The role of remote wind forcing in the subinertial current variability in the central and northern parts of the South Brazil Bight

NASA Astrophysics Data System (ADS)

Dottori, Marcelo; Castro, Belmiro Mendes

2018-05-01

Data analysis of continental shelf currents and coastal sea level, together with the application of a semi-analytical model, are used to estimate the importance of remote wind forcing on the subinertial variability of the current in the central and northern areas of the South Brazil Bight. Results from both the data analysis and from the semi-analytical model are robust in showing subinertial variability that propagates along-shelf leaving the coast to the left in accordance with theoretical studies of Continental Shelf Waves (CSW). Both the subinertial variability observed in along-shelf currents and sea level oscillations present different propagation speeds for the narrow northern part of the SBB ( 6-7 m/s) and the wide central SBB region ( 11 m/s), those estimates being in agreement with the modeled CSW propagation speed. On the inner and middle shelf, observed along-shelf subinertial currents show higher correlation coefficients with the winds located southward and earlier in time than with the local wind at the current meter mooring position and at the time of measurement. The inclusion of the remote (located southwestward) wind forcing improves the prediction of the subinertial currents when compared to the currents forced only by the local wind, since the along-shelf-modeled currents present correlation coefficients with observed along-shelf currents up to 20% higher on the inner and middle shelf when the remote wind is included. For most of the outer shelf, on the other hand, this is not observed since usually, the correlation between the currents and the synoptic winds is not statistically significant.

Wave-Current Interaction in Coastal Inlets and River Mouths

DTIC Science & Technology

2014-09-30

the Astoria Canyon buoy operated by the Coastal Data Information Program ( CDIP , buoy # 46248). Three-dimensional current fields and bathymetry were...bar show considerable differences. The SWAN model uses observations from CDIP buoy # 46248 as boundary condition; three- dimensional current data and

Upstream ionization instability associated with a current-free double layer.

PubMed

Aanesland, A; Charles, C; Lieberman, M A; Boswell, R W

2006-08-18

A low frequency instability has been observed using various electrostatic probes in a low-pressure expanding helicon plasma. The instability is associated with the presence of a current-free double layer (DL). The frequency of the instability increases linearly with the potential drop of the DL, and simultaneous measurements show their coexistence. A theory for an upstream ionization instability has been developed, which shows that electrons accelerated through the DL increase the ionization upstream and are responsible for the observed instability. The theory is in good agreement with the experimental results.

Dynamics of Intense Currents in the Solar Wind

NASA Astrophysics Data System (ADS)

Artemyev, Anton V.; Angelopoulos, Vassilis; Halekas, Jasper S.; Vinogradov, Alexander A.; Vasko, Ivan Y.; Zelenyi, Lev M.

2018-06-01

Transient currents in the solar wind are carried by various magnetic field discontinuities that contribute significantly to the magnetic field fluctuation spectrum. Internal instabilities and dynamics of these discontinuities are believed to be responsible for magnetic field energy dissipation and corresponding charged particle acceleration and heating. Accurate modeling of these phenomena requires detailed investigation of transient current formation and evolution. By examining such evolution using a unique data set compiled from observations of the same solar wind flow by two spacecraft at Earth’s and Mars’s orbits, we show that it consists of several processes: discontinuity thinning (decrease in thickness normalized by the ion inertial length), intensification of currents normalized to the proton thermal current (i.e., the product of proton charge, density, and thermal velocity), and increase in the compressional component of magnetic field variations across discontinuities. The significant proton temperature variation around most observed discontinuities indicates possible proton heating. Plasma velocity jumps across the discontinuities are well correlated with Alfvén velocity changes. We discuss possible explanations of the observed discontinuity evolution. We also compare the observed evolution with predictions of models describing discontinuity formation due to Alfvén wave steepening. Our results show that discontinuity modeling likely requires taking into account both the effects of nonlinear Alfvén wave dynamics and solar wind expansion.

Solar Energetic Particle Transport Near a Heliospheric Current Sheet

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

Battarbee, Markus; Dalla, Silvia; Marsh, Mike S., E-mail: mbattarbee@uclan.ac.uk

2017-02-10

Solar energetic particles (SEPs), a major component of space weather, propagate through the interplanetary medium strongly guided by the interplanetary magnetic field (IMF). In this work, we analyze the implications that a flat Heliospheric Current Sheet (HCS) has on proton propagation from SEP release sites to the Earth. We simulate proton propagation by integrating fully 3D trajectories near an analytically defined flat current sheet, collecting comprehensive statistics into histograms, fluence maps, and virtual observer time profiles within an energy range of 1–800 MeV. We show that protons experience significant current sheet drift to distant longitudes, causing time profiles to exhibitmore » multiple components, which are a potential source of confusing interpretations of observations. We find that variation of the current sheet thickness within a realistic parameter range has little effect on particle propagation. We show that the IMF configuration strongly affects the deceleration of protons. We show that in our model, the presence of a flat equatorial HCS in the inner heliosphere limits the crossing of protons into the opposite hemisphere.« less

Multiple-Station Observation of Frequency Dependence and Polarization Characteristics of ELF/VLF waves generated via Ionospheric Modification

NASA Astrophysics Data System (ADS)

Maxworth, A. S.; Golkowski, M.; Cohen, M.; Moore, R. C.

2014-12-01

Generation of Extremely Low Frequency (ELF) and Very Low Frequency (VLF) signals through ionospheric modification has been practiced for many years. Heating the lower ionosphere with high power HF waves allows for modulation of natural current systems. Our experiments were carried out at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska, USA. In this experiment, the ionosphere was heated with a vertical amplitude modulating signal and the modulation frequency was changed sequentially within an array of 40 frequencies followed by a frequency ramp. The observed magnetic field amplitude and polarization of the generated ELF/VLF signals were analyzed for multiple sites and as a function of modulation frequency. Our three observation sites: Chistochina, Paxson and Paradise are located within 36km (azimuth 47.7°), 50.2km (azimuth -20°) and 99km (azimuth 80.3°) respectively. We show that the peak amplitudes observed as a function of frequency result from vertical resonance in the Earth-ionosphere waveguide and can be used to diagnose the D-region profile. Polarization analysis showed that out of the three sites Paxson shows the highest circularity in the magnetic field polarization, compared to Chistochina and Paradise which show highly linear polarizations. The experimental results were compared with a theoretical simulation model results and it was clear that in both cases, the modulated Hall current dominates the observed signals at Chistochina and Paradise sites and at Paxson there is an equal contribution from Hall and Pedersen currents. The Chistochina site shows the highest magnetic field amplitudes in both experimental and simulation environments. Depending upon the experimental and simulation observations at the three sites, a radiation pattern for the HAARP ionospheric heater can be mapped

Equatorial disc and dawn-dusk currents in the frontside magnetosphere of Jupiter - Pioneer 10 and 11

NASA Technical Reports Server (NTRS)

Jones, D. E.; Thomas, B. T.; Melville, J. G., II

1981-01-01

Observations by Pioneer 10 and 11 show that the strongest azimuthal fields are observed near the dawn meridian (Pioneer 10) while the weakest occur near the noon meridian (Pioneer 11), suggesting a strong local time dependence for the corresponding radial current system. Modeling studies of the radial component of the field observed by both spacecraft suggest that the corresponding azimuthal current system must also be a strong function of local time. Both the azimuthal and the radial field component signatures exhibit sharp dips and reversals, requiring thin radial and azimuthal current systems. There is also a suggestion that these two current systems either are interacting or are due, at least in part, to the same current. It is suggested that a plausible current model consists of the superposition of a thin, local-time-independent azimuthal current system plus the equatorial portion of a tail-like current system that extends into the dayside magnetosphere.

An embedding structure of the cross-tail CSs and its relation to the ion composition according to MAVEN observations in the Martian magnetotai

NASA Astrophysics Data System (ADS)

Grigorenko, E. E.; Shuvalov, S. D.; Malova, H. V.; Zelenyi, L. M.

2017-12-01

The multilayered (embedded) Current Sheets (CS) are often observed in the Earth's magnetotail. Simulations based on quasi-adiabatic dynamics of different ion components showed that the observed embedding structures can be reconstructed by taking into account the net electric currents carried by ions with different masses and, thus, with different gyroradii. The last determines the spatial scales of the corresponding current layers. The embedding can be quantitatively described by the ratio of the magnetic field value at the edges of a thin embedded layer Bext to the value of the magnetic field outside a thick CS, B0. For the Earth's magnetotail it was shown that there is a relation between the Bext/B0 and the relative densities of heavy and light ion components. In the Martian magnetotail the embedding feature is also often observed in the cross-tail CS formed by the draping of the IMF field lines. The analysis of 100 CS crossings by MAVEN spacecraft showed that in the Martian magnetotail the relation between the embedding characteristics and ion composition is similar to the one observed in the Earth's magnetotail and the spatial scales of the embedded layers are defined by the gyroradii of the current carrying ion component.

Long-Term Variability of Jupiter's Magnetodisk and Implications for the Aurora

NASA Astrophysics Data System (ADS)

Vogt, Marissa F.; Bunce, Emma J.; Nichols, Jonathan D.; Clarke, John T.; Kurth, William S.

2017-12-01

Observations of Jupiter's UV auroral emissions collected over several years show that the ionospheric positions of the main emission and the Ganymede footprint can vary by as much as 3° in latitude. One explanation for this shift is a change of Jupiter's current sheet current density, which would alter the amount of field line stretching and displace the ionospheric mapping of field lines from a given radial distance in the magnetosphere. In this study we measure the long-term variability of Jupiter's magnetodisk using Galileo magnetometer data collected from 1996 to 2003. Using the Connerney et al. (1981) current sheet model, we calculate the current sheet density parameter that gives the best fit to the data from each orbit and find that the current density parameter varies by about 15% of its average value during the Galileo era. We investigate possible relationships between the observed current sheet variability and quantities such as Io's plasma torus production rate inferred from volcanic activity and external solar wind conditions extrapolated from data at 1 AU but find only a weak correlation. Finally, we trace Khurana (1997) model field lines to show that the observed changes in Jupiter's current sheet are sufficient to shift the ionospheric footprint of Ganymede and main auroral emission by a few degrees of latitude, consistent with the magnitude of auroral variability observed by Hubble Space Telescope (HST). However, we find that the measured auroral shifts in HST images are not consistent with concurrent changes in the current density parameter measured by Galileo.

Telluric currents: A meeting of theory and observation

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

Boteler, D.H.; Seager, W.H.

Pipe-to-soil (P/S) potential variations resulting from telluric currents have been observed on pipelines in many locations. However, it has never teen clear which parts of a pipeline will experience the worst effects. Two studies were conducted to answer this question. Distributed-source transmission line (DSTL) theory was applied to the problem of modeling geomagnetic induction in pipelines. This theory predicted that the largest P/S potential variations would occur at the ends of the pipeline. The theory also predicted that large P/S potential variations, of opposite sign, should occur on either side of an insulating flange. Independently, an observation program was conductedmore » to determine the change in telluric current P/S potential variations and to design counteractive measures along a pipeline in northern Canada. Observations showed that the amplitude of P/S potential fluctuations had maxima at the northern and southern ends of the pipeline. A further set of recordings around an insulating flange showed large P/S potential variations, of opposite sign, on either side of the flange. Agreement between the observations and theoretical predictions was remarkable. While the observations confirmed the theory, the theory explains how P/S potential variations are produced by telluric currents and provides the basis for design of cathodic protection systems for pipelines that can counteract any adverse telluric effects.« less

Long-term geomagnetically induced current observations in New Zealand: Earth return corrections and geomagnetic field driver

NASA Astrophysics Data System (ADS)

Mac Manus, Daniel H.; Rodger, Craig J.; Dalzell, Michael; Thomson, Alan W. P.; Clilverd, Mark A.; Petersen, Tanja; Wolf, Moritz M.; Thomson, Neil R.; Divett, Tim

2017-08-01

Transpower New Zealand Limited has measured DC currents in transformer neutrals in the New Zealand electrical network at multiple South Island locations. Near-continuous archived DC current data exist since 2001, starting with 12 different substations and expanding from 2009 to include 17 substations. From 2001 to 2015 up to 58 individual transformers were simultaneously monitored. Primarily, the measurements were intended to monitor the impact of the high-voltage DC system linking the North and South Islands when it is operating in "Earth return" mode. However, after correcting for Earth return operation, as described here, the New Zealand measurements provide an unusually long and spatially detailed set of geomagnetically induced current (GIC) measurements. We examine the peak GIC magnitudes observed from these observations during two large geomagnetic storms on 6 November 2001 and 2 October 2013. Currents of 30-50 A are observed, depending on the measurement location. There are large spatial variations in the GIC observations over comparatively small distances, which likely depend upon network layout and ground conductivity. We then go on to examine the GIC in transformers throughout the South Island during more than 151 h of geomagnetic storm conditions. We compare the GIC to the various magnitude and rate of change components of the magnetic field. Our results show that there is a strong correlation between the magnitude of the GIC and the rate of change of the horizontal magnetic field (H'). This correlation is particularly clear for transformers that show large GIC current during magnetic storms.

Observations of near-bottom currents in Bornholm Basin, Slupsk Furrow and Gdansk Deep

NASA Astrophysics Data System (ADS)

Bulczak, A. I.; Rak, D.; Schmidt, B.; Beldowski, J.

2016-06-01

Dense bottom currents are responsible for transport of the salty inflow waters from the North Sea driving ventilation and renewal of Baltic deep waters. This study characterises dense currents in three deep locations of the Baltic Proper: Bornholm Basin (BB), Gdansk Basin (GB) and Slupsk Furrow (SF). These locations are of fundamental importance for the transport and pollution associated with chemical munitions deposited in BB and GB after 2nd World War. Of further importance the sub-basins are situated along the pathway of dense inflowing water.Current velocities were measured in the majority of the water column during regular cruises of r/v Oceania and r/v Baltica in 2001-2012 (38 cruises) by 307 kHz vessel mounted (VM), downlooking ADCP. Additionally, the high-resolution CTD and oxygen profiles were collected. Three moorings measured current velocity profiles in SF and GB over the summer 2012. In addition, temperature, salinity, oxygen and turbidity were measured at about 1 m above the bottom in GB. The results showed that mean current speed across the Baltic Proper was around 12 cm s-1 and the stronger flow was characteristic to the regions located above the sills, in the Bornholm and Slupsk Channels, reaching on average about 20 cm s-1. The results suggest that these regions are important for the inflow of saline waters into the eastern Baltic and are the areas of intense vertical mixing. The VM ADCP observations indicate that the average near-bottom flow across the basin can reach 35±6 cm s-1. The mooring observations also showed similar near-bottom flow velocities. However, they showed that the increased speed of the near-bottom layer occurred frequently in SF and GB during short time periods lasting for about few to several days or 10-20% of time. The observations showed that the bottom mixed layer occupies at least 10% of the water column and the turbulent mixing induced by near-bottom currents is likely to produce sediment resuspension and transport within the layer in all three sub-basins. The turbidity measurements, performed for 5-month-long time period over the summer 2012 in GB show that increased sediment resuspension is associated with a faster near-bottom flow.

Field-Aligned Currents in Saturn's Magnetosphere: Observations From the F-Ring Orbits

NASA Astrophysics Data System (ADS)

Hunt, G. J.; Provan, G.; Bunce, E. J.; Cowley, S. W. H.; Dougherty, M. K.; Southwood, D. J.

2018-05-01

We investigate the azimuthal magnetic field signatures associated with high-latitude field-aligned currents observed during Cassini's F-ring orbits (October 2016-April 2017). The overall ionospheric meridional current profiles in the northern and southern hemispheres, that is, the regions poleward and equatorward of the field-aligned currents, differ most from the 2008 observations. We discuss these differences in terms of the seasonal change between data sets and local time (LT) differences, as the 2008 data cover the nightside while the F-ring data cover the post-dawn and dusk sectors in the northern and southern hemispheres, respectively. The F-ring field-aligned currents typically have a similar four current sheet structure to those in 2008. We investigate the properties of the current sheets and show that the field-aligned currents in a hemisphere are modulated by that hemisphere's "planetary period oscillation" (PPO) systems. We separate the PPO-independent and PPO-related currents in both hemispheres using their opposite symmetry. The average PPO-independent currents peak at 1.5 MA/rad just equatorward of the open closed field line boundary, similar to the 2008 observations. However, the PPO-related currents in both hemispheres are reduced by 50% to 0.4 MA/rad. This may be evidence of reduced PPO amplitudes, similar to the previously observed weaker equatorial oscillations at similar dayside LTs. We do not detect the PPO current systems' interhemispheric component, likely a result of the weaker PPO-related currents and their closure within the magnetosphere. We also do not detect previously proposed lower latitude discrete field-aligned currents that act to "turn off" the PPOs.

Controlling heat and particle currents in nanodevices by quantum observation

NASA Astrophysics Data System (ADS)

Biele, Robert; Rodríguez-Rosario, César A.; Frauenheim, Thomas; Rubio, Angel

2017-07-01

We demonstrate that in a standard thermo-electric nanodevice the current and heat flows are not only dictated by the temperature and potential gradient, but also by the external action of a local quantum observer that controls the coherence of the device. Depending on how and where the observation takes place, the direction of heat and particle currents can be independently controlled. In fact, we show that the current and heat flow in a quantum material can go against the natural temperature and voltage gradients. Dynamical quantum observation offers new possibilities for the control of quantum transport far beyond classical thermal reservoirs. Through the concept of local projections, we illustrate how we can create and directionality control the injection of currents (electronic and heat) in nanodevices. This scheme provides novel strategies to construct quantum devices with application in thermoelectrics, spintronic injection, phononics, and sensing among others. In particular, highly efficient and selective spin injection might be achieved by local spin projection techniques.

Evolution of Flow channels and Dipolarization Using THEMIS Observations and Global MHD Simulations

NASA Astrophysics Data System (ADS)

El-Alaoui, M.; McPherron, R. L.; Nishimura, Y.

2017-12-01

We have extensively analyzed a substorm on March 14, 2008 for which we have observations from THEMIS spacecraft located beyond 9 RE near 2100 local time. The available data include an extensive network of all sky cameras and ground magnetometers that establish the times of various auroral and magnetic events. This arrangement provided an excellent data set with which to investigate meso-scale structures in the plasma sheet. We have used a global magnetohydrodynamic simulation to investigate the structure and dynamics of the magnetotail current sheet during this substorm. Both earthward and tailward flows were found in the observations as well as the simulations. The simulation shows that the flow channels follow tortuous paths that are often reflected or deflected before arriving at the inner magnetosphere. The simulation shows a sequence of fast flows and dipolarization events similar to what is seen in the data, though not at precisely the same times or locations. We will use our simulation results combined with the observations to investigate the global convection systems and current sheet structure during this event, showing how meso-scale structures fit into the context of the overall tail dynamics during this event. Our study includes determining the location, timing and strength of several current wedges and expansion onsets during an 8-hour interval.

Observation of spinon spin currents in one-dimensional spin liquid

NASA Astrophysics Data System (ADS)

Hirobe, Daichi; Sato, Masahiro; Kawamata, Takayuki; Shiomi, Yuki; Uchida, Ken-Ichi; Iguchi, Ryo; Koike, Yoji; Maekawa, Sadamichi; Saitoh, Eiji

To date, two types of spin current have been explored experimentally: conduction-electron spin current and spin-wave spin current. Here, we newly present spinon spin current in quantum spin liquid. An archetype of quantum spin liquid is realized in one-dimensional spin-1/2 chains with the spins coupled via antiferromagnetic interaction. Elementary excitation in such a system is known as a spinon. Theories have predicted that the correlation of spinons reaches over a long distance. This suggests that spin current may propagate via one-dimensional spinons even in spin liquid states. In this talk, we report the experimental observation that a spin liquid in a spin-1/2 quantum chain generates and conveys spin current, which is attributed to spinon spin current. This is demonstrated by observing an anisotropic negative spin Seebeck effect along the spin chains in Sr2CuO3. The results show that spin current can flow via quantum fluctuation in spite of the absence of magnetic order, suggesting that a variety of quantum spin systems can be applied to spintronics. Spin Quantum Rectification Project, ERATO, JST, Japan; PRESTO, JST, Japan.

Current-voltage hysteresis and dielectric properties of PVA coated MWCNT film

NASA Astrophysics Data System (ADS)

Das, Amit Kumar; Meikap, Ajit Kumar

2017-12-01

In this work, we have prepared polyvinyl alcohol (PVA) coated multiwall carbon nanotube (MWCNT) film by an in situ chemical oxidative preparation technique. The thermogravimetric analysis clearly explains the thermal degradation of pure polymer and polymer nanocomposite film. We have studied the AC electrical transport properties and current-voltage (I-V) characteristic of PVA-MWCNT composites within the temperature range 300 ≤ T ≤ 423 K and frequency range 150 Hz ≤ f ≤ 2 MHz. It is observed that the dielectric constant of the composite film increases significantly. The frequency variation of AC conductivity follows the power law ( ωS ) and a sharp transition from small polaron tunneling to correlated barrier hopping model is found. The imaginary part of electric modulus shows non-Debye type asymmetric behaviour. The impedance spectroscopy shows the negative temperature coefficient of resistance of the composite film. Nyquist plot of the composite film at different temperatures is established from impedance measurement. The current-voltage characteristic (under ± 20 V) shows hysteresis behaviour and field dependent resistance. We simulate the experimentally observed current density-electric field data with the established theory.

Current-voltage hysteresis and dielectric properties of PVA coated MWCNT film

NASA Astrophysics Data System (ADS)

Das, Amit Kumar; Meikap, Ajit Kumar

2018-06-01

In this work, we have prepared polyvinyl alcohol (PVA) coated multiwall carbon nanotube (MWCNT) film by an in situ chemical oxidative preparation technique. The thermogravimetric analysis clearly explains the thermal degradation of pure polymer and polymer nanocomposite film. We have studied the AC electrical transport properties and current-voltage (I-V) characteristic of PVA-MWCNT composites within the temperature range 300 ≤ T ≤ 423 K and frequency range 150 Hz ≤ f ≤ 2 MHz. It is observed that the dielectric constant of the composite film increases significantly. The frequency variation of AC conductivity follows the power law ( ωS ) and a sharp transition from small polaron tunneling to correlated barrier hopping model is found. The imaginary part of electric modulus shows non-Debye type asymmetric behaviour. The impedance spectroscopy shows the negative temperature coefficient of resistance of the composite film. Nyquist plot of the composite film at different temperatures is established from impedance measurement. The current-voltage characteristic (under ± 20 V) shows hysteresis behaviour and field dependent resistance. We simulate the experimentally observed current density-electric field data with the established theory.

Heating the sun's lower transition region with fine-scale electric currents

NASA Technical Reports Server (NTRS)

Rabin, D.; Moore, R.

1984-01-01

Analytical and observational data are presented to show that the lower transition zone, a 100 km thick region at 10,000-200,000 K between the solar chromosphere and corona, is heated by local electric currents. The study was spurred by correlations between the enhanced atmospheric heating and magnetospheric flux in the chromospheric network and active regions. Field aligned current heated flux loops are asserted to mainly reside in and make up most of the transition region. It is shown that thermal conduction from the sides of hot gas columns generated by the current dissipation is the source of the observed temperature distribution in the transition regions.

Does Solar Wind also Drive Convection in Jupiter's Magnetosphere?

NASA Astrophysics Data System (ADS)

Khurana, K. K.

2001-05-01

Using a simple model of magnetic field and plasma velocity, Brice and Ioannidis [1970] showed that the corotation electric field exceeds convection electric field throughout the Jovian magnetosphere. Since that time it has been tacitly assumed that Jupiter's magnetosphere is driven from within. If Brice and Ioannidis conjecture is correct then one would not expect major asymmetries in the field and plasma parameters in the middle magnetosphere of Jupiter. Yet, new field and plasma observations from Galileo and simultaneous auroral observations from HST show that there are large dawn/dusk and day/night asymmetries in many magnetospheric parameters. For example, the magnetic observations show that a partial ring current and an associated Region-2 type field-aligned current system exist in the magnetosphere of Jupiter. In the Earth's magnetosphere it is well known that the region-2 current system is created by the asymmetries imposed by a solar wind driven convection. Thus, we are getting first hints that the solar wind driven convection is important in Jupiter's magnetosphere as well. Other in-situ observations also point to dawn-dusk asymmetries imposed by the solar wind. For example, first order anisotropies in the Energetic Particle Detector show that the plasma is close to corotational on the dawn side but lags behind corotation in the dusk sector. Magnetic field data show that the current sheet is thin and highly organized on the dawn side but thick and disturbed on the dusk side. I will discuss the reasons why Brice and Ioannidis calculation may not be valid. I will show that both the magnetic field and plasma velocity estimates used by Brice and Ioannidis were rather excessive. Using more modern estimates of the field and velocity values I show that the solar wind convection can penetrate as deep as 40 RJ on the dawnside. I will present a new model of convection that invokes in addition to a distant neutral line spanning the whole magnetotail, a near-Jupiter neutral line only on the dawnside. I will discuss how the internal and external drivers together set up a convection system and transport plasma and magnetic flux in Jupiter's magnetosphere. I will explore the consequences of this convection system on the flows, current sheet and the Jovian aurorae.

Observation and analysis of tidal and residual current in the North Yellow Sea in the spring

NASA Astrophysics Data System (ADS)

Miao, Qingsheng; Yang, Jinkun; Yang, Yang; Wan, Fangfang; Yu, Jia

2018-02-01

In order to study the current characteristics of the North Yellow Sea (NYS), 4 moored ADCPs (Acoustic Doppler Current Profilers) were deployed and Current characteristics were analyzed based on the observations. Results show that tidal current is the dominant and M2 is the main constituent. Shallow water constituents are obvious in the near-shore area, and tidal current ellipses directions have relations with topography. Residual currents in the Bohai Strait point to the Bohai Sea interior and the magnitude have a connection with terrain. Residual current in south NYS can be divided into two layers, and energy of residual current only accounts for about 13% of the total energy. Barotropic eddy kinetic energy plays a major role and the average in NYS accounts for 87%, baroclinic mean kinetic energy is larger in north NYS, in other regions barotropic mean kinetic energy take the leading position.

Spatial Heterodyne Observation of Water (SHOW) from a high altitude aircraft

NASA Astrophysics Data System (ADS)

Bourassa, A. E.; Langille, J.; Solheim, B.; Degenstein, D. A.; Letros, D.; Lloyd, N. D.; Loewen, P.

2017-12-01

The Spatial Heterodyne Observations of Water instrument (SHOW) is limb-sounding satellite prototype that is being developed in collaboration between the University of Saskatchewan, York University, the Canadian Space Agency and ABB. The SHOW instrument combines a field-widened SHS with an imaging system to observe limb-scattered sunlight in a vibrational band of water (1363 nm - 1366 nm). Currently, the instrument has been optimized for deployment on NASA's ER-2 aircraft. Flying at an altitude of 70, 000 ft the ER-2 configuration and SHOW viewing geometry provides high spatial resolution (< 500 m) limb-measurements of water vapor in the Upper troposphere and lower stratosphere region. During an observation campaign from July 15 - July 22, the SHOW instrument performed 10 hours of observations from the ER-2. This paper describes the SHOW measurement technique and presents the preliminary analysis and results from these flights. These observations are used to validate the SHOW measurement technique and demonstrate the sampling capabilities of the instrument.

Evaluating Surface Radiation Fluxes Observed From Satellites in the Southeastern Pacific Ocean

NASA Astrophysics Data System (ADS)

Pinker, R. T.; Zhang, B.; Weller, R. A.; Chen, W.

2018-03-01

This study is focused on evaluation of current satellite and reanalysis estimates of surface radiative fluxes in a climatically important region. It uses unique observations from the STRATUS Ocean Reference Station buoy in a region of persistent marine stratus clouds 1,500 km off northern Chile during 2000-2012. The study shows that current satellite estimates are in better agreement with buoy observations than model outputs at a daily time scale and that satellite data depict well the observed annual cycle in both shortwave and longwave surface radiative fluxes. Also, buoy and satellite estimates do not show any significant trend over the period of overlap or any interannual variability. This verifies the stability and reliability of the satellite data and should make them useful to examine El Niño-Southern Oscillation variability influences on surface radiative fluxes at the STRATUS site for longer periods for which satellite record is available.

Evolution of flare ribbons, electric currents, and quasi-separatrix layers during an X-class flare

NASA Astrophysics Data System (ADS)

Janvier, M.; Savcheva, A.; Pariat, E.; Tassev, S.; Millholland, S.; Bommier, V.; McCauley, P.; McKillop, S.; Dougan, F.

2016-07-01

Context. The standard model for eruptive flares has been extended to three dimensions (3D) in the past few years. This model predicts typical J-shaped photospheric footprints of the coronal current layer, forming at similar locations as the quasi-separatrix layers (QSLs). Such a morphology is also found for flare ribbons observed in the extreme ultraviolet (EUV) band, and in nonlinear force-free field (NLFFF) magnetic field extrapolations and models. Aims: We study the evolution of the photospheric traces of the current density and flare ribbons, both obtained with the Solar Dynamics Observatory instruments. We aim to compare their morphology and their time evolution, before and during the flare, with the topological features found in a NLFFF model. Methods: We investigated the photospheric current evolution during the 06 September 2011 X-class flare (SOL2011-09-06T22:20) occurring in NOAA AR 11283 from observational data of the magnetic field obtained with the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory. We compared this evolution with that of the flare ribbons observed in the EUV filters of the Atmospheric Imager Assembly. We also compared the observed electric current density and the flare ribbon morphology with that of the QSLs computed from the flux rope insertion method-NLFFF model. Results: The NLFFF model shows the presence of a fan-spine configuration of overlying field lines, due to the presence of a parasitic polarity, embedding an elongated flux rope that appears in the observations as two parts of a filament. The QSL signatures of the fan configuration appear as a circular flare ribbon that encircles the J-shaped ribbons related to the filament ejection. The QSLs, evolved via a magnetofrictional method, also show similar morphology and evolution as both the current ribbons and the EUV flare ribbons obtained several times during the flare. Conclusions: For the first time, we propose a combined analysis of the photospheric traces of an eruptive flare, in a complex topology, with direct measurements of electric currents and QSLs from observational data and a magnetic field model. The results, obtained by two different and independent approaches 1) confirm previous results of current increase during the impulsive phase of the flare and 2) show how NLFFF models can capture the essential physical signatures of flares even in a complex magnetic field topology. A movie associated to Fig. 1 is available in electronic form at http://www.aanda.org

Non-neutralized Electric Currents in Solar Active Regions and Flare Productivity

NASA Astrophysics Data System (ADS)

Kontogiannis, Ioannis; Georgoulis, Manolis K.; Park, Sung-Hong; Guerra, Jordan A.

2017-11-01

We explore the association of non-neutralized currents with solar flare occurrence in a sizable sample of observations, aiming to show the potential of such currents in solar flare prediction. We used the high-quality vector magnetograms that are regularly produced by the Helioseismic Magnetic Imager, and more specifically, the Space weather HMI Active Region Patches (SHARP). Through a newly established method that incorporates detailed error analysis, we calculated the non-neutralized currents contained in active regions (AR). Two predictors were produced, namely the total and the maximum unsigned non-neutralized current. Both were tested in AR time-series and a representative sample of point-in-time observations during the interval 2012 - 2016. The average values of non-neutralized currents in flaring active regions are higher by more than an order of magnitude than in non-flaring regions and correlate very well with the corresponding flare index. The temporal evolution of these parameters appears to be connected to physical processes, such as flux emergence and/or magnetic polarity inversion line formation, that are associated with increased solar flare activity. Using Bayesian inference of flaring probabilities, we show that the total unsigned non-neutralized current significantly outperforms the total unsigned magnetic flux and other well-established current-related predictors. It therefore shows good prospects for inclusion in an operational flare-forecasting service. We plan to use the new predictor in the framework of the FLARECAST project along with other highly performing predictors.

Inclined gravity currents filling basins: The influence of Reynolds number on entrainment into gravity currents

NASA Astrophysics Data System (ADS)

Hogg, Charlie A. R.; Dalziel, Stuart B.; Huppert, Herbert E.; Imberger, Jörg

2015-09-01

In many important natural and industrial systems, gravity currents of dense fluid feed basins. Examples include lakes fed by dense rivers and auditoria supplied with cooled air by ventilation systems. As we will show, the entrainment into such buoyancy driven currents can be influenced by viscous forces. Little work, however, has examined this viscous influence and how entrainment varies with the Reynolds number, Re. Using the idea of an entrainment coefficient, E, we derive a mathematical expression for the rise of the front at the top of the dense fluid ponding in a basin, where the horizontal cross-sectional area of the basin varies linearly with depth. We compare this expression to experiments on gravity currents with source Reynolds numbers, Res, covering the broad range 100 < Res < 1500. The form of the observed frontal rises was well approximated by our theory. By fitting the observed frontal rises to the theoretical form with E as the free parameter, we find a linear trend for E(Res) over the range 350 < Res < 1100, which is in the transition to turbulent flow. In the experiments, the entrainment coefficient, E, varied from 4 × 10-5 to 7 × 10-2. These observations show that viscous damping can be a dominant influence on gravity current entrainment in the laboratory and in geophysical flows in this transitional regime.

Dephasing effects on ac-driven triple quantum dot systems

NASA Astrophysics Data System (ADS)

Maldonado, I.; Villavicencio, J.; Contreras-Pulido, L. D.; Cota, E.; Maytorena, J. A.

2018-05-01

We analyze the effect of environmental dephasing on the electrical current in an ac-driven triple quantum dot system in a symmetric Λ configuration. The current is explored by solving the time evolution equation of the density matrix as a function of the frequency and amplitude of the driving field. Two characteristic spectra are observed depending on the field amplitude. At the resonance condition, when the frequency matches the interdot energy difference, one spectrum shows a distinctive Fano-type peak, while the other, occurring at larger values of the field amplitude, exhibits a strong current suppression due to dynamic localization. In the former case we observe that the current maximum is reduced due to dephasing, while in the latter it is shown that dephasing partially alleviates the localization. In both cases, away from resonance, we observe current oscillations which are dephasing-enhanced for a wide range of frequencies. These effects are also discussed using Floquet theory, and analytical expressions for the electrical current are obtained within the rotating wave approximation.

A comparison of coronal and interplanetary current sheet inclinations

NASA Technical Reports Server (NTRS)

Behannon, K. W.; Burlaga, L. F.; Hundhausen, A. J.

1983-01-01

The HAO white light K-coronameter observations show that the inclination of the heliospheric current sheet at the base of the corona can be both large (nearly vertical with respect to the solar equator) or small during Cararington rotations 1660 - 1666 and even on a single solar rotation. Voyager 1 and 2 magnetic field observations of crossing of the heliospheric current sheet at distances from the Sun of 1.4 and 2.8 AU. Two cases are considered, one in which the corresponding coronameter data indicate a nearly vertical (north-south) current sheet and another in which a nearly horizontal, near equatorial current sheet is indicated. For the crossings of the vertical current sheet, a variance analysis based on hour averages of the magnetic field data gave a minimum variance direction consistent with a steep inclination. The horizontal current sheet was observed by Voyager as a region of mixed polarity and low speeds lasting several days, consistent with multiple crossings of a horizontal but irregular and fluctuating current sheet at 1.4 AU. However, variance analysis of individual current sheet crossings in this interval using 1.92 see averages did not give minimum variance directions consistent with a horizontal current sheet.

Sea Surface Wakes Observed by Spaceborne SAR in the Offshore Wind Farms

NASA Astrophysics Data System (ADS)

Li, Xiaoming; Lehner, Susanne; Jacobsen, Sven

2014-11-01

In the paper, we present some X-band spaceborne synthetic aperture radar (SAR) TerraSAR-X (TS-X) images acquired at the offshore wind farms in the North Sea and the East China Sea. The high spatial resolution SAR images show different sea surface wake patterns downstream of the offshore wind turbines. The analysis suggests that there are major two types of wakes among the observed cases. The wind turbine wakes generated by movement of wind around wind turbines are the most often observed cases. In contrast, due to the strong local tidal currents in the near shore wind farm sites, the tidal current wakes induced by tidal current impinging on the wind turbine piles are also observed in the high spatial resolution TS-X images. The discrimination of the two types of wakes observed in the offshore wind farms is also described in the paper.

Water mass characteristic in the outflow region of the Indonesian throughflow during and post 2016 negative Indian ocean dipole event

NASA Astrophysics Data System (ADS)

Bayhaqi, A.; Iskandar, I.; Surinati, D.; Budiman, A. S.; Wardhana, A. K.; Dirhamsyah; Yuan, D.; Lestari, D. O.

2018-05-01

Strong El Niño and positive Indian Ocean Dipole (pIOD) events in 2015/2016 followed by relatively strong negative Indian Ocean Dipole (nIOD) and weak La Niña in 2016 events have affected hydrography conditions in the Indonesian Throughflow (ITF) region. Two research cruises were conducted using RV Baruna Jaya VIII in August and November 2016. These cruises aim to evaluate possible impact of those two climate mode events on the water mass characteristic in the outflow region of the ITF. Hydrographic data from those two cruises were combined with the sea surface temperature (SST) from the Advanced Very High Resolution Radiometer (AVHRR) and surface wind data from the European Centre for Medium-Range Weather Forecasts (ECMWF). The results showed that in the 2016 anomaly year, the cooler sea surface temperature was observed during the negative IOD (nIOD) event while the warmer temperature was found in the post of nIOD event. The observed water mass characteristics in the outflow region of the ITF revealed that the upper layer was dominated by the Indian Ocean water mass, while the Pacific Ocean water mass was observed in the deeper layer. The observed current data across the Sumba Strait showed that the South Java Coastal Current (SJCC) was observed in the upper layer, propagating eastward toward the Savu Sea. A few days later, the observed currents in the upper layer of the Ombai Strait revealed the ITF flow towards the Indian Ocean. Meanwhile, the lower layer showed an eastward flow towards the Ombai Strait.

Generation of the displacement current by the transformation of J-aggregates in spreading monolayers of squarylium dye

NASA Astrophysics Data System (ADS)

Iwamoto, Mitsumasa; Majima, Yutaka; Hirayama, Fuminori; Furuki, Makoto; Pu, Lyong Sun

1992-07-01

Maxwell displacement currents generated from monolayers of squarylium dye with propyl groups (SQ) and from mixed monolayers with arachidic acid were investigated during the course of monolayer compression in connection with the formation of J-aggregates in the monolayers. Abrupt changes in the generation of displacement current were observed for monolayers of SQ due to the transformation between two types of J-aggregates with different absorption spectra. In contrast, for mixed monolayers with arachidic acid which show no transition of J-aggregates, abrupt changes in the displacement current were not observed. It was concluded that displacement current measurement is effective in the detection of the transformation of the molecular arrangement in aggregates.

Microstructures of Ni-AlN composite coatings prepared by pulse electrodeposition technology

NASA Astrophysics Data System (ADS)

Xia, Fafeng; Xu, Huibin; Liu, Chao; Wang, Jinwu; Ding, Junjie; Ma, Chunhua

2013-04-01

Ni-AlN composite coating was fabricated onto the surface of steel substrates by using pulse electrodeposition (PED) technique in this work. The effect of pulse current on the nucleation and growth of grains was investigated using transmission electronic microscopy (TEM), X-ray diffraction (XRD), scanning electronic microscopy (SEM) and atomic force microscopy (AFM), respectively. The results show that the contents of AlN nanoparticles increase with density of pulse current and on-duty ratio of pulse current increasing. Whereas the size of nickel grains decreases with density of pulse current increasing and on-duty ratio of pulse current decreasing. Ni-AlN composite coating consists of crystalline nickel (˜68 nm) and AlN particles (˜38 nm). SEM and AFM observations show that the composite coatings obtained by PED showed more compact surfaces and less grain sizes, whereas those obtained by direct current electrodepositing have rougher surfaces and bigger grain sizes.

Flare Energy Release: Internal Conflict, Contradiction with High Resolution Observations, Possible Solutions

NASA Astrophysics Data System (ADS)

Pustilnik, L.

2017-06-01

All accepted paradigm of solar and stellar flares energy release based on 2 whales: 1. Source of energy is free energy of non-potential force free magnetic field in atmosphere above active region; 2. Process of ultrafast dissipation of magnetic fields is Reconnection in Thin Turbulent Current Sheet (RTTCS). Progress in observational techniques in last years provided ultra-high spatial resolution and in physics of turbulent plasma showed that real situation is much more complicated and standard approach is in contradiction both with observations and with problem of RTTCS stability. We present critical analysis of classic models of pre-flare energy accumulation and its dissipation during flare energy release from pioneer works Giovanelli (1939, 1947) up to topological reconnection. We show that all accepted description of global force-free fields as source of future flare cannot be agreed with discovered in last years fine and ultra-fine current-magnetic structure included numerouse arcs-threads with diameters up to 100 km with constant sequence from photosphere to corona. This magnetic skeleton of thin current magnetic threads with strong interaction between them is main source of reserved magnetic energy insolar atmosphere. Its dynamics will be controlled by percolation of magnetic stresses through network of current-magnetic threads with transition to flare state caused by critical value of global current. We show that thin turbulent current sheet is absolutely unstable configuration both caused by splitting to numerous linear currents by dissipative modes like to tearing, and as sequence of suppress of plasma turbulence caused by anomalous heating of turbulent plasma. In result of these factors primary RTTCS will be disrupted in numerous turbulent and normal plasma domains like to resistors network. Current propagation through this network will have percolation character with all accompanied properties of percolated systems: self-organization with formation power spectrum of distribution of flares and micro-flares, and possibility of phase transition to flare energy release with huge increasing of energy release.

EVIDENCE FOR QUASI-ADIABATIC MOTION OF CHARGED PARTICLES IN STRONG CURRENT SHEETS IN THE SOLAR WIND

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

Malova, H. V.; Popov, V. Yu.; Grigorenko, E. E.

We investigate quasi-adiabatic dynamics of charged particles in strong current sheets (SCSs) in the solar wind, including the heliospheric current sheet (HCS), both theoretically and observationally. A self-consistent hybrid model of an SCS is developed in which ion dynamics is described at the quasi-adiabatic approximation, while the electrons are assumed to be magnetized, and their motion is described in the guiding center approximation. The model shows that the SCS profile is determined by the relative contribution of two currents: (i) the current supported by demagnetized protons that move along open quasi-adiabatic orbits, and (ii) the electron drift current. The simplestmore » modeled SCS is found to be a multi-layered structure that consists of a thin current sheet embedded into a much thicker analog of a plasma sheet. This result is in good agreement with observations of SCSs at ∼1 au. The analysis of fine structure of different SCSs, including the HCS, shows that an SCS represents a narrow current layer (with a thickness of ∼10{sup 4} km) embedded into a wider region of about 10{sup 5} km, independently of the SCS origin. Therefore, multi-scale structuring is very likely an intrinsic feature of SCSs in the solar wind.« less

Characteristics of inertial currents observed in offshore wave records

NASA Astrophysics Data System (ADS)

Gemmrich, J.; Garrett, C.

2012-04-01

It is well known that ambient currents can change the amplitude, direction and frequency of ocean surface waves. Regions with persistent strong currents, such as the Agulhas current off the east coast of South Africa, are known as areas of extreme waves, and wave height modulations of up to 50% observed in the shallow North Sea have been linked to tidal currents. In the open ocean, inertial currents, while intermittent, are typically the most energetic currents with speeds up to 0.5 m/s, and can interact with the surface wave field to create wave modulation, though this has not previously been reported. We use long records of significant wave heights from buoy observations in the northeast Pacific and show evidence of significant modulation at frequencies that are slightly higher than the local inertial frequency. Quite apart from the relevance to surface waves, this result can provide a consistent and independent measurement, over a wide range of latitudes, of the frequency blue-shift, the strength and intermittency of ocean surface inertial currents. Near-inertial waves constitute the most energetic portion of the internal wave band and play a significant role in deep ocean mixing. So far, observational data on near-surface inertial currents has tended to come from short records that do not permit the reliable determination of the frequency blue-shift, though this is an important factor affecting the energy flux from the surface into deeper waters. Long records from routine wave height observations are widely available and could help to shed new light globally on the blue-shift and on the characteristics of inertial currents.

Observation and numerical modeling of tidal dune dynamics

NASA Astrophysics Data System (ADS)

Doré, Arnaud; Bonneton, Philippe; Marieu, Vincent; Garlan, Thierry

2018-05-01

Tidal sand dune dynamics is observed for two tidal cycles in the Arcachon tidal inlet, southwest France. An array of instruments is deployed to measure bathymetric and current variations along dune profiles. Based on the measurements, dune crest horizontal and vertical displacements are quantified and show important dynamics in phase with tidal currents. We observed superimposed ripples on the dune stoss side and front, migrating and changing polarity as tidal currents reverse. A 2D RANS numerical model is used to simulate the morphodynamic evolution of a flat non-cohesive sand bed submitted to a tidal current. The model reproduces the bed evolution until a field of sand bedforms is obtained that are comparable with observed superimposed ripples in terms of geometrical dimensions and dynamics. The model is then applied to simulate the dynamics of a field of large sand dunes of similar size as the dunes observed in situ. In both cases, simulation results compare well with measurements qualitatively and quantitatively. This research allows for a better understanding of tidal sand dune and superimposed ripple morphodynamics and opens new perspectives for the use of numerical models to predict their evolution.

Variation of the North Equatorial Current, Mindanao Current, and Kuroshio Current in a high-resolution data assimilation during 2008-2012

NASA Astrophysics Data System (ADS)

Zhai, Fangguo; Wang, Qingye; Wang, Fujun; Hu, Dunxin

2014-11-01

Outputs from a high-resolution data assimilation system, the global Hybrid Coordinate Ocean Model and Navy Coupled Ocean Data Assimilation (HYCOM+NCODA) 1/12° analysis, were analyzed for the period September 2008 to February 2012. The objectives were to evaluate the performance of the system in simulating ocean circulation in the tropical northwestern Pacific and to examine the seasonal to interannual variations of the western boundary currents. The HYCOM assimilation compares well with altimetry observations and mooring current measurements. The mean structures and standard deviations of velocities of the North Equatorial Current (NEC), Mindanao Current (MC) and Kuroshio Current (KC) also compare well with previous observations. Seasonal to interannual variations of the NEC transport volume are closely correlated with the MC transport volume, instead of that of the KC. The NEC and MC transport volumes mainly show well-defined annual cycles, with their maxima in spring and minima in fall, and are closely related to the circulation changes in the Mindanao Dome (MD) region. In seasons of transport maxima, the MD region experiences negative SSH anomalies and a cyclonic gyre anomaly, and in seasons of transport minima the situation is reversed. The sea surface NEC bifurcation latitude (NBL) in the HYCOM assimilation also agrees well with altimetry observations. In 2009, the NBL shows an annual cycle similar to previous studies, reaching its southernmost position in summer and its northernmost position in winter. In 2010 and 2011, the NBL variations are dominantly influenced by La Niña events. The dynamics responsible for the seasonal to interannual variations of the NEC-MC-KC current system are also discussed.

The role of Internal Solitary Waves on deep-water sedimentary processes: the case of up-slope migrating sediment waves off the Messina Strait.

PubMed

Droghei, R; Falcini, F; Casalbore, D; Martorelli, E; Mosetti, R; Sannino, G; Santoleri, R; Chiocci, F L

2016-11-03

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary "current" that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

EXPERIMENTAL MEASUREMENT AND INTERPRETATION OF VOLT-AMPERE CURVES

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

Gingrich, J.E.; Warner, C.; Weeks, C.C.

1962-07-01

Cylindrical and parallel-plane cesium vapor thermionic converters were used for obtaining volt-ampere curves for systematic variations of emitter, collector, and cesium reservoir temperatures, with electrode spacings ranging from a few to many mean free paths, and with space charge conditions varying from electron-rich to ion-rich. The resulting curves exhibit much variety. The saturation currents agree well with the data of Houston and Aamodt for the space charge neutralized, few-mean-free-path cases. Apparent'' saturation currents for space charge limited cases were observed and were always less than the currents predicted by Houston and Aamodt. Several discontinuities in slope were observed in themore » reverse current portion of the curves and these have tentatively been identified with volume ionization of atoms in both the ground and excited states. Similar processes may be important for obtaining the ignited mode. The methods used to measure static and dynamic volt-ampere curves are described. The use of a controlled-current load has yielded a negative resistance'' region in the curves which show the ignited mode. The curves obtained with poor current control do not show this phenomenon. Extinction is considered from the standpoint of Kaufmann' s criterion for stability. (auth)« less

The Origin of the Tsushima Warm Current in a High Resolution Model

NASA Astrophysics Data System (ADS)

Park, Y.; Yeh, S.; Hwang, J.

2008-12-01

Using a high resolution global ocean circulation model results, the present study investigates the origin of the Tsushima Warm Current and related East China Sea Circulation. The simulated Tsushima Warm Current is weaker than the observations by about 30 %, but the persistence of the Taiwan-Tsushima Current System shows that the Taiwan Warm Current is the main source of the Tsushima Warm Current. The high resolution model results allow us to distinguish the Kuroshio intrusion north of Taiwan and west of Kyushu from the Taiwan-Tsushima Current System. West of Kyushu the onshore intrusion of the Kuroshio is strong between September and February, and north of Taiwan between June and November. The annual mean strength of the intrusion is 0.32 Sv west of Kyushu, and 0.22 Sv north of Taiwan. Since the simulated Tsushima Warm Current is weaker than the observation while that of the Taiwan Current is comparable to the observations, the strength of the intrusion is weaker than the reality. In addition, a linear relation is found between the transport of the Tsushima Warm Current and the sea level difference between the Korea/Tsushima Strait and the Tsugaru/Soya Straits, and we can conclude that the sea level difference is the main driving force of the current.

Modeling Jupiter's current disc - Pioneer 10 outbound

NASA Astrophysics Data System (ADS)

Jones, D. E.; Melville, J. G.; Blake, M. L.

1980-07-01

A model of the magnetic field of the Jovian current disk is presented. The model uses Euler functions and the Biot-Savart law applied to a series of concentric, but not necessarily coplanar current rings. It was found that the best fit to the Pioneer 10 outbound perturbation magnetic field data is obtained if the current disk is twisted, and also bent to tend toward parallelism with the Jovigraphic equator. The inner and outer radii of the disk appear to be about 7 and 150 Jovian radii, respectively; because of the observed current disk penetrations, the bent disk also requires a deformation in the form of a bump or wrinkle whose axis tends to exhibit spiraling. Modeling of the azimuthal field shows that it is due to a thin radial current sheet, but it may actually be due in large part to penetration of a tail current sheet as suggested by Voyager observations.

Remote sensing of ocean currents using ERTS imagery

NASA Technical Reports Server (NTRS)

Maul, G. A.

1973-01-01

Major ocean currents such as the Loop Current in the eastern Gulf of Mexico have surface manifestations which can be exploited for remote sensing. Surface chlorophyll-a concentrations, which contribute to the shift in color from blue to green in the open sea, were found to have high spatial variability; significantly lower concentrations were observed in the current. The cyclonic edge of the current is an accumulation zone which causes a peak in chlorophyll concentration. The dynamics also cause surface concentrations of algae, which have a high reflectance in the near infrared. Combining these observations gives rise to an edge effect which can show up as a bright lineation on multispectral imagery delimiting the current's boundary under certain environmental conditions. When high seas introduce bubbles, white caps, and foam, the reflectance is dominated by scattering rather than absorption. This has been detected in ERTS imagery and used for current location.

Formation and disruption of current paths of anodic porous alumina films by conducting atomic force microscopy

NASA Astrophysics Data System (ADS)

Oyoshi, K.; Nigo, S.; Inoue, J.; Sakai, O.; Kitazawa, H.; Kido, G.

2010-11-01

Anodic porous alumina (APA) films have a honeycomb cell structure of pores and a voltage-induced bi-stable switching effect. We have applied conducting atomic force microscopy (CAFM) as a method to form and to disrupt current paths in the APA films. A bi-polar switching operation was confirmed. We have firstly observed terminals of current paths as spots or areas typically on the center of the triangle formed by three pores. In addition, though a part of the current path showed repetitive switching, most of them were not observed again at the same position after one cycle of switching operations in the present experiments. This suggests that a part of alumina structure and/or composition along the current paths is modified during the switching operations.

Sharp burnout failure observed in high current-carrying double-walled carbon nanotube fibers

NASA Astrophysics Data System (ADS)

Song, Li; Toth, Geza; Wei, Jinquan; Liu, Zheng; Gao, Wei; Ci, Lijie; Vajtai, Robert; Endo, Morinobu; Ajayan, Pulickel M.

2012-01-01

We report on the current-carrying capability and the high-current-induced thermal burnout failure modes of 5-20 µm diameter double-walled carbon nanotube (DWNT) fibers made by an improved dry-spinning method. It is found that the electrical conductivity and maximum current-carrying capability for these DWNT fibers can reach up to 5.9 × 105 S m - 1 and over 1 × 105 A cm - 2 in air. In comparison, we observed that standard carbon fiber tended to be oxidized and burnt out into cheese-like morphology when the maximum current was reached, while DWNT fiber showed a much slower breakdown behavior due to the gradual burnout in individual nanotubes. The electron microscopy observations further confirmed that the failure process of DWNT fibers occurs at localized positions, and while the individual nanotubes burn they also get aligned due to local high temperature and electrostatic field. In addition a finite element model was constructed to gain better understanding of the failure behavior of DWNT fibers.

Quench dynamics of the Josephson current in a topological Josephson junction

NASA Astrophysics Data System (ADS)

Sun, Dihao; Liu, Jie

2018-01-01

The 4 π -periodic Josephson effect is a distinguishing feature of a topological Josephson junction. However, stringent conditions make it hard to observe in experiments. In this work, we study the transient transport properties in a topological Josephson junction numerically. We show that the 4 π Josephson current can be sustained under nonequilibrium conditions. The properties of the Josephson current are analyzed for different conditions and three main regimes are identified. First, when both the superconducting wires of the Josephson junction lie in the topologically nontrivial region, a 4 π Josephson current can appear upon suddenly applying a dc voltage. Second, when one superconducting wire lies in the trivial region, while the other wire lies in the nontrivial region, the Josephson current is 2 π periodic but the component of the higher-order Josephson current increases. Third, when both wires lie in the trivial region, a stable 2 π Josephson current is observed. Most importantly, the fractional Josephson effect is fragile in the presence of disorder. Hence experiments should be designed carefully to eliminate the effect of disorder. These results could be helpful to optimize fine-tuning of the experimental parameters to observe the 4 π -periodic Josephson current in a topological Josephson junction.

Sex differences in spatial ability: a lateralization of function approach.

PubMed

Rilea, Stacy L; Roskos-Ewoldsen, Beverly; Boles, David

2004-12-01

The current study was designed to examine whether the extent of the male advantage in performance on a spatial task was determined by the extent to which the task was right-hemisphere dependent. Participants included 108 right-handed men and women who completed the mental rotation, waterlevel, and paperfolding tasks, all of which were presented bilaterally. The results partially supported the hypothesis. On the mental rotation task, men showed a right-hemisphere advantage, whereas women showed no hemispheric differences; however, no overall sex differences were observed. On the waterlevel task, men outperformed women, and both men and women showed a right-hemisphere advantage. On the paperfolding task, no sex or hemispheric differences were observed. Although the findings of the current study were mixed, the study provides a framework for examining sex differences across different types of spatial ability.

Field-aligned currents and magnetospheric convection - A comparison between MHD simulations and observations

NASA Technical Reports Server (NTRS)

Walker, Raymond J.; Ogino, Tatsuki

1988-01-01

A time-dependent three-dimensional MHD model was used to investigate the magnetospheric configuration as a function of the interplanetary magnetic field direction when it was in the y-z plane in geocentric solar magnetospheric coordinates. The model results show large global convection cells, tail lobe cells, high-latitude polarcap cells, and low latitude cells. The field-aligned currents generated in the model magnetosphere and the model convection system are compared with observations from low-altitude polar orbiting satellites.

Noise in CdZnTe detectors

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

Luke, P. N.; Amman, M.; Lee J. S.

2000-10-10

Noise in CdZnTe devices with different electrode configurations was investigated. Measurements on devices with guard-ring electrode structures showed that surface leakage current does not produce any significant noise. The parallel white noise component of the devices appeared to be generated by the bulk current alone, even though the surface current was substantially higher. This implies that reducing the surface leakage current of a CdZnTe detector may not necessarily result in a significant improvement in noise performance. The noise generated by the bulk current is also observed to be below full shot noise. This partial suppression of shot noise may bemore » the result of Coulomb interaction between carriers or carrier trapping. Devices with coplanar strip electrodes were observed to produce a 1/f noise term at the preamplifier output. Higher levels of this 1/f noise were observed with decreasing gap widths between electrodes. The level of this 1/f noise appeared to be independent of bias voltage and leakage current but was substantially reduced after certain surface treatments.« less

Observations and Modeling for Source Characterization

DTIC Science & Technology

2011-02-25

Sequim Bay Road Sequim , WA 98382 Phone: (360) 681 -3616 Fax: (360) 681 -3699 Email: lyle.hibler@pnl.gov Grant Number: N00014-08-1-0508 LONG...currents south of the opening of San Diego Bay show a northerly propagation resulting in an eddy off of Point Loma. The currents around the Tijuana

Teacher Evaluation: The Limits of Looking.

ERIC Educational Resources Information Center

Stodolsky, Susan S.

1984-01-01

Reviews current teacher evaluation practices with particular focus on the use of observation. Argues that direct observation is an inadequate evaluation technique because it assumes that stability and consistency are necessary for effective teaching. Presents data showing that flexibility is a more accurate characterization of elementary level…

DMSP F7 observations of a substorm field-aligned current

NASA Technical Reports Server (NTRS)

Lopez, R. E.; Spence, H. E.; Meng, C.-I.

1991-01-01

Observations are described of a substorm field-aligned current (FAC) system traversed by the DMSP F7 spacecraft just after 0300 UT on April 25, 1985. It is shown that the substorm FAC portion of the current system was located equatorward of the boundary between open and closed field lines. The equatorward boundary of the substorm FAC into the magnetotail was mapped using the Tsyganenko (1987) model, showing that the boundary corresponds to 6.9 earth radii. The result is consistent with the suggestion of Akasofu (1972) and Lopez and Lui (1990) that the region of substorm initiation lies relatively close to the earth and the concept that an essential feature of substorms is the disruption and diversion of the near-earth current sheet.

Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors

NASA Technical Reports Server (NTRS)

Sadleir, John E.; Smith, Stephen J.; Bandler, SImon R.; Chervenak, James A.; Clem, John R.

2009-01-01

We have found experimentally that the critical current of a square superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T. As a consequence, the effective transition temperature T(sub c) of the TES is current-dependent and at fixed current scales as 1/L(sup 2). We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. The observed behavior has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. We have observed the proximity effect in these devices over extraordinarily long lengths exceeding 100 microns.

Multiple-Satellite Observation of Magnetic Dip Event During the Substorm on 10 October 2013

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

He, Zhaoguo; Chen, Lunjin; Zhu, Hui

Here, we present a multiple-satellite observation of the magnetic dip event during the substorm on 10 October 2013. The observation illustrates the temporal and spatial evolution of the magnetic dip and gives a compelling evidence that ring current ions induce the magnetic dip by enhanced plasma beta. The dip moves with the energetic ions in a comparable drift velocity and affects the dynamics of relativistic electrons in the radiation belt. In addition, the magnetic dip provides a favorable condition for the electromagnetic ion cyclotron (EMIC) wave generation based on the linear theory analysis. The calculated proton diffusion coefficients show thatmore » the observed EMIC wave can lead to the pitch angle scattering losses of the ring current ions, which in turn partially relax the magnetic dip in the observations. This study enriches our understanding of magnetic dip evolution and demonstrates the important role of the magnetic dip for the coupling of radiation belt and ring current.« less

Multiple-Satellite Observation of Magnetic Dip Event During the Substorm on 10 October 2013

NASA Astrophysics Data System (ADS)

He, Zhaoguo; Chen, Lunjin; Zhu, Hui; Xia, Zhiyang; Reeves, G. D.; Xiong, Ying; Xie, Lun; Cao, Yong

2017-09-01

We present a multiple-satellite observation of the magnetic dip event during the substorm on 10 October 2013. The observation illustrates the temporal and spatial evolution of the magnetic dip and gives a compelling evidence that ring current ions induce the magnetic dip by enhanced plasma beta. The dip moves with the energetic ions in a comparable drift velocity and affects the dynamics of relativistic electrons in the radiation belt. In addition, the magnetic dip provides a favorable condition for the electromagnetic ion cyclotron (EMIC) wave generation based on the linear theory analysis. The calculated proton diffusion coefficients show that the observed EMIC wave can lead to the pitch angle scattering losses of the ring current ions, which in turn partially relax the magnetic dip in the observations. This study enriches our understanding of magnetic dip evolution and demonstrates the important role of the magnetic dip for the coupling of radiation belt and ring current.

Multiple-Satellite Observation of Magnetic Dip Event During the Substorm on 10 October 2013

DOE PAGES

He, Zhaoguo; Chen, Lunjin; Zhu, Hui; ...

2017-09-05

Here, we present a multiple-satellite observation of the magnetic dip event during the substorm on 10 October 2013. The observation illustrates the temporal and spatial evolution of the magnetic dip and gives a compelling evidence that ring current ions induce the magnetic dip by enhanced plasma beta. The dip moves with the energetic ions in a comparable drift velocity and affects the dynamics of relativistic electrons in the radiation belt. In addition, the magnetic dip provides a favorable condition for the electromagnetic ion cyclotron (EMIC) wave generation based on the linear theory analysis. The calculated proton diffusion coefficients show thatmore » the observed EMIC wave can lead to the pitch angle scattering losses of the ring current ions, which in turn partially relax the magnetic dip in the observations. This study enriches our understanding of magnetic dip evolution and demonstrates the important role of the magnetic dip for the coupling of radiation belt and ring current.« less

Link between EMIC waves in a plasmaspheric plume and a detached sub-auroral proton arc with observations of Cluster and IMAGE satellites

NASA Astrophysics Data System (ADS)

Yuan, Zhigang; Deng, Xiaohua; Lin, Xi; Pang, Ye; Zhou, Meng; Décréau, P. M. E.; Trotignon, J. G.; Lucek, E.; Frey, H. U.; Wang, Jingfang

2010-04-01

In this paper, we report observations from a Cluster satellite showing that ULF wave occurred in the outer boundary of a plasmaspheric plume on September 4, 2005. The band of observed ULF waves is between the He+ ion gyrofrequency and O+ ion gyrofrequency at the equatorial plane, implying that those ULF waves can be identified as EMIC waves generated by ring current ions in the equatorial plane and strongly affected by rich cold He+ ions in plasmaspheric plumes. During the interval of observed EMIC waves, the footprint of Cluster SC3 lies in a subauroral proton arc observed by the IMAGE FUV instrument, demonstrating that the subauroral proton arc was caused by energetic ring current protons scattered into the loss cone under the Ring Current (RC)-EMIC interaction in the plasmaspheric plume. Therefore, the paper provides a direct proof that EMIC waves can be generated in the plasmaspheric plume and scatter RC ions to cause subauroral proton arcs.

Electrical transport and low-frequency noise in chemical vapor deposited single-layer MoS2 devices.

PubMed

Sharma, Deepak; Amani, Matin; Motayed, Abhishek; Shah, Pankaj B; Birdwell, A Glen; Najmaei, Sina; Ajayan, Pulickel M; Lou, Jun; Dubey, Madan; Li, Qiliang; Davydov, Albert V

2014-04-18

We have studied temperature-dependent (77-300 K) electrical characteristics and low-frequency noise (LFN) in chemical vapor deposited (CVD) single-layer molybdenum disulfide (MoS2) based back-gated field-effect transistors (FETs). Electrical characterization and LFN measurements were conducted on MoS2 FETs with Al2O3 top-surface passivation. We also studied the effect of top-surface passivation etching on the electrical characteristics of the device. Significant decrease in channel current and transconductance was observed in these devices after the Al2O3 passivation etching. For passivated devices, the two-terminal resistance variation with temperature showed a good fit to the activation energy model, whereas for the etched devices the trend indicated a hopping transport mechanism. A significant increase in the normalized drain current noise power spectral density (PSD) was observed after the etching of the top passivation layer. The observed channel current noise was explained using a standard unified model incorporating carrier number fluctuation and correlated surface mobility fluctuation mechanisms. Detailed analysis of the gate-referred noise voltage PSD indicated the presence of different trapping states in passivated devices when compared to the etched devices. Etched devices showed weak temperature dependence of the channel current noise, whereas passivated devices exhibited near-linear temperature dependence.

Non-axisymmetric equilibrium reconstruction and suppression of density limit disruptions in a current-carrying stellarator

NASA Astrophysics Data System (ADS)

Ma, Xinxing; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Knowlton, S. F.; Maurer, D. A.

2017-10-01

Non-axisymmetric equilibrium reconstructions have been routinely performed with the V3FIT code in the Compact Toroidal Hybrid (CTH), a stellarator/tokamak hybrid. In addition to 50 external magnetic measurements, 160 SXR emissivity measurements are incorporated into V3FIT to reconstruct the magnetic flux surface geometry and infer the current distribution within the plasma. Improved reconstructions of current and q profiles provide insight into understanding the physics of density limit disruptions observed in current-carrying discharges in CTH. It is confirmed that the final scenario of the density limit of CTH plasmas is consistent with classic observations in tokamaks: current profile shrinkage leads to growing MHD instabilities (tearing modes) followed by a loss of MHD equilibrium. It is also observed that the density limit at a given current linearly increases with increasing amounts of 3D shaping fields. Consequently, plasmas with densities up to two times the Greenwald limit are attained. Equilibrium reconstructions show that addition of 3D fields effectively moves resonance surfaces towards the edge of the plasma where the current profile gradient is less, providing a stabilizing effect. This work is supported by US Department of Energy Grant No. DE-FG02-00ER54610.

Assimilation of the seabird and ship drift data in the north-eastern sea of Japan into an operational ocean nowcast/forecast system

PubMed Central

Miyazawa, Yasumasa; Guo, Xinyu; Varlamov, Sergey M.; Miyama, Toru; Yoda, Ken; Sato, Katsufumi; Kano, Toshiyuki; Sato, Keiji

2015-01-01

At the present time, ocean current is being operationally monitored mainly by combined use of numerical ocean nowcast/forecast models and satellite remote sensing data. Improvement in the accuracy of the ocean current nowcast/forecast requires additional measurements with higher spatial and temporal resolution as expected from the current observation network. Here we show feasibility of assimilating high-resolution seabird and ship drift data into an operational ocean forecast system. Data assimilation of geostrophic current contained in the observed drift leads to refinement in the gyre mode events of the Tsugaru warm current in the north-eastern sea of Japan represented by the model. Fitting the observed drift to the model depends on ability of the drift representing geostrophic current compared to that representing directly wind driven components. A preferable horizontal scale of 50 km indicated for the seabird drift data assimilation implies their capability of capturing eddies with smaller horizontal scale than the minimum scale of 100 km resolved by the satellite altimetry. The present study actually demonstrates that transdisciplinary approaches combining bio-/ship- logging and numerical modeling could be effective for enhancement in monitoring the ocean current. PMID:26633309

THE ORIGIN OF NET ELECTRIC CURRENTS IN SOLAR ACTIVE REGIONS

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

Dalmasse, K.; Aulanier, G.; Démoulin, P.

There is a recurring question in solar physics regarding whether or not electric currents are neutralized in active regions (ARs). This question was recently revisited using three-dimensional (3D) magnetohydrodynamic (MHD) numerical simulations of magnetic flux emergence into the solar atmosphere. Such simulations showed that flux emergence can generate a substantial net current in ARs. Other sources of AR currents are photospheric horizontal flows. Our aim is to determine the conditions for the occurrence of net versus neutralized currents with this second mechanism. Using 3D MHD simulations, we systematically impose line-tied, quasi-static, photospheric twisting and shearing motions to a bipolar potentialmore » magnetic field. We find that such flows: (1) produce both direct and return currents, (2) induce very weak compression currents—not observed in 2.5D—in the ambient field present in the close vicinity of the current-carrying field, and (3) can generate force-free magnetic fields with a net current. We demonstrate that neutralized currents are in general produced only in the absence of magnetic shear at the photospheric polarity inversion line—a special condition that is rarely observed. We conclude that  photospheric flows, as magnetic flux emergence, can build up net currents in the solar atmosphere, in agreement with recent observations. These results thus provide support for eruption models based on pre-eruption magnetic fields that possess a net coronal current.« less

Internationally coordinated multi-mission planning is now critical to sustain the space-based rainfall observations needed for managing floods globally

NASA Astrophysics Data System (ADS)

Reed, Patrick M.; Chaney, Nathaniel W.; Herman, Jonathan D.; Ferringer, Matthew P.; Wood, Eric F.

2015-02-01

At present 4 of 10 dedicated rainfall observing satellite systems have exceeded their design life, some by more than a decade. Here, we show operational implications for flood management of a ‘collapse’ of space-based rainfall observing infrastructure as well as the high-value opportunities for a globally coordinated portfolio of satellite missions and data services. Results show that the current portfolio of rainfall missions fails to meet operational data needs for flood management, even when assuming a perfectly coordinated data product from all current rainfall-focused missions (i.e., the full portfolio). In the full portfolio, satellite-based rainfall data deficits vary across the globe and may preclude climate adaptation in locations vulnerable to increasing flood risks. Moreover, removing satellites that are currently beyond their design life (i.e., the reduced portfolio) dramatically increases data deficits globally and could cause entire high intensity flood events to be unobserved. Recovery from the reduced portfolio is possible with internationally coordinated replenishment of as few as 2 of the 4 satellite systems beyond their design life, yielding rainfall data coverages that outperform the current full portfolio (i.e., an optimized portfolio of eight satellites can outperform ten satellites). This work demonstrates the potential for internationally coordinated satellite replenishment and data services to substantially enhance the cost-effectiveness, sustainability and operational value of space-based rainfall observations in managing evolving flood risks.

Ionospheric Alfvén resonator and aurora: Modeling of MICA observations

NASA Astrophysics Data System (ADS)

Tulegenov, B.; Streltsov, A. V.

2017-07-01

We present results from a numerical study of small-scale, intense magnetic field-aligned currents observed in the vicinity of the discrete auroral arc by the Magnetosphere-Ionosphere Coupling in the Alfvén Resonator (MICA) sounding rocket launched from Poker Flat, Alaska, on 19 February 2012. The goal of the MICA project was to investigate the hypothesis that such currents can be produced inside the ionospheric Alfvén resonator by the ionospheric feedback instability (IFI) driven by the system of large-scale magnetic field-aligned currents interacting with the ionosphere. The trajectory of the MICA rocket crossed two discrete auroral arcs and detected packages of intense, small-scale currents at the edges of these arcs, in the most favorable location for the development of the ionospheric feedback instability, predicted by the IFI theory. Simulations of the reduced MHD model derived in the dipole magnetic field geometry with realistic background parameters confirm that IFI indeed generates small-scale ULF waves inside the ionospheric Alfvén resonator with frequency, scale size, and amplitude showing a good, quantitative agreement with the observations. The comparison between numerical results and observations was performed by "flying" a virtual MICA rocket through the computational domain, and this comparison shows that, for example, the waves generated in the numerical model have frequencies in the range from 0.30 to 0.45 Hz, and the waves detected by the MICA rocket have frequencies in the range from 0.18 to 0.50 Hz.

Turbulence between two inline hemispherical obstacles under wave-current interactions

NASA Astrophysics Data System (ADS)

Barman, K.; Debnath, K.; Mazumder, B. S.

2016-02-01

This paper reports an experimental investigation of open channel turbulent flow between two inline surface mounted hemispherical obstacles in tandem arrangement. A series of experiments are performed under combined wave-current interaction with seven relative spacing L/h, where L is center to center spacing distance and h is the obstacle height for Reynolds number Re = 5.88 × 104. The observations are particularly focused on the changes induced in the mean velocity components, turbulence intensities and Reynolds shear stress due to superposition of surface waves on the ambient flow, and are compared to that of flat-surface and a single hemisphere. The paper also investigates the dominant turbulent bursting events that contribute to the Reynolds shear stress for different relative depth influenced by hemispheres. It is observed that the contributions to the total shear stress due to ejection and sweep are dominant at the wake region for single and double hemisphere near the bed, while towards the surface outward and inward interactions show significant effect for wave-current interactions which is largely different from that over the flat-surface case. Spectral analysis of the observed velocity fluctuations reveals the existence of two distinct power law scaling regime near the bed. At high frequency, an inertial sub-range of turbulence with -5/3 Kolmogorov scaling is observed for the flat-surface. The spectral slope is calculated to show the shifting of standard Kolmogorov scale for both only current and wave-induced tests.

Transient tidal eddy motion in the western Gulf of Maine, part 1: Primary structure

NASA Astrophysics Data System (ADS)

Brown, W. S.; Marques, G. M.

2013-07-01

High frequency radar-derived surface current maps of the Great South Channel (GSC) in the western Gulf of Maine in 2005 revealed clockwise (CW) and anticlockwise (ACW) eddy motion associated with the strong regional tidal currents. To better elucidate the kinematics and dynamics of these transient tidal eddy motions, an observational and modeling study was conducted during the weakly stratified conditions of winter 2008-2009. Our moored bottom pressure and ADCP current measurements in 13m depth were augmented by historical current measurements in about 30m in documenting the dominance of highly polarized M2 semidiurnal currents in our nearshore study region. The high-resolution finite element coastal ocean model (QUODDY) - forced by the five principal tidal constituents - produced maps depicting the formation and evolution of the CW and ACW eddy motions that regularly follow maximum ebb and flood flows, respectively. Observation versus model current comparison required that the model bottom current drag coefficient be set to at an unusually high Cd=0.01 - suggesting the importance of form drag in the study region. The observations and model results were consistent in diagnosing CW or ACW eddy motions that (a) form nearshore in the coastal boundary layer (CBL) for about 3h after the respective tidal current maxima and then (b) translate southeastward across the GSC along curved 50m isobath at speeds of about 25m/s. Observation-based and model-based momentum budget estimates were consistent in showing a first order forced semidiurnal standing tidal wave dynamics (like the adjacent Gulf of Maine) which was modulated by adverse pressure gradient/bottom stress forcing to generate the eddy motions. Observation-based estimates of terms in the transport vorticity budget showed that in the shallower Inner Zone subregion (average depth=23m) that the diffusion of nearshore vorticity was dominant in feeding the growth of eddy motion vorticity; while in the somewhat deeper Outer Zone subregion (33m) bottom current lateral shear and water column stretching/squashing was significant in modulating the eddy motion. We conclude that the transient eddy motions in the GSC region are phase eddies that accompany the change of tide across the GSC and are (1) generated by bottom stress gradients in the shallower nearshore - an issue which needs to be better understood for improved future forecasting.

The Deep Western Boundary Current in the Labrador Sea From Observations and a High-Resolution Model

NASA Astrophysics Data System (ADS)

Handmann, Patricia; Fischer, Jürgen; Visbeck, Martin; Karstensen, Johannes; Biastoch, Arne; Böning, Claus; Patara, Lavinia

2018-04-01

Long-term observations from a 17 year long mooring array at the exit of the Labrador Sea at 53°N are compared to the output of a high-resolution model (VIKING20). Both are analyzed to define robust integral properties on basin and regional scale, which can be determined and evaluated equally well. While both, the observations and the model, show a narrow DWBC cyclonically engulfing the Labrador Sea, the model's boundary current system is more barotropic than in the observations and spectral analysis indicates stronger monthly to interannual transport variability. Compared to the model, the observations show a stronger density gradient, hence a stronger baroclinicity, from center to boundary. Despite this, the observed temporal evolution of the temperature in the central Labrador Sea is reproduced. The model results yield a mean export of North Atlantic Deep Water (NADW) (33.0 ± 5.7 Sv), which is comparable to the observed transport (31.2 ± 5.5 Sv) at 53°N. The results also include a comparable spatial pattern and March mixed layer depth in the central Labrador Sea (maximum depth ˜2,000 m). During periods containing enhanced deep convection (1990s) our analyses show increased correlation between LSW and LNADW model transport at 53°N. Our results indicate that the transport variability in LSW and LNADW at 53°N is a result of a complex modulation of wind stress and buoyancy forcing on regional and basin wide scale.

Large mesopelagic fishes biomass and trophic efficiency in the open ocean.

PubMed

Irigoien, Xabier; Klevjer, T A; Røstad, A; Martinez, U; Boyra, G; Acuña, J L; Bode, A; Echevarria, F; Gonzalez-Gordillo, J I; Hernandez-Leon, S; Agusti, S; Aksnes, D L; Duarte, C M; Kaartvedt, S

2014-01-01

With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters.

Large mesopelagic fishes biomass and trophic efficiency in the open ocean

PubMed Central

Irigoien, Xabier; Klevjer, T. A.; Røstad, A.; Martinez, U.; Boyra, G.; Acuña, J. L.; Bode, A.; Echevarria, F.; Gonzalez-Gordillo, J. I.; Hernandez-Leon, S.; Agusti, S.; Aksnes, D. L.; Duarte, C. M.; Kaartvedt, S.

2014-01-01

With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters. PMID:24509953

Progress on Artist Improvements

DTIC Science & Technology

1988-11-01

without Elimination of Multiple Es 13 10 ARTIST Printout to Show the Current Version Number 16 1 1 ARTIST Autoscaling lonogram 18 12 ARTIST Autoscaling ...subroutines used in that version. Another area of concern has been the often observed roughness of the h’(f) traces. The ARTIST autoscaling often...1 2 3 4 [MHz] F 3(:) 0 53 58 E C) ES 22 46 57 Figure 10. ARTIST Printout to Show the Current Version Number 4.0 SMOOTHING OF THE AUTOSCALED TRACES The

Do substorms energise the ring current?

NASA Astrophysics Data System (ADS)

Sandhu, J. K.; Rae, J.; Freeman, M. P.; Forsyth, C.; Jackman, C. M.; Lam, M. M.

2017-12-01

The substorm phenomenon is a highly dynamic and variable process that results in the global reconfiguration and redistribution of energy within the magnetosphere. There are many open questions surrounding substorms, particularly how the energy released during a substorm is distributed throughout the magnetosphere, and how the energy loss varies from one substorm to the next. In this study, we explore whether energy lost during the substorm plays a role in energising the ring current. Using observations of the particle energy flux from RBSPICE/RBSP, we are able to quantitatively observe how the energy is distributed spatially and across the different ion species (H+, He+, and O+). Furthermore, we can observe how the total energy content of the ring current changes during the substorm process, using substorm phases defined by the SOPHIE algorithm. This analysis provides information on how the energy released from a substorm is partitioned throughout the magnetosphere, and on the processes determining the energy provided to the ring current. Overall, our results show that the substorm-ring current coupling is more complex than originally thought, and we discuss the reasons behind this complex response.

STS-65 Earth observation of island wake at Oahu, Hawaii, taken from OV-102

NASA Technical Reports Server (NTRS)

1994-01-01

STS-65 Earth observation taken aboard Columbia, Orbiter Vehicle (OV) 102, shows Oahu, Hawaii. The island wake emerging to the lower left side of Oahu is caused by wind currents blowing from the northeast being obstructed by the northwest-southeast trending, cloud covered, Koolau mountain range. The lighter colored water indicates a more smooth surface with a slower water current that the darker, rougher, faster moving water current. Pearl Harbor is visible to the south of the Koolau Range. To the right, or east, of Pearl Harbor is the city of Honolulu. The circular, brown feature to the east of Honolulu is the dormant volcano Diamond Head.

Sliding mode observers for automotive alternator

NASA Astrophysics Data System (ADS)

Chen, De-Shiou

Estimator development for synchronous rectification of the automotive alternator is a desirable approach for estimating alternator's back electromotive forces (EMFs) without a direct mechanical sensor of the rotor position. Recent theoretical studies show that estimation of the back EMF may be observed based on system's phase current model by sensing electrical variables (AC phase currents and DC bus voltage) of the synchronous rectifier. Observer design of the back EMF estimation has been developed for constant engine speed. In this work, we are interested in nonlinear observer design of the back EMF estimation for the real case of variable engine speed. Initial back EMF estimate can be obtained from a first-order sliding mode observer (SMO) based on the phase current model. A fourth-order nonlinear asymptotic observer (NAO), complemented by the dynamics of the back EMF with time-varying frequency and amplitude, is then incorporated into the observer design for chattering reduction. Since the cost of required phase current sensors may be prohibitive, the most applicable approach in real implementation by measuring DC current of the synchronous rectifier is carried out in the dissertation. It is shown that the DC link current consists of sequential "windows" with partial information of the phase currents, hence, the cascaded NAO is responsible not only for the purpose of chattering reduction but also for necessarily accomplishing the process of estimation. Stability analyses of the proposed estimators are considered for most linear and time-varying cases. The stability of the NAO without speed information is substantiated by both numerical and experimental results. Prospective estimation algorithms for the case of battery current measurements are investigated. Theoretical study indicates that the convergence of the proposed LAO may be provided by high gain inputs. Since the order of the LAO/NAO for the battery current case is one order higher than that of the link current measurements, it is hard to find moderate values of the input gains for the real-time sampled-data systems. Technical difficulties in implementation of such high order discrete-time nonlinear estimators have been discussed. Directions of further investigations have been provided.

Minimal Unified Resolution to R_{K^{(*)}} and R(D^{(*)}) Anomalies with Lepton Mixing.

PubMed

Choudhury, Debajyoti; Kundu, Anirban; Mandal, Rusa; Sinha, Rahul

2017-10-13

It is a challenging task to explain, in terms of a simple and compelling new physics scenario, the intriguing discrepancies between the standard model expectations and the data for the neutral-current observables R_{K} and R_{K^{*}}, as well as the charged-current observables R(D) and R(D^{*}). We show that this can be achieved in an effective theory with only two unknown parameters. In addition, this class of models predicts some interesting signatures in the context of both B decays as well as high-energy collisions.

Direct observation of current-induced conductive path in colossal-electroresistance manganite thin films

NASA Astrophysics Data System (ADS)

Wei, Wengang; Zhu, Yinyan; Bai, Yu; Liu, Hao; Du, Kai; Zhang, Kai; Kou, Yunfang; Shao, Jian; Wang, Wenbin; Hou, Denglu; Dong, Shuai; Yin, Lifeng; Shen, Jian

2016-01-01

Manganites are known to often show colossal electroresistance (CER) in addition to colossal magnetoresistance. The (La1-yP ry) 1 -xC axMn O3 (LPCMO) system has a peculiar CER behavior in that little change of magnetization occurs. We use a magnetic force microscope to uncover the CER mechanism in the LPCMO system. In contrast to the previous belief that current reshapes the ferromagnetic metallic (FMM) domains, we show that the shape of the FMM domains remain virtually unchanged after passing electric current. Instead, it is the appearance of a tiny fraction of FMM "bridges" that is responsible for the CER behavior.

Analysis of tidal currents in the North Sea from shipboard acoustic Doppler current profiler data

NASA Astrophysics Data System (ADS)

Vindenes, Håvard; Orvik, Kjell Arild; Søiland, Henrik; Wehde, Henning

2018-06-01

North Sea tidal currents are determined by applying harmonic analysis to ship-borne acoustic Doppler current profiler data recorded from 1999 to 2016, covering large areas of the northern North Sea. Direct current measurement data sets of this magnitude are rare in the otherwise well investigated North Sea, and thus it is a valuable asset in studying and expanding our understanding of its tidal currents and circulation in general. The harmonic analysis is applied to a least squares fit of the current observations at a set of knot points. Results from the harmonic analysis compare favorably to tidal parameters estimated from observations from moored instruments. The analysis shows that the tides are characterized by strong semi-diurnal component, with amplitudes of the principal Lunar constituent ranging from 1.6 cm/s in the Skagerrak to 67 cm/s in the Fair Isle Channel. Diurnal tides are found to be approximately one fifth the strength of the predominant semi-diurnal constituent. Output from a regional barotropic tide model compares well to tidal current determined from the harmonic analysis of the Acoustic Doppler Current Profiler data.

Accaleration of Electrons of the Outer Electron Radiation Belt and Auroral Oval Dynamics

NASA Astrophysics Data System (ADS)

Antonova, Elizaveta; Ovchinnikov, Ilya; Riazantseva, Maria; Znatkova, Svetlana; Pulinets, Maria; Vorobjev, Viachislav; Yagodkina, Oksana; Stepanova, Marina

2016-07-01

We summarize the results of experimental observations demonstrating the role of auroral processes in the formation of the outer electron radiation belt and magnetic field distortion during magnetic storms. We show that the auroral oval does not mapped to the plasma sheet proper (region with magnetic field lines stretched in the tailward direction). It is mapped to the surrounding the Earth plasma ring in which transverse currents are closed inside the magnetosphere. Such currents constitute the high latitude continuation of the ordinary ring current. Mapping of the auroral oval to the region of high latitude continuation of the ordinary ring current explains the ring like shape of the auroral oval with finite thickness near noon and auroral oval dynamics during magnetic storms. The auroral oval shift to low latitudes during storms. The development of the ring current produce great distortion of the Earth's magnetic field and corresponding adiabatic variations of relativistic electron fluxes. Development of the asymmetric ring current produce the dawn-dusk asymmetry of such fluxes. We analyze main features of the observed processes including formation of sharp plasma pressure profiles during storms. The nature of observed pressure peak is analyzed. It is shown that the observed sharp pressure peak is directly connected with the creation of the seed population of relativistic electrons. The possibility to predict the position of new radiation belt during recovery phase of the magnetic storm using data of low orbiting and ground based observations is demonstrated.

Comparison of dark energy models after Planck 2015

NASA Astrophysics Data System (ADS)

Xu, Yue-Yao; Zhang, Xin

2016-11-01

We make a comparison for ten typical, popular dark energy models according to their capabilities of fitting the current observational data. The observational data we use in this work include the JLA sample of type Ia supernovae observation, the Planck 2015 distance priors of cosmic microwave background observation, the baryon acoustic oscillations measurements, and the direct measurement of the Hubble constant. Since the models have different numbers of parameters, in order to make a fair comparison, we employ the Akaike and Bayesian information criteria to assess the worth of the models. The analysis results show that, according to the capability of explaining observations, the cosmological constant model is still the best one among all the dark energy models. The generalized Chaplygin gas model, the constant w model, and the α dark energy model are worse than the cosmological constant model, but still are good models compared to others. The holographic dark energy model, the new generalized Chaplygin gas model, and the Chevalliear-Polarski-Linder model can still fit the current observations well, but from an economically feasible perspective, they are not so good. The new agegraphic dark energy model, the Dvali-Gabadadze-Porrati model, and the Ricci dark energy model are excluded by the current observations.

High electric field conduction in low-alkali boroaluminosilicate glass

NASA Astrophysics Data System (ADS)

Dash, Priyanka; Yuan, Mengxue; Gao, Jun; Furman, Eugene; Lanagan, Michael T.

2018-02-01

Electrical conduction in silica-based glasses under a low electric field is dominated by high mobility ions such as sodium, and there is a transition from ionic transport to electronic transport as the electric field exceeds 108 V/m at low temperatures. Electrical conduction under a high electric field was investigated in thin low-alkali boroaluminosilicate glass samples, showing nonlinear conduction with the current density scaling approximately with E1/2, where E is the electric field. In addition, thermally stimulated depolarization current (TSDC) characterization was carried out on room-temperature electrically poled glass samples, and an anomalous discharging current flowing in the same direction as the charging current was observed. High electric field conduction and TSDC results led to the conclusion that Poole-Frenkel based electronic transport occurs in the mobile-cation-depleted region adjacent to the anode, and accounts for the observed anomalous current.

Observations of currents and density structure across a buoyant plume front

USGS Publications Warehouse

Gelfenbaum, G.; Stumpf, R.P.

1993-01-01

Observations of the Mobile Bay, Alabama, plume during a flood event in April 1991 reveal significant differences in the current field on either side of a front associated with the buoyant plume. During a strong southeasterly wind, turbid, low salinity water from Mobile Bay was pushed through an opening in the west side of the ebb-tidal delta and moved parallel to the coast. A stable front developed between the low salinity water of the buoyant plume (11‰) and the high salinity coastal water (>23‰) that was being forced landward by the prevailing winds. Despite the shallow water depth of 6 m, measurements of currents, temperature, and salinity show large shears and density gradients in both the vertical and the horizontal directions. At a station outside of the buoyant plume, currents at 0.5 m and 1.5 m below the surface were in the same direction as the wind. Inside the plume, however, currents at 0.5 m below the surface were parallel to the coast, 45°, off the direction of the wind and the magnitude was 45% larger than the magnitude of the surface currents outside the plume. Beneath the level of the plume, the currents were identical to the wind-driven currents in the ambient water south of the front. Our observations suggest that the wind-driven surface currents of the ambient water converged with the buoyant plume at the front and were subducted beneath the plume. The motion of the ambient coastal surface water was in the direction of the local wind stress, however, the motion of the plume had no northerly component of motion. The plume also did not show any flow toward the front, suggesting a balance between the northerly component of wind stress and the southerly component of buoyant spreading. In addition, the motion of the plume did not appear to affect the motion of the underlying ambient water, suggesting a lack of mixing between the two waters.

Spectral and Imaging Observations of a Current Sheet Region in a Small-scale Magnetic Reconnection Event

NASA Astrophysics Data System (ADS)

Xue, Zhike; Yan, Xiaoli; Yang, Liheng; Wang, Jincheng; Feng, Song; Li, Qiaoling; Ji, Kaifan; Zhao, Li

2018-05-01

We report a possible current sheet region associated with a small-scale magnetic reconnection event by using the spectral and imaging observations of the Interface Region Imaging Spectrograph (IRIS) and the magnetograms obtained by the Solar Dynamics Observatory on 2016 August 08. The length and width of the current sheet region are estimated to be from 1.4 ± 0.1 Mm to 3.0 ± 0.3 Mm and from 0.34 ± 0.01 Mm to 0.64 ± 0.09 Mm, respectively. The evolutions of the length of the current sheet region are positively correlated with that of the width. These measurements are among the smallest reported. When the IRIS slit scans the current sheet region, the spectroscopic observations show that the Si IV line is broadened in the current sheet region and the plasma has a blueshifted feature at the middle and a redshifted feature at the ends of the current sheet region. The maximum measured blueshifted and redshifted Doppler velocities are ‑20.8 ± 0.9 and 34.1 ± 0.4 km s‑1, respectively. Additionally, the electron number densities of the plasma in the current sheet region are computed to be around 1011 cm‑3 based on the spectrums of the two O IV lines. The emergence, movement, and cancellation of a small sunspot with negative polarity are observed during the formation and shift of the current sheet region. We suggest that the occurrence and evolution of the magnetic reconnection are driven by the movement of the small sunspot in the photosphere.

We still fail to account for Mendel's observations.

PubMed

Porteous, John W

2004-08-16

The present article corrects common textbook accounts of Mendel's experiments by re-establishing what he wrote and how he accounted for his observations. It notes the long-established tests for the validity of any explanations that purport to explain observations obtained by experiment. Application of these tests to Mendel's paper shows that the arguments he used to explain his observations were internally consistent but were, on one crucial issue, implausible. The same tests are applied to the currently accepted explanation for Mendel's observations. The currently favoured explanation for Mendel's observations is untenable. It misrepresents Mendel, fails to distinguish between the parameters and the variables of any system of interacting components, its arguments are inconsistent, it repeats the implausibility in Mendel's paper, fails to give a rational explanation for his observed 3:1 trait ratio and cannot explain why this ratio is not always observed in experimental practice. A rational explanation for Mendel's observations is initiated. Readers are challenged to complete the process before a further article appears.

Properties of the Agulhas Current's Inshore Front During The Shelf Agulhas Glider Experiment (SAGE)

NASA Astrophysics Data System (ADS)

Krug, M.; Swart, S.; Goschen, W.

2016-02-01

The response of coastal and shelf regions to changes in the Agulhas Current remains poorly studied. This is partly due to observational challenges associated with sampling western boundary currents. Cross-shelf exchange in such energetic current systems occurs through a range of meso- ( 50-200 km) and sub-meso (<10 km) scale processes which are difficult to observe using moored current arrays or Lagrangian platforms. Profiling gliders offer a revolutionary technology to continuously sample the energetic inshore regions of the Agulhas Current at a high spatial (100's of meters to 3km - well within the sub-mesoscale range) and temporal (0.5-4 hourly) resolution. In April 2015, two SeaGliders were deployed off Port Elizabeth (34S) at the inshore edge of the Agulhas Current as part of the Shelf Agulhas Glider Experiment (SAGE), testing for the very 1st time the feasibility of operating autonomous platforms in this highly turbulent and energetic western boundary current system. For a period of approximately two months, the Seagliders provided continuous observations at the inshore boundary of the Agulhas Current at an unprecedented spatial resolution. Observations from the Seagliders showed that at the inshore edge of the Agulhas Current, both surface and depth averaged currents are aligned in a south-west / north- east direction, with stronger flows encountered over deeper regions of the shelf, when the gliders are closer to the Agulhas Current. In the absence of large meanders, the mean flow at the inshore boundary of the Agulhas Current is characterised by strong shear with a counter current flowing in opposite direction to the mean current field. Instances of counter currents occur 45% of the time in the surface flow and 54% of the time in the depth-averaged record. More than 80% of return flow occurrences occur when glider is in water depth of less than 200m.

Atmospheric Signature of the Agulhas Current

NASA Astrophysics Data System (ADS)

Nkwinkwa Njouodo, Arielle Stela; Koseki, Shunya; Keenlyside, Noel; Rouault, Mathieu

2018-05-01

Western boundary currents play an important role in the climate system by transporting heat poleward and releasing it to the atmosphere. While their influence on extratropical storms and oceanic rainfall is becoming appreciated, their coastal influence is less known. Using satellite and climate reanalysis data sets and a regional atmospheric model, we show that the Agulhas Current is a driver of the observed band of rainfall along the southeastern African coast and above the Agulhas Current. The Agulhas current's warm core is associated with sharp gradients in sea surface temperature and sea level pressure, a convergence of low-level winds, and a co-located band of precipitation. Correlations among wind convergence, sea level pressure, and sea surface temperature indicate that these features show high degree of similarity to those in the Gulf Stream region. Model experiments further indicate that the Agulhas Current mostly impacts convective rainfall.

Direct measurements of mean Reynolds stress and ripple roughness in the presence of energetic forcing by surface waves

USGS Publications Warehouse

Scully, Malcolm; Trowbridge, John; Sherwood, Christopher R.; Jones, Katie R.; Traykovski, Peter A.

2018-01-01

Direct covariance observations of the mean flow Reynolds stress and sonar images of the seafloor collected on a wave‐exposed inner continental shelf demonstrate that the drag exerted by the seabed on the overlying flow is consistent with boundary layer models for wave‐current interaction, provided that the orientation and anisotropy of the bed roughness are appropriately quantified. Large spatial and temporal variations in drag result from nonequilibrium ripple dynamics, ripple anisotropy, and the orientation of the ripples relative to the current. At a location in coarse sand characterized by large two‐dimensional orbital ripples, the observed drag shows a strong dependence on the relative orientation of the mean current to the ripple crests. At a contrasting location in fine sand, where more isotropic sub‐orbital ripples are observed, the sensitivity of the current to the orientation of the ripples is reduced. Further, at the coarse site under conditions when the currents are parallel to the ripple crests and the wave orbital diameter is smaller than the wavelength of the relic orbital ripples, the flow becomes hydraulically smooth. This transition is not observed at the fine site, where the observed wave orbital diameter is always greater than the wavelength of the observed sub‐orbital ripples. Paradoxically, the dominant along‐shelf flows often experience lower drag at the coarse site than at the fine site, despite the larger ripples, highlighting the complex dynamics controlling drag in wave‐exposed environments with heterogeneous roughness.

Direct Measurements of Mean Reynolds Stress and Ripple Roughness in the Presence of Energetic Forcing by Surface Waves

NASA Astrophysics Data System (ADS)

Scully, Malcolm E.; Trowbridge, John H.; Sherwood, Christopher R.; Jones, Katie R.; Traykovski, Peter

2018-04-01

Direct covariance observations of the mean flow Reynolds stress and sonar images of the seafloor collected on a wave-exposed inner continental shelf demonstrate that the drag exerted by the seabed on the overlying flow is consistent with boundary layer models for wave-current interaction, provided that the orientation and anisotropy of the bed roughness are appropriately quantified. Large spatial and temporal variations in drag result from nonequilibrium ripple dynamics, ripple anisotropy, and the orientation of the ripples relative to the current. At a location in coarse sand characterized by large two-dimensional orbital ripples, the observed drag shows a strong dependence on the relative orientation of the mean current to the ripple crests. At a contrasting location in fine sand, where more isotropic sub-orbital ripples are observed, the sensitivity of the current to the orientation of the ripples is reduced. Further, at the coarse site under conditions when the currents are parallel to the ripple crests and the wave orbital diameter is smaller than the wavelength of the relic orbital ripples, the flow becomes hydraulically smooth. This transition is not observed at the fine site, where the observed wave orbital diameter is always greater than the wavelength of the observed sub-orbital ripples. Paradoxically, the dominant along-shelf flows often experience lower drag at the coarse site than at the fine site, despite the larger ripples, highlighting the complex dynamics controlling drag in wave-exposed environments with heterogeneous roughness.

Coronal Current Sheet Evolution in the Aftermath of a CME

NASA Technical Reports Server (NTRS)

Bemporad, A.; Poletto, G.; Suess, S. T.; Ko, Y.-K.; Schwadron, N. A.; Elliott, H. A.; Raymond, J. C.

2005-01-01

We report on SOHO-UVCS observations of coronal restructuring following a Coronal Mass Ejection (CME) on November 26, 2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after the CME, which was directed towards Ulysses, UVCS began taking spectra at 1.7 solar radii, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6x10(6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by SWICS throughout the magnetic cloud associated with the CME, although the rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Investigation on Microstructure and Mechanical Properties of Continuous and Pulsed Current Gas Tungsten Arc Welded alloy 600

NASA Astrophysics Data System (ADS)

Srikanth, A.; Manikandan, M.

2018-02-01

The present study investigates the microstructure and mechanical properties of joints fabricated by Continuous and pulsed current gas tungsten arc welded alloy 600. Welding was done by autogenous mode. The macro examination was carried out to evaluate the welding defects in the weld joints. Optical and Scanning Electron Microscope (SEM) were performed to assess the microstructural changes in the fusion zone. Energy Dispersive Spectroscopy (EDS) analysis was carried to evaluate the microsegregation of alloying elements in the fusion zone. The tensile test was conducted to assess the strength of the weld joints. The results show that no welding defects were observed in the fusion zones of Continuous and Pulsed current Gas Tungsten Arc Welding. The refined microstructure was found in the pulsed current compared to continuous current mode. Microsegregation was not noticed in the weld grain boundary of continuous and pulsed current mode. The pulsed current shows improved mechanical properties compared to the continuous current mode.

HST observations of Europa's atmospheric UV emission

NASA Astrophysics Data System (ADS)

Saur, J. S.; Feldman, P. D.; Strobel, D. F.; Retherford, K. D.; Roth, L.; McGrath, M. A.; Gerard, J. M.; Grodent, D. C.; Schilling, N.

2009-12-01

The Advanced Camera for Surveys on the Hubble Space Telescope observed Europa on June 29, 2008 during five consecutive orbits. Europa was at eastern elongation and crossed the Jovian current sheet during the observing interval. The observations were performed with ACS/SBC with prism PR130L to separate the two prominent FUV oxygen lines OI 1304 A, OI 1356 A and to discriminate reflected solar light from Europa's surface. After addressing the strong red leak contained in the measurements, we find that Europa's atmospheric emission clearly depends on Europa's position in Jupiter's current sheet. We also see that the atmospheric emissions of Europa's leading side do not show pronounced asymmetries with respect to Europa's sub-Jovian and anti-Jovian side. Previous observations of the atmospheric emissions, in contrast, found a strong asymmetry on Europa's trailing side [McGrath et al. 2004].

Observations of Hall Reconnection Physics Far Downstream of the X Line.

PubMed

Mistry, R; Eastwood, J P; Haggerty, C C; Shay, M A; Phan, T D; Hietala, H; Cassak, P A

2016-10-28

Observations made using the Wind spacecraft of Hall magnetic fields in solar wind reconnection exhausts are presented. These observations are consistent with the generation of Hall fields by a narrow ion inertial scale current layer near the separatrix, which is confirmed with an appropriately scaled particle-in-cell simulation that shows excellent agreement with observations. The Hall fields are observed thousands of ion inertial lengths downstream from the reconnection X line, indicating that narrow regions of kinetic dynamics can persist extremely far downstream.

Multispacecraft Observations and Modeling of the 22/23 June 2015 Geomagnetic Storm

NASA Technical Reports Server (NTRS)

Reiff, P. H.; Daou, A. G.; Sazykin, S. Y.; Nakamura, R.; Hairston, M. R.; Coffey, V.; Chandler, M. O.; Anderson, B. J.; Russell, C. T.; Welling, D.;

Effective Thermodynamics for a Marginal Observer

NASA Astrophysics Data System (ADS)

Polettini, Matteo; Esposito, Massimiliano

2017-12-01

Thermodynamics is usually formulated on the presumption that the observer has complete information about the system he or she deals with: no parasitic current, exact evaluation of the forces that drive the system. For example, the acclaimed fluctuation relation (FR), relating the probability of time-forward and time-reversed trajectories, assumes that the measurable transitions suffice to characterize the process as Markovian (in our case, a continuous-time jump process). However, most often the observer only measures a marginal current. We show that he or she will nonetheless produce an effective description that does not dispense with the fundamentals of thermodynamics, including the FR and the 2nd law. Our results stand on the mathematical construction of a hidden time reversal of the dynamics, and on the physical requirement that the observed current only accounts for a single transition in the configuration space of the system. We employ a simple abstract example to illustrate our results and to discuss the feasibility of generalizations.

ISEE 1 observations of electrostatic ion cyclotron waves in association with ion beams on auroral field lines from about 2.5 to 4.5 R(E)

NASA Technical Reports Server (NTRS)

Catell, C. A.; Mozer, F. S.; Roth, I.; Anderson, R. R.; Elphic, R. C.

1991-01-01

Quasi-monochromatic waves at about the hydrogen cyclotron frequency were observed as the ISEE 1 satellite traversed auroral field lines at radial distances of about 2.5-4.5 R(E) near midnight on June 19, 1981. Waves and both lower and higher frequencies were observed at higher altitudes, and possible electrostatic helium cyclotron and oxygen cyclotron waves occurred at lower altitudes. Upflowing hydrogen and oxygen beams and field-aligned currents occurred simultaneously. The features of the waves are most consistent with the current-driven mode. In addition, numerical studies of the linear dispersion relation, using parameters based on the observations, show that both the parallel and oblique two-stream modes and the ion-beam-driven modes were stable while oblique current-driven modes were unstable. The O(+) and H(+) distributions provide evidence for interactions with local electrostatic ion cyclotron waves and for the H(+)-O(+) two-stream instability at altitudes below the satellite.

Mercury's magnetosphere after MESSENGER's first flyby.

PubMed

Slavin, James A; Acuña, Mario H; Anderson, Brian J; Baker, Daniel N; Benna, Mehdi; Gloeckler, George; Gold, Robert E; Ho, George C; Killen, Rosemary M; Korth, Haje; Krimigis, Stamatios M; McNutt, Ralph L; Nittler, Larry R; Raines, Jim M; Schriver, David; Solomon, Sean C; Starr, Richard D; Trávnícek, Pavel; Zurbuchen, Thomas H

2008-07-04

Observations by MESSENGER show that Mercury's magnetosphere is immersed in a comet-like cloud of planetary ions. The most abundant, Na+, is broadly distributed but exhibits flux maxima in the magnetosheath, where the local plasma flow speed is high, and near the spacecraft's closest approach, where atmospheric density should peak. The magnetic field showed reconnection signatures in the form of flux transfer events, azimuthal rotations consistent with Kelvin-Helmholtz waves along the magnetopause, and extensive ultralow-frequency wave activity. Two outbound current sheet boundaries were observed, across which the magnetic field decreased in a manner suggestive of a double magnetopause. The separation of these current layers, comparable to the gyro-radius of a Na+ pickup ion entering the magnetosphere after being accelerated in the magnetosheath, may indicate a planetary ion boundary layer.

A coronal magnetic field model with horizontal volume and sheet currents

NASA Technical Reports Server (NTRS)

Zhao, Xuepu; Hoeksema, J. Todd

1994-01-01

When globally mapping the observed photospheric magnetic field into the corona, the interaction of the solar wind and magnetic field has been treated either by imposing source surface boundary conditions that tacitly require volume currents outside the source surface or by limiting the interaction to thin current sheets between oppositely directed field regions. Yet observations and numerical Magnetohydrodynamic (MHD) calculations suggest the presence of non-force-free volume currents throughout the corona as well as thin current sheets in the neighborhoods of the interfaces between closed and open field lines or between oppositely directed open field lines surrounding coronal helmet-streamer structures. This work presents a model including both horizontal volume currents and streamer sheet currents. The present model builds on the magnetostatic equilibria developed by Bogdan and Low and the current-sheet modeling technique developed by Schatten. The calculation uses synoptic charts of the line-of-sight component of the photospheric magnetic field measured at the Wilcox Solar Observatory. Comparison of an MHD model with the calculated model results for the case of a dipole field and comparison of eclipse observations with calculations for CR 1647 (near solar minimum) show that this horizontal current-current-sheet model reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces polar plumes and axes of corona streamers better than the source-surface model and reproduces coro nal helmet structures better than the current-sheet model.

The effects of vertical motion on the performance of current meters

USGS Publications Warehouse

Thibodeaux, K.G.; Futrell, J. C.

1987-01-01

A series of tests to determine the correction coefficients for Price type AA and Price type OAA current meters, when subjected to vertical motion in a towing tank, have been conducted. During these tests, the meters were subjected to vertical travel that ranged from 1.0 to 4.0 ft and vertical rates of travel that ranged from 0.33 to 1.20 ft/sec while being towed through the water at speeds ranging from 0 to 8 ft/sec. The tests show that type AA and type OAA current meters are affected adversely by the rate of vertical motion and the distance of vertical travel. In addition, the tests indicate that when current meters are moved vertically, correction coefficients must be applied to the observed meter velocities to correct for the registration errors that are induced by the vertical motion. The type OAA current meter under-registers and the type AA current meter over-registers in observed meter velocity. These coefficients for the type OAA current meter range from 0.99 to 1.49 and for the type AA current meter range from 0.33 to 1.07. When making current meter measurements from a boat or a cableway, errors in observed current meter velocity will occur when the bobbing of a boat or cableway places the current meter into vertical motion. These errors will be significant when flowing water is < 2 ft/sec and the rate of vertical motion is > 0.3 ft/sec. (Author 's abstract)

THEMIS two‐point measurements of the cross‐tail current density: A thick bifurcated current sheet in the near‐Earth plasma sheet

PubMed Central

2015-01-01

Abstract The basic properties of the near‐Earth current sheet from 8 RE to 12 RE were determined based on Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations from 2007 to 2013. Ampere's law was used to estimate the current density when the locations of two spacecraft were suitable for the calculation. A total of 3838 current density observations were obtained to study the vertical profile. For typical solar wind conditions, the current density near (off) the central plane of the current sheet ranged from 1 to 2 nA/m2 (1 to 8 nA/m2). All the high current densities appeared off the central plane of the current sheet, indicating the formation of a bifurcated current sheet structure when the current density increased above 2 nA/m2. The median profile also showed a bifurcated structure, in which the half thickness was about 3 RE. The distance between the peak of the current density and the central plane of the current sheet was 0.5 to 1 RE. High current densities above 4 nA/m2 were observed in some cases that occurred preferentially during substorms, but they also occurred in quiet times. In contrast to the commonly accepted picture, these high current densities can form without a high solar wind dynamic pressure. In addition, these high current densities can appear in two magnetic configurations: tail‐like and dipolar structures. At least two mechanisms, magnetic flux depletion and new current system formation during the expansion phase, other than plasma sheet compression are responsible for the formation of the bifurcated current sheets. PMID:27722039

Accurate Modelling of Surface Currents and Internal Tides in a Semi-enclosed Coastal Sea

NASA Astrophysics Data System (ADS)

Allen, S. E.; Soontiens, N. K.; Dunn, M. B. H.; Liu, J.; Olson, E.; Halverson, M. J.; Pawlowicz, R.

2016-02-01

The Strait of Georgia is a deep (400 m), strongly stratified, semi-enclosed coastal sea on the west coast of North America. We have configured a baroclinic model of the Strait of Georgia and surrounding coastal waters using the NEMO ocean community model. We run daily nowcasts and forecasts and publish our sea-surface results (including storm surge warnings) to the web (salishsea.eos.ubc.ca/storm-surge). Tides in the Strait of Georgia are mixed and large. The baroclinic model and previous barotropic models accurately represent tidal sea-level variations and depth mean currents. The baroclinic model reproduces accurately the diurnal but not the semi-diurnal baroclinic tidal currents. In the Southern Strait of Georgia, strong internal tidal currents at the semi-diurnal frequency are observed. Strong semi-diurnal tides are also produced in the model, but are almost 180 degrees out of phase with the observations. In the model, in the surface, the barotropic and baroclinic tides reinforce, whereas the observations show that at the surface the baroclinic tides oppose the barotropic. As such the surface currents are very poorly modelled. Here we will present evidence of the internal tidal field from observations. We will discuss the generation regions of the tides, the necessary modifications to the model required to correct the phase, the resulting baroclinic tides and the improvements in the surface currents.

Constraining Modified Theories of Gravity with Gravitational-Wave Stochastic Backgrounds

NASA Astrophysics Data System (ADS)

Maselli, Andrea; Marassi, Stefania; Ferrari, Valeria; Kokkotas, Kostas; Schneider, Raffaella

2016-08-01

The direct discovery of gravitational waves has finally opened a new observational window on our Universe, suggesting that the population of coalescing binary black holes is larger than previously expected. These sources produce an unresolved background of gravitational waves, potentially observable by ground-based interferometers. In this Letter we investigate how modified theories of gravity, modeled using the parametrized post-Einsteinian formalism, affect the expected signal, and analyze the detectability of the resulting stochastic background by current and future ground-based interferometers. We find the constraints that Advanced LIGO would be able to set on modified theories, showing that they may significantly improve the current bounds obtained from astrophysical observations of binary pulsars.

On Alfvenic Waves and Stochastic Ion Heating with 1Re Observations of Strong Field-aligned Currents, Electric Fields, and O+ ions

NASA Technical Reports Server (NTRS)

Coffey, Victoria; Chandler, Michael; Singh, Nagendra

2008-01-01

The role that the cleft/cusp has in ionosphere/magnetosphere coupling makes it a very dynamic region having similar fundamental processes to those within the auroral regions. With Polar passing through the cusp at 1 Re in the Spring of 1996, we observe a strong correlation between ion heating and broadband ELF (BBELF) emissions. This commonly observed relationship led to the study of the coupling of large field-aligned currents, burst electric fields, and the thermal O+ ions. We demonstrate the role of these measurements to Alfvenic waves and stochastic ion heating. Finally we will show the properties of the resulting density cavities.

Strongly scale-dependent CMB dipolar asymmetry from super-curvature fluctuations

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

Byrnes, Christian; Domènech, Guillem; Sasaki, Misao

2016-12-01

We reconsider the observed CMB dipolar asymmetry in the context of open inflation, where a supercurvature mode might survive the bubble nucleation. If such a supercurvature mode modulates the amplitude of the curvature power spectrum, it would easily produce an asymmetry in the power spectrum. We show that current observational data can be accommodated in a three-field model, with simple quadratic potentials and a non-trivial field-space metric. Despite the presence of three fields, we believe this model is so far the simplest that can match current observations. We are able to match the observed strong scale dependence of the dipolarmore » asymmetry, without a fine tuning of initial conditions, breaking slow roll or adding a feature to the evolution of any field.« less

Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water.

PubMed

Darelius, E; Fer, I; Nicholls, K W

2016-08-02

The average rate of melting at the base of the large Filchner-Ronne Ice Shelf in the southern Weddell Sea is currently low, but projected to increase dramatically within the next century. In a model study, melt rates increase as changing ice conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner Ice Shelf cavity. Here we present observations from near Filchner Ice Shelf and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the ice front. This southward heat transport follows the eastern flank of the Filchner Depression and is found to be directly linked to the strength of a wind-driven coastal current. Our observations emphasize the potential sensitivity of Filchner-Ronne Ice Shelf melt rates to changes in wind forcing.

Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water

PubMed Central

Darelius, E.; Fer, I.; Nicholls, K. W.

2016-01-01

The average rate of melting at the base of the large Filchner-Ronne Ice Shelf in the southern Weddell Sea is currently low, but projected to increase dramatically within the next century. In a model study, melt rates increase as changing ice conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner Ice Shelf cavity. Here we present observations from near Filchner Ice Shelf and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the ice front. This southward heat transport follows the eastern flank of the Filchner Depression and is found to be directly linked to the strength of a wind-driven coastal current. Our observations emphasize the potential sensitivity of Filchner-Ronne Ice Shelf melt rates to changes in wind forcing. PMID:27481659

Memory perspective and self-concept in social anxiety: an exploratory study.

PubMed

Stopa, Lusia; Bryant, Tess

2004-07-01

The mental representation of self and observer perspective images are important maintaining factors in cognitive models of social phobia (Clark & Wells, 1995; Rapee & Heimberg, 1997). This study investigates Libby and Eibach's (2002) hypothesis that the observer perspective is used to recall memories that are incongruent with current self-concept. A total of 60 participants (divided into high and low social anxiety groups) completed a questionnaire in which they described current self-concept, recalled four memories of social occasions (two congruent, two incongruent), and rated memory age and vividness. Congruence was defined as memories that "fit" with current self-descriptions. A qualitative analysis of self-concept showed that both groups used a similar range of themes. High socially anxious participants recalled more observer perspective memories in the second incongruent memory. Congruence did not influence vividness, but public self-consciousness did. The implications of the results are discussed and suggestions made for future research.

Hamiltonian term for a uniform dc electric field under the adiabatic approximation

NASA Astrophysics Data System (ADS)

Siu, Zhuo Bin; Jalil, Mansoor B. A.; Tan, Seng Ghee

2018-02-01

In this work, we show that the disorder-free Kubo formula for the nonequilibrium value of an observable due to a dc electric field, represented by Exx ̂ in the Hamiltonian, can be interpreted as the standard time-independent theory response of the observable due to a time- and position-independent perturbation HMF. We derive the explicit expression for HMF and show that it originates from the adiabatic approximation to

Initial leakage current paths in the vertical-type GaN-on-GaN Schottky barrier diodes

NASA Astrophysics Data System (ADS)

Sang, Liwen; Ren, Bing; Sumiya, Masatomo; Liao, Meiyong; Koide, Yasuo; Tanaka, Atsushi; Cho, Yujin; Harada, Yoshitomo; Nabatame, Toshihide; Sekiguchi, Takashi; Usami, Shigeyoshi; Honda, Yoshio; Amano, Hiroshi

2017-09-01

Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations with a screw-type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current-voltage characteristics.

Random Telegraph Signal-Like Fluctuation Created by Fowler-Nordheim Stress in Gate Induced Drain Leakage Current of the Saddle Type Dynamic Random Access Memory Cell Transistor

NASA Astrophysics Data System (ADS)

Kim, Heesang; Oh, Byoungchan; Kim, Kyungdo; Cha, Seon-Yong; Jeong, Jae-Goan; Hong, Sung-Joo; Lee, Jong-Ho; Park, Byung-Gook; Shin, Hyungcheol

2010-09-01

We generated traps inside gate oxide in gate-drain overlap region of recess channel type dynamic random access memory (DRAM) cell transistor through Fowler-Nordheim (FN) stress, and observed gate induced drain leakage (GIDL) current both in time domain and in frequency domain. It was found that the trap inside gate oxide could generate random telegraph signal (RTS)-like fluctuation in GIDL current. The characteristics of that fluctuation were similar to those of RTS-like fluctuation in GIDL current observed in the non-stressed device. This result shows the possibility that the trap causing variable retention time (VRT) in DRAM data retention time can be located inside gate oxide like channel RTS of metal-oxide-semiconductor field-effect transistors (MOSFETs).

The role of Internal Solitary Waves on deep-water sedimentary processes: the case of up-slope migrating sediment waves off the Messina Strait

NASA Astrophysics Data System (ADS)

Droghei, R.; Falcini, F.; Casalbore, D.; Martorelli, E.; Mosetti, R.; Sannino, G.; Santoleri, R.; Chiocci, F. L.

2016-11-01

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary “current” that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

Effects of wave-current interaction on storm surge in the Taiwan Strait: Insights from Typhoon Morakot

NASA Astrophysics Data System (ADS)

Yu, Xiaolong; Pan, Weiran; Zheng, Xiangjing; Zhou, Shenjie; Tao, Xiaoqin

2017-08-01

The effects of wave-current interaction on storm surge are investigated by a two-dimensional wave-current coupling model through simulations of Typhoon Morakot in the Taiwan Strait. The results show that wind wave and slope of sea floor govern wave setup modulations within the nearshore surf zone. Wave setup during Morakot can contribute up to 24% of the total storm surge with a maximum value of 0.28 m. The large wave setup commonly coincides with enhanced radiation stress gradient, which is itself associated with transfer of wave momentum flux. Water levels are to leading order in modulating significant wave height inside the estuary. High water levels due to tidal change and storm surge stabilize the wind wave and decay wave breaking. Outside of the estuary, waves are mainly affected by the current-induced modification of wind energy input to the wave generation. By comparing the observed significant wave height and water level with the results from uncoupled and coupled simulations, the latter shows a better agreement with the observations. It suggests that wave-current interaction plays an important role in determining the extreme storm surge and wave height in the study area and should not be neglected in a typhoon forecast.

Measurement of magnetic field fluctuations and diamagnetic currents within a laser ablation plasma interacting with an axial magnetic field

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

Ikeda, S.; Horioka, K.; Okamura, M.

Here, the guiding of laser ablation plasmas with axial magnetic fields has been used for many applications, since its effectiveness has been proven empirically. For more sophisticated and complicated manipulations of the plasma flow, the behavior of the magnetic field during the interaction and the induced diamagnetic current in the plasma plume needs to be clearly understood. To achieve the first milestone for establishing magnetic plasma manipulation, we measured the spatial and temporal fluctuations of the magnetic field caused by the diamagnetic current. We showed that the small fluctuations of the magnetic field can be detected by using a simplemore » magnetic probe. We observed that the field penetrates to the core of the plasma plume. The diamagnetic current estimated from the magnetic field had temporal and spatial distributions which were confirmed to be correlated with the transformation of the plasma plume. Our results show that the measurement by the magnetic probe is an effective method to observe the temporal and spatial distributions of the magnetic field and diamagnetic current. The systematic measurement of the magnetic field variations is a valuable method to establish the magnetic field manipulation of the laser ablation plasma.« less

Measurement of magnetic field fluctuations and diamagnetic currents within a laser ablation plasma interacting with an axial magnetic field

DOE PAGES

Ikeda, S.; Horioka, K.; Okamura, M.

2017-10-10

Here, the guiding of laser ablation plasmas with axial magnetic fields has been used for many applications, since its effectiveness has been proven empirically. For more sophisticated and complicated manipulations of the plasma flow, the behavior of the magnetic field during the interaction and the induced diamagnetic current in the plasma plume needs to be clearly understood. To achieve the first milestone for establishing magnetic plasma manipulation, we measured the spatial and temporal fluctuations of the magnetic field caused by the diamagnetic current. We showed that the small fluctuations of the magnetic field can be detected by using a simplemore » magnetic probe. We observed that the field penetrates to the core of the plasma plume. The diamagnetic current estimated from the magnetic field had temporal and spatial distributions which were confirmed to be correlated with the transformation of the plasma plume. Our results show that the measurement by the magnetic probe is an effective method to observe the temporal and spatial distributions of the magnetic field and diamagnetic current. The systematic measurement of the magnetic field variations is a valuable method to establish the magnetic field manipulation of the laser ablation plasma.« less

Trap densities and transport properties of pentacene metal-oxide-semiconductor transistors. I. Analytical modeling of time-dependent characteristics

NASA Astrophysics Data System (ADS)

Basile, A. F.; Cramer, T.; Kyndiah, A.; Biscarini, F.; Fraboni, B.

2014-06-01

Metal-oxide-semiconductor (MOS) transistors fabricated with pentacene thin films were characterized by temperature-dependent current-voltage (I-V) characteristics, time-dependent current measurements, and admittance spectroscopy. The channel mobility shows almost linear variation with temperature, suggesting that only shallow traps are present in the semiconductor and at the oxide/semiconductor interface. The admittance spectra feature a broad peak, which can be modeled as the sum of a continuous distribution of relaxation times. The activation energy of this peak is comparable to the polaron binding energy in pentacene. The absence of trap signals in the admittance spectra confirmed that both the semiconductor and the oxide/semiconductor interface have negligible density of deep traps, likely owing to the passivation of SiO2 before pentacene growth. Nevertheless, current instabilities were observed in time-dependent current measurements following the application of gate-voltage pulses. The corresponding activation energy matches the energy of a hole trap in SiO2. We show that hole trapping in the oxide can explain both the temperature and the time dependences of the current instabilities observed in pentacene MOS transistors. The combination of these experimental techniques allows us to derive a comprehensive model for charge transport in hybrid architectures where trapping processes occur at various time and length scales.

Long-Term Geomagnetically Induced Current Observations From New Zealand: Peak Current Estimates for Extreme Geomagnetic Storms

NASA Astrophysics Data System (ADS)

Rodger, Craig J.; Mac Manus, Daniel H.; Dalzell, Michael; Thomson, Alan W. P.; Clarke, Ellen; Petersen, Tanja; Clilverd, Mark A.; Divett, Tim

2017-11-01

Geomagnetically induced current (GIC) observations made in New Zealand over 14 years show induction effects associated with a rapidly varying horizontal magnetic field (dBH/dt) during geomagnetic storms. This study analyzes the GIC observations in order to estimate the impact of extreme storms as a hazard to the power system in New Zealand. Analysis is undertaken of GIC in transformer number six in Islington, Christchurch (ISL M6), which had the highest observed currents during the 6 November 2001 storm. Using previously published values of 3,000 nT/min as a representation of an extreme storm with 100 year return period, induced currents of 455 A were estimated for Islington (with the 95% confidence interval range being 155-605 A). For 200 year return periods using 5,000 nT/min, current estimates reach 755 A (confidence interval range 155-910 A). GIC measurements from the much shorter data set collected at transformer number 4 in Halfway Bush, Dunedin, (HWB T4), found induced currents to be consistently a factor of 3 higher than at Islington, suggesting equivalent extreme storm effects of 460-1,815 A (100 year return) and 460-2,720 A (200 year return). An estimate was undertaken of likely failure levels for single-phase transformers, such as HWB T4 when it failed during the 6 November 2001 geomagnetic storm, identifying that induced currents of 100 A can put such transformer types at risk of damage. Detailed modeling of the New Zealand power system is therefore required to put this regional analysis into a global context.

Observing Inflationary Reheating

NASA Astrophysics Data System (ADS)

Martin, Jérôme; Ringeval, Christophe; Vennin, Vincent

2015-02-01

Reheating is the epoch which connects inflation to the subsequent hot big-bang phase. Conceptually very important, this era is, however, observationally poorly known. We show that the current Planck satellite measurements of the cosmic microwave background (CMB) anisotropies constrain the kinematic properties of the reheating era for most of the inflationary models. This result is obtained by deriving the marginalized posterior distributions of the reheating parameter for about 200 models of slow-roll inflation. Weighted by the statistical evidence of each model to explain the data, we show that the Planck 2013 measurements induce an average reduction of the posterior-to-prior volume by 40%. Making some additional assumptions on reheating, such as specifying a mean equation of state parameter, or focusing the analysis on peculiar scenarios, can enhance or reduce this constraint. Our study also indicates that the Bayesian evidence of a model can substantially be affected by the reheating properties. The precision of the current CMB data is therefore such that estimating the observational performance of a model now requires incorporating information about its reheating history.

Space Technology 5 Multipoint Observations of Temporal and Spatial Variability of Field-Aligned Currents

NASA Technical Reports Server (NTRS)

Le, G.; Wang, Y.; Slavin, J. A.; Strangeway, R. L.

2009-01-01

Space Technology 5 (ST5) is a constellation mission consisting of three microsatellites. It provides the first multipoint magnetic field measurements in low Earth orbit, which enables us to separate spatial and temporal variations. In this paper, we present a study of the temporal variability of field-aligned currents using the ST5 data. We examine the field-aligned current observations during and after a geomagnetic storm and compare the magnetic field profiles at the three spacecraft. The multipoint data demonstrate that mesoscale current structures, commonly embedded within large-scale current sheets, are very dynamic with highly variable current density and/or polarity in approx.10 min time scales. On the other hand, the data also show that the time scales for the currents to be relatively stable are approx.1 min for mesoscale currents and approx.10 min for large-scale currents. These temporal features are very likely associated with dynamic variations of their charge carriers (mainly electrons) as they respond to the variations of the parallel electric field in auroral acceleration region. The characteristic time scales for the temporal variability of mesoscale field-aligned currents are found to be consistent with those of auroral parallel electric field.

A generalised model of secondary circulation for a wide range of geophysical flows from direct observations of natural turbidity currents

NASA Astrophysics Data System (ADS)

Azpiroz, M.; Cartigny, M.; Sumner, E. J.; Talling, P.; Parsons, D. R.; Clare, M. A.; Cooper, C.

2017-12-01

Turbidity currents transport sediment through submarine channel systems for hundreds of kilometres to form vast deposits of sediment in the deep sea called submarine fans. The largest submarine fans are fed by meandering channels suggesting that bends may enhance sediment transport distances. The interaction between meander bends and turbidity currents has been a topic of intense debate. Due to the absence of observations of deep-sea turbidity currents flowing through meander bends, our understanding has been based on experimental and numerical models. Measurements of geophysical flows demonstrate a common helical flow structure around meanders. Previous work has demonstrated that helical circulation in rivers is dominated by a single helix that rotates towards the inner bend at near-bed depths. In contrast, initial numerical and experimental models for turbidity currents found both river-like and river-reversed circulations. Saline flows in well-mixed estuaries show a river-like basal helical circulation, while stratified estuaries and saline flows are river-reversed. The existence of lateral stratification in stratified flows is thought to be the key factor in the change of direction of rotation. Stratification causes lateral pressure gradients that can govern the rotation of the flow helix. Turbidity currents are stratified due to their upwards-decreasing sediment load. It has therefore been proposed that stratified turbidity currents behave like stratified saline flow, but this hypothesis remains so far untested. Here we present the first observations of the helical flow in turbidity currents, which occurred within the deep-sea Congo Canyon. The measurements show a consistent river-reversed pattern downstream of the bend apex. Those results lead us to develop a new generalised model for a wide range of flows around meanders. Our conclusions have implications for understanding the flow erosional and depositional patterns, the evolution of channel systems and the architecture of the depositional record.

Characterizing frontal eddies along the East Australian Current from HF radar observations

NASA Astrophysics Data System (ADS)

Schaeffer, Amandine; Gramoulle, A.; Roughan, M.; Mantovanelli, A.

2017-05-01

The East Australian Current (EAC) dominates the ocean circulation along south-eastern Australia, however, little is known about the submesoscale frontal instabilities associated with this western boundary current. One year of surface current measurements from HF radars, in conjunction with mooring and satellite observations, highlight the occurrence and propagation of meanders and frontal eddies along the inshore edge of the EAC. Eddies were systematically identified using the geometry of the high spatial resolution (˜1.5 km) surface currents, and tracked every hour. Cyclonic eddies were observed irregularly, on average every 7 days, with inshore radius ˜10 km. Among various forms of structures, frontal eddies associated with EAC meanders were characterized by poleward advection speeds of ˜0.3-0.4 m/s, migrating as far as 500 km south, based on satellite imagery. Flow field kinematics show that cyclonic eddies have high Rossby numbers (0.6-1.9) and enhance particle dispersion. Patches of intensified surface divergence at the leading edge of the structures are expected to generate vertical uplift. This is confirmed by subsurface measurements showing temperature uplift of up to 55 m over 24 h and rough estimates of vertical velocities of 10s of meters per day. While frontal eddies propagate through the radar domain independently of local wind stress, upfront wind can influence their stalling and growth, and can also generate large cold core eddies through intense shear. Such coherent structures are a major mechanism for the transport and entrainment of nutrient rich coastal or deep waters, influencing physical and biological dynamics, and connectivity over large distances.

The force-free configuration of flux ropes in geomagnetotail: Cluster observations

NASA Astrophysics Data System (ADS)

Yang, Y. Y.; Shen, C.; Zhang, Y. C.; Rong, Z. J.; Li, X.; Dunlop, M.; Ma, Y. H.; Liu, Z. X.; Carr, C. M.; Rème, H.

2014-08-01

Unambiguous knowledge of magnetic field structure and the electric current distribution is critical for understanding the origin, evolution, and related dynamic properties of magnetic flux ropes (MFRs). In this paper, a survey of 13 MFRs in the Earth's magnetotail are conducted by Cluster multipoint analysis, so that their force-free feature, i.e., the kind of magnetic field structure satisfying J × B = 0, can be probed directly. It is showed that the selected flux ropes with the bipolar signature of the south-north magnetic field component generally lie near the equatorial plane, as expected, and that the magnetic field gradient is rather weak near the axis center, where the curvature radius is large. The current density (up to several tens of nA/m2) reaches their maximum values as the center is approached. It is found that the stronger the current density, the smaller the angles between the magnetic field and current in MFRs. The direct observations show that only quasi force-free structure is observed, and it tends to appear in the low plasma beta regime (in agreement with the theoretic results). The quasi force-free region is generally found to be embedded in the central portion of the MFRs, where the current is approximately field aligned and proportional to the strength of core field. It is shown that ~60% of surveyed MFRs can be globally approximated as force free. The force-free factor α is found to be nonconstantly varied through the quasi force-free MFR, suggesting that the force-free structure is nonlinear.

Potential effects of climate change on the distribution range of the main silicate sinker of the Southern Ocean.

PubMed

Pinkernell, Stefan; Beszteri, Bánk

2014-08-01

Fragilariopsis kerguelensis, a dominant diatom species throughout the Antarctic Circumpolar Current, is coined to be one of the main drivers of the biological silicate pump. Here, we study the distribution of this important species and expected consequences of climate change upon it, using correlative species distribution modeling and publicly available presence-only data. As experience with SDM is scarce for marine phytoplankton, this also serves as a pilot study for this organism group. We used the maximum entropy method to calculate distribution models for the diatom F. kerguelensis based on yearly and monthly environmental data (sea surface temperature, salinity, nitrate and silicate concentrations). Observation data were harvested from GBIF and the Global Diatom Database, and for further analyses also from the Hustedt Diatom Collection (BRM). The models were projected on current yearly and seasonal environmental data to study current distribution and its seasonality. Furthermore, we projected the seasonal model on future environmental data obtained from climate models for the year 2100. Projected on current yearly averaged environmental data, all models showed similar distribution patterns for F. kerguelensis. The monthly model showed seasonality, for example, a shift of the southern distribution boundary toward the north in the winter. Projections on future scenarios resulted in a moderately to negligibly shrinking distribution area and a change in seasonality. We found a substantial bias in the publicly available observation datasets, which could be reduced by additional observation records we obtained from the Hustedt Diatom Collection. Present-day distribution patterns inferred from the models coincided well with background knowledge and previous reports about F. kerguelensis distribution, showing that maximum entropy-based distribution models are suitable to map distribution patterns for oceanic planktonic organisms. Our scenario projections indicate moderate effects of climate change upon the biogeography of F. kerguelensis.

An Assessment of Potential Detectors to Monitor the Man-made Orbital Debris Environment. [space debris

NASA Technical Reports Server (NTRS)

Reynolds, R. C.; Ruck, G. T.

1983-01-01

Observations using NORAD radar showed that man made debris exceeds the natural environment for large objects. For short times (a few days to a few weeks) after solid rocket motor (SRM) firings in LEO, man made debris in the microparticle size range also appears to exceed the meteoroid environment. The properties of the debris population between these size regimes is currently unknown as there has been no detector system able to perform the required observations. The alternatives for obtaining data on this currently unobserved segment of the population are assessed.

Solar wind and coronal structure near sunspot minimum - Pioneer and SMM observations from 1985-1987

NASA Technical Reports Server (NTRS)

Mihalov, J. D.; Barnes, A.; Hundhausen, A. J.; Smith, E. J.

1990-01-01

Changes in solar wind speed and magnetic polarity observed at the Pioneer spacecraft are discussed here in terms of the changing magnetic geometry implied by SMM coronagraph observations over the period 1985-1987. The pattern of recurrent solar wind streams, the long-term average speed, and the sector polarity of the interplanetary magnetic field all changed in a manner suggesting both a temporal variation, and a changing dependence on heliographic latitude. Coronal observations during this epoch show a systematic variation in coronal structure and the magnetic structure imposed on the expanding solar wind. These observations suggest interpretation of the solar wind speed variations in terms of the familiar model where the speed increases with distance from a nearly flat interplanetary current sheet, and where this current sheet becomes aligned with the solar equatorial plane as sunspot minimum approaches, but deviates rapidly from that orientation after minimum.

Steadiness in Dilute Pyroclastic Density Currents

NASA Astrophysics Data System (ADS)

Andrews, B. J.

2015-12-01

Pyroclastic density currents (PDCs) are often unsteady, as evidenced by direct observations of dilute lobes or jets emerging from the fronts of larger currents and by deposits that indicate transient transport and depositional regimes. We used scaled experiments to investigate unsteadiness in dilute PDCs. The experimental currents were run in an 8.5x6.1x2.6 m tank and comprised heated or ambient temperature 20-μm talc powder turbulently suspended in air. Experiments were scaled such that densimetric and thermal Richardson numbers, Froude number, and particle Stokes and settling numbers were dynamically similar to natural dilute PDCs. Although the experiment Reynolds numbers are substantially lower than those of natural PDCs, the experiments are fully turbulent. Experiments were observed with video and high-speed cameras and high-frequency thermocouples. Currents were generated with total eruption durations of 100 s. Unsteadiness in source conditions was produced by interrupting supply for intervals, t, with durations of 1, 2.5, 5, and 10 s in the experimental runs at 35 and 70 s. When t<2.5 s, the currents are indistinguishable from currents with steady supply. In runs with t=2.5-5 s, the individual pulses comprising each current are readily apparent near the source, but decay with distance downstream until the currents appear as single (e.g. steady) flows. In experiments with t=10 s, the 3 pulses comprising each run never merge and the currents remain unsteady. Comparison with the integral turbulent timescale, τ, and current velocity, U, show that unsteadiness is persistent when t>3<τ but currents are steady when t<τ. In currents with 3τ>t>τ, unsteadiness decays such that at a distance of ~4Ut, the currents are again steady. Applied to natural dilute PDCs, our results suggest that currents and their resulting deposits, will only show evidence of unsteadiness if they are disrupted for many seconds and those breaks may "heal" over distances of 100s of meters.

Observation of water mass characteristics in the southwestern Mariana Trench

NASA Astrophysics Data System (ADS)

Xu, H.; Xie, Q.; Hong, B.

2016-12-01

The identification of large water mass characteristic can help oceanographer to better understand the oceanic circulation structures and other physical processes in open oceans. In current stage, the water mass characteristics were recognized well by extensive observation in the upper ocean, however, it was rarely studied in deep oceans, especially for deep trench with > 6000 m depth. In this study, we use observed data collected by CTDs during several surveys to investigate the water mass physical characteristic and transport in the world deepest trench, `Challenger Deep', in the southwestern Mariana Trench. The preliminary results show complex vertical structures of water mass in this trench. From surface to 4500 m, the water masses are occupied by typical tropical surface water, NPTUW, NPMW, NPIW and NPDW. Under 4500m, the water mass shows mixing characteristics of NPDW and AABW, which indicate AABW can be transported by form the deep ocean of the South Ocean to Northwestern Pacific and it can affect local water mass characteristics. The baroclinic geostrophic current calculated from the CTDs data shows the westerly transport of water mass can reach about 1.0 SV in the trench which is close to previous results.

Magnetoacoustic waves propagating along a dense slab and Harris current sheet and their wavelet spectra

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

Mészárosová, Hana; Karlický, Marian; Jelínek, Petr

Currently, there is a common endeavor to detect magnetoacoustic waves in solar flares. This paper contributes to this topic using an approach of numerical simulations. We studied a spatial and temporal evolution of impulsively generated fast and slow magnetoacoustic waves propagating along the dense slab and Harris current sheet using two-dimensional magnetohydrodynamic numerical models. Wave signals computed in numerical models were used for computations of the temporal and spatial wavelet spectra for their possible comparison with those obtained from observations. It is shown that these wavelet spectra allow us to estimate basic parameters of waveguides and perturbations. It was foundmore » that the wavelet spectra of waves in the dense slab and current sheet differ in additional wavelet components that appear in association with the main tadpole structure. These additional components are new details in the wavelet spectrum of the signal. While in the dense slab this additional component is always delayed after the tadpole head, in the current sheet this component always precedes the tadpole head. It could help distinguish a type of the waveguide in observed data. We present a technique based on wavelets that separates wave structures according to their spatial scales. This technique shows not only how to separate the magnetoacoustic waves and waveguide structure in observed data, where the waveguide structure is not known, but also how propagating magnetoacoustic waves would appear in observations with limited spatial resolutions. The possibilities detecting these waves in observed data are mentioned.« less

A flexible and transparent graphene/ZnO nanorod hybrid structure fabricated by exfoliating a graphite substrate

NASA Astrophysics Data System (ADS)

Nam, Gwang-Hee; Baek, Seong-Ho; Cho, Chang-Hee; Park, Il-Kyu

2014-09-01

We demonstrate the fabrication of a graphene/ZnO nanorod (NR) hybrid structure by mechanical exfoliation of ZnO NRs grown on a graphite substrate. We confirmed the existence of graphene sheets on the hybrid structure by analyzing the Raman spectra and current-voltage (I-V) characteristics. The Raman spectra of the exfoliated graphene/ZnO NR hybrid structure show G and 2D band peaks that are shifted to lower wavenumbers, indicating that the exfoliated graphene layer exists under a significant amount of strain. The I-V characteristics of the graphene/ZnO NR hybrid structure show current flow through the graphene layer, while no current flow is observed on the ZnO NR/polydimethylsiloxane (PDMS) composite without graphene, thereby indicating that the few-layer graphene was successfully transferred onto the hybrid structure. A piezoelectric nanogenerator is demonstrated by using the fabricated graphene/ZnO NR hybrid structure. The nanogenerator exhibits stable output voltage up to 3.04 V with alternating current output characteristics.We demonstrate the fabrication of a graphene/ZnO nanorod (NR) hybrid structure by mechanical exfoliation of ZnO NRs grown on a graphite substrate. We confirmed the existence of graphene sheets on the hybrid structure by analyzing the Raman spectra and current-voltage (I-V) characteristics. The Raman spectra of the exfoliated graphene/ZnO NR hybrid structure show G and 2D band peaks that are shifted to lower wavenumbers, indicating that the exfoliated graphene layer exists under a significant amount of strain. The I-V characteristics of the graphene/ZnO NR hybrid structure show current flow through the graphene layer, while no current flow is observed on the ZnO NR/polydimethylsiloxane (PDMS) composite without graphene, thereby indicating that the few-layer graphene was successfully transferred onto the hybrid structure. A piezoelectric nanogenerator is demonstrated by using the fabricated graphene/ZnO NR hybrid structure. The nanogenerator exhibits stable output voltage up to 3.04 V with alternating current output characteristics. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr02318h

Design and flight performance evaluation of the Mariners 6, 7, and 9 short-circuit current, open-circuit voltage transducers

NASA Technical Reports Server (NTRS)

Patterson, R. E.

1973-01-01

The purpose of the short-circuit voltage transducer is to provide engineering data to aid the evaluation of array performance during flight. The design, fabrication, calibration, and in-flight performance of the transducers onboard the Mariner 6, 7 and 9 spacecrafts are described. No significant differences were observed in the in-flight electrical performance of the three transducers. The transducers did experience significant losses due to coverslides or adhesive darkening, increased surface reflection, or spectral shifts within coverslide assembly. Mariner 6, 7 and 9 transducers showed non-cell current degradations of 3-1/2%, 3%, and 4%, respectively at Mars encounter and 6%, 3%, and 4-12%, respectively at end of mission. Mariner 9 solar Array Test 2 showed 3-12% current degradation while the transducer showed 4-12% degradation.

The wind-forced response on a buoyant coastal current: Observations of the western Gulf of Maine plume

USGS Publications Warehouse

Fong, D.A.; Geyer, W.R.; Signell, R.P.

1997-01-01

The Freshwater plume in the western Gulf of Maine is being studied as part of an interdisciplinary investigation of the physical transport of a toxic alga. A field program was conducted in the springs of 1993 and 1994 to map the spatial and temporal patterns of salinity, currents and algal toxicity. The observations suggest that the plume's cross-shore structure varies markedly as a function of fluctuations in alongshore wind forcing. Consistent with Ekman drift dynamics, upwelling favorable winds spread the plume offshore, at times widening it to over 50 km in offshore extent, while downwelling favorable winds narrow the plume width to as little as 10 km. Using a simple slab model, we find qualitative agreement between the observed variations of plume width and those predicted by Ekman theory for short time scales of integration. Near surface current meters show significant correlations between cross-shore currents and alongshore wind stress, consistent with Ekman theory. Estimates of the terms in the alongshore momentum equation calculated from moored current meter arrays also indicate a dominant Ekman balance within the plume. A significant correlation between alongshore currents and winds suggests that interfacial drag may be important, although inclusion of a Raleigh drag term does not significantly improve the alongshore momentum balance.

Albireo: 260 Years of Astrometric Observations

NASA Astrophysics Data System (ADS)

Hass, Jacob; Phung, Kevin; Carro, Joseph; Hock, Emily; Loveland, Donald; Nibbe, Tristan; Sharp, Zoe; Smit, Jenny; Genet, Russell

2016-03-01

The historical record of Albireo's observations reflects the progress of double star research. Some 294 astrometric observations have been published starting with Bradley's 1755 observation and ending with our 2015 observation. Several observation techniques were used over this 260 year span. Noteworthy are the historic contributions of astronomers such as James Bradley, Christian Mayer, William Herschel, Giuseppe Piazzi, Friedrich Georg Wilhelm von Struve, Sir John Herschel, Sir James South, Edward Skinner King, and Andrei Tokovinin. Overall trend lines of the past observations of Albireo are compared to our current observation, and are generally concurrent. Dividing Albireo's past observations of separation into time segments shows evidence of a known third star in Albireo's system.

Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope.

PubMed

Nichols, J D; Badman, S V; Baines, K H; Brown, R H; Bunce, E J; Clarke, J T; Cowley, S W H; Crary, F J; Dougherty, M K; Gérard, J-C; Grocott, A; Grodent, D; Kurth, W S; Melin, H; Mitchell, D G; Pryor, W R; Stallard, T S

2014-05-28

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ∼330% rigid corotation from near ∼01 h LT toward ∼08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current.

Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope

PubMed Central

Nichols, J D; Badman, S V; Baines, K H; Brown, R H; Bunce, E J; Clarke, J T; Cowley, S W H; Crary, F J; Dougherty, M K; Gérard, J-C; Grocott, A; Grodent, D; Kurth, W S; Melin, H; Mitchell, D G; Pryor, W R; Stallard, T S

2014-01-01

We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ∼330% rigid corotation from near ∼01 h LT toward ∼08 h LT. We suggest that these are indicative of ongoing, bursty reconnection of lobe flux in the magnetotail, providing strong evidence that Saturn's auroral storms are caused by large-scale flux closure. We also discuss the later evolution of a similar storm and show that the emission maps to the trailing region of an energetic neutral atom enhancement. We thus identify the auroral form with the upward field-aligned continuity currents flowing into the associated partial ring current. PMID:26074636

Finite Gyroradius Effects in the Electron Outflow of Asymmetric Magnetic Reconnection

NASA Technical Reports Server (NTRS)

Norgren, C.; Graham, D. B.; Khotyaintsev, Yu. V.; Andre, M.; Vaivads, A.; Chen, Li-Jen; Lindqvist, P.-A.; Marklund, G. T.; Ergun, R. E.; Magnes, W.;

Studies of Current Circulation at Ocean Waste Disposal Sites

NASA Technical Reports Server (NTRS)

Klemas, V. (Principal Investigator); Davis, G.; Henry, R.

1976-01-01

The author has identified the following significant results. Acid waste plume was observed in LANDSAT imagery fourteen times ranging from during dump up to 54 hours after dump. Circulation processes at the waste disposal site are highly storm-dominated, with the majority of the water transport occurring during strong northeasterlies. There is a mean flow to the south along shore. This appears to be due to the fact that northeasterly winds produce stronger currents than those driven by southeasterly winds and by the thermohaline circulation. During the warm months (May through October), the ocean at the dump site stratifies with a distinct thermocline observed during all summer cruising at depths ranging from 10 to 21 m. During stratified conditions, the near-bottom currents were small. Surface currents responded to wind conditions resulting in rapid movement of surface drogues on windy days. Mid-depth drogues showed an intermediate behavior, moving more rapidly as wind velocities increased.

Electrical Counting and Sizing of Mammalian Cells in Suspension

PubMed Central

Gregg, E. C.; Steidley, K. David

1965-01-01

A recently developed method of determining the number and size of particles suspended in a conducting solution is to pump the suspension through a small orifice having an immersed electrode on each side to supply electrical current. The current changes due to the passage of particles of resistivity different from that of the solution. Theoretical expressions are developed which relate the current change caused by such particles to their volume and shape. It is found that most biological cells may be treated as dielectric particles whose capacitive effects are negligible. Electrolytic tank measurements on models confirm the theoretical development, and electric field plots of model orifices are used to predict the observed pulse shapes. An equivalent circuit of the orifice-electrode system is analyzed and shows that the current pulse may be made conductivity-independent when observed with a zero input impedance amplifier. PMID:5861698

Response of the Equatorial Ionosphere to the Geomagnetic DP 2 Current System

NASA Technical Reports Server (NTRS)

Yizengaw, E.; Moldwin, M. B.; Zesta, E.; Magoun, M.; Pradipta, R.; Biouele, C. M.; Rabiu, A. B.; Obrou, O. K.; Bamba, Z.; Paula, E. R. De

2016-01-01

The response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground-based multiinstrument observations. The interaction between the solar wind and fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high-latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.

Effects of 1- and 2-MeV electrons on photomultiplier tubes

NASA Technical Reports Server (NTRS)

Beatty, M. E., III; Debnam, W. J., Jr.; Meredith, B. D.

1976-01-01

Various types of photomultiplier tubes useful for space applications were irradiated with 1- and 2-MeV electrons at Van Allen radiation belt fluxes of 100,000 to 10 millions electrons/sq cm-sec. The increase in the dark current due to electron irradiation was observed at various bias voltages under worst-case conditions (no shielding). Results were presented in the form of dark current plotted against electron flux. All the tubes tested showed extremely large increases in dark current. Tube types 541A, 6217, 6199, and 6903 exhibited the largest increases under irradiation, whereas type 1P22 was affected the least. All the damage observed was transient. The luminescence produced in the optical window probably accounts for a large part of the dark-current increases, but there were some effects possibly due to direct irradiation of the photocathode and dynode chain.

Generation of Near-Inertial Currents on the Mid-Atlantic Bight by Hurricane Arthur (2014)

NASA Astrophysics Data System (ADS)

Zhang, Fan; Li, Ming; Miles, Travis

2018-04-01

Near-inertial currents (NICs) were observed on the Mid-Atlantic Bight (MAB) during the passage of Hurricane Arthur (2014). High-frequency radars showed that the surface currents were weak near the coast but increased in the offshore direction. The NICs were damped out in 3-4 days in the southern MAB but persisted for up to 10 days in the northern MAB. A Slocum glider deployed on the shelf recorded two-layer baroclinic currents oscillating at the inertial frequency. A numerical model was developed to interpret the observed spatial and temporal variabilities of the NICs and their vertical modal structure. Energy budget analysis showed that most of the differences in the NICs between the shelf and the deep ocean were determined by the spatial variations in wind energy input. In the southern MAB, energy dissipation quickly balanced the wind energy input, causing a rapid damping of the NICs. In the northern MAB, however, the dissipation lagged the wind energy input such that the NICs persisted. The model further showed that mode-1 waves dominated throughout the MAB shelf and accounted for over 70% of the current variability in the NICs. Rotary spectrum analyses revealed that the NICs were the largest component of the total kinetic energy except in the southern MAB and the inner shelf regions with strong tides. The NICs were also a major contributor to the shear spectrum over an extensive area of the MAB shelf and thus may play an important role in producing turbulent mixing and cooling of the surface mixed layer.

PLANETARY SYSTEM FORMATION IN THE PROTOPLANETARY DISK AROUND HL TAURI

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

Akiyama, Eiji; Hasegawa, Yasuhiro; Hayashi, Masahiko

2016-02-20

We reprocess the Atacama Large Millimeter/Submillimeter Array (ALMA) long-baseline science verification data taken toward HL Tauri. Assuming the observed gaps are opened up by currently forming, unseen bodies, we estimate the mass of such hypothetical bodies based on the following two approaches: the Hill radius analysis and a more elaborate approach developed from the angular momentum transfer analysis in gas disks. For the former, the measured gap widths are used for estimating the mass of the bodies, while for the latter, the measured gap depths are utilized. We show that their masses are comparable to or less than the mass of Jovian planets.more » By evaluating Toomre’s gravitational instability (GI) condition and cooling effect, we find that the GI might be a mechanism to form the bodies in the outer region of the disk. As the disk might be gravitationally unstable only in the outer region of the disk, inward planetary migration would be needed to construct the current architecture of the observed disk. We estimate the gap-opening mass and show that type II migration might be able to play such a role. Combining GIs with inward migration, we conjecture that all of the observed gaps may be a consequence of bodies that might have originally formed at the outer part of the disk, and have subsequently migrated to the current locations. While ALMA’s unprecedented high spatial resolution observations can revolutionize our picture of planet formation, more dedicated observational and theoretical studies are needed to fully understand the HL Tauri images.« less

Comparison of five different defibrillators using recommended energy protocols.

PubMed

Zelinka, M; Buić, D; Zelinka, I

2007-09-01

Biphasic defibrillators represent a great step ahead in defibrillation. The manufacturers claim that biphasic defibrillators are able to compensate for differences in transthoracic impedance. That should mean that all patients should be defibrillated with approximately the same amount of current, regardless of their transthoracic impedance. We assessed one monophasic and four biphasic defibrillators. The defibrillators were discharged into resistive loads of 50, 90 and 130 Omega, simulating transthoracic impedance. For each waveform we used energy protocols recommended by the manufacturers and guidelines 2005. Waveforms were observed with on a digitising oscilloscope on a current sensing resistor. We compared the electrical properties of different waveforms and two defibrillators with the same type of waveform. The influence of different impedance on shape, duration and amplitude of current flow were also observed for each waveform. Measurements showed a significant difference in current flow at different impedance loads. At low impedance the mean current is well above expectations for all the defibrillators studied and at high impedance load we observed a big reduction of current amplitude. We can conclude that the compensating mechanisms of biphasic defibrillators are, from electrical point of view, negligible. From the laws of physics it is practically impossible to keep same level of current at given time with same energy at higher impedance. That is why we should reconsider the use of different energy equivalents between patients with different transthoracic impedance and not between different defibrillation impulses.

Bottom currents and sediment transport in Long Island Sound: A modeling study

USGS Publications Warehouse

Signell, R.P.; List, J.H.; Farris, A.S.

2000-01-01

A high resolution (300-400 m grid spacing), process oriented modeling study was undertaken to elucidate the physical processes affecting the characteristics and distribution of sea-floor sedimentary environments in Long Island Sound. Simulations using idealized forcing and high-resolution bathymetry were performed using a three-dimensional circulation model ECOM (Blumberg and Mellor, 1987) and a stationary shallow water wave model HISWA (Holthuijsen et al., 1989). The relative contributions of tide-, density-, wind- and wave-driven bottom currents are assessed and related to observed characteristics of the sea-floor environments, and simple bedload sediment transport simulations are performed. The fine grid spacing allows features with scales of several kilometers to be resolved. The simulations clearly show physical processes that affect the observed sea-floor characteristics at both regional and local scales. Simulations of near-bottom tidal currents reveal a strong gradient in the funnel-shaped eastern part of the Sound, which parallels an observed gradient in sedimentary environments from erosion or nondeposition, through bedload transport and sediment sorting, to fine-grained deposition. A simulation of estuarine flow driven by the along-axis gradient in salinity shows generally westward bottom currents of 2-4 cm/s that are locally enhanced to 6-8 cm/s along the axial depression of the Sound. Bottom wind-driven currents flow downwind along the shallow margins of the basin, but flow against the wind in the deeper regions. These bottom flows (in opposition to the wind) are strongest in the axial depression and add to the estuarine flow when winds are from the west. The combination of enhanced bottom currents due to both estuarine circulation and the prevailing westerly winds provide an explanation for the relatively coarse sediments found along parts of the axial depression. Climatological simulations of wave-driven bottom currents show that frequent high-energy events occur along the shallow margins of the Sound, explaining the occurrence of relatively coarse sediments in these regions. Bedload sediment transport calculations show that the estuarine circulation coupled with the oscillatory tidal currents result in a net westward transport of sand in much of the eastern Sound. Local departures from this regional westward trend occur around topographic and shoreline irregularities, and there is strong predicted convergence of bedload transport over most of the large, linear sand ridges in the eastern Sound, providing a mechanism which prevents their decay. The strong correlation between the near-bottom current intensity based on the model results and the sediment response, as indicated by the distribution of sedimentary environments, provides a framework for predicting the long-term effects of anthropogenic activities.

A Description of Local Time Asymmetries in the Kronian Current Sheet

NASA Astrophysics Data System (ADS)

Nickerson, J. S.; Hansen, K. C.; Gombosi, T. I.

2012-12-01

Cassini observations imply that Saturn's magnetospheric current sheet is displaced northward above the rotational equator [C.S. Arridge et al., Warping of Saturn's magnetospheric and magnetotail current sheets, Journal of Geophysical Research, Vol. 113, August 2008]. Arridge et al. show that this hinging of the current sheet above the equator occurs over the noon, midnight, and dawn local time sectors. They present an azimuthally independent model to describe this paraboloid-like geometry. We have used our global MHD model, BATS-R-US/SWMF, to study Saturn's magnetospheric current sheet under various solar wind dynamic pressure and solar zenith angle conditions. We show that under reasonable conditions the current sheet does take on the basic shape of the Arridge model in the noon, midnight, and dawn sectors. However, the hinging distance parameter used in the Arridge model is not a constant and does in fact vary in Saturn local time. We recommend that the Arridge model should be adjusted to account for this azimuthal dependence. Arridge et al. does not discuss the shape of the current sheet in the dusk sector due to an absence of data but does presume that the current sheet will assume the same geometry in this region. On the contrary, our model shows that this is not the case. On the dusk side the current sheet hinges (aggressively) southward and cannot be accounted for by the Arridge model. We will present results from our simulations showing the deviation from axisymmetry and the general behavior of the current sheet under different conditions.

Entanglement of two qubits coupled to an XY spin chain: Role of energy current

NASA Astrophysics Data System (ADS)

Liu, Ben-Qiong; Shao, Bin; Zou, Jian

2009-12-01

We investigate the entanglement dynamics of a two-qubit system which interacts with a Heisenberg XY spin chain constrained to carry an energy current. We show an explicit connection between the decoherence factor and entanglement, and numerically and analytically study the dynamical process of entanglement in both weak- and strong-coupling cases for two initial states, the general pure state and the mixed Werner state. We provide results that the entanglement evolution depends not only on the energy current, the anisotropy parameter and the system-environment couplings but also on the size of degrees of freedom of environment. In particular, our results imply that entanglement will be strongly suppressed by the introduction of energy current on the environmental spin chain in the weak-coupling region while it is not sensitive to the energy current in the strong-coupling region. We also observe the sudden death of entanglement in the system and show how the energy current affects the phenomenon.

Bowhead whales feed on plankton concentrated by estuarine and tidal currents in Academy Bay, Sea of Okhotsk

NASA Astrophysics Data System (ADS)

Rogachev, Konstantin A.; Carmack, Eddy C.; Foreman, Michael G. G.

2008-08-01

Academy Bay in the Sea of Okhotsk is an important summertime feeding ground for pelagic-feeding Bowhead whales ( Balaena mysticetus) in the western subarctic North Pacific. The present work combines satellite observations with physical (CTD, currents, tides) and biological (zooplankton sampling) measurements. Data obtained aboard the RV Lugovoe in August-September 2003 and July-August 2004 show dense populations of zooplankton (such as copepods Calanus glacialis, Pseudocalanus sp., pteropods Limacina helicina, and chaetognaths Sagitta sp.) that are concentrated by physical mechanisms within this critically important ecosystem. We show that near-bottom, cold water intrusions from the northern Sea of Okhotsk associated with the estuarine circulation advect arctic herbivorous calanoids ( Calanus glacialis) and mollusks Limacina helicina into the region. Satellite and in situ observations that include conductivity-temperature-depth (CTD) data and measurements of tidal currents are used to study the nature of the estuarine circulation. Results show an anticyclonic circulation, associated with the effect of earth's rotation. An analytical model shows horizontally convergent flows in the lower layer toward the western coast of the bay that push water upward along the steep slope. This together with zooplankton vertical migration leads to aggregation. Thus the combination of the residual eddy formation and swimming behavior act to concentrate zooplankton near the cape and to provide the necessary densities of planktonic food supply for Bowhead whales.

Current-driven non-linear magnetodynamics in exchange-biased spin valves

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

Seinige, Heidi; Wang, Cheng; Tsoi, Maxim, E-mail: tsoi@physics.utexas.edu

2015-05-07

This work investigates the excitation of parametric resonance in exchange-biased spin valves (EBSVs). Using a mechanical point contact, high density dc and microwave currents were injected into the EBSV sample. Observing the reflected microwave power and the small rectification voltage that develops across the contact allows detecting the current-driven magnetodynamics not only in the bulk sample but originating exclusively from the small contact region. In addition to ferromagnetic resonance (FMR), parametric resonance at twice the natural FMR frequency was observed. In contrast to FMR, this non-linear resonance was excited only in the vicinity of the point contact where current densitiesmore » are high. Power-dependent measurements displayed a typical threshold-like behavior of parametric resonance and a broadening of the instability region with increasing power. Parametric resonance showed a linear shift as a function of applied dc bias which is consistent with the field-like spin-transfer torque induced by current on magnetic moments in EBSV.« less

Io's Interaction with the Jovian Magnetosphere: Models of Particle Acceleration and Scattering

NASA Astrophysics Data System (ADS)

Crary, Frank Judson

1998-09-01

I develop models of electron acceleration and ion scattering which result from Io's interaction with the jovian magnetosphere. According to my models, Io initially generates transient currents and an Alfvenic disturbance when it first encounters a jovian magnetic field line, and the interaction would eventually settle into a system of steady Birkeland currents as the field line is advected downstream past Io and into Io's wake. I derive a model of wave propagation and electron acceleration by the Alfvenic transient, due to electron inertial effects. My numerical calculations show that the power and particle energy of the resulting electron beam are consistent with observations of the Io-related auroral spot and of Jupiter's S-burst decametric emissions. In the case of the steady currents and Io's wake. I show that these currents would drive instabilities and argue that electrostatic double layers would form in the high latitudes of the Io/Io wake flux tubes. I examine the role of these double layers in producing energetic electrons and estimate the likely electron energies and power. This model agrees with observations of a long arc in the jovian aurora, extending away from the Io-related spot, the L-burst decametric radio emissions and electron beams observed by the Galileo spacecraft in Io's wake. Finally, I consider the Galileo observations of ion cyclotron waves near Io. I use the absence of waves near the S and O gyrofrequencies to place limits on the source rate of heavy ions near Io. For a sufficiently low source rate, the thermal core population prevents ion cyclotron instabilities and wave growth. I use these limits to constrain the neutral column density of Io's exosphere and amount of plasma produced within 2 to 10 body radii of Io.

Multiple current peaks in room-temperature atmospheric pressure homogenous dielectric barrier discharge plasma excited by high-voltage tunable nanosecond pulse in air

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

Yang, De-Zheng; Wang, Wen-Chun; Zhang, Shuai

2013-05-13

Room temperature homogenous dielectric barrier discharge plasma with high instantaneous energy efficiency is acquired by using nanosecond pulse voltage with 20-200 ns tunable pulse width. Increasing the voltage pulse width can lead to the generation of regular and stable multiple current peaks in each discharge sequence. When the voltage pulse width is 200 ns, more than 5 organized current peaks can be observed under 26 kV peak voltage. Investigation also shows that the organized multiple current peaks only appear in homogenous discharge mode. When the discharge is filament mode, organized multiple current peaks are replaced by chaotic filament current peaks.

On Verifying Currents and Other Features in the Hawaiian Islands Region Using Fully Coupled Ocean/Atmosphere Mesoscale Prediction System Compared to Global Ocean Model and Ocean Observations

NASA Astrophysics Data System (ADS)

Jessen, P. G.; Chen, S.

2014-12-01

This poster introduces and evaluates features concerning the Hawaii, USA region using the U.S. Navy's fully Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS-OS™) coupled to the Navy Coastal Ocean Model (NCOM). It also outlines some challenges in verifying ocean currents in the open ocean. The system is evaluated using in situ ocean data and initial forcing fields from the operational global Hybrid Coordinate Ocean Model (HYCOM). Verification shows difficulties in modelling downstream currents off the Hawaiian islands (Hawaii's wake). Comparing HYCOM to NCOM current fields show some displacement of small features such as eddies. Generally, there is fair agreement from HYCOM to NCOM in salinity and temperature fields. There is good agreement in SSH fields.

A decay of gap junctions associated with ganglion cell differentiation during retinal regeneration of the adult newt.

PubMed

Oi, Hanako; Chiba, Chikafumi; Saito, Takehiko

2003-12-01

Changes in the gap junctional coupling and maturation of voltage-activated Na(+) currents during regeneration of newt retinas were examined by whole-cell patch-clamping in slice preparations. Progenitor cells in regenerating retinas did not exhibit Na(+) currents but showed prominent electrical and tracer couplings. Cells identified by LY-fills were typically slender. Na(+) currents were detected in premature ganglion cells with round somata in the 'intermediate-II' regenerating retina. No electrical and tracer couplings were observed between these cells. Mature ganglion cells did not exhibit electrical coupling, but showed tracer coupling. On average, the maximum Na(+) current amplitude recorded from premature ganglion cells was roughly 2.5-fold smaller than that of mature ganglion cells. In addition, the activation threshold of the Na(+) current was nearly 11 mV more positive than that of mature cells. We provide morphological and physiological evidence showing that loss of gap junctions between progenitor cells is associated with ganglion cell differentiation during retinal regeneration and that new gap junctions are recreated between mature ganglion cells. Also we provide evidence suggesting that the loss of gap junctions correlates with the appearance of voltage-activated Na(+) currents in ganglion cells.

The off-shore Transport of China Coastal Current over Taiwan Bank in Winter

NASA Astrophysics Data System (ADS)

Liao, E.; Yan, X. H.; Oey, L. Y.; Jiang, Y.

2016-12-01

In winter, an off-shore flow of China Coastal Current can be inferred from satellite and in-situ data over the Taiwan Bank. The dynamics related to this off-shore flow have not been previously explained and are examined here using observations and model. Influenced by southward wind stress and opposing pressure gradient, currents over the Taiwan Bank can be classified into three regimes. The southward China Coastal Current flows pass the Taiwan Bank when the wind stress is stronger than a critical value which depends on the opposite pressure gradient force. The coastal current turns northward under a weak wind stress. Two opposite currents converge over the bank and a branch of the coastal current then turns into the northward warm current when these two forces are in balance. Analysis of the vorticity balance shows that the cross-isobath movement is related to a negative bottom stress curl over the Taiwan Bank. Both bottom Ekman transport and shear and curvature vorticity related to the weak bottom slope over the Taiwan Bank contribute to the bottom stress curl. Composite analyses using observations tend to support the model results.

Discoveries in plasmas while teaching simulation

NASA Astrophysics Data System (ADS)

Birdsall, Charles K.(Ned); Estacio, Edison T.; Plasma Theory; Simulation Group (PTSG)

2004-12-01

Once PC's became ubiquitous, we have been using them for teaching plasma simulation, hands-on by instructors and by students. The transfer of skills from instructor to class has been very rapid (most desirable). However, occasionally some unanticipated results are observed with plausible explanations expected from the instructor (scary). Our examples are all one-dimensional. First, we show the famous two-stream instability in a periodic model, starting either cold or warm, which does not (quite) Maxwellianize; why not? Second, we show Landau damping also in a periodic model, with what appears to be small (hence linear) excitation, but observe trapping in the wave frame; going to very small excitation the trapping diminishes and the damping rate approaches that from Landau linear theory. Lastly, we show a warm plasma bounded by two grounded metal planar walls, uniform in density at t=0, bounded, one-dimensional. For t>0 we observe spontaneous plasma frequency oscillations in the midplane, sheath formation at ion sound speed at both walls, trapping of electrons, and acceleration of the ions to the walls; however, we also observe an oscillatory axial current, and 'staircasing' of the number of electrons in time. Both can come only from some degree of asymmetry in the system. The frequency of the current is the series resonance between the sheath capacitance (almost no electrons, so vacuum) and the bulk plasma 'inductance' (as ωseries≪ ωp).

Structural and critical current properties in Al-doped MgB 2

NASA Astrophysics Data System (ADS)

Zheng, D. N.; Xiang, J. Y.; Lang, P. L.; Li, J. Q.; Che, G. C.; Zhao, Z. W.; Wen, H. H.; Tian, H. Y.; Ni, Y. M.; Zhao, Z. X.

2004-08-01

A series of Al-doped Mg 1- xAl xB 2 samples have been fabricated and systematic study on structure and superconducting properties have been carried out for the samples. In addition to a structural transition observed by XRD, TEM micrographs showed the existence of a superstructure of double c-axis lattice constant along the direction perpendicular to the boron honeycomb sheet. In order to investigate the effect of Al doping on flux pinning and critical current properties in MgB 2, measurements on the superconducting transition temperature Tc, irreversible field Birr and critical current density Jc were performed too, for the samples with the doping levels lower than 0.15 in particular. These experimental observations were discussed in terms of Al doping induced changes in carrier concentration.

Generation of valley-polarized electron beam in bilayer graphene

NASA Astrophysics Data System (ADS)

Park, Changsoo

2015-12-01

We propose a method to produce valley-polarized electron beams using a bilayer graphene npn junction. By analyzing the transmission properties of electrons through the junction with zigzag interface in the presence of trigonal warping, we observe that there exist a range of incident energies and barrier heights in which transmitted electrons are well polarized and collimated. From this observation and by performing numerical simulations, it is demonstrated that valley-dependent electronic currents with nearly perfect polarization can be generated. We also show that the peak-to-peak separation angle between the polarized currents is tunable either by incident energy or by barrier height each of which is controlled by using top and back gate voltages. The results can be used for constructing an electron beam splitter to produce valley-polarized currents.

Observations of the interaction between near-inertial waves and mesoscale eddies

NASA Astrophysics Data System (ADS)

Martínez-Marrero, Antonio; Sangrá, Pablo; Caldeira, Rui; Aguiar-González, Borja; Rodríguez-Santana, Ángel

2014-05-01

Trajectories of eight drifters dragged below the surface mixed layer and current meter data from a mooring are used to analyse the interaction between near-inertial waves and mesoscale eddies. Drifters were deployed within eddies generated downstream of Canary and Madeira islands between 1998 and 2007. The mooring was installed in the passage of cyclonic eddies induced by Gran Canaria island during 2006. Rotatory wavelet analysis of Lagrangian velocities shows a clear relationship between the near-inertial waves' intrinsic frequencies and the eddy angular velocities. The results reveal that near-inertial waves reach a minimum frequency of half the planetary vorticity (f/2) in the inner core of young anticyclonic eddies rotating with its maximum absolute angular speed of f/2. The highest amplitudes of the observed inertial motions are also found within anticyclonic eddies evidencing the trapping of inertial waves. Finally, the analysis of the current meter series show frequency fluctuations of the near-inertial currents in the upper 500 meters that are related to the passage of cyclonic eddies. These fluctuations appear to be consistent with the variation of the background vorticity produced by the eddies.

A Gradually Varied Approach to Model Turbidity Currents in Submarine Channels

NASA Astrophysics Data System (ADS)

Bolla Pittaluga, M.; Frascati, A.; Falivene, O.

2018-01-01

We develop a one-dimensional model to describe the dynamics of turbidity current flowing in submarine channels. We consider the flow as a steady state polydisperse suspension accounting for water detrainment from the clear water-turbid interface, for spatial variations of the channel width and for water and sediment lateral overspill from the channel levees. Moreover, we account for sediment exchange with the bed extending the model to deal with situations where the current meets a nonerodible bed. Results show that when water detrainment is accounted for, the flow thickness becomes approximately constant proceeding downstream. Similarly, in the presence of channel levees, the flow tends to adjust to channel relief through the lateral loss of water and sediment. As more mud is spilled above the levees relative to sand, the flow becomes more sand rich proceeding downstream when lateral overspill is present. Velocity and flow thickness predicted by the model are then validated by showing good agreement with laboratory observations. Finally, the model is applied to the Monterey Canyon bathymetric data matching satisfactorily the December 2002 event field measurements and predicting a runout length consistent with observations.

Wave-current interaction study in the Gulf of Alaska for detection of eddies by synthetic aperture radar

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Peng, Chich Y.; Schumacher, James D.

1994-01-01

High resolution Esa Remote Sensing Satellite-1 (ERS-1) Synthetic Aperture Radar (SAR) images are used to detect a mesoscale eddy. Such features limit dispersal of pollock larvae and therefore likely influence recruitment of fish in the Gulf of Alaska. During high sea states and high winds, the direct surface signature of the eddy was not clearly visible, but the wave refraction in the eddy area was observed. The rays of the wave field are traced out directly from the SAR image. The ray pattern gives information on the refraction pattern and on the relative variation of the wave energy along a ray through wave current interaction. These observations are simulated by a ray-tracing model which incorporates a surface current field associated with the eddy. The numerical results of the model show that the waves are refracted and diverge in the eddy field with energy density decreasing. The model-data comparison for each ray shows the model predictions are in good agreement with the SAR data.

Current Sheet Evolution in the Aftermath of a CME Event

NASA Technical Reports Server (NTRS)

Bemporad, A.; Poletto, G.; Suess, S. T.; Ko, Y.-K.; Schwadron, N. A.; Elliott, H. A.; Raymond, J. C.

2005-01-01

We report on SOHO-UVCS observations of the coronal restructuring following a Coronal Mass Ejection (CME) on November 26,2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after a CME in the NW quadrant, UVCS began taking spectra at 1.7 solar radius, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the Fe XVIII emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by Ulysses-SWICS throughout the magnetic cloud associated with the CME. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Depth-averaged instantaneous currents in a tidally dominated shelf sea from glider observations

NASA Astrophysics Data System (ADS)

Merckelbach, Lucas

2016-12-01

Ocean gliders have become ubiquitous observation platforms in the ocean in recent years. They are also increasingly used in coastal environments. The coastal observatory system COSYNA has pioneered the use of gliders in the North Sea, a shallow tidally energetic shelf sea. For operational reasons, the gliders operated in the North Sea are programmed to resurface every 3-5 h. The glider's dead-reckoning algorithm yields depth-averaged currents, averaged in time over each subsurface interval. Under operational conditions these averaged currents are a poor approximation of the instantaneous tidal current. In this work an algorithm is developed that estimates the instantaneous current (tidal and residual) from glider observations only. The algorithm uses a first-order Butterworth low pass filter to estimate the residual current component, and a Kalman filter based on the linear shallow water equations for the tidal component. A comparison of data from a glider experiment with current data from an acoustic Doppler current profilers deployed nearby shows that the standard deviations for the east and north current components are better than 7 cm s-1 in near-real-time mode and improve to better than 6 cm s-1 in delayed mode, where the filters can be run forward and backward. In the near-real-time mode the algorithm provides estimates of the currents that the glider is expected to encounter during its next few dives. Combined with a behavioural and dynamic model of the glider, this yields predicted trajectories, the information of which is incorporated in warning messages issued to ships by the (German) authorities. In delayed mode the algorithm produces useful estimates of the depth-averaged currents, which can be used in (process-based) analyses in case no other source of measured current information is available.

Impact of the Fraser River Geometry on Tides and the River Plumes in a Model of the Fraser River Plume

NASA Astrophysics Data System (ADS)

Liu, J.; Allen, S. E.; Soontiens, N. K.

2016-02-01

Fraser River is the largest river on the west coast of Canada. It empties into the Strait of Georgia, which is a large, semi-enclosed body of water between Vancouver Island and the mainland of British Columbia. We have developed a three-dimensional model of the Strait of Georgia, including the Fraser River plume, using the NEMO model in its regional configuration. This operational model produces daily nowcasts and forecasts for salinity, temperature, currents and sea surface heights. Observational data available for evaluation of the model includes daily British Columbia ferry salinity data, profile data and surface drifter data. The salinity of the modelled Fraser River plume agrees well with ferry based measurements of salinity. However, large discrepencies exist between the modelled and observed position of the plume. Modelled surface currents compared to drifter observations show that the model has too strong along-strait velocities and too weak cross-strait velocities. We investigated the impact of river geometry. A sensitivity experiment was performed comparing the original, short, shallow river channel to an extended and deepened river channel. With the latter bathymetry, tidal amplitudes within Fraser River correspond well with observations. Comparisons to drifter tracks show that the surface currents have been improved with the new bathymetry. However, substantial discrepencies remain. We will discuss how reducing vertical eddy viscosity and other changes further improve the modelled position of the plume.

The role of Internal Solitary Waves on deep-water sedimentary processes: the case of up-slope migrating sediment waves off the Messina Strait

PubMed Central

Droghei, R.; Falcini, F.; Casalbore, D.; Martorelli, E.; Mosetti, R.; Sannino, G.; Santoleri, R.; Chiocci, F. L.

2016-01-01

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary “current” that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities. PMID:27808239

Excited cosmic strings with superconducting currents

NASA Astrophysics Data System (ADS)

Hartmann, Betti; Michel, Florent; Peter, Patrick

2017-12-01

We present a detailed analysis of excited cosmic string solutions that possess superconducting currents. These currents can be excited inside the string core, and—if the condensate is large enough—can lead to the excitations of the Higgs field. Next to the case with global unbroken symmetry, we discuss also the effects of the gauging of this symmetry and show that excited condensates persist when coupled to an electromagnetic field. The space-time of such strings is also constructed by solving the Einstein equations numerically and we show how the local scalar curvature is modified by the excitation. We consider the relevance of our results on the cosmic string network evolution as well as observations of primordial gravitational waves and cosmic rays.

Current Sheet Evolution In The Aftermath Of A CME Event

NASA Technical Reports Server (NTRS)

Bemporad, A.; Poletto, G.; Seuss, S. T.; Schwardron, N. A.; Elliott, H. A.; Raymond, J. C.

2006-01-01

We report on SOHO UVCS observations of the coronal restructuring following a coronal mass ejection (CME) on 2002 November 26, at the time of a SOHO-Ulysses quadrature campaign. Starting about 1.5 hr after a CME in the northwest quadrant, UVCS began taking spectra at 1.7 R, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 A line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature versus time in the current sheet and estimate its density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by the Ulysses SWICS throughout the magnetic cloud associated with the CME, although its rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. The SOHO-Ulysses data set provided us with the unique opportunity of analyzing a current sheet structure from its lowest coronal levels out to its in situ properties. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Observed variability in the upper layers at the Equator, 90°E in the Indian Ocean during 2001-2008, 1: zonal currents

NASA Astrophysics Data System (ADS)

Rao, R. R.; Horii, T.; Masumoto, Y.; Mizuno, K.

2017-08-01

The observed variability of zonal currents (ZC) at the Equator, 90°E shows a strong seasonal cycle in the near-surface 40-350 m water column with periodic east-west reversals most pronounced at semiannual frequency. Superposed on this, a strong intraseasonal variability of 30-90 day periodicity is also prominently seen in the near-surface layer (40-80 m) almost throughout the year with the only exception of February-March. An eastward flowing equatorial undercurrent (EUC) is present in the depth range of 80-160 m during March-April and October-November. The observed intraseasonal variability in the near-surface layer is primarily determined by the equatorial zonal westerly wind bursts (WWBs) through local frictional coupling between the zonal flow in the surface layer and surface zonal winds and shows large interannual variability. The eastward flowing EUC maintained by the ZPG set up by the east-west slope of the thermocline remotely controlled by the zonal wind (ZW) and zonally propagating wave fields also shows significant interannual variability. This observed variability on interannual time scales appears to be controlled by the corresponding variability in the alongshore winds off the Somalia coast during the preceding boreal winter, the ZW field along the equator, and the associated zonally propagating Kelvin and Rossby waves. The salinity induced vertical stratification observed in the near-surface layer through barrier layer thickness (BLT) effects also shows a significant influence on the ZC field on intraseasonal time scale. Interestingly, among all the 8 years (2001-2008), relatively weaker annual cycle is seen in both ZC in the 40-350 m water column and boreal spring sea surface temperature (SST) only during 2001 and 2008 along the equator caused through propagating wave dynamics.

ICRF antenna-plasma interactions and its influence on W sputtering in ASDEX upgrade

NASA Astrophysics Data System (ADS)

ASDEX Upgrade Team Bobkov, Vl.; Braun, F.; Colas, L.; Dux, R.; Faugel, H.; Giannone, L.; Herrmann, A.; Kallenbach, A.; Müller, H. W.; Neu, R.; Noterdaeme, J.-M.; Pütterich, Th.; Siegl, G.; Wolfrum, E.

2011-08-01

Analysis of the W concentration during ICRF over AUG experimental campaigns confirms the critical role of W antenna limiters for the W content in plasma, though other structures connected to antennas along magnetic field lines cannot be neglected as W sources.Abrupt changes of spectroscopically measured W sputtering patterns are observed which correlate with step-wise changes of connection lengths at antenna limiters. Analysis of discharges with the reversed direction of toroidal magnetic field shows less W release compared to identical discharges with the normal direction. The lower W release is accompanied by lower intensity of fluctuations of reflected ICRF power in the 1-60 kHz range. The observations suggest that local magnetic geometry and density convection at the antennas are at least as important for the W sputtering as the distribution of RF near-fields at the antenna.Measurements of DC currents flowing through the antenna limiters show that the limiters at the active antenna collect predominantly negative DC currents whereas those distant from the active antenna collect predominantly positive DC currents. The latter decrease and become more negative when the intensity of the RF pickup measured at the limiters increases. The mutual compensation between the positive and negative currents can lead to lower values of the DC current than those expected from simplified theoretical models of the RF/DC circuit.

ICRF antenna-plasma interactions and its influence on W sputtering in ASDEX upgrade

NASA Astrophysics Data System (ADS)

Bobkov, Vl.; Braun, F.; Colas, L.; Dux, R.; Faugel, H.; Giannone, L.; Herrmann, A.; Kallenbach, A.; Müller, H. W.; Neu, R.; Noterdaeme, J.-M.; Pütterich, Th.; Siegl, G.; Wolfrum, E.; ASDEX Upgrade Team

2011-08-01

Analysis of the W concentration during ICRF over AUG experimental campaigns confirms the critical role of W antenna limiters for the W content in plasma, though other structures connected to antennas along magnetic field lines cannot be neglected as W sources. Abrupt changes of spectroscopically measured W sputtering patterns are observed which correlate with step-wise changes of connection lengths at antenna limiters. Analysis of discharges with the reversed direction of toroidal magnetic field shows less W release compared to identical discharges with the normal direction. The lower W release is accompanied by lower intensity of fluctuations of reflected ICRF power in the 1-60 kHz range. The observations suggest that local magnetic geometry and density convection at the antennas are at least as important for the W sputtering as the distribution of RF near-fields at the antenna. Measurements of DC currents flowing through the antenna limiters show that the limiters at the active antenna collect predominantly negative DC currents whereas those distant from the active antenna collect predominantly positive DC currents. The latter decrease and become more negative when the intensity of the RF pickup measured at the limiters increases. The mutual compensation between the positive and negative currents can lead to lower values of the DC current than those expected from simplified theoretical models of the RF/DC circuit.

Adjunctation and Scalar Product in the Dirac Equation - II

NASA Astrophysics Data System (ADS)

Dima, M.

2017-02-01

Part-I Dima (Int. J. Theor. Phys. 55, 949, 2016) of this paper showed in a representation independent way that γ 0 is the Bergmann-Pauli adjunctator of the Dirac { γ μ } set. The distiction was made between similarity (MATH) transformations and PHYS transformations - related to the (covariant) transformations of physical quantities. Covariance is due solely to the gauging of scalar products between systems of reference and not to the particular action of γ 0 on Lorentz boosts - a matter that in the past led inadvertently to the definition of a second scalar product (the Dirac-bar product). Part-II shows how two scalar products lead to contradictions and eliminates this un-natural duality in favour of the canonical scalar product and its gauge between systems of reference. What constitutes a proper observable is analysed and for instance spin is revealed not to embody one (except as projection on the boost direction - helicity). A thorough investigation into finding a proper-observable current for the theory shows that the Dirac equation does not possess one in operator form. A number of problems with the Dirac current operator are revealed - its Klein-Gordon counterpart being significantly more physical. The alternative suggested is finding a current for the Dirac theory in scalar form j^{μ } = < ρ rangle _{_{ψ }}v^{μ }_{ψ }.

Automated and manual patch clamp data of human induced pluripotent stem cell-derived dopaminergic neurons.

PubMed

Franz, Denise; Olsen, Hervør Lykke; Klink, Oliver; Gimsa, Jan

2017-04-25

Human induced pluripotent stem cells can be differentiated into dopaminergic neurons (Dopa.4U). Dopa.4U neurons expressed voltage-gated Na V and K V channels and showed neuron-like spontaneous electrical activity. In automated patch clamp measurements with suspended Dopa.4U neurons, delayed rectifier K + current (delayed K V ) and rapidly inactivating A-type K + current (fast K V ) were identified. Examination of the fast K V current with inhibitors yielded IC 50 values of 0.4 mM (4-aminopyridine) and 0.1 mM (tetraethylammonium). In manual patch clamp measurements with adherent Dopa.4U neurons, fast K V current could not be detected, while the delayed K V current showed an IC 50 of 2 mM for 4-aminopyridine. The Na V channels in adherent and suspended Dopa.4U neurons showed IC 50 values for tetrodotoxin of 27 and 2.9 nM, respectively. GABA-induced currents that could be observed in adherent Dopa.4U neurons could not be detected in suspended cells. Application of current pulses induced action potentials in approx. 70 % of the cells. Our results proved the feasibility of automated electrophysiological characterization of neuronal cells.

SAR observation and numerical modeling of tidal current wakes at the East China Sea offshore wind farm

NASA Astrophysics Data System (ADS)

Li, XiaoMing; Chi, Lequan; Chen, Xueen; Ren, YongZheng; Lehner, Susanne

2014-08-01

A TerraSAR-X (TS-X) Synthetic Aperture Radar (SAR) image acquired at the East China Sea offshore wind farm presents distinct wakes at a kilometer scale on the lee of the wind turbines. The presumption was that these wakes were caused by wind movement around turbine blades. However, wind analysis using spaceborne radiometer data, numerical weather prediction, and in situ measurements suggest that the prevailing wind direction did not align with the wakes. By analyzing measurement at the tidal gauge station and modeling of the tidal current field, these trailing wakes are interpreted to have formed when a strong tidal current impinged on the cylindrical monopiles of the wind turbines. A numerical simulation was further conducted to reproduce the tidal current wake under such conditions. Comparison of the simulated surface velocity in the wake region with the TS-X sea surface backscatter intensity shows a similar trend. Consequently, turbulence intensity (T.I.) of the tidal current wakes over multiple piles is studied using the TS-X observation. It is found that the T.I. has a logarithmic relation with distance. Furthermore, another case study showing wakes due to wind movement around turbine blades is presented to discuss the differences in the tidal current wakes and wind turbine wakes. The conclusion is drawn that small-scale wakes formed by interaction of the tidal current and the turbine piles could be also imaged by SAR when certain conditions are satisfied. The study is anticipated to draw more attentions to the impacts of offshore wind foundations on local hydrodynamic field.

Multi-instrument Observations of Transient Luminous Events Associated with a Small-scale Winter Thunderstorm

NASA Astrophysics Data System (ADS)

Kolmasova, I.; Santolik, O.; Spurny, P.; Borovicka, J.; Mlynarczyk, J.; Popek, M.; Lan, R.; Uhlir, L.; Diendorfer, G.; Slosiar, R.

2017-12-01

We present observations of transient luminous events (TLEs) produced by a small-scale winter thunderstorm which occurred on 2 April 2017 in the southwest of Czechia. Elves, sprites and associated positive lightning strokes have been simultaneously recorded by different observational techniques. Optical data include video recordings of TLEs from Nydek (Czechia) and data recorded by high time-resolution photometers at several stations of the Czech fireball network which measured the all-sky brightness originating from lightning return strokes. Electromagnetic data sets include 3-component VLF measurements conducted in Rustrel (France), 2-component ELF measurements recorded at the Hylaty station (Poland) and signal intensity variations of a VLF transmitter (DHO38, Rhauderfehn, Germany) recorded in Bojnice (Slovakia). Optical and electromagnetic data are completed by positions and peak currents of all strokes recorded during the observed thunderstorm by the EUCLID lightning detection network. We focus our analysis on positive lightning discharges with high peak currents and we compare properties of those which produced TLE with properties of discharges for which TLE was not detected. The current moment waveforms and charge moment changes associated with the TLE events are reconstructed from the ELF electromagnetic signals. Obtained current moment waveforms show excellent agreement with high time-resolution optical data.

Vertical structure of mean cross-shore currents across a barred surf zone

USGS Publications Warehouse

Haines, John W.; Sallenger, Asbury H.

1994-01-01

Mean cross-shore currents observed across a barred surf zone are compared to model predictions. The model is based on a simplified momentum balance with a turbulent boundary layer at the bed. Turbulent exchange is parameterized by an eddy viscosity formulation, with the eddy viscosity Aυ independent of time and the vertical coordinate. Mean currents result from gradients due to wave breaking and shoaling, and the presence of a mean setup of the free surface. Descriptions of the wave field are provided by the wave transformation model of Thornton and Guza [1983]. The wave transformation model adequately reproduces the observed wave heights across the surf zone. The mean current model successfully reproduces the observed cross-shore flows. Both observations and predictions show predominantly offshore flow with onshore flow restricted to a relatively thin surface layer. Successful application of the mean flow model requires an eddy viscosity which varies horizontally across the surf zone. Attempts are made to parameterize this variation with some success. The data does not discriminate between alternative parameterizations proposed. The overall variability in eddy viscosity suggested by the model fitting should be resolvable by field measurements of the turbulent stresses. Consistent shortcomings of the parameterizations, and the overall modeling effort, suggest avenues for further development and data collection.

Transport and sedimentation in unconfined experimental dilute pyroclastic density currents

NASA Astrophysics Data System (ADS)

Ramirez, G.; Andrews, B. J.; Dennen, R. L.

2013-12-01

We present results from experiments conducted in a new facility that permits the study of large, unconfined particle laden density currents that are dynamically similar to natural dilute pyroclastic density currents (PDCs). Experiments were run in a sealed, air-filled tank measuring 8.5 m long by 6.1 m wide by 2.6 m tall. Currents were generated by feeding mixture of heated particles (5 μm aluminum oxide, 25 μm talc, 27 μm walnut shell, 76 μm glass beads) down a chute at controlled rates to produce dilute, turbulent gravity currents. Comparison of experimental currents with natural PDCs shows good agreement between Froude, densimetric and thermal Richardson, and particle Stokes and settling numbers; experimental currents have lower Reynolds numbers than natural PDCs, but are fully turbulent. Currents were illuminated with 3 orthogonal laser sheets (650, 532, and 450 nm wavelengths) and recorded with an array of HD video cameras and a high speed camera (up to 3000 fps). Deposits were mapped using a grid of sedimentation traps. We observe distinct differences between ambient temperature and warm currents: * warm currents have shorter run out distances, narrow map view distributions of currents and deposits, thicken with distance from the source, and lift off to form coignimbrite plumes; * ambient temperature currents typically travel farther, spread out radially, do not thicken greatly with transport distance, and do not form coignimbrite plumes. Long duration currents (600 s compared to 30-100 s) oscillate laterally with time (e.g. transport to the right, then the left, and back); this oscillation happens prior to any interaction with the tank walls. Isopach maps of the deposits show predictable trends in sedimentation versus distance in response to eruption parameters (eruption rate, duration, temperature, and initial current mass), but all sedimentation curves can be fit with 2nd order polynomials (R2>.9). Proximal sedimentation is similar in comparable warm and ambient temperature currents, but distal sedimentation (beyond the current runout) increases in warm currents reflecting deposition from coignimbrite plumes. We are currently developing analytical models to link the observed transport and sedimentation results.

Interventions addressing general parenting to prevent or treat childhood obesity.

PubMed

Gerards, Sanne M P L; Sleddens, Ester F C; Dagnelie, Pieter C; de Vries, Nanne K; Kremers, Stef P J

2011-06-01

Observational studies increasingly emphasize the impact of general parenting on the development of childhood overweight and obesity. The aim of the current literature review was to provide an overview of interventions addressing general parenting in order to prevent or treat childhood obesity. Electronic literature databases were systematically searched for relevant studies. Seven studies were eligible for inclusion. The studies described four different general parenting programs, which were supplemented with lifestyle components (i.e., physical activity and nutrition). All studies showed significant small to moderate intervention effects on at least one weight-related outcome measure. The current review shows that despite the emerging observational evidence for the role of parenting in children's weight-related outcomes, few interventions have been developed that address general parenting in the prevention of childhood obesity. These interventions provide evidence that the promotion of authoritative parenting is an effective strategy for the prevention and management of childhood obesity.

Use of sand wave habitats by silver hake

USGS Publications Warehouse

Auster, P.J.; Lindholm, J.; Schaub, S.; Funnell, G.; Kaufman, L.S.; Valentine, P.C.

2003-01-01

Silver hake Merluccius bilinearis are common members of fish communities in sand wave habitats on Georges Bank and on Stellwagen Bank in the Gulf of Maine. Observations of fish size v. sand wave period showed that silver hake are not randomly distributed within sand wave landscapes. Regression analyses showed a significant positive relationship between sand wave period and fish length. Correlation coefficients, however, were low, suggesting other interactions with sand wave morphology, the range of current velocities, and available prey may also influence their distribution. Direct contact with sand wave habitats varied over diel periods, with more fish resting on the seafloor during daytime than at night. Social foraging, in the form of polarized groups of fish swimming in linear formations during crepuscular and daytime periods, was also observed. Sand wave habitats may provide shelter from current flows and mediate fish-prey interactions. ?? 2003 The Fisheries Society of the British Isles.

Constraints on the dark matter neutralinos from the radio emissions of galaxy clusters

NASA Astrophysics Data System (ADS)

Kiew, Ching-Yee; Hwang, Chorng-Yuan; Zainal Abibin, Zamri

2017-05-01

By assuming the dark matter to be composed of neutralinos, we used the detection of upper limit on diffuse radio emission in a sample of galaxy clusters to put constraint on the properties of neutralinos. We showed the upper limit constraint on <σv>-mχ space with neutralino annihilation through b\\bar{b} and μ+μ- channels. The best constraint is from the galaxy clusters A2199 and A1367. We showed the uncertainty due to the density profile and cluster magnetic field. The largest uncertainty comes from the uncertainty in dark matter spatial distribution. We also investigated the constraints on minimal Supergravity (mSUGRA) and minimal supersymmetric standard model (MSSM) parameter space by scanning the parameters using the darksusy package. By using the current radio observation, we managed to exclude 40 combinations of mSUGRA parameters. On the other hand, 573 combinations of MSSM parameters can be excluded by current observation.

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

Parkin, William M.; Balan, Adrian; Liang, Liangbo

Here, we report how the presence of electron-beam-induced sulfur vacancies affects first-order Raman modes and correlate the effects with the evolution of the in situ transmission-electron microscopy (TEM) two-terminal conductivity of monolayer MoS 2 under electron irradiation. We observe a redshift in the E Raman peak and a less pronounced blueshift in the A' 1 peak with increasing electron dose. Using energy-dispersive X-ray spectroscopy (EDS), we show that irradiation causes partial removal of sulfur and correlate the dependence of the Raman peak shifts with S vacancy density (a few %), which is confirmed by first-principles density functional theory calculations. Inmore » situ device current measurements show exponential decrease in channel current upon irradiation. Our analysis demonstrates that the observed frequency shifts are intrinsic properties of the defective systems and that Raman spectroscopy can be used as a quantitative diagnostic tool to characterize MoS 2-based transport channels.« less

Trends in the Brazil/Malvinas Confluence region

NASA Astrophysics Data System (ADS)

Combes, Vincent; Matano, Ricardo P.

2014-12-01

Observations show abrupt changes in the oceanic circulation of the southwestern Atlantic. These studies report a southward drift of the Brazil/Malvinas Confluence (BMC) and a change in the spectral characteristics of the Malvinas Current (MC) transport. We address the cause of these changes using the result of a high-resolution numerical experiment. The experiment, which is consistent with observations, shows a southward BMC displacement at a rate of 0.62°/decade between 1993 and 2008, and a shift of the spectral characteristics of the MC transport after 1999. We find that these changes are driven by a weakening of the northern branch of the Antarctic Circumpolar Current, which translates to a weakening of the MC transport and a southward BMC drift. The drift changes the spectral characteristics of the MC transport, which becomes more influenced by annual and semiannual variations associated with the BMC.

Finite element simulation of thunderstorm electrodynamics in the proximity of the storm

NASA Technical Reports Server (NTRS)

Baginski, Michael Edward

1988-01-01

Observations of electric fields, Maxwell current density, and air conductivity over thunderstorms were presented. The measurements were obtained using electric field mils and conductivity probes installed on a U2 aircraft as the aircraft passed approximately directly over an active thunderstorm at an altitude of 18 to 20 km. Accurate electrical observations of this type are rare and provide important information to those involved in numerically modeling a thunderstorm. A preliminary set of computer simulations based on this data were conducted and are described. The simulations show good agreement with measurements and are used to infer the thundercloud's charging current and amount of charge exchanged per flash.

Size dependent tunnel diode effects in gold tipped CdSe nanodumbbells.

PubMed

Saraf, Deepashri; Kumar, Ashok; Kanhere, Dilip; Kshirsagar, Anjali

2017-02-07

We report simulation results for scanning tunneling spectroscopy of gold-tipped CdSe nanodumbbells of lengths ∼27 Å and ∼78 Å. Present results are based on Bardeen, Tersoff, and Hamann formalism that takes inputs from ab initio calculations. For the shorter nanodumbbell, the current-voltage curves reveal negative differential conductance, the characteristic of a tunnel diode. This behaviour is attributed to highly localized metal induced gap states that rapidly decay towards the center of the nanodumbbell leading to suppression in tunneling. In the longer nanodumbbell, these gap states are absent in the central region, as a consequence of which zero tunneling current is observed in that region. The overall current-voltage characteristics for this nanodumbbell are observed to be largely linear near the metal-semiconductor interface and become rectifying at the central region, the nature being similar to its parent nanorod. The cross-sectional heights of these nanodumbbells also show bias-dependence where we begin to observe giant Stark effect features in the semiconducting central region of the longer nanodumbbell.

United Kingdom Infrared Telescope's Spectrograph Observations of Human-Made Space Objects

NASA Technical Reports Server (NTRS)

Buckalew, Brent; Abercromby, Kira; Lederer, Susan; Frith, James; Cowardin, Heather

2017-01-01

Presented here are the results of the United Kingdom Infrared Telescope (UKIRT) spectral observations of human-made space objects taken from 2014 to 2015. The data collected using the UIST infrared spectrograph cover the wavelength range 0.7-2.5 micrometers. Overall, data were collected on 18 different orbiting objects at or near the geosynchronous (GEO) regime. Thirteen of the objects are spacecraft, one is a rocket body, and four are cataloged as debris pieces. The remotely collected data are compared to the laboratory-collected reflectance data on typical spacecraft materials; thereby general materials are identified but not specific types. These results highlight the usefulness of observations in the infrared by focusing on features from hydrocarbons and silicon. The spacecraft show distinct features due to the presence of solar panels. Signature variations between rocket bodies, due to the presence of various metals and paints on their surfaces, show a clear distinction from those objects with solar panels, demonstrating that one can distinguish most spacecraft from rocket bodies through infrared spectrum analysis. Finally, the debris pieces tend to show featureless, dark spectra. These results show that the laboratory data in its current state give excellent indications as to the nature of the surface materials on the objects. Further telescopic data collection and model updates to include more materials, noise, surface roughness, and material degradation are necessary to make better assessments of orbital object material types. A comparison conducted between objects observed previously with the NASA Infrared Telescope Facility (IRTF) shows similar materials and trends from the two telescopes and from the two distinct data sets. However, based on the current state of the model, infrared spectroscopic data are adequate to classify objects in GEO as spacecraft, rocket bodies, or debris.

Merging altimeter data with Argo profiles to improve observation of tropical Pacific thermocline circulation and ENSO

NASA Astrophysics Data System (ADS)

Zhang, D.; Lee, T.; Wang, F.; McPhaden, M. J.; Kessler, W. S.

2016-12-01

Meridional thermocline currents play an important role in the recharge and discharge of tropical Pacific warm water during the development and transition of ENSO cycles. Previous analyses have shown large variations of the equatorward meridional thermocline convergence/divergence on ENSO and decadal time scales in the interior ocean. The total convergence/divergence is however unknown due to the lack of long term observation in the western boundary currents. Numerical modelling studies suggested a tendency of compensation between the interior and western boundary currents, but the exact compensation is model dependent. While Argo floats provide reasonable data coverage in the interior ocean, few floats are in the western boundary currents. Recent multi-mission satellite altimeter data and advanced processing techniques have resulted in higher resolution sea surface height anomaly (SSHA) products with better accuracy closer to the coasts. This study utilizes the statistical relationship between Argo dynamic height profiles and altimeter SSHA to calculate geostrophic thermocline currents in both the interior ocean and the western boundary of the tropical Pacific. The derived thermocline currents in the western boundary are validated by a 3.5-year moored Acoustic Doppler Current Profiler (ADCP) measurement in the Mindanao Current and by a series of glider surveys (Davis et al. 2012) in the Solomon Sea. The meridional transport timeseries of the interior and western boundary currents in the thermocline show different lead-lag relationships to the Nino 3.4 index. Results will be discussed in the context of recent 2014-2015 El Nino development and the potential contribution to the Tropical Pacific Observing System (TPOS).

Degradation of (La(0.8)Sr(0.2))(0.98)MnO(3-δ)-Zr(0.84)Y(0.16)O(2-γ) composite electrodes during reversing current operation.

PubMed

Hughes, Gareth A; Railsback, Justin G; Yakal-Kremski, Kyle J; Butts, Danielle M; Barnett, Scott A

2015-01-01

Reversing-current operation of solid oxide cell (La(0.8)Sr(0.2))(0.98)MnO(3-δ)-Zr(0.84)Y(0.16)O(2-γ) (LSM-YSZ) oxygen electrodes is described. Degradation was characterized by impedance spectroscopy in symmetric cells tested at 800 °C in air with a symmetric current cycle with a period of 12 hours. No change in cell resistance could be detected, in 1000 h tests with a sensitivity of ∼1% per kh, at a current density of 0.5 A cm(-2) corresponding to an overpotential of 0.18 V. At a current density to 0.6 A cm(-2) (0.33 V overpotential) measurable resistance degradation at a rate of 3% per kh was observed, while higher current/overpotential values led to faster degradation. Degradation was observed mainly in the ohmic resistance for current densities of 0.6, 0.8 and 0.9 A cm(-2), with little change in the polarization resistance. Polarization degradation, mainly observed at higher current density, was present as an increase in an impedance response at ∼30 kHz, apparently associated with the resistance of YSZ grain boundaries within the electrode. Microstructural and chemical analysis showed significant changes in electrode structure after the current cycling, including an increase in LSM particle size and a reduction in the amount of YSZ and LSM at the electrode/electrolyte interface - the latter presumably a precursor to delamination.

Electrical overstress in AlGaN/GaN HEMTs: study of degradation processes

NASA Astrophysics Data System (ADS)

Kuzmík, J.; Pogany, D.; Gornik, E.; Javorka, P.; Kordoš, P.

2004-02-01

We study degradation mechanisms in 50 μm gate width/0.45 μm length AlGaN/GaN HEMTs after electrical overstresses. One hundred nanosecond long rectangular current pulses are applied on the drain contact keeping either both of the source and gate grounded or the source grounded and gate floating. Source-drain pulsed I- V characteristics show similar shape for both connections. After the HEMT undergoes the source-drain breakdown, a negative differential resistance region transits into a low voltage/high current region. Changes in the Schottky contact dc I- V characteristics and in the source and drain ohmic contacts are investigated as a function of the current stress level and are related to the HEMT dc performance. Catastrophic HEMT degradation was observed after Istress=1.65 A in case of the 'gate floating' connection due to ohmic contacts burnout. In case of the 'gate grounded' connection, Istress=0.45 A was sufficient for the gate failure showing a high gate susceptibility to overstress. Backside transient interferometric mapping technique experiment reveals a current filament formation under both HEMT stress connections. Infrared camera observations lead to conclusion that the filament formation together with a consequent high-density electron flow is responsible for a dark spot formation and gradual ohmic contact degradation.

In situ hydrostatic pressure induced improvement of critical current density and suppression of magnetic relaxation in Y(Dy0.5)Ba2Cu3O7‑δ coated conductors

NASA Astrophysics Data System (ADS)

Sang, Lina; Gutiérrez, Joffre; Cai, Chuanbing; Dou, Shixue; Wang, Xiaolin

2018-07-01

We report on the effect of in situ hydrostatic pressure on the enhancement of the in-magnetic-field critical current density parallel to the crystallographic c-axis and vortex pinning in epitaxial Y(Dy0.5)Ba2Cu3O7‑δ coated conductors prepared by metal organic deposition. Our results show that in situ hydrostatic pressure greatly enhances the critical current density at high fields and high temperatures. At 80 K and 5 T we observe a ten-fold increase in the critical current density under the pressure of 1.2 GPa, and the irreversibility line is shifted to higher fields without changing the critical temperature. The normalized magnetic relaxation rate shows that vortex creep rates are strongly suppressed due to applied pressure, and the pinning energy is significantly increased based on the collective creep theory. After releasing the pressure, we recover the original superconducting properties. Therefore, we speculate that the in situ hydrostatic pressure exerted on the coated conductor enhances the pinning of existing extended defects. This is totally different from what has been observed in REBa2Cu3O7‑δ melt-textured crystals, where the effect of pressure generates point-like defects.

ALMA Long Baseline Observations of the Dynamical Atmospheres of AGB Stars

NASA Astrophysics Data System (ADS)

Vlemmings, Wouter

2018-04-01

I will present the current status of ALMA long baseline observations of W Hya, R Leo, R Dor and Mira. We have recently obtained band 4, 6 and 7 observations of the line and continuum emission tracing the temperature and dynamics in their extended atmosphere. Our preliminary analysis confirms our previous detection of a hotspot on W Hya, and reveals unexpected lines in most of the sources, as well as possible fast rotation in the atmopshere of one of the stars. The observations show the unique power of ALMA in observing the extended stellar atmospheres.

A Network Model of Observation and Imitation of Speech

PubMed Central

Mashal, Nira; Solodkin, Ana; Dick, Anthony Steven; Chen, E. Elinor; Small, Steven L.

2012-01-01

Much evidence has now accumulated demonstrating and quantifying the extent of shared regional brain activation for observation and execution of speech. However, the nature of the actual networks that implement these functions, i.e., both the brain regions and the connections among them, and the similarities and differences across these networks has not been elucidated. The current study aims to characterize formally a network for observation and imitation of syllables in the healthy adult brain and to compare their structure and effective connectivity. Eleven healthy participants observed or imitated audiovisual syllables spoken by a human actor. We constructed four structural equation models to characterize the networks for observation and imitation in each of the two hemispheres. Our results show that the network models for observation and imitation comprise the same essential structure but differ in important ways from each other (in both hemispheres) based on connectivity. In particular, our results show that the connections from posterior superior temporal gyrus and sulcus to ventral premotor, ventral premotor to dorsal premotor, and dorsal premotor to primary motor cortex in the left hemisphere are stronger during imitation than during observation. The first two connections are implicated in a putative dorsal stream of speech perception, thought to involve translating auditory speech signals into motor representations. Thus, the current results suggest that flow of information during imitation, starting at the posterior superior temporal cortex and ending in the motor cortex, enhances input to the motor cortex in the service of speech execution. PMID:22470360

On Leakage Current Measured at High Cell Voltages in Lithium-Ion Batteries

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

Vadivel, Nicole R.; Ha, Seungbum; He, Meinan

2017-01-01

In this study, parasitic side reactions in lithium-ion batteries were examined experimentally using a potentiostatic hold at high cell voltage. The experimental leakage current measured during the potentiostatic hold was compared to the Tafel expression and showed poor agreement with the expected transfer coefficient values, indicating that a more complicated expression could be needed to accurately capture the physics of this side reaction. Here we show that cross-talk between the electrodes is the primary contribution to the observed leakage current after the relaxation of concentration gradients has ceased. This cross-talk was confirmed with experiments using a lithium-ion conducting glass ceramicmore » (LICGC) separator, which has high conductance only for lithium cations. The cells with LICGC separators showed significantly less leakage current during the potentiostatic hold test compared to cells with standard microporous separators where cross-talk is present. In addition, direct-current pulse power tests show an impedance rise for cells held at high potentials and for cells held at high temperatures, which could be attributed to film formation from the parasitic side reaction. Based on the experimental findings, a phenomenological mechanism is proposed for the parasitic side reaction which accounts for cross-talk and mass transport of the decomposition products across the separator.« less

Experimental investigation of large-scale vortices in a freely spreading gravity current

NASA Astrophysics Data System (ADS)

Yuan, Yeping; Horner-Devine, Alexander R.

2017-10-01

A series of laboratory experiments are presented to compare the dynamics of constant-source buoyant gravity currents propagating into laterally confined (channelized) and unconfined (spreading) environments. The plan-form structure of the spreading current and the vertical density and velocity structures on the interface are quantified using the optical thickness method and a combined particle image velocimetry and planar laser-induced fluorescence method, respectively. With lateral boundaries, the buoyant current thickness is approximately constant and Kelvin-Helmholtz instabilities are generated within the shear layer. The buoyant current structure is significantly different in the spreading case. As the current spreads laterally, nonlinear large-scale vortex structures are observed at the interface, which maintain a coherent shape as they propagate away from the source. These structures are continuously generated near the river mouth, have amplitudes close to the buoyant layer thickness, and propagate offshore at speeds approximately equal to the internal wave speed. The observed depth and propagation speed of the instabilities match well with the fastest growing mode predicted by linear stability analysis, but with a shorter wavelength. The spreading flows have much higher vorticity, which is aggregated within the large-scale structures. Secondary instabilities are generated on the leading edge of the braids between the large-scale vortex structures and ultimately break and mix on the lee side of the structures. Analysis of the vortex dynamics shows that lateral stretching intensifies the vorticity in the spreading currents, contributing to higher vorticity within the large-scale structures in the buoyant plume. The large-scale instabilities and vortex structures observed in the present study provide new insights into the origin of internal frontal structures frequently observed in coastal river plumes.

Anomalous Ion Heating, Intrinsic and Induced Rotation in the Pegasus Toroidal Experiment

NASA Astrophysics Data System (ADS)

Burke, M. G.; Barr, J. L.; Bongard, M. W.; Fonck, R. J.; Hinson, E. T.; Perry, J. M.; Redd, A. J.; Thome, K. E.

2014-10-01

Pegasus plasmas are initiated through either standard, MHD stable, inductive current drive or non-solenoidal local helicity injection (LHI) current drive with strong reconnection activity, providing a rich environment to study ion dynamics. During LHI discharges, a large amount of anomalous impurity ion heating has been observed, with Ti ~ 800 eV but Te < 100 eV. The ion heating is hypothesized to be a result of large-scale magnetic reconnection activity, as the amount of heating scales with increasing fluctuation amplitude of the dominant, edge localized, n = 1 MHD mode. Chordal Ti spatial profiles indicate centrally peaked temperatures, suggesting a region of good confinement near the plasma core surrounded by a stochastic region. LHI plasmas are observed to rotate, perhaps due to an inward radial current generated by the stochastization of the plasma edge by the injected current streams. H-mode plasmas are initiated using a combination of high-field side fueling and Ohmic current drive. This regime shows a significant increase in rotation shear compared to L-mode plasmas. In addition, these plasmas have been observed to rotate in the counter-Ip direction without any external momentum sources. The intrinsic rotation direction is consistent with predictions from the saturated Ohmic confinement regime. Work supported by US DOE Grant DE-FG02-96ER54375.

Discharge Oscillations in a Permanent Magnet Cylindrical Hall-Effect Thruster

NASA Technical Reports Server (NTRS)

Polzin, K. A.; Sooby, E. S.; Raitses, Y.; Merino, E.; Fisch, N. J.

2009-01-01

Measurements of the discharge current in a cylindrical Hall thruster are presented to quantify plasma oscillations and instabilities without introducing an intrusive probe into the plasma. The time-varying component of the discharge current is measured using a current monitor that possesses a wide frequency bandwidth and the signal is Fourier transformed to yield the frequency spectra present, allowing for the identification of plasma oscillations. The data show that the discharge current oscillations become generally greater in amplitude and complexity as the voltage is increased, and are reduced in severity with increasing flow rate. The breathing mode ionization instability is identified, with frequency as a function of discharge voltage not increasing with discharge voltage as has been observed in some traditional Hall thruster geometries, but instead following a scaling similar to a large-amplitude, nonlinear oscillation mode recently predicted in for annular Hall thrusters. A transition from lower amplitude oscillations to large relative fluctuations in the oscillating discharge current is observed at low flow rates and is suppressed as the mass flow rate is increased. A second set of peaks in the frequency spectra are observed at the highest propellant flow rate tested. Possible mechanisms that might give rise to these peaks include ionization instabilities and interactions between various oscillatory modes.

Contribution of energetic and heavy ions to the plasma pressure: The 27 September to 3 October 2002 storm

NASA Astrophysics Data System (ADS)

Kronberg, E. A.; Welling, D.; Kistler, L. M.; Mouikis, C.; Daly, P. W.; Grigorenko, E. E.; Klecker, B.; Dandouras, I.

2017-09-01

Magnetospheric plasma sheet ions drift toward the Earth and populate the ring current. The ring current plasma pressure distorts the terrestrial internal magnetic field at the surface, and this disturbance strongly affects the strength of a magnetic storm. The contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure in the near-Earth plasma sheet is not always considered. In this study, we evaluate the contribution of low-energy and energetic ions of different species to the total plasma pressure for the storm observed by the Cluster mission from 27 September until 3 October 2002. We show that the contribution of energetic ions (>40 keV) and of heavy ions to the total plasma pressure is ≃76-98.6% in the ring current and ≃14-59% in the magnetotail. The main source of oxygen ions, responsible for ≃56% of the plasma pressure of the ring current, is located at distances earthward of XGSE ≃ -13.5 RE during the main phase of the storm. The contribution of the ring current particles agrees with the observed Dst index. We model the magnetic storm using the Space Weather Modeling Framework (SWMF). We assess the plasma pressure output in the ring current for two different ion outflow models in the SWMF through comparison with observations. Both models yield reasonable results. The model which produces the most heavy ions agrees best with the observations. However, the data suggest that there is still potential for refinement in the simulations.

Dependence of transition width on current and critical current in transition-edge sensors

NASA Astrophysics Data System (ADS)

Morgan, K. M.; Pappas, C. G.; Bennett, D. A.; Gard, J. D.; Hays-Wehle, J. P.; Hilton, G. C.; Reintsema, C. D.; Schmidt, D. R.; Ullom, J. N.; Swetz, D. S.

2017-05-01

In superconducting transition-edge sensor X-ray detectors, we observe that as the thermal conductance (G) to the heat bath increases, the resistive transition broadens. Consequently, the sensitivity of films to deposited energy worsens. Using a two-fluid model for the superconducting-to-normal transition in a thin film, we show that this broadening can be attributed to the larger current (I0) necessary for biasing the film at a given point in the transition for higher-G devices, resulting in a higher Ic0/I0 ratio (Ic0 is the film's critical current at zero temperature). To recover a sharper transition, we fabricated rectangular films with varying numbers of internal normal-metal structures while keeping G constant, allowing the independent variation of both I0 and Ic0. We show that it is possible to manipulate the transition width and G independently, thus enabling fast thermal sensors with an excellent energy resolution.

Spin-orbit torque-induced switching in ferrimagnetic alloys: Experiments and modeling

NASA Astrophysics Data System (ADS)

Je, Soong-Geun; Rojas-Sánchez, Juan-Carlos; Pham, Thai Ha; Vallobra, Pierre; Malinowski, Gregory; Lacour, Daniel; Fache, Thibaud; Cyrille, Marie-Claire; Kim, Dae-Yun; Choe, Sug-Bong; Belmeguenai, Mohamed; Hehn, Michel; Mangin, Stéphane; Gaudin, Gilles; Boulle, Olivier

2018-02-01

We investigate spin-orbit torque (SOT)-induced switching in rare-earth-transition metal ferrimagnetic alloys using W/CoTb bilayers. The switching current is found to vary continuously with the alloy concentration, and no reduction in the switching current is observed at the magnetic compensation point despite a very large SOT efficiency. A model based on coupled Landau-Lifschitz-Gilbert (LLG) equations shows that the switching current density scales with the effective perpendicular anisotropy which does not exhibit strong reduction at the magnetic compensation, explaining the behavior of the switching current density. This model also suggests that conventional SOT effective field measurements do not allow one to conclude whether the spins are transferred to one sublattice or just simply to the net magnetization. The effective spin Hall angle measurement shows an enhancement of the spin Hall angle with the Tb concentration which suggests an additional SOT contribution from the rare earth Tb atoms.

The morphology of flare phenomena, magnetic fields, and electric currents in active regions. II - NOAA active region 5747 (1989 October)

NASA Technical Reports Server (NTRS)

Leka, K. D.; Canfield, Richard C.; Mcclymont, A. N.; De La Beaujardiere, J.-F.; Fan, Yuhong; Tang, F.

1993-01-01

The paper describes October 1989 observations in NOAA Active Region 5747 of the morphology of energetic electron precipitation and high-pressure coronal flare plasmas of three flares and their relation to the vector magnetic field and vertical electric currents. The H-alpha spectroheliograms were coaligned with the vector magnetograms using continuum images of sunspots, enabling positional accuracy of a few arcsec. It was found that, during the gradual phase, the regions of the H-alpha flare that show the effects of enhanced pressure in the overlying corona often encompass extrema of the vertical current density, consistent with earlier work showing a close relationship between H-alpha emission and line-of-sight currents. The data are also consistent with the overall morphology and evolution described by erupting-filament models such as those of Kopp and Pneuman (1976) and Sturrock (1989).

Time-dependent density-functional theory simulation of local currents in pristine and single-defect zigzag graphene nanoribbons

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

He, Shenglai, E-mail: shenglai.he@vanderbilt.edu; Russakoff, Arthur; Li, Yonghui

2016-07-21

The spatial current distribution in H-terminated zigzag graphene nanoribbons (ZGNRs) under electrical bias is investigated using time-dependent density-functional theory solved on a real-space grid. A projected complex absorbing potential is used to minimize the effect of reflection at simulation cell boundary. The calculations show that the current flows mainly along the edge atoms in the hydrogen terminated pristine ZGNRs. When a vacancy is introduced to the ZGNRs, loop currents emerge at the ribbon edge due to electrons hopping between carbon atoms of the same sublattice. The loop currents hinder the flow of the edge current, explaining the poor electric conductancemore » observed in recent experiments.« less

Magnetic Field Dependence of the Critical Current in S-N Bilayer Thin Films

NASA Technical Reports Server (NTRS)

Sadleir, John E.; Lee, Sang-Jun; Smith, Stephen James; Bandler, Simon; Chervenak, James; Kilbourne, Caroline A.; Finkbeiner, Fred M.; Porter, Frederick S.; Kelley, Richard L.; Adams, Joseph S.;

North American vegetation patterns observed with the NOAA-7 advanced very high resolution radiometer. [North America

NASA Technical Reports Server (NTRS)

Goward, S. N.; Tucker, C. J.; Dye, D. G.

1985-01-01

Spectral vegetation index measurements derived from remotely sensed observations show great promise as a means to improve knowledge of land vegetation patterns. The daily, global observations acquired by the advanced very high resolution radiometer, a sensor on the current series of U.S. National Oceanic and Atmospheric Administration meteorological satellites, may be particularly well suited for global studies of vegetation. Preliminary results from analysis of North American observations, extending from April to November 1982, show that the vegetation index patterns observed correspond to the known seasonality of North American natural and cultivated vegetation. Integration of the observations over the growing season produced measurements that are related to net primary productivity patterns of the major North American natural vegetation formations. Regions of intense cultivation were observed as anomalous areas in the integrated growing season measurements. Significant information on seasonality, annual extent and interannual variability of vegetation photosynthetic activity at continental and global scales can be derived from these satellite observations.

Coherent Control of Nanoscale Ballistic Currents in Transition Metal Dichalcogenide ReS2.

PubMed

Cui, Qiannan; Zhao, Hui

2015-04-28

Transition metal dichalcogenides are predicted to outperform traditional semiconductors in ballistic devices with nanoscale channel lengths. So far, experimental studies on charge transport in transition metal dichalcogenides are limited to the diffusive regime. Here we show, using ReS2 as an example, all-optical injection, detection, and coherent control of ballistic currents. By utilizing quantum interference between one-photon and two-photon interband transition pathways, ballistic currents are injected in ReS2 thin film samples by a pair of femtosecond laser pulses. We find that the current decays on an ultrafast time scale, resulting in an electron transport of only a fraction of one nanometer. Following the relaxation of the initially injected momentum, backward motion of the electrons for about 1 ps is observed, driven by the Coulomb force from the oppositely moved holes. We also show that the injected current can be controlled by the phase of the laser pulses. These results demonstrate a new platform to study ballistic transport of nonequilibrium carriers in transition metal dichalcogenides.

Effect of spin transfer torque on domain wall motion regimes in [Co/Ni] superlattice wires

NASA Astrophysics Data System (ADS)

Le Gall, S.; Vernier, N.; Montaigne, F.; Thiaville, A.; Sampaio, J.; Ravelosona, D.; Mangin, S.; Andrieu, S.; Hauet, T.

2017-05-01

The combined effect of magnetic field and current on domain wall motion is investigated in epitaxial [Co/Ni] microwires. Both thermally activated and flow regimes are found to be strongly affected by current. All experimental data can be understood by taking into account both adiabatic and nonadiabatic components of the spin transfer torque, the parameters of which are extracted. In the precessional flow regime, it is shown that the domain wall can move in the electron flow direction against a strong applied field, as previously observed. In addition, for a large range of applied magnetic field and injected current, a stochastic domain wall displacement after each pulse is observed. Two-dimensional micromagnetic simulations, including some disorder, show a random fluctuation of the domain wall position that qualitatively matches the experimental results.

Investigating storm-time magnetospheric electrodynamics: Multi-spacecraft observations of the June 22, 2015 magnetic storm

NASA Astrophysics Data System (ADS)

Reiff, P. H.; Sazykin, S. Y.; Bala, R.; Coffey, V. N.; Chandler, M. O.; Minow, J. I.; Anderson, B. J.; Wolf, R.; Huba, J.; Baker, D. N.; Mauk, B.; Russell, C. T.

2015-12-01

The magnetic storm that commenced on June 22, 2015 was one of the largest storms in the current solar cycle. Availability of in situ observations from Magnetospheric Multiscale (MMS), the Van Allen Probes (VAP), and THEMIS in the magnetosphere, field-aligned currents from AMPERE, as well as the ionospheric data from the Floating Potential Measurement Unit (FPMU) instrument suite on board the International Space Station (ISS) represents an exciting opportunity to analyze storm-related dynamics. Our real-time space weather alert system sent out a "red alert" warning users of the event 2 hours in advance, correctly predicting Kp indices greater than 8. During this event, the MMS observatories were taking measurements in the magnetotail, VAP were in the inner magnetosphere, THEMIS was on the dayside, and the ISS was orbiting at 400 km every 90 minutes. Among the initial findings are the crossing of the dayside magnetopause into the region earthward of 8 RE, strong dipolarizations in the MMS magnetometer data, and dropouts in the particle fluxes seen by the MMS FPI instrument suite. At ionospheric altitudes, the FMPU measurements of the ion densities show dramatic post-sunset depletions at equatorial latitudes that are correlated with the particle flux dropouts measured by the MMS FPI. AMPERE data show highly variable currents varying from intervals of intense high latitude currents to currents at maximum polar cap expansion to 50 deg MLAT and exceeding 20 MA. In this paper, we use numerical simulations with global magnetohydrodynamic (MHD) models and the Rice Convection Model (RCM) of the inner magnetosphere in an attempt to place the observations in the context of storm-time global electrodynamics and cross-check the simulation global Birkeland currents with AMPERE distributions. Specifically, we will look at model-predicted effects of dipolarizations and the global convection on the inner magnetosphere via data-model comparison.

First direct observation of the link between supercritical flow processes, crescent-shape bedforms and massive sand deposits

NASA Astrophysics Data System (ADS)

Hage, Sophie; Cartigny, Matthieu; Clare, Michael; Sumner, Esther; Talling, Peter; Vendettuoli, Daniela; Hughes Clarke, John; Hubbard, Stephen

2017-04-01

Massive sandstones have been studied in many outcrops worldwide as they form a building stone of good subsurface petroleum reservoirs. Massive sands are often associated with turbidites sequences in ancient sedimentary successions. Turbidites are widely known to result from the deceleration of turbidity currents, these underwater flows driven by the excess density of sediments they carry in suspension. Depositional processes that are associated with the formation of massive sands are still under debate in the literature and many theoretical mechanisms have been suggested based on outcrops interpretations, lab experiments and numerical models. Here we present the first field observations that show how massive sands are generated from flow instabilities associated with supercritical flow processes occurring in turbidity currents. We combine turbidity current measurements with seafloor topography observations on the active Squamish Delta, British Columbia (Canada). We show that supercritical flow processes shape crescent-shape bedforms on the seafloor, and how these crescent-shape bedforms are built by massive sands. This modern process-product link is then used to interpret massive sandstone successions found in ancient outcrops. We demonstrate that supercritical-flow processes can be recognised in outcrops and that these processes produce highly diachronous stratigraphic surfaces in the rock record. This has profound implications on how to interpret ancient geological successions and the Earth history they archive.

Effects of space weather on GOCE electrostatic gravity gradiometer measurements

NASA Astrophysics Data System (ADS)

Ince, E. Sinem; Pagiatakis, Spiros D.

2016-12-01

We examine the presence of residual nongravitational signatures in gravitational gradients measured by GOCE electrostatic gravity gradiometer. These signatures are observed over the magnetic poles during geomagnetically active days and can contaminate the trace of the gravitational gradient tensor by up to three to five times the expected noise level of the instrument (˜ 11 mE). We investigate these anomalies in the gradiometer measurements along many satellite tracks and examine possible causes using external datasets, such as interplanetary electric field measurements from the ACE (advanced composition explorer) and WIND spacecraft, and Poynting vector (flux) estimated from equivalent ionospheric currents derived from spherical elementary current systems over North America and Greenland. We show that the variations in the east-west and vertical electrical currents and Poynting vector components at the satellite position are highly correlated with the disturbances observed in the gradiometer measurements. The results presented in this paper reveal that the disturbances are due to intense ionospheric current variations that are enhanced by increased solar activity that causes a very dynamic drag environment. Moreover, successful modelling and removal of a high percentage of these disturbances are possible using external geomagnetic field observations.

Giant spin torque in hybrids with anisotropic p-d exchange interaction

NASA Astrophysics Data System (ADS)

Korenev, V. L.

2014-03-01

Control of magnetic domain wall movement by the spin-polarized current looks promising for creation of a new generation of magnetic memory devices. A necessary condition for this is the domain wall shift by a low-density current. Here, I show that a strongly anisotropic exchange interaction between mobile heavy holes and localized magnetic moments enormously increases the current-induced torque on the domain wall as compared to systems with isotropic exchange. This enables one to control the domain wall motion by current density 104 A/cm2 in ferromagnet/semiconductor hybrids. The experimental observation of the anisotropic torque will facilitate the integration of ferromagnetism into semiconductor electronics.

Using multi-scale entropy and principal component analysis to monitor gears degradation via the motor current signature analysis

NASA Astrophysics Data System (ADS)

Aouabdi, Salim; Taibi, Mahmoud; Bouras, Slimane; Boutasseta, Nadir

2017-06-01

This paper describes an approach for identifying localized gear tooth defects, such as pitting, using phase currents measured from an induction machine driving the gearbox. A new tool of anomaly detection based on multi-scale entropy (MSE) algorithm SampEn which allows correlations in signals to be identified over multiple time scales. The motor current signature analysis (MCSA) in conjunction with principal component analysis (PCA) and the comparison of observed values with those predicted from a model built using nominally healthy data. The Simulation results show that the proposed method is able to detect gear tooth pitting in current signals.

Coherent (photon) vs incoherent (current) detection of multidimensional optical signals from single molecules in open junctions

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

Agarwalla, Bijay Kumar; Hua, Weijie; Zhang, Yu

2015-06-07

The nonlinear optical response of a current-carrying single molecule coupled to two metal leads and driven by a sequence of impulsive optical pulses with controllable phases and time delays is calculated. Coherent (stimulated, heterodyne) detection of photons and incoherent detection of the optically induced current are compared. Using a diagrammatic Liouville space superoperator formalism, the signals are recast in terms of molecular correlation functions which are then expanded in the many-body molecular states. Two dimensional signals in benzene-1,4-dithiol molecule show cross peaks involving charged states. The correlation between optical and charge current signal is also observed.

Deep drivers of mesoscale circulation in the central Rockall Trough

NASA Astrophysics Data System (ADS)

Sherwin, T. J.; Alyenik, D.; Dumont, E.; Inall, M.

2014-11-01

Mesoscale variability in the central Rockall Trough between about 56 and 58° N has been investigated using a combination of ship-borne, underwater glider and gridded satellite altimeter measurements. Altimeter observations show that mesoscale features such as eddies and large scale circulation cells are ubiquitous phenomena. They have horizontal length scales of order 100 km with vertical scales of over 1000 m and are associated with mean current speeds (over the upper 1000 m) of 15 ± 7 cm s-1. Monthly area averaged surface Eddy Kinetic Energy (EKE) has substantial inter-annual variability, which at times can dominate a mean seasonal signal that varies from a maximum in May (74 cm2 s-2) to a minimum in October (52 cm2 s-2) and has increased gradually since 1992 at about 1.1 cm2 s-2 per year. A five month glider mission in the Trough showed that much of this energy comes from features that are located over 1000 m below the surface in the deep cold waters of the Trough (possibly from eddies associated the North Atlantic Current). The surface currents from altimeters had similar magnitude to the drift currents averaged over 1000 m from the glider in the stratified autumn, but were half the deep water speed during late winter. Although the mesoscale features move in an apparent random manner they may also be quasi-trapped by submarine topography such as seamounts. Occasionally anti-cyclonic and cyclonic cells combine to cause a coherent westward deflection of the European slope current that warms the Rockall side of the Trough. Such deflections contribute to the inter-annual variability in the observed temperature and salinity that are monitored in the upper 800 m of the Trough. By combining glider and altimeter measurements it is shown that altimeter measurements fail to observe a 15 cm s-1 northward flowing slope current on the eastern side and a small persistent southward current on the western side. There is much to be gained from the synergy between satellite altimetry and in situ glider observations both in the interpretation of their separate data sets and in aiding glider pilots to steer their vehicles through EKE active regions such as the north-east Atlantic.

Temperature Dependent Electron Transport Properties of Gold Nanoparticles and Composites: Scanning Tunneling Spectroscopy Investigations.

PubMed

Patil, Sumati; Datar, Suwarna; Dharmadhikari, C V

2018-03-01

Scanning tunneling spectroscopy (STS) is used for investigating variations in electronic properties of gold nanoparticles (AuNPs) and its composite with urethane-methacrylate comb polymer (UMCP) as function of temperature. Films are prepared by drop casting AuNPs and UMCP in desired manner on silicon substrates. Samples are further analyzed for morphology under scanning electron microscopy (SEM) and atomic force microscopy (AFM). STS measurements performed in temperature range of 33 °C to 142 °C show systematic variation in current versus voltage (I-V) curves, exhibiting semiconducting to metallic transition/Schottky behavior for different samples, depending upon preparation method and as function of temperature. During current versus time (I-t) measurement for AuNPs, random telegraphic noise is observed at room temperature. Random switching of tunneling current between two discrete levels is observed for this sample. Power spectra derived from I-t show 1/f2 dependence. Statistical analysis of fluctuations shows exponential behavior with time width τ ≈ 7 ms. Local density of states (LDOS) plots derived from I-V curves of each sample show systematic shift in valance/conduction band edge towards/away from Fermi level, with respect to increase in temperature. Schottky emission is best fitted electron emission mechanism for all samples over certain range of bias voltage. Schottky plots are used to calculate barrier heights and temperature dependent measurements helped in measuring activation energies for electron transport in all samples.

Study on electrochemically deposited Mg metal

NASA Astrophysics Data System (ADS)

Matsui, Masaki

An electrodeposition process of magnesium metal from Grignard reagent based electrolyte was studied by comparing with lithium. The electrodeposition of magnesium was performed at various current densities. The obtained magnesium deposits did not show dendritic morphologies while all the lithium deposits showed dendritic products. Two different crystal growth modes in the electrodeposition process of magnesium metal were confirmed by an observation using scanning electron micro scope (SEM) and a crystallographic analysis using X-ray diffraction (XRD). An electrochemical study of the deposition/dissolution process of the magnesium showed a remarkable dependency of the overpotential of magnesium deposition on the electrolyte concentration compared with lithium. This result suggests that the dependency of the overpotential on the electrolyte concentration prevent the locally concentrated current resulting to form very uniform deposits.

Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

NASA Astrophysics Data System (ADS)

Nishimura, Yukitoshi; Kikuchi, Takashi; Ebihara, Yusuke; Yoshikawa, Akimasa; Imajo, Shun; Li, Wen; Utada, Hisashi

2016-08-01

We investigated evolution of ionospheric currents during sudden commencements using a ground magnetometer network in conjunction with an all-sky imager, which has the advantage of locating field-aligned currents much more accurately than ground magnetometers. Preliminary (PI) and main (MI) impulse currents showed two-cell patterns propagating antisunward, particularly during a southward interplanetary magnetic field (IMF). Although this overall pattern is consistent with the Araki (solar wind sources of magnetospheric ultra-low-frequency waves. Geophysical monograph series, vol 81. AGU, Washington, DC, pp 183-200, 1994. doi: 10.1029/GM081p0183) model, we found several interesting features. The PI and MI currents in some events were highly asymmetric with respect to the noon-midnight meridian; the post-noon sector did not show any notable PI signal, but only had an MI starting earlier than the pre-noon MI. Not only equivalent currents but also aurora and equatorial magnetometer data supported the much weaker PI response. We suggest that interplanetary shocks impacting away from the subsolar point caused the asymmetric current pattern. Additionally, even when PI currents form in both pre- and post-noon sectors, they can initiate and disappear at different timings. The PI currents did not immediately disappear but coexisted with the MI currents for the first few minutes of the MI. During a southward IMF, the MI currents formed equatorward of a preexisting DP-2, indicating that the MI currents are a separate structure from a preexisting DP-2. In contrast, the MI currents under a northward IMF were essentially an intensification of a preexisting DP-2. The magnetometer and imager combination has been shown to be a powerful means for tracing evolution of ionospheric currents, and we showed various types of ionospheric responses under different upstream conditions.

EVIDENCE FOR NEWLY INITIATED RECONNECTION IN THE SOLAR WIND AT 1 AU

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

Xu, Xiaojun; Ma, Yonghui; Wong, Hon-Cheng

2015-08-10

We report the first evidence for a large-scale reconnection exhaust newly initiated in the solar wind using observations from three spacecraft: ACE, Wind, and ARTEMIS P2. We identified a well-structured X-line exhaust using measurements from ARTEMIS P2 in the downstream solar wind. However, in the upstream solar wind, ACE detected the same current sheet that corresponds to the exhaust identified by ARTEMIS P2 data without showing any reconnection signals. We cannot find any reconnection signals from Wind located between ACE and ARTEMIS P2. Within the exhaust, a magnetic island is identified, which is not consistent with the quasi-steady feature asmore » previously reported and provides further evidence that the reconnection is newly initiated. Our observations show that the entering of energetic particles, probably from Earth's bow shock, makes the crucial difference between the non-reconnecting current sheet and the exhaust. Since no obvious driving factors are responsible for the reconnection initiation, we infer that these energetic particles probably play an important role in the reconnection initiation. Theoretical analysis also shows support for this potential mechanism.« less

Validation of a new plasmapause model derived from CHAMP field-aligned current signatures

NASA Astrophysics Data System (ADS)

Heilig, Balázs; Darrouzet, Fabien; Vellante, Massimo; Lichtenberger, János; Lühr, Hermann

2014-05-01

Recently a new model for the plasmapause location in the equatorial plane was introduced based on magnetic field observations made by the CHAMP satellite in the topside ionosphere (Heilig and Lühr, 2013). Related signals are medium-scale field-aligned currents (MSFAC) (some 10km scale size). An empirical model for the MSFAC boundary was developed as a function of Kp and MLT. The MSFAC model then was compared to in situ plasmapause observations of IMAGE RPI. By considering this systematic displacement resulting from this comparison and by taking into account the diurnal variation and Kp-dependence of the residuals an empirical model of the plasmapause location that is based on MSFAC measurements from CHAMP was constructed. As a first step toward validation of the new plasmapause model we used in-situ (Van Allen Probes/EMFISIS, Cluster/WHISPER) and ground based (EMMA) plasma density observations. Preliminary results show a good agreement in general between the model and observations. Some observed differences stem from the different definitions of the plasmapause. A more detailed validation of the method can take place as soon as SWARM and VAP data become available. Heilig, B., and H. Lühr (2013) New plasmapause model derived from CHAMP field-aligned current signatures, Ann. Geophys., 31, 529-539, doi:10.5194/angeo-31-529-2013

Current driven transition from Abrikosov-Josephson to Josephson-like vortex in mesoscopic lateral S/S’/S superconducting weak links

PubMed Central

Carapella, G.; Sabatino, P.; Barone, C.; Pagano, S.; Gombos, M.

2016-01-01

Vortices are topological defects accounting for many important effects in superconductivity, superfluidity, and magnetism. Here we address the stability of a small number of such excitations driven by strong external forces. We focus on Abrikosov-Josephson vortex that appears in lateral superconducting S/S’/S weak links with suppressed superconductivity in S’. In such a system the vortex is nucleated and confined in the narrow S’ region by means of a small magnetic field and moves under the effect of a force proportional to an applied electrical current with a velocity proportional to the measured voltage. Our numerical simulations show that when a slow moving Abrikosov-Josephson vortex is driven by a strong constant current it becomes unstable with respect to a faster moving excitation: the Josephon-like vortex. Such a current-driven transition explains the structured dissipative branches that we observe in the voltage-current curve of the weak link. When vortex matter is strongly confined phenomena as magnetoresistance oscillations and reentrance of superconductivity can possibly occur. We experimentally observe these phenomena in our weak links. PMID:27752137

Mapping thunder sources by inverting acoustic and electromagnetic observations

NASA Astrophysics Data System (ADS)

Anderson, J. F.; Johnson, J. B.; Arechiga, R. O.; Thomas, R. J.

2014-12-01

We present a new method of locating current flow in lightning strikes by inversion of thunder recordings constrained by Lightning Mapping Array observations. First, radio frequency (RF) pulses are connected to reconstruct conductive channels created by leaders. Then, acoustic signals that would be produced by current flow through each channel are forward modeled. The recorded thunder is considered to consist of a weighted superposition of these acoustic signals. We calculate the posterior distribution of acoustic source energy for each channel with a Markov Chain Monte Carlo inversion that fits power envelopes of modeled and recorded thunder; these results show which parts of the flash carry current and produce thunder. We examine the effects of RF pulse location imprecision and atmospheric winds on quality of results and apply this method to several lightning flashes over the Magdalena Mountains in New Mexico, USA. This method will enable more detailed study of lightning phenomena by allowing researchers to map current flow in addition to leader propagation.

Leakage current phenomena in Mn-doped Bi(Na,K)TiO{sub 3}-based ferroelectric thin films

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

Walenza-Slabe, J.; Gibbons, B. J., E-mail: brady.gibbons@oregonstate.edu

2016-08-28

Mn-doped 80(Bi{sub 0.5}Na{sub 0.5})TiO{sub 3}-20(Bi{sub 0.5}K{sub 0.5})TiO{sub 3} thin films were fabricated by chemical solution deposition on Pt/TiO{sub 2}/SiO{sub 2}/Si substrates. Steady state and time-dependent leakage current were investigated from room temperature to 180 °C. Undoped and low-doped films showed space-charge-limited current (SCLC) at high temperatures. The electric field marking the transition from Ohmic to trap-filling-limited current increased monotonically with Mn-doping. With 2 mol. % Mn, the current was Ohmic up to 430 kV/cm, even at 180 °C. Modeling of the SCLC showed that all films exhibited shallow trap levels and high trap concentrations. In the regime of steady state leakage, theremore » were also observations of negative differential resistivity and positive temperature coefficient of resistivity near room temperature. Both of these phenomena were confined to relatively low temperatures (below ∼60 °C). Transient currents were observed in the time-dependent leakage data, which was measured out to several hundred seconds. In the undoped films, these were found to be a consequence of oxygen vacancy migration modulating the electronic conductivity. The mobility and thermal activation energy for oxygen vacancies was extracted as μ{sub ion} ≈ 1.7 × 10{sup −12} cm{sup 2} V{sup −1} s{sup −1} and E{sub A,ion} ≈ 0.92 eV, respectively. The transient current displayed different characteristics in the 1 mol. % Mn-doped films which were not readily explained by oxygen vacancy migration.« less

Field-aligned Currents Induced by Electrostatic Polarization at the Ionosphere: Application to the Poleward Boundary Intensification (PBI) of Auroral Emission

NASA Astrophysics Data System (ADS)

Ohtani, S.; Yoshikawa, A.

2016-12-01

Although the field-aligned currents (Birkeland currents) are generally considered to be driven by magnetospheric processes, it is possible that some field-aligned currents are locally induced in the ionosphere in the presence of sharp conductance gradient. In this presentation we shall discuss the poleward boundary intensification (PBI) of auroral emission as an example effect of such electrostatic polarization. The observations show that the PBIs are very often preceded by the fast polar cap convection approaching the nightside auroral oval. We propose that the ionospheric currents driven by the associated electric field diverges/converges at the poleward boundary of the auroral oval as the background ionospheric conductance changes sharply in space, and they close with field-aligned currents. The associated upward field-aligned current is accompanied by electron precipitation, which may cause auroral emission as observed as PBIs. We test this idea by modeling the ionosphere as a slab-shaped enhancement of conductance and the polar cap flow channel as a pair of upward and downward FACs. The results show that (i) a pair of upward and downward FACs is induced at the poleward boundary when the front of the polar cap flow channel approaches the auroral oval; (ii) the upward FAC extends westward much wider in longitude than the flow channel; (iii) the peak FAC density is significantly larger than the incident FAC; and (iv) the induced upward and downward FACs are distributed almost symmetrically in longitude, indicating that the Pedersen polarization dominates the Hall polarization. These results are consistent with some general characteristics of PBIs, which are rather difficult to explain if the PBIs are the ionospheric manefestation of distant reconnection as often suggested.

Current-oriented swimming by jellyfish and its role in bloom maintenance.

PubMed

Fossette, Sabrina; Gleiss, Adrian Christopher; Chalumeau, Julien; Bastian, Thomas; Armstrong, Claire Denise; Vandenabeele, Sylvie; Karpytchev, Mikhail; Hays, Graeme Clive

2015-02-02

Cross-flows (winds or currents) affect animal movements [1-3]. Animals can temporarily be carried off course or permanently carried away from their preferred habitat by drift depending on their own traveling speed in relation to that of the flow [1]. Animals able to only weakly fly or swim will be the most impacted (e.g., [4]). To circumvent this problem, animals must be able to detect the effects of flow on their movements and respond to it [1, 2]. Here, we show that a weakly swimming organism, the jellyfish Rhizostoma octopus, can orientate its movements with respect to currents and that this behavior is key to the maintenance of blooms and essential to reduce the probability of stranding. We combined in situ observations with first-time deployment of accelerometers on free-ranging jellyfish and simulated the behavior observed in wild jellyfish within a high-resolution hydrodynamic model. Our results show that jellyfish can actively swim countercurrent in response to current drift, leading to significant life-history benefits, i.e., increased chance of survival and facilitated bloom formation. Current-oriented swimming may be achieved by jellyfish either directly detecting current shear across their body surface [5] or indirectly assessing drift direction using other cues (e.g., magnetic, infrasound). Our coupled behavioral-hydrodynamic model provides new evidence that current-oriented swimming contributes to jellyfish being able to form aggregations of hundreds to millions of individuals for up to several months, which may have substantial ecosystem and socioeconomic consequences [6, 7]. It also contributes to improve predictions of jellyfish blooms' magnitude and movements in coastal waters. Copyright © 2015 Elsevier Ltd. All rights reserved.

Cosmology and convention

NASA Astrophysics Data System (ADS)

Merritt, David

2017-02-01

I argue that some important elements of the current cosmological model are 'conventionalist' in the sense defined by Karl Popper. These elements include dark matter and dark energy; both are auxiliary hypotheses that were invoked in response to observations that falsified the standard model as it existed at the time. The use of conventionalist stratagems in response to unexpected observations implies that the field of cosmology is in a state of 'degenerating problemshift' in the language of Imre Lakatos. I show that the 'concordance' argument, often put forward by cosmologists in support of the current paradigm, is weaker than the convergence arguments that were made in the past in support of the atomic theory of matter or the quantization of energy.

Existence of a return direction for plasma escaping from a pinched column in a plasma focus discharge

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

Kubes, P.; Cikhardt, J.; Klir, D.

2015-05-15

The use of multi-frame interferometry used on the PF-1000 device with the deuterium filling showed the existence of a return motion of the top of several lobules of the pinched column formed at the pinched plasma column. This phenomenon was observed in the presence of an over-optimal mass in front of the anode, which depressed the intensity of the implosion and the smooth surface of the pinched plasma column. The observed evolution was explored through the use of closed poloidal currents transmitted outside the pinched plasma. This interpretation complements the scenario of the closed currents flowing within the structures insidemore » the pinched column, which has been published recently on the basis of observations from interferometry, neutron, and magnetic probe diagnostics on this device.« less

Data Assimilation with the Extended Cmam: Nudging to Re-Analyses of the Lower Atmosphere

NASA Astrophysics Data System (ADS)

Fomichev, V. I.; Beagley, S. R.; Shepherd, M. G.; Semeniuk, K.; Mclandress, C. W.; Scinocca, J.; McConnell, J. C.

2012-12-01

The extended CMAM is currently being run in a forecast mode allowing the use of the model to simulate specific events. The current analysis period covers 1990-2010. The model is forced using ERA-Interim re-analyses via a nudging technique for the troposphere/stratosphere in combination with the GCM evolution in the lower atmosphere. Thus a transient forced model state is created in the lower atmosphere. The upper atmosphere is allowed to evolve in response to the observed conditions occurring in the lower atmosphere and in response to other transient forcing's such as SSTs, solar flux, and CO2 and CFC boundary changes. This methodology allows specific events and observations to be more successfully compared with the model. The model results compared to TOMS and ACE observations show a good agreement.

Laboratory experiment on the 3D tide-induced Lagrangian residual current using the PIV technique

NASA Astrophysics Data System (ADS)

Chen, Yang; Jiang, Wensheng; Chen, Xu; Wang, Tao; Bian, Changwei

2017-12-01

The 3D structure of the tide-induced Lagrangian residual current was studied using the particle image velocimetry (PIV) technique in a long shallow narrow tank in the laboratory. At the mouth of the tank, a wave generator was used to make periodic wave which represents the tide movement, and at the head of the tank, a laterally sloping topography with the length of one fifth of the water tank was installed, above which the tide-induced Lagrangian residual current was studied. Under the weakly nonlinear condition in the present experiment setup, the results show that the Lagrangian residual velocity (LRV) field has a three-layer structure. The residual current flows inwards (towards the head) in the bottom layer and flows outwards in the middle layer, while in the surface layer, it flows inwards along the shallow side of the sloping topography and outwards along the deep side. The depth-averaged and breadth-averaged LRV are also analyzed based on the 3D LRV observations. Our results are in good agreement with the previous experiment studies, the analytical solutions with similar conditions and the observational results in real bays. Moreover, the volume flux comparison between the Lagrangian and Eulerian residual currents shows that the Eulerian residual velocity violates the mass conservation law while the LRV truly represents the inter-tidal water transport. This work enriches the laboratory studies of the LRV and offers valuable references for the LRV studies in real bays.

Extremely Nonthermal Monoenergetic Precipitation in the Auroral Acceleration Region: In Situ Observations

NASA Astrophysics Data System (ADS)

Hatch, S.; Chaston, C. C.; Labelle, J. W.

2017-12-01

We report in situ measurements through the auroral acceleration region that reveal extremely nonthermal monoenergetic electron distributions. These auroral primaries are indicative of source populations in the plasma sheet well described as kappa distributions with κ ≲ 2. We show from observations and modeling how this large deviation from Maxwellian form may modify the acceleration potential required to drive current closure through the auroral ionosphere.

Deep-water bedforms induced by refracting Internal Solitary Waves

NASA Astrophysics Data System (ADS)

Falcini, Federico; Droghei, Riccardo; Casalbore, Daniele; Martorelli, Eleonora; Mosetti, Renzo; Sannino, Gianmaria; Santoleri, Rosalia; Latino Chiocci, Francesco

2017-04-01

Subaqueous bedforms (or sand waves) are typically observed in those environments that are exposed to strong currents, characterized by a dominant unidirectional flow. However, sand-wave fields may be also observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs), induced by tides, can produce an effective, unidirectional boundary flow filed that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

Bottom currents observed in and around a submarine valley on the continental slope of the northern South China Sea

NASA Astrophysics Data System (ADS)

Wu, Lunyu; Xiong, Xuejun; Li, Xiaolong; Shi, Maochong; Guo, Yongqing; Chen, Liang

2016-12-01

Bottom currents at about 1000 m depth in and around a submarine valley on the continental slope of the northern South China Sea were studied by a 14-month long experiment from July 2013 to September 2014. The observations reveal that bottom currents are strongly influenced by the topography, being along valley axis or isobaths. Power density spectrum analysis shows that all the currents have significant peaks at diurnal and semi-diurnal frequencies. Diurnal energy is dominant at the open slope site, which is consistent with many previous studies. However, at the site inside the valley the semi-diurnal energy dominates, although the distance between the two sites of observation is quite small (11 km) compared to a typical horizontal first-mode internal tide wavelength (200 km). We found this phenomenon is caused by the focusing of internal waves of certain frequencies in the valley. The inertial peak is found only at the open slope site in the first deployment but missing at the inside valley site and the rest of the deployments. Monthly averaged residual currents reveal that the near-bottom currents on the slope flow southwestward throughout the year except in August and September, 2013, from which we speculate that this is a result of the interaction between a mesoscale eddy and the canyon/sag topography. Currents inside the valley within about 10 mab basically flow along slope and in the layers above the 10 mab the currents are northwestward, that is, from the deep ocean to the shelf. The monthly mean current vectors manifest an Ekman layer-like vertical structure at both sites, which rotate counter-clockwise looking from above.

Studying the start of the Maunder Minimum to understand the current situation

NASA Astrophysics Data System (ADS)

Neuhäuser, Ralph; Neuhäuser, Dagmar L.

2016-04-01

To investigate whether we now enter a Maunder-like grand minimum, we have to compare the current situation with the time around the start of the Maunder minimum. Sunspot observations in the 1610s are of particular importance and relevance, because they are shortly before the start of the Maunder Grand Minimum. While the Maunder Minimum it is usually dated from 1645 to 1715, Vaquero & Trigo (2015) argue that what they call the "Extended Maunder Minimum" would have started in 1618 during or around a Schwabe cycle minimum around that time. We have therefore studied the sunspot record of that time in detail. Hoyt & Schatten (1998) compiled for all known telescopic observers a list of their observations; recent solar activity studies for the past four centuries are based on their compilation. In addition to 12 observers listed by Hoyt & Schatten (1998) for the 1610s, we list six more observers with datable spot observations. Furthermore, while Hoyt & Schatten (1998) argue that Simon Marius would have observed from mid 1617 to the end of 1618 almost every day, but would have never seen a spot, we can show with the original reports by Marius that he observed from Aug 1611 to spring 1619 with a lot of sunspot detections. Similar, while Hoyt & Schatten (1998) argue that Giovanni Riccioli would have observed on almost every day in 1618, but would have never seen a spot, he did not report any own observations at all that year, but quoted Argoli for that there were no spots during the periods with comets in 1618. The data base by Hoyt & Schatten (1998) has several more errors in the 1610s, as we show also for the observations by Harriot, Scheiner, Malapert, Saxonius, and Tarde. We also compare drawings from Jungius with the observations by Harriot, Galilei, and Marius. In contrast to what is specified in Hoyt & Schatten (1998), after Harriot, the two Fabricius (father and son), Scheiner and Cysat, Marius and Schmidnerus are among the earliest datable telescopic sunspot observers (1611 Aug 3, Julian). It is very important to go back to the original drawings and observational reports (written often in Latin or German). The active day fractions was high from 1611 to 1616 (1.0 to 0.9), but then dropped to much lower values 1617 to 1620. Sunspots records by Malapert from 1618 to 1621 show that the last low-latitude spot was seen in Dec 1620, while the first high-latitude spots were noticed in June and Oct 1620 (we show his drawings), so that the turnover from one Schwabe cycle to the next (minimum) took place around that time, also seen in longer periods without naked-eye and telescopic spots nor any likely true aurorae. Did the Maunder Minimum start with or right after this Schwabe cycle minimum in the second half of 1620 or one or two cycles later? We will then compare the start of the Maunder minimum with the current situation.

Did Irving Langmuir Observe Langmuir Circulations?

NASA Astrophysics Data System (ADS)

D'Asaro, E. A.; Harcourt, R. R.; Shcherbina, A.; Thomson, J. M.; Fox-Kemper, B.

2012-12-01

Although surface waves are known to play an important role in mixing the upper ocean, the current generation of upper ocean boundary layer parameterizations does not include the explicit effects of surface waves. Detailed simulations using LES models which include the Craik-Leibovich wave-current interactions, now provide quantitative predictions of the enhancement of boundary layer mixing by waves. Here, using parallel experiments in Lake Washington and at Ocean Station Papa, we show a clear enhancement of vertical kinetic energy across the entire upper ocean boundary layer which can be attributed to surface wave effects. The magnitude of this effect is close to that predicted by LES models, but is not large, less than a factor of 2 on average, and increased by large Stokes drift and shallow mixed layers. Global estimates show the largest wave enhancements occur on the equatorial side of the westerlies in late Spring, due to the combination of large waves, shallow mixed layers and weak winds. In Lakes, however, the waves and the Craik-Leibovich interactions are weak, making it likely that the counter-rotating vortices famously observed by Irving Langmuir in Lake George were not driven by wave-current interactions.

Geometrical control of pure spin current induced domain wall depinning.

PubMed

Pfeiffer, A; Reeve, R M; Voto, M; Savero-Torres, W; Richter, N; Vila, L; Attané, J P; Lopez-Diaz, L; Kläui, Mathias

2017-03-01

We investigate the pure spin-current assisted depinning of magnetic domain walls in half ring based Py/Al lateral spin valve structures. Our optimized geometry incorporating a patterned notch in the detector electrode, directly below the Al spin conduit, provides a tailored pinning potential for a transverse domain wall and allows for a precise control over the magnetization configuration and as a result the domain wall pinning. Due to the patterned notch, we are able to study the depinning field as a function of the applied external field for certain applied current densities and observe a clear asymmetry for the two opposite field directions. Micromagnetic simulations show that this can be explained by the asymmetry of the pinning potential. By direct comparison of the calculated efficiencies for different external field and spin current directions, we are able to disentangle the different contributions from the spin transfer torque, Joule heating and the Oersted field. The observed high efficiency of the pure spin current induced spin transfer torque allows for a complete depinning of the domain wall at zero external field for a charge current density of [Formula: see text] A m -2 , which is attributed to the optimal control of the position of the domain wall.

Hydrography and circulation west of Sardinia in June 2014

NASA Astrophysics Data System (ADS)

Knoll, Michaela; Borrione, Ines; Fiekas, Heinz-Volker; Funk, Andreas; Hemming, Michael P.; Kaiser, Jan; Onken, Reiner; Queste, Bastien; Russo, Aniello

2017-11-01

In the frame of the REP14-MED sea trial in June 2014, the hydrography and circulation west of Sardinia, observed by means of gliders, shipborne CTD (conductivity, temperature, depth) instruments, towed devices, and vessel-mounted ADCPs (acoustic doppler current profilers), are presented and compared with previous knowledge. So far, the circulation is not well-known in this area, and the hydrography is subject to long-term changes. Potential temperature, salinity, and potential density ranges as well as core values of the observed water masses were determined. Modified Atlantic Water (MAW), with potential density anomalies below 28.72 kg m-3, showed a salinity minimum of 37.93 at 50 dbar. Levantine Intermediate Water (LIW), with a salinity maximum of about 38.70 at 400 dbar, was observed within a range of 28.72<σΘ/(kg m-3) < 29.10. MAW and LIW showed slightly higher salinities than previous investigations. During the trial, LIW covered the whole area from the Sardinian shelf to 7°15' E. Only north of 40° N was it tied to the continental slope. Within the MAW, a cold and saline anticyclonic eddy was observed in the southern trial area. The strongest variability in temperature and salinity appeared around this eddy, and in the southwestern part of the domain, where unusually low saline surface water entered the area towards the end of the experiment. An anticyclonic eddy of Winter Intermediate Water was recorded moving northward at 0.014 m s-1. Geostrophic currents and water mass transports calculated across zonal and meridional transects showed a good agreement with vessel-mounted ADCP measurements. Within the MAW, northward currents were observed over the shelf and offshore, while a southward transport of about 1.5 Sv occurred over the slope. A net northward transport of 0.38 Sv across the southern transect decreased to zero in the north. Within the LIW, northward transports of 0.6 Sv across the southern transects were mainly observed offshore, and decreased to 0.3 Sv in the north where they were primarily located over the slope. This presentation of the REP14-MED observations helps to further understand the long-term evolution of hydrography and circulation in the Western Mediterranean, where considerable changes occurred after the Eastern Mediterranean Transient and the Western Mediterranean Transition.

Sand waves on an epicontinental shelf: Northern Bering Sea

USGS Publications Warehouse

Field, M.E.; Nelson, C.H.; Cacchione, D.A.; Drake, D.E.

1981-01-01

Sand waves and current ripples occupy the crests and flanks of a series of large linear sand ridges (20 km ?? 5 km ?? 10 m high) lying in an open-marine setting in the northern Bering Sea. The sand wave area, which lies west of Seward Peninsula and southeast of Bering Strait, is exposed to the strong continuous flow of coastal water northward toward Bering Strait. A hierarchy of three sizes of superimposed bedforms, all facing northward, was observed in successive cruises in 1976 and 1977. Large sand waves (height 2 m; spacing 200 m) have smaller sand waves (height 1 m; spacing 20 m) lying at a small oblique angle on their stoss slopes. The smaller sand waves in turn have linguoid ripples on their stoss slopes. Repeated studies of the sand wave fields were made both years with high-resolution seismic-reflection profiles, side-scan sonographs, underwater photographs, current-meter stations, vibracores, and suspended-sediment samplers. Comparison of seismic and side-scan data collected along profile lines run both years showed changes in sand wave shape that indicate significant bedload transport within the year. Gouge marks made in sediment by keels of floating ice also showed significantly different patterns each year, further documenting modification to the bottom by sediment transport. During calm sea conditions in 1977, underwater video and camera observations showed formation and active migration of linguoid and straight-crested current ripples. Current speeds 1 m above the bottom were between 20 and 30 cm/s. Maximum current velocities and sand wave migration apparently occur when strong southwesterly winds enhance the steady northerly flow of coastal water. Many cross-stratified sand bodies in the geologic record are interpreted as having formed in a tidal- or storm-dominated setting. This study provides an example of formation and migration of large bedforms by the interaction of storms with strong uniform coastal currents in an open-marine setting. ?? 1981.

Anomalous current in diffusive ferromagnetic Josephson junctions

NASA Astrophysics Data System (ADS)

Silaev, M. A.; Tokatly, I. V.; Bergeret, F. S.

2017-05-01

We demonstrate that in diffusive superconductor/ferromagnet/superconductor (S/F/S) junctions a finite, anomalous Josephson current can flow even at zero phase difference between the S electrodes. The conditions for the observation of this effect are noncoplanar magnetization distribution and a broken magnetization inversion symmetry of the superconducting current. The latter symmetry is intrinsic for the widely used quasiclassical approximation and prevented previous works based on this approximation from obtaining the Josephson anomalous current. We show that this symmetry can be removed by introducing spin-dependent boundary conditions for the quasiclassical equations at the superconducting/ferromagnet interfaces in diffusive systems. Using this recipe, we consider generic multilayer magnetic systems and determine the ideal experimental conditions in order to maximize the anomalous current.

Feeding practices of low-income mothers: how do they compare to current recommendations?

PubMed

Power, Thomas G; Hughes, Sheryl O; Goodell, L Suzanne; Johnson, Susan L; Duran, J Andrea Jaramillo; Williams, Kimberly; Beck, Ashley D; Frankel, Leslie A

2015-03-07

Despite a growing consensus on the feeding practices associated with healthy eating patterns, few observational studies of maternal feeding practices with young children have been conducted, especially in low-income populations. The aim of this study was to provide such data on a low income sample to determine the degree to which observed maternal feeding practices compare with current recommendations. Eighty low-income mothers and their preschool children were videotaped at dinner in their homes. Mothers were chosen from a larger study to create a 2 X 2 X 2 design: maternal ethnicity (African American vs. Latina) by child gender by child weight status (healthy weight vs. overweight/obese). Observers coded videotapes for a range of maternal feeding strategies and other behaviors. Many mothers spent considerable time encouraging eating--often in spite of the child's insistence that he or she was finished. Mothers talked little about food characteristics, rarely referred to feelings of hunger and fullness, and made more attempts to enforce table manners than to teach eating skills. Latina mothers showed higher levels of teaching eating skills and encouraging their children to eat; African American mothers showed higher levels of enforcing table manners and getting children to clear their plates. Mothers of boys used more unelaborated commands and less questions/suggestions than mothers of girls. Finally, compared to mothers of overweight/obese children, mothers of healthy weight children showed higher levels of encouraging eating and lower levels of discouraging eating. Most of the mothers in this study did not engage in feeding practices that are consistent with current recommendations. They did this, despite the fact that they knew they were being observed. These results should be used to inform future research about the motivations behind mothers' feeding practices and the development of interventions by helping identify areas in greatest need of change.

Secure Identifications of the Electron Diffusion Region with Spacecraft Observations

NASA Astrophysics Data System (ADS)

Scudder, J. D.; Karimabadi, H.; Daughton, W. S.

2009-12-01

The Electron Diffusion Region (EDR) plays a key role in the reconnection process and its detection in spacecraft data is one of the major goals of MMS. However, the observable and diagnostic properties of entry into the EDR of collisionless magnetic reconnection remain a matter of much debate. There are also even some theoretical disagreements as to how to define secondary and tertiary properties of the EDR, that may be the only properties that are practically observable. Here we start with first principles of what the EDR is in a general magnetic topology including anti-parallel and guide field regimes. We motivate the EDR as the site in the reconnection layer where magnetic flux is not preserved for the comoving electron observer. Observable diagnostics were then found based on kinetic theory that (i) can be measured in the data, and (ii) that also highlight the theoretically motivated EDR found in the PIC simulations. We compare and contrast our diagnostics with those used by others. We present results from PIC simulations of an RD, an EDR layer, and a fast shock to illustrate their degeneracy under evidence presented in the literature to support EDR “sightings”. Seven (7) properties are shared by these layers. Invariably one of these seven inspecific tests are invoked in the literature when “EDR’s” are identified. A particularly common inspecific test is any and all violations of the Ideal Electron MHD (IEMHD) condition: E+UexB=0, whether from parallel E field detection or perpendicular deviations from IEMHD=0. PIC simulations clearly show that all three current layers possess violations of the ideal electron MHD condition; this result implies that the common usage of violations of IEMHD=0 to define, identify or corroborate a current layer as the EDR are not theoretically appropriate. Our kinetic, observable diagnostics however do differentiate amongst this degenerate class of propagating current layers. For example, these observables clearly differentiate a freely propagating RD - Alfven wave from an EDR layer, although both degenerately would satisfy the Walen test performed with electron flow and magnetic variables. We also show that the first principles definition of the EDR only selects the EDR layers from amongst this degenerate set of current layers.

Observations of field-aligned currents, waves, and electric fields at substorm onset

NASA Technical Reports Server (NTRS)

Smits, D. P.; Hughes, W. J.; Cattell, C. A.; Russell, C. T.

1986-01-01

Substorm onsets, identified Pi 2 pulsations observed on the Air Force Geophysics Laboratory Magnetometer Network, are studied using magnetometer and electric field data from ISEE 1 as well as magnetometer data from the geosynchronous satellites GOES 2 and 3. The mid-latitude magnetometer data provides the means of both timing and locating the substorm onset so that the spacecraft locations with respect to the substorm current systems are known. During two intervals, each containing several onsets or intensifications, ISEE 1 observed field-aligned current signatures beginning simultaneously with the mid-latitude Pi 2 pulsation. Close to the earth broadband bursts of wave noise were observed in the electric field data whenever field-aligned currents were detected. One onset occurred when ISEE 1 and GOES 2 were on the same field line but in opposite hemispheres. During this onset ISEE 1 and GOES 2 saw magnetic signatures which appear to be due to conjugate field-aligned currents flowing out of the western end of the westward auroral electrojets. The ISEE 1 signature is of a line current moving westward past the spacecraft. During the other interval, ISEE 1 was in the near-tail region near the midnight meridian. Plasma data confirms that the plasma sheet thinned and subsequently expanded at onset. Electric field data shows that the plasma moved in the opposite direction to the plasma sheet boundary as the boundary expanded which implies that there must have been an abundant source of hot plasma present. The plasma motion was towards the center of the plasma sheet and earthwards and consisted of a series of pulses rather than a steady flow.

Infrared Telescope Facility's Spectrograph Observations of Human-Made Space Objects

NASA Technical Reports Server (NTRS)

Abercromby, K.; Buckalew, B.; Abell, P.; Cowardin, H.

2015-01-01

Presented here are the results of the Infrared Telescope Facility (IRTF) spectral observations of human-made space objects taken from 2006 to 2008. The data collected using the SpeX infrared spectrograph cover the wavelength range 0.7-2.5 micrometers. Overall, data were collected on 20 different orbiting objects at or near the geosynchronous (GEO) regime. Four of the objects were controlled spacecraft, seven were non-controlled spacecraft, five were rocket bodies, and the final four were cataloged as debris pieces. The remotely collected data are compared to the laboratory-collected reflectance data on typical spacecraft materials, thereby general materials are identified but not specific types. These results highlight the usefulness of observations in the infrared by focusing on features from hydrocarbons, silicon, and thermal emission. The spacecraft, both the controlled and non-controlled, show distinct features due to the presence of solar panels, whereas the rocket bodies do not. Signature variations between rocket bodies, due to the presence of various metals and paints on their surfaces, show a clear distinction from those objects with solar panels, demonstrating that one can distinguish most spacecraft from rocket bodies through infrared spectrum analysis. Finally, the debris pieces tend to show featureless, dark spectra. These results show that the laboratory data in its current state give excellent indications as to the nature of the surface materials on the objects. Further telescopic data collection and model updates to include noise, surface roughness, and material degradation are necessary to make better assessments of orbital object material types. However, based on the current state of the comparison between the observations and the laboratory data, infrared spectroscopic data are adequate to classify objects in GEO as spacecraft, rocket bodies, or debris.

Je pense donc je fais: transcranial direct current stimulation modulates brain oscillations associated with motor imagery and movement observation.

PubMed

Lapenta, Olivia M; Minati, Ludovico; Fregni, Felipe; Boggio, Paulo S

2013-01-01

Motor system neural networks are activated during movement imagery, observation and execution, with a neural signature characterized by suppression of the Mu rhythm. In order to investigate the origin of this neurophysiological marker, we tested whether transcranial direct current stimulation (tDCS) modifies Mu rhythm oscillations during tasks involving observation and imagery of biological and non-biological movements. We applied tDCS (anodal, cathodal, and sham) in 21 male participants (mean age 23.8 ± 3.06), over the left M1 with a current of 2 mA for 20 min. Following this, we recorded the EEG at C3, C4, and Cz and surrounding C3 and C4 electrodes. Analyses of C3 and C4 showed significant effects for biological vs. non-biological movement (p = 0.005), and differential hemisphere effects according to the type of stimulation (p = 0.04) and type of movement (p = 0.02). Analyses of surrounding electrodes revealed significant interaction effects considering type of stimulation and imagery or observation of biological or non-biological movement (p = 0.03). The main findings of this study were (1) Mu desynchronization during biological movement of the hand region in the contralateral hemisphere after sham tDCS; (2) polarity-dependent modulation effects of tDCS on the Mu rhythm, i.e., anodal tDCS led to Mu synchronization while cathodal tDCS led to Mu desynchronization during movement observation and imagery (3) specific focal and opposite inter-hemispheric effects, i.e., contrary effects for the surrounding electrodes during imagery condition and also for inter-hemispheric electrodes (C3 vs. C4). These findings provide insights into the cortical oscillations during movement observation and imagery. Furthermore, it shows that tDCS can be highly focal when guided by a behavioral task.

Evaluation of OSCAR ocean surface current product in the tropical Indian Ocean using in situ data

NASA Astrophysics Data System (ADS)

Sikhakolli, Rajesh; Sharma, Rashmi; Basu, Sujit; Gohil, B. S.; Sarkar, Abhijit; Prasad, K. V. S. R.

2013-02-01

The OSCAR (ocean surface current analysis real-time), which is a product derived from various satellite observations, has been evaluated in the tropical Indian Ocean (TIO) in two different ways. First, the OSCAR-derived monthly climatology has been compared with available drifter-derived climatology in the TIO. From the comparison of the two climatologies, one can infer that OSCAR product is able to capture the variabilities of the well-known surface current systems in the TIO reasonably well. Fourier analysis of the major current systems, as reproduced by OSCAR, shows that the dominant annual and semiannual periodicities, known to exist in these systems, have been faithfully picked up by OSCAR. Next, the evaluation has been carried out by comparing the OSCAR currents with currents measured by moored buoys. The zonal component of OSCAR-current is in good agreement with corresponding component of buoy-observed current with a correlation exceeding 0.7, while the match between the meridional components is poorer. The locations of the peaks of the mean and eddy kinetic energies are matching in both the climatologies, although the peak in the drifter climatology is stronger than the same in the OSCAR product. Finally, an important feature of Indian Ocean circulation, namely the reverse Wyrtki jet, occurring during anomalous dipole years, has been well-reproduced by OSCAR currents.

Observations of transitional tidal boundary layers and their impact on sediment transport in the Great Bay, NH

NASA Astrophysics Data System (ADS)

Koetje, K. M.; Foster, D. L.; Lippmann, T. C.

2017-12-01

Observations of the vertical structure of tidal flows obtained in 2016 and 2017 in the Great Bay Estuary, NH show evidence of transitional tidal boundary layers at deployment locations on shallow mudflats. High-resolution bottom boundary layer currents, hydrography, turbidity, and bed characteristics were observed with an acoustic Doppler current profiler (ADCP), an acoustic Doppler velocimeter (ADV), conductivity-depth-temperature (CTD) sensors, optical backscatter sensors, multibeam bathymetric surveys, and sediment grab samples and cores. Over the 2.5 m tidal range and at water depths ranging from 0.3 m to 1.5 m at mean lower low water, peak flows ranged from 10 cm/s to 30 cm/s and were primarily driven by the tides. A downward-looking ADCP captured the velocity profile over the lowest 1 m of the water column. Results consistently show a dual-log layer system, with evidence of a lower layer within 15 cm of the bed, another layer above approximately 30 cm from the bed, and a transitional region where the flow field rotates between that the two layers that can be as much as 180 degrees out of phase. CTD casts collected over a complete tidal cycle suggest that the weak thermohaline stratification is not responsible for development of the two layers. On the other hand, acoustic and optical backscatter measurements show spatial and temporal variability in suspended sediments that are dependant on tidal phase. Current work includes an examination of the relationship between sediment concentrations in the water column and velocity profile characteristics, along with an effort to quantify the impact of rotation and dual-log layers on bed stress.

Dopant induced single electron tunneling within the sub-bands of single silicon NW tri-gate junctionless n-MOSFET

NASA Astrophysics Data System (ADS)

Uddin, Wasi; Georgiev, Yordan M.; Maity, Sarmistha; Das, Samaresh

2017-09-01

We report 1D electron transport of silicon junctionless tri-gate n-type transistor at 4.2 K. The step like curve observed in the current voltage characteristic suggests 1D transport. Besides the current steps for 1D transport, we found multiple spikes within individual steps, which we relate to inter-band single electron tunneling, mediated by the charged dopants available in the channel region. Clear Coulomb diamonds were observed in the stability diagram of the device. It is shown that a uniformly doped silicon nanowire can provide us the window for the single electron tunnelling. Back-gate versus front-gate color plot, where current is in a color scale, shows a crossover of the increased conduction region. This is a clear indication of the dopant-dopant interaction. It has been shown that back-gate biasing can be used to tune the coupling strength between the dopants.

Direct Observation of Zhang-Li Torque Expansion of Magnetic Droplet Solitons

NASA Astrophysics Data System (ADS)

Chung, Sunjae; Le, Q. Tuan; Ahlberg, Martina; Awad, Ahmad A.; Weigand, Markus; Bykova, Iuliia; Khymyn, Roman; Dvornik, Mykola; Mazraati, Hamid; Houshang, Afshin; Jiang, Sheng; Nguyen, T. N. Anh; Goering, Eberhard; Schütz, Gisela; Gräfe, Joachim; Åkerman, Johan

2018-05-01

Magnetic droplets are nontopological dynamical solitons that can be nucleated in nanocontact based spin torque nano-oscillators (STNOs) with perpendicular magnetic anisotropy free layers. While theory predicts that the droplet should be of the same size as the nanocontact, its inherent drift instability has thwarted attempts at observing it directly using microscopy techniques. Here, we demonstrate highly stable magnetic droplets in all-perpendicular STNOs and present the first detailed droplet images using scanning transmission X-ray microscopy. In contrast to theoretical predictions, we find that the droplet diameter is about twice as large as the nanocontact. By extending the original droplet theory to properly account for the lateral current spread underneath the nanocontact, we show that the large discrepancy primarily arises from current-in-plane Zhang-Li torque adding an outward pressure on the droplet perimeter. Electrical measurements on droplets nucleated using a reversed current in the antiparallel state corroborate this picture.

Experimental study of current loss and plasma formation in the Z machine post-hole convolute

NASA Astrophysics Data System (ADS)

Gomez, M. R.; Gilgenbach, R. M.; Cuneo, M. E.; Jennings, C. A.; McBride, R. D.; Waisman, E. M.; Hutsel, B. T.; Stygar, W. A.; Rose, D. V.; Maron, Y.

2017-01-01

The Z pulsed-power generator at Sandia National Laboratories drives high energy density physics experiments with load currents of up to 26 MA. Z utilizes a double post-hole convolute to combine the current from four parallel magnetically insulated transmission lines into a single transmission line just upstream of the load. Current loss is observed in most experiments and is traditionally attributed to inefficient convolute performance. The apparent loss current varies substantially for z-pinch loads with different inductance histories; however, a similar convolute impedance history is observed for all load types. This paper details direct spectroscopic measurements of plasma density, temperature, and apparent and actual plasma closure velocities within the convolute. Spectral measurements indicate a correlation between impedance collapse and plasma formation in the convolute. Absorption features in the spectra show the convolute plasma consists primarily of hydrogen, which likely forms from desorbed electrode contaminant species such as H2O , H2 , and hydrocarbons. Plasma densities increase from 1 ×1016 cm-3 (level of detectability) just before peak current to over 1 ×1017 cm-3 at stagnation (tens of ns later). The density seems to be highest near the cathode surface, with an apparent cathode to anode plasma velocity in the range of 35 - 50 cm /μ s . Similar plasma conditions and convolute impedance histories are observed in experiments with high and low losses, suggesting that losses are driven largely by load dynamics, which determine the voltage on the convolute.

Personality changes in patients with beginning Alzheimer disease.

PubMed

Pocnet, Cornelia; Rossier, Jérôme; Antonietti, Jean-Philippe; von Gunten, Armin

2011-07-01

To investigate personality traits in patients with Alzheimer disease, compared with mentally healthy control subjects. We compared both current personality characteristics using structured interviews as well as current and previous personality traits as assessed by proxies. Fifty-four patients with mild Alzheimer disease and 64 control subjects described their personality traits using the Structured Interview for the Five-Factor Model. Family members filled in the Revised NEO Personality Inventory, Form R, to evaluate their proxies' current personality traits, compared with 5 years before the estimated beginning of Alzheimer disease or 5 years before the control subjects. After controlling for age, the Alzheimer disease group presented significantly higher scores than normal control subjects on current neuroticism, and significantly lower scores on current extraversion, openness, and conscientiousness, while no significant difference was observed on agreeableness. A similar profile, though less accentuated, was observed when considering personality traits as the patients' proxies remembered them. Diachronic personality assessment showed again significant differences between the 2 groups for the same 4 domains, with important personality changes only for the Alzheimer disease group. Group comparison and retrospective personality evaluation are convergent. Significant personality changes follow a specific trend in patients with Alzheimer disease and contrast with the stability generally observed in mentally healthy people in their personality profile throughout their lives. Whether or not the personality assessment 5 years before the current status corresponds to an early sign of Alzheimer disease or real premorbid personality differences in people who later develop Alzheimer disease requires longitudinal studies.

SSV Launch Monitoring Strategies: HGDS Design and Development Through System Maturity

NASA Technical Reports Server (NTRS)

Shoemaker, Marc D.; Crimi, Thomas

2010-01-01

This poster presentation reviews the design and development of the Hazardous Gas Detection System (HGDS). It includes a overview schematic of the HGDS, pictures of the shuttle on the Mobile Launch platform, the original HGDS, the current HGDS and parts of the original and current system. There are charts showing the dynamics of the orbiter during external tank loading, and transient leaks observed on HGDS during Power Reactant Storage and Distribution (PRSD) load.

Multi-Component Current Sheets in the Martian Magnetotail. MAVEN Observations

NASA Astrophysics Data System (ADS)

Grigorenko, E.; Zelenyi, L. M.; Vaisberg, O. L.; Ermakov, V.; Dubinin, E.; Malova, H. V.

2016-12-01

Current sheets (CSs) are the wide-spread objects in space and laboratory plasmas. The capability of CSs to maintain their stability, efficiently store and convert energy is a challenge to space physicists for many decades. Extensive studies of the CSs showed that the presence of multi-component plasma distribution can significantly affect the CS structure and dynamics. Such features like CS thinning, embedding and bifurcation are often related to the anisotropy of particle velocity distribution functions and multi-component ion composition, and they can be a source for generation of plasma instabilities and current disruption/reconnection. The MAVEN mission equipped with comprehensive instrument suite allows the observations of plasma and magnetic field characteristics with a high time resolution and provides an opportunity to study different processes in the Martian plasma environment. In this work we present the analysis of the CSs observed by MAVEN in the Martian magnetotail and discuss the peculiarities of their structure in relation to the thermal/energy characteristics of different plasma components. The relation to the existing CS models is also discussed. This work is supported by Russian Science Foundation (grant Nr.16-42-01103)

Transcriptomic Modification in the Cerebral Cortex following Noninvasive Brain Stimulation: RNA-Sequencing Approach

PubMed Central

Holmes, Ben; Jung, Seung Ho; Lu, Jing; Wagner, Jessica A.; Rubbi, Liudmilla; Pellegrini, Matteo

2016-01-01

Transcranial direct current stimulation (tDCS) has been shown to modulate neuroplasticity. Beneficial effects are observed in patients with psychiatric disorders and enhancement of brain performance in healthy individuals has been observed following tDCS. However, few studies have attempted to elucidate the underlying molecular mechanisms of tDCS in the brain. This study was conducted to assess the impact of tDCS on gene expression within the rat cerebral cortex. Anodal tDCS was applied at 3 different intensities followed by RNA-sequencing and analysis. In each current intensity, approximately 1,000 genes demonstrated statistically significant differences compared to the sham group. A variety of functional pathways, biological processes, and molecular categories were found to be modified by tDCS. The impact of tDCS on gene expression was dependent on current intensity. Results show that inflammatory pathways, antidepressant-related pathways (GTP signaling, calcium ion binding, and transmembrane/signal peptide pathways), and receptor signaling pathways (serotonergic, adrenergic, GABAergic, dopaminergic, and glutamate) were most affected. Of the gene expression profiles induced by tDCS, some changes were observed across multiple current intensities while other changes were unique to a single stimulation intensity. This study demonstrates that tDCS can modify the expression profile of various genes in the cerebral cortex and that these tDCS-induced alterations are dependent on the current intensity applied. PMID:28119786

The effect of photoelectrons on boom-satellite potential differences during electron beam ejection

NASA Technical Reports Server (NTRS)

Lai, Shu T.; Cohen, Herbert A.; Aggson, Thomas L.; Mcneil, William J.

1987-01-01

Data taken on the SCATHA satellite at geosynchronous altitudes during periods of electron beam ejection in sunlight showed that the potential difference between an electrically isolated boom and the satellite main body was a function of beam current, energy, and boom-sun angle. The potential difference decreased as the boom area illuminated by the sun increased; the maximum and minimum potential differences were measured when minimum and maximum boom areas, respectively, were exposed to the sun. It is shown that photoelectrons, created on the boom, could be engulfed in the electrostatic field of the highly charged satellite main body. Theoretical calculations made using a simple current balance model showed that these electrons could provide a substantial discharging current to the main body and cause the observed variations in the potential difference between the main body and the booms.

Analytical Estimation of the Scale of Earth-Like Planetary Magnetic Fields

NASA Astrophysics Data System (ADS)

Bologna, Mauro; Tellini, Bernardo

2014-10-01

In this paper we analytically estimate the magnetic field scale of planets with physical core conditions similar to that of Earth from a statistical physics point of view. We evaluate the magnetic field on the basis of the physical parameters of the center of the planet, such as density, temperature, and core size. We look at the contribution of the Seebeck effect on the magnetic field, showing that a thermally induced electrical current can exist in a rotating fluid sphere. We apply our calculations to Earth, where the currents would be driven by the temperature difference at the outer-inner core boundary, Jupiter and the Jupiter's satellite Ganymede. In each case we show that the thermal generation of currents leads to a magnetic field scale comparable to the observed fields of the considered celestial bodies.

Origin of large dark current increase in InGaAs/InP avalanche photodiode

NASA Astrophysics Data System (ADS)

Wen, J.; Wang, W. J.; Chen, X. R.; Li, N.; Chen, X. S.; Lu, W.

2018-04-01

The large dark current increase near the breakdown voltage of an InGaAs/InP avalanche photodiode is observed and analyzed from the aspect of bulk defects in the device materials. The trap level information is extracted from the temperature-dependent electrical characteristics of the device and the low temperature photoluminescence spectrum of the materials. Simulation results with the extracted trap level taken into consideration show that the trap is in the InP multiplication layer and the trap assisted tunneling current induced by the trap is the main cause of the large dark current increase with the bias from the punch-through voltage to 95% breakdown voltage.

An analysis of USSPACECOM's space surveillance network sensor tasking methodology

NASA Astrophysics Data System (ADS)

Berger, Jeff M.; Moles, Joseph B.; Wilsey, David G.

1992-12-01

This study provides the basis for the development of a cost/benefit assessment model to determine the effects of alterations to the Space Surveillance Network (SSN) on orbital element (OE) set accuracy. It provides a review of current methods used by NORAD and the SSN to gather and process observations, an alternative to the current Gabbard classification method, and the development of a model to determine the effects of observation rate and correction interval on OE set accuracy. The proposed classification scheme is based on satellite J2 perturbations. Specifically, classes were established based on mean motion, eccentricity, and inclination since J2 perturbation effects are functions of only these elements. Model development began by creating representative sensor observations using a highly accurate orbital propagation model. These observations were compared to predicted observations generated using the NORAD Simplified General Perturbation (SGP4) model and differentially corrected using a Bayes, sequential estimation, algorithm. A 10-run Monte Carlo analysis was performed using this model on 12 satellites using 16 different observation rate/correction interval combinations. An ANOVA and confidence interval analysis of the results show that this model does demonstrate the differences in steady state position error based on varying observation rate and correction interval.

Observational Constraints on the Water Vapor Feedback Using GPS Radio Occultations

NASA Astrophysics Data System (ADS)

Vergados, P.; Mannucci, A. J.; Ao, C. O.; Fetzer, E. J.

2016-12-01

The air refractive index at L-band frequencies depends on the air's density and water vapor content. Exploiting these relationships, we derive a theoretical model to infer the specific humidity response to surface temperature variations, dq/dTs, given knowledge of how the air refractive index and temperature vary with surface temperature. We validate this model using 1.2-1.6 GHz Global Positioning System Radio Occultation (GPS RO) observations from 2007 to 2010 at 250 hPa, where the water vapor feedback on surface warming is strongest. Current research indicates that GPS RO data sets can capture the amount of water vapor in very dry and very moist air more efficiently than other observing platforms, possibly suggesting larger water vapor feedback than previously known. Inter-comparing the dq/dTs among different data sets will provide us with additional constraints on the water vapor feedback. The dq/dTs estimation from GPS RO observations shows excellent agreement with previously published results and the responses estimated using Atmospheric Infrared Sounder (AIRS) and NASA's Modern-Era Retrospective Analysis for Research and Applications (MERRA) data sets. In particular, the GPS RO-derived dq/dTs is larger by 6% than that estimated using the AIRS data set. This agrees with past evidence that AIRS may be dry-biased in the upper troposphere. Compared to the MERRA estimations, the GPS RO-derived dq/dTs is 10% smaller, also agreeing with previous results that show that MERRA may have a wet bias in the upper troposphere. Because of their high sensitivity to fractional changes in water vapor, and their inherent long-term accuracy, current and future GPS RO observations show great promise in monitoring climate feedbacks and their trends.

Use of Multiangle Satellite Observations to Retrieve Aerosol Properties and Ocean Color

NASA Technical Reports Server (NTRS)

Martonchik, John V.; Diner, David; Khan, Ralph

2005-01-01

A new technique is described for retrieving aerosol over ocean water and the associated ocean color using multiangle satellite observations. Unlike current satellite aerosol retrieval algorithms which only utilize observations at red wavelengths and longer, with the assumption that these wavelengths have a negligible ocean (water-leaving radiance), this new algorithm uses all available spectral bands and simultaneously retrieves both aerosol properties and the spectral ocean color. We show some results of case studies using MISR data, performed over different water conditions (coastal water, blooms, and open water).

Primordial non-Gaussianity and power asymmetry with quantum gravitational effects in loop quantum cosmology

NASA Astrophysics Data System (ADS)

Zhu, Tao; Wang, Anzhong; Kirsten, Klaus; Cleaver, Gerald; Sheng, Qin

2018-02-01

Loop quantum cosmology provides a resolution of the classical big bang singularity in the deep Planck era. The evolution, prior to the usual slow-roll inflation, naturally generates excited states at the onset of the slow-roll inflation. It is expected that these quantum gravitational effects could leave its fingerprints on the primordial perturbation spectrum and non-Gaussianity, and lead to some observational evidences in the cosmic microwave background. While the impact of the quantum effects on the primordial perturbation spectrum has been already studied and constrained by current data, in this paper we continue to study such effects but now on the non-Gaussianity of the primordial curvature perturbations. We present detailed and analytical calculations of the non-Gaussianity and show explicitly that the corrections due to the quantum effects are at the same magnitude of the slow-roll parameters in the observable scales and thus are well within current observational constraints. Despite this, we show that the non-Gaussianity in the squeezed limit can be enhanced at superhorizon scales and it is these effects that can yield a large statistical anisotropy on the power spectrum through the Erickcek-Kamionkowski-Carroll mechanism.

Evaluation of Alkylamine Modified Pt Nanoparticles as Oxygen Reduction Reaction Electrocatalyst for Fuel Cells via Electrochemical Impedance Spectroscopy.

PubMed

Joshi, Prerna; Okada, Toshihiko; Miyabayashi, Keiko; Miyake, Mikio

2018-05-15

Organically (octyl amine, OA) surface modified electrocatalyst (OA-Pt/CB) was studied for its oxygen reduction reaction (ORR) activity via dc methods and its charge and mass transfer properties were studied via electrochemical impedance spectroscopy (EIS). Comparison with a commercial catalyst (TEC10V30E) with similar Pt content was also carried out. In EIS, both the catalysts showed a single time-constant with an emerging high-frequency semicircle of very small diameter which was fitted using suitable equivalent circuits. The organically modified catalyst showed lower charge-transfer resistance and hence, low polarization resistance in high potential region as compared to the commercial catalyst. The dominance of kinetic processes was observed at 0.925-1.000 V, whereas domination of diffusion based processes was observed at lower potential region for the organic catalyst. No effect due to the presence of carbon was observed in the EIS spectra. Using the hydrodynamic method, higher current penetration depth was obtained for the organically modified catalyst at 1600 rpm. Exchange current density and Tafel slopes for both the electrocatalysts were calculated from the polarization resistance obtained from EIS which was in correlation with the results obtained from dc methods.

El paradigma jerarquico de formacion de estructuras

NASA Astrophysics Data System (ADS)

Lambas, D. G.

This contribution aims at showing our current understanding of the hierarchical clustering scenario for structure formation, its main success in terms of agreement of theoretical predictions and observations, and the most direct tests that provide confidence on the validity of the paradigm. FULL TEXT IN SPANISH

Foveated model observers to predict human performance in 3D images

NASA Astrophysics Data System (ADS)

Lago, Miguel A.; Abbey, Craig K.; Eckstein, Miguel P.

2017-03-01

We evaluate 3D search requires model observers that take into account the peripheral human visual processing (foveated models) to predict human observer performance. We show that two different 3D tasks, free search and location-known detection, influence the relative human visual detectability of two signals of different sizes in synthetic backgrounds mimicking the noise found in 3D digital breast tomosynthesis. One of the signals resembled a microcalcification (a small and bright sphere), while the other one was designed to look like a mass (a larger Gaussian blob). We evaluated current standard models observers (Hotelling; Channelized Hotelling; non-prewhitening matched filter with eye filter, NPWE; and non-prewhitening matched filter model, NPW) and showed that they incorrectly predict the relative detectability of the two signals in 3D search. We propose a new model observer (3D Foveated Channelized Hotelling Observer) that incorporates the properties of the visual system over a large visual field (fovea and periphery). We show that the foveated model observer can accurately predict the rank order of detectability of the signals in 3D images for each task. Together, these results motivate the use of a new generation of foveated model observers for predicting image quality for search tasks in 3D imaging modalities such as digital breast tomosynthesis or computed tomography.

Selection rules for harmonic generation in solids

NASA Astrophysics Data System (ADS)

Moiseyev, Nimrod

2015-05-01

High-order harmonic generation (HHG) in a bulk crystal was first observed in 2011 [S. Ghimire, A. D. DiChiara, E. Sistrunk, P. Agostini, L. F. DiMauro, and D. A. Reis, Nat. Phys. 7, 138 (2011), 10.1038/nphys1847]. Only odd-order harmonics were observed as expected on the basis of the selection rules in solids, which were derived when only the interband currents were taken into consideration. Here we study HHG in solids when the intraband currents are taken into consideration as well. We show that the dynamical selection rules are broken in solids and the possibility of generation of even-order harmonics cannot be excluded on the basis of the dynamical symmetry analysis. However, a simple analysis of the expression we obtained for the amplitude of the emitted high-order harmonics shows, without the need to carry out numerical calculations, that the even-order harmonics are suppressed due to the localization of the field-free one-electron density probability on the atoms in the solids.

The Aro 1 mm Survey of the Oxygen-Rich Envelope of Supergiant Star NML Cygnus

NASA Astrophysics Data System (ADS)

Edwards, Jessica L.; Ziurys, L. M.; Woolf, N. J.

2011-06-01

Although a number of molecular line surveys of carbon-rich circumstellar envelopes (CSE) have been performed, only one oxygen-rich CSE, that of VY Canis Majoris (VY CMa), has been studied in depth. The Arizona Radio Observatory (ARO) 1 mm survey of VY CMa showed a very different and interesting chemistry dominated by sulfur- and silicon-bearing compounds as well as a number of more exotic species. A similar survey of the oxygen rich star NML Cygnus (NML Cyg) from 215 to 285 GHz is currently under way using the ARO Sub-millimeter Telescope. Initial observations show that this circumstellar envelope appears to be as chemically rich as that of VY CMa. Molecules including 12CO, 13CO, 12CN, 13CN, HCN, HCO+, CS, SO{_2}, SiO and 30SiO have been observed in NML Cyg. Line profiles of this source also suggest that there may be multiple outflows and that the circumstellar envelope is not spherically symmetric. Current results will be presented.

Site-specific Installation and Study of Electroactive Units in Every Layer of Dendrons

PubMed Central

Azagarsamy, Malar A.; Krishnamoorthy, Kothandam; Sivanandan, Kulandaivelu; Thayumanavan, S.

2009-01-01

While encapsulation of functional groups at the core of dendrimers is well-understood, very little is known about their intermediate layers or even the periphery. Here we report on a systematic investigation of every layer of dendrimers by incorporating a single ferrocene unit in well-defined locations in dendrons. Site-specific incorporation of the ferrocene unit was achieved utilizing the dendrimer sequencing methodology. We show here that the redox potential values of ferrocene at intermediate layers were remarkably different from that at the core and the periphery. While redox potential values were location-dependent, no significant change in the rate of heterogeneous electron transfer (k0) was observed with respect to locations. This was attributed to the possibility that free rotation of dendrimer nullifies the distance between the electrode and ferrocene unit. Finally, we also show that no Faradaic current was observed for the amphiphilic assemblies of these dendrons, while the same dendron did exhibit significant Faradaic current in non-assembling solvent environments. PMID:19905006

Raman shifts in electron-irradiated monolayer MoS 2

DOE PAGES

Parkin, William M.; Balan, Adrian; Liang, Liangbo; ...

2016-03-21

Here, we report how the presence of electron-beam-induced sulfur vacancies affects first-order Raman modes and correlate the effects with the evolution of the in situ transmission-electron microscopy (TEM) two-terminal conductivity of monolayer MoS 2 under electron irradiation. We observe a redshift in the E Raman peak and a less pronounced blueshift in the A' 1 peak with increasing electron dose. Using energy-dispersive X-ray spectroscopy (EDS), we show that irradiation causes partial removal of sulfur and correlate the dependence of the Raman peak shifts with S vacancy density (a few %), which is confirmed by first-principles density functional theory calculations. Inmore » situ device current measurements show exponential decrease in channel current upon irradiation. Our analysis demonstrates that the observed frequency shifts are intrinsic properties of the defective systems and that Raman spectroscopy can be used as a quantitative diagnostic tool to characterize MoS 2-based transport channels.« less

Observations of Enhanced Radar Backscatter (ERB) from Millstone Hill

NASA Technical Reports Server (NTRS)

Lee, M. C.

1991-01-01

Intense enhancements of the incoherent radar backscatter spectrum from the topside ionosphere were observed with the Millstone Hill UHF radar. Enhancements occurring at the local ion acoustic frequency causing large asymmetries in the measured ion line may be produced by current driven instabilities. These enhancements pose a practical problem for space surveillance systems because their cross section and spectral width are characteristic of satellites. Conversely, their hard target signature complicates the study of naturally occurring ERB events; it is nearly impossible to distinguish them from satellites based on a single measurement. Statistical comparisons of observed coherent echo distributions with predictions from a satellite catalog were used to broadly identify periods of ERB activity. A series of experiments using multiple diagnostics, including satellite instruments, for simultaneous observations have established the association of ERB with large fluxes of soft suprathermal electrons carrying field aligned currents. Zenith data are also presented which show the asymmetric growth of ion acoustic waves directly above Millstone Hill. Details of these results are presented.

La Serra d'Almos (Tarragona): an example of phenological data rescue and preservation in Catalonia

NASA Astrophysics Data System (ADS)

Busto, Montserrat; Cunillera, Jordi; de Yzaguirre, Xavi; Borrell, Josep

2016-04-01

The interruption of important phenological series and the progressive disappearance of phenological observations in Catalonia led the Meteorological Service of Catalonia (SMC) to design and impulse a new phenological network promoted by the Climate Change Unit of this Met Service. The "Fenocat" network was born in March 2013, and currently has around fifty observers distributed throughout Catalonia that observe plants, birds and butterflies. We are providing data from different plant phenophases to PEP725 database. Besides this new phenological network (Fenocat), one of the aims of SMC is to rescue and preserve historical data from different observation points in Catalonia. We show in this poster the example of rescue and preservation of phenological data from la Serra d'Almos (in Tivissa, near Tarragona, Catalonia, NE Iberian Peninsula), an observation series that began in 1973. After digitalization process and quality control tasks, we show preliminary results of this phenological series, and we compare them with those of similar European series. We show the evolution trends for different observed species, such as almond tree (Prunus dulcis), hazel (Corylus avellana), plum (Prunus domestica), olive tree (Olea europea), apple tree (Malus domestica) or vineyard (Vitis vinifera).

Near-bed observations of high-concentration sediment transport in the Changjiang Estuary

NASA Astrophysics Data System (ADS)

Zhou, Z.; Ge, J.; Ding, P.

2017-12-01

The North Passage, the core of turbidity maximum in the Changjiang Estuary, is now under the strong sedimentation due to the abundant sediment supply from the upstream Changjiang River and the river-tide interacted dynamics. Recent studies suggested that strong siltation could be attributed to bottom high-concentration sediment transport, which however is very difficult to be detected and observed by vessel-anchored survey methods. To better understand the mechanisms of sediment transport and deposition in the channel region of the North Passage and its adjacent areas, we conducted continuous field observations which covered spring and neap tide period in the wintertime of 2016, the summertime of 2015 and 2017, focusing on near-bottom sediment transport. Tripods mounted with multiple instruments, including up-looking and down-looking Acoustic Doppler Current Profilers(ADCP), Vector Current Meter(ADV), Optical Backscatter Sensor(OBS), ASM, ALEC and RBR were used to observe the near-bottom physical process and its induced sediment dynamics. Results of these observations clearly described the current-wave-sediment interaction, which produced different patterns of bottom mud suspension at different tripods. Both hydrodynamic features and suspended sediment showed variations between spring and neap tide. Taking data of 2016 as an example, averaged suspended sediment concentration(SSC) at two tripods was 1.52 g/L and 2.13 g/L during the neap tide, 4.51 g/L and 5.75 g/L with the peak value reaching 25 g/L during the spring tide. At the tripod which was closer to the channel region, three peaks of SSC during the spring tide occurred near the flood slack with notable salinity increase, indicating the impact of saltwater intrusion on the bottom hydrodynamics. The results showed the occurrence of high-concentration suspended sediment was probably related to combined effects of bottom salinity intrusion, turbulent kinetic energy(TKE) and local stratification due to density gradient from intruded salinity and local sediment suspension. Meanwhile, tripods' monitoring identified a significant cross-channel component of residual current, which could produce potential bottom sediment accumulation in the channel region within the North Passage.

Cocaine acute "binge" administration results in altered thalamocortical interactions in mice.

PubMed

Urbano, Francisco J; Bisagno, Verónica; Wikinski, Silvia I; Uchitel, Osvaldo D; Llinás, Rodolfo R

2009-10-15

Abnormalities in both thalamic and cortical areas have been reported in human cocaine addicts with noninvasive functional magnetic resonance imaging. Given the substantial involvement of the thalamocortical system in sensory processing and perception, we defined electrophysiology-based protocols to attempt a characterization of cocaine effects on thalamocortical circuits. Thalamocortical function was studied in vivo and in vitro in mice after cocaine "binge" administration. In vivo awake electroencephalography (EEG) was implemented in mice injected with saline, 1 hour or 24 hours after the last cocaine "binge" injection. In vitro current- and voltage-clamp whole-cell patch-clamp recordings were performed from slices including thalamic relay ventrobasal (VB) neurons. In vivo EEG recordings after cocaine "binge" administration showed a significant increment, compared with saline, in low frequencies while observing no changes in high-frequency gamma activity. In vitro patch recordings from VB neurons after cocaine "binge" administration showed low threshold spikes activation at more negative membrane potentials and increments in both I(h) and low voltage activated T-type calcium currents. Also, a 10-mV negative shift on threshold activation level of T-type current and a remarkable increment in both frequency and amplitudes of gamma-aminobutyric acid-A-mediated minis were observed. Our data indicate that thalamocortical dysfunctions observed in cocaine abusers might be due to two distinct but additive events: 1) increased low frequency oscillatory thalamocortical activity, and 2) overinhibition of VB neurons that can abnormally "lock" the whole thalamocortical system at low frequencies.

Kinetic and functional analysis of transient, persistent and resurgent sodium currents in rat cerebellar granule cells in situ: an electrophysiological and modelling study

PubMed Central

Magistretti, Jacopo; Castelli, Loretta; Forti, Lia; D'Angelo, Egidio

2006-01-01

Cerebellar neurones show complex and differentiated mechanisms of action potential generation that have been proposed to depend on peculiar properties of their voltage-dependent Na+ currents. In this study we analysed voltage-dependent Na+ currents of rat cerebellar granule cells (GCs) by performing whole-cell, patch-clamp experiments in acute rat cerebellar slices. A transient Na+ current (INaT) was always present and had the properties of a typical fast-activating/inactivating Na+ current. In addition to INaT, robust persistent (INaP) and resurgent (INaR) Na+ currents were observed. INaP peaked at ∼−40 mV, showed half-maximal activation at ∼−55 mV, and its maximal amplitude was about 1.5% of that of INaT. INaR was elicited by repolarizing pulses applied following step depolarizations able to activate/inactivate INaT, and showed voltage- and time-dependent activation and voltage-dependent decay kinetics. The conductance underlying INaR showed a bell-shaped voltage dependence, with peak at −35 mV. A significant correlation was found between GC INaR and INaT peak amplitudes; however, GCs expressing INaT of similar size showed marked variability in terms of INaR amplitude, and in a fraction of cells INaR was undetectable. INaT, INaP and INaR could be accounted for by a 13-state kinetic scheme comprising closed, open, inactivated and blocked states. Current-clamp experiments carried out to identify possible functional correlates of INaP and/or INaR revealed that in GCs single action potentials were followed by depolarizing afterpotentials (DAPs). In a majority of cells, DAPs showed properties consistent with INaR playing a role in their generation. Computer modelling showed that INaR promotes DAP generation and enhances high-frequency firing, whereas INaP boosts near-threshold firing activity. Our findings suggest that special properties of voltage-dependent Na+ currents provides GCs with mechanisms suitable for shaping activity patterns, with potentially important consequences for cerebellar information transfer and computation. PMID:16527854

Particle-in-cell simulations of anomalous transport in a Penning discharge

NASA Astrophysics Data System (ADS)

Carlsson, Johan; Kaganovich, Igor; Powis, Andrew; Raitses, Yevgeny; Romadanov, Ivan; Smolyakov, Andrei

2018-06-01

Electrostatic particle-in-cell simulations of a Penning discharge are performed in order to investigate azimuthally asymmetric, spoke-like structures previously observed in experiments. Two-dimensional simulations show that for Penning-discharge conditions, a persistent nonlinear spoke-like structure forms readily and rotates in the direction of E × B and electron diamagnetic drifts. The azimuthal velocity is within about a factor of 2 of the ion acoustic speed. The spoke frequency follows the experimentally observed scaling with ion mass, which indicates the importance of ion inertia in spoke formation. The spoke provides enhanced (anomalous) radial electron transport, and the effective cross-field conductivity is several times larger than the classical (collisional) value. The level of anomalous current obtained in the simulations is in good agreement with the experimental data. The rotating spoke channels most of the radial current, observable by an edge probe as short pulses.

Field enhancement of electronic conductance at ferroelectric domain walls

DOE PAGES

Vasudevan, Rama K.; Cao, Ye; Laanait, Nouamane; ...

2017-11-06

Ferroelectric domain walls have continued to attract widespread attention due to both the novelty of the phenomena observed and the ability to reliably pattern them in nanoscale dimensions. But, the conductivity mechanisms remain in debate, particularly around nominally uncharged walls. Here, we posit a conduction mechanism relying on field-modification effect from polarization re-orientation and the structure of the reverse-domain nucleus. Through conductive atomic force microscopy measurements on an ultra-thin (001) BiFeO 3 thin film, in combination with phase-field simulations, we show that the field-induced twisted domain nucleus formed at domain walls results in local-field enhancement around the region of themore » atomic force microscope tip. In conjunction with slight barrier lowering, these two effects are sufficient to explain the observed emission current distribution. Our results suggest that different electronic properties at domain walls are not necessary to observe localized enhancement in domain wall currents.« less

Non Thermal Emission from Clusters of Galaxies: the Importance of a Joint LOFAR/Simbol-X View

NASA Astrophysics Data System (ADS)

Ferrari, C.

2009-05-01

Deep radio observations of galaxy clusters have revealed the existence of diffuse radio sources (``halos'' and ``relics'') related to the presence of relativistic electrons and weak magnetic fields in the intracluster volume. I will outline our current knowledge about the presence and properties of this non-thermal cluster component. Despite the recent progress made in observational and theoretical studies of the non-thermal emission in galaxy clusters, a number of open questions about its origin and its effects on the thermo-dynamical evolution of galaxy clusters need to be answered. I will show the importance of combining galaxy cluster observations by new-generation instruments such as LOFAR and Simbol-X. A deeper knowledge of the non-thermal cluster component, together with statistical studies of radio halos and relics, will allow to test the current cluster formation scenario and to better constrain the physics of large scale structure evolution.

Ogo 5 observations of LHR noise, emissions, and whistlers near the plasmapause at several earth radii during a large magnetic storm.

NASA Technical Reports Server (NTRS)

Scarf, F. L.; Fredricks, R. W.; Smith, E. J.; Frandsen, A. M. A.; Serbu, G. P.

1972-01-01

On May 15, 1969, Ogo 5 crossed the plasmapause during a major storm that produced severe geomagnetic disturbances (Kp up to 8-), large and rapid variations in ring-current intensity (as measured by Dst), intense low-latitude aurora, and persistent SAR arcs. Near the highly structured plasmasphere boundary, the electric- and magnetic-field sensors on Ogo 5 detected lower-hybrid-resonance noise bursts, whistlers, ELF hiss, and other discrete signals or emissions. Some LHR noise bursts were associated with whistlers, and these high-altitude phenomena resembled the corresponding ionospheric ones. This report contains a description of the VLF observations. We also show that intense ULF magnetic signals were present near the plasmapause, and we attempt to relate these observations to the predictions of various theories of proton ring-current decay and SAR-arc formation.

Sound diffraction at wall impedance discontinuities in a circular cylinder - Investigated using Wiener-Hopf technique

NASA Technical Reports Server (NTRS)

Cho, Y.-C.

1983-01-01

The results of ground observations as well as high resolution rocket electric field and particle observations during a breakup event of an intense magnetospheric substorm over northern Scandinavia are discussed. In particular, the characteristics of the substorm-associated electric field, ionospheric currents, and power dissipation during a time period about 15 minutes after substorm onset are addressed. A comparison of the observations with those of a pre-breakup event earlier in the day (Marklund et al., 1982) showed that the ionospheric substorm-related electric field could be split up into two parts: (1) an ambient LT-dependent field, probably of magnetospheric origin; and (2) a small-scale electric field associated with the bright auroral structures, which is superimposed on the LT-dependent field. The consequences for the location of the ionospheric currents and the Joule energy dissipation relative to the auroral forms are discussed. Previously announced in STAR as N83-23117

Observation of Gigawatt-Class THz Pulses from a Compact Laser-Driven Particle Accelerator

NASA Astrophysics Data System (ADS)

Gopal, A.; Herzer, S.; Schmidt, A.; Singh, P.; Reinhard, A.; Ziegler, W.; Brömmel, D.; Karmakar, A.; Gibbon, P.; Dillner, U.; May, T.; Meyer, H.-G.; Paulus, G. G.

2013-08-01

We report the observation of subpicosecond terahertz (T-ray) pulses with energies ≥460μJ from a laser-driven ion accelerator, thus rendering the peak power of the source higher even than that of state-of-the-art synchrotrons. Experiments were performed with intense laser pulses (up to 5×1019W/cm2) to irradiate thin metal foil targets. Ion spectra measured simultaneously showed a square law dependence of the T-ray yield on particle number. Two-dimensional particle-in-cell simulations show the presence of transient currents at the target rear surface which could be responsible for the strong T-ray emission.

Protein kinase A stimulates Kv7.1 surface expression by regulating Nedd4-2-dependent endocytic trafficking.

PubMed

Andersen, Martin N; Hefting, Louise L; Steffensen, Annette B; Schmitt, Nicole; Olesen, Søren-Peter; Olsen, Jesper V; Lundby, Alicia; Rasmussen, Hanne B

2015-11-15

The potassium channel Kv7.1 plays critical physiological roles in both heart and epithelial tissues. In heart, Kv7.1 and the accessory subunit KCNE1 forms the slowly activating delayed-rectifier potassium current current, which is enhanced by protein kinase A (PKA)-mediated phosphorylation. The observed current increase requires both phosphorylation of Kv7.1 and the presence of KCNE1. However, PKA also stimulates Kv7.1 currents in epithelial tissues, such as colon, where the channel does not coassemble with KCNE1. Here, we demonstrate that PKA activity significantly impacts the subcellular localization of Kv7.1 in Madin-Darby canine kidney cells. While PKA inhibition reduced the fraction of channels at the cell surface, PKA activation increased it. We show that PKA inhibition led to intracellular accumulation of Kv7.1 in late endosomes/lysosomes. By mass spectroscopy we identified eight phosphorylated residues on Kv7.1, however, none appeared to play a role in the observed response. Instead, we found that PKA acted by regulating endocytic trafficking involving the ubiquitin ligase Nedd4-2. We show that a Nedd4-2-resistant Kv7.1-mutant displayed significantly reduced intracellular accumulation upon PKA inhibition. Similar effects were observed upon siRNA knockdown of Nedd4-2. However, although Nedd4-2 is known to regulate Kv7.1 by ubiquitylation, biochemical analyses demonstrated that PKA did not influence the amount of Nedd4-2 bound to Kv7.1 or the ubiquitylation level of the channel. This suggests that PKA influences Nedd4-2-dependent Kv7.1 transport though a different molecular mechanism. In summary, we identify a novel mechanism whereby PKA can increase Kv7.1 current levels, namely by regulating Nedd4-2-dependent Kv7.1 transport. Copyright © 2015 the American Physiological Society.

Protein kinase A stimulates Kv7.1 surface expression by regulating Nedd4-2-dependent endocytic trafficking

PubMed Central

Andersen, Martin N.; Hefting, Louise L.; Steffensen, Annette B.; Schmitt, Nicole; Olesen, Søren-Peter; Olsen, Jesper V.; Lundby, Alicia

2015-01-01

The potassium channel Kv7.1 plays critical physiological roles in both heart and epithelial tissues. In heart, Kv7.1 and the accessory subunit KCNE1 forms the slowly activating delayed-rectifier potassium current current, which is enhanced by protein kinase A (PKA)-mediated phosphorylation. The observed current increase requires both phosphorylation of Kv7.1 and the presence of KCNE1. However, PKA also stimulates Kv7.1 currents in epithelial tissues, such as colon, where the channel does not coassemble with KCNE1. Here, we demonstrate that PKA activity significantly impacts the subcellular localization of Kv7.1 in Madin-Darby canine kidney cells. While PKA inhibition reduced the fraction of channels at the cell surface, PKA activation increased it. We show that PKA inhibition led to intracellular accumulation of Kv7.1 in late endosomes/lysosomes. By mass spectroscopy we identified eight phosphorylated residues on Kv7.1, however, none appeared to play a role in the observed response. Instead, we found that PKA acted by regulating endocytic trafficking involving the ubiquitin ligase Nedd4-2. We show that a Nedd4-2-resistant Kv7.1-mutant displayed significantly reduced intracellular accumulation upon PKA inhibition. Similar effects were observed upon siRNA knockdown of Nedd4-2. However, although Nedd4-2 is known to regulate Kv7.1 by ubiquitylation, biochemical analyses demonstrated that PKA did not influence the amount of Nedd4-2 bound to Kv7.1 or the ubiquitylation level of the channel. This suggests that PKA influences Nedd4-2-dependent Kv7.1 transport though a different molecular mechanism. In summary, we identify a novel mechanism whereby PKA can increase Kv7.1 current levels, namely by regulating Nedd4-2-dependent Kv7.1 transport. PMID:26405101

Remote sensing of ocean currents. [Loop Current in Gulf of Mexico

NASA Technical Reports Server (NTRS)

Maul, G. A. (Principal Investigator)

1974-01-01

The author has identified the following significant results. A time series of the Loop Current in the Gulf of Mexico, covering an annual cycle of growth, spreading, and decay, has been obtained in synchronization with ERTS-1. Computer enhanced images, which are necessary to extract useful oceanic information, show that the current can be observed either by color or sea state effects associated with the cyclonic boundary. The color effect relates to the spectral variations in the optical properties of the water and its suspended particles, and is studied by radiative transfer theory. Significant oceanic parameters identified are: the probability of forward scattering, and the ratio of scattering to total attenuation. Several spectra of upwelling diffuse light are computed as a function of the concentration of particles and yellow substance. These calculations compare favorably with experimental measurements and show that the ratio of channels method gives ambiguous interpretative results. These results are used to discuss features in images where surface measurements were obtained and are extended to tentative explanation in others.

A flexible and transparent graphene/ZnO nanorod hybrid structure fabricated by exfoliating a graphite substrate.

PubMed

Nam, Gwang-Hee; Baek, Seong-Ho; Cho, Chang-Hee; Park, Il-Kyu

2014-10-21

We demonstrate the fabrication of a graphene/ZnO nanorod (NR) hybrid structure by mechanical exfoliation of ZnO NRs grown on a graphite substrate. We confirmed the existence of graphene sheets on the hybrid structure by analyzing the Raman spectra and current-voltage (I-V) characteristics. The Raman spectra of the exfoliated graphene/ZnO NR hybrid structure show G and 2D band peaks that are shifted to lower wavenumbers, indicating that the exfoliated graphene layer exists under a significant amount of strain. The I-V characteristics of the graphene/ZnO NR hybrid structure show current flow through the graphene layer, while no current flow is observed on the ZnO NR/polydimethylsiloxane (PDMS) composite without graphene, thereby indicating that the few-layer graphene was successfully transferred onto the hybrid structure. A piezoelectric nanogenerator is demonstrated by using the fabricated graphene/ZnO NR hybrid structure. The nanogenerator exhibits stable output voltage up to 3.04 V with alternating current output characteristics.

Observation of the Spin Nernst Effect in Platinum

NASA Astrophysics Data System (ADS)

Goennenwein, Sebastian

Thermoelectric effects - arising from the interplay between thermal and charge transport phenomena - have been extensively studied and are considered well established. Upon taking into account the spin degree of freedom, however, qualitatively new phenomena arise. A prototype example for these so-called magneto-thermoelectric or spin-caloritronic effects is the spin Seebeck effect, in which a thermal gradient drives a pure spin current. In contrast to their thermoelectric counterparts, not all the spin-caloritronic effects predicted from theory have yet been observed in experiment. One of these `missing' phenomena is the spin Nernst effect, in which a thermal gradient gives rise to a transverse pure spin current. We have observed the spin Nernst effect in yttrium iron garnet/platinum (YIG/Pt) thin film bilayers. Upon applying a thermal gradient within the YIG/Pt bilayer plane, a pure spin current flows in the direction orthogonal to the thermal drive. We detect this spin current as a thermopower voltage, generated via magnetization-orientation dependent spin transfer into the adjacent YIG layer. Our data shows that the spin Nernst and the spin Hall effect in in Pt have different sign, but comparable magnitude, in agreement with first-principles calculations. Financial support via Deutsche Forschungsgemeinschaft Priority Programme SPP 1538 Spin-Caloric Transport is gratefully acknowledged.

Effect of various electrokinetic treatment regimes on solids surface properties and thermal behavior of oil sediments.

PubMed

Kariminezhad, Esmaeel; Elektorowicz, Maria

2018-04-10

The electrokinetic process has shown its ability to separate the different material phases. However, not much is known about the effect of the electric fields on the surface properties of solids in the oil sediments and their behavior under different electrical regimes. In this study, the effect of four different types of electrical current on the surface properties of oil sediments was investigated, namely constant direct current (CDC), pulsed direct current (PDC), incremental direct current (IDC) and decremental direct current (DDC). X-ray photoelectron spectroscopy (XPS) analyses showed a decrease in the concentration of carbon from 99% in centrifuged samples to 63% on the surface of the solids in the PDC-treated oil sediment. Wettability alteration and contact angle studies showed an enhance in hydrophilicity of the solids following electrokinetic treatment. A significant change in carbon and oxygen-containing functionalities at the surface solids of the DDC-treated sediment was also observed. Thermogravimetric analyses (TGA) confirmed the ability of electrokinetic treatment in separating the phases by shifting the thermogram profiles towards lower temperatures. The findings showed that the electrokinetic process exerts its effect by altering the surface properties of the sediment solids and destabilizing water-in-oil emulsions to facilitate phase separation of this complex waste. Copyright © 2018 Elsevier B.V. All rights reserved.

Time and space resolved current density mapping in three dimensions using magnetic field probe array in a high voltage coaxial gap

NASA Astrophysics Data System (ADS)

Cordaro, S. W.; Bott-Suzuki, S. C.

2017-12-01

We present an experimental analysis of the symmetry of current density in a coaxial geometry, diagnosed using a magnetic field probe array and calculations of the Fowler-Nordheim enhancement factor. Data were collected on the coaxial gap breakdown device (240 A, 25 kV, 150 ns, ˜0.1 Hz), and data from experiments using 2 different gap sizes and different penetration depths are compared over runs comprising 50 shots for each case. The magnetic field probe array quantifies the distribution of current density at three axial locations, on either sides of a vacuum breakdown, and tracks the evolution with time and space. The results show asymmetries in current density, which can be influenced by changes in the gap size and the penetration depth (of the center electrode into the outer electrode). For smaller gap sizes (400 μm), symmetric current profiles were not observed, and the change in the penetration depth changes both the symmetric behavior of the current density and the enhancement factor. For larger gaps (900 μm), current densities were typically more uniform and less influenced by the penetration depth, which is reflected in the enhancement factor values. It is possible that the change in inductance caused by the localization of current densities plays a role in the observed behavior.

Tearing modes induced by perpendicular electron cyclotron resonance heating in the KSTAR tokamak

NASA Astrophysics Data System (ADS)

Lee, H. H.; Lee, S. G.; Seol, J.; Aydemir, A. Y.; Bae, C.; Yoo, J. W.; Na, Y. S.; Kim, H. S.; Woo, M. H.; Kim, J.; Joung, M.; You, K. I.; Park, B. H.

2014-10-01

This paper reports on experimental evidence that shows perpendicular electron cyclotron resonance heating (ECRH) can trigger classical tearing modes when deposited near a rational flux surface. The complex evolution of an m = 2 island is followed during current ramp-up in KSTAR plasmas, from its initial onset as the rational surface enters the ECRH resonance layer to its eventual lock on the wall after the rational surface leaves the layer. Stability analysis coupled to a transport calculation of the current profile with ECRH shows that the perpendicular ECRH may play a significant role in triggering and destabilizing classical m = 2 tearing modes, in agreement with our experimental observation.

Magnetic vortex excitation as spin torque oscillator and its unusual trajectories

NASA Astrophysics Data System (ADS)

Natarajan, Kanimozhi; Muthuraj, Ponsudana; Rajamani, Amuda; Arumugam, Brinda

2018-05-01

We report an interesting observation of unusual trajectories of vortex core oscillations in a spin valve pillar. Micromagnetic simulation in the composite free layer spin valve nano-pillar shows magnetic vortex excitation under critical current density. When current density is slightly increased and wave vector is properly tuned, for the first time we observe a star like and square gyration. Surprisingly this star like and square gyration also leads to steady, coherent and sustained oscillations. Moreover, the frequency of gyration is also very high for this unusual trajectories. The power spectral analysis reveals that there is a marked increase in output power and frequency with less distortions. Our investigation explores the possibility of these unusual trajectories to exhibit spin torque oscillations.

Enhancement of minority carrier injection in ambipolar carbon nanotube transistors using double-gate structures

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

Kim, Bongjun; Liang, Kelly; Dodabalapur, Ananth, E-mail: ananth.dodabalapur@engr.utexas.edu

We show that double-gate ambipolar thin-film transistors can be operated to enhance minority carrier injection. The two gate potentials need to be significantly different for enhanced injection to be observed. This enhancement is highly beneficial in devices such as light-emitting transistors where balanced electron and hole injections lead to optimal performance. With ambipolar single-walled carbon nanotube semiconductors, we demonstrate that higher ambipolar currents are attained at lower source-drain voltages, which is desired for portable electronic applications, by employing double-gate structures. In addition, when the two gates are held at the same potential, the expected advantages of the double-gate transistors suchmore » as enhanced on-current are also observed.« less

Poker flat radar observations of the magnetosphere-ionosphere coupling electrodynamics of the earthward penetrating plasma sheet following convection enhancements

NASA Astrophysics Data System (ADS)

Lyons, L. R.; Zou, S.; Heinselman, C. J.; Nicolls, M. J.; Anderson, P. C.

2009-05-01

The plasma sheet moves earthward (equatorward in the ionosphere) after enhancements in convection, and the electrodynamics of this response is strongly influenced by Region 2 magnetosphere-ionosphere coupling. We have used Poker Flat Advanced Modular Incoherent Scatter Radar (PFISR) observations associated with two relatively abrupt southward turnings of the IMF to provide an initial evaluation of aspects of this response. The observations show that strong westward sub-auroral polarization streams (SAPS) flow regions moved equatorward as the plasma sheet electron precipitation (the diffuse aurora) penetrated equatorward following the IMF southward turnings. Consistent with our identification of these flows as SAPS, concurrent DMSP particle precipitation measurements show the equatorial boundary of ion precipitation equatorward of the electron precipitation boundary and that westward flows lie within the low-conductivity region between the two boundaries where the plasma sheet ion pressure gradient is expected to drive downward R2 currents. Evidence for these downward currents is seen in the DMSP magnetometer observations. Preliminary examination indicates that the SAPS response seen in the examples presented here may be common. However, detailed analysis will be required for many more events to reliably determine if this is the case. If so, it would imply that SAPS are frequently an important aspect of the inner magnetospheric electric field distribution, and that they are critical for understanding the response of the magnetosphere-ionosphere system to enhancements in convection, including understanding the earthward penetration of the plasma sheet. This earthward penetration is critical to geomagnetic disturbance phenomena such as the substorm growth phase and the formation of the stormtime ring current. Additionally, for one example, a prompt electric field response to the IMF southward turnings is seen within the inner plasma sheet.

The role of convection in the buildup of the ring current pressure during the 17 March 2013 storm

NASA Astrophysics Data System (ADS)

Menz, A. M.; Kistler, L. M.; Mouikis, C. G.; Spence, H. E.; Skoug, R. M.; Funsten, H. O.; Larsen, B. A.; Mitchell, D. G.; Gkioulidou, M.

2017-01-01

On 17 March 2013, the Van Allen Probes measured the H+ and O+ fluxes of the ring current during a large geomagnetic storm. Detailed examination of the pressure buildup during the storm shows large differences in the pressure measured by the two spacecraft, with measurements separated by only an hour, and large differences in the pressure measured at different local times. In addition, while the H+ and O+ pressure contributions are about equal during the main phase in the near-Earth plasma sheet outside L = 5.5, the O+ pressure dominates at lower L values. We test whether adiabatic convective transport from the near-Earth plasma sheet (L > 5.5) to the inner magnetosphere can explain these observations by comparing the observed inner magnetospheric distributions with the source distribution at constant magnetic moment, mu. We find that adiabatic convection can account for the enhanced pressure observed during the storm. Using a Weimer 1996 electric field we model the drift trajectories to show that the key features can be explained by variation in the near-Earth plasma sheet population and particle access that changes with energy and L shell. Finally, we show that the dominance of O+ at low L shells is due partly to a near-Earth plasma sheet that is preferentially enhanced in O+ at lower energies (5-10 keV) and partly due to the time dependence in the source combined with longer drift times to low L shells. No source of O+ inside L = 5.5 is required to explain the observations at low L shells.

Current and efficiency of Brownian particles under oscillating forces in entropic barriers

NASA Astrophysics Data System (ADS)

Nutku, Ferhat; Aydιner, Ekrem

2015-04-01

In this study, considering the temporarily unbiased force and different forms of oscillating forces, we investigate the current and efficiency of Brownian particles in an entropic tube structure and present the numerically obtained results. We show that different force forms give rise to different current and efficiency profiles in different optimized parameter intervals. We find that an unbiased oscillating force and an unbiased temporal force lead to the current and efficiency, which are dependent on these parameters. We also observe that the current and efficiency caused by temporal and different oscillating forces have maximum and minimum values in different parameter intervals. We conclude that the current or efficiency can be controlled dynamically by adjusting the parameters of entropic barriers and applied force. Project supported by the Funds from Istanbul University (Grant No. 45662).

Dependences of contraction/expansion of stacking faults on temperature and current density in 4H-SiC p–i–n diodes

NASA Astrophysics Data System (ADS)

Okada, Aoi; Nishio, Johji; Iijima, Ryosuke; Ota, Chiharu; Goryu, Akihiro; Miyazato, Masaki; Ryo, Mina; Shinohe, Takashi; Miyajima, Masaaki; Kato, Tomohisa; Yonezawa, Yoshiyuki; Okumura, Hajime

2018-06-01

To investigate the mechanism of contraction/expansion behavior of Shockley stacking faults (SSFs) in 4H-SiC p–i–n diodes, the dependences of the SSF behavior on temperature and injection current density were investigated by electroluminescence image observation. We investigated the dependences of both triangle- and bar-shaped SSFs on the injection current density at four temperature levels. All SSFs in this study show similar temperature and injection current density dependences. We found that the expansion of SSFs at a high current density was converted to contraction at a certain value as the current decreased and that the value is temperature-dependent. It has been confirmed that SSF behavior, which was considered complex or peculiar, might be explained mainly by the energy change caused by SSFs.

Pion Condensation by Rotation in a Magnetic Field

NASA Astrophysics Data System (ADS)

Liu, Yizhuang; Zahed, Ismail

2018-01-01

We show that the combined effects of a rotation plus a magnetic field can cause charged pion condensation. We suggest that this phenomenon may yield to observable effects in current heavy ion collisions at collider energies, where large magnetism and rotations are expected in off-central collisions.

Behaviour Recognition from Sensory Streams in Smart Environments

NASA Astrophysics Data System (ADS)

Chua, Sook-Ling; Marsland, Stephen; Guesgen, Hans W.

One application of smart homes is to take sensor activations from a variety of sensors around the house and use them to recognise the particular behaviours of the inhabitants. This can be useful for monitoring of the elderly or cognitively impaired, amongst other applications. Since the behaviours themselves are not directly observed, only the observations by sensors, it is common to build a probabilistic model of how behaviours arise from these observations, for example in the form of a Hidden Markov Model (HMM). In this paper we present a method of selecting which of a set of trained HMMs best matches the current observations, together with experiments showing that it can reliably detect and segment the sensor stream into behaviours. We demonstrate our algorithm on real sensor data obtained from the MIT PlaceLab. The results show a significant improvement in the recognition accuracy over other approaches.

A Statistical Survey of the 630.0-nm Optical Signature of Periodic Auroral Arcs Resulting From Magnetospheric Field Line Resonances

NASA Astrophysics Data System (ADS)

Gillies, D. Megan; Knudsen, David; Rankin, Robert; Milan, Stephen; Donovan, Eric

2018-05-01

Advances in networks of ground-based optical instrumentation have enabled us to identify over 400 examples of auroral arcs with an infrequently observed, temporally periodic auroral morphology. This study focuses on these arcs observed via the 630-nm ("redline") auroral emission wavelength and connects them to global magnetospheric wave modes known as field line resonances (FLRs). We show that optical redline FLR auroral arcs occur most frequently near 20 and 4 magnetic local time, in contrast to nonperiodic redline arcs, which occur most frequently near midnight. We find that this periodic type of auroral arc is rare, occurring in approximately 5% of redline aurora observed by the Redline Emission Geospace Observatory all-sky imagers. We also show Swarm satellite observations of two separate instances of 630-nm FLR arcs with strong upward field-aligned currents of the order of 3-6 μA/m2.

Conduction at domain walls in insulating Pb(Zr0.2 Ti0.8)O3 thin films.

PubMed

Guyonnet, Jill; Gaponenko, Iaroslav; Gariglio, Stefano; Paruch, Patrycja

2011-12-01

Domain wall conduction in insulating Pb(Zr(0.2) Ti(0.8))O(3) thin films is demonstrated. The observed electrical conduction currents can be clearly differentiated from displacement currents associated with ferroelectric polarization switching. The domain wall conduction, nonlinear and highly asymmetric due to the specific local probe measurement geometry, shows thermal activation at high temperatures, and high stability over time. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Gravitational circulation in a tidal strait

USGS Publications Warehouse

Smith, P.E.; Cheng, R.T.; Burau, J.R.; Simpson, M.R.; ,

1991-01-01

Eight months of continuous measurements of tidal current profiles with an acoustic Doppler current profiler (ADCP) were made in Carquinez Strait, California, during 1988 for the purpose of estimating long-term variations in vertical profiles of Eulerian residual currents. Salinity stratification near the ADCP deployment site also was analyzed. The strength of density-driven gravitational circulation and the amount of salinity stratification in the strait varied significantly over the spring-neap tidal cycle. Density currents and stratification were greater during neap tides when vertical mixing from the tide is at a minimum. Landward residual currents along the bottom were observed only during neap tides. Simulations made with a three-dimensional model to supplement the field measurements show a significant, tidally induced lateral variation in residual currents across the strait. The Stokes drift of 1-2 cm/s in the strait is small relative to the speed of gravitational currents.

Field-aligned current associated with a distorted two-cell convection pattern during northward interplanetary magnetic field

NASA Technical Reports Server (NTRS)

Zhu, L.; Schunk, R. W.; Sojka, J. J.

1991-01-01

The influence of the ionospheric conductance on the field-aligned current associated with a distorted two-cell convection pattern during northward IMF was investigated using the Heppner-Maynard (1987) convection model and the Utah State University conductivity model described by Rasmussen and Schunk (1987). Results show that the variation of the ionospheric conductivity distribution can significantly affect the features of the field-aligned current for northward IMF, where matching or mismatching between the conductance gradient and the convection electric field plays a key role. It was found that the increase of the field-aligned current in the polar cap observed during summer is mainly due to the increasing contribution from the Pedersen current, and that the increase of the field-aligned current in both the oval region and the evening-midnight sector during the active aurora period is mainly due to the increasing contribution from the Hall current.

United Kingdom Infrared Telescope's Spectrograph Observations of Human-Made Space Objects

NASA Technical Reports Server (NTRS)

Buckalew, Brent; Abercromby, Kira; Lederer, Susan; Cowardin, Heather; Frith, James

2017-01-01

Presented here are the results of the United Kingdom Infrared Telescope (UKIRT) spectral observations of human-made space objects taken from 2014 to 2015. The data collected using the UKIRT 1-5 micron Imager Spectrometer (UIST) cover the wavelength range 0.7-2.5 micrometers. Overall, data were collected on 18 different orbiting objects at or near geosynchronous orbit (GEO). Two of the objects are controlled spacecraft, twelve are non-controlled spacecraft, one is a rocket body, and three are cataloged as debris. The remotely collected data are compared to the laboratory-collected reflectance data on typical spacecraft materials; thereby general materials are identified but not specific types. These results highlight the usefulness of observations in the infrared by focusing on features from hydrocarbons and silicon. The spacecraft, both the controlled and non-controlled, show distinct features due to the presence of solar panels whereas the rocket bodies do not. Signature variations between rocket bodies, due to the presence of various metals and paints on their surfaces, show a clear distinction from those objects with solar panels, demonstrating that one can distinguish most spacecraft from rocket bodies through infrared spectrum analysis. Finally, the debris pieces tend to show featureless, dark spectra. These results show that the laboratory data in its current state give well-correlated indications as to the nature of the surface materials on the objects. Further telescopic data collection and model updates to include noise, surface roughness, and material degradation are necessary to make better assessments of orbital object material types. A comparison conducted between objects observed previously with the NASA Infrared Telescope Facility (IRTF) shows similar materials and trends from the two telescopes and different times. However, based on the current state of the model, infrared spectroscopic data are adequate to classify objects in GEO as spacecraft, rocket bodies, or debris.

Heat current through an artificial Kondo impurity beyond linear response

NASA Astrophysics Data System (ADS)

Sierra, Miguel A.; Sánchez, David

2018-03-01

We investigate the heat current of a strongly interacting quantum dot in the presence of a voltage bias in the Kondo regime. Using the slave-boson mean-field theory, we discuss the behavior of the energy flow and the Joule heating. We find that both contributions to the heat current display interesting symmetry properties under reversal of the applied dc bias. We show that the symmetries arise from the behavior of the dot transmission function. Importantly, the transmission probability is a function of both energy and voltage. This allows us to analyze the heat current in the nonlinear regime of transport. We observe that nonlinearities appear already for voltages smaller than the Kondo temperature. Finally, we suggest to use the contact and electric symmetry coefficients as a way to measure pure energy currents.

Interfacial contributions of H2O2 decomposition-induced reaction current on mesoporous Pt/TiO2 systems

NASA Astrophysics Data System (ADS)

Ray, Nathan J.; Styrov, Vladislav V.; Karpov, Eduard G.

2017-12-01

We report on conversion of energy released due to chemical reactions into current for the decomposition of aqueous hydrogen peroxide solution on single phases Pt and TiO2, in addition to Pt and TiO2 simultaneously. We observe that H2O2 decomposition-induced current on TiO2 drastically overshadows the current generated by H2O2 decomposition on Pt. Photo-effects avoided, H2O2 decomposition was found to yield a conversion efficiency of 10-3 electrons generated per H2O2 molecule. Further understanding of chemical reaction-induced current shows promise as a metric with which the surface reaction may be monitored and could be greatly extended into the field of analytical chemistry.

Indirect resin composite restorations bonded to dentin using self-adhesive resin cements applied with an electric current-assisted method.

PubMed

Gotti, Valeria Bisinoto; Feitosa, Victor Pinheiro; Sauro, Salvatore; Correr-Sobrinho, Lourenço; Correr, Americo Bortolazzo

2014-10-01

To evaluate the effects of an electric current-assisted application on the bond strength and interfacial morphology of self-adhesive resin cements bonded to dentin. Indirect resin composite build-ups were luted to prepared dentin surfaces using two self-adhesive resin cements (RelyX Unicem and BisCem) and an ElectroBond device under 0, 20, or 40 μA electrical current. All specimens were submitted to microtensile bond strength test and to interfacial SEM analysis. The electric current-assisted application induced no change (P > 0.05) on the overall bond strength, although RelyX Unicem showed significantly higher bond strength (P < 0.05) than BisCem. Similarly, no differences were observed in terms of interfacial integrity when using the electrical current applicator.

Fibrinogen adsorption onto 316L stainless steel under polarized conditions.

PubMed

Gettens, Robert T T; Gilbert, Jeremy L

2008-04-01

Adsorption of the plasma protein fibrinogen onto electrically polarized 316L stainless steel was observed and quantified using both in situ and ex situ atomic force microscopy (AFM) techniques. Significant differences in fibrinogen adsorption were observed across voltages. Ex situ studies showed significantly lower area coverage (theta) and height of adsorbed Fb on cathodically polarized surfaces when compared to anodically polarized surfaces. Conformational differences in the protein may explain the distinctions in Fb surface area coverage (theta) and height between the anodic and cathodic cases. In situ studies showed significantly slower kinetics of Fb adsorption onto surfaces below -100 mV (vs. Ag/AgCl) compared to surfaces polarized above -100 mV. Electrochemical current density data showed large charge transfer processes (approximately 1 x 10(-5) to 1 x 10(-4) A/cm(2)) taking place on the 316L SS surfaces at voltages below -100 mV (vs. Ag/AgCl). These relatively large current densities point to flux of ionic species away from the surface as a major source of the reduction in adsorption kinetics rather than just hydrophilic or electrostatic effects. Copyright 2007 Wiley Periodicals, Inc.

Embedded binaries and their dense cores

NASA Astrophysics Data System (ADS)

Sadavoy, Sarah I.; Stahler, Steven W.

2017-08-01

We explore the relationship between young, embedded binaries and their parent cores, using observations within the Perseus Molecular Cloud. We combine recently published Very Large Array observations of young stars with core properties obtained from Submillimetre Common-User Bolometer Array 2 observations at 850 μm. Most embedded binary systems are found towards the centres of their parent cores, although several systems have components closer to the core edge. Wide binaries, defined as those systems with physical separations greater than 500 au, show a tendency to be aligned with the long axes of their parent cores, whereas tight binaries show no preferred orientation. We test a number of simple, evolutionary models to account for the observed populations of Class 0 and I sources, both single and binary. In the model that best explains the observations, all stars form initially as wide binaries. These binaries either break up into separate stars or else shrink into tighter orbits. Under the assumption that both stars remain embedded following binary break-up, we find a total star formation rate of 168 Myr-1. Alternatively, one star may be ejected from the dense core due to binary break-up. This latter assumption results in a star formation rate of 247 Myr-1. Both production rates are in satisfactory agreement with current estimates from other studies of Perseus. Future observations should be able to distinguish between these two possibilities. If our model continues to provide a good fit to other star-forming regions, then the mass fraction of dense cores that becomes stars is double what is currently believed.

Circulation on the Inner-Shelf of Long Bay, South Carolina: Vertical Current Variability and Evidence for Cross-Shelf Variation in Near-Bed Currents

NASA Astrophysics Data System (ADS)

Gutierrez, B. T.; Voulgaris, G.; Work, P. A.; Seim, H.; Warner, J. C.

2004-12-01

Cross-shelf variations of near-bed currents and variations in vertical flow were investigated on the inner shelf of Long Bay, South Carolina during the spring and fall of 2001. Current meters sampled near-bed currents at six locations as well as vertical current profiles at three of the sites. The observations showed that the tides accounted for approximately 45-66% of the flow variability. The dominant tidal component, the semi-diurnal constituent M2, exhibited tidal ellipse orientations that are increasingly aligned with the coast closer to the shore. The largest M2 current magnitudes were identified closest to shore and over the top of a sand shoal located 5.5 km offshore of Myrtle Beach. The remaining flow variability was associated with sub-tidal flows which respond to the passage of low-pressure systems across the region. These weather systems were characterized by periods of southwesterly winds in advance of low-pressure centers followed by northeasterly winds as the systems passed over the study area. When strong southwesterly winds persisted, surface flow was oriented approximately in the direction of the wind. At the same time near-bottom flows were also directed to the northeast in the direction of the wind except during periods of stratification when vertical current profiles suggest near-bed onshore flow. The stratified flows were observed mainly during the spring deployment. For periods of strong northeasterly winds, currents were directed alongshore to the southwest and exhibited little variation throughout the water column. These observations are consistent with recent field and modeling studies for the inner-shelf. Comparison of the near-bed flow measurements during the fall deployment revealed a cross-shore gradient in alongshore flow during periods of strong northeasterly winds. During these episodes flows at the offshore measurement stations were oriented in the direction of the wind, while flows closest to shore occurred in the opposite direction. These observations reveal 1) conditions which contribute to cross-shore transport and 2) the presence of an alongshore flow gradient which may affect sediment transport patterns during certain meteorological conditions.

Discharge current distribution in stratified soil under impulse discharge

NASA Astrophysics Data System (ADS)

Eniola Fajingbesi, Fawwaz; Shahida Midi, Nur; Elsheikh, Elsheikh M. A.; Hajar Yusoff, Siti

2017-06-01

The mobility of charge particles traversing a material defines its electrical properties. Soil (earth) have long been the universal grounding before and after the inception of active ground systems for electrical appliance purpose due to it semi-conductive properties. The soil can thus be modelled as a single material exhibiting semi-complex inductive-reactive impedance. Under impulse discharge such as lightning strikes to soil this property of soil could result in electric potential level fluctuation ranging from ground potential rise/fall to electromagnetic pulse coupling that could ultimately fail connected electrical appliance. In this work we have experimentally model the soil and lightning discharge using point to plane electrode setup to observe the current distribution characteristics at different soil conductivity [mS/m] range. The result presented from this research indicate above 5% shift in conductivity before and after discharge which is significant for consideration when dealing with grounding designs. The current distribution in soil have also be successfully observed and analysed from experimental result using mean current magnitude in relation to electrode distance and location, current density variation with depth all showing strong correlation with theoretical assumptions of a semi-complex impedance material.

Preliminary lightning observations over Greece

NASA Astrophysics Data System (ADS)

Chronis, Themis G.

2012-02-01

The first Precision Lightning Network, monitoring the Cloud-to-Ground (CG) lightning stroke activity over Greece and surrounding waters is operated and maintained by the Hellenic National Meteorological Service. This paper studies the regional (land/water interface), seasonal and diurnal variability of the CG strokes as a function of density, polarity and peak current. Additional investigation uniquely links the CG stroke current to sea surface salinity and cloud electrical capacitance. In brief, this study's major findings area as follows: (1) The seasonal maps of thunder days agree well with the regional climatic convective characteristics of the study area, (2) the CG diurnal variability is consistent with the global lightning activity observations over land and ocean, (3) the maxima of monthly averaged CG counts are located over land and water during typical summer and fall months respectively for both polarities, (4) CG peak currents show a distinct seasonality with larger currents during relatively colder months and smaller currents during summer months, and (5) strong linear trends between -CGs and sea surface salinity; (6) this trend is absent for +CGs data analysis of the employed database relate to the thunderstorm's RC constant and agrees with previous numerical modeling studies.

Simultaneous observations of traveling convection vortices: Ionosphere-thermosphere coupling

NASA Astrophysics Data System (ADS)

Kim, Hyomin; Lessard, Marc R.; Jones, Sarah L.; Lynch, Kristina A.; Fernandes, Philip A.; Aruliah, Anasuya L.; Engebretson, Mark J.; Moen, Jøran I.; Oksavik, Kjellmar; Yahnin, Alexander G.; Yeoman, Timothy K.

2017-05-01

We present simultaneous observations of magnetosphere-ionosphere-thermosphere coupling over Svalbard during a traveling convection vortex (TCV) event. Various spaceborne and ground-based instruments made coordinated measurements, including magnetometers, particle detectors, an all-sky camera, European Incoherent Scatter (EISCAT) Svalbard Radar, Super Dual Auroral Radar Network (SuperDARN), and SCANning Doppler Imager (SCANDI). The instruments recorded TCVs associated with a sudden change in solar wind dynamic pressure. The data display typical features of TCVs including vortical ionospheric convection patterns seen by the ground magnetometers and SuperDARN radars and auroral precipitation near the cusp observed by the all-sky camera. Simultaneously, electron and ion temperature enhancements with corresponding density increase from soft precipitation are also observed by the EISCAT Svalbard Radar. The ground magnetometers also detected electromagnetic ion cyclotron waves at the approximate time of the TCV arrival. This implies that they were generated by a temperature anisotropy resulting from a compression on the dayside magnetosphere. SCANDI data show a divergence in thermospheric winds during the TCVs, presumably due to thermospheric heating associated with the current closure linked to a field-aligned current system generated by the TCVs. We conclude that solar wind pressure impulse-related transient phenomena can affect even the upper atmospheric dynamics via current systems established by a magnetosphere-ionosphere-thermosphere coupling process.

Geminids 2012 - a spectacular show from Oman

NASA Astrophysics Data System (ADS)

Weiland, Thomas; Bettonvil, Felix

2014-02-01

The Geminids are the most reliable prominent meteor shower currently visible. They can be observed from the whole northern hemisphere and even low southern latitudes as well. Nevertheless, as the weather is often unfavourable in Central Europe during December, a six-day-long visual observing campaign was carried out from Oman in 2012. There observing conditions were nearly perfect, especially in the Rub al-Khali desert in the western part of the country. As a consequence, we managed to record more than 1800 Geminids within almost 45 hours of effective observing time. An impression of the campaign together with a summary of the results is given.

The electrons and ion characteristics of Saturn's plasma disk inside the Enceladus orbit

NASA Astrophysics Data System (ADS)

Morooka, Michiko; Wahlund, Jan-Erik; Ye, Sheng-Yi; Kurth, William; Persoon, Ann; Holmberg, Mika

2017-04-01

Cassini observations revealed that Saturn's icy moon Enceladus and surrounding E ring are the significant plasma source of the magnetosphere. However, the observations sometimes show the electron density enhancement even inside the Enceladus orbiting distance, 4RS. Further plasma contribution from the inner rings, the G and the F rings and main A ring are the natural candidate as an additional plasma source. The Cassini/RPWS Langmuir Probe (LP) measurement provides the characteristics of the electrons and ions independently in a cold dense plasma. The observations near the center of the E ring showed that the ion density being larger than the electron density, indicating that there is additional particle as a negative charge carrier. Those are the small nm and μm sized dust grains that are negatively charged by the electron attachments. The faint F and G rings, located at R=2RS and 3RS, consist of small grains and similar electron/ion density discrepancies can be expected. We will show different types of the LP observations when Cassini traveled the equator region of the plasma disk down to 3RS. One with the electron density increasing inside 4RS, and another with the electron density decreasing inside 4RS. During the orbit 016 (2005 doy-284/285), the electron density continued to increase toward the planet. On the other hand, the ion currents, the LP measured currents from the negative bias voltage, turn to decreasing inside 4RS, implying the density decrease of the ions. By comparing the observed LP ion current characteristics and the modeled values using the obtained electron density, we found that the characteristic ion mass can be several times larger than the water ions (AMU=18) that we expected in this region. During the orbit 015 (2005 doy-266/267), on the other hand, the LP observed sharp electron density drop near 3RS. The dust signals from the RPWS antenna showed the density enhancement of the μm sized grains coincide the electron density drop and we have estimated that the characteristic ion mass can exceed AMU=100. Throughout the whole Cassini observation near the equator inside 4RS, we didn't find the case with the ion densities larger than the electron densities as were found near the E ring and the Enceladus plume. We suggest that Saturn's plasmadisk inside the Enceladus orbit is dynamic in ion characteristics where the water molecules coagulate and grow into a small icy dust grains. In the presentation we discuss the relationship between the electron/ion density and the density of the nm and μm sized grains.

Ultrafast Mid-Infrared Dynamics in Quantum Cascade Lasers

DTIC Science & Technology

2010-01-01

bias . In Fig. 2(a), selected bias - dependent DT results at 30 K are displayed. For positive pump-probe delay, negative DT signals were observed at all...lifetime is weakly bias - dependent . Just below threshold, the photon density in the cavity becomes of the order of a few hundred, which is sufficient to...component, on the time scale of 2 ps, shows a characteristic inverse dependence on the bias current. We have observed this component in a variety of

Combining Remote and In Situ Observations with MHD models to Understand the Formation of the Slow Solar Wind

NASA Astrophysics Data System (ADS)

Viall, N. M.; Kepko, L.; Antiochos, S. K.; Lepri, S. T.; Vourlidas, A.; Linker, J.

2017-12-01

Connecting the structure and variability in the solar corona to the Heliosphere and solar wind is one of the main goals of Heliophysics and space weather research. The instrumentation and viewpoints of the Parker Solar Probe and Solar Orbiter missions will provide an unprecedented opportunity to combine remote sensing with in situ data to determine how the corona drives the Heliosphere, especially as it relates to the origin of the slow solar wind. We present analysis of STEREO coronagraph and heliospheric imager observations and of in situ ACE and Wind measurements that reveal an important connection between the dynamics of the corona and of the solar wind. We show observations of quasi-periodic release of plasma into the slow solar wind occurring throughout the corona - including regions away from the helmet streamer and heliospheric current sheet - and demonstrate that these observations place severe constraints on the origin of the slow solar wind. We build a comprehensive picture of the dynamic evolution by combining remote imaging data, in situ composition and magnetic connectivity information, and MHD models of the solar wind. Our results have critical implications for the magnetic topology involved in slow solar wind formation and magnetic reconnection dynamics. Crucially, this analysis pushes the limits of current instrument resolution and sensitivity, showing the enormous potential science to be accomplished with the Parker Solar Probe and Solar Orbiter missions.

Are weather models better than gridded observations for precipitation in the mountains? (Invited)

NASA Astrophysics Data System (ADS)

Gutmann, E. D.; Rasmussen, R.; Liu, C.; Ikeda, K.; Clark, M. P.; Brekke, L. D.; Arnold, J.; Raff, D. A.

2013-12-01

Mountain snowpack is a critical storage component in the water cycle, and it provides drinking water for tens of millions of people in the Western US alone. This water store is susceptible to climate change both because warming temperatures are likely to lead to earlier melt and a temporal shift of the hydrograph, and because changing atmospheric conditions are likely to change the precipitation patterns that produce the snowpack. Current measurements of snowfall in complex terrain are limited in number due in part to the logistics of installing equipment in complex terrain. We show that this limitation leads to statistical artifacts in gridded observations of current climate including errors in precipitation season totals of a factor of two or more, increases in wet day fraction, and decreases in storm intensity. In contrast, a high-resolution numerical weather model (WRF) is able to reproduce observed precipitation patterns, leading to confidence in its predictions for areas without measurements and new observations support this. Running WRF for a future climate scenario shows substantial changes in the spatial patterns of precipitation in the mountains related to the physics of hydrometeor production and detrainment that are not captured by statistical downscaling products. The stationarity in statistical downscaling products is likely to lead to important errors in our estimation of future precipitation in complex terrain.

Laboratory-based geoelectric monitoring of water infiltration in consolidated ground

NASA Astrophysics Data System (ADS)

Yang, Lining; Sun, Qiang; Yang, Haiping

2018-04-01

Infiltration usually plays a significant role in construction failures and transfer of contaminants. Therefore, it is very important to monitor underground water migration. In this study, a soil infiltration experiment was carried out using an indoor model test. The water infiltration characteristics were recorded and analyzed based on the response of the geoelectric field, including the primary field potential, self-potential, excitation current and apparent resistivity. The phreatic water surface and the infiltration velocity were determined. The inversion results were compared with direct observations. The results showed that the changes in the geoelectric field parameters explain the principles of groundwater flow. The infiltration velocity and the phreatic surface can be determined based on the primary field potential response and the excitation current. When the phreatic surface reached the location of the electrodes, the primary field potential and self-potential decreased rapidly whereas the excitation current increased rapidly. The height of the phreatic surface and the infiltration time exhibited a linear relationship for both the observation data and the calculations of the excitation current. The apparent resistivity described the infiltration status in the soil and tracked the phreatic surface accurately.

Analysis of Dark Current in BRITE Nanostellite CCD Sensors †

PubMed Central

Popowicz, Adam

2018-01-01

The BRightest Target Explorer (BRITE) is the pioneering nanosatellite mission dedicated for photometric observations of the brightest stars in the sky. The BRITE charge coupled device (CCD) sensors are poorly shielded against extensive flux of energetic particles which constantly induce defects in the silicon lattice. In this paper we investigate the temporal evolution of the generation of the dark current in the BRITE CCDs over almost four years after launch. Utilizing several steps of image processing and employing normalization of the results, it was possible to obtain useful information about the progress of thermal activity in the sensors. The outcomes show a clear and consistent linear increase of induced damage despite the fact that only about 0.14% of CCD pixels were probed. By performing the analysis of temperature dependencies of the dark current, we identified the observed defects as phosphorus-vacancy (PV) pairs, which are common in proton irradiated CCD matrices. Moreover, the Meyer-Neldel empirical rule was confirmed in our dark current data, yielding EMN=24.8 meV for proton-induced PV defects. PMID:29415471

Differences observed in the surface morphology and microstructure of Ni-Fe-Cu ternary thin films electrochemically deposited at low and high applied current densities

NASA Astrophysics Data System (ADS)

Sarac, U.; Kaya, M.; Baykul, M. C.

2016-10-01

In this research, nanocrystalline Ni-Fe-Cu ternary thin films using electrochemical deposition technique were produced at low and high applied current densities onto Indium Tin Oxide (ITO) coated conducting glass substrates. Change of surface morphology and microstructural properties of the films were investigated. Energy dispersive X-ray spectroscopy (EDX) measurements showed that the Ni-Fe-Cu ternary thin films exhibit anomalous codeposition behaviour during the electrochemical deposition process. From the X-ray diffraction (XRD) analyses, it was revealed that there are two segregated phases such as Cu- rich and Ni-rich within the films. The crystallographic structure of the films was face-centered cubic (FCC). It was also observed that the film has lower lattice micro-strain and higher texture degree at high applied current density. Scanning electron microscopy (SEM) studies revealed that the films have rounded shape particles on the base part and cauliflower-like structures on the upper part. The film electrodeposited at high current density had considerably smaller rounded shape particles and cauliflower-like structures. From the atomic force microscopy (AFM) analyses, it was shown that the film deposited at high current density has smaller particle size and surface roughness than the film grown at low current density.

In Vitro Assessment of Electric Currents Increasing the Effectiveness of Vancomycin Against Staphylococcus epidermidis Biofilms.

PubMed

Haddad, Peter A; Mah, Thien-Fah; Mussivand, Tofy

2016-08-01

Biofilms are communities of bacteria that can cause infections which are resistant to the immune system and antimicrobial treatments, posing a significant threat for patients with implantable and indwelling medical devices. The purpose of our research was to determine if utilizing specific parameters for electric currents in conjunction with antibiotics could effectively treat a highly resistant biofilm. Our study evaluated the impact of 16 μg/mL of vancomycin with or without 22 or 333 μA of direct electric current (DC) generated by stainless steel electrodes against 24-, 48-, and 72-h-old Staphylococcus epidermidis biofilms formed on titanium coupons. An increase in effectiveness of vancomycin was observed with the combination of 333 μA of electric current against 48-h-old biofilms (P value = 0.01) as well as in combination with 22 μA of electric current against 72-h-old biofilms (P value = 0.04); 333 μA of electric current showed the most significant impact on the effectiveness of vancomycin against S. epidermidis biofilms demonstrating a bioelectric effect previously not observed against this strain of bacteria. © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Turbulent structures in cylindrical density currents in a rotating frame of reference

NASA Astrophysics Data System (ADS)

Salinas, Jorge S.; Cantero, Mariano I.; Dari, Enzo A.; Bonometti, Thomas

2018-06-01

Gravity currents are flows generated by the action of gravity on fluids with different densities. In some geophysical applications, modeling such flows makes it necessary to account for rotating effects, modifying the dynamics of the flow. While previous works on rotating stratified flows focused on currents of large Coriolis number, the present work focuses on flows with small Coriolis numbers (i.e. moderate-to-large Rossby numbers). In this work, cylindrical rotating gravity currents are investigated by means of highly resolved simulations. A brief analysis of the mean flow evolution to the final state is presented to provide a complete picture of the flow dynamics. The numerical results, showing the well-known oscillatory behavior of the flow (inertial waves) and a final state lens shape (geostrophic adjustment), are in good agreement with experimental observations and theoretical models. The turbulent structures in the flow are visualized and described using, among others, a stereoscopic visualization and videos as supplementary material. In particular, the structure of the lobes and clefts at the front of the current is presented in association to local turbulent structures. In rotating gravity currents, the vortices observed at the lobes front are not of hairpin type but are rather of Kelvin-Helmholtz type.

Electroosmotic pump performance is affected by concentration polarizations of both electrodes and pump

PubMed Central

Suss, Matthew E.; Mani, Ali; Zangle, Thomas A.; Santiago, Juan G.

2010-01-01

Current methods of optimizing electroosmotic (EO) pump performance include reducing pore diameter and reducing ionic strength of the pumped electrolyte. However, these approaches each increase the fraction of total ionic current carried by diffuse electric double layer (EDL) counterions. When this fraction becomes significant, concentration polarization (CP) effects become important, and traditional EO pump models are no longer valid. We here report on the first simultaneous concentration field measurements, pH visualizations, flow rate, and voltage measurements on such systems. Together, these measurements elucidate key parameters affecting EO pump performance in the CP dominated regime. Concentration field visualizations show propagating CP enrichment and depletion fronts sourced by our pump substrate and traveling at order mm/min velocities through millimeter-scale channels connected serially to our pump. The observed propagation in millimeter-scale channels is not explained by current propagating CP models. Additionally, visualizations show that CP fronts are sourced by and propagate from the electrodes of our system, and then interact with the EO pump-generated CP zones. With pH visualizations, we directly detect that electrolyte properties vary sharply across the anode enrichment front interface. Our observations lead us to hypothesize possible mechanisms for the propagation of both pump- and electrode-sourced CP zones. Lastly, our experiments show the dynamics associated with the interaction of electrode and membrane CP fronts, and we describe the effect of these phenomena on EO pump flow rates and applied voltages under galvanostatic conditions. PMID:21516230

Forcing and variability of nonstationary rip currents

USGS Publications Warehouse

Long, Joseph W.; H.T. Özkan-Haller,

2016-01-01

Surface wave transformation and the resulting nearshore circulation along a section of coast with strong alongshore bathymetric gradients outside the surf zone are modeled for a consecutive 4 week time period. The modeled hydrodynamics are compared to in situ measurements of waves and currents collected during the Nearshore Canyon Experiment and indicate that for the entire range of observed conditions, the model performance is similar to other studies along this stretch of coast. Strong alongshore wave height gradients generate rip currents that are observed by remote sensing data and predicted qualitatively well by the numerical model. Previous studies at this site have used idealized scenarios to link the rip current locations to undulations in the offshore bathymetry but do not explain the dichotomy between permanent offshore bathymetric features and intermittent rip current development. Model results from the month‐long simulation are used to track the formation and location of rip currents using hourly statistics, and results show that the direction of the incoming wave energy strongly controls whether rip currents form. In particular, most of the offshore wave spectra were bimodal and we find that the ratio of energy contained in each mode dictates rip current development, and the alongshore rip current position is controlled by the incident wave period. Additionally, model simulations performed with and without updating the nearshore morphology yield no significant change in the accuracy of the predicted surf zone hydrodyanmics indicating that the large‐scale offshore features (e.g., submarine canyon) predominately control the nearshore wave‐circulation system.

Utilizing Peer Observation as a Professional Development Tool to Learn in Context

ERIC Educational Resources Information Center

Hirsch, Linda J.

2011-01-01

De-contextualized professional development is the common route taken by school districts to addresses pedagogical skills and address change within an educational organization. Research suggests that the current process of professional development activities is limited if not ineffective. Research shows that another model of professional…

Controlling charge current through a DNA based molecular transistor

NASA Astrophysics Data System (ADS)

Behnia, S.; Fathizadeh, S.; Ziaei, J.

2017-01-01

Molecular electronics is complementary to silicon-based electronics and may induce electronic functions which are difficult to obtain with conventional technology. We have considered a DNA based molecular transistor and study its transport properties. The appropriate DNA sequence as a central chain in molecular transistor and the functional interval for applied voltages is obtained. I-V characteristic diagram shows the rectifier behavior as well as the negative differential resistance phenomenon of DNA transistor. We have observed the nearly periodic behavior in the current flowing through DNA. It is reported that there is a critical gate voltage for each applied bias which above it, the electrical current is always positive.

Tunneling current spectroscopy of a nanostructure junction involving multiple energy levels.

PubMed

Kuo, David M-T; Chang, Yia-Chung

2007-08-24

A multilevel Anderson model is employed to simulate the system of a nanostructure tunnel junction with any number of one-particle energy levels. The tunneling current, including both shell-tunneling and shell-filling cases, is theoretically investigated via the nonequilibrium Green's function method. We obtain a closed form for the spectral function, which is used to analyze the complicated tunneling current spectra of a quantum dot or molecule embedded in a double-barrier junction. We also show that negative differential conductance can be observed in a quantum dot tunnel junction when the Coulomb interactions with neighboring quantum dots are taken into account.

Electron Cooling and Isotropization during Magnetotail Current Sheet Thinning: Implications for Parallel Electric Fields

NASA Astrophysics Data System (ADS)

Lu, San; Artemyev, A. V.; Angelopoulos, V.

2017-11-01

Magnetotail current sheet thinning is a distinctive feature of substorm growth phase, during which magnetic energy is stored in the magnetospheric lobes. Investigation of charged particle dynamics in such thinning current sheets is believed to be important for understanding the substorm energy storage and the current sheet destabilization responsible for substorm expansion phase onset. We use Time History of Events and Macroscale Interactions during Substorms (THEMIS) B and C observations in 2008 and 2009 at 18 - 25 RE to show that during magnetotail current sheet thinning, the electron temperature decreases (cooling), and the parallel temperature decreases faster than the perpendicular temperature, leading to a decrease of the initially strong electron temperature anisotropy (isotropization). This isotropization cannot be explained by pure adiabatic cooling or by pitch angle scattering. We use test particle simulations to explore the mechanism responsible for the cooling and isotropization. We find that during the thinning, a fast decrease of a parallel electric field (directed toward the Earth) can speed up the electron parallel cooling, causing it to exceed the rate of perpendicular cooling, and thus lead to isotropization, consistent with observation. If the parallel electric field is too small or does not change fast enough, the electron parallel cooling is slower than the perpendicular cooling, so the parallel electron anisotropy grows, contrary to observation. The same isotropization can also be accomplished by an increasing parallel electric field directed toward the equatorial plane. Our study reveals the existence of a large-scale parallel electric field, which plays an important role in magnetotail particle dynamics during the current sheet thinning process.

Very rare outburst of the symbiotic variable AG Peg

NASA Astrophysics Data System (ADS)

Waagen, Elizabeth O.

2015-06-01

The symbiotic variable AG Peg is in outburst, the first one observed since its only known outburst, which occurred in 1860-1870. Currently at visual/V magnitude 7.2 (B=7.8), it is an excellent target for visual, PEP, CCD, and DSLR observers and spectroscopists. The current outburst began after 2015 May 27 UT (T. Markham, Leek, Staffordshire, England, from the BAAVSS online database) and was underway by June 13.90 (A. Kosa-Kiss, Salonta, Romania). AG Peg has a very interesting history. Regarding the 1860-1870 outburst, data collected by E. Zinner (Merrill, 1959, S&T, 18, 9, 490) show AG Peg slowly brightening from visual magnitude 9.2 in 1821 to 8.0 in 1855, then at 6.2 in 1860 and brightening to 6.0 in 1870, then in decline at 6.8 by 1903, and continuing to decline slowly ( 6.9 in 1907, 8.0 in 1920, 8.3 in 1940). Observations in the AAVSO International Database since July 1941 show that the decline has continued without interruption from an average magnitude of 7.7 to an average magnitude of 8.8-9.0 by mid-January 2015. The AAVSO data since 1941 also show the periodic 0.4-magnitude variations ( 825 days) that have been present since the 1920s. Thus, after taking about 10 years to brighten from its minimum magnitude of about 9 to its maximum magnitude of 6.0, and then fading gradually over 140-145 years, AG Peg is now in outburst again. There are no observations of the 1860-1870 outburst that show the outburst's beginning. This time, however, in 2015, the opportunity is here to follow the outburst itself closely and learn just what this system does during outburst. Observations in all bands and visual observations are strongly encouraged. AG Peg is bright enough to be a very good PEP target. For spectroscopists, AG Peg has an extremely complex spectrum that undergoes substantial changes and would make a very interesting target. Finder charts with sequence may be created using the AAVSO Variable Star Plotter (https://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. Precise observing instructions and other details are given in the full Alert Notice.

Determination of the Flux-distance Relationship for Pulsars in the Parkes Multibeam Survey: Violation of the Inverse Square Law Gives Support for a New Model of Pulsar Emission

NASA Astrophysics Data System (ADS)

Singleton, John; Sengupta, P.; Middleditch, J.; Graves, T.; Schmidt, A.; Perez, M.; Ardavan, H.; Ardavan, A.; Fasel, J.

2010-01-01

Soon after the discovery of pulsars, it was realized that their unique periodic emissions must be associated with a source that rotates. Despite this insight and forty one years of subsequent effort, a detailed understanding of the pulsar emission mechanism has proved elusive. Here, using data for 983 pulsars taken from the Parkes Multibeam Survey, we show that their fluxes at 1400 MHz (S(1400)) decay with distance d according to a non-standard power-law; we suggest that S(1400) is proportional to 1/d. This distance dependence is revealed by two independent statistical techniques, (i) the Maximum Likelihood Method and (ii) analysis of the distance evolution of the cumulative distribution functions of pulsar flux. Moreover, the derived power law is valid for both millisecond and longer-period pulsars, and is robust against possible errors in the NE2001 method for obtaining pulsar distances from dispersion measure. This observation provides strong support for a mechanism of pulsar emission due to superluminal (faster than light in vacuo) polarization currents. Such superluminal polarization currents have been extensively studied by Bolotovskii, Ginzburg and others, who showed both that they do not violate Special Relativity (since the oppositely-charged particles that make them move relatively slowly) and that they form a bona-fide source term in Maxwell's equations. Subsequently, emission of radiation by superluminal polarization currents was demonstrated in laboratory experiments. By extending these ideas to a superluminal polarization current whose distribution pattern follows a circular orbit, we can explain the 1/d dependence of the flux suggested by our analyses of the observational data. In addition, we show that a model of pulsar emission due to such a rotating superluminal polarization current can predict the the frequency spectrum of nine pulsars over 16 orders of magnitude of frequency quantitatively. This work is supported by the DoE LDRD program at Los Alamos.

Alfven resonance mode conversion in the Phaedrus-T current drive experiments: Modelling and density fluctuations measurements

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

Vukovic, M.; Harper, M.; Breun, R.

1995-12-31

Current drive experiments on the Phaedrus-T tokamak performed with a low field side two-strap fast wave antenna at frequencies below {omega}{sub cH} show loop volt drops of up to 30% with strap phasing (0, {pi}/2). RF induced density fluctuations in the plasma core have also been observed with a microwave reflectometer. It is believed that they are caused by kinetic Alfven waves generated by mode conversion of fast waves at the Alfven resonance. Correlation of the observed density fluctuations with the magnitude of the {Delta}V{sub loop} suggest that the {Delta}V{sub loop} is attributable to current drive/heating due to mode convertedmore » kinetic Alfven waves. The toroidal cold plasma wave code LION is used to model the Alfven resonance mode conversion surfaces in the experiments while the cylindrical hot plasma kinetic wave code ISMENE is used to model the behavior of kinetic Alfven waves at the Alfven resonance location. Initial results obtained from limited density, magnetic field, antenna phase, and impurity scans show good agreement between the RF induced density fluctuations and the predicted behavior of the kinetic Alfven waves. Detailed comparisons between the density fluctuations and the code predictions are presented.« less

Limacina helicina shell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem

PubMed Central

Bednaršek, N.; Feely, R. A.; Reum, J. C. P.; Peterson, B.; Menkel, J.; Alin, S. R.; Hales, B.

2014-01-01

Few studies to date have demonstrated widespread biological impacts of ocean acidification (OA) under conditions currently found in the natural environment. From a combined survey of physical and chemical water properties and biological sampling along the Washington–Oregon–California coast in August 2011, we show that large portions of the shelf waters are corrosive to pteropods in the natural environment. We show a strong positive correlation between the proportion of pteropod individuals with severe shell dissolution damage and the percentage of undersaturated water in the top 100 m with respect to aragonite. We found 53% of onshore individuals and 24% of offshore individuals on average to have severe dissolution damage. Relative to pre-industrial CO2 concentrations, the extent of undersaturated waters in the top 100 m of the water column has increased over sixfold along the California Current Ecosystem (CCE). We estimate that the incidence of severe pteropod shell dissolution owing to anthropogenic OA has doubled in near shore habitats since pre-industrial conditions across this region and is on track to triple by 2050. These results demonstrate that habitat suitability for pteropods in the coastal CCE is declining. The observed impacts represent a baseline for future observations towards understanding broader scale OA effects. PMID:24789895

Hemispheric Patterns in Electric Current Helicity of Solar Magnetic Fields During Solar Cycle 24: Results from SOLIS, SDO and Hinode

NASA Astrophysics Data System (ADS)

Gusain, S.

2017-12-01

We study the hemispheric patterns in electric current helicity distribution on the Sun. Magnetic field vector in the photosphere is now routinely measured by variety of instruments. SOLIS/VSM of NSO observes full disk Stokes spectra in photospheric lines which are used to derive vector magnetograms. Hinode SP is a space based spectropolarimeter which has the same observable as SOLIS albeit with limited field-of-view (FOV) but high spatial resolution. SDO/HMI derives vector magnetograms from full disk Stokes measurements, with rather limited spectral resolution, from space in a different photospheric line. Further, these datasets now exist for several years. SOLIS/VSM from 2003, Hinode SP from 2006, and SDO HMI since 2010. Using these time series of vector magnetograms we compute the electric current density in active regions during solar cycle 24 and study the hemispheric distributions. Many studies show that the helicity parameters and proxies show a strong hemispheric bias, such that Northern hemisphere has preferentially negative and southern positive helicity, respectively. We will confirm these results for cycle 24 from three different datasets and evaluate the statistical significance of the hemispheric bias. Further, we discuss the solar cycle variation in the hemispheric helicity pattern during cycle 24 and discuss its implications in terms of solar dynamo models.

Study of Ag/RGO/ITO sandwich structure for resistive switching behavior deposited on plastic substrate

NASA Astrophysics Data System (ADS)

Vartak, Rajdeep; Rag, Adarsh; De, Shounak; Bhat, Somashekhara

2018-05-01

We report here the use of facile and environmentally benign way synthesized reduced graphene oxide (RGO) for low-voltage non-volatile memory device as charge storing element. The RGO solutions have been synthesized using electrochemical exfoliation of battery electrode. The solution processed based RGO solution is suitable for large area and low-cost processing on plastic substrate. Room-temperature current-voltage characterisation has been carried out in Ag/RGO/ITO PET sandwich configuration to study the type of trap distribution. It is observed that in the low-voltage sweep, ohmic current is the main mechanism of current flow and trap filled/assisted conduction is observed at high-sweep voltage region. The Ag/RGO/ITO PET sandwich structure showed bipolar resistive switching behavior. These mechanisms can be analyzed based on oxygen availability and vacancies in the RGO giving rise to continuous least resistive path (conductive) and high resistance path along the structure. An Ag/RGO/ITO arrangement demonstrates long retention time with low operating voltage, low set/reset voltage, good ON/OFF ratio of 103 (switching transition between lower resistance state and higher resistance state and decent switching performance. The RGO memory showed decent results with an almost negligible degradation in switching properties which can be used for low-voltage and low-cost advanced flexible electronics.

Limacina helicina shell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem.

PubMed

Bednaršek, N; Feely, R A; Reum, J C P; Peterson, B; Menkel, J; Alin, S R; Hales, B

2014-06-22

Few studies to date have demonstrated widespread biological impacts of ocean acidification (OA) under conditions currently found in the natural environment. From a combined survey of physical and chemical water properties and biological sampling along the Washington-Oregon-California coast in August 2011, we show that large portions of the shelf waters are corrosive to pteropods in the natural environment. We show a strong positive correlation between the proportion of pteropod individuals with severe shell dissolution damage and the percentage of undersaturated water in the top 100 m with respect to aragonite. We found 53% of onshore individuals and 24% of offshore individuals on average to have severe dissolution damage. Relative to pre-industrial CO2 concentrations, the extent of undersaturated waters in the top 100 m of the water column has increased over sixfold along the California Current Ecosystem (CCE). We estimate that the incidence of severe pteropod shell dissolution owing to anthropogenic OA has doubled in near shore habitats since pre-industrial conditions across this region and is on track to triple by 2050. These results demonstrate that habitat suitability for pteropods in the coastal CCE is declining. The observed impacts represent a baseline for future observations towards understanding broader scale OA effects.

Van Allen Probes observations of drift-bounce resonance and energy transfer between energetic ring current protons and poloidal Pc4 wave

NASA Astrophysics Data System (ADS)

Oimatsu, S.; Masahito, N.; Takahashi, K.; Yamamoto, K.; Keika, K.; Kletzing, C.; MacDowall, R. J.; Smith, C.; Mitchell, D. G.

2017-12-01

Poloidal Pc4 wave and proton flux oscillation due to the drift-bounce resonance are observed in the inner magnetosphere on the dayside near the magnetic equator by the Van Allen Probes spacecraft on 2 March 2014. The flux modulation is observed in the energy range of 67.0 keV to 268.8 keV with the same frequency of poloidal Pc4 wave. We estimate the resonant energy to be 120 keV for pitch angle (α) of 20º-40º or 140º-160º, and 170-180 keV for α=40º-60º or 120º-140º. The drift-bounce resonance theory gives the resonant energy of 110-120 keV, which is consistent with the observation for small α (or large α when α≥90º), but slightly higher than the observation for large α (or small α when α≥90º). We consider that this discrepancy of the resonant energy is due to the drift shell splitting. In order to examine the direction of energy flow between protons and the wave, we calculate the sign of the gradient of proton phase space density (df/dW) in both outbound and inbound paths. Results showed positive gradient in both paths, which means that the energy is transferred from the protons to the wave. During the appearance of poloidal Pc4 wave, the Dst* index shows a sudden increase of 6.7 nT. We estimate the total energy loss of the ring current from the recovery of the Dst* index and the variation of proton flux by the drift-bounce resonance. The estimated energy loss is almost comparable for both cases. Therefore, we suggest that the energy transfer from the ring current protons to the wave via the drift-bounce resonance cause the increase of Dst* index.

Measurement and analysis of time-domain characteristics of corona-generated radio interference from a single positive corona source

NASA Astrophysics Data System (ADS)

Li, Xuebao; Li, Dayong; Chen, Bo; Cui, Xiang; Lu, Tiebing; Li, Yinfei

2018-04-01

The corona-generated electromagnetic interference commonly known as radio interference (RI) has become a limiting factor for the design of high voltage direct current transmission lines. In this paper, a time-domain measurement system is developed to measure the time-domain characteristics of corona-generated RI from a single corona source under a positive corona source. In the experiments, the corona current pulses are synchronously measured through coupling capacitors. The one-to-one relationship between the corona current pulse and measured RI voltage pulse is observed. The statistical characteristics of pulse parameters are analyzed, and the correlations between the corona current pulse and RI voltage pulse in the time-domain and frequency-domain are analyzed. Depending on the measured corona current pulses, the time-domain waveform of corona-generated RI is calculated on the basis of the propagation model of corona current on the conductor, the dipolar model for electric field calculation, and the antenna model for inducing voltage calculation. The well matched results between measured and simulated waveforms of RI voltage can show the validity of the measurement and calculation method presented in this paper, which also further show the close correlation between corona current and corona-generated RI.

Geomorphology and sediment transport on a submerged back-reef sand apron: One Tree Reef, Great Barrier Reef

NASA Astrophysics Data System (ADS)

Harris, Daniel L.; Vila-Concejo, Ana; Webster, Jody M.

2014-10-01

Back-reef sand aprons are conspicuous and dynamic sedimentary features in coral reef systems. The development of these features influences the evolution and defines the maturity of coral reefs. However, the hydrodynamic processes that drive changes on sand aprons are poorly understood with only a few studies directly assessing sediment entrainment and transport. Current and wave conditions on a back-reef sand apron were measured during this study and a digital elevation model was developed through topographic and bathymetric surveying of the sand apron, reef flats and lagoon. The current and wave processes that may entrain and transport sediment were assessed using second order small amplitude (Stokes) wave theory and Shields equations. The morphodynamic interactions between current flow and geomorphology were also examined. The results showed that sediment transport occurs under modal hydrodynamic conditions with waves the main force entraining sediment rather than average currents. A morphodynamic relationship between current flow and geomorphology was also observed with current flow primarily towards the lagoon in shallow areas of the sand apron and deeper channel-like areas directing current off the sand apron towards the lagoon or the reef crest. These results show that the short-term mutual interaction of hydrodynamics and geomorphology in coral reefs can result in morphodynamic equilibrium.

Electric current variations and 3D magnetic configuration of coronal jets

NASA Astrophysics Data System (ADS)

Schmieder, Brigitte; Harra, Louise K.; Aulanier, Guillaume; Guo, Yang; Demoulin, Pascal; Moreno-Insertis, Fernando, , Prof

Coronal jets (EUV) were observed by SDO/AIA on September 17, 2010. HMI and THEMIS measured the vector magnetic field from which we derived the magnetic flux, the phostospheric velocity and the vertical electric current. The magnetic configuration was computed with a non linear force-free approach. The phostospheric current pattern of the recurrent jets were associated with the quasi-separatrix layers deduced from the magnetic extrapolation. The large twisted near-by Eiffel-tower-shape jet was also caused by reconnection in current layers containing a null point. This jet cannot be classified precisely within either the quiescent or the blowout jet types. We will show the importance of the existence of bald patches in the low atmosphere

Cross-Cultural Agreement in Facial Attractiveness Preferences: The Role of Ethnicity and Gender

PubMed Central

Coetzee, Vinet; Greeff, Jaco M.; Stephen, Ian D.; Perrett, David I.

2014-01-01

Previous work showed high agreement in facial attractiveness preferences within and across cultures. The aims of the current study were twofold. First, we tested cross-cultural agreement in the attractiveness judgements of White Scottish and Black South African students for own- and other-ethnicity faces. Results showed significant agreement between White Scottish and Black South African observers' attractiveness judgements, providing further evidence of strong cross-cultural agreement in facial attractiveness preferences. Second, we tested whether cross-cultural agreement is influenced by the ethnicity and/or the gender of the target group. White Scottish and Black South African observers showed significantly higher agreement for Scottish than for African faces, presumably because both groups are familiar with White European facial features, but the Scottish group are less familiar with Black African facial features. Further work investigating this discordance in cross-cultural attractiveness preferences for African faces show that Black South African observers rely more heavily on colour cues when judging African female faces for attractiveness, while White Scottish observers rely more heavily on shape cues. Results also show higher cross-cultural agreement for female, compared to male faces, albeit not significantly higher. The findings shed new light on the factors that influence cross-cultural agreement in attractiveness preferences. PMID:24988325

Cross-cultural agreement in facial attractiveness preferences: the role of ethnicity and gender.

PubMed

Coetzee, Vinet; Greeff, Jaco M; Stephen, Ian D; Perrett, David I

2014-01-01

Previous work showed high agreement in facial attractiveness preferences within and across cultures. The aims of the current study were twofold. First, we tested cross-cultural agreement in the attractiveness judgements of White Scottish and Black South African students for own- and other-ethnicity faces. Results showed significant agreement between White Scottish and Black South African observers' attractiveness judgements, providing further evidence of strong cross-cultural agreement in facial attractiveness preferences. Second, we tested whether cross-cultural agreement is influenced by the ethnicity and/or the gender of the target group. White Scottish and Black South African observers showed significantly higher agreement for Scottish than for African faces, presumably because both groups are familiar with White European facial features, but the Scottish group are less familiar with Black African facial features. Further work investigating this discordance in cross-cultural attractiveness preferences for African faces show that Black South African observers rely more heavily on colour cues when judging African female faces for attractiveness, while White Scottish observers rely more heavily on shape cues. Results also show higher cross-cultural agreement for female, compared to male faces, albeit not significantly higher. The findings shed new light on the factors that influence cross-cultural agreement in attractiveness preferences.

THE EVOLUTION OF THE ELECTRIC CURRENT DURING THE FORMATION AND ERUPTION OF ACTIVE-REGION FILAMENTS

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

Wang, Jincheng; Yan, Xiaoli; Qu, Zhongquan

We present a comprehensive study of the electric current related to the formation and eruption of active region filaments in NOAA AR 11884. The vertical current on the solar surface was investigated by using vector magnetograms (VMs) observed by HMI on board the Solar Dynamics Observatory. To obtain the electric current along the filament's axis, we reconstructed the magnetic fields above the photosphere by using nonlinear force-free field extrapolation based on photospheric VMs. Spatio-temporal evolutions of the vertical current on the photospheric surface and the horizontal current along the filament's axis were studied during the long-term evolution and eruption-related period,more » respectively. The results show that the vertical currents of the entire active region behaved with a decreasing trend and the magnetic fields also kept decreasing during the long-term evolution. For the eruption-related evolution, the mean transverse field strengths decreased before two eruptions and increased sharply after two eruptions in the vicinity of the polarity inversion lines underneath the filament. The related vertical current showed different behaviors in two of the eruptions. On the other hand, a very interesting feature was found: opposite horizontal currents with respect to the current of the filament's axis appeared and increased under the filament before the eruptions and disappeared after the eruptions. We suggest that these opposite currents were carried by the new flux emerging from the photosphere bottom and might be the trigger mechanism for these filament eruptions.« less

Inception of Snapover and Gas Induced Glow Discharges

NASA Technical Reports Server (NTRS)

Galofaro, J. T.; Vayner, B. V.; Degroot, W. A.; Ferguson, D. C.; Thomson, C. D.; Dennison, J. R.; Davies, R. E.

2000-01-01

Ground based experiments of the snapover phenomenon were conducted in the large vertical simulation chamber at the Glenn Research Center (GRC) Plasma Interaction Facility (PIF). Two Penning sources provided both argon and xenon plasmas for the experiments. The sources were used to simulate a variety of ionospheric densities pertaining to a spacecraft in a Low Earth Orbital (LEO) environment. Secondary electron emission is believed responsible for dielectric surface charging, and all subsequent snapover phenomena observed. Voltage sweeps of conductor potentials versus collected current were recorded in order to examine the specific charging history of each sample. The average time constant for sample charging was estimated between 25 and 50 seconds for all samples. It appears that current drops off by approximately a factor of 3 over the charging time of the sample. All samples charged in the forward and reverse bias directions, demonstrated hysteresis. Current jumps were only observed in the forward or positive swept voltage direction. There is large dispersion in tile critical snapover potential when repeating sweeps on any one sample. The current ratio for the first snapover region jumps between 2 and 4.6 times, with a standard deviation less than 1.6. Two of the samples showed even larger current ratios. It is believed the second large snapover region is due to sample outgassing. Under certain preset conditions, namely at the higher neutral gas background pressures, a perceptible blue-green glow was observed around the conductor. The glow is believed to be a result of secondary electrons undergoing collisions with an expelled tenuous cloud of gas, that is outgassed from the sample. Spectroscopic measurements of the glow discharge were made in an attempt to identify specific lines contributing to the observed glow.

Kinetic Electric Field Signatures Associated with Magnetic Turbulence and Their Impact on Space Plasma Environments

NASA Astrophysics Data System (ADS)

Goodrich, K. A.

Magnetic turbulence is a universal phenomenon that occurs in space plasma physics, the small-scale processes of which is not well understood. This thesis presents on observational analysis of kinetic electric field signatures associated with magnetic turbulence, in an attempt to examine its underlying microphysics. Such kinetic signatures include small-scale magnetic holes, double layers, and phase-space holes. The first and second parts of this thesis presents observations of small-scale magnetic holes, observed depressions in total magnetic field strength with spatial widths on the order of or less than the ion Larmor radius, in the near-Earth plasmasheet. Here I demonstrate electric field signatures associated small-scale magnetic holes are consistent with the presence of electron Hall currents, currents oriented perpendicularly to the magnetic field. Further investigation of these fields indicates that the Hall electron current is primarily responsible for the depletion of | B| associated with small-scale magnetic holes. I then present evidence that suggests these currents can descend to smaller spatial scales, indicating they participate in a turbulent cascade to smaller scales, a link that has not been observable suggested until now. The last part of this thesis investigates the presence of double layers and phase-space holes in a magnetically turbulent region of the terrestrial bow shock. In this part, I present evidence that these same signatures can be generated via field-aligned currents generated by strong magnetic fluctuations. I also show that double layers and phase-space holes, embedded within localized nonlinear ion acoustic waves, correlate with localized electron heating and possible ion deceleration, indicating they play a role in turbulent dissipation of kinetic to thermal energy. This thesis clearly demonstrates that energy dissipation in turbulent plasma is closely linked to the small-scale electric field environment.

Local wind forcing of the Monterey Bay area inner shelf

USGS Publications Warehouse

Drake, P.T.; McManus, M.A.; Storlazzi, C.D.

2005-01-01

Wind forcing and the seasonal cycles of temperature and currents were investigated on the inner shelf of the Monterey Bay area of the California coast for 460 days, from June 2001 to September 2002. Temperature measurements spanned an approximate 100 km stretch of coastline from a bluff just north of Monterey Bay south to Point Sur. Inner shelf currents were measured at two sites near the bay's northern shore. Seasonal temperature variations were consistent with previous observations from the central California shelf. During the spring, summer and fall, a seasonal mean alongshore current was observed flowing northwestward in the northern bay, in direct opposition to a southeastward wind stress. A barotropic alongshore pressure gradient, potentially driving the northwestward flow, was needed to balance the alongshore momentum equation. With the exception of the winter season, vertical profiles of mean cross-shore currents were consistent with two-dimensional upwelling and existing observations from upwelling regions with poleward subsurface flow. At periods of 15-60 days, temperature fluctuations were coherent both throughout the domain and with the regional wind field. Remote wind forcing was minimal. During the spring upwelling season, alongshore currents and temperatures in the northern bay were most coherent with winds measured at a nearby land meteorological station. This wind site showed relatively low correlations to offshore buoy wind stations, indicating localized wind effects are important to the circulation along this stretch of Monterey Bay's inner shelf. ?? 2004 Elsevier Ltd. All rights reserved.

Near-inertial motions in the Brazil Current at 24°S-36°S: Observations by satellite tracked drifters

NASA Astrophysics Data System (ADS)

Assireu, Arcilan T.; Dauhut, Thibaut; dos Santos, Francisco A.; Lorenzzetti, João A.

2017-08-01

Increased spatial and temporal resolution of recent observations and modeling have pointed out the importance of small scale structures (in the range of 1-50 km) for the mixing processes in the ocean. Based on high-frequency drifter measurements, we show here that the near-inertial currents (NICs) can contribute significantly to the surface kinetic energy in the Brazil Current (BC) region and, therefore, should be properly taken into account in the studies of transport and mixing processes. To characterize these submesoscale features, we examine the current response to the wind forcing in the Brazilian ocean margin between 24°S and 36°S using 3-hourly sampled trajectories of satellite-tracked drifters. Our results indicate a preference for anti-cyclonic circular motions, with a rotating period close to the local inertial period, consistent with near-inertial motions in the Southern Hemisphere (SH). Wind stress time series, from three months of wind measurements, along with synoptic weather charts, are used to relate the observed NICs to the atmospheric forcing. During SH spring, NICs occur in 4.7-15 day bursts and account for 15-45% of the total surface current variance. This intermittency is related to atmospheric cold frontal passages, low pressure systems, and sea breeze/land breeze circulations. The predominance of NICs south of 28°S appears to be related to the increased Effective Inertial Frequency (EIF), which is the inertial frequency changed by the sub-inertial background flow.

Small scale currents and ocean wave heights: from today's models to future satellite observations with CFOSAT and SKIM

NASA Astrophysics Data System (ADS)

Ardhuin, Fabrice; Gille, Sarah; Menemenlis, Dimitris; Rocha, Cesar; Rascle, Nicolas; Gula, Jonathan; Chapron, Bertrand

2017-04-01

Tidal currents and large oceanic currents, such as the Agulhas, Gulf Stream and Kuroshio, are known to modify ocean wave properties, causing extreme sea states that are a hazard to navigation. Recent advances in the understanding and modeling capability of ocean currents at scales of 10 km or less have revealed the ubiquitous presence of fronts and filaments. Based on realistic numerical models, we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km, including important variations at 10 km. This current-induced variability creates gradients in wave heights that were previously overlooked and are relevant for extreme wave heights and remote sensing. The spectrum of significant wave heights is found to be of the order of 70⟨Hs ⟩2/(g2⟨Tm0,-1⟩2) times the current spectrum, where ⟨Hs ⟩ is the spatially-averaged significant wave height, ⟨Tm0,-1⟩ is the average energy period, and g is the gravity acceleration. This small scale variability is consistent with Jason-3 and SARAL along-track variability. We will discuss how future satellite mission with wave spectrometers can help observe these wave-current interactions. CFOSAT is due for launch in 2018, and SKIM is a proposal for ESA Earth Explorer 9.

Cusp field-aligned currents and ion outflows

NASA Astrophysics Data System (ADS)

Strangeway, R. J.; Russell, C. T.; Carlson, C. W.; McFadden, J. P.; Ergun, R. E.; Temerin, M.; Klumpar, D. M.; Peterson, W. K.; Moore, T. E.

2000-09-01

On September 24 and 25, 1998, the Polar spacecraft observed intense outflows of terrestrial ions in association with the passage of an interplanetary shock and coronal mass ejection. The orbit of the Fast Auroral Snapshot (FAST) Explorer was in the noon-midnight meridian during this ion outflow event, and FAST passed through the day side cusp region at ˜4000 km altitude every 2.2 hours. FAST was therefore able to monitor the ion outflows subsequently observed by Polar. We show that while the outflows were more intense after the shock passage, the overall particle and field signatures within the cusp region were qualitatively similar both before and after the shock passage. FAST observations show that the cusp particle precipitation marks the lower latitude leg of a pair of field-aligned currents and further, that both field-aligned current sheets appear to be on open field lines. Moreover, the polarity of the cusp currents is controlled by the polarity of the interplanetary magnetic field (IMF) y-component, such that the magnetic field perturbation associated with the pair of cusp currents is in the same direction as the IMF By. This is a consequence of the reconnection of cusp-region field lines at the magnetopause, with the flux transport resulting in electromagnetic energy being transmitted along field lines to the ionosphere as Poynting flux. We show that this Poynting flux can be as high as 120 mW m-2 (120 ergs cm-2 s-1) at FAST altitudes (˜500 mW m-2 at ionospheric altitudes), presumably because of the strong IMF By (˜40 nT), and is the dominant energy input to the cusp-region ionosphere. Furthermore, we find that the peak ion outflow flux is correlated with the peak downward Poynting flux, although only a few passes through the cusp centered around the time of the shock passage were used to determine this correlation. The energy carried by Poynting flux is dissipated as heat within the ionosphere, through Joule dissipation. The heating will tend to increase the ionospheric scale height, allowing greater access of ionospheric ions to the altitudes where transverse ion heating via ELF waves can occur. Thus electromagnetic energy supplied by the transport of reconnected magnetic flux is the essential first step in a multistep process that enhances the outflow of ionospheric plasma in the dayside cusp.

Global GNSS processing based on the raw observation approach

NASA Astrophysics Data System (ADS)

Strasser, Sebastian; Zehentner, Norbert; Mayer-Gürr, Torsten

2017-04-01

Many global navigation satellite system (GNSS) applications, e.g. Precise Point Positioning (PPP), require high-quality GNSS products, such as precise GNSS satellite orbits and clocks. These products are routinely determined by analysis centers of the International GNSS Service (IGS). The current processing methods of the analysis centers make use of the ionosphere-free linear combination to reduce the ionospheric influence. Some of the analysis centers also form observation differences, in general double-differences, to eliminate several additional error sources. The raw observation approach is a new GNSS processing approach that was developed at Graz University of Technology for kinematic orbit determination of low Earth orbit (LEO) satellites and subsequently adapted to global GNSS processing in general. This new approach offers some benefits compared to well-established approaches, such as a straightforward incorporation of new observables due to the avoidance of observation differences and linear combinations. This becomes especially important in view of the changing GNSS landscape with two new systems, the European system Galileo and the Chinese system BeiDou, currently in deployment. GNSS products generated at Graz University of Technology using the raw observation approach currently comprise precise GNSS satellite orbits and clocks, station positions and clocks, code and phase biases, and Earth rotation parameters. To evaluate the new approach, products generated using the Global Positioning System (GPS) constellation and observations from the global IGS station network are compared to those of the IGS analysis centers. The comparisons show that the products generated at Graz University of Technology are on a similar level of quality to the products determined by the IGS analysis centers. This confirms that the raw observation approach is applicable to global GNSS processing. Some areas requiring further work have been identified, enabling future improvements of the method.

The aluminum electrode in AlCl3-alkali-halide melts.

NASA Technical Reports Server (NTRS)

Holleck, G. L.; Giner, J.

1972-01-01

Passivation phenomena have been observed upon cathodic and anodic polarization of the Al electrode in AlCl3-KCl-NaCl melts between 100 and 160 C. They are caused by formation of a solid salt layer at the electrode surface resulting from concentration changes upon current flow. The anodic limiting currents increased with temperature and with decreasing AlCl3 content of the melt. Current voltage curves obtained on a rotating aluminum disk showed a linear relationship between the anodic limiting current and omega to the minus 1/2 power. Upon cathodic polarization, dendrite formation occurs at the Al electrode. The activation overvoltage in AlCl3-KCl-NaCl was determined by galvanostatic current step methods. An apparent exchange current density of 270 mA/sq cm at 130 C and a double layer capacity of 40 plus or minus 10 microfarad/sq cm were measured.

Effect of high current density to defect generation of blue LED and its characterization with transmission electron microscope

NASA Astrophysics Data System (ADS)

Gunawan, R.; Sugiarti, E.; Isnaeni; Purawiardi, R. I.; Widodo, H.; Muslimin, A. N.; Yuliasari; Ronaldus, C. E.; Prastomo, N.; Hastuty, S.

2018-03-01

The optical, electrical and structural characteristics of InGaN-based blue light-emitting diodes (LEDs) were investigated to identify the degradation of LED before and after current injection. The sample was injected by high current of 200 A/cm2 for 5 and 20 minutes. It was observed that injection of current shifts light intensity and wavelength characteristics that indicated defect generation. Transmission Electron Microscopy (TEM) characterization was carried out in order to clarify the structure degradation caused by defect in active layer which consisted of 14 quantum well with thickness of about 5 nm and confined with barrier layer with thickness of about 12 nm. TEM results showed pre-existing defect in LED before injection with high current. Furthermore, discontinue and edge defect was found in dark spot region of LED after injection with high current.

Observations of nonlinear and nonuniform kink dynamics in a laboratory flux rope

NASA Astrophysics Data System (ADS)

Sears, J.; Intrator, T.; Feng, Y.; Swan, H.; Gao, K.; Chapdelaine, L.

2013-12-01

A plasma column with axial magnetic field and current has helically twisted field lines. When current density in the column exceeds the kink instability threshold this magnetic configuration becomes unstable. Flux ropes in the solar wind and some solar prominences exhibit this topology, with their dynamics strongly and nonlinearly coupled to the ratio of axial current to magnetic field. The current-driven kink mode is ubiquitous in laboratory plasmas and well suited to laboratory study. In the Reconnection Scaling Experiment (RSX), nonlinear stability properties beyond the simple perturbative kink model are observed and readily diagnosed. We use a plasma gun to generate a single plasma column 0.50 m in length, in which we then drive an axial plasma current at the limit of marginal kink stability. With plasma current maintained at this threshold, we observe a deformation to a new dynamic equilibrium with finite gyration amplitude, where the currents and magnetic fields that support the force balance have surprising axial structure. Three dimensional measurements of magnetic field, plasma density, plasma potential, and ion flow velocity in the deformed plasma column show variation in the axial direction of the instability parameter and in the terms of the momentum equation. Likewise the pitch of the kink is measured to be nonuniform over the column length. In addition there is a return current antiparallel to the driven plasma current at distances up to 0.30 m from the gun that also modifies the force balance. These axial inhomogeneities, which are not considered in the model of an ideal kink, may be the terms that allow the deformed equilibrium of the RSX plasma to exist. Supported by DOE Office of Fusion Energy Sciences under LANS contract DE-AC52-06NA25369, NASA Geospace NNHIOA044I, Basic. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Cluster observations of quasi-periodic impulsive signatures in the dayside northern lobe: High-latitude flux transfer events?

NASA Technical Reports Server (NTRS)

Thompson, S. M.; Kivelson, M. G.; Khurana, K. K.; Balogh, A.; Reme, H.; Fazakerley, A. N.; Kistler, L. M.

2004-01-01

We report on a series of quasi-periodic reversals in GSM B(sub Z) observed by the four Cluster spacecraft in the northern dayside lobe poleward of the cusp on 23 February 2001. During an interval of about 35 min, multiple reversals (negative to positive) in B(sub Z) of approximately 1-min duration with an approximate 8-min recurrence time were observed. The individual structures do not resemble low-latitude flux transfer events (FTE) [Russell and Elphic, 1979] but the 8-min recurrence frequency suggests that intermittent reconnection may be occurring .Measurements (appropriately lagged) of the solar wind at ACE show that the IMF was southward-oriented with a strong B(sub X) and that a modest dynamic pressure increased as the events started. The multi-point observations afforded by the Cluster spacecraft were used to infer the motion (direction and speed) of the observed magnetic field reversals. The associated currents were also calculated and they are consistent with the spatial confinement of the observed magnetic field reversals. We propose that the observed reversals are due to flux tubes reconnecting with closed field lines on the dayside. Ancillary data from the Cluster Ion Spectrometry (CIS) and Plasma Electron And Current Experiment (PEACE) instruments were used to develop a physical picture of the reversals.

An Undergraduate Endeavor: Assembling a Live Planetarium Show About Mars

NASA Astrophysics Data System (ADS)

McGraw, Allison M.

2016-10-01

Viewing the mysterious red planet Mars goes back thousands of years with just the human eye but in more recent years the growth of telescopes, satellites and lander missions unveil unrivaled detail of the Martian surface that tells a story worth listening to. This planetarium show will go through the observations starting with the ancients to current understandings of the Martian surface, atmosphere and inner-workings through past and current Mars missions. Visual animations of its planetary motions, display of high resolution images from the Hi-RISE (High Resolution Imaging Science Experiment) and CTX (Context Camera) data imagery aboard the MRO (Mars Reconnaissance Orbiter) as well as other datasets will be used to display the terrain detail and imagery of the planet Mars with a digital projection system. Local planetary scientists and Mars specialists from the Lunar and Planetary Lab at the University of Arizona (Tucson, AZ) will be interviewed and used in the show to highlight current technology and understandings of the red planet. This is an undergraduate project that is looking for collaborations and insight in order gain structure in script writing that will teach about this planetary body to all ages in the format of a live planetarium show.

Magnetic effects of magnetospheric currents at ground and in low orbit

NASA Astrophysics Data System (ADS)

Stolle, C.; Willer, A.; Finlay, C. C.; Olsen, N.

2012-12-01

Since the advent of high precision vector magnetic field observations from satellites in low orbit it has been recognized that magnetospheric currents contribute by about 20nT to the geomagnetic field even during quiet times (when Dst=0nT) (Langel et al., 1980). Comparing spherical harmonic models of the magnetospheric field derived from ground observations with satellite data shows a similar offset. A robust linear fit between these two quantities reveals a slope of about 0.9, indicating that only 90% of the magnetospheric field as monitored on ground is seen by satellites. The intercept of ~20nT is found to diminish with reducing solar activity (as was previously noted by Lühr & Maus, 2010), while the slope is hardly affected. There have been several suggestions for the origin of this systematic difference between ground and space based observations of magnetospheric fields. We compare magnetic residuals of selected observatories with those of CHAMP satellite observations at times of conjunctions, separating the data pairs by criteria including local time and longitude, season, solar and magnetic activity. Obtaining rough estimates of the ionospheric conductivity in this way, we are able to discuss possible ionospheric sources for the observed intercept. Consideration of appropriate ordering in local time, also enables us to test for possible contributions from field aligned currents connecting the ionosphere and the magnetosphere. Langel RA, Mead GD, Lancaster ER, Estes RH, Fabiano EB. 1980. Initial geomagnetic field model from Magsat vector data. Geophys. Res. Lett. 7:793-96 Lühr H, Maus S. 2010. Solar cycle dependence of quiet-time magnetospheric currents and a model of their near-Earth magnetic fields. Earth Planets Space 62:843-48

In search of a Self-Consistent Explanation of Saturn's Magnetospheric Periodicities

NASA Astrophysics Data System (ADS)

Brandt, P. C.; Mitchell, D. G.; Carbary, J. F.; Tsyganenko, N. A.; Ebihara, Y.

2011-12-01

A global picture of Saturn's magnetospheric periodicities is emerging from several observations and modeling efforts. In this presentation we demonstrate that these observations likely contain sufficient information to explain the mysterious periodicities at Saturn, without the need of any prescribed (and often, unobservable) longitudinal anomalies. In this picture plasmoids are released quasi-periodically down the tail, leading to fast planet-ward flows and particle energization ("injections") that enhance the plasma pressure in the night side magnetosphere in the 8-20 Rs region as clearly observed in energetic neutral atom (ENA) observations by the Ion Neutral Camera (INCA) on board Cassini. Both the fast flows and the enhanced pressure drive a 3D current system that closes through the ionosphere, whose upward field-aligned component can be linked to bursts of Saturn Kilometric Radition (SKR). The current system driven by the energetic particle pressure - the partial ring current (PRC) - also distorts the magnetic field significantly leading to its periodic oscillations as the enhanced particle pressure island drifts around Saturn with a period between 10-11 h. The missing link is how the plasmoid release can be periodic. We present global INCA observations showing that pre-existing energetic particle pressure distributions from a previous injection seem to trigger the next injection. This is likely to happen due to the inflation of the magnetic field and modification of the properties of the night side current sheet, leading to an unstable current sheet. The presence of a PRC rotating around Saturn also modifies the electric field in the magnetosphere due to its closure through the ionosphere. Such a modification is called a shielding electric field, and is commonly observed at Earth associated with a radially outward density enhancement of the cold, dense plasmasphere below the PRC. This can further contribute to triggering the plasmoid release. In regards to the "dual" SKR and field periodicities that appear to be different in the northern and southern hemispheres, we investigate the possibilities that this could be a combined effect of injections in to two different radial ranges and inter-hemispheric field-aligned currents (FAC) set up by the seasonal conductance differences of the two hemispheres. Injections have been observed in the two radial ranges of roughly 9-12 Rs and >15Rs where the drift periods differ. We will attempt to quantify if this holds statistically and visualize what the combination of a rotating PRC and inter hemispheric currents look like.

Temporal variations of volume transport through the Taiwan Strait, as identified by three-year measurements

NASA Astrophysics Data System (ADS)

Chen, Hsien-Wen; Liu, Cho-Teng; Matsuno, Takeshi; Ichikawa, Kaoru; Fukudome, Ken-ichi; Yang, Yih; Doong, Dong-Jiing; Tsai, Wei-Ling

2016-02-01

The water characteristics of the East China Sea depend on influxes from river run-off, the Kuroshio, and the Taiwan Strait. A three-year observation using an acoustic Doppler current profiler (ADCP) operated on a ferry provides the first nearly continuous data set concerning the seasonal flow pattern and the volume transport from the Taiwan Strait to the East China Sea. The observed volume transport shows strong seasonality and linkage to the along-strait wind stress. An empirical regression formula between the volume transport and wind was derived to fill the gaps of observation so as to obtain a continuous data set. Based on this unique data set, the three-year mean of monthly volume transport is northeastward throughout the year, large (nearly 3 Sv) in summer and low (nearly zero) in winter. The China Coastal Current flows southward in winter, while the northward-flowing Taiwan Strait Current may reverse direction during severe northeasterly winds in the winter or under typhoons. The sea level difference across Taiwan Strait is closely correlated to the transport through the strait, and their relation is found seasonally nearly stable.

First laboratory insight on the behavioral rhythms of the bathyal crab Geryon longipes

NASA Astrophysics Data System (ADS)

Nuñez, J. D.; Sbragaglia, V.; García, J. A.; Company, J. B.; Aguzzi, J.

2016-10-01

The deep sea is the largest and at the same time least explored biome on Earth, but quantitative studies on the behavior of bathyal organisms are scarce because of the intrinsic difficulties related to in situ observations and maintaining animals in aquaria. In this study, we reported, for the first time, laboratory observations on locomotor rhythms and other behavioral observations (i.e. feeding, exploring and self-grooming) for the bathyal crab Geryon longipes. Crabs were collected on the middle-lower slope (720-1750 m) off the coast of Blanes (Spain). Inertial (18 h) water currents and monochromatic blue (i.e. 470 nm) light-darkness (24 h) cycles were simulated in two different experiments in flume tanks endowed with burrows. Both cycles were simulated in order to investigate activity rhythms regulation in Mediterranean deep-sea benthos. Crabs showed rhythmic locomotor activity synchronized to both water currents and light-darkness cycles. In general terms, feeding and exploring behaviors also followed the same pattern. Results presented here indicate the importance of local inertial (18 h) periodicity of water currents at the seabed as a temporal cue regulating the behavior of bathyal benthic fauna in all continental margin areas where the effects of tides is negligible.

Video, LMA and ULF observations of a negative gigantic jet in North Texas

NASA Astrophysics Data System (ADS)

Bruning, E. C.; Cummer, S.; Palivec, K.; Lyons, W. A.; Chmielewski, V.; MacGorman, D. R.

2017-12-01

On 8 September 2016 at 0125:38 UTC video of a negative gigantic jet was captured from Hawley, TX. VHF Lightning Mapping Arrays in West Texas and Oklahoma also observed the parent flash (duration of about 1 s) and, for the first time, mapped dozens of points along ascending negative leaders, lasting about 50 ms, which extended well above cloud top to about 35 km MSL altitude. A few well-located VHF sources were also detected near 50 km. Together, the video and VHF observations provide additional confirmation of the altitude at which the leader-to-streamer transition takes place in gigantic jet discharges. ULF magnetic field data from the Duke iCMC network show a current excursion associated with the onset of the upward movement of negative charge and leaders in the VHF. As the gigantic jet reached its full height, current spiked to 80 kA, followed by several hundred milliseconds of continuing current of 10-20 kA. Total charge moment change was about 6000 C km. The storm complex produced predominantly negative large charge moment change events, which is characteristic of storms that produce negative gigantic jets.

Association between cotinine-verified smoking status and hypertension in 167,868 Korean adults.

PubMed

Kim, Byung Jin; Han, Ji Min; Kang, Jung Gyu; Kim, Bum Soo; Kang, Jin Ho

2017-10-01

Previous studies showed inconsistent results concerning the relationship between chronic smoking and blood pressure. Most of the studies involved self-reported smoking status. This study was performed to evaluate the association of urinary cotinine or self-reported smoking status with hypertension and blood pressure in Korean adults. Among individuals enrolled in the Kangbuk Samsung Health Study and Kangbuk Samsung Cohort Study, 167,868 participants (men, 55.7%; age, 37.5 ± 6.9 years) between 2011 and 2013 who had urinary cotinine measurements were included. Individuals with urinary cotinine levels ≥50 ng/mL were defined as cotinine-verified current smokers. The prevalence of hypertension and cotinine-verified current smokers in the overall population was 6.8% and 22.7%, respectively (10.0% in men and 2.8% in women for hypertension: 37.7% in men and 3.9% in women for cotinine-verified current smokers). In a multivariate regression analysis adjusted for age, sex, body mass index, waist circumference, alcohol drinking, vigorous exercise, and diabetes, cotinine-verified current smoking was associated with lower prevalence of hypertension compared with cotinine-verified never smoking (OR[95% CI], 0.79 [0.75, 0.84]). Log-transformed cotinine levels and unobserved smoking were negatively associated with hypertension, respectively (0.96 [0.96, 0.97] and 0.55 [0.39, 0.79]). In a multivariate linear regression analysis, the cotinine-verified current smoking was inversely associated with systolic and diastolic blood pressure (BP) (regression coefficient[95% CI], -1.23[-1.39, -1.07] for systolic BP and -0.71 [-0.84, -0.58] for diastolic BP). In subgroup analyses according to sex, the inverse associations between cotinine-verified current smoking and hypertension were observed only in men. This large observational study showed that cotinine-verified current smoking and unobserved smoking were inversely associated with hypertension in Korean adults, especially only in men.

A note on sea level variability at Clipperton Island from GEOSAT and in-situ observations

NASA Astrophysics Data System (ADS)

Maul, George A.; Hansen, Donald V.; Bravo, Nicolas J.

During the 1986-1989 Exact Repeat Mission (ERM) of GEOSAT, in-situ observations of sea level at Clipperton Island (10°N/109°W) and satellite-tracked free-drifting drogued buoys in the eastern tropical Pacific Ocean are concurrently available. A map of the standard deviations of GEOSAT sea surface heights (2.9 years) shows a variance maximum along ˜12°N from Central America, past Clipperton to ˜160°W. Sea floor pressure gauge observations from a shallow (10m depth) site on Clipperton Island and an ERM crossover point in deep water nearby show a correlation of r = 0.76 with a residual of ±6.7 cm RMS. Approximately 17% of the difference (GEOSAT minus sea level) is characterized by a 4 cm amplitude 0° phase annual harmonic, which is probably caused by unaccounted-for tropospheric water vapor affecting the altimeter and/or ERM orbit error removal. Wintertime anticyclonic mesoscale eddies advecting past Clipperton Island each year have GEOSAT sea surface height and in-situ sea level signals of more than 30 cm, some of which are documented by the satellite-tracked drifters. Meridional profiles of the annual harmonic of zonal geostrophic current from GEOSAT and from the drifters both show synchronous maxima in the North Equatorial Countercurrent and the North Equatorial Current. Other Clipperton sea level maxima seen during late spring of each year may involve anticyclonic vortices formed along Central America the previous winter.

Magnetosphere-Regolith/Exosphere Coupling: Differences and Similarities to the Earth Magnetosphere-Ionosphere Coupling

NASA Technical Reports Server (NTRS)

Gjerleov, J. W.; Slavin, J. A.

2001-01-01

Of the three Mercury passes made by Mariner 10, the first and third went through the Mercury magnetosphere. The third encounter which occurred during northward IMF (interplanetary magnetic field) showed quiet time magnetic fields. In contrast the third encounter observed clear substorm signatures including dipolarization, field-aligned currents (FACs) and injection of energetic electrons at geosynchronous orbit. However, the determined cross-tail potential drop and the assumed height integrated conductance indicate that the FAC should be 2-50 times weaker than observed. We address this inconsistency and the fundamental problem of FAC closure whether this takes place in the regolith or in the exosphere. The current state of knowledge of the magnetosphere-exosphere/regolith coupling is addressed and similarities and differences to the Earth magnetosphere-ionosphere coupling are discussed.

Observer-based higher order sliding mode control of power factor in three-phase AC/DC converter for hybrid electric vehicle applications

NASA Astrophysics Data System (ADS)

Liu, Jianxing; Laghrouche, Salah; Wack, Maxime

2014-06-01

In this paper, a full-bridge boost power converter topology is studied for power factor control, using output higher order sliding mode control. The AC/DC converters are used for charging the battery and super-capacitor in hybrid electric vehicles from the utility. The proposed control forces the input currents to track the desired values, which can control the output voltage while keeping the power factor close to one. Super-twisting sliding mode observer is employed to estimate the input currents and load resistance only from the measurement of output voltage. Lyapunov analysis shows the asymptotic convergence of the closed-loop system to zero. Multi-rate simulation illustrates the effectiveness and robustness of the proposed controller in the presence of measurement noise.

Observational viability and stability of nonlocal cosmology

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

Deser, S.; Woodard, R.P., E-mail: deser@brandeis.edu, E-mail: woodard@phys.ufl.edu

2013-11-01

We show that the nonlocal gravity models, proposed to explain current cosmic acceleration without dark energy, pass two essential tests: first, they can be defined so as not to alter the, observationally correct, general relativity predictions for gravitationally bound systems. Second, they are stable, ghost-free, with no additional excitations beyond those of general relativity. In this they differ from their, ghostful, localized versions. The systems' initial value constraints are the same as in general relativity, and our nonlocal modifications never convert the original gravitons into ghosts.

Investigation of Post-mortem Tissue Effects Using Long-time Decorrelation Ultrasound

NASA Astrophysics Data System (ADS)

Csány, Gergely; Balogh, Lajos; Gyöngy, Miklós

Decorrelation ultrasound is being increasingly used to investigate long-term biological phenomena. In the current work, ultrasound image sequences of mice who did not survive anesthesia (in a separate investigation) were analyzed and post-mortem tissue effects were observed via decorrelation calculation. A method was developed to obtain a quantitative parameter characterizing the rate of decorrelation. The results show that ultrasound decorrelation imaging is an effective method of observing post-mortem tissue effects and point to further studies elucidating the mechanism behind these effects.

Mumps outbreaks in a highly vaccinated population: Investigation of a neutralization titre against the current circulating wildtype genotype G5 mumps virus.

PubMed

Kenny, Lena; O'Kelly, Edwin; Connell, Jeff; De Gascun, Cillian; Hassan, Jaythoon

2016-01-01

Mumps outbreaks continue to occur globally, despite high levels of uptake of the mumps vaccine. In order to address immunity to the current circulating wildtype virus, we sought to determine a mumps G5 specific IgG quantitative value which correlates with genotype G5 specific neutralization ability in vitro. Sera from 199 individuals including controls and acute mumps cases were assessed for mumps specific IgG titres using five different enzyme immunoassays coated with antigen from different mumps virus strains. A subset of 66 sera was also assessed for in vitro neutralizing antibody against a contemporary circulating genotype G5 mumps virus. For all the different antigenic targets, mumps specific IgG titres were higher in patients following acute mumps infection compared to controls. In acute mumps infected patients, females showed significantly higher serum titres of anti-G5 IgG compared to males (p<0.05). Furthermore, control males did not show any change in G5 specific IgG with increasing age whereas females show a progressive rise in titre. Linear regression analysis revealed a significant association between the mumps G5 specific IgG levels in the EIA and the in vitro neutralization titres (r(2)=0.59). Specific IgG to the current circulating genotype G5 mumps strain showed significantly lower titres in males which supports our previous observation that there is a male gender bias in cases of acute mumps infection. Furthermore, in this preliminary study, the data indicate that genotype G5 specific IgG levels of >40 RU/ml are required for neutralization capability to be observed in vitro. Copyright © 2015 Elsevier B.V. All rights reserved.

Demonstration of Hole Transport and Voltage Equilibration in Self-Assembled π-Conjugated Peptide Nanostructures Using Field-Effect Transistor Architectures.

PubMed

Besar, Kalpana; Ardoña, Herdeline Ann M; Tovar, John D; Katz, Howard E

2015-12-22

π-Conjugated peptide materials are attractive for bioelectronics due to their unique photophysical characteristics, biofunctional interfaces, and processability under aqueous conditions. In order to be relevant for electrical applications, these types of materials must be able to support the passage of current and the transmission of applied voltages. Presented herein is an investigation of both the current and voltage transmission activities of one-dimensional π-conjugated peptide nanostructures. Observations of the nanostructures as both semiconducting and gate layers in organic field-effect transistors (OFETs) were made, and the effect of systematic changes in amino acid composition on the semiconducting/conducting functionality of the nanostructures was investigated. These molecular variations directly impacted the hole mobility values observed for the nanomaterial active layers over 3 orders of magnitude (∼0.02 to 5 × 10(-5) cm(2) V(-1) s(-1)) when the nanostructures had quaterthiophene cores and the assembled peptide materials spanned source and drain electrodes. Peptides without the quaterthiophene core were used as controls and did not show field-effect currents, verifying that the transport properties of the nanostructures rely on the semiconducting behavior of the π-electron core and not just ionic rearrangements. We also showed that the nanomaterials could act as gate electrodes and assessed the effect of varying the gate dielectric layer thickness in devices where the conventional organic semiconductor pentacene spanned the source and drain electrodes in a top-contact OFET, showing an optimum performance with 35-40 nm dielectric thickness. This study shows that these peptides that self-assemble in aqueous environments can be used successfully to transmit electronic signals over biologically relevant distances.

Effect of annealing temperature on the PEC performance of electrodeposited copper oxides

NASA Astrophysics Data System (ADS)

Marathey, Priyanka; Pati, Ranjan; Mukhopadhyay, Indrajit; Ray, Abhijit

2018-05-01

In this work, we have deposited Cu2O film on fluorine doped tin oxide (FTO) substrate by electrodeposition. Pure CuO phase has been obtained by annealing the electrodeposited Cu2O film at optimized temperature (500°C) for two hours in air. Copper(I) oxide films showed good photo response with a current density of 0.54mA/cm2 at 0 V vs RHE. It is evident from UV-Visible spectroscopic analysis that the bandgap of Cu(I) and Cu(II) oxides differs from each other resulting in significant change in photo current for these two phases, observed in the PEC study. However CuO film showed better stability as compared to Cu2O film.

U-shaped relationship between current and pitch in helicene molecules

NASA Astrophysics Data System (ADS)

Guo, Yan-Dong; Yan, Xiao-Hong; Xiao, Yang; Liu, Chun-Sheng

2015-11-01

The helicene is constructed by twisted benzene or other aromatic rings, exhibiting a helical structure. Using first-principles calculations, we investigate the electronic transport of helicenes under stretching or compressing. Interestingly, a U-shaped curve of the current against d (the pitch of a helicene) is observed. Further analysis shows that, it is the result of the nonmonotonic change of HOMO-LUMO gap with d. The change of overlap between orbitals induced by conformational deformation is found to be the underlying mechanism. Moreover, the U-curve phenomenon is an intrinsic feature of the helicene molecules, being robust to the electrode materials or doping. This U-curve behavior is expected to be extended to helical graphene or other related structures, showing great application potential.

U-shaped relationship between current and pitch in helicene molecules.

PubMed

Guo, Yan-Dong; Yan, Xiao-Hong; Xiao, Yang; Liu, Chun-Sheng

2015-11-19

The helicene is constructed by twisted benzene or other aromatic rings, exhibiting a helical structure. Using first-principles calculations, we investigate the electronic transport of helicenes under stretching or compressing. Interestingly, a U-shaped curve of the current against d (the pitch of a helicene) is observed. Further analysis shows that, it is the result of the nonmonotonic change of HOMO-LUMO gap with d. The change of overlap between orbitals induced by conformational deformation is found to be the underlying mechanism. Moreover, the U-curve phenomenon is an intrinsic feature of the helicene molecules, being robust to the electrode materials or doping. This U-curve behavior is expected to be extended to helical graphene or other related structures, showing great application potential.

Large-scale traveling ionospheric disturbances observed by GPS dTEC maps over North and South America on Saint Patrick's Day storm in 2015

NASA Astrophysics Data System (ADS)

Figueiredo, C. A. O. B.; Wrasse, C. M.; Takahashi, H.; Otsuka, Y.; Shiokawa, K.; Barros, D.

2017-04-01

Large-scale traveling ionospheric disturbances (LSTIDs) were detected in both Northern and Southern Hemispheres over American sector during the geomagnetic storm on 17-18 March 2015, also known as the Saint Patrick's Day storm. Detrended total electronic content (dTEC) maps were made using dense GNSS network receiver data. The retrieved LSTIDs showed wavelengths of 1000 to 2000 km, phase velocity of 300-1000 m/s, and period of 30-50 min. Among them, three couples of LSTIDs were observed propagating from the polar regions to low latitudes. Two wave events observed in daytime showed the propagation direction of southwest in the Northern Hemisphere and northeast in the Southern Hemisphere, which means an asymmetric propagation against the geographic equator. The other wave event observed during the evening hour showed symmetric propagation direction, i.e., southwest in the Northern Hemisphere and northwest in the Southern Hemisphere, whereas their wavelength and phase velocity are significantly different between NH and SH. These observations indicate that the two groups of LSTID have different propagation conditions from polar to low-latitude regions. The observed asymmetric/symmetric propagation forms suggest asymmetric/symmetric auroral current activity between the northern and southern polar regions.

Declining Rotation Curves at z = 2 in ΛCDM Galaxy Formation Simulations

NASA Astrophysics Data System (ADS)

Teklu, Adelheid F.; Remus, Rhea-Silvia; Dolag, Klaus; Arth, Alexander; Burkert, Andreas; Obreja, Aura; Schulze, Felix

2018-02-01

Selecting disk galaxies from the cosmological, hydrodynamical simulation Magneticum Pathfinder, we show that almost half of our poster child disk galaxies at z = 2 show significantly declining rotation curves and low dark matter fractions, very similar to recently reported observations. These galaxies do not show any anomalous behavior, they reside in standard dark matter halos, and they typically grow significantly in mass until z = 0, where they span all morphological classes, including disk galaxies matching present-day rotation curves and observed dark matter fractions. Our findings demonstrate that declining rotation curves and low dark matter fractions in rotation-dominated galaxies at z = 2 appear naturally within the ΛCDM paradigm and reflect the complex baryonic physics, which plays a role at the peak epoch of star formation. In addition, we find some dispersion-dominated galaxies at z = 2 that host a significant gas disk and exhibit similar shaped rotation curves as the disk galaxy population, rendering it difficult to differentiate between these two populations with currently available observation techniques.

Role of cold water and beta-effect in the formation of the East Korean Warm Current in the East/Japan Sea: a numerical experiment

NASA Astrophysics Data System (ADS)

Kim, Yong-Yub; Cho, Yang-Ki; Kim, Young Ho

2018-06-01

The contributions of bottom cold water and planetary β-effect to the formation of the East Korean Warm Current (EKWC), the western boundary current in the East/Japan Sea (EJS), were evaluated using an idealized three-dimensional numerical model. The model results suggest that the bottom cold water and, to a lesser extent, the planetary β-effect both contribute to the formation of the EKWC. The cold water functions as the bottom of the upper layer, to control the EKWC via conservation of potential vorticity. It is known that cold waters, such as the North Korean Cold Water and Korea Strait Bottom Cold Water often observed during summer along the southwestern coast of the EJS, originate from the winter convection in the northern area. Observational studies consistently show that the EKWC strengthens in summer when the cold water extends further south along the western boundary.

Submesoscale Rossby waves on the Antarctic circumpolar current.

PubMed

Taylor, John R; Bachman, Scott; Stamper, Megan; Hosegood, Phil; Adams, Katherine; Sallee, Jean-Baptiste; Torres, Ricardo

2018-03-01

The eastward-flowing Antarctic circumpolar current (ACC) plays a central role in the global ocean overturning circulation and facilitates the exchange of water between the ocean surface and interior. Submesoscale eddies and fronts with scales between 1 and 10 km are regularly observed in the upper ocean and are associated with strong vertical circulations and enhanced stratification. Despite their importance in other locations, comparatively little is known about submesoscales in the Southern Ocean. We present results from new observations, models, and theories showing that submesoscales are qualitatively changed by the strong jet associated with the ACC in the Scotia Sea, east of Drake Passage. Growing submesoscale disturbances develop along a dense filament and are transformed into submesoscale Rossby waves, which propagate upstream relative to the eastward jet. Unlike their counterparts in slower currents, the submesoscale Rossby waves do not destroy the underlying frontal structure. The development of submesoscale instabilities leads to strong net subduction of water associated with a dense outcropping filament, and later, the submesoscale Rossby waves are associated with intense vertical circulations.

Atomically Resolved STM Characterization of the 3-D Dirac Semimetal Cd3As2

NASA Astrophysics Data System (ADS)

Butler, Christopher; Tseng, Yi; Hsing, Cheng-Rong; Wu, Yu-Mi; Sankar, Raman; Wang, Mei-Fang; Wei, Ching-Ming; Chou, Fang-Cheng; Lin, Minn-Tsong

Dirac semimetals such as Cd3As2 are a recently discovered class of materials which host three-dimensional linear dispersion around point-like band crossings in the bulk Brillouin zone, and hence represent three-dimensional analogues of graphene. This electronic phase is enabled by specific crystal symmetries: In the case of Cd3As2, a C4 rotational symmetry associated with its peculiar corkscrew arrangement of systematic Cd vacancies. Although this arrangement underpins the current crystallographic understanding of Cd3As2, and all its theoretical implications, it is strangely absent in surface microscopic investigations reported previously. Here we use a combined approach of scanning tunneling microscopy and ab initio calculations to show that the currently held crystallographic model of Cd3As2 is indeed predictive of a periodic zig-zag superstructure at the (112) surface, which we observe in scanning tunneling microscopy images. This helps to reconcile the current state of microscopic surface observations with the prevailing crystallographic and theoretical models.

Size-controlled InGaN/GaN nanorod LEDs with an ITO/graphene transparent layer

NASA Astrophysics Data System (ADS)

Shim, Jae-Phil; Seong, Won-Seok; Min, Jung-Hong; Kong, Duk-Jo; Seo, Dong-Ju; Kim, Hyung-jun; Lee, Dong-Seon

2016-11-01

We introduce ITO on graphene as a current-spreading layer for separated InGaN/GaN nanorod LEDs for the purpose of passivation-free and high light-extraction efficiency. Transferred graphene on InGaN/GaN nanorods effectively blocks the diffusion of ITO atoms to nanorods, facilitating the production of transparent ITO/graphene contact on parallel-nanorod LEDs, without filling the air gaps, like a bridge structure. The ITO/graphene layer sufficiently spreads current in a lateral direction, resulting in uniform and reliable light emission observed from the whole area of the top surface. Using KOH treatment, we reduce series resistance and reverse leakage current in nanorod LEDs by recovering the plasma-damaged region. We also control the size of the nanorods by varying the KOH treatment time and observe strain relaxation via blueshift in electroluminescence. As a result, bridge-structured LEDs with 8 min of KOH treatment show 15 times higher light-emitting efficiency than with 2 min of KOH treatment.

Robust Engineering Designs for Infrastructure Adaptation to a Changing Climate

NASA Astrophysics Data System (ADS)

Samaras, C.; Cook, L.

2015-12-01

Infrastructure systems are expected to be functional, durable and safe over long service lives - 50 to over 100 years. Observations and models of climate science show that greenhouse gas emissions resulting from human activities have changed climate, weather and extreme events. Projections of future changes (albeit with uncertainties caused by inadequacies of current climate/weather models) can be made based on scenarios for future emissions, but actual future emissions are themselves uncertain. Most current engineering standards and practices for infrastructure assume that the probabilities of future extreme climate and weather events will match those of the past. Climate science shows that this assumption is invalid, but is unable, at present, to define these probabilities over the service lives of existing and new infrastructure systems. Engineering designs, plans, and institutions and regulations will need to be adaptable for a range of future conditions (conditions of climate, weather and extreme events, as well as changing societal demands for infrastructure services). For their current and future projects, engineers should: Involve all stakeholders (owners, financers, insurance, regulators, affected public, climate/weather scientists, etc.) in key decisions; Use low regret, adaptive strategies, such as robust decision making and the observational method, comply with relevant standards and regulations, and exceed their requirements where appropriate; Publish design studies and performance/failure investigations to extend the body of knowledge for advancement of practice. The engineering community should conduct observational and modeling research with climate/weather/social scientists and the concerned communities and account rationally for climate change in revised engineering standards and codes. This presentation presents initial research on decisionmaking under uncertainty for climate resilient infrastructure design.

Enhanced Brain Responses to Pain-Related Words in Chronic Back Pain Patients and Their Modulation by Current Pain.

PubMed

Ritter, Alexander; Franz, Marcel; Puta, Christian; Dietrich, Caroline; Miltner, Wolfgang H R; Weiss, Thomas

2016-08-10

Previous functional magnetic resonance imaging (fMRI) studies in healthy controls (HC) and pain-free migraine patients found activations to pain-related words in brain regions known to be activated while subjects experience pain. The aim of the present study was to identify neural activations induced by pain-related words in a sample of chronic back pain (CBP) patients experiencing current chronic pain compared to HC. In particular, we were interested in how current pain influences brain activations induced by pain-related adjectives. Subjects viewed pain-related, negative, positive, and neutral words; subjects were asked to generate mental images related to these words during fMRI scanning. Brain activation was compared between CBP patients and HC in response to the different word categories and examined in relation to current pain in CBP patients. Pain-related words vs. neutral words activated a network of brain regions including cingulate cortex and insula in subjects and patients. There was stronger activation in medial and dorsolateral prefrontal cortex (DLPFC) and anterior midcingulate cortex in CPB patients than in HC. The magnitude of activation for pain-related vs. negative words showed a negative linear relationship to CBP patients' current pain. Our findings confirm earlier observations showing that pain-related words activate brain networks similar to noxious stimulation. Importantly, CBP patients show even stronger activation of these structures while merely processing pain-related words. Current pain directly influences on this activation.

A Comparison of ARTEMIS Observations and Particle-in-cell Modeling of the Lunar Photoelectron Sheath in the Terrestrial Magnetotail

NASA Technical Reports Server (NTRS)

Poppe, A. R.; Halekas, J. S.; Delory, G. T.; Farrell, W. M.; Angelopoulos, V.; McFadden, J. P.; Bonnell, J. W.; Ergun, R. E.

2012-01-01

As an airless body in space with no global magnetic field, the Moon is exposed to both solar ultraviolet radiation and ambient plasmas. Photoemission from solar UV radiation and collection of ambient plasma are typically opposing charging currents and simple charging current balance predicts that the lunar dayside surface should charge positively; however, the two ARTEMIS probes have observed energydependent loss cones and high-energy, surface-originating electron beams above the dayside lunar surface for extended periods in the magnetosphere, which are indicative of negative surface potentials. In this paper, we compare observations by the ARTEMIS P1 spacecraft with a one dimensional particle-in-cell simulation and show that the energy-dependent loss cones and electron beams are due to the presence of stable, non-monotonic, negative potentials above the lunar surface. The simulations also show that while the magnitude of the non-monotonic potential is mainly driven by the incoming electron temperature, the incoming ion temperature can alter this magnitude, especially for periods in the plasma sheet when the ion temperature is more than twenty times the electron temperature. Finally, we note several other plasma phenomena associated with these non-monotonic potentials, such as broadband electrostatic noise and electron cyclotron harmonic emissions, and offer possible generation mechanisms for these phenomena.

CCD BVI c observations of Cepheids

NASA Astrophysics Data System (ADS)

Berdnikov, L. N.; Kniazev, A. Yu.; Sefako, R.; Kravtsov, V. V.; Zhujko, S. V.

2014-02-01

In 2008-2013, we obtained 11333 CCD BVI c frames for 57 Cepheids from the General Catalogue of Variable Stars. We performed our observations with the 76-cm telescope of the South African Astronomical Observatory (SAAO, South Africa) and the 40-cm telescope of the Cerro Armazones Astronomical Observatory of the Universidad Católica del Norte (OCA, Chile) using the SBIG ST-10XME CCD camera. The tables of observations, the plots of light curves, and the current light elements are presented. Comparison of our light curves with those constructed from photoelectric observations shows that the differences between their mean magnitudes exceed 0ṃ05 in 20% of the cases. This suggests the necessity of performing CCD observations for all Cepheids.

Gas discharge plasma treatment of poly(ethylene glycol-co-1,3/1,4 cyclohexanedimethanol terephthalate) for enhanced paint adhesion

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

Salapare, Hernando S., E-mail: hssalapare@up.edu.ph; Department of Physical Sciences and Mathematics, College of Arts and Sciences, University of the Philippines Manila, Manila City 1000; College of Science, Pamantasan ng Lungsod ng Maynila, Intramuros, Manila City 1002

Low-energy hydrogen-ions and tetrafluoromethane-ions produced from a gas discharge ion source were irradiated to poly(ethylene glycol-co-1,3/1,4 cyclohexanedimethanol terephthalate) (PETG) sheets for enhancing paint adhesion. The ion beams were characterized using a cast steel mass spectrometer, while the untreated and treated samples were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, contact angle measurements, and profilometry. The paint adhesion was determined by using the standard method for evaluating adhesion by knife [ASTM D6677-07, Standard Test Method for Evaluating Adhesion by Knife (ASTM International, West Conshohocken, PA, 2012)] and was correlated with the calculation of the work of adhesion derived frommore » the Young–Dupré equation. After plasma treatment, a significant decrease in the contact angle was observed in all samples, except for the CF{sub 4} ion-treated samples with the discharge current of 3 mA and an irradiation time of 30 min. At longer irradiation times, the treated samples showed lesser changes in the contact angle measurement. The increase in the average and root-mean-square surface roughness was observed on the samples after plasma treatment. The samples treated with either H{sub 2} or CF{sub 4} ions for 15 min showed a direct correlation between the discharge current and surface roughness. The samples treated for 30 min showed no significant correlation between the surface roughness and discharge current, which can be attributed to the possible melting of the samples since PETG has a low melting point. The observation made in this study on the relationship of wettability and surface roughness is consistent with the Wenzel wetting mode. Scanning electron micrographs showed surface etching on the hydrogen ion-treated samples while no significant surface changes were observed for the CF{sub 4} ion-treated samples. In general, paint adhesion was stronger for samples that exhibited enhanced wettability and high work of adhesion. The optimal work of adhesion to double the paint adhesion performance was at least 84.79 mN/m. The increase in the surface roughness after the treatment provided an increased friction between the paint and the PETG surface. The increase in the paint adhesion was also due to the covalent, hydrogen, and van der Waals bonding that are typically observed for highly wettable surfaces.« less

The role of convection in the buildup of the ring current pressure during the 17 March 2013 storm

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

Menz, A. M.; Kistler, L. M.; Mouikis, C. G.

We report on 17 March 2013, the Van Allen Probes measured the H + and O + fluxes of the ring current during a large geomagnetic storm. Detailed examination of the pressure buildup during the storm shows large differences in the pressure measured by the two spacecraft, with measurements separated by only an hour, and large differences in the pressure measured at different local times. In addition, while the H + and O + pressure contributions are about equal during the main phase in the near-Earth plasma sheet outside L = 5.5, the O + pressure dominates at lower Lmore » values. We test whether adiabatic convective transport from the near-Earth plasma sheet (L > 5.5) to the inner magnetosphere can explain these observations by comparing the observed inner magnetospheric distributions with the source distribution at constant magnetic moment, mu. We find that adiabatic convection can account for the enhanced pressure observed during the storm. Using a Weimer 1996 electric field we model the drift trajectories to show that the key features can be explained by variation in the near-Earth plasma sheet population and particle access that changes with energy and L shell. Finally, we show that the dominance of O + at low L shells is due partly to a near-Earth plasma sheet that is preferentially enhanced in O + at lower energies (5–10 keV) and partly due to the time dependence in the source combined with longer drift times to low L shells. Lastly, no source of O + inside L = 5.5 is required to explain the observations at low L shells.« less

The role of convection in the buildup of the ring current pressure during the 17 March 2013 storm

DOE PAGES

Menz, A. M.; Kistler, L. M.; Mouikis, C. G.; ...

2017-01-21

We report on 17 March 2013, the Van Allen Probes measured the H + and O + fluxes of the ring current during a large geomagnetic storm. Detailed examination of the pressure buildup during the storm shows large differences in the pressure measured by the two spacecraft, with measurements separated by only an hour, and large differences in the pressure measured at different local times. In addition, while the H + and O + pressure contributions are about equal during the main phase in the near-Earth plasma sheet outside L = 5.5, the O + pressure dominates at lower Lmore » values. We test whether adiabatic convective transport from the near-Earth plasma sheet (L > 5.5) to the inner magnetosphere can explain these observations by comparing the observed inner magnetospheric distributions with the source distribution at constant magnetic moment, mu. We find that adiabatic convection can account for the enhanced pressure observed during the storm. Using a Weimer 1996 electric field we model the drift trajectories to show that the key features can be explained by variation in the near-Earth plasma sheet population and particle access that changes with energy and L shell. Finally, we show that the dominance of O + at low L shells is due partly to a near-Earth plasma sheet that is preferentially enhanced in O + at lower energies (5–10 keV) and partly due to the time dependence in the source combined with longer drift times to low L shells. Lastly, no source of O + inside L = 5.5 is required to explain the observations at low L shells.« less

Asymmetric Magnetic Reconnection in the Solar Atmosphere

NASA Astrophysics Data System (ADS)

Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

2013-12-01

Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasmoid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

Asymmetric Magnetic Reconnection in the Solar Atmosphere

NASA Astrophysics Data System (ADS)

Murphy, N. A.; Miralles, M. P.; Ranquist, D. A.; Pope, C. L.; Raymond, J. C.; Lukin, V. S.; McKillop, S. C.; Shen, C.; Winter, H. D.; Reeves, K. K.; Lin, J.

2013-12-01

Models of solar flares and coronal mass ejections typically predict the development of an elongated current sheet in the wake behind the rising flux rope. In reality, reconnection in these current sheets will be asymmetric along the inflow, outflow, and out-of-plane directions. We perform resistive MHD simulations to investigate the consequences of asymmetry during solar reconnection. We predict several observational signatures of asymmetric reconnection, including flare loops with a skewed candle flame shape, slow drifting of the current sheet into the strong field upstream region, asymmetric footpoint speeds and hard X-ray emission, and rolling motions within the erupting flux rope. There is net plasma flow across the magnetic field null along both the inflow and outflow directions. We compare simulations to SDO/AIA, Hinode/XRT, and STEREO observations of flare loop shapes, current sheet drifting, and rolling motions during prominence eruptions. Simulations of the plasm! oid instability with different upstream magnetic fields show that the reconnection rate remains enhanced even during the asymmetric case. The islands preferentially grow into the weak field upstream region. The islands develop net vorticity because the outflow jets impact them obliquely rather than directly. Asymmetric reconnection in the chromosphere occurs when emerging flux interacts with pre-existing overlying flux. We present initial results on asymmetric reconnection in partially ionized chromospheric plasmas. Finally, we discuss how comparisons to observations are necessary to understand the role of three-dimensional effects.

The ion temperature gradient: An intrinsic property of Earth's magnetotail

NASA Astrophysics Data System (ADS)

Lu, San; Artemyev, A. V.; Angelopoulos, V.; Lin, Y.; Wang, X. Y.

2017-08-01

Although the ion temperature gradient along (XGSM) and across (ZGSM) the Earth's magnetotail, which plays a key role in generating the cross-tail current and establishing pressure balance with the lobes, has been extensively observed by spacecraft, the mechanism responsible for its formation is still unknown. We use multispacecraft observations and three-dimensional (3-D) global hybrid simulations to reveal this mechanism. Using THEMIS (Time History of Events and Macroscale Interactions during Substorms), Geotail, and ARTEMIS (Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun) observations during individual, near-simultaneous plasma sheet crossings from 10 to 60 RE, we demonstrate that the ion temperature ZGSM profile is bell-shaped at different geocentric distances. This ZGSM profile is also prevalent in statistics of 200 THEMIS current sheet crossings in the near-Earth region. Using 3-D global hybrid simulations, we show that mapping of the XGSM gradient of ion temperature along magnetic field lines produces such a bell-shaped profile. The ion temperature mapping along magnetic field lines in the magnetotail enables construction of two-dimensional distributions of these quantities from vertical (north-south) spacecraft crossings. Our findings suggest that the ion temperature gradient is an intrinsic property of the magnetotail that should be considered in kinetic descriptions of the magnetotail current sheet. Toward this goal, we use theoretical approaches to incorporate the temperature gradient into kinetic current sheet models, making them more realistic.

Radiometric and Radiation Response of Visible FPAs

NASA Technical Reports Server (NTRS)

Hubbs, John

2007-01-01

The readout integrated circuit (ROIC) used in these devices was originally developed for use in space based infrared systems operating at deep cryogenic temperatures and was selected because of its proven tolerance to total ionizing radiation? The detectors are a 128 x 128 array of 60 pm x 60 pm pixel elements that have been anti-reflection (AR) coated to improve the response at very short wavelengths. These visible focal plane arrays were operated at -40 C (233 K). Two focal planes were characterized using cobalt-60 radiation to produce ionizing total dose damage in the VFPAs. Both operational and performance data were obtained as functions of total dose. The first device tested showed no appreciable change in responsivity or noise up to 300 krad(Si). However, at the next dose level of 600 krad(Si), the readout was non-operational due to failure in the digital circuitry. The second device was characterized to a total dose of 750 krad(Si) with no observed change in responsivity. An increase dark current was observed in both devices, and in the second device, the dark current caused an increase in noise at low irradiance at 400 krad(Si) and above. The increase in dark current was somewhat un-expected for visible PIN detectors. The median dark current increased more than two orders of magnitude at 300 krad(Si) for the first device and a factor of 350 at 750 krad(Si) for pixels near the edge for the second device. The dark current was found to be a strong function of detector bias, with pixels near the edge of the array showing a greater increase in dark current with bias than those near the center. Since the optical response was not a function of bias, it is hypothesized that the dark current is a surface effect and that the variation in dark current with location is due to a variation in pixel bias, caused by a voltage drop across the pixel common lead. As the total dose increased, the dark current and the voltage drop increased

Broadening of divertor heat flux profile with increasing number of ELM filaments in NSTX

DOE PAGES

Ahn, J. -W.; Maingi, R.; Canik, J. M.; ...

2014-11-13

Edge localized modes (ELMs) represent a challenge to future fusion devices, owing to cyclical high peak heat fluxes on divertor plasma facing surfaces. One ameliorating factor has been that the heat flux characteristic profile width has been observed to broaden with the size of the ELM, as compared with the inter-ELM heat flux profile. In contrast, the heat flux profile has been observed to narrow during ELMs under certain conditions in NSTX. Here we show that the ELM heat flux profile width increases with the number of filamentary striations observed, i.e., profile narrowing is observed with zero or very fewmore » striations. Because NSTX often lies on the long wavelength current-driven mode side of ideal MHD instabilities, few filamentary structures can be expected under many conditions. Lastly, ITER is also projected to lie on the current driven low-n stability boundary, and therefore detailed projections of the unstable modes expected in ITER and the heat flux driven in ensuing filamentary structures is needed.« less

AGN-driven helium reionization and the incidence of extended He III regions at redshift z > 3

NASA Astrophysics Data System (ADS)

Compostella, Michele; Cantalupo, Sebastiano; Porciani, Cristiano

2014-12-01

We use hydrodynamic simulations post-processed with the radiative-transfer code RADAMESH to assess recent claims that the low He II opacity observed in z > 3 quasar spectra may be incompatible with models of He II reionization driven by the observed population of active galactic nuclei (AGNs). In particular, building upon our previous work, we consider an early population of sources and start the radiative-transfer calculation at redshifts z ≥ 5. Our model faithfully reproduces the emissivity of optically selected AGNs as inferred from measurements of their luminosity function. We find that He II reionization is very extended in redshift (Δz ≥ 2) and highly spatially inhomogeneous. In fact, mock spectra extracted from the simulations show a large variability in the evolution of the He II effective optical depth within chunks of size Δz = 0.04. Regions with low opacity (τ_ {He {II}}^eff < 3) can be found at high redshift, in agreement with the most recent observations of UV-transmitting quasars. At the highest redshift currently probed by observations (z ˜ 3.4), our updated model predicts a much lower He II effective optical depth than previous simulations in the literature relieving most of the tension with the current data, that, however, still persists at about the (Gaussian) 1σ to 2σ level. Given the very small number of observed lines of sight, our analysis indicates that current data cannot rule out a purely AGN-driven scenario with high statistical significance.

Cultural Differences in the Development of Cognitive Shifting: East-West Comparison

ERIC Educational Resources Information Center

Moriguchi, Yusuke; Evans, Angela D.; Hiraki, Kazuo; Itakura, Shoji; Lee, Kang

2012-01-01

Prior research has documented that Japanese children's performance on the Dimensional Change Card Sorting (DCCS) task can be influenced by their observation of another person completing the task, which is referred to as social transmission of disinhibition. The current study explored whether Canadian children would also show a social transmission…

Dramatic Change in Jupiter's Great Red Spot

NASA Technical Reports Server (NTRS)

Simon, A. A.; Wong, M. H.; Rogers, J. H.; Orton, G. S.; de Pater, I.; Asay-Davis, X.; Carlson, R. W.; Marcus, P. S.

2015-01-01

Jupiter's Great Red Spot (GRS) is one of its most distinct and enduring features, having been continuously observed since the 1800's. It currently spans the smallest latitude and longitude size ever recorded. Here we show analyses of 2014 Hubble spectral imaging data to study the color, structure and internal dynamics of this long-live storm.

Testing Viable f(T) Models with Current Observations

NASA Astrophysics Data System (ADS)

Xu, Bing; Yu, Hongwei; Wu, Puxun

2018-03-01

We perform observational tests on the f(T) gravity with the BAO data (including the BOSS DR 12 galaxy sample, the DR12 Lyα-Forests measurement, the new eBOSS DR14 quasar sample, the 6dFGS, and the SDSS), the CMB distance priors from the Planck 2015, the SNIa data from the joint light-curve analysis, the latest H(z) data, and the local value of the Hubble constant. Six different f(T) models are investigated. Furthermore, the ΛCDM is also considered. All models are compared by using the Akaike information criteria (AIC) and the Bayesian information criteria (BIC). Our results show that the ΛCDM remains to be the most favored model by current observations. However, there are also the Hubble constant tension between the Planck measurements and the local Universe observations and the tension between the CMB data and the H(z) data in the ΛCDM. For f(T) models considered in this paper, half, which can reduce to the ΛCDM, have values of {{χ }2}\\min smaller than that of the ΛCDM and can relieve the tensions existing in the ΛCDM. However, they are punished slightly by the BIC due to one extra parameter. Two of six f(T) models, in which the crossing of the phantom divide line can be realized for the equation of state of the effective dark energy and this crossing is shown in this paper to be favored by current observations, are punished by the information criteria. In addition, we find that the logarithmic f(T) model is excluded by cosmological observations.

A Tailward Moving Current Sheet Normal Magnetic Field Front Followed by an Earthward Moving Dipolarization Front

NASA Technical Reports Server (NTRS)

Hwang, K.-J.; Goldstein, M. L.; Moore, T. E.; Walsh, B. M.; Baishev, D. G.; Moiseyev, A. V.; Shevtsov, B. M.; Yumoto, K.

2014-01-01

A case study is presented using measurements from the Cluster spacecraft and ground-based magnetometers that show a substorm onset propagating from the inner to outer plasma sheet. On 3 October 2005, Cluster, traversing an ion-scale current sheet at the near-Earth plasma sheet, detected a sudden enhancement of Bz, which was immediately followed by a series of flux rope structures. Both the local Bz enhancement and flux ropes propagated tailward. Approximately 5 min later, another Bz enhancement, followed by a large density decrease, was observed to rapidly propagate earthward. Between the two Bz enhancements, a significant removal of magnetic flux occurred, possibly resulting from the tailward moving Bz enhancement and flux ropes. In our scenario, this flux removal caused the magnetotail to be globally stretched so that the thinnest sheet formed tailward of Cluster. The thinned current sheet facilitated magnetic reconnection that quickly evolved from plasma sheet to lobe and generated the later earthward moving dipolarization front (DF) followed by a reduction in density and entropy. Ground magnetograms located near the meridian of Cluster's magnetic foot points show two-step bay enhancements. The positive bay associated with the first Bz enhancement indicates that the substorm onset signatures propagated from the inner to the outer plasma sheet, consistent with the Cluster observation. The more intense bay features associated with the later DF are consistent with the earthward motion of the front. The event suggests that current disruption signatures that originated in the near-Earth current sheet propagated tailward, triggering or facilitating midtail reconnection, thereby preconditioning the magnetosphere for a later strong substorm enhancement.

Evidence of negative leaders which precede fast rise ICC pulses of upward

NASA Astrophysics Data System (ADS)

Yoshida, S.; Akita, M.; Morimoto, T.; Ushio, T.; Kawasaki, Z.; Wang, D.; Takagi, N.

2008-12-01

During winter thunderstorm season in Japan, a lightning observation campaign was conducted with using a VHF broadband digital interferometer (DITF), a capacitive antenna, and Rogowski coils to study the charge transfer mechanism associated with ICC pulses of upward lightning. All the detection systems recorded one upward negative lightning stroke hitting a lightning protection tower. The upward lightning consists of only the Initial Stage (IS) with one upward positive leader and six ICC pulses. The six ICC pulses are sub-classified clearly into two types according to current pulse shapes. The type 1 ICC pulses have a higher geometric mean (GM) current peak of 17 kA and a shorter GM 10-90% risetime of 8.9 μs, while the type 2 ICC pulses have a lower GM current peak of 0.34 kA and longer GM 10-90% risetime of 55 μs. The type 1 ICC pulses have the preceding negative leaders connecting to the channel of the continuing current, while the type 2 ICC pulses have no clear preceding negative leader. These negative leaders prior to the type 1 ICC pulses probably caused the current increases of the ICC pulses, which means that the negative leaders created the channels for the ICC pulses. The height of the space charge transferred by one of the type 1 ICC pulses was estimated about 700 m above sea level at most. This observation result is the first evidence to show explicitly the existence of the negative leaders prior to the fast rise ICC pulse. Furthermore, the result shows that space charge could exist at a low attitude such as 700 m above sea level. This fact is one of the reasons why upward lightning occurs even from rather low structures during winter thunderstorm season in Japan.

Loss of ring current O+ ions due to interaction with Pc 5 waves

NASA Astrophysics Data System (ADS)

Hudson, Mary; Chan, Anthony; Roth, Ilan

1993-01-01

The behavior of ring current ions in low-frequency geomagnetic pulsations is investigated analytically and numerically. We focus primarily on ring current O+ ions, whose flux increases dramatically during geomagnetic storms and decays at a rate which is not fully explained by collisional processes. This paper presents a new loss mechanism for the O+ ions due to the combined effects of convection and corotation electric fields and interaction with Pc 5 waves (wave period: 150-600 s) via a magnetic drift-bounce resonance. A test particle code has been developed to calculate the motion of the ring current O+ ions in a time-independent dipole magnetic field, and convection and corotation electric fields, plus Pc 5 wave fields, for which a simple analytical model has been formulated based on spacecraft observations. For given fields, whether a particle gains or loses energy depends on its initial kinetic energy, pitch angle at the equatorial plane, and the position of its guiding center with respect to the azimuthal phase of the wave. The ring current O+ ions show a dispersion in energies and L values with decreasing local time across the dayside, and a bulk shift to lower energies and higher L values. The former is due to the wave-particle interaction causing the ion to gain or lose energy, while the latter is due to the convection electric field. Our simulations show that, due to the interaction with the Pc 5 waves, the particle's kinetic energy can drop below that required to overcome the convection potential and the particle will be lost to the dayside magnetopause by a sunward E×B drift. This may contribute to the loss of O+ ions at intermediate energies (tens of keV) observed during the recovery phase of geomagnetic storms.

Causal Imprinting in Causal Structure Learning

PubMed Central

Taylor, Eric G.; Ahn, Woo-kyoung

2012-01-01

Suppose one observes a correlation between two events, B and C, and infers that B causes C. Later one discovers that event A explains away the correlation between B and C. Normatively, one should now dismiss or weaken the belief that B causes C. Nonetheless, participants in the current study who observed a positive contingency between B and C followed by evidence that B and C were independent given A, persisted in believing that B causes C. The authors term this difficulty in revising initially learned causal structures “causal imprinting.” Throughout four experiments, causal imprinting was obtained using multiple dependent measures and control conditions. A Bayesian analysis showed that causal imprinting may be normative under some conditions, but causal imprinting also occurred in the current study when it was clearly non-normative. It is suggested that causal imprinting occurs due to the influence of prior knowledge on how reasoners interpret later evidence. Consistent with this view, when participants first viewed the evidence showing that B and C are independent given A, later evidence with only B and C did not lead to the belief that B causes C. PMID:22859019

Electric modulation of conduction in multiferroic Ni-doped GaFeO3 ceramics

NASA Astrophysics Data System (ADS)

Ghani, Awais; Yang, Sen; Rajput, S. S.; Ahmed, S.; Murtaza, Adil; Zhou, Chao; Yu, Zhonghai; Zhang, Yin; Song, Xiaoping; Ren, Xiaobing

2018-06-01

In this work, the effects of Ni substitution on the electrical leakage and multiferroic properties of GaFeO3 were examined. Structural analysis of grown ceramics using x-ray diffraction and Raman shows that all ceramics have pure phases with an orthorhombic structure and space group. Ni substitutions slightly modify lattice parameters and induce lattice distortion within the same crystalline structure. It is observed that with increasing Ni-content up to 0.10, the magnetic transition temperature () increases from 196 K to 407 K. Ni-doped samples showed better ferroelectric properties and a drastic reduction in leakage current (~three orders of magnitude) at room temperature. Enhanced characteristics behavior is observed for 10% Ni substitution (GaFe0.9Ni0.1O3) and higher substitution leads to deterioration of properties with a larger leakage current. It is proposed that the role of Ni substitution can reduce hopping between Fe+3 and Fe+2 as well as suppressing the oxygen vacancies. This work would open new possibilities for integrating polycrystalline GaFeO3 at room temperature for magnetoelectric applications.

Direct observation of in-plane anisotropy of the superconducting critical current density in Ba (Fe1-xCox) 2As2 crystals

NASA Astrophysics Data System (ADS)

Hecher, J.; Ishida, S.; Song, D.; Ogino, H.; Iyo, A.; Eisaki, H.; Nakajima, M.; Kagerbauer, D.; Eisterer, M.

2018-01-01

The phase diagram of iron-based superconductors exhibits structural transitions, electronic nematicity, and magnetic ordering, which are often accompanied by an electronic in-plane anisotropy and a sharp maximum of the superconducting critical current density (Jc) near the phase boundary of the tetragonal and the antiferromagnetic-orthorhombic phase. We utilized scanning Hall-probe microscopy to visualize the Jc of twinned and detwinned Ba (Fe1-xCox) 2As2 (x =5 %-8 % ) crystals to compare the electronic normal state properties with superconducting properties. We find that the electronic in-plane anisotropy continues into the superconducting state. The observed correlation between the electronic and the Jc anisotropy agrees qualitatively with basic models, however, the Jc anisotropy is larger than predicted from the resistivity data. Furthermore, our measurements show that the maximum of Jc at the phase boundary does not vanish when the crystals are detwinned. This shows that twin boundaries are not responsible for the large Jc, suggesting an exotic pinning mechanism.

NASA Astrophysics Data System (ADS)

Nishimura, A.; Takeuchi, T.; Nishijima, S.; Ochiai, K.; Nishijima, G.; Watanabe, K.; Shikama, T.

2010-04-01

To investigate the effect of neutron irradiation on superconducting properties, a collaboration network was established among superconducting material engineering and neutronics fields. Within the framework, irradiation test of Nb3Sn and Nb3Al wires by 14 MeV fusion neutron was planned and carried out at Fusion Neutronics Source in Japan Atomic Energy Agency. After the irradiation, critical current and critical magnetic field were measured with 28 T hybrid magnet at Institute for Metals Research in Tohoku University. The irradiation to 3.52×1020 n/m2 showed a slight increase of the critical current of the Nb3Sn wire, and the irradiation to 1.78×1021 n/m2 made the critical current appreciably larger. Regarding the critical magnetic field, no clear change was observed. In the case of Nb3Al wire, a sample irradiated to 1.78×1021 n/m2 showed no increase of the critical current below 200 A which was the limit of the power supply. As for the critical magnetic field, there was no clear improvement similar to the Nb3Sn wire. The increase of the critical current would be caused by knock-on effect of the fast neutron.

Beam steering via resonance detuning in coherently coupled vertical cavity laser arrays

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

Johnson, Matthew T., E-mail: matthew.johnson.9@us.af.mil; Siriani, Dominic F.; Peun Tan, Meng

2013-11-11

Coherently coupled vertical-cavity surface-emitting laser arrays offer unique advantages for nonmechanical beam steering applications. We have applied dynamic coupled mode theory to show that the observed temporal phase shift between vertical-cavity surface-emitting array elements is caused by the detuning of their resonant wavelengths. Hence, a complete theoretical connection between the differential current injection into array elements and the beam steering direction has been established. It is found to be a fundamentally unique beam-steering mechanism with distinct advantages in efficiency, compactness, speed, and phase-sensitivity to current.

Phase slip process and charge density wave dynamics in a one dimensional conductor

NASA Astrophysics Data System (ADS)

Habiballah, N.; Zouadi, M.; Arbaoui, A.; Qjani, M.; Dumas, J.

In this paper, we study the phase slip effect on the charge density wave (CDW) dynamics in a one-dimensional conductor in the weak pinning limit. A considerable enhancement of JCDW is observed in the presence of phase slips. In addition, a spatial dependence of the CDW current density JCDW is also studied showing that a decrease of JCDW with distance from the current contact occurs. The results are discussed in terms the relationship between additional phase slips and the mobility of phase dislocations nucleated at electrical contacts.

Correnti atmosferiche su Giove

NASA Astrophysics Data System (ADS)

Adamoli, Gianluigi

2006-06-01

UAI observations are presented concerning the surveillance of Jupiter's atmospheric currents by means of digital images. General statistics are derived about the latitude and speed of individual spots and currents in the period 2000-04, compared with the Voyager wind profile. Attention is drawn to the wind shear present at distinct latitudes, namely on the South edge of the SEB, across the NTB and across the NEB. Especially interesting were the 2003 remnants of the disappearing NTB, which showed a motion intermediate between the NTC and the NTBs jet streams. Vorticity was derived in all cases.

The Quest for Dusty Primeval Galaxies

NASA Astrophysics Data System (ADS)

Mancuso, C.; Lapi, A.; Danese, L.

2016-06-01

We exploit the continuity equation approach and the 'main sequence' star-formation timescales to show that the observed high abundance of galaxies with stellar masses ? a few >10^10 M_⊙ at redshift z >? 4 implies the existence of a galaxy population featuring large star formation rates (SFRs) ψ >? 10^2 M_⊙ yr^-1 in heavily dust-obscured conditions. These galaxies constitute the high-redshift counterparts of the dusty star-forming population already surveyed for z<3 in the far-IR band by the Herschel space observatory. We work out specific predictions for the evolution of the corresponding stellar mass and SFR functions out to z ˜ 10, elucidating that the number density at z 30 M_⊙ yr^-1 cannot be estimated relying on the UV luminosity function alone, even when standard corrections for dust extinction based on the UV slope are applied. We compute the number counts and redshift distributions (including galaxy-scale gravitational lensing) of this galaxy population, and show that current data from AzTEC-LABOCA, SCUBA-2 and ALMA-SPT surveys are already digging into it. We substantiate how an observational strategy based on a color preselection in the far-IR or (sub-)mm band with Herschel and SCUBA-2, supplemented by photometric data via on-source observations with ALMA, can allow to reconstruct the bright end of the SFR functions out to z ? 8. In parallel, such a challenging task can be managed by exploiting current UV surveys in combination with (sub-)mm observations by ALMA and NIKA2 and/or radio observations by SKA and its precursors.

Observation of EHO in NSTX and Theoretical Study of its Active Control Using HHFW Antenna

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

J.-K. Park, et. al.

2013-01-14

Two important topics in the tokamak ELM control, using the non-axisymmetric (3D) magnetic perturbations, are studied in NSTX and combined envisioning ELM control in the future NSTX-U operation: Experimental observations of the edge harmonic oscillation in NSTX (not necessarily the same as EHOs in DIII-D), and theoretical study of its external drive using the high harmonic fast wave (HHFW) antenna as a 3D field coil. Edge harmonic oscillations were observed particularly well in NSTX ELM-free operation with low n core modes, with various diagnostics confirming n = 4 ~ 6 edge-localized and coherent oscillations in 2 ~ 8kHz frequency range.more » These oscillations seem to have a favored operational window in rotational shear, similarly to EHOs in DIII-D QH modes . However, in NSTX, they are not observed to provide particle or impurity control, possibly due to their weak amplitudes, of a few mm displacements, as measured by reflectometry. The external drive of these modes has been proposed in NSTX, by utilizing audio-frequency currents in the HHFW antenna straps. Analysis shows that the HHFW straps can be optimized to maximize n = 4 ~ 6 while minimizing n = 1 ~ 3. Also, IPEC calculations show that the optimized configuration with only 1kAt current can produce comparable or larger displacements than the observed internal modes. If this optimized external drive can be constructively combined, or further resonated with the internal modes, the edge harmonic oscillations in NSTX may be able to produce sufficient particle control to modify ELMs.« less

Lateral eddy diffusivity estimates from simulated and observed drifter trajectories: a case study for the Agulhas Current system

NASA Astrophysics Data System (ADS)

Rühs, Siren; Zhurbas, Victor; Durgadoo, Jonathan V.; Biastoch, Arne

2017-04-01

The Lagrangian description of fluid motion by sets of individual particle trajectories is extensively used to characterize connectivity between distinct oceanic locations. One important factor influencing the connectivity is the average rate of particle dispersal, generally quantified as Lagrangian diffusivity. In addition to Lagrangian observing programs, Lagrangian analyses are performed by advecting particles with the simulated flow field of ocean general circulation models (OGCMs). However, depending on the spatio-temporal model resolution, not all scale-dependent processes are explicitly resolved in the simulated velocity fields. Consequently, the dispersal of advective Lagrangian trajectories has been assumed not to be sufficiently diffusive compared to observed particle spreading. In this study we present a detailed analysis of the spatially variable lateral eddy diffusivity characteristics of advective drifter trajectories simulated with realistically forced OGCMs and compare them with estimates based on observed drifter trajectories. The extended Agulhas Current system around South Africa, known for its intricate mesoscale dynamics, serves as a test case. We show that a state-of-the-art eddy-resolving OGCM indeed features theoretically derived dispersion characteristics for diffusive regimes and realistically represents Lagrangian eddy diffusivity characteristics obtained from observed surface drifter trajectories. The estimates for the maximum and asymptotic lateral single-particle eddy diffusivities obtained from the observed and simulated drifter trajectories show a good agreement in their spatial pattern and magnitude. We further assess the sensitivity of the simulated lateral eddy diffusivity estimates to the temporal and lateral OGCM output resolution and examine the impact of the different eddy diffusivity characteristics on the Lagrangian connectivity between the Indian Ocean and the South Atlantic.

Redshift drift constraints on holographic dark energy

NASA Astrophysics Data System (ADS)

He, Dong-Ze; Zhang, Jing-Fei; Zhang, Xin

2017-03-01

The Sandage-Loeb (SL) test is a promising method for probing dark energy because it measures the redshift drift in the spectra of Lyman- α forest of distant quasars, covering the "redshift desert" of 2 ≲ z ≲ 5, which is not covered by existing cosmological observations. Therefore, it could provide an important supplement to current cosmological observations. In this paper, we explore the impact of SL test on the precision of cosmological constraints for two typical holographic dark energy models, i.e., the original holographic dark energy (HDE) model and the Ricci holographic dark energy (RDE) model. To avoid data inconsistency, we use the best-fit models based on current combined observational data as the fiducial models to simulate 30 mock SL test data. The results show that SL test can effectively break the existing strong degeneracy between the present-day matter density Ωm0 and the Hubble constant H 0 in other cosmological observations. For the considered two typical dark energy models, not only can a 30-year observation of SL test improve the constraint precision of Ωm0 and h dramatically, but can also enhance the constraint precision of the model parameters c and α significantly.

Generation and Propagation of Nonlinear Internal Waves in Sheared Currents Over the Washington Continental Shelf

NASA Astrophysics Data System (ADS)

Hamann, Madeleine M.; Alford, Matthew H.; Mickett, John B.

2018-04-01

The generation, propagation, and dissipation of nonlinear internal waves (NLIW) in sheared background currents is examined using 7 days of shipboard microstructure surveys and two moorings on the continental shelf offshore of Washington state. Surveys near the hypothesized generation region show semi-diurnal (D2) energy flux is onshore and that the ratio of energy flux to group speed times energy (F/cgE) increases sharply at the shelf break, suggesting that the incident D2 internal tide is partially reflected and partially transmitted. NLIW appear at an inshore mooring at the leading edge of the onshore phase of the baroclinic tide, consistent with nonlinear transformation of the shoaling internal tide as their generation mechanism. Of the D2 energy flux observed at the eastern extent of the generation region (133 ± 18 Wm-1), approximately 30% goes into the NLIW observed inshore (36 ± 11 Wm-1). Inshore of the moorings, 7 waves are tracked into shallow (30-40 m) water, where a vertically sheared, southward current becomes strong. As train-like waves propagate onshore, wave amplitudes of 25-30 m and energies of 5 MJ decrease to 12 m and 10 kJ, respectively. The observed direction of propagation rotates from 30° N of E to ˜30° S of E in the strongly sheared region. Linear ray tracing using the Taylor-Goldstein equation to incorporate parallel shear effects accounts for only a small portion of the observed rotation, suggesting that three-dimensionality of the wave crests and the background currents is important here.

Investigation of 1/f Noise Mechanisms in Midwave Infrared HgCdTe Gated Photodiodes

NASA Astrophysics Data System (ADS)

Westerhout, R. J.; Musca, C. A.; Antoszewski, J.; Dell, J. M.; Faraone, L.

2007-08-01

In this work, gated midwave infrared (MWIR) Hg1 x Cd x Te photodiodes are used to investigate the physical origin of 1/f noise generation. Gated photodiodes were fabricated on liquid-phase epitaxy p-type HgCdTe MWIR material with a vacancy-doped concentration of 1.6 × 1016 cm-3 and x = 0.31. CdTe was thermally deposited and used as both a passivant and a mask for the plasma-based type conversion, and ZnS was used as an insulator. Fabricated devices show a R 0 A of 1 5 × 104 Ωcm2 with zero gate bias. Application of 2 V to the gate improves the R 0 A by more than two orders of magnitude to 6.0 × 106 Ωcm2, which corresponds to the p-type surface being at transition between depletion and weak inversion. Trap-assisted tunneling (TAT) current was observed at negative gate biases and reverse junction biases. For gate biases greater than 3 V, a field-induced junction breakdown was observed. An I n = α I β f -0.5 trend was observed above 200 pA reverse bias dark current, with α = 3.5 × 10-5 and β = 0.82, which corresponds to the TAT dominated region. Below 200 pA, junction generation-recombination (GR) current starts to dominate and this previously mentioned trend is no longer observed. Junction GR current was not seen to be correlated with 1/f noise in these photodiodes.

The Reality of Well-Being-Focused Design in Dementia Care: A Case Study of Acute Dementia Wards in the United Kingdom.

PubMed

Catt, Megan; Giridharan, Renganathan

2018-01-01

The study explored design for well-being within dementia care by investigating the adoption of well-being-focused design in real-world practice, through observing National Health Service (NHS) wards. Design for well-being is an approach that considers the psychological and physiological effects of architecture to improve health and well-being. The high psychological care requirement for dementia patients makes them a significant group to study in the evaluation of current hospital facilities. A literature review was conducted to frame the current theoretical perception of the key characteristics of a good environment for dementia care. A framework was generated to summarize and used as an assessment tool in a series of observational visits to NHS wards. Interviews with clinical staff focused on care outcomes and practicalities of implementing well-being-focused design, considering the historical and economical context. Key findings from the observations and interviews were analyzed for recurring themes. The ward observations and interviews provided insight into the current progression of well-being-led design in NHS hospitals in England. The research highlights key areas of success and factors that inhibit further progression. The case studies showed a good degree of ambition to utilize well-being-focused design, with belief among staff that the physical environment has a substantial role in the health and well-being of patients. Staff also felt that this approach is most effective for those in the less advanced stages of dementia. Despite the high level of support, the current degree of implementation appears to be varied.

Monetary Shocks in Models with Inattentive Producers.

PubMed

Alvarez, Fernando E; Lippi, Francesco; Paciello, Luigi

2016-04-01

We study models where prices respond slowly to shocks because firms are rationally inattentive. Producers must pay a cost to observe the determinants of the current profit maximizing price, and hence observe them infrequently. To generate large real effects of monetary shocks in such a model the time between observations must be long and/or highly volatile. Previous work on rational inattentiveness has allowed for observation intervals that are either constant-but-long ( e.g . Caballero, 1989 or Reis, 2006) or volatile-but-short ( e.g . Reis's, 2006 example where observation costs are negligible), but not both. In these models, the real effects of monetary policy are small for realistic values of the duration between observations. We show that non-negligible observation costs produce both of these effects: intervals between observations are infrequent and volatile. This generates large real effects of monetary policy for realistic values of the average time between observations.

Monetary Shocks in Models with Inattentive Producers

PubMed Central

Alvarez, Fernando E.; Lippi, Francesco; Paciello, Luigi

2016-01-01

We study models where prices respond slowly to shocks because firms are rationally inattentive. Producers must pay a cost to observe the determinants of the current profit maximizing price, and hence observe them infrequently. To generate large real effects of monetary shocks in such a model the time between observations must be long and/or highly volatile. Previous work on rational inattentiveness has allowed for observation intervals that are either constant-but-long (e.g. Caballero, 1989 or Reis, 2006) or volatile-but-short (e.g. Reis's, 2006 example where observation costs are negligible), but not both. In these models, the real effects of monetary policy are small for realistic values of the duration between observations. We show that non-negligible observation costs produce both of these effects: intervals between observations are infrequent and volatile. This generates large real effects of monetary policy for realistic values of the average time between observations. PMID:27516627

Coherent current-carrying filaments during nonlinear reconnecting ELMs and VDEs

NASA Astrophysics Data System (ADS)

Ebrahimi, Fatima

2017-10-01

We have examined plasmoid-mediated reconnection in a spherical tokamak using global nonlinear three-dimensional resistive MHD simulations with NIMROD. We have shown that physical current sheets/layers develop near the edge as a peeling component of ELMs or during vertical displacement events (associated with the scrape-off layer currents - halo currents), can become unstable to nonaxisymmetric 3-D current-sheet instabilities (peeling- or tearing-like) and nonlinearly form edge coherent current-carrying filaments. Time-evolving edge current sheets with reconnecting nature in NSTX and NSTX-U configurations are identified. In the case of peeling-like edge localized modes, the longstanding problem of quasiperiodic ELMs cycles is explained through the relaxation of edge current via direct numerical calculations of reconnecting emf terms. For the VDEs during disruption, we show that as the plasma is vertically displaced, edge halo current sheet becomes MHD unstable and forms coherent edge current filament structures, which would eventually bleed into the walls. Our model explains some essential asymmetric physics relevant to the experimental observations. Supported by DOE Grants DE-SC0010565, DE-AC02-09CH11466.

The Distributions of Voltage-Gated K+ current Subtypes in Different Cell Sizes from Adult Mouse Dorsal Root Ganglia.

PubMed

Sheng, Anqi; Hong, Jiangru; Zhang, Lulu; Zhang, Yan; Zhang, Guangqin

2018-03-29

Voltage-gated K + (K V ) currents play a crucial role in regulating pain by controlling neuronal excitability, and are divided into transient A-type currents (I A ) and delayed rectifier currents (I K ). The dorsal root ganglion (DRG) neurons are heterogeneous and the subtypes of K V currents display different levels in distinct cell sizes. To observe correlations of the subtypes of K V currents with DRG cell sizes, K V currents were recorded by whole-cell patch clamp in freshly isolated mouse DRG neurons. Results showed that I A occupied a high proportion in K V currents in medium- and large-diameter DRG neurons, whereas I K possessed a larger proportion of K V currents in small-diameter DRG neurons. A lower correlation was found between the proportion of I A or I K in K V currents and cell sizes. These data suggest that I A channels are mainly expressed in medium and large cells and I K channels are predominantly expressed in small cells.

Remote sensing of ocean current boundary layer. [Loop Current in Gulf of Mexico

NASA Technical Reports Server (NTRS)

Maul, G. A. (Principal Investigator)

1973-01-01

The author has identified the following significant results. A time series of the Loop Current in the Gulf of Mexico, covering an annual cycle of growth, spreading, and decay, has been obtained in synchronization with ERTS-1. Computer enhanced images, which are necessary to extract useful oceanic information, show that the current can be observed either by color or sea state effects associated with the cyclonic boundary. The color effect relates to the spectral variations in the optical properties of the water and its suspended particles, and is studied by radiative transfer theory. Significant oceanic parameters identified are: the probability of forward scattering, and the ratio of scattering to total attenuation. Several spectra of upwelling diffuse light are computed as a function of the concentration of particles and yellow substance. These calculations compare favorably with experimental measurements and show that the ratio of channels method gives ambiguous interpretative results. These results are used to discuss features in images where surface measurements were obtained and are extended to tentative explanation in others.

AC Glow Discharge Plasma in N2O

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

Yousif, F. B.; Martinez, H.; Robledo-Martinez, A.

2006-12-04

This paper considers the optical and electrical characterization of AC glow discharge plasma in the abnormal glow mode used for optical emission spectroscopy. The total discharge current and applied voltage are measured using conventional techniques. The electrical characteristics of the planer-cathode glow discharge confirmed that the plasma is operating at abnormal discharge mode characterized by the increases in the operating voltage as the current was raised under given pressure. Optical emission spectroscopy was used to determine the main emission lines of the glow discharge plasma of N2O at pressures between 0.5 and 4.0 Torr. It shows that the discharge emissionmore » range is mainly within 300-400 nm. The emission lines correspond to NO, O2, and O{sub 2}{sup +} are the dominant lines in the glow discharge plasma in the present study. Intensity of the emission lines show linear increase with the discharge current up to 0.4 A followed by saturation at higher currents. No emission lines were observed in this work corresponding to atomic oxygen or nitrogen.« less

Observations of the sub-inertial, near-surface East India Coastal Current

NASA Astrophysics Data System (ADS)

Mukhopadhyay, S.; Shankar, D.; Aparna, S. G.; Mukherjee, A.

2017-09-01

We present surface current measurements made using two pairs of HF (high-frequency) radars deployed on the east coast of India. The radar data, used in conjunction with data from acoustic Doppler current profiler (ADCP) measurements on the shelf and slope off the Indian east coast, confirm that the East India Coastal Current (EICC) flows poleward as a deep current during February-March. During the summer monsoon, when the EICC flows poleward, and October-December, when the EICC flows equatorward, the current is shallow (< 40 m deep), except towards the northern end of the coast. Data from Argo floats confirm a shallow mixed layer that leads to a strong vertical shear off southeast India during October-December. A consequence of the strong stratification is that the upward propagation of phase evident in the ADCP data does not always extend to the surface. Even within the seasons, however, the poleward and equatorward flows show variability at periods of the order of 20-45 days, implying that the EICC direction is the same over the top ∼100 m for short durations. The high spatial resolution of the HF radar data brings out features at scales shorter than those resolved by the altimeter and the high temporal resolution captures short bursts that are not captured in satellite-derived estimates of surface currents. The radar data show that the EICC, which is a boundary current, leaves a strong imprint on the current at the coast. Since the EICC is known to be affected significantly by remote forcing, this correlation between the boundary and nearshore current implies the need to use large-domain models even for simulating the nearshore current. Comparison with a simulation by a state-of-the-art Ocean General Circulation Model, run at a resolution of 0.1 ° × 0.1 ° , shows that the model is able to simulate only the low-frequency variability.

Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors

NASA Technical Reports Server (NTRS)

Sadlier, John E.; Smith, Stephen J.; Bandler, Simon R.; Chervenak, James A.; Clem, John R.

2009-01-01

We have found experimentally that the critical current of a square thin-film superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T, a behavior that has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. As a consequence, the effective transition temperature T(sub c) of the TES is current-dependent and at fixed current scales as 1/L(sup 2). We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. We have observed the longitudinal proximity effect in these devices over extraordinarily long lengths up to 290 micrometers, 1450 times the mean-free path.

Indirectly pumped 3.7 THz InGaAs/InAlAs quantum-cascade lasers grown by metal-organic vapor-phase epitaxy.

PubMed

Fujita, Kazuue; Yamanishi, Masamichi; Furuta, Shinichi; Tanaka, Kazunori; Edamura, Tadataka; Kubis, Tillmann; Klimeck, Gerhard

2012-08-27

Device-performances of 3.7 THz indirect-pumping quantum-cascade lasers are demonstrated in an InGaAs/InAlAs material system grown by metal-organic vapor-phase epitaxy. The lasers show a low threshold-current-density of ~420 A/cm2 and a peak output power of ~8 mW at 7 K, no sign of parasitic currents with recourse to well-designed coupled-well injectors in the indirect pump scheme, and a maximum operating temperature of Tmax ~100 K. The observed roll-over of output intensities in current ranges below maximum currents and limitation of Tmax are discussed with a model for electron-gas heating in injectors. Possible ways toward elevation of Tmax are suggested.

Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors

NASA Technical Reports Server (NTRS)

Sadleir, John E.; Smith, Stephen J.; Bandler, Simon R.; Chervenak, James A.; Clem, John R.

2010-01-01

We have found experimentally that the critical current of a square thin-film superconducting transition-edge sensor (TES) depends exponentially upon the side length L and the square root of the temperature T, a behavior that has a natural theoretical explanation in terms of longitudinal proximity effects if the TES is regarded as a weak link between superconducting leads. As a consequence, the effective transition temperature T(sub c) of the TES is current-dependent and at fixed current scales as 1/L(sup 2). We also have found that the critical current can show clear Fraunhofer-like oscillations in an applied magnetic field, similar to those found in Josephson junctions. We have observed the longitudinal proximity effect in these devices over extraordinarily long lengths up to 290 micrometers, 1450 times the mean-free path.

New Inspiring Planetarium Show Introduces ALMA to the Public

NASA Astrophysics Data System (ADS)

2009-03-01

As part of a wide range of education and public outreach activities for the International Year of Astronomy 2009 (IYA2009), ESO, together with the Association of French Language Planetariums (APLF), has produced a 30-minute planetarium show, In Search of our Cosmic Origins. It is centred on the global ground-based astronomical Atacama Large Millimeter/submillimeter Array (ALMA) project and represents a unique chance for planetariums to be associated with the IYA2009. ESO PR Photo 09a/09 Logo of the ALMA Planetarium Show ESO PR Photo 09b/09 Galileo's first observations with a telescope ESO PR Photo 09c/09 The ALMA Observatory ESO PR Photo 09d/09 The Milky Way band ESO PR Video 09a/09 Trailer in English ALMA is the leading telescope for observing the cool Universe -- the relic radiation of the Big Bang, and the molecular gas and dust that constitute the building blocks of stars, planetary systems, galaxies and life itself. It is currently being built in the extremely arid environment of the Chajnantor plateau, at 5000 metres altitude in the Chilean Andes, and will start scientific observations around 2011. ALMA, the largest current astronomical project, is a revolutionary telescope, comprising a state-of-the-art array of 66 giant 12-metre and 7-metre diameter antennas observing at millimetre and submillimetre wavelengths. In Search of our Cosmic Origins highlights the unprecedented window on the Universe that this facility will open for astronomers. "The show gives viewers a fascinating tour of the highest observatory on Earth, and takes them from there out into our Milky Way, and beyond," says Douglas Pierce-Price, the ALMA Public Information Officer at ESO. Edited by world fulldome experts Mirage3D, the emphasis of the new planetarium show is on the incomparable scientific adventure of the ALMA project. A young female astronomer guides the audience through a story that includes unique animations and footage, leading the viewer from the first observations by Galileo, 400 years ago, to the world of modern astronomy, moving from the visible wavelength domain to explore the millimetre-wave view of the Universe, and leaving light-polluted cities for unique settings in some of the highest and driest places on Earth. "The fascinating topic, the breathtaking ESO astronomical images, the amazing 3D computer animations, and the very clever use of the music, all make this a really inspiring show," says Agnès Acker, President of the APLF. In search of our Cosmic Origins is available in three different formats: fulldome video, classical with video windows, and classical with slides. Fulldome video shows immerse the audience in a true 360-degree projected computer-generated virtual environment. The ALMA planetarium show is currently available in French and English. Several other language versions are in preparation: German, Italian, Spanish and Chilean Spanish, while further languages are planned: Danish, Dutch, Greek, Japanese, Portuguese and Brazilian Portuguese. The show will be available to all planetariums worldwide for a small fee, depending on the type and the size of the planetarium, to cover basic costs. The media are invited to attend, and see firsthand, the official screening during the European Film Festival, between 24 and 26 April 2009 in Espinho, Portugal. For media accreditation, please go to http://iff.multimeios.pt/index.php?option=com_wrapper&Itemid=45 A set of educational materials is also being prepared and will be finished in late April. To learn more about the show, please go to www.cosmicorigins.org

Depth of origin of ocean-circulation-induced magnetic signals

NASA Astrophysics Data System (ADS)

Irrgang, Christopher; Saynisch-Wagner, Jan; Thomas, Maik

2018-01-01

As the world ocean moves through the ambient geomagnetic core field, electric currents are generated in the entire ocean basin. These oceanic electric currents induce weak magnetic signals that are principally observable outside of the ocean and allow inferences about large-scale oceanic transports of water, heat, and salinity. The ocean-induced magnetic field is an integral quantity and, to first order, it is proportional to depth-integrated and conductivity-weighted ocean currents. However, the specific contribution of oceanic transports at different depths to the motional induction process remains unclear and is examined in this study. We show that large-scale motional induction due to the general ocean circulation is dominantly generated by ocean currents in the upper 2000 m of the ocean basin. In particular, our findings allow relating regional patterns of the oceanic magnetic field to corresponding oceanic transports at different depths. Ocean currents below 3000 m, in contrast, only contribute a small fraction to the ocean-induced magnetic signal strength with values up to 0.2 nT at sea surface and less than 0.1 nT at the Swarm satellite altitude. Thereby, potential satellite observations of ocean-circulation-induced magnetic signals are found to be likely insensitive to deep ocean currents. Furthermore, it is shown that annual temporal variations of the ocean-induced magnetic field in the region of the Antarctic Circumpolar Current contain information about sub-surface ocean currents below 1000 m with intra-annual periods. Specifically, ocean currents with sub-monthly periods dominate the annual temporal variability of the ocean-induced magnetic field.

InP electroluminescence as a tool to directly monitor carrier leakage in InGaAsP/InP buried heterostructure lasers

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

Stern, M.B.; Brody, E.; Sowell, B.

1987-12-15

Direct measurements of homojunction and heterojunction carrier leakage currents in InGaAsP/InP buried heterostructure lasers have been made by monitoring the electroluminescence (EL) at 0.96 ..mu..m in the InP confinement layers. These EL measurements show directly, for the first time, a correlation between homojunction leakage currents and the sublinearity in the 1.3-..mu..m light output-current characteristic. The observed decrease in the 0.96-..mu..m intensity with increasing p-dopant concentration is a direct confirmation that heterojunction leakage is reduced when the doping level in the p-InP confinement layer is increased.

Electric-field-driven phase transition in vanadium dioxide

NASA Astrophysics Data System (ADS)

Wu, B.; Zimmers, A.; Aubin, H.; Ghosh, R.; Liu, Y.; Lopez, R.

2011-12-01

We report on local probe measurements of current-voltage and electrostatic force-voltage characteristics of electric-field-induced insulator to metal transition in VO2 thin film. In conducting AFM mode, switching from the insulating to metallic state occurs for electric-field threshold E˜6.5×107Vm-1 at 300K. Upon lifting the tip above the sample surface, we find that the transition can also be observed through a change in electrostatic force and in tunneling current. In this noncontact regime, the transition is characterized by random telegraphic noise. These results show that electric field alone is sufficient to induce the transition; however, the electronic current provides a positive feedback effect that amplifies the phenomena.

Role of silver nanotube on conductivity, dielectric permittivity and current voltage characteristics of polyvinyl alcohol-silver nanocomposite film

NASA Astrophysics Data System (ADS)

Mukherjee, P. S.; Das, A. K.; Dutta, B.; Meikap, A. K.

2017-12-01

A comprehensive study on the prevailing conduction mechanism, dielectric relaxation and current voltage behaviour of Polyvinyl alcohol (PVA) - Silver (Ag) nanotube composite film has been reported. Introduction of Ag nanotubes enhances the conductivity and dielectric permittivity of film. Film shows semiconducting behaviour with two activation energies. The dc conductivity of the nanocomposite film obeys the adiabatic small polaron model. The dielectric permittivity can be analysed by modified Cole-Cole model. A non-Debye type asymmetric behaviour has been observed in the sample. The back to back Schottky diode concept has been used to describe the current-voltage characteristic of the composite film.

Strain-induced chiral magnetic effect in Weyl semimetals

DOE PAGES

Cortijo, Alberto; Kharzeev, Dmitri; Landsteiner, Karl; ...

2016-12-19

Here, we argue that strain applied to a time-reversal and inversion breaking Weyl semimetal in a magnetic field can induce an electric current via the chiral magnetic effect. A tight-binding model is used to show that strain generically changes the locations in the Brillouin zone but also the energies of the band touching points (tips of the Weyl cones). Since axial charge in a Weyl semimetal can relax via intervalley scattering processes, the induced current will decay with a time scale given by the lifetime of a chiral quasiparticle. Lastly, we estimate the strength and lifetime of the current formore » typical material parameters and find that it should be experimentally observable.« less

Simultaneous observations of traveling convection vortices: Ionosphere-thermosphere coupling: M-I-T COUPLING OF TCV

DOE PAGES

Kim, Hyomin; Lessard, Marc R.; Jones, Sarah L.; ...

2017-03-11

We present simultaneous observations of magnetosphere-ionosphere-thermosphere coupling over Svalbard during a traveling convection vortex (TCV) event. Various spaceborne and ground-based instruments made coordinated measurements, including magnetometers, particle detectors, an all-sky camera, European Incoherent Scatter (EISCAT) Svalbard Radar, Super Dual Auroral Radar Network (SuperDARN), and SCANning Doppler Imager (SCANDI). The instruments recorded TCVs associated with a sudden change in solar wind dynamic pressure. The data display typical features of TCVs including vortical ionospheric convection patterns seen by the ground magnetometers and SuperDARN radars and auroral precipitation near the cusp observed by the all-sky camera. Simultaneously, electron and ion temperature enhancements withmore » corresponding density increase from soft precipitation are also observed by the EISCAT Svalbard Radar. The ground magnetometers also detected electromagnetic ion cyclotron waves at the approximate time of the TCV arrival. This implies that they were generated by a temperature anisotropy resulting from a compression on the dayside magnetosphere. SCANDI data show a divergence in thermospheric winds during the TCVs, presumably due to thermospheric heating associated with the current closure linked to a field-aligned current system generated by the TCVs. We conclude that solar wind pressure impulse-related transient phenomena can affect even the upper atmospheric dynamics via current systems established by a magnetosphere-ionosphere-thermosphere coupling process.« less

Simultaneous observations of traveling convection vortices: Ionosphere-thermosphere coupling: M-I-T COUPLING OF TCV

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

Kim, Hyomin; Lessard, Marc R.; Jones, Sarah L.

We present simultaneous observations of magnetosphere-ionosphere-thermosphere coupling over Svalbard during a traveling convection vortex (TCV) event. Various spaceborne and ground-based instruments made coordinated measurements, including magnetometers, particle detectors, an all-sky camera, European Incoherent Scatter (EISCAT) Svalbard Radar, Super Dual Auroral Radar Network (SuperDARN), and SCANning Doppler Imager (SCANDI). The instruments recorded TCVs associated with a sudden change in solar wind dynamic pressure. The data display typical features of TCVs including vortical ionospheric convection patterns seen by the ground magnetometers and SuperDARN radars and auroral precipitation near the cusp observed by the all-sky camera. Simultaneously, electron and ion temperature enhancements withmore » corresponding density increase from soft precipitation are also observed by the EISCAT Svalbard Radar. The ground magnetometers also detected electromagnetic ion cyclotron waves at the approximate time of the TCV arrival. This implies that they were generated by a temperature anisotropy resulting from a compression on the dayside magnetosphere. SCANDI data show a divergence in thermospheric winds during the TCVs, presumably due to thermospheric heating associated with the current closure linked to a field-aligned current system generated by the TCVs. We conclude that solar wind pressure impulse-related transient phenomena can affect even the upper atmospheric dynamics via current systems established by a magnetosphere-ionosphere-thermosphere coupling process.« less

Steady state scenario development with elevated minimum safety factor on DIII-D

DOE PAGES

Holcomb, Christopher T.; Ferron, John R.; Luce, Timothy C.; ...

2014-08-15

On DIII-D, a high β scenario with minimum safety factor (q min) near 1.4 has been optimized with new tools and shown to be a favourable candidate for long pulse or steady state operation in future devices. Furthermore, the new capability to redirect up to 5 MW of neutral beam injection (NBI) from on- to off-axis improves the ability to sustain elevated q min with a less peaked pressure profile. The observed changes increase the ideal magnetohydrodynamics (MHD) n = 1 mode β N limit thus providing a path forward for increasing the noninductive current drive fraction by operating atmore » high β N. Quasi-stationary discharges free of tearing modes have been sustained at βN = 3.5 and β T = 3.6% for two current profile diffusion timescales (about 3 s) limited by neutral beam duration. The discharge performance has normalized fusion performance expected to give fusion gain Q ≈ 5 in a device the size of ITER. Analysis of the poloidal flux evolution and current drive balance show that the loop voltage profile is almost relaxed even with 25% of the current driven inductively, and q min remains elevated near 1.4. Our observations increase confidence that the current profile will not evolve to one unstable to a tearing mode. In preliminary tests a divertor heat flux reduction technique based on producing a radiating mantle with neon injection appears compatible with this operating scenario. 0D model extrapolations suggest it may be possible to push this scenario up to 100% noninductive current drive by raising β N. Similar discharges with q min = 1.5–2 were susceptible to tearing modes and off-axis fishbones, and with q min > 2 lower normalized global energy confinement time is observed.« less

Current-driven ion-acoustic and potential-relaxation instabilities excited in plasma plume during electron beam welding

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

Trushnikov, D. N., E-mail: trdimitr@yandex.ru; Mladenov, G. M., E-mail: gmmladenov@abv.bg; Koleva, E. G., E-mail: eligeorg@abv.bg

Many papers have sought correlations between the parameters of secondary particles generated above the beam/work piece interaction zone, dynamics of processes in the keyhole, and technological processes. Low- and high-frequency oscillations of the current, collected by plasma have been observed above the welding zone during electron beam welding. Low-frequency oscillations of secondary signals are related to capillary instabilities of the keyhole, however; the physical mechanisms responsible for the high-frequency oscillations (>10 kHz) of the collected current are not fully understood. This paper shows that peak frequencies in the spectra of the collected high-frequency signal are dependent on the reciprocal distancemore » between the welding zone and collector electrode. From the relationship between current harmonics frequency and distance of the collector/welding zone, it can be estimated that the draft velocity of electrons or phase velocity of excited waves is about 1600 m/s. The dispersion relation with the properties of ion-acoustic waves is related to electron temperature 10 000 K, ion temperature 2 400 K and plasma density 10{sup 16} m{sup −3}, which is analogues to the parameters of potential-relaxation instabilities, observed in similar conditions. The estimated critical density of the transported current for creating the anomalous resistance state of plasma is of the order of 3 A·m{sup −2}, i.e. 8 mA for a 3–10 cm{sup 2} collector electrode. Thus, it is assumed that the observed high-frequency oscillations of the current collected by the positive collector electrode are caused by relaxation processes in the plasma plume above the welding zone, and not a direct demonstration of oscillations in the keyhole.« less

Current-driven ion-acoustic and potential-relaxation instabilities excited in plasma plume during electron beam welding

NASA Astrophysics Data System (ADS)

Trushnikov, D. N.; Mladenov, G. M.; Belenkiy, V. Ya.; Koleva, E. G.; Varushkin, S. V.

2014-04-01

Many papers have sought correlations between the parameters of secondary particles generated above the beam/work piece interaction zone, dynamics of processes in the keyhole, and technological processes. Low- and high-frequency oscillations of the current, collected by plasma have been observed above the welding zone during electron beam welding. Low-frequency oscillations of secondary signals are related to capillary instabilities of the keyhole, however; the physical mechanisms responsible for the high-frequency oscillations (>10 kHz) of the collected current are not fully understood. This paper shows that peak frequencies in the spectra of the collected high-frequency signal are dependent on the reciprocal distance between the welding zone and collector electrode. From the relationship between current harmonics frequency and distance of the collector/welding zone, it can be estimated that the draft velocity of electrons or phase velocity of excited waves is about 1600 m/s. The dispersion relation with the properties of ion-acoustic waves is related to electron temperature 10 000 K, ion temperature 2 400 K and plasma density 1016 m-3, which is analogues to the parameters of potential-relaxation instabilities, observed in similar conditions. The estimated critical density of the transported current for creating the anomalous resistance state of plasma is of the order of 3 A.m-2, i.e. 8 mA for a 3-10 cm2 collector electrode. Thus, it is assumed that the observed high-frequency oscillations of the current collected by the positive collector electrode are caused by relaxation processes in the plasma plume above the welding zone, and not a direct demonstration of oscillations in the keyhole.

Phonetic imitation by young children and its developmental changes.

PubMed

Nielsen, Kuniko

2014-12-01

In the current study, the author investigated the developmental course of phonetic imitation in childhood, and further evaluated existing accounts of phonetic imitation. Sixteen preschoolers, 15 third graders, and 18 college students participated in the current study. An experiment with a modified imitation paradigm with a picture-naming task was conducted, in which participants' voice-onset time (VOT) was compared before and after they were exposed to target speech with artificially increased VOT. Extended VOT in the target speech was imitated by preschoolers and 3rd graders as well as adults, confirming previous findings in phonetic imitation. Furthermore, an age effect of phonetic imitation was observed; namely, children showed greater imitation than adults, whereas the degree of imitation was comparable between preschoolers and 3rd graders. No significant effect of gender or word specificity was observed. Young children imitated fine phonetic details of the target speech, and greater degree of phonetic imitation was observed in children compared to adults. These findings suggest that the degree of phonetic imitation negatively correlates with phonological development.

Deterministic Creation of Macroscopic Cat States

PubMed Central

Lombardo, Daniel; Twamley, Jason

2015-01-01

Despite current technological advances, observing quantum mechanical effects outside of the nanoscopic realm is extremely challenging. For this reason, the observation of such effects on larger scale systems is currently one of the most attractive goals in quantum science. Many experimental protocols have been proposed for both the creation and observation of quantum states on macroscopic scales, in particular, in the field of optomechanics. The majority of these proposals, however, rely on performing measurements, making them probabilistic. In this work we develop a completely deterministic method of macroscopic quantum state creation. We study the prototypical optomechanical Membrane In The Middle model and show that by controlling the membrane’s opacity, and through careful choice of the optical cavity initial state, we can deterministically create and grow the spatial extent of the membrane’s position into a large cat state. It is found that by using a Bose-Einstein condensate as a membrane high fidelity cat states with spatial separations of up to ∼300 nm can be achieved. PMID:26345157

Discrepancy between simulated and observed ethane and propane levels explained by underestimated fossil emissions

NASA Astrophysics Data System (ADS)

Dalsøren, Stig B.; Myhre, Gunnar; Hodnebrog, Øivind; Myhre, Cathrine Lund; Stohl, Andreas; Pisso, Ignacio; Schwietzke, Stefan; Höglund-Isaksson, Lena; Helmig, Detlev; Reimann, Stefan; Sauvage, Stéphane; Schmidbauer, Norbert; Read, Katie A.; Carpenter, Lucy J.; Lewis, Alastair C.; Punjabi, Shalini; Wallasch, Markus

2018-03-01

Ethane and propane are the most abundant non-methane hydrocarbons in the atmosphere. However, their emissions, atmospheric distribution, and trends in their atmospheric concentrations are insufficiently understood. Atmospheric model simulations using standard community emission inventories do not reproduce available measurements in the Northern Hemisphere. Here, we show that observations of pre-industrial and present-day ethane and propane can be reproduced in simulations with a detailed atmospheric chemistry transport model, provided that natural geologic emissions are taken into account and anthropogenic fossil fuel emissions are assumed to be two to three times higher than is indicated in current inventories. Accounting for these enhanced ethane and propane emissions results in simulated surface ozone concentrations that are 5-13% higher than previously assumed in some polluted regions in Asia. The improved correspondence with observed ethane and propane in model simulations with greater emissions suggests that the level of fossil (geologic + fossil fuel) methane emissions in current inventories may need re-evaluation.

Sensorless control for permanent magnet synchronous motor using a neural network based adaptive estimator

NASA Astrophysics Data System (ADS)

Kwon, Chung-Jin; Kim, Sung-Joong; Han, Woo-Young; Min, Won-Kyoung

2005-12-01

The rotor position and speed estimation of permanent-magnet synchronous motor(PMSM) was dealt with. By measuring the phase voltages and currents of the PMSM drive, two diagonally recurrent neural network(DRNN) based observers, a neural current observer and a neural velocity observer were developed. DRNN which has self-feedback of the hidden neurons ensures that the outputs of DRNN contain the whole past information of the system even if the inputs of DRNN are only the present states and inputs of the system. Thus the structure of DRNN may be simpler than that of feedforward and fully recurrent neural networks. If the backpropagation method was used for the training of the DRNN the problem of slow convergence arise. In order to reduce this problem, recursive prediction error(RPE) based learning method for the DRNN was presented. The simulation results show that the proposed approach gives a good estimation of rotor speed and position, and RPE based training has requires a shorter computation time compared to backpropagation based training.

Initial measurements of O-ion and He-ion decay rates observed from the Van Allen probes RBSPICE instrument

PubMed Central

Gerrard, Andrew; Lanzerotti, Louis; Gkioulidou, Matina; Mitchell, Donald; Manweiler, Jerry; Bortnik, Jacob; Keika, Kunihiro

2014-01-01

H-ion (∼45 keV to ∼600 keV), He-ion (∼65 keV to ∼520 keV), and O-ion (∼140 keV to ∼1130 keV) integral flux measurements, from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft B, are reported. These abundance data form a cohesive picture of ring current ions during the first 9 months of measurements. Furthermore, the data presented herein are used to show injection characteristics via the He-ion/H-ion abundance ratio and the O-ion/H-ion abundance ratio. Of unique interest to ring current dynamics are the spatial-temporal decay characteristics of the two injected populations. We observe that He-ions decay more quickly at lower L shells, on the order of ∼0.8 day at L shells of 3–4, and decay more slowly with higher L shell, on the order of ∼1.7 days at L shells of 5–6. Conversely, O-ions decay very rapidly (∼1.5 h) across all L shells. The He-ion decay time are consistent with previously measured and calculated lifetimes associated with charge exchange. The O-ion decay time is much faster than predicted and is attributed to the inclusion of higher-energy (> 500 keV) O-ions in our decay rate estimation. We note that these measurements demonstrate a compelling need for calculation of high-energy O-ion loss rates, which have not been adequately studied in the literature to date. Key Points We report initial observations of ring current ions We show that He-ion decay rates are consistent with theory We show that O-ions with energies greater than 500 keV decay very rapidly PMID:26167435

Plasmoid formation in the elongated current sheet during transient CHI on HIST

NASA Astrophysics Data System (ADS)

Nagata, Masayoshi; Fujita, Akihiro; Matsui, Takahiro; Kikuchi, Yusuke; Fukumoto, Naoyuki; Kanki, Takashi

2016-10-01

The Transient-Coaxial Helicity Injection (T-CHI) is a promising candidate for the non-inductive plasma start-up on Spherical Torus (ST). The problem of the flux closure in the T-CHI is important and related to understand the physics of fast magnetic reconnection. The recent MHD simulation (F. Ebrahimi and R. Raman, Phys. Rev. Lett. 114, 205003 (2015)) on T-CHI for NSTX predicts the formation and breakup of an elongated Sweet-Parker (S-P) current sheet and a transient to plasmoid instability. According to this simulation, the reconnection rate based on the plasmoid instability is faster than that by S-P model and becomes nearly independent of the Lundquist number S. In this meeting, we will present that the formation of multiple X-points and plasmoids has been observed in T-CHI start-up plasmas on HIST. The stronger external guide (toroidal) magnetic field makes plasma less compressible, leading to slower reconnection time and longer current sheet. The experimental observation shows that 2/3 plasmoids are generated in the elongated current sheet with the narrow width comparable to the ion skin depth or the ion sound gyro-radius. The small plasmoids develop to a large-scale flux structure due to a current inward diffusion during the decay phase.

Poole Frenkel current and Schottky emission in SiN gate dielectric in AlGaN/GaN metal insulator semiconductor heterostructure field effect transistors

NASA Astrophysics Data System (ADS)

Hanna, Mina J.; Zhao, Han; Lee, Jack C.

2012-10-01

We analyze the anomalous I-V behavior in SiN prepared by plasma enhanced chemical vapor deposition for use as a gate insulator in AlGaN/GaN metal insulator semiconductor heterostructure filed effect transistors (HFETs). We observe leakage current across the dielectric with opposite polarity with respect to the applied electric field once the voltage sweep reaches a level below a determined threshold. This is observed as the absolute minimum of the leakage current does not occur at minimum voltage level (0 V) but occurs earlier in the sweep interval. Curve-fitting analysis suggests that the charge-transport mechanism in this region is Poole-Frenkel current, followed by Schottky emission due to band bending. Despite the current anomaly, the sample devices have shown a notable reduction of leakage current of over 2 to 6 order of magnitudes compared to the standard Schottky HFET. We show that higher pressures and higher silane concentrations produce better films manifesting less trapping. This conforms to our results that we reported in earlier publications. We found that higher chamber pressure achieves higher sheet carrier concentration that was found to be strongly dependent on the trapped space charge at the SiN/GaN interface. This would suggest that a lower chamber pressure induces more trap states into the SiN/GaN interface.

Twilight observation by the naked eye of the dawn sincere at Hail and other areas in Saudi Arabia

NASA Astrophysics Data System (ADS)

Khalifa, N. S.; Hassan, A. H.; Taha, A. I.

2018-06-01

Naked eye observations of morning twilight phenomenon at Hail and other areas of Saudi Arabia are recorded. During the interval from 2014 to 2015, about 80 morning twilight observations were carried out in Hail at longitude λ = 41°42‧E and latitude φ = 27°31‧N for a desert background. The phenomena was followed over azimuth angles ranged from 0° to 20° of solar vertical direction and from 0° to 10° along the altitudinal range. By selecting 32 days with a very good visibility, it was found that Sun depression, Do, lies in a range between 13.48° and 14.69° with an average of 14.014° ±0.317. The difference between our obtained value and that one which is currently applicable in Saudi Arabia is about 4°. The results indicate that dawn (white thread browser) occurs at a sun vertical depression angle Do = 14.66° (mean + 2SD) according to the normal eye estimations. The results at different areas in the deep desert in KSA showed that the beginning of morning twilight and true dawn is at sun vertical depression Do = 14.88° (mean + 1SD). The current study shows significant results, which are comparable with both naked eye observations and photoelectric measurements of true dawn in both Egypt and Libya for desert background.

Connecting Variability and Metals in White Dwarfs

NASA Astrophysics Data System (ADS)

Kilic, Mukremin

2016-10-01

The Kepler and K2 missions have revealed that about half of the observed white dwarfs with sufficient signal-to-noise ratio light curves have low-level photometric variations at hour to day timescales. Potential explanations for the observed variability include the relativistic beaming effect, ellipsodial variations, eclipses, and reflection off of giant planets in close orbits. However, these are all rare events. Roughly 10% of white dwarfs are magnetic, and magnetic fields can explain part of this puzzle. However, the high incidence (50%) of variability is currently unexplained. HST COS spectroscopy of nearby white dwarfs show that about half of them have metals on their surface. Hence, we propose that the observed variability is due to the rotation of the star coupled with an inhomogeneous surface distribution of accreted metals. We have recently discovered an ideal system to test this hypothesis. J1529 is an apparently non-magnetic white dwarf that shows 5.9% photometric dips in the optical every 38 min. We propose to obtain COS TIME-TAG spectroscopy of J1529 over 4 orbits to search for surface abundance differences throughout the orbit and look for the flux redistribution effect in the optical. These observations will confirm or rule out the idea that inhomogeneous metal accretion on white dwarfs can explain the high incidence of variability. We predict that the LSST will identify 100,000 variable white dwarfs. Hence, understanding the source of variability in white dwarfs has implications for the current and future transient surveys.

Current at domain walls, roughly speaking: nanoscales studies of disorder roughening and conduction

NASA Astrophysics Data System (ADS)

Paruch, Patrycja

2013-03-01

Domain walls in (multi)ferroic materials are the thin elastic interfaces separating regions with different orientations of magnetisation, electric polarisation, or spontaneous strain. Understanding their behaviour, and controlling domain size and stability, is key for their integration into applications, while fundamentally, domain walls provide an excellent model system in which the rich physics of disordered elastic interfaces can be accesses. In addition, domain walls can present novel properties, quite different from those of their parent materials, making them potentially useful as active components in future nano-devices. Here, we present our atomic force microscopy studies of ferroelectric domain walls in epitaxial Pb(Zr0.2Ti0.8)O3 and BiFeO3 thin films, in which we use piezorespose force microscopy to show unusual domain wall roughening behaviour, with very localised disorder regions in the sample leading to a complex, multi-affine scaling of the domain wall shape. We also show the effects of temperature, environmental conditions, and defects on switching dynamics and domain wall roughness. We combine these observations with parallel conductive-tip atomic force microscopy current measurements, which also show highly localised variations in conduction, and highlight the key role played by oxygen vacancies in the observed domain wall conduction.

Search for sterile neutrinos in holographic dark energy cosmology: Reconciling Planck observation with the local measurement of the Hubble constant

NASA Astrophysics Data System (ADS)

Zhao, Ming-Ming; He, Dong-Ze; Zhang, Jing-Fei; Zhang, Xin

2017-08-01

We search for sterile neutrinos in the holographic dark energy cosmology by using the latest observational data. To perform the analysis, we employ the current cosmological observations, including the cosmic microwave background temperature power spectrum data from the Planck mission, the baryon acoustic oscillation measurements, the type Ia supernova data, the redshift space distortion measurements, the shear data of weak lensing observation, the Planck lensing measurement, and the latest direct measurement of H0 as well. We show that, compared to the Λ CDM cosmology, the holographic dark energy cosmology with sterile neutrinos can relieve the tension between the Planck observation and the direct measurement of H0 much better. Once we include the H0 measurement in the global fit, we find that the hint of the existence of sterile neutrinos in the holographic dark energy cosmology can be given. Under the constraint of the all-data combination, we obtain Neff=3.76 ±0.26 and mν,sterile eff<0.215 eV , indicating that the detection of Δ Neff>0 in the holographic dark energy cosmology is at the 2.75 σ level and the massless or very light sterile neutrino is favored by the current observations.

Supra Arcade Downflows with XRT Informed by Dipolarization Fronts with THEMIS

NASA Technical Reports Server (NTRS)

Kobelski, Adam; Savage, Sabrina Leah; Malaspina, David

2016-01-01

Magnetic reconnection can rapidly reconfigure the magnetic field of the corona, accelerating plasma through the site of reconnection. Ambiguities due to the nature of remote sensing have complicated the interpretation of observations of the inflowing and outflowing plasma in reconnecting regions. In particular, the interpretation of sunward moving density depletions above flare arcades (known as Supra Arcade Downflows - SADs) is still debated. Hinode/XRT has provided a wealth of observations for SADs and helped inform our current understanding of these structures. SADs have been interpreted as wakes behind newly reconnected and outflowing loops (Supra Arcade Downflowing Loops - SADLs). Models have shown the plausibility of this interpretation, though this interpretation has not yet been fully accepted. We present here observations of newly reconnected outflowing loops observed via in situ instruments in the magnetosphere. These observations, provided by five THEMIS spacecraft, show that around retracting loops (dipolarization fronts in this context) similar dynamic temperature and density structures are found as seen in SADs. We compare data from multiple SADs and dipolarization fronts to show that the observational signatures implied in the corona can be directly observed in similar plasma regimes in the magnetosphere, strongly favoring the interpretation of SADs as wakes behind retracting loops.

Using EFSO/PQC to Improve the Quality of Observations and Analyses

NASA Astrophysics Data System (ADS)

Chen, T. C.; Kalnay, E.

2017-12-01

Massive amounts of observations are assimilated every day into modern Numerical Weather Prediction (NWP) systems. This makes difficult to estimate the impact of a new observing system using the current approach (Observing System Experiments, OSEs) because there is already so much information provided by existing observations. In addition, the large volume of data also prevents monitoring the impact of each assimilated observation with OSEs. We demonstrate here how using Ensemble Forecast Sensitivity to Observations (EFSO) allows monitoring and improving the impact of observations on the analyses and forecasts in the Hybrid GSI/LETKF system. In addition, we show how EFSO can identify flow dependent detrimental observations from observing systems that, on the average, are beneficial. For example, using EFSO we find that positive zonal wind innovations in MODIS polar winds are generally detrimental, whereas no such bias is present in other satellite wind systems. We also show how EFSO can be used to identify and reject very detrimental observations (Proactive Quality Control, PQC). The withdrawal of these detrimental observations leads to improved analyses and 5-day forecasts, which also serves as a verification of EFSO. The operational implementation of PQC/EFSO is computationally very feasible, and will provide detailed QC monitoring of every observing system. Finally, we provide a theoretical justification of the PQC and its connection to dynamical instabilities with a simple Lorenz 96 model.

Impact of Microplastic Beads and Fibers on Waterflea (Ceriodaphnia dubia) Survival, Growth, and Reproduction: Implications of Single and Mixture Exposures.

PubMed

Ziajahromi, Shima; Kumar, Anupama; Neale, Peta A; Leusch, Frederic D L

2017-11-21

There is limited knowledge regarding the adverse effects of wastewater-derived microplastics, particularly fibers, on aquatic biota. In this study, we examined the acute (48 h) and chronic (8 d) effects of microplastic polyester fibers and polyethylene (PE) beads on freshwater zooplankton Ceriodaphnia dubia. We also assessed the acute response of C. dubia to a binary mixture of microplastic beads and fibers for the first time. Acute exposure to fibers and PE beads both showed a dose-dependent effect on survival. An equitoxic binary mixture of beads and fibers resulted in a toxic unit of 1.85 indicating less than additive effects. Chronic exposure to lower concentrations did not significantly affect survival of C. dubia, but a dose-dependent effect on growth and reproduction was observed. Fibers showed greater adverse effects than PE beads. While ingestion of fibers was not observed, scanning electron microscopy showed carapace and antenna deformities after exposure to fibers, with no deformities observed after exposure to PE beads. While much of the current research has focused on microplastic beads, our study shows that microplastic fibers pose a greater risk to C. dubia, with reduced reproductive output observed at concentrations within an order of magnitude of reported environmental levels.

Cardiac structural changes and electrical remodeling in a thiamine-deficiency model in rats.

PubMed

Roman-Campos, D; Campos, A C; Gioda, C R; Campos, P P; Medeiros, M A A; Cruz, J S

2009-06-05

Thiamine is an important cofactor present in many biochemical reactions, and its deprivation can lead to heart dysfunction. Little is known about the influence of thiamine deprivation on the electrophysiological behavior of the isolated heart cells and information about thiamine deficiency in heart morphology is controversial. Thus, we decided to investigate the major repolarizing conductances and their influence in the action potential (AP) waveform as well as the changes in the heart structure in a set of thiamine deficiency in rats. Using the patch-clamp technique, we investigated inward (I(K1)) and outward K(+) currents (I(to)), T-type and L-type Ca(2+) currents and APs. To evaluate heart morphology we used hematoxylin and eosin in transversal heart sections. Thiamine deficiency caused a marked decrease in left ventricle thickness, cardiomyocyte number, cell length and width, and membrane capacitance. When evaluating I(to) we did not find difference in current amplitude; however an acceleration of I(to) inactivation was observed. I(K1) showed a reduction in the amplitude and slope conductance, which implicated a less negative resting membrane potential in cardiac myocytes isolated from thiamine-deficient rats. We did not find any difference in L-type Ca(2+) current density. T-type Ca(2+) current was not observed. In addition, we did not observe significant changes in AP repolarization. Based on our study we can conclude that thiamine deficiency causes heart hypotrophy and not heart hypertrophy. Moreover, we provided evidence that there is no major electrical remodeling during thiamine deficiency, a feature of heart failure models.

Terminator field-aligned current system: A new finding from model-assimilated data set (MADS)

NASA Astrophysics Data System (ADS)

Zhu, L.; Schunk, R. W.; Scherliess, L.; Sojka, J. J.; Gardner, L. C.; Eccles, J. V.; Rice, D.

2013-12-01

Physics-based data assimilation models have been recognized by the space science community as the most accurate approach to specify and forecast the space weather of the solar-terrestrial environment. The model-assimilated data sets (MADS) produced by these models constitute an internally consistent time series of global three-dimensional fields whose accuracy can be estimated. Because of its internal consistency of physics and completeness of descriptions on the status of global systems, the MADS has also been a powerful tool to identify the systematic errors in measurements, reveal the missing physics in physical models, and discover the important dynamical physical processes that are inadequately observed or missed by measurements due to observational limitations. In the past years, we developed a data assimilation model for the high-latitude ionospheric plasma dynamics and electrodynamics. With a set of physical models, an ensemble Kalman filter, and the ingestion of data from multiple observations, the data assimilation model can produce a self-consistent time-series of the complete descriptions of the global high-latitude ionosphere, which includes the convection electric field, horizontal and field-aligned currents, conductivity, as well as 3-D plasma densities and temperatures, In this presentation, we will show a new field-aligned current system discovered from the analysis of the MADS produced by our data assimilation model. This new current system appears and develops near the ionospheric terminator. The dynamical features of this current system will be described and its connection to the active role of the ionosphere in the M-I coupling will be discussed.

Effects of wall electrodes on Hall effect thruster plasma

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

Langendorf, S., E-mail: samuel.langendorf@gatech.edu; Walker, M., E-mail: mitchell.walker@ae.gatech.edu; High-Power Electric Propulsion Laboratory, 625 Lambert St NW, Atlanta, Georgia 30318

2015-02-15

This paper investigates the physical mechanisms that cause beneficial and detrimental performance effect observed to date in Hall effect thrusters with wall electrodes. It is determined that the wall electrode sheath can reduce ion losses to the wall if positioned near the anode (outside the dense region of the plasma) such that an ion-repelling sheath is able to form. The ability of the wall electrode to form an ion-repelling sheath is inversely proportional to the current drawn—if the wall electrode becomes the dominant sink for the thruster discharge current, increases in wall electrode bias result in increased local plasma potentialmore » rather than an ion-repelling sheath. A single-fluid electron flow model gives results that mimic the observed potential structures and the current-sharing fractions between the anode and wall electrodes, showing that potential gradients in the presheath and bulk plasma come at the expense of current draw to the wall electrodes. Secondary electron emission from the wall electrodes (or lack thereof) is inferred to have a larger effect if the electrodes are positioned near the exit plane than if positioned near the anode, due to the difference in energy deposition from the plasma.« less

Power Generation from a Radiative Thermal Source Using a Large-Area Infrared Rectenna

NASA Astrophysics Data System (ADS)

Shank, Joshua; Kadlec, Emil A.; Jarecki, Robert L.; Starbuck, Andrew; Howell, Stephen; Peters, David W.; Davids, Paul S.

2018-05-01

Electrical power generation from a moderate-temperature thermal source by means of direct conversion of infrared radiation is important and highly desirable for energy harvesting from waste heat and micropower applications. Here, we demonstrate direct rectified power generation from an unbiased large-area nanoantenna-coupled tunnel diode rectifier called a rectenna. Using a vacuum radiometric measurement technique with irradiation from a temperature-stabilized thermal source, a generated power density of 8 nW /cm2 is observed at a source temperature of 450 °C for the unbiased rectenna across an optimized load resistance. The optimized load resistance for the peak power generation for each temperature coincides with the tunnel diode resistance at zero bias and corresponds to the impedance matching condition for a rectifying antenna. Current-voltage measurements of a thermally illuminated large-area rectenna show current zero crossing shifts into the second quadrant indicating rectification. Photon-assisted tunneling in the unbiased rectenna is modeled as the mechanism for the large short-circuit photocurrents observed where the photon energy serves as an effective bias across the tunnel junction. The measured current and voltage across the load resistor as a function of the thermal source temperature represents direct current electrical power generation.

Observation of reflected waves on the SABRE positive polarity inductive adder MITL

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

Cuneo, M.E.; Poukey, J.W.; Mendel, C.W.

We are studying the coupling of extraction applied-B ion diodes to Magnetically Insulated Transmission Line (MITLs) on the SABRE (Sandia Accelerator and Beam Research Experiment, 6 MV, 300 kA) positive polarity inductive voltage adder. Our goal is to determine conditions under which efficient coupling occurs. The best total power efficiency for an ideal ion diode load (i.e., without parasitic losses) is obtained by maximizing the product of cathode current and gap voltage. MITLs require that the load impedance be undermatched to the self-limited line operating impedance for efficient transfer of power to ion diodes, independent of transit time isolation, andmore » even in the case of multiple cathode system with significant vacuum electron flow. We observe that this undermatched condition results in a reflected wave which decreases the line voltage and gap electron sheath current, and increases the anode and cathode current in a time-dependent way. The MITL diode coupling is determined by the flow impedance at the adder exit. We also show that the flow impedance increases along the extension MITL on SABRE. Experimental measurements of current and peak voltage are compared to analytical models and TWOQUICK 2.5-D PIC code simulations.« less

Tidal and residual currents across the northern Ryukyu Island chain observed by ferryboat ADCP

NASA Astrophysics Data System (ADS)

Liu, Zhao-Jun; Nakamura, Hirohiko; Zhu, Xiao-Hua; Nishina, Ayako; Dong, Menghong

2017-09-01

Ferryboat Acoustic Doppler Current Profiler (ADCP) data from 2003 to 2012 are used to estimate the tidal and residual currents across the northern Ryukyu Island chain (RIC) between the islands of Okinawa and Amamioshima. In this region, the M2 tide current is the strongest tidal component, and the K1 tide current is the strongest diurnal tidal component. The corresponding maximum amplitudes are 40 and 34 cm s-1, respectively. After removal of the tidal currents, the mean volume transport, 1.5 ± 2.7 Sv, flows into the East China Sea (ECS) from the western North Pacific through four channels in this area. In an empirical orthogonal function (EOF) analysis performed to clarify the temporal and spatial variability of currents through the four channels, the first two EOF modes account for 71% and 18% of the total variance, respectively. The EOF1 mode shows a clear bottom-intensified mode through the deep channel, which is likely to be formed by the propagation of bottom-trapped long topographic Rossby wave caused by the impingement of westward-propagating mesoscale eddies upon the eastern slope of the northern RIC. The EOF2 mode has significant seasonal variability and may be driven by the wind stress prevailing over the Kuroshio flow region around the northern RIC in October-November. This study provides observational evidence of the water exchanges across the northern RIC, which is essential for constructing a circulation scheme in the North Pacific subtropical western boundary region.

Structure of high latitude currents in magnetosphere-ionosphere models

NASA Astrophysics Data System (ADS)

Wiltberger, M. J.; Lyon, J.; Merkin, V. G.; Rigler, E. J.

2016-12-01

Using three resolutions of the Lyon-Fedder-Mobarry global magnetosphere-ionosphere model (LFM) and the Weimer 2005 empirical model the structure of the high latitude field-aligned current patterns is examined. Each LFM resolution was run for the entire Whole Heliosphere Interval (WHI), which contained two high-speed solar wind streams and modest interplanetary magnetic field strengths. Average states of the field-aligned current (FAC) patterns for 8 interplanetary magnetic field clock angle directions are computed using data from these runs. Generally speaking the patterns obtained agree well with results from the Weimer 2005 computed using the solar wind and IMF conditions that correspond to each bin. As the simulation resolution increases the currents become more intense and confined. A machine learning analysis of the FAC patterns shows that the ratio of Region 1 (R1) to Region 2 (R2) currents decreases as the simulation resolution increases. This brings the simulation results into better agreement with observational predictions and the Weimer 2005 model results. The increase in R2 current strengths in the model also results in a better shielding of mid- and low-latitude ionosphere from the polar cap convection, also in agreement with observations. Current-voltage relationships between the R1 strength and the cross-polar cap potential (CPCP) are quite similar at the higher resolutions indicating the simulation is converging on a common solution. We conclude that LFM simulations are capable of reproducing the statistical features of FAC patterns.

DNA Sequence-Dependent Ionic Currents in Ultra-Small Solid-State Nanopores†

PubMed Central

Comer, Jeffrey

2016-01-01

Measurements of ionic currents through nanopores partially blocked by DNA have emerged as a powerful method for characterization of the DNA nucleotide sequence. Although the effect of the nucleotide sequence on the nanopore blockade current has been experimentally demonstrated, prediction and interpretation of such measurements remain a formidable challenge. Using atomic resolution computational approaches, here we show how the sequence, molecular conformation, and pore geometry affect the blockade ionic current in model solid-state nanopores. We demonstrate that the blockade current from a DNA molecule is determined by the chemical identities and conformations of at least three consecutive nucleotides. We find the blockade currents produced by the nucleotide triplets to vary considerably with their nucleotide sequence despite having nearly identical molecular conformations. Encouragingly, we find blockade current differences as large as 25% for single-base substitutions in ultra small (1.6 nm × 1.1 nm cross section; 2 nm length) solid-state nanopores. Despite the complex dependence of the blockade current on the sequence and conformation of the DNA triplets, we find that, under many conditions, the number of thymine bases is positively correlated with the current, whereas the number of purine bases and the presence of both purine and pyrimidines in the triplet are negatively correlated with the current. Based on these observations, we construct a simple theoretical model that relates the ion current to the base content of a solid-state nanopore. Furthermore, we show that compact conformations of DNA in narrow pores provide the greatest signal-to-noise ratio for single base detection, whereas reduction of the nanopore length increases the ionic current noise. Thus, the sequence dependence of nanopore blockade current can be theoretically rationalized, although the predictions will likely need to be customized for each nanopore type. PMID:27103233

Observation of chiral currents at the magnetic domain boundary of a topological insulator

DOE PAGES

Wang, Y. H.; Kirtley, J. R.; Katmis, F.; ...

2015-08-28

A magnetic domain boundary on the surface of a three-dimensional topological insulator is predicted to host a chiral edge state, but direct demonstration is challenging. Here, we used a scanning superconducting quantum interference device to show that current in a magnetized EuS/Bi 2Se 3 heterostructure flows at the edge when the Fermi level is gate-tuned to the surface band gap. We further induced micron-scale magnetic structures on the heterostructure, and detected a chiral edge current at the magnetic domain boundary. The chirality of the current was determined by magnetization of the surrounding domain and its magnitude by the local chemicalmore » potential rather than the applied current. As a result, such magnetic structures, provide a platform for detecting topological magnetoelectric effects and may enable progress in quantum information processing and spintronics.« less

Effects of Current Density on Microstructure and Corrosion Property of Coating on AZ31 Mg Alloy Processed via Plasma Electrolytic Oxidation

NASA Astrophysics Data System (ADS)

Lee, Kang Min; Einkhah, Feryar; Sani, Mohammad Ali Faghihi; Ko, Young Gun; Shin, Dong Hyuk

The effects of the current density on the micro structure and the corrosion property of the coating on AZ31 Mg alloy processed by the plasma electrolytic oxidation (PEO) were investigated. The present coatings were produced in an acid electrolyte containing K2ZrF6 with three different current densities, i.e., 100, 150, and 200 mA/cm2. From the microstructural observations, as the applied current density was increased, the diameter of micro-pores formed by the plasma discharges with high temperature increased. The coatings on AZ31 Mg alloy were mainly composed of MgO, ZrO2, MgF2, and Mg2Zr5O12 phases. The results of potentiodynamic polarization clearly showed that the PEO-treated AZ31 Mg alloy applied at 100 mA/cm2 of current density exhibited better corrosion properties than the others.

Mid-Atomic-Number Cylindrical Wire Array Precursor Plasma Studies on Zebra

DOE PAGES

Stafford, A; Safronova, A. S.; Kantsyrev, V. L.; ...

2014-12-30

The precursor plasmas from low wire number cylindrical wire arrays (CWAs) were previously shown to radiate at temperatures >300 eV for Ni-60 (94% Cu and 6% Ni) wires in experiments on the 1-MA Zebra generator. Continued research into precursor plasmas has studied additional midatomic-number materials including Cu and Alumel (95% Ni, 2% Al, 2% Mn, and 1% Si) to determine if the >300 eV temperatures are common for midatomic-number materials. Additionally, current scaling effects were observed by performing CWA precursor experiments at an increased current of 1.5 MA using a load current multiplier. Our results show an increase in amore » linear radiation yield of ~50% (16 versus 10 kJ/cm) for the experiments at increased current. However, plasma conditions inferred through the modeling of X-ray time-gated spectra are very similar for the precursor plasma in both current conditions.« less

Dark current in multilayer stabilized amorphous selenium based photoconductive x-ray detectors

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

Frey, Joel B.; Belev, George; Kasap, Safa O.

2012-07-01

We report on experimental results which show that the dark current in n-i-p structured, amorphous selenium films is independent of i-layer thickness in samples with consistently thick blocking layers. We have observed, however, a strong dependence on the n-layer thickness and positive contact metal chosen. These results indicate that the dominant source of the dark current is carrier injection from the contacts and any contribution from carriers thermally generated in the bulk of the photoconductive layer is negligible. This conclusion is supported by a description of the dark current transients at different applied fields by a model which assumes onlymore » carrier emission over a Schottky barrier. This model also predicts that while hole injection is initially dominant, some time after the application of the bias, electron injection may become the dominant source of dark current.« less

Significance of the model considering mixed grain-size for inverse analysis of turbidites

NASA Astrophysics Data System (ADS)

Nakao, K.; Naruse, H.; Tokuhashi, S., Sr.

2016-12-01

A method for inverse analysis of turbidity currents is proposed for application to field observations. Estimation of initial condition of the catastrophic events from field observations has been important for sedimentological researches. For instance, there are various inverse analyses to estimate hydraulic conditions from topography observations of pyroclastic flows (Rossano et al., 1996), real-time monitored debris-flow events (Fraccarollo and Papa, 2000), tsunami deposits (Jaffe and Gelfenbaum, 2007) and ancient turbidites (Falcini et al., 2009). These inverse analyses need forward models and the most turbidity current models employ uniform grain-size particles. The turbidity currents, however, are the best characterized by variation of grain-size distribution. Though there are numerical models of mixed grain-sized particles, the models have difficulty in feasibility of application to natural examples because of calculating costs (Lesshaft et al., 2011). Here we expand the turbidity current model based on the non-steady 1D shallow-water equation at low calculation costs for mixed grain-size particles and applied the model to the inverse analysis. In this study, we compared two forward models considering uniform and mixed grain-size particles respectively. We adopted inverse analysis based on the Simplex method that optimizes the initial conditions (thickness, depth-averaged velocity and depth-averaged volumetric concentration of a turbidity current) with multi-point start and employed the result of the forward model [h: 2.0 m, U: 5.0 m/s, C: 0.01%] as reference data. The result shows that inverse analysis using the mixed grain-size model found the known initial condition of reference data even if the condition where the optimization started is deviated from the true solution, whereas the inverse analysis using the uniform grain-size model requires the condition in which the starting parameters for optimization must be in quite narrow range near the solution. The uniform grain-size model often reaches to local optimum condition that is significantly different from true solution. In conclusion, we propose a method of optimization based on the model considering mixed grain-size particles, and show its application to examples of turbidites in the Kiyosumi Formation, Boso Peninsula, Japan.

Observation of Terahertz Radiation via the Two-Color Laser Scheme with Uncommon Frequency Ratios

NASA Astrophysics Data System (ADS)

Zhang, Liang-Liang; Wang, Wei-Min; Wu, Tong; Zhang, Rui; Zhang, Shi-Jing; Zhang, Cun-Lin; Zhang, Yan; Sheng, Zheng-Ming; Zhang, Xi-Cheng

2017-12-01

In the widely studied two-color laser scheme for terahertz (THz) radiation from a gas, the frequency ratio of the two lasers is usually fixed at ω2/ω1=1 :2 . We investigate THz generation with uncommon frequency ratios. Our experiments show, for the first time, efficient THz generation with new ratios of ω2/ω1=1 :4 and 2 ∶3 . We observe that the THz polarization can be adjusted by rotating the longer-wavelength laser polarization and the polarization adjustment becomes inefficient by rotating the other laser polarization; the THz energy shows similar scaling laws with different frequency ratios. These observations are inconsistent with multiwave mixing theory, but support the gas-ionization or plasma-current model. This study pushes the development of the two-color scheme and provides a new dimension to explore the long-standing problem of the THz generation mechanism.

Observation of Terahertz Radiation via the Two-Color Laser Scheme with Uncommon Frequency Ratios.

PubMed

Zhang, Liang-Liang; Wang, Wei-Min; Wu, Tong; Zhang, Rui; Zhang, Shi-Jing; Zhang, Cun-Lin; Zhang, Yan; Sheng, Zheng-Ming; Zhang, Xi-Cheng

2017-12-08

In the widely studied two-color laser scheme for terahertz (THz) radiation from a gas, the frequency ratio of the two lasers is usually fixed at ω_{2}/ω_{1}=1:2. We investigate THz generation with uncommon frequency ratios. Our experiments show, for the first time, efficient THz generation with new ratios of ω_{2}/ω_{1}=1:4 and 2∶3. We observe that the THz polarization can be adjusted by rotating the longer-wavelength laser polarization and the polarization adjustment becomes inefficient by rotating the other laser polarization; the THz energy shows similar scaling laws with different frequency ratios. These observations are inconsistent with multiwave mixing theory, but support the gas-ionization or plasma-current model. This study pushes the development of the two-color scheme and provides a new dimension to explore the long-standing problem of the THz generation mechanism.

Cognitive-Processing Bias in Chinese Student Teachers with Strong and Weak Professional Identity.

PubMed

Wang, Xin-Qiang; Zhu, Jun-Cheng; Liu, Lu; Chen, Xiang-Yu

2017-01-01

Professional identity plays an important role in career development. Although many studies have examined professional identity, differences in cognitive-processing biases between Chinese student teachers with strong and weak professional identity are poorly understood. The current study adopted Tversky's social-cognitive experimental paradigm to explore cognitive-processing biases in Chinese student teachers with strong and weak professional identity. Experiment 1 showed that participants with strong professional identity exhibited stronger positive-coding bias toward positive profession-related life events, relative to that observed in those with weak professional identity. Experiment 2 showed that participants with strong professional identity exhibited greater recognition bias for previously read items, relative to that observed in those with weak professional identity. Overall, the results suggested that participants with strong professional identity exhibited greater positive cognitive-processing bias relative to that observed in those with weak professional identity.

Cognitive-Processing Bias in Chinese Student Teachers with Strong and Weak Professional Identity

PubMed Central

Wang, Xin-qiang; Zhu, Jun-cheng; Liu, Lu; Chen, Xiang-yu

2017-01-01

Professional identity plays an important role in career development. Although many studies have examined professional identity, differences in cognitive-processing biases between Chinese student teachers with strong and weak professional identity are poorly understood. The current study adopted Tversky’s social-cognitive experimental paradigm to explore cognitive-processing biases in Chinese student teachers with strong and weak professional identity. Experiment 1 showed that participants with strong professional identity exhibited stronger positive-coding bias toward positive profession-related life events, relative to that observed in those with weak professional identity. Experiment 2 showed that participants with strong professional identity exhibited greater recognition bias for previously read items, relative to that observed in those with weak professional identity. Overall, the results suggested that participants with strong professional identity exhibited greater positive cognitive-processing bias relative to that observed in those with weak professional identity. PMID:28555123

Technique for the comparison of light spectra from natural and laboratory generated lightning current arcs

NASA Astrophysics Data System (ADS)

Mitchard, D.; Clark, D.; Carr, D.; Haddad, A.

2016-08-01

A technique was developed for the comparison of observed emission spectra from lightning current arcs generated through self-breakdown in air and the use of two types of initiation wire, aluminum bronze and nichrome, against previously published spectra of natural lightning events. A spectrograph system was used in which the wavelength of light emitted by the lightning arc was analyzed to derive elemental interactions. A lightning impulse of up to 100 kA was applied to a two hemispherical tungsten electrode configuration which allowed the effect of the lightning current and lightning arc length to be investigated. A natural lightning reference spectrum was reconstructed from literature, and generated lightning spectra were obtained from self-breakdown across a 14.0 mm air gap and triggered along initiation wires of length up to 72.4 mm. A comparison of the spectra showed that the generated lightning arc induced via self-breakdown produced a very similar spectrum to that of natural lightning, with the addition of only a few lines from the tungsten electrodes. A comparison of the results from the aluminum bronze initiation wire showed several more lines, whereas results from the nichrome initiation wire differed greatly across large parts of the spectrum. This work highlights the potential use for spectrographic techniques in the study of lightning interactions with surrounding media and materials, and in natural phenomena such as recently observed ball lightning.

Variability of Surface pollutants and aerosol concentration over Abu Dhabi, UAE - sources, transport and current levels

NASA Astrophysics Data System (ADS)

Phanikumar, Devulapalli V.; Basha, Ghouse; Ouarda, Taha B. M. J.

2015-04-01

In the view of recent economic, industrial, and rapid development, Abu Dhabi (24.4oN; 54.4oE; 27m msl) has become one of the most populated regions in the world despite of extreme heat, frequent dust storms, and with distinctive topography. The major sources of air pollution are from the dust and sand storms, greenhouse gas emissions, and to some extent from industrial pollution. In order to realize the accurate and comprehensive understanding of air quality and plausible sources over this region, we have made a detailed analysis of three years simultaneous measurements during 2011-13 of pollutants such as O3, SO2, NO2, CO, and PM10 concentrations. Diurnal variation of meteorological parameters such as temperature and wind speed/relative humidity clearly shows daytime maximum/minimum in summer followed by pre-monsoon, post-monsoon and winter. The prevailing winds over this region are mostly from northwesterly direction (Shamal wind). Diurnal wind pattern showed a clear contrast with the majority of the wind pattern during nighttime and early morning is from the westerly/northwesterly and daytime is from southwesterly/southeasterly directions. The diurnal pattern of O3 shows minimum during 08 LT and increases thereafter reaching maximum at 17 LT and decreases during nighttime. However, the diurnal pattern of SO2 and NO2 show a peak at ~ 08 LT and dip at ~ 14 LT during all the seasons with some variability in each season. On the other hand, the diurnal pattern of CO shows a peculiar picture of elevated levels during daytime peaking at ~ 10 LT (prominent in summer and post-monsoon) followed by a sharp decrease and minimum is ~14 LT. PM10 concentration has an early morning peak at ~ 02 LT and then decreases to a minimum value at ~11 LT and again increases in the afternoon hours (maximum at ~17 LT) depicting a forenoon-afternoon asymmetry. Monthly variation of PM10 shows maximum in pre-monsoon season and minimum in winter. Our observations show the diurnal pattern of pollutants are in contrast with the diurnal pattern of wind speed as evident from the previous observations. Wind rose diagram of pollutants reveal that the dominant source directions are scattered from northwesterly to southwesterly. Our results (2011-13) are compared with earlier observations from the same region (2007-08) and no alarming differences were observed in the pollutant levels. Our observations are discussed in the light of current understanding of pollutants sources over this region.

The Current Driven Kink Instability and its Relationship to Delta-Spot Active Regions

NASA Astrophysics Data System (ADS)

Linton, Mark George

The current driven kink instability may be the cause of both the unusual morphology of solar δ-spot active regions and the tendency of these regions to be significantly more flare active than most active regions. We investigate the current driven kink instability of flux tubes in the solar interior both with a linear stability analysis and with nonlinear MHD simulations. The linear analysis shows that there is a critical twist, which depends on the axial magnetic field profile, that a flux tube needs to become kink unstable. This critical twist decreases as the tube expands, so twisted flux tubes will become increasingly unstable as they rise through the convection zone. The nonlinear simulations show that a twisted tube excited by a single unstable kink mode will evolve to a helical equilibrium state. The emergence through the photosphere of such a kinked tube would create an active region which was tilted with respect to Hale's law and which would rotate as it evolved, as δ-spots are observed to do. We then find that, when excited by multiple unstable kink modes, highly twisted flux tubes develop concentrated kinks. These concentrated kinks would produce more of the observed characteristics of δ-spot active regions. They would create active regions which, in addition to emerging tilted and then rotating, would remain compact as they evolved, and develop strong shear along their magnetic neutral line. Finally, we find that a strong concentrated kink develops a current sheet at which the magnetic field reconnects, which may be the cause of the high flare activity of δ-spots.

Temporal and Spatial Variability of the Ras Al-Hadd Jet/Front in the Northwest Arabian Sea

NASA Astrophysics Data System (ADS)

Al Shaqsi, Hilal Mohamed Said

Thirteen years of 1.1 km resolution daily satellites remote sensing sea surface temperature datasets (2002-2014), sea surface winds, sea surface height, Argo floats, daily three-hour interval wind datasets, and hourly records of oceanography physical parameters from mooring current meters were processed and analyzed to investigate the dynamics, temporal and spatial variability of the Ras Al-Hadd Jet off the northwest Arabian Sea. Cayula and Cornillon single image edge detection algorithm was used to detect these thermal fronts. The Ras Al-Hadd thermal front was found to have two seasonal peaks. The first peak occurred during the intensified southwest monsoon period (July/August), while the second peak was clearly observed during the transitional period or the Post-Southwest monsoon (September-October). Interannual and intraseasonal variability showed the occurrence of the Ras Al-Hadd thermal fronts in the northwest Arabian Sea. The southwest monsoon winds, the Somalia Current, the East Arabian Current, and the warmer high salinity waters from the Sea of Oman are the main factors influencing the creation of the Ras Al-Hadd Jet. Based on direct observations, current velocity in the Cape Ras Al-Hadd Jet exceeded 120 cms-1, and the wind speed was over 12 ms-1 during the southwest monsoon seasons. The mean width and the mean length of the Jet were approximately 40 km and 260 km, respectively. Neither the winter monsoon, nor the Pre-Southwest monsoon seasons showed signs of the Ras Al-Hadd Jet or fronts in the northwest Arabian Sea.

Open issues in hadronic interactions for air showers

NASA Astrophysics Data System (ADS)

Pierog, Tanguy

2017-06-01

In detailed air shower simulations, the uncertainty in the prediction of shower observables for different primary particles and energies is currently dominated by differences between hadronic interaction models. With the results of the first run of the LHC, the difference between post-LHC model predictions has been reduced to the same level as experimental uncertainties of cosmic ray experiments. At the same time new types of air shower observables, like the muon production depth, have been measured, adding new constraints on hadronic models. Currently no model is able to consistently reproduce all mass composition measurements possible within the Pierre Auger Observatory for instance. Comparing the different models, and with LHC and cosmic ray data, we will show that the remaining open issues in hadronic interactions in air shower development are now in the pion-air interactions and in nuclear effects.

Fish-Eye Observing with Phased Array Radio Telescopes

NASA Astrophysics Data System (ADS)

Wijnholds, S. J.

The radio astronomical community is currently developing and building several new radio telescopes based on phased array technology. These telescopes provide a large field-of-view, that may in principle span a full hemisphere. This makes calibration and imaging very challenging tasks due to the complex source structures and direction dependent radio wave propagation effects. In this thesis, calibration and imaging methods are developed based on least squares estimation of instrument and source parameters. Monte Carlo simulations and actual observations with several prototype show that this model based approach provides statistically and computationally efficient solutions. The error analysis provides a rigorous mathematical framework to assess the imaging performance of current and future radio telescopes in terms of the effective noise, which is the combined effect of propagated calibration errors, noise in the data and source confusion.

Effect of beta-amyloid block of the fast-inactivating K+ channel on intracellular Ca2+ and excitability in a modeled neuron.

PubMed

Good, T A; Murphy, R M

1996-12-24

beta-Amyloid peptide (A beta), one of the primary protein components of senile plaques found in Alzheimer disease, is believed to be toxic to neurons by a mechanism that may involve loss of intracellular calcium regulation. We have previously shown that A beta blocks the fast-inactivating potassium (A) current. In this work, we show, through the use of a mathematical model, that the A beta-mediated block of the A current could result in increased intracellular calcium levels and increased membrane excitability, both of which have been observed in vitro upon acute exposure to A beta. Simulation results are compared with experimental data from the literature; the simulations quantitatively capture the observed concentration dependence of the neuronal response and the level of increase in intracellular calcium.

The mass of Lutetia from Rosetta RSI radio tracking

NASA Astrophysics Data System (ADS)

Pätzold, Martin; Andert, Thomas; Haeusler, Bernd; Tellmann, Silvia; Anderson, John D.; Asmar, Sami; Barriot, Jean-Pierre; Bird, Michael

The Rosetta spacecraft will flyby at its second target asteroid (21) Lutetia on 10 July 2010. Simulations based on the currently known size of Lutetia and assumptions on the bulk density show that the tracking of the two radio carrier frequencies at X-band (8.4 GHz) and S-band (2.3 GHz) during the flyby will yield a mass determination of less than a few percent accuracy, assuming noise conditions similar to those observed during several in-flight payload checkouts. The derivation of the asteroid volume by camera observation will be the driver for the un-certainty in the derivation of the bulk density. The mass determination alone, however, can already give clues for the currently unknown taxonomy of the asteroid type. If possible, first impressions and results from the flyby will be presented at the conference.

Structural and electronic properties of chiral single-wall copper nanotubes

NASA Astrophysics Data System (ADS)

Duan, YingNi; Zhang, JianMin; Xu, KeWei

2014-04-01

The structural, energetic and electronic properties of chiral ( n, m) (3⩽ n⩽6, n/2⩽ m⩽ n) single-wall copper nanotubes (CuNTs) have been investigated by using projector-augmented wave method based on density-functional theory. The (4, 3) CuNT is energetically stable and should be observed experimentally in both free-standing and tip-suspended conditions, whereas the (5, 5) and (6, 4) CuNTs should be observed in free-standing and tip-suspended conditions, respectively. The number of conductance channels in the CuNTs does not always correspond to the number of atomic strands comprising the nanotube. Charge density contours show that there is an enhanced interatomic interaction in CuNTs compared with Cu bulk. Current transporting states display different periods and chirality, the combined effects of which lead to weaker chiral currents on CuNTs.

Intrathecal Baclofen Therapy for the Treatment of Spasticity in Sjögren-Larsson Syndrome.

PubMed

Hidalgo, Eveline Teresa; Orillac, Cordelia; Hersh, Andrew; Harter, David H; Rizzo, William B; Weiner, Howard L

2017-01-01

Intrathecal baclofen therapy is widely accepted as a treatment option for patients with severe spasticity. The current treatment of spasticity in patients with Sjögren-Larsson syndrome is largely symptomatic, given that no effective causal therapy treatments are available. We report the outcome of 2 patients with Sjögren-Larsson syndrome who had pump implantation for intrathecal baclofen. We observed a positive response, with a decrease of spasticity, reflecting in the Modified Ashworth Scale, and parents and caregivers observed a functional improvement in both patients. One patient experienced skin irritation 15 months after surgery, necessitating pump repositioning. No infection occurred. Our report shows that intrathecal baclofen therapy can have a positive therapeutic effect on spasticity in patients with Sjögren-Larsson syndrome, and therefore may be a promising addition to current treatments.

Estimation of the processes controlling variability in phytoplankton pigment distributions on the southeastern U.S. continental shelf

NASA Technical Reports Server (NTRS)

Mcclain, Charles R.; Ishizaka, Joji; Hofmann, Eileen E.

1990-01-01

Five coastal-zone-color-scanner images from the southeastern U.S. continental shelf are combined with concurrent moored current meter measurements to assess the processes controlling the variability in chlorophyll concentration and distribution in this region. An equation governing the space and time distribution of a nonconservative quantity such as chlorophyll is used in the calculations. The terms of the equation, estimated from observations, show that advective, diffusive, and local processes contribute to the plankton distributions and vary with time and location. The results from this calculation are compared with similar results obtained using a numerical physical-biological model with circulation fields derived from an optimal interpolation of the current meter observations and it is concluded that the two approaches produce different estimates of the processes controlling phytoplankton variability.

PHYSICAL MODEL FOR RECOGNITION TUNNELING

PubMed Central

Krstić, Predrag; Ashcroft, Brian; Lindsay, Stuart

2015-01-01

Recognition tunneling (RT) identifies target molecules trapped between tunneling electrodes functionalized with recognition molecules that serve as specific chemical linkages between the metal electrodes and the trapped target molecule. Possible applications include single molecule DNA and protein sequencing. This paper addresses several fundamental aspects of RT by multiscale theory, applying both all-atom and coarse-grained DNA models: (1) We show that the magnitude of the observed currents are consistent with the results of non-equilibrium Green's function calculations carried out on a solvated all-atom model. (2) Brownian fluctuations in hydrogen bond-lengths lead to current spikes that are similar to what is observed experimentally. (3) The frequency characteristics of these fluctuations can be used to identify the trapped molecules with a machine-learning algorithm, giving a theoretical underpinning to this new method of identifying single molecule signals. PMID:25650375

On magnetic reconnection in the Venusian wake. The experimental evidences

NASA Astrophysics Data System (ADS)

Fedorov, A.; Volwerk, M.; Zhang, T.; Barabash, S.; Sauvaud, J.

2009-12-01

The Venusian magnetotail is formed by solar wind magnetic flux tubes draping around the planet and stretched antisunward. The magnetotail topology represents two magnetic lobes separated by a thin current sheet. Such a configuration is a free energy reservoir. The accumulated energy is generally released by acceleration of planetary ions antisunward. But in the case of a magnetic reconnection, hypothetically appeared somewhere in the equatorial current sheet, some part of the planetary ions filling the tail, should be accelerated toward the planet. The present paper is devoted to the study of such sunward flows observed by IMA mass spectrometer onboard of the Venus Express orbiter. The case study shows rare accidently observed precipitations of the heavy ions in the nightside of the planet. The statistical study gives us the spatial distribution of such precipitations and conditions of their appearance.

Ponderomotive lower hybrid wave growth in electric fields associated with electron beam injection and transverse ion acceleration

NASA Astrophysics Data System (ADS)

Bale, S. D.; Kellogg, P. J.; Erickson, K. N.; Monson, S. J.; Arnoldy, R. L.

During electron beam injection, the Echo 7 rocket experiment observed large bursts of transversely accelerated ions. These ions seem to have been energized in the region of the beam or the payload return current. Electric field waveforms (<= 30 kHz) during gun operation show both low frequency fluctuations and broad band power. An analysis of the waveforms shows nonlinear mode coupling between waves near the ion cyclotron frequency and waves above the lower hybrid frequency.

Associating ground magnetometer observations with current or voltage generators

NASA Astrophysics Data System (ADS)

Hartinger, M. D.; Xu, Z.; Clauer, C. R.; Yu, Y.; Weimer, D. R.; Kim, H.; Pilipenko, V.; Welling, D. T.; Behlke, R.; Willer, A. N.

2017-07-01

A circuit analogy for magnetosphere-ionosphere current systems has two extremes for drivers of ionospheric currents: ionospheric electric fields/voltages constant while current/conductivity vary—the "voltage generator"—and current constant while electric field/conductivity vary—the "current generator." Statistical studies of ground magnetometer observations associated with dayside Transient High Latitude Current Systems (THLCS) driven by similar mechanisms find contradictory results using this paradigm: some studies associate THLCS with voltage generators, others with current generators. We argue that most of this contradiction arises from two assumptions used to interpret ground magnetometer observations: (1) measurements made at fixed position relative to the THLCS field-aligned current and (2) negligible auroral precipitation contributions to ionospheric conductivity. We use observations and simulations to illustrate how these two assumptions substantially alter expectations for magnetic perturbations associated with either a current or a voltage generator. Our results demonstrate that before interpreting ground magnetometer observations of THLCS in the context of current/voltage generators, the location of a ground magnetometer station relative to the THLCS field-aligned current and the location of any auroral zone conductivity enhancements need to be taken into account.

Magnetosphere dynamics during the 14 November 2012 storm inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US-CRCM

NASA Astrophysics Data System (ADS)

Buzulukova, Natalia; Goldstein, Jerry; Fok, Mei-Ching; Glocer, Alex; Valek, Phil; McComas, David; Korth, Haje; Anderson, Brian

2018-01-01

During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases (dropouts) in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global magnetosphere dynamics and magnetosphere-ionosphere (M-I) coupling during the dropout events using multipoint measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US-CRCM model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1) weak nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensification of Region 2 currents after the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by large-scale motions of the OCB (open-closed boundary) during substorm activity. We show the new result that this OCB motion was associated with global changes in Birkeland (M-I coupling) currents and strong modulation of low-altitude ion precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M-I coupling aspects that have not previously been investigated.

Magnetosphere dynamics during the 14 November 2012 storm inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US–CRCM

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

Buzulukova, Natalia; Goldstein, Jerry; Fok, Mei-Ching

During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases ("dropouts") in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global magnetosphere dynamics and magnetosphere–ionosphere (M–I) coupling during the dropout events using multipoint measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US–CRCM model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1) weak nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensificationmore » of Region 2 currents after the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by large-scale motions of the OCB (open–closed boundary) during substorm activity. We show the new result that this OCB motion was associated with global changes in Birkeland (M–I coupling) currents and strong modulation of low-altitude ion precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M–I coupling aspects that have not previously been investigated.« less

Magnetosphere Dynamics During the 14 November 2012 Storm Inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US-CRCM

NASA Technical Reports Server (NTRS)

Buzulukova, Natalia; Goldstein, Jerry; Fok, Mei-Ching; Glocer, Alex; Valek, Phil; McComas, David; Korth, Haje; Anderson, Brian

2018-01-01

During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases ('dropouts') in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global magnetosphere dynamics and magnetosphere- ionosphere (M-I) coupling during the dropout events using multipoint measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US-CRCM model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1) weak nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensification of Region 2 currents after the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by large-scale motions of the OCB (open-closed boundary) during substorm activity. We show the new result that this OCB motion was associated with global changes in Birkeland (M-I coupling) currents and strong modulation of low-altitude ion precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M-I coupling aspects that have not previously been investigated.

Magnetosphere dynamics during the 14 November 2012 storm inferred from TWINS, AMPERE, Van Allen Probes, and BATS-R-US–CRCM

DOE PAGES

Buzulukova, Natalia; Goldstein, Jerry; Fok, Mei-Ching; ...

2018-01-25

During the 14 November 2012 geomagnetic storm, the Van Allen Probes spacecraft observed a number of sharp decreases ("dropouts") in particle fluxes for ions and electrons of different energies. In this paper, we investigate the global magnetosphere dynamics and magnetosphere–ionosphere (M–I) coupling during the dropout events using multipoint measurements by Van Allen Probes, TWINS, and AMPERE together with the output of the two-way coupled global BATS-R-US–CRCM model. We find different behavior for two pairs of dropouts. For one pair, the same pattern was repeated: (1) weak nightside Region 1 and 2 Birkeland currents before and during the dropout; (2) intensificationmore » of Region 2 currents after the dropout; and (3) a particle injection detected by TWINS after the dropout. The model predicted similar behavior of Birkeland currents. TWINS low-altitude emissions demonstrated high variability during these intervals, indicating high geomagnetic activity in the near-Earth tail region. For the second pair of dropouts, the structure of both Birkeland currents and ENA emissions was relatively stable. The model also showed quasi-stationary behavior of Birkeland currents and simulated ENA emissions with gradual ring current buildup. We confirm that the first pair of dropouts was caused by large-scale motions of the OCB (open–closed boundary) during substorm activity. We show the new result that this OCB motion was associated with global changes in Birkeland (M–I coupling) currents and strong modulation of low-altitude ion precipitation. The second pair of dropouts is the result of smaller OCB disturbances not related to magnetospheric substorms. The local observations of the first pair of dropouts result from a global magnetospheric reconfiguration, which is manifested by ion injections and enhanced ion precipitation detected by TWINS and changes in the structure of Birkeland currents detected by AMPERE. This study demonstrates that multipoint measurements along with the global model results enable the reconstruction of a more complete system-level picture of the dropout events and provides insight into M–I coupling aspects that have not previously been investigated.« less

Tethered by Self-Generated Flow: Mucus String Augmented Feeding Current Generation in Larval Oysters

NASA Astrophysics Data System (ADS)

Jiang, H.; Wheeler, J.; Anderson, E.

2016-02-01

Marine zooplankton live in a nutritionally dilute environment. To survive, they must process an enormous volume of water relative to their own body volume for food. To achieve this, many zooplankters including copepods, invertebrate larvae, and protists create a feeding current to concentrate and transport food items to their food gathering structures. To enhance the efficiency of the feeding current, these zooplankters often rely on certain "tethering" mechanisms to retard their translational motion for producing a strong feeding current. The tethering force may include excess weight due to gravity, force from attachment to solid surfaces, and drag experienced by strategically placed morphological structures. Larval oysters are known from previous studies to release mucus strings during feeding, presumably for supplying a tethering force to enhance their feeding-current efficiency. But the underlying mechanism is unclear. In this study, we used a high-speed microscale imaging system (HSMIS) to observe the behavior of freely swimming and feeding larval oysters. We also used HSMIS to measure larval imposed feeding currents via a micro-particle image velocimetry (µPIV) technique. HSMIS allows observations along a vertically oriented focal plane in a relatively large water vessel with unprecedented spatial and temporal resolutions. Our high-speed videos show that a feeding larval oyster continuously released a long mucus string into its feeding current that flows downward; the feeding current subsequently dragged the mucus string downward. Analysis of our µPIV data combined with a hydrodynamic model further suggests that the drag force experienced by the mucus string in the feeding current contributes significantly to the tethering force required to generate the feeding current. Thus, mucus strings in larval oysters act as "anchors" in larval self-generated flow to actively tether the feeding larvae.

Modelling the Auroral Magnetosphere-Ionosphere Coupling System at Jupiter

NASA Astrophysics Data System (ADS)

Bunce, E. J.; Cowley, S.; Provan, G.

2016-12-01

The magnetosphere-ionosphere coupling system at Jupiter is a topic of central significance in understanding the fundamental properties of its large-scale plasma environment. Theoretical discussion of this topic typically considers the properties of the field-aligned current systems that form part of a large-scale magnetosphere-ionosphere coupling current system associated with momentum exchange between the ionosphere and the magnetosphere, communicated via the magnetic field. The current system associated with the main oval is believed to be related to centrifugally-driven outward radial transport of iogenic plasma that leads to sub-corotation in the middle magnetosphere. In addition to the magnetosphere-ionosphere coupling current system, upward-directed field-aligned currents may flow at the open-closed field line boundary due to the shear between outer closed field lines and open field lines, which may relate to emission poleward of the main oval. An axi-symmetric model of the plasma flow in the jovian system, the related coupling currents, and the consequent auroral precipitation based on these combined ideas was initially devised to represent typical steady-state conditions for the system and later extended to consider auroral effects resulting from sudden compressions of the magnetosphere. More recently, the model has been extended along model magnetic field lines into the magnetosphere in order to relate them to in situ observations from the NASA Juno spacecraft at Jupiter. The field-aligned coupling currents associated with the modelled current systems produce a readily-observable azimuthal field signature that bends the field lines out of magnetic meridians. Here we show the computed azimuthal fields produced by our model auroral current system throughout the region between the ionosphere and the magnetic equator, and illustrate the results by evaluation of various model parameters (e.g. field-aligned current density, accelerating voltages, accelerated energy flux) along the Juno orbits.

Reinjected water return at Miravalles geothermal reservoir, Costa Rica: Numerical modelling and observations

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

Parini, Mauro; Acuna, Jorge A.; Laudiano, Michele

1996-01-24

The first 55 MW power plant at Miravalles started operation in March, 1994. During the first few months of production, a gradual increase in chloride content was observed in some production wells. The cause was assumed to be a rapid return of injectate from two in.jection wells located fairly near to the main production area. A tracer test was performed and showed a relatively rapid breakthrough, confirming the assumption made. Numerical modeling was then carried out to try to reproduce the observed behavior. The reservoir was modelled with an idealized three-dimensional network of fractures embedded into a low permeability matrix.more » The “two waters” feature of TOUGH2 simulator was used. The numerical simulation showed good agreement with observations. A “porous medium” model with equivalent hydraulic characteristics was unable to reproduce the observations. The fractured model, when applied to investigate the mid and long term expected behavior, indicated a reservoir cooling risk associated to the present injection scheme. Work is currently underway to modify this scheme.« less

Reinjected water return at Miravalles geothermal reservoir, Costa Rica: Numerical modelling and observations

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

Parini, M.; Laudiano, M.; Acuna, J.A.

1996-12-31

The first 55 MW power plant at Miravalles started operation in March, 1994. During the first few months of production, a gradual increase in chloride content was observed in some production wells. The cause was assumed to be a rapid return of injectate from two injection wells located fairly near to the main production area. A tracer test was performed and showed a relatively rapid breakthrough, confirming the assumption made. Numerical modeling was then carried out to try to reproduce the observed behavior. The reservoir was modelled with an idealized three-dimensional network of fractures embedded into a low permeability matrix.more » The {open_quotes}two waters{close_quotes} feature of TOUGH2 simulator was used. The numerical simulation showed good agreement with observations. A {open_quotes}porous medium{close_quotes} model with equivalent hydraulic characteristics was unable to reproduce the observations. The fractured model, when applied to investigate the mid and long term expected behavior, indicated a reservoir cooling risk associated to the present injection scheme. Work is currently underway to modify this scheme.« less

DE 1 observations of type 1 counterstreaming electrons and field-aligned currents

NASA Technical Reports Server (NTRS)

Lin, C. S.; Burch, J. L.; Barfield, J. N.; Sugiura, M.; Nielsen, E.

1984-01-01

Dynamics Explorer 1 satellite observations of plasma and magnetic fields during type one counterstreaming electron events are presented. Counterstreaming electrons are observed at high altitudes in the region of field-aligned current. The total current density computed from the plasma data in the 18-10,000 eV energy range is generally about 1-2 micro-A/sq m. For the downward current, low-energy electrons contribute more than 40 percent of the total plasma current density integrated above 18 eV. For the upward current, such electrons contribute less than 50 percent of that current density. Electron beams in the field-aligned direction are occasionally detected. The pitch angle distributions of counterstreaming electrons are generally enhanced at both small and large pitch angles. STARE simultaneous observations for one DE 1 pass indicated that the field-aligned current was closed through Pedersen currents in the ionosphere. The directions of the ionospheric current systems are consistent with the DE 1 observations at high altitudes.

Impact of Ring Current Ions on Electromagnetic Ion Cyclotron Wave Dispersion Relation

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Gamayunov, K. V.

2007-01-01

Effect of the ring current ions in the real part of electromagnetic ion Cyclotron wave dispersion relation is studied on global scale. Recent Cluster observations by Engebretson et al. showed that although the temperature anisotropy of is energetic (> 10 keV) ring current protons was high during the entire 22 November 2003 perigee pass, electromagnetic ion cyclotron waves were observed only in conjunction with intensification of the ion fluxes below 1 keV by over an order of magnitude. To study the effect of the ring current ions on the wave dispersive properties and the corresponding global wave redistribution, we use a self-consistent model of interacting ring current and electromagnetic ion cyclotron waves, and simulate the May 1998 storm. The main findings of our simulation can be summarized as follows: First, the plasma density enhancement in the night MLT sector during the main and recovery storm phases is mostly caused by injection of suprathermal plasma sheet H + (approximately < 1 keV), which dominate the thermal plasma density. Second, during the recovery storm phases, the ring current modification of the wave dispersion relation leads to a qualitative change of the wave patterns in the postmidnight-dawn sector for L > 4.75. This "new" wave activity is well organized by outward edges of dense suprathermal ring current spots, and the waves are not observed if the ring current ions are not included in the real part of dispersion relation. Third, the most intense wave-induced ring current precipitation is located in the night MLT sector and caused by modification of the wave dispersion relation. The strongest precipitating fluxes of about 8 X 10(exp 6)/ (cm(exp 2) - s X st) are found near L=5.75, MLT=2 during the early recovery phase on 4 May. Finally, the nightside precipitation is more intense than the dayside fluxes, even if there are less intense waves, because the convection field moves ring current ions into the loss cone on the nightside, but drives them out of the loss cone on the dayside. So convection and wave scattering reinforce each other in the nightside, but interfere in the dayside sector.

Magnetoresistive DNA chips based on ac field focusing of magnetic labels

NASA Astrophysics Data System (ADS)

Ferreira, H. A.; Cardoso, F. A.; Ferreira, R.; Cardoso, S.; Freitas, P. P.

2006-04-01

A study was made on the sensitivity of a magnetoresistive DNA-chip platform being developed for cystic fibrosis diagnostics. The chip, comprised of an array of 2.5×80 μm2 U-shaped spin-valve sensors integrated within current line structures for magnetic label manipulation, enabled the detection at 30 Hz of 250 nm magnetic nanoparticles from 100 pM down to the pM range (or a target DNA concentration of 500 pM). It was observed that the sensor response increased linearly with label concentration. Noise spectra obtained for these sensors showed a thermal noise of 10-17 V2/Hz with a 1/f knee at 50 kHz at a 1 mA sense current, showing that lower detection limits are possible.

Numerical simulation of the observed near-surface East India Coastal Current on the continental slope

NASA Astrophysics Data System (ADS)

Mukherjee, A.; Shankar, D.; Chatterjee, Abhisek; Vinayachandran, P. N.

2018-06-01

We simulate the East India Coastal Current (EICC) using two numerical models (resolution 0.1° × 0.1°), an oceanic general circulation model (OGCM) called Modular Ocean Model and a simpler, linear, continuously stratified (LCS) model, and compare the simulated current with observations from moorings equipped with acoustic Doppler current profilers deployed on the continental slope in the western Bay of Bengal (BoB). We also carry out numerical experiments to analyse the processes. Both models simulate well the annual cycle of the EICC, but the performance degrades for the intra-annual and intraseasonal components. In a model-resolution experiment, both models (run at a coarser resolution of 0.25° × 0.25°) simulate well the currents in the equatorial Indian Ocean (EIO), but the performance of the high-resolution LCS model as well as the coarse-resolution OGCM, which is good in the EICC regime, degrades in the eastern and northern BoB. An experiment on forcing mechanisms shows that the annual EICC is largely forced by the local alongshore winds in the western BoB and remote forcing due to Ekman pumping over the BoB, but forcing from the EIO has a strong impact on the intra-annual EICC. At intraseasonal periods, local (equatorial) forcing dominates in the south (north) because the Kelvin wave propagates equatorward in the western BoB. A stratification experiment with the LCS model shows that changing the background stratification from EIO to BoB leads to a stronger surface EICC owing to strong coupling of higher order vertical modes with wind forcing for the BoB profiles. These high-order modes, which lead to energy propagating down into the ocean in the form of beams, are important only for the current and do not contribute significantly to the sea level.

A data-assimilative ocean forecasting system for the Prince William sound and an evaluation of its performance during sound Predictions 2009

NASA Astrophysics Data System (ADS)

Farrara, John D.; Chao, Yi; Li, Zhijin; Wang, Xiaochun; Jin, Xin; Zhang, Hongchun; Li, Peggy; Vu, Quoc; Olsson, Peter Q.; Schoch, G. Carl; Halverson, Mark; Moline, Mark A.; Ohlmann, Carter; Johnson, Mark; McWilliams, James C.; Colas, Francois A.

2013-07-01

The development and implementation of a three-dimensional ocean modeling system for the Prince William Sound (PWS) is described. The system consists of a regional ocean model component (ROMS) forced by output from a regional atmospheric model component (the Weather Research and Forecasting Model, WRF). The ROMS ocean model component has a horizontal resolution of 1km within PWS and utilizes a recently-developed multi-scale 3DVAR data assimilation methodology along with freshwater runoff from land obtained via real-time execution of a digital elevation model. During the Sound Predictions Field Experiment (July 19-August 3, 2009) the system was run in real-time to support operations and incorporated all available real-time streams of data. Nowcasts were produced every 6h and a 48-h forecast was performed once a day. In addition, a sixteen-member ensemble of forecasts was executed on most days. All results were published at a web portal (http://ourocean.jpl.nasa.gov/PWS) in real time to support decision making.The performance of the system during Sound Predictions 2009 is evaluated. The ROMS results are first compared with the assimilated data as a consistency check. RMS differences of about 0.7°C were found between the ROMS temperatures and the observed vertical profiles of temperature that are assimilated. The ROMS salinities show greater discrepancies, tending to be too salty near the surface. The overall circulation patterns observed throughout the Sound are qualitatively reproduced, including the following evolution in time. During the first week of the experiment, the weather was quite stormy with strong southeasterly winds. This resulted in strong north to northwestward surface flow in much of the central PWS. Both the observed drifter trajectories and the ROMS nowcasts showed strong surface inflow into the Sound through the Hinchinbrook Entrance and strong generally northward to northwestward flow in the central Sound that was exiting through the Knight Island Passage and Montague Strait entrance. During the latter part of the second week when surface winds were light and southwesterly, the mean surface flow at the Hinchinbrook Entrance reversed to weak outflow and a cyclonic eddy formed in the central Sound. Overall, RMS differences between ROMS surface currents and observed HF radar surface currents in the central Sound were generally between 5 and 10cm/s, about 20-40% of the time mean current speeds.The ROMS reanalysis is then validated against independent observations. A comparison of the ROMS currents with observed vertical current profiles from moored ADCPs in the Hinchinbrook Entrance and Montague Strait shows good qualitative agreement and confirms the evolution of the near surface inflow/outflow at these locations described above. A comparison of the ROMS surface currents with drifter trajectories provided additional confirmation that the evolution of the surface flow described above was realistic. Forecasts of drifter locations had RMS errors of less than 10km for up to 36h. One and two-day forecasts of surface temperature, salinity and current fields were more skillful than persistence forecasts. In addition, ensemble mean forecasts were found to be slightly more skillful than single forecasts. Two case studies demonstrated the system's qualitative skill in predicting subsurface changes within the mixed layer measured by ships and autonomous underwater vehicles. In summary, the system is capable of producing a realistic evolution of the near-surface circulation within PWS including forecasts of up to two days of this evolution. Use of the products provided by the system during the experiment as part of the asset deployment decision making process demonstrated the value of accurate regional ocean forecasts in support of field experiments.

Gender-Based Wage Differentials in a Predominantly Female Profession: Observations from Nursing

ERIC Educational Resources Information Center

Jones, Cheryl, Bland; Gates, Michael

2004-01-01

Despite numerous studies examining nursing wages, very little attention has focused on nursing wage differentials. We build on previous research by modeling nursing wages and examining male-female wage differences within the context of the current nursing shortage. Our results show that male nurses do earn a wage premium, largely explained by…

Interrater Reliability among Elementary Principals Using the North Carolina Teacher Evaluation Process

ERIC Educational Resources Information Center

Mazurek, Sharon Ann

2012-01-01

Teacher observation remains one of the primary data collection methods for analyzing teaching behaviors. States use various evaluation instruments and current trends across the United States show that more states are working to tie teacher evaluation to student performance. The purpose of this study was to determine to what extent there was…

High-latitude ionospheric inhomogeneities according to measurements on Kosmos 348

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

Dzhordzhio, N.V.

1975-01-01

The Kosmos 348 measurements showed that considerable ionospheric inhomogeneities are virtually always observed in the precipitation region of the high-latitude nighttime ionosphere in the presence of fluxes of injected electrons with E = 0.03 to 5 keV that exceed the critical value for current instability, unlike the situation in the presence of small fluxes.

Insights on landscape evolution and climatic forcing on Titan

NASA Astrophysics Data System (ADS)

Lucas, A.; Daudon, C.; Rodriguez, S.; Cornet, T.; Perron, J. T.

2017-12-01

The landscapes of Titan were observed for nearly 13 years by the Cassini spacecraft and Huygens probe. With dunes, mountains, seas, lakes, rivers..., the great morphological variety observed testifies to the geological richness that Titan shares with the Earth. In this study, we combine analysis of radar and hyperspectral data provided by the Cassini-Huygens mission, with models of valley and river network evolution to better understand the processes at work that sculpt these familiar landscapes. We develop quantitative criteria for comparing 3D morphologies obtained by numerical simulation with those derived for Titan by photogrammetry. These criteria are validated on Earth's landscapes. We simulate morphologies similar to those observed and show that landscapes at the equator and poles are mainly controlled by river incision and mass wasting such as landslides for which we quantify their respective contribution. Subsequently, we relate modeling to precipitation rates of methane and show values that are to be compared with general circulation model predictions (GCM). Our results also show a very young age of formation of the observed morphologies, less than a few million years. Finally, we provide new constraints on current amplitude of the tidal effects and organic precipitation rates from atmosphere chemistry.

Current and future constraints on extended Bekenstein-type models for a varying fine-structure constant

NASA Astrophysics Data System (ADS)

Alves, C. S.; Leite, A. C. O.; Martins, C. J. A. P.; Silva, T. A.; Berge, S. A.; Silva, B. S. A.

2018-01-01

There is a growing interest in astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant α , as an optimal probe of new physics. The imminent arrival of the ESPRESSO spectrograph will soon enable significant gains in the precision and accuracy of these tests and widen the range of theoretical models that can be tightly constrained. Here we illustrate this by studying proposed extensions of the Bekenstein-type models for the evolution of α that allow different couplings of the scalar field to both dark matter and dark energy. We use a combination of current astrophysical and local laboratory data (from tests with atomic clocks) to show that these couplings are constrained to parts per million level, with the constraints being dominated by the atomic clocks. We also quantify the expected improvements from ESPRESSO and other future spectrographs, and briefly discuss possible observational strategies, showing that these facilities can improve current constraints by more than an order of magnitude.

Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides

NASA Astrophysics Data System (ADS)

Gu, Mingqiang; Rondinelli, James M.

2016-04-01

We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.

Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides.

PubMed

Gu, Mingqiang; Rondinelli, James M

2016-04-29

We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.

Impact of E × B flow shear on turbulence and resulting power fall-off width in H-mode plasmas in experimental advanced superconducting tokamak

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

Yang, Q. Q., E-mail: yangqq@ipp.ac.cn; Zhong, F. C., E-mail: gsxu@ipp.ac.cn, E-mail: fczhong@dhu.edu.cn; Jia, M. N.

2015-06-15

The power fall-off width in the H-mode scrape-off layer (SOL) in tokamaks shows a strong inverse dependence on the plasma current, which was noticed by both previous multi-machine scaling work [T. Eich et al., Nucl. Fusion 53, 093031 (2013)] and more recent work [L. Wang et al., Nucl. Fusion 54, 114002 (2014)] on the Experimental Advanced Superconducting Tokamak. To understand the underlying physics, probe measurements of three H-mode discharges with different plasma currents have been studied in this work. The results suggest that a higher plasma current is accompanied by a stronger E×B shear and a shorter radial correlation lengthmore » of turbulence in the SOL, thus resulting in a narrower power fall-off width. A simple model has also been applied to demonstrate the suppression effect of E×B shear on turbulence in the SOL and shows relatively good agreement with the experimental observations.« less

Rapid response to coastal upwelling in a semienclosed bay

NASA Astrophysics Data System (ADS)

Gilcoto, Miguel; Largier, John L.; Barton, Eric D.; Piedracoba, Silvia; Torres, Ricardo; Graña, Rocío.; Alonso-Pérez, Fernando; Villacieros-Robineau, Nicolás.; de la Granda, Francisco

2017-03-01

Bays/estuaries forced by local wind show bidirectional exchange flow. When forced by remote wind, they exhibit unidirectional flow adjustment to coastal sea level. Acoustic Doppler Current Profiler observations over 1 year show that the Ria de Vigo (Iberian Upwelling) responds to coastal wind events with bidirectional exchange flow. The duration of the upwelling and downwelling events, estimated from the current variability, was 3.3 days and 2.6 days, respectively. Vectorial correlations reveal a rapid response to upwelling/downwelling, in which currents lag local wind by <6 h and remote wind by <14 h, less than the Ekman spinup (17.8 h). This rapidity arises from the ria's narrowness (nonrotational local response), equatorward orientation (additive remote and local wind responses), depth greater than the Ekman depth (penetration of shelf circulation into the interior), and vertical stratification (shear reinforcing shelf circulation). Similar rapid responses are expected in other narrow bays where local and remote winds act together and stratification enhances bidirectional flow.

Investigation from Japanese MAGSAT Team. Part A. Crustal structure near Japan and in Antarctic station. Part B. Electric currents and hydromagnetic waves in the ionosphere and the magnetosphere

NASA Technical Reports Server (NTRS)

Fukushima, N. (Principal Investigator)

1981-01-01

Preliminary results of MAGSAT data analysis are described. Regional anomaly maps (deviations from the MGST model field) for X,Y,Z, and F in the area of 115 to 155 deg E and 20 to 60 deg N were obtained. A similar map for the geomagnetic total force anomaly in the vicinity of Japan showed that the observed anomaly can be explained by the difference in crustal magnetization between the Japan Sea and the Japan Island, which reflects a difference of 25 km in the thickness of the magnetized layer. The MAGSAT record of a sudden commencement of a magnetic storm above the South Atlantic Ocean showed a reverse impulse particularly in the D-component. Results relating to toroidal currents in the ionosphere, transverse and parallel perturbations over the polar regions, the relationship between field aligned currents and precipitating electrons, and the calculation of the subsatellite electric field are also discussed.