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Sample records for multi-frequency local field

  1. Far-field imaging with a multi-frequency metalens

    SciTech Connect

    Jouvaud, C. Ourir, A.; Rosny, J. de

    2014-06-16

    A metalens, i.e., a dense array of identical resonators, allows to image an object pattern at subwavelength scale from far field radiation field. Here, we show that the efficiency can be improved when the resonant frequencies of the cell are distributed over a given frequency range. Because in such systems each eigen mode is localized, the subwavelength image is built from a spectral analysis of the radiated field. A simple model based on coupled resonant dipoles is used to find the best frequency distribution. This multifrequency metalens approach is validated using a flat array of split ring resonators. We experimentally demonstrate the subwavelength resolution of such a device at microwave range.

  2. Multi-frequency local wavenumber analysis and ply correlation of delamination damage.

    PubMed

    Juarez, Peter D; Leckey, Cara A C

    2015-09-01

    Wavenumber domain analysis through use of scanning laser Doppler vibrometry has been shown to be effective for non-contact inspection of damage in composites. Qualitative and semi-quantitative local wavenumber analysis of realistic delamination damage and quantitative analysis of idealized damage scenarios (Teflon inserts) have been performed previously in the literature. This paper presents a new methodology based on multi-frequency local wavenumber analysis for quantitative assessment of multi-ply delamination damage in carbon fiber reinforced polymer (CFRP) composite specimens. The methodology is presented and applied to a real world damage scenario (impact damage in an aerospace CFRP composite). The methodology yields delamination size and also correlates local wavenumber results from multiple excitation frequencies to theoretical dispersion curves in order to robustly determine the delamination ply depth. Results from the wavenumber based technique are validated against a traditional nondestructive evaluation method.

  3. Fourier method for recovering acoustic sources from multi-frequency far-field data

    NASA Astrophysics Data System (ADS)

    Wang, Xianchao; Guo, Yukun; Zhang, Deyue; Liu, Hongyu

    2017-03-01

    We consider an inverse source problem of determining a source term in the Helmholtz equation from multi-frequency far-field measurements. Based on the Fourier series expansion, we develop a novel non-iterative reconstruction method for solving the problem. A promising feature of this method is that it utilizes the data from only a few observation directions for each frequency. Theoretical uniqueness and stability analysis are provided. Numerical experiments are conducted to illustrate the effectiveness and efficiency of the proposed method in both two and three dimensions.

  4. The matched-phase coherent multi-frequency matched-field processor

    PubMed

    Orris; Nicholas; Perkins

    2000-05-01

    Coherent multi-frequency matched-field processing is investigated using a matched-phase coherent matched-field processor. Its main difference from previous coherent processors is that the relative phases of the Fourier components contained within the recorded signal are not assumed to be known a priori. Rather they are considered free parameters that can be determined using a global functional minimization algorithm. Additionally, this processor uses only the cross-frequency terms, making it less susceptible to the detrimental effects of ambient noise; in one example, this processor shows a five decibel improvement over a similar coherent processor. Along with its increased sensitivity with respect to the broadcast source levels, this coherent processor exhibits superior range resolution as compared with multi-frequency incoherent processors, due to the cross-frequency interference of the vertical eigenmodes. Within this work we explore the efficacy of the algorithms used to determine the relative phases along with the performance of the matched-phase coherent processor itself, performed within the context of data collected during an event from the SWellEx-96 experiment. Performance comparisons between this processor, an incoherent processor, and another coherent processor are demonstrated using this data set.

  5. Array processing for RFID tag localization exploiting multi-frequency signals

    NASA Astrophysics Data System (ADS)

    Zhang, Yimin; Li, Xin; Amin, Moeness G.

    2009-05-01

    RFID is an increasingly valuable business and technology tool for electronically identifying, locating, and tracking products, assets, and personnel. As a result, precise positioning and tracking of RFID tags and readers have received considerable attention from both academic and industrial communities. Finding the position of RFID tags is considered an important task in various real-time locating systems (RTLS). As such, numerous RFID localization products have been developed for various applications. The majority of RFID positioning systems is based on the fusion of pieces of relevant information, such as the range and the direction-of-arrival (DOA). For example, trilateration can determine the tag position by using the range information of the tag estimated from three or more spatially separated reader antennas. Triangulation is another method to locate RFID tags that use the direction-of-arrival (DOA) information estimated at multiple spatially separated locations. The RFID tag positions can also be determined through hybrid techniques that combine the range and DOA information. The focus of this paper to study the design and performance of the localization of passive RFID tags using array processing techniques in a multipath environment, and exploiting multi-frequency CW signals. The latter are used to decorrelate the coherent multipath signals for effective DOA estimation and for the purpose of accurate range estimation. Accordingly, the spatial and frequency dimensionalities are fully utilized for robust and accurate positioning of RFID tags.

  6. Simulation of multi-frequency EPR spectra for a distribution of the zero-field splitting.

    PubMed

    Azarkh, Mykhailo; Groenen, Edgar J J

    2015-06-01

    We present a numerical procedure called 'grid-of-errors' to extract the distribution of magnetic interactions from continuous-wave electron-paramagnetic-resonance (EPR) spectra at multiple microwave frequencies. The approach is based on the analysis of the lineshape of the spectra and explicitly worked out for high-spin systems for which the lineshape is determined by a distribution of the zero-field splitting. Initial principal values of the zero-field splitting tensor are obtained from the EPR spectrum at a microwave frequency in the high-field limit, and the initial distribution is taken Gaussian. Subsequently, the grid-of-errors procedure optimizes this distribution, without any restriction to its shape, taking into account spectra at various microwave frequencies. The numerical procedure is illustrated for the Fe(III)-EDTA complex. An optimized distribution of the zero-field splitting is obtained, which provides a proper description of the EPR spectra at 9.5, 34, 94, and 275 GHz. The proposed approach can be used as well for distributions of magnetic interactions other than the zero-field splitting.

  7. A multi-frequency radiometric measurement of soil moisture content over bare and vegetated fields

    NASA Technical Reports Server (NTRS)

    Wang, J. R.; Schmugge, T. J.; Gould, W. I.; Glazar, W. S.; Fuchs, J. E.; Mcmurtrey, J. E., III

    1982-01-01

    An experiment on soil moisture remote sensing was conducted during July to September 1981 on bare, grass, and alfalfa fields at frequencies of 0.6, 1.4, 5.0, and 10.6 GHz with radiometers mounted on mobile towers. The results confirm the frequency dependence of sensitivity reduction due to the presence of vegetation cover. For the type of vegetated fields reported here, the vegetation effect is appreciable even at 0.6 GHz. Measurements over bare soil show that when the soil is wet, the measured brightness temperature is lowest at 5.0 GHz and highest at 0.6 GHz, a result contrary to the expectation based on the estimated dielectric permittivity of soil-water mixtures and the current radiative transfer model in that frequency range.

  8. A multi-frequency radiometric measurement of soil moisture content over bare and vegetated fields

    NASA Technical Reports Server (NTRS)

    Wang, J. R.; Schmugge, T. J.; Mcmurtrey, J. E., III; Gould, W. I.; Glazar, W. S.; Fuchs, J. E. (Principal Investigator)

    1981-01-01

    A USDA Beltsville Agricultural Research Center site was used for an experiment in which soil moisture remote sensing over bare, grass, and alfalfa fields was conducted over a three-month period using 0.6 GHz, 1.4 GHz, and 10.6 GHz Dicke-type microwave radiometers mounted on mobile towers. Ground truth soil moisture content and ambient air and sil temperatures were obtained concurrently with the radiometric measurements. Biomass of the vegetation cover was sampled about once a week. Soil density for each of the three fields was measured several times during the course of the experiment. Results of the radiometric masurements confirm the frequency dependence of moisture sensing sensitivity reduction reported earlier. Observations over the bare, wet field show that the measured brightness temperature is lowest at 5.0 GHz and highest of 0.6 GHz frequency, a result contrary to expectation based on the estimated dielectric permittivity of soil water mixtures and current radiative transfer model in that frequency range.

  9. Multi-frequency SAR data for soil surface moisture estimation over agricultural fields

    NASA Astrophysics Data System (ADS)

    Zribi, Mehrez; Baghdadi, Nicolas

    2015-04-01

    Soil moisture plays a crucial role in the continental water cycle, in particular through its influence on the distribution of precipitation between surface runoff and infiltration, which is the main driver behind most hydrological and geomorphologic processes. Although there is now a good understanding of soil hydrodynamics and water transfer in porous media, the development of reliable techniques allowing field heterogeneities to be fully analyzed in space and time remains a key issue. In recent decades, various inversion models have been proposed for the retrieval of surface parameters (mainly soil moisture and surface roughness) from Synthetic Aperture Radar (SAR) high resolution measurements. The proposed techniques depend particularly on two instrumental parameters: the radar system's spatial resolution and the number of configurations measured during satellite acquisitions (mainly incidence angle and polarization). In this paper, our objective is to illustrate different applications of SAR data to estimate soil moisture over bare soil and vegetation cover areas (wheat, olive groves, meadows ...). Potential of very high resolution data, with the availability of TerraSAR-X and COSMO-SkyMed constellations is also discussed. This study is based on different experimental campaigns organized over different sites in humid and semi-arid regions. Ground measurements (soil moisture, soil roughness, vegetation description) over test fields were carried out simultaneously to SAR measurements. Effect of vegetation attenuation on radar signal is considered through a synergy with optical remote sensing. Soil moisture precision for all proposed applications is generally ranged between 3 and 5% of volumetric moisture. These methodologies are developed in the context of the preparation for having a high soil moisture operational product, with SENTINEL and/or the other planned constellations. After an analysis of radar data sensitivity (C and X bands) to surface parameters

  10. Multi-Frequency Synthesis

    NASA Astrophysics Data System (ADS)

    Conway, J. E.; Sault, R. J.

    Introduction; Image Fidelity; Multi-Frequency Synthesis; Spectral Effects; The Spectral Expansion; Spectral Dirty Beams; First Order Spectral Errors; Second Order Spectral Errors; The MFS Deconvolution Problem; Nature of The Problem; Map and Stack; Direct Assault; Data Weighting Methods; Double Deconvolution; The Sault Algorithm; Multi-Frequency Self-Calibration; Practical MFS; Conclusions

  11. Multi-Frequency Synthesis

    NASA Astrophysics Data System (ADS)

    Sault, R. J.; Conway, J. E.

    Multi-frequency synthesis is the practice of using visibility data measured over a range of frequencies when forming a continuum image. Because observing frequency is easier to vary than antenna location, it is an effective way of filling the (u,v) plane for an observation. Here we consider the artifacts in MFS images caused by source spectral variation. For frequency ranges of about 30%, for observations where only modest dynamic range is required, the artifacts of MFS can be completely ignored. For higher dynamic range observations, some calibration techniques and deconvolution algorithms are described which minimize the artifacts.

  12. Multi-frequency inversion-charge pumping for charge separation and mobility analysis in high-k/InGaAs metal-oxide-semiconductor field-effect transistors

    SciTech Connect

    Djara, V.; Cherkaoui, K.; Negara, M. A.; Hurley, P. K.

    2015-11-28

    An alternative multi-frequency inversion-charge pumping (MFICP) technique was developed to directly separate the inversion charge density (N{sub inv}) from the trapped charge density in high-k/InGaAs metal-oxide-semiconductor field-effect transistors (MOSFETs). This approach relies on the fitting of the frequency response of border traps, obtained from inversion-charge pumping measurements performed over a wide range of frequencies at room temperature on a single MOSFET, using a modified charge trapping model. The obtained model yielded the capture time constant and density of border traps located at energy levels aligned with the InGaAs conduction band. Moreover, the combination of MFICP and pulsed I{sub d}-V{sub g} measurements enabled an accurate effective mobility vs N{sub inv} extraction and analysis. The data obtained using the MFICP approach are consistent with the most recent reports on high-k/InGaAs.

  13. Optical multi-frequency swept sensing for wide-field vibration measurement of interior surfaces in biological tissue

    NASA Astrophysics Data System (ADS)

    Choi, S.; Nin, F.; Hibino, H.; Suzuki, T.

    2015-12-01

    Multifrequency sensing technique adopting the wide field heterodyne detection technique is demonstrated for interior surface vibration measurements in thick biological tissue. These arrangements allow obtaining not only 3D tomographic images but also various vibration parameters such as spatial amplitude, phase, and frequency, with high temporal and transverse resolutions over a wide field. The axial resolution and the accuracy of vibration amplitude measurement were estimated to be 2.5 μm and 3 nm, respectively. This wide-field tomographic sensing method can be applied for measuring microdynamics of a variety of biological samples, thus contributing to the progress in life sciences research.

  14. DERIVATION OF THE MAGNETIC FIELD IN A CORONAL MASS EJECTION CORE VIA MULTI-FREQUENCY RADIO IMAGING

    SciTech Connect

    Tun, Samuel D.; Vourlidas, A.

    2013-04-01

    The magnetic field within the core of a coronal mass ejection (CME) on 2010 August 14 is derived from analysis of multi-wavelength radio imaging data. This CME's core was found to be the source of a moving type IV radio burst, whose emission is here determined to arise from the gyrosynchrotron process. The CME core's true trajectory, electron density, and line-of-sight depth are derived from stereoscopic observations, constraining these parameters in the radio emission models. We find that the CME carries a substantial amount of mildly relativistic electrons (E < 100 keV) in a strong magnetic field (B < 15 G), and that the spectra at lower heights are preferentially suppressed at lower frequencies through absorption from thermal electrons. We discuss the results in light of previous moving type IV burst studies, and outline a plan for the eventual use of radio methods for CME magnetic field diagnostics.

  15. Improved regionalization of soil surface properties using multi-frequency remote sensing data and geo-statistics at field scale

    NASA Astrophysics Data System (ADS)

    Meyer, Swen; Marzahn, Philip; Krüger, Karsten; Duttmann, Rainer; Ludwig, Ralf

    2010-05-01

    Land Surface Models (LSM) have become indispensable tools to quantify the most important physical, chemical and biological processes to determine water and nutrient fluxes in support of land management strategies or the prediction of climate change impacts. However, the utilization of LSM requires numerous soil and vegetation parameters, which are seldom available in spatial distribution or an appropriate temporal frequency. The quality of these model input parameters, especially the spatial heterogeneity and temporal variability of soil parameters, has a strong effect on LSM simulations. Conventional measurements of soil characteristics (texture, bulk density, moisture) remain time consuming and non-cost effective and are therefore continuously reduced. Thus, the presentation focuses on the regionalization of soil physical properties such as surface texture, bulk density, soil roughness and soil moisture using microwave airborne SAR data at different frequencies and polarisations, calculated terrain attributes from a Digital Elevation Model (DEM) and geo-statistical approaches. Stochastic and deterministic approaches comprised different prediction methods, such as IDW, linear- and multiple linear regressions, Simple Kriging and Ordinary Kriging as well as hybrid approaches such as Regression Kriging. Different co- variables were integrated in the spatial prediction process using the Regression-Kriging Models A, B and C first introduced by Odeh et al. (1995). Co-variables were derived using: a.) An interferometric high resolution DEM and its quantified first and second order terrain attributes. b.) Spatially distributed dielectric properties of the soil surface derived from SAR imagery following a semi empirical approach (Oh et al. 1992) and a physically based approach (Hajnsek et al. 2003). The developed approach was validated against in-situ data from different field campaigns carried out over a test site located in the young moraine area in northern Mecklenburg

  16. Field application of a multi-frequency acoustic instrument to monitor sediment for silt erosion study in Pelton turbine in Himalayan region, India

    NASA Astrophysics Data System (ADS)

    Rai, A. K.; Kumar, A.; Hies, T.; Nguyen, H. H.

    2016-11-01

    High sediment load passing through hydropower components erodes the hydraulic components resulting in loss of efficiency, interruptions in power production and downtime for repair/maintenance, especially in Himalayan regions. The size and concentration of sediment play a major role in silt erosion. The traditional process of collecting samples manually to analyse in laboratory cannot suffice the need of monitoring temporal variation in sediment properties. In this study, a multi-frequency acoustic instrument was applied at desilting chamber to monitor sediment size and concentration entering the turbine. The sediment size and concentration entering the turbine were also measured with manual samples collected twice daily. The samples collected manually were analysed in laboratory with a laser diffraction instrument for size and concentration apart from analysis by drying and filtering methods for concentration. A conductivity probe was used to calculate total dissolved solids, which was further used in results from drying method to calculate suspended solid content of the samples. The acoustic instrument was found to provide sediment concentration values similar to drying and filtering methods. However, no good match was found between mean grain size from the acoustic method with the current status of development and laser diffraction method in the first field application presented here. The future versions of the software and significant sensitivity improvements of the ultrasonic transducers are expected to increase the accuracy in the obtained results. As the instrument is able to capture the concentration and in the future most likely more accurate mean grain size of the suspended sediments, its application for monitoring silt erosion in hydropower plant shall be highly useful.

  17. Field test of a multi-frequency electromagnetic induction sensor for the study of soil moisture in different land-soil units

    NASA Astrophysics Data System (ADS)

    Calamita, Giuseppe; Onorati, Beniamino; Perrone, Angela; Manfreda, Salvatore; Brocca, Luca

    2015-04-01

    appealing compared to satellite remote sensing (RS) methods. However, similarly to RS, the interpretation of the EMI measurements is not straightforward due to the simultaneous influence of different soil properties. So far, the great majority of the studies have used mono-frequency EMI sensors for periods of time shorter than one year. Moreover studies over area with medium to high vegetation density are still quite rare. The focus of this work is to evaluate the usability of the GEM-300 multi-frequency EMI sensor for spatial and temporal SM retrieval at the hillslope scale over a number of diverse land-soil units including some of the less explored types, like highland forested areas. Further, some aspects relating to the inherent stability of the GEM-300 sensor, which were never addressed before in this research area, are also explored. The test sites are located in the "Fiumarella di Corleto" experimental basin, located in Basilicata region (southern Italy). The experimentation lasted from May 2012 to May 2013. Regular grids (80 x 80 mq) and a transect (60 m) were used as spatial sampling schemes. A TDR mobile probe was used for SM measurements on the 25 points of each grid whereas fixed buried TDR probes were used on the 11 points of transect. The obtained results allowed us to investigate the spatial and temporal variability and relation between TDR and EMI sensors.

  18. Temperature rise in tissue ablation using multi-frequency ultrasound.

    PubMed

    Sijia Guo; Yun Jing; Xiaoning Jiang

    2013-08-01

    High-intensity focused ultrasound (HIFU) is becoming an increasingly important noninvasive surgical tool, despite the challenges in temperature rise control and unwanted heating problems. In this study, experiments and simulations on tissue ablation effectiveness were performed using multi-frequency HIFU with frequency differences of more than 500 kHz (center frequencies are 950 kHz, 1.5 MHz, and 3.3 MHz). In the experiments, the temperature was recorded as chicken breast tissue was heated by single-frequency, dual-frequency, and tri-frequency HIFU configurations at controlled acoustic power and exposure time. 5% to 10% temperature rise differences were observed between single- and multi-frequency modes, indicating that multi-frequency HIFU is more effective at producing faster temperature rises. Cavitation detection tests were conducted to compare the cavitation pressure fields between single- and multi-frequency ultrasound. Moreover, simulations on single-frequency and multi-frequency acoustic fields as well as bio-heating-induced temperature fields were performed. With the comparison between experimental and simulation results, we believe that the more effective tissue ablation using multi-frequency ultrasound is likely attributed to the enhanced cavitation, a promising result for HIFU applications.

  19. Measurement of hyperfine fields and the Δg-effect in π-conjugated polymer-based OLEDs using multi-frequency electrically detected magnetic resonance

    NASA Astrophysics Data System (ADS)

    Joshi, Gajadhar; Malissa, Hans; Miller, Richard; Ogden, Lillie; Baird, Douglas; Jamali, Shirin; Kavand, Marzieh; Ambal, Kapil; van Tol, Johan; Lupton, John; Boehme, Christoph

    Magneto-opto-electronic properties of organic semiconductors, such as organic magnetoresistance or magneto-electroluminescence, are strongly influenced by the interplay of proton induced hyperfine fields to which charge carrier spins are coupled [Nguyen et al., Nat. Mater. 9, 345-352 (2010), McCamey et al. Phys. Rev. Lett. 104, 017601 (2010)]. In addition, the weak but non-negligible and highly inhomogeneously distributed spin-orbit effects caused by the material's structural disorder can affect spin-dependent processes. In order to quantitatively access and discriminate between these mechanisms, we investigate the inhomogeneous broadening of polaron spin-resonances using electrically detected magnetic resonance (EDMR) spectroscopy at various magnetic fields between 3mT and 12T. While random local hyperfine fields cause an external magnetic field-independent line broadening, spin-orbit contributions give rise to a distribution of the charge carrier g-factors. This Δg effect leads to a resonance line-width contribution that is proportional to the external magnetic field. We observe an EDMR line that is largely field-independent in the low-magnetic field, but shows substantial broadening of line shape at higher fields.

  20. Field demonstration of simultaneous wind and temperature measurements from 5 to 50 km with a Na double-edge magneto-optic filter in a multi-frequency Doppler lidar.

    PubMed

    Huang, Wentao; Chu, Xinzhao; Wiig, Johannes; Tan, Bo; Yamashita, Chihoko; Yuan, T; Yue, J; Harrell, S D; She, C-Y; Williams, B P; Friedman, J S; Hardesty, R M

    2009-05-15

    We report the first (to our knowledge) field demonstration of simultaneous wind and temperature measurements with a Na double-edge magneto-optic filter implemented in the receiver of a three-frequency Na Doppler lidar. Reliable winds and temperatures were obtained in the altitude range of 10-45 km with 1 km resolution and 60 min integration under the conditions of 0.4 W lidar power and 75 cm telescope aperture. This edge filter with a multi-frequency lidar concept can be applied to other direct-detection Doppler lidars for profiling both wind and temperature simultaneously from the lower to the upper atmosphere.

  1. Wearable Multi-Frequency and Multi-Segment Bioelectrical Impedance Spectroscopy for Unobtrusively Tracking Body Fluid Shifts during Physical Activity in Real-Field Applications: A Preliminary Study

    PubMed Central

    Villa, Federica; Magnani, Alessandro; Maggioni, Martina A.; Stahn, Alexander; Rampichini, Susanna; Merati, Giampiero; Castiglioni, Paolo

    2016-01-01

    Bioelectrical Impedance Spectroscopy (BIS) allows assessing the composition of body districts noninvasively and quickly, potentially providing important physiological/clinical information. However, neither portable commercial instruments nor more advanced wearable prototypes simultaneously satisfy the demanding needs of unobtrusively tracking body fluid shifts in different segments simultaneously, over a broad frequency range, for long periods and with high measurements rate. These needs are often required to evaluate exercise tests in sports or rehabilitation medicine, or to assess gravitational stresses in aerospace medicine. Therefore, the aim of this work is to present a new wearable prototype for monitoring multi-segment and multi-frequency BIS unobtrusively over long periods. Our prototype guarantees low weight, small size and low power consumption. An analog board with current-injecting and voltage-sensing electrodes across three body segments interfaces a digital board that generates square-wave current stimuli and computes impedance at 10 frequencies from 1 to 796 kHz. To evaluate the information derivable from our device, we monitored the BIS of three body segments in a volunteer before, during and after physical exercise and postural shift. We show that it can describe the dynamics of exercise-induced changes and the effect of a sit-to-stand maneuver in active and inactive muscular districts separately and simultaneously. PMID:27187389

  2. Wearable Multi-Frequency and Multi-Segment Bioelectrical Impedance Spectroscopy for Unobtrusively Tracking Body Fluid Shifts during Physical Activity in Real-Field Applications: A Preliminary Study.

    PubMed

    Villa, Federica; Magnani, Alessandro; Maggioni, Martina A; Stahn, Alexander; Rampichini, Susanna; Merati, Giampiero; Castiglioni, Paolo

    2016-05-11

    Bioelectrical Impedance Spectroscopy (BIS) allows assessing the composition of body districts noninvasively and quickly, potentially providing important physiological/clinical information. However, neither portable commercial instruments nor more advanced wearable prototypes simultaneously satisfy the demanding needs of unobtrusively tracking body fluid shifts in different segments simultaneously, over a broad frequency range, for long periods and with high measurements rate. These needs are often required to evaluate exercise tests in sports or rehabilitation medicine, or to assess gravitational stresses in aerospace medicine. Therefore, the aim of this work is to present a new wearable prototype for monitoring multi-segment and multi-frequency BIS unobtrusively over long periods. Our prototype guarantees low weight, small size and low power consumption. An analog board with current-injecting and voltage-sensing electrodes across three body segments interfaces a digital board that generates square-wave current stimuli and computes impedance at 10 frequencies from 1 to 796 kHz. To evaluate the information derivable from our device, we monitored the BIS of three body segments in a volunteer before, during and after physical exercise and postural shift. We show that it can describe the dynamics of exercise-induced changes and the effect of a sit-to-stand maneuver in active and inactive muscular districts separately and simultaneously.

  3. Localization of dexamethasone within dendritic core-multishell (CMS) nanoparticles and skin penetration properties studied by multi-frequency electron paramagnetic resonance (EPR) spectroscopy.

    PubMed

    Saeidpour, S; Lohan, S B; Anske, M; Unbehauen, M; Fleige, E; Haag, R; Meinke, M C; Bittl, R; Teutloff, C

    2016-10-15

    The skin and especially the stratum corneum (SC) act as a barrier and protect epidermal cells and thus the whole body against xenobiotica of the external environment. Topical skin treatment requires an efficient drug delivery system (DDS). Polymer-based nanocarriers represent novel transport vehicles for dermal application of drugs. In this study dendritic core-multishell (CMS) nanoparticles were investigated as promising candidates. CMS nanoparticles were loaded with a drug (analogue) and were applied to penetration studies of skin. We determined by dual-frequency electron paramagnetic resonance (EPR) how dexamethasone (Dx) labelled with 3-carboxy-2,2,5,5-tetramethyl-1-pyrrolidinyloxy (PCA) is associated with the CMS. The micro-environment of the drug loaded to CMS nanoparticles was investigated by pulsed high-field EPR at cryogenic temperature, making use of the fact that magnetic parameters (g-, A-matrices, and spin-lattice relaxation time) represent specific probes for the micro-environment. Additionally, the rotational correlation time of spin-labelled Dx was probed by continuous wave EPR at ambient temperature, which provides independent information on the drug environment. Furthermore, the penetration depth of Dx into the stratum corneum of porcine skin after different topical applications was investigated. The location of Dx in the CMS nanoparticles is revealed and the function of CMS as penetration enhancers for topical application is shown.

  4. Multi-frequency imaging in VLBI

    NASA Astrophysics Data System (ADS)

    Likhachev, S.

    The new technique, multi-frequency imaging ( MFI) is developed. In VLBI, Multi-Frequency Imaging (MFI) consists of multi-frequency synthesis (MFS) and multi-frequency analysis (MFA) of the VLBI data obtained from observations on various frequencies. A set of linear deconvolution MFI algorithms is described. The algorithms make it possible to obtain high quality images interpolated on any given frequency inside any given bandwidth, and to derive reliable estimates of spectral indexes for radio sources with continuum spectrum. Thus MFI approach makes it is possible not only to improve the quality and fidelity of the images and also essentially to derive the morphology of the observed radio sources. (astro-ph/0412470)

  5. Multi-Frequency Band Pyroelectric Sensors

    PubMed Central

    Hsiao, Chun-Ching; Liu, Sheng-Yi

    2014-01-01

    A methodology is proposed for designing a multi-frequency band pyroelectric sensor which can detect subjects with various frequencies or velocities. A structure with dual pyroelectric layers, consisting of a thinner sputtered ZnO layer and a thicker aerosol ZnO layer, proved helpful in the development of the proposed sensor. The thinner sputtered ZnO layer with a small thermal capacity and a rapid response accomplishes a high-frequency sensing task, while the thicker aerosol ZnO layer with a large thermal capacity and a tardy response is responsible for low-frequency sensing tasks. A multi-frequency band pyroelectric sensor is successfully designed, analyzed and fabricated in the present study. The range of the multi-frequency sensing can be estimated by means of the proposed design and analysis to match the thicknesses of the sputtered and the aerosol ZnO layers. The fabricated multi-frequency band pyroelectric sensor with a 1 μm thick sputtered ZnO layer and a 20 μm thick aerosol ZnO layer can sense a frequency band from 4000 to 40,000 Hz without tardy response and low voltage responsivity. PMID:25429406

  6. Multi-Frequency Intravascular Ultrasound (IVUS) Imaging

    PubMed Central

    Ma, Teng; Yu, Mingyue; Chen, Zeyu; Fei, Chunlong; Shung, K. Kirk; Zhou, Qifa

    2015-01-01

    Acute coronary syndrome (ACS) is frequently associated with the sudden rupture of a vulnerable atherosclerotic plaque within the coronary artery. Several unique physiological features, including a thin fibrous cap accompanied by a necrotic lipid core, are the targeted indicators for identifying the vulnerable plaques. Intravascular ultrasound (IVUS), a catheter-based imaging technology, has been routinely performed in clinics for more than 20 years to describe the morphology of the coronary artery and guide percutaneous coronary interventions. However, conventional IVUS cannot facilitate the risk assessment of ACS because of its intrinsic limitations, such as insufficient resolution. Renovation of the IVUS technology is essentially needed to overcome the limitations and enhance the coronary artery characterization. In this paper, a multi-frequency intravascular ultrasound (IVUS) imaging system was developed by incorporating a higher frequency IVUS transducer (80 to 150 MHz) with the conventional IVUS (30–50 MHz) system. The newly developed system maintains the advantage of deeply penetrating imaging with the conventional IVUS, while offering an improved higher resolution image with IVUS at a higher frequency. The prototyped multi-frequency catheter has a clinically compatible size of 0.95 mm and a favorable capability of automated image co-registration. In vitro human coronary artery imaging has demonstrated the feasibility and superiority of the multi-frequency IVUS imaging system to deliver a more comprehensive visualization of the coronary artery. This ultrasonic-only intravascular imaging technique, based on a moderate refinement of the conventional IVUS system, is not only cost-effective from the perspective of manufacturing and clinical practice, but also holds the promise of future translation into clinical benefits. PMID:25585394

  7. Multi-frequency communication system and method

    DOEpatents

    Carrender, Curtis Lee; Gilbert, Ronald W.

    2004-06-01

    A multi-frequency RFID remote communication system is provided that includes a plurality of RFID tags configured to receive a first signal and to return a second signal, the second signal having a first frequency component and a second frequency component, the second frequency component including data unique to each remote RFID tag. The system further includes a reader configured to transmit an interrogation signal and to receive remote signals from the tags. A first signal processor, preferably a mixer, removes an intermediate frequency component from the received signal, and a second processor, preferably a second mixer, analyzes the IF frequency component to output data that is unique to each remote tag.

  8. Generalized Linear Multi-Frequency Imaging in VLBI

    NASA Astrophysics Data System (ADS)

    Likhachev, S.; Ladygin, V.; Guirin, I.

    2004-07-01

    In VLBI, generalized Linear Multi-Frequency Imaging (MFI) consists of multi-frequency synthesis (MFS) and multi-frequency analysis (MFA) of the VLBI data obtained from observations on various frequencies. A set of linear deconvolution MFI algorithms is described. The algorithms make it possible to obtain high quality images interpolated on any given frequency inside any given bandwidth, and to derive reliable estimates of spectral indexes for radio sources with continuum spectrum.

  9. High Field and Multi-Frequency EPR in Single Crystals of Sperm Whale Met-Myoglobin: Determination of the Axial Zero-Field Splitting Constant and Frequency Dependence of the Linewidth

    NASA Astrophysics Data System (ADS)

    Miyajima, Yoshiharu; Yashiro, Haruhiko; Kashiwagi, Takanari; Hagiwara, Masayuki; Hori, Hiroshi

    2004-01-01

    Electron paramagnetic resonance (EPR) measurements for frequencies from 28.5 GHz to 608.1 GHz and magnetic field up to 14 T have been performed on single crystals of sperm whale high-spin (S=5/2) met-myoglobin. The EPR resonance field along the c*-axis deviates from the g=5.71 straight line at high frequencies. The axial zero-field splitting constant (D) of the met-myoglobin sample is evaluated to be 9.47± 0.05 cm-1 by analyzing the resonance fields with the S=5/2 spin Hamiltonian including the D term. The angular dependence of EPR spectra in the ab plane has been also investigated at high frequencies. Two kinds of EPR spectra are observed corresponding to two kinds of different heme sites in the unit cell. A notable change in the linewidth of the spectrum along the c*-axis occurs above 350 GHz, suggesting that the dominant relaxation process changes around 350 GHz. The origins of the linewidth are discussed.

  10. Tensor gauge field localization in branes

    SciTech Connect

    Tahim, M. O.; Cruz, W. T.; Almeida, C. A. S.

    2009-04-15

    In this work we study localization of a Kalb-Ramond tensorial gauge field on a membrane described by real scalar fields. The membrane is embedded in an AdS-type five-dimensional bulk space, which mimics a Randall-Sundrum scenario. First, we consider a membrane described by only a single real scalar field. In that scenario we find that there is no localized tensorial zero mode. When we take into account branes described by two real scalar fields with internal structures, we obtain again a nonlocalized zero mode for a Kalb-Ramond tensorial gauge field. After modifying our model of one single scalar field by coupling the dilaton to the Kalb-Ramond field, we find that this result is changed. Furthermore, we analyze Kaluza-Klein massive modes and resonance structures.

  11. A multi-scale multi-frequency deconvolution algorithm for synthesis imaging in radio interferometry

    NASA Astrophysics Data System (ADS)

    Rau, U.; Cornwell, T. J.

    2011-08-01

    Aims: We describe MS-MFS, a multi-scale multi-frequency deconvolution algorithm for wide-band synthesis-imaging, and present imaging results that illustrate the capabilities of the algorithm and the conditions under which it is feasible and gives accurate results. Methods: The MS-MFS algorithm models the wide-band sky-brightness distribution as a linear combination of spatial and spectral basis functions, and performs image-reconstruction by combining a linear-least-squares approach with iterative χ2 minimization. This method extends and combines the ideas used in the MS-CLEAN and MF-CLEAN algorithms for multi-scale and multi-frequency deconvolution respectively, and can be used in conjunction with existing wide-field imaging algorithms. We also discuss a simpler hybrid of spectral-line and continuum imaging methods and point out situations where it may suffice. Results: We show via simulations and application to multi-frequency VLA data and wideband EVLA data, that it is possible to reconstruct both spatial and spectral structure of compact and extended emission at the continuum sensitivity level and at the angular resolution allowed by the highest sampled frequency.

  12. Experimental diagnostics of multi-frequency quasiperiodic oscillations

    NASA Astrophysics Data System (ADS)

    Stankevich, N. V.; Kuznetsov, A. P.; Popova, E. S.; Seleznev, E. P.

    2017-02-01

    We suggest a new technique of fold Poincaré section, allowing one to visualize an invariant curve of a multi-frequency invariant torus in a physical experiment. Details of the technique are presented, along with examples of its application to various experimental studies. Examples of how an invariant curve is visualized in double-, triple- and four-fold Poincaré sections are shown.

  13. Gauge Field Localization on Deformed Branes

    NASA Astrophysics Data System (ADS)

    Tofighi, A.; Moazzen, M.; Farokhtabar, A.

    2016-02-01

    In this paper, we utilise the Chumbes-Holf da Silva-Hott (CHH) mechanism to investigate the issue of gauge field localization on a deformed brane constructed with one scalar field, which can be coupled to gravity minimally or non-minimally. The study of deformed defects is important because they contain internal structures which may have implications in braneworld models. With the CHH mechanism, we find that the massless zero mode of gauge field, in the case of minimal or non-minimal coupling is localized on the brane. Moreover, in the case of non-minimal coupling, it is shown that, when the non-minimal coupling constant is larger than its critical value, then the zero mode is localized on each sub brane.

  14. The Local Group: the ultimate deep field

    NASA Astrophysics Data System (ADS)

    Boylan-Kolchin, Michael; Weisz, Daniel R.; Bullock, James S.; Cooper, Michael C.

    2016-10-01

    Near-field cosmology - using detailed observations of the Local Group and its environs to study wide-ranging questions in galaxy formation and dark matter physics - has become a mature and rich field over the past decade. There are lingering concerns, however, that the relatively small size of the present-day Local Group (˜2 Mpc diameter) imposes insurmountable sample-variance uncertainties, limiting its broader utility. We consider the region spanned by the Local Group's progenitors at earlier times and show that it reaches 3 arcmin ≈ 7 comoving Mpc in linear size (a volume of ≈350 Mpc3) at z = 7. This size at early cosmic epochs is large enough to be representative in terms of the matter density and counts of dark matter haloes with Mvir(z = 7) ≲ 2 × 109 M⊙. The Local Group's stellar fossil record traces the cosmic evolution of galaxies with 103 ≲ M⋆(z = 0)/M⊙ ≲ 109 (reaching M1500 > -9 at z ˜ 7) over a region that is comparable to or larger than the Hubble Ultra-Deep Field (HUDF) for the entire history of the Universe. In the JWST era, resolved stellar populations will probe regions larger than the HUDF and any deep JWST fields, further enhancing the value of near-field cosmology.

  15. The Effect of Subcutaneous Fat on Electrical Impedance Myography: Electrode Configuration and Multi-Frequency Analyses

    PubMed Central

    Li, Le; Li, Xiaoyan; Hu, Huijing; Shin, Henry

    2016-01-01

    This study investigates the impact of the subcutaneous fat layer (SFL) thickness on localized electrical impedance myography (EIM), as well as the effects of different current electrodes, varying in distance and direction, on EIM output. Twenty-three healthy subjects underwent localized multi-frequency EIM on their biceps brachii muscles with a hand-held electrode array. The EIM measurements were recorded under three different configurations: wide (or outer) longitudinal configuration 6.8 cm, narrow (or inner) longitudinal configuration 4.5 cm, and narrow transverse configuration 4.5 cm. Ultrasound was applied to measure the SFL thickness. Coefficients of determination (R2) of three EIM variables (resistance, reactance, and phase) and SFL thickness were calculated. For the longitudinal configuration, the wide distance could reduce the effects of the subcutaneous fat when compared with the narrow distance, but a significant correlation still remained for all three EIM parameters. However, there was no significant correlation between SFL thickness and reactance in the transverse configuration (R2 = 0.0294, p = 0.434). Utilizing a ratio of 50kHz/100kHz phase was found to be able to help reduce the correlation with SFL thickness for all the three configurations. The findings indicate that the appropriate selection of the current electrode distance, direction and the multi-frequency phase ratio can reduce the impact of subcutaneous fat on EIM. These settings should be evaluated for future clinical studies using hand-held localized arrays to perform EIM. PMID:27227876

  16. Localizing periodicity in near-field images

    NASA Astrophysics Data System (ADS)

    Fraundorf, P.

    1990-02-01

    We show that Bayesian Physical inference, like that used in statistical mechanics, can guide the systematic construction of Fourier dark-field methods for localizing periodicity in near-field (e.g., scanning tunneling and electron phase contrast) images. For crystals in an aperiodic field, the Fourier coefficient Zeicphi combines with a prior estimate for background amplitude B to predict background phase (β) values distributed with a probability p(β-φ||Z,φ,B) inversely proportional to amplitude P of the signal of interest, when the latter is treated as an unknown translation scaled to B.

  17. Gauge field localization on brane worlds

    SciTech Connect

    Guerrero, Rommel; Rodriguez, R. Omar; Melfo, Alejandra; Pantoja, Nelson

    2010-04-15

    We consider the effects of spacetime curvature and brane thickness on the localization of gauge fields on a brane via kinetic terms induced by localized fermions. We find that in a warped geometry with an infinitely thin brane, both the infrared and the ultraviolet behavior of the electromagnetic propagator are affected, providing a more stringent bound on the brane's tension than that coming from the requirement of four-dimensional gravity on the brane. On the other hand, for a thick wall in a flat spacetime, where the fermions are localized by means of a Yukawa coupling, we find that four-dimensional electromagnetism is recovered in a region bounded from above by the same critical distance appearing in the thin case, but also from below by a new scale related to the brane's thickness and the electromagnetic couplings. This imposes very stringent bounds on the brane's thickness which seem to invalidate the localization mechanism for this case.

  18. Multi-frequency analysis of neutralino dark matter annihilations in the Coma cluster

    NASA Astrophysics Data System (ADS)

    Colafrancesco, S.; Profumo, S.; Ullio, P.

    2006-08-01

    We study the astrophysical implications of neutralino dark matter annihilations in galaxy clusters, with a specific application to the Coma cluster. We first address the determination of the dark halo models for Coma, starting from structure formation models and observational data, and we discuss in detail the role of sub-halos. We then perform a thorough analysis of the transport and diffusion properties of neutralino annihilation products, and investigate the resulting multi-frequency signals, from radio to gamma-ray frequencies. We also study other relevant astrophysical effects of neutralino annihilations, like the DM-induced Sunyaev-Zel'dovich effect and the intracluster gas heating. As for the particle physics setup, we adopt a two-fold approach, resorting both to model-independent bottom-up scenarios and to benchmark, GUT-motivated frameworks. We show that the Coma radio-halo data (the spectrum and the surface brightness) can be nicely fitted by the neutralino-induced signal for peculiar particle physics models and for magnetic field values, which we outline in detail. Fitting the radio data and moving to higher frequencies, we find that the multi-frequency spectral energy distributions are typically dim at EUV and X-ray frequencies (with respect to the data), but show a non-negligible gamma-ray emission, depending on the amplitude of the Coma magnetic field. A simultaneous fit to the radio, EUV and HXR data is not possible without violating the gamma-ray EGRET upper limit. The best-fit particle physics models yields substantial heating of the intracluster gas, but not sufficient energy injection as to explain the quenching of cooling flows in the innermost region of clusters. Due to the specific multi-frequency features of the DM-induced spectral energy distribution in Coma, we find that supersymmetric models can be significantly and optimally constrained either in the gamma-rays or at radio and microwave frequencies.

  19. Application of Multi-Frequency Modulation (MFM) facsimile machines

    NASA Astrophysics Data System (ADS)

    Nickerson, James T.

    1990-09-01

    Multi-Frequency Modulation (MFM) has been developed at NPS using both differential quadrature-amplitude-modulation (DQAM) and differential quadrature-phase-shift-keying (DQPSK) encoding formats. This report discusses the use of each of these formats in transmitting a facsimile encoded message over a voice frequency channel. The satisfactory transmission and receipt of facsimile messages was achieved using both DQPSK and D16-QAM encoding formats. Research and testing for this report included the use of variable facsimile transmission rates in an attempt to optimize MFM operating parameters. Experimental results revealed a higher error rate when decoding messages contained similar contiguous characters.

  20. Beginning stages of local magnetic field formation

    NASA Astrophysics Data System (ADS)

    Bumba, V.

    Based on a study of the initial stages of local magnetic field formation, the appearance of a new magnetic flux in the photosphere is studied. This magnetic flux is found to occur both under the influence of different modes of convective motion as well as under the action of Paleomagnetic fields. Waldmeier's Heliographic Maps of the Photosphere and Mt. Wilson Observatory daily magnetic maps were used in the analysis. Observed regularities could not be explained by a model of magnetic flux tubes emerging on the photospheric surface. This model can not account for the practically simultaneous development of separate active regions, belonging to different solar hemispheres and different cycles of solar activity in one, relatively narrow, 'unipolar' sector of the background field. It is also difficult to explain the different roles and velocities of negative and positive polarities during the formation of new magnetic fields. The importance of velocity measurements and maps for solving the observed phenomenon is stressed.

  1. Inversion of multi-frequency electromagnetic induction data for 3D characterization of hydraulic conductivity

    USGS Publications Warehouse

    Brosten, T.R.; Day-Lewis, F. D.; Schultz, G.M.; Curtis, G.P.; Lane, J.W.

    2011-01-01

    Electromagnetic induction (EMI) instruments provide rapid, noninvasive, and spatially dense data for characterization of soil and groundwater properties. Data from multi-frequency EMI tools can be inverted to provide quantitative electrical conductivity estimates as a function of depth. In this study, multi-frequency EMI data collected across an abandoned uranium mill site near Naturita, Colorado, USA, are inverted to produce vertical distribution of electrical conductivity (EC) across the site. The relation between measured apparent electrical conductivity (ECa) and hydraulic conductivity (K) is weak (correlation coefficient of 0.20), whereas the correlation between the depth dependent EC obtained from the inversions, and K is sufficiently strong to be used for hydrologic estimation (correlation coefficient of -0.62). Depth-specific EC values were correlated with co-located K measurements to develop a site-specific ln(EC)-ln(K) relation. This petrophysical relation was applied to produce a spatially detailed map of K across the study area. A synthetic example based on ECa values at the site was used to assess model resolution and correlation loss given variations in depth and/or measurement error. Results from synthetic modeling indicate that optimum correlation with K occurs at ~0.5m followed by a gradual correlation loss of 90% at 2.3m. These results are consistent with an analysis of depth of investigation (DOI) given the range of frequencies, transmitter-receiver separation, and measurement errors for the field data. DOIs were estimated at 2.0??0.5m depending on the soil conductivities. A 4-layer model, with varying thicknesses, was used to invert the ECa to maximize available information within the aquifer region for improved correlations with K. Results show improved correlation between K and the corresponding inverted EC at similar depths, underscoring the importance of inversion in using multi-frequency EMI data for hydrologic estimation. ?? 2011.

  2. A Multi-frequency Beam-forming HF Radar for Tsunami Detection

    NASA Astrophysics Data System (ADS)

    Trizna, D. B.

    2007-05-01

    local radio frequency allocation authorities, assuming just a single frequency is used at a time. Alternatively, one may choose four to eight frequencies operating simultaneously, to allow the clearest channel and best signal strength channel for enhanced processing. We will discuss the tradeoffs on multiple frequency use versus single optimum frequency use, both using a multi-frequency radar capability. Results of preliminary testing of a prototype system at Duck, NC will also be presented.

  3. Multi-frequency complex network from time series for uncovering oil-water flow structure

    PubMed Central

    Gao, Zhong-Ke; Yang, Yu-Xuan; Fang, Peng-Cheng; Jin, Ning-De; Xia, Cheng-Yi; Hu, Li-Dan

    2015-01-01

    Uncovering complex oil-water flow structure represents a challenge in diverse scientific disciplines. This challenge stimulates us to develop a new distributed conductance sensor for measuring local flow signals at different positions and then propose a novel approach based on multi-frequency complex network to uncover the flow structures from experimental multivariate measurements. In particular, based on the Fast Fourier transform, we demonstrate how to derive multi-frequency complex network from multivariate time series. We construct complex networks at different frequencies and then detect community structures. Our results indicate that the community structures faithfully represent the structural features of oil-water flow patterns. Furthermore, we investigate the network statistic at different frequencies for each derived network and find that the frequency clustering coefficient enables to uncover the evolution of flow patterns and yield deep insights into the formation of flow structures. Current results present a first step towards a network visualization of complex flow patterns from a community structure perspective. PMID:25649900

  4. Utilisation of multi-frequency VEMPs improves diagnostic accuracy for Meniere's disease.

    PubMed

    Maxwell, Rebecca; Jerin, Claudia; Gürkov, Robert

    2017-01-01

    To determine whether vestibular evoked myogenic potential (VEMP) measurements that combine the VEMP 500/1000 Hz frequency tuning ratio and the inter-aural asymmetry ratio can reliably detect unilateral Meniere's disease ears as compared to healthy controls. Forty-two consecutive patients with certain unilateral Meniere's disease (as confirmed using a locally enhanced inner ear MRI (LEIM)) were assessed. Cervical vestibular evoked myogenic potentials (cVEMP) and ocular vestibular evoked myogenic potentials (oVEMP) were recorded at 500 and 1000 Hz. The VEMP amplitudes, asymmetry ratios, and the 500/1000 Hz amplitude ratios were compared with those of 21 age-matched healthy controls. A multi-frequency VEMPs score that combined: (1) the cVEMP 500/1000 Hz amplitude ratio, (2) the oVEMP 500/1000 Hz amplitude ratio, (3) the 500 Hz cVEMP asymmetry ratio, (4) the 1000 Hz cVEMP asymmetry ratio, produced a ROC curve with an area under the curve (AUC) of 0.814. The inclusion of audiology data further improved the result to 0.906. This score can be used to discriminate with a good degree of clinical accuracy between Meniere's ears (unilateral) and those of healthy controls. Multi-frequency VEMP analysis offers a simple, cost-effective solution to the diagnostic difficulties presented by Meniere's disease.

  5. Magnetic fields in Local Group dwarf irregulars

    NASA Astrophysics Data System (ADS)

    Chyży, K. T.; Weżgowiec, M.; Beck, R.; Bomans, D. J.

    2011-05-01

    Aims: We wish to clarify whether strong magnetic fields can be effectively generated in typically low-mass dwarf galaxies and to assess the role of dwarf galaxies in the magnetization of the Universe. Methods: We performed a search for radio emission and magnetic fields in an unbiased sample of 12 Local Group (LG) irregular and dwarf irregular galaxies with the 100-m Effelsberg telescope at 2.64 GHz. Three galaxies were detected. A higher frequency (4.85 GHz) was used to search for polarized emission in five dwarfs that are the most luminous ones in the infrared domain, of which three were detected. Results: Magnetic fields in LG dwarfs are weak, with a mean value of the total field strength of <4.2 ± 1.8 μG, three times lower than in the normal spirals. The strongest field among all LG dwarfs of 10 μG (at 2.64 GHz) is observed in the starburst dwarf IC 10. The production of total magnetic fields in dwarf systems appears to be regulated mainly by the star-formation surface density (with the power-law exponent of 0.30 ± 0.04) or by the gas surface density (with the exponent 0.47 ± 0.09). In addition, we find systematically stronger fields in objects of higher global star-formation rate. The dwarf galaxies follow a similar far-infrared relationship (with a slope of 0.91 ± 0.08) to that determined for high surface brightness spiral galaxies. The magnetic field strength in dwarf galaxies does not correlate with their maximum rotational velocity, indicating that a small-scale rather than a large-scale dynamo process is responsible for producting magnetic fields in dwarfs. If magnetization of the Universe by galactic outflows is coeval with its metal enrichment, we show that more massive objects (such as Lyman break galaxies) can efficiently magnetize the intergalactic medium with a magnetic field strength of about 0.8 nG out to a distance of 160-530 kpc at redshifts 5-3, respectively. Magnetic fields that are several times weaker and shorter magnetization

  6. A multi-frequency method for ultrasonic ranging.

    PubMed

    Queirós, Ricardo; Corrêa Alegria, Francisco; Silva Girão, Pedro; Cruz Serra, António

    2015-12-01

    This paper presents a method for ultrasonic ranging based on the cross-correlation of two multi-frequency signals. The stimulus signal is composed by multiple sine-wave bursts/segments, each containing a different frequency and an integer number of periods. The frequency of each sine-wave burst is different from that of the adjacent bursts, but it is very close to the transducer resonant frequency. The time-of-flight (TOF) is estimated by finding the maximum of the cross-correlation. Interpolation is used to increase the measurement resolution. The experimental error corresponding to two standard deviations, for a range up to 1 m, is less than 0.3 mm.

  7. Microfabricated multi-frequency particle impedance characterization system

    SciTech Connect

    Fuller, C K; Hamilton, J; Ackler, H; Krulevitch, P; Boser, B; Eldredge, A; Becker, F; Yang, J; Gascoyne, P

    2000-03-01

    We have developed a microfabricated flow-through impedance characterization system capable of performing AC, multi-frequency measurements on cells and other particles. The sensor measures both the resistive and reactive impedance of passing particles, at rates of up to 100 particles per second. Its operational bandwidth approaches 10 MHz with a signal-to-noise ratio of approximately 40 dB. Particle impedance is measured at three or more frequencies simultaneously, enabling the derivation of multiple particle parameters. This constitutes an improvement to the well-established technique of DC particle sizing via the Coulter Principle. Human peripheral blood granulocyte radius, membrane capacitance, and cytoplasmic conductivity were measured (r = 4.1 {micro}m, C{sub mem} = 0.9 {micro}F/cm{sup 2}, {sigma}{sub int} = 0.66 S/m) and were found to be consistent with published values.

  8. A multi-frequency MRCSI algorithm with phaseless data

    NASA Astrophysics Data System (ADS)

    Hu, Zheng; Lianlin, Li; Fang, Li

    2009-06-01

    This paper presents a novel multi-frequency multiplicative regularized contrast source inversion (MRCSI) algorithm with phaseless data (PD-MRCSI) for solving a two-dimensional scalar inverse scattering problem. The MRCSI method resolves the inverse scattering problem by minimization of a cost functional which is a linear combination of mismatches in the data equation and the state equation. Through modifying the mismatch in the data equation, we construct a new cost functional which is suitable for the inverse scattering problem with phaseless data. Similar to the MRCSI algorithm, the new cost functional can be minimized by alternatively updating the unknown contrast source and contrast using the so-called Polak-Ribere conjugate gradient method. Numerical results show that the proposed algorithm works effectively and efficiently for solving the inverse scattering problem with phaseless data.

  9. III-V-on-silicon multi-frequency lasers.

    PubMed

    Keyvaninia, S; Verstuyft, S; Pathak, S; Lelarge, F; Duan, G-H; Bordel, D; Fedeli, J-M; De Vries, T; Smalbrugge, B; Geluk, E J; Bolk, J; Smit, M; Roelkens, G; Van Thourhout, D

    2013-06-03

    Compact multi-frequency lasers are realized by combining III-V based optical amplifiers with silicon waveguide optical demultiplexers using a heterogeneous integration process based on adhesive wafer bonding. Both devices using arrayed waveguide grating routers as well as devices using ring resonators as the demultiplexer showed lasing with threshold currents between 30 and 40 mA and output powers in the order of a few mW. Laser operation up to 60°C is demonstrated. The small bending radius allowable for the silicon waveguides results in a short cavity length, ensuring stable lasing in a single longitudinal mode, even with relaxed values for the intra-cavity filter bandwidths.

  10. Acoustic metamaterial panels based on multi frequency vibration absorbers

    NASA Astrophysics Data System (ADS)

    Shi, Chao; Sun, Hongwei; Hu, Xiaolei; Gu, Jinliang

    2016-04-01

    Presented here is a new metamaterial panel based on multi-frequency vibration absorbers for broadband vibration absorption. The proposed metamaterial panel consists of a uniform isotropic panel and small two-mass spring-mass-damper subsystem many locations along the panel to act as multi-frequency vibration absorbers. The existence of two stopbands is demonstrated using a model based on averaging material properties over a cell length and a model based on finite element modeling and the Bloch-Floquet theory for periodic structures. For a finite metamaterial panel, because these two idealized models can not be used for finite panels and/or elastic waves having short wavelengths, a finite-element method is used for detailed modeling and analysis. The concepts of negative effective stiffness is explained in detail. For an incoming wave with a frequency in one of the two stopbands, the absorbers are excited to vibrate in their optical modes to create shear forces to straighten the panel and stop the wave propagation. For an incoming wave with a frequency outside of but between the two stopbands, it can be efficiently damped out by the damper with these mass of each absorber. Hence, the two stopbands are connected in to a wide stopband. Numerical examples validate the concept and show that the structures boundary conditions do not have significant influence on the absorption of high-frequency waves. However, for absorption of low-frequency waves, the structures boundary conditions and resonance frequencies and the location and spatial distribution of absorbers need to be considered in design, and it is better to use heavier masses for absorbers.

  11. A multi-frequency approach to soil moisture measurements

    NASA Astrophysics Data System (ADS)

    Castiglione, Paolo; Campbell, Colin S.; Cobos, Doug R.; Campbell, Gaylon S.

    2014-05-01

    clay) and four salinities (pore water from 0 to 15 dS/m). The regression analysis with multi-frequency predictors was carried out through an artificial neural network. Results show considerable improvement of the proposed multi-frequency approach over conventional single frequency measurements.

  12. Acoustic metamaterial structures based on multi-frequency vibration absorbers

    NASA Astrophysics Data System (ADS)

    Pai, P. Frank; Peng, Hao

    2014-03-01

    This paper presents a new metamaterial beam based on multi-frequency vibration absorbers for broadband vibration absorption. The proposed metamaterial beam consists of a uniform isotropic beam and small two-mass spring-mass- damper subsystems at many locations along the beam to act as multi-frequency vibration absorbers. For an infinite metamaterial beam, governing equations of a unit cell are derived using the extended Hamilton principle. The existence of two stopbands is demonstrated using a model based on averaging material properties over a cell length and a model based on finite element modeling and the Bloch-Floquet theory for periodic structures. For a finite metamaterial beam, because these two idealized models cannot be used for finite beams and/or elastic waves having short wavelengths, a finite-element method is used for detailed modeling and analysis. The concepts of negative effective mass and effective stiffness and how the spring-mass-damper subsystem creates two stopbands are explained in detail. Numerical simulations reveal that the actual working mechanism of the proposed metamaterial beam is based on the concept of conventional mechanical vibration absorbers. For an incoming wave with a frequency in one of the two stopbands, the absorbers are excited to vibrate in their optical modes to create shear forces to straighten the beam and stop the wave propagation. For an incoming wave with a frequency outside of but between the two stopbands, it can be efficiently damped out by the damper with the second mass of each absorber. Hence, the two stopbands are connected into a wide stopband. Numerical examples validate the concept and show that the structure's boundary conditions do not have significant influence on the absorption of high-frequency waves. However, for absorption of low-frequency waves, the structure's boundary conditions and resonance frequencies and the location and spatial distribution of absorbers need to be considered in design, and it

  13. Composite Characterization Using Laser Doppler Vibrometry and Multi-Frequency Wavenumber Analysis

    NASA Technical Reports Server (NTRS)

    Juarez, Peter; Leckey, Cara

    2015-01-01

    NASA has recognized the need for better characterization of composite materials to support advances in aeronautics and the next generation of space exploration vehicles. An area of related research is the evaluation of impact induced delaminations. Presented is a non-contact method of measuring the ply depth of impact delamination damage in a composite through use of a Scanning Laser Doppler Vibrometer (SLDV), multi-frequency wavenumber analysis, and a wavenumber-ply correlation algorithm. A single acquisition of a chirp excited lamb wavefield in an impacted composite is post-processed into a numerous single frequency excitation wavefields through a deconvolution process. A spatially windowed wavenumber analysis then extracts local wavenumbers from the wavefield, which are then correlated to theoretical dispersion curves for ply depth determination. SLDV based methods to characterize as-manufactured composite variation using wavefield analysis will also be discussed.

  14. [Cross Frequency Coupling Characteristic Analysis in Subthalamic Local Field Potentials of Parkinson's Disease].

    PubMed

    Wang, Zongbao; Huang, Yongzhi; Zhang, Xinjing; Geng, Xinyi; Chen, Xiao; Wang, Shouyan

    2015-08-01

    Pathological neural activity in subthalamic nucleus (STN) is closely related to the symptoms of Parkinson' s disease. Local field potentials (LFPs) recordings from subthalamic nucleus show that power spectral peaks exist at tremor, double tremor and tripble tremor frequencies, respectively. The interaction between these components in the multi-frequency tremor may be related to the generation of tremor. To study the linear and nonlinear relationship between those components, we analyzed STN LFPs from 9 Parkinson's disease patients using time frequency, cross correlation, Granger casuality and bi-spectral analysis. Results of the time-frequency analysis and cross-frequency correlation analysis demonstrated that the power density of those components significantly decreased as the alleviation of tremor and cross-correlation (0.18-0.50) exists during tremor period. Granger causality of the time-variant amplitude showed stronger contribution from tremor to double tremor components, and contributions from both tremor and double tremor components to triple tremor component. Quadratic phase couplings among these three components were detected by the bispectral approaches. The linear and nonlinear relationships existed among the multi-components and certainly confirmed that the dependence cross those frequencies and neurological mechanism of tremor involved complicate neural processes.

  15. Multi-frequency metal detector in high mineralization

    NASA Astrophysics Data System (ADS)

    Stamatescu, Laurence; Harmer, Gregory; Nesper, Oliver; Bordean, Dorin; Tkachenko, Yuri

    2009-05-01

    The successful detection and discrimination of mines is very difficult in areas of high soil mineralization. In these areas, the soil can make a significant contribution to the received signal that causes false detections or masks the true mine response. To address this problem, Minelab has developed a continuous wave (CW) multi-frequency digital detector (MFDD). It transmits four frequencies (between 1 kHz and 45 kHz) and each has a high dynamic range that approaches 120 dB. The mineralized soil with high magnetic susceptibility affects the characteristics of the sensor-head, in particular the inductance of the transmitting and receiving windings. These in turn affect the front-end electronics and measuring circuits and can lead to excessive ground noise that makes detection difficult. Minelab has modeled the effect that the soil has on the sensor-head and developed methods to monitor these effects. By having a well calibrated detector, which is demonstrated by the tight agreement of raw ground signals with theoretical ground models, the tasks of ground balance and discrimination become much more reliable and robust.

  16. Local Field Potentials: Myths and Misunderstandings

    PubMed Central

    Herreras, Oscar

    2016-01-01

    The intracerebral local field potential (LFP) is a measure of brain activity that reflects the highly dynamic flow of information across neural networks. This is a composite signal that receives contributions from multiple neural sources, yet interpreting its nature and significance may be hindered by several confounding factors and technical limitations. By and large, the main factor defining the amplitude of LFPs is the geometry of the current sources, over and above the degree of synchronization or the properties of the media. As such, similar levels of activity may result in potentials that differ in several orders of magnitude in different populations. The geometry of these sources has been experimentally inaccessible until intracerebral high density recordings enabled the co-activating sources to be revealed. Without this information, it has proven difficult to interpret a century's worth of recordings that used temporal cues alone, such as event or spike related potentials and frequency bands. Meanwhile, a collection of biophysically ill-founded concepts have been considered legitimate, which can now be corrected in the light of recent advances. The relationship of LFPs to their sources is often counterintuitive. For instance, most LFP activity is not local but remote, it may be larger further from rather than close to the source, the polarity does not define its excitatory or inhibitory nature, and the amplitude may increase when source's activity is reduced. As technological developments foster the use of LFPs, the time is now ripe to raise awareness of the need to take into account spatial aspects of these signals and of the errors derived from neglecting to do so. PMID:28018180

  17. A robust multi-frequency mixing algorithm for suppression of rivet signal in GMR inspection of riveted structures

    NASA Astrophysics Data System (ADS)

    Safdernejad, Morteza S.; Karpenko, Oleksii; Ye, Chaofeng; Udpa, Lalita; Udpa, Satish

    2016-02-01

    The advent of Giant Magneto-Resistive (GMR) technology permits development of novel highly sensitive array probes for Eddy Current (EC) inspection of multi-layer riveted structures. Multi-frequency GMR measurements with different EC pene-tration depths show promise for detection of bottom layer notches at fastener sites. However, the distortion of the induced magnetic field due to flaws is dominated by the strong fastener signal, which makes defect detection and classification a challenging prob-lem. This issue is more pronounced for ferromagnetic fasteners that concentrate most of the magnetic flux. In the present work, a novel multi-frequency mixing algorithm is proposed to suppress rivet signal response and enhance defect detection capability of the GMR array probe. The algorithm is baseline-free and does not require any assumptions about the sample geometry being inspected. Fastener signal suppression is based upon the random sample consensus (RANSAC) method, which iteratively estimates parameters of a mathematical model from a set of observed data with outliers. Bottom layer defects at fastener site are simulated as EDM notches of different length. Performance of the proposed multi-frequency mixing approach is evaluated on finite element data and experimental GMR measurements obtained with unidirectional planar current excitation. Initial results are promising demonstrating the feasibility of the approach.

  18. The status of the QUIJOTE multi-frequency instrument

    NASA Astrophysics Data System (ADS)

    Hoyland, R. J.; Aguiar-González, M.; Aja, B.; Ariño, J.; Artal, E.; Barreiro, R. B.; Blackhurst, E. J.; Cagigas, J.; Cano de Diego, J. L.; Casas, F. J.; Davis, R. J.; Dickinson, C.; Arriaga, B. E.; Fernandez-Cobos, R.; de la Fuente, L.; Génova-Santos, R.; Gómez, A.; Gomez, C.; Gómez-Reñasco, F.; Grainge, K.; Harper, S.; Herran, D.; Herreros, J. M.; Herrera, G. A.; Hobson, M. P.; Lasenby, A. N.; Lopez-Caniego, M.; López-Caraballo, C.; Maffei, B.; Martinez-Gonzalez, E.; McCulloch, M.; Melhuish, S.; Mediavilla, A.; Murga, G.; Ortiz, D.; Piccirillo, L.; Pisano, G.; Rebolo-López, R.; Rubiño-Martin, J. A.; Ruiz, J. Luis; Sanchez de la Rosa, V.; Sanquirce, R.; Vega-Moreno, A.; Vielva, P.; Viera-Curbelo, T.; Villa, E.; Vizcargüenaga, A.; Watson, R. A.

    2012-09-01

    The QUIJOTE-CMB project has been described in previous publications. Here we present the current status of the QUIJOTE multi-frequency instrument (MFI) with five separate polarimeters (providing 5 independent sky pixels): two which operate at 10-14 GHz, two which operate at 16-20 GHz, and a central polarimeter at 30 GHz. The optical arrangement includes 5 conical corrugated feedhorns staring into a dual reflector crossed-draconian system, which provides optimal cross-polarization properties (designed to be < -35 dB) and symmetric beams. Each horn feeds a novel cryogenic on-axis rotating polar modulator which can rotate at a speed of up to 1 Hz. The science driver for this first instrument is the characterization of the galactic emission. The polarimeters use the polar modulator to derive linear polar parameters Q, U and I and switch out various systematics. The detection system provides optimum sensitivity through 2 correlated and 2 total power channels. The system is calibrated using bright polarized celestial sources and through a secondary calibration source and antenna. The acquisition system, telescope control and housekeeping are all linked through a real-time gigabit Ethernet network. All communication, power and helium gas are passed through a central rotary joint. The time stamp is synchronized to a GPS time signal. The acquisition software is based on PLCs written in Beckhoffs TwinCat and ethercat. The user interface is written in LABVIEW. The status of the QUIJOTE MFI will be presented including pre-commissioning results and laboratory testing.

  19. Model to localize gauge and tensor fields on thick branes

    NASA Astrophysics Data System (ADS)

    Chumbes, A. E. R.; Hoff da Silva, J. M.; Hott, M. B.

    2012-04-01

    It is shown that the introduction of a suitable function in the higher-dimensional gauge field action may be used in order to achieve gauge bosons localization on a thick brane. The model is constructed upon analogies to the effective coupling of neutral scalar field to electromagnetic field and to the Friedberg-Lee model for hadrons. After that we move forward studying the localization of the Kalb-Ramond field via this procedure.

  20. Local field distribution near corrugated interfaces: Green's function formulation

    NASA Astrophysics Data System (ADS)

    Yu, K. W.; Wan, Jones T. K.

    2001-12-01

    We have developed a Green's function formalism to compute the local field distribution near an interface separating two media of different dielectric constants. The Maxwell's equations are converted into a surface integral equation; thus it greatly simplifies the solutions and yields accurate results for interfaces of arbitrary shape. The integral equation is solved and the local field distribution is obtained for a periodic interface.

  1. Noise-resilient multi-frequency surface sensor for nuclear quadrupole resonance.

    PubMed

    Peshkovsky, A S; Cattena, C J; Cerioni, L M; Osán, T M; Forguez, J G; Peresson, W J; Pusiol, D J

    2008-10-01

    A planar nuclear quadrupole resonance (NQR) sensor has been developed. The sensor is resilient to environmental noise and is capable of simultaneous independent multi-frequency operation. The device was constructed as an open multimodal birdcage structure, in which the higher modes, generally not used in magnetic resonance, are utilized for NQR detection. These modes have smooth distributions of the amplitudes of the corresponding radiofrequency magnetic fields everywhere along the sensor's surface. The phases of the fields, on the other hand, are cyclically shifted across the sensor's surface. Noise signals coming from distant sources, therefore, induce equal-magnitude cyclically phase-shifted currents in different parts of the sensor. When such cyclically phase-shifted currents arrive at the mode connection point, they destructively interfere with each other and are cancelled out. NQR signals of polycrystalline or disordered substances, however, are efficiently detected by these modes because they are insensitive to the phases of the excitation/detection. No blind spots exist along the sensor's surface. The sensor can be used for simultaneous detection of one or more substances in locations with environmental noise.

  2. PAGaN I: Multi-Frequency Polarimetry of AGN Jets with KVN

    NASA Astrophysics Data System (ADS)

    Kim, Jae-Young; Trippe, Sascha; Sohn, Bong Won; Oh, Junghwan; Park, Jong-Ho; Lee, Sang-Sung; Lee, Taeseok; Kim, Daewon

    2015-10-01

    Active Galactic Nuclei (AGN) with bright radio jets offer the opportunity to study the structure of and physical conditions in relativistic outflows. For such studies, multi-frequency polarimetric very long baseline interferometric (VLBI) observations are important as they directly probe particle densities, magnetic field geometries, and several other parameters. We present results from first-epoch data obtained by the Korean VLBI Network (KVN) within the frame of the Plasma Physics of Active Galactic Nuclei (PAGaN) project. We observed seven radio-bright nearby AGN at frequencies of 22, 43, 86, and 129 GHz in dual polarization mode. Our observations constrain apparent brightness temperatures of jet components and radio cores in our sample to >10^{8.01} K and >10^{9.86} K, respectively. Degrees of linear polarization m_{L} are relatively low overall: less than 10%. This indicates suppression of polarization by strong turbulence in the jets. We found an exceptionally high degree of polarization in a jet component of BL Lac at 43 GHz, with m_{L} ˜ 40%. Assuming a transverse shock front propagating downstream along the jet, the shock front being almost parallel to the line of sight can explain the high degree of polarization.

  3. Multi-frequency electron paramagnetic resonance study of irradiated human finger phalanxes

    NASA Astrophysics Data System (ADS)

    Zdravkova, M.; Vanhaelewyn, G.; Callens, F.; Gallez, B.; Debuyst, R.

    2005-10-01

    Electron paramagnetic resonance (EPR) is often used in dosimetry using biological samples such as teeth and bones. It is generally assumed that the radicals, formed after irradiation, are similar in both tissues as the mineral part of bone and tooth is carbonated hydroxyapatite. However, there is a lack of experimental evidence to support this assumption. The aim of the present study was to contribute to that field by studying powder and block samples of human finger phalanxes that were irradiated and analyzed by multi-frequency EPR. The results obtained from bones are different from the ones obtained in enamel by several respects: the ordering of the apatite crystallites is much smaller in bone, complicating the assignment of the observed CO 2- radicals to a specific location, and one type of CO 33- radical was only found in enamel. Moreover, a major difference was found in the non-CO 2- and non-CO 33- signals. The elucidation of the nature of these native signals (in bone and tooth enamel) still represents a big challenge.

  4. Advantages in using multi-frequency driving ultrasound for optimizing echo particle image velocimetry techniques.

    PubMed

    Zheng, Hairong; Mukdadi, Osama; Hertzberg, Jean; Shandas, Robin

    2004-01-01

    We have recently developed an ultrasound based velocimetry technique, termed echo particle image velocimetry (echo PIV). This method takes advantage of the non-linear backscatter characteristics of ultrasound contrast microbubbles when exposed to certain ultrasonic field. Preliminary in vitro, animal and clinical studies have shown significant promise of this method for measuring multiple velocity components with good temporal and spatial resolution. However, there is still difficulty in maximizing the non-linearity of bubble backscatter using conventional Gaussian-pulse excitation techniques because significant harmonic components may not be produced at modest pressure amplitudes and the higher incident pressure amplitudes required to induce non-linear behavior may cause bubble destruction. We present here a potential solution to this problem through the use of multi-frequency excitation. A rectangular pulse with multiple harmonics is used to drive the bubble. The backscatter process is studied through a modified Rayleigh-Plesset equation. Results show that the rectangular wave is effective in improving the visibility of microbubbles with ultrasound backscattered efficiency significantly higher than the widely used Gaussian waveform. Use of rectangular pulses with 4 and 2 harmonics showed no significant difference in bubble backscatter behavior, indicating that a two-frequency excitation may be sufficient to induce non-linear behavior of the microbubbles practically at modest incident pressures.

  5. Sonic IR crack detection of aircraft turbine engine blades with multi-frequency ultrasound excitations

    SciTech Connect

    Zhang, Ding; Han, Xiaoyan; Newaz, Golam

    2014-02-18

    Effectively and accurately detecting cracks or defects in critical engine components, such as turbine engine blades, is very important for aircraft safety. Sonic Infrared (IR) Imaging is such a technology with great potential for these applications. This technology combines ultrasound excitation and IR imaging to identify cracks and flaws in targets. In general, failure of engine components, such as blades, begins with tiny cracks. Since the attenuation of the ultrasound wave propagation in turbine engine blades is small, the efficiency of crack detection in turbine engine blades can be quite high. The authors at Wayne State University have been developing the technology as a reliable tool for the future field use in aircraft engines and engine parts. One part of the development is to use finite element modeling to assist our understanding of effects of different parameters on crack heating while experimentally hard to achieve. The development has been focused with single frequency ultrasound excitation and some results have been presented in a previous conference. We are currently working on multi-frequency excitation models. The study will provide results and insights of the efficiency of different frequency excitation sources to foster the development of the technology for crack detection in aircraft engine components.

  6. Local field effect as a function of pulse duration

    SciTech Connect

    Novitsky, Denis V.

    2010-07-15

    In this brief report we give semiclassical consideration to the role of pulse duration in the observation of local field effects in the regime of optical switching. We show that the main parameter governing local field influence is the ratio of peak Rabi frequency corresponding to medium inversion and Lorentz frequency of the medium. To obtain significant local field effect, this parameter should be near unity that is valid only for long enough pulses. We also discuss the role of relaxation and pulse shape in this process.

  7. Asymptotic behavior of local dipolar fields in thin films

    NASA Astrophysics Data System (ADS)

    Bowden, G. J.; Stenning, G. B. G.; van der Laan, G.

    2016-10-01

    A simple method, based on layer by layer direct summation, is used to determine the local dipolar fields in uniformly magnetized thin films. The results show that the dipolar constants converge ~1/m where the number of spins in a square film is given by (2m+1)2. Dipolar field results for sc, bcc, fcc, and hexagonal lattices are presented and discussed. The results can be used to calculate local dipolar fields in films with either ferromagnetic, antiferromagnetic, spiral, exponential decay behavior, provided the magnetic order only changes normal to the film. Differences between the atomistic (local fields) and macroscopic fields (Maxwellian) are also examined. For the latter, the macro B-field inside the film is uniform and falls to zero sharply outside, in accord with Maxwell boundary conditions. In contrast, the local field for the atomistic point dipole model is highly non-linear inside and falls to zero at about three lattice spacing outside the film. Finally, it is argued that the continuum field B (used by the micromagnetic community) and the local field Bloc(r) (used by the FMR community) will lead to differing values for the overall demagnetization energy.

  8. Acoustic source localization in mixed field using spherical microphone arrays

    NASA Astrophysics Data System (ADS)

    Huang, Qinghua; Wang, Tong

    2014-12-01

    Spherical microphone arrays have been used for source localization in three-dimensional space recently. In this paper, a two-stage algorithm is developed to localize mixed far-field and near-field acoustic sources in free-field environment. In the first stage, an array signal model is constructed in the spherical harmonics domain. The recurrent relation of spherical harmonics is independent of far-field and near-field mode strengths. Therefore, it is used to develop spherical estimating signal parameter via rotational invariance technique (ESPRIT)-like approach to estimate directions of arrival (DOAs) for both far-field and near-field sources. In the second stage, based on the estimated DOAs, simple one-dimensional MUSIC spectrum is exploited to distinguish far-field and near-field sources and estimate the ranges of near-field sources. The proposed algorithm can avoid multidimensional search and parameter pairing. Simulation results demonstrate the good performance for localizing far-field sources, or near-field ones, or mixed field sources.

  9. Imaging Local Electric Field Distribution by Plasmonic Impedance Microscopy.

    PubMed

    Wang, Yixian; Shan, Xiaonan; Wang, Shaopeng; Tao, Nongjian; Blanchard, Pierre-Yves; Hu, Keke; Mirkin, Michael V

    2016-02-02

    We report on imaging of local electric field on an electrode surface with plasmonic electrochemical impedance microscopy (P-EIM). The local electric field is created by putting an electrode inside a micropipet positioned over the electrode and applying a voltage between the two electrodes. We show that the distribution of the surface charge as well as the local electric field at the electrode surface can be imaged with P-EIM. The spatial distribution and the dependence of the local charge density and electric field on the distance between the micropipet and the surface are measured, and the results are compared with the finite element calculations. The work also demonstrates the possibility of integrating plasmonic imaging with scanning ion conductance microscopy (SICM) and other scanning probe microscopies.

  10. A new narrow-beam, multi-frequency, scanning radiometer and its application to in-flight icing detection

    NASA Astrophysics Data System (ADS)

    Serke, David J.; Reed, Kimberly A.; Negus, James; Blanchette, Levi; Ware, Randolph; Kennedy, Patrick C.

    2017-03-01

    A one degree beamwidth, multi-frequency (20 to 30 and 89GHz), dual-polarization radiometer with full azimuth and elevation scanning capabilities was built with the purpose of improving the detection of in-flight icing hazards to aircraft in the near airport environment. This goal was achieved by collocating the radiometer with Colorado State University's CHILL polarized Doppler radar and leveraging the similar beamwidth and volume scan regiments of the two instruments. The collocated instruments allowed for the liquid water path and water vapor measurements derived from the radiometer to be merged with the radar moment fields to determine microphysical and water phase characteristics aloft. The radiometer was field tested at Colorado State University's CHILL radar site near Greeley, Colorado during the summer of 2009. Instrument design, calibration, and initial field testing results are discussed in this paper.

  11. Dynamical localization: Hydrogen atoms in magnetic and microwave fields

    SciTech Connect

    Benvenuto, F.; Casati, G.; Shepelyansky, D.L.

    1997-03-01

    We show that dynamical localization for excited hydrogen atoms in magnetic and microwave fields takes place at quite low microwave frequency ({omega}n{sup 3}{lt}1). Estimates of the localization length are given for different parameter regimes, showing that the quantum delocalization border drops significantly as compared to the case of zero magnetic field. This opens up broad possibilities for laboratory investigations. {copyright} {ital 1997} {ital The American Physical Society}

  12. Local Ambipolar Graphene Field Effect Transistors via Metal Side Gates

    NASA Astrophysics Data System (ADS)

    Tian, Jifa; Jauregui, Luis; Lopez, Gabriel; Cao, Helin; Chen, Yong

    2010-03-01

    We fabricated local graphene field effect transistors (FET) based on metal side gates. The characteristic ambipolar field effect of graphene device was observed by sweeping only the voltage of a local metal side gate. The local charge neutrality point of the side-gate graphene FET can be tuned in a large voltage range from positive to negative by a second side gate. Furthermore, we observed that the field effect due to the side gate can be appreciably weakened by electrically grounding the back gate compared to floating the back gate. The experimental results can be well explained by electrostatic simulation using COMSOL. Our technique offers a simple method for local tuning of charge density of graphene nanodevices while avoiding coating graphene surface with dielectrics, which may cause contamination and degradation of graphene.

  13. Anisotropies in magnetic field evolution and local Lyapunov exponents

    SciTech Connect

    Tang, X.Z.; Boozer, A.H.

    2000-01-13

    The natural occurrence of small scale structures and the extreme anisotropy in the evolution of a magnetic field embedded in a conducting flow is interpreted in terms of the properties of the local Lyapunov exponents along the various local characteristic (un)stable directions for the Lagrangian flow trajectories. The local Lyapunov exponents and the characteristic directions are functions of Lagrangian coordinates and time, which are completely determined once the flow field is specified. The characteristic directions that are associated with the spatial anisotropy of the problem, are prescribed in both Lagrangian and Eulerian frames. Coordinate transformation techniques are employed to relate the spatial distributions of the magnetic field, the induced current density, and the Lorentz force, which are usually followed in Eulerian frame, to those of the local Lyapunov exponents, which are naturally defined in Lagrangian coordinates.

  14. Local versus average field failure criterion in amorphous polymers

    NASA Astrophysics Data System (ADS)

    Xie, Yuesong; Mao, Yunzhe; Sun, Lin; Koslowski, Marisol

    2015-03-01

    There is extensive work developing laws that predict yielding in amorphous polymers, ranging from the pioneer experimental work of Sternstein et al (1968 Appl. Polym. Symp. 7 175-99) to the novel molecular dynamics simulations of Jaramillo et al (2012 Phys. Rev. B 85 024114). While atomistic models render damage criteria in terms of local values of the stress and strain fields, experiments provide yield conditions in terms of the average values of these fields. Unfortunately, it is not possible to compare these results due to the differences in time and length scales. Here, we use a micromechanical phase-field damage model with parameters calculated from atomistic simulations to connect atomistic and macroscopic scale experiments. The phase-field damage model is used to study failure in composite materials. We find that the yield criterion should be described in terms of local stress and strains fields and cannot be extended directly from applied stress field values to determine yield conditions.

  15. Local and nonlocal parallel heat transport in general magnetic fields

    SciTech Connect

    Del-Castillo-Negrete, Diego B; Chacon, Luis

    2011-01-01

    A novel approach for the study of parallel transport in magnetized plasmas is presented. The method avoids numerical pollution issues of grid-based formulations and applies to integrable and chaotic magnetic fields with local or nonlocal parallel closures. In weakly chaotic fields, the method gives the fractal structure of the devil's staircase radial temperature profile. In fully chaotic fields, the temperature exhibits self-similar spatiotemporal evolution with a stretched-exponential scaling function for local closures and an algebraically decaying one for nonlocal closures. It is shown that, for both closures, the effective radial heat transport is incompatible with the quasilinear diffusion model.

  16. Bulk from bi-locals in Thermo field CFT

    DOE PAGES

    Jevicki, Antal; Yoon, Junggi

    2016-02-15

    For this research, we study the Large N dynamics of the O(N) field theory in the Thermo field dynamics approach. The question of recovering the high temperature phase and the corresponding O(N) gauging is clarified. Through the associated bi-local representation we discuss the emergent bulk space-time and construction of (Higher spin) fields. In addition, we note the presence of ‘evanescent’ modes in this construction and also the mixing of spins at finite temperature.

  17. Generalized conservation laws in non-local field theories

    NASA Astrophysics Data System (ADS)

    Kegeles, Alexander; Oriti, Daniele

    2016-04-01

    We propose a geometrical treatment of symmetries in non-local field theories, where the non-locality is due to a lack of identification of field arguments in the action. We show that the existence of a symmetry of the action leads to a generalized conservation law, in which the usual conserved current acquires an additional non-local correction term, obtaining a generalization of the standard Noether theorem. We illustrate the general formalism by discussing the specific physical example of complex scalar field theory of the type describing the hydrodynamic approximation of Bose-Einstein condensates. We expect our analysis and results to be of particular interest for the group field theory formulation of quantum gravity.

  18. Localized electron heating by strong guide-field magnetic reconnection

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Inomoto, Michiaki; Sugawara, Takumichi; Yamasaki, Kotaro; Ushiki, Tomohiko; Ono, Yasushi

    2015-10-01

    Localized electron heating of magnetic reconnection was studied under strong guide-field using two merging spherical tokamak plasmas in the University of Tokyo Spherical Tokamak experiment. Our new slide-type two-dimensional Thomson scattering system is documented for the first time the electron heating localized around the X-point. Shape of the high electron temperature area does not agree with that of energy dissipation term Et.jt . If we include a guide-field effect term Bt/(Bp+αBt) for Et.jt , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point.

  19. Monopole and dipole estimation for multi-frequency sky maps by linear regression

    NASA Astrophysics Data System (ADS)

    Wehus, I. K.; Fuskeland, U.; Eriksen, H. K.; Banday, A. J.; Dickinson, C.; Ghosh, T.; Górski, K. M.; Lawrence, C. R.; Leahy, J. P.; Maino, D.; Reich, P.; Reich, W.

    2017-01-01

    We describe a simple but efficient method for deriving a consistent set of monopole and dipole corrections for multi-frequency sky map data sets, allowing robust parametric component separation with the same data set. The computational core of this method is linear regression between pairs of frequency maps, often called T-T plots. Individual contributions from monopole and dipole terms are determined by performing the regression locally in patches on the sky, while the degeneracy between different frequencies is lifted whenever the dominant foreground component exhibits a significant spatial spectral index variation. Based on this method, we present two different, but each internally consistent, sets of monopole and dipole coefficients for the nine-year WMAP, Planck 2013, SFD 100 μm, Haslam 408 MHz and Reich & Reich 1420 MHz maps. The two sets have been derived with different analysis assumptions and data selection, and provide an estimate of residual systematic uncertainties. In general, our values are in good agreement with previously published results. Among the most notable results are a relative dipole between the WMAP and Planck experiments of 10-15μK (depending on frequency), an estimate of the 408 MHz map monopole of 8.9 ± 1.3 K, and a non-zero dipole in the 1420 MHz map of 0.15 ± 0.03 K pointing towards Galactic coordinates (l,b) = (308°,-36°) ± 14°. These values represent the sum of any instrumental and data processing offsets, as well as any Galactic or extra-Galactic component that is spectrally uniform over the full sky.

  20. Vortex configuration in the presence of local magnetic field and locally applied stress

    NASA Astrophysics Data System (ADS)

    Wissberg, Shai; Kremen, Anna; Shperber, Yishai; Kalisky, Beena

    2017-02-01

    Vortex configuration is determined by the repulsive interaction, which becomes dominant with increasing vortex density, by the pinning potential, and by other considerations such as the local magnetic fields, currents flowing in the sample, or as we showed recently, by local stress applied on the sample. In this work we describe different ways to control vortex configuration using scanning SQUID microscopy.

  1. Detection of oyster habitat in tidal flats using multi-frequency polarimetric SAR data

    NASA Astrophysics Data System (ADS)

    Choe, Byung-Hun; Kim, Duk-jin; Hwang, Ji-Hwan; Oh, Yisok; Moon, Wooil M.

    2012-01-01

    Exposed oyster reefs in tidal flats have complex and rough surfaces because of their unique surface texture, which are quite distinct from the surrounding mud or sand flats. Here we investigate the microwave signatures, backscattered from naturally distributed oyster reefs in tidal flats, utilizing the polarimetric analysis techniques to fully polarimetric RADARSAT-2 (C-band) and ALOS PALSAR (L-band) data. The study areas include the tidal flats around Jebu Island and Hampyung Bay on the west coast of the Korean peninsula. We analyzed the microwave scattering mechanisms associated with oyster reefs and surrounding areas using the polarimetric target decomposition theorem and quantitatively measu ρHHVV red target depolarization effects (the cross-polarized ratio (HV/VV), the co-polarized correlation coefficient ( ρHHVV), and the co-polarized phase difference between HH and VV). On the basis of a large increase in the cross-polarized backscattering (HV) in the C-band SAR data, one can observe strong volume (or multiple) scattering and depolarization effects over oyster reefs areas, whereas only surface scattering was dominant in most parts of the background tidal areas. In oyster reefs, the proportion of volume scattering and the cross-polarized ratio were greater than 0.7 and -8 dB, respectively. These scattering characteristics were also verified from in-situ measurements in the field using a ground-based polarimetric scatterometer system. However, almost no difference was observed between the scattering signatures of oyster reefs and background mudflat areas from L-band data, which have a considerably longer wavelength than C-band. The study clearly suggests that multi-frequency (C- and L-band) polarimetric SAR systems can be used to detect the naturally distributed oyster reefs in tidal flats.

  2. THE DOUBLE PULSAR ECLIPSES. I. PHENOMENOLOGY AND MULTI-FREQUENCY ANALYSIS

    SciTech Connect

    Breton, R. P.; Kaspi, V. M.; McLaughlin, M. A.; Lyutikov, M.; Kramer, M.; Stairs, I. H.; Ransom, S. M.; Ferdman, R. D.; Camilo, F.; Possenti, A.

    2012-03-10

    The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise around conjunction when the radio waves emitted by pulsar A are absorbed as they propagate through the magnetosphere of its companion pulsar B. These eclipses offer a unique opportunity to directly probe the magnetospheric structure and the plasma properties of pulsar B. We have performed a comprehensive analysis of the eclipse phenomenology using multi-frequency radio observations obtained with the Green Bank Telescope. We have characterized the periodic flux modulations previously discovered at 820 MHz by McLaughlin et al. and investigated the radio frequency dependence of the duration and depth of the eclipses. Based on their weak radio frequency evolution, we conclude that the plasma in pulsar B's magnetosphere requires a large multiplicity factor ({approx}10{sup 5}). We also found that, as expected, flux modulations are present at all radio frequencies in which eclipses can be detected. Their complex behavior is consistent with the confinement of the absorbing plasma in the dipolar magnetic field of pulsar B as suggested by Lyutikov and Thompson and such a geometric connection explains that the observed periodicity is harmonically related to pulsar B's spin frequency. We observe that the eclipses require a sharp transition region beyond which the plasma density drops off abruptly. Such a region defines a plasmasphere that would be well inside the magnetospheric boundary of an undisturbed pulsar. It is also two times smaller than the expected standoff radius calculated using the balance of the wind pressure from pulsar A and the nominally estimated magnetic pressure of pulsar B.

  3. Localized Dictionaries Based Orientation Field Estimation for Latent Fingerprints.

    PubMed

    Xiao Yang; Jianjiang Feng; Jie Zhou

    2014-05-01

    Dictionary based orientation field estimation approach has shown promising performance for latent fingerprints. In this paper, we seek to exploit stronger prior knowledge of fingerprints in order to further improve the performance. Realizing that ridge orientations at different locations of fingerprints have different characteristics, we propose a localized dictionaries-based orientation field estimation algorithm, in which noisy orientation patch at a location output by a local estimation approach is replaced by real orientation patch in the local dictionary at the same location. The precondition of applying localized dictionaries is that the pose of the latent fingerprint needs to be estimated. We propose a Hough transform-based fingerprint pose estimation algorithm, in which the predictions about fingerprint pose made by all orientation patches in the latent fingerprint are accumulated. Experimental results on challenging latent fingerprint datasets show the proposed method outperforms previous ones markedly.

  4. Multi-Frequency Soliton Complex in Er/Yb-Doped Fiber Amplifier

    NASA Technical Reports Server (NTRS)

    Kang, Jin U.; Kim, Do-Hyun; Khurgin, Jacob B.; Akhmediev, Nail N.; Han, Haewook; Shaw, Harry; Day, John H. (Technical Monitor)

    2001-01-01

    We experimentally investigated presence of multi-frequency soliton complex that exist in high power Er/Yb-doped Fiber Amplifier. The complex with the spectral bandwidth in excess of 100 nm is bound by the Kerr nonlinearity and exhibit stable propagation.

  5. THE PLANCHEREL FORMULA FOR SL(2) OVER A LOCAL FIELD*

    PubMed Central

    Sally, P. J.; Shalika, J. A.

    1969-01-01

    More than two decades ago, in his classical paper on the irreducible unitary representations of the Lorentz group, V. Bargmann initiated the concrete study of Fourier analysis on real Lie groups and obtained the analogue of the classical Fourier expansion theorem in the case of the Lorentz group. Since then the general theory for real semisimple Lie groups has been extensively developed, chiefly through the work of Harish-Chandra. More generally, one may consider groups defined by algebraic equations over locally compact fields, in particular local fields, and ask for an explicit Fourier expansion formula. In the present article the authors obtain this formula for the group SL(2). PMID:16591775

  6. Locally oriented potential field for controlling multi-robots

    NASA Astrophysics Data System (ADS)

    Romero, Roseli A. F.; Prestes, Edson; Idiart, Marco A. P.; Faria, Gedson

    2012-12-01

    In this paper, we present an extension of the boundary value problem path planner (BVP PP) to control multiple robots in a robot soccer scenario. This extension is called Locally Oriented Potential Field (LOPF) and computes a potential field from the numerical solution of a BVP using local relaxations in different patches of the solution space. This permits that a single solution of the BVP endows distinct robots with different behaviors in a team. We present the steps to implement LOPF as well as several results obtained in simulation.

  7. Field Theory Approach to Many-Body Localization

    NASA Astrophysics Data System (ADS)

    Altland, Alexander; Micklitz, Tobias

    2017-03-01

    We introduce an analytic approach to many-body localization (MBL) in random spin chains. We consider MBL within a first quantized framework where it becomes a localization phenomenon in the high-dimensional lattice defined by the Hilbert space of the clean system. Designed in analogy with the field-theory description of single particle localization, our approach describes wave package propagation on that lattice after a disorder average has been performed and the system is controlled by only a few universal parameters. We discuss the stability of an ergodic weak disorder and a localized strong disorder phase, respectively, and demonstrate that the latter is protected by mechanisms which put MBL outside the universality class of Anderson localization.

  8. Localized Electron Heating by Strong Guide-Field Magnetic Reconnection

    NASA Astrophysics Data System (ADS)

    Guo, Xuehan; Sugawara, Takumichi; Inomoto, Michiaki; Yamasaki, Kotaro; Ono, Yasushi; UTST Team

    2015-11-01

    Localized electron heating of magnetic reconnection was studied under strong guide-field (typically Bt 15Bp) using two merging spherical tokamak plasmas in Univ. Tokyo Spherical Tokamak (UTST) experiment. Our new slide-type two-dimensional Thomson scattering system documented for the first time the electron heating localized around the X-point. The region of high electron temperature, which is perpendicular to the magnetic field, was found to have a round shape with radius of 2 [cm]. Also, it was localized around the X-point and does not agree with that of energy dissipation term Et .jt . When we include a guide-field effect term Bt / (Bp + αBt) for Et .jt where α =√{ (vin2 +vout2) /v∥2 } , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus,'' a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) Fellows 15J03758.

  9. Ion beams extraction and measurements of plasma parameters on a multi-frequencies microwaves large bore ECRIS with permanent magnets

    SciTech Connect

    Nozaki, Dai; Kiriyama, Ryutaro; Takenaka, Tomoya; Kurisu, Yosuke; Yano, Keisuke; Sato, Fuminobu; Kato, Yushi; Iida, Toshiyuki

    2012-11-06

    We have developed an all-permanent magnet large bore electron cyclotron resonance ion source (ECRIS) for broad ion beam processing. The cylindrically comb-shaped magnetic field configuration is adopted for efficient plasma production and good magnetic confinement. To compensate for disadvantages of fixed magnetic configuration, a traveling wave tube amplifier (TWTA) is used. In the comb-shaped ECRIS, it is difficult to achieve controlling ion beam profiles in the whole inside the chamber by using even single frequency-controllable TWTA (11-13GHz), because of large bore size with all-magnets. We have tried controlling profiles of plasma parameters and then those of extracted ion beams by launching two largely different frequencies simultaneously, i.e., multi-frequencies microwaves. Here we report ion beam profiles and corresponding plasma parameters under various experimental conditions, dependence of ion beams against extraction voltages, and influence of different electrode positions on the electron density profile.

  10. Wedge-local quantum fields on a nonconstant noncommutative spacetime

    SciTech Connect

    Much, A.

    2012-08-15

    Within the framework of warped convolutions we deform the massless free scalar field. The deformation is performed by using the generators of the special conformal transformations. The investigation shows that the deformed field turns out to be wedge-local. Furthermore, it is shown that the spacetime induced by the deformation with the special conformal operators is nonconstant noncommutative. The noncommutativity is obtained by calculating the deformed commutator of the coordinates.

  11. Local approximations for effective scalar field equations of motion

    NASA Astrophysics Data System (ADS)

    Berera, Arjun; Moss, Ian G.; Ramos, Rudnei O.

    2007-10-01

    Fluctuation and dissipation dynamics is examined at all temperature ranges for the general case of a background time evolving scalar field coupled to heavy intermediate quantum fields which in turn are coupled to light quantum fields. The evolution of the background field induces particle production from the light fields through the action of the intermediate catalyzing heavy fields. Such field configurations are generically present in most particle physics models, including grand unified and supersymmetry theories, with application of this mechanism possible in inflation, heavy ion collision, and phase transition dynamics. The effective evolution equation for the background field is obtained and a fluctuation-dissipation theorem is derived for this system. The effective evolution, in general, is nonlocal in time. Appropriate conditions are found for when these time nonlocal effects can be approximated by local terms. Here careful distinction is made between a local expansion and the special case of a derivative expansion to all orders, which requires analytic behavior of the evolution equation in Fourier space.

  12. Formation of the residual stress field under local thermal actions

    NASA Astrophysics Data System (ADS)

    Burenin, A. A.; Dats, E. P.; Murashkin, E. V.

    2014-03-01

    The one-dimensional process of material deformation due to local heating and subsequent cooling is analyzed in the framework of the classical theory of elastoplastic deformations. The problem of formation of residual stresses in a thin plate made of an elastoplastic material under a given thermal action is solved. The graphs of fields of residual stresses and displacements are constructed.

  13. Convective Flow Induced by Localized Traveling Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Mazuruk, Konstantin; Rose, M. Franklin (Technical Monitor)

    2001-01-01

    An axisymmetric traveling magnetic field induces a meridional base flow in a cylindrical zone of an electrically conducting liquid. This remotely induced flow can be conveniently controlled, in magnitude and direction, and can have benefits for crystal growth applications. In particular, it can be used to offset natural convection. For long vertical cylinders, non-uniform and localized in the propagating direction, magnetic fields are required for this purpose. Here we investigate a particular form of this field, namely that induced by a set of a few electric current coils. An order of magnitude reduction of buoyancy convection is theoretically demonstrated for a vertical Bridgman crystal growth configuration.

  14. Locally smeared operator product expansions in scalar field theory

    DOE PAGES

    Monahan, Christopher; Orginos, Kostas

    2015-04-01

    We propose a new locally smeared operator product expansion to decompose non-local operators in terms of a basis of smeared operators. The smeared operator product expansion formally connects nonperturbative matrix elements determined numerically using lattice field theory to matrix elements of non-local operators in the continuum. These nonperturbative matrix elements do not suffer from power-divergent mixing on the lattice, which significantly complicates calculations of quantities such as the moments of parton distribution functions, provided the smearing scale is kept fixed in the continuum limit. The presence of this smearing scale complicates the connection to the Wilson coefficients of the standardmore » operator product expansion and requires the construction of a suitable formalism. We demonstrate the feasibility of our approach with examples in real scalar field theory.« less

  15. Locally smeared operator product expansions in scalar field theory

    SciTech Connect

    Monahan, Christopher; Orginos, Kostas

    2015-04-01

    We propose a new locally smeared operator product expansion to decompose non-local operators in terms of a basis of smeared operators. The smeared operator product expansion formally connects nonperturbative matrix elements determined numerically using lattice field theory to matrix elements of non-local operators in the continuum. These nonperturbative matrix elements do not suffer from power-divergent mixing on the lattice, which significantly complicates calculations of quantities such as the moments of parton distribution functions, provided the smearing scale is kept fixed in the continuum limit. The presence of this smearing scale complicates the connection to the Wilson coefficients of the standard operator product expansion and requires the construction of a suitable formalism. We demonstrate the feasibility of our approach with examples in real scalar field theory.

  16. Localization of vector field on dynamical domain wall

    NASA Astrophysics Data System (ADS)

    Higuchi, Masafumi; Nojiri, Shin'ichi

    2017-03-01

    In the previous works (arxiv:arXiv:1202.5375 and arxiv:arXiv:1402.1346), the dynamical domain wall, where the four dimensional FRW universe is embedded in the five dimensional space-time, has been realized by using two scalar fields. In this paper, we consider the localization of vector field in three formulations. The first formulation was investigated in the previous paper (arxiv:arXiv:1510.01099) for the U (1) gauge field. In the second formulation, we investigate the Dvali-Shifman mechanism (arxiv:arXiv:hep-th/9612128), where the non-abelian gauge field is confined in the bulk but the gauge symmetry is spontaneously broken on the domain wall. In the third formulation, we investigate the Kaluza-Klein modes coming from the five dimensional graviton. In the Randall-Sundrum model, the graviton was localized on the brane. We show that the (5 , μ) components (μ = 0 , 1 , 2 , 3) of the graviton are also localized on the domain wall and can be regarded as the vector field on the domain wall. There are, however, some corrections coming from the bulk extra dimension if the domain wall universe is expanding.

  17. Quantum entanglement of local operators in conformal field theories.

    PubMed

    Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi

    2014-03-21

    We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including Einstein-Podolsky-Rosen states. They agree with a heuristic picture of propagations of entangled particles.

  18. Quantum Entanglement of Local Operators in Conformal Field Theories

    NASA Astrophysics Data System (ADS)

    Nozaki, Masahiro; Numasawa, Tokiro; Takayanagi, Tadashi

    2014-03-01

    We introduce a series of quantities which characterize a given local operator in any conformal field theory from the viewpoint of quantum entanglement. It is defined by the increased amount of (Rényi) entanglement entropy at late time for an excited state defined by acting the local operator on the vacuum. We consider a conformal field theory on an infinite space and take the subsystem in the definition of the entanglement entropy to be its half. We calculate these quantities for a free massless scalar field theory in two, four and six dimensions. We find that these results are interpreted in terms of quantum entanglement of a finite number of states, including Einstein-Podolsky-Rosen states. They agree with a heuristic picture of propagations of entangled particles.

  19. Dynamic-local-field approximation for the quantum solids

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Danilowicz, R. L.

    1974-01-01

    A local-molecular-field description for the ground-state properties of the quantum solids is presented. The dynamical behavior of atoms contributing to the local field, which acts on an arbitrary pair of test particles, is incorporated by decoupling the pair correlations between these field atoms. The energy, pressure, compressibility, single-particle-distribution function, and the rms atomic deviations about the equilibrium lattice sites are calculated for H2, He-3, and He-4 over the volume range from 5 to 24.5 cu cm/mole. The results are in close agreement with existing Monte Carlo calculations wherever comparisons are possible. At very high pressure, the results agree with simplified descriptions which depend on negligible overlap of the system wave function between neighboring lattice sites.

  20. Light scattering, field localization and local density of states in co-axial plasmonic nanowires.

    PubMed

    Lawrence, Nate; Dal Negro, Luca

    2010-07-19

    Based on analytical scattering theory, we develop a multipolar expansion method to investigate systematically the near-field enhancement, far-field scattering and Local Density of States (LDOS) spectra in concentric metal-insulator-metal (MIM) cylindrical nanostructures, or coaxial plasmonic nanowires (CPNs). We demonstrate that these structures support distinctive plasmonic resonances with strongly reduced scattering in the far-field zone and significant electric field enhancement in deep sub-wavelength dielectric regions. Additionally, we study systematically the effects of geometrical parameters and dielectric index on the near-field and far-field plasmonic response of CPNs in the visible and near infrared spectral range. Finally, we demonstrate that CPNs provide a convenient approach for engineering strong (almost three orders of magnitude) LDOS enhancement in sub-wavelength dielectric gaps at multiple frequencies. These results enable the engineering of multiband optical detectors and CPNs-based light emitters with simultaneously enhanced excitation and emission rates for nanoplasmonics.

  1. Localization of disordered bosons and magnets in random fields

    SciTech Connect

    Yu, Xiaoquan; Müller, Markus

    2013-10-15

    We study localization properties of disordered bosons and spins in random fields at zero temperature. We focus on two representatives of different symmetry classes, hard-core bosons (XY magnets) and Ising magnets in random transverse fields, and contrast their physical properties. We describe localization properties using a locator expansion on general lattices. For 1d Ising chains, we find non-analytic behavior of the localization length as a function of energy at ω=0, ξ{sup −1}(ω)=ξ{sup −1}(0)+A|ω|{sup α}, with α vanishing at criticality. This contrasts with the much smoother behavior predicted for XY magnets. We use these results to approach the ordering transition on Bethe lattices of large connectivity K, which mimic the limit of high dimensionality. In both models, in the paramagnetic phase with uniform disorder, the localization length is found to have a local maximum at ω=0. For the Ising model, we find activated scaling at the phase transition, in agreement with infinite randomness studies. In the Ising model long range order is found to arise due to a delocalization and condensation initiated at ω=0, without a closing mobility gap. We find that Ising systems establish order on much sparser (fractal) subgraphs than XY models. Possible implications of these results for finite-dimensional systems are discussed. -- Highlights: •Study of localization properties of disordered bosons and spins in random fields. •Comparison between XY magnets (hard-core bosons) and Ising magnets. •Analysis of the nature of the magnetic transition in strong quenched disorder. •Ising magnets: activated scaling, no closing mobility gap at the transition. •Ising order emerges on sparser (fractal) support than XY order.

  2. Spectral investigation of nonlinear local field effects in Ag nanoparticles

    SciTech Connect

    Sato, Rodrigo Takeda, Yoshihiko; Ohnuma, Masato; Oyoshi, Keiji

    2015-03-21

    The capability of Ag nanoparticles to modulate their optical resonance condition, by optical nonlinearity, without an external feedback system was experimentally demonstrated. These optical nonlinearities were studied in the vicinity of the localized surface plasmon resonance (LSPR), using femtosecond pump-and-probe spectroscopy with a white-light continuum probe. Transient transmission changes ΔT/T exhibited strong photon energy and particle size dependence and showed a complex and non-monotonic change with increasing pump light intensity. Peak position and change of sign redshift with increasing pump light intensity demonstrate the modulation of the LSPR. These features are discussed in terms of the intrinsic feedback via local field enhancement.

  3. Multi-frequency Imaging Algorithms and Simulation of Space VLBI Using the VLA

    NASA Astrophysics Data System (ADS)

    Likhachev, S.; Kogan, L.; Fomalont, E.; Owen, F.

    2009-08-01

    New Multi-Frequency Synthesis (MFS) algorithms were developed and implemented in the Astro Space Locator (ASL) operating under MS Windows system. In November 2005 multi-frequency VLA observations of the radio source M87 were carried out at the following frequencies: 14.7, 15.2 21.3, 22.2, 23.0, and 23.4 GHz. We used the new MFS algorithms to determine the structure of M87 at the central frequency (19 GHz) and obtained both the image and spectral index map of the source. Comparison with more straight-forward imaging techniques (with single frequency images) shows that the new MFS algorithms increase the fidelity of the image by at least a factor of two and provides accurate spectral indices across the emission. Application to simulated Radioastron data is also shown.

  4. Multi-Frequency Target Detection Techniques for DVB-T Based Passive Radar Sensors

    PubMed Central

    Martelli, Tatiana; Colone, Fabiola; Tilli, Enrico; Di Lallo, Annarita

    2016-01-01

    This paper investigates the possibility to improve target detection capability in a DVB-T- based passive radar sensor by jointly exploiting multiple digital television channels broadcast by the same transmitter of opportunity. Based on the remarkable results obtained by such a multi-frequency approach using other signals of opportunity (i.e., FM radio broadcast transmissions), we propose appropriate modifications to the previously devised signal processing techniques for them to be effective in the newly considered scenarios. The resulting processing schemes are extensively applied against experimental DVB-T-based passive radar data pertaining to different surveillance applications. The obtained results clearly show the effectiveness of the proposed multi-frequency approaches and demonstrate their suitability for application in the considered scenarios. PMID:27690036

  5. Multi-Frequency Target Detection Techniques for DVB-T Based Passive Radar Sensors.

    PubMed

    Martelli, Tatiana; Colone, Fabiola; Tilli, Enrico; Di Lallo, Annarita

    2016-09-28

    This paper investigates the possibility to improve target detection capability in a DVB-T- based passive radar sensor by jointly exploiting multiple digital television channels broadcast by the same transmitter of opportunity. Based on the remarkable results obtained by such a multi-frequency approach using other signals of opportunity (i.e., FM radio broadcast transmissions), we propose appropriate modifications to the previously devised signal processing techniques for them to be effective in the newly considered scenarios. The resulting processing schemes are extensively applied against experimental DVB-T-based passive radar data pertaining to different surveillance applications. The obtained results clearly show the effectiveness of the proposed multi-frequency approaches and demonstrate their suitability for application in the considered scenarios.

  6. OCT based on multi-frequency sweeping Fizeau interferometer with phase modulating method

    NASA Astrophysics Data System (ADS)

    Choi, S.; Watanabe, T.; Sasaki, O.; Suzuki, T.

    2013-09-01

    The Multi-frequency sweeping Fizeau-type interferometer (MFS-FI) for optical coherence tomography (OCT) is demonstrated. The multi-frequency sweeping by a variable Fabry-Perot filter permits detection of high-order low-coherence interferometric signals in the Fizeau interferometer. The sinusoidal phase modulation technique was utilized to detect accurate interference amplitude and phase distributions of back scattered light from surfaces of a sample. OCT measurements by the MFS-FI were conducted for vibrating glass plates with a frequency of 1 kHz, and cellular tissues fixed with formalin and embedded in paraffin. The tomographic 3-dimensional volume and cross-sectional surface displacements were detected with an accuracy of nano-meters.

  7. Analysis of photonic crystal and multi-frequency terahertz microstrip patch antenna

    NASA Astrophysics Data System (ADS)

    Yang, Lechen; Shi, Xueshun; Chen, Kunfeng; Fu, Kai; Zhang, Baoshun

    2013-12-01

    In this paper, two-dimensional photonic crystals working at terahertz (THz) frequency is analyzed, a multi-frequency terahertz microstrip patch antenna on photonic crystal substrate is presented and its electromagnetic wave propagation phenomenon is investigated. The proposed antenna can work at five frequency points' scope at terahertz frequency regions, and the radiation efficiency is as high as ~96%. The photonic crystal structure of the substrate is used to enhance the gain, directivity and radiation efficiency of the antenna.

  8. A Kernel Machine Framework for Feature Optimization in Multi-frequency Sonar Imagery

    DTIC Science & Technology

    2006-09-01

    best performance with the fewest number of basis Table III OBJECT MEASUREMENTS USED TO CONSTRUCT FEATURES Textural Measurements GLCM Contrast...each object in each image, 17 measurements are made and used to construct the features . Of these 17 measurements, 5 are textural based and are...A Kernel Machine Framework for Feature Optimization in Multi-frequency Sonar Imagery J.R. Stack and R. Arrieta Naval Surface Warfare Center

  9. Reconstruction of Flaw Profiles Using Neural Networks and Multi-Frequency Eddy Current System

    SciTech Connect

    Chady, T.; Caryk, M.

    2005-04-09

    The objective of this paper is to identify profiles of flaws in conducting plates. To solve this problem, application of a multi-frequency eddy current system (MFES) and artificial neural networks is proposed. Dynamic feed-forward neural networks with various architectures are investigated. Extended experiments with all neural models are carried out in order to select the most promising configuration. Data utilized for the experiments were obtained from the measurements performed on the Inconel plates with EDM flaws.

  10. Classifying multi-frequency fisheries acoustic data using a robust probabilistic classification technique.

    PubMed

    Anderson, C I H; Horne, J K; Boyle, J

    2007-06-01

    A robust probabilistic classification technique, using expectation maximization of finite mixture models, is used to analyze multi-frequency fisheries acoustic data. The number of clusters is chosen using the Bayesian Information Criterion. Probabilities of membership to clusters are used to classify each sample. The utility of the technique is demonstrated using two examples: the Gulf of Alaska representing a low-diversity, well-known system; and the Mid-Atlantic Ridge, a species-rich, relatively unknown system.

  11. Fermion localization and resonances on two-field thick branes

    SciTech Connect

    Almeida, C. A. S.; Casana, R.; Ferreira, M. M. Jr.; Gomes, A. R.

    2009-06-15

    We consider (4, 1)-dimensional branes constructed with two scalar fields {phi} and {chi} coupled to a Dirac spinor field by means of a general Yukawa coupling. The equation of motion for the coefficients of the chiral decomposition of the spinor in curved spacetime leads to a Schroedinger-like equation whose solutions allow to obtain the masses of the fermionic modes. The simplest Yukawa coupling {psi}{phi}{chi}{psi} is considered for the Bloch brane model and fermion localization is studied. We found resonances for both chiralities and related their appearance to branes with internal structure.

  12. Near-field beamforming analysis for acoustic emission source localization.

    PubMed

    He, Tian; Pan, Qiang; Liu, Yaoguang; Liu, Xiandong; Hu, Dayong

    2012-07-01

    This paper attempts to introduce a near-field acoustic emission (AE) beamforming method to estimate the AE source locations by using a small array of sensors closely placed in a local region. The propagation characteristics of AE signals are investigated based on guided wave theory to discuss the feasibility of using beamforming techniques in AE signal processing. To validate the effectiveness of the AE beamforming method, a series of pencil lead break tests at various regions of a thin steel plate are conducted. The potential of this method for engineering applications are explored through rotor-stator rubbing tests. The experimental results demonstrate that the proposed method can effectively determine the region where rubbing occurs. It is expected that the work of this paper may provide a helpful analysis tool for near-field AE source localization.

  13. Fatigue crack localization with near-field acoustic emission signals

    NASA Astrophysics Data System (ADS)

    Zhou, Changjiang; Zhang, Yunfeng

    2013-04-01

    This paper presents an AE source localization technique using near-field acoustic emission (AE) signals induced by crack growth and propagation. The proposed AE source localization technique is based on the phase difference in the AE signals measured by two identical AE sensing elements spaced apart at a pre-specified distance. This phase difference results in canceling-out of certain frequency contents of signals, which can be related to AE source direction. Experimental data from simulated AE source such as pencil breaks was used along with analytical results from moment tensor analysis. It is observed that the theoretical predictions, numerical simulations and the experimental test results are in good agreement. Real data from field monitoring of an existing fatigue crack on a bridge was also used to test this system. Results show that the proposed method is fairly effective in determining the AE source direction in thick plates commonly encountered in civil engineering structures.

  14. Multi-frequency AOM for multi-beam laser scanning exposure system

    NASA Astrophysics Data System (ADS)

    Shinada, Hidetoshi

    2016-10-01

    Digital printing systems recorded on films or computer to plates (CTPs) have been required to improve their productivity and image quality. Under the circumstance, a printing technology of the multi-beam laser scanning for the drum capstan system, which is almost the same as optics configuration as the flat bed system, was developed using a newly developed multi-frequency acousto-optic modulator (AOM) as a key device instead of ultra-fast scanning devices toward a main scan direction. The multi-frequency AOM was developed with phased array-type transducers, achieving a wider bandwidth of over 160 MHz. The design consisted of a simultaneous three beams generation with interlace scan to avoid the beat effect by adjacent Doppler-shifted beams, which consequently attained the fastest recording speed of 5.0 mm/s compared with 2.0-3.0 mm/s of existing systems in those days. Furthermore, a couple of critical parameters of the multi-frequency AOM are studied, for example, a treatment of third-order intermodulation and also beat effect in connection with photosensitive media. As a result, the necessity of interlaces scanning to obtain good image quality without beat effect and also to allow a lower laser power to apply is proposed.

  15. A practical implementation of multi-frequency widefield frequency-domain FLIM

    PubMed Central

    Chen, Hongtao

    2013-01-01

    Widefield frequency-domain fluorescence lifetime imaging microscopy (FD-FLIM) is a fast and accurate method to measure the fluorescence lifetime, especially in kinetic studies in biomedical researches. However, the small range of modulation frequencies available in commercial instruments makes this technique limited in its applications. Here we describe a practical implementation of multi-frequency widefield FD-FLIM using a pulsed supercontinuum laser and a direct digital synthesizer. In this instrument we use a pulse to modulate the image intensifier rather than the more conventional sine wave modulation. This allows parallel multi-frequency FLIM measurement using the Fast Fourier Transform and the cross-correlation technique, which permits precise and simultaneous isolation of individual frequencies. In addition, the pulse modulation at the cathode of image intensifier restored the loss of optical resolution caused by the defocusing effect when the voltage at the cathode is sinusoidally modulated. Furthermore, in our implementation of this technique, data can be graphically analyzed by the phasor method while data are acquired, which allows easy fit-free lifetime analysis of FLIM images. Here our measurements of standard fluorescent samples and a Föster resonance energy transfer pair demonstrate that the widefield multi-frequency FLIM system is a valuable and simple tool in fluorescence imaging studies. PMID:23296945

  16. The local dayside reconnection rate for oblique interplanetary magnetic fields

    NASA Astrophysics Data System (ADS)

    Komar, C. M.; Cassak, P. A.

    2016-06-01

    We present an analysis of local properties of magnetic reconnection at the dayside magnetopause for various interplanetary magnetic field (IMF) orientations in global magnetospheric simulations. This has heretofore not been practical because it is difficult to locate where reconnection occurs for oblique IMF, but new techniques make this possible. The approach is to identify magnetic separators, the curves separating four regions of differing magnetic topology, which map the reconnection X line. The electric field parallel to the X line is the local reconnection rate. We compare results to a simple model of local two-dimensional asymmetric reconnection. To do so, we find the plasma parameters that locally drive reconnection in the magnetosheath and magnetosphere in planes perpendicular to the X line at a large number of points along the X line. The global magnetohydrodynamic simulations are from the three-dimensional Block-Adaptive, Tree Solarwind Roe-type Upwind Scheme (BATS-R-US) code with a uniform resistivity, although the techniques described here are extensible to any global magnetospheric simulation model. We find that the predicted local reconnection rates scale well with the measured values for all simulations, being nearly exact for due southward IMF. However, the absolute predictions differ by an undetermined constant of proportionality, whose magnitude increases as the IMF clock angle changes from southward to northward. We also show similar scaling agreement in a simulation with oblique southward IMF and a dipole tilt. The present results will be an important component of a full understanding of the local and global properties of dayside reconnection.

  17. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Makarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism.We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) = (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) = (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star...

  18. New localization mechanism and Hodge duality for q -form field

    NASA Astrophysics Data System (ADS)

    Fu, Chun-E.; Liu, Yu-Xiao; Guo, Heng; Zhang, Sheng-Li

    2016-03-01

    In this paper, we investigate the problem of localization and the Hodge duality for a q -form field on a p -brane with codimension one. By a general Kaluza-Klein (KK) decomposition without gauge fixing, we obtain two Schrödinger-like equations for two types of KK modes of the bulk q -form field, which determine the localization and mass spectra of these KK modes. It is found that there are two types of zero modes (the 0-level modes): a q -form zero mode and a (q -1 )-form one, which cannot be localized on the brane at the same time. For the n -level KK modes, there are two interacting KK modes, a massive q -form KK mode and a massless (q -1 )-form one. By analyzing gauge invariance of the effective action and choosing a gauge condition, the n -level massive q -form KK mode decouples from the n -level massless (q -1 )-form one. It is also found that the Hodge duality in the bulk naturally becomes two dualities on the brane. The first one is the Hodge duality between a q -form zero mode and a (p -q -1 )-form one, or between a (q -1 )-form zero mode and a (p -q )-form one. The second duality is between two group KK modes: one is an n -level massive q -form KK mode with mass mn and an n -level massless (q -1 )-form mode; another is an n -level (p -q )-form one with the same mass mn and an n -level massless (p -q -1 )-form mode. Because of the dualities, the effective field theories on the brane for the KK modes of the two dual bulk form fields are physically equivalent.

  19. Chemical and biochemical analysis using microfluidic-localized field platforms

    NASA Astrophysics Data System (ADS)

    Sepaniak, Michael; Abu-Hatab, Nahla; Wellman, Amber; John, Joshy; Connatser, Maggie

    2007-09-01

    Microfluidics offer the advantages of multiplexed analysis on small, inexpensive platforms. We describe herein two distinct optical detection techniques that have the common point of sequestering and measuring analyte signals in highly localized EM fields. The first technique mates a microfluidic polydimethylsiloxane (PDMS) platform with colloidal-based surface enhanced Raman scattering (SERS) in order to perform parallel, high throughput vibrational spectroscopy. Spectra are acquired for analytes localized in surface plasmon fields associated with conventional and uniquely synthesized cubic silver colloids. SERS studies such as pH of the colloidal solution, and the type of colloid are used to demonstrate the efficiency and applicability of the method. In addition, a facile passive pumping method is used to deliver Ag colloids and analytes into the channels where all SERS measurements were completed under nondestructive flowing conditions. With this approach, SERS signal reproducibility was found to be better than 7%. A calibration curve for the drug mitoxantrone (resonance enhanced) was generated. The second technique seeks to integrate a passively-pumped, microfluidic, PDMS platform and planar waveguide technology, utilizing magnetic beads as solid supports for fluoro-assays with direct detection of bound analyte within the sample mixture accomplished by selectively driving functionalized beads to a localized evanescent field. Because analyte binding occurs in free solution, the reaction is not diffusion limited and, once magnetically delivered to the evanescent wave, the analyte can be detected with fewer complications arising from non-optically homogeneous, biological matrices. Additionally, the evanescent sensing surface can be easily regenerated by simply removing the bead-retaining magnetic field. Initial testing, optimization and calibration were performed using a model sandwich immunoassay system for the detection of rabbit IgG, with which we demonstrate a

  20. Multi-frequency electrical impedance tomography as a non-invasive tool to characterize and monitor crop root systems

    NASA Astrophysics Data System (ADS)

    Weigand, Maximilian; Kemna, Andreas

    2017-02-01

    A better understanding of root-soil interactions and associated processes is essential in achieving progress in crop breeding and management, prompting the need for high-resolution and non-destructive characterization methods. To date, such methods are still lacking or restricted by technical constraints, in particular the charactization and monitoring of root growth and function in the field. A promising technique in this respect is electrical impedance tomography (EIT), which utilizes low-frequency (< 1 kHz)- electrical conduction- and polarization properties in an imaging framework. It is well established that cells and cell clusters exhibit an electrical polarization response in alternating electric-current fields due to electrical double layers which form at cell membranes. This double layer is directly related to the electrical surface properties of the membrane, which in turn are influenced by nutrient dynamics (fluxes and concentrations on both sides of the membranes). Therefore, it can be assumed that the electrical polarization properties of roots are inherently related to ion uptake and translocation processes in the root systems. We hereby propose broadband (mHz to hundreds of Hz) multi-frequency EIT as a non-invasive methodological approach for the monitoring and physiological, i.e., functional, characterization of crop root systems. The approach combines the spatial-resolution capability of an imaging method with the diagnostic potential of electrical-impedance spectroscopy. The capability of multi-frequency EIT to characterize and monitor crop root systems was investigated in a rhizotron laboratory experiment, in which the root system of oilseed plants was monitored in a water-filled rhizotron, that is, in a nutrient-deprived environment. We found a low-frequency polarization response of the root system, which enabled the successful delineation of its spatial extension. The magnitude of the overall polarization response decreased along with the

  1. Acquiring local field potential information from amperometric neurochemical recordings

    PubMed Central

    Zhang, Hao; Lin, Shih-Chieh; Nicolelis, Miguel A.L.

    2009-01-01

    Simultaneous acquisition of in vivo electrophysiological and neurochemical information is essential for understanding how endogenous neurochemicals modulate the dynamics of brain activity. However, up to now such a task has rarely been accomplished due to the major technical challenge of operating two independent recording systems simultaneously in real-time. Here we propose a simpler solution for achieving this goal by using only a standard electrochemical technique - amperometry. To demonstrate its feasibility, we compared amperometric signals with simultaneously recorded local field potential (LFP) signals. We found that the high frequency component (HFC) of the amperometric signals did not reflect neurochemical fluctuations, but instead it resembled LFPs in several aspects, including: (1) coherent spectral fluctuations; (2) clear characterization of different brain states; (3) identical hippocampal theta depth profile. As such, our findings provide the first demonstration that both LFP and local neurochemical information can be simultaneously acquired from electrochemical sensors alone. PMID:19428527

  2. Reality, measurement and locality in Quantum Field Theory

    NASA Astrophysics Data System (ADS)

    Tommasini, Daniele

    2002-07-01

    It is currently believed that the local causality of Quantum Field Theory (QFT) is destroyed by the measurement process. This belief is also based on the Einstein-Podolsky-Rosen (EPR) paradox and on the so-called Bell's theorem, that are thought to prove the existence of a mysterious, instantaneous action between distant measurements. However, I have shown recently that the EPR argument is removed, in an interpretation-independent way, by taking into account the fact that the Standard Model of Particle Physics prevents the production of entangled states with a definite number of particles. This result is used here to argue in favor of a statistical interpretation of QFT and to show that it allows for a full reconciliation with locality and causality. Within such an interpretation, as Ballentine and Jarret pointed out long ago, Bell's theorem does not demonstrate any nonlocality.

  3. Localization and Dualities in Three-dimensional Superconformal Field Theories

    NASA Astrophysics Data System (ADS)

    Willett, Brian

    In this thesis we apply the technique of localization to three-dimensional N = 2 superconformal field theories. We consider both theories which are exactly superconformal, and those which are believed to flow to nontrivial superconformal fixed points, for which we consider implicitly these fixed points. We find that in such theories, the partition function and certain supersymmetric observables, such as Wilson loops, can be computed exactly by a matrix model. This matrix model consists of an integral over g , the Lie algebra of the gauge group of the theory, of a certain product of 1-loop factors and classical contributions. One can also consider a space of supersymmetric deformations of the partition function corresponding to the set of abelian global symmetries. In the second part of the thesis we apply these results to test dualities. We start with the case of ABJM theory, which is dual to M-theory on an asymptotically AdS4 x S7 background. We extract strong coupling results in the field theory, which can be compared to semiclassical, weak coupling results in the gravity theory, and a nontrivial agreement is found. We also consider several classes of dualities between two three-dimensional field theories, namely, 3D mirror symmetry, Aharony duality, and Giveon-Kutasov duality. Here the dualities are typically between the IR limits of two Yang-Mills theories, which are strongly coupled in three dimensions since Yang-Mills theory is asymptotically free here. Thus the comparison is again very nontrivial, and relies on the exactness of the localization computation. We also compare the deformed partition functions, which tests the mapping of global symmetries of the dual theories. Finally, we discuss some recent progress in the understanding of general three-dimensional theories in the form of the F-theorem, a conjectured analogy to the a-theorem in four dimensions and c-theorem in two dimensions, which is closely related to the localization computation.

  4. Investigation of nanogap localized field enhancement in gold plasmonic structures

    NASA Astrophysics Data System (ADS)

    Debu, Desalegn Tadesse; Bauman, Stephen; Saylor, Cameron; Novak, Eric; French, David; Herzog, Joseph

    2015-03-01

    Nanogaps between plasmonic structures allow confining the localized electric field with moreenhancements. Based on previously implemented two-step lithography process, we introducea nano-masking technique to fabricate nanostructrues and nanogaps for various geometrical patterns. This new method can fabricate gold nanostructures as well as nanogaps that are less than 10nm, below the limiting scale of lithography. Simulation from finite element method (FEM) shows strong gap dependence of optical properties and peak enhancement of these devices. The fabricated plasmonic nanostructure provides wide range of potential future application including highly sensitive optical antenna, surface enhanced Raman spectroscopy and biosensing.

  5. Local electric fields in optical glasses during field-assisted ionic exchanges

    NASA Astrophysics Data System (ADS)

    Lupascu, Alexandru I.; Kevorkian, Antoine P.; Cristescu, Constantin P.; Popescu, Ion M.

    2000-02-01

    We study the phenomena connected with high concentration of incoming ions emerging during field-assisted migration in otpical glass. We find that ion dynamics are very different at concentrations higher and lower than a certain parameter called the transition concentration. To explain anomalies at high ionic concentrations, we introduce a supplementary local electric field. This field opposes to the field E0 existing in the glass at all concentrations of incoming ions and is connected with a local space charge. We investigate its dependence on concentration and on E0. These effects are studied using a model with concentration-dependent diffusion coefficients and mobilities. We present a method to obtain the concentration dependence of the relevant quantities. Theoretical curves are compared with experimental results measured in usual silicate glasses, during Ag+-Na+ exchanges.

  6. Exponentially localized Wannier functions in periodic zero flux magnetic fields

    NASA Astrophysics Data System (ADS)

    De Nittis, G.; Lein, M.

    2011-11-01

    In this work, we investigate conditions which ensure the existence of an exponentially localized Wannier basis for a given periodic hamiltonian. We extend previous results [Panati, G., Ann. Henri Poincare 8, 995-1011 (2007), 10.1007/s00023-007-0326-8] to include periodic zero flux magnetic fields which is the setting also investigated by Kuchment [J. Phys. A: Math. Theor. 42, 025203 (2009), 10.1088/1751-8113/42/2/025203]. The new notion of magnetic symmetry plays a crucial rôle; to a large class of symmetries for a non-magnetic system, one can associate "magnetic" symmetries of the related magnetic system. Observing that the existence of an exponentially localized Wannier basis is equivalent to the triviality of the so-called Bloch bundle, a rank m hermitian vector bundle over the Brillouin zone, we prove that magnetic time-reversal symmetry is sufficient to ensure the triviality of the Bloch bundle in spatial dimension d = 1, 2, 3. For d = 4, an exponentially localized Wannier basis exists provided that the trace per unit volume of a suitable function of the Fermi projection vanishes. For d > 4 and d ⩽ 2m (stable rank regime) only the exponential localization of a subset of Wannier functions is shown; this improves part of the analysis of Kuchment [J. Phys. A: Math. Theor. 42, 025203 (2009), 10.1088/1751-8113/42/2/025203]. Finally, for d > 4 and d > 2m (unstable rank regime) we show that the mere analysis of Chern classes does not suffice in order to prove triviality and thus exponential localization.

  7. Influence of magnetic field on electric-field-induced local polar states in manganites

    SciTech Connect

    Mamin, R. F.; Strle, J.; Kabanov, V. V.; Kranjec, A.; Borovsak, M.; Mihailovic, D.; Bizyaev, D. A.; Yusupov, R. V.; Bukharaev, A. A.

    2015-11-09

    It is shown that creation of local charged states at the surface of the lanthanum-strontium manganite single crystals by means of bias application via a conducting atomic force microscope tip is strongly affected by magnetic field. Both a charge and a size of created structures increase significantly on application of the magnetic field during the induction. We argue that the observed phenomenon originates from a known tendency of manganites toward charge segregation and its intimate relation to magnetic ordering.

  8. Multi-frequency study of jet in HH 80-81

    NASA Astrophysics Data System (ADS)

    Pal, Sabyasachi; Chakrabarti, Sandip Kumar; Patra, Dusmanta

    2016-07-01

    We present multi-wavelength radio observation of the large radio jet from Herbig-Halo object HH 80-81 to study morphology of the jet in detail. We have combined the low frequency data of Giant Metrewave Radio Telescope (GMRT) with high frequency Jansky Very Large Array (JVLA) archival data for multi-frequency study. We have seen a highly collimated jet emitting from central source and the jet is collinear with the central source and HH 80-81. The spectrum of the source is studied in detail and we find the signature of spectral absorption towards the low frequency region.

  9. Multi-frequency acoustic metasurface for extraordinary reflection and sound focusing

    NASA Astrophysics Data System (ADS)

    Zhu, Yi-Fan; Fan, Xu-Dong; Liang, Bin; Yang, Jing; Yang, Jun; Yin, Lei-lei; Cheng, Jian-Chun

    2016-12-01

    We theoretically and numerically present the design of multi-frequency acoustic metasurfaces (MFAMs) with simple structure that can work not only at fundamental frequency, but also at their harmonic frequencies, which breaks the single frequency limitation in conventional resonance-based acoustic metasurfaces. The phase matched condition for achromatic manipulation is discussed. We demonstrate achromatic extraordinary reflection and sound focusing at 1700Hz, 3400Hz, and 5100Hz, that is, they have the same reflection direction and the same focusing position. This significant feature may pave the way to new type of acoustic metasurface, and will also extend acoustic metasurface applications to strongly nonlinear source cases.

  10. Simultaneous multi-frequency topological edge modes between one-dimensional photonic crystals.

    PubMed

    Choi, Ka Hei; Ling, C W; Lee, K F; Tsang, Y H; Fung, Kin Hung

    2016-04-01

    We show theoretically that, in the limit of weak dispersion, one-dimensional binary centrosymmetric photonic crystals can support topological edge modes in all photonic bandgaps. By analyzing their bulk band topology, these "harmonic" topological edge modes can be designed in a way that they exist at all photonic bandgaps opened at the center of the Brillouin zone, at all gaps opened at the zone boundaries, or both. The results may suggest a new approach to achieve robust multi-frequency coupled modes for applications in nonlinear photonics, such as frequency upconversion.

  11. Computed Linear/Nonlinear Acoustic Response of a Cascade for Single/Multi Frequency Excitation

    NASA Technical Reports Server (NTRS)

    Nallasamy, M.; Hixon, R.; Sawyer, S.

    2004-01-01

    This paper examines mode generation and propagation characteristics of a 2-D cascade due to incident vortical disturbances using a time domain approach. Full nonlinear Euler equations are solved employing high order accurate spatial differencing and time marching techniques. The solutions show the generation and propagation of mode orders that are expected from theory. Single frequency excitations show linear response over a wide range of amplitudes. The response for multi-frequency excitations tend to become nonlinear due to interaction between frequencies and self interaction.

  12. Towards a reference cavitating vessel Part III—design and acoustic pressure characterization of a multi-frequency sonoreactor

    NASA Astrophysics Data System (ADS)

    Wang, Lian; Memoli, Gianluca; Hodnett, Mark; Butterworth, Ian; Sarno, Dan; Zeqiri, Bajram

    2015-08-01

    A multi-frequency cavitation vessel (RV-multi) has been commissioned at the National Physical Laboratory (NPL, UK), with the aim of establishing a standard source of acoustic cavitation in water, with reference to which details of the cavitation process can be studied and cavitation measurement techniques evaluated. The vessel is a cylindrical cavity with a maximum capacity up to 17 L, and is designed to work at six frequency ranges, from 21 kHz to 136 kHz, under controlled temperature conditions. This paper discusses the design of RV-multi and reports experiments carried out to establish the reproducibility of the acoustic pressure field established within the vessel and its operating envelope, including sensitivity to aspects such as water depth and temperature. The acoustic field distribution was determined along the radial and depth directions within the vessel using a miniature hydrophone, for two input voltage levels under low power transducer excitation conditions (e.g. below the cavitation threshold). Particular care was taken in determining peak acoustic pressure locations, as these are critical for accompanying cavitation studies. Perturbations of the vessel by the measuring hydrophone were also monitored with a bottom-mounted pressure sensor.

  13. Matched field localization based on CS-MUSIC algorithm

    NASA Astrophysics Data System (ADS)

    Guo, Shuangle; Tang, Ruichun; Peng, Linhui; Ji, Xiaopeng

    2016-04-01

    The problem caused by shortness or excessiveness of snapshots and by coherent sources in underwater acoustic positioning is considered. A matched field localization algorithm based on CS-MUSIC (Compressive Sensing Multiple Signal Classification) is proposed based on the sparse mathematical model of the underwater positioning. The signal matrix is calculated through the SVD (Singular Value Decomposition) of the observation matrix. The observation matrix in the sparse mathematical model is replaced by the signal matrix, and a new concise sparse mathematical model is obtained, which means not only the scale of the localization problem but also the noise level is reduced; then the new sparse mathematical model is solved by the CS-MUSIC algorithm which is a combination of CS (Compressive Sensing) method and MUSIC (Multiple Signal Classification) method. The algorithm proposed in this paper can overcome effectively the difficulties caused by correlated sources and shortness of snapshots, and it can also reduce the time complexity and noise level of the localization problem by using the SVD of the observation matrix when the number of snapshots is large, which will be proved in this paper.

  14. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Astrophysics Data System (ADS)

    Makarov, V. V.; Murphy, D. W.

    2007-07-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (VX,VY,VZ)=(10.5,18.5,7.3)+/-0.1 km s-1 not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (VX,VY,VZ)=(9.9,15.6,6.9)+/-0.2 km s-1. The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0+/-1.4, B=-13.1+/-1.2, K=1.1+/-1.8, and C=-2.9+/-1.4 km s-1 kpc-1. The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at ~-20 km s-1 kpc-1. A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z>1 kpc), but here we surmise its existence in the thin disk at z<200 pc. The most unexpected and unexplained term within

  15. The Local Stellar Velocity Field via Vector Spherical Harmonics

    NASA Technical Reports Server (NTRS)

    Markarov, V. V.; Murphy, D. W.

    2007-01-01

    We analyze the local field of stellar tangential velocities for a sample of 42,339 nonbinary Hipparcos stars with accurate parallaxes, using a vector spherical harmonic formalism. We derive simple relations between the parameters of the classical linear model (Ogorodnikov-Milne) of the local systemic field and low-degree terms of the general vector harmonic decomposition. Taking advantage of these relationships, we determine the solar velocity with respect to the local stars of (V(sub X), V(sub Y), V(sub Z)) (10.5, 18.5, 7.3) +/- 0.1 km s(exp -1) not corrected for the asymmetric drift with respect to the local standard of rest. If only stars more distant than 100 pc are considered, the peculiar solar motion is (V(sub X), V(sub Y), V(sub Z)) (9.9, 15.6, 6.9) +/- 0.2 km s(exp -1). The adverse effects of harmonic leakage, which occurs between the reflex solar motion represented by the three electric vector harmonics in the velocity space and higher degree harmonics in the proper-motion space, are eliminated in our analysis by direct subtraction of the reflex solar velocity in its tangential components for each star. The Oort parameters determined by a straightforward least-squares adjustment in vector spherical harmonics are A=14.0 +/- 1.4, B=13.1 +/- 1.2, K=1.1 +/- 1.8, and C=2.9 +/- 1.4 km s(exp -1) kpc(exp -1). The physical meaning and the implications of these parameters are discussed in the framework of a general linear model of the velocity field. We find a few statistically significant higher degree harmonic terms that do not correspond to any parameters in the classical linear model. One of them, a third-degree electric harmonic, is tentatively explained as the response to a negative linear gradient of rotation velocity with distance from the Galactic plane, which we estimate at approximately -20 km s(exp -1) kpc(exp -1). A similar vertical gradient of rotation velocity has been detected for more distant stars representing the thick disk (z greater than 1 kpc

  16. Local Field Distribution Function and High Order Field Moments for metal-dielectric composites.

    NASA Astrophysics Data System (ADS)

    Genov, Dentcho A.; Sarychev, Andrey K.; Shalaev, Vladimir M.

    2001-11-01

    In a span of two decades the physics of nonlinear optics saw vast improvement in our understanding of optical properties for various inhomogeneous mediums. One such medium is the metal-dielectric composite, where the metal inclusions have a surface coverage fraction of p, while the rest (1-p) is assumed to represent the dielectric host. The computations carried out by using different theoretical models and the experimental data show existence of giant local electric and magnetic field fluctuations. In this presentation we will introduce a new developed 2D model that determines exactly the Local Field Distribution Function (LFDF) and all other relevant parameters of the film. The LFDF for small filling factors will be shown to transform from lognormal distribution into a single-dipole distribution function. We also will confirm the predictions of the scaling theory for the high field moments, which have a power law dependence on the loss factor.

  17. Dynamic analysis of parametrically excited system under uncertainties and multi-frequency excitations

    NASA Astrophysics Data System (ADS)

    Wei, Sha; Han, Qinkai; Peng, Zhike; Chu, Fulei

    2016-05-01

    Some system parameters in mechanical systems are always uncertain due to uncertainties in geometric and material properties, lubrication condition and wear. For a more reasonable estimation of dynamic analysis of the parametrically excited system, the effect of uncertain parameters should be taken into account. This paper presents a new non-probabilistic analysis method for solving the dynamic responses of parametrically excited systems under uncertainties and multi-frequency excitations. By using the multi-dimensional harmonic balance method (MHBM) and the Chebyshev inclusion function (CIF), an interval multi-dimensional harmonic balance method (IMHBM) is obtained. To illustrate the accuracy of the proposed method, a time-varying geared system of wind turbine with different kinds of uncertainties is demonstrated. By comparing with the results of the scanning method, it is shown that the presented method is valid and effective for the parametrically excited system with uncertainties and multi-frequency excitations. The effects of some uncertain system parameters including uncertain mesh stiffnesses and uncertain bearing stiffnesses on the frequency responses of the system are also discussed in detail. It is shown that the dynamic responses of the system are insensitive to the uncertain mesh stiffness and bearing stiffnesses of the planetary gear stage. The uncertain bearing stiffnesses of the intermediate and high-speed stages will lead to relatively large uncertainties in the dynamic responses around resonant regions. It will provide valuable guidance for the optimal design and condition monitoring of wind turbine gearboxes.

  18. A multi-frequency impedance analysing instrument for eddy current testing

    NASA Astrophysics Data System (ADS)

    Yin, W.; Dickinson, S. J.; Peyton, A. J.

    2006-02-01

    This paper presents the design of a high-performance multi-frequency impedance analysing instrument (MFIA) for eddy current testing which has been developed primarily for monitoring a steel production process using an inductive sensor. The system consists of a flexible multi-frequency waveform generator and a voltage/current measurement unit. The impedance of the sensor is obtained by cross-spectral analysis of the current and voltage signals. The system contains high-speed digital-to-analogue, analogue-to-digital converters and dual DSPs with one for control and interface and one dedicated to frequency-spectra analysis using fast Fourier transformation (FFT). The frequency span of the signal that can be analysed ranges from 1 kHz to 8 MHz. The system also employs a high-speed serial port interface (USB) to communicate with a personal computer (PC) and to allow for fast transmission of data and control commands. Overall, the system is capable of delivering over 250 impedance spectra per second. Although the instrument has been developed mainly for use with an inductive sensor, the system is not restricted to inductive measurement. The flexibility of the design architecture is demonstrated with capacitive and resistive measurements by using appropriate input circuitry. Issues relating to optimizing the phase of the spectra components in the excitation waveform are also discussed.

  19. PULSAR TIMING ERRORS FROM ASYNCHRONOUS MULTI-FREQUENCY SAMPLING OF DISPERSION MEASURE VARIATIONS

    SciTech Connect

    Lam, M. T.; Cordes, J. M.; Chatterjee, S.; Dolch, T.

    2015-03-10

    Free electrons in the interstellar medium cause frequency-dependent delays in pulse arrival times due to both scattering and dispersion. Multi-frequency measurements are used to estimate and remove dispersion delays. In this paper, we focus on the effect of any non-simultaneity of multi-frequency observations on dispersive delay estimation and removal. Interstellar density variations combined with changes in the line of sight from pulsar and observer motions cause dispersion measure (DM) variations with an approximately power-law power spectrum, augmented in some cases by linear trends. We simulate time series, estimate the magnitude and statistical properties of timing errors that result from non-simultaneous observations, and derive prescriptions for data acquisition that are needed in order to achieve a specified timing precision. For nearby, highly stable pulsars, measurements need to be simultaneous to within about one day in order for the timing error from asynchronous DM correction to be less than about 10 ns. We discuss how timing precision improves when increasing the number of dual-frequency observations used in DM estimation for a given epoch. For a Kolmogorov wavenumber spectrum, we find about a factor of two improvement in precision timing when increasing from two to three observations but diminishing returns thereafter.

  20. Research of frequency modulation to amplitude modulation with multi-frequency modulation

    NASA Astrophysics Data System (ADS)

    Zhou, Yuliang; Zhan, Sui; Geng, Yuanchao; Liu, Lanqin; Xu, Lixin; Ming, Hai

    2013-12-01

    For better performance of laser coupling in inertial confinement fusion (ICF), beam shaping of the focus spot is required. Among all the beam smoothing methods, the multi frequency modulation smoothing by spectral dispersion (MultiFM-SSD) proposed by LLE has the advantages of the faster smoothing and better operability. Strong frequency modulation to amplitude modulation conversion(FM-to-AM) will take place because of the complex spectrum imposed by the multi frequency modulators applied in the Multi FM-SSD method. The FM-to-AM effect is studied with numerical simulation including the polarization mode dispersion and group velocity dispersion. The results reveal that the modulation frequencies and bandwidths of multi modulators will influence the contrast degree of the FM-to-AM effect. The compensation of the FM-to-AM with arbitrary waveform generator (AWG) is also numerically simulated. The FM-to-AM effect is effectively suppressed, i.e. the non-uniformity of the pulse decreases substantially, by applying multiple intensity and phase compensation (the compensation function is obtained via G-S algorithm).

  1. Advanced multi-frequency radar: Design, preliminary measurements and particle size distribution retrieval

    NASA Astrophysics Data System (ADS)

    Majurec, Ninoslav

    In the spring of 2001 the Microwave Remote Sensing Laboratory (MIRSL) at the University of Massachusetts began the development of an advanced Multi-Frequency Radar (AMFR) system for studying clouds and precipitation. This mobile radar was designed to consist of three polarimetric Doppler subsystems operating at Ku-band (13.4 GHz), Ka-band (35.6 GHz) and W-band (94.92 GHz). This combination of frequency bands allows a measurement of a wide range of atmospheric targets ranging from weakly reflecting clouds to strong precipitation. The antenna beamwidths at each frequency were intentionally matched, ensuring consistent sampling volume. Multi-frequency radar remote sensing techniques are not widely used because few multi-frequency radars are available to the science community. One exception is the 33 GHz/95 GHz UMass Cloud Profiling Radar System (CPRS), which AMFR is intended to replace. AMFR's multi-parameter capabilities are designed for characterizing the complex microphysics of layer clouds and precipitation processes in winter storms. AMFR will also play an important role in developing algorithms and validating measurements for an upcoming generation of space-borne radars. The frequency bands selected for AMFR match those of several sensors that have been deployed or are under development. These include the Japanese Aerospace Exploration Agencies (JAXA's) Tropical Rainfall Measuring Mission (TRMM) satellite Ku-band (13 GHz) radar, the CloudSat W-band (95 GHz) radar, and the Global Precipitation Mission (GPM) satellite radars at Ku-band and Ka-band. This dissertation describes the AMFR hardware design and development. Compared to CPRS, the addition of one extra frequency band (Ku) will extend AMFR's measurement capabilities towards the larger particle sizes (precipitation). AMFR's design is based around high-power klystron amplifiers. This ensures complete coherency (CPRS uses magnetrons and coherent-on-receive technique). The partial loss in sensitivity due to

  2. Trapped energetic ion dynamics affected by localized electric field perturbations

    NASA Astrophysics Data System (ADS)

    Nishimura, Seiya

    2016-01-01

    Trapped energetic ion orbits in helical systems are numerically simulated using the Lorentz model. Simulation results of precession drift frequencies of trapped energetic ions are benchmarked by those of analytic solutions. The effects of the electric field perturbation localized at the rational surface on trapped energetic ions are examined, where the perturbation has an arbitrary rotation frequency and an amplitude fixed in time. It is found that the trapped energetic ions resonantly interact with the perturbation, when the rotation frequency of the perturbation is comparable to the precession drift frequencies of trapped energetic ions. The simulation results are suggestive to a mechanism of the energetic-ion-induced interchange mode, which might be associated with the fishbone mode observed in helical systems.

  3. System Description and First Application of an FPGA-Based Simultaneous Multi-Frequency Electrical Impedance Tomography

    PubMed Central

    Aguiar Santos, Susana; Robens, Anne; Boehm, Anna; Leonhardt, Steffen; Teichmann, Daniel

    2016-01-01

    A new prototype of a multi-frequency electrical impedance tomography system is presented. The system uses a field-programmable gate array as a main controller and is configured to measure at different frequencies simultaneously through a composite waveform. Both real and imaginary components of the data are computed for each frequency and sent to the personal computer over an ethernet connection, where both time-difference imaging and frequency-difference imaging are reconstructed and visualized. The system has been tested for both time-difference and frequency-difference imaging for diverse sets of frequency pairs in a resistive/capacitive test unit and in self-experiments. To our knowledge, this is the first work that shows preliminary frequency-difference images of in-vivo experiments. Results of time-difference imaging were compared with simulation results and shown that the new prototype performs well at all frequencies in the tested range of 60 kHz–960 kHz. For frequency-difference images, further development of algorithms and an improved normalization process is required to correctly reconstruct and interpreted the resulting images. PMID:27463715

  4. Multi-frequency and polarimetric radar backscatter signatures for discrimination between agricultural crops at the Flevoland experimental test site

    NASA Technical Reports Server (NTRS)

    Freeman, A.; Villasenor, J.; Klein, J. D.

    1991-01-01

    We describe the calibration and analysis of multi-frequency, multi-polarization radar backscatter signatures over an agriculture test site in the Netherlands. The calibration procedure involved two stages: in the first stage, polarimetric and radiometric calibrations (ignoring noise) were carried out using square-base trihedral corner reflector signatures and some properties of the clutter background. In the second stage, a novel algorithm was used to estimate the noise level in the polarimetric data channels by using the measured signature of an idealized rough surface with Bragg scattering (the ocean in this case). This estimated noise level was then used to correct the measured backscatter signatures from the agriculture fields. We examine the significance of several key parameters extracted from the calibrated and noise-corrected backscatter signatures. The significance is assessed in terms of the ability to uniquely separate among classes from 13 different backscatter types selected from the test site data, including eleven different crops, one forest and one ocean area. Using the parameters with the highest separation for a given class, we use a hierarchical algorithm to classify the entire image. We find that many classes, including ocean, forest, potato, and beet, can be identified with high reliability, while the classes for which no single parameter exhibits sufficient separation have higher rates of misclassification. We expect that modified decision criteria involving simultaneous consideration of several parameters increase performance for these classes.

  5. System Description and First Application of an FPGA-Based Simultaneous Multi-Frequency Electrical Impedance Tomography.

    PubMed

    Aguiar Santos, Susana; Robens, Anne; Boehm, Anna; Leonhardt, Steffen; Teichmann, Daniel

    2016-07-25

    A new prototype of a multi-frequency electrical impedance tomography system is presented. The system uses a field-programmable gate array as a main controller and is configured to measure at different frequencies simultaneously through a composite waveform. Both real and imaginary components of the data are computed for each frequency and sent to the personal computer over an ethernet connection, where both time-difference imaging and frequency-difference imaging are reconstructed and visualized. The system has been tested for both time-difference and frequency-difference imaging for diverse sets of frequency pairs in a resistive/capacitive test unit and in self-experiments. To our knowledge, this is the first work that shows preliminary frequency-difference images of in-vivo experiments. Results of time-difference imaging were compared with simulation results and shown that the new prototype performs well at all frequencies in the tested range of 60 kHz-960 kHz. For frequency-difference images, further development of algorithms and an improved normalization process is required to correctly reconstruct and interpreted the resulting images.

  6. Non-contact multi-frequency magnetic induction spectroscopy system for industrial-scale bio-impedance measurement

    NASA Astrophysics Data System (ADS)

    O'Toole, M. D.; Marsh, L. A.; Davidson, J. L.; Tan, Y. M.; Armitage, D. W.; Peyton, A. J.

    2015-03-01

    Biological tissues have a complex impedance, or bio-impedance, profile which changes with respect to frequency. This is caused by dispersion mechanisms which govern how the electromagnetic field interacts with the tissue at the cellular and molecular level. Measuring the bio-impedance spectra of a biological sample can potentially provide insight into the sample’s properties and its cellular structure. This has obvious applications in the medical, pharmaceutical and food-based industrial domains. However, measuring the bio-impedance spectra non-destructively and in a way which is practical at an industrial scale presents substantial challenges. The low conductivity of the sample requires a highly sensitive instrument, while the demands of industrial-scale operation require a fast high-throughput sensor of rugged design. In this paper, we describe a multi-frequency magnetic induction spectroscopy (MIS) system suitable for industrial-scale, non-contact, spectroscopic bio-impedance measurement over a bandwidth of 156 kHz-2.5 MHz. The system sensitivity and performance are investigated using calibration and known reference samples. It is shown to yield rapid and consistently sensitive results with good long-term stability. The system is then used to obtain conductivity spectra of a number of biological test samples, including yeast suspensions of varying concentration and a range of agricultural produce, such as apples, pears, nectarines, kiwis, potatoes, oranges and tomatoes.

  7. Differential cohomology and locally covariant quantum field theory

    NASA Astrophysics Data System (ADS)

    Becker, Christian; Schenkel, Alexander; Szabo, Richard J.

    We study differential cohomology on categories of globally hyperbolic Lorentzian manifolds. The Lorentzian metric allows us to define a natural transformation whose kernel generalizes Maxwell's equations and fits into a restriction of the fundamental exact sequences of differential cohomology. We consider smooth Pontryagin duals of differential cohomology groups, which are subgroups of the character groups. We prove that these groups fit into smooth duals of the fundamental exact sequences of differential cohomology and equip them with a natural presymplectic structure derived from a generalized Maxwell Lagrangian. The resulting presymplectic Abelian groups are quantized using the CCR-functor, which yields a covariant functor from our categories of globally hyperbolic Lorentzian manifolds to the category of C∗-algebras. We prove that this functor satisfies the causality and time-slice axioms of locally covariant quantum field theory, but that it violates the locality axiom. We show that this violation is precisely due to the fact that our functor has topological subfunctors describing the Pontryagin duals of certain singular cohomology groups. As a byproduct, we develop a Fréchet-Lie group structure on differential cohomology groups.

  8. Quantum dynamical simulations of local field enhancement in metal nanoparticles.

    PubMed

    Negre, Christian F A; Perassi, Eduardo M; Coronado, Eduardo A; Sánchez, Cristián G

    2013-03-27

    Field enhancements (Γ) around small Ag nanoparticles (NPs) are calculated using a quantum dynamical simulation formalism and the results are compared with electrodynamic simulations using the discrete dipole approximation (DDA) in order to address the important issue of the intrinsic atomistic structure of NPs. Quite remarkably, in both quantum and classical approaches the highest values of Γ are located in the same regions around single NPs. However, by introducing a complete atomistic description of the metallic NPs in optical simulations, a different pattern of the Γ distribution is obtained. Knowing the correct pattern of the Γ distribution around NPs is crucial for understanding the spectroscopic features of molecules inside hot spots. The enhancement produced by surface plasmon coupling is studied by using both approaches in NP dimers for different inter-particle distances. The results show that the trend of the variation of Γ versus inter-particle distance is different for classical and quantum simulations. This difference is explained in terms of a charge transfer mechanism that cannot be obtained with classical electrodynamics. Finally, time dependent distribution of the enhancement factor is simulated by introducing a time dependent field perturbation into the Hamiltonian, allowing an assessment of the localized surface plasmon resonance quantum dynamics.

  9. Enhanced Soundings for Local Coupling Studies Field Campaign Report

    SciTech Connect

    Ferguson, Craig R; Santanello, Joseph A; Gentine, Pierre

    2016-04-01

    This document presents initial analyses of the enhanced radiosonde observations obtained during the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility Enhanced Soundings for Local Coupling Studies Field Campaign (ESLCS), which took place at the ARM Southern Great Plains (SGP) Central Facility (CF) from June 15 to August 31, 2015. During ESLCS, routine 4-times-daily radiosonde measurements at the ARM-SGP CF were augmented on 12 days (June 18 and 29; July 11, 14, 19, and 26; August 15, 16, 21, 25, 26, and 27) with daytime 1-hourly radiosondes and 10-minute ‘trailer’ radiosondes every 3 hours. These 12 intensive operational period (IOP) days were selected on the basis of prior-day qualitative forecasts of potential land-atmosphere coupling strength. The campaign captured 2 dry soil convection advantage days (June 29 and July 14) and 10 atmospherically controlled days. Other noteworthy IOP events include: 2 soil dry-down sequences (July 11-14-19 and August 21-25-26), a 2-day clear-sky case (August 15-16), and the passing of Tropical Storm Bill (June 18). To date, the ESLCS data set constitutes the highest-temporal-resolution sampling of the evolution of the daytime planetary boundary layer (PBL) using radiosondes at the ARM-SGP. The data set is expected to contribute to: 1) improved understanding and modeling of the diurnal evolution of the PBL, particularly with regard to the role of local soil wetness, and (2) new insights into the appropriateness of current ARM-SGP CF thermodynamic sampling strategies.

  10. Optimizing an Actuator Array for the Control of Multi-Frequency Noise in Aircraft Interiors

    NASA Technical Reports Server (NTRS)

    Palumbo, D. L.; Padula, S. L.

    1997-01-01

    Techniques developed for selecting an optimized actuator array for interior noise reduction at a single frequency are extended to the multi-frequency case. Transfer functions for 64 actuators were obtained at 5 frequencies from ground testing the rear section of a fully trimmed DC-9 fuselage. A single loudspeaker facing the left side of the aircraft was the primary source. A combinatorial search procedure (tabu search) was employed to find optimum actuator subsets of from 2 to 16 actuators. Noise reduction predictions derived from the transfer functions were used as a basis for evaluating actuator subsets during optimization. Results indicate that it is necessary to constrain actuator forces during optimization. Unconstrained optimizations selected actuators which require unrealistically large forces. Two methods of constraint are evaluated. It is shown that a fast, but approximate, method yields results equivalent to an accurate, but computationally expensive, method.

  11. Classification and Monitoring of Salt Marsh Habitats with Multi-Polarimetric and Multi-Frequency SAR

    NASA Astrophysics Data System (ADS)

    van Beijma, Sybrand; Comber, Alexis; Lamb, Alistair; Brown, Sarah

    2013-08-01

    Within GMES there is much interest in the ability of remote sensing technology to deliver operational solutions to many areas of life including environmental management. This paper describes research focused on the application for Earth Observation for Integrated Coastal Zone Management. The main topic of this research is to explore to which extent salt marsh habitats from can be identified from SAR remotely sensed data. Multi-frequency, multi-polarimetric SAR images from airborne (S- and X-Band quad-polarimetric from the Astrium airborne SAR Demonstrator) is used to examine salt marsh habitat classification potential in the Llanrhidian salt marshes in South Wales, UK. This is achieved by characterizing their botanical and structural composition, flooding regimes as well as fluctuations in soil moisture. Different SAR features as backscatter coefficient, band ratios and polarimetric decomposition are extracted.

  12. Design and characterization of a multi-frequency bioimpedance measurement prototype

    NASA Astrophysics Data System (ADS)

    Mattia Neto, O. E.; Porto, R. W.; Aya, J. C. C.

    2012-12-01

    A multi-frequency bioimpedance measurement prototype is proposed, validated and characterized. It consists of an Improved Howland Current Source controlled by voltage, a load voltage sensing scheme through a discrete 3-opamp instrumentation amplifier, a phase and quadrature demodulation setup through analog multipliers, and digitization and processing of the signals using a digital benchtop multimeter. The electrical characterization of the measurement channel was done for resistive loads only, on four different circuits. Measurements were made on 10 frequencies, from 100 kHz to 1 MHz, with 10 load resistances, from 100 Ω to 1 kΩ, to obtain linearity, absolute error and frequency response. The best performance among the four circuits was a maximum absolute error of 5.55 %, and -1.93 % of load current variation at the worst case scenario.

  13. Three-dimensional ground penetrating radar imaging using multi-frequency diffraction tomography

    SciTech Connect

    Mast, J.E.; Johansson, E.M.

    1994-11-15

    In this talk we present results from a three-dimensional image reconstruction algorithm for impulse radar operating in monostatic pule-echo mode. The application of interest to us is the nondestructive evaluation of civil structures such as bridge decks. We use a multi-frequency diffraction tomography imaging technique in which coherent backward propagations of the received reflected wavefield form a spatial image of the scattering interfaces within the region of interest. This imaging technique provides high-resolution range and azimuthal visualization of the subsurface region. We incorporate the ability to image in planarly layered conductive media and apply the algorithm to experimental data from an offset radar system in which the radar antenna is not directly coupled to the surface of the region. We present a rendering in three-dimensions of the resulting image data which provides high-detail visualization.

  14. Three-dimensional ground penetrating radar imaging using multi-frequency diffraction tomography

    SciTech Connect

    Mast, J.E.; Johansson, E.M.

    1994-07-01

    In this paper we present results from a three-dimensional image reconstruction algorithm for impulse radar operating in monostatic pulse-echo mode. The application of interest to us is the nondestructive evaluation of civil structures such as bridge decks. We use a multi-frequency diffraction tomography imaging technique in which coherent backward propagations of the received reflected wavefield form a spatial image of the scattering interfaces within the region of interest. This imaging technique provides high-resolution range and azimuthal visualization of the subsurface region. We incorporate the ability to image in planarly layered conductive media and apply the algorithm to experimental data from an offset radar system in which the radar antenna is not directly coupled to the surface of the region. We present a rendering in three-dimensions of the resulting image data which provides high-detail visualization.

  15. Multi-Frequency Investigation into Scattering from Vegetation over the Growth Cycle

    NASA Technical Reports Server (NTRS)

    Lang, R. H.; Kurum, M.; O'Neill, P. E.; Joseph, A. T.; Deshpande, M. D.; Cosh, M. H.

    2016-01-01

    In this investigation, we aim to collect and use time-series multi-frequency microwave data over winter wheat during entire growth cycle to characterize vegetation dynamics and to quantify its effects on soil moisture retrievals. We plan to incorporate C-band radar and VHF receiver within the existing L-band radarradiometer system called ComRAD (SMAPs ground based simulator). With C-bands ability to sense vegetation details and VHFs root-zone soil moisture within ComRADs footprint, we will be able to test our discrete scatterer vegetation models and parameters at various surface conditions. The purpose of this study is to determine optical depth and effective scattering albedo of vegetation of a given type (i.e. winter wheat) at various stages of growth that are need to refine soil moisture retrieval algorithms being developed for the SMAP mission.

  16. Recovering Inner Slices of Layered Translucent Objects by Multi-Frequency Illumination.

    PubMed

    Tanaka, Kenichiro; Mukaigawa, Yasuhiro; Kubo, Hiroyuki; Matsushita, Yasuyuki; Yagi, Yasushi

    2017-04-01

    This paper describes a method for recovering appearance of inner slices of translucent objects. The appearance of a layered translucent object is the summed appearance of all layers, where each layer is blurred by a depth-dependent point spread function (PSF). By exploiting the difference of low-pass characteristics of depth-dependent PSFs, we develop a multi-frequency illumination method for obtaining the appearance of individual inner slices. Specifically, by observing the target object with varying the spatial frequency of checker-pattern illumination, our method recovers the appearance of inner slices via computation. We study the effect of non-uniform transmission due to inhomogeneity of translucent objects and develop a method for recovering clear inner slices based on the pixel-wise PSF estimates under the assumption of spatial smoothness of inner slice appearances. We quantitatively evaluate the accuracy of the proposed method by simulations and qualitatively show faithful recovery using real-world scenes.

  17. Active subthreshold dendritic conductances shape the local field potential

    PubMed Central

    Ness, Torbjørn V.; Remme, Michiel W. H.

    2016-01-01

    Key points The local field potential (LFP), the low‐frequency part of extracellular potentials recorded in neural tissue, is often used for probing neural circuit activity. Interpreting the LFP signal is difficult, however.While the cortical LFP is thought mainly to reflect synaptic inputs onto pyramidal neurons, little is known about the role of the various subthreshold active conductances in shaping the LFP.By means of biophysical modelling we obtain a comprehensive qualitative understanding of how the LFP generated by a single pyramidal neuron depends on the type and spatial distribution of active subthreshold currents.For pyramidal neurons, the h‐type channels probably play a key role and can cause a distinct resonance in the LFP power spectrum.Our results show that the LFP signal can give information about the active properties of neurons and imply that preferred frequencies in the LFP can result from those cellular properties instead of, for example, network dynamics. Abstract The main contribution to the local field potential (LFP) is thought to stem from synaptic input to neurons and the ensuing subthreshold dendritic processing. The role of active dendritic conductances in shaping the LFP has received little attention, even though such ion channels are known to affect the subthreshold neuron dynamics. Here we used a modelling approach to investigate the effects of subthreshold dendritic conductances on the LFP. Using a biophysically detailed, experimentally constrained model of a cortical pyramidal neuron, we identified conditions under which subthreshold active conductances are a major factor in shaping the LFP. We found that, in particular, the hyperpolarization‐activated inward current, I h, can have a sizable effect and cause a resonance in the LFP power spectral density. To get a general, qualitative understanding of how any subthreshold active dendritic conductance and its cellular distribution can affect the LFP, we next performed a systematic

  18. SU-E-I-52: Validation of Multi-Frequency Electrical Impedance Tomography Using Computed Tomography

    SciTech Connect

    Kohli, K; Liu, F; Krishnan, K

    2014-06-01

    Purpose: Multi-frequency EIT has been reported to be a potential tool in distinguishing a tissue anomaly from background. In this study, we investigate the feasibility of acquiring functional information by comparing multi-frequency EIT images in reference to the structural information from the CT image through fusion. Methods: EIT data was acquired from a slice of winter melon using sixteen electrodes around the phantom, injecting a current of 0.4mA at 100, 66, 24.8 and 9.9 kHz. Differential EIT images were generated by considering different combinations of pair frequencies, one serving as reference data and the other as test data. The experiment was repeated after creating an anomaly in the form of an off-centered cavity of diameter 4.5 cm inside the melon. All EIT images were reconstructed using Electrical Impedance Tomography and Diffuse Optical Tomography Reconstruction Software (EIDORS) package in 2-D differential imaging mode using one-step Gaussian Newton minimization solver. CT image of the melon was obtained using a Phillips CT Scanner. A segmented binary mask image was generated based on the reference electrode position and the CT image to define the regions of interest. The region selected by the user was fused with the CT image through logical indexing. Results: Differential images based on the reference and test signal frequencies were reconstructed from EIT data. Result illustrated distinct structural inhomogeneity in seeded region compared to fruit flesh. The seeded region was seen as a higherimpedance region if the test frequency was lower than the base frequency in the differential EIT reconstruction. When the test frequency was higher than the base frequency, the signal experienced less electrical impedance in the seeded region during the EIT data acquisition. Conclusion: Frequency-based differential EIT imaging can be explored to provide additional functional information along with structural information from CT for identifying different tissues.

  19. Design and verification of wide-band, simultaneous, multi-frequency, tuning circuits for large moment transmitter loops

    NASA Astrophysics Data System (ADS)

    Dvorak, Steven L.; Sternberg, Ben K.; Feng, Wanjie

    2017-03-01

    In this paper we discuss the design and verification of wide-band, multi-frequency, tuning circuits for large-moment Transmitter (TX) loops. Since these multi-frequency, tuned-TX loops allow for the simultaneous transmission of multiple frequencies at high-current levels, they are ideally suited for frequency-domain geophysical systems that collect data while moving, such as helicopter mounted systems. Furthermore, since multi-frequency tuners use the same TX loop for all frequencies, instead of using separate tuned-TX loops for each frequency, they allow for the use of larger moment TX loops. In this paper we discuss the design and simulation of one- and three-frequency tuned TX loops and then present measurement results for a three-frequency, tuned-TX loop.

  20. The Local Interstellar Magnetic Field Determined from the IBEX Ribbon

    NASA Astrophysics Data System (ADS)

    Zirnstein, E.; Funsten, H. O.; Heerikhuisen, J.; Livadiotis, G.; McComas, D. J.; Pogorelov, N. V.

    2015-12-01

    As the solar wind plasma flows away from the Sun, it eventually collides with the local interstellar medium, creating the heliosphere. Neutral atoms from interstellar space travel inside the heliosphere and charge-exchange with the solar wind plasma, creating energetic neutral atoms (ENAs). Some of these ENAs travel outside the heliosphere, undergo two charge-exchange events, and travel back inside the heliosphere towards Earth, with the strongest intensity in directions perpendicular to the interstellar magnetic field (IMF). It is widely believed that this process generates the "ribbon" of enhanced ENA intensity observed by the Interstellar Boundary Explorer (IBEX), and has been shown to explain many key features of the observations. IBEX observations of the ribbon are composed of a complex, line-of-sight integration of ENAs that come from different distances beyond the heliopause, and thus the ENAs detected by IBEX over a wide range of energies are uniquely coupled to the IMF draped around the heliosphere. We present a detailed analysis of the IBEX ribbon measurements using 3D simulations of the heliosphere and computations of the ribbon flux at Earth based on IBEX capabilities, and derive the magnitude and direction of the IMF required to reproduce the position of the IBEX ribbon in the sky. These results have potentially large implications for our understanding of the solar-interstellar environment.

  1. On the photovoltaic effect in local field potential recordings

    PubMed Central

    Mikulovic, Sanja; Pupe, Stefano; Peixoto, Helton Maia; Do Nascimento, George C.; Kullander, Klas; Tort, Adriano B. L.; Leão, Richardson N.

    2016-01-01

    Abstract. Optogenetics allows light activation of genetically defined cell populations and the study of their link to specific brain functions. While it is a powerful method that has revolutionized neuroscience in the last decade, the shortcomings of directly stimulating electrodes and living tissue with light have been poorly characterized. Here, we assessed the photovoltaic effects in local field potential (LFP) recordings of the mouse hippocampus. We found that light leads to several artifacts that resemble genuine LFP features in animals with no opsin expression, such as stereotyped peaks at the power spectrum, phase shifts across different recording channels, coupling between low and high oscillation frequencies, and sharp signal deflections that are detected as spikes. Further, we tested how light stimulation affected hippocampal LFP recordings in mice expressing channelrhodopsin 2 in parvalbumin neurons (PV/ChR2 mice). Genuine oscillatory activity at the frequency of light stimulation could not be separated from light-induced artifacts. In addition, light stimulation in PV/ChR2 mice led to an overall decrease in LFP power. Thus, genuine LFP changes caused by the stimulation of specific cell populations may be intermingled with spurious changes caused by photovoltaic effects. Our data suggest that care should be taken in the interpretation of electrophysiology experiments involving light stimulation. PMID:26835485

  2. On the photovoltaic effect in local field potential recordings.

    PubMed

    Mikulovic, Sanja; Pupe, Stefano; Peixoto, Helton Maia; Do Nascimento, George C; Kullander, Klas; Tort, Adriano B L; Leão, Richardson N

    2016-01-01

    Optogenetics allows light activation of genetically defined cell populations and the study of their link to specific brain functions. While it is a powerful method that has revolutionized neuroscience in the last decade, the shortcomings of directly stimulating electrodes and living tissue with light have been poorly characterized. Here, we assessed the photovoltaic effects in local field potential (LFP) recordings of the mouse hippocampus. We found that light leads to several artifacts that resemble genuine LFP features in animals with no opsin expression, such as stereotyped peaks at the power spectrum, phase shifts across different recording channels, coupling between low and high oscillation frequencies, and sharp signal deflections that are detected as spikes. Further, we tested how light stimulation affected hippocampal LFP recordings in mice expressing channelrhodopsin 2 in parvalbumin neurons (PV/ChR2 mice). Genuine oscillatory activity at the frequency of light stimulation could not be separated from light-induced artifacts. In addition, light stimulation in PV/ChR2 mice led to an overall decrease in LFP power. Thus, genuine LFP changes caused by the stimulation of specific cell populations may be intermingled with spurious changes caused by photovoltaic effects. Our data suggest that care should be taken in the interpretation of electrophysiology experiments involving light stimulation.

  3. Performance of FFT methods in local gravity field modelling

    NASA Technical Reports Server (NTRS)

    Forsberg, Rene; Solheim, Dag

    1989-01-01

    Fast Fourier transform (FFT) methods provide a fast and efficient means of processing large amounts of gravity or geoid data in local gravity field modelling. The FFT methods, however, has a number of theoretical and practical limitations, especially the use of flat-earth approximation, and the requirements for gridded data. In spite of this the method often yields excellent results in practice when compared to other more rigorous (and computationally expensive) methods, such as least-squares collocation. The good performance of the FFT methods illustrate that the theoretical approximations are offset by the capability of taking into account more data in larger areas, especially important for geoid predictions. For best results good data gridding algorithms are essential. In practice truncated collocation approaches may be used. For large areas at high latitudes the gridding must be done using suitable map projections such as UTM, to avoid trivial errors caused by the meridian convergence. The FFT methods are compared to ground truth data in New Mexico (xi, eta from delta g), Scandinavia (N from delta g, the geoid fits to 15 cm over 2000 km), and areas of the Atlantic (delta g from satellite altimetry using Wiener filtering). In all cases the FFT methods yields results comparable or superior to other methods.

  4. Field-independent source localization of Neptune's radio bursts

    NASA Technical Reports Server (NTRS)

    Farrell, W. M.; Desch, M. D.; Kaiser, M. L.

    1990-01-01

    During the Voyager 2 encounter with Neptune, a narrowbanded bursty radio component was observed between 500 and 1326 kHz by the Planetary Radio Astronomy instrument. Based on the emission occurrence pattern, the radio source has been localized without the explicit use of the Neptunian offset-tilted dipole magnetic field model, which is accurate only at distances greater than 4 R(N) (Neptune radii) from the planet. Only assumptions based upon the general nature of radio wave propagation in planetary magnetospheres were used. A number of different candidate radial positions were sampled. For example, at 1.5 R(N), the derived source location was positioned only about 10 deg from the south magnetic pole. The radiation from this source was beamed into a cone of 77.5 + or - 6.3 deg half-angle that was tilted about 10 deg from the radial direction to the north-northeast. At other sampled radial positions, similar source locations were obtained. Due to its proximity to the south magnetic pole, the kilometric emission radio source is believed to be associated with an active auroral region, similar in nature to those found at earth and Saturn.

  5. Threshold Region Performance Prediction for Adaptive Matched Field Processing Localization

    DTIC Science & Technology

    2007-11-02

    significant non-local estimation errors at low signal-to-noise ratios ( SNRs )-errors not modeled by traditional localization measures such as the Cramer...as a function of SNR , for apertures and environments of interest. Particular attention will be given to the "threshold SNR " (below which localization...performance degrades rapidly due to global estimation errors) and to the minimum SNR required to achieve acceptable range/depth localization. Initial

  6. Rapid ambiguity resolution over medium-to-long baselines based on GPS/BDS multi-frequency observables

    NASA Astrophysics Data System (ADS)

    Gong, Xiaopeng; Lou, Yidong; Liu, Wanke; Zheng, Fu; Gu, Shengfeng; Wang, Hua

    2017-02-01

    Medium-long baseline RTK positioning generally needs a long initial time to find an accurate position due to non-negligible atmospheric delay residual. In order to shorten the initial or re-convergence time, a rapid phase ambiguity resolution method is employed based on GPS/BDS multi-frequency observables in this paper. This method is realized by two steps. First, double-differenced un-combined observables (i.e., L1/L2 and B1/B2/B3 observables) are used to obtain a float solution with atmospheric delay estimated as random walk parameter by using Kalman filter. This model enables an easy and consistent implementation for different systems and different frequency observables and can readily be extended to use more satellite navigation systems (e.g., Galileo, QZSS). Additional prior constraints for atmospheric information can be quickly added as well, because atmospheric delay is parameterized. Second, in order to fix ambiguity rapidly and reliably, ambiguities are divided into three types (extra-wide-lane (EWL), wide-lane (WL) and narrow-lane (NL)) according to their wavelengths and are to be fixed sequentially by using the LAMBDA method. Several baselines ranging from 61 km to 232 km collected by Trimble and Panda receivers are used to validate the method. The results illustrate that it only takes approximately 1, 2 and 6 epochs (30 s intervals) to fix EWL, WL and NL ambiguities, respectively. More epochs' observables are needed to fix WL and NL ambiguity around local time 14:00 than other time mainly due to more active ionosphere activity. As for the re-convergence time, the simulated results show that 90% of epochs can be fixed within 2 epochs by using prior atmospheric delay information obtained from previously 5 min. Finally, as for positioning accuracy, meter, decimeter and centimeter level positioning results are obtained according to different ambiguity resolution performances, i.e., EWL, WL and NL fixed solutions.

  7. Multi-Frequency and Multi-Polarization Study on SAR-Based Coastal AReas Characterization: The Case of the Yellow River Delta

    NASA Astrophysics Data System (ADS)

    Buono, Andrea; Nunziata, Ferdinando; Migliaccio, Maurizio; Li, Xiaofeng; Shen, Dongliang; Ding, Xianwen

    2016-08-01

    The Yellow River is the most sediment-filled river and the sixth-longest one in the world. It is of paramount importance for safe navigation, local economy and environment due to the presence of floods, farms, aquacultures and pollution. Further, the Yellow River delta is characterized by several physical phenomena due to both natural and anthropogenic processes: sedimentation, erosion, floods, pollution, etc.In this study, actual partially-overlapped L-/C-band fully- polarimetric (FP) synthetic aperture radar (SAR) data are used to investigate the scattering properties of the Yellow River delta, whose very complex area is characterized by different environments as recorded by ground truth data acquired during a ship-based in-situ campaign. Preliminary results witness that multi-polarization and multi-frequency SAR measurements allow inferring more physical information in such a complex environment that can be used as starting point for developing ad hoc classification algorithms.

  8. Multi-frequency properties of synthetic blazar radio light curves within the shock-in-jet scenario

    NASA Astrophysics Data System (ADS)

    Fromm, C. M.; Fuhrmann, L.; Perucho, M.

    2015-08-01

    Context. Blazars are among the most powerful extragalactic objects as a sub-class of active galactic nuclei. They launch relativistic jets and their emitted radiation shows strong variability across the entire electro-magnetic spectrum. The mechanisms producing the variability are still controversial, and different models have been proposed to explain the observed variations in multi-frequency blazar light curves. Aims: We investigate the capabilities of the classical shock-in-jet model to explain and reconstruct the observed evolution of flares in the turnover frequency - turnover flux density (νm-Sm) plane and their frequency dependent light curve parameters. With a detailed parameter space study, we provide the framework for future, detailed comparisons of observed flare signatures with the shock-in-jet scenario. Methods: Based on the shock model, we compute synthetic single-dish light curves at different radio frequencies (2.6 to 345 GHz) and for different physical conditions in a conical jet (e.g. magnetic field geometry and Doppler factor). From those we extract the slopes of the different energy loss stages within the (νm-Sm) plane and deduce the frequency dependence of different light curve parameters, such as flare amplitude, time scale, and cross-band delays. Results: The evolution of the Doppler factor along the jet has the strongest influence on the evolution of the flare and on the frequency dependent light curve parameters. The synchrotron stage can be hidden in the Compton or in the adiabatic stage, depending mainly on the evolution of the Doppler factor, which makes it difficult to detect its signature in observations. In addition, we show that the time lags between different frequencies can be used as an efficient tool to better constrain the physical properties of these objects. Appendix A is available in electronic form at http://www.aanda.org

  9. Perceptual and Attentional Influences on Continuous 2:1 and 3:2 Multi-Frequency Bimanual Coordination

    ERIC Educational Resources Information Center

    Kovacs, Attila J.; Buchanan, John J.; Shea, Charles H.

    2010-01-01

    Two experiments were conducted to determine if multi-frequency (2:1 and 3:2) coordination between the limbs is enhanced when integrated feedback is provided in the form of Lissajous plots, attention demands are reduced, and attempts to consciously coordinate the limbs are not encouraged. To determine the influence of vision of the limbs, covered…

  10. [Study on spectral gain characterization of FWM processes with multi-frequency pumps in photonic crystal fiber].

    PubMed

    Hui, Zhan-Qiang

    2011-10-01

    Spectral gain induced by four-wave-mixing with multi-frequency pump was investigated by exploiting the data signal and continue lights co-propagation in dispersion flattened high nonlinear photonic crystal fiber (PCF). The effects of wavelength drift of pump lights, polarization state of orthogonal or parallel of pump lights, polarization mismatch of signal light versus orthogonal pump lights, total power of signal and probe light on the spectrum gain were analyzed. The results show that good FWM gain effects with multi-frequency pump can be obtained in 36.4 nm wavelength range when power ratio of pump to probe light is appropriate and with identical polarization. Furthermore, the gain of FWM with multi-frequency pump is very sensitive to polarization fluctuation and the different idle waves obtain different gain with the variation in signal polarization state. Moreover, the impact of pump numbers was investigated. The obtained results would be helpful for further research on ultrahigh-speed all optical signal processing devices exploiting the FWM with multi-frequency pump in PCF for future photonics network.

  11. Delaunay Tessellation Field Estimator analysis of the PSCz local Universe: density field and cosmic flow

    NASA Astrophysics Data System (ADS)

    Romano-Díaz, Emilio; van de Weygaert, Rien

    2007-11-01

    We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyse the matter distribution and cosmic velocity flows in the local Universe on the basis of the PSCz galaxy survey. The prime objective of this study is the production of optimal resolution 3D maps of the volume-weighted velocity and density fields throughout the nearby universe, the basis for a detailed study of the structure and dynamics of the cosmic web at each level probed by underlying galaxy sample. Fully volume-covering 3D maps of the density and (volume-weighted) velocity fields in the cosmic vicinity, out to a distance of 150h-1Mpc, are presented. Based on the Voronoi and Delaunay tessellation defined by the spatial galaxy sample, DTFE involves the estimate of density values on the basis of the volume of the related Delaunay tetrahedra and the subsequent use of the Delaunay tessellation as natural multidimensional (linear) interpolation grid for the corresponding density and velocity fields throughout the sample volume. The linearized model of the spatial galaxy distribution and the corresponding peculiar velocities of the PSCz galaxy sample, produced by Branchini et al., forms the input sample for the DTFE study. The DTFE maps reproduce the high-density supercluster regions in optimal detail, both their internal structure as well as their elongated or flattened shape. The corresponding velocity flows trace the bulk and shear flows marking the region extending from the Pisces-Perseus supercluster, via the Local Superclusters, towards the Hydra-Centaurus and the Shapley concentration. The most outstanding and unique feature of the DTFE maps is the sharply defined radial outflow regions in and around underdense voids, marking the dynamical importance of voids in the local Universe. The maximum expansion rate of voids defines a sharp cut-off in the DTFE velocity divergence probability distribution function. We found that on the basis of this cut-off DTFE manages to consistently

  12. Electromagnetic field enhancement and light localization in deterministic aperiodic nanostructures

    NASA Astrophysics Data System (ADS)

    Gopinath, Ashwin

    The control of light matter interaction in periodic and random media has been investigated in depth during the last few decades, yet structures with controlled degree of disorder such as Deterministic Aperiodic Nano Structures (DANS) have been relatively unexplored. DANS are characterized by non-periodic yet long-range correlated (deterministic) morphologies and can be generated by the mathematical rules of symbolic dynamics and number theory. In this thesis, I have experimentally investigated the unique light transport and localization properties in planar dielectric and metal (plasmonics) DANS. In particular, I have focused on the design, nanofabrication and optical characterization of DANS, formed by arranging metal/dielectric nanoparticles in an aperiodic lattice. This effort is directed towards development of on-chip nanophotonic applications with emphasis on label-free bio-sensing and enhanced light emission. The DANS designed as Surface Enhanced Raman Scattering (SERS) substrate is composed of multi-scale aperiodic nanoparticle arrays fabricated by e-beam lithography and are capable of reproducibly demonstrating enhancement factors as high as ˜107. Further improvement of SERS efficiency is achieved by combining DANS formed by top-down approach with bottom-up reduction of gold nanoparticles, to fabricate novel nanostructures called plasmonic "nano-galaxies" which increases the SERS enhancement factors by 2--3 orders of magnitude while preserving the reproducibility. In this thesis, along with presenting details of fabrication and SERS characterization of these "rationally designed" SERS substrates, I will also present results on using these substrates for detection of DNA nucleobases, as well as reproducible label-free detection of pathogenic bacteria with species specificity. In addition to biochemical detection, the combination of broadband light scattering behavior and the ability for the generation of reproducible high fields in DANS make these

  13. Infinite-time average of local fields in an integrable quantum field theory after a quantum quench.

    PubMed

    Mussardo, G

    2013-09-06

    The infinite-time average of the expectation values of local fields of any interacting quantum theory after a global quench process are key quantities for matching theoretical and experimental results. For quantum integrable field theories, we show that they can be obtained by an ensemble average that employs a particular limit of the form factors of local fields and quantities extracted by the generalized Bethe ansatz.

  14. Spin noise explores local magnetic fields in a semiconductor

    NASA Astrophysics Data System (ADS)

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-02-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new – magnetometric – potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates.

  15. Spin noise explores local magnetic fields in a semiconductor

    PubMed Central

    Ryzhov, Ivan I.; Kozlov, Gleb G.; Smirnov, Dmitrii S.; Glazov, Mikhail M.; Efimov, Yurii P.; Eliseev, Sergei A.; Lovtcius, Viacheslav A.; Petrov, Vladimir V.; Kavokin, Kirill V.; Kavokin, Alexey V.; Zapasskii, Valerii S.

    2016-01-01

    Rapid development of spin noise spectroscopy of the last decade has led to a number of remarkable achievements in the fields of both magnetic resonance and optical spectroscopy. In this report, we demonstrate a new – magnetometric – potential of the spin noise spectroscopy and use it to study magnetic fields acting upon electron spin-system of an n-GaAs layer in a high-Q microcavity probed by elliptically polarized light. Along with the external magnetic field, applied to the sample, the spin noise spectrum revealed the Overhauser field created by optically oriented nuclei and an additional, previously unobserved, field arising in the presence of circularly polarized light. This “optical field” is directed along the light propagation axis, with its sign determined by sign of the light helicity. We show that this field results from the optical Stark effect in the field of the elliptically polarized light. This conclusion is supported by theoretical estimates. PMID:26882994

  16. Heuristic approximations for sound fields produced by spherical waves incident on locally and non-locally reacting planar surfaces.

    PubMed

    Li, Kai Ming; Tao, Hongdan

    2014-01-01

    The classic Weyl-van der Pol (WVDP) formula is a well-known asymptotic solution for accurately predicting sound fields above a locally reacting ground surface. However, the form of the WVDP formula is inadequate for predicting sound fields in the vicinity of non-locally reacting surfaces; a correction term is often required in the formula to provide accurate numerical solutions. Even with this correction, there is a singularity in the diffraction wave term when the source is located directly above or below the receiver. This paper explores a heuristic method to remove this singularity and suggests an analytical form comparable to the WVDP formula. This improved formula offers a physically interpretable solution and allows for accurate predictions of the total sound field above locally and non-locally reacting surfaces for all geometrical configurations.

  17. Lightfast optical current in dielectric by plasmonically induced local field

    NASA Astrophysics Data System (ADS)

    Kim, Seungchul; Kwon, Ojoon; Lee, Tae-Woo

    2014-08-01

    Recently, ultrafast strong field induced optical current in SiO2 dielectric medium has demonstrated. By foaming laser intensity more than 1013 W•cm-2 in the dielectric material, the optical current was generated in a dielectric gap without any DC bias. This phenomenon is affected by the strength electric field of incident laser field and the generated electrons follow the speed of optical frequency enabling lightfast electronics in the future. In this study, we especially adopted nanoplasmonic field to trigger and control current flow in a nanometer spatial resolution. Nanoplasmonic field enables to manipulate light field in nanoscale domain. By using nanoplasmonic field, optically induced current flow can be selectively controlled by characteristic of nanoplasmonic nanostructure. For the first demonstration, saw tooth like 2-D nano Au pattern was numerically and experimentally investigated to boost up the laser intensity of incident 4.5 fs laser pulse with minimum field distortion and broadening. The intensity enhancement factor of plasmonic field at the saw tooth tip was ~40, enabling Wannier-Stark effect with incidence intensity level of only 1011W•cm-2 in the TiO2 substrate. The carrier envelope phase of laser pulse is controlled to measure ultrafast optical current generation in dielectric medium by plasmonically induced strong near-field. This will be the basis for developing practical lightfast optical electronics in the future.

  18. Extraction of Benthic Fauna Habitat in Tidal Flats Using Multi-Frequency Polarimetric SAR Data

    NASA Astrophysics Data System (ADS)

    Choe, Byung-Hun; Kim, Duk-Jin; Hwang, Ji-Hwan; Moon, Wooil M.

    2011-03-01

    Benthic faunas form a relatively rough surface structure in tidal flats by their unique surface structure or their survival activities. In particular, oyster reefs are exposed and distributed intensively on those tidal flats at low tide. In this study, we investigated the microwave scattering signatures occurred by the regional distribution of oysters in tidal flats, applying polarimetric analysis techniques to fully polarimetric RADARSAT-2 (C-band) and ALOS PALSAR (L-band) data. Tidal flats of Jebu Island in the western coastal region of the Korean peninsula were selected for the investigation. The scattering mechanisms in tidal flats were analyzed by Freeman-Durden target decomposition and the target depolarization effects were quantitatively measured using the cross- polarized ratio, co-polarized correlation coefficient, and phase difference between HH and VV. From C-band SAR data, we observed strong volume (or multiple) scattering and depolarization effects in the oyster reefs, while only surface scattering was dominant in mud flat areas. These scattering signatures were also verified in-situ measurenments using a ground-based polarimetric scatterometer system. However, no difference was observed between the scattering signatures of oyster reefs and mud flat areas from L-band data, which have a relatively longer wavelength. In conclusion, this study suggests that multi-frequency polarimetric SAR measurements can be used to detect the naturally distributed oysters in tidal flats.

  19. The study of multi-frequency scattering of 10 radio pulsars

    NASA Astrophysics Data System (ADS)

    Lewandowski, Wojciech; Rożko, Karolina; Kijak, Jarosław; Bhattacharyya, Bhaswati; Roy, Jayanta

    2015-12-01

    We present the results of the multi-frequency scatter time measurements for 10 radio pulsars that were relatively less studied in this regard. The observations were performed using the Giant Metrewave Radio Telescope at the observing frequencies of 150, 235, 325, 610 and 1060 MHz. The data we collected, in conjunction with the results from other frequencies published earlier, allowed us to estimate the scatter time frequency scaling indices for eight of these sources. For PSR J1852-0635, it became evident that its profile undergoes a strong evolution with frequency, which makes the scatter time measurements difficult to perform, and for PSR J1835-1020 we were able to obtain reliable pulse broadening estimates at only two frequencies. We used the eight frequency scaling indices to estimate both: the electron density fluctuation strengths along the respective lines of sight and the standardized amount of scattering at the frequency of 1 GHz. Combining the new data with the results published earlier by Lewandowski et al., we revisited the scaling index versus the dispersion measure (DM) relation, and similarly to some of the earlier studies, we show that the average value of the scaling index deviates from the theoretical predictions for large-DM pulsars; however, it reaches the magnitude claimed by Löhmer et al. only for pulsars with very large DMs (>650 pc cm-3). We also investigated the dependence of the scattering strength indicators on the pulsar distance, DM and the position of the source in the Milky Way Galaxy.

  20. A frequency based constraint for a multi-frequency linear sampling method

    NASA Astrophysics Data System (ADS)

    Alqadah, H. F.; Valdivia, N.

    2013-09-01

    The linear sampling method (LSM) has become a well established non-iterative technique for a variety of inverse scattering problems. The method offers a number of advantages over competing inverse scattering methods, mainly it is based on solving a linear problem while being able to account for multi-path effects. Unfortunately under the current framework the method is only effective when using a large number of multi-static data, and therefore may be impractical for many imaging applications. While primarily developed under a single frequency framework, recently the extension of the method to multi-banded data sets has been considered. It is known in general that the availability of multi-frequency data should compensate for reduced spatial diversity, but it is not clear how this can be accomplished for the LSM. In this work we take a step in this direction by considering a frequency based partial variation approach. We first establish that on bands absent of any corresponding Dirichlet eigenvalues the Herglotz density exhibits bounded variation. We then consider a regularization method incorporating this prior knowledge. The proposed approach exhibited a good estimate of the unknown Dirichlet eigenvalues of the obstacle in question when using reduced data. This observation also correlated with higher quality 3D reconstructions.

  1. A multi-frequency EIT system design based on telecommunication signal processors.

    PubMed

    Robitaille, Nicolas; Guardo, Robert; Maurice, Isabelle; Hartinger, Alzbeta E; Gagnon, Hervé

    2009-06-01

    A multi-frequency electrical impedance tomography system for cardiopulmonary monitoring has been designed with specialized digital signal processors developed primarily for the telecommunications sector. The system consists of two modules: a scan-head and a base-station. The scan-head, located close to the patient's torso, contains front-end circuits for measuring transfer impedance with a 16-electrode array. The base-station, placed at the bedside, comprises 16 direct digital synthesizers, 32 digital down-converters, digital circuits to control the data acquisition sequence and a USB-2.0 microcontroller. At every step of the scan sequence, the system simultaneously measures four complex variables at eight frequencies. These variables are the potential difference between the selected pair of sense electrodes, the currents applied by the source and sink electrodes, and the current flowing through the ground electrode. Frequencies are programmable from 10 kHz to 2 MHz with a resolution of 2 mHz. Characterization tests were performed with a precision mesh phantom connected to the scan-head. For a 5 Hz frame rate, the mean signal-to-noise ratio and accuracy are, respectively, 43 dB and 95.4% for eight frequencies logarithmically spaced from 70 to 950 kHz. In vitro and in vivo time-difference images have been reconstructed.

  2. The Galactic Center Radio Arc: A Multi-Frequency Spectro-Polarimetric Study

    NASA Astrophysics Data System (ADS)

    Toomey, James Edward; Lang, Cornelia C.; Ludovici, Dominic

    2014-06-01

    Despite the Radio Arc non-thermal filaments (NTFs) being discovered 30 years ago, their origin remain poorly understood. The Radio Arc NTFs have an unusually flat spectrum in the centimeter to millimeter spectrum with a predicted, though poorly constrained, turn-over between 30- 200 GHz. With the recently upgraded wide-band capabilities of the VLA, we conducted a multi-frequency spectro-polarimetric study of the Radio Arc region. With observations at a set of low radio frequencies (continuous coverage over 2-6 GHz & 10-12 GHz), we imaged both the total and polarized intensity distributions at high angular resolution (≤ 1”). Presented here are the preliminary results from four observations spanning May 2013 to February 2014 using the DnC, CnB, B & BnA array configurations. This study has produced the deepest continuum intensity images of the Radio Arc region to date, with a sensitivity an order of magnitude greater than previous surveys, and resulted in the detection of new structure and compact emission sources. These observations will serve as a pilot polarization study for larger, more complete polarimetric surveys of the Galactic center region.

  3. The galactic center radio arc: A multi-frequency polarimetric study

    NASA Astrophysics Data System (ADS)

    Toomey, James, IV

    Despite the Radio Arc non-thermal filaments (NTFs) being discovered 30 years ago, their origin remain poorly understood. The Radio Arc NTFs have an unusually flat spectrum in the centimeter to millimeter spectrum with a predicted, though poorly constrained, turn-over between 30-200 GHz. With the recently upgraded wide-band capabilities of the VLA, we conducted a multi-frequency polarimetric study of the Radio Arc region. With observations at a set of low radio frequencies (continuous coverage over 2-6 GHz & 10-12 GHz), we imaged both the total and polarized intensity distributions at high angular resolution (< 1''). Presented here are the preliminary results from four observations spanning May 2013 to February 2014 using the DnC, CnB, B & BnA array configurations. This study has produced the deepest continuum intensity images of the Radio Arc region to date, with a sensitivity an order of magnitude greater than previous surveys, and resulted in the detection of new structure and compact emission sources. These observations will serve as a pilot polarization study for larger, more complete polarimetric surveys of the Galactic center region.

  4. Data Acquisition System for Multi-Frequency Radar Flight Operations Preparation

    NASA Technical Reports Server (NTRS)

    Leachman, Jonathan

    2010-01-01

    A three-channel data acquisition system was developed for the NASA Multi-Frequency Radar (MFR) system. The system is based on a commercial-off-the-shelf (COTS) industrial PC (personal computer) and two dual-channel 14-bit digital receiver cards. The decimated complex envelope representations of the three radar signals are passed to the host PC via the PCI bus, and then processed in parallel by multiple cores of the PC CPU (central processing unit). The innovation is this parallelization of the radar data processing using multiple cores of a standard COTS multi-core CPU. The data processing portion of the data acquisition software was built using autonomous program modules or threads, which can run simultaneously on different cores. A master program module calculates the optimal number of processing threads, launches them, and continually supplies each with data. The benefit of this new parallel software architecture is that COTS PCs can be used to implement increasingly complex processing algorithms on an increasing number of radar range gates and data rates. As new PCs become available with higher numbers of CPU cores, the software will automatically utilize the additional computational capacity.

  5. Altered Effective Connectivity Network in Childhood Absence Epilepsy: A Multi-frequency MEG Study.

    PubMed

    Wu, Caiyun; Xiang, Jing; Jiang, Wenwen; Huang, Shuyang; Gao, Yuan; Tang, Lu; Zhou, Yuchen; Wu, Di; Chen, Qiqi; Hu, Zheng; Wang, Xiaoshan

    2017-03-12

    Using multi-frequency magnetoencephalography (MEG) data, we investigated whether the effective connectivity (EC) network of patients with childhood absence epilepsy (CAE) is altered during the inter-ictal period in comparison with healthy controls. MEG data from 13 untreated CAE patients and 10 healthy controls were recorded. Correlation analysis and Granger causality analysis were used to construct an EC network at the source level in eight frequency bands. Alterations in the spatial pattern and topology of the network in CAE were investigated by comparing the patients with the controls. The network pattern was altered mainly in 1-4 Hz, showing strong connections within the frontal cortex and weak connections in the anterior-posterior pathways. The EC involving the precuneus/posterior cingulate cortex (PC/PCC) significantly decreased in low-frequency bands. In addition, the parameters of graph theory were significantly altered in several low- and high-frequency bands. CAE patients display frequency-specific abnormalities in the network pattern even during the inter-ictal period, and the frontal cortex and PC/PCC might play crucial roles in the pathophysiology of CAE. The EC network of CAE patients was over-connective and random during the inter-ictal period. This study is the first to reveal the frequency-specific alteration in the EC network during the inter-ictal period in CAE patients. Multiple-frequency MEG data are useful in investigating the pathophysiology of CAE, which can serve as new biomarkers of this disorder.

  6. Performance evaluation of KHU Mark2 parallel multi-frequency EIT system

    NASA Astrophysics Data System (ADS)

    Kim, D. Y.; Wi, H.; Yoo, P. J.; Oh, T. I.; Woo, E. J.

    2010-04-01

    We describe a new parallel multi-frequency EIT system, KHU Mark2. It is based on the impedance measurement module (IMM), which comprises a single-ended constant current source and a voltmeter. Each IMM has an FPGA for its independent operations including current injection at multiple frequencies, voltage amplification, ADC, digital phase-sensitive demodulation and intra-networking with a main controller of the system. The main controller is based on a DSP and an isolated USB for its connection to a PC. There is an FPGA-based intranet controller, which arbitrates data exchanges between the DSP and multiple IMMs. Unlike its precursor, KHU Mark1, it is a true parallel system with no switching for both current injection and voltage sensing. The small size of the IMM results in a much reduced dimension of a multi-channel system. The KHU Mark2 can be assembled in any channels between 1 and 64. Depending on a chosen application, we custom design an analog backplane that interfaces multiple IMMs with electrodes. Special care was given to the system calibration to maximize its performance in frequency-difference EIT imaging as well as time-difference. Flexibility is the key improvement factor compared with the KHU Mark1. The new system can accommodate any current injection and voltage sensing protocol including the optimal injection current pattern. Reduced size and new internal architecture significantly improved mechanical as well as electrical stability of the system.

  7. Impurities and electron spin relaxations in nanodiamonds studied by multi-frequency electron spin resonance

    NASA Astrophysics Data System (ADS)

    Cho, Franklin; Takahashi, Susumu

    2014-03-01

    Nano-sized diamond or nanodiamond is a fascinating material for potential applications of fluorescence imaging and magnetic sensing of biological systems via nitrogen-vacancy defect centers in diamonds. Sensitivity of the magnetic sensing strongly depends on coupling to surrounding environmental noises, thus understanding of the environment is critical to realize the application. In the present study, we employ multi-frequency (X-band, 115 GHz and 230 GHz) continuous-wave (cw) and pulsed electron spin resonance (ESR) spectroscopy to investigate impurity contents and spin relaxation properties in various sizes of nanodiamonds. Spectra taken with our home-built 230/115 GHz cw/pulsed ESR spectrometer shows presence of two major impurity contents; single substitutional nitrogen impurities (P1) also common in bulk diamonds and paramagnetic impurities (denoted as X) unique to nanodiamonds. The ESR measurement also shows a strong dependence of the population ratio between P1 and X on particle size. Furthermore, we will discuss the nature of spin-lattice relaxation time T1 of nanodiamonds studied by pulsed ESR measurements at X-band, 115 GHz and 230 GHz.

  8. A Multi-Frequency Wide-Swath Spaceborne Cloud and Precipitation Imaging Radar

    NASA Technical Reports Server (NTRS)

    Li, Lihua; Racette, Paul; Heymsfield, Gary; McLinden, Matthew; Venkatesh, Vijay; Coon, Michael; Perrine, Martin; Park, Richard; Cooley, Michael; Stenger, Pete; Spence, Thomas; Retelny, Tom

    2016-01-01

    Microwave and millimeter-wave radars have proven their effectiveness in cloud and precipitation observations. The NASA Earth Science Decadal Survey (DS) Aerosol, Cloud and Ecosystems (ACE) mission calls for a dual-frequency cloud radar (W band 94 GHz and Ka-band 35 GHz) for global measurements of cloud microphysical properties. Recently, there have been discussions of utilizing a tri-frequency (KuKaW-band) radar for a combined ACE and Global Precipitation Measurement (GPM) follow-on mission that has evolved into the Cloud and Precipitation Process Mission (CaPPM) concept. In this presentation we will give an overview of the technology development efforts at the NASA Goddard Space Flight Center (GSFC) and at Northrop Grumman Electronic Systems (NGES) through projects funded by the NASA Earth Science Technology Office (ESTO) Instrument Incubator Program (IIP). Our primary objective of this research is to advance the key enabling technologies for a tri-frequency (KuKaW-band) shared-aperture spaceborne imaging radar to provide unprecedented, simultaneous multi-frequency measurements that will enhance understanding of the effects of clouds and precipitation and their interaction on Earth climate change. Research effort has been focused on concept design and trade studies of the tri-frequency radar; investigating architectures that provide tri-band shared-aperture capability; advancing the development of the Ka band active electronically scanned array (AESA) transmitreceive (TR) module, and development of the advanced radar backend electronics.

  9. Development of a Multi-frequency Interferometer Telescope for Radio Astronomy (MITRA)

    NASA Astrophysics Data System (ADS)

    Ingala, Dominique Guelord Kumamputu

    2015-03-01

    This dissertation describes the development and construction of the Multi-frequency Interferometer Telescope for Radio Astronomy (MITRA) at the Durban University of Technology. The MITRA station consists of 2 antenna arrays separated by a baseline distance of 8 m. Each array consists of 8 Log-Periodic Dipole Antennas (LPDAs) operating from 200 MHz to 800 MHz. The design and construction of the LPDA antenna and receiver system is described. The receiver topology provides an equivalent noise temperature of 113.1 K and 55.1 dB of gain. The Intermediate Frequency (IF) stage was designed to produce a fixed IF frequency of 800 MHz. The digital Back-End and correlator were implemented using a low cost Software Defined Radio (SDR) platform and Gnu-Radio software. Gnu-Octave was used for data analysis to generate the relevant received signal parameters including total power, real, and imaginary, magnitude and phase components. Measured results show that interference fringes were successfully detected within the bandwidth of the receiver using a Radio Frequency (RF) generator as a simulated source. This research was presented at the IEEE Africon 2013 / URSI Session Mauritius, and published in the proceedings.

  10. Sub-10 nm near-field localization by plasmonic metal nanoaperture arrays with ultrashort light pulses

    PubMed Central

    Lee, Hongki; Kim, Chulhong; Kim, Donghyun

    2015-01-01

    Near-field localization by ultrashort femtosecond light pulses has been investigated using simple geometrical nanoapertures. The apertures employ circular, rhombic, and triangular shapes to localize the distribution of surface plasmon. To understand the geometrical effect on the localization, aperture length and period of the nanoapertures were varied. Aperture length was shown to affect the performance more than aperture period due mainly to intra-aperture coupling of near-fields. Triangular apertures provided the strongest spatial localization below 10 nm in size as well as the highest enhancement of field intensity by more than 7000 times compared to the incident light pulse. Use of ultrashort pulses was found to allow much stronger light localization than with continuous-wave light. The results can be used for super-localization sensing and imaging applications where spatially localized fields can break through the limits in achieving improved sensitivity and resolution. PMID:26628326

  11. Trapping and injecting single domain walls in magnetic wire by local fields.

    PubMed

    Vázquez, Manuel; Basheed, G A; Infante, Germán; Del Real, Rafael P

    2012-01-20

    A single domain wall (DW) moves at linearly increasing velocity under an increasing homogeneous drive magnetic field. Present experiments show that the DW is braked and finally trapped at a given position when an additional antiparallel local magnetic field is applied. That position and its velocity are further controlled by suitable tuning of the local field. In turn, the parallel local field of small amplitude does not significantly affect the effective wall speed at long distance, although it generates tail-to-tail and head-to-head pairs of walls moving along opposite directions when that field is strong enough.

  12. Localization from near-source quasi-static electromagnetic fields

    SciTech Connect

    Mosher, John Compton

    1993-09-01

    A wide range of research has been published on the problem of estimating the parameters of electromagnetic and acoustical sources from measurements of signals measured at an array of sensors. In the quasi-static electromagnetic cases examined here, the signal variation from a point source is relatively slow with respect to the signal propagation and the spacing of the array of sensors. As such, the location of the point sources can only be determined from the spatial diversity of the received signal across the array. The inverse source localization problem is complicated by unknown model order and strong local minima. The nonlinear optimization problem is posed for solving for the parameters of the quasi-static source model. The transient nature of the sources can be exploited to allow subspace approaches to separate out the signal portion of the spatial correlation matrix. Decomposition techniques are examined for improved processing, and an adaptation of MUtiple SIgnal Characterization (MUSIC) is presented for solving the source localization problem. Recent results on calculating the Cramer-Rao error lower bounds are extended to the multidimensional problem here. This thesis focuses on the problem of source localization in magnetoencephalography (MEG), with a secondary application to thunderstorm source localization. Comparisons are also made between MEG and its electrical equivalent, electroencephalography (EEG). The error lower bounds are examined in detail for several MEG and EEG configurations, as well as localizing thunderstorm cells over Cape Canaveral and Kennedy Space Center. Time-eigenspectrum is introduced as a parsing technique for improving the performance of the optimization problem.

  13. Species-Independent Femtosecond Localized Electric Field Measurement

    NASA Astrophysics Data System (ADS)

    Dogariu, Arthur; Goldberg, Benjamin M.; O'Byrne, Sean; Miles, Richard B.

    2017-02-01

    We present an optical measurement method using a femtosecond laser for nonintrusive measurements of electric field strength and orientation in virtually any gas or gas mixture via second-harmonic generation. This simple method takes advantage of the asymmetry in polarizability induced by an applied electric field, which enables the otherwise forbidden second-harmonic generation in any centrosymmetric or homogeneous media. The use of a femtosecond laser source permits high intensities without avalanche breakdown and leads to the measurement of electric field strength down to approximately 100 V / cm in air with submillimeter spatial resolution governed by the confocal parameter and femtosecond temporal resolution governed by the laser-pulse duration.

  14. Performance Monitoring Local Field Potentials in the Medial Frontal Cortex of Primates: Supplementary Eye Field

    PubMed Central

    Emeric, Erik E.; Leslie, Melanie; Pouget, Pierre

    2010-01-01

    We describe intracranial local field potentials (LFPs) recorded in the supplementary eye field (SEF) of macaque monkeys performing a saccade countermanding task. The most prominent feature at 90% of the sites was a negative-going polarization evoked by a contralateral visual target. At roughly 50% of sites a negative-going polarization was observed preceding saccades, but in stop signal trials this polarization was not modulated in a manner sufficient to control saccade initiation. When saccades were canceled in stop signal trials, LFP modulation increased with the inferred magnitude of response conflict derived from the coactivation of gaze-shifting and gaze-holding neurons. At 30% of sites, a pronounced negative-going polarization occurred after errors. This negative polarity did not appear in unrewarded correct trials. Variations of response time with trial history were not related to any features of the LFP. The results provide new evidence that error-related and conflict-related but not feedback-related signals are conveyed by the LFP in the macaque SEF and are important for identifying the generator of the error-related negativity. PMID:20660423

  15. Frequency-dependent local field factors in dielectric liquids by a polarizable force field and molecular dynamics simulations

    SciTech Connect

    Davari, Nazanin; Haghdani, Shokouh; Åstrand, Per-Olof

    2015-12-31

    A force field model for calculating local field factors, i.e. the linear response of the local electric field for example at a nucleus in a molecule with respect to an applied electric field, is discussed. It is based on a combined charge-transfer and point-dipole interaction model for the polarizability, and thereby it includes two physically distinct terms for describing electronic polarization: changes in atomic charges arising from transfer of charge between the atoms and atomic induced dipole moments. A time dependence is included both for the atomic charges and the atomic dipole moments and if they are assumed to oscillate with the same frequency as the applied electric field, a model for frequency-dependent properties are obtained. Furthermore, if a life-time of excited states are included, a model for the complex frequency-dependent polariability is obtained including also information about excited states and the absorption spectrum. We thus present a model for the frequency-dependent local field factors through the first molecular excitation energy. It is combined with molecular dynamics simulations of liquids where a large set of configurations are sampled and for which local field factors are calculated. We are normally not interested in the average of the local field factor but rather in configurations where it is as high as possible. In electrical insulation, we would like to avoid high local field factors to reduce the risk for electrical breakdown, whereas for example in surface-enhanced Raman spectroscopy, high local field factors are desired to give dramatically increased intensities.

  16. Microvasculature alters the dispersion properties of shear waves--a multi-frequency MR elastography study.

    PubMed

    Jugé, Lauriane; Petiet, Anne; Lambert, Simon A; Nicole, Pascal; Chatelin, Simon; Vilgrain, Valerie; Van Beers, Bernard E; Bilston, Lynne E; Sinkus, Ralph

    2015-12-01

    Magnetic Resonance Elastography (MRE) uses macroscopic shear wave propagation to quantify mechanical properties of soft tissues. Micro-obstacles are capable of affecting the macroscopic dispersion properties of shear waves. Since disease or therapy can change the mechanical integrity and organization of vascular structures, MRE should be able to sense these changes if blood vessels represent a source for wave scattering. To verify this, MRE was performed to quantify alteration of the shear wave speed cs due to the presence of vascular outgrowths using an aortic ring model. Eighteen fragments of rat aorta included in a Matrigel matrix (n=6 without outgrowths, n=6 with a radial outgrowth extent of ~600 µm and n=6 with ~850 µm) were imaged using a 7 Tesla MR scanner (Bruker, PharmaScan). High resolution anatomical images were acquired in addition to multi-frequency MRE (ν = 100, 115, 125, 135 and 150 Hz). Average cs was measured within a ring of ~900 µm thickness encompassing the aorta and were normalized to cs0 of the corresponding Matrigel. The frequency dependence was fit to the power law model cs ~ν(y). After scanning, optical microscopy was performed to visualize outgrowths. Results demonstrated that in presence of vascular outgrowths (1) normalized cs significantly increased for the three highest frequencies (Kruskal-Wallis test, P = 0.0002 at 125 Hz and P = 0.002 at 135 Hz and P = 0.003 at 150 Hz) but not for the two lowest (Kruskal-Wallis test, P = 0.63 at 100 Hz and P = 0.87 at 115 Hz), and (2) normalized cs followed a power law behavior not seen in absence of vascular outgrowths (ANOVA test, P < 0.0001). These results showed that vascular outgrowths acted as micro-obstacles altering the dispersion relationships of propagating shear waves and that MRE could provide valuable information about microvascular changes.

  17. A glimpse beneath Antarctic sea ice: observation of platelet-layer thickness and ice-volume fraction with multi-frequency EM

    NASA Astrophysics Data System (ADS)

    Hendricks, S.; Hoppmann, M.; Hunkeler, P. A.; Kalscheuer, T.; Gerdes, R.

    2015-12-01

    In Antarctica, ice crystals (platelets) form and grow in supercooled waters below ice shelves. These platelets rise and accumulate beneath nearby sea ice to form a several meter thick sub-ice platelet layer. This special ice type is a unique habitat, influences sea-ice mass and energy balance, and its volume can be interpreted as an indicator for ice - ocean interactions. Although progress has been made in determining and understanding its spatio-temporal variability based on point measurements, an investigation of this phenomenon on a larger scale remains a challenge due to logistical constraints and a lack of suitable methodology. In the present study, we applied a lateral constrained Marquardt-Levenberg inversion to a unique multi-frequency electromagnetic (EM) induction sounding dataset obtained on the ice-shelf influenced fast-ice regime of Atka Bay, eastern Weddell Sea. We adapted the inversion algorithm to incorporate a sensor specific signal bias, and confirmed the reliability of the algorithm by performing a sensitivity study using synthetic data. We inverted the field data for sea-ice and sub-ice platelet-layer thickness and electrical conductivity, and calculated ice-volume fractions from platelet-layer conductivities using Archie's Law. The thickness results agreed well with drill-hole validation datasets within the uncertainty range, and the ice-volume fraction also yielded plausible results. Our findings imply that multi-frequency EM induction sounding is a suitable approach to efficiently map sea-ice and platelet-layer properties. However, we emphasize that the successful application of this technique requires a break with traditional EM sensor calibration strategies due to the need of absolute calibration with respect to a physical forward model.

  18. Geometrical parameters effects on local electric field enhancement of silver-dielectric-silver multilayer nanoshell

    SciTech Connect

    Shirzaditabar, Farzad; Saliminasab, Maryam

    2013-05-15

    The local electric field enhancement at different points of silver-dielectric-silver nanoshell is investigated using quasi-static theory. Because of the symmetric and anti-symmetric coupling between surface plasmon of inner silver core and outer silver shell, the local electric field spectrum of silver-dielectric-silver has two distinct peaks at resonance wavelengths. The silver core size and middle dielectric thickness affect the local electric field enhancement at different points of silver-dielectric-silver nanoshell. Increasing the silver core radius always leads to blue shift of shorter resonance wavelength and red shift of longer resonance wavelength. We observed two distinct local electric field peaks, which are corresponded to the symmetric and anti-symmetric coupling between inner and outer surface plasmons. In a system with thick silver shell, local electric field enhancement is greater than a system with thin silver shell. However, the local electric field variations as a function of silver core radius in both systems are different at different points of nanoshell. The effects of the dielectric thickness variations on local electric field are different from those from silver core size variations. As the dielectric thickness is about 3 nm, the highest local electric field enhancement occurs at the surface of the inner silver core, where the symmetric and anti-symmetric modes are mixed together.

  19. Radio frequency current-voltage probe for impedance and power measurements in multi-frequency unmatched loads.

    PubMed

    Lafleur, T; Delattre, P A; Booth, J P; Johnson, E V; Dine, S

    2013-01-01

    A broad-band, inline current-voltage probe, with a characteristic impedance of 50 Ω, is presented for the measurement of voltage and current waveforms, impedance, and power in rf systems. The probe, which uses capacitive and inductive sensors to determine the voltage and current, respectively, can be used for the measurement of single or multi-frequency signals into both matched and unmatched loads, over a frequency range of about 1-100 MHz. The probe calibration and impedance/power measurement technique are described in detail, and the calibrated probe results are compared with those obtained from a vector network analyzer and other commercial power meters. Use of the probe is demonstrated with the measurement of power into an unmatched capacitively coupled plasma excited by multi-frequency tailored voltage waveforms.

  20. Local Properties of Index-Alpha Stable Fields.

    DTIC Science & Technology

    1986-12-01

    not exhaust that class, e.g. Cambanis and Soltani (1983). Sufficient conditions for (3.1) and (3.2) to hold are respectively (3.5) lim suP XIN+aP4...The Geometry of Random Fields, John Wiley and Sons, New York. 2. Cambanis, S. and Soltani , A.R. (1983) "Prediction of stable processes: spectral and

  1. Efficient Simulation and Downscaling of Large Non-Stationary Fields with Varying Local Anisotropy

    NASA Astrophysics Data System (ADS)

    Dodov, B.

    2015-12-01

    Simulation of locally anisotropic, non-stationary random fields is a relatively new topic in geostatistics with applications currently restricted to the construction of an admissible covariance matrix. In this paper, we introduce an efficient algorithm for constructing large non-stationary random fields with arbitrary local covariance structure and anisotropy. At the heart of our approach is a newly developed robust directional multiresolution framework combined with a local tensor anisotropy model. The use of our algorithm is illustrated with local anisotropy analysis, simulation and downscaling of complex pseudo-precipitation (PP) fields* related to tropical and extra-tropical cyclones. The efficiency of the algorithm allows obtaining realistic downscaled global GCM precipitation fields down to a few kilometers resolution in seconds.* Reference: Unpublished work by Huiling Yuan and Zoltan Toth. PP fields are constructed by taking the precipitation as the positive component of the field and the water vapor saturation deficit as its negative complement.

  2. Multi-DOF rotor model based measurement of stiffness and damping for active magnetic bearing using multi-frequency excitation

    NASA Astrophysics Data System (ADS)

    Jiang, Kejian; Zhu, Changsheng; Chen, Liangliang; Qiao, Xiaoli

    2015-08-01

    To represent the support characteristic of active magnetic bearings (AMB), the commonly used parameters are the equivalent stiffness and the equivalent damping, which inherit the parameters of the stiffness and the damping from traditional mechanical bearings. First, by analyzing the diversity and the similarity between traditional mechanical bearing and AMB, the prior condition for applying the parametric representation of equivalent stiffness and equivalent damping to AMB is illuminated. Then, a method for measuring the equivalent stiffness and the equivalent damping of AMB-rotor system is proposed with multi-frequency excitation. One of its outstanding features is that the proposed method is based on the multi-degree of freedom (DOF) rotor model, not the single- DOF model, because the single DOF model cannot be suitably applied to the multi-DOF AMB-rotor systems. Otherwise, in order to decrease the identification error, the multi-frequency excitation can achieve the lowest peak value by means of appropriate selection for the relative phasing of each component, so that the possibility of the rotor displacement exceeding clearances of AMB and the magnetic force reaching saturation is minimized. Finally, the experiments, which are carried out on an AMB-rotor test rig with a vertical shaft, indicate that the proposed method can efficiently reduce the peak value for the superimposed multi-frequency excitation and correctly identify the equivalent stiffness and equivalent damping of AMB-rotor system.

  3. Dark Field Technology - A Practical Approach To Local Alignment

    NASA Astrophysics Data System (ADS)

    Beaulieu, David R.; Hellebrekers, Paul P.

    1987-01-01

    A fully automated direct reticle reference alignment system for use in step and repeat camera systems is described. The technique, first outlined by Janus S. Wilczynski, ("Optical Step and Repeat Camera with Dark Field Alignment", J. Vac. Technol., 16(6), Nov./Dec. 1979), has been implemented on GCA Corporation's DSW Wafer Stepper. Results from various process levels covering the typical CMOS process have shown that better than ±0.2μm alignment accuracy can be obtained with minimal process sensitivity. The technique employs fixed illumination and microscope optics to achieve excellent registration stability and maintenance-free operation. Latent image techniques can be exploited for intra-field, grid and focus characterization.

  4. Switching local magnetization by electric-field-induced domain wall motion

    NASA Astrophysics Data System (ADS)

    Kakizakai, Haruka; Ando, Fuyuki; Koyama, Tomohiro; Yamada, Kihiro; Kawaguchi, Masashi; Kim, Sanghoon; Kim, Kab-Jin; Moriyama, Takahiro; Chiba, Daichi; Ono, Teruo

    2016-06-01

    Electric field effect on magnetism is an appealing technique for manipulating magnetization at a low energy cost. Here, we show that the local magnetization of an ultrathin Co film can be switched by simply applying a gate electric field without the assistance of any external magnetic field or current flow. The local magnetization switching is explained by nucleation and annihilation of magnetic domains through domain wall motion induced by the electric field. Our results lead to external-field-free and ultralow-energy spintronic applications.

  5. Multi-Frequency Synthesis - a New Technique in Radio Interferometric Imaging

    NASA Astrophysics Data System (ADS)

    Conway, J. E.; Cornwell, T. J.; Wilkinson, P. N.

    1990-10-01

    We describe an extension to aperture synthesis, multi-frequency synthesis or MFS, whose principal goal is to allow high-quality radio images to be obtained from spars interferometric arrays. The idea is to use data from a relatively narrow range of frequencies (typically +/- 10 per cent) to produce a major improvement in the aperture-plane coverage of an array. From these data one can reconstruct an image at a single reference frequency in which the 'reconstruction errors', which normally occur as a result of large 'holes' in the aperture plane, are much reduced. The obvious problem to -be overcome is that the source brightness distribution is slightly different at each frequency. We analyse the 'spectral errors' introduced into the reconstructed image by this frequency-dependent structure. For a +/- 1 2.5 per cent range of frequencies we show that typically, spectral errors will be below the thermal noise level provided that the ratio of the peak brightness (excluding any compact component such as a radio core) to rms noise is less than a thousand-to-one, Unresolved features can be identified easily and effectively removed from the data a each frequency and hence they need not be a source of spectral errors. When this spectral errors are above the noise they can be recognized and removed by an extension to the well-established CLEAN deconvolution methodi We call the new method 'double deconvolution', or DD, and demonstrate its effectiveness 0 simulated data. The primary motivation beyond narrow-band MFS observations is to produce improved intensity images, rather than to determine spectral index distributions. Although the DD algorithm effectively estimates the spectral index distribution in the course of removing spectral effects, these estimates will be crude and not generally of astrophysical use. We briefly consider the practical problems involved in making MFS observations and conclude that the major limiting factor is likely to be radio

  6. Land subsidence in the Yangtze River Delta, China revealed from multi-frequency SAR Interferometry

    NASA Astrophysics Data System (ADS)

    Li, Zhenhong; Motagh, Mahdi; Yu, Jun; Gong, Xulong; Wu, Jianqiang; Zhu, Yefei; Chen, Huogen; Zhang, Dengming; Xu, Yulin

    2014-05-01

    of multi-frequency SAR datasets allows a long record (~20 years) of historic deformation to be measured over a large region. Ultimately this should help inform land managers in assessing land subsidence and planning appropriate remedial measures.

  7. Multi-frequency survey of background radiations of the Universe. The "Cosmological Gene" project. First results

    NASA Astrophysics Data System (ADS)

    Parijskij, Yu. N.; Mingaliev, M. G.; Nizhel'Skii, N. A.; Bursov, N. N.; Berlin, A. B.; Grechkin, A. A.; Zharov, V. I.; Zhekanis, G. V.; Majorova, E. K.; Semenova, T. A.; Stolyarov, V. A.; Tsybulev, P. G.; Kratov, D. V.; Udovitskii, R. Yu.; Khaikin, V. B.

    2011-10-01

    The results of the first stage of the "Cosmological Gene" project of the Russian Academy of Sciences are reported. These results consist in the accumulation of multi-frequency data in 31 frequency channels in the wavelength interval 1-55 cm with maximum achievable statistical sensitivity limited by the noise of background radio sources at all wavelengths exceeding 1.38 cm. The survey region is determined by constraints 00 h < RA < 24 h and 40°30' < DEC < 42°30'. The scientific goals of the project are refined in view of recent proposals to use cosmological background radiation data for the development of a unified physical theory. Experimental data obtained with the RATAN-600 radio telescope are used to refine the contribution of the main "screens" located between the observer and the formation epoch of cosmic background radiation ( z = 1100). Experimental data for synchrotron radiation and free-free noise on scales that are of interest for the anisotropy of cosmic microwave background are reported as well as the contribution of these noise components in millimeter-wave experiments to be performed in the nearest years. The role of dipole radio emission of fullerene-type dust nanostructures is shown to be small. The most precise estimates of the role of background radio sources with inverted spectra are given and these sources are shown to create no serious interference in experiments. The average spectral indices of the weakest sources of the NVSS and FIRST catalogs are estimated. The "saturation" data for all wavelengths allowed a constraint to be imposed on the Sunyaev-Zeldovich noise (the SZ noise) at all wavelengths, and made it possible to obtain independent estimates of the average sky temperature from sources, substantially weaker than those listed in the NVSS catalog. These estimates are inconsistent with the existence of powerful extragalactic synchrotron background associated with radio sources. Appreciable "quadrupole" anisotropy in is detected in the

  8. A multi-frequency study of an X ray selected sample of active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Grossan, Bruce Alan

    1992-01-01

    The LASS (Large Area Sky Survey) experiment, which flew aboard the HEAO-1 spacecraft, carried out a 2-20 keV survey of the sky during 1977-1978. The X-ray sources from this survey make up the LASS catalog (Wood et al. 1979). Optical counterparts have been identified for greater than 86 percent of the LASS sources above a flux of approx. 0.95 microns (mu)Jy Q 5 keV (Remillard 1992b). The LASS error boxes, along with the more precise positions from the Modulation Collimator (MC) X-ray experiment (also aboard HEAO-1), subsequent X-ray imaging, and optical search techniques were all used to identify the LASS sources. From these identifications, a high-latitude (absolute value of b greater than 20 deg.), flux limited (greater than or equal to 0.95 (mu)Jy) sample of 96 emission line Active Galactic Nuclei (AGN) have been selected for study. The sample is referred to as the LMA (for the LASS/MC identified sample of AGN). The objective of this work is to produce multi-frequency spectra of this sample of objects, in order to determine and interpret the statistical properties of the sample over nearly the full range of observable wavelengths. Data were obtained for as much of the radio through hard X-ray (less than 20 keV) spectrum as possible for each object in the LMA. Radio, near infrared, and other measurements were taken from the literature, far IR fluxes were extracted from co-added observations from IRAS, UV spectra were obtained from the IUE archives, and original observations were performed (with the help of collaborators) in the radio, near IR, optical, UV, and X-ray to fulfill this goal. Correlation studies of the continuum bands found poor correlations of X-ray and radio flux, good correlations for 12 and 26 micron flux with X-ray flux, excellent correlations for optical and near IR fluxes with X-rays, and poor correlations of UV and X-ray fluxes. Correlation studies of the line and X-ray continuum flux yield a good correlation between the flux of (OIII), the

  9. Electrostatic Kelvin-Helmholtz instability produced by a localized electric field perpendicular to an external magnetic field

    NASA Technical Reports Server (NTRS)

    Pritchett, P. L.

    1987-01-01

    The evolution of a plasma with a localized electric field perpendicular to an external magnetic field is shown to be dominated by the Kelvin-Helmholtz instability. For small ion gyroradius, the instability is similar to the fluid mode. When the ion gyroradius is an appreciable fraction of the spatial extent of the electric field, the plasma is not in equilibrium, and the initial drift profile relaxes. Subsequent evolution still leads to vortex flows.

  10. Insights into lateral marsh retreat mechanism through localized field measurements

    NASA Astrophysics Data System (ADS)

    Bendoni, M.; Mel, R.; Solari, L.; Lanzoni, S.; Francalanci, S.; Oumeraci, H.

    2016-02-01

    Deterioration of salt marshes may be due to several factors related to increased anthropic pressure, sea level rise, and erosive processes. While salt marshes can reach equilibrium in the vertical direction, adapting to sea level rise, they are inherently unstable in the horizontal direction. Marsh boundaries are characterized by scarps with bare sediment below the vegetated surface layer that can be easily removed by wave-induced erosion. In this work, we explore the different mechanisms involved in the erosion of marsh borders through the interpretation of field data. The analysis is based on a systematic field monitoring of a salt marsh in the Venice Lagoon subject to lateral erosion. Measurements included horizontal retreat of the scarp at various locations and wave height in front of the marsh during three storm surges. Continuous erosion and mass failures alternated during the observed period, leading to an average retreat up to 80 cm/yr. The data, collected roughly every month for 1.5 year, indicate that the linear relation that links the observed erosion rate to the impinging wave power exhibits a larger slope than that already estimated in literature on the basis of long-term surveys. Moreover, an increase in the gradient of erodibility is detected along the marsh scarp, due to the combined action of soil strengthening by vegetation on the marsh surface and the impact of wave breaking at the bank toe, which promote cantilever failures and increase the lateral erosion rate.

  11. Synthetic Dimensions with Magnetic Fields and Local Interactions in Photonic Lattices.

    PubMed

    Ozawa, Tomoki; Carusotto, Iacopo

    2017-01-06

    We discuss how one can realize a photonic device that combines synthetic dimensions and synthetic magnetic fields with spatially local interactions. Using an array of ring cavities, the angular coordinate around each cavity spans the synthetic dimension. The synthetic magnetic field arises as the intercavity photon hopping is associated with a change of angular momentum. Photon-photon interactions are local in the periodic angular coordinate around each cavity. Experimentally observable consequences of the synthetic magnetic field and of the local interactions are pointed out.

  12. Direct subwavelength imaging and control of near-field localization in individual silver nanocubes

    SciTech Connect

    Mårsell, Erik; Svärd, Robin; Miranda, Miguel; Guo, Chen; Harth, Anne; Lorek, Eleonora; Mauritsson, Johan; Arnold, Cord L.; L'Huillier, Anne; Mikkelsen, Anders; Losquin, Arthur; Xu, Hongxing

    2015-11-16

    We demonstrate the control of near-field localization within individual silver nanocubes through photoemission electron microscopy combined with broadband, few-cycle laser pulses. We find that the near-field is concentrated at the corners of the cubes, and that it can be efficiently localized to different individual corners depending on the polarization of the incoming light. The experimental results are confirmed by finite-difference time-domain simulations, which also provide an intuitive picture of polarization dependent near-field localization in nanocubes.

  13. Removal of the local geomagnetic field affects reproductive growth in Arabidopsis.

    PubMed

    Xu, Chunxiao; Wei, Shufeng; Lu, Yan; Zhang, Yuxia; Chen, Chuanfang; Song, Tao

    2013-09-01

    The influence of the geomagnetic field-removed environment on Arabidopsis growth was investigated by cultivation of the plants in a near-null magnetic field and local geomagnetic field (45 µT) for the whole growth period under laboratory conditions. The biomass accumulation of plants in the near-null magnetic field was significantly suppressed at the time when plants were switching from vegetative growth to reproductive growth compared with that of plants grown in the local geomagnetic field, which was caused by a delay in the flowering of plants in the near-null magnetic field. At the early or later growth stage, no significant difference was shown in the biomass accumulation between the plants in the near-null magnetic field and local geomagnetic field. The average number of siliques and the production of seeds per plant in the near-null magnetic field was significantly lower by about 22% and 19%, respectively, than those of control plants. These resulted in a significant reduction of about 20% in the harvest index of plants in the near-null magnetic field compared with that of the controls. These results suggest that the removal of the local geomagnetic field negatively affects the reproductive growth of Arabidopsis, which thus affects the yield and harvest index.

  14. The lure of local SETI: Fifty years of field experiments

    NASA Astrophysics Data System (ADS)

    Ailleris, Philippe

    2011-01-01

    With the commemoration in October 2007 of the Sputnik launch, space exploration celebrated its 50th anniversary. Despite impressive technological and scientific achievements the fascination for space has weakened during the last decades. One contributing factor has been the gradual disappearance of mankind's hope of discovering extraterrestrial life within its close neighbourhood. In striking contrast and since the middle of the 20th century, a non-negligible proportion of the population have already concluded that intelligent beings from other worlds do exist and visit Earth through space vehicles popularly called Unidentified Flying Objects (UFOs). In light of the continuous public interest for the UFO enigma symbolized by the recent widely diffused media announcements on the release of French and English governmental files; and considering the approach of broadening the strategies of the "Active SETI" approach and the existence of a rich multi-disciplinary UFO documentation of potential interest for SETI; this paper describes some past scientific attempts to demonstrate the physical reality of the phenomena and potentially the presence on Earth of probes of extraterrestrial origin. Details of the different instrumented field studies deployed by scientists and organizations during the period 1950-1990 in the USA, Canada and Europe are provided. In conclusion it will be argued that while continuing the current radio/optical SETI searches, there is the necessity to maintain sustaining attention to the topic of anomalous aerospace phenomena and to develop new rigorous research approaches.

  15. Localization of incipient tip vortex cavitation using ray based matched field inversion method

    NASA Astrophysics Data System (ADS)

    Kim, Dongho; Seong, Woojae; Choo, Youngmin; Lee, Jeunghoon

    2015-10-01

    Cavitation of marine propeller is one of the main contributing factors of broadband radiated ship noise. In this research, an algorithm for the source localization of incipient vortex cavitation is suggested. Incipient cavitation is modeled as monopole type source and matched-field inversion method is applied to find the source position by comparing the spatial correlation between measured and replicated pressure fields at the receiver array. The accuracy of source localization is improved by broadband matched-field inversion technique that enhances correlation by incoherently averaging correlations of individual frequencies. Suggested localization algorithm is verified through known virtual source and model test conducted in Samsung ship model basin cavitation tunnel. It is found that suggested localization algorithm enables efficient localization of incipient tip vortex cavitation using a few pressure data measured on the outer hull above the propeller and practically applicable to the typically performed model scale experiment in a cavitation tunnel at the early design stage.

  16. Using local fields to tailor hybrid quantum-dot/metal nanoparticle systems

    NASA Astrophysics Data System (ADS)

    Artuso, Ryan D.; Bryant, Garnett W.; Garcia-Etxarri, Aitzol; Aizpurua, Javier

    2011-06-01

    We study hybrid-molecule structures consisting of a metal nanoparticle (MNP) nanorod coupled to a semiconductor quantum dot (SQD). MNP geometry can be used to tailor the local fields that determine the SQD-MNP coupling and to engineer the hybrid dynamical response. We identify regimes where dark modes and higher-order multipolar modes can influence hybrid response. Strong local-field coupling via dark modes changes the interference and self-interaction effects dramatically. External fields do not directly drive this MNP dark mode, so SQD-MNP coupling is dominated by the local induced self-coupling. By utilizing more complex structures that provide substantial local-field enhancement, we show the strong SQD-MNP coupling regimes can be made much more accessible. All of these aspects could enhance the capabilities of metal nanostructures to provide spatial and spectral control of the optical properties of single emitters.

  17. On the local Hurst exponent of geomagnetic field fluctuations: Spatial distribution for different geomagnetic activity levels

    NASA Astrophysics Data System (ADS)

    Michelis, Paola De; Consolini, Giuseppe

    2015-04-01

    This study attempts to characterize the spatial distribution of the scaling features of the short time scale magnetic field fluctuations obtained from 45 ground-based geomagnetic observatories distributed in the Northern Hemisphere. We investigate the changes of the scaling properties of the geomagnetic field fluctuations by evaluating the local Hurst exponent and reconstruct maps of this index as a function of the geomagnetic activity level. These maps permit us to localize the different latitudinal structures responsible for disturbances and related to the ionospheric current systems. We find that the geomagnetic field fluctuations associated with the different ionospheric current systems have different scaling features, which can be evidenced by the local Hurst exponent. We also find that in general, the local Hurst exponent for quiet magnetospheric periods is higher than that for more active periods suggesting that the dynamical processes that are activated during disturbed times are responsible for changes in the nature of the geomagnetic field fluctuations.

  18. Externally controlled local magnetic field in a conducting mesoscopic ring coupled to a quantum wire

    SciTech Connect

    Maiti, Santanu K.

    2015-01-14

    In the present work, the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an in-plane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the in-plane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designing spin-based quantum devices is also analyzed.

  19. Accurate color tuning of firefly chromophore by modulation of local polarization electrostatic fields.

    PubMed

    Cai, Duanjun; Marques, Miguel A L; Nogueira, Fernando

    2011-01-20

    Although many microenvironmental factors contribute to the color shift of light emission from the firefly chromophore, the dominant one is the local electrostatic field. This opens up the possibility of accurate color tuning the bioluminescent absorption and emission by adjusting the local charged residues. With this aim, the optical response of oxyluciferin for different electrostatic fields is computed by using time-dependent density-functional theory. We find that the wavelength shift is correlated to the projection of the electrostatic field on the molecular plane, and that the fluorescent intensity of the second excitation peak can be effectively enhanced or suppressed (±30%) by field modulation. A model is formulated by correlating the shift in the spectral maxima with the projection of the local electrostatic field on the molecular plane. This method provides a predictable determination of the structural modifications leading to a particular color shift and/or fluorescent efficiency enhancement.

  20. Effect of local field enhancement on the nonlinear terahertz response of a silicon-based metamaterial

    NASA Astrophysics Data System (ADS)

    Al-Naib, Ibraheem; Sharma, Gargi; Dignam, Marc M.; Hafez, Hassan; Ibrahim, Akram; Cooke, David G.; Ozaki, Tsuneyuki; Morandotti, Roberto

    2013-11-01

    We demonstrate the strong effect of the local field enhancement on the nonlinear terahertz response of a hybrid photoexcited silicon/double concentric ring metamaterial structure. The ring resonators enhance the local terahertz electric field by more than a factor of ten, pushing the terahertz-semiconductor interaction into the high-field regime even for moderate-strength incident terahertz pulses. In this regime, terahertz field-induced intervalley scattering in the photoexcited silicon substrate dynamically alters the substrate conductivity, which in turn strongly modifies the pulse transmission. The spatial distribution of the local field enhancement within the resonator structure results in a modified bandwidth, amplitude, and central frequency of the transmission resonance occurring on a subcycle time scale. These results demonstrate an enhancement of the nonlinear terahertz response of silicon-based metamaterials that must be accounted for in the design of terahertz nonlinear devices.

  1. Retrieving small features in reflection-mode raster-scan optoacoustic mesoscopy (RSOM) using multi-frequency reconstruction

    NASA Astrophysics Data System (ADS)

    Omar, Murad; Soliman, Dominik; Gateau, Jérôme; Ntziachristos, Vasilis

    2015-03-01

    We developed a reflection-mode, raster-scan optoacoustic mesoscopy system, based on a custom-made ultrasonic detector, with an ultra wide bandwidth of 20-180 MHz. To optimally use this bandwidth, we implemented multifrequency reconstruction. System characterization reveals a 4 μm axial, and 18 μm transverse resolution, at penetration depths reaching 5 mm. After characterization, the system was applied to image a zebrafish ex vivo, and an excised mouse ear. In the zebrafish, the lateral line, intestines, eyes, and melanocytes are seen, while in the mouse ear, multi-frequency reconstruction recovered the small vessels, otherwise not seen on the image.

  2. Stimulated Brillouin scattering in the field of a two-dimensionally localized pumping wave

    NASA Astrophysics Data System (ADS)

    Solikhov, D. K.; Dvinin, S. A.

    2016-06-01

    Stimulated Brillouin scattering of electromagnetic waves in the field of a two-dimensionally localized pump wave at arbitrary scattering angles in the regime of forward scattering is analyzed. Spatial variations in the amplitudes of interacting waves are studied for different values of the pump field and different dimensions of the pump wave localization region. The intensity of scattered radiation is determined as a function of the scattering angle and the dimensions of the pump wave localization region. It is shown that the intensity increases with increasing scattering angle.

  3. Near-field localization by two dimensional metallic nano-post arrays with ultrashort light pulses

    NASA Astrophysics Data System (ADS)

    Lee, Hongki; Kim, Chulhong; Kim, Donghyun

    2016-03-01

    Locally amplified near-fields can be induced with nanostructures within a sub-diffraction-limited volume, which is useful for biomedical imaging and sensing applications. Employment of field localization in the biomedical applications where the pulsed light is used necessitates the spatial and temporal characteristics of fields near nanostructures. We considered the gold nano-post arrays of three different shapes to localize the near-fields which are circular, rhombic, and triangular. They were modeled to be located on an ITO film and a quartz substrate with periods changing from 300 to 900 nm by 200 nm. Their size changes from 50 to 250 nm which corresponds to the radius for the case of circular nanoposts and the distance between the center and the vertices for equilateral rhombic and triangular nanoposts. Numerical calculation of near-fields at the top of nanoposts was performed with finite difference time domain method when the Gaussian pulses at center wavelengths of 532, 633, and 850 nm were normally incident. Near-fields localization occurred mainly at vertices of the nanoposts, which makes the triangular nanoposts of primary interest with an observation of the strongest field intensity within a diffraction limited field-of-view. The observed fields on the triangular vertices were enhanced by 7.85, 51.54, and 7268 when the center wavelengths were 532, 633, and 850 nm respectively. Their temporal peaks were delayed by 2.05, 4.03, and 14.49 fs, which indicates the correlation between field enhancement and time delay associated with electron damping process. It was shown that with rhombic and triangular nanoposts fields can be localized below 10 nm on vertices and their signal-to-noise ratio increased with a larger period.

  4. Thinking Globally, Planning Nationally and Acting Locally: Nested Organizational Fields and the Adoption of Environmental Practices

    ERIC Educational Resources Information Center

    Vasi, Ion Bogdan

    2007-01-01

    The study of the adoption of activities to protect the natural environment has tended to focus on the role of organizational fields. This article advances existing research by simultaneously examining conflicting processes that operate in nested organizational fields at local, national and supra-national levels. It examines the recent spread of an…

  5. Stabilization of the Vertical Mode in Tokamaks by Localized Nonaxisymmetric Fields

    SciTech Connect

    A. Reiman

    2007-10-02

    Vertical instability of a tokamak plasma can be controlled by nonaxisymmetric magnetic fields localized near the plasma edge at the bottom and top of the torus. The required magnetic fields can be produced by a relatively simple set of parallelogram-shaped coils.

  6. Local field enhancement on metallic periodic surface structures produced by femtosecond laser pulses

    SciTech Connect

    Ionin, Andrei A; Kudryashov, Sergei I; Ligachev, A E; Makarov, Sergei V; Mel'nik, N N; Rudenko, A A; Seleznev, L V; Sinitsyn, D V; Khmelnitskii, R A

    2013-04-30

    Periodic surface structures on aluminium are produced by femtosecond laser pulses for efficient excitation of surface electromagnetic waves using a strong objective (NA = 0.5). The local electromagnetic field enhancement on the structures is measured using the technique of surface-enhanced Raman scattering from pyridine molecules. (extreme light fields and their applications)

  7. Local ζ -functions, stress-energy tensor, field fluctuations, and all that, in curved static spacetime

    NASA Astrophysics Data System (ADS)

    Moretti, Valter

    This is a quick review on some technology concerning the local zeta function applied to Quantum Field Theory in curved static (thermal) spacetime to regularize the stress energy tensor and the field fluctuations. Dedicated to Prof. Emilio Elizalde on the occasion of his 60th birthday.

  8. A localized ELF magnetic field exposure system for microscope cover-slips.

    PubMed

    Wang, Paul K C

    2014-07-01

    In extremely low frequency (ELF) magnetic field exposure systems for the inverted microscope stage where the cells grown on the entire microscope cover-slip are exposed to the magnetic field, the effects of variations in cell characteristics from one cover-slip to another on the experimental data cannot be readily identified. To overcome this drawback, a localized ELF magnetic field exposure system for cells grown on cover-slips was designed. The basic idea is to expose only a marked portion of the cover-slip to the magnetic field so that the effect of the ELF magnetic field on the cells grown on the same cover-slip can be observed under a microscope. A prototype system was built and tested. Experimental test results pertaining to the prototype system performance validate the proposed design approach. The paper concludes with a discussion of alternative approaches to the design of localized ELF magnetic field exposure systems.

  9. Deformation-induced spatiotemporal fluctuation, evolution and localization of strain fields in a bulk metallic glass

    DOE PAGES

    Wu, Yuan; Bei, Hongbin; Wang, Yanli; ...

    2015-05-16

    Deformation behavior and local strain evolutions upon loading and unloading of a bulk metallic glass (BMG) were systematically investigated by in situ digital image correlation (DIC). Distinct fluctuations and irreversible local strains were observed before the onset of macroscopic yielding. Statistical analysis shows that these fluctuations might be related to intrinsic structural heterogeneities, and that the evolution history and characteristics of local strain fields play an important role in the subsequent initiation of shear bands. Effects of sample size, pre-strain, and loading conditions were systematically analyzed in terms of the probability distributions of the resulting local strain fields. It ismore » found that a higher degree of local shear strain heterogeneity corresponds to a more ductile stressestrain curve. Implications of these findings are discussed for the design of new materials.« less

  10. Local conductance: A means to extract polarization and depolarizing fields near domain walls in ferroelectrics

    SciTech Connect

    Douglas, A. M.; Kumar, A.; Gregg, J. M.; Whatmore, R. W.

    2015-10-26

    Conducting atomic force microscopy images of bulk semiconducting BaTiO{sub 3} surfaces show clear stripe domain contrast. High local conductance correlates with strong out-of-plane polarization (mapped independently using piezoresponse force microscopy), and current-voltage characteristics are consistent with dipole-induced alterations in Schottky barriers at the metallic tip-ferroelectric interface. Indeed, analyzing current-voltage data in terms of established Schottky barrier models allows relative variations in the surface polarization, and hence the local domain structure, to be determined. Fitting also reveals the signature of surface-related depolarizing fields concentrated near domain walls. Domain information obtained from mapping local conductance appears to be more surface-sensitive than that from piezoresponse force microscopy. In the right materials systems, local current mapping could therefore represent a useful complementary technique for evaluating polarization and local electric fields with nanoscale resolution.

  11. Deformation-induced spatiotemporal fluctuation, evolution and localization of strain fields in a bulk metallic glass

    SciTech Connect

    Wu, Yuan; Bei, Hongbin; Wang, Yanli; Lu, Zhaoping; George, Easo P.; Gao, Yanfei

    2015-05-16

    Deformation behavior and local strain evolutions upon loading and unloading of a bulk metallic glass (BMG) were systematically investigated by in situ digital image correlation (DIC). Distinct fluctuations and irreversible local strains were observed before the onset of macroscopic yielding. Statistical analysis shows that these fluctuations might be related to intrinsic structural heterogeneities, and that the evolution history and characteristics of local strain fields play an important role in the subsequent initiation of shear bands. Effects of sample size, pre-strain, and loading conditions were systematically analyzed in terms of the probability distributions of the resulting local strain fields. It is found that a higher degree of local shear strain heterogeneity corresponds to a more ductile stressestrain curve. Implications of these findings are discussed for the design of new materials.

  12. Selective domain wall depinning by localized Oersted fields and Joule heating

    NASA Astrophysics Data System (ADS)

    Ilgaz, Dennis; Kläui, Mathias; Heyne, Lutz; Boulle, Olivier; Zinser, Fabian; Krzyk, Stephen; Fonin, Mikhail; Rüdiger, Ulrich; Backes, Dirk; Heyderman, Laura J.

    2008-09-01

    Using low temperature magnetoresistance measurements, the possibility to selectively move a domain wall locally by applying current pulses through a Au nanowire adjacent to a permalloy element is studied. We find that the domain wall depinning field is drastically modified with increasing current density due to the Joule heating and the Oersted field of the current, and controlled motion due to the Oersted field without any externally applied fields is achieved. By placing the domain wall at various distances from the Au wire, we determine the range of the Joule heating and the Oersted field and both effects can be separated.

  13. A Multi-frequency Look at Gas Seeps on the Eastern Siberian Margin

    NASA Astrophysics Data System (ADS)

    Mayer, L. A.; Jerram, K.; Weidner, E.; Weber, T.; Jakobsson, M.; Chernykh, D.; Ananiev, R.; Mohammad, R.; Semiletov, I. P.

    2015-12-01

    The Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) is a multi-investigator, multi-disciplinary program aimed at increasing our understanding of the climate-cryosphere-carbon system of the Eastern Siberian Arctic Ocean. In 2014 SWERUS-C3 carried out a two-leg field program on the Swedish Icebreaker ODEN. A component of the SWERUS-C3 program focused on water column mapping of the spatial distribution and geologic context of gas seeps using the acoustic systems on board ODEN (12 kHz EM122 multibeam echo sounder, 2-8 kHz SBP120 subbottom profiler, and an 18 kHz EK60 split-beam sonar). On Leg 2 of the 2014 expedition, a new wideband transceiver (EK80) was added to the split-beam echo sounder and calibrated, providing the ability to measure the acoustic response of the gas seeps over a much broader range of frequencies (15-30 kHz). While the broader bandwidth unquestionably provides higher target resolution a further objective of the broadband mapping was to determine whether information on bubble size distribution could be determined so as to help model the flux of gas coming from the seeps. On Leg 2 approximately 34 seeps were mapped, mostly in the vicinity of Herald Canyon. The wide-swath, high-resolution multibeam bathymetry (from the EM122) and high-resolution chirp sub-bottom profiling (from the SBP120 multibeam sub-bottom profiler) combined with water column imaging of seeps collected at both 12 kHz (from the EM122) and 15-30 kHz (from the EK80) offer an important opportunity to understand the spatial distribution of seeps and their relationship to local and regional processes as determined from seafloor and subsurface structure, as well as to explore the potential of extracting quantitative information about the magnitude of gas transport from the seeps.

  14. Impact of mask CDU and local CD variation on intra-field CDU

    NASA Astrophysics Data System (ADS)

    Miyazaki, Junji; Mouraille, Orion; Finders, Jo; Higuchi, Masaru; Kojima, Yosuke; Sato, Shunsuke; Morimoto, Hiroaki

    2012-11-01

    The control of critical dimension uniformity (CDU), especially intra-field CDU, is an important aspect for advanced lithography, and this property must be controlled very tightly since it affects all of the exposure fields. It is well known that the influence of the mask CDU on the wafer intra-field CDU is becoming dominant because the mask error enhancement factor (MEEF) is quite high for low-k1 lithography. Additionally, the abovementioned factors impact the CDU through global (field-level) and local (grating-level) variations. In this paper, we analyze in detail CDU budgets by clarifying the impact of local CD variation. The 50-nm staggered hole features using Att-PSM showed a mask global CDU of 1.64 nm (3sigma at the mask level) and a wafer intra-field CDU of 2.30 nm, indicating that the mask global CDU was a major part of the intra-field CDU. By compensating for the contribution of the mask CD, the wafer intra-field CDU can be reduced to 0.986 nm. We analyzed the budgets of wafer intra-field CDU, which is caused by local CD variation (mask and process) and measurement noise. We determined that a primary cause of the wafer intra-field CDU after applying a mask CD correction was these local CD variations, which might disturb the proper use of dose correction for the mask CD. We demonstrated that the impact of mask local CD variation on the correction flow can be greatly reduced by averaging multiple point measurements within a small area, and therefore discuss the optimum conditions allowing for an accurate intra-field CDU determination. We also consider optimization of the CD sampling scheme in order to apply a dose correction on an exposure system to compensate for the mask CDU.

  15. Quasi locality of the GGE in interacting-to-free quenches in relativistic field theories

    NASA Astrophysics Data System (ADS)

    Bastianello, Alvise; Sotiriadis, Spyros

    2017-02-01

    We study the quench dynamics in continuous relativistic quantum field theory, more specifically the locality properties of the large time stationary state. After a quantum quench in a one-dimensional integrable model, the expectation values of local observables are expected to relax to a generalized Gibbs ensemble (GGE), constructed out of the conserved charges of the model. Quenching to a free bosonic theory, it has been shown that the system indeed relaxes to a GGE described by the momentum mode occupation numbers. We first address the question whether the latter can be written directly in terms of local charges and we find that, in contrast to the lattice case, this is not possible in continuous field theories. We then investigate the less stringent requirement of the existence of a sequence of truncated local GGEs that converges to the correct steady state, in the sense of the expectation values of the local observables. While we show that such a sequence indeed exists, in order to unequivocally determine the so-defined GGE, we find that information about the expectation value of the recently discovered quasi-local charges is in the end necessary, the latter being the suitable generalization of the local charges while passing from the lattice to the continuum. Lastly, we study the locality properties of the GGE and show that the latter is completely determined by the knowledge of the expectation value of a countable set of suitably defined quasi-local charges.

  16. Evaluation of Long-Term Cloud-Resolving Model Simulations Using Satellite Radiance Observations and Multi-Frequency Satellite Simulators

    NASA Technical Reports Server (NTRS)

    Matsui, Toshihisa; Zeng, Xiping; Tao, Wei-Kuo; Masunaga, Hirohiko; Olson, William S.; Lang, Stephen

    2008-01-01

    This paper proposes a methodology known as the Tropical Rainfall Measuring Mission (TRMM) Triple-Sensor Three-step Evaluation Framework (T3EF) for the systematic evaluation of precipitating cloud types and microphysics in a cloud-resolving model (CRM). T3EF utilizes multi-frequency satellite simulators and novel statistics of multi-frequency radiance and backscattering signals observed from the TRMM satellite. Specifically, T3EF compares CRM and satellite observations in the form of combined probability distributions of precipitation radar (PR) reflectivity, polarization-corrected microwave brightness temperature (Tb), and infrared Tb to evaluate the candidate CRM. T3EF is used to evaluate the Goddard Cumulus Ensemble (GCE) model for cases involving the South China Sea Monsoon Experiment (SCSMEX) and Kwajalein Experiment (KWAJEX). This evaluation reveals that the GCE properly captures the satellite-measured frequencies of different precipitating cloud types in the SCSMEX case but underestimates the frequencies of deep convective and deep stratiform types in the KWAJEX case. Moreover, the GCE tends to simulate excessively large and abundant frozen condensates in deep convective clouds as inferred from the overestimated GCE-simulated radar reflectivities and microwave Tb depressions. Unveiling the detailed errors in the GCE s performance provides the best direction for model improvements.

  17. Classification of heavy metal ions present in multi-frequency multi-electrode potable water data using evolutionary algorithm

    NASA Astrophysics Data System (ADS)

    Karkra, Rashmi; Kumar, Prashant; Bansod, Baban K. S.; Bagchi, Sudeshna; Sharma, Pooja; Krishna, C. Rama

    2016-12-01

    Access to potable water for the common people is one of the most challenging tasks in the present era. Contamination of drinking water has become a serious problem due to various anthropogenic and geogenic events. The paper demonstrates the application of evolutionary algorithms, viz., particle swan optimization and genetic algorithm to 24 water samples containing eight different heavy metal ions (Cd, Cu, Co, Pb, Zn, Ar, Cr and Ni) for the optimal estimation of electrode and frequency to classify the heavy metal ions. The work has been carried out on multi-variate data, viz., single electrode multi-frequency, single frequency multi-electrode and multi-frequency multi-electrode water samples. The electrodes used are platinum, gold, silver nanoparticles and glassy carbon electrodes. Various hazardous metal ions present in the water samples have been optimally classified and validated by the application of Davis Bouldin index. Such studies are useful in the segregation of hazardous heavy metal ions found in water resources, thereby quantifying the degree of water quality.

  18. Frozen Gaussian approximation-based two-level methods for multi-frequency Schrödinger equation

    NASA Astrophysics Data System (ADS)

    Lorin, E.; Yang, X.

    2016-10-01

    In this paper, we develop two-level numerical methods for the time-dependent Schrödinger equation (TDSE) in multi-frequency regime. This work is motivated by attosecond science (Corkum and Krausz, 2007), which refers to the interaction of short and intense laser pulses with quantum particles generating wide frequency spectrum light, and allowing for the coherent emission of attosecond pulses (1 attosecond=10-18 s). The principle of the proposed methods consists in decomposing a wavefunction into a low/moderate frequency (quantum) contribution, and a high frequency contribution exhibiting a semi-classical behavior. Low/moderate frequencies are computed through the direct solution to the quantum TDSE on a coarse mesh, and the high frequency contribution is computed by frozen Gaussian approximation (Herman and Kluk, 1984). This paper is devoted to the derivation of consistent, accurate and efficient algorithms performing such a decomposition and the time evolution of the wavefunction in the multi-frequency regime. Numerical simulations are provided to illustrate the accuracy and efficiency of the derived algorithms.

  19. Local Heat Transfer to an Evaporating Sessile Droplet in an Electric Field

    NASA Astrophysics Data System (ADS)

    Gibbons, M. J.; Howe, C. M.; Di Marco, P.; Robinson, A. J.

    2016-09-01

    Local heat transfer of an evaporating sessile droplet under a static electric field is an underdeveloped topic. In this research an 80 μl water droplet is placed in the centre of a 25 μm thick stainless steel substrate. A static electric field is applied by an electrode positioned 10 mm above the substrate. A high speed thermal imaging camera is placed below the substrate to capture the thermal footprint of the evaporating droplet. Four electric fields were characterised; 0, 5, 10 and 11 kV/cm. As the electric field is increased the contact angle was observed to decrease. The local heat flux profile, peak and radial location of this peek were observed to be independent of the applied electric field for all test points for this working fluid and surface combination.

  20. Simplest relationship between local field potential and intracellular signals in layered neural tissue.

    PubMed

    Chizhov, Anton V; Sanchez-Aguilera, Alberto; Rodrigues, Serafim; de la Prida, Liset Menendez

    2015-12-01

    The relationship between the extracellularly measured electric field potential resulting from synaptic activity in an ensemble of neurons and intracellular signals in these neurons is an important but still open question. Based on a model neuron with a cylindrical dendrite and lumped soma, we derive a formula that substantiates a proportionality between the local field potential and the total somatic transmembrane current that emerges from the difference between the somatic and dendritic membrane potentials. The formula is tested by intra- and extracellular recordings of evoked synaptic responses in hippocampal slices. Additionally, the contribution of different membrane currents to the field potential is demonstrated in a two-population mean-field model. Our formalism, which allows for a simple estimation of unknown dendritic currents directly from somatic measurements, provides an interpretation of the local field potential in terms of intracellularly measurable synaptic signals. It is also applicable to the study of cortical activity using two-compartment neuronal population models.

  1. Simplest relationship between local field potential and intracellular signals in layered neural tissue

    NASA Astrophysics Data System (ADS)

    Chizhov, Anton V.; Sanchez-Aguilera, Alberto; Rodrigues, Serafim; de la Prida, Liset Menendez

    2015-12-01

    The relationship between the extracellularly measured electric field potential resulting from synaptic activity in an ensemble of neurons and intracellular signals in these neurons is an important but still open question. Based on a model neuron with a cylindrical dendrite and lumped soma, we derive a formula that substantiates a proportionality between the local field potential and the total somatic transmembrane current that emerges from the difference between the somatic and dendritic membrane potentials. The formula is tested by intra- and extracellular recordings of evoked synaptic responses in hippocampal slices. Additionally, the contribution of different membrane currents to the field potential is demonstrated in a two-population mean-field model. Our formalism, which allows for a simple estimation of unknown dendritic currents directly from somatic measurements, provides an interpretation of the local field potential in terms of intracellularly measurable synaptic signals. It is also applicable to the study of cortical activity using two-compartment neuronal population models.

  2. A Method to Localize RF B1 Field in High-Field Magnetic Resonance Imaging Systems

    PubMed Central

    Yoo, Hyoungsuk; Gopinath, Anand; Vaughan, J. Thomas

    2014-01-01

    In high-field magnetic resonance imaging (MRI) systems, B0 fields of 7 and 9.4 T, the RF field shows greater inhomogeneity compared to clinical MRI systems with B0 fields of 1.5 and 3.0 T. In multichannel RF coils, the magnitude and phase of the input to each coil element can be controlled independently to reduce the nonuniformity of the RF field. The convex optimization technique has been used to obtain the optimum excitation parameters with iterative solutions for homogeneity in a selected region of interest. The pseudoinverse method has also been used to find a solution. The simulation results for 9.4- and 7-T MRI systems are discussed in detail for the head model. Variation of the simulation results in a 9.4-T system with the number of RF coil elements for different positions of the regions of interest in a spherical phantom are also discussed. Experimental results were obtained in a phantom in the 9.4-T system and are compared to the simulation results and the specific absorption rate has been evaluated. PMID:22929360

  3. A tailored multi-frequency EPR approach to accurately determine the magnetic resonance parameters of dynamic nuclear polarization agents: application to AMUPol.

    PubMed

    Gast, P; Mance, D; Zurlo, E; Ivanov, K L; Baldus, M; Huber, M

    2017-02-01

    To understand the dynamic nuclear polarization (DNP) enhancements of biradical polarizing agents, the magnetic resonance parameters need to be known. We describe a tailored EPR approach to accurately determine electron spin-spin coupling parameters using a combination of standard (9 GHz), high (95 GHz) and ultra-high (275 GHz) frequency EPR. Comparing liquid- and frozen-solution continuous-wave EPR spectra provides accurate anisotropic dipolar interaction D and isotropic exchange interaction J parameters of the DNP biradical AMUPol. We found that D was larger by as much as 30% compared to earlier estimates, and that J is 43 MHz, whereas before it was considered to be negligible. With the refined data, quantum mechanical calculations confirm that an increase in dipolar electron-electron couplings leads to higher cross-effect DNP efficiencies. Moreover, the DNP calculations qualitatively reproduce the difference of TOTAPOL and AMUPol DNP efficiencies found experimentally and suggest that AMUPol is particularly effective in improving the DNP efficiency at magnetic fields higher than 500 MHz. The multi-frequency EPR approach will aid in predicting the optimal structures for future DNP agents.

  4. Lorentz factor determination for local electric fields in semiconductor devices utilizing hyper-thin dielectrics

    SciTech Connect

    McPherson, J. W.

    2015-11-28

    The local electric field (the field that distorts, polarizes, and weakens polar molecular bonds in dielectrics) has been investigated for hyper-thin dielectrics. Hyper-thin dielectrics are currently required for advanced semiconductor devices. In the work presented, it is shown that the common practice of using a Lorentz factor of L = 1/3, to describe the local electric field in a dielectric layer, remains valid for hyper-thin dielectrics. However, at the very edge of device structures, a rise in the macroscopic/Maxwell electric field E{sub diel} occurs and this causes a sharp rise in the effective Lorentz factor L{sub eff}. At capacitor and transistor edges, L{sub eff} is found to increase to a value 2/3 < L{sub eff} < 1. The increase in L{sub eff} results in a local electric field, at device edge, that is 50%–100% greater than in the bulk of the dielectric. This increase in local electric field serves to weaken polar bonds thus making them more susceptible to breakage by standard Boltzmann and/or current-driven processes. This has important time-dependent dielectric breakdown (TDDB) implications for all electronic devices utilizing polar materials, including GaN devices that suffer from device-edge TDDB.

  5. Local high-resolution crustal magnetic field analysis from satellite data

    NASA Astrophysics Data System (ADS)

    Plattner, Alain; Simons, Frederik J.

    2016-04-01

    Planetary crustal magnetic fields are key to understanding a planet or moon's structure and history. Due to satellite orbit parameters such as aerobraking (Mars) or only partial coverage (Mercury), or simply because of the strongly heterogeneous crustal field strength, satellite data of planetary magnetic fields vary regionally in their signal-to noise ratio and data coverage. To take full advantage of data quality within one region of a planet or moon without diluting the data with lower quality measurements outside of that region we resort to local methods. Slepian functions are linear combinations of spherical harmonics that provide local sensitivity to structure. Here we present a selection of crustal magnetic field models obtained from vector-valued variable-altitude satellite observations using an altitude-cognizant gradient-vector Slepian approach. This method is based on locally maximizing energy concentration within the region of data availability while simultaneously bandlimiting the model in terms of its spherical-harmonic degree and minimizing noise amplification due to downward continuation. For simple regions such as spherical caps, our method is computationally efficient and allows us to calculate local crustal magnetic field solutions beyond spherical harmonic degree 800, if the data permit. We furthermore discuss extensions of the method that are optimized for the analysis and separation of internal and external magnetic fields.

  6. Direct mapping of local director field of nematic liquid crystals at the nano-scale

    NASA Astrophysics Data System (ADS)

    Xia, Yu; Serra, Francesca; Yang, Shu; Kamien, Randall

    2015-03-01

    The director field in liquid crystals (LCs) has been characterized mainly via polarized optical microscopy, fluorescence confocal microscopy, and Raman spectroscopy, all of which are limited by optical wavelengths - from hundreds of nanometers to several micrometers. Since LC orientation cannot be resolved directly by these methods, theory is needed to interpret the local director field of LC alignment. In this work, we introduce a new approach to directly visualize the local director field of a nematic LC (NLC) at the nano-scale using scanning electron microscopy (SEM). A new type of NLC monomer bearing crosslinkable groups was designed and synthesized. It can be well-oriented at particle surfaces and patterned polymer substrates, including micron-sized silica colloids, porous membranes, micropillar arrays, and 1D channels. After carefully crosslinking, the molecular orientation of NLCs around the particles or within the patterns could be directly visualized by SEM, showing oriented nanofibers representing LC director from the fractured samples. Here, we could precisely resolve not only the local director field by this approach, but the defect structures of NLCs, including hedgehogs and line defects. The direct mapping of LC directors at the nanoscale using this method will improve our understanding of NLC local director field, and thus their manipulation and applications. More importantly, a theoretical interpretation will no longer be a necessity to resolve a new material system in this field.

  7. Effects of the local structure dependence of evaporation fields on field evaporation behavior

    SciTech Connect

    Yao, Lan; Marquis, Emmanuelle A.; Withrow, Travis; Restrepo, Oscar D.; Windl, Wolfgang

    2015-12-14

    Accurate three dimensional reconstructions of atomic positions and full quantification of the information contained in atom probe microscopy data rely on understanding the physical processes taking place during field evaporation of atoms from needle-shaped specimens. However, the modeling framework for atom probe microscopy has only limited quantitative justification. Building on the continuum field models previously developed, we introduce a more physical approach with the selection of evaporation events based on density functional theory calculations. This model reproduces key features observed experimentally in terms of sequence of evaporation, evaporation maps, and depth resolution, and provides insights into the physical limit for spatial resolution.

  8. Unmasking local activity within local field potentials (LFPs) by removing distal electrical signals using independent component analysis.

    PubMed

    Whitmore, Nathan W; Lin, Shih-Chieh

    2016-05-15

    Local field potentials (LFPs) are commonly thought to reflect the aggregate dynamics in local neural circuits around recording electrodes. However, we show that when LFPs are recorded in awake behaving animals against a distal reference on the skull as commonly practiced, LFPs are significantly contaminated by non-local and non-neural sources arising from the reference electrode and from movement-related noise. In a data set with simultaneously recorded LFPs and electroencephalograms (EEGs) across multiple brain regions while rats perform an auditory oddball task, we used independent component analysis (ICA) to identify signals arising from electrical reference and from volume-conducted noise based on their distributed spatial pattern across multiple electrodes and distinct power spectral features. These sources of distal electrical signals collectively accounted for 23-77% of total variance in unprocessed LFPs, as well as most of the gamma oscillation responses to the target stimulus in EEGs. Gamma oscillation power was concentrated in volume-conducted noise and was tightly coupled with the onset of licking behavior, suggesting a likely origin of muscle activity associated with body movement or orofacial movement. The removal of distal signal contamination also selectively reduced correlations of LFP/EEG signals between distant brain regions but not within the same region. Finally, the removal of contamination from distal electrical signals preserved an event-related potential (ERP) response to auditory stimuli in the frontal cortex and also increased the coupling between the frontal ERP amplitude and neuronal activity in the basal forebrain, supporting the conclusion that removing distal electrical signals unmasked local activity within LFPs. Together, these results highlight the significant contamination of LFPs by distal electrical signals and caution against the straightforward interpretation of unprocessed LFPs. Our results provide a principled approach to

  9. Localized heating on silicon field effect transistors: device fabrication and temperature measurements in fluid.

    PubMed

    Elibol, Oguz H; Reddy, Bobby; Nair, Pradeep R; Dorvel, Brian; Butler, Felice; Ahsan, Zahab S; Bergstrom, Donald E; Alam, Muhammad A; Bashir, Rashid

    2009-10-07

    We demonstrate electrically addressable localized heating in fluid at the dielectric surface of silicon-on-insulator field-effect transistors via radio-frequency Joule heating of mobile ions in the Debye layer. Measurement of fluid temperatures in close vicinity to surfaces poses a challenge due to the localized nature of the temperature profile. To address this, we developed a localized thermometry technique based on the fluorescence decay rate of covalently attached fluorophores to extract the temperature within 2 nm of any oxide surface. We demonstrate precise spatial control of voltage dependent temperature profiles on the transistor surfaces. Our results introduce a new dimension to present sensing systems by enabling dual purpose silicon transistor-heaters that serve both as field effect sensors as well as temperature controllers that could perform localized bio-chemical reactions in Lab on Chip applications.

  10. Single-field inflation and the local ansatz: Distinguishability and consistency

    NASA Astrophysics Data System (ADS)

    de Putter, Roland; Doré, Olivier; Green, Daniel; Meyers, Joel

    2017-03-01

    The single-field consistency conditions and the local ansatz have played separate but important roles in characterizing the non-Gaussian signatures of single- and multifield inflation respectively. We explore the precise relationship between these two approaches and their predictions. We demonstrate that the predictions of the single-field consistency conditions can never be satisfied by a general local ansatz with deviations necessarily arising at order (ns-1 )2 . This implies that there is, in principle, a minimum difference between single- and (fully local) multifield inflation in observables sensitive to the squeezed limit such as scale-dependent halo bias. We also explore some potential observational implications of the consistency conditions and its relationship to the local ansatz. In particular, we propose a new scheme to test the consistency relations. In analogy with delensing of the cosmic microwave background, one can deproject the coupling of the long wavelength modes with the short wavelength modes and test for residual anomalous coupling.

  11. A dark-field scanning spectroscopy platform for localized scatter and fluorescence imaging of tissue

    NASA Astrophysics Data System (ADS)

    Krishnaswamy, Venkataramanan; Laughney, Ashley M.; Paulsen, Keith D.; Pogue, Brian W.

    2011-03-01

    Tissue ultra-structure and molecular composition provide native contrast mechanisms for discriminating across pathologically distinct tissue-types. Multi-modality optical probe designs combined with spatially confined sampling techniques have been shown to be sensitive to this type of contrast but their extension to imaging has only been realized recently. A modular scanning spectroscopy platform has been developed to allow imaging localized morphology and molecular contrast measures in breast cancer surgical specimens. A custom designed dark-field telecentric scanning spectroscopy system forms the core of this imaging platform. The system allows imaging localized elastic scatter and fluorescence measures over fields of up to 15 mm x 15 mm at 100 microns resolution in tissue. Results from intralipid and blood phantom measurements demonstrate the ability of the system to quantify localized scatter parameters despite significant changes in local absorption. A co-registered fluorescence spectroscopy mode is also demonstrated in a protophorphyrin-IX phantom.

  12. Local recording of biological magnetic fields using Giant Magneto Resistance-based micro-probes

    PubMed Central

    Barbieri, Francesca; Trauchessec, Vincent; Caruso, Laure; Trejo-Rosillo, Josué; Telenczuk, Bartosz; Paul, Elodie; Bal, Thierry; Destexhe, Alain; Fermon, Claude; Pannetier-Lecoeur, Myriam; Ouanounou, Gilles

    2016-01-01

    The electrical activity of brain, heart and skeletal muscles generates magnetic fields but these are recordable only macroscopically, such as in magnetoencephalography, which is used to map neuronal activity at the brain scale. At the local scale, magnetic fields recordings are still pending because of the lack of tools that can come in contact with living tissues. Here we present bio-compatible sensors based on Giant Magneto-Resistance (GMR) spin electronics. We show on a mouse muscle in vitro, using electrophysiology and computational modeling, that this technology permits simultaneous local recordings of the magnetic fields from action potentials. The sensitivity of this type of sensor is almost size independent, allowing the miniaturization and shaping required for in vivo/vitro magnetophysiology. GMR-based technology can constitute the magnetic counterpart of microelectrodes in electrophysiology, and might represent a new fundamental tool to investigate the local sources of neuronal magnetic activity. PMID:27991562

  13. Local field-induced optical properties of Ag-coated CdS quantum dots.

    PubMed

    Je, Koo-Chul; Ju, Honglyoul; Treguer, Mona; Cardinal, Thierry; Park, Seung-Han

    2006-08-21

    Local field-induced optical properties of Ag-coated CdS quantum dot structures are investigated. We experimentally observe a clear exciton peak due to the quantum confinement effect in uncoated CdS quantum dots, and surface plasmon resonance and red-shifted exciton peak in Ag-coated CdS composite quantum dot structures. We have calculated the Stark shift of the exciton peak as a function of the local field for different silver thicknesses and various sizes of quantum dots based on the effective-mass Hamiltonian using the numerical-matrix-diagonalization method. Our theoretical calculations strongly indicate that the exciton peak is red-shifted in the metal-semiconductor composite quantum dots due to a strong local field, i.e., the quantum confined Stark effect.

  14. Far-ultraviolet studies. VII - The spectrum and latitude dependence of the local interstellar radiation field

    NASA Technical Reports Server (NTRS)

    Henry, R. C.; Anderson, R. C.; Fastie, W. G.

    1980-01-01

    A direct measurement has been made of the spectrum (1180-1680 A) and Gould-latitude dependence of the local interstellar radiation field, over about one-third of the sky. The result is corrected to give expected values for the entire sky. The average local 1180-1680 A energy density is 5.8 x 10 to the -17th ergs/cu cm A. The surface brightness falls off toward high latitudes much more steeply than published models predict.

  15. Sounding of Europa's interior using multi-frequency electromagnetic induction from a Europa orbiter

    NASA Astrophysics Data System (ADS)

    Khurana, K. K.; Kivelson, M. G.; Russell, C. T.

    2000-12-01

    Magnetic field observations from Galileo have shown that Europa induces a strong response to the varying field of Jupiter's magnetosphere. These observations are consistent with a global conductor located close to the surface. Khurana et al. [1998] and Kivelson et al. [1999] have shown that a moon-wide ocean with a conductivity similar to the Earth's ocean and having a thickness of at least 6 km could produce the observed induction signature. Many other geological and geophysical observations are consistent with this interpretation (See Pappalardo et al. [1999] for further details.). The magnetic induction signature at a single frequency can also be explained with a model in which the conducting layer is thinner (thicker) but has higher (lower) conductivity. The initial work relied on the variations of the time varying field at the synodic rotation period of Jupiter (as seen in the rest frame of the moon) to infer the interior structure of Europa. We have extended the initial analysis by showing that the spectrum of the primary field contains several other important frequencies. We single out one frequency-corresponding to the orbital period of Europa-for further examination. We show that by modeling the induction response at this frequency in addition to the previously used synodic frequency for a range of ocean shell thicknesses and conductivities, the ocean conductivity and the thickness of the ocean at Europa can be determined uniquely. We discuss how the measurements from an orbiting spacecraft can be decomposed into the internal (which is the secondary field) and external (the primary imposed field) components not only for the steady field but also for the varying field.

  16. Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna

    DOE PAGES

    Caselli, Niccolò; La China, Federico; Bao, Wei; ...

    2015-06-05

    Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magneticmore » intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. In conclusion, by exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions.« less

  17. Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna

    SciTech Connect

    Caselli, Niccolò; La China, Federico; Bao, Wei; Riboli, Francesco; Gerardino, Annamaria; Li, Lianhe; Linfield, Edmund H.; Pagliano, Francesco; Fiore, Andrea; Schuck, P. James; Cabrini, Stefano; Weber-Bargioni, Alexander; Gurioli, Massimo; Intonti, Francesca

    2015-06-05

    Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. In conclusion, by exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions.

  18. Deep-subwavelength imaging of both electric and magnetic localized optical fields by plasmonic campanile nanoantenna

    PubMed Central

    Caselli, Niccolò; La China, Federico; Bao, Wei; Riboli, Francesco; Gerardino, Annamaria; Li, Lianhe; Linfield, Edmund H.; Pagliano, Francesco; Fiore, Andrea; Schuck, P. James; Cabrini, Stefano; Weber-Bargioni, Alexander; Gurioli, Massimo; Intonti, Francesca

    2015-01-01

    Tailoring the electromagnetic field at the nanoscale has led to artificial materials exhibiting fascinating optical properties unavailable in naturally occurring substances. Besides having fundamental implications for classical and quantum optics, nanoscale metamaterials provide a platform for developing disruptive novel technologies, in which a combination of both the electric and magnetic radiation field components at optical frequencies is relevant to engineer the light-matter interaction. Thus, an experimental investigation of the spatial distribution of the photonic states at the nanoscale for both field components is of crucial importance. Here we experimentally demonstrate a concomitant deep-subwavelength near-field imaging of the electric and magnetic intensities of the optical modes localized in a photonic crystal nanocavity. We take advantage of the “campanile tip”, a plasmonic near-field probe that efficiently combines broadband field enhancement with strong far-field to near-field coupling. By exploiting the electric and magnetic polarizability components of the campanile tip along with the perturbation imaging method, we are able to map in a single measurement both the electric and magnetic localized near-field distributions. PMID:26045401

  19. Rational Conformal Correlation Functions of Gauge-Invariant Local Fields in Four Dimensions

    SciTech Connect

    Nikolov, N.M.; Stanev, Ya.S.; Todorov, I.T.

    2005-11-01

    Global conformal invariance in Minkowski space and the Wightman axioms imply strong locality (Huygens principle) and rationality of correlation functions, thus providing an extension of the concept of a vertex algebra to higher (even) dimensions D. We (p)review current work on a model of a Hermitian scalar field L of scale dimension 4 (D = 4) which can be interpreted as the Lagrangian of a gauge field theory that generates the algebra of gauge-invariant local observables in a conformally invariant renormalization group fixed point.

  20. Spin polarization induced by an electric field in the presence of weak localization effects

    NASA Astrophysics Data System (ADS)

    Guerci, Daniele; Borge, Juan; Raimondi, Roberto

    2016-01-01

    We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.

  1. Reprint of : Spin polarization induced by an electric field in the presence of weak localization effects

    NASA Astrophysics Data System (ADS)

    Guerci, Daniele; Borge, Juan; Raimondi, Roberto

    2016-08-01

    We evaluate the spin polarization (Edelstein or inverse spin galvanic effect) and the spin Hall current induced by an applied electric field by including the weak localization corrections for a two-dimensional electron gas. We show that the weak localization effects yield logarithmic corrections to both the spin polarization conductivity relating the spin polarization and the electric field and to the spin Hall angle relating the spin and charge currents. The renormalization of both the spin polarization conductivity and the spin Hall angle combine to produce a zero correction to the total spin Hall conductivity as required by an exact identity. Suggestions for the experimental observation of the effect are given.

  2. Estimation of inter-modular connectivity from the local field potentials in a hierarchical modular network

    NASA Astrophysics Data System (ADS)

    Cui, Xue-Mei; Kim, Won Sup; Hwang, Dong-Uk; Han, Seung Kee

    2015-05-01

    We propose a method of estimating inter-modular connectivity in a hierarchical modular network. The method is based on an analysis of inverse phase synchronization applied to the local field potentials on a hierarchical modular network of phase oscillators. For a strong-coupling strength, the inverse phase synchronization index of the local field potentials for two modules depends linearly on the corresponding inter-modular connectivity defined as the number of links connecting the modules. The method might enable us to estimate the inter-modular connectivity in various complex systems from the inverse phase synchronization index of the mesoscopic modular activities.

  3. Ultrahigh-field MRI whole-slice and localized RF field excitations using the same RF transmit array.

    PubMed

    Ibrahim, Tamer S

    2006-10-01

    In this paper, a multiport driving mechanism is numerically implemented at ultra high-field (UHF) magnetic resonance imaging (MRI) to provide 1) homogenous whole-slice (axial, sagittal, or coronal) and 2) highly localized radio frequency (RF) field excitation within the same slices, all with the same RF transmit array (here chosen to be a standard transverse electromagnetic (TEM) resonator/coil). The method is numerically tested using a full-wave model of a TEM coil loaded with a high-resolution/18-tissue/anatomically detailed human head mesh. The proposed approach is solely based on electromagnetic and phased array antenna theories. The results demonstrate that both homogenous whole-slice as well as localized RF excitation can be achieved within any slice of the head at 7 T (298 MHz for proton imaging).

  4. Localization and mass spectra of various matter fields on scalar-tensor brane

    SciTech Connect

    Xie, Qun-Ying; Zhao, Zhen-Hua; Zhong, Yi; Yang, Jie; Zhou, Xiang-Nan

    2015-03-10

    Recently, a new scalar-tensor braneworld model was presented in [http://dx.doi.org/10.1103/PhysRevD.86.127502]. It not only solves the gauge hierarchy problem but also reproduces a correct Friedmann-like equation on the brane. In this new model, there are two different brane solutions, for which the mass spectra of gravity on the brane are the same. In this paper, we investigate localization and mass spectra of various bulk matter fields (i.e., scalar, vector, Kalb-Ramond, and fermion fields) on the brane. It is shown that the zero modes of all the matter fields can be localized on the positive tension brane under some conditions, and the mass spectra of each kind of bulk matter field for the two brane solutions are different except for some special cases, which implies that the two brane solutions are not physically equivalent. When the coupling constants between the dilaton and bulk matter fields take special values, the mass spectra for both solutions are the same, and the scalar and vector zero modes are localized on the negative tension brane, while the KR zero mode is still localized on the positive tension brane.

  5. Soil moisture from the recent AMSR2 and FY3B multi-frequency passive microwave sensors

    NASA Astrophysics Data System (ADS)

    Parinussa, Robert; Wang, Guojie; de Jeu, Richard

    2014-05-01

    Over the years several different multi-frequency passive microwave sensors were used to estimate surface soil moisture. An historical multi-frequency passive microwave database from these satellite platforms was already used to generate a long term (32 years) surface soil moisture dataset. The Land Parameter Retrieval Algorithm (LPRM) was applied to this historical multi-frequency passive microwave database, including the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E), that plays a dominant role in the 2002-2011 period. The Advanced Microwave Scanning Radiometer 2 (AMSR2) shares a similar design with its predecessor, it was improved based on general technical development as well as the valuable heritage that AMSR-E left behind. Most recently, the Japanese Aerospace Exploration Agency (JAXA) started offering brightness temperature observations from the AMSR2 radiometer. In the recent years, China's National Satellite Meteorological Center (NSMC) developed meteorological satellites. The NSMC has polar orbiting sun-synchronized meteorological satellites in operation since 1988 in the so-called FengYun (FY) satellite series. FY3 is China's 2nd generation polar orbiting satellite series, its design was based on the previous polar orbiting satellite series and FY3 will ultimately become series of four satellites (FY3A to FY3D). The FY3B satellite is the 2nd satellite of the FY3 series and it's the 1st in the series to carry a microwave imager (MWRI) onboard observing the Earth's surface in 10 microwave channels. Brightness temperature observations of these recently developed sensors were compared to the existing database. An inter-calibration step was performed in order to overcome small difference in brightness temperature observations as a result of the different sensor calibration procedures. The LPRM was applied to observations made by the FY3B and AMSR2 sensors resulting in global soil moisture products. After the implementation of the

  6. Local motion detectors are required for the computation of expansion flow-fields

    PubMed Central

    Schilling, Tabea; Borst, Alexander

    2015-01-01

    ABSTRACT Avoidance of predators or impending collisions is important for survival. Approaching objects can be mimicked by expanding flow-fields. Tethered flying fruit flies, when confronted with an expansion flow-field, reliably turn away from the pole of expansion when presented laterally, or perform a landing response when presented frontally. Here, we show that the response to an expansion flow-field is independent of the overall luminance change and edge acceleration. As we demonstrate by blocking local motion-sensing neurons T4 and T5, the response depends crucially on the neural computation of appropriately aligned local motion vectors, using the same hardware that also controls the optomotor response to rotational flow-fields. PMID:26231626

  7. High-Resolution Local Crustal Magnetic Field Modeling of the Martian South Pole

    NASA Astrophysics Data System (ADS)

    Plattner, A.; Simons, F. J.

    2014-12-01

    The Mars Global Surveyor (MGS) satellite mission has brought us a wealth of information about the Martian magnetic field. Besides determining that Mars currently does not possess an active core field, MGS revealed that Mars contains an unexpectedly wide crustal magnetic field intensity range. In its orbit insertion, MGS performed a series of low altitude passes down to around 100 km above surface. During this mission phase the magnetic field measurements were active. In particular the nighttime low-altitude data are of high interest because they contain minimal noise from solar wind. Since these data only cover a small portion of the planet's surface, to date all Martian crustal magnetic field models blend the highest-quality data with lower quality measurements collected either at higher satellite altitudes or during daytime. In this contribution we present a locally inverted crustal magnetic field model for the Martian South Polar region calculated from only the highest-quality MGS data using locally constructed altitude vector Slepian functions. The South Polar region of Mars contains the southern part of the strongly magnetized Terra Sirenum and the area south of the Tharsis volcanic highland. Besides parts of planetary scale features our area of data coverage also contains local features such as the presumably volcanic Australe Montes and the Prometheus impact crater. These ingredients compose a highly heterogeneous crustal magnetic field. We show that even for our dense low-altitude low-noise data set the inversion for the crustal magnetic field of a weakly magnetized region adjacent to a region containing a strong magnetic field leads to artifacts in the weak region. With our local method we can avoid these artifacts by selecting subregions of roughly homogeneous field intensity and individually invert for crustal magnetic fields from data within only these subregions. This regional and subregional modeling allows us to reveal previously obscured crustal

  8. A method of analysis of distributions of local electric fields in composites

    NASA Astrophysics Data System (ADS)

    Kolesnikov, V. I.; Yakovlev, V. B.; Bardushkin, V. V.; Lavrov, I. V.; Sychev, A. P.; Yakovleva, E. N.

    2016-03-01

    A method of prediction of distributions of local electric fields in composite media based on analysis of the tensor operators of the concentration of intensity and induction is proposed. Both general expressions and the relations for calculating these operators are obtained in various approximations. The analytical expressions are presented for the operators of the concentration of electric fields in various types of inhomogeneous structures obtained in the generalized singular approximation.

  9. Multi-frequency ferromagnetic resonance investigation of nickel nanocubes encapsulated in diamagnetic magnesium oxide matrix

    NASA Astrophysics Data System (ADS)

    Nellutla, Saritha; Nori, Sudhakar; Singamaneni, Srinivasa R.; Prater, John T.; Narayan, Jagdish; Smirnov, Alex I.

    2016-12-01

    Partially aligned nickel nanocubes were grown epitaxially in a diamagnetic magnesium oxide (MgO:Ni) host and studied by a continuous wave ferromagnetic resonance (FMR) spectroscopy at the X-band (9.5 GHz) from ca. 117 to 458 K and then at room temperature for multiple external magnetic fields/resonant frequencies from 9.5 to 330 GHz. In contrast to conventional magnetic susceptibility studies that provided data on the bulk magnetization, the FMR spectra revealed the presence of three different types of magnetic Ni nanocubes in the sample. Specifically, three different ferromagnetic resonances were observed in the X-band spectra: a line 1 assigned to large nickel nanocubes, a line 2 corresponding to the nanocubes exhibiting saturated magnetization even at ca. 0.3 T field, and a high field line 3 (geff ˜ 6.2) tentatively assigned to small nickel nanocubes likely having their hard magnetization axis aligned along or close to the direction of the external magnetic field. Based on the analysis of FMR data, the latter nanocubes possess an anisotropic internal magnetic field of at least ˜1.0 T in magnitude.

  10. Performance analysis of multi-frequency topological derivative for reconstructing perfectly conducting cracks

    NASA Astrophysics Data System (ADS)

    Park, Won-Kwang

    2017-04-01

    This paper concerns a fast, one-step iterative technique of imaging extended perfectly conducting cracks with Dirichlet boundary condition. In order to reconstruct the shape of cracks from scattered field data measured at the boundary, we introduce a topological derivative-based electromagnetic imaging functional operated at several nonzero frequencies. The structure of the imaging functionals is carefully analyzed by establishing relationships with infinite series of Bessel functions for the configurations of both symmetric and non-symmetric incident field directions. Identified structure explains why the application of incident fields with symmetric direction operated at multiple frequencies guarantees a successful reconstruction. Various numerical simulations with noise-corrupted data are conducted to assess the performance, effectiveness, robustness, and limitations of the proposed technique.

  11. Multi-frequency, multi-technique pulsed EPR investigation of the copper binding site of murine amyloid β peptide.

    PubMed

    Kim, Donghun; Bang, Jeong Kyu; Kim, Sun Hee

    2015-01-26

    Copper-amyloid peptides are proposed to be the cause of Alzheimer's disease, presumably by oxidative stress. However, mice do not produce amyloid plaques and thus do not suffer from Alzheimer's disease. Although much effort has been focused on the structural characterization of the copper- human amyloid peptides, little is known regarding the copper-binding mode in murine amyloid peptides. Thus, we investigated the structure of copper-murine amyloid peptides through multi-frequency, multi-technique pulsed EPR spectroscopy in conjunction with specific isotope labeling. Based on our pulsed EPR results, we found that Ala2, Glu3, His6, and His14 are directly coordinated with the copper ion in murine amyloid β peptides at pH 8.5. This is the first detailed structural characterization of the copper-binding mode in murine amyloid β peptides. This work may advance the knowledge required for developing inhibitors of Alzheimer's disease.

  12. Comparison Of Multi-Frequency SAR Land Cover Signatures For Multi-Site Semi-Arid Regions Of Africa

    NASA Astrophysics Data System (ADS)

    Spies, Bernard; Lamb, Alistair; Brown, Sarah, Balzter, Heiko; Fisher, Peter

    2013-12-01

    This study shows the analysis and comparison of different SAR backscatter signatures (σ0 distributions) for distinguishable land cover types over two semi-arid test sites in Africa. The two sites that were chosen are located in Tanzania and Chad, where existing multi- frequency data was available from the different synthetic aperture radar (SAR) archives. Images were grouped into wet and dry season for the Tanzania site, whereas only dry season imagery was available for the Chad site. An IsoData unsupervised classification was applied on all three sets of images to classify seven land cover classes. Random samples were taken from each of the classes, resulting in σ0 distributions for the different classes for each site. These SAR land cover signatures are interpreted and discussed, with further steps identified.

  13. Mapping power-law rheology of living cells using multi-frequency force modulation atomic force microscopy

    SciTech Connect

    Takahashi, Ryosuke; Okajima, Takaharu

    2015-10-26

    We present multi-frequency force modulation atomic force microscopy (AFM) for mapping the complex shear modulus G* of living cells as a function of frequency over the range of 50–500 Hz in the same measurement time as the single-frequency force modulation measurement. The AFM technique enables us to reconstruct image maps of rheological parameters, which exhibit a frequency-dependent power-law behavior with respect to G{sup *}. These quantitative rheological measurements reveal a large spatial variation in G* in this frequency range for single cells. Moreover, we find that the reconstructed images of the power-law rheological parameters are much different from those obtained in force-curve or single-frequency force modulation measurements. This indicates that the former provide information about intracellular mechanical structures of the cells that are usually not resolved with the conventional force measurement methods.

  14. 2WHSP: A multi-frequency selected catalog of VHE gamma-ray blazars and blazar candidates

    NASA Astrophysics Data System (ADS)

    Chang, Yu Lin; Arsioli, Bruno; Giommi, Paolo; Padovani, Paolo

    2016-08-01

    High Synchrotron Peaked Blazars (HSPs) are extremely important for VHE astronomy. We built the largest existing catalog of High Synchrotron Blazars (2WHSP) based on multi-frequency data. The catalog is an extension of the 1WHSP list. We compared several general properties of HSPs such as the synchrotron peak, the redshift and IR the color-color diagram. We also built the logN-logS for the sources, trying to see the evolution and the deficiency of the catalog. The catalog will provide a unique sample of targets for VHE observations in future since the HSPs are the dominant extra-Galactic sources in VHE sky. This might help find more VHE sources later. In the future, we will use this catalog to estimate other VHE properties of HSPs.

  15. Application of Multi-Frequency Modulation (MFM) for high-speed data communications to a voice frequency channel

    NASA Astrophysics Data System (ADS)

    Salsman, Charles P.

    1990-06-01

    Multi-Frequency Modulation (MFM) has been developed at NPS using both differential quadrature-phase-shift-keying (DQPSK) and differential-quadrature-amplitude-modulation (DQAM) encoding formats. Previous applications of these encoding formats were on industry standard computers (PC) over a 16 to 20 kHz channel. This report discusses the implementation of MFM to a voice frequency channel of 200 to 3400 Hz, for possible future use with high-speed modems over switched telephone networks. Research and testing for this report included the DQPSK and differential 16 quadrature-amplitude-modulation (D16-QAM) encoding formats implemented on PCs. Experimental results of the implemented MFM signal were comparable to theory with acceptable bit error rates for input signal-to-noise ratios (SNR) of 15 dB and higher.

  16. AGN Astrophysics via Multi-Frequency Monitoring of γ-ray Blazars in the Fermi-GST Era

    NASA Astrophysics Data System (ADS)

    Angelakis, E.; Angelakis, E.; Fuhrmann, L.; Zensus, J. A.; Nestoras, I.; Marchili, N.; Krichbaum, T. P.; Ungerechts, H.; Max-Moerbeck, W.; Pavlidou, V.; Pearson, T. J.; Readhead, A. C. S.; Richards, J. L.; Stevenson, M. A.

    2010-10-01

    The F-GAMMA-project is the coordinated effort of several observatories to understand the AGN phenomenon and specifically blazars via multi-frequency monitoring in collaboration with the Fermi-GST satellite since January 2007. The core observatories are: the Effelsberg 100-m, the IRAM 30-m and the OVRO 40-m telescope covering the range between 2.6 and 270 GHz. Effelsberg and IRAM stations do a monthly monitoring of the cm to sub-mm radio spectra of 60 selected blazars whereas the OVRO telescope is observing roughly 1200 objects at 15 GHz with a dense sampling of 2 points per week. The calibration uncertainty even at high frequencies, is of a few percent. 47% of the Effelsberg/Pico Veleta sample is included in the LBAS list. An update of the monitored sample is currently underway.

  17. A new method for matched field localization based on two-hydrophone

    NASA Astrophysics Data System (ADS)

    Li, Kun; Fang, Shi-liang

    2015-03-01

    The conventional matched field processing (MFP) uses large vertical arrays to locate an underwater acoustic target. However, the use of large vertical arrays increases equipment and computational cost, and causes some problems such as element failures, and array tilting to degrade the localization performance. In this paper, the matched field localization method using two-hydrophone is proposed for underwater acoustic pulse signals with an unknown emitted signal waveform. Using the received signal of hydrophones and the ocean channel pulse response which can be calculated from an acoustic propagation model, the spectral matrix of the emitted signal for different source locations can be estimated by employing the method of frequency domain least squares. The resulting spectral matrix of the emitted signal for every grid region is then multiplied by the ocean channel frequency response matrix to generate the spectral matrix of replica signal. Finally, the matched field localization using two-hydrophone for underwater acoustic pulse signals of an unknown emitted signal waveform can be estimated by comparing the difference between the spectral matrixes of the received signal and the replica signal. The simulated results from a shallow water environment for broadband signals demonstrate the significant localization performance of the proposed method. In addition, the localization accuracy in five different cases are analyzed by the simulation trial, and the results show that the proposed method has a sharp peak and low sidelobes, overcoming the problem of high sidelobes in the conventional MFP due to lack of the number of elements.

  18. Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics

    PubMed Central

    Usher, Tedi-Marie; Levin, Igor; Daniels, John E.; Jones, Jacob L.

    2015-01-01

    The atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO3 and Na½Bi½TiO3, and dielectric SrTiO3. For Na½Bi½TiO3, the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO3 and SrTiO3, the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively. PMID:26424360

  19. Measuring Earth's Local Magnetic Field Using a Helmholtz Coil

    ERIC Educational Resources Information Center

    Williams, Jonathan E.

    2014-01-01

    In this paper, I present a low-cost interactive experiment for measuring the strength of Earth's local magnetic field. This activity can be done in most high schools or two-year physics laboratories with limited resources, yet will have a tremendous learning impact. This experiment solidifies the three-dimensional nature of Earth's…

  20. Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics

    SciTech Connect

    Usher, Tedi -Marie; Levin, Igor; Daniels, John E.; Jones, Jacob L.

    2015-10-01

    In this study, the atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO3 and Na½Bi½TiO3, and dielectric SrTiO3. For Na½Bi½TiO3, the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO3 and SrTiO3, the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively.

  1. Nonperturbative renormalization group for scalar fields in de Sitter space: Beyond the local potential approximation

    NASA Astrophysics Data System (ADS)

    Guilleux, Maxime; Serreau, Julien

    2017-02-01

    Nonperturbative renormalization group techniques have recently proven a powerful tool to tackle the nontrivial infrared dynamics of light scalar fields in de Sitter space. In the present article, we develop the formalism beyond the local potential approximation employed in earlier works. In particular, we consider the derivative expansion, a systematic expansion in powers of field derivatives, appropriate for long wavelength modes, that we generalize to the relevant case of a curved metric with Lorentzian signature. The method is illustrated with a detailed discussion of the so-called local potential approximation prime which, on top of the full effective potential, includes a running (but field-independent) field renormalization. We explicitly compute the associated anomalous dimension for O (N ) theories. We find that it can take large values along the flow, leading to sizable differences as compared to the local potential approximation. However, it does not prevent the phenomenon of gravitationally induced dimensional reduction pointed out in previous studies. We show that, as a consequence, the effective potential at the end of the flow is unchanged as compared to the local potential approximation, the main effect of the running anomalous dimension being merely to slow down the flow. We discuss some consequences of these findings.

  2. Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics

    DOE PAGES

    Usher, Tedi -Marie; Levin, Igor; Daniels, John E.; ...

    2015-10-01

    In this study, the atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO3 and Na½Bi½TiO3,more » and dielectric SrTiO3. For Na½Bi½TiO3, the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO3 and SrTiO3, the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively.« less

  3. Comparison of Phase-Based 3D Near-Field Source Localization Techniques for UHF RFID

    PubMed Central

    Parr, Andreas; Miesen, Robert; Vossiek, Martin

    2016-01-01

    In this paper, we present multiple techniques for phase-based narrowband backscatter tag localization in three-dimensional space with planar antenna arrays or synthetic apertures. Beamformer and MUSIC localization algorithms, known from near-field source localization and direction-of-arrival estimation, are applied to the 3D backscatter scenario and their performance in terms of localization accuracy is evaluated. We discuss the impact of different transceiver modes known from the literature, which evaluate different send and receive antenna path combinations for a single localization, as in multiple input multiple output (MIMO) systems. Furthermore, we propose a new Singledimensional-MIMO (S-MIMO) transceiver mode, which is especially suited for use with mobile robot systems. Monte-Carlo simulations based on a realistic multipath error model ensure spatial correlation of the simulated signals, and serve to critically appraise the accuracies of the different localization approaches. A synthetic uniform rectangular array created by a robotic arm is used to evaluate selected localization techniques. We use an Ultra High Frequency (UHF) Radiofrequency Identification (RFID) setup to compare measurements with the theory and simulation. The results show how a mean localization accuracy of less than 30 cm can be reached in an indoor environment. Further simulations demonstrate how the distance between aperture and tag affects the localization accuracy and how the size and grid spacing of the rectangular array need to be adapted to improve the localization accuracy down to orders of magnitude in the centimeter range, and to maximize array efficiency in terms of localization accuracy per number of elements. PMID:27347976

  4. Behavior of Caenorhabditis elegans in alternating electric field and its application to their localization and control

    NASA Astrophysics Data System (ADS)

    Rezai, Pouya; Siddiqui, Asad; Selvaganapathy, Ponnambalam Ravi; Gupta, Bhagwati P.

    2010-04-01

    Caenorhabditis elegans is an attractive model organism because of its genetic similarity to humans and the ease of its manipulation in the laboratory. Recently, it was shown that a direct current electric field inside microfluidic channel induces directed movement that is highly sensitive, reliable, and benign. In this letter, we describe the worm's movement response to alternating electric fields in a similar channel setup. We demonstrate that the 1 Hz and higher frequency of alternating current field can effectively localize worms in the channel. This discovery could potentially help design microfluidic devices for high throughput automated analysis of worms.

  5. Locality and efficient evaluation of lattice composite fields: Overlap-based gauge operators

    NASA Astrophysics Data System (ADS)

    Alexandru, Andrei; Horváth, Ivan

    2017-01-01

    We propose a novel general approach to locality of lattice composite fields, which in case of QCD involves locality in both quark and gauge degrees of freedom. The method is applied to gauge operators based on the overlap Dirac matrix elements, showing for the first time their local nature on realistic path-integral backgrounds. The framework entails a method for efficient evaluation of such nonultralocal operators, whose computational cost is volume independent at fixed accuracy, and only grows logarithmically as this accuracy approaches zero. This makes computation of useful operators, such as overlap-based topological density, practical. The key notion underlying these features is that of exponential insensitivity to distant fields, made rigorous by introducing the procedure of statistical regularization. The scales associated with insensitivity property are useful characteristics of nonlocal continuum operators.

  6. Multi-frequency Phase Unwrap from Noisy Data: Adaptive Least Squares Approach

    NASA Astrophysics Data System (ADS)

    Katkovnik, Vladimir; Bioucas-Dias, José

    2010-04-01

    Multiple frequency interferometry is, basically, a phase acquisition strategy aimed at reducing or eliminating the ambiguity of the wrapped phase observations or, equivalently, reducing or eliminating the fringe ambiguity order. In multiple frequency interferometry, the phase measurements are acquired at different frequencies (or wavelengths) and recorded using the corresponding sensors (measurement channels). Assuming that the absolute phase to be reconstructed is piece-wise smooth, we use a nonparametric regression technique for the phase reconstruction. The nonparametric estimates are derived from a local least squares criterion, which, when applied to the multifrequency data, yields denoised (filtered) phase estimates with extended ambiguity (periodized), compared with the phase ambiguities inherent to each measurement frequency. The filtering algorithm is based on local polynomial (LPA) approximation for design of nonlinear filters (estimators) and adaptation of these filters to unknown smoothness of the spatially varying absolute phase [9]. For phase unwrapping, from filtered periodized data, we apply the recently introduced robust (in the sense of discontinuity preserving) PUMA unwrapping algorithm [1]. Simulations give evidence that the proposed algorithm yields state-of-the-art performance for continuous as well as for discontinues phase surfaces, enabling phase unwrapping in extraordinary difficult situations when all other algorithms fail.

  7. Steady flows in rotating spherical cavity excited by multi-frequency oscillations of free inner core

    NASA Astrophysics Data System (ADS)

    Kozlov, Victor G.; Kozlov, Nikolai V.; Subbotin, Stanislav V.

    2017-01-01

    Fluid motion in a rotating spherical cavity in the conditions of resonant oscillations of free inner core is experimentally investigated. The centrifugal force retains a solid core with density less than the fluid density near the center of the cavity. In the absence of external force field the system "solid core - liquid" performs solid body rotation. The oscillations of the core are excited by an external oscillating force field and this results in differential rotation of the core with respect to the cavity. The direction of rotation is determined by the ratio of the oscillation frequency to the cavity angular velocity. The core oscillations with the radian frequency, which exceeds the cavity angular velocity, are investigated. It is found that a steady flow in the form of a system of nested fluid columns of circular cross section, which rotate at different angular velocities, is generated in the cavity as a result of oscillations of the core and the fluid. It is shown that at simultaneous influence of several oscillating fields the resulting steady flow is determined by a linear superposition of the flows, which are excited by the oscillations of the inner core with different frequencies. At a certain ratio of the vibration frequency to the rotation one the transformation of the circular shape of the column into the elliptical one is observed.

  8. Non-linear non-local molecular electrodynamics with nano-optical fields.

    PubMed

    Chernyak, Vladimir Y; Saurabh, Prasoon; Mukamel, Shaul

    2015-10-28

    The interaction of optical fields sculpted on the nano-scale with matter may not be described by the dipole approximation since the fields may vary appreciably across the molecular length scale. Rather than incrementally adding higher multipoles, it is advantageous and more physically transparent to describe the optical process using non-local response functions that intrinsically include all multipoles. We present a semi-classical approach for calculating non-local response functions based on the minimal coupling Hamiltonian. The first, second, and third order response functions are expressed in terms of correlation functions of the charge and the current densities. This approach is based on the gauge invariant current rather than the polarization, and on the vector potential rather than the electric and magnetic fields.

  9. Local magnetic fields diagnostics in solar faculae using Fel 5233 line

    NASA Astrophysics Data System (ADS)

    Lozitsky, V.; Osyka, O.; Liakh, V.

    2015-12-01

    The bisectors of I ± V Stokes profiles are analyzed for measurements of local magnetic field strengths in solar faculae of 7 August 2013observed on Echelle spectrograph of horizontal solar telescope of the Astronomical Observatory of Kyiv Taras Shevchenko National University. Obtained observational data indicate the inapplicability the weak-field and one-component approximation for this line. This follows from essential (till five times) differences of bisector splitting in different parts of line profile. A fine effect was found from analysis of mean-square deviation of observed bisector splitting from linear trend. This deviation has a maximum (relatively error level) on distance nearly 120 mǺ from line center that could indicate the presence of local magnetic field of about 7.4 kG.

  10. Local Magnetic Field Diagnostics in Solar Faculae Using FeI 5233 Line

    NASA Astrophysics Data System (ADS)

    Lozitsky, V.; Osyka, O.; Lyakh, V.

    2015-06-01

    The bisectors of I ± V Stokes profiles are analyzed for measurements of local magnetic field strengths in solar faculae of 7 August 2013 observed on Echelle spectrograph of horizontal solar telescope of the Astronomical Observatory of Kyiv Taras Shevchenko National University. Obtained observational data indicate the inapplicability the weak-field and one-component approximation for this line. This follows from essential (till five times) differences of bisector splitting in different parts of line profile. A fine effect was found from analysis of mean-square deviation of observed bisector splitting from linear trend. This deviation has a maximum (relatively error level) on distance nearly 120 mÅ from line center that could indicate the presence of local magnetic field of about 7.4 kG.

  11. Dust Grain Alignment and Magnetic Field Strength in the Wall of the Local Bubble

    NASA Astrophysics Data System (ADS)

    Andersson, B.-G.; Medan, Ilija

    2017-01-01

    We use archival data on polarization (Berdyugin 2014) and extinction in the wall of the Local Bubble to study the grain alignment efficiency and the magnetic field strength. We find that the grain alignment efficiency variations can be directly tied to the location of the known OB-associations within 200pc from the Sun, strongly supporting modern, radiation-driven dust grain alignment. Based on the Davis-Chandrasekhar-Fermi method, we find a bimodal magnetic field-strength distribution, where the locations of the strongest fields correlate with the directions towards the near-by OB associations. We hypothesize that this strengthening is due to compression of the bubble wall by the opposing outflows in the Local Bubble and from the surrounding OB associations.

  12. Local and global effects of the cross-field current instability

    NASA Technical Reports Server (NTRS)

    Lui, A. T. Y.

    1996-01-01

    The cross-field current instability (CCI) was proposed elsewhere as a plausible mechanism for the initiation and intensification of substorm expansions. This instability encompasses the modified two stream, the ion-Weibel and the lower hybrid drift modes. The work carried out in relation to this instability and its local and global effects is reviewed. Predicted local effects include current reduction, particle acceleration, the excitation of oblique whistlers and lower hybrid drift waves, and the breakdown of the frozen-in-field condition through anomalous dissipation. The predicted global effects of CCI include the offset of force equilibrium and the generation of field aligned currents at the disruption site, which allow the efficient large scale transportation of mass, momentum and energy within the magnetosphere.

  13. Field Effect and Strongly Localized Carriers in the Metal-Insulator Transition Material VO(2).

    PubMed

    Martens, K; Jeong, J W; Aetukuri, N; Rettner, C; Shukla, N; Freeman, E; Esfahani, D N; Peeters, F M; Topuria, T; Rice, P M; Volodin, A; Douhard, B; Vandervorst, W; Samant, M G; Datta, S; Parkin, S S P

    2015-11-06

    The intrinsic field effect, the change in surface conductance with an applied transverse electric field, of prototypal strongly correlated VO(2) has remained elusive. Here we report its measurement enabled by epitaxial VO(2) and atomic layer deposited high-κ dielectrics. Oxygen migration, joule heating, and the linked field-induced phase transition are precluded. The field effect can be understood in terms of field-induced carriers with densities up to ∼5×10(13)  cm(-2) which are trongly localized, as shown by their low, thermally activated mobility (∼1×10(-3)  cm(2)/V s at 300 K). These carriers show behavior consistent with that of Holstein polarons and strongly impact the (opto)electronics of VO(2).

  14. Wired/wireless access integrated RoF-PON with scalable generation of multi-frequency MMWs enabled by polarization multiplexed FWM in SOA.

    PubMed

    Xiang, Yu; Chen, Chen; Zhang, Chongfu; Qiu, Kun

    2013-01-14

    In this paper, we propose and demonstrate a novel integrated radio-over-fiber passive optical network (RoF-PON) system for both wired and wireless access. By utilizing the polarization multiplexed four-wave mixing (FWM) effect in a semiconductor optical amplifier (SOA), scalable generation of multi-frequency millimeter-waves (MMWs) can be provided so as to assist the configuration of multi-frequency wireless access for the wire/wireless access integrated ROF-PON system. In order to obtain a better performance, the polarization multiplexed FWM effect is investigated in detail. Simulation results successfully verify the feasibility of our proposed scheme.

  15. Si dielectric function in a local basis representation: Optical properties, local field effects, excitons, and stopping power

    NASA Astrophysics Data System (ADS)

    Gómez, M.; González, P.; Ortega, J.; Flores, F.

    2014-11-01

    An atomiclike basis representation is used to analyze the dielectric function ɛ (q ⃗+G ⃗,q ⃗+G⃗';ω ) of Si. First, we show that a s p3d5 local basis set yields good results for the electronic band structure of this crystal and, then, we analyze the Si optical properties including local field and excitonic effects. In our formulation, we follow Hanke and Sham [W. Hanke and L. J. Sham, Phys. Rev. B 12, 4501 (1975), 10.1103/PhysRevB.12.4501; Phys. Rev. B 21, 4656 (1980), 10.1103/PhysRevB.21.4656], and introduce excitonic effects using a many-body formulation that incorporates a static screened electron-hole interaction. Dynamical effects in this interaction are also analyzed and shown to introduce non-negligible corrections in the optical spectrum. Our results are found in reasonable agreement with the experimental evidence and with other theoretical results calculated with the computationally more demanding plane-wave representation. Finally, calculations for the stopping power of Si are also presented.

  16. Multi-Frequency and Multi-Polarization Scattering Analysis for Model-Based Coastal Areas Classification

    NASA Astrophysics Data System (ADS)

    Buono, A.; Nunziata, F.; Migliaccio, M.; Li, X.; Wei, Y.; Shen, D.

    2016-08-01

    The Yellow River (in Chinese, Huang He) is the most sediment-filled river and the sixth-longest one in the world. The Yellow River is of paramount importance for safe navigation, local economy and environment due to the presence of floods, farms, aquacultures and pollution. Nonetheless, its delta area it is characterized by of several physical phenomena due to both natural and anthropogenic processes: sedimentation, erosion, floods, pollution, etc.In this study, actual partially overlapped L-/C-band FP SAR data collected from Radarsat-2 and ALOS PalSAR-2, respectively, are used to investigate the scattering properties of the Yellow River delta, whose very challenging area is characterized by different scenarios as recorded by ground truth data acquired during an in-situ campaign. 10 different classes have been codified: sea, river, forest, pond, swamp, tide-land, sand, saline soil, rural and industrial urban areas. However, no ground truth data is available in some codified areas.

  17. Local energy and power in many-particle quantum systems driven by an external electrical field

    NASA Astrophysics Data System (ADS)

    Albareda, Guillermo; Traversa, Fabio Lorenzo; Oriols, Xavier

    2016-05-01

    We derive expressions for the expectation values of the local energy and the local power for a many-particle system of (scalar) charged particles interacting with an external electrical field. In analogy with the definition of the (local) current probability density, we construct a local energy operator such that the time-rate of change of its expectation value provides information on the spatial distribution of power. Results are presented as functions of an arbitrarily small volume Ω , and physical insights are discussed by means of the quantum hydrodynamical representation of the wavefunction, which is proven to allow for a clear-cut separation into contributions with and without classical correspondence. Quantum features of the local power are mainly manifested through the presence of non-local sources/sinks of power and through the action of forces with no classical counterpart. Many-particle classical-like effects arise in the form of current-force correlations and through the inflow/outflow of energy across the boundaries of the volume Ω . Interestingly, all these intriguing features are only reflected in the expression of the local power when the volume Ω is finite. Otherwise, for closed systems with Ω \\to ∞ , we recover a classical-like single-particle expression.

  18. A multi-frequency study of the SZE in giant radio galaxies

    NASA Astrophysics Data System (ADS)

    Colafrancesco, S.; Marchegiani, P.; de Bernardis, P.; Masi, S.

    2013-02-01

    Context. Radio galaxy (RG) lobes contain relativistic electrons embedded in a tangled magnetic field that produce, in addition to low-frequency synchrotron radio emission, inverse-Compton scattering (ICS) of the cosmic microwave background (CMB) photons. This produces a relativistic, non-thermal Sunyaev-Zel'dovich effect (SZE). Aims: We study the spectral and spatial properties of the non-thermal SZE in a sample of radio galaxies and make predictions for their detectability in both the negative and the positive part of the SZE, with space experiments like Planck, OLIMPO, and Herschel-SPIRE. These cover a wide range of frequencies, from radio to sub-mm. Methods: We model the SZE in a general formalism that is equivalent to the relativistic covariant one and describe the electron population contained in the lobes of the radio galaxies with parameters derived from their radio observations, namely, flux, spectral index, and spatial extension. We further constrain the electron spectrum and the magnetic field of the RG lobes using X-ray, gamma-ray, and microwave archival observations. Results: We determine the main spectral features of the SZE in RG lobes, namely, the minimum, the crossover, and the maximum of the SZE. We show that these typical spectral features fall in the frequency ranges probed by the available space experiments. We provide the most reliable predictions for the amplitude and spectral shape of the SZE in a sample of selected RGs with extended lobes. In three of these objects, we also derive an estimate of the magnetic field in the lobe at the ~μG level by combining radio (synchrotron) observations and X-ray (ICS) observations. These data, together with the WMAP upper limits, set constraints on the minimum momentum of the electrons residing in the RG lobes and allow realistic predictions for the visibility of their SZE to be derived with Planck, OLIMPO, and Herschel-SPIRE. Conclusions: We show that the SZE from several RG lobes can be observed with mm

  19. Relative localization in wireless sensor networks for measurement of electric fields under HVDC transmission lines.

    PubMed

    Cui, Yong; Wang, Qiusheng; Yuan, Haiwen; Song, Xiao; Hu, Xuemin; Zhao, Luxing

    2015-02-04

    In the wireless sensor networks (WSNs) for electric field measurement system under the High-Voltage Direct Current (HVDC) transmission lines, it is necessary to obtain the electric field distribution with multiple sensors. The location information of each sensor is essential to the correct analysis of measurement results. Compared with the existing approach which gathers the location information by manually labelling sensors during deployment, the automatic localization can reduce the workload and improve the measurement efficiency. A novel and practical range-free localization algorithm for the localization of one-dimensional linear topology wireless networks in the electric field measurement system is presented. The algorithm utilizes unknown nodes' neighbor lists based on the Received Signal Strength Indicator (RSSI) values to determine the relative locations of nodes. The algorithm is able to handle the exceptional situation of the output permutation which can effectively improve the accuracy of localization. The performance of this algorithm under real circumstances has been evaluated through several experiments with different numbers of nodes and different node deployments in the China State Grid HVDC test base. Results show that the proposed algorithm achieves an accuracy of over 96% under different conditions.

  20. Effect of the local morphology in the field emission properties of conducting polymer surfaces

    NASA Astrophysics Data System (ADS)

    de Assis, T. A.; Benito, R. M.; Losada, J. C.; Andrade, R. F. S.; Miranda, J. G. V.; de Souza, Nara C.; de Castilho, C. M. C.; Mota, F. de B.; Borondo, F.

    2013-07-01

    In this work, we present systematic theoretical evidence of a relationship between the point local roughness exponent (PLRE) (which quantifies the heterogeneity of an irregular surface) and the cold field emission properties (indicated by the local current density and the macroscopic current density) of real polyaniline (PANI) surfaces, considered nowadays as very good candidates in the design of field emission devices. The latter are obtained from atomic force microscopy data. The electric field and potential are calculated in a region bounded by the rough PANI surface and a distant plane, both boundaries held at distinct potential values. We numerically solve Laplace’s equation subject to appropriate Dirichlet’s condition. Our results show that local roughness reveals the presence of specific sharp emitting spots with a smooth geometry, which are the main ones responsible (but not the only) for the emission efficiency of such surfaces for larger deposition times. Moreover, we have found, with a proper choice of a scale interval encompassing the experimentally measurable average grain length, a highly structured dependence of local current density on PLRE, considering different ticks of PANI surfaces.

  1. Relative Localization in Wireless Sensor Networks for Measurement of Electric Fields under HVDC Transmission Lines

    PubMed Central

    Cui, Yong; Wang, Qiusheng; Yuan, Haiwen; Song, Xiao; Hu, Xuemin; Zhao, Luxing

    2015-01-01

    In the wireless sensor networks (WSNs) for electric field measurement system under the High-Voltage Direct Current (HVDC) transmission lines, it is necessary to obtain the electric field distribution with multiple sensors. The location information of each sensor is essential to the correct analysis of measurement results. Compared with the existing approach which gathers the location information by manually labelling sensors during deployment, the automatic localization can reduce the workload and improve the measurement efficiency. A novel and practical range-free localization algorithm for the localization of one-dimensional linear topology wireless networks in the electric field measurement system is presented. The algorithm utilizes unknown nodes' neighbor lists based on the Received Signal Strength Indicator (RSSI) values to determine the relative locations of nodes. The algorithm is able to handle the exceptional situation of the output permutation which can effectively improve the accuracy of localization. The performance of this algorithm under real circumstances has been evaluated through several experiments with different numbers of nodes and different node deployments in the China State Grid HVDC test base. Results show that the proposed algorithm achieves an accuracy of over 96% under different conditions. PMID:25658390

  2. High Accuracy Passive Magnetic Field-Based Localization for Feedback Control Using Principal Component Analysis.

    PubMed

    Foong, Shaohui; Sun, Zhenglong

    2016-08-12

    In this paper, a novel magnetic field-based sensing system employing statistically optimized concurrent multiple sensor outputs for precise field-position association and localization is presented. This method capitalizes on the independence between simultaneous spatial field measurements at multiple locations to induce unique correspondences between field and position. This single-source-multi-sensor configuration is able to achieve accurate and precise localization and tracking of translational motion without contact over large travel distances for feedback control. Principal component analysis (PCA) is used as a pseudo-linear filter to optimally reduce the dimensions of the multi-sensor output space for computationally efficient field-position mapping with artificial neural networks (ANNs). Numerical simulations are employed to investigate the effects of geometric parameters and Gaussian noise corruption on PCA assisted ANN mapping performance. Using a 9-sensor network, the sensing accuracy and closed-loop tracking performance of the proposed optimal field-based sensing system is experimentally evaluated on a linear actuator with a significantly more expensive optical encoder as a comparison.

  3. High Accuracy Passive Magnetic Field-Based Localization for Feedback Control Using Principal Component Analysis

    PubMed Central

    Foong, Shaohui; Sun, Zhenglong

    2016-01-01

    In this paper, a novel magnetic field-based sensing system employing statistically optimized concurrent multiple sensor outputs for precise field-position association and localization is presented. This method capitalizes on the independence between simultaneous spatial field measurements at multiple locations to induce unique correspondences between field and position. This single-source-multi-sensor configuration is able to achieve accurate and precise localization and tracking of translational motion without contact over large travel distances for feedback control. Principal component analysis (PCA) is used as a pseudo-linear filter to optimally reduce the dimensions of the multi-sensor output space for computationally efficient field-position mapping with artificial neural networks (ANNs). Numerical simulations are employed to investigate the effects of geometric parameters and Gaussian noise corruption on PCA assisted ANN mapping performance. Using a 9-sensor network, the sensing accuracy and closed-loop tracking performance of the proposed optimal field-based sensing system is experimentally evaluated on a linear actuator with a significantly more expensive optical encoder as a comparison. PMID:27529253

  4. Local and Global Magnetic Fields of Late-Type Dwarfs OT Ser and YZ CMi

    NASA Astrophysics Data System (ADS)

    Bychkov, V. D.; Bychkova, L. V.; Madej, J.; Panferov, A. A.

    2015-04-01

    Differential rotation is the primary energy source for generation of local magnetic fields in the atmospheres of late-type stars (Moss et al. 1995). Moreover, the colder a star, the greater the effect, which was confirmed by observations. For instance, Saar (1988) measured the surface magnetic fields of late-type stars using the integral method Robinson (1980) and drew attention to the fact that the average magnetic field in the spots reaches the values of 1500 G for the G-type dwarfs, 2500 G for the K dwarfs, and 3500 G for the M-dwarf stars. The fraction of the surface of a star covered by spots also increases towards the latest spectral types. These well-known observational facts were explained by theoretical models, such as the α2 mechanism, for instance (Moss et al. 1995). Late-type dwarfs exhibit periodic eruptions resulting from the field line reconnection of newly generated local magnetic fields. This feature is observed in G, K, and M dwarfs, constituting 95%of all the stars in our Galaxy. The most prominent are the field reconnections in the so-called flare stars, which are the M dwarfs. This is understandable, since the peak flux of M dwarfs is placed in the red and infrared regions of the spectrum, whereas a flash has the maximum emission in the violet spectral region. Analysis of long-term photometric observations revealed that, on the average, energy of flares was found constant over a long time period for each flare star. That is to say, this conclusion implies that the power of the local magnetic field generator remains constant at this stage of evolution of stars.

  5. Field theoretic approach to dynamical orbital localization in ab initio molecular dynamics

    NASA Astrophysics Data System (ADS)

    Thomas, Jordan W.; Iftimie, Radu; Tuckerman, Mark E.

    2004-03-01

    Techniques from gauge-field theory are employed to derive an alternative formulation of the Car-Parrinello ab initio molecular-dynamics method that allows maximally localized Wannier orbitals to be generated dynamically as the calculation proceeds. In particular, the Car-Parrinello Lagrangian is mapped onto an SU(n) non-Abelian gauge-field theory and the fictitious kinetic energy in the Car-Parrinello Lagrangian is modified to yield a fully gauge-invariant form. The Dirac gauge-fixing method is then employed to derive a set of equations of motion that automatically maintain orbital locality by restricting the orbitals to remain in the “Wannier gauge.” An approximate algorithm for integrating the equations of motion that is stable and maintains orbital locality is then developed based on the exact equations of motion. It is shown in a realistic application (64 water molecules plus one hydrogen-chloride molecule in a periodic box) that orbital locality can be maintained with only a modest increase in CPU time. The ability to keep orbitals localized in an ab initio molecular-dynamics calculation is a crucial ingredient in the development of emerging linear scaling approaches.

  6. Effects of reconstructed magnetic field from sparse noisy boundary measurements on localization of active neural source.

    PubMed

    Shen, Hui-min; Lee, Kok-Meng; Hu, Liang; Foong, Shaohui; Fu, Xin

    2016-01-01

    Localization of active neural source (ANS) from measurements on head surface is vital in magnetoencephalography. As neuron-generated magnetic fields are extremely weak, significant uncertainties caused by stochastic measurement interference complicate its localization. This paper presents a novel computational method based on reconstructed magnetic field from sparse noisy measurements for enhanced ANS localization by suppressing effects of unrelated noise. In this approach, the magnetic flux density (MFD) in the nearby current-free space outside the head is reconstructed from measurements through formulating the infinite series solution of the Laplace's equation, where boundary condition (BC) integrals over the entire measurements provide "smooth" reconstructed MFD with the decrease in unrelated noise. Using a gradient-based method, reconstructed MFDs with good fidelity are selected for enhanced ANS localization. The reconstruction model, spatial interpolation of BC, parametric equivalent current dipole-based inverse estimation algorithm using reconstruction, and gradient-based selection are detailed and validated. The influences of various source depths and measurement signal-to-noise ratio levels on the estimated ANS location are analyzed numerically and compared with a traditional method (where measurements are directly used), and it was demonstrated that gradient-selected high-fidelity reconstructed data can effectively improve the accuracy of ANS localization.

  7. Place as a social space: fields of encounter relating to the local sustainability process.

    PubMed

    Dumreicher, Heidi; Kolb, Bettina

    2008-04-01

    The paper shows how sustainability questions relate to the local space. The local place is not a static entity, but a dynamic one, undergoing constant changes, and it is the rapid social and material processes within the given local situation that is a challenge for the Chinese villages and their integrity. The following article considers the cohesion between the dwellers' emotional co-ownership of their local space and the sustainability process as a driving force in social, economic and ecological development. We bring together the classification of the seven fields of encounter, which were developed out of the empirical data of the Chinese case study villages, and sustainability oriented management considerations for all levels of this concept. We do not pretend to know the solutions, but describe a set of interrelated fields that can be anchor points for placing the solutions and show in which fields action and intervention is possible. In our concept of sustainability, every spatial field has its special meaning, needs special measures and policies and has different connotations to concepts like responsibility, family values or communication systems. We see the social sustainability process as a support for the empowerment of the local dwellers, and the SUCCESS research has encouraged the villages to find suitable sustainability oriented solutions for their natural and societal situation. Before entering the discussion about the chances and potential of a sustainability approach for the Chinese villages, it is first necessary to accept the fact that rural villages play a primordial role in Chinese society and that their potential can strengthen future pathways for China.

  8. A Multi-Frequency Study of Nearby MSP J1400-1431

    NASA Astrophysics Data System (ADS)

    Swiggum, Joe K.; Kaplan, David L. A.; McLaughlin, Maura; Lorimer, Duncan; Barlow, Brad

    2017-01-01

    Millisecond pulsar (MSP) J1400-1431 was discovered by Pulsar Search Collaboratory (PSC) students in 2012 and a preliminary timing solution was published a year later by Rosen et al. (2013). Using a new localization method and additional measured pulse times of arrival, we find that the initial published position was incorrect. With the improved position, we have obtained a phase-connected timing solution spanning 4.5 years, also measuring proper motion, spin period, period derivative, dispersion measure, and five Keplerian binary parameters to high precision. PSR J1400-1431 is in a nearly circular, 9.5 day orbit around a white dwarf (Mwd > 0.26 Msun) companion. Using the Southern Astrophysical Research (SOAR) and Keck Low-Resolution Imaging Spectrometer (LRIS) optical telescopes, we observe J1400-1431's white dwarf companion in R, I, and V bands to measure absolute magnitudes, color and temperature; this provides valuable information about the white dwarf companion's composition and therefore, clues about the binary system's evolutionary history. We also report faint detections of MSP J1400-1431 in gamma rays (Fermi) and X-rays (XMM).

  9. Multi-frequency Craik Criminale solutions of the Navier Stokes equations

    NASA Astrophysics Data System (ADS)

    Fabijonas, Bruce R.; Holm, Darryl D.

    2004-05-01

    An exact Craik Criminale (CC) solution to the incompressible Navier Stokes (NS) equations describes the instability of an elliptical columnar flow interacting with a single Kelvin wave. These CC solutions are extended to allow multi-harmonic Kelvin waves to interact with any exact ‘base’ solution of the NS equations. The interaction is evaluated along an arbitrarily chosen flowline of the base solution, so exact nonlinear instability in this context is locally convective, rather than absolute. Furthermore, an iterative method called ‘WKB-bootstrapping’ is introduced which successively adds Kelvin waves with incommensurate phases to the extended CC solutions. In illustrating WKB bootstrapping, we construct a succession of extended nonlinear CC solutions consisting of a circular columnar flow interacting progressively with one (Kelvin 1887), two (Fabijonas & Lifschitz 1996), or three waves with incommensurate phases. The phase of each wave packet is frozen into the previous flow and we examine the exact nonlinear convective instability induced at each stage (primary, secondary, tertiary). At each stage, the flow becomes progressively more unstable.

  10. Stress fields and energy of disclination-type defects in zones of localized elastic distortions

    NASA Astrophysics Data System (ADS)

    Sukhanov, Ivan I.; Tyumentsev, Alexander N.; Ditenberg, Ivan A.

    2016-11-01

    This paper studies theoretically the elastically deformed state and analyzes deformation mechanisms in nanocrystals in the zones of localized elastic distortions and related disclination-type defects, such as dipole, quadrupole and multipole of partial disclinations. Significant differences in the energies of quadrupole and multipole configurations in comparison with nanodipole are revealed. The mechanism of deformation localization in the field of elastic distortions is proposed, which is a quasi-periodic sequence of formation and relaxation of various disclination ensembles with a periodic change in the energy of the defect.

  11. Three-dimensional atom localization by laser fields in a four-level tripod system

    NASA Astrophysics Data System (ADS)

    Ivanov, Vladimir S.; Rozhdestvensky, Yuri V.; Suominen, Kalle-Antti

    2014-12-01

    We present a scheme for high-precision three-dimensional (3D) localization by the measurement of the atomic-level population. The scheme is applied to a four-level tripod-type atom coupled by three strong standing waves and a probe running wave. As a result, the atom can be localized in volumes that are substantially smaller than a cubic optical wavelength, which is achieved by the increase of standing-wave intensities. The upper-level distribution depends crucially on the atom-field coupling and it forms 3D periodic structures composed of spheres, hourglasses, bowls, donuts, or deformed barrels.

  12. Coulomb's law corrections and fermion field localization in a tachyonic de Sitter thick braneworld

    NASA Astrophysics Data System (ADS)

    Cartas-Fuentevilla, Roberto; Escalante, Alberto; Germán, Gabriel; Herrera-Aguilar, Alfredo; Rigel Mora-Luna, Refugio

    2016-05-01

    Following recent studies which show that it is possible to localize gravity as well as scalar and gauge vector fields in a tachyonic de Sitter thick braneworld, we investigate the solution of the gauge hierarchy problem, the localization of fermion fields in this model, the recovering of the Coulomb law on the non-relativistic limit of the Yukawa interaction between bulk fermions and gauge bosons localized in the brane, and confront the predicted 5D corrections to the photon mass with its upper experimental/observational bounds, finding the model physically viable since it passes these tests. In order to achieve the latter aims we first consider the Yukawa interaction term between the fermionic and the tachyonic scalar fields MF(T)ΨΨ̅ in the action and analyze four distinct tachyonic functions F(T) that lead to four different structures of the respective fermionic mass spectra with different physics. In particular, localization of the massless left-chiral fermion zero mode is possible for three of these cases. We further analyze the phenomenology of these Yukawa interactions among fermion fields and gauge bosons localized on the brane and obtain the crucial and necessary information to compute the corrections to Coulomb's law coming from massive KK vector modes in the non-relativistic limit. These corrections are exponentially suppressed due to the presence of the mass gap in the mass spectrum of the bulk gauge vector field. From our results we conclude that corrections to Coulomb's law in the thin brane limit have the same form (up to a numerical factor) as far as the left-chiral massless fermion field is localized on the brane. Finally we compute the corrections to the Coulomb's law for an arbitrarily thick brane scenario which can be interpreted as 5D corrections to the photon mass. By performing consistent estimations with brane phenomenology, we found that the predicted corrections to the photon mass, which are well bounded by the experimentally observed or

  13. Coulomb’s law corrections and fermion field localization in a tachyonic de Sitter thick braneworld

    SciTech Connect

    Cartas-Fuentevilla, Roberto; Escalante, Alberto; Germán, Gabriel; Herrera-Aguilar, Alfredo; Mora-Luna, Refugio Rigel

    2016-05-11

    Following recent studies which show that it is possible to localize gravity as well as scalar and gauge vector fields in a tachyonic de Sitter thick braneworld, we investigate the solution of the gauge hierarchy problem, the localization of fermion fields in this model, the recovering of the Coulomb law on the non-relativistic limit of the Yukawa interaction between bulk fermions and gauge bosons localized in the brane, and confront the predicted 5D corrections to the photon mass with its upper experimental/observational bounds, finding the model physically viable since it passes these tests. In order to achieve the latter aims we first consider the Yukawa interaction term between the fermionic and the tachyonic scalar fields MF(T)ΨΨ-bar in the action and analyze four distinct tachyonic functions F(T) that lead to four different structures of the respective fermionic mass spectra with different physics. In particular, localization of the massless left-chiral fermion zero mode is possible for three of these cases. We further analyze the phenomenology of these Yukawa interactions among fermion fields and gauge bosons localized on the brane and obtain the crucial and necessary information to compute the corrections to Coulomb’s law coming from massive KK vector modes in the non-relativistic limit. These corrections are exponentially suppressed due to the presence of the mass gap in the mass spectrum of the bulk gauge vector field. From our results we conclude that corrections to Coulomb’s law in the thin brane limit have the same form (up to a numerical factor) as far as the left-chiral massless fermion field is localized on the brane. Finally we compute the corrections to the Coulomb’s law for an arbitrarily thick brane scenario which can be interpreted as 5D corrections to the photon mass. By performing consistent estimations with brane phenomenology, we found that the predicted corrections to the photon mass, which are well bounded by the experimentally

  14. Rapid tsunami models and earthquake source parameters: Far-field and local applications

    USGS Publications Warehouse

    Geist, E.L.

    2005-01-01

    Rapid tsunami models have recently been developed to forecast far-field tsunami amplitudes from initial earthquake information (magnitude and hypocenter). Earthquake source parameters that directly affect tsunami generation as used in rapid tsunami models are examined, with particular attention to local versus far-field application of those models. First, validity of the assumption that the focal mechanism and type of faulting for tsunamigenic earthquakes is similar in a given region can be evaluated by measuring the seismic consistency of past events. Second, the assumption that slip occurs uniformly over an area of rupture will most often underestimate the amplitude and leading-wave steepness of the local tsunami. Third, sometimes large magnitude earthquakes will exhibit a high degree of spatial heterogeneity such that tsunami sources will be composed of distinct sub-events that can cause constructive and destructive interference in the wavefield away from the source. Using a stochastic source model, it is demonstrated that local tsunami amplitudes vary by as much as a factor of two or more, depending on the local bathymetry. If other earthquake source parameters such as focal depth or shear modulus are varied in addition to the slip distribution patterns, even greater uncertainty in local tsunami amplitude is expected for earthquakes of similar magnitude. Because of the short amount of time available to issue local warnings and because of the high degree of uncertainty associated with local, model-based forecasts as suggested by this study, direct wave height observations and a strong public education and preparedness program are critical for those regions near suspected tsunami sources.

  15. Full-Field Strain Measurement On Titanium Welds And Local Elasto-Plastic Identification With The Virtual Fields Method

    SciTech Connect

    Tattoli, F.; Casavola, C.; Pierron, F.; Rotinat, R.; Pappalettere, C.

    2011-01-17

    One of the main problems in welding is the microstructural transformation within the area affected by the thermal history. The resulting heterogeneous microstructure within the weld nugget and the heat affected zones is often associated with changes in local material properties. The present work deals with the identification of material parameters governing the elasto--plastic behaviour of the fused and heat affected zones as well as the base material for titanium hybrid welded joints (Ti6Al4V alloy). The material parameters are identified from heterogeneous strain fields with the Virtual Fields Method. This method is based on a relevant use of the principle of virtual work and it has been shown to be useful and much less time consuming than classical finite element model updating approaches applied to similar problems. The paper will present results and discuss the problem of selection of the weld zones for the identification.

  16. Full-Field Strain Measurement On Titanium Welds And Local Elasto-Plastic Identification With The Virtual Fields Method

    NASA Astrophysics Data System (ADS)

    Tattoli, F.; Pierron, F.; Rotinat, R.; Casavola, C.; Pappalettere, C.

    2011-01-01

    One of the main problems in welding is the microstructural transformation within the area affected by the thermal history. The resulting heterogeneous microstructure within the weld nugget and the heat affected zones is often associated with changes in local material properties. The present work deals with the identification of material parameters governing the elasto—plastic behaviour of the fused and heat affected zones as well as the base material for titanium hybrid welded joints (Ti6Al4V alloy). The material parameters are identified from heterogeneous strain fields with the Virtual Fields Method. This method is based on a relevant use of the principle of virtual work and it has been shown to be useful and much less time consuming than classical finite element model updating approaches applied to similar problems. The paper will present results and discuss the problem of selection of the weld zones for the identification.

  17. Reconstruction of the shape of conductivity spectra using differential multi-frequency magnetic induction tomography.

    PubMed

    Brunner, Patricia; Merwa, Robert; Missner, Andreas; Rosell, Javier; Hollaus, Karl; Scharfetter, Hermann

    2006-05-01

    Magnetic induction tomography (MIT) of biological tissue is used for the reconstruction of the complex conductivity distribution kappa inside the object under investigation. It is based on the perturbation of an alternating magnetic field caused by the object and can be used in all applications of electrical impedance tomography (EIT) such as functional lung monitoring and assessment of tissue fluids. In contrast to EIT, MIT does not require electrodes and magnetic fields can also penetrate non-conducting barriers such as the skull. As in EIT, the reconstruction of absolute conductivity values is very difficult because of the method's sensitivity to numerical errors and noise. To overcome this problem, image reconstruction in EIT is often done differentially. Analogously, this concept has been adopted for MIT. Two different methods for differential imaging are applicable. The first one is state-differential, for example when the conductivity change between inspiration and expiration in the lung regions is being detected. The second one is frequency-differential, which is of high interest in motionless organs like the brain, where a state-differential method cannot be applied. An equation for frequency-differential MIT was derived taking into consideration the frequency dependence of the sensitivity matrix. This formula is valid if we can assume that only small conductivity changes occur. In this way, the non-linear inverse problem of MIT can be approximated by a linear one (depending only on the frequency), similar to in EIT. Keeping this limitation in mind, the conductivity changes between one or more reference frequencies and several measurement frequencies were reconstructed, yielding normalized conductivity spectra. Due to the differential character of the method, these spectra do not provide absolute conductivities but preserve the shape of the spectrum. The validity of the method was tested with artificial data generated with a spherical perturbation within a

  18. Electric-field control of magnetic domain wall motion and local magnetization reversal

    PubMed Central

    Lahtinen, Tuomas H. E.; Franke, Kévin J. A.; van Dijken, Sebastiaan

    2012-01-01

    Spintronic devices currently rely on magnetic switching or controlled motion of domain walls by an external magnetic field or spin-polarized current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including enhanced functionality and low power consumption. Here we report on an approach to electrically control local magnetic properties, including the writing and erasure of regular ferromagnetic domain patterns and the motion of magnetic domain walls, in CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer from ferroelastic domains in ferroelectric media to continuous magnetostrictive films with negligible magnetocrystalline anisotropy. Optical polarization microscopy of both ferromagnetic and ferroelectric domain structures reveals that domain correlations and strong inter-ferroic domain wall pinning persist in an applied electric field. This leads to an unprecedented electric controllability over the ferromagnetic microstructure, an accomplishment that produces giant magnetoelectric coupling effects and opens the way to electric-field driven spintronics. PMID:22355770

  19. The role of localized inductive electric fields in electron injections around dipolarizing flux bundles

    NASA Astrophysics Data System (ADS)

    Gabrielse, Christine; Harris, Camilla; Angelopoulos, Vassilis; Artemyev, Anton; Runov, Andrei

    2016-10-01

    We study energetic electron injections by using an analytical model that self-consistently describes electric and magnetic field perturbations of a transient, localized dipolarizing flux bundle (DFB). This simple model reproduces most injection signatures at multiple locations simultaneously, reaffirming earlier findings that an earthward-traveling DFB can both transport and accelerate electrons to suprathermal energies, and can thus be considered an important driver of short-lived ( < 10 min) injections. We find that energetic electron drift paths are greatly influenced by the sharp magnetic field gradients around a localized DFB. Because a DFB is so localized (only a few RE wide across the tail), there are strong duskward magnetic field gradients on the DFB's dawn flank and strong dawnward magnetic field gradients on its dusk flank. Electrons on the DFB's dawnside therefore ∇B drift farther earthward from the reconnection site, whereas electrons on its duskside can potentially evacuate the inner magnetosphere by ∇B drifting tailward. This results in flux decrease at the front's duskside. As a result, the source of electrons observed during injection depends sensitively on the spacecraft location relative to the DFB and on the DFB's properties. We similarly find that the process of electron energization depends on how the electrons interact with the DFB. The initial injection signature is from electrons that interact with the front and gain the majority of their energy from the increasing magnetic field (∂B/∂t), whereas populations that arrive later gain most of their energy from ∇B drifting across the flow channel and against the DFB's electric fields.

  20. SPECTRUM AND ANISOTROPY OF TURBULENCE FROM MULTI-FREQUENCY MEASUREMENT OF SYNCHROTRON POLARIZATION

    SciTech Connect

    Lazarian, A.; Pogosyan, D.

    2016-02-20

    We consider turbulent synchrotron-emitting media that also exhibit Faraday rotation and provide a statistical description of synchrotron polarization fluctuations. In particular, we consider these fluctuations as a function of the spatial separation of the direction of the measurements and as a function of wavelength for the same line of sight. On the basis of our general analytical approach, we introduce several measures that can be used to obtain the spectral slopes and correlation scales of both the underlying magnetic turbulence responsible for emission and the spectrum of the Faraday rotation fluctuations. We show the synergetic nature of these measures and discuss how the study can be performed using sparsely sampled interferometric data. We also discuss how additional characteristics of turbulence can be obtained, including the turbulence anisotropy and the three-dimensional direction of the mean magnetic field. In addition, we consider the cases when the synchrotron emission and Faraday rotation regions are spatially separated. Appealing to our earlier study, we explain that our new results are applicable to a wide range of spectral indexes of relativistic electrons responsible for synchrotron emission. We expect wide application of our techniques, both with existing synchrotron data sets and with big forthcoming data sets from LOFAR and SKA.

  1. In Vivo Magnetic Particle Targeting by Local Gradient Field of Interstitial Seeds Magnetized in an Ex Vivo Uniform Field

    NASA Astrophysics Data System (ADS)

    Li, Xiao-Qiang; Zheng, Lu; Wang, Xu-Fei

    2014-02-01

    The possibility of in vivo magnetic particle targeting by the locally induced gradient field of interstitial ferromagnetic implants, magnetized in an ex vivo uniform field, is evaluated by a modelling analysis. A simplified 3D model analogous to a torso size, with a continuous laminar flow through the volume with the typical velocity and viscosity values of in vivo blood flow and a ferromagnetic seed inserted in the volume center vertical to the flow, is used to evaluate the magnetic particle capturing efficiency by the seed, which is magnetized in a uniform field. The initial modelling results indicate that for 1-10 μm iron oxide particles transporting with a blood flow of 0.5-5 mm/s, the seeds of tungsten steel, magnet steel and cast cobalt all present an effective particle capturing efficiency, which shows a fast initial increase and a slow saturation with the increasing magnetic field, a quasilinear increase with the increasing particle size, and a nonlinear decrease with the increasing blood velocity.

  2. Local switching of two-dimensional superconductivity using the ferroelectric field effect

    NASA Astrophysics Data System (ADS)

    Takahashi, K. S.; Gabay, M.; Jaccard, D.; Shibuya, K.; Ohnishi, T.; Lippmaa, M.; Triscone, J.-M.

    2006-05-01

    Correlated oxides display a variety of extraordinary physical properties including high-temperature superconductivity and colossal magnetoresistance. In these materials, strong electronic correlations often lead to competing ground states that are sensitive to many parameters-in particular the doping level-so that complex phase diagrams are observed. A flexible way to explore the role of doping is to tune the electron or hole concentration with electric fields, as is done in standard semiconductor field effect transistors. Here we demonstrate a model oxide system based on high-quality heterostructures in which the ferroelectric field effect approach can be studied. We use a single-crystal film of the perovskite superconductor Nb-doped SrTiO3 as the superconducting channel and ferroelectric Pb(Zr,Ti)O3 as the gate oxide. Atomic force microscopy is used to locally reverse the ferroelectric polarization, thus inducing large resistivity and carrier modulations, resulting in a clear shift in the superconducting critical temperature. Field-induced switching from the normal state to the (zero resistance) superconducting state was achieved at a well-defined temperature. This unique system could lead to a field of research in which devices are realized by locally defining in the same material superconducting and normal regions with `perfect' interfaces, the interface being purely electronic. Using this approach, one could potentially design one-dimensional superconducting wires, superconducting rings and junctions, superconducting quantum interference devices (SQUIDs) or arrays of pinning centres.

  3. Local switching of two-dimensional superconductivity using the ferroelectric field effect.

    PubMed

    Takahashi, K S; Gabay, M; Jaccard, D; Shibuya, K; Ohnishi, T; Lippmaa, M; Triscone, J-M

    2006-05-11

    Correlated oxides display a variety of extraordinary physical properties including high-temperature superconductivity and colossal magnetoresistance. In these materials, strong electronic correlations often lead to competing ground states that are sensitive to many parameters--in particular the doping level--so that complex phase diagrams are observed. A flexible way to explore the role of doping is to tune the electron or hole concentration with electric fields, as is done in standard semiconductor field effect transistors. Here we demonstrate a model oxide system based on high-quality heterostructures in which the ferroelectric field effect approach can be studied. We use a single-crystal film of the perovskite superconductor Nb-doped SrTiO3 as the superconducting channel and ferroelectric Pb(Zr,Ti)O3 as the gate oxide. Atomic force microscopy is used to locally reverse the ferroelectric polarization, thus inducing large resistivity and carrier modulations, resulting in a clear shift in the superconducting critical temperature. Field-induced switching from the normal state to the (zero resistance) superconducting state was achieved at a well-defined temperature. This unique system could lead to a field of research in which devices are realized by locally defining in the same material superconducting and normal regions with 'perfect' interfaces, the interface being purely electronic. Using this approach, one could potentially design one-dimensional superconducting wires, superconducting rings and junctions, superconducting quantum interference devices (SQUIDs) or arrays of pinning centres.

  4. On the Lorentz local electric field in soft-matter systems.

    PubMed

    Tan, P; Tian, W J; Zhou, L W; Huang, J P

    2009-04-23

    In electric-field-responsive soft-matter systems, the suspended particles respond to the Lorentz local field (LLF), yielding abundant important phenomena. Even though the particles can easily rotate, the LLF was conventionally adopted as a quantity that is independent of rotations in the literature. In contrast, here we design an experiment to measure the LLF between two metallic spheres, one of which is rotating, and report a rotation-driven reduction. Excellent agreement between our experiment and theory reveals the role of the relaxation of dipole moments. Its relevance to biophysics, colloidal physics, and nonlinear physics is also discussed.

  5. A photonic-crystal optical antenna for extremely large local-field enhancement.

    PubMed

    Chang, Hyun-Joo; Kim, Se-Heon; Lee, Yong-Hee; Kartalov, Emil P; Scherer, Axel

    2010-11-08

    We propose a novel design of an all-dielectric optical antenna based on photonic-band-gap confinement. Specifically, we have engineered the photonic-crystal dipole mode to have broad spectral response (Q~70) and well-directed vertical-radiation by introducing a plane mirror below the cavity. Considerably large local electric-field intensity enhancement~4,500 is expected from the proposed design for a normally incident planewave. Furthermore, an analytic model developed based on coupled-mode theory predicts that the electric-field intensity enhancement can easily be over 100,000 by employing reasonably high-Q (~10,000) resonators.

  6. Graviton localization and Newton's law for brane models with a nonminimally coupled bulk scalar field

    SciTech Connect

    Farakos, K.; Koutsoumbas, G.; Pasipoularides, P.

    2007-09-15

    Brane world models with a nonminimally coupled bulk scalar field have been studied recently. In this paper we consider metric fluctuations around an arbitrary gravity-scalar background solution, and we show that the corresponding spectrum includes a localized zero mode which strongly depends on the profile of the background scalar field. For a special class of solutions, with a warp factor of the RS form, we solve the linearized Einstein equations, for a pointlike mass source on the brane, by using the brane bending formalism. We see that general relativity on the brane is recovered only if we impose restrictions on the parameter space of the models under consideration.

  7. Comparison of Quantum and Classical Local-field Effects on Two-Level Atoms in a Dielectric

    DTIC Science & Technology

    2010-12-24

    applies to nonlinear me- dia. Bloembergen [10] investigated nonlinear optics in the presence of a linear host medium and found that a local-field...dielectric enhancement factor of ℓ = n2 + 2 3 (2.3) accompanies each appearance of a macroscopic field in the nonlinear susceptibility. In our notation, ε...Bowden and Dowling [18] showed that the field that drives the atoms is the local field (2.1). With that substitution, one obtains the gen- eralized

  8. Localized ultrahigh frequency acoustic fields induced micro-vortices for submilliseconds microfluidic mixing

    NASA Astrophysics Data System (ADS)

    Cui, Weiwei; Zhang, Hao; Zhang, Hongxiang; Yang, Yang; He, Meihang; Qu, Hemi; Pang, Wei; Zhang, Daihua; Duan, Xuexin

    2016-12-01

    We present an acoustic microfluidic mixing approach via acousto-mechanically induced micro-vortices sustained by localized ultrahigh frequency (UHF) acoustic fields. A micro-fabricated solid-mounted thin-film piezoelectric resonator (SMR) with a frequency of 1.54 GHz has been integrated into microfluidic systems. Experimental and simulation results show that UHF-SMR triggers strong acoustic field gradients to produce efficient and highly localized acoustic streaming vortices, providing a powerful source for microfluidic mixing. Homogeneous mixing with 87% mixing efficiency at a Peclet number of 35520 within 1 ms has been achieved. The proposed strategy shows a great potential for microfluidic mixing and enhanced molecule transportation in minimized analytical systems.

  9. Single domain wall manipulation in curved nanowires using a mobile, local, circular field

    NASA Astrophysics Data System (ADS)

    Shortt, Madeline; Bickel, Jessica; Khan, Mina; Tuominen, Mark; Aidala, Katherine

    2014-03-01

    Ferromagnetic nanostructures present exciting physics with a range of potential applications in data storage devices, such as magnetoresistive random access memory (MRAM). These proposals require precise control and understanding of domain wall (DW) movement and interactions. We developed a technique that generates a local circular Oersted field at a precise location by applying current through the tip of the atomic force microscope (AFM). We previously used this technique to control DW motion in nanorings. We extend this method to control individual DW movement in curved nanowires by placing the tip near a 180 DW at the vertex of a curved wire and generating a local field. In this way, we can examine the motion of domain walls through regions with different curvature and the effects of pinning. This work was supported in part by NSF DMR-1207924 and the UMass Center for Hierarchical Manufacturing, NSF CMMI-1025020.

  10. Scaling of high-field transport and localized heating in graphene transistors.

    PubMed

    Bae, Myung-Ho; Islam, Sharnali; Dorgan, Vincent E; Pop, Eric

    2011-10-25

    We use infrared thermal imaging and electrothermal simulations to find that localized Joule heating in graphene field-effect transistors on SiO(2) is primarily governed by device electrostatics. Hot spots become more localized (i.e., sharper) as the underlying oxide thickness is reduced, such that the average and peak device temperatures scale differently, with significant long-term reliability implications. The average temperature is proportional to oxide thickness, but the peak temperature is minimized at an oxide thickness of ∼90 nm due to competing electrostatic and thermal effects. We also find that careful comparison of high-field transport models with thermal imaging can be used to shed light on velocity saturation effects. The results shed light on optimizing heat dissipation and reliability of graphene devices and interconnects.

  11. Squeezed bispectrum in the δ N formalism: local observer effect in field space

    NASA Astrophysics Data System (ADS)

    Tada, Yuichiro; Vennin, Vincent

    2017-02-01

    The prospects of future galaxy surveys for non-Gaussianity measurements call for the development of robust techniques for computing the bispectrum of primordial cosmological perturbations. In this paper, we propose a novel approach to the calculation of the squeezed bispectrum in multiple-field inflation. With use of the δ N formalism, our framework sheds new light on the recently pointed out difference between the squeezed bispectrum for global observers and that for local observers, while allowing one to calculate both. For local observers in particular, the squeezed bispectrum is found to vanish in single-field inflation. Furthermore, our framework allows one to go beyond the near-equilateral ("small hierarchy") limit, and to automatically include intrinsic non-Gaussianities that do not need to be calculated separately. The explicit computational programme of our method is given and illustrated with a few examples.

  12. Local Electric Field Effects on Rhodium-Porphyrin and NHC-Gold Catalysts

    DTIC Science & Technology

    2015-01-05

    AFRL-OSR-VA-TR-2015-0023 (NII) - Local Electric Field Effects on Rhodium-Porphyrin and NHC-Gold Catalysts MATTHEW KANAN LELAND STANFORD JUNIOR UNIV...Effects on Rhodium-Porphyrin and NHC-Gold Catalysts Principal Investigator: Matthew W. Kanan Project Publications: 1. “An Electric Field–Induced Change...design—i.e. controlling selectivity by changing the molecular structure of the reactants, catalysts or other reaction components. The overall goal of

  13. Localization and Classification of Paddy Field Pests using a Saliency Map and Deep Convolutional Neural Network

    NASA Astrophysics Data System (ADS)

    Liu, Ziyi; Gao, Junfeng; Yang, Guoguo; Zhang, Huan; He, Yong

    2016-02-01

    We present a pipeline for the visual localization and classification of agricultural pest insects by computing a saliency map and applying deep convolutional neural network (DCNN) learning. First, we used a global contrast region-based approach to compute a saliency map for localizing pest insect objects. Bounding squares containing targets were then extracted, resized to a fixed size, and used to construct a large standard database called Pest ID. This database was then utilized for self-learning of local image features which were, in turn, used for classification by DCNN. DCNN learning optimized the critical parameters, including size, number and convolutional stride of local receptive fields, dropout ratio and the final loss function. To demonstrate the practical utility of using DCNN, we explored different architectures by shrinking depth and width, and found effective sizes that can act as alternatives for practical applications. On the test set of paddy field images, our architectures achieved a mean Accuracy Precision (mAP) of 0.951, a significant improvement over previous methods.

  14. Quiet sun magnetic fields vs. polar faculae - local vs. global dynamo?

    NASA Astrophysics Data System (ADS)

    Okunev, O. V.; Domínguez Cerdeña, I.; Puschmann, K. G.; Kneer, F.; Sánchez Almeida, J.

    2005-04-01

    Quiet Sun magnetic fields in the internetwork are almost ubiquitous. Simultaneous observations in infra-red and visible lines and high spatial resolution (< 0.5'') data in visible lines show that their field strengths range from below few hundred Gauss to kilo-Gauss. Most of the flux is contained in small-scale, strong-field features located mainly in intergranular lanes. The average unsigned flux density exceeds 20 Gauss. The new detections are confirmed by recent quiet Sun observations in the G band. The generation of the strong fields in the internetwork, which may be due to a local dynamo, poses a challenging problem. - Polar faculae (PFe) are small-scale magnetic features at the polar caps of the Sun. They take part in the solar cycle and are thus likely to be rooted deeply in the solar interior. They are the result of the global dynamo at the solar poles. PFe also possess kilo-Gauss magnetic fields which have the same polarity as the global magnetic field. The rôle of quiet Sun magnetic field structures and of PFe for the dynamics of the corona and for the solar wind are addressed.

  15. Evidence of Toroidally Localized Turbulence with Applied 3D Fields in the DIII-D Tokamak.

    PubMed

    Wilcox, R S; Shafer, M W; Ferraro, N M; McKee, G R; Zeng, L; Rhodes, T L; Canik, J M; Paz-Soldan, C; Nazikian, R; Unterberg, E A

    2016-09-23

    New evidence indicates that there is significant 3D variation in density fluctuations near the boundary of weakly 3D tokamak plasmas when resonant magnetic perturbations are applied to suppress transient edge instabilities. The increase in fluctuations is concomitant with an increase in the measured density gradient, suggesting that this toroidally localized gradient increase could be a mechanism for turbulence destabilization in localized flux tubes. Two-fluid magnetohydrodynamic simulations find that, although changes to the magnetic field topology are small, there is a significant 3D variation of the density gradient within the flux surfaces that is extended along field lines. This modeling agrees qualitatively with the measurements. The observed gradient and fluctuation asymmetries are proposed as a mechanism by which global profile gradients in the pedestal could be relaxed due to a local change in the 3D equilibrium. These processes may play an important role in pedestal and scrape-off layer transport in ITER and other future tokamak devices with small applied 3D fields.

  16. Place field repetition and purely local remapping in a multicompartment environment.

    PubMed

    Spiers, Hugo J; Hayman, Robin M A; Jovalekic, Aleksandar; Marozzi, Elizabeth; Jeffery, Kathryn J

    2015-01-01

    Hippocampal place cells support spatial memory using sensory information from the environment and self-motion information to localize their firing fields. Currently, there is disagreement about whether CA1 place cells can use pure self-motion information to disambiguate different compartments in environments containing multiple visually identical compartments. Some studies report that place cells can disambiguate different compartments, while others report that they do not. Furthermore, while numerous studies have examined remapping, there has been little examination of remapping in different subregions of a single environment. Is remapping purely local or do place fields in neighboring, unaffected, regions detect the change? We recorded place cells as rats foraged across a 4-compartment environment and report 3 new findings. First, we find that, unlike studies in which rats foraged in 2 compartments, place fields showed a high degree of spatial repetition with a slight degree of rate-based discrimination. Second, this repetition does not diminish with extended experience. Third, remapping was found to be purely local for both geometric change and contextual change. Our results reveal the limited capacity of the path integrator to drive pattern separation in hippocampal representations, and suggest that doorways may play a privileged role in segmenting the neural representation of space.

  17. Finite-temperature electron correlations in the framework of a dynamic local-field correction

    SciTech Connect

    Schweng, H.K.; Boehm, H.M. )

    1993-07-15

    The quantum-mechanical version of the Singwi-Tosi-Land-Sjoelander (STLS) approximation is applied to finite temperatures. This approximation has two main advantages. First, it includes a dynamic local-field correction and second, it gives positive values for the pair-distribution function in the short-range region at zero temperature. This is even valid for rather low densities. After a description of the numerical difficulties arising with the use of a dynamic approximation, the results for the static-structure factor and the pair-distribution function are discussed thoroughly. Detailed work is performed on the static part of the local-field correction, with special emphasis put on the investigation of its structure. A peak is found at a wave vector [ital q][approx]2.8 (in units of the Fermi wave vector) for small temperatures, which tends towards higher values of [ital q] with increasing temperature. This peak causes an attractive particle-hole interaction in a certain [ital q] region and thus gives rise to the appearance of a charge-density wave. A parametric description is given for the static local-field correction in order to simplify further applications. Furthermore, the exchange-and-correlation free energy is considered. The results are compared with the STLS results and with the modified convolution approach.

  18. Evidence of toroidally localized turbulence with applied 3D fields in the DIII-D tokamak

    DOE PAGES

    Wilcox, R. S.; Shafer, M. W.; Ferraro, N. M.; ...

    2016-09-21

    New evidence indicates that there is significant 3D variation in density fluctuations near the boundary of weakly 3D tokamak plasmas when resonant magnetic perturbations are applied to suppress transient edge instabilities. The increase in fluctuations is concomitant with an increase in the measured density gradient, suggesting that this toroidally localized gradient increase could be a mechanism for turbulence destabilization in localized flux tubes. Two-fluid magnetohydrodynamic simulations find that, although changes to the magnetic field topology are small, there is a significant 3D variation of the density gradient within the flux surfaces that is extended along field lines. This modeling agreesmore » qualitatively with the measurements. The observed gradient and fluctuation asymmetries are proposed as a mechanism by which global profile gradients in the pedestal could be relaxed due to a local change in the 3D equilibrium. In conclusion, these processes may play an important role in pedestal and scrape-off layer transport in ITER and other future tokamak devices with small applied 3D fields.« less

  19. Local and nonlocal strain rate fields and vorticity alignment in turbulent flows.

    PubMed

    Hamlington, Peter E; Schumacher, Jörg; Dahm, Werner J A

    2008-02-01

    Local and nonlocal contributions to the total strain rate tensor S(ij) at any point x in a flow are formulated from an expansion of the vorticity field in a local spherical neighborhood of radius R centered on x. The resulting exact expression allows the nonlocal (background) strain rate tensor S(ij)(B)(x) to be obtained from S(ij)(x). In turbulent flows, where the vorticity naturally concentrates into relatively compact structures, this allows the local alignment of vorticity with the most extensional principal axis of the background strain rate tensor to be evaluated. In the vicinity of any vortical structure, the required radius R and corresponding order n to which the expansion must be carried are determined by the viscous length scale lambda(nu). We demonstrate the convergence to the background strain rate field with increasing R and n for an equilibrium Burgers vortex, and show that this resolves the anomalous alignment of vorticity with the intermediate eigenvector of the total strain rate tensor. We then evaluate the background strain field S(ij)(B)(x) in direct numerical simulations of homogeneous isotropic turbulence where, even for the limited R and n corresponding to the truncated series expansion, the results show an increase in the expected equilibrium alignment of vorticity with the most extensional principal axis of the background strain rate tensor.

  20. Evidence of toroidally localized turbulence with applied 3D fields in the DIII-D tokamak

    SciTech Connect

    Wilcox, R. S.; Shafer, M. W.; Ferraro, N. M.; McKee, G. R.; Zeng, L.; Rhodes, T. L.; Canik, J. M.; Paz-Soldan, C.; Nazikian, R.; Unterberg, E. A.

    2016-09-21

    New evidence indicates that there is significant 3D variation in density fluctuations near the boundary of weakly 3D tokamak plasmas when resonant magnetic perturbations are applied to suppress transient edge instabilities. The increase in fluctuations is concomitant with an increase in the measured density gradient, suggesting that this toroidally localized gradient increase could be a mechanism for turbulence destabilization in localized flux tubes. Two-fluid magnetohydrodynamic simulations find that, although changes to the magnetic field topology are small, there is a significant 3D variation of the density gradient within the flux surfaces that is extended along field lines. This modeling agrees qualitatively with the measurements. The observed gradient and fluctuation asymmetries are proposed as a mechanism by which global profile gradients in the pedestal could be relaxed due to a local change in the 3D equilibrium. In conclusion, these processes may play an important role in pedestal and scrape-off layer transport in ITER and other future tokamak devices with small applied 3D fields.

  1. Evolution of localized blobs of swirling or buoyant fluid with and without an ambient magnetic field

    NASA Astrophysics Data System (ADS)

    Davidson, P. A.; Sreenivasan, Binod; Aspden, A. J.

    2007-02-01

    We investigate the evolution of localized blobs of swirling or buoyant fluid in an infinite, inviscid, electrically conducting fluid. We consider the three cases of a strong imposed magnetic field, a weak imposed magnetic field, and no magnetic field. For a swirling blob in the absence of a magnetic field, we find, in line with others, that the blob bursts radially outward under the action of the centrifugal force, forming a thin annular vortex sheet. A simple model of this process predicts that the vortex sheet thins exponentially fast and that it moves radially outward with constant velocity. These predictions are verified by high-resolution numerical simulations. When an intense magnetic field is applied, this phenomenon is suppressed, with the energy and angular momentum of the blob now diffusing axially along the magnetic field lines, converting the blob into a columnar structure. For modest or weak magnetic fields, there are elements of both types of behavior, with the radial bursting dominating over axial diffusion for weak fields. However, even when the magnetic field is very weak, the flow structure is quite distinct to that of the nonmagnetic case. In particular, a small but finite magnetic field places a lower bound on the thickness of the annular vortex sheet and produces an annulus of counter-rotating fluid that surrounds the vortex core. The behavior of the buoyant blob is similar. In the absence of a magnetic field, it rapidly develops the mushroomlike shape of a thermal, with a thin vortex sheet at the top and sides of the mushroom. Again, a simple model of this process predicts that the vortex sheet at the top of the thermal thins exponentially fast and rises with constant velocity. These predictions are consistent with earlier numerical simulations. Curiously, however, it is shown that the net vertical momentum associated with the blob increases linearly in time, despite the fact that the vertical velocity at the front of the thermal is constant

  2. Evolution of localized blobs of swirling or buoyant fluid with and without an ambient magnetic field

    SciTech Connect

    Davidson, P. A.; Sreenivasan, Binod; Aspden, A. J.

    2007-02-15

    We investigate the evolution of localized blobs of swirling or buoyant fluid in an infinite, inviscid, electrically conducting fluid. We consider the three cases of a strong imposed magnetic field, a weak imposed magnetic field, and no magnetic field. For a swirling blob in the absence of a magnetic field, we find, in line with others, that the blob bursts radially outward under the action of the centrifugal force, forming a thin annular vortex sheet. A simple model of this process predicts that the vortex sheet thins exponentially fast and that it moves radially outward with constant velocity. These predictions are verified by high-resolution numerical simulations. When an intense magnetic field is applied, this phenomenon is suppressed, with the energy and angular momentum of the blob now diffusing axially along the magnetic field lines, converting the blob into a columnar structure. For modest or weak magnetic fields, there are elements of both types of behavior, with the radial bursting dominating over axial diffusion for weak fields. However, even when the magnetic field is very weak, the flow structure is quite distinct to that of the nonmagnetic case. In particular, a small but finite magnetic field places a lower bound on the thickness of the annular vortex sheet and produces an annulus of counter-rotating fluid that surrounds the vortex core. The behavior of the buoyant blob is similar. In the absence of a magnetic field, it rapidly develops the mushroomlike shape of a thermal, with a thin vortex sheet at the top and sides of the mushroom. Again, a simple model of this process predicts that the vortex sheet at the top of the thermal thins exponentially fast and rises with constant velocity. These predictions are consistent with earlier numerical simulations. Curiously, however, it is shown that the net vertical momentum associated with the blob increases linearly in time, despite the fact that the vertical velocity at the front of the thermal is constant

  3. Hidden local symmetry of Eu{sup 3+} in xenotime-like crystals revealed by high magnetic fields

    SciTech Connect

    Han, Yibo; Ma, Zongwei; Zhang, Junpei; Wang, Junfeng; Du, Guihuan; Xia, Zhengcai; Han, Junbo Li, Liang; Yu, Xuefeng

    2015-02-07

    The excellent optical properties of europium-doped crystals in visible and near infrared wavelength regions enable them to have broad applications in optoelectronics, laser crystals and sensing devices. The local site crystal fields can affect the intensities and peak positions of the photo-emission lines strongly, but they are usually difficult to be clarified due to magnetically degenerate 4f electronic levels coupling with the crystal fields. Here, we provide an effective way to explore the hidden local symmetry of the Eu{sup 3+} sites in different hosts by taking photoluminescence measurements under pulsed high magnetic fields up to 46 T. The zero-field photoluminescence peaks split further at high magnetic fields when the Zeeman splitting energy is comparable to or larger than that of the crystal field induced zero-field splitting. In particular, a magnetic field induced crossover of the local crystal fields has been observed in the GdVO{sub 4}:Eu{sup 3+} crystal, which resulted from the alignment of Gd{sup 3+} magnetic moment in high magnetic fields; and a hexagonally symmetric local crystal fields was observed in the YPO{sub 4} nanocrystals at the Eu{sup 3+} sites characterized by the special axial and rhombic crystal field terms. These distinct Zeeman splitting behaviors uncover the crystal fields-related local symmetry of luminescent Eu{sup 3+} centers in different hosts or magnetic environments, which are significant for their applications in optics and optoelectronics.

  4. Tailored Fano resonance and localized electromagnetic field enhancement in Ag gratings

    NASA Astrophysics Data System (ADS)

    Li, Zhaozhu; Klopf, J. Michael; Wang, Lei; Yang, Kaida; Lukaszew, Rosa A.

    2017-03-01

    Metallic gratings can support Fano resonances when illuminated with EM radiation, and their characteristic reflectivity versus incident angle lineshape can be greatly affected by the surrounding dielectric environment and the grating geometry. By using conformal oblique incidence thin film deposition onto an optical grating substrate, it is possible to increase the grating amplitude due to shadowing effects, thereby enabling tailoring of the damping processes and electromagnetic field couplings of the Fano resonances, hence optimizing the associated localized electric field intensity. To investigate these effects we compare the optical reflectivity under resonance excitation in samples prepared by oblique angle deposition (OAD) and under normal deposition (ND) onto the same patterned surfaces. We observe that by applying OAD method, the sample exhibits a deeper and narrower reflectivity dip at resonance than that obtained under ND. This can be explained in terms of a lower damping of Fano resonance on obliquely deposited sample and leads to a stronger localized electric field. This approach opens a fabrication path for applications where tailoring the electromagnetic field induced by Fano resonance can improve the figure of merit of specific device characteristics, e.g. quantum efficiency (QE) in grating-based metallic photocathodes.

  5. Tailored Fano resonance and localized electromagnetic field enhancement in Ag gratings

    PubMed Central

    Li, Zhaozhu; Klopf, J. Michael; Wang, Lei; Yang, Kaida; Lukaszew, Rosa A.

    2017-01-01

    Metallic gratings can support Fano resonances when illuminated with EM radiation, and their characteristic reflectivity versus incident angle lineshape can be greatly affected by the surrounding dielectric environment and the grating geometry. By using conformal oblique incidence thin film deposition onto an optical grating substrate, it is possible to increase the grating amplitude due to shadowing effects, thereby enabling tailoring of the damping processes and electromagnetic field couplings of the Fano resonances, hence optimizing the associated localized electric field intensity. To investigate these effects we compare the optical reflectivity under resonance excitation in samples prepared by oblique angle deposition (OAD) and under normal deposition (ND) onto the same patterned surfaces. We observe that by applying OAD method, the sample exhibits a deeper and narrower reflectivity dip at resonance than that obtained under ND. This can be explained in terms of a lower damping of Fano resonance on obliquely deposited sample and leads to a stronger localized electric field. This approach opens a fabrication path for applications where tailoring the electromagnetic field induced by Fano resonance can improve the figure of merit of specific device characteristics, e.g. quantum efficiency (QE) in grating-based metallic photocathodes. PMID:28290545

  6. Mesoscopic turbulence and local order in Janus particles self-propelling under an ac electric field

    NASA Astrophysics Data System (ADS)

    Nishiguchi, Daiki; Sano, Masaki

    2015-11-01

    To elucidate mechanisms of mesoscopic turbulence exhibited by active particles, we experimentally study turbulent states of nonliving self-propelled particles. We realize an experimental system with dense suspensions of asymmetrical colloidal particles (Janus particles) self-propelling on a two-dimensional surface under an ac electric field. Velocity fields of the Janus particles in the crowded situation can be regarded as a sort of turbulence because it contains many vortices and their velocities change abruptly. Correlation functions of their velocity field reveal the coexistence of polar alignment and antiparallel alignment interactions, which is considered to trigger mesoscopic turbulence. Probability distributions of local order parameters for polar and nematic orders indicate the formation of local clusters with particles moving in the same direction. A broad peak in the energy spectrum of the velocity field appears at the spatial scales where the polar alignment and the cluster formation are observed. Energy is injected at the particle scale and conserved quantities such as energy could be cascading toward the larger clusters.

  7. Nine years of multi-frequency monitoring of the blazar PKS 0048-097: spectral and temporal variability

    NASA Astrophysics Data System (ADS)

    Wierzcholska, Alicja

    2015-08-01

    Context. Blazars are highly variable, radio-loud active galactic nuclei with jets oriented at a small angle to the line of sight. The observed emission of these sources covers the whole electromagnetic spectrum from radio frequencies up to the high or even very high energy gamma-ray range. To understand the complex physics of these objects, multi-wavelength observations and studies on the variability and correlations between different wavelengths are therefore essential. Aims: The long-term multi-frequency observations of PKS 0048-097 are analysed here to investigate its spectral and temporal features. The studies includes nine years of observations of the blazar, which is well studied in the optical and radio domain, but not in the other frequencies. Methods: Multi-wavelength data collected with OVRO, KAIT, Catalina, Swift/UVOT, Swift/XRT, and Fermi/LAT were studied. Results: The performed analysis revealed strong variability in all wavelengths that is most clearly manifested in the X-ray range. The correlation studies do not exhibit any relation between different wavelengths, except for the very strong positive correlation between the optical emission in V and R bands.

  8. Continuous-scanning laser Doppler vibrometry: Extensions to arbitrary areas, multi-frequency and 3D capture

    SciTech Connect

    Weekes, B.; Ewins, D.; Acciavatti, F.

    2014-05-27

    To date, differing implementations of continuous scan laser Doppler vibrometry have been demonstrated by various academic institutions, but since the scan paths were defined using step or sine functions from function generators, the paths were typically limited to 1D line scans or 2D areas such as raster paths or Lissajous trajectories. The excitation was previously often limited to a single frequency due to the specific signal processing performed to convert the scan data into an ODS. In this paper, a configuration of continuous-scan laser Doppler vibrometry is demonstrated which permits scanning of arbitrary areas, with the benefit of allowing multi-frequency/broadband excitation. Various means of generating scan paths to inspect arbitrary areas are discussed and demonstrated. Further, full 3D vibration capture is demonstrated by the addition of a range-finding facility to the described configuration, and iteratively relocating a single scanning laser head. Here, the range-finding facility was provided by a Microsoft Kinect, an inexpensive piece of consumer electronics.

  9. MULTI-FREQUENCY STUDIES OF RADIO RELICS IN THE GALAXY CLUSTERS A4038, A1664, AND A786

    SciTech Connect

    Kale, Ruta; Dwarakanath, K. S.

    2012-01-01

    We present a multi-frequency study of radio relics associated with the galaxy clusters A4038, A1664, and A786. Radio images, integrated spectra, spectral index maps, and fits to the integrated spectra in the framework of the adiabatic compression model are presented. Images of the relic in A4038 at 150, 240, and 606 MHz with the Giant Meterwave Radio Telescope have revealed extended ultra-steep spectrum ({alpha} {approx} -1.8 to -2.7) emission of extent 210 Multiplication-Sign 80 kpc{sup 2}. The model of passively evolving radio lobes compressed by a shock fits the integrated spectrum best. The relic with a circular morphology at the outskirts of the cluster A1664 has an integrated spectral index of {approx} - 1.10 {+-} 0.06 and is best fit by the model of radio lobes lurking for {approx}4 Multiplication-Sign 10{sup 7} yr. The relic near A786 has a curved spectrum and is best fit by a model of radio lobes lurking for {approx}3 Multiplication-Sign 10{sup 7} yr. At 4.7 GHz, a compact radio source, possibly the progenitor of the A786 relic, is detected near the center of the radio relic. The A786 radio relic is thus likely a lurking radio galaxy rather than a site of cosmological shock as has been considered in earlier studies.

  10. On the self-excitation mechanisms of plasma series resonance oscillations in single- and multi-frequency capacitive discharges

    SciTech Connect

    Schüngel, Edmund; Brandt, Steven; Schulze, Julian; Korolov, Ihor; Derzsi, Aranka; Donkó, Zoltán

    2015-04-15

    The self-excitation of plasma series resonance (PSR) oscillations is a prominent feature in the current of low pressure capacitive radio frequency discharges. This resonance leads to high frequency oscillations of the charge in the sheaths and enhances electron heating. Up to now, the phenomenon has only been observed in asymmetric discharges. There, the nonlinearity in the voltage balance, which is necessary for the self-excitation of resonance oscillations with frequencies above the applied frequencies, is caused predominantly by the quadratic contribution to the charge-voltage relation of the plasma sheaths. Using Particle In Cell/Monte Carlo collision simulations of single- and multi-frequency capacitive discharges and an equivalent circuit model, we demonstrate that other mechanisms, such as a cubic contribution to the charge-voltage relation of the plasma sheaths and the time dependent bulk electron plasma frequency, can cause the self-excitation of PSR oscillations, as well. These mechanisms have been neglected in previous models, but are important for the theoretical description of the current in symmetric or weakly asymmetric discharges.

  11. Development of a multi-frequency diffuse photon density wave device for the characterization of tissue damage at multiple depths

    NASA Astrophysics Data System (ADS)

    Diaz, David; Weingarten, Michael S.; Neidrauer, Michael T.; Samuels, Joshua A.; Huneke, Richard B.; Kuzmin, Vladimir L.; Lewin, Peter A.; Zubkov, Leonid A.

    2014-02-01

    The ability to determine the depth and degree of cutaneous and subcutaneous tissue damage is critical for medical applications such as burns and pressure ulcers. The Diffuse Photon Density Wave (DPDW) methodology at near infrared wavelengths can be used to non-invasively measure the optical absorption and reduced scattering coefficients of tissue at depths of several millimeters. A multi-frequency DPDW system with one light source and one detector was constructed so that light is focused onto the tissue surface using an optical fiber and lens mounted to a digitally-controlled actuator which changes the distance between light source and detector. A variable RF generator enables the modulation frequency to be selected between 50 to 400MHz. The ability to digitally control both source-detector separation distance and modulation frequency allows for virtually unlimited number of data points, enabling precise selection of the volume and depth of tissue that will be characterized. Suspensions of Intralipid and india ink with known absorption and reduced scattering coefficients were used as optical phantoms to assess device accuracy. Solid silicon phantoms were formulated for stability testing. Standard deviations for amplitude and phase shift readings were found to be 0.9% and 0.2 degrees respectively, over a one hour period. The ability of the system to quantify tissue damage in vivo at multiple depths was tested in a porcine burn model.

  12. The Multi-Frequency Correlation Between Eua and sCER Futures Prices: Evidence from the Emd Approach

    NASA Astrophysics Data System (ADS)

    Zhang, Yue-Jun; Huang, Yi-Song

    2015-05-01

    Currently European Union Allowances (EUA) and secondary Certified Emission Reduction (sCER) have become two dominant carbon trading assets for investors and their linkage attracts much attention from academia and practitioners in recent years. Under this circumstance, we use the empirical mode decomposition (EMD) approach to decompose the two carbon futures contract prices and discuss their correlation from the multi-frequency perspective. The empirical results indicate that, first, the EUA and sCER futures price movements can be divided into those triggered by the long-term, medium-term and short-term market impacts. Second, the price movements in the EUA and sCER futures markets are primarily caused by the long-term impact, while the short-term impact can only explain a small fraction. Finally, the long-term (short-term) effect on EUA prices is statistically uncorrelated with the short-term (long-term) effect of sCER prices, and there is a medium or strong lead-and-lag correlation between the EUA and sCER price components with the same time scales. These results may provide some important insights of price forecast and arbitraging activities for carbon futures market investors, analysts and regulators.

  13. Effects of multi-frequency power ultrasound on the enzymolysis of corn gluten meal: Kinetics and thermodynamics study.

    PubMed

    Jin, Jian; Ma, Haile; Qu, Wenjuan; Wang, Kai; Zhou, Cunshan; He, Ronghai; Luo, Lin; Owusu, John

    2015-11-01

    The effects of multi-frequency power ultrasound (MPU) pretreatment on the kinetics and thermodynamics of corn gluten meal (CGM) were investigated in this research. The apparent constant (KM), apparent break-down rate constant (kA), reaction rate constants (k), energy of activation (Ea), enthalpy of activation (ΔH), entropy of activation (ΔS) and Gibbs free energy of activation (ΔG) were determined by means of the Michaelis-Menten equation, first-order kinetics model, Arrhenius equation and transition state theory, respectively. The results showed that MPU pretreatment can accelerate the enzymolysis of CGM under different enzymolysis conditions, viz. substrate concentration, enzyme concentration, pH, and temperature. Kinetics analysis revealed that MPU pretreatment decreased the KM value by 26.1% and increased the kA value by 7.3%, indicating ultrasound pretreatment increased the affinity between enzyme and substrate. In addition, the values of k for ultrasound pretreatment were increased by 84.8%, 41.9%, 28.9%, and 18.8% at the temperature of 293, 303, 313 and 323 K, respectively. For the thermodynamic parameters, ultrasound decreased Ea, ΔH and ΔS by 23.0%, 24.3% and 25.3%, respectively, but ultrasound had little change in ΔG value in the temperature range of 293-323 K. In conclusion, MPU pretreatment could remarkably enhance the enzymolysis of CGM, and this method can be applied to protein proteolysis industry to produce peptides.

  14. Continuous-scanning laser Doppler vibrometry: Extensions to arbitrary areas, multi-frequency and 3D capture

    NASA Astrophysics Data System (ADS)

    Weekes, B.; Ewins, D.; Acciavatti, F.

    2014-05-01

    To date, differing implementations of continuous scan laser Doppler vibrometry have been demonstrated by various academic institutions, but since the scan paths were defined using step or sine functions from function generators, the paths were typically limited to 1D line scans or 2D areas such as raster paths or Lissajous trajectories. The excitation was previously often limited to a single frequency due to the specific signal processing performed to convert the scan data into an ODS. In this paper, a configuration of continuous-scan laser Doppler vibrometry is demonstrated which permits scanning of arbitrary areas, with the benefit of allowing multi-frequency/broadband excitation. Various means of generating scan paths to inspect arbitrary areas are discussed and demonstrated. Further, full 3D vibration capture is demonstrated by the addition of a range-finding facility to the described configuration, and iteratively relocating a single scanning laser head. Here, the range-finding facility was provided by a Microsoft Kinect, an inexpensive piece of consumer electronics.

  15. Fractionated Wide-Field Radiation Therapy Followed by Fractionated Local-Field Irradiation for Treating Widespread Painful Bone Metastasis

    SciTech Connect

    Ki, Yongkan; Kim, Wontaek; Nam, Jiho; Kim, Donghyun; Jeon, Hosang; Park, Dahl; Kim, Dongwon

    2011-01-01

    Purpose: Wide-field radiation therapy (WFRT) is an effective treatment for widespread bone metastasis. We evaluated local-field irradiation (LFI) after fractionated WFRT (f-WFRT) for treating the patients with multiple painful bone lesions. Methods and Materials: From 1998 to 2007, 32 patients with multiple bone metastases were treated with fractionated LFI (f-LFI) after f-WFRT. All patients initially received 15 Gy in 5 fractions to a wide field, followed by LFI (9-15 Gy in 3 Gy fractions). Response was assessed by evaluating the degree of pain relief using a visual analog scale before radiotherapy, after f-WFRT, and after f-LFI. Results: Fractionated LFI following f-WFRT yielded an overall relief rate of 93.8% and a complete relief rate of 43.8%. The rate of the appearance of new disease was 6.3% for the patients with complete relief, 20.5% for the patients with a partial relief, and 50% for the patients with no relief. Conclusion: Fractionated LFI after f-WFRT is a well-tolerated and effective treatment for multiple metastatic bone disease.

  16. Local and Global Bifurcations of Flow Fields During Physical Vapor Transport: Application to a Microgravity Experiment

    NASA Technical Reports Server (NTRS)

    Duval, W. M. B.; Singh, N. B.; Glicksman, M. E.

    1996-01-01

    The local bifurcation of the flow field, during physical vapor transport for a parametric range of experimental interest, shows that its dynamical state ranges from steady to aperiodic. Comparison of computationally predicted velocity profiles with laser doppler velocimetry measurements shows reasonable agreement in both magnitude and planform. Correlation of experimentally measured crystal quality with the predicted dynamical state of the flow field shows a degradation of quality with an increase in Rayleigh number. The global bifurcation of the flow field corresponding to low crystal quality indicates the presence of a traveling wave for Ra = 1.09 x 10(exp 5). For this Rayleigh number threshold a chaotic transport state occurs. However, a microgravity environment for this case effectively stabilizes the flow to diffusive-advective and provides the setting to grow crystals with optimal quality.

  17. Image dipoles approach to the local field enhancement in nanostructured Ag-Au hybrid devices.

    PubMed

    David, Christin; Richter, Marten; Knorr, Andreas; Weidinger, Inez M; Hildebrandt, Peter

    2010-01-14

    We have investigated the plasmonic enhancement in the radiation field at various nanostructured multilayer devices that may be applied in surface enhanced Raman spectroscopy. We apply an image dipole method to describe the effect of surface morphology on the field enhancement in a quasistatic limit. In particular, we compare the performance of a nanostructured silver surface and a layered silver-gold hybrid device. It is found that localized surface plasmon states provide a high field enhancement in silver-gold hybrid devices, where symmetry breaking due to surface defects is a supporting factor. These results are compared to those obtained for multishell nanoparticles of spherical symmetry. Calculated enhancement factors are discussed on the background of recent experimental data.

  18. Local equilibria and state transfer of charged classical particles on a helix in an electric field

    NASA Astrophysics Data System (ADS)

    Plettenberg, J.; Stockhofe, J.; Zampetaki, A. V.; Schmelcher, P.

    2017-01-01

    We explore the effects of a homogeneous external electric field on the static properties and dynamical behavior of two charged particles confined to a helix. In contrast to the field-free setup which provides a separation of the center-of-mass and relative motion, the existence of an external force perpendicular to the helix axis couples the center-of-mass to the relative degree of freedom leading to equilibria with a localized center of mass. By tuning the external field various fixed points are created and/or annihilated through different bifurcation scenarios. We provide a detailed analysis of these bifurcations based on which we demonstrate a robust state transfer between essentially arbitrary equilibrium configurations of the two charges that can be induced by making the external force time dependent.

  19. Narrow band perfect absorber for maximum localized magnetic and electric field enhancement and sensing applications

    NASA Astrophysics Data System (ADS)

    Yong, Zhengdong; Zhang, Senlin; Gong, Chensheng; He, Sailing

    2016-04-01

    Plasmonics offer an exciting way to mediate the interaction between light and matter, allowing strong field enhancement and confinement, large absorption and scattering at resonance. However, simultaneous realization of ultra-narrow band perfect absorption and electromagnetic field enhancement is challenging due to the intrinsic high optical losses and radiative damping in metals. Here, we propose an all-metal plasmonic absorber with an absorption bandwidth less than 8 nm and polarization insensitive absorptivity exceeding 99%. Unlike traditional Metal-Dielectric-Metal configurations, we demonstrate that the narrowband perfect absorption and field enhancement are ascribed to the vertical gap plasmonic mode in the deep subwavelength scale, which has a high quality factor of 120 and mode volume of about 10-4 × (λres/n)3. Based on the coupled mode theory, we verify that the diluted field enhancement is proportional to the absorption, and thus perfect absorption is critical to maximum field enhancement. In addition, the proposed perfect absorber can be operated as a refractive index sensor with a sensitivity of 885 nm/RIU and figure of merit as high as 110. It provides a new design strategy for narrow band perfect absorption and local field enhancement, and has potential applications in biosensors, filters and nonlinear optics.

  20. Narrow band perfect absorber for maximum localized magnetic and electric field enhancement and sensing applications

    PubMed Central

    Yong, Zhengdong; Zhang, Senlin; Gong, Chensheng; He, Sailing

    2016-01-01

    Plasmonics offer an exciting way to mediate the interaction between light and matter, allowing strong field enhancement and confinement, large absorption and scattering at resonance. However, simultaneous realization of ultra-narrow band perfect absorption and electromagnetic field enhancement is challenging due to the intrinsic high optical losses and radiative damping in metals. Here, we propose an all-metal plasmonic absorber with an absorption bandwidth less than 8 nm and polarization insensitive absorptivity exceeding 99%. Unlike traditional Metal-Dielectric-Metal configurations, we demonstrate that the narrowband perfect absorption and field enhancement are ascribed to the vertical gap plasmonic mode in the deep subwavelength scale, which has a high quality factor of 120 and mode volume of about 10−4 × (λres/n)3. Based on the coupled mode theory, we verify that the diluted field enhancement is proportional to the absorption, and thus perfect absorption is critical to maximum field enhancement. In addition, the proposed perfect absorber can be operated as a refractive index sensor with a sensitivity of 885 nm/RIU and figure of merit as high as 110. It provides a new design strategy for narrow band perfect absorption and local field enhancement, and has potential applications in biosensors, filters and nonlinear optics. PMID:27046540

  1. Are the Faraday Rotating Magnetic Fields Local to Intracluster Radio Galaxies?

    NASA Astrophysics Data System (ADS)

    Ensslin, Torsten A.; Vogt, Corina; Clarke, T. E.; Taylor, Greg B.

    2003-11-01

    We investigate the origin of the high Faraday rotation measures (RMs) found for polarized radio galaxies in clusters. The two most likely origins are magnetic fields local to the source or magnetic fields located in the foreground intracluster medium. The latter is identified as the null hypothesis. Rudnick & Blundell have recently suggested that the presence of magnetic fields local to the source may be revealed in correlations of the position angles (PAs) of the source-intrinsic linear polarization and the RMs. We investigate the claim of Rudnick & Blundell that they have found a relationship between the intrinsic PA0 of the radio source PKS 1246-410 and its RM by testing the clustering strength of the PA0-RM scatter plot. We show that the claimed relationship is an artifact of an improperly performed null experiment. We describe a gradient alignment statistic aimed at finding correlations between PA0 and RM maps. This statistic does not require any null experiment since it gives a unique (zero) result in the case of uncorrelated maps. We apply it to a number of extended radio sources in galaxy clusters (PKS 1246-410, Cygnus A, Hydra A, and 3C 465). In no case is a significant large-scale alignment of PA0 and RM maps detected. We find significant small-scale co-alignment in all cases, but we are able to fully identify this with map-making artifacts through a suitable statistical test. We conclude that there is presently no existing evidence for Faraday rotation local to radio lobes. Given the existing independent pieces of evidence, we favor the null hypothesis that the observed Faraday screens are produced by intracluster magnetic fields.

  2. Tip-enhanced Raman nanographs: mapping topography and local electric fields.

    PubMed

    El-Khoury, Patrick Z; Gong, Yu; Abellan, Patricia; Arey, Bruce W; Joly, Alan G; Hu, Dehong; Evans, James E; Browning, Nigel D; Hess, Wayne P

    2015-04-08

    We report tip-enhanced Raman imaging experiments in which information on sample topography and local electric fields is simultaneously obtained using an all-optical detection scheme. We demonstrate how a Raman-active 4,4'-dimercaptostilbene (DMS)-coated gold tip of an atomic force microscope can be used to simultaneously map the topography and image the electric fields localized at nanometric (20 and 5 nm wide) slits lithographically etched in silver, all using optical signals. Bimodal imaging is feasible by virtue of the frequency-resolved optical response of the functionalized metal probe. Namely, the probe position-dependent signals can be subdivided into two components. The first is a 500-2250 cm(-1) Raman-shifted signal, characteristic of the tip-bound DMS molecules. The molecules report on topography through the intensity contrast observed as the tip scans across the nanoscale features. The variation in molecular Raman activity arises from the absence/formation of a plasmonic junction between the scanning probe and patterned silver surface, which translates into dimmed/enhanced Raman signatures of DMS. Using these molecular signals, we demonstrate that sub-15 nm spatial resolution is attainable using a 30 nm DMS-coated gold tip. The second response consists of two correlated sub-500 cm(-1) signals arising from mirror-like reflections of (i) the incident laser field and (ii) the Raman scattered response of an underlying glass support (at 100-500 cm(-1)) off the gold tip. We show that both the reflected low-wavenumber signals trace the local electric fields in the vicinity of the nanometric slits.

  3. Nonlinear effects of locally heterogeneous hydraulic conductivity fields on regional stream-aquifer exchanges

    NASA Astrophysics Data System (ADS)

    Zhu, J.; Winter, C. L.; Wang, Z.

    2015-11-01

    Computational experiments are performed to evaluate the effects of locally heterogeneous conductivity fields on regional exchanges of water between stream and aquifer systems in the Middle Heihe River basin (MHRB) of northwestern China. The effects are found to be nonlinear in the sense that simulated discharges from aquifers to streams are systematically lower than discharges produced by a base model parameterized with relatively coarse effective conductivity. A similar, but weaker, effect is observed for stream leakage. The study is organized around three hypotheses: (H1) small-scale spatial variations of conductivity significantly affect regional exchanges of water between streams and aquifers in river basins, (H2) aggregating small-scale heterogeneities into regional effective parameters systematically biases estimates of stream-aquifer exchanges, and (H3) the biases result from slow paths in groundwater flow that emerge due to small-scale heterogeneities. The hypotheses are evaluated by comparing stream-aquifer fluxes produced by the base model to fluxes simulated using realizations of the MHRB characterized by local (grid-scale) heterogeneity. Levels of local heterogeneity are manipulated as control variables by adjusting coefficients of variation. All models are implemented using the MODFLOW (Modular Three-dimensional Finite-difference Groundwater Flow Model) simulation environment, and the PEST (parameter estimation) tool is used to calibrate effective conductivities defined over 16 zones within the MHRB. The effective parameters are also used as expected values to develop lognormally distributed conductivity (K) fields on local grid scales. Stream-aquifer exchanges are simulated with K fields at both scales and then compared. Results show that the effects of small-scale heterogeneities significantly influence exchanges with simulations based on local-scale heterogeneities always producing discharges that are less than those produced by the base model

  4. Field-Scale Modeling of Local Capillary Trapping During CO2 Injection into a Saline Aquifer

    NASA Astrophysics Data System (ADS)

    Ren, B.; Lake, L. W.; Bryant, S. L.

    2015-12-01

    Local capillary trapping is the small-scale (10-2 to 10+1 m) CO2 trapping that is caused by the capillary pressure heterogeneity. The benefit of LCT, applied specially to CO2 sequestration, is that saturation of stored CO2 is larger than the residual gas, yet these CO2 are not susceptible to leakage through failed seals. Thus quantifying the extent of local capillary trapping is valuable in design and risk assessment of geologic storage projects. Modeling local capillary trapping is computationally expensive and may even be intractable using a conventional reservoir simulator. In this paper, we propose a novel method to model local capillary trapping by combining geologic criteria and connectivity analysis. The connectivity analysis originally developed for characterizing well-to-reservoir connectivity is adapted to this problem by means of a newly defined edge weight property between neighboring grid blocks, which accounts for the multiphase flow properties, injection rate, and gravity effect. Then the connectivity is estimated from shortest path algorithm to predict the CO2 migration behavior and plume shape during injection. A geologic criteria algorithm is developed to estimate the potential local capillary traps based only on the entry capillary pressure field. The latter is correlated to a geostatistical realization of permeability field. The extended connectivity analysis shows a good match of CO2 plume computed by the full-physics simulation. We then incorporate it into the geologic algorithm to quantify the amount of LCT structures identified within the entry capillary pressure field that can be filled during CO2 injection. Several simulations are conducted in the reservoirs with different level of heterogeneity (measured by the Dykstra-Parsons coefficient) under various injection scenarios. We find that there exists a threshold Dykstra-Parsons coefficient, below which low injection rate gives rise to more LCT; whereas higher injection rate increases LCT

  5. Localized field-aligned currents in the polar cap associated with airglow patches

    NASA Astrophysics Data System (ADS)

    Zou, Ying; Nishimura, Yukitoshi; Burchill, Johnathan K.; Knudsen, David J.; Lyons, Larry R.; Shiokawa, Kazuo; Buchert, Stephan; Chen, Steve; Nicolls, Michael J.; Ruohoniemi, J. Michael; McWilliams, Kathryn A.; Nishitani, Nozomu

    2016-10-01

    Airglow patches have been recently associated with channels of enhanced antisunward ionospheric flows propagating across the polar cap from the dayside to nightside auroral ovals. However, how these flows maintain their localized nature without diffusing away remains unsolved. We examine whether patches and collocated flows are associated with localized field-aligned currents (FACs) in the polar cap by using coordinated observations of the Swarm spacecraft, a polar cap all-sky imager, and Super Dual Auroral Radar Network (SuperDARN) radars. We commonly (66% of cases) identify substantial FAC enhancements around patches, particularly near the patches' leading edge and center, in contrast to what is seen in the otherwise quiet polar cap. These FACs have densities of 0.1-0.2 μA/m-2 and have a distribution of width peaking at 75 km. They can be approximated as infinite current sheets that are orientated roughly parallel to patches. They usually exhibit a Region 1 sense, i.e., a downward FAC lying eastward of an upward FAC. With the addition of Resolute Bay Incoherent Scatter radar data, we find that the FACs can close through Pedersen currents in the ionosphere, consistent with the locally enhanced dawn-dusk electric field across the patch. Our results suggest that ionospheric polar cap flow channels are imposed by structures in the magnetospheric lobe via FACs, and thus manifest mesoscale magnetosphere-ionosphere coupling embedded in large-scale convection.

  6. Nanoscale Imaging of Local Few-Femtosecond Near-Field Dynamics within a Single Plasmonic Nanoantenna

    PubMed Central

    2015-01-01

    The local enhancement of few-cycle laser pulses by plasmonic nanostructures opens up for spatiotemporal control of optical interactions on a nanometer and few-femtosecond scale. However, spatially resolved characterization of few-cycle plasmon dynamics poses a major challenge due to the extreme length and time scales involved. In this Letter, we experimentally demonstrate local variations in the dynamics during the few strongest cycles of plasmon-enhanced fields within individual rice-shaped silver nanoparticles. This was done using 5.5 fs laser pulses in an interferometric time-resolved photoemission electron microscopy setup. The experiments are supported by finite-difference time-domain simulations of similar silver structures. The observed differences in the field dynamics across a single particle do not reflect differences in plasmon resonance frequency or dephasing time. They instead arise from a combination of retardation effects and the coherent superposition between multiple plasmon modes of the particle, inherent to a few-cycle pulse excitation. The ability to detect and predict local variations in the few-femtosecond time evolution of multimode coherent plasmon excitations in rationally synthesized nanoparticles can be used in the tailoring of nanostructures for ultrafast and nonlinear plasmonics. PMID:26375959

  7. The gravity of dark vortices: effective field theory for branes and strings carrying localized flux

    NASA Astrophysics Data System (ADS)

    Burgess, C. P.; Diener, R.; Williams, M.

    2015-11-01

    A Nielsen-Olesen vortex usually sits in an environment that expels the flux that is confined to the vortex, so flux is not present both inside and outside. We construct vortices for which this is not true, where the flux carried by the vortex also permeates the `bulk' far from the vortex. The idea is to mix the vortex's internal gauge flux with an external flux using off-diagonal kinetic mixing. Such `dark' vortices could play a phenomenological role in models with both cosmic strings and a dark gauge sector. When coupled to gravity they also provide explicit ultra-violet completions for codimension-two brane-localized flux, which arises in extra-dimensional models when the same flux that stabilizes extra-dimensional size is also localized on space-filling branes situated around the extra dimensions. We derive simple formulae for observables such as defect angle, tension, localized flux and on-vortex curvature when coupled to gravity, and show how all of these are insensitive to much of the microscopic details of the solutions, and are instead largely dictated by low-energy quantities. We derive the required effective description in terms of a world-sheet brane action, and derive the matching conditions for its couplings. We consider the case where the dimensions transverse to the bulk compactify, and determine how the on- and off-vortex curvatures and other bulk features depend on the vortex properties. We find that the brane-localized flux does not gravitate, but just renormalizes the tension in a magnetic-field independent way. The existence of an explicit UV completion puts the effective description of these models on a more precise footing, verifying that brane-localized flux can be consistent with sensible UV physics and resolving some apparent paradoxes that can arise with a naive (but commonly used) delta-function treatment of the brane's localization within the bulk.

  8. The Contribution of Local Stresses in the Western Europe Stress Field

    NASA Astrophysics Data System (ADS)

    Kusters, D.; Camelbeeck, T.; de Viron, O.; Van Camp, M. J.

    2013-12-01

    The analysis of the World Stress Map (WSM) has evidenced first and second stress patterns (Heidbach et al. 2013) in Western Europe. The long wavelength pattern is controlled by plate boundary forces and transmitted into the plate interior. The second order is due to local topography, density and strength contrasts and can modify significantly the long wavelength component of the stress field. We propose to use the second spatial derivatives of a geoid height grid to evaluate the stress generated at the local scale by the spatial variations of the Gravitational Potential Energy (GPE), which is related to inhomogeneous topography and mass distribution in the lithosphere (Camelbeeck et al., 2013). This allows estimating whether this local component could be dominant in the tectonic stress, mainly by comparing our results with the WSM dataset and earthquake fault-plane solutions. For the northern Alps, we obtain results similar to the ones obtained for the Pyrenees by Camelbeeck et al. (Lithosphere, 2013), i.e. 70% of focal mechanisms are in agreement with the local stresses inferred from the geoid. This agrees with Heidbach et al. (2007), who showed that the short wavelength stress pattern is predominant in the Alps In Great Britain, the first order pattern is expected to be the main factor in the global stress field such that in principle, our method may not be appropriate. However, our tectonic style predicted from the geoid agrees with most of the earthquake focal mechanisms, of which 70% correspond to our main horizontal stress direction (σH). Hence, the local stresses should not be neglected when assessing the overall stress state in the UK. On the South Norway shelf, Pascal and Cloetingh (2009) computed the gravitational potential stresses (GPSt). This model generally reflects the WSM and has an intermediate wavelength pattern. However, it does not allow estimating the local stresses due to small geological structures. At such short wavelength, our method

  9. Local signals from beyond the receptive fields of striate cortical neurons.

    PubMed

    Müller, James R; Metha, Andrew B; Krauskopf, John; Lennie, Peter

    2003-08-01

    We examined in anesthetized macaque how the responses of a striate cortical neuron to patterns inside the receptive field were altered by surrounding patterns outside it. The changes in a neuron's response brought about by a surround are immediate and transient: they arise with the same latency as the response to a stimulus within the receptive field (this argues for a source locally in striate cortex) and become less effective as soon as 27 ms later. Surround signals appeared to exert their influence through divisive interaction (normalization) with those arising in the receptive field. Surrounding patterns presented at orientations slightly oblique to the preferred orientation consistently deformed orientation tuning curves of complex (but not simple) cells, repelling the preferred orientation but without decreasing the discriminability of the preferred grating and ones at slightly oblique orientations. By reducing responsivity and changing the tuning of complex cells locally in stimulus space, surrounding patterns reduce the correlations among responses of neurons to a particular stimulus, thus reducing the redundancy of image representation.

  10. Generalized local-frame-transformation theory for excited species in external fields

    NASA Astrophysics Data System (ADS)

    Giannakeas, P.; Greene, Chris H.; Robicheaux, F.

    2016-07-01

    A rigorous theoretical framework is developed for a generalized local-frame-transformation theory (GLFT). The GLFT is applicable to the following systems: Rydberg atoms or molecules in an electric field and negative ions in any combination of electric and/or magnetic fields. A first test application to the photoionization spectra of Rydberg atoms in an external electric field demonstrates dramatic improvement over the first version of the local-frame-transformation theory developed initially by U. Fano [Phys. Rev. A 24, 619 (1981), 10.1103/PhysRevA.24.619] and D. A. Harmin [Phys. Rev. A 26, 2656 (1982), 10.1103/PhysRevA.26.2656]. This revised GLFT theory yields nontrivial corrections because it now includes the full on-shell Hilbert space without adopting the truncations in the original theory. Comparisons of the semianalytical GLFT Stark spectra with ab initio numerical simulations yield errors in the range of a few tens of MHz, an improvement over the original Fano-Harmin theory, whose errors are 10-100 times larger. Our analysis provides a systematic pathway to precisely describe the corresponding photoabsorption spectra that should be accurate enough to meet most modern experimental standards.

  11. Scalar field localization on 3-branes placed at a warped resolved conifold

    SciTech Connect

    Silva, J. E. G.; Almeida, C. A. S.

    2011-10-15

    We have studied the localization of a scalar field on a 3-brane embedded in a six-dimensional warped bulk of the form M{sub 4}xC{sub 2}, where M{sub 4} is a 3-brane and C{sub 2} is a 2-cycle of a six-dimensional resolved conifold C{sub 6} over a T{sup 1,1} space. Since the resolved conifold is singularity-free in r=0 depending on a resolution parameter a, we have analyzed the behavior of the localization of a scalar field when we vary the resolution parameter. On one hand, this enables us to study the effects that a singularity has on the field. On the other hand we can use the resolution parameter as a fine-tuning between the bulk Planck mass and 3-brane Planck mass and so it opens a new perspective to extend the hierarchy problem. Using a linear and a nonlinear warp factor, we have found that the massive and massless modes are trapped to the brane even in the singular cone (a{ne}0). We have also compared the results obtained in this geometry and those obtained in other six-dimensional models, such as stringlike geometry and cigarlike universe geometry.

  12. Localization and mass spectrum of q-form fields on branes

    NASA Astrophysics Data System (ADS)

    Fu, Chun-E.; Zhong, Yuan; Xie, Qun-Ying; Liu, Yu-Xiao

    2016-06-01

    In this paper, we investigate localization of a bulk massless q-form field on codimension-one branes by using a new Kaluza-Klein (KK) decomposition, for which there are two types of KK modes for the bulk q-form field, the q-form and (q - 1)-form modes. The first modes may be massive or massless while the second ones are all massless. These two types of KK modes satisfy two Schrödinger-like equations. For a five-dimensional brane model with a finite extra dimension, the spectrum of a bulk 3-form field on the brane consists of some massive bound 3-form KK modes as well as some massless bound 2-form ones with different configuration along the extra dimension. These 2-form modes are different from those obtained from a bulk 2-form field. For a five-dimensional degenerated Bloch brane model with an infinite extra dimension, some massive 3-form resonant KK modes and corresponding massless 2-form resonant ones are obtained for a bulk 3-form field.

  13. Plasmonic plano-semi-cylindrical nanocavities with high-efficiency local-field confinement

    NASA Astrophysics Data System (ADS)

    Liu, Feifei; Zhang, Xinping; Fang, Xiaohui

    2017-01-01

    Plasmonic nanocavity arrays were achieved by producing isolated silver semi-cylindrical nanoshells periodically on a continuous planar gold film. Hybridization between localized surface plasmon resonance (LSPR) in the Ag semi-cylindrical nanoshells (SCNS) and surface plasmon polaritons (SPP) in the gold film was observed as split bonding and anti-bonding resonance modes located at different spectral positions. This led to strong local field enhancement and confinement in the plano-concave nanocavites. Narrow-band optical extinction with an amplitude as high as 1.5 OD, corresponding to 97% reduction in the transmission, was achieved in the visible spectrum. The resonance spectra of this hybrid device can be extended from the visible to the near infrared by adjusting the structural parameters.

  14. Plasmonic plano-semi-cylindrical nanocavities with high-efficiency local-field confinement

    PubMed Central

    Liu, Feifei; Zhang, Xinping; Fang, Xiaohui

    2017-01-01

    Plasmonic nanocavity arrays were achieved by producing isolated silver semi-cylindrical nanoshells periodically on a continuous planar gold film. Hybridization between localized surface plasmon resonance (LSPR) in the Ag semi-cylindrical nanoshells (SCNS) and surface plasmon polaritons (SPP) in the gold film was observed as split bonding and anti-bonding resonance modes located at different spectral positions. This led to strong local field enhancement and confinement in the plano-concave nanocavites. Narrow-band optical extinction with an amplitude as high as 1.5 OD, corresponding to 97% reduction in the transmission, was achieved in the visible spectrum. The resonance spectra of this hybrid device can be extended from the visible to the near infrared by adjusting the structural parameters. PMID:28074853

  15. Resolving phase information of the optical local density of state with scattering near-field probes

    NASA Astrophysics Data System (ADS)

    Prasad, R.; Vincent, R.

    2016-10-01

    We theoretically discuss the link between the phase measured using a scattering optical scanning near-field microscopy (s-SNOM) and the local density of optical states (LDOS). A remarkable result is that the LDOS information is directly included in the phase of the probe. Therefore by monitoring the spatial variation of the trans-scattering phase, we locally measure the phase modulation associated with the probe and the optical paths. We demonstrate numerically that a technique involving two-phase imaging of a sample with two different sized tips should allow to obtain the image the pLDOS. For this imaging method, numerical comparison with extinction probe measurement shows crucial qualitative and quantitative improvement.

  16. Local-field effects and nanostructuring for controlling optical properties and enabling novel optical phenomena

    NASA Astrophysics Data System (ADS)

    Dolgaleva, Ksenia

    My Ph. D. thesis is devoted to the investigation of the methods of controlling and improving the linear and nonlinear optical properties of materials. Within my studies, two approaches are considered: nanostructuring and invoking local-field effects. These broad topics involve various projects that I have undertaken during my Ph. D. research. The first project is on composite laser gain media. It involves both nanostructuring and using local-field effects to control the basic laser parameters, such as the radiative lifetime, small-signal gain and absorption, and the saturation intensity. While being involved in this project, I have performed both theoretical and experimental studies of laser characteristics of composite materials. In particular, I have developed simple theoretical models for calculating the effective linear susceptibilities of layered and Maxwell Garnett composite materials with a gain resonance in one of their components. The analysis of the results given by the models suggests that local-field effects provide considerable freedom in controlling the optical properties of composite laser gain media. I have also experimentally measured the radiative lifetime of Nd:YAG nanopowder suspended in different liquids to extract information regarding local-field effects. The second project is devoted to the investigation of a not-well-known phenomenon that local-field effects can induce, which is microscopic cascading in nonlinear optics. This project involves the theoretical prediction of local-field-induced microscopic cascading effect in the fifth-order nonlinear response and its first experimental observation. This effect has been mostly overlooked or underestimated, but could prove useful in quantum optics. I have shown that, under certain conditions, the microscopic cascaded contribution can be a dominant effect in high-order nonlinearities. The third project is about characterization of laser performance of a new dye, oligofluorene, embedded into

  17. Measuring electromagnetic properties of superconductors in high and localized rf magnetic field

    NASA Astrophysics Data System (ADS)

    Tai, Tamin

    Niobium-based Superconducting Radio Frequency (SRF) particle accelerator cavity performance is sensitive to localized defects that give rise to quenches at high accelerating gradients. In order to identify these material defects on bulk Nb surfaces at their operating frequency and temperature, it is important to develop a new kind of wide bandwidth microwave microscopy with localized and strong RF magnetic fields. A novel near-field magnetic field microwave microscope that enables mapping of the local electrodynamic response in the multi-GHz frequency regime at liquid helium cryogenic temperatures was successful built via the combination of a magnetic writer and a near field-microwave microscope [1] [2]. This magnetic writer can create a localized and strong RF magnetic field and should achieve a condition with Bsurface ~150 mT and sub-micron resolution (Chapter 3). Our objective is to study the extreme and local electrodynamic properties of Niobium (Nb), and to relate these properties to specific defects that limit the ultimate RF performance of superconducting radio frequency cavities made from Nb. Therefore, in this dissertation, many superconducting materials, especially the candidate materials for superconducting RF cavities, were tested at a fixed location to analyze the local electrodynamic response through linear and nonlinear microwave measurements. For the linear measurement (Chapter 4), many fundamental properties of RF superconductivity such as the critical temperature Tc and penetration depth lambda can be identified. For the nonlinear response measurement (Chapter 5), both the intrinsic and extrinsic nonlinearities from the superconductors are excited by our magnetic write head probe. Many models are introduced to identify the measured nonlinearity, including the intrinsic nonlinearity from the modulation of the superconducting order parameter near Tc, and the extrinsic nonlinearity from the moving vortex model, weak-link Josephson effect, and the

  18. AMUSE-Field I: NUCLEAR X-RAY PROPERTIES OF LOCAL FIELD AND GROUP SPHEROIDS ACROSS THE STELLAR MASS SCALE

    SciTech Connect

    Miller, Brendan; Gallo, Elena; Treu, Tommaso; Woo, Jong-Hak

    2012-03-01

    We present the first results from AMUSE-Field, a Chandra survey designed to characterize the occurrence and intensity of low-level accretion onto supermassive black holes (SMBHs) at the center of local early-type field galaxies. This is accomplished by means of a Large Program targeting a distance-limited (<30 Mpc) sample of 103 early types spanning a wide range in stellar masses. We acquired new ACIS-S observations for 61 objects down to a limiting (0.3-10 keV) luminosity of 2.5 Multiplication-Sign 10{sup 38} erg s{sup -1}, and we include an additional 42 objects with archival (typically deeper) coverage. A nuclear X-ray source is detected in 52 out of the 103 galaxies. After accounting for potential contamination from low-mass X-ray binaries, we estimate that the fraction of accreting SMBHs within the sample is 45% {+-} 7%, which sets a firm lower limit on the occupation fraction within the field. The measured nuclear X-ray luminosities are invariably highly sub-Eddington, with L{sub X}/L{sub Edd} ratios between {approx}10{sup -4} and 10{sup -8}. As also found in a companion survey targeting Virgo early types, the active fraction increases with increasing host galaxy stellar mass, reflective of 'Eddington incompleteness' within the lower-mass objects. For the Field sample, the average nuclear X-ray luminosity scales with the host stellar mass as M{sup 0.71{+-}0.10}{sub star}, with an intrinsic scatter of 0.73 {+-} 0.09 dex. Qualitatively similar results hold for morphologically homogeneous (type E) or uniform sensitivity (new observations only) subsets. A majority of the AMUSE-Field galaxies (78%) inhabit groups, enabling us to investigate the influence of group richness on nuclear activity. We see no evidence for a positive correlation between nuclear X-ray luminosity, normalized to host properties, and galaxy density. Rather, while the scatter is substantial, it appears that the Eddington-scaled X-ray luminosity of group members may be slightly lower than for

  19. AMUSE-Field I: Nuclear X-Ray Properties of Local Field and Group Spheroids across the Stellar Mass Scale

    NASA Astrophysics Data System (ADS)

    Miller, Brendan; Gallo, Elena; Treu, Tommaso; Woo, Jong-Hak

    2012-03-01

    We present the first results from AMUSE-Field, a Chandra survey designed to characterize the occurrence and intensity of low-level accretion onto supermassive black holes (SMBHs) at the center of local early-type field galaxies. This is accomplished by means of a Large Program targeting a distance-limited (<30 Mpc) sample of 103 early types spanning a wide range in stellar masses. We acquired new ACIS-S observations for 61 objects down to a limiting (0.3-10 keV) luminosity of 2.5 × 1038 erg s-1, and we include an additional 42 objects with archival (typically deeper) coverage. A nuclear X-ray source is detected in 52 out of the 103 galaxies. After accounting for potential contamination from low-mass X-ray binaries, we estimate that the fraction of accreting SMBHs within the sample is 45% ± 7%, which sets a firm lower limit on the occupation fraction within the field. The measured nuclear X-ray luminosities are invariably highly sub-Eddington, with L X/L Edd ratios between ~10-4 and 10-8. As also found in a companion survey targeting Virgo early types, the active fraction increases with increasing host galaxy stellar mass, reflective of "Eddington incompleteness" within the lower-mass objects. For the Field sample, the average nuclear X-ray luminosity scales with the host stellar mass as M 0.71 ± 0.10 star, with an intrinsic scatter of 0.73 ± 0.09 dex. Qualitatively similar results hold for morphologically homogeneous (type E) or uniform sensitivity (new observations only) subsets. A majority of the AMUSE-Field galaxies (78%) inhabit groups, enabling us to investigate the influence of group richness on nuclear activity. We see no evidence for a positive correlation between nuclear X-ray luminosity, normalized to host properties, and galaxy density. Rather, while the scatter is substantial, it appears that the Eddington-scaled X-ray luminosity of group members may be slightly lower than for isolated galaxies, and that this trend continues to cluster early types.

  20. Posteroventrolateral pallidotomy through implanted DBS electrodes monitored by recording local field potentials.

    PubMed

    Franzini, Angelo; Cordella, Roberto; Penner, Federica; Rosa, Manuela; Messina, Giuseppe; Rizzi, Michele; Nardocci, Nardo; Priori, Alberto

    2015-01-01

    This paper describes the use of globus pallidus internus (Gpi) local field potentials recorded through pre-implanted deep brain stimulation (DBS) electrodes on a patient affected by generalized dystonia. The recordings were made both before and after radiofrequency-induced posteroventrolateral bilateral stereotactic pallidotomy. LFP patterns and macroelectrode impedances were modified after the pallidotomy, along with the improvement of dystonic symptoms. After implantation, the DBS electrodes were used for subsequent bedside pallidotomies that were required by the evolution and/or persistence of symptoms. In our hands, LFPs were safe and effective in monitoring pallidotomy performed through DBS electrodes.

  1. Enhancement of Optical Nonlinearities in Composite Media and Structures via Local Fields and Electromagnetic Coupling Effects

    NASA Technical Reports Server (NTRS)

    Smith, David D.

    2002-01-01

    This talk will review the linear and nonlinear optical properties of metal nanoparticles and dielectric microparticles, with an emphasis on local field effects, and whispering gallery modes (WGMs), as well as the conjunction of these two effects for enhanced Raman. In particular, enhanced optical properties that result from electromagnetic coupling effects will be discussed in the context of Mie scattering from concentric spheres and bispheres. Predictions of mode splitting and photonic bandgaps in micro-spheres will be presented and will be shown to be analogous to effects that occur in coupled resonator optical waveguides (CROW). Slow and fast light in SCISSOR / CROW configurations will also be discussed.

  2. Isotropic proton-detected local-field nuclear magnetic resonancein solids

    SciTech Connect

    Havlin, Robert H.; Walls, Jamie D.; Pines, Alexander

    2004-08-04

    A new nuclear magnetic resonance (NMR) method is presented which produces linear, isotropic proton-detected local-field spectra for InS spin systems in powdered samples. The method, HETeronuclear Isotropic Evolution (HETIE), refocuses the anisotropic portion of the heteronuclear dipolar coupling frequencies by evolving the system under a series of specially designed Hamiltonians and evolution pathways. The theory behind HETIE is represented along with experimental studies conducted on a powdered sample of ferrocene, demonstrating the methodology outlined in this paper. Applications of HETIE for structural determination in solid-state NMR are discussed.

  3. Multipartite non-locality and entanglement signatures of a field-induced quantum phase transition

    NASA Astrophysics Data System (ADS)

    Batle, Josep; Alkhambashi, Majid; Farouk, Ahmed; Naseri, Mosayeb; Ghoranneviss, Mahmood

    2017-02-01

    Quantum correlation measures are limited in practice to a few number of parties, since no general theory is still capable of reaching the thermodynamic limit. In the present work we study entanglement and non-locality for a cluster of spins belonging to a compound that displays a magnetocaloric effect. A quantum phase transition (QPT) is induced by an external magnetic field B, in such a way that the corresponding quantum fluctuations are reproduced at a much smaller scale than the experimental outcomes, and then described by means of the aforementioned quantum measures.

  4. Performance assessment of multi-frequency processing of ICU chest images for enhanced visualization of tubes and catheters

    NASA Astrophysics Data System (ADS)

    Wang, Xiaohui; Couwenhoven, Mary E.; Foos, David H.; Doran, James; Yankelevitz, David F.; Henschke, Claudia I.

    2008-03-01

    An image-processing method has been developed to improve the visibility of tube and catheter features in portable chest x-ray (CXR) images captured in the intensive care unit (ICU). The image-processing method is based on a multi-frequency approach, wherein the input image is decomposed into different spatial frequency bands, and those bands that contain the tube and catheter signals are individually enhanced by nonlinear boosting functions. Using a random sampling strategy, 50 cases were retrospectively selected for the study from a large database of portable CXR images that had been collected from multiple institutions over a two-year period. All images used in the study were captured using photo-stimulable, storage phosphor computed radiography (CR) systems. Each image was processed two ways. The images were processed with default image processing parameters such as those used in clinical settings (control). The 50 images were then separately processed using the new tube and catheter enhancement algorithm (test). Three board-certified radiologists participated in a reader study to assess differences in both detection-confidence performance and diagnostic efficiency between the control and test images. Images were evaluated on a diagnostic-quality, 3-megapixel monochrome monitor. Two scenarios were studied: the baseline scenario, representative of today's workflow (a single-control image presented with the window/level adjustments enabled) vs. the test scenario (a control/test image pair presented with a toggle enabled and the window/level settings disabled). The radiologists were asked to read the images in each scenario as they normally would for clinical diagnosis. Trend analysis indicates that the test scenario offers improved reading efficiency while providing as good or better detection capability compared to the baseline scenario.

  5. IBEX RIBBON: WHAT COULD IT TELL ABOUT THE LOCAL INTERSTELLAR MAGNETIC FIELD?

    SciTech Connect

    Grygorczuk, J.; Ratkiewicz, R.; Strumik, M.; Grzedzielski, S.

    2011-02-01

    We show that the shape of the IBEX Ribbon can be reproduced assuming energetic neutral atoms originate in regions beyond the heliopause where the interstellar magnetic field is the strongest and perpendicular to radial directions from the Sun. The best fit to the observed ribbon was obtained for the local interstellar magnetic field B{sub {infinity}} = 3.0 {+-} 1.0 {mu}G pointing from ecliptic/galactic coordinates ({lambda}, {beta})/(l, b) = (225{sup 0} {+-} 5{sup 0}, 35{sup 0} {+-} 5{sup 0})/(27{sup 0} {+-} 5{sup 0}, 51{sup 0} {+-} 5{sup 0}) close to the apparent ribbon center ({lambda}, {beta})/(l, b) = (221{sup 0}, 39{sup 0})/(33{sup 0}, 55{sup 0}). The geometrical considerations presented below should prove useful in identifying the mechanism of ribbon formation.

  6. Method for formation of high quality back contact with screen-printed local back surface field

    DOEpatents

    Rohatgi, Ajeet; Meemongkolkiat, Vichai

    2010-11-30

    A thin silicon solar cell having a back dielectric passivation and rear contact with local back surface field is described. Specifically, the solar cell may be fabricated from a crystalline silicon wafer having a thickness from 50 to 500 micrometers. A barrier layer and a dielectric layer are applied at least to the back surface of the silicon wafer to protect the silicon wafer from deformation when the rear contact is formed. At least one opening is made to the dielectric layer. An aluminum contact that provides a back surface field is formed in the opening and on the dielectric layer. The aluminum contact may be applied by screen printing an aluminum paste having from one to 12 atomic percent silicon and then applying a heat treatment at 750 degrees Celsius.

  7. Ultra-fast magnetic vortex core reversal by a local field pulse

    SciTech Connect

    Rückriem, R.; Albrecht, M.; Schrefl, T.

    2014-02-03

    Magnetic vortex core reversal of a 20-nm-thick permalloy disk with a diameter of 100 nm was studied by micromagnetic simulations. By applying a global out-of-plane magnetic field pulse, it turned out that the final core polarity is very sensitive to pulse width and amplitude, which makes it hard to control. The reason for this phenomenon is the excitation of radial spin waves, which dominate the reversal process. The excitation of spin waves can be strongly suppressed by applying a local field pulse within a small area at the core center. With this approach, ultra-short reversal times of about 15 ps were achieved, which are ten times faster compared to a global pulse.

  8. Massively parallel recording of unit and local field potentials with silicon-based electrodes.

    PubMed

    Csicsvari, Jozsef; Henze, Darrell A; Jamieson, Brian; Harris, Kenneth D; Sirota, Anton; Barthó, Péter; Wise, Kensall D; Buzsáki, György

    2003-08-01

    Parallel recording of neuronal activity in the behaving animal is a prerequisite for our understanding of neuronal representation and storage of information. Here we describe the development of micro-machined silicon microelectrode arrays for unit and local field recordings. The two-dimensional probes with 96 or 64 recording sites provided high-density recording of unit and field activity with minimal tissue displacement or damage. The on-chip active circuit eliminated movement and other artifacts and greatly reduced the weight of the headgear. The precise geometry of the recording tips allowed for the estimation of the spatial location of the recorded neurons and for high-resolution estimation of extracellular current source density. Action potentials could be simultaneously recorded from the soma and dendrites of the same neurons. Silicon technology is a promising approach for high-density, high-resolution sampling of neuronal activity in both basic research and prosthetic devices.

  9. Local fields in conductor surface electromigration: A first-principles study in the low-bias ballistic limit

    SciTech Connect

    Bevan, Kirk H; Zhu, Wenguang; Stocks, George Malcolm; Guo, Hong; Zhang, Zhenyu

    2012-01-01

    Utilizing first-principles quantum transport calculations, we investigate the role of local fields in conductor surface electromigration. A nanometer-thick Ag(100) thin film is adopted as our prototypical conductor, where we demonstrate the existence of intense local electric fields at atomic surface defects under an external bias. It is shown that such local fields can play an important role in driving surface electromigration and electrical breakdown. The intense fields originate from the relatively short (atomic-scale) screening lengths common to most elemental metals. This general short-range screening trend is established self-consistently within an intuitive picture of linear response electrostatics. The findings shed new light on the underlying physical origins of surface electromigration and point to the possibility of harnessing local fields to engineer electromigration at the nanoscale.

  10. Limits of the measurability of the local quantum electromagnetic-field amplitude

    NASA Astrophysics Data System (ADS)

    Compagno, G.; Persico, F.

    1998-03-01

    The precision with which the amplitude of the free electromagnetic field can be measured locally in QED is evaluated by analyzing a well-known gedanken experiment originally proposed by Bohr and Rosenfeld (BR). The analysis is performed by applying standard theoretical techniques familiar in quantum optics. The main result obtained for the precision is significantly different from the generally accepted Bohr-Rosenfeld result. This leads to questioning the widely accepted notion of the compensating field, fostered by these authors. A misconception at the origin of this notion is pointed out by a careful investigation of the self-force acting on the apparatus designed to measure the field. The correct expression for this self-force is found to be at variance with that proposed by Bohr and Rosenfeld and generally accepted. It is argued that, as a consequence of this new expression and in contrast with the generally accepted view, no compensating force of nonelectromagnetic nature is required in order to perform measurements of the quantum field amplitude with any desired accuracy. It is shown that the only limitations to the precision of the measurement, in the BR gedanken experiment, arise from the time-energy uncertainty principle, as well as from the finite dimensions of the measuring apparatus.

  11. Nano-patterning photosensitive polymers using local field enhancement at the end of apertureless SNOM tips.

    PubMed

    H'dhili, F; Bachelot, R; Rumyantseva, A; Lerondel, G; Royer, P

    2003-03-01

    We show experimentally that local optical field enhancement can occur at the end of an apertureless SNOM tip illuminated by an external light source. Our approach consists in the use of a photosensitive polymer, placed in the tip near-field, to record intensity distribution in the vicinity of the tip end. The excited nanometre-size light source permits us to produce nano-patterns on the polymer surface which are then characterized by atomic force microscopy. Experimental images show the influence, on the field enhancement, of three important experimental parameters: the polarization state of the incident light, the geometry of the external illumination and the radius of curvature of the tip apex. These results are shown to be in good agreement with two-dimensional numerical calculations based on the finite-difference time-domain method. We show preliminary nanometre-size patterns created by this nano-source excited at a metallic tip extremity and discuss the potential of this approach for near-field optical lithography.

  12. Tissue heterogeneity as a mechanism for localized neural stimulation by applied electric fields

    NASA Astrophysics Data System (ADS)

    Miranda, P. C.; Correia, L.; Salvador, R.; Basser, P. J.

    2007-09-01

    We investigate the heterogeneity of electrical conductivity as a new mechanism to stimulate excitable tissues via applied electric fields. In particular, we show that stimulation of axons crossing internal boundaries can occur at boundaries where the electric conductivity of the volume conductor changes abruptly. The effectiveness of this and other stimulation mechanisms was compared by means of models and computer simulations in the context of transcranial magnetic stimulation. While, for a given stimulation intensity, the largest membrane depolarization occurred where an axon terminates or bends sharply in a high electric field region, a slightly smaller membrane depolarization, still sufficient to generate action potentials, also occurred at an internal boundary where the conductivity jumped from 0.143 S m-1 to 0.333 S m-1, simulating a white-matter-grey-matter interface. Tissue heterogeneity can also give rise to local electric field gradients that are considerably stronger and more focal than those impressed by the stimulation coil and that can affect the membrane potential, albeit to a lesser extent than the two mechanisms mentioned above. Tissue heterogeneity may play an important role in electric and magnetic 'far-field' stimulation.

  13. Model-independent mean-field theory as a local method for approximate propagation of information.

    PubMed

    Haft, M; Hofmann, R; Tresp, V

    1999-02-01

    We present a systematic approach to mean-field theory (MFT) in a general probabilistic setting without assuming a particular model. The mean-field equations derived here may serve as a local, and thus very simple, method for approximate inference in probabilistic models such as Boltzmann machines or Bayesian networks. Our approach is 'model-independent' in the sense that we do not assume a particular type of dependences; in a Bayesian network, for example, we allow arbitrary tables to specify conditional dependences. In general, there are multiple solutions to the mean-field equations. We show that improved estimates can be obtained by forming a weighted mixture of the multiple mean-field solutions. Simple approximate expressions for the mixture weights are given. The general formalism derived so far is evaluated for the special case of Bayesian networks. The benefits of taking into account multiple solutions are demonstrated by using MFT for inference in a small and in a very large Bayesian network. The results are compared with the exact results.

  14. Decoding intravesical pressure from local field potentials in rat lumbosacral spinal cord

    NASA Astrophysics Data System (ADS)

    Im, Changkyun; Park, Hae Yong; Koh, Chin Su; Ryu, Sang Baek; Seo, In Seok; Kim, Yong Jung; Kim, Kyung Hwan; Shin, Hyung-Cheul

    2016-10-01

    Chronic monitoring of intravesical pressure is required to detect the onset of intravesical hypertension and the progression of a more severe condition. Recent reports demonstrate the bladder state can be monitored from the spiking activity of the dorsal root ganglia or lumbosacral spinal cord. However, one of the most serious challenges for these methods is the difficulty of sustained spike signal acquisition due to the high-electrode-location-sensitivity of spikes or neuro-degeneration. Alternatively, it has been demonstrated that local field potential recordings are less affected by encapsulation reactions or electrode location changes. Here, we hypothesized that local field potential (LFP) from the lumbosacral dorsal horn may provide information concerning the intravesical pressure. LFP and spike activities were simultaneously recorded from the lumbosacral spinal cord of anesthetized rats during bladder filling. The results show that the LFP activities carry significant information about intravesical pressure along with spiking activities. Importantly, the intravesical pressure is decoded from the power in high-frequency bands (83.9-256 Hz) with a substantial performance similar to that of the spike train decoding. These findings demonstrate that high-frequency LFP activity can be an alternative intravesical pressure monitoring signal, which could lead to a proper closed loop system for urinary control.

  15. Anisotropy of the local field of the light wave in cholesteric liquid crystals

    NASA Astrophysics Data System (ADS)

    Aver'yanov, E. M.

    2010-05-01

    The experimental values of the L j components of the Lorentz tensor have been obtained for the first time for the quasinematic layer of the cholesteric phase and in the smectic phase A for homologs of cholesteric fatty ethers using the dispersion dependences of the refraction indices for the planar texture of cholesteric liquid crystals (CLCs). The dependence of the L j components on the homolog number, mesophase temperature, the magnitude of birefringence, and the change in the orientational ordering of molecules in the cholesteric phase and at the cholesteric-smectic A phase transition was determined. Isotropization of the Lorentz tensor L and the local field tensor f was found for CLCs when the birefringence of LCs and the anisotropy of molecular polarizability decreased simultaneously. The anisotropy Δ f was found to be negative for the quasinematic layer of CLCs and the smectic phase in the visible range of the spectrum. The values of L j , obtained with known local field models for CLCs and smectics A, gave positive Δ f irrespective of the chemical structure of molecules, optical anisotropy of LCs, and the spectral region, which contradicts to the experiment.

  16. Local field potentials primarily reflect inhibitory neuron activity in human and monkey cortex

    PubMed Central

    Teleńczuk, Bartosz; Dehghani, Nima; Le Van Quyen, Michel; Cash, Sydney S.; Halgren, Eric; Hatsopoulos, Nicholas G.; Destexhe, Alain

    2017-01-01

    The local field potential (LFP) is generated by large populations of neurons, but unitary contribution of spiking neurons to LFP is not well characterised. We investigated this contribution in multi-electrode array recordings from human and monkey neocortex by examining the spike-triggered LFP average (st-LFP). The resulting st-LFPs were dominated by broad spatio-temporal components due to ongoing activity, synaptic inputs and recurrent connectivity. To reduce the spatial reach of the st-LFP and observe the local field related to a single spike we applied a spatial filter, whose weights were adapted to the covariance of ongoing LFP. The filtered st-LFPs were limited to the perimeter of 800 μm around the neuron, and propagated at axonal speed, which is consistent with their unitary nature. In addition, we discriminated between putative inhibitory and excitatory neurons and found that the inhibitory st-LFP peaked at shorter latencies, consistently with previous findings in hippocampal slices. Thus, in human and monkey neocortex, the LFP reflects primarily inhibitory neuron activity. PMID:28074856

  17. Census of the Local Universe (CLU) Galaxy Survey: Results Within Preliminary Fields

    NASA Astrophysics Data System (ADS)

    Cook, David O.; Kasliwal, Mansi M.; Van Sistine, Angela; Dale, Daniel A.; Sutter, Jessica; Turner, Jordan; Parziale, Ryan; iPTF Team

    2017-01-01

    We present an analysis of galaxy candidates in 15 (out of ~3600) preliminary fields of the Census of the Local Universe (CLU) galaxy survey. The intermediate Palomar Transient Factory (iPTF) is undertaking the CLU project to complete our survey of galaxies out to 200 Mpc (z ˜ 0.05) and deploys 4 wavelength-adjacent, narrowband filters to search for emission line (Hα) sources across 3π (~28,000 deg^2) of the sky. Using the Palomar 200-inch Hale telescope, we have obtained spectroscopic follow-up observations with which we can verify each candidate’s redshift and derive galaxy properties. In addition, we present some interesting galaxies in our candidate list (e.g., green peas) whose extreme properties (e.g., low metallicity and high star formation rate) are similar to those of higher redshift galaxies (z>2). We will expand our analysis to all ~3600 fields and anticipate finding tens-of-thousands of new galaxies in the local Universe over the next year.

  18. Localizing gauge fields on a topological Abelian string and the Coulomb law

    SciTech Connect

    Torrealba S, Rafael S.

    2010-07-15

    The confinement of electromagnetic field is studied in axial symmetrical, warped, six-dimensional brane world, using a recently proposed topological Abelian string-vortex solution as background. It was found, that the massless gauge field fluctuations follow four-dimensional Maxwell equations in the Lorenz gauge. The massless zero mode is localized when the thickness of the string vortex is less than 5{beta}/4{pi}e{sup 2}v{sup 2} and there are no other localized massless modes. There is also an infinite of nonlocalized massive Fourier modes, that follow four-dimensional Proca equations with a continuous spectrum. To compute the corrections to the Coulomb potential, a radial cutoff was introduced, in order to achieve a discrete mass spectrum. As a main result, a (R{sub o}/{beta}R{sup 2}) correction was found for the four-dimensional effective Coulomb law; the result is in correspondence with the observed behavior of the Coulomb potential at today's measurable distances.

  19. Electrocoalescence mechanisms of microdroplets using localized electric fields in microfluidic channels.

    PubMed

    Zagnoni, Michele; Le Lain, Guillaume; Cooper, Jonathan M

    2010-09-21

    Electrocoalescence of water-in-oil microdroplets in microfluidic channels is an active technique that enables droplet-based mixing functionalities to be achieved in lab-on-a-chip applications. In this work, a characterization of the electrocoalescence mechanisms of water microdroplets in oil is presented, using localized electric field systems. We report a theoretical and experimental description of the electrocoalscence behavior of droplet pairs by varying the physical and fluid dynamic conditions of the phases. Our results demonstrate that localized electric field systems can be reliably used to merge droplets in pairs, regardless of the distance between the drops. The coalescence behavior was dependent upon the viscosity of the continuous phase for water droplets that were separated by a thick layer of oil and upon interfacial tension for droplets that were in close proximity. We showed that these systems have the potential to be used for high-throughput applications and that, unlike other examples of active systems in the literature, the need of droplet synchronization and the application of high voltages is considerably reduced.

  20. Consistent Feature Extraction From Vector Fields: Combinatorial Representations and Analysis Under Local Reference Frames

    SciTech Connect

    Bhatia, Harsh

    2015-05-01

    This dissertation presents research on addressing some of the contemporary challenges in the analysis of vector fields—an important type of scientific data useful for representing a multitude of physical phenomena, such as wind flow and ocean currents. In particular, new theories and computational frameworks to enable consistent feature extraction from vector fields are presented. One of the most fundamental challenges in the analysis of vector fields is that their features are defined with respect to reference frames. Unfortunately, there is no single “correct” reference frame for analysis, and an unsuitable frame may cause features of interest to remain undetected, thus creating serious physical consequences. This work develops new reference frames that enable extraction of localized features that other techniques and frames fail to detect. As a result, these reference frames objectify the notion of “correctness” of features for certain goals by revealing the phenomena of importance from the underlying data. An important consequence of using these local frames is that the analysis of unsteady (time-varying) vector fields can be reduced to the analysis of sequences of steady (timeindependent) vector fields, which can be performed using simpler and scalable techniques that allow better data management by accessing the data on a per-time-step basis. Nevertheless, the state-of-the-art analysis of steady vector fields is not robust, as most techniques are numerical in nature. The residing numerical errors can violate consistency with the underlying theory by breaching important fundamental laws, which may lead to serious physical consequences. This dissertation considers consistency as the most fundamental characteristic of computational analysis that must always be preserved, and presents a new discrete theory that uses combinatorial representations and algorithms to provide consistency guarantees during vector field analysis along with the uncertainty

  1. Ultrafast electronic response of graphene to a strong and localized electric field

    NASA Astrophysics Data System (ADS)

    Gruber, Elisabeth; Wilhelm, Richard A.; Pétuya, Rémi; Smejkal, Valerie; Kozubek, Roland; Hierzenberger, Anke; Bayer, Bernhard C.; Aldazabal, Iñigo; Kazansky, Andrey K.; Libisch, Florian; Krasheninnikov, Arkady V.; Schleberger, Marika; Facsko, Stefan; Borisov, Andrei G.; Arnau, Andrés; Aumayr, Friedrich

    2016-12-01

    The way conduction electrons respond to ultrafast external perturbations in low dimensional materials is at the core of the design of future devices for (opto)electronics, photodetection and spintronics. Highly charged ions provide a tool for probing the electronic response of solids to extremely strong electric fields localized down to nanometre-sized areas. With ion transmission times in the order of femtoseconds, we can directly probe the local electronic dynamics of an ultrathin foil on this timescale. Here we report on the ability of freestanding single layer graphene to provide tens of electrons for charge neutralization of a slow highly charged ion within a few femtoseconds. With values higher than 1012 A cm-2, the resulting local current density in graphene exceeds previously measured breakdown currents by three orders of magnitude. Surprisingly, the passing ion does not tear nanometre-sized holes into the single layer graphene. We use time-dependent density functional theory to gain insight into the multielectron dynamics.

  2. High-energy localized eigenstates of an electronic resonator in a magnetic field

    NASA Astrophysics Data System (ADS)

    Zalipaev, V. V.; Kusmartsev, F. V.; Popov, M. M.

    2008-02-01

    We present a semiclassical analysis of the high-energy eigenstates of an electron inside a closed resonator. An asymptotic method of the construction of the energy spectrum and eigenfunctions, localized in the small neighborhood of a periodic orbit, is developed in the presence of a homogeneous magnetic field and arbitrary scalar potential. The isolated periodic orbit is confined between two interfaces which could be planar, concave or even convex. Such a system represents a quantum electronic resonator, an analog of the well-known high-frequency optical or acoustic resonator with eigenmodes called 'bouncing ball vibrations'. The first step in the asymptotic analysis involves constructing a solitary localized asymptotic solution to the Schrödinger equation (electronic Gaussian beam—wavepackage). Then, the stability of a closed continuous family of periodic trajectories confined between two reflecting surfaces of the resonator boundary was studied. The asymptotics of the eigenfunctions were constructed as a superposition of two electronic Gaussian beams propagating in opposite directions between two reflecting points of the periodic orbits. The asymptotics of the energy spectrum are obtained by the generalized Bohr-Sommerfeld quantization condition derived as a requirement for the eigenfunction asymptotics to be periodic. For one class of periodic orbits, localized eigenstates were computed numerically by the finite element method using FEMLAB and proved to be in a very good agreement with those computed semiclassically.

  3. Ultrafast electronic response of graphene to a strong and localized electric field

    PubMed Central

    Gruber, Elisabeth; Wilhelm, Richard A.; Pétuya, Rémi; Smejkal, Valerie; Kozubek, Roland; Hierzenberger, Anke; Bayer, Bernhard C.; Aldazabal, Iñigo; Kazansky, Andrey K.; Libisch, Florian; Krasheninnikov, Arkady V.; Schleberger, Marika; Facsko, Stefan; Borisov, Andrei G.; Arnau, Andrés; Aumayr, Friedrich

    2016-01-01

    The way conduction electrons respond to ultrafast external perturbations in low dimensional materials is at the core of the design of future devices for (opto)electronics, photodetection and spintronics. Highly charged ions provide a tool for probing the electronic response of solids to extremely strong electric fields localized down to nanometre-sized areas. With ion transmission times in the order of femtoseconds, we can directly probe the local electronic dynamics of an ultrathin foil on this timescale. Here we report on the ability of freestanding single layer graphene to provide tens of electrons for charge neutralization of a slow highly charged ion within a few femtoseconds. With values higher than 1012 A cm−2, the resulting local current density in graphene exceeds previously measured breakdown currents by three orders of magnitude. Surprisingly, the passing ion does not tear nanometre-sized holes into the single layer graphene. We use time-dependent density functional theory to gain insight into the multielectron dynamics. PMID:28000666

  4. Mycorrhizal symbiosis and local adaptation in Aster amellus: a field transplant experiment.

    PubMed

    Pánková, Hana; Raabová, Jana; Münzbergová, Zuzana

    2014-01-01

    Many plant populations have adapted to local soil conditions. However, the role of arbuscular mycorrhizal fungi is often overlooked in this context. Only a few studies have used reciprocal transplant experiments to study the relationships between soil conditions, mycorrhizal colonisation and plant growth. Furthermore, most of the studies were conducted under controlled greenhouse conditions. However, long-term field experiments can provide more realistic insights into this issue. We conducted a five-year field reciprocal transplant experiment to study the relationships between soil conditions, arbuscular mycorrhizal fungi and plant growth in the obligate mycotrophic herb Aster amellus. We conducted this study in two regions in the Czech Republic that differ significantly in their soil nutrient content, namely Czech Karst (region K) and Ceske Stredohori (region S). Plants that originated from region S had significantly higher mycorrhizal colonisation than plants from region K, indicating that the percentage of mycorrhizal colonisation has a genetic basis. We found no evidence of local adaptation in Aster amellus. Instead, plants from region S outperformed the plants from region K in both target regions. Similarly, plants from region S showed more mycorrhizal colonisation in all cases, which was likely driven by the lower nutrient content in the soil from that region. Thus, plant aboveground biomass and mycorrhizal colonisation exhibited corresponding differences between the two target regions and regions of origin. Higher mycorrhizal colonisation in the plants from region with lower soil nutrient content (region S) in both target regions indicates that mycorrhizal colonisation is an adaptive trait. However, lower aboveground biomass in the plants with lower mycorrhizal colonisation suggests that the plants from region K are in fact maladapted by their low inherent mycorrhizal colonization. We conclude that including mycorrhizal symbiosis in local adaptation studies

  5. Nonperturbative measurement of the local magnetic field using pulsed polarimetry for fusion reactor conditions (invited).

    PubMed

    Smith, Roger J

    2008-10-01

    A novel diagnostic technique for the remote and nonperturbative sensing of the local magnetic field in reactor relevant plasmas is presented. Pulsed polarimetry [Patent No. 12/150,169 (pending)] combines optical scattering with the Faraday effect. The polarimetric light detection and ranging (LIDAR)-like diagnostic has the potential to be a local B(pol) diagnostic on ITER and can achieve spatial resolutions of millimeters on high energy density (HED) plasmas using existing lasers. The pulsed polarimetry method is based on nonlocal measurements and subtle effects are introduced that are not present in either cw polarimetry or Thomson scattering LIDAR. Important features include the capability of simultaneously measuring local T(e), n(e), and B(parallel) along the line of sight, a resiliency to refractive effects, a short measurement duration providing near instantaneous data in time, and location for real-time feedback and control of magnetohydrodynamic (MHD) instabilities and the realization of a widely applicable internal magnetic field diagnostic for the magnetic fusion energy program. The technique improves for higher n(e)B(parallel) product and higher n(e) and is well suited for diagnosing the transient plasmas in the HED program. Larger devices such as ITER and DEMO are also better suited to the technique, allowing longer pulse lengths and thereby relaxing key technology constraints making pulsed polarimetry a valuable asset for next step devices. The pulsed polarimetry technique is clarified by way of illustration on the ITER tokamak and plasmas within the magnetized target fusion program within present technological means.

  6. Improved iris localization by using wide and narrow field of view cameras for iris recognition

    NASA Astrophysics Data System (ADS)

    Kim, Yeong Gon; Shin, Kwang Yong; Park, Kang Ryoung

    2013-10-01

    Biometrics is a method of identifying individuals by their physiological or behavioral characteristics. Among other biometric identifiers, iris recognition has been widely used for various applications that require a high level of security. When a conventional iris recognition camera is used, the size and position of the iris region in a captured image vary according to the X, Y positions of a user's eye and the Z distance between a user and the camera. Therefore, the searching area of the iris detection algorithm is increased, which can inevitably decrease both the detection speed and accuracy. To solve these problems, we propose a new method of iris localization that uses wide field of view (WFOV) and narrow field of view (NFOV) cameras. Our study is new as compared to previous studies in the following four ways. First, the device used in our research acquires three images, one each of the face and both irises, using one WFOV and two NFOV cameras simultaneously. The relation between the WFOV and NFOV cameras is determined by simple geometric transformation without complex calibration. Second, the Z distance (between a user's eye and the iris camera) is estimated based on the iris size in the WFOV image and anthropometric data of the size of the human iris. Third, the accuracy of the geometric transformation between the WFOV and NFOV cameras is enhanced by using multiple matrices of the transformation according to the Z distance. Fourth, the searching region for iris localization in the NFOV image is significantly reduced based on the detected iris region in the WFOV image and the matrix of geometric transformation corresponding to the estimated Z distance. Experimental results showed that the performance of the proposed iris localization method is better than that of conventional methods in terms of accuracy and processing time.

  7. Mycorrhizal Symbiosis and Local Adaptation in Aster amellus: A Field Transplant Experiment

    PubMed Central

    Pánková, Hana; Raabová, Jana; Münzbergová, Zuzana

    2014-01-01

    Many plant populations have adapted to local soil conditions. However, the role of arbuscular mycorrhizal fungi is often overlooked in this context. Only a few studies have used reciprocal transplant experiments to study the relationships between soil conditions, mycorrhizal colonisation and plant growth. Furthermore, most of the studies were conducted under controlled greenhouse conditions. However, long-term field experiments can provide more realistic insights into this issue. We conducted a five-year field reciprocal transplant experiment to study the relationships between soil conditions, arbuscular mycorrhizal fungi and plant growth in the obligate mycotrophic herb Aster amellus. We conducted this study in two regions in the Czech Republic that differ significantly in their soil nutrient content, namely Czech Karst (region K) and Ceske Stredohori (region S). Plants that originated from region S had significantly higher mycorrhizal colonisation than plants from region K, indicating that the percentage of mycorrhizal colonisation has a genetic basis. We found no evidence of local adaptation in Aster amellus. Instead, plants from region S outperformed the plants from region K in both target regions. Similarly, plants from region S showed more mycorrhizal colonisation in all cases, which was likely driven by the lower nutrient content in the soil from that region. Thus, plant aboveground biomass and mycorrhizal colonisation exhibited corresponding differences between the two target regions and regions of origin. Higher mycorrhizal colonisation in the plants from region with lower soil nutrient content (region S) in both target regions indicates that mycorrhizal colonisation is an adaptive trait. However, lower aboveground biomass in the plants with lower mycorrhizal colonisation suggests that the plants from region K are in fact maladapted by their low inherent mycorrhizal colonization. We conclude that including mycorrhizal symbiosis in local adaptation studies

  8. Multi-frequency weak signal detection based on wavelet transform and parameter compensation band-pass multi-stable stochastic resonance

    NASA Astrophysics Data System (ADS)

    Han, Dongying; li, Pei; An, Shujun; Shi, Peiming

    2016-03-01

    In actual fault diagnosis, useful information is often submerged in heavy noise, and the feature information is difficult to extract. A novel weak signal detection method aimed at the problem of detecting multi-frequency signals buried under heavy background noise is proposed based on wavelet transform and parameter compensation band-pass multi-stable stochastic resonance (SR). First, the noisy signal is processed by parameter compensation, with the noise and system parameters expanded 10 times to counteract the effect of the damping term. The processed signal is decomposed into multiple signals of different scale frequencies by wavelet transform. Following this, we adjust the size of the scaled signals' amplitudes and reconstruct the signals; the weak signal frequency components are then enhanced by multi-stable stochastic resonance. The enhanced components of the signal are processed through a band-pass filter, leaving the enhanced sections of the signal. The processed signal is analyzed by FFT to achieve detection of the multi-frequency weak signals. The simulation and experimental results show that the proposed method can enhance the signal amplitude, can effectively detect multi-frequency weak signals buried under heavy noise and is valuable and usable for bearing fault signal analysis.

  9. Use of Dual-Pulse Lithotripter to Generate a Localized Intensified Cavitation Field

    SciTech Connect

    Sokolov, Dihlia L.; Bailey, Michael R.; Crum, Lawrence A.

    2001-09-01

    Localizing cavitation to the kidney stone in extracorporeal shock wave lithotripsy may be desirable since cavitation appears to play a major role in both stone comminution and renal tissue damage. A method has been developed to localize and intensify cavitation damage in vitro. Cavitation fields in water were filmed with a high-speed digital video camera. In a conventional lithotripter (CL), the shock wave produced by a single source creates a 2 x 10 cm cylindrical cloud of bubbles in water. Bubbles in the CL field collapse simultaneously along the focal axis to produce a nearly uniform 1-mm x 8-cm line of pits in 25- mm-thick aluminum foil. Our dual-pulse lithotripter (DPL) uses two shock wave sources, facing each other, confocal, and triggered simultaneously to create a 4 x 5 cm cylindrical cloud of bubbles that collapse over a range of times and strengths such that the greatest pit damage on foils is contained within a few square millimeters of the focus. The time for bubbles to grow and collapse was measured with a focused hydrophone and compared with calculations based on the Gilmore equation. Pressure doubling due to synchronous arrival of the two pulses at the focus created increased bubble growth and increased foil pit depth. Asynchronous timing between the two pulses elsewhere in the DPL field resulted in disruption of radial dynamics and negligible pitting to foils. Translation of bubbles was also investigated, both numerically and experimentally. While net translation was calculated to be ,0.3 mm in all cases, the rapid

  10. Free-field study on auditory localization and discrimination performance in older adults.

    PubMed

    Freigang, Claudia; Schmiedchen, Kristina; Nitsche, Ines; Rübsamen, Rudolf

    2014-04-01

    Localization accuracy and acuity for low- (0.375-0.75 kHz; LN) and high-frequency (2.25-4.5 kHz; HN) noise bands were examined in young (20-29 years) and older adults (65-83 years) in the acoustic free-field. A pointing task was applied to quantify accuracy, while acuity was inferred from minimum audible angle (MAA) thresholds measured with an adaptive 3-alternative forced-choice procedure. Accuracy decreased with laterality and age. From young to older adults, the accuracy declined by up to 23 % for the low-frequency noise band across all lateralities. The mean age effect was even more pronounced on MAA thresholds. Thus, age was a strong predictor for MAA thresholds for both LN and HN bands. There was no significant correlation between hearing status and localization performance. These results suggest that central auditory processing of space declines with age and is mainly driven by age-related changes in the processing of binaural cues (interaural time difference and interaural intensity difference) and not directly induced by peripheral hearing loss. We conclude that the representation of the location of sound sources becomes blurred with age as a consequence of declined temporal processing, the effect of which becomes particularly evident for MAA thresholds, where two closely adjoining sound sources have to be separated. While localization accuracy and MAA were not correlated in older adults, only a weak correlation was found in young adults. These results point to an employment of different processing strategies for localization accuracy and acuity.

  11. Spatio-spectral characterization of local field potentials in the subthalamic nucleus via multitrack microelectrode recordings.

    PubMed

    Telkes, I; Ince, N F; Onaran, I; Abosch, A

    2015-08-01

    Deep brain stimulation of the subthalamic nucleus (STN) is a highly effective treatment for motor symptoms of Parkinson's disease. However, precise intraoperative localization of STN remains a procedural challenge. In the present study, local field potentials (LFPs) were recorded from three tracks during microelectrode recording-based (MER) targeting of STN, in five patients. The raw LFP data were preprocessed in original recording setup and then data quality was compared to data with common average derivation. The depth-frequency maps were generated according to preprocessing results for each patient and spectral characteristics of LFPs were explored at each depth across different tracks and different subjects. Spatio-spectral analysis of LFP was investigated to see whether LFP activity can be used for optimal track selection and STN border identification. Analysis show that monopolar derivation suffer from various artifacts and/or power line noise which makes the interpretation of target localization very difficult in most of the subjects. Unlikely, bipolar derivation helps to recover the neurological signals and investigation of signal characteristics. The frequency-vs-depth maps using a modified Welch periodogram with robust statistics, demonstrated that a median-based spectrum estimation approach eliminates outliers pretty well by preserving band-specific LFP activity. The results indicate that there is a clear oscillatory beta activity around 20 Hz in all subjects. 1/f normalization reveals the high frequency oscillations (HFOs) between 200-to-350 Hz in two subjects. It's noted that the optimal track selection is not consistent with the track having highest beta band oscillations in two out of five subjects. In conclusion, microelectrode-derived LFP recordings may provide an alternative approach to single unit activity (SUA)-based MER, for localizing the target STN borders during DBS surgery. Despite the small number of subjects, the present study adds to

  12. A Modified Brain MR Image Segmentation and Bias Field Estimation Model Based on Local and Global Information

    PubMed Central

    Cong, Wang; Luan, Kuan; Liang, Hong; Ma, Xingcheng

    2016-01-01

    Because of the poor radio frequency coil uniformity and gradient-driven eddy currents, there is much noise and intensity inhomogeneity (bias) in brain magnetic resonance (MR) image, and it severely affects the segmentation accuracy. Better segmentation results are difficult to achieve by traditional methods; therefore, in this paper, a modified brain MR image segmentation and bias field estimation model based on local and global information is proposed. We first construct local constraints including image neighborhood information in Gaussian kernel mapping space, and then the complete regularization is established by introducing nonlocal spatial information of MR image. The weighting between local and global information is automatically adjusted according to image local information. At the same time, bias field information is coupled with the model, and it makes the model reduce noise interference but also can effectively estimate the bias field information. Experimental results demonstrate that the proposed algorithm has strong robustness to noise and bias field is well corrected. PMID:27660649

  13. Field Dependence-Field Independence Cognitive Style, Gender, Career Choice and Academic Achievement of Secondary School Students in Emohua Local Government Area of Rivers State

    ERIC Educational Resources Information Center

    Onyekuru, Bruno Uchenna

    2015-01-01

    This is a descriptive study that investigated the relationships among field dependence-field independence cognitive style and gender, career choice and academic achievement of secondary school students in Emohua Local Government Area of Rivers State, Nigeria. From the initial sample of 320 senior secondary school one (SS1) students drawn from the…

  14. Suppression of edge localized mode crashes by multi-spectral non-axisymmetric fields in KSTAR

    NASA Astrophysics Data System (ADS)

    Kim, Jayhyun; Park, Gunyoung; Bae, Cheonho; Yoon, Siwoo; Han, Hyunsun; Yoo, Min-Gu; Park, Young-Seok; Ko, Won-Ha; Juhn, June-Woo; Na, Yong Su; The KSTAR Team

    2017-02-01

    Among various edge localized mode (ELM) crash control methods, only non-axisymmetric magnetic perturbations (NAMPs) yield complete suppression of ELM crashes beyond their mitigation, and thus attract more attention than others. No other devices except KSTAR, DIII-D, and recently EAST have successfully achieved complete suppression with NAMPs. The underlying physics mechanisms of these successful ELM crash suppressions in a non-axisymmetric field environment, however, still remain uncertain. In this work, we investigate the ELM crash suppression characteristics of the KSTAR ELMy H-mode discharges in a controlled multi-spectral field environment, created by both n=2 middle reference and n=1 top/bottom proxy in-vessel control coils. Interestingly, the attempts have produced a set of contradictory findings, one expected (ELM crash suppression enhancement with the addition of n  =  1 to the n  =  2 field at relatively low heating discharges) and another unexpected (ELM crash suppression degradation at relatively high heating discharges) from the earlier findings in DIII-D. This contradiction indicates the dependence of the ELM crash suppression characteristics on the heating level and the associated kink-like plasma responses. Preliminary linear resistive MHD plasma response simulation shows the unexpected suppression performance degradation to be likely caused by the dominance of kink-like plasma responses over the island gap-filling effects.

  15. Numerical modeling of diffusive heat transport across magnetic islands and local stochastic field

    SciTech Connect

    Yu, Q.

    2006-06-15

    The heat diffusion across magnetic islands is studied numerically and compared with analytical results. For a single island, the enhanced radial heat diffusivity, {chi}{sub r}, due to the parallel transport along the field lines is increased over a region of about the island width w. The maximum enhanced heat conductivity at the rational surface is proportional to w{sup 2}({chi}{sub parallel}{chi}{sub perpendicular}){sup 1/2} for sufficiently high values of {chi}{sub parallel}/{chi}{sub perpendicular}, where {chi}{sub parallel}/{chi}{sub perpendicular} is the ratio between the parallel and the perpendicular heat diffusivity. For low ratios of {chi}{sub parallel}/{chi}{sub perpendicular}, however, the maximum value of {chi}{sub r} is proportional to w{sup 4}{chi}{sub parallel}. In a locally stochastic magnetic field, {chi}{sub r} is again proportional to w{sup 4}{chi}{sub parallel} for low {chi}{sub parallel}/{chi}{sub perpendicular}, which is in agreement with the analytical results. With increasing {chi}{sub parallel/}{chi}{sub perpendicular}, {chi}{sub r} is dominated first by the additive effect of individual islands and then by the field ergodicity.

  16. Boosting Local Field Enhancement by on-Chip Nanofocusing and Impedance-Matched Plasmonic Antennas.

    PubMed

    Zenin, Vladimir A; Andryieuski, Andrei; Malureanu, Radu; Radko, Ilya P; Volkov, Valentyn S; Gramotnev, Dmitri K; Lavrinenko, Andrei V; Bozhevolnyi, Sergey I

    2015-12-09

    Strongly confined surface plasmon-polariton modes can be used for efficiently delivering the electromagnetic energy to nanosized volumes by reducing the cross sections of propagating modes far beyond the diffraction limit, that is, by nanofocusing. This process results in significant local-field enhancement that can advantageously be exploited in modern optical nanotechnologies, including signal processing, biochemical sensing, imaging, and spectroscopy. Here, we propose, analyze, and experimentally demonstrate on-chip nanofocusing followed by impedance-matched nanowire antenna excitation in the end-fire geometry at telecom wavelengths. Numerical and experimental evidence of the efficient excitation of dipole and quadrupole (dark) antenna modes are provided, revealing underlying physical mechanisms and analogies with the operation of plane-wave Fabry-Pérot interferometers. The unique combination of efficient nanofocusing and nanoantenna resonant excitation realized in our experiments offers a major boost to the field intensity enhancement up to ∼12000, with the enhanced field being evenly distributed over the gap volume of 30 × 30 × 10 nm(3), and promises thereby a variety of useful on-chip functionalities within sensing, nonlinear spectroscopy and signal processing.

  17. Sensitivity of resistive and Hall measurements to local inhomogeneities: Finite-field, intensity, and area corrections

    NASA Astrophysics Data System (ADS)

    Koon, Daniel W.; Wang, Fei; Petersen, Dirch Hjorth; Hansen, Ole

    2014-10-01

    We derive exact, analytic expressions for the sensitivity of sheet resistance and Hall sheet resistance measurements to local inhomogeneities for the cases of nonzero magnetic fields, strong perturbations, and perturbations over a finite area, extending our earlier results on weak perturbations. We express these sensitivities for conductance tensor components and for other charge transport quantities. Both resistive and Hall sensitivities, for a van der Pauw specimen in a finite magnetic field, are a superposition of the zero-field sensitivities to both sheet resistance and Hall sheet resistance. Strong perturbations produce a nonlinear correction term that depends on the strength of the inhomogeneity. Solution of the specific case of a finite-sized circular inhomogeneity coaxial with a circular specimen suggests a first-order correction for the general case. Our results are confirmed by computer simulations on both a linear four-point probe array on a large circular disc and a van der Pauw square geometry. Furthermore, the results also agree well with Náhlík et al. published experimental results for physical holes in a circular copper foil disc.

  18. Voyager 1 and 2 Observations of the Local Interstellar Magnetic Field and Heliosheath

    NASA Astrophysics Data System (ADS)

    Richardson, J. D.; Burlaga, L. F.; Ness, N. F.

    2015-12-01

    Voyager 1 (V1) observed compressive interstellar turbulence in the local interstellar medium (LISM) with a Kolmogorov spectrum from 2013.36 to 2014.64. Observations of the magnetic field by V1 during 2015 will be presented. Preliminary heliosheath observations by Voyager 2 (V2) indicate that the magnetic field strength (B) began to increase in mid-2011, possibly reaching 0.3 nT during mid-2012. A similar increase in B was observed by V1 shortly before it crossed the heliopause. However, it is possible that the strong magnetic fields observed by V2, if confirmed, were associated with increasing solar activity. The plasma speed was lowest during the middle of 2012, but there was no clear relationship between V and B. The magnetic flux continued to be conserved by V2 during 2011 and 2012, whereas the magnetic flux at V1 decreased in the heliosheath with increasing distance. At least 30 magnetic holes, magnetic humps and other microscale features were observed in the heliosheath by V2 during 2012. Such features were not observed by V1 in the LISM.

  19. Morphogenetic fields in embryogenesis, regeneration, and cancer: Non-local control of complex patterning

    PubMed Central

    Levin, Michael

    2012-01-01

    Establishment of shape during embryonic development, and the maintenance of shape against injury or tumorigenesis, requires constant coordination of cell behaviors toward the patterning needs of the host organism. Molecular cell biology and genetics have made great strides in understanding the mechanisms that regulate cell function. However, generalized rational control of shape is still largely beyond our current capabilities. Significant instructive signals function at long range to provide positional information and other cues to regulate organism-wide systems properties like anatomical polarity and size control. Is complex morphogenesis best understood as the emergent property of local cell interactions, or as the outcome of a computational process that is guided by a physically-encoded map or template of the final goal state? Here I review recent data and molecular mechanisms relevant to morphogenetic fields: large-scale systems of physical properties that have been proposed to store patterning information during embryogenesis, regenerative repair, and cancer suppression that ultimately controls anatomy. Placing special emphasis on the role of endogenous bioelectric signals as an important component of the morphogenetic field, I speculate on novel approaches for the computational modeling and control of these fields with applications to synthetic biology, regenerative medicine, and evolutionary developmental biology. PMID:22542702

  20. Tumor treating fields perturb the localization of septins and cause aberrant mitotic exit.

    PubMed

    Gera, Nidhi; Yang, Aaron; Holtzman, Talia S; Lee, Sze Xian; Wong, Eric T; Swanson, Kenneth D

    2015-01-01

    The anti-tumor effects of chemotherapy and radiation are thought to be mediated by triggering G1/S or G2/M cell cycle checkpoints, while spindle poisons, such as paclitaxel, block metaphase exit by initiating the spindle assembly checkpoint. In contrast, we have found that 150 kilohertz (kHz) alternating electric fields, also known as Tumor Treating Fields (TTFields), perturbed cells at the transition from metaphase to anaphase. Cells exposed to the TTFields during mitosis showed normal progression to this point, but exhibited uncontrolled membrane blebbing that coincided with metaphase exit. The ability of such alternating electric fields to affect cellular physiology is likely to be dependent on their interactions with proteins possessing high dipole moments. The mitotic Septin complex consisting of Septin 2, 6 and 7, possesses a high calculated dipole moment of 2711 Debyes (D) and plays a central role in positioning the cytokinetic cleavage furrow, and governing its contraction during ingression. We showed that during anaphase, TTFields inhibited Septin localization to the anaphase spindle midline and cytokinetic furrow, as well as its association with microtubules during cell attachment and spreading on fibronectin. After aberrant metaphase exit as a consequence of TTFields exposure, cells exhibited aberrant nuclear architecture and signs of cellular stress including an overall decrease in cellular proliferation, followed by apoptosis that was strongly influenced by the p53 mutational status. Thus, TTFields are able to diminish cell proliferation by specifically perturbing key proteins involved in cell division, leading to mitotic catastrophe and subsequent cell death.

  1. Tumor Treating Fields Perturb the Localization of Septins and Cause Aberrant Mitotic Exit

    PubMed Central

    Holtzman, Talia S.; Lee, Sze Xian; Wong, Eric T.; Swanson, Kenneth D.

    2015-01-01

    The anti-tumor effects of chemotherapy and radiation are thought to be mediated by triggering G1/S or G2/M cell cycle checkpoints, while spindle poisons, such as paclitaxel, block metaphase exit by initiating the spindle assembly checkpoint. In contrast, we have found that 150 kilohertz (kHz) alternating electric fields, also known as Tumor Treating Fields (TTFields), perturbed cells at the transition from metaphase to anaphase. Cells exposed to the TTFields during mitosis showed normal progression to this point, but exhibited uncontrolled membrane blebbing that coincided with metaphase exit. The ability of such alternating electric fields to affect cellular physiology is likely to be dependent on their interactions with proteins possessing high dipole moments. The mitotic Septin complex consisting of Septin 2, 6 and 7, possesses a high calculated dipole moment of 2711 Debyes (D) and plays a central role in positioning the cytokinetic cleavage furrow, and governing its contraction during ingression. We showed that during anaphase, TTFields inhibited Septin localization to the anaphase spindle midline and cytokinetic furrow, as well as its association with microtubules during cell attachment and spreading on fibronectin. After aberrant metaphase exit as a consequence of TTFields exposure, cells exhibited aberrant nuclear architecture and signs of cellular stress including an overall decrease in cellular proliferation, followed by apoptosis that was strongly influenced by the p53 mutational status. Thus, TTFields are able to diminish cell proliferation by specifically perturbing key proteins involved in cell division, leading to mitotic catastrophe and subsequent cell death. PMID:26010837

  2. Estimating the correlation between bursty spike trains and local field potentials.

    PubMed

    Li, Zhaohui; Ouyang, Gaoxiang; Yao, Li; Li, Xiaoli

    2014-09-01

    To further understand rhythmic neuronal synchronization, an increasingly useful method is to determine the relationship between the spiking activity of individual neurons and the local field potentials (LFPs) of neural ensembles. Spike field coherence (SFC) is a widely used method for measuring the synchronization between spike trains and LFPs. However, due to the strong dependency of SFC on the burst index, it is not suitable for analyzing the relationship between bursty spike trains and LFPs, particularly in high frequency bands. To address this issue, we developed a method called weighted spike field correlation (WSFC), which uses the first spike in each burst multiple times to estimate the relationship. In the calculation, the number of times that the first spike is used is equal to the spike count per burst. The performance of this method was demonstrated using simulated bursty spike trains and LFPs, which comprised sinusoids with different frequencies, amplitudes, and phases. This method was also used to estimate the correlation between pyramidal cells in the hippocampus and gamma oscillations in rats performing behaviors. Analyses using simulated and real data demonstrated that the WSFC method is a promising measure for estimating the correlation between bursty spike trains and high frequency LFPs.

  3. A multi-frequency sparse hemispherical ultrasound phased array for microbubble-mediated transcranial therapy and simultaneous cavitation mapping.

    PubMed

    Deng, Lulu; O'Reilly, Meaghan A; Jones, Ryan M; An, Ran; Hynynen, Kullervo

    2016-12-21

    Focused ultrasound (FUS) phased arrays show promise for non-invasive brain therapy. However, the majority of them are limited to a single transmit/receive frequency and therefore lack the versatility to expose and monitor the treatment volume. Multi-frequency arrays could offer variable transmit focal sizes under a fixed aperture, and detect different spectral content on receive for imaging purposes. Here, a three-frequency (306, 612, and 1224 kHz) sparse hemispherical ultrasound phased array (31.8 cm aperture; 128 transducer modules) was constructed and evaluated for microbubble-mediated transcranial therapy and simultaneous cavitation mapping. The array is able to perform effective electronic beam steering over a volume spanning (-40, 40) and (-30, 50) mm in the lateral and axial directions, respectively. The focal size at the geometric center is approximately 0.9 (2.1) mm, 1.7 (3.9) mm, and 3.1 (6.5) mm in lateral (axial) pressure full width at half maximum (FWHM) at 1224, 612, and 306 kHz, respectively. The array was also found capable of dual-frequency excitation and simultaneous multi-foci sonication, which enables the future exploration of more complex exposure strategies. Passive acoustic mapping of dilute microbubble clouds demonstrated that the point spread function of the receive array has a lateral (axial) intensity FWHM between 0.8-3.5 mm (1.7-11.7 mm) over a volume spanning (-25, 25) mm in both the lateral and axial directions, depending on the transmit/receive frequency combination and the imaging location. The device enabled both half and second harmonic imaging through the intact skull, which may be useful for improving the contrast-to-tissue ratio or imaging resolution, respectively. Preliminary in vivo experiments demonstrated the system's ability to induce blood-brain barrier opening and simultaneously spatially map microbubble cavitation activity in a rat model. This work presents a tool to investigate optimal strategies for non

  4. A multi-frequency sparse hemispherical ultrasound phased array for microbubble-mediated transcranial therapy and simultaneous cavitation mapping

    NASA Astrophysics Data System (ADS)

    Deng, Lulu; O'Reilly, Meaghan A.; Jones, Ryan M.; An, Ran; Hynynen, Kullervo

    2016-12-01

    Focused ultrasound (FUS) phased arrays show promise for non-invasive brain therapy. However, the majority of them are limited to a single transmit/receive frequency and therefore lack the versatility to expose and monitor the treatment volume. Multi-frequency arrays could offer variable transmit focal sizes under a fixed aperture, and detect different spectral content on receive for imaging purposes. Here, a three-frequency (306, 612, and 1224 kHz) sparse hemispherical ultrasound phased array (31.8 cm aperture; 128 transducer modules) was constructed and evaluated for microbubble-mediated transcranial therapy and simultaneous cavitation mapping. The array is able to perform effective electronic beam steering over a volume spanning (-40, 40) and (-30, 50) mm in the lateral and axial directions, respectively. The focal size at the geometric center is approximately 0.9 (2.1) mm, 1.7 (3.9) mm, and 3.1 (6.5) mm in lateral (axial) pressure full width at half maximum (FWHM) at 1224, 612, and 306 kHz, respectively. The array was also found capable of dual-frequency excitation and simultaneous multi-foci sonication, which enables the future exploration of more complex exposure strategies. Passive acoustic mapping of dilute microbubble clouds demonstrated that the point spread function of the receive array has a lateral (axial) intensity FWHM between 0.8-3.5 mm (1.7-11.7 mm) over a volume spanning (-25, 25) mm in both the lateral and axial directions, depending on the transmit/receive frequency combination and the imaging location. The device enabled both half and second harmonic imaging through the intact skull, which may be useful for improving the contrast-to-tissue ratio or imaging resolution, respectively. Preliminary in vivo experiments demonstrated the system’s ability to induce blood-brain barrier opening and simultaneously spatially map microbubble cavitation activity in a rat model. This work presents a tool to investigate optimal strategies for non

  5. Design of smoothed multi-flared antenna for multi-frequency reception of direct transmission from meteorological satellites

    NASA Astrophysics Data System (ADS)

    Yasodha, Polisetti; Jayaraman, Achuthan; Kesarkar, Amit P.; Thawait, Prateek

    2016-07-01

    The direct radiance data assimilation is found to be advantageous for the numerical weather prediction over short and medium range. Therefore reception of satellite radiance in real time is important. Satellite earth station is the preferred choice for direct reception of this data, which is voluminous. High Rate Information being transmitted from these satellites operating in L, S, C and X bands needs to be received. A commercial wide band antenna is not preferred for such application, as it operates uniformly over the entire frequency range in these bands and may create interference over the unwanted frequencies. As the frequencies of interest occupy only a small portion of these bands, it is essential to design a horn antenna, which receives only specified frequencies and filter other frequencies. In this work, we have designed a multi-flare multi-frequency cylindrical horn antenna for reception of direct transmission from meteorological satellites. This earth station antenna tracks selected satellites working over specified frequency ranges, which are 1.694-1.703 GHz, 2.0-2.06 GHz, 4.5-4.6 GHz and 7.8-7.9 GHz in L, S, C and X bands respectively. Cylindrical waveguides for the frequencies, 1.6, 2, 4.5 and 8 GHz are designed and they are joined in the increasing order of radius with suitable conical shapes. The slope of the cones is adjusted experimentally. With this design, the return loss is simulated and found to be better than 20 dB upto 4.5 GHz and later it became poor. To overcome this difficulty, the abrupt transitions at the joints of the conical and cylindrical waveguides are made smoothen by increasing the diameter of one mouth of the cylinder and reducing the other mouth to match with the cylinders corresponding to next higher and lower frequency respectively. As a result, a smooth flared antenna is obtained and the simulated results are satisfactory. A parabolic reflector of 4 m diameter is designed and the smooth multi-flared antenna is kept at the

  6. Multi-frequency polarimetry of the Galactic radio background around 350 MHz. I. A region in Auriga around l = 161 deg, b = 16 deg

    NASA Astrophysics Data System (ADS)

    Haverkorn, M.; Katgert, P.; de Bruyn, A. G.

    2003-06-01

    With the Westerbork Synthesis Radio Telescope (WSRT), multi-frequency polarimetric images were taken of the diffuse radio synchrotron background in a ~ 5 deg times 7 deg region centered on (l,b) = (161 deg ,16 deg ) in the constellation of Auriga. The observations were done simultaneously in 5 frequency bands, from 341 MHz to 375 MHz, and have a resolution of ~ 5.0arcminx5 .0arcmin cosec delta . The polarized intensity P and polarization angle phi show ubiquitous structure on arcminute and degree scales, with polarized brightness temperatures up to about 13 K. On the other hand, no structure at all is observed in total intensity I to an rms limit of 1.3 K, indicating that the structure in the polarized radiation must be due to Faraday rotation and depolarization mostly in the warm component of the nearby Galactic interstellar medium (ISM). Different depolarization processes create structure in polarized intensity P. Beam depolarization creates ``depolarization canals'' of one beam wide, while depth depolarization is thought to be responsible for creating most of the structure on scales larger than a beam width. Rotation measures (RM) can be reliably determined, and are in the range -17 <~ RM <~ 10 rad m-2 with a non-zero average RM0 ~ -3.4 rad m-2. The distribution of RMs on the sky shows both abrupt changes on the scales of the beam and a gradient in the direction of positive Galactic longitude of ~ 1 rad m-2 per degree. The gradient and average RM are consistent with a regular magnetic field of ~ 1 mu G which has a pitch angle of p = -14 deg. There are 13 extragalactic sources in the field for which RMs could be derived, and those have |RM| <~ 13 rad m-2, with an estimated intrinsic source contribution of ~ 3.6 rad m-2. The RMs of the extragalactic sources show a gradient that is about 3 times larger than the gradient in the RMs of the diffuse emission and that is approximately in Galactic latitude. This difference is ascribed to a vastly different effective

  7. Manipulation of local optical properties and structures in molybdenum-disulfide monolayers using electric field-assisted near-field techniques

    PubMed Central

    Nozaki, Junji; Fukumura, Musashi; Aoki, Takaaki; Maniwa, Yutaka; Yomogida, Yohei; Yanagi, Kazuhiro

    2017-01-01

    Remarkable optical properties, such as quantum light emission and large optical nonlinearity, have been observed in peculiar local sites of transition metal dichalcogenide monolayers, and the ability to tune such properties is of great importance for their optoelectronic applications. For that purpose, it is crucial to elucidate and tune their local optical properties simultaneously. Here, we develop an electric field-assisted near-field technique. Using this technique we can clarify and tune the local optical properties simultaneously with a spatial resolution of approximately 100 nm due to the electric field from the cantilever. The photoluminescence at local sites in molybdenum-disulfide (MoS2) monolayers is reversibly modulated, and the inhomogeneity of the charge neutral points and quantum yields is suggested. We successfully etch MoS2 crystals and fabricate nanoribbons using near-field techniques in combination with an electric field. This study creates a way to tune the local optical properties and to freely design the structural shapes of atomic monolayers using near-field optics. PMID:28378804

  8. Millisecond Coupling of Local Field Potentials to Synaptic Currents in the Awake Visual Cortex

    PubMed Central

    Haider, Bilal; Schulz, David P.A.; Häusser, Michael; Carandini, Matteo

    2016-01-01

    Summary The cortical local field potential (LFP) is a common measure of population activity, but its relationship to synaptic activity in individual neurons is not fully established. This relationship has been typically studied during anesthesia and is obscured by shared slow fluctuations. Here, we used patch-clamp recordings in visual cortex of anesthetized and awake mice to measure intracellular activity; we then applied a simple method to reveal its coupling to the simultaneously recorded LFP. LFP predicted membrane potential as accurately as synaptic currents, indicating a major role for synaptic currents in the relationship between cortical LFP and intracellular activity. During anesthesia, cortical LFP predicted excitation far better than inhibition; during wakefulness, it predicted them equally well, and visual stimulation further enhanced predictions of inhibition. These findings reveal a central role for synaptic currents, and especially inhibition, in the relationship between the subthreshold activity of individual neurons and the cortical LFP during wakefulness. PMID:27021173

  9. Decoding gripping force based on local field potentials recorded from subthalamic nucleus in humans.

    PubMed

    Tan, Huiling; Pogosyan, Alek; Ashkan, Keyoumars; Green, Alexander L; Aziz, Tipu; Foltynie, Thomas; Limousin, Patricia; Zrinzo, Ludvic; Hariz, Marwan; Brown, Peter

    2016-11-18

    The basal ganglia are known to be involved in the planning, execution and control of gripping force and movement vigour. Here we aim to define the nature of the basal ganglia control signal for force and to decode gripping force based on local field potential (LFP) activities recorded from the subthalamic nucleus (STN) in patients with deep brain stimulation (DBS) electrodes. We found that STN LFP activities in the gamma (55-90 Hz) and beta (13-30m Hz) bands were most informative about gripping force, and that a first order dynamic linear model with these STN LFP features as inputs can be used to decode the temporal profile of gripping force. Our results enhance the understanding of how the basal ganglia control gripping force, and also suggest that deep brain LFPs could potentially be used to decode movement parameters related to force and movement vigour for the development of advanced human-machine interfaces.

  10. Characteristics of thalamic local field potentials in patients with disorders of consciousness.

    PubMed

    Huang, Yongzhi; He, Jianghong; Green, Alexander L; Aziz, Tipu Z; Stein, John F; Wang, Shouyan

    2015-08-01

    A functioning thalamus is essential for treatment of patients with disorders of consciousness (DOC) using deep brain stimulation (DBS). This work aims to identify the potential biomarkers related to consciousness from the thalamic deep brain local field potentials (LFPs) in DOC patients. The frequency features of central thalamic LFPs were characterized with spectral analysis. The features were further compared to those of LFPs from the ventroposterior lateral nucleus of the thalamus (VPL) in patients with pain. There are several distinct characteristics of thalamic LFPs found in patients with DOC. The most important feature is the oscillation around 10Hz which could be relevant to the existence of residual consciousness, whereas high power below 8Hz seemed to be associated with loss of consciousness. The invasive deep brain recording tool opens a unique way to explore the brain function in consciousness, awareness and alertness and clarify the potential mechanisms of thalamic stimulation in DOC.

  11. Many-body localization in a long range XXZ model with random-field

    NASA Astrophysics Data System (ADS)

    Li, Bo

    2016-12-01

    Many-body localization (MBL) in a long range interaction XXZ model with random field are investigated. Using the exact diagonal method, the MBL phase diagram with different tuning parameters and interaction range is obtained. It is found that the phase diagram of finite size results supplies strong evidence to confirm that the threshold interaction exponent α = 2. The tuning parameter Δ can efficiently change the MBL edge in high energy density stats, thus the system can be controlled to transfer from thermal phase to MBL phase by changing Δ. The energy level statistics data are consistent with result of the MBL phase diagram. However energy level statistics data cannot detect the thermal phase correctly in extreme long range case.

  12. J Cross-Polarization Methods for Localized NMR without Magnetic Field Gradients

    NASA Astrophysics Data System (ADS)

    Kostler, H.; Kimmich, R.

    1993-10-01

    This work predominantly refers to 13C in vivo spectroscopy and has two objectives. First, heteronuclear editing is considered for proton-detected NMR spectroscopy of rare nuclei. The second aspect refers to localized heteronuclear NMR spectroscopy implying the editing option. Both purposes are achieved by employing J cross polarization (or coherent rotating-frame polarization transfer). The spatial selectivity is due to different in-homogeneities of the superimposed double-resonance radiofrequency fields of the J cross-polarization experiment. A 13C surface coil, for instance, was combined with a 1H birdcage resonator, so that J cross polarization is restricted to the region where the Hartmann/Hahn condition is approached. Heteronuclear editing of NMR lines for proton-detected 13C spectroscopy was performed by the aid of a cyclic cross-polarization pathway. Test experiments demonstrating the volume selectivity of the transfer process and the editing efficiency of the cyclic cross-polarization procedure are reported.

  13. Tissue motion tracking at the edges of a radiation treatment field using local optical flow analysis

    NASA Astrophysics Data System (ADS)

    Teo, P. T.; Pistorius, S.

    2014-03-01

    This paper investigates the feasibility and accuracy of tracking the motion of an intruding organ-at-risk (OAR) at the edges of a treatment field using a local optical flow analysis of electronic portal images. An intruding OAR was simulated by modifying the portal images obtained by irradiating a programmable phantom's lung tumour. A rectangular treatment aperture was assumed and the edges of the beam's eye view (BEV) were partitioned into clusters/grids according to the width of the multi-leaf collimators (MLC). The optical flow velocities were calculated and the motion accuracy in these clusters was analysed. A velocity error of 0.4 ± 1.4 mm/s with a linearity of 1.04 for tracking an object intruding at 10mm/s (max) was obtained.

  14. Measuring Instantaneous Frequency of Local Field Potential Oscillations using the Kalman Smoother

    PubMed Central

    Nguyen, David P.; Wilson, Matthew A.; Brown, Emery N.; Barbieri, Riccardo

    2009-01-01

    Rhythmic local field potentials (LFP) arise from coordinated neural activity. Inference of neural function based on the properties of brain rhythms remains a challenging data analysis problem. Algorithms that characterize non-stationary rhythms with high temporal and spectral resolution may be useful for interpreting LFP activity on the timescales in which they are generated. We propose a Kalman smoother based dynamic autoregressive model for tracking the instantaneous frequency (iFreq) and frequency modulation (FM) of noisy and non-stationary sinusoids such as those found in LFP data. We verify the performance of our algorithm using simulated data with broad spectral content, and demonstrate its application using real data recorded from behavioral learning experiments. In analyses of ripple oscillations (100-250 Hz) recorded from the rodent hippocampus, our algorithm identified novel repetitive, short timescale frequency dynamics. Our results suggest that iFreq and FM may be useful measures for the quantification of small timescale LFP dynamics. PMID:19699763

  15. Large developing receptive fields using a distributed and locally reprogrammable address-event receiver.

    PubMed

    Bamford, Simeon A; Murray, Alan F; Willshaw, David J

    2010-02-01

    A distributed and locally reprogrammable address-event receiver has been designed, in which incoming address-events are monitored simultaneously by all synapses, allowing for arbitrarily large axonal fan-out without reducing channel capacity. Synapses can change the address of their presynaptic neuron, allowing the distributed implementation of a biologically realistic learning rule, with both synapse formation and elimination (synaptic rewiring). Probabilistic synapse formation leads to topographic map development, made possible by a cross-chip current-mode calculation of Euclidean distance. As well as synaptic plasticity in rewiring, synapses change weights using a competitive Hebbian learning rule (spike-timing-dependent plasticity). The weight plasticity allows receptive fields to be modified based on spatio-temporal correlations in the inputs, and the rewiring plasticity allows these modifications to become embedded in the network topology.

  16. Sum rules and static local-field corrections of electron liquids in two and three dimensions

    NASA Technical Reports Server (NTRS)

    Iwamoto, N.

    1984-01-01

    The dielectric functions of electron liquids which take into account short-range electron-electron correlations via the static local-field corrections are examined in the light of the frequency-moment sum rules. The formation is given for degenerate as well as classical electron liquids in arbitrary (d) spatial dimensions, which is suitable for comparison between the two- and three-dimensional cases. By using the virial equations of state it is shown that such dielectric functions cannot satisfy the compressibility sum rule and the third-frequency-moment sum rule simultaneously. In the degenerate case, the plasmon, single-pair, and multipair contributions to the sum rules are analyzed, and the reason for this incompatibility is discussed.

  17. Bandgap- and local field-dependent photoactivity of Ag/black phosphorus nanohybrids

    DOE PAGES

    Lei, Wanying; Zhang, Tingting; Liu, Ping; ...

    2016-10-18

    Black phosphorus (BP) is the most exciting post-graphene layered nanomaterial that serendipitously bridges the 2D materials gap between semimetallic graphene and large bandgap transition-metal dichalcogenides in terms of high charge-carrier mobility and tunable direct bandgap, yet research into BP-based solar to chemical energy conversion is still in its infancy. Herein, a novel hybrid photocatalyst with Ag nanoparticles supported on BP nanosheets is prepared using a chemical reduction approach. Spin-polarized density functional theory (DFT) calculations show that Ag nanoparticles are stabilized on BP by covalent bonds at the Ag/BP interface and Ag–Ag interactions. In the visible-light photocatalysis of rhodamine B bymore » Ag/BP plasmonic nanohybrids, a significant rise in photoactivity compared with pristine BP nanosheets is observed either by decreasing BP layer thickness or increasing Ag particle size, with the greatest enhancement being up to ~20-fold. By virtue of finite-difference time domain (FDTD) simulations and photocurrent measurements, we give insights into the enhanced photocatalytic performance of Ag/BP nanohybrids, including the effects of BP layer thickness and Ag particle size. In comparison with BP, Ag/BP nanohybrids present intense local field amplification at the perimeter of Ag NPs, which is increased by either decreasing the BP layer thickness from multiple to few layers or increasing the Ag particle size from 20 to 40 nm. Additionally, when the BP layer thickness is decreased from multiple to few layers, the bandgap becomes favorable to generate more strongly oxidative holes in the proximity of the Ag/BP interface to enhance photoactivity. Our findings illustrate a synergy between locally enhanced electric fields and BP bandgap, in which BP layer thickness and Ag particle size can be independently tuned to enhance photoactivity. Lastly, this study may open a new avenue for further exploiting BP-based plasmonic nanostructures in

  18. Determining the True Polarity and Amplitude of Synaptic Currents Underlying Gamma Oscillations of Local Field Potentials

    PubMed Central

    Makarov, Valeri A.; Herreras, Oscar

    2013-01-01

    Fluctuations in successive waves of oscillatory local field potentials (LFPs) reflect the ongoing processing of neuron populations. However, their amplitude, polarity and synaptic origin are uncertain due to the blending of electric fields produced by multiple converging inputs, and the lack of a baseline in standard AC-coupled recordings. Consequently, the estimation of underlying currents by laminar analysis yields spurious sequences of inward and outward currents. We devised a combined analytical/experimental approach that is suitable to study laminated structures. The approach was essayed on an experimental oscillatory LFP as the Schaffer-CA1 gamma input in anesthetized rats, and it was verified by parallel processing of model LFPs obtained through a realistic CA1 aggregate of compartmental units. This approach requires laminar LFP recordings and the isolation of the oscillatory input from other converging pathways, which was achieved through an independent component analysis. It also allows the spatial and temporal components of pathway-specific LFPs to be separated. While reconstructed Schaffer-specific LFPs still show spurious inward/outward current sequences, these were clearly stratified into distinct subcellular domains. These spatial bands guided the localized delivery of neurotransmitter blockers in experiments. As expected, only Glutamate but not GABA blockers abolished Schaffer LFPs when applied to the active but not passive subcellular domains of pyramidal cells. The known chemical nature of the oscillatory LFP allowed an empirical offset of the temporal component of Schaffer LFPs, such that following reconstruction they yield only sinks or sources at the appropriate sites. In terms of number and polarity, some waves increased and others decreased proportional to the concomitant inputs in native multisynaptic LFPs. Interestingly, the processing also retrieved the initiation time for each wave, which can be used to discriminate afferent from

  19. Bandgap- and local field-dependent photoactivity of Ag/black phosphorus nanohybrids

    SciTech Connect

    Lei, Wanying; Zhang, Tingting; Liu, Ping; Rodriguez, Jose A.; Liu, Gang; Liu, Minghua

    2016-10-18

    Black phosphorus (BP) is the most exciting post-graphene layered nanomaterial that serendipitously bridges the 2D materials gap between semimetallic graphene and large bandgap transition-metal dichalcogenides in terms of high charge-carrier mobility and tunable direct bandgap, yet research into BP-based solar to chemical energy conversion is still in its infancy. Herein, a novel hybrid photocatalyst with Ag nanoparticles supported on BP nanosheets is prepared using a chemical reduction approach. Spin-polarized density functional theory (DFT) calculations show that Ag nanoparticles are stabilized on BP by covalent bonds at the Ag/BP interface and Ag–Ag interactions. In the visible-light photocatalysis of rhodamine B by Ag/BP plasmonic nanohybrids, a significant rise in photoactivity compared with pristine BP nanosheets is observed either by decreasing BP layer thickness or increasing Ag particle size, with the greatest enhancement being up to ~20-fold. By virtue of finite-difference time domain (FDTD) simulations and photocurrent measurements, we give insights into the enhanced photocatalytic performance of Ag/BP nanohybrids, including the effects of BP layer thickness and Ag particle size. In comparison with BP, Ag/BP nanohybrids present intense local field amplification at the perimeter of Ag NPs, which is increased by either decreasing the BP layer thickness from multiple to few layers or increasing the Ag particle size from 20 to 40 nm. Additionally, when the BP layer thickness is decreased from multiple to few layers, the bandgap becomes favorable to generate more strongly oxidative holes in the proximity of the Ag/BP interface to enhance photoactivity. Our findings illustrate a synergy between locally enhanced electric fields and BP bandgap, in which BP layer thickness and Ag particle size can be independently tuned to enhance photoactivity. Lastly, this study may open a new avenue for further exploiting BP-based plasmonic nanostructures in photocatalysis

  20. Determining the true polarity and amplitude of synaptic currents underlying gamma oscillations of local field potentials.

    PubMed

    Martín-Vázquez, Gonzalo; Makarova, Julia; Makarov, Valeri A; Herreras, Oscar

    2013-01-01

    Fluctuations in successive waves of oscillatory local field potentials (LFPs) reflect the ongoing processing of neuron populations. However, their amplitude, polarity and synaptic origin are uncertain due to the blending of electric fields produced by multiple converging inputs, and the lack of a baseline in standard AC-coupled recordings. Consequently, the estimation of underlying currents by laminar analysis yields spurious sequences of inward and outward currents. We devised a combined analytical/experimental approach that is suitable to study laminated structures. The approach was essayed on an experimental oscillatory LFP as the Schaffer-CA1 gamma input in anesthetized rats, and it was verified by parallel processing of model LFPs obtained through a realistic CA1 aggregate of compartmental units. This approach requires laminar LFP recordings and the isolation of the oscillatory input from other converging pathways, which was achieved through an independent component analysis. It also allows the spatial and temporal components of pathway-specific LFPs to be separated. While reconstructed Schaffer-specific LFPs still show spurious inward/outward current sequences, these were clearly stratified into distinct subcellular domains. These spatial bands guided the localized delivery of neurotransmitter blockers in experiments. As expected, only Glutamate but not GABA blockers abolished Schaffer LFPs when applied to the active but not passive subcellular domains of pyramidal cells. The known chemical nature of the oscillatory LFP allowed an empirical offset of the temporal component of Schaffer LFPs, such that following reconstruction they yield only sinks or sources at the appropriate sites. In terms of number and polarity, some waves increased and others decreased proportional to the concomitant inputs in native multisynaptic LFPs. Interestingly, the processing also retrieved the initiation time for each wave, which can be used to discriminate afferent from

  1. Low-dimensional attractor for neural activity from local field potentials in optogenetic mice

    PubMed Central

    Oprisan, Sorinel A.; Lynn, Patrick E.; Tompa, Tamas; Lavin, Antonieta

    2015-01-01

    We used optogenetic mice to investigate possible nonlinear responses of the medial prefrontal cortex (mPFC) local network to light stimuli delivered by a 473 nm laser through a fiber optics. Every 2 s, a brief 10 ms light pulse was applied and the local field potentials (LFPs) were recorded with a 10 kHz sampling rate. The experiment was repeated 100 times and we only retained and analyzed data from six animals that showed stable and repeatable response to optical stimulations. The presence of nonlinearity in our data was checked using the null hypothesis that the data were linearly correlated in the temporal domain, but were random otherwise. For each trail, 100 surrogate data sets were generated and both time reversal asymmetry and false nearest neighbor (FNN) were used as discriminating statistics for the null hypothesis. We found that nonlinearity is present in all LFP data. The first 0.5 s of each 2 s LFP recording were dominated by the transient response of the networks. For each trial, we used the last 1.5 s of steady activity to measure the phase resetting induced by the brief 10 ms light stimulus. After correcting the LFPs for the effect of phase resetting, additional preprocessing was carried out using dendrograms to identify “similar” groups among LFP trials. We found that the steady dynamics of mPFC in response to light stimuli could be reconstructed in a three-dimensional phase space with topologically similar “8”-shaped attractors across different animals. Our results also open the possibility of designing a low-dimensional model for optical stimulation of the mPFC local network. PMID:26483665

  2. Local and transient structural changes in stratum corneum at high electric fields: contribution of Joule heating.

    PubMed

    Pliquett, U; Gallo, S; Hui, S W; Gusbeth, Ch; Neumann, E

    2005-09-01

    Electroporation of skin is accompanied by local heating, such that thermally induced structural changes of the stratum corneum (SC) accompany the field effect. Comparing on the time scale, the local changes in structure, temperature and conductance of the SC, during and after the pulse, it is seen that Joule heating also facilitates the subsequent molecular transport. It is found that the transport of medium-sized, ionic molecules occurs through localized transport regions (LTR). The size of a LTR increases with the pulse length, whereas the density of the LTRs increases with increasing voltage, for instance at U(SC=)80 V, the LTR cover approximately 0.02--1% of the surface area. The state of low resistance within the LTR is long-lived. During high voltage application, the center of the LTR is heated above the phase transition temperature of the SC lipids (70 degrees C) and the heat front propagates outwards. Inside the SC, the pulse causes aggregates of small-sized vesicles. At a higher temperature, the aggregate formation and their disappearance are delayed. Multiple pulses with the applied voltage of U(appl)=80 V induce the formation of long-lasting vesicle aggregates with a diameter of slashed circle=1--30 microm, covering 0.05--0.5% of the total sample area. The electric energy dissipated within the LTR during high voltage application is apparently sufficient to raise the temperature well above the phase transition temperature of the lipids of the SC, accounting for the conformational changes from the multi-lamella to the vesicular structures.

  3. Stimulus selectivity and spatial coherence of gamma components of the local field potential

    PubMed Central

    Jia, Xiaoxuan; Smith, Matthew A.; Kohn, Adam

    2011-01-01

    The gamma frequencies of the local field potential (LFP) provide a physiological correlate for numerous perceptual and cognitive phenomena and have been proposed to play a role in cortical function. Understanding the spatial extent of gamma and its relationship to spiking activity is critical for interpreting this signal and elucidating its function, but previous studies have provided widely disparate views of these properties. We addressed these issues by simultaneously recording LFPs and spiking activity using microelectrode arrays implanted in the primary visual cortex of macaque monkeys. We find that the spatial extent of gamma and its relationship to local spiking activity is stimulus dependent. Small gratings, and those masked with noise, induce a broadband increase in spectral power. This signal is tuned similarly to spiking activity and has limited spatial coherence. Large gratings, on the other hand, induce a gamma rhythm characterized by a distinctive spectral “bump”, which is coherent across widely separated sites. This signal is well tuned, but its stimulus preference is similar across millimeters of cortex. The preference of this global gamma rhythm is sensitive to adaptation, in a manner consistent with it magnifying a bias in the neuronal representation of visual stimuli. Gamma thus arises from two sources that reflect different spatial scales of neural ensemble activity. Our results show that there is not a single, fixed ensemble contributing to gamma and that the selectivity of gamma cannot be used to infer its spatial extent. PMID:21697389

  4. Assessing local instrument reliability and validity: a field-based example from northern Uganda.

    PubMed

    Betancourt, Theresa S; Bass, Judith; Borisova, Ivelina; Neugebauer, Richard; Speelman, Liesbeth; Onyango, Grace; Bolton, Paul

    2009-08-01

    This paper presents an approach for evaluating the reliability and validity of mental health measures in non-Western field settings. We describe this approach using the example of our development of the Acholi psychosocial assessment instrument (APAI), which is designed to assess depression-like (two tam, par and kumu), anxiety-like (ma lwor) and conduct problems (kwo maraco) among war-affected adolescents in northern Uganda. To examine the criterion validity of this measure in the absence of a traditional gold standard, we derived local syndrome terms from qualitative data and used self reports of these syndromes by indigenous people as a reference point for determining caseness. Reliability was examined using standard test-retest and inter-rater methods. Each of the subscale scores for the depression-like syndromes exhibited strong internal reliability ranging from alpha = 0.84-0.87. Internal reliability was good for anxiety (0.70), conduct problems (0.83), and the pro-social attitudes and behaviors (0.70) subscales. Combined inter-rater reliability and test-retest reliability were good for most subscales except for the conduct problem scale and prosocial scales. The pattern of significant mean differences in the corresponding APAI problem scale score between self-reported cases vs. noncases on local syndrome terms was confirmed in the data for all of the three depression-like syndromes, but not for the anxiety-like syndrome ma lwor or the conduct problem kwo maraco.

  5. Generalized local frame transformation theory for Rydberg atoms in external fields

    NASA Astrophysics Data System (ADS)

    Giannakeas, Panagiotis; Robicheaux, Francis; Greene, Chris H.

    2016-05-01

    In this work a rigorous theoretical framework is developed generalizing the local frame transformation theory (GLFT) and it is applied to the photoionization spectra of Rydberg atoms in an external electric field. The resulting development is compared with previous theoretical treatments, including the first version of local frame transformation theory, developed initially by Fano and Harmin. Our revised version of the theory yields non-trivial corrections because we now take into account the full Hilbert space on the energy shell without adopting truncations utilized by the original Fano-Harmin theory. The semi-analytical calculations from GLFT approach are compared with ab initio numerical simulations yielding errors of few tens of MHz whereas the errors in the original Fano-Harmin theory are one or two orders of magnitude larger. Our analysis provides a systematic pathway to precisely describe the corresponding photoabsorption spectra that should be accurate enough to meet modern experimental standards. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award numbers DE-SC0010545 (for PG and CHG) and DE-SC0012193 (for FR).

  6. Approximate light cone effects in a nonrelativistic quantum field theory after a local quench

    NASA Astrophysics Data System (ADS)

    Bertini, Bruno

    2017-02-01

    We study the spreading of correlations after a local quench in a nonrelativistic quantum field theory. We focus on noninteracting nonrelativistic fermions and study the time evolution after two identical systems in their ground states are suddenly joined together with a localized impurity at the junction. We find that, even if the quasiparticles of the system have unbounded dispersion, the correlations show light cone effects. We carry out a detailed study of these effects by developing an accurate asymptotic expansion of the two-point function and determining exactly the density of particles at any time after the quench. In particular, we find that the width of the light cone region is ∝t1 /2 . The structure of correlations, however, does not show a pure light cone form: "superluminal corrections" are much larger than in the bounded-dispersion case. These findings can be explained by inspecting the structure of excitations generated by the initial state. We show that a similar picture also emerges in the presence of a harmonic trapping potential and when more than two systems are suddenly joined at a single point.

  7. Dark-field spectral imaging microscope for localized surface plasmon resonance-based biosensing

    NASA Astrophysics Data System (ADS)

    Yim, Sang-Youp; Park, Jin-Ho; Kim, Min-Gon

    2015-07-01

    Localized surface plasmon resonance (LSPR) of metal nanoparticles makes red-shift of extinction wavelength with an increase in the refractive index at the surface of the metal nanoparticles. Since biomolecules bound to the metal nanoparticle's surface induce refractive index change, biosensing based on LSPR effect can be possible by monitoring scattering or absorption spectrum changes. Generally, however, conventional method detects ensemble averaged LSPR signal of a huge number of metal nanoparticles. Here, we have constructed a dark-field spectral imaging microscope in order to monitor the scattering spectra of individual metal nanoparticles, simultaneously. Gold nanorod (GNR) and aptamer are employed to detect ochratoxin A (OTA) related to a carcinogenic illness. An aptamer-target binding mechanism promotes wavelength shift of extinction spectra due to refractive index change within sensing volume of GNR by structural change of aptamer. A number of GNRs can be identified in a dark-field LSPR image, simultaneously. A typical spectrum of a GNR exhibits red-shift after target binding of molecules and OTA detection is extended to the very low concentration of 1 pM level.

  8. Performance Monitoring Local Field Potentials in the Medial Frontal Cortex of Primates: Anterior Cingulate Cortex

    PubMed Central

    Emeric, Erik E.; Brown, Joshua W.; Leslie, Melanie; Pouget, Pierre; Stuphorn, Veit; Schall, Jeffrey D.

    2009-01-01

    We describe intracranial local field potentials (LFP) recorded in the anterior cingulate cortex (ACC) of macaque monkeys performing a saccade countermanding task. The most prominent feature at ∼70% of sites was greater negative polarity after errors than after rewarded correct trials. This negative polarity was also evoked in unrewarded correct trials. The LFP evoked by the visual target was much less polarized, and the weak presaccadic modulation was insufficient to control the initiation of saccades. When saccades were cancelled, LFP modulation decreased slightly with the magnitude of response conflict that corresponds to the coactivation of gaze-shifting and -holding neurons estimated from the probability of canceling. However, response time adjustments on subsequent trials were not correlated with LFP polarity on individual trials. The results provide clear evidence that error- and feedback-related, but not conflict-related, signals are carried by the LFP in the macaque ACC. Finding performance monitoring field potentials in the ACC of macaque monkeys establishes a bridge between event-related potential and functional brain-imaging studies in humans and neurophysiology studies in non-human primates. PMID:18077665

  9. Local dissipation effects in two-dimensional quantum Josephson junction arrays with a magnetic field

    SciTech Connect

    Polak, T.P.; Kopec, T.K.

    2005-07-01

    We study the quantum phase transitions in two-dimensional arrays of Josephson-couples junctions with short range Josephson couplings (given by the Josephson energy E{sub J}) and the charging energy E{sub C}. We map the problem onto the solvable quantum generalization of the spherical model that improves over the mean-field theory method. The arrays are placed on the top of a two-dimensional electron gas separated by an insulator. We include effects of the local dissipation in the presence of an external magnetic flux f={phi}/{phi}{sub 0} in square lattice for several rational fluxes f=0,(1/2),(1/3),(1/4), and (1/6). We also have examined the T=0 superconducting-insulator phase boundary as a function of a dissipation {alpha}{sub 0} for two different geometry of the lattice: square and triangular. We have found a critical value of the dissipation parameter independent on geometry of the lattice and presence magnetic field.

  10. Directly resolving particles in an electric field: local charge, force, torque, and applications

    NASA Astrophysics Data System (ADS)

    Liu, Qianlong

    2011-11-01

    Prosperetti's seminal Physalis method for fluid flows with suspended particles is extended to electric fields to directly resolve finite-sized particles and to investigate accurately the mutual fluid-particle, particle-particle, and particle-boundary interactions. The method can be used for uncharged/charged dielectrics, uncharged/charged conductors, conductors with specified voltage, and general weak and strong discontinuous interface conditions. These interface conditions can be in terms of field variable, its gradients, and surface integration which has not been addesed by other numerical methods. In addition, for the first time, we rigorously derive the force and torque on the finite-sized particles resulting from the interactions between harmonics. The method, for the first time, directly resolves the particles with accurate local charge distribution, force, and torque on the particles, making many applications in engineering, mechanics, physics, chemistry, and biology possible, such as heterogeneous materials, microfluidics, electrophotography, electric double layer capacitors, and microstructures of nanodispersions. The efficiency of the method is demonstrated with up to one hundred thousand 3D particles, which suggests that the method can be used for many important engineering applications of broad interest. This research is supported by the Department of Energy under funding for an EFRC (the HeteroFoaM Center), grant no. DE-SC0001061.

  11. Vector meson masses from a hidden local symmetry in a constant magnetic field

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Mamiya; Matsuzaki, Shinya

    2016-06-01

    We discuss the magnetic responses of vector meson masses based on the hidden local symmetry (HLS) model in a constant magnetic field, described by the lightest two-flavor system including the pion, rho and omega mesons in the spectrum. The effective masses influenced under the magnetic field are evaluated according to the derivative or chiral expansion established in the HLS model. At the leading order O (p2), the g factor of the charged rho meson is fixed to be 2, implying that the rho meson at this order is treated just like a pointlike spin-1 particle. Beyond the leading order, one finds anomalous magnetic interactions of the charged rho meson, involving the anomalous magnetic moment, which give corrections to the effective mass. It is then suggested that up to O (p4) the charged rho meson tends to become massless. Of interest is that nontrivial magnetic dependence of neutral mesons emerges to give rise to the significant mixing among neutral mesons. Consequently, it leads to the dramatic enhancement of the omega meson mass, which is testable in future lattice simulations. Corrections from terms beyond O (p4) are also addressed.

  12. Global and local perceptual style, field-independence, and central coherence: An attempt at concept validation.

    PubMed Central

    Milne, Elizabeth; Szczerbinski, Marcin

    2009-01-01

    Historically, the concepts of field-independence, closure flexibility, and weak central coherence have been used to denote a locally, rather globally, dominated perceptual style. To date, there has been little attempt to clarify the relationship between these constructs, or to examine the convergent validity of the various tasks purported to measure them. To address this, we administered 14 tasks that have been used to study visual perceptual styles to a group of 90 neuro-typical adults. The data were subjected to exploratory factor analysis. We found evidence for the existence of a narrowly defined weak central coherence (field-independence) factor that received loadings from only a few of the tasks used to operationalise this concept. This factor can most aptly be described as representing the ability to dis-embed a simple stimulus from a more complex array. The results suggest that future studies of perceptual styles should include tasks whose theoretical validity is empirically verified, as such validity cannot be established merely on the basis of a priori task analysis. Moreover, the use of multiple indices is required to capture the latent dimensions of perceptual styles reliably. PMID:20523847

  13. Extreme Local Extrema of Two-Dimensional Discrete Gaussian Free Field

    NASA Astrophysics Data System (ADS)

    Biskup, Marek; Louidor, Oren

    2016-07-01

    We consider the discrete Gaussian Free Field in a square box in {mathbb{Z}^2} of side length N with zero boundary conditions and study the joint law of its properly-centered extreme values ( h) and their scaled spatial positions ( x) in the limit as {N to infty}. Restricting attention to extreme local maxima, i.e., the extreme points that are maximal in an r N -neighborhood thereof, we prove that the associated process tends, whenever {r_N to infty} and {r_N/N to 0}, to a Poisson point process with intensity measure {Z{(dx)}e^{-α h} dh}, where {α:= 2/√{g}} with g: = 2/π and where Z(dx) is a random Borel measure on [0, 1]2. In particular, this yields an integral representation of the law of the absolute maximum, similar to that found in the context of Branching Brownian Motion. We give evidence that the random measure Z is a version of the derivative martingale associated with the continuum Gaussian Free Field.

  14. Spectral properties and localization of an electron in a two-dimensional system with point scatterers in a magnetic field

    NASA Astrophysics Data System (ADS)

    Gredeskul, S. A.; Zusman, M.; Avishai, Y.; Azbel', M. Ya.

    1997-09-01

    Electron spectral properties and localization in a two-dimensional system with point potentials subject to a perpendicular magnetic field are studied. A brief review of the known results concerning electron dynamics in such systems is presented. For a set of periodic point potentials, exact dispersion laws and energy-flux diagram (Hofstadter-type butterfly) are obtained. It is shown that, in the case of one-dimensional disorder, the electron localization in a strong magnetic field is described by the random Harper equation. Energy-flux diagram for the localization length is presented and the fractal structure of the localization length is demonstrated. Near the Landau levels an exact formula for the localization length as a function of energy and disorder is obtained. The corresponding critical exponent is equal to unity which is reminiscent of one-dimensional characteristics.

  15. Locally covariant quantum field theory and the problem of formulating the same physics in all space-times.

    PubMed

    Fewster, Christopher J

    2015-08-06

    The framework of locally covariant quantum field theory is discussed, motivated in part using 'ignorance principles'. It is shown how theories can be represented by suitable functors, so that physical equivalence of theories may be expressed via natural isomorphisms between the corresponding functors. The inhomogeneous scalar field is used to illustrate the ideas. It is argued that there are two reasonable definitions of the local physical content associated with a locally covariant theory; when these coincide, the theory is said to be dynamically local. The status of the dynamical locality condition is reviewed, as are its applications in relation to (i) the foundational question of what it means for a theory to represent the same physics in different space-times and (ii) a no-go result on the existence of natural states.

  16. Statistical thermodynamics of lattice models in zeolites: Implications of local versus global mean field interactions

    NASA Astrophysics Data System (ADS)

    Ayappa, K. G.

    1999-09-01

    The statistical thermodynamics of adsorption in caged zeolites is developed by treating the zeolite as an ensemble of M identical cages or subsystems. Within each cage adsorption is assumed to occur onto a lattice of n identical sites. Expressions for the average occupancy per cage are obtained by minimizing the Helmholtz free energy in the canonical ensemble subject to the constraints of constant M and constant number of adsorbates N. Adsorbate-adsorbate interactions in the Brag-Williams or mean field approximation are treated in two ways. The local mean field approximation (LMFA) is based on the local cage occupancy and the global mean field approximation (GMFA) is based on the average coverage of the ensemble. The GMFA is shown to be equivalent in formulation to treating the zeolite as a collection of interacting single site subsystems. In contrast, the treatment in the LMFA retains the description of the zeolite as an ensemble of identical cages, whose thermodynamic properties are conveniently derived in the grand canonical ensemble. For a z coordinated lattice within the zeolite cage, with ɛaa as the adsorbate-adsorbate interaction parameter, the comparisons for different values of ɛaa*=ɛaaz/2kT, and number of sites per cage, n, illustrate that for -1<ɛaa*<0 and n⩾10, the adsorption isotherms and heats of adsorption predicted with the two approaches are similar. In general, the deviation between the LMFA and GMFA is greater for smaller n and less sensitive to n for ɛaa*>0. We compare the isotherms predicted with the LMFA with previous GMFA predictions [K. G. Ayappa, C. R. Kamala, and T. A. Abinandanan, J. Chem. Phys. 110, 8714 (1999)] (which incorporates both the site volume reduction and a coverage-dependent ɛaa) for xenon and methane in zeolite NaA. In all cases the predicted isotherms are very similar, with the exception of a small steplike feature present in the LMFA for xenon at higher coverages.

  17. Benthic processes and coastal aquaculture: merging models and field data at a local scale

    NASA Astrophysics Data System (ADS)

    Brigolin, Daniele; Rabouille, Christophe; Bombled, Bruno; Colla, Silvia; Pastres, Roberto; Pranovi, Fabio

    2016-04-01

    Shellfish farming is regarded as an organic extractive aquaculture activity. However, the production of faeces and pseudofaeces, in fact, leads to a net transfer of organic matter from the water column to the surface sediment. This process, which is expected to locally affect the sediment biogeochemistry, may also cause relevant changes in coastal areas characterized by a high density of farms. In this paper, we present the result of a study recently carried out in the Gulf of Venice (northern Adriatic sea), combining mathematical modelling and field sampling efforts. The work aimed at using a longline mussel farm as an in-situ test-case for modelling the differences in soft sediments biogeochemical processes along a gradient of organic deposition. We used an existing integrated model, allowing to describe biogeochemical fluxes towards the mussel farm and to predict the extent of the deposition area underneath it. The model framework includes an individual-based population dynamic model of the Mediterranean mussel coupled with a Lagrangian deposition model and a 1D benthic model of early diagenesis. The work was articulated in 3 steps: 1) the integrated model allowed to simulate the downward fluxes of organic matter originated by the farm, and the extent of its deposition area; 2) based on the first model application, two stations were localized, at which sediment cores were collected during a field campaign, carried out in June 2015. Measurements included O2 and pH microprofiling, porosity and micro-porosity, Total Organic Carbon, and pore waters NH4, PO4, SO4, Alkalinity, and Dissolved Inorganic Carbon; 3) two distinct early diagenesis models were set-up, reproducing observed field data in the sampled cores. Observed oxygen microprofiles showed a different behavior underneath the farm with respect to the outside reference station. In particular, a remarkable decrease in the oxygen penetration depth, and an increase in the O2 influx calculated from the

  18. Analysis of rainfall-induced slope instability using a field of local factor of safety

    USGS Publications Warehouse

    Lu, Ning; Şener-Kaya, Başak; Wayllace, Alexandra; Godt, Jonathan W.

    2012-01-01

    Slope-stability analyses are mostly conducted by identifying or assuming a potential failure surface and assessing the factor of safety (FS) of that surface. This approach of assigning a single FS to a potentially unstable slope provides little insight on where the failure initiates or the ultimate geometry and location of a landslide rupture surface. We describe a method to quantify a scalar field of FS based on the concept of the Coulomb stress and the shift in the state of stress toward failure that results from rainfall infiltration. The FS at each point within a hillslope is called the local factor of safety (LFS) and is defined as the ratio of the Coulomb stress at the current state of stress to the Coulomb stress of the potential failure state under the Mohr-Coulomb criterion. Comparative assessment with limit-equilibrium and hybrid finite element limit-equilibrium methods show that the proposed LFS is consistent with these approaches and yields additional insight into the geometry and location of the potential failure surface and how instability may initiate and evolve with changes in pore water conditions. Quantitative assessments applying the new LFS field method to slopes under infiltration conditions demonstrate that the LFS has the potential to overcome several major limitations in the classical FS methodologies such as the shape of the failure surface and the inherent underestimation of slope instability. Comparison with infinite-slope methods, including a recent extension to variably saturated conditions, shows further enhancement in assessing shallow landslide occurrence using the LFS methodology. Although we use only a linear elastic solution for the state of stress with no post-failure analysis that require more sophisticated elastoplastic or other theories, the LFS provides a new means to quantify the potential instability zones in hillslopes under variably saturated conditions using stress-field based methods.

  19. Assessment of outdoor radiofrequency electromagnetic field exposure through hotspot localization using kriging-based sequential sampling.

    PubMed

    Aerts, Sam; Deschrijver, Dirk; Verloock, Leen; Dhaene, Tom; Martens, Luc; Joseph, Wout

    2013-10-01

    In this study, a novel methodology is proposed to create heat maps that accurately pinpoint the outdoor locations with elevated exposure to radiofrequency electromagnetic fields (RF-EMF) in an extensive urban region (or, hotspots), and that would allow local authorities and epidemiologists to efficiently assess the locations and spectral composition of these hotspots, while at the same time developing a global picture of the exposure in the area. Moreover, no prior knowledge about the presence of radiofrequency radiation sources (e.g., base station parameters) is required. After building a surrogate model from the available data using kriging, the proposed method makes use of an iterative sampling strategy that selects new measurement locations at spots which are deemed to contain the most valuable information-inside hotspots or in search of them-based on the prediction uncertainty of the model. The method was tested and validated in an urban subarea of Ghent, Belgium with a size of approximately 1 km2. In total, 600 input and 50 validation measurements were performed using a broadband probe. Five hotspots were discovered and assessed, with maximum total electric-field strengths ranging from 1.3 to 3.1 V/m, satisfying the reference levels issued by the International Commission on Non-Ionizing Radiation Protection for exposure of the general public to RF-EMF. Spectrum analyzer measurements in these hotspots revealed five radiofrequency signals with a relevant contribution to the exposure. The radiofrequency radiation emitted by 900 MHz Global System for Mobile Communications (GSM) base stations was always dominant, with contributions ranging from 45% to 100%. Finally, validation of the subsequent surrogate models shows high prediction accuracy, with the final model featuring an average relative error of less than 2dB (factor 1.26 in electric-field strength), a correlation coefficient of 0.7, and a specificity of 0.96.

  20. Geophysical Summer Field Camp: Answering questions about the subsurface for the local community

    NASA Astrophysics Data System (ADS)

    van Wijk, K.; Batzle, M.; Liberty, L.; Raynolds, R.

    2008-12-01

    Summer Geophysics Field Camp is part of the core requirement for undergraduate Geophysics majors at Boise State University (CSM), as well as at Colorado School of Mines (CSM). We have found it to be most effectively taught when the target of the camp involves answering questions, which impact society. For example, currently the CSM/BSU geophysics summer camp focuses on ground water resources and geothermal potential in the Upper Arkansas River Basin, a part of the Rio Grande Rift system in Chaffee County, Colorado. A prime goal is to train students how to combine diverse sources of information into a unified interpretation: Students examine lithologies and structures on the periphery of the basin. Cross sections are constructed to predict the geophysical signature. Geophysical tools then are used to ascertain the gross structure and examine subsurface conditions in greater detail. These tools include surveying, regional gravity, deep and shallow seismic surveys, magnetics, DC resistivity, Ground Penetrating Radar, electromagnetics, hydrochemistry, and karaoke. While BSU and CSM own a considerable amount of geophysical hardware, our field camps are only possible because of extensive support by corporations and governmental agencies. In addition, the Society of Exploration Geohysics (SEG) Foundation provides financial support, Chaffee County assists with housing costs, and local land owners provide open access. In turn, the field camp results aid the community of Chaffee County in assessing their water resources for long term growth planning, as well as understanding the geothermal potential for hydroelectric power generation. BSU is currently exploring with the SEG Foundation under the Geophysicists Without Borders program to apply this model of combined education and social outreach in the form a geophysics camp for Southeast Asia, where we propose to study geohazards,geoarcheology and groundwater issues.

  1. Anisotropies in TeV Cosmic Rays Related to the Local Interstellar Magnetic Field from the IBEX Ribbon

    NASA Astrophysics Data System (ADS)

    Schwadron, N. A.; Adams, F. C.; Christian, E.; Desiati, P.; Frisch, P.; Funsten, H. O.; Jokipii, J. R.; McComas, D. J.; Moebius, E.; Zank, G. P.

    2015-01-01

    The Interstellar Boundary Explorer (IBEX) observes enhanced Energetic Neutral Atoms (ENAs) emission in the keV energy range from a narrow (~20° wide) "ribbon" in the sky that appears to be centered on the direction of the local interstellar (LIS) magnetic field. The Milagro collaboration, the Asγ collaboration and the IceCube observatory have recently made global maps of cosmic ray fluxes in the TeV energy range, revealing anisotropic structures ordered in part by the local interstellar magnetic field and the interstellar flow. This paper following from a recent publication in Science makes the link between these disparate observations by developing a simple model of the magnetic structure surrounding the heliosphere in the Local Interstellar Medium (LISM) that is consistent with both IBEX ENA fluxes and TeV cosmic ray anisotropies. The model also employs the revised velocity direction of the LIC derived from neutral He observations by IBEX. By modeling the propagation of cosmic rays through this magnetic field structure, we specifically show that (1) the large-scale TeV anisotropy provides a roughly consistent orientation for the local interstellar magnetic field at the center of the IBEX Ribbon and corroborates the ~ 3 μG magnitude of the local interstellar magnetic field derived from IBEX observations of the global heliosphere; (2) and small-scale structures in cosmic rays (over < 30° angular scales) are influenced by the interstellar field interaction with the heliosphere at energies < 10 TeV. Thus, we provide a link between IBEX ENA observations, IBEX neutral observations of interstellar He, and TeV cosmic ray anisotropies, which are strongly influenced by the interactions between the local interstellar magnetic field, the flow of the local interstellar plasma, and the global heliosphere.

  2. Working Close to Home. WIRE-Net's Hire Locally Program. Workforce Development Report to the Field. Field Report Series.

    ERIC Educational Resources Information Center

    Ma, Patricia; Proscio, Tony

    In 1986, three neighborhood development organizations in Cleveland, Ohio, created the Westside Industrial Retention Network (WIRE-Net) to retain manufacturing jobs on the city's West Side. In 1989, WIRE-Net launched its Hire Locally program, which was designed to provide local business with candidates judged to be effective workers and help…

  3. Stress Field in Brazil with Focal Mechanism: Regional and Local Patterns

    NASA Astrophysics Data System (ADS)

    Dias, F.; Assumpcao, M.

    2013-05-01

    The knowledge of stress field is fundamental not only to understand driving forces and plate deformation but also in the study of intraplate seismicity. The stress field in Brazil has been determined mainly using focal mechanisms and a few breakout data and in-situ measurements. However the stress field still is poorly known in Brazil. The focal mechanisms of recent earthquakes (magnitude lower than 5 mb) were studied using waveform modeling. We stacked the record of several teleseismic stations ( delta > 30°) stacked groups of stations separated according to distance and azimuth. Every record was visually inspected and those with a good signal/noise ratio (SNR) were grouped in windows of ten degrees distance and stacked. The teleseismic P-wave of the stacked signals was modeled using the hudson96 program of Herrmann seismology package (Herrmann, 2002) and the consistency of focal mechanism with the first-motion was checked. Some events in central Brazil were recorded by closer stations (~ 1000 km) and the moment tensor was determined with the ISOLA code (Sokos & Zahradnik, 2008). With the focal mechanisms available in literature and those obtained in this work, we were able to identify some patterns: the central region shows a purely compressional pattern (E-W SHmax), which is predicted by regional theoretical models (Richardson & Coblentz, 1996 and the TD0 model of Lithgow & Bertelloni, 2004). Meanwhile in the Amazon we find an indication of SHmax oriented in the SE-NW direction, probably caused by the Caribbean plate interaction (Meijer, 1995). In northern coastal region, the compression rotates following the coastline, which indicates an important local component related to spreading effects at the continental/oceanic transition (Assumpção, 1998) and flexural stresses caused by sedimentary load in Amazon Fan. We determine the focal mechanism of several events in Brazil using different techniques according to the available data. The major difficulty is to

  4. Deep multi-frequency radio imaging in the Lockman Hole - II. The spectral index of submillimetre galaxies

    NASA Astrophysics Data System (ADS)

    Ibar, Edo; Ivison, R. J.; Best, P. N.; Coppin, K.; Pope, A.; Smail, Ian; Dunlop, J. S.

    2010-01-01

    We have employed the Giant Metre-wave Radio Telescope and the Very Large Array to map the Lockman Hole. At 610 and 1400MHz, we reach noise levels of 15 and 6μJybeam-1, respectively, with well-matched resolutions (~5arcsec). At this depth, we obtained reliable detections for about half of the known sub-mm galaxies (SMGs) in the field. For radio-identified SMGs, which are typically at z ~ 2, we measure a mean radio spectral index of α1400610 = -0.75 +/- 0.06 (where Sν ~ να) and standard deviation of 0.29, between approximate rest-frame frequencies of 1.8 and 4.2GHz. The slope of their continuum emission is indistinguishable from that of local star-forming galaxies and suggests that extended optically thin synchrotron emission dominates the radio output of SMGs. Cooling effects by synchrotron emission and Inverse Compton scattering off the cosmic microwave background do not seem to affect their radio spectral energy distributions. For those SMGs judged by Spitzer mid-infrared colours and spectroscopy to host obscured active galactic nuclei (AGN), we find a clear deviation from the rest of the sample - they typically have steeper radio spectral indices, α1400610 <~ -1.0. These findings suggest these mid-IR-/AGN-selected SMGs may have an intrinsically different injection mechanism for relativistic particles, or they might reside in denser environments. This work provides a reliable spectral template for the estimation of far-IR/radio photometric redshifts, and will enable accurate statistical K-corrections for the large samples of SMGs expected with SCUBA-2 and Herschel.

  5. Analysis of fracture patterns and local stress field variations in fractured reservoirs

    NASA Astrophysics Data System (ADS)

    Deckert, Hagen; Drews, Michael; Fremgen, Dominik; Wellmann, J. Florian

    2010-05-01

    independently estimated regional stress tensor is put as a boundary condition into the BE Model. The computed BE model allows to recognize local 3D stress tensor perturbations caused by the larger faults that act as mechanical inhomogeneities. The geometry of the fracture network from field work together with the local stress tensors derived from the 3D BE models allows examining normal and shear stresses on single fractures in different domains of the investigated area. This in turn is used to evaluate, which of the fractures might preferably act as fluid conduits by describing the dilation potential of single fractures. The combination of an improved understanding of the fracture network along with local stress tensors variations from mechanical models will provide a sound evaluation of fluid pathways in fractured reservoirs. In future applications the accurate investigation of large discontinuity pattern in outcrops might be used for a better mathematical definition of fracture networks which could be implemented into numerical simulations of fluid flow.

  6. Spectral distribution of local field potential responses to electrical stimulation of the retina

    NASA Astrophysics Data System (ADS)

    Wong, Yan T.; Halupka, Kerry; Kameneva, Tatiana; Cloherty, Shaun L.; Grayden, David B.; Burkitt, Anthony N.; Meffin, Hamish; Shivdasani, Mohit N.

    2016-06-01

    Objective. Different frequency bands of the local field potential (LFP) have been shown to reflect neuronal activity occurring at varying cortical scales. As such, recordings of the LFP may offer a novel way to test the efficacy of neural prostheses and allow improvement of stimulation strategies via neural feedback. Here we use LFP measurements from visual cortex to characterize neural responses to electrical stimulation of the retina. We aim to show that the LFP is a viable signal that contains sufficient information to optimize the performance of sensory neural prostheses. Approach. Clinically relevant electrode arrays were implanted in the suprachoroidal space of one eye in four felines. LFPs were simultaneously recorded in response to stimulation of individual electrodes using penetrating microelectrode arrays from the visual cortex. The frequency response of each electrode was extracted using multi-taper spectral analysis and the uniqueness of the responses was determined via a linear decoder. Main results. We found that cortical LFPs are reliably modulated by electrical stimulation of the retina and that the responses are spatially localized. We further characterized the spectral distribution of responses, with maximum information being contained in the low and high gamma bands. Finally, we found that LFP responses are unique to a large range of stimulus parameters (∼40) with a maximum conveyable information rate of 6.1 bits. Significance. These results show that the LFP can be used to validate responses to electrical stimulation of the retina and we provide the first steps towards using these responses to provide more efficacious stimulation strategies.

  7. LOCAL INTERSTELLAR MAGNETIC FIELD DETERMINED FROM THE INTERSTELLAR BOUNDARY EXPLORER RIBBON

    SciTech Connect

    Zirnstein, E. J.; Livadiotis, G.; McComas, D. J.; Heerikhuisen, J.; Pogorelov, N. V.; Funsten, H. O.

    2016-02-10

    The solar wind emanating from the Sun interacts with the local interstellar medium (LISM), forming the heliosphere. Hydrogen energetic neutral atoms (ENAs) produced by the solar-interstellar interaction carry important information about plasma properties from the boundaries of the heliosphere, and are currently being measured by NASA's Interstellar Boundary Explorer (IBEX). IBEX observations show the existence of a “ribbon” of intense ENA emission projecting a circle on the celestial sphere that is centered near the local interstellar magnetic field (ISMF) vector. Here we show that the source of the IBEX ribbon as a function of ENA energy outside the heliosphere, uniquely coupled to the draping of the ISMF around the heliopause, can be used to precisely determine the magnitude (2.93 ± 0.08 μG) and direction (227.°28 ± 0.°69, 34.°62 ± 0.°45 in ecliptic longitude and latitude) of the pristine ISMF far (∼1000 AU) from the Sun. We find that the ISMF vector is offset from the ribbon center by ∼8.°3 toward the direction of motion of the heliosphere through the LISM, and their vectors form a plane that is consistent with the direction of deflected interstellar neutral hydrogen, thought to be controlled by the ISMF. Our results yield draped ISMF properties close to that observed by Voyager 1, the only spacecraft to directly measure the ISMF close to the heliosphere, and give predictions of the pristine ISMF that Voyager 1 has yet to sample.

  8. Relationships between spike-free local field potentials and spike timing in human temporal cortex

    PubMed Central

    Zanos, Theodoros P.; Marmarelis, Vasilis Z.; Ojemann, George A.; Fetz, Eberhard E.

    2012-01-01

    Intracortical recordings comprise both fast events, action potentials (APs), and slower events, known as local field potentials (LFPs). Although it is believed that LFPs mostly reflect local synaptic activity, it is unclear which of their signal components are most closely related to synaptic potentials and would therefore be causally related to the occurrence of individual APs. This issue is complicated by the significant contribution from AP waveforms, especially at higher LFP frequencies. In recordings of single-cell activity and LFPs from the human temporal cortex, we computed quantitative, nonlinear, causal dynamic models for the prediction of AP timing from LFPs, at millisecond resolution, before and after removing AP contributions to the LFP. In many cases, the timing of a significant number of single APs could be predicted from spike-free LFPs at different frequencies. Not surprisingly, model performance was superior when spikes were not removed. Cells whose activity was predicted by the spike-free LFP models generally fell into one of two groups: in the first group, neuronal spike activity was associated with specific phases of low LFP frequencies, lower spike activity at high LFP frequencies, and a stronger linear component in the spike-LFP model; in the second group, neuronal spike activity was associated with larger amplitude of high LFP frequencies, less frequent phase locking, and a stronger nonlinear model component. Spike timing in the first group was better predicted by the sign and level of the LFP preceding the spike, whereas spike timing in the second group was better predicted by LFP power during a certain time window before the spike. PMID:22157112

  9. Cascading and local-field effects in non-linear optics revisited: a quantum-field picture based on exchange of photons.

    PubMed

    Bennett, Kochise; Mukamel, Shaul

    2014-01-28

    The semi-classical theory of radiation-matter coupling misses local-field effects that may alter the pulse time-ordering and cascading that leads to the generation of new signals. These are then introduced macroscopically by solving Maxwell's equations. This procedure is convenient and intuitive but ad hoc. We show that both effects emerge naturally by including coupling to quantum modes of the radiation field that are initially in the vacuum state to second order. This approach is systematic and suggests a more general class of corrections that only arise in a QED framework. In the semi-classical theory, which only includes classical field modes, the susceptibility of a collection of N non-interacting molecules is additive and scales as N. Second-order coupling to a vacuum mode generates an effective retarded interaction that leads to cascading and local field effects both of which scale as N(2).

  10. Cascading and local-field effects in non-linear optics revisited: A quantum-field picture based on exchange of photons

    SciTech Connect

    Bennett, Kochise Mukamel, Shaul

    2014-01-28

    The semi-classical theory of radiation-matter coupling misses local-field effects that may alter the pulse time-ordering and cascading that leads to the generation of new signals. These are then introduced macroscopically by solving Maxwell's equations. This procedure is convenient and intuitive but ad hoc. We show that both effects emerge naturally by including coupling to quantum modes of the radiation field that are initially in the vacuum state to second order. This approach is systematic and suggests a more general class of corrections that only arise in a QED framework. In the semi-classical theory, which only includes classical field modes, the susceptibility of a collection of N non-interacting molecules is additive and scales as N. Second-order coupling to a vacuum mode generates an effective retarded interaction that leads to cascading and local field effects both of which scale as N{sup 2}.

  11. A Model of the Medial Superior Olive Explains Spatiotemporal Features of Local Field Potentials

    PubMed Central

    Mc Laughlin, Myles; Verschooten, Eric; Joris, Philip X.; Rinzel, John

    2014-01-01

    Local field potentials are important indicators of in vivo neural activity. Sustained, phase-locked, sound-evoked extracellular fields in the mammalian auditory brainstem, known as the auditory neurophonic, reflect the activity of neurons in the medial superior olive (MSO). We develop a biophysically based model of the neurophonic that accounts for features of in vivo extracellular recordings in the cat auditory brainstem. By making plausible idealizations regarding the spatial symmetry of MSO neurons and the temporal synchrony of their afferent inputs, we reduce the challenging problem of computing extracellular potentials in a 3D volume conductor to a one-dimensional problem. We find that postsynaptic currents in bipolar MSO neuron models generate extracellular voltage responses that strikingly resemble in vivo recordings. Simulations reproduce distinctive spatiotemporal features of the in vivo neurophonic response to monaural pure tones: large oscillations (hundreds of microvolts to millivolts), broad spatial reach (millimeter scale), and a dipole-like spatial profile. We also explain how somatic inhibition and the relative timing of bilateral excitation may shape the spatial profile of the neurophonic. We observe in simulations, and find supporting evidence in in vivo data, that coincident excitatory inputs on both dendrites lead to a drastically reduced spatial reach of the neurophonic. This outcome surprises because coincident inputs are thought to evoke maximal firing rates in MSO neurons, and it reconciles previously puzzling evoked potential results in humans and animals. The success of our model, which has no axon or spike-generating sodium currents, suggests that MSO spikes do not contribute appreciably to the neurophonic. PMID:25164666

  12. MAGIC gamma-ray and multi-frequency observations of flat spectrum radio quasar PKS 1510-089 in early 2012

    NASA Astrophysics Data System (ADS)

    Aleksić, J.; Ansoldi, S.; Antonelli, L. A.; Antoranz, P.; Babic, A.; Bangale, P.; Barres de Almeida, U.; Barrio, J. A.; Becerra González, J.; Bednarek, W.; Bernardini, E.; Biland, A.; Blanch, O.; Bonnefoy, S.; Bonnoli, G.; Borracci, F.; Bretz, T.; Carmona, E.; Carosi, A.; Carreto Fidalgo, D.; Colin, P.; Colombo, E.; Contreras, J. L.; Cortina, J.; Covino, S.; Da Vela, P.; Dazzi, F.; De Angelis, A.; De Caneva, G.; De Lotto, B.; Delgado Mendez, C.; Doert, M.; Domínguez, A.; Dominis Prester, D.; Dorner, D.; Doro, M.; Einecke, S.; Eisenacher, D.; Elsaesser, D.; Farina, E.; Ferenc, D.; Fonseca, M. V.; Font, L.; Frantzen, K.; Fruck, C.; García López, R. J.; Garczarczyk, M.; Garrido Terrats, D.; Gaug, M.; Godinović, N.; González Muñoz, A.; Gozzini, S. R.; Hadasch, D.; Hayashida, M.; Herrera, J.; Herrero, A.; Hildebrand, D.; Hose, J.; Hrupec, D.; Idec, W.; Kadenius, V.; Kellermann, H.; Kodani, K.; Konno, Y.; Krause, J.; Kubo, H.; Kushida, J.; La Barbera, A.; Lelas, D.; Lewandowska, N.; Lindfors, E.; Lombardi, S.; López, M.; López-Coto, R.; López-Oramas, A.; Lorenz, E.; Lozano, I.; Makariev, M.; Mallot, K.; Maneva, G.; Mankuzhiyil, N.; Mannheim, K.; Maraschi, L.; Marcote, B.; Mariotti, M.; Martínez, M.; Mazin, D.; Menzel, U.; Meucci, M.; Miranda, J. M.; Mirzoyan, R.; Moralejo, A.; Munar-Adrover, P.; Nakajima, D.; Niedzwiecki, A.; Nilsson, K.; Nishijima, K.; Noda, K.; Nowak, N.; Orito, R.; Overkemping, A.; Paiano, S.; Palatiello, M.; Paneque, D.; Paoletti, R.; Paredes, J. M.; Paredes-Fortuny, X.; Partini, S.; Persic, M.; Prada, F.; Prada Moroni, P. G.; Prandini, E.; Preziuso, S.; Puljak, I.; Reinthal, R.; Rhode, W.; Ribó, M.; Rico, J.; Rodriguez Garcia, J.; Rügamer, S.; Saggion, A.; Saito, T.; Saito, K.; Satalecka, K.; Scalzotto, V.; Scapin, V.; Schultz, C.; Schweizer, T.; Shore, S. N.; Sillanpää, A.; Sitarek, J.; Snidaric, I.; Sobczynska, D.; Spanier, F.; Stamatescu, V.; Stamerra, A.; Steinbring, T.; Storz, J.; Strzys, M.; Sun, S.; Surić, T.; Takalo, L.; Takami, H.; Tavecchio, F.; Temnikov, P.; Terzić, T.; Tescaro, D.; Teshima, M.; Thaele, J.; Tibolla, O.; Torres, D. F.; Toyama, T.; Treves, A.; Uellenbeck, M.; Vogler, P.; Wagner, R. M.; Zandanel, F.; Zanin, R.; MAGIC Collaboration; Lucarelli, F.; Pittori, C.; Vercellone, S.; Verrecchia, F.; AGILE Collaboration; Buson, S.; D'Ammando, F.; Stawarz, L.; Giroletti, M.; Orienti, M.; Fermi-LAT Collaboration; Mundell, C.; Steele, I.; Zarpudin, B.; Raiteri, C. M.; Villata, M.; Sandrinelli, A.; Lähteenmäki, A.; Tammi, J.; Tornikoski, M.; Hovatta, T.; Readhead, A. C. S.; Max-Moerbeck, W.; Richards, J. L.; Jorstad, S.; Marscher, A.; Gurwell, M. A.; Larionov, V. M.; Blinov, D. A.; Konstantinova, T. S.; Kopatskaya, E. N.; Larionova, L. V.; Larionova, E. G.; Morozova, D. A.; Troitsky, I. S.; Mokrushina, A. A.; Pavlova, Yu. V.; Chen, W. P.; Lin, H. C.; Panwar, N.; Agudo, I.; Casadio, C.; Gómez, J. L.; Molina, S. N.; Kurtanidze, O. M.; Nikolashvili, M. G.; Kurtanidze, S. O.; Chigladze, R. A.; Acosta-Pulido, J. A.; Carnerero, M. I.; Manilla-Robles, A.; Ovcharov, E.; Bozhilov, V.; Metodieva, I.; Aller, M. F.; Aller, H. D.; Fuhrman, L.; Angelakis, E.; Nestoras, I.; Krichbaum, T. P.; Zensus, J. A.; Ungerechts, H.; Sievers, A.

    2014-09-01

    Aims: Amongst more than fifty blazars detected in very high energy (VHE, E> 100 GeV) γ rays, only three belong to the subclass of flat spectrum radio quasars (FSRQs). The detection of FSRQs in the VHE range is challenging, mainly because of their soft spectra in the GeV-TeV regime. MAGIC observed PKS 1510-089 (z = 0.36) starting 2012 February 3 until April 3 during a high activity state in the high energy (HE, E> 100 MeV) γ-ray band observed by AGILE and Fermi. MAGIC observations result in the detection of a source with significance of 6.0 standard deviations (σ). We study the multi-frequency behaviour of the source at the epoch of MAGIC observation, collecting quasi-simultaneous data at radio and optical (GASP-WEBT and F-Gamma collaborations, REM, Steward, Perkins, Liverpool, OVRO, and VLBA telescopes), X-ray (Swift satellite), and HE γ-ray frequencies. Methods: We study the VHE γ-ray emission, together with the multi-frequency light curves, 43 GHz radio maps, and spectral energy distribution (SED) of the source. The quasi-simultaneous multi-frequency SED from the millimetre radio band to VHE γ rays is modelled with a one-zone inverse Compton model. We study two different origins of the seed photons for the inverse Compton scattering, namely the infrared torus and a slow sheath surrounding the jet around the Very Long Baseline Array (VLBA) core. Results: We find that the VHE γ-ray emission detected from PKS 1510-089 in 2012 February-April agrees with the previous VHE observations of the source from 2009 March-April. We find no statistically significant variability during the MAGIC observations on daily, weekly, or monthly time scales, while the other two known VHE FSRQs (3C 279 and PKS 1222+216) have shown daily scale to sub-hour variability. The γ-ray SED combining AGILE, Fermi and MAGIC data joins smoothly and shows no hint of a break. The multi-frequency light curves suggest a common origin for the millimetre radio and HE γ-ray emission, and the HE

  13. A Multi-frequency analysis of dark matter annihilation interpretations of recent anti-particle and γ-ray excesses in cosmic structures

    NASA Astrophysics Data System (ADS)

    Beck, G.; Colafrancesco, S.

    2016-05-01

    The Fermi-LAT observation of a γ-ray excess from the galactic-centre, as well as the PAMELA, AMS, and AMS-2 anti-particle excesses, and the recent indications of a Fermi-LAT γ-ray excess in the Reticulum II dwarf galaxy have all been variously put forward as possible indirect signatures of supersymmetric neutralino dark matter. These are of particular interest as the neutralino annihilation models which fit these observations must have observable consequences across the frequency spectrum, from radio to γ-ray emission. Moreover, since dark matter is expected to be a major constituent of cosmic structure, these multi-frequency consequences should be common to such structures across the mass spectrum, from dwarf galaxies to galaxy clusters. Thus, in this work we make predictions for the multi-frequency spectra of three well-known sources dominated by dark matter on cluster, galaxy and dwarf galaxy scales, e.g. the Coma cluster, the galaxy M81, and the Draco dwarf galaxy, using models favoured by dark matter interpretations of the aforementioned observations. We pay special attention to the consequences for these models when their cross-sections are renormalised to reproduce the recent γ-ray excess observed in the Reticulum II dwarf galaxy, as well as using cross-sections from the Fermi-LAT dwarf galaxy limits, which throw a dark matter interpretation of this excess into doubt. We find that the multi-frequency data of Coma and Draco are in conflict with the dark matter interpretation of the AMS, PAMELA and Fermi positron excess. Additionally, models derived from Fermi-LAT galactic centre observations, and AMS-2 re-analysis, present similar but less extensive conflicts. Using the sensitivity projections for the Square Kilometre Array, the Cherenkov Telescope Array, as well as the ASTROGAM and ASTRO-H satellites, we determine the detection prospects for a subset of neutralino models that remain consistent with Planck cosmological constraints. Although the SKA has

  14. Localized states in an unbounded neural field equation with smooth firing rate function: a multi-parameter analysis.

    PubMed

    Faye, Grégory; Rankin, James; Chossat, Pascal

    2013-05-01

    The existence of spatially localized solutions in neural networks is an important topic in neuroscience as these solutions are considered to characterize working (short-term) memory. We work with an unbounded neural network represented by the neural field equation with smooth firing rate function and a wizard hat spatial connectivity. Noting that stationary solutions of our neural field equation are equivalent to homoclinic orbits in a related fourth order ordinary differential equation, we apply normal form theory for a reversible Hopf bifurcation to prove the existence of localized solutions; further, we present results concerning their stability. Numerical continuation is used to compute branches of localized solution that exhibit snaking-type behaviour. We describe in terms of three parameters the exact regions for which localized solutions persist.

  15. Field emission properties and strong localization effect in conduction mechanism of nanostructured perovskite LaNiO3

    NASA Astrophysics Data System (ADS)

    Kamble, Ramesh B.; Tanty, Narendra; Patra, Ananya; Prasad, V.

    2016-08-01

    We report the potential field emission of highly conducting metallic perovskite lanthanum nickelate (LaNiO3) from the nanostructured pyramidal and whisker shaped tips as electron emitters. Nano particles of lanthanum nickelate (LNO) were prepared by sol-gel route. Structural and morphological studies have been carried out. Field emission of LNO exhibited high emission current density, J = 3.37 mA/cm2 at a low threshold electric field, Eth = 16.91 V/μm, obeying Fowler-Nordheim tunneling. The DC electrical resistivity exhibited upturn at 11.6 K indicating localization of electron at low temperature. Magnetoresistance measurement at different temperatures confirmed strong localization in nanostructured LNO obeying Anderson localization effect at low temperature.

  16. U(1) gauge field localization on a Bloch brane with Chumbes-Holf da Silva-Hott mechanism

    NASA Astrophysics Data System (ADS)

    Zhao, Zhen-Hua; Liu, Yu-Xiao; Zhong, Yuan

    2014-08-01

    We follow the Chumbes-Holf da Silva-Hott mechanism to study the (quasi)localization of the U(1) gauge field on the Bloch brane. The localization and resonances of the U(1) gauge field are discussed for four kinds of Bloch brane solutions: the original and generalized Bloch brane solutions, as well as the degenerate Bloch brane solutions I and II. With the Chumbes-Holf da Silva-Hott mechanism, we find that the mass spectrum of the gauge field Kaluza-Klein modes is continuous and there is no tachyonic mode. The zero mode is localized on all the branes and there are resonant Kaluza-Klein modes on the degenerate Bloch branes.

  17. Continuous Force Decoding from Local Field Potentials of the Primary Motor Cortex in Freely Moving Rats

    PubMed Central

    Khorasani, Abed; Heydari Beni, Nargess; Shalchyan, Vahid; Daliri, Mohammad Reza

    2016-01-01

    Local field potential (LFP) signals recorded by intracortical microelectrodes implanted in primary motor cortex can be used as a high informative input for decoding of motor functions. Recent studies show that different kinematic parameters such as position and velocity can be inferred from multiple LFP signals as precisely as spiking activities, however, continuous decoding of the force magnitude from the LFP signals in freely moving animals has remained an open problem. Here, we trained three rats to press a force sensor for getting a drop of water as a reward. A 16-channel micro-wire array was implanted in the primary motor cortex of each trained rat, and obtained LFP signals were used for decoding of the continuous values recorded by the force sensor. Average coefficient of correlation and the coefficient of determination between decoded and actual force signals were r = 0.66 and R2 = 0.42, respectively. We found that LFP signal on gamma frequency bands (30–120 Hz) had the most contribution in the trained decoding model. This study suggests the feasibility of using low number of LFP channels for the continuous force decoding in freely moving animals resembling BMI systems in real life applications. PMID:27767063

  18. Selective excitation for spectral editing and assignment in separated local field experiments of oriented membrane proteins

    NASA Astrophysics Data System (ADS)

    Koroloff, Sophie N.; Nevzorov, Alexander A.

    2017-01-01

    Spectroscopic assignment of NMR spectra for oriented uniformly labeled membrane proteins embedded in their native-like bilayer environment is essential for their structure determination. However, sequence-specific assignment in oriented-sample (OS) NMR is often complicated by insufficient resolution and spectral crowding. Therefore, the assignment process is usually done by a laborious and expensive "shotgun" method involving multiple selective labeling of amino acid residues. Presented here is a strategy to overcome poor spectral resolution in crowded regions of 2D spectra by selecting resolved "seed" residues via soft Gaussian pulses inserted into spin-exchange separated local-field experiments. The Gaussian pulse places the selected polarization along the z-axis while dephasing the other signals before the evolution of the 1H-15N dipolar couplings. The transfer of magnetization is accomplished via mismatched Hartmann-Hahn conditions to the nearest-neighbor peaks via the proton bath. By optimizing the length and amplitude of the Gaussian pulse, one can also achieve a phase inversion of the closest peaks, thus providing an additional phase contrast. From the superposition of the selective spin-exchanged SAMPI4 onto the fully excited SAMPI4 spectrum, the 15N sites that are directly adjacent to the selectively excited residues can be easily identified, thereby providing a straightforward method for initiating the assignment process in oriented membrane proteins.

  19. Filaments from the galaxy distribution and from the velocity field in the local universe

    NASA Astrophysics Data System (ADS)

    Libeskind, Noam I.; Tempel, Elmo; Hoffman, Yehuda; Tully, R. Brent; Courtois, Hélène

    2015-10-01

    The cosmic web that characterizes the large-scale structure of the Universe can be quantified by a variety of methods. For example, large redshift surveys can be used in combination with point process algorithms to extract long curvilinear filaments in the galaxy distribution. Alternatively, given a full 3D reconstruction of the velocity field, kinematic techniques can be used to decompose the web into voids, sheets, filaments and knots. In this Letter, we look at how two such algorithms - the Bisous model and the velocity shear web - compare with each other in the local Universe (within 100 Mpc), finding good agreement. This is both remarkable and comforting, given that the two methods are radically different in ideology and applied to completely independent and different data sets. Unsurprisingly, the methods are in better agreement when applied to unbiased and complete data sets, like cosmological simulations, than when applied to observational samples. We conclude that more observational data is needed to improve on these methods, but that both methods are most likely properly tracing the underlying distribution of matter in the Universe.

  20. Attention Influences Single Unit and Local Field Potential Response Latencies in Visual Cortical Area V4

    PubMed Central

    Sundberg, Kristy A.; Mitchell, Jude F.; Gawne, Timothy J.

    2012-01-01

    Many previous studies have demonstrated that changes in selective attention can alter the response magnitude of visual cortical neurons, but there has been little evidence for attention affecting response latency. Small latency differences, though hard to detect, can potentially be of functional importance, and may also give insight into the mechanisms of neuronal computation. We therefore reexamined the effect of attention on the response latency of both single units and the local field potential (LFP) in primate visual cortical area V4. We find that attention does produce small (1–2 ms) but significant reductions in the latency of both the spiking and LFP responses. Though attention, like contrast elevation, reduces response latencies, we find that the two have different effects on the magnitude of the LFP. Contrast elevations increase and attention decreases the magnitude of the initial deflection of the stimulus-evoked LFP. Both contrast elevation and attention increase the magnitude of the spiking response. We speculate that latencies may be reduced at higher contrast because stronger stimulus inputs drive neurons more rapidly to spiking threshold, while attention may reduce latencies by placing neurons in a more depolarized state closer to threshold before stimulus onset. PMID:23136440

  1. Decoding spoken words using local field potentials recorded from the cortical surface

    NASA Astrophysics Data System (ADS)

    Kellis, Spencer; Miller, Kai; Thomson, Kyle; Brown, Richard; House, Paul; Greger, Bradley

    2010-10-01

    Pathological conditions such as amyotrophic lateral sclerosis or damage to the brainstem can leave patients severely paralyzed but fully aware, in a condition known as 'locked-in syndrome'. Communication in this state is often reduced to selecting individual letters or words by arduous residual movements. More intuitive and rapid communication may be restored by directly interfacing with language areas of the cerebral cortex. We used a grid of closely spaced, nonpenetrating micro-electrodes to record local field potentials (LFPs) from the surface of face motor cortex and Wernicke's area. From these LFPs we were successful in classifying a small set of words on a trial-by-trial basis at levels well above chance. We found that the pattern of electrodes with the highest accuracy changed for each word, which supports the idea that closely spaced micro-electrodes are capable of capturing neural signals from independent neural processing assemblies. These results further support using cortical surface potentials (electrocorticography) in brain-computer interfaces. These results also show that LFPs recorded from the cortical surface (micro-electrocorticography) of language areas can be used to classify speech-related cortical rhythms and potentially restore communication to locked-in patients.

  2. Using human extra-cortical local field potentials to control a switch

    NASA Astrophysics Data System (ADS)

    Kennedy, Philip; Andreasen, Dinal; Ehirim, Princewill; King, Brandon; Kirby, Todd; Mao, Hui; Moore, Melody

    2004-06-01

    Individuals with profound paralysis and mutism require a communication channel. Traditional assistive technology devices eventually fail, especially in the case of amyotrophic lateral sclerosis (ALS) subjects who gradually become totally locked-in. A direct brain-to-computer interface that provides switch functions can provide a direct communication channel to the external world. Electroencephalographic (EEG) signals recorded from scalp electrodes are significantly degraded due to skull and scalp attenuation and ambient noise. The present system using conductive skull screws allows more reliable access to cortical local field potentials (LFPs) without entering the brain itself. We describe an almost locked-in human subject with ALS who activated a switch using online time domain detection techniques. Frequency domain analysis of his LFP activity demonstrates this to be an alternative method of detecting switch activation intentions. With this brain communicator system it is reasonable to expect that locked-in, but cognitively intact, humans will always be able to communicate. Financial disclosure. Authors PK and DA may derive some financial gain from the sale of this device. A patent has been applied under US and international law: 10/675,703.

  3. Decoding gripping force based on local field potentials recorded from subthalamic nucleus in humans

    PubMed Central

    Tan, Huiling; Pogosyan, Alek; Ashkan, Keyoumars; Green, Alexander L; Aziz, Tipu; Foltynie, Thomas; Limousin, Patricia; Zrinzo, Ludvic; Hariz, Marwan; Brown, Peter

    2016-01-01

    The basal ganglia are known to be involved in the planning, execution and control of gripping force and movement vigour. Here we aim to define the nature of the basal ganglia control signal for force and to decode gripping force based on local field potential (LFP) activities recorded from the subthalamic nucleus (STN) in patients with deep brain stimulation (DBS) electrodes. We found that STN LFP activities in the gamma (55–90 Hz) and beta (13–30m Hz) bands were most informative about gripping force, and that a first order dynamic linear model with these STN LFP features as inputs can be used to decode the temporal profile of gripping force. Our results enhance the understanding of how the basal ganglia control gripping force, and also suggest that deep brain LFPs could potentially be used to decode movement parameters related to force and movement vigour for the development of advanced human-machine interfaces. DOI: http://dx.doi.org/10.7554/eLife.19089.001 PMID:27855780

  4. The utility of multichannel local field potentials for brain-machine interfaces

    NASA Astrophysics Data System (ADS)

    Hwang, Eun Jung; Andersen, Richard A.

    2013-08-01

    Objective. Local field potentials (LFPs) that carry information about the subject's motor intention have the potential to serve as a complement or alternative to spike signals for brain-machine interfaces (BMIs). The goal of this study is to assess the utility of LFPs for BMIs by characterizing the largely unknown information coding properties of multichannel LFPs. Approach. Two monkeys were implanted, each with a 16-channel electrode array, in the parietal reach region where both LFPs and spikes are known to encode the subject's intended reach target. We examined how multichannel LFPs recorded during a reach task jointly carry reach target information, and compared the LFP performance to simultaneously recorded multichannel spikes. Main Results. LFPs yielded a higher number of channels that were informative about reach targets than spikes. Single channel LFPs provided more accurate target information than single channel spikes. However, LFPs showed significantly larger signal and noise correlations across channels than spikes. Reach target decoders performed worse when using multichannel LFPs than multichannel spikes. The underperformance of multichannel LFPs was mostly due to their larger noise correlation because noise de-correlated multichannel LFPs produced a decoding accuracy comparable to multichannel spikes. Despite the high noise correlation, decoders using LFPs in addition to spikes outperformed decoders using only spikes. Significance. These results demonstrate that multichannel LFPs could effectively complement spikes for BMI applications by yielding more informative channels. The utility of multichannel LFPs may be further augmented if their high noise correlation can be taken into account by decoders.

  5. Out Flow in a Virtual Mtr Station Using a Local View Floor Field Model

    NASA Astrophysics Data System (ADS)

    Leng, Biao; Wang, Jianyuan; Zhao, Xiaoxi; Fang, Jun; Xiong, Zhang

    2013-06-01

    The floor field (FF) model, up until now, has been the most widely used simulation in pedestrian flow dynamics for simple based scenarios. This paper presents an improvement on and upon the local view FF model by simulating pedestrian flow in more complex scenarios with typical goals and obstacles that may block or assist the sight of the pedestrian. In addition this model will also provide a detailed analysis entailing the simulation of multi-goal selections. This involves the visibility information on each cell being set, and a dynamic priority list of goals for every pedestrian being updated as he/she moves. The pedestrians select the convenient goal according to the priority of goals, the distances to the candidate goals and the degree of congestion. To aid in the theory of this and to make a better understanding of reality, a simulation scenario is conducted on a virtual MTR station, where parameter settings are discussed and some regular phenomena helpful to the designers of stations is put forward.

  6. Nociceptive Local Field Potentials Recorded from the Human Insula Are Not Specific for Nociception

    PubMed Central

    Liberati, Giulia; Klöcker, Anne; Safronova, Marta M.; Ferrão Santos, Susana; Ribeiro Vaz, Jose-Geraldo; Raftopoulos, Christian; Mouraux, André

    2016-01-01

    The insula, particularly its posterior portion, is often regarded as a primary cortex for pain. However, this interpretation is largely based on reverse inference, and a specific involvement of the insula in pain has never been demonstrated. Taking advantage of the high spatiotemporal resolution of direct intracerebral recordings, we investigated whether the human insula exhibits local field potentials (LFPs) specific for pain. Forty-seven insular sites were investigated. Participants received brief stimuli belonging to four different modalities (nociceptive, vibrotactile, auditory, and visual). Both nociceptive stimuli and non-nociceptive vibrotactile, auditory, and visual stimuli elicited consistent LFPs in the posterior and anterior insula, with matching spatial distributions. Furthermore, a blind source separation procedure showed that nociceptive LFPs are largely explained by multimodal neural activity also contributing to non-nociceptive LFPs. By revealing that LFPs elicited by nociceptive stimuli reflect activity unrelated to nociception and pain, our results confute the widespread assumption that these brain responses are a signature for pain perception and its modulation. PMID:26734726

  7. Oscillatory pallidal local field potential activity inversely correlates with limb dyskinesias in Parkinson's disease.

    PubMed

    Silberstein, Paul; Oliviero, Antonio; Di Lazzaro, Vincenzo; Insola, Angelo; Mazzone, Paolo; Brown, Peter

    2005-08-01

    Levodopa induced dyskinesias (LIDs) are poorly understood and yet are a major cause of disability in Parkinson's disease (PD). The activity of neurons in the basal ganglia of patients with PD tends to be strongly synchronized at frequencies under 30 Hz, leading to oscillatory local field potentials (LFPs). As dopaminergic therapy acutely suppresses this synchronization, we investigated whether this suppression may contribute to LIDs. Accordingly, we sought an inverse correlation between oscillatory synchronization and dyskinesia activity across time. To this end, we recorded pallidal LFPs in two Parkinsonian subjects exhibiting LIDs following surgery for deep brain stimulation. We correlated LFP power with simultaneously recorded EMG from the dyskinetic contralateral upper limb. We found highly significant inverse correlations between the oscillatory LFP activity under 30 Hz and dyskinetic EMG (maximum r = -0.65, P < 0.001 and r = -0.33, P < 0.001 for activities over 13-30 Hz in each subject). The inverse relationship between oscillatory pallidal LFP activity and dyskinetic EMG was maintained over time periods of a few seconds and was focal. This observation links the suppression of oscillatory synchronization in the pallidum with dyskinetic muscle activity in PD.

  8. A priori complete active space self consistent field localized orbitals: an application on linear polyenes

    NASA Astrophysics Data System (ADS)

    Angeli, Celestino; Sparta, Manuel; Cimiraglia, Renzo

    2006-03-01

    A recently proposed a priori localization technique is used to exploit the possibility to reduce the number of active orbitals in a Complete Active Space Self Consistent Field calculation. The work relies on the fact that the new approach allows a strict control on the nature of the active orbitals and therefore makes it possible to include in the active space only the relevant orbitals. The idea is tested on the calculation of the energy barrier for rigid rotation of linear polyenes. In order to obtain a relevant set of data, a number of possible rotations around double bonds have been considered in the ethylene, butadiene, hexatriene, octatetraene, decapentaene, dodecahexaene molecules. The possibility to reduce the dimension of the active space has been investigated, considering for each possible rotation different active spaces ranging from the minimal dimension of 2 electrons in 2 π orbitals to the π-complete space. The results show that the rigid isomerization in the polyene molecules can be described with a negligible loss in accuracy with active spaces no larger than ten orbitals and ten electrons. In the special case of the rotation around the terminal double bond, the space can be further reduced to six orbitals and six electrons with a large decrease of the computational cost. An interesting summation rule has been found and verified for the stabilization of the energy barriers as a function of the dimension of the conjugated lateral chains and of the dimension of the active space.

  9. Computational Modeling of Single Neuron Extracellular Electric Potentials and Network Local Field Potentials using LFPsim

    PubMed Central

    Parasuram, Harilal; Nair, Bipin; D'Angelo, Egidio; Hines, Michael; Naldi, Giovanni; Diwakar, Shyam

    2016-01-01

    Local Field Potentials (LFPs) are population signals generated by complex spatiotemporal interaction of current sources and dipoles. Mathematical computations of LFPs allow the study of circuit functions and dysfunctions via simulations. This paper introduces LFPsim, a NEURON-based tool for computing population LFP activity and single neuron extracellular potentials. LFPsim was developed to be used on existing cable compartmental neuron and network models. Point source, line source, and RC based filter approximations can be used to compute extracellular activity. As a demonstration of efficient implementation, we showcase LFPs from mathematical models of electrotonically compact cerebellum granule neurons and morphologically complex neurons of the neocortical column. LFPsim reproduced neocortical LFP at 8, 32, and 56 Hz via current injection, in vitro post-synaptic N2a, N2b waves and in vivo T-C waves in cerebellum granular layer. LFPsim also includes a simulation of multi-electrode array of LFPs in network populations to aid computational inference between biophysical activity in neural networks and corresponding multi-unit activity resulting in extracellular and evoked LFP signals. PMID:27445781

  10. Auxiliary field quantum Monte Carlo with a localized basis--applications to atoms and molecules

    NASA Astrophysics Data System (ADS)

    Al-Saidi, Wissam A.; Zhang, Shiwei; Krakauer, Henry

    2006-03-01

    We extended the recently introduced phaseless auxiliary field quantum Monte Carlo approach [1] to any single-particle basis, and applied it to study atoms and molecules using localized Gaussian basis. This method maps the interacting many-body problem into a linear combination of non-interacting problems using a complex Hubbard-Stratonovich transformation, and controls the phase/sign problem using a trial wave function. It employs a random walk approach in Slater determinant space to project the many-body ground state of the system. The computational cost scales as a low power of system size. In all of the presented results the trial wave function was from a Hartree-Fock calculation. The obtained total energies of the atoms and molecules agree to within a few milli Hartrees with the exact value from full configuration interaction or density matrix renormalization group. The results are comparable in accuracy to those of CCSD(T) for equilibrium geometries but are superior for bond breaking. [1] S. Zhang and H. Krakauer, Phys. Rev. Lett. 90, 136401 (2003).

  11. Reduced local field potential power in the medial prefrontal cortex by noxious stimuli.

    PubMed

    Li, Ai-Ling; Yang, Xiaofei; Chiao, Jung-Chih; Peng, Yuan Bo

    2016-10-01

    Nociceptive signals produced by noxious stimuli at the periphery reach the brain through ascending pathways. These signals are processed by various brain areas and lead to activity changes in those areas. The medial prefrontal cortex (mPFC) is involved in higher cognitive functions and emotional processing. It receives projections from brain areas involved in nociception. In this study, we investigated how nociceptive input from the periphery changes the local field potential (LFP) activity in the mPFC. Three different types of noxious stimuli were applied to the hind paw contralateral to the LFP recording site. They were transcutaneous electrical stimulations, mechanical stimuli and a chemical stimulus (formalin injection). High intensity transcutaneous stimulations (10V to 50V) and noxious mechanical stimulus (pinch) significantly reduced the LFP power during the stimulating period (p<0.05), but not the low intensity subcutaneous stimulations (0.1V to 5V) and other innocuous mechanical stimuli (brush and pressure). More frequency bands were inhibited with increased intensity of transcutaneous electrical stimulation, and almost all frequency bands were inhibited by stimulations at or higher than 30v. Pinch significantly reduced the power for beta band and formalin injection significantly reduced the power of alpha and beta band. Our data demonstrated the noxious stimuli-induced reduction of LFP power in the mPFC, which indicates the active processing of nociceptive information by the mPFC.

  12. Local-field enhancement of optical nonlinearities in the AGZO nano-triangle array

    NASA Astrophysics Data System (ADS)

    Long, Hua; Bao, Lijiao; Wang, Kai; Liu, Shuhui; Wang, Bing

    2016-10-01

    Enhancement of the third order optical nonlinearities in Ga and Al co-doped ZnO (AGZO) nano-triangle array was investigated by performing a Z-scan method with a femtosecond laser (800 nm, 40 fs). The AGZO nano-triangle array was fabricated on silica substrates by nanosphere lithography (NSL) method, showing a surface plasmon resonance (SPR) peak around 3 μm. The two photon absorption (TPA) coefficient and nonlinear refractive index of the AGZO nano-triangle array were determined to be 340 cm/GW and 3.22 × 10-2 cm2/GW under an excitation intensity of 26 GW/cm2. It shows a 3.4-fold enhancement of the nonlinear refraction in the AGZO array with respect to that in the AGZO film, which attributes to the local field enhancement effect. The finite-difference time-domain (FDTD) simulation was in agreement with the experimental results. It indicates that the AGZO nano-triangle arrays have potential applications for nonlinear optical devices like all-optical switching, optical limiting and other types of signal processing.

  13. Deleterious localized stress fields: the effects of boundaries and stiffness tailoring in anisotropic laminated plates

    PubMed Central

    Weaver, P. M.

    2016-01-01

    The safe design of primary load-bearing structures requires accurate prediction of stresses, especially in the vicinity of geometric discontinuities where deleterious three-dimensional stress fields can be induced. Even for thin-walled structures significant through-thickness stresses arise at edges and boundaries, and this is especially precarious for laminates of advanced fibre-reinforced composites because through-thickness stresses are the predominant drivers in delamination failure. Here, we use a higher-order equivalent single-layer model derived from the Hellinger–Reissner mixed variational principle to examine boundary layer effects in laminated plates comprising constant-stiffness and variable-stiffness laminae and deforming statically in cylindrical bending. The results show that zigzag deformations, which arise due to layerwise differences in the transverse shear moduli, drive boundary layers towards clamped edges and are therefore critically important in quantifying localized stress gradients. The relative significance of the boundary layer scales with the degree of layerwise anisotropy and the thickness to characteristic length ratio. Finally, we demonstrate that the phenomenon of alternating positive and negative transverse shearing deformation through the thickness of composite laminates, previously only observed at clamped boundaries, can also occur at other locations as a result of smoothly varying the material properties over the in-plane dimensions of the laminate. PMID:27843401

  14. Computational Modeling of Single Neuron Extracellular Electric Potentials and Network Local Field Potentials using LFPsim.

    PubMed

    Parasuram, Harilal; Nair, Bipin; D'Angelo, Egidio; Hines, Michael; Naldi, Giovanni; Diwakar, Shyam

    2016-01-01

    Local Field Potentials (LFPs) are population signals generated by complex spatiotemporal interaction of current sources and dipoles. Mathematical computations of LFPs allow the study of circuit functions and dysfunctions via simulations. This paper introduces LFPsim, a NEURON-based tool for computing population LFP activity and single neuron extracellular potentials. LFPsim was developed to be used on existing cable compartmental neuron and network models. Point source, line source, and RC based filter approximations can be used to compute extracellular activity. As a demonstration of efficient implementation, we showcase LFPs from mathematical models of electrotonically compact cerebellum granule neurons and morphologically complex neurons of the neocortical column. LFPsim reproduced neocortical LFP at 8, 32, and 56 Hz via current injection, in vitro post-synaptic N2a, N2b waves and in vivo T-C waves in cerebellum granular layer. LFPsim also includes a simulation of multi-electrode array of LFPs in network populations to aid computational inference between biophysical activity in neural networks and corresponding multi-unit activity resulting in extracellular and evoked LFP signals.

  15. Hybrid Scheme for Modeling Local Field Potentials from Point-Neuron Networks.

    PubMed

    Hagen, Espen; Dahmen, David; Stavrinou, Maria L; Lindén, Henrik; Tetzlaff, Tom; van Albada, Sacha J; Grün, Sonja; Diesmann, Markus; Einevoll, Gaute T

    2016-12-01

    With rapidly advancing multi-electrode recording technology, the local field potential (LFP) has again become a popular measure of neuronal activity in both research and clinical applications. Proper understanding of the LFP requires detailed mathematical modeling incorporating the anatomical and electrophysiological features of neurons near the recording electrode, as well as synaptic inputs from the entire network. Here we propose a hybrid modeling scheme combining efficient point-neuron network models with biophysical principles underlying LFP generation by real neurons. The LFP predictions rely on populations of network-equivalent multicompartment neuron models with layer-specific synaptic connectivity, can be used with an arbitrary number of point-neuron network populations, and allows for a full separation of simulated network dynamics and LFPs. We apply the scheme to a full-scale cortical network model for a ∼1 mm(2) patch of primary visual cortex, predict laminar LFPs for different network states, assess the relative LFP contribution from different laminar populations, and investigate effects of input correlations and neuron density on the LFP. The generic nature of the hybrid scheme and its public implementation in hybridLFPy form the basis for LFP predictions from other and larger point-neuron network models, as well as extensions of the current application with additional biological detail.

  16. Subthalamic nucleus local field potential activity helps encode motor effort rather than force in parkinsonism.

    PubMed

    Tan, Huiling; Pogosyan, Alek; Ashkan, Keyoumars; Cheeran, Binith; FitzGerald, James J; Green, Alexander L; Aziz, Tipu; Foltynie, Thomas; Limousin, Patricia; Zrinzo, Ludvic; Brown, Peter

    2015-04-15

    Local field potential (LFP) recordings from patients with deep brain stimulation electrodes in the basal ganglia have suggested that frequency-specific activities correlate with force or effort, but previous studies have not been able to disambiguate the two. Here, we dissociated effort from actual force generated by contrasting the force generation of different fingers while recording LFP activity from the subthalamic nucleus (STN) in patients with Parkinson's disease who had undergone functional surgery. Patients were studied while on their normal dopaminergic medication. We investigated the relationship between frequency-specific oscillatory activity in the STN and voluntary flexion of either the index or little finger at different effort levels. At each tested effort level (10%, 25%, and 40% of the maximal voluntary contraction force of each individual finger), the index finger generated larger force than the little finger. Movement-related suppression of beta-band power in the STN LFP was significantly modulated by effort, but not by which finger was used, suggesting that the beta suppression in the STN LFP during sustained contraction serves as a proxy for effort. The absolute force scaled with beta power suppression, but with the scaling determined by the maximal voluntary contraction force of the motor effector. Our results argue against the hypothesis that the basal ganglia are directly involved in the parameterization of force during movement and support a role of the STN in the control of motor effort to be attributed to a response.

  17. Spatial spread of local field potential is band-pass in the primary visual cortex

    PubMed Central

    Dubey, Agrita

    2016-01-01

    Local field potential (LFP) is a valuable tool in understanding brain function and in brain machine-interfacing applications. However, there is no consensus on the spatial extent of the cortex that contributes to the LFP (its “spatial spread”), with different studies reporting values between a few hundred micrometers and several millimeters. Furthermore, the dependency of the spatial spread on frequency, which could reflect properties of the network architecture and extracellular medium, is not well studied, with theory and models predicting either “all-pass” (frequency-independent) or “low-pass” behavior. Surprisingly, we found the LFP spread to be “band-pass” in the primate primary visual cortex, with the greatest spread in the high-gamma range (60–150 Hz). This was accompanied by an increase in phase coherency across neighboring sites in the same frequency range, consistent with the findings of a recent model that reconciles previous studies by suggesting that spatial spread depends on neuronal correlations. PMID:27489369

  18. System Identification of Local Field Potentials under Deep Brain Stimulation in a Healthy Primate

    PubMed Central

    Pedoto, Gilda; Santaniello, Sabato; Montgomery, Erwin B.; Gale, John T.; Fiengo, Giovanni; Glielmo, Luigi; Sarma, Sridevi V.

    2013-01-01

    High frequency (HF) Deep Brain Stimulation (DBS) in the Sub-Thalamic Nucleus (STN) is a clinically recognized therapy for the treatment of motor disorders in Parkinson Disease (PD). The underlying mechanisms of DBS and how it impacts neighboring nuclei, however, are not yet completely understood. Electrophysiological data has been collected in PD patients and primates to better understand the impact of DBS on STN and the entire Basal Ganglia (BG) motor circuit. We use single unit recordings from Globus Pallidus, both pars interna and externa segments (GPi and GPe) in the BG, in a normal primate before and after DBS to reconstruct Local Field Potentials (LFPs) in the region. We then use system identification techniques to understand how GPe LFP activity and the DBS signal applied to STN influence GPi LFP activity. Our models suggest that when no stimulation is applied, the GPe LFPs have an inhibitory effect on GPi LFPs with a 2-3 ms delay, as is the case for single unit neuronal activity. On the other hand, when DBS is ON the models suggest that stimulation has a dominant effect on GPi LFPs which mask the inhibitory effects of GPe. PMID:21096635

  19. Generation of spatiotemporally correlated spike trains and local field potentials using a multivariate autoregressive process.

    PubMed

    Gutnisky, Diego A; Josić, Kresimir

    2010-05-01

    Experimental advances allowing for the simultaneous recording of activity at multiple sites have significantly increased our understanding of the spatiotemporal patterns in neural activity. The impact of such patterns on neural coding is a fundamental question in neuroscience. The simulation of spike trains with predetermined activity patterns is therefore an important ingredient in the study of potential neural codes. Such artificially generated spike trains could also be used to manipulate cortical neurons in vitro and in vivo. Here, we propose a method to generate spike trains with given mean firing rates and cross-correlations. To capture this statistical structure we generate a point process by thresholding a stochastic process that is continuous in space and discrete in time. This stochastic process is obtained by filtering Gaussian noise through a multivariate autoregressive (AR) model. The parameters of the AR model are obtained by a nonlinear transformation of the point-process correlations to the continuous-process correlations. The proposed method is very efficient and allows for the simulation of large neural populations. It can be optimized to the structure of spatiotemporal correlations and generalized to nonstationary processes and spatiotemporal patterns of local field potentials and spike trains.

  20. Evoked Potentials in Motor Cortical Local Field Potentials Reflect Task Timing and Behavioral Performance

    PubMed Central

    Confais, Joachim; Ponce-Alvarez, Adrián; Diesmann, Markus; Riehle, Alexa

    2010-01-01

    Evoked potentials (EPs) are observed in motor cortical local field potentials (LFPs) during movement execution (movement-related potentials [MRPs]) and in response to relevant visual cues (visual evoked potentials [VEPs]). Motor cortical EPs may be directionally selective, but little is known concerning their relation to other aspects of motor behavior, such as task timing and performance. We recorded LFPs in motor cortex of two monkeys during performance of a precued arm-reaching task. A time cue at the start of each trial signaled delay duration and thereby the pace of the task and the available time for movement preparation. VEPs and MRPs were strongly modulated by the delay duration, VEPs being systematically larger in short-delay trials and MRPs larger in long-delay trials. Despite these systematic modulations related to the task timing, directional selectivity was similar in short and long trials. The behavioral reaction time was positively correlated with MRP size and negatively correlated with VEP size, within sessions. In addition, the behavioral performance improved across sessions, in parallel with a slow decrease in the size of VEPs and MRPs. Our results clearly show the strong influence of the behavioral context and performance on motor cortical population activity during movement preparation and execution. PMID:20884766