Survey of Pc3-5 ULF velocity oscillations in SuperDARN THEMIS-mode data: Occurrence statistics and driving mechanisms

NASA Astrophysics Data System (ADS)

Shi, X.; Ruohoniemi, J. M.; Baker, J. B.; Lin, D.; Bland, E. C.; Hartinger, M.; Scales, W.

2017-12-01

Ultra-low frequency (ULF: 1 mHz-10 Hz) waves are believed to play an important role in the energization and transport of plasma within the magnetosphere-ionosphere system, as well as the transfer of energy from the solar wind. Most previous statistical studies of ionospheric ULF waves using Super Dual Auroral Radar Network (SuperDARN) data have been constrained to the Pc5 band ( 1-7 mHz) and/or one or two radars covering a limited range of latitudes. This is partially due to lack of a database cataloging high time resolution data and an efficient way to identify wave events. In this study, we conducted a comprehensive survey of ULF wave signatures in the Pc3-5 band using 6 s resolution data from all SuperDARN radars in the northern hemisphere operating in THEMIS-mode from 2010 to 2016. Numerical experiments were conducted to derive dynamic thresholds for automated detection of ULF waves at different frequencies using the Lomb-Scargle periodogram technique. The spatial occurrence distribution, frequency characteristics, seasonal effects, solar wind condition and geomagnetic activity level dependence have been studied. We found Pc5 events dominate at high latitudes with a most probable frequency of 2 mHz while Pc3-4 are relatively more common at mid-latitudes on the nightside with a most probable frequency of 11 mHz. At high latitudes the occurrence rate of poloidal Pc3-5 peaks in the dusk sector and in winter while at mid-latitudes the poloidal Pc3-4 occurrence rate peaks at pre-midnight. This pre-midnight occurrence peak becomes more prominent with increasing AE index value, in equinox and during southward IMF, which suggests many of these events are most likely Pi2 pulsations associated with magnetotail dynamics during active geomagnetic intervals.

Low-energy (< 200 eV) electron acceleration by ULF waves in the plasmaspheric boundary layer: Van Allen Probes observation

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

Ren, Jie; Zong, Q. G.; Miyoshi, Y.

Here, we report observational evidence of cold plamsmaspheric electron (< 200 eV) acceleration by ultra-low-frequency (ULF) waves in the plasmaspheric boundary layer on 10 September 2015. Strongly enhanced cold electron fluxes in the energy spectrogram were observed along with second harmonic mode waves with a period of about 1 minute which lasted several hours during two consecutive Van Allen Probe B orbits. Cold electron (<200 eV) and energetic proton (10-20 keV) bi-directional pitch angle signatures observed during the event are suggestive of the drift-bounce resonance mechanism. The correlation between enhanced energy fluxes and ULF waves leads to the conclusions thatmore » plasmaspheric dynamics is strongly affected by ULF waves. Van Allen Probe A and B, GOES 13, GOES 15 and MMS 1 observations suggest ULF waves in the event were strongest on the dusk-side magnetosphere. Measurements from MMS 1 contain no evidence of an external wave source during the period when ULF waves and injected energetic protons with a bump-on-tail distribution were detected by Van Allen Probe B. This suggests that the observed ULF waves were probably excited by a localized drift-bounce resonant instability, with the free energy supplied by substorm-injected energetic protons. The observations by Van Allen Probe B suggest that energy transfer between particle species in different energy ranges can take place through the action of ULF waves, demonstrating the important role of these waves in the dynamical processes of the inner magnetosphere.« less

Low-energy (< 200 eV) electron acceleration by ULF waves in the plasmaspheric boundary layer: Van Allen Probes observation

DOE PAGES

Ren, Jie; Zong, Q. G.; Miyoshi, Y.; ...

2017-08-30

Here, we report observational evidence of cold plamsmaspheric electron (< 200 eV) acceleration by ultra-low-frequency (ULF) waves in the plasmaspheric boundary layer on 10 September 2015. Strongly enhanced cold electron fluxes in the energy spectrogram were observed along with second harmonic mode waves with a period of about 1 minute which lasted several hours during two consecutive Van Allen Probe B orbits. Cold electron (<200 eV) and energetic proton (10-20 keV) bi-directional pitch angle signatures observed during the event are suggestive of the drift-bounce resonance mechanism. The correlation between enhanced energy fluxes and ULF waves leads to the conclusions thatmore » plasmaspheric dynamics is strongly affected by ULF waves. Van Allen Probe A and B, GOES 13, GOES 15 and MMS 1 observations suggest ULF waves in the event were strongest on the dusk-side magnetosphere. Measurements from MMS 1 contain no evidence of an external wave source during the period when ULF waves and injected energetic protons with a bump-on-tail distribution were detected by Van Allen Probe B. This suggests that the observed ULF waves were probably excited by a localized drift-bounce resonant instability, with the free energy supplied by substorm-injected energetic protons. The observations by Van Allen Probe B suggest that energy transfer between particle species in different energy ranges can take place through the action of ULF waves, demonstrating the important role of these waves in the dynamical processes of the inner magnetosphere.« less

ULF radio monitoring network in a seismic area

NASA Astrophysics Data System (ADS)

Toader, Victorin; Moldovan, Iren-Adelina; Ionescu, Constantin; Marmureanu, Alexandru

2017-04-01

ULF monitoring is a part of a multidisciplinary network (AeroSolSys) located in Vrancea (Curvature Carpathian Mountains). Four radio receivers (100 kHz - microwave) placed on faults in a high seismic area characterized by deep earthquakes detect fairly weak radio waves. The radio power is recorded in correlation with many other parameters related to near surface low atmosphere phenomena (seismicity, solar radiation, air ionization, electromagnetic activity, radon, CO2 concentration, atmospheric pressure, telluric currents, infrasound, seismo-acoustic emission, meteorological information). We follow variations in the earth's surface propagate radio waves avoiding reflection on ionosphere. For this reason the distance between stations is less than 60 km and the main source of emission is near (Bod broadcasting transmitter for long- and medium-wave radio, next to Brasov city). In the same time tectonic stress affects the radio propagation in air and it could generates ULF waves in ground (LAI coupling). To reduce the uncertainty is necessary to monitor a location for extended periods of time to outline local and seasonal fluctuations. Solar flares do not affect seismic activity but they produce disturbances in telecommunications networks and power grids. Our ULF monitoring correlated with two local magnetometers does not indicate this so far with our receivers. Our analysis was made during magnetic storms with Kp 7 and 8 according to NOAA satellites. To correlate the results we implemented an application that monitors the satellite EUTELSAT latency compared to WiMAX land communication in the same place. ULF band radio monitoring showed that our receiver is dependent on temperature and that it is necessary to introduce a band pass filter in data analysis. ULF data acquisition is performed by Kinemetrics and National Instruments digitizers with a sampling rate of 100 Hz in Miniseed format and then converted into text files with 1 Hz rate for analysis in very low

ULF Wave Activity in the Magnetosphere: Resolving Solar Wind Interdependencies to Identify Driving Mechanisms

NASA Astrophysics Data System (ADS)

Bentley, S. N.; Watt, C. E. J.; Owens, M. J.; Rae, I. J.

2018-04-01

Ultralow frequency (ULF) waves in the magnetosphere are involved in the energization and transport of radiation belt particles and are strongly driven by the external solar wind. However, the interdependency of solar wind parameters and the variety of solar wind-magnetosphere coupling processes make it difficult to distinguish the effect of individual processes and to predict magnetospheric wave power using solar wind properties. We examine 15 years of dayside ground-based measurements at a single representative frequency (2.5 mHz) and a single magnetic latitude (corresponding to L ˜ 6.6RE). We determine the relative contribution to ULF wave power from instantaneous nonderived solar wind parameters, accounting for their interdependencies. The most influential parameters for ground-based ULF wave power are solar wind speed vsw, southward interplanetary magnetic field component Bz<0, and summed power in number density perturbations δNp. Together, the subordinate parameters Bz and δNp still account for significant amounts of power. We suggest that these three parameters correspond to driving by the Kelvin-Helmholtz instability, formation, and/or propagation of flux transfer events and density perturbations from solar wind structures sweeping past the Earth. We anticipate that this new parameter reduction will aid comparisons of ULF generation mechanisms between magnetospheric sectors and will enable more sophisticated empirical models predicting magnetospheric ULF power using external solar wind driving parameters.

An initial ULF wave index derived from 2 years of Swarm observations

NASA Astrophysics Data System (ADS)

Papadimitriou, Constantinos; Balasis, Georgios; Daglis, Ioannis A.; Giannakis, Omiros

2018-03-01

The ongoing Swarm satellite mission provides an opportunity for better knowledge of the near-Earth electromagnetic environment. Herein, we use a new methodological approach for the detection and classification of ultra low-frequency (ULF) wave events observed by Swarm based on an existing time-frequency analysis (TFA) tool and utilizing a state-of-the-art high-resolution magnetic field model and Swarm Level 2 products (i.e., field-aligned currents - FACs - and the Ionospheric Bubble Index - IBI). We present maps of the dependence of ULF wave power with magnetic latitude and magnetic local time (MLT) as well as geographic latitude and longitude from the three satellites at their different locations in low-Earth orbit (LEO) for a period spanning 2 years after the constellation's final configuration. We show that the inclusion of the Swarm single-spacecraft FAC product in our analysis eliminates all the wave activity at high altitudes, which is physically unrealistic. Moreover, we derive a Swarm orbit-by-orbit Pc3 wave (20-100 MHz) index for the topside ionosphere and compare its values with the corresponding variations of solar wind variables and geomagnetic activity indices. This is the first attempt, to our knowledge, to derive a ULF wave index from LEO satellite data. The technique can be potentially used to define a new Level 2 product from the mission, the Swarm ULF wave index, which would be suitable for space weather applications.

ULF Waves in the Earth's Inner Magnetosphere: Role in Radiation Belt and Ring Current Dynamics

NASA Astrophysics Data System (ADS)

Mann, I. R.; Murphy, K. R.; Rae, J.; Claudepierre, S. G.; Fennell, J. F.; Baker, D. N.; Reeves, G. D.; Spence, H. E.; Ozeke, L.; Milling, D. K.

2013-05-01

Ultra-low frequency (ULF) waves in the Pc4-5 band can be excited in the magnetosphere by the solar wind. Much recent work has shown how ULF wave power is strongly correlated with solar wind speed. However, little attention has been paid the dynamics of ULF wave power penetration onto low L-shells in the inner magnetosphere. We use more than a solar cycle of ULF wave data, derived from ground-based magnetometer networks, to examine this ULF wave power penetration and its dependence on solar wind and geomagnetic activity indices. In time domain data, we show very clearly that dayside ULF wave power, spanning more than 4 orders of magnitude, follows solar wind speed variations throughout the whole solar cycle - during periods of sporadic solar maximum ICMEs, during declining phase fast solar wind streams, and at solar minimum, alike. We also show that time domain ULF wave power increases during magnetic storms activations, and significantly demonstrate that a deeper ULF wave power penetration into the inner magnetosphere occurs during larger negative excursions in Dst. We discuss potential explanations for this low-L ULF wave power penetration, including the role of plasma mass density (such as during plasmaspheric erosion), or ring current ion instabilities during near-Earth ring current penetration. Interestingly, we also show that both ULF wave power and SAMPEX MeV electron flux show a remarkable similarity in their penetration to low-L, which suggests that ULF wave power penetration may be important for understanding and explaining radiation belt dynamics. Moreover, the correlation of ULF wave power with Dst, which peaks at one day lag, suggests the ULF waves might also be important for the inward transport of ions into the ring current. Current ring current models, which exclude long period ULF wave transport, under-estimate the ring current during fast solar wind streams which is consistent with a potential role for ULF waves in ring current energisation

The Quasi-monochromatic ULF Wave Boundary in the Venusian Foreshock: Venus Express Observations

NASA Astrophysics Data System (ADS)

Shan, Lican; Mazelle, Christian; Meziane, Karim; Romanelli, Norberto; Ge, Yasong S.; Du, Aimin; Lu, Quanming; Zhang, Tielong

2018-01-01

The location of ultralow-frequency (ULF) quasi-monochromatic wave onset upstream of Venus bow shock is explored using Venus Express magnetic field data. We report the existence of a spatial foreshock boundary behind which ULF waves are present. We have found that the ULF wave boundary at Venus is sensitive to the interplanetary magnetic field (IMF) direction like the terrestrial one and appears well defined for a cone angle larger than 30°. In the Venusian foreshock, the inclination angle of the wave boundary with respect to the Sun-Venus direction increases with the IMF cone angle. We also found that for the IMF nominal direction (θBX = 36°) at Venus' orbit, the value of this inclination angle is 70°. Moreover, we have found that the inferred velocity of an ion traveling along the ULF boundary is in a qualitative agreement with a quasi-adiabatic reflection of a portion of the solar wind at the bow shock. For an IMF nominal direction at Venus, the inferred bulk speed of ions traveling along this boundary is 1.07 VSW, sufficiently enough to overcome the solar wind convection. This strongly suggests that the backstreaming ions upstream of the Venusian bow shock provide the main energy source for the ULF waves.

Use of the Wigner-Ville distribution in interpreting and identifying ULF waves in triaxial magnetic records

NASA Astrophysics Data System (ADS)

Chi, P. J.; Russell, C. T.

2008-01-01

Magnetospheric ultra-low-frequency (ULF) waves (f = 1 mHz to 1 Hz) exhibit highly time-dependent characteristics due to the dynamic properties of these waves and, for observations in space, the spacecraft motion. These time-dependent features may not be properly resolved by conventional Fourier techniques. In this study we examine how the Wigner-Ville distribution (WVD) can be used to analyze ULF waves. We find that this approach has unique advantages over the conventional Fourier spectrograms and wavelet scalograms. In particular, for Pc1 wave packets, field line/cavity mode resonances in the Pc 3-4 band, and Pi2 pulsations, the start and end times of each wave packet can be well identified and the frequency better defined. In addition, we demonstrate that the Wigner-Ville distribution can be used to calculate the polarization of wave signals in triaxial magnetic field data in a way analogous to Fourier analysis. Motivated by the large amount of ULF wave observations, we have also developed a WVD-based algorithm to identify ULF waves as a way to facilitate the rapid processing of the data collected by satellite missions and the vast network of ground magnetometers.

Global distribution of ULF waves during magnetic storms on March 27, 2017 and April 4, 2017

NASA Astrophysics Data System (ADS)

Takahashi, N.; Seki, K.; Teramoto, M.; Matsuoka, A.; Higashio, N.; Fok, M. C. H.

2017-12-01

The relativistic electron population in the Earth's outer radiation belt is drastically variable, especially during the active condition of the magnetosphere such as magnetic storms. One of the candidate mechanisms to cause the increase or decrease of relativistic electrons is the radial diffusion of the electrons driven by ultra-low-frequency (ULF) waves in Pc5 frequency ranges. However, how much ULF Pc5 waves contribute to the evolution of the radiation belt is still an open issue. In particular, previous papers have investigated the radial distribution of ULF Pc5 waves in the inner magnetosphere, but the spatial distribution is not well understood because of the limited number of satellite. In December 2016, the Arase satellite was launched into the inner magnetosphere, and the campaign observations between Arase and ground-based observations are now operated. During the first campaign observation from the end of March to April 2017, two distinct magnetic storms were occurred. The first storm was occurred on March 27, 2017 (Storm 1), which lasted for about six days. On the other hand, the second storm on April 4, 2017 (Storm 2) lasted for about two days. The temporal variation of the dynamic pressure and density of solar wind during each storm is almost similar. However, the solar wind flow speed data shows that Storm 1 is caused by the CIR, while Storm 2 might be caused by the CME. Therefore, background field variations that excite ULF Pc5 waves in the inner magnetosphere can be different between Storm 1 and 2. In addition, the Extremely High-Energy Electron Experiment (XEP) data onboard Arase clearly show the increase of high-energy electrons (400 keV-20 MeV) during the recovery phase of Storm 1, while they did not recover to the pre-storm level during Storm 2. Remarkable difference between two storms is the substorm activities in the recovery phase. The AE index continuously increased in Storm 1, while in Storm 2, it stayed in low level. The global simulation

A contribution to ULF activity in the Pc 3-4 range correlated with IMF radial orientation. [geomagnetic micropulsations

NASA Technical Reports Server (NTRS)

Greenstadt, E. W.; Olson, J. V.

1977-01-01

The paper describes an experiment to determine whether the radial orientation of the interplanetary magnetic field (IMF) is associated with ULF activity in the Pc 3-4 range. Data are obtained from base levels, undisturbed intervals, IMF and disturbance selection, and trigonometric correlation. The results obtained are discussed, noting particularly that for low Kp, the probability of enhanced amplitude noise rises as IMF orientation with respect to the nominal solar wind flow decreases in both Pc 3 and Pc 4 channels.

Role of the Ionosphere in the Generation of Large-Amplitude Ulf Waves at High Latitudes

NASA Astrophysics Data System (ADS)

Tulegenov, B.; Guido, T.; Streltsov, A. V.

2014-12-01

We present results from the statistical study of ULF waves detected by the fluxgate magnetometer in Gakona, Alaska during several experimental campaigns conducted at the High Frequency Active Auroral Research Program (HAARP) facility in years 2011-2013. We analyzed frequencies of ULF waves recorded during 26 strongly disturbed geomagnetic events (substorms) and compared them with frequencies of ULF waves detected during magnetically quite times. Our analysis demonstrates that the frequency of the waves carrying most of the power almost in all these events is less than 1 mHz. We also analyzed data from the ACE satellite, measuring parameters of the solar wind in the L1 Lagrangian point between Earth and Sun, and found that in several occasions there is a strong correlation between oscillations of the magnetic field in the solar wind and oscillations detected on the ground. We also found several cases when there is no correlation between signals detected on ACE and on the ground. This finding suggests that these frequencies correspond to the fundamental eigenfrequency of the coupled magnetosphere-ionosphere system. The low frequency of the oscillations is explained by the effect of the ionosphere, where the current is carried by ions through highly collisional media. The amplitude of these waves can reach significant magnitude when the system is driven by the external driver (for example, the solar wind) with this particular frequency. When the frequency of the driver does not match the frequency of the system, the waves still are observed, but their amplitudes are much smaller.

Are there new findings in the search for ULF magnetic precursors to earthquakes?

NASA Astrophysics Data System (ADS)

Masci, F.; Thomas, J. N.

2015-12-01

Moore (1964) in a letter published in Nature reported disturbances in geomagnetic field data prior to the 27 March 1964 Alaska earthquake. After the publication of this report, many papers have shown magnetic changes preceding earthquakes. However, a causal relationship between preearthquake magnetic changes and impending earthquakes has never been demonstrated. As a consequence, after 50 years, magnetic disturbances in the geomagnetic field are still candidate precursory phenomena. Some researchers consider the investigation of ultra low frequency (ULF: 0.001-10 Hz) magnetic data the correct approach for identifying precursory signatures of earthquakes. Other researchers, instead, have recently reviewed many published ULF magnetic changes that preceded earthquakes and have shown that these are not actual precursors. The recent studies by Currie and Waters (2014) and Han et al. (2014) aim to provide relevant new findings in the search for ULF magnetic precursory signals. However, in order to contribute to science, alleged precursors must be shown to be valid and reproducible by objective testing. Here we will briefly discuss the state of the art in the search for ULF magnetic precursors, paying special attention to the recent findings of Currie and Waters (2014) and Han et al. (2014). We do not see in these two reports significant evidence that may support the observation of precursory signatures of earthquakes in ULF magnetic records.

Determining magnetospheric ULF wave activity from external drivers using the most influential solar wind parameters

NASA Astrophysics Data System (ADS)

Bentley, S.; Watt, C.; Owens, M. J.

2017-12-01

Ultra-low frequency (ULF) waves in the magnetosphere are involved in the energisation and transport of radiation belt particles and are predominantly driven by the external solar wind. By systematically examining the instantaneous relative contribution of non-derived solar wind parameters and accounting for their interdependencies using fifteen years of ground-based measurements (CANOPUS) at a single frequency and magnetic latitude, we conclude that the dominant causal parameters for ground-based ULF wave power are solar wind speed v, interplanetary magnetic field component Bz and summed power in number density perturbations δNp. We suggest that these correspond to driving by the Kelvin-Helmholtz instability, flux transfer events and direct perturbations from solar wind structures sweeping past. We will also extend our analysis to a stochastic wave model at multiple magnetic latitudes that will be used in future to predict background ULF wave power across the radiation belts in different magnetic local time sectors, and to examine the relative contribution of the parameters v, Bz and var(Np) in these sectors.

Changes in the transmissibility of the mid-latitude ionosphere related to the ULF (Pc1) signal

NASA Astrophysics Data System (ADS)

Prikner, Karel; Vagner, Vladimir

The frequency dependences of the transmissibility of a stratified inhomogeneous anisotropic and dissipative model of the ionosphere in relation to the ordinary Alfven wave mode, which is incident under various angles in the meridional plane, are studied. A method for the numerical modeling of the ionospheric filtration of Fourier components of the micropulsation (ULF) signals in the Pc1 range was used. The specific features of filtration in the daytime and nighttime ionosphere under low and enhanced solar activity are pointed out.

System engineering study of electrodynamic tether as a spaceborne generator and radiator of electromagnetic waves in the ULF/ELF frequency band

NASA Technical Reports Server (NTRS)

Estes, R. D.; Grossi, M. D.; Lorenzini, E. C.

1986-01-01

The transmission and generation by orbiting tethered satellite systems of information carrying electromagnetic waves in the ULF/ELF frequency band to the Earth at suitably high signal intensities was examined and the system maintaining these intensities in their orbits for long periods of time without excessive onboard power requirements was investigated. The injection quantity power into electromagnetic waves as a function of system parameters such as tether length and orbital height was estimated. The basic equations needed to evaluate alternataing current tethered systems for external energy requirements are presented. The energy equations to tethered systems with various lengths, tether resistances, and radiation resistances, operating at different current values are applied. Radiation resistance as a function of tether length and orbital height is discussed. It is found that ULF/ELF continuously radiating systems could be maintained in orbit with moderate power requirements. The effect of tether length on the power going into electromagnetic waves and whether a single or dual tether system is preferable for the self-driven mode is discussed. It is concluded that the single tether system is preferable over the dual system.

ULF Waves in the Ionospheric Alfven Resonator: Modeling of MICA Observations

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Tulegenov, B.

2017-12-01

We present results from a numerical study of physical processes responsible for the generation of small-scale, intense electromagnetic structures in the ultra-low-frequency range frequently observed in the close vicinity of bright discrete auroral arcs. In particular, our research is focused on the role of the ionosphere in generating these structures. A significant body of observations demonstrate that small-scale electromagnetic waves with frequencies below 1 Hz are detected at high latitudes where the large-scale, downward magnetic field-aligned current (FAC) interact with the ionosphere. Some theoretical studies suggest that these waves can be generated by the ionospheric feedback instability (IFI) inside the ionospheric Alfven resonator (IAR). The IAR is the region in the low-altitude magnetosphere bounded by the strong gradient in the Alfven speed at high altitude and the conducting bottom of the ionosphere (ionospheric E-region) at low altitude. To study ULF waves in this region we use a numerical model developed from reduced two fluid MHD equations describing shear Alfven waves in the ionosphere and magnetosphere of the earth. The active ionospheric feedback on structure and amplitude of magnetic FACs that interact with the ionosphere is implemented through the ionospheric boundary conditions that link the parallel current density with the plasma density and the perpendicular electric field in the ionosphere. Our numerical results are compared with the in situ measurements performed by the Magnetosphere-Ionosphere Coupling in the Alfven Resonator (MICA) sounding rocket, launched on February 19, 2012 from Poker Flat Research Range in Alaska to measure fields and particles during a passage through a discreet auroral arc. Parameters of the simulations are chosen to match actual MICA parameters, allowing the comparison in the most precise and rigorous way. Waves generated in the numerical model have frequencies between 0.30 and 0.45 Hz, while MICA measured

Global MHD modeling of resonant ULF waves: Simulations with and without a plasmasphere.

PubMed

Claudepierre, S G; Toffoletto, F R; Wiltberger, M

2016-01-01

We investigate the plasmaspheric influence on the resonant mode coupling of magnetospheric ultralow frequency (ULF) waves using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) model. We present results from two different versions of the model, both driven by the same solar wind conditions: one version that contains a plasmasphere (the LFM coupled to the Rice Convection Model, where the Gallagher plasmasphere model is also included) and another that does not (the stand-alone LFM). We find that the inclusion of a cold, dense plasmasphere has a significant impact on the nature of the simulated ULF waves. For example, the inclusion of a plasmasphere leads to a deeper (more earthward) penetration of the compressional (azimuthal) electric field fluctuations, due to a shift in the location of the wave turning points. Consequently, the locations where the compressional electric field oscillations resonantly couple their energy into local toroidal mode field line resonances also shift earthward. We also find, in both simulations, that higher-frequency compressional (azimuthal) electric field oscillations penetrate deeper than lower frequency oscillations. In addition, the compressional wave mode structure in the simulations is consistent with a radial standing wave oscillation pattern, characteristic of a resonant waveguide. The incorporation of a plasmasphere into the LFM global MHD model represents an advance in the state of the art in regard to ULF wave modeling with such simulations. We offer a brief discussion of the implications for radiation belt modeling techniques that use the electric and magnetic field outputs from global MHD simulations to drive particle dynamics.

A tale of two theories: How the adiabatic response and ULF waves affect relativistic electrons

NASA Astrophysics Data System (ADS)

Green, J. C.; Kivelson, M. G.

2001-11-01

Using data from the Comprehensive Energetic Particle and Pitch Angle Distribution (CEPPAD)-High Sensitivity Telescope (HIST) instrument on the Polar spacecraft and ground magnetometer data from the 210 meridian magnetometer chain, we test the ULF wave drift resonance theory proposed to explain relativistic electron phase space density enhancements. We begin by investigating changes in electron flux due to the ``Dst effect.'' The Dst effect refers to the adiabatic response of relativistic electrons to changes in the magnetic field characterized by the Dst index. The Dst effect, assuming no loss or addition of new electrons, produces reversible order of magnitude changes in relativistic electrons flux measured at fixed energy, but it cannot account for the flux enhancement that occurs in the recovery phase of most storms. Liouville's theorem states that phase space density expressed in terms of constant adiabatic invariants is unaffected by adiabatic field changes and thus is insensitive to the Dst effect. It is therefore useful to express flux measurements in terms of phase space densities at constant first, second and third adiabatic invariants. The phase space density is determined from the CEPPAD-HIST electron detector that measures differential directional flux of electrons from 0.7 to 9 MeV and the Tsyganenko 96 field model. The analysis is done for January to June 1997. The ULF wave drift resonance theory that we test proposes that relativistic electrons are accelerated by an m=2 toroidal or poloidal mode wave whose frequency equals the drift frequency of the electron. The theory is tested by comparing the relativistic electron phase space densities to wave power determined at three ground stations with L* values of 4.0, 5.7 and 6.2. Comparison of the wave data to the phase space densities shows that five out of nine storm events are consistent with the ULF wave drift resonance mechanism, three out of nine give ambiguous support to the model, and one event has

Effects of ULF waves on local and global energetic particles: Particle energy and species dependences

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

Li, L. Y.; Yu, J.; Cao, J. B.

After 06:13 UT on 24 August 2005, an interplanetary shock triggers large-amplitude ultralow-frequency (ULF) waves (|δB| ≥ 15 nT) in the Pc4–Pc5 wave band (1.6–9 mHz) near the noon geosynchronous orbit (6.6 RE). The local and global effects of ULF waves on energetic particles are observed by five Los Alamos National Laboratory satellites at different magnetic local times. The large-amplitude ULF waves cause the synchronous oscillations of energetic electrons and protons (≥75 keV) at the noon geosynchronous orbit. When the energetic particles have a negative phase space density radial gradient, they undergo rapid outward radial diffusion and loss in themore » wave activity region. In the particle drift paths without strong ULF waves, only the rapidly drifting energetic electrons (≥225 keV) display energy-dispersive oscillations and flux decays, whereas the slowly drifting electrons (<225 keV) and protons (75–400 keV) have no ULF oscillation and loss feature. When the dayside magnetopause is compressed to the geosynchronous orbit, most of energetic electrons and protons are rapidly lost because of open drift trajectories. Furthermore, the global and multicomposition particle measurements demonstrate that the effect of ULF waves on nonlocal particle flux depends on the particle energy and species, whereas magnetopause shadowing effect is independent of the energetic particle species. For the rapidly drifting outer radiation belt particles (≥225 keV), nonlocal particle loss/acceleration processes could also change their fluxes in the entire drift trajectory in the absence of “ Dst effect” and substorm injection.« less

Effects of ULF waves on local and global energetic particles: Particle energy and species dependences

DOE PAGES

Li, L. Y.; Yu, J.; Cao, J. B.; ...

2016-11-05

After 06:13 UT on 24 August 2005, an interplanetary shock triggers large-amplitude ultralow-frequency (ULF) waves (|δB| ≥ 15 nT) in the Pc4–Pc5 wave band (1.6–9 mHz) near the noon geosynchronous orbit (6.6 RE). The local and global effects of ULF waves on energetic particles are observed by five Los Alamos National Laboratory satellites at different magnetic local times. The large-amplitude ULF waves cause the synchronous oscillations of energetic electrons and protons (≥75 keV) at the noon geosynchronous orbit. When the energetic particles have a negative phase space density radial gradient, they undergo rapid outward radial diffusion and loss in themore » wave activity region. In the particle drift paths without strong ULF waves, only the rapidly drifting energetic electrons (≥225 keV) display energy-dispersive oscillations and flux decays, whereas the slowly drifting electrons (<225 keV) and protons (75–400 keV) have no ULF oscillation and loss feature. When the dayside magnetopause is compressed to the geosynchronous orbit, most of energetic electrons and protons are rapidly lost because of open drift trajectories. Furthermore, the global and multicomposition particle measurements demonstrate that the effect of ULF waves on nonlocal particle flux depends on the particle energy and species, whereas magnetopause shadowing effect is independent of the energetic particle species. For the rapidly drifting outer radiation belt particles (≥225 keV), nonlocal particle loss/acceleration processes could also change their fluxes in the entire drift trajectory in the absence of “ Dst effect” and substorm injection.« less

Convective and diffusive ULF wave driven radiation belt electron transport

NASA Astrophysics Data System (ADS)

Degeling, A. W.; Rankin, R.; Elkington, S. R.

2011-12-01

The process of magnetospheric radiation belt electron transport driven by ULF waves is studied using a 2-D ideal MHD model for ULF waves in the equatorial plane including day/night asymmetry and a magnetopause boundary, and a test kinetic model for equatorially mirroring electrons. We find that ULF wave disturbances originating along the magnetopause flanks in the afternoon sector can act to periodically inject phase space density from these regions into the magnetosphere. Closely spaced drift-resonant surfaces for electrons with a given magnetic moment in the presence of the ULF waves create a layer of stochastic dynamics for L-shells above 6.5-7 in the cases examined, extending to the magnetopause. The phase decorrelation time scale for the stochastic region is estimated by the relaxation time for the diffusion coefficient to reach a steady value. This is found to be of the order of 10-15 wave periods, which is commensurate with the typical duration of observed ULF wave packets in the magnetosphere. For L-shells earthward of the stochastic layer, transport is limited to isolated drift-resonant islands in the case of narrowband ULF waves. We examine the effect of increasing the bandwidth of the ULF wave driver by summing together wave components produced by a set of independent runs of the ULF wave model. The wave source spectrum is given a flat-top amplitude of variable width (adjusted for constant power) and random phase. We find that increasing bandwidth can significantly enhance convective transport earthward of the stochastic layer and extend the stochastic layer to lower L-shells.

Conjugate Event Study of Geomagnetic ULF Pulsations with Wavelet-based Indices

NASA Astrophysics Data System (ADS)

Xu, Z.; Clauer, C. R.; Kim, H.; Weimer, D. R.; Cai, X.

2013-12-01

The interactions between the solar wind and geomagnetic field produce a variety of space weather phenomena, which can impact the advanced technology systems of modern society including, for example, power systems, communication systems, and navigation systems. One type of phenomena is the geomagnetic ULF pulsation observed by ground-based or in-situ satellite measurements. Here, we describe a wavelet-based index and apply it to study the geomagnetic ULF pulsations observed in Antarctica and Greenland magnetometer arrays. The wavelet indices computed from these data show spectrum, correlation, and magnitudes information regarding the geomagnetic pulsations. The results show that the geomagnetic field at conjugate locations responds differently according to the frequency of pulsations. The index is effective for identification of the pulsation events and measures important characteristics of the pulsations. It could be a useful tool for the purpose of monitoring geomagnetic pulsations.

Penetration of Solar Wind Driven ULF Waves into the Earth's Inner Magnetosphere: Role in Radiation Belt and Ring Current Dynamics

NASA Astrophysics Data System (ADS)

Mann, Ian; Murphy, Kyle; Rae, Jonathan; Ozeke, Louis; Milling, David

2013-04-01

Ultra-low frequency (ULF) waves in the Pc4-5 band can be excited in the magnetosphere by the solar wind. Much recent work has shown how ULF wave power is strongly correlated with solar wind speed. However, little attention has been paid the dynamics of ULF wave power penetration onto low L-shells in the inner magnetosphere. We use more than a solar cycle of ULF wave data, derived from ground-based magnetometer networks, to examine this ULF wave power penetration and its dependence on solar wind and geomagnetic activity indices. In time domain data, we show very clearly that dayside ULF wave power, spanning more than 4 orders of magnitude, follows solar wind speed variations throughout the whole solar cycle - during periods of sporadic solar maximum ICMEs, during declining phase fast solar wind streams, and at solar minimum, alike. We also show that time domain ULF wave power increases during magnetic storms activations, and significantly demonstrate that a deeper ULF wave power penetration into the inner magnetosphere occurs during larger negative excursions in Dst. We discuss potential explanations for this low-L ULF wave power penetration, including the role of plasma mass density (such as during plasmaspheric erosion), or ring current ion instabilities during near-Earth ring current penetration. Interestingly, we also show that both ULF wave power and SAMPEX MeV electron flux show a remarkable similarity in their penetration to low-L, which suggests that ULF wave power penetration may be important for understanding and explaining radiation belt dynamics. Moreover, the correlation of ULF wave power with Dst, which peaks at one day lag, suggests the ULF waves might also be important for the inward transport of ions into the ring current. Current ring current models, which exclude long period ULF wave transport, under-estimate the ring current during fast solar wind streams which is consistent with a potential role for ULF waves in ring current energisation. The

Dynamic cross correlation studies of wave particle interactions in ULF phenomena

NASA Technical Reports Server (NTRS)

Mcpherron, R. L.

1979-01-01

Magnetic field observations made by satellites in the earth's magnetic field reveal a wide variety of ULF waves. These waves interact with the ambient particle populations in complex ways, causing modulation of the observed particle fluxes. This modulation is found to be a function of species, pitch angle, energy and time. The characteristics of this modulation provide information concerning the wave mode and interaction process. One important characteristic of wave-particle interactions is the phase of the particle flux modulation relative to the magnetic field variations. To display this phase as a function of time a dynamic cross spectrum program has been developed. The program produces contour maps in the frequency time plane of the cross correlation coefficient between any particle flux time series and the magnetic field vector. This program has been utilized in several studies of ULF wave-particle interactions at synchronous orbit.

Modeling and observations of ULF waves trapped in a plasmaspheric density plume

NASA Astrophysics Data System (ADS)

Degeling, A. W.; Zhang, S.; Foster, J. C.; Shi, Q.; Zong, Q. G.; Rankin, R.

2017-12-01

In order for ULF waves to effectively energise radiation belt electrons by drift-resonance, wave power must be significant in regions within the magnetosphere where the ULF wave phase propagation and electron drift directions are roughly aligned. For waves launched along the dayside magnetopause, such a region would be located in the afternoon - dusk sector of the inner magnetosphere. During periods of storm activity and enhanced convection, the plasma density in this region is highly dynamic due to the development of plasmaspheric drainage plume (PDP) structure. This significantly affects the local Alfvén speed, and alters the propagation of ULF waves launched from the magnetopause. It can therefore be expected that the accessibility of ULF wave power for radiation belt energisation is sensitively dependent on the recent history of magnetospheric convection, and the stage of development of the PDP. This is investigated using a 3D model for ULF waves within the magnetosphere in which the plasma density distribution is evolved using an advection model for cold plasma, driven by a (Volland - Stern) convection electrostatic field (resulting in PDP structure). The wave model includes magnetic-field day/night asymmetry, and extends to a paraboloid dayside magnetopause, from which ULF waves are launched at various stages during the PDP development. We find that the plume structure significantly alters the field line resonance (FLR) location, and the turning point for MHD fast waves, introducing strong asymmetry in the ULF wave distribution across the noon meridian. Moreover, the density enhancement within the PDP creates a waveguide or local cavity for MHD fast waves, such that eigenmodes formed allow the penetration of ULF wave power to much lower L within the plume than outside. This may explain satellite observations of the appearance of ULF wave activity within localized density enhancements associated with a PDP. Such an example, made by THEMIS following a

Survey of Ionospheric Pc3-5 ULF Wave Signatures in SuperDARN High Time Resolution Data

NASA Astrophysics Data System (ADS)

Shi, X.; Ruohoniemi, J. M.; Baker, J. B. H.; Lin, D.; Bland, E. C.; Hartinger, M. D.; Scales, W. A.

2018-05-01

Ionospheric signatures of ultralow frequency (ULF) wave in the Pc3-5 band (1.7-40.0 mHz) were surveyed using ˜6-s resolution data from Super Dual Auroral Radar Network (SuperDARN) radars in the Northern Hemisphere from 2010 to 2016. Numerical experiments were conducted to derive wave period-dependent thresholds for automated detection of ULF waves using the Lomb-Scargle periodogram technique. The spatial occurrence distribution, frequency characteristics, seasonal effects, solar wind condition, and geomagnetic activity level dependence have been studied. Pc5 wave events were found to dominate at high and polar latitudes with a most probable frequency of 2.08 ± 0.07 mHz, while Pc3-4 waves were relatively more common at midlatitudes on the nightside with a most probable frequency of 11.39 ± 0.14 mHz. At high latitudes, the occurrence rate of Pc4-5 waves maximizes in the dusk sector and during winter. These events tend to occur during low geomagnetic activity and northward interplanetary magnetic field. For the category of radially bounded but longitudinally extended Pc4 events in the duskside ionosphere, an internal driving source is suggested. At midlatitudes, the poloidal Pc3-4 occurrence rate maximizes premidnight and during equinox. This tendency becomes more prominent with increasing auroral electrojet (AE) index and during southward interplanetary magnetic field, which suggests that many of these events are Pi2 and Pc3-4 pulsations associated with magnetotail dynamics during active geomagnetic intervals. The overall occurrence rate of Pc3-5 wave events is lowest in summer, which suggests that the ionospheric conductivity plays a role in controlling ULF wave occurrence.

MESSENGER Observations of ULF Waves in Mercury's Foreshock Region

NASA Technical Reports Server (NTRS)

Le, Guan; Chi, Peter J.; Bardsen, Scott; Blanco-Cano, Xochitl; Slavin, James A.; Korth, Haje

2012-01-01

The region upstream from a planetary bow shock is a natural plasma laboratory containing a variety of wave particle phenomena. The study of foreshocks other than the Earth s is important for extending our understanding of collisionless shocks and foreshock physics since the bow shock strength varies with heliocentric distance from the Sun, and the sizes of the bow shocks are different at different planets. The Mercury s bow shock is unique in our solar system as it is produced by low Mach number solar wind blowing over a small magnetized body with a predominately radial interplanetary magnetic field. Previous observations of Mercury upstream ultra-low frequency (ULF) waves came exclusively from two Mercury flybys of Mariner 10. The MESSENGER orbiter data enable us to study of upstream waves in the Mercury s foreshock in depth. This paper reports an overview of upstream ULF waves in the Mercury s foreshock using high-time resolution magnetic field data, 20 samples per second, from the MESSENGER spacecraft. The most common foreshock waves have frequencies near 2 Hz, with properties similar to the 1-Hz waves in the Earth s foreshock. They are present in both the flyby data and in every orbit of the orbital data we have surveyed. The most common wave phenomenon in the Earth s foreshock is the large-amplitude 30-s waves, but similar waves at Mercury have frequencies at 0.1 Hz and occur only sporadically with short durations (a few wave cycles). Superposed on the "30-s" waves, there are spectral peaks at 0.6 Hz, not reported previously in Mariner 10 data. We will discuss wave properties and their occurrence characteristics in this paper.

Seafloor Pressure Array Studies at Ultra-Low Frequencies

DTIC Science & Technology

1991-01-01

broadband instrument design and deployment. In order to measure broadband noise routinely, a low frequency pressure gauge designed for deep ocean...below the microseism band (Moore et al, 1981). A differential pressure gauge , developed for low frequency recordings by Cox et al (1984) and sensitive to...design differential pressure gauge (Cox et al, 1984) with a sensitivity -3- ULF Seafloor Pressure Array Studies range of 0.01-5 Hz. The high

Kinetic Alfvén waves and particle response associated with a shock-induced, global ULF perturbation of the terrestrial magnetosphere

DOE PAGES

Malaspina, David M.; Claudepierre, Seth G.; Takahashi, Kazue; ...

2015-11-14

On 2 October 2013, the arrival of an interplanetary shock compressed the Earth's magnetosphere and triggered a global ULF (ultra low frequency) oscillation. Furthermore, the Van Allen Probe B spacecraft observed this large-amplitude ULF wave in situ with both magnetic and electric field data. Broadband waves up to approximately 100 Hz were observed in conjunction with, and modulated by, this ULF wave. Detailed analysis of fields and particle data reveals that these broadband waves are Doppler-shifted kinetic Alfvén waves. This event then suggests that magnetospheric compression by interplanetary shocks can induce abrupt generation of kinetic Alfvén waves over large portionsmore » of the inner magnetosphere, potentially driving previously unconsidered wave-particle interactions throughout the inner magnetosphere during the initial response of the magnetosphere to shock impacts.« less

Rethinking the polar cap: Eccentric dipole structuring of ULF power at the highest corrected geomagnetic latitudes

NASA Astrophysics Data System (ADS)

Urban, Kevin D.; Gerrard, Andrew J.; Lanzerotti, Louis J.; Weatherwax, Allan T.

2016-09-01

The day-to-day evolution and statistical features of Pc3-Pc7 band ultralow frequency (ULF) power throughout the southern polar cap suggest that the corrected geomagnetic (CGM) coordinates do not adequately organize the observed hydromagnetic spatial structure. It is shown that that the local-time distribution of ULF power at sites along CGM latitudinal parallels exhibit fundamental differences and that the CGM latitude of a site in general is not indicative of the site's projection into the magnetosphere. Thus, ULF characteristics observed at a single site in the polar cap cannot be freely generalized to other sites of similar CGM latitude but separated in magnetic local time, and the inadequacy of CGM coordinates in the polar cap has implications for conjugacy/mapping studies in general. In seeking alternative, observationally motivated systems of "polar cap latitudes," it is found that eccentric dipole (ED) coordinates have several strengths in organizing the hydromagnetic spatial structure in the polar cap region. ED latitudes appear to better classify the local-time ULF power in both magnitude and morphology and better differentiate the "deep polar cap" (where the ULF power is largely UT dependent and nearly free of local-time structure) from the "peripheral polar cap" (where near-magnetic noon pulsations dominate at lower and lower frequencies as one increases in ED latitude). Eccentric local time is shown to better align the local-time profiles in the magnetic east component over several PcX bands but worsen in the magnetic north component. It is suggested that a hybrid ED-CGM coordinate system might capture the strengths of both CGM and ED coordinates. It is shown that the local-time morphology of median ULF power at high-latitude sites is dominantly driven by where they project into the magnetosphere, which is best quantified by their proximity to the low-altitude cusp on the dayside (which is not necessarily quantified by a site's CGM latitude), and that

Determining the VLF/ULF source height using phase measurements

NASA Astrophysics Data System (ADS)

Ryabov, A.; Kotik, D. S.

2012-12-01

Generation of ULF/VLF waves in the ionosphere using powerful RF facilities has been studied for the last 40 years, both theoretically and experimentally. During this time, it was proposed several mechanisms for explaining the experimental results: modulation of ionospheric currents based on thermal nonlinearity, ponderomotive mechanisms for generation both VLF and ULF signals, cubic nonlinearity, etc. According mentioned above mechanisms the VLF/ULF signal source could be located in the lower or upper ionosphere. The group velocity of signal propagation in the ionosphere is significantly smaller than speed of light. As a result the appreciable time delay of the received signals will occur at the earth surface. This time delay could be determine by measuring the phase difference between received and reference signals, which are GPS synchronized. The experiment on determining the time delay of ULF signal propagation from the ionospheric source was carried out at SURA facility in 2012 and the results are presented in this paper. The comparison with numerical simulation of the time delay using the adjusted IRI model and ionosonde data shows well agreement with the experimental observations. The work was supported by RFBR grant 11-02-00419-a and RF Ministry of education and science by state contract 16.518.11.7066.

The Effects of High Frequency ULF Wave Activity on the Spectral Characteristics of Coherent HF Radar Returns

NASA Astrophysics Data System (ADS)

Wright, D. M.; Yeoman, T. K.; Woodfield, E. E.

2003-12-01

It is now a common practice to employ ground-based radars in order to distinguish between those regions of the Earth's upper atmosphere which are magnetically conjugate to open and closed field lines. Radar returns from ionospheric irregularities inside the polar cap and cusp regions generally exhibit large spectral widths in contrast to those which exist on closed field lines at lower latitudes. It has been suggested that the so-called Spectral Width Boundary (SWB) might act as a proxy for the open-closed field line boundary (OCFLB), which would then be an invaluable tool for investigating reconnection rates in the magnetosphere. The exact cause of the increased spectral widths observed at very high latitudes is still subject to considerable debate. Several mechanisms have been proposed. This paper compares a dusk-sector interval of coherent HF radar data with measurements made by an induction coil magnetometer located at Tromso, Norway (66° N geomagnetic). On this occasion, a series of transient regions of radar backscatter exhibiting large spectral widths are accompanied by increases in spectral power of ULF waves in the Pc1-2 frequency band. These observations would then, seem to support the possibility that high frequency magnetospheric wave activity at least contribute to the observed spectral characteristics and that such wave activity might play a significant role in the cusp and polar cap ionospheres.

Quasiperiodic modulations of energetic electron fluxes in the ULF range observed by the ERG satellite

NASA Astrophysics Data System (ADS)

Teramoto, M.; Hori, T.; Kurita, S.; Yoshizumi, M.; Saito, S.; Higashio, N.; Mitani, T.; Matsuoka, A.; Park, I.; Takashima, T.; Nomura, R.; Nose, M.; Fujimoto, A.; Tanaka, Y.; Shinohara, M.; Shinohara, I.

2017-12-01

Exploration of energization and Radiation in Geospace (ERG) satellite was successfully launched on December 20, 2016. The Extremely High-Energy Electron Experiment (XEP) and High-Energy Electron Experiments (HEP-L and HEP-H) are carried by the ERG satellite to observe energetic electrons. These instruments frequently observed quasiperiodic modulations of energetic electron fluxes with period of 100-600 sec. Continuous flux modulations with the period of 600 s appeared in the 700keV-3.6MeV energy range during the period 0920UT-1120UT on March 31, 2017 when the ERG satellite was located at L 5.5-6.1 and MLT 3-4 h. We compare these flux modulations with the magnetic field observed by the Magnetic Field Experiment (MGF) on the ERG satellite. It is found that these flux modulations are not accompanied by corresponding magnetic signatures. It indicates that these quasiperiodic flux modulations are not caused by drift-resonant interactions between ULF waves and energetic electrons, at least locally. In this study, we will show several events and discuss possible mechanism for quasiperiodic flux modulations of energetic electrons on XEP and HEP.

Vortex, ULF wave and Aurora Observation after Solar Wind Dynamic Pressure Change

NASA Astrophysics Data System (ADS)

Shi, Q.

2017-12-01

Here we will summarize our recent study and show some new results on the Magnetosphere and Ionosphere Response to Dynamic Pressure Change/disturbances in the Solar Wind and foreshock regions. We study the step function type solar wind dynamic pressure change (increase/decrease) interaction with the magnetosphere using THEMIS satellites at both dayside and nightside in different geocentric distances. Vortices generated by the dynamic pressure change passing along the magnetopause are found and compared with model predictions. ULF waves and vortices are excited in the dayside and nightside plasma sheet when dynamic pressure change hit the magnetotail. The related ionospheric responses, such as aurora and TCVs, are also investigated. We compare Global MHD simulations with the observations. We will also show some new results that dayside magnetospheric FLRs might be caused by foreshock structures.Shi, Q. Q. et al. (2013), THEMIS observations of ULF wave excitation in the nightside plasma sheet during sudden impulse events, J. Geophys. Res. Space Physics, 118, doi:10.1029/2012JA017984. Shi, Q. Q. et al. (2014), Solar wind pressure pulse-driven magnetospheric vortices and their global consequences, J. Geophys. Res. Space Physics, 119, doi:10.1002/2013JA019551. Tian, A.M. et al.(2016), Dayside magnetospheric and ionospheric responses to solar wind pressure increase: Multispacecraft and ground observations, J. Geophys. Res., 121, doi:10.1002/2016JA022459. Shen, X.C. et al.(2015), Magnetospheric ULF waves with increasing amplitude related to solar wind dynamic pressure changes: THEMIS observations, J. Geophys. Res., 120, doi:10.1002/2014JA020913Zhao, H. Y. et al. (2016), Magnetospheric vortices and their global effect after a solar wind dynamic pressure decrease, J. Geophys. Res. Space Physics, 121, doi:10.1002/2015JA021646. Shen, X. C., et al. (2017), Dayside magnetospheric ULF wave frequency modulated by a solar wind dynamic pressure negative impulse, J. Geophys. Res

Substorm Related ULF waves Observed in the Magnetosphere by BD-IES and Van Allan Probes

NASA Astrophysics Data System (ADS)

Zong, Q.

2017-12-01

By using the data return from the BD-IES instrument onboard an inclined (55°) geosynchronous orbit (IGSO) satellite together with geo-transfer orbit (GTO) Van Allen Probe A&B satellite, we analysis a substorm related ULF waves occurred on Feb 5, 2016 in the dawnside of the magnetosphere. Immediately after the substorm injection followed by energetic electron drift echoes, the electron flux was clearly and strongly varying on the ULF wave time scale. It is found that both toroidal and poloidal mode ULF waves with a period of 320 s. During the substorm injection, the IES onboard IGSO is outbound while both Van Allen Probe A&B satellites are inbound. This configuration of multiple satellite trajectories provides an unique opportunity to investigate substorm related ULF waves. When substorm injections are observed simultaneously with multiple spacecraft, they help elucidate potential mechanisms for particle transport and energization, a topic of great importance for understanding and modeling the magnetosphere. Two possible scenaria on ULF wave triggering are discussed: fast-mode compressional waves -driven field line resonance and ULF wave growth through drift resonance.

The Role of Solar Wind Structures in the Generation of ULF Waves in the Inner Magnetosphere

NASA Astrophysics Data System (ADS)

Alves, L. R.; Souza, V. M.; Jauer, P. R.; da Silva, L. A.; Medeiros, C.; Braga, C. R.; Alves, M. V.; Koga, D.; Marchezi, J. P.; de Mendonça, R. R. S.; Dallaqua, R. S.; Barbosa, M. V. G.; Rockenbach, M.; Dal Lago, A.; Mendes, O.; Vieira, L. E. A.; Banik, M.; Sibeck, D. G.; Kanekal, S. G.; Baker, D. N.; Wygant, J. R.; Kletzing, C. A.

2017-07-01

The plasma of the solar wind incident upon the Earth's magnetosphere can produce several types of geoeffective events. Among them, an important phenomenon consists of the interrelation of the magnetospheric-ionospheric current systems and the charged-particle population of the Earth's Van Allen radiation belts. Ultra-low-frequency (ULF) waves resonantly interacting with such particles have been claimed to play a major role in the energetic particle flux changes, particularly at the outer radiation belt, which is mainly composed of electrons at relativistic energies. In this article, we use global magnetohydrodynamic simulations along with in situ and ground-based observations to evaluate the ability of two different solar wind transient (SWT) events to generate ULF (few to tens of mHz) waves in the equatorial region of the inner magnetosphere. Magnetic field and plasma data from the Advanced Composition Explorer (ACE) satellite were used to characterize these two SWT events as being a sector boundary crossing (SBC) on 24 September 2013, and an interplanetary coronal mass ejection (ICME) in conjunction with a shock on 2 October 2013. Associated with these events, the twin Van Allen Probes measured a depletion of the outer belt relativistic electron flux concurrent with magnetic and electric field power spectra consistent with ULF waves. Two ground-based observatories apart in 90°C longitude also showed evidence of ULF-wave activity for the two SWT events. Magnetohydrodynamic (MHD) simulation results show that the ULF-like oscillations in the modeled electric and magnetic fields observed during both events are a result from the SWT coupling to the magnetosphere. The analysis of the MHD simulation results together with the observations leads to the conclusion that the two SWT structures analyzed in this article can be geoeffective on different levels, with each one leading to distinct ring current intensities, but both SWTs are related to the same disturbance in the

Control of ULF Wave Accessibility to the Inner Magnetosphere by the Convection of Plasma Density

NASA Astrophysics Data System (ADS)

Degeling, A. W.; Rae, I. J.; Watt, C. E. J.; Shi, Q. Q.; Rankin, R.; Zong, Q.-G.

2018-02-01

During periods of storm activity and enhanced convection, the plasma density in the afternoon sector of the magnetosphere is highly dynamic due to the development of plasmaspheric drainage plume (PDP) structure. This significantly affects the local Alfvén speed and alters the propagation of ULF waves launched from the magnetopause. Therefore, it can be expected that the accessibility of ULF wave power for radiation belt energization is sensitively dependent on the recent history of magnetospheric convection and the stage of development of the PDP. This is investigated using a 3-D model for ULF waves within the magnetosphere in which the plasma density distribution is evolved using an advection model for cold plasma, driven by a (VollandStern) convection electrostatic field (resulting in PDP structure). The wave model includes magnetic field day/night asymmetry and extends to a paraboloid dayside magnetopause, from which ULF waves are launched at various stages during the PDP development. We find that the plume structure significantly alters the field line resonance location, and the turning point for MHD fast waves, introducing strong asymmetry in the ULF wave distribution across the noon meridian. Moreover, the density enhancement within the PDP creates a waveguide or local cavity for MHD fast waves, such that eigenmodes formed allow the penetration of ULF wave power to much lower L within the plume than outside, providing an avenue for electron energization.

Sensory trigeminal ULF-TENS stimulation reduces HRV response to experimentally induced arithmetic stress: A randomized clinical trial.

PubMed

Monaco, Annalisa; Cattaneo, Ruggero; Ortu, Eleonora; Constantinescu, Marian Vladimir; Pietropaoli, Davide

2017-05-01

Ultra Low Frequency Transcutaneous Electric Nervous Stimulation (ULF-TENS) is extensively used for pain relief and for the diagnosis and treatment of temporomandibular disorders (TMD). In addition to its local effects, ULF-TENS acts on the autonomic nervous system (ANS), with particular reference to the periaqueductal gray (PAG), promoting the release of endogenous opioids and modulating descending pain systems. It has been suggested that the PAG participates in the coupling between the emotional stimulus and the appropriate behavioral autonomic response. This function is successfully investigated by HRV. Therefore, our goal is to investigate the effects of trigeminal ULF-TENS stimulation on autonomic behavior in terms of HRV and respiratory parameters during an experimentally-induced arithmetic stress test in healthy subjects. Thirty healthy women between 25 and 35years of age were enrolled and randomly assigned to either the control (TENS stimulation off) or test group (TENS stimulation on). Heart (HR, LF, HF, LF/HF ratio, DET, RMSSD, PNN50, RR) and respiratory (BR) rate were evaluated under basal, T1 (TENS off/on), and stress (mathematical task) conditions. Results showed that HRV parameters and BR significantly changed during the arithmetic stress paradigm (p<0.01). Independently of stress conditions, TENS and control group could be discriminated only by non-linear HRV data, namely RR and DET (p=0.038 and p=0.027, respectively). During the arithmetic task, LF/HF ratio was the most sensitive parameter to discriminate between groups (p=0.019). Our data suggest that trigeminal sensory ULF-TENS reduces the autonomic response in terms of HRV and BR during acute mental stress in healthy subjects. Future directions of our work aim at applying the HRV and BR analysis, with and without TENS stimulation, to individuals with dysfunctional ANS among those with TMD. Copyright © 2017 Elsevier Inc. All rights reserved.

Distribution of ULF energy (f is less than 80 mHz) in the inner magnetosphere - A statistical analysis of AMPTE CCE magnetic field data

NASA Technical Reports Server (NTRS)

Takahashi, Kazue; Anderson, Brian J.

1992-01-01

Magnetic field measurements made with the AMPTE CCE spacecraft are used to investigate the distribution of ULF energy in the inner magnetosphere. The data base is employed to examine the spatial distribution of ULF energy. The spatial distribution of wave power and spectral structures are used to identify several pulsation types, including multiharmonic toroidal oscillations; equatorial compressional Pc 3 oscillations; second harmonic poloidal oscillations; and nightside compressional oscillations. The frequencies of the toroidal oscillations are applied to determine the statistical radial profile of the plasma mass density and Alfven velocity. A clear signature of the plasma pause in the profiles of these average parameters is found.

Correlated Pc4-5 ULF waves, whistler-mode chorus, and pulsating aurora observed by the Van Allen Probes and ground-based systems

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

Jaynes, A. N.; Lessard, M. R.; Takahashi, K.

Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch angle scattering of tens of keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and tens of keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4–5 compressional pulsations and modulation of whistler-mode chorus using Time History of Events and Macroscale Interactions during Substorms. In the current study, we present simultaneous in situ observations of structured chorusmore » waves and an apparent field line resonance (in the Pc4–5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4–5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth's atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. As a result, such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades and may be a result of nonlinear chorus wave interactions in the equatorial region.« less

Correlated Pc4-5 ULF waves, whistler-mode chorus, and pulsating aurora observed by the Van Allen Probes and ground-based systems

DOE PAGES

Jaynes, A. N.; Lessard, M. R.; Takahashi, K.; ...

2015-10-28

Theory and observations have linked equatorial VLF waves with pulsating aurora for decades, invoking the process of pitch angle scattering of tens of keV electrons in the equatorial magnetosphere. Recently published satellite studies have strengthened this argument, by showing strong correlation between pulsating auroral patches and both lower-band chorus and tens of keV electron modulation in the vicinity of geosynchronous orbit. Additionally, a previous link has been made between Pc4–5 compressional pulsations and modulation of whistler-mode chorus using Time History of Events and Macroscale Interactions during Substorms. In the current study, we present simultaneous in situ observations of structured chorusmore » waves and an apparent field line resonance (in the Pc4–5 range) as a result of a substorm injection, observed by Van Allen Probes, along with ground-based observations of pulsating aurora. We demonstrate the likely scenario being one of substorm-driven Pc4–5 ULF pulsations modulating chorus waves, and thus providing the driver for pulsating particle precipitation into the Earth's atmosphere. Interestingly, the modulated chorus wave and ULF wave periods are well correlated, with chorus occurring at half the periodicity of the ULF waves. We also show, for the first time, a particular few-Hz modulation of individual chorus elements that coincides with the same modulation in a nearby pulsating aurora patch. As a result, such modulation has been noticed as a high-frequency component in ground-based camera data of pulsating aurora for decades and may be a result of nonlinear chorus wave interactions in the equatorial region.« less

Digital techniques for ULF wave polarization analysis

NASA Technical Reports Server (NTRS)

Arthur, C. W.

1979-01-01

Digital power spectral and wave polarization analysis are powerful techniques for studying ULF waves in the earth's magnetosphere. Four different techniques for using the spectral matrix to perform such an analysis have been presented in the literature. Three of these techniques are similar in that they require transformation of the spectral matrix to the principal axis system prior to performing the polarization analysis. The differences in the three techniques lie in the manner in which determine this transformation. A comparative study of these three techniques using both simulated and real data has shown them to be approximately equal in quality of performance. The fourth technique does not require transformation of the spectral matrix. Rather, it uses the measured spectral matrix and state vectors for a desired wave type to design a polarization detector function in the frequency domain. The design of various detector functions and their application to both simulated and real data will be presented.

Documentation for a web site to serve ULF-EM (Ultra-Low Frequency Electromagnetic) data to the public

USGS Publications Warehouse

Neumann, Danny A.; McPherson, Selwyn; Klemperer, Simon L.; Glen, Jonathan M.G.; McPhee, Darcy K.; Kappler, Karl

2011-01-01

The Stanford Ultra-Low Frequency Electromagnetic (ULF-EM) Monitoring Project is recording naturally varying electromagnetic signals adjacent to active earthquake faults, in an attempt to establish whether there is any variation in these signals associated with earthquakes. Our project is collaborative between Stanford University, the U.S. Geological Survey (USGS), and UC Berkeley. Lead scientists are Simon Klemperer (Stanford University), Jonathan Glen (USGS) and Darcy Karakelian McPhee (USGS). Our initial sites are in the San Francisco Bay Area, monitoring different strands of the San Andreas fault system, at Stanford University's Jasper Ridge Biological Preserve (JRSC), Marin Headlands of the Golden Gate National Recreation Area (MHDL), and the UC Berkeley's Russell Reservation Field Station adjacent to Briones Regional Park (BRIB). In addition, we maintain in conjunction with the Berkeley Seismological Laboratory (BSL) two remote reference stations at the Bear Valley Ranch in Parkfield, Calif., (PKD) and the San Andreas Geophysical Observatory at Hollister, Calif., (SAO). Metadata about our site can be found at http://ulfem-data.stanford.edu/info.html. Site descriptions can be found at the BSL at http://seismo.berkeley.edu/, and seismic data can be obtained from the Northern California Earthquake Data Center at http://www.ncedc.org/. The site http://ulfem-data.stanford.edu/ allows access to data from the Stanford-USGS sites JRSC, MHDL and BRIB, as well as UC Berkeley sites PKD and SAO.

System engineering study of electrodynamic tether as a spaceborne generator and radiator of electromagnetic waves in the ULF/ELF frequency band

NASA Technical Reports Server (NTRS)

Estes, Robert D.

1987-01-01

An electrodynamic tether deployed from a satellite in low-Earth orbit can perform, if properly instrumented, as a partially self-powered generator of electromagnetic waves in the ULF/ELF band, potentially at power levels high enough to be of practical use. Two basic problems are examined. The first is that of the level of wave power that the system can be expected to generate in the ULF/ELF radiation band. The second major question is whether an electrodynamic tethered satellite system for transmitting waves can be made partially self-powering so that power requirements for drag compensation can be met within economical constraints of mass, cost, and complexity. The theoretical developments and the system applications study are presented. The basic design criteria, the drag-compensation method, the effects on the propagation paths from orbit to Earth surface of high-altitude nuclear debris patches, and the estimate of masses and sizes are covered. An outline of recommended analytical work, to be performed as a follow-on to the present study, is contained.

A study of the coherence length of ULF waves in the earth's foreshock

NASA Technical Reports Server (NTRS)

Le, G.; Russell, C. T.

1990-01-01

High-time-resolution magnetic-field data for different separations of ISEE 1 and 2 in the earth's ion foreshock region are examined to study the coherence length of upstream ULF waves. Examining the correlation coefficients of the low-frequency waves as a function of separation distance shows that the correlation coefficient depends mainly on the separation distance of ISEE 1 and 2 transverse to the solar-wind flow. It drops to about 0.5 when the transverse separation is about 1 earth radius, a distance much larger than the proton thermal gyroradius in the solar wind. Thus the coherence length of the low-frequency waves is about one earth radius, which is of the order of the wavelength, and is consistent with that estimated from the bandwidth of the waves.

A new ULF wave analysis for Seismo-Electromagnetics using CPMN/MAGDAS data

NASA Astrophysics Data System (ADS)

Yumoto, K.; Ikemoto, S.; Cardinal, M. G.; Hayakawa, M.; Hattori, K.; Liu, J. Y.; Saroso, S.; Ruhimat, M.; Husni, M.; Widarto, D.; Ramos, E.; McNamara, D.; Otadoy, R. E.; Yumul, G.; Ebora, R.; Servando, N.

The Space Environment Research Center of Kyushu University has obtained geomagnetic data in the Circum-pan Pacific Magnetometer Network (CPMN) region for over 10 years, and has recently deployed a new real-time Magnetic Data Acquisition System (MAGDAS) in the CPMN region and an FM-CW radar network along the 210° magnetic meridian (MM) for space weather research and applications. This project intends to get the MAGDAS network fully operational and provide data for studies on space and lithosphere weather. In connection with this project, we propose a new ultra-low frequency (ULF) wave analysis method to study ULF anomalies associated with large earthquakes using magnetic data. From a case study of the 1999/05/12 Kushiro earthquake with magnitude M = 6.4, we found a peculiar increase of H-component power ratio AR/ AM of Pc 3 magnetic pulsations a few weeks before the earthquake, where AR is the power obtained at Rikubetsu station ( r = 61 km) near the epicenter and AM is the power obtained at a remote reference station, Moshiri ( r = 205 km). It is also found that the H-component power ratio AD/ AY of Pc 3 increased three times just a few weeks before the earthquake and after one week decreased to the normal level, where AD is one-day power at Rikubetsu station and AY is the one-year-average power.

On the Role of Solar Wind Discontinuities in the ULF Power Spectral Density at the Earth's Outer Radiation Belt: a Case Study

NASA Astrophysics Data System (ADS)

Lago, A.; Alves, L. R.; Braga, C. R.; Mendonca, R. R. S.; Jauer, P. R.; Medeiros, C.; Souza, V. M. C. E. S.; Mendes, O., Jr.; Marchezi, J.; da Silva, L.; Vieira, L.; Rockenbach, M.; Sibeck, D. G.; Kanekal, S. G.; Baker, D. N.; Wygant, J. R.; Kletzing, C.

2016-12-01

The solar wind incident upon the Earth's magnetosphere can produce either enhancement, depletion or no change in the flux of relativistic electrons at the outer radiation belt. During geomagnetic storms progress, solar wind parameters may change significantly, and occasionally relativistic electron fluxes at the outer radiation belt show dropouts in a range of energy and L-shells. Wave-particle interactions observed within the Van Allen belts have been claimed to play a significant role in energetic particle flux changes. The relation between changes on the solar wind parameters and the radiation belt is still a hot topic nowadays, particularly the role played by the solar wind on sudden electron flux decreases. The twin satellite Van Allen Probes measured a relativistic electron flux dropout concurrent to broad band Ultra-low frequency (ULF) waves, i.e. from 1 mHz to 10 Hz, on October 2, 2013. Magnetic field and plasma data from both ACE and WIND satellites allowed the characterization of this event as being an interplanetary coronal mass ejection in conjunction with shock. The interaction of this event with the Earth's magnetosphere was modeled using a global magnetohydrodynamic simulation and the magnetic field perturbation deep in magnetosphere could be analyzed from the model outputs. Results show the contribution of time-varying solar wind parameters to the generation of ULF waves. The power spectral densities, as a function of L-shell, were evaluated considering changes in the input parameters, e.g. magnitude and duration of dynamic pressure and magnetic field. The modeled power spectral densities are compared with Van Allen Probes data. The results provide us a clue on the solar wind characteristics that might be able to drive ULF waves in the inner magnetosphere, and also which wave modes are expected to be excited under a specific solar wind driving.

STS-132/ULF4 Flight Controllers on Console

NASA Image and Video Library

2010-05-18

JSC2010-E-081946 (18 May 2010) --- ISS flight director Emily Nelson monitors data at her console in the space station flight control room in the Mission Control Center at NASA's Johnson Space Center during STS-132/ULF-4 mission flight day five activities.

STS-132/ULF4 Flight Controllers on Console

NASA Image and Video Library

2010-05-18

JSC2010-E-081914 (18 May 2010) --- ISS flight director Holly Ridings reviews data at her console in the space station flight control room in the Mission Control Center at NASA's Johnson Space Center during STS-132/ULF-4 mission flight day five activities.

ULF geomagnetic activity effects on tropospheric temperature, specific humidity, and cloud cover in Antarctica, during 2003-2010

NASA Astrophysics Data System (ADS)

Regi, Mauro; Redaelli, Gianluca; Francia, Patrizia; De Lauretis, Marcello

2017-06-01

In the present study we investigated the possible relationship between the ULF geomagnetic activity and the variations of several atmospheric parameters. In particular, we compared the ULF activity in the Pc1-2 frequency band (100 mHz-5 Hz), computed from geomagnetic field measurements at Terra Nova Bay in Antarctica, with the tropospheric temperature T, specific humidity Q, and cloud cover (high cloud cover, medium cloud cover, and low cloud cover) obtained from reanalysis data set. The statistical analysis was conducted during the years 2003-2010, using correlation and Superposed Epoch Analysis approaches. The results show that the atmospheric parameters significantly change following the increase of geomagnetic activity within 2 days. These changes are evident in particular when the interplanetary magnetic field Bz component is oriented southward (Bz<0) and the By component duskward (By>0). We suggest that both the precipitation of electrons induced by Pc1-2 activity and the intensification of the polar cap potential difference, modulating the microphysical processes in the clouds, can affect the atmosphere conditions.

On precursory ULF/ELF electromagnetic signatures for the Kobe earthquake on April 12, 2013

NASA Astrophysics Data System (ADS)

Schekotov, A.; Izutsu, J.; Hayakawa, M.

2015-12-01

After the 2011 Tohoku earthquake (EQ), there have been numerous aftershocks in the eastern and Pacific Ocean of Japan, but EQs are still rare in the western part of Japan. In this situation a relatively large (magnitude (M) ∼ 6) EQ happened on April 12 (UT), 2013 at a place close to the 1995 Kobe EQ (M ∼ 7), so we have tried to find whether there existed any electromagnetic precursors to this EQ. Two precursory signatures are detected: one is the depression of ULF (ultra-low-frequency, 0.01-0.02 Hz) geomagnetic variations on April 9, and the second is wideband ELF (extremely low frequency) electromagnetic radiation on April 11. These results for the 2013 Kobe EQ are compared with the corresponding results for the former 1995 Kobe EQ.

A Review of the Low-Frequency Waves in the Giant Magnetospheres

NASA Astrophysics Data System (ADS)

Delamere, P. A.

2016-02-01

The giant magnetospheres harbor a plethora of low-frequency waves with both internal (i.e., moons) and external (i.e., solar wind) source mechanisms. This chapter summarizes the observation of low-frequency waves at Jupiter and Saturn and postulates the underlying physics based on our understanding of magnetodisc generation mechanisms. The source mechanisms of ULF pulsations at the giant magnetospheres are numerous. The satellite-magnetosphere interactions and mass loading of corotational flows generate many low-frequency waves. Observations of low-frequency bursts of radio emissions serve as an excellent diagnostic for understanding satellite-magnetosphere interactions. The outward radial transport of plasma through the magnetodisc and related magnetic flux circulation is a significant source of ULF pulsations; however, it is uncertain how the radial transport mechanism compares with solar wind induced perturbations.

STS-132/ULF4 Flight Controllers on Console

NASA Image and Video Library

2010-05-18

JSC2010-E-081916 (18 May 2010) --- ISS flight directors Holly Ridings (seated) and Emily Nelson monitor data at their console in the space station flight control room in the Mission Control Center at NASA's Johnson Space Center during STS-132/ULF-4 mission flight day five activities.

Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

NASA Astrophysics Data System (ADS)

Xu, Xiang; Zhou, Chen; Shi, Run; Ni, Binbin; Zhao, Zhengyu; Zhang, Yuannong

2016-09-01

Powerful high-frequency (HF) radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF) drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012) model and the neutral atmosphere model (NRLMSISE-00), including the High Frequency Active Auroral Research Program (HAARP; 62.39° N, 145.15° W), Wuhan (30.52° N, 114.32° E) and Jicamarca (11.95° S, 76.87° W) at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature oscillation decreases with

The role of localised Ultra-Low Frequency waves in energetic electron precipitation

NASA Astrophysics Data System (ADS)

Rae, J.; Murphy, K. R.; Watt, C.; Mann, I. R.; Ozeke, L.; Halford, A. J.; Sibeck, D. G.; Clilverd, M. A.; Rodger, C. J.; Degeling, A. W.; Singer, H. J.

2016-12-01

Electromagnetic waves play pivotal roles in radiation belt dynamics through a variety of different means. Typically, Ultra-Low Frequency (ULF) waves have historically been invoked for radial diffusive transport leading to both acceleration and loss of outer radiation belt electrons. Very-Low Frequency (VLF) and Extremely-Low Frequency (ELF) waves are generally thought to provide a mechanism for localized acceleration and loss through precipitation into the ionosphere. In this study we present a new mechanism for electron loss through precipitation into the ionosphere due to direct modulation of the loss cone via localized compressional ULF waves. Observational evidence is presented demonstrating that modulation of the equatorial loss cone can occur via localized compressional wave activity. We then perform statistical computations of the probability distribution to determine how likely a given magnetic perturbation would produce a given percentage change in the bounce loss-cone (BLC). We discuss the ramifications of the action of coherent, localized compressional ULF waves on drifting electron populations; their precipitation response can be a complex interplay between electron energy, the shape of the phase space density profile at pitch angles close to the loss cone, ionospheric decay timescales, and the time-dependence of the electron source. We present a case study of compressional wave activity in tandem with riometer and balloon-borne electron precipitation across keV-MeV energies to demonstrate that the experimental measurements can be explained by our new enhanced loss cone mechanism. We determine that the two pivotal components not usually considered are localized ULF wave fields and ionospheric decay timescales. We conclude that ULF wave modulation of the loss cone is a viable candidate for direct precipitation of radiation belt electrons without any additional requirement for gyroresonant wave-particle interaction. Additional mechanisms would be

Effect of Upstream ULF Waves on the Energetic Ion Diffusion at the Earth's Foreshock. I. Theory and Simulation

NASA Astrophysics Data System (ADS)

Otsuka, Fumiko; Matsukiyo, Shuichi; Kis, Arpad; Nakanishi, Kento; Hada, Tohru

2018-02-01

Field-aligned diffusion of energetic ions in the Earth’s foreshock is investigated by using the quasi-linear theory (QLT) and test particle simulation. Non-propagating MHD turbulence in the solar wind rest frame is assumed to be purely transverse with respect to the background field. We use a turbulence model based on a multi-power-law spectrum including an intense peak that corresponds to upstream ULF waves resonantly generated by the field-aligned beam (FAB). The presence of the ULF peak produces a concave shape of the diffusion coefficient when it is plotted versus the ion energy. The QLT including the effect of the ULF wave explains the simulation result well, when the energy density of the turbulent magnetic field is 1% of that of the background magnetic field and the power-law index of the wave spectrum is less than 2. The numerically obtained e-folding distances from 10 to 32 keV ions match with the observational values in the event discussed in the companion paper, which contains an intense ULF peak in the spectra generated by the FAB. Evolution of the power spectrum of the ULF waves when approaching the shock significantly affects the energy dependence of the e-folding distance.

Generation of ULF waves by electric or magnetic dipoles. [propagation from earth surface to ionosphere

NASA Technical Reports Server (NTRS)

Harker, K. J.

1975-01-01

The generation of ULF waves by ground-based magnetic and electric dipoles is studied with a simplified model consisting of three adjoining homogeneous regions representing the groud, the vacuum (free space) region, and the ionosphere. The system is assumed to be immersed in a homogeneous magnetic field with an arbitrary tilt angle. By the use of Fourier techniques and the method of stationary phase, analytic expressions are obtained for the field strength of the compressional Alfven waves in the ionosphere. Expressions are also obtained for the strength of the torsional Alfven wave in the ionosphere and the ULF magnetic field at ground level. Numerical results are obtained for the compressional Alfven-wave field strength in the ionosphere with a nonvertical geomagnetic field and for the ULF magnetic field at ground level for a vertical geomagnetic field.

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

NASA Astrophysics Data System (ADS)

Rae, I. J.; Murphy, K. R.; Watt, Clare E. J.; Mann, Ian R.; Yao, Zhonghua; Kalmoni, Nadine M. E.; Forsyth, Colin; Milling, David K.

2017-12-01

Substorm onset is marked in the ionosphere by the sudden brightening of an existing auroral arc or the creation of a new auroral arc. Also present is the formation of auroral beads, proposed to play a key role in the detonation of the substorm, as well as the development of the large-scale substorm current wedge (SCW), invoked to carry the current diversion. Both these phenomena, auroral beads and the SCW, have been intimately related to ultra-low frequency (ULF) waves of specific frequencies as observed by ground-based magnetometers. We present a case study of the absolute and relative timing of Pi1 and Pi2 ULF wave bands with regard to a small substorm expansion phase onset. We find that there is both a location and frequency dependence for the onset of ULF waves. A clear epicentre is observed in specific wave frequencies concurrent with the brightening of the substorm onset arc and the presence of "auroral beads". At higher and lower wave frequencies, different epicentre patterns are revealed, which we conclude demonstrate different characteristics of the onset process; at higher frequencies, this epicentre may demonstrate phase mixing, and at intermediate and lower frequencies these epicentres are characteristic of auroral beads and cold plasma approximation of the "Tamao travel time" from near-earth neutral line reconnection and formation of the SCW.

Remembrances of Ulf Svante von Euler.

PubMed

Igić, Rajko

2018-05-21

I first met Ulf Svante von Euler when he came to Belgrade, in 1968, to attend an international symposium on the occasion of the 50 th anniversary of the Medical Faculty. I was at that time a graduate student at the Medical Faculty in Sarajevo, and a new researcher. I had finished medical school in Belgrade and had worked for two years as a physician in the northern part of Serbia. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

The frequency range of TMJ sounds.

PubMed

Widmalm, S E; Williams, W J; Djurdjanovic, D; McKay, D C

2003-04-01

There are conflicting opinions about the frequency range of temporomandibular joint (TMJ) sounds. Some authors claim that the upper limit is about 650 Hz. The aim was to test the hypothesis that TMJ sounds may contain frequencies well above 650 Hz but that significant amounts of their energy are lost if the vibrations are recorded using contact sensors and/or travel far through the head tissues. Time-frequency distributions of 172 TMJ clickings (three subjects) were compared between recordings with one microphone in the ear canal and a skin contact transducer above the clicking joint and between recordings from two microphones, one in each ear canal. The energy peaks of the clickings recorded with a microphone in the ear canal on the clicking side were often well above 650 Hz and always in a significantly higher area (range 117-1922 Hz, P < 0.05 or lower) than in recordings obtained with contact sensors (range 47-375 Hz) or in microphone recordings from the opposite ear canal (range 141-703 Hz). Future studies are required to establish normative frequency range values of TMJ sounds but need methods also capable of recording the high frequency vibrations.

Analytic expressions for ULF wave radiation belt radial diffusion coefficients

PubMed Central

Ozeke, Louis G; Mann, Ian R; Murphy, Kyle R; Jonathan Rae, I; Milling, David K

2014-01-01

We present analytic expressions for ULF wave-derived radiation belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global radiation belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV—even though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp. Key Points Analytic expressions for the radial diffusion coefficients are presented The coefficients do not dependent on energy or wave m value The electric field diffusion coefficient dominates over the magnetic PMID:26167440

Ion flux oscillations and ULF waves observed by ARASE satellite and their origin

NASA Astrophysics Data System (ADS)

Yamamoto, K.; Masahito, N.; Kasahara, S.; Yokota, S.; Keika, K.; Matsuoka, A.; Teramoto, M.; Nomura, R.; Fujimoto, A.; Tanaka, Y.; Shinohara, M.; Shinohara, I.; Yoshizumi, M.

2017-12-01

The ARASE satellite, which was launched on December 20, 2016, is now observing thenightside inner magnetosphere. The inclination of the orbit is larger than those of otherrecent spacecraft flying in the inner magnetosphere such as THMEIS and Van Allen Probes.This unique orbit provides us new information on ULF waves since ULF waves havelatitudinal structure and the antinode of magnetic fluctuations of fundamental mode is athigh magnetic latitudes.Although Pc pulsations are predominantly observed on the dayside, ARASE satellitesometimes observes Pc4-5 pulsations on the nightside. Some of these waves are accompaniedwith energetic particle flux modulations. We found 6 events of the particle flux modulationsaccompanying Pc pulsations on the dawnside and nightside. Theoretical studies suggest thatULF waves detected at afternoon are generated by plasma instabilities like drift-mirror instability [Hasegawa, 1969] and drift-bounce resonance [Southwood et al, 1969].These instabilities cause plasma pressure disturbances or flux modulation of ions. Nonresonant ion clouds injected on the duskside are also considered to be one of the candidates ofULF wave driver [Zolotukhina, 1974]. We therefore discuss whether the ULF waves observedby ARASE satellite are generated internally or externally, and the flux modulations arecreated by plasma instabilities or the other non-resonant effects.On March 31, 2017, Medium-Energy Particle Experiments - Ion Mass Analyzer (MEPi)onboard ARASE detected ion flux oscillations at 12-70 keV with a period of 120 seconds inthe normal (NML) mode observation. NML mode observation provides details of the directionof particle movements. The pitch angle distribution of proton flux showed isotropic fluxoscillations. At the same time, Pc4 pulsations with the same oscillation period were observed.These flux and field perturbations were seen on the dawnside (4.3-5.9 MLT).ARASE found oscillations of ion count with a period of 130 seconds in the time

The interaction of ultra-low-frequency pc3-5 waves with charged particles in Earth's magnetosphere

NASA Astrophysics Data System (ADS)

Zong, Qiugang; Rankin, Robert; Zhou, Xuzhi

2017-12-01

One of the most important issues in space physics is to identify the dominant processes that transfer energy from the solar wind to energetic particle populations in Earth's inner magnetosphere. Ultra-low-frequency (ULF) waves are an important consideration as they propagate electromagnetic energy over vast distances with little dissipation and interact with charged particles via drift resonance and drift-bounce resonance. ULF waves also take part in magnetosphere-ionosphere coupling and thus play an essential role in regulating energy flow throughout the entire system. This review summarizes recent advances in the characterization of ULF Pc3-5 waves in different regions of the magnetosphere, including ion and electron acceleration associated with these waves.

Variability of ULF wave power at the magnetopause: a study at low latitude with Cluster data

NASA Astrophysics Data System (ADS)

Cornilleau-Wehrlin, N.; Grison, B.; Belmont, G.; Rezeau, L.; Chanteur, G.; Robert, P.; Canu, P.

2012-04-01

Strong ULF wave activity has been observed at magnetopause crossings since a long time. Those turbulent-like waves are possible contributors to particle penetration from the Solar Wind to the Magnetosphere through the magnetopause. Statistical studies have been performed to understand under which conditions the ULF wave power is the most intense and thus the waves can be the most efficient for particle transport from one region to the other. Clearly the solar wind pressure organizes the data, the stronger the pressure, the higher the ULF power (Attié et al 2008). Double STAR-Cluster comparison has shown that ULF wave power is stronger at low latitude than at high latitude (Cornilleau-Wehrlin et al, 2008). The different studies performed have not, up to now, shown a stronger power in the vicinity of local noon. Nevertheless under identical activity conditions, the variability of this power, even at a given location in latitude and local time is very high. The present work intends at understanding this variability by means of the multi spacecraft mission Cluster. The data used are from spring 2008, while Cluster was crossing the magnetopause at low latitude, in particularly quite Solar Wind conditions. The first region of interest of this study is the sub-solar point vicinity where the long wavelength surface wave effects are most unlikely.

47 CFR 18.309 - Frequency range of measurements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... MEDICAL EQUIPMENT Technical Standards § 18.309 Frequency range of measurements. (a) For field strength measurements: Frequency band in which device operates (MHz) Range of frequency measurements Lowest frequency...

Variations of the ionospheric parameters obtained from ground based measurements of ULF magnetic noise

NASA Astrophysics Data System (ADS)

Ermakova, Elena; Kotik, Dmitry; Bösinger, Tilmann

2016-07-01

The dynamics of the amplitude spectra and polarization parameter (epsilon)[1] of magnetic ULF noise were investigated during different seasons and high geomagnetic activity time using the data on the horizontal magnetic components monitoring at mid-latitude (New Life, Russia, 56 N, 46 E) and low-latitude stations (Crete, 35.15 N, 25.20 E). It was found that abrupt changes in the spectral polarization parameters can be linked as with variation of height of maximum and the electron density of the F-layer, and with a change in ionospheric parameters profiles at lower altitudes, for example, with the appearance of sporadic Es-layers and intermediate layers, located between the E and F-layers. It was detected the peculiarities in the daily dynamics of the epsilon parameter at low latitudes: a) the appearance in some cases more complicated than in the mid-latitudes, epsilon structure of the spectrum associated with the presence of two different values of the boundary frequency fB [2]; b) a decreasing of fB near local midnight observed in 70% of cases; c) observation of typical for dark time epsilon spectra after sunrise in the winter season. The numerical calculations of epsilon parameter were made using the IRI-2012 model with setting the models of sporadic and intermediate layers. The results revealed the dependence of the polarization spectra of the intensity and height of such thin layers. The specific changes in the electron density at altitudes of 80-350 km during the recovery phase of strong magnetic storms were defined basing on a comparative analysis of the experimental spectra and the results of the numerical calculations. References. 1. E. N. Ermakova, D. S. Kotik, A. V.Ryabov, A. V.Pershin, T. B.osinger, and Q. Zhou, Studying the variation of the broadband spectral maximum parameters in the natural ULF fields, Radiophysics and Quantum Electronics, Vol. 55, No. 10-11, March, 2013 p. 605-615. 2. T. Bosinger, A. G. Demekhov, E. N. Ermakova, C. Haldoupis and Q

The Role of Localized Compressional Ultra-low Frequency Waves in Energetic Electron Precipitation

NASA Astrophysics Data System (ADS)

Rae, I. Jonathan; Murphy, Kyle R.; Watt, Clare E. J.; Halford, Alexa J.; Mann, Ian R.; Ozeke, Louis G.; Sibeck, David G.; Clilverd, Mark A.; Rodger, Craig J.; Degeling, Alex W.; Forsyth, Colin; Singer, Howard J.

2018-03-01

Typically, ultra-low frequency (ULF) waves have historically been invoked for radial diffusive transport leading to acceleration and loss of outer radiation belt electrons. At higher frequencies, very low frequency waves are generally thought to provide a mechanism for localized acceleration and loss through precipitation into the ionosphere of radiation belt electrons. In this study we present a new mechanism for electron loss through precipitation into the ionosphere due to a direct modulation of the loss cone via localized compressional ULF waves. We present a case study of compressional wave activity in tandem with riometer and balloon-borne electron precipitation across keV-MeV energies to demonstrate that the experimental measurements can be explained by our new enhanced loss cone mechanism. Observational evidence is presented demonstrating that modulation of the equatorial loss cone can occur via localized compressional wave activity, which greatly exceeds the change in pitch angle through conservation of the first and second adiabatic invariants. The precipitation response can be a complex interplay between electron energy, the localization of the waves, the shape of the phase space density profile at low pitch angles, ionospheric decay time scales, and the time dependence of the electron source; we show that two pivotal components not usually considered are localized ULF wave fields and ionospheric decay time scales. We conclude that enhanced precipitation driven by compressional ULF wave modulation of the loss cone is a viable candidate for direct precipitation of radiation belt electrons without any additional requirement for gyroresonant wave-particle interaction. Additional mechanisms would be complementary and additive in providing means to precipitate electrons from the radiation belts during storm times.

STS-132/ULF-4 Flight Control Team in FCR-1

NASA Image and Video Library

2010-05-20

JSC2010-E-085365 (20 May 2010) --- The members of the STS-132/ULF-4 ISS Orbit 2 flight control team pose for a group portrait in the space station flight control room in the Mission Control Center at NASA's Johnson Space Center. Flight director Emily Nelson holds the Expedition 23 mission logo.

STS-132/ULF-4 Flight Control Team in FCR-1

NASA Image and Video Library

2010-05-19

JSC2010-E-086277 (19 May 2010) --- The members of the STS-132/ULF-4 ISS Orbit 1 flight control team pose for a group portrait in the space station flight control room in the Mission Control Center at NASA's Johnson Space Center. Flight director Holly Ridings holds the STS-132 mission logo.

STS-132/ULF-4 Flight Control Team in FCR-1

NASA Image and Video Library

2010-05-20

JSC2010-E-086504 (20 May 2010) --- The members of the STS-132/ULF-4 ISS Orbit 3 flight control team pose for a group portrait in the space station flight control room in the Mission Control Center at NASA's Johnson Space Center. Flight director Scott Stover holds the Expedition 23 mission logo.

STS-132/ULF4 Flight Controllers on Console - Bldg. 30 south

NASA Image and Video Library

2010-05-20

JSC2010-E-086341 (20 May 2010) --- ISS flight director Holly Ridings monitors data at her console in the space station flight control room in the Mission Control Center at NASA's Johnson Space Center during STS-132/ULF-4 mission flight day seven activities.

Frequency up-converted piezoelectric energy harvester for ultralow-frequency and ultrawide-frequency-range operation

NASA Astrophysics Data System (ADS)

Zhang, Xiyang; Gao, Shiqiao; Li, Dongguang; Jin, Lei; Wu, Qinghe; Liu, Feng

2018-04-01

At present, frequency up-converted piezoelectric energy harvesters are disadvantaged by their narrow range of operating frequencies and low efficiency at ultralow-frequency excitation. To address these shortcomings, we propose herein an impact-driven frequency up-converted piezoelectric energy harvester composed of two driving beams and a generating beam. We find experimentally that the proposed device offers efficient energy output over an ultrawide-frequency-range and performs very well in the ultralow-frequency excitation. A maximum peak power of 29.3 mW is achieved under 0.5g acceleration at the excitation frequency of 12.7 Hz. The performance of the energy harvester can be adjusted and optimized by adjusting the spacing between the driving and generating beams. The results show that the proposed harvester has the potential to power miniaturized portable devices and wireless sensor nodes.

Compendium of the ULF/ELF Electromagnetic Fields Generated above a Sea of Finite Depth by Submerged Harmonic Dipoles

DTIC Science & Technology

1980-01-01

CATALOG NUMBER Tech. Report No. E715-1 4. TTE (ln tlitts LTYPE RPOT’ QcOIJj. Compendium of the ULF/ELF Electromagnetic Fields nccnicat Generated above...sidi if noeess’ry arid Identify hy bulock mriifi.rnb) ULF/ELF Electromagnetic Fields VMD, VED, HED, HMD Submerged Dipoles Undersea /Air Communication...a whole, it appears that the vertical electric component produced by th HED in the plane of the dipole (• =0) should be the most useful for undersea

47 CFR 15.202 - Certified operating frequency range.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 47 Telecommunication 1 2010-10-01 2010-10-01 false Certified operating frequency range. 15.202 Section 15.202 Telecommunication FEDERAL COMMUNICATIONS COMMISSION GENERAL RADIO FREQUENCY DEVICES Intentional Radiators § 15.202 Certified operating frequency range. Client devices that operate in a master...

Ulf Fernström (1915-1985) and his Contributions to the Development of Artificial Disc Replacements.

PubMed

Fisahn, Christian; Burgess, Brittni; Iwanaga, Joe; Chapman, Jens R; Oskouian, Rod J; Tubbs, R Shane

2017-02-01

Artificial disc replacements, which serve the function of separating vertebrae to allow for proper spinal alignment, can help treat debilitating low back pain in patients who have failed other conservative methods of treatment. A Swedish surgeon, Ulf Fernström, was the pioneer of artificial disc replacement, and his contribution in the form of Fernström balls dramatically altered spinal surgery and technique by showing the proper technique and implant that should be used for areas requiring motion in many planes. Ulf Fernström created his artificial disc inspired by the movement of the hip and knee joints. His implants attempted to restore disc spacing and articulation in patients who had failed conservative measures of treatment. Fernström balls were the first implants of their kind and represent the first attempt at artificial disc replacement. However, many surgeons and researchers questioned Fernström balls, claiming that their lack of elastic properties could damage patients. Of the wide range of implants on the market for the intervertebral disc space, all designs and applications of products stem from the initial discovery made by Fernström, thus making him a pioneer in disc replacement. Copyright © 2016 Elsevier Inc. All rights reserved.

Compressional ULF waves in the outer magnetosphere. 2: A case study of Pc 5 type wave activity

NASA Technical Reports Server (NTRS)

Zhu, Xiaoming; Kivelson, Margaret G.

1994-01-01

In previously published work (Zhu and Kivelson, 1991) the spatial distribution of compressional magnetic pulsations of period 2 - 20 min in the outer magnetosphere was described. In this companion paper, we study some specific compressional events within our data set, seeking to determine the structure of the waves and identifying the wave generation mechanism. We use both the magnetic field and three-dimensional plasma data observed by the International Sun-Earth Explorer (ISEE) 1 and/or 2 spacecraft to characterize eight compressional ultra low frequency (ULF) wave events with frequencies below 8 mHz in the outer magnetosphere. High time resolution plasma data for the event of July 24, 1978, made possible a detailed analysis of the waves. Wave properties specific to the event of July 24, 1978, can be summarized as follows: (1) Partial plasma pressures in the different energy ranges responded to the magnetic field pressure differently. In the low-energy range they oscillated in phase with the magnetic pressure, while oscillations in higher-energy ranges were out-of-phase; (2) Perpendicular wavelengths for the event were determined to be 60,000 and 30,000 km in the radial and azimuthal directions, respectively. Wave properties common to all events can be summarized as follows: (1) Compressional Pc 5 wave activity is correlated with Beta, the ratio of the plasma pressure to the magnetic pressure; the absolute magnitude of the plasma pressure plays a minor role for the wave activity; (2) The magnetic equator is a node of the compressional perturbation of the magnetic field; (3) The criterion for the mirror mode instability is often satisfied near the equator in the outer magnetosphere when the compressional waves are present. We believe these waves are generated by internal magnetohydrodynamic (MHD) instabilities.

SC- and SI-associated ULF and HF-Doppler oscillations during the great magnetic storm of February 1986

NASA Technical Reports Server (NTRS)

Yumoto, K.; Watanabe, T.; Takahashi, K.; Ogawa, T.

1989-01-01

Results are presented of an investigation of SC- and SI-associated ULF and HF-Doppler pulsations observed during the great geomagnetic storm of February 1986, which began with a sudden commmencement on February 6 at about 13:12 UT, developed slowly over the next two days, and, after a rapid intensification late on February 8, reached a minimum. It is shown that these ULF and geomagnetic pulsations can be explained by the dynamo-motor mechanism of ionospheric electric fields and by global compressional oscillations in the magnetosphere and ionosphere, respectively.

Spacecraft Observations of a ULF Wave Injected Onto Field Lines by SPEAR

NASA Astrophysics Data System (ADS)

Badman, S. V.; Wright, D. M.; Yeoman, T. K.; Clausen, L. B.; Fear, R. C.; Fazakerley, A. N.; Lucek, E. A.

2008-12-01

SPEAR (Space Exploration by Active Radar) is an ionospheric heating facility situated on Svalbard which is capable of exciting ULF waves on local magnetic field lines. Field-guided ULF waves can interact with the ionospheric Alfvén resonator (IAR) and produce parallel electric fields, which then accelerate electrons along the field line. Detection and study of these waves thus provides information on the properties of the IAR and auroral acceleration processes. We examine an interval from 1 February 2006 when SPEAR was transmitting with a 5 min on-off cycle. During this interval the Cluster spacecraft passed over the heater site. We discuss signatures of the SPEAR-generated wave identified in the Cluster field and electron measurements. One feature of interest is the periodic enhancement of electron fluxes in two broad energy bands (~10-100 eV and ~100-1000 eV) which occur out of phase with each other in the two different energy bands.

Energetic electrons response to ULF waves induced by interplanetary shocks in the outer radiation belt

NASA Astrophysics Data System (ADS)

Zong, Qiugang

Strong interplanetary shocks interaction with the Earth's magnetosphere would have great impacts on the Earth's magnetosphere. Cluster and Double Star constellation provides an ex-cellent opportunity to study the inner magnetospheric response to a powerful interplanetary solar wind forcing. An interplanetary shock on Nov.7 2004 with the solar wind dynamic pres-sure ˜ 70 nPa (Maximum) induced a large bipolar electric field in the plasmasphere boundary layer as observed by Cluster fleet, the peak-to-peak ∆Ey is more than 60 mV/m. Energetic elec-trons in the outer radiation belt are accelerated almost simultaneously when the interplanetary shock impinges upon the Earth's magnetosphere. Energetic electron bursts are coincident with the induced large electric field, energetic electrons (30 to 500 keV) with 900 pitch angles are accelerated first whereas those electrons are decelerated when the shock-induced electric field turns to positive value. Both toroidal and poloidal mode waves are found to be important but interacting with energetic electron at a different L-shell and a different period. At the Cluster's position (L = 4.4,), poloidal is predominant wave mode whereas at the geosynchronous orbits (L = 6.6), the ULF waves observed by the GOES -10 and -12 satellites are mostly toroidal. For comparison, a rather weak interplanetary shock on Aug. 30, 2001 (dynamic pressure ˜ 2.7 nPa) is also investigated in this paper. It is found that interplanetary shocks or solar wind pressure pulses with even small dynamic pressure change would have non-ignorable role in the radiation belt dynamic. Further, in this paper, our results also reveal the excitation of ULF waves re-sponses on the passing interplanetary shock, especially the importance of difference ULF wave modes when interacting with the energetic electrons in the radiation belt. The damping of the shock induced ULF waves could be separated into two terms: one term corresponds to the generalized Landau damping, the

Parameters of 1-4 mHz (Pc5/Pi3) ULF pulsations during the intervals preceding non-triggered substorms at high geomagnetic latitudes

NASA Astrophysics Data System (ADS)

Nosikova, Nataliya; Yagova, Nadezda; Baddeley, Lisa; Kozyreva, Olga; Lorentzen, Dag; Pilipenko, Vyacheslav

2017-04-01

One of the important questions for understanding substorm generation is the possible existence of specific pre-substorm variations of plasma, particles and electromagnetic field parameters. In this case analyzing of isolated non-triggered substorms (i.e. substorms that occur under quiet geomagnetic conditions without any visible triggers in IMF or SW) gives benefits for investigation of processes of substorm preparation. It was shown in previous studies that during a few hours preceding a non-triggered isolated substorm, coherent geomagnetic and aurroral luminosity pulsations are observed. Moreover, PSD, amplitudes of geomagnetic fluctuations in Pc5/Pi3 (1-4 mHz) frequency range and some spectral parameters differ from those registered on days without substorms. In present work this sort of pulsations has been studied in details. Features of longitudinal and latitudinal profiles are presented. Possible correlation with ULF disturbances in IMF and SW as well as in the magnetotail/magnetosheath are discussed.

New advanced tools for combined ULF wave analysis of multipoint space-borne and ground observations: application to single event and statistical studies

NASA Astrophysics Data System (ADS)

Balasis, G.; Papadimitriou, C.; Daglis, I. A.; Georgiou, M.; Giamini, S. A.

2013-12-01

In the past decade, a critical mass of high-quality scientific data on the electric and magnetic fields in the Earth's magnetosphere and topside ionosphere has been progressively collected. This data pool will be further enriched by the measurements of the upcoming ESA/Swarm mission, a constellation of three satellites in three different polar orbits between 400 and 550 km altitude, which is expected to be launched in November 2013. New analysis tools that can cope with measurements of various spacecraft at various regions of the magnetosphere and in the topside ionosphere as well as ground stations will effectively enhance the scientific exploitation of the accumulated data. Here, we report on a new suite of algorithms based on a combination of wavelet spectral methods and artificial neural network techniques and demonstrate the applicability of our recently developed analysis tools both for individual case studies and statistical studies of ultra-low frequency (ULF) waves. First, we provide evidence for a rare simultaneous observation of a ULF wave event in the Earth's magnetosphere, topside ionosphere and surface: we have found a specific time interval during the Halloween 2003 magnetic storm, when the Cluster and CHAMP spacecraft were in good local time (LT) conjunction, and have examined the ULF wave activity in the Pc3 (22-100 mHz) and Pc4-5 (1-22 mHz) bands using data from the Geotail, Cluster and CHAMP missions, as well as the CARISMA and GIMA magnetometer networks. Then, we perform a statistical study of Pc3 wave events observed by CHAMP for the full decade (2001-2010) of the satellite vector magnetic data: the creation of a database of such events enabled us to derive valuable statistics for many important physical properties relating to the spatio-temporal location of these waves, the wave power and frequency, as well as other parameters and their correlation with solar wind conditions, magnetospheric indices, electron density data, ring current decay

Functional Testing and Evaluation of Actiwatch Spectrum Devices for Launch on STS-133/ULF5

NASA Technical Reports Server (NTRS)

Rollins, Selisa F.; Humbert, Scott; Tysdal, Jessica A.

2010-01-01

The Actiwatch Spectrum (AWS) is a wrist-worn device that may be used for obtaining ground or on-orbit light exposure patterns and movement data. The objective of this project was to prepare AWS devices for launch on STS-133/ULF5 by a means of implementing functional tests and engineering evaluations. The data obtained from these tests and evaluations served as a means for detecting any plausible issues that the AWS may encounter while on-orbit. Subsequent steps after detecting anomalies with AWS devices encompassed identifying their root causes and taking the steps needed to mitigate them. As a result of this study, the overall success of sleep/wake research studies for STS-133/ULF5 and future missions will be enhanced.

Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons

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

Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang

The Van Allen radiation belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer radiation belt electrons are accelerated to relativistic energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique radiation belt event with intense ULF waves but no detectable VLF chorus waves. So, our results demonstrate that the ULFmore » waves moved the inner edge of the outer radiation belt earthward 0.3 Earth radii and enhanced the relativistic electron fluxes by up to one order of magnitude near the slot region within about 10 h, providing strong evidence for the radial diffusion of radiation belt relativistic electrons.« less

Ultra-low-frequency wave-driven diffusion of radiation belt relativistic electrons

DOE PAGES

Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; ...

2015-12-22

The Van Allen radiation belts are typically two zones of energetic particles encircling the Earth separated by the slot region. How the outer radiation belt electrons are accelerated to relativistic energies remains an unanswered question. Recent studies have presented compelling evidence for the local acceleration by very-low-frequency (VLF) chorus waves. However, there has been a competing theory to the local acceleration, radial diffusion by ultra-low-frequency (ULF) waves, whose importance has not yet been determined definitively. Here we report a unique radiation belt event with intense ULF waves but no detectable VLF chorus waves. So, our results demonstrate that the ULFmore » waves moved the inner edge of the outer radiation belt earthward 0.3 Earth radii and enhanced the relativistic electron fluxes by up to one order of magnitude near the slot region within about 10 h, providing strong evidence for the radial diffusion of radiation belt relativistic electrons.« less

Range-azimuth decouple beamforming for frequency diverse array with Costas-sequence modulated frequency offsets

NASA Astrophysics Data System (ADS)

Wang, Zhe; Wang, Wen-Qin; Shao, Huaizong

2016-12-01

Different from the phased-array using the same carrier frequency for each transmit element, the frequency diverse array (FDA) uses a small frequency offset across the array elements to produce range-angle-dependent transmit beampattern. FDA radar provides new application capabilities and potentials due to its range-dependent transmit array beampattern, but the FDA using linearly increasing frequency offsets will produce a range and angle coupled transmit beampattern. In order to decouple the range-azimuth beampattern for FDA radar, this paper proposes a uniform linear array (ULA) FDA using Costas-sequence modulated frequency offsets to produce random-like energy distribution in the transmit beampattern and thumbtack transmit-receive beampattern. In doing so, the range and angle of targets can be unambiguously estimated through matched filtering and subspace decomposition algorithms in the receiver signal processor. Moreover, random-like energy distributed beampattern can also be utilized for low probability of intercept (LPI) radar applications. Numerical results show that the proposed scheme outperforms the standard FDA in focusing the transmit energy, especially in the range dimension.

On the elimination of pulse wave velocity in stroke volume determination from the ultralow-frequency displacement ballistocardiogram.

DOT National Transportation Integrated Search

1964-03-01

A hydrodynamic model of the systemic circulatory system was mounted on an ultralow-frequency ballistocardiograph (ULF-BCG). The relationship between stroke volume and ballistocardiographic amplitude was investigated for different pulse wave velocitie...

Characteristics of different frequency ranges in scanning electron microscope images

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

Sim, K. S., E-mail: kssim@mmu.edu.my; Nia, M. E.; Tan, T. L.

2015-07-22

We demonstrate a new approach to characterize the frequency range in general scanning electron microscope (SEM) images. First, pure frequency images are generated from low frequency to high frequency, and then, the magnification of each type of frequency image is implemented. By comparing the edge percentage of the SEM image to the self-generated frequency images, we can define the frequency ranges of the SEM images. Characterization of frequency ranges of SEM images benefits further processing and analysis of those SEM images, such as in noise filtering and contrast enhancement.

Discrete-time model reduction in limited frequency ranges

NASA Technical Reports Server (NTRS)

Horta, Lucas G.; Juang, Jer-Nan; Longman, Richard W.

1991-01-01

A mathematical formulation for model reduction of discrete time systems such that the reduced order model represents the system in a particular frequency range is discussed. The algorithm transforms the full order system into balanced coordinates using frequency weighted discrete controllability and observability grammians. In this form a criterion is derived to guide truncation of states based on their contribution to the frequency range of interest. Minimization of the criterion is accomplished without need for numerical optimization. Balancing requires the computation of discrete frequency weighted grammians. Close form solutions for the computation of frequency weighted grammians are developed. Numerical examples are discussed to demonstrate the algorithm.

Fast flows, ULF waves, firehose instability and their association in the Earth's mid-tail current sheet

NASA Astrophysics Data System (ADS)

Wang, C. P.; Xing, X.

2017-12-01

Ultra-Low Frequency (ULF) plasma waves with frequency range between 1 mHz to 10 Hz are widely observed in the Earth's magnetosphere and on the ground. In particular, Pi2 and Pc4 waves have been found to be closely related to many important dynamic processes in the magnetotail, e.g., fast flows (V > 300 km/s). Observations have shown Pi2 waves in association with fast flows in the near-Earth plasma sheet (X>-30 RE). However, in the mid-tail region, where fast flows are more frequently observed than those in the near-Earth magnetotail, this association has not been evaluated. Our preliminary study using ARTEMIS probes in the mid-tail region (X -60 RE) shows close association between Pi2 and Pc4 waves with the presence of fast flows. Strong connection between mid-tail Pi2 pulsations and high-latitude ground Pi2 signatures are also observed. Among many proposed theories for Pi2 wave, ballooning and firehose instabilities are plausible mechanisms in leading to the generation of plasma waves around Pi2 frequency band. Ballooning instability is widely admitted for fast flow associated Pi2 pulsations in the near-Earth region. However, firehose instability is expected to occur more easily in mid-tail and beyond due to the specific pressure anisotropy in that region. We examined the pressure anisotropy conditions and evaluated firehose instability condition for both Pi2 and Pc4 events in mid-tail. It is found that the plasma is unstable against firehose instability in association with the initiation of Pi2 and Pc4 waves. These may suggest that firehose instability can be a wave generation mechanism in the mid-tail region.

Predicting Achievable Fundamental Frequency Ranges in Vocalization Across Species

PubMed Central

Titze, Ingo; Riede, Tobias; Mau, Ted

2016-01-01

Vocal folds are used as sound sources in various species, but it is unknown how vocal fold morphologies are optimized for different acoustic objectives. Here we identify two main variables affecting range of vocal fold vibration frequency, namely vocal fold elongation and tissue fiber stress. A simple vibrating string model is used to predict fundamental frequency ranges across species of different vocal fold sizes. While average fundamental frequency is predominantly determined by vocal fold length (larynx size), range of fundamental frequency is facilitated by (1) laryngeal muscles that control elongation and by (2) nonlinearity in tissue fiber tension. One adaptation that would increase fundamental frequency range is greater freedom in joint rotation or gliding of two cartilages (thyroid and cricoid), so that vocal fold length change is maximized. Alternatively, tissue layers can develop to bear a disproportionate fiber tension (i.e., a ligament with high density collagen fibers), increasing the fundamental frequency range and thereby vocal versatility. The range of fundamental frequency across species is thus not simply one-dimensional, but can be conceptualized as the dependent variable in a multi-dimensional morphospace. In humans, this could allow for variations that could be clinically important for voice therapy and vocal fold repair. Alternative solutions could also have importance in vocal training for singing and other highly-skilled vocalizations. PMID:27309543

A Frequency Domain Approach to Pretest Analysis Model Correlation and Model Updating for the Mid-Frequency Range

DTIC Science & Technology

2009-02-01

range of modal analysis and the high frequency region of statistical energy analysis , is referred to as the mid-frequency range. The corresponding...frequency range of modal analysis and the high frequency region of statistical energy analysis , is referred to as the mid-frequency range. The...predictions. The averaging process is consistent with the averaging done in statistical energy analysis for stochastic systems. The FEM will always

Statistical study of ULF wave occurrence in the dayside magnetosphere

NASA Technical Reports Server (NTRS)

Cao, M.; Mcpherron, R. L.; Russell, C. T.

1994-01-01

Ultralow-frequency (ULF) waves are observed almost everywhere in the dayside magnetosphere. The mechanism by which these waves are generated and transformed in the dayside magnetosphere is still not understood. Here we report a statistical study of these waves based on magnetic field data from the International Sun-Earth Explorer 1 (ISEE 1) spacecraft. Data from the first traversal of the spacecraft through the entire dayside magnetosphere have been examined to determine the spatial distribution of wave occurrence. Successive 20-min segments of data were transformed to a field-aligned coordinate system. The parallel component was detrended and all three components of the field spectrally analyzed. Wave occurrence was defined by the presence of significant peaks in the power spectra. Wave events were categorized by three wave frequency bands: Pc 3 with T approximately 10-45 s; Pc 4 with T approximately 45-150 s; the short-period part of the Pc 5 wave band with T approximately 150-324 s. Properties of the spectral peaks were then entered into a data base. The data base was next sorted to determine the spatial occurrence pattern for the waves. Our results show that Pc 3 waves most frequently occur just outside synchronous orbit and are approximately centered on local noon. Pc 4 waves have a similar distribution with its peak further out. Pc 5 waves have high occurrence rate at the two flanks of the magnetosphere. Peaks in spectra obtained near the magnetopause are less clearly defined than those deeper in the magnetosphere.

Active laser ranging with frequency transfer using frequency comb

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

Zhang, Hongyuan; Wei, Haoyun; Yang, Honglei

2016-05-02

A comb-based active laser ranging scheme is proposed for enhanced distance resolution and a common time standard for the entire system. Three frequency combs with different repetition rates are used as light sources at the two ends where the distance is measured. Pulse positions are determined through asynchronous optical sampling and type II second harmonic generation. Results show that the system achieves a maximum residual of 379.6 nm and a standard deviation of 92.9 nm with 2000 averages over 23.6 m. Moreover, as for the frequency transfer, an atom clock and an adjustable signal generator, synchronized to the atom clock, are used asmore » time standards for the two ends to appraise the frequency deviation introduced by the proposed system. The system achieves a residual fractional deviation of 1.3 × 10{sup −16} for 1 s, allowing precise frequency transfer between the two clocks at the two ends.« less

Theory and experiment research for ultra-low frequency maglev vibration sensor.

PubMed

Zheng, Dezhi; Liu, Yixuan; Guo, Zhanshe; Zhao, Xiaomeng; Fan, Shangchun

2015-10-01

A new maglev sensor is proposed to measure ultra-low frequency (ULF) vibration, which uses hybrid-magnet levitation structure with electromagnets and permanent magnets as the supporting component, rather than the conventional spring structure of magnetoelectric vibration sensor. Since the lower measurement limit needs to be reduced, the equivalent bearing stiffness coefficient and the equivalent damping coefficient are adjusted by the sensitivity unit structure of the sensor and the closed-loop control system, which realizes both the closed-loop control and the solving algorithms. A simple sensor experimental platform is then assembled based on a digital hardware system, and experimental results demonstrate that the lower measurement limit of the sensor is increased to 0.2 Hz under these experimental conditions, indicating promising results of the maglev sensor for ULF vibration measurements.

Theory and experiment research for ultra-low frequency maglev vibration sensor

NASA Astrophysics Data System (ADS)

Zheng, Dezhi; Liu, Yixuan; Guo, Zhanshe; Zhao, Xiaomeng; Fan, Shangchun

2015-10-01

A new maglev sensor is proposed to measure ultra-low frequency (ULF) vibration, which uses hybrid-magnet levitation structure with electromagnets and permanent magnets as the supporting component, rather than the conventional spring structure of magnetoelectric vibration sensor. Since the lower measurement limit needs to be reduced, the equivalent bearing stiffness coefficient and the equivalent damping coefficient are adjusted by the sensitivity unit structure of the sensor and the closed-loop control system, which realizes both the closed-loop control and the solving algorithms. A simple sensor experimental platform is then assembled based on a digital hardware system, and experimental results demonstrate that the lower measurement limit of the sensor is increased to 0.2 Hz under these experimental conditions, indicating promising results of the maglev sensor for ULF vibration measurements.

Field-aligned currents, convection electric fields, and ULF-ELF waves in the cusp

NASA Technical Reports Server (NTRS)

Saflekos, N. A.; Potemra, T. A.; Kintner, P. M., Jr.; Green, J. L.

1979-01-01

Nearly simultaneous observations from the Triad and Hawkeye satellites over the Southern Hemisphere, at low altitudes near the noon meridian and close to the usual polar cusp latitudes, show that in and near the polar cusp there exist several relationships between field-aligned currents (FACs), convection electric fields, ULF-ELF magnetic noise, broadband electrostatic noise and interplanetary magnetic fields. The most important findings are (1) the FACs directed into the ionosphere in the noon-to-dusk local time sector and directed away from the ionosphere in the noon-to-dawn local time sector and identified as region-1 permanent FACs (Iijima and Potemra, 1976a) and are located equatorward of the regions of antisunward (westward) convection; (2) the observations are consistent with a two-cell convection pattern symmetric in one case (throat positioned at noon) and asymmetric in another (throat located in a sector on the forenoon side in juxtaposition to the region of strong convection on the afternoon side); and (3) fine-structure FACs are responsible for the generation of ULF-ELF noise in the polar cusp.

Van Allen Probes, THEMIS, GOES, and Cluster Observations of EMIC Waves, ULF Pulsations, and an Electron Flux Dropout

NASA Technical Reports Server (NTRS)

Sigsbee, K.; Kletzing, C. A.; Smith, C. W.; Macdowall, R.; Spence, H.; Reeves, G.; Blake, J. B.; Baker, D. N.; Green, J. C.; Singer, H. J.;

Acceleration of Magnetospheric Relativistic Electrons by Ultra-Low Frequency Waves: A Comparison between Two Cases Observed by Cluster and LANL Satellites

NASA Technical Reports Server (NTRS)

Shao, X.; Fung, S. F.; Tan, L. C.; Sharma, A. S.

2010-01-01

Understanding the origin and acceleration of magnetospheric relativistic electrons (MREs) in the Earth's radiation belt during geomagnetic storms is an important subject and yet one of outstanding questions in space physics. It has been statistically suggested that during geomagnetic storms, ultra-low-frequency (ULF) Pc-5 wave activities in the magnetosphere are correlated with order of magnitude increase of MRE fluxes in the outer radiation belt. Yet, physical and observational understandings of resonant interactions between ULF waves and MREs remain minimum. In this paper, we show two events during storms on September 25, 2001 and November 25, 2001, the solar wind speeds in both cases were > 500 km/s while Cluster observations indicate presence of strong ULF waves in the magnetosphere at noon and dusk, respectively, during a approx. 3-hour period. MRE observations by the Los Alamos (LANL) spacecraft show a quadrupling of 1.1-1.5 MeV electron fluxes in the September 25, 2001 event, but only a negligible increase in the November 2.5, 2001 event. We present a detailed comparison between these two events. Our results suggest that the effectiveness of MRE acceleration during the September 25, 2001 event can be attributed to the compressional wave mode with strong ULF wave activities and the physical origin of MRE acceleration depends more on the distribution of toroidal and poloidal ULF waves in the outer radiation belt.

Oscillator or Amplifier With Wide Frequency Range

NASA Technical Reports Server (NTRS)

Kleinberg, L.; Sutton, J.

1987-01-01

Inductive and capacitive effects synthesized with feedback circuits. Oscillator/amplifier resistively tunable over wide frequency range. Feedback circuits containing operational amplifiers, resistors, and capacitors synthesize electrical effects of inductance and capacitance in parallel between input terminals. Synthetic inductance and capacitance, and, therefore, resonant frequency of input admittance, adjusted by changing potentiometer setting.

A multispacecraft event study of Pc5 ultralow-frequency waves in the magnetosphere and their external drivers

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

Wang, Chih-Ping; Thorne, Richard; Liu, Terry Z.

We investigate a quiet time event of magnetospheric Pc5 ultralow-frequency (ULF) waves and their likely external drivers using multiple spacecraft observations. Enhancements of electric and magnetic field perturbations in two narrow frequency bands, 1.5–2 mHz and 3.5–4 mHz, were observed over a large radial distance range from r ~ 5 to 11 RE. During the first half of this event, perturbations were mainly observed in the transverse components and only in the 3.5–4 mHz band. In comparison, enhancements were stronger during the second half in both transverse and compressional components and in both frequency bands. No indication of field linemore » resonances was found for these magnetic field perturbations. Perturbations in these two bands were also observed in the magnetosheath, but not in the solar wind dynamic pressure perturbations. For the first interval, good correlations between the flow perturbations in the magnetosphere and magnetosheath and an indirect signature for Kelvin-Helmholtz (K-H) vortices suggest K-H surface waves as the driver. For the second interval, good correlations are found between the magnetosheath dynamic pressure perturbations, magnetopause deformation, and magnetospheric waves, all in good correspondence to interplanetary magnetic field (IMF) discontinuities. The characteristics of these perturbations can be explained by being driven by foreshock perturbations resulting from these IMF discontinuities. This event shows that even during quiet periods, K-H-unstable magnetopause and ion foreshock perturbations can combine to create a highly dynamic magnetospheric ULF wave environment« less

A multispacecraft event study of Pc5 ultralow-frequency waves in the magnetosphere and their external drivers

DOE PAGES

Wang, Chih-Ping; Thorne, Richard; Liu, Terry Z.; ...

2017-05-09

We investigate a quiet time event of magnetospheric Pc5 ultralow-frequency (ULF) waves and their likely external drivers using multiple spacecraft observations. Enhancements of electric and magnetic field perturbations in two narrow frequency bands, 1.5–2 mHz and 3.5–4 mHz, were observed over a large radial distance range from r ~ 5 to 11 RE. During the first half of this event, perturbations were mainly observed in the transverse components and only in the 3.5–4 mHz band. In comparison, enhancements were stronger during the second half in both transverse and compressional components and in both frequency bands. No indication of field linemore » resonances was found for these magnetic field perturbations. Perturbations in these two bands were also observed in the magnetosheath, but not in the solar wind dynamic pressure perturbations. For the first interval, good correlations between the flow perturbations in the magnetosphere and magnetosheath and an indirect signature for Kelvin-Helmholtz (K-H) vortices suggest K-H surface waves as the driver. For the second interval, good correlations are found between the magnetosheath dynamic pressure perturbations, magnetopause deformation, and magnetospheric waves, all in good correspondence to interplanetary magnetic field (IMF) discontinuities. The characteristics of these perturbations can be explained by being driven by foreshock perturbations resulting from these IMF discontinuities. This event shows that even during quiet periods, K-H-unstable magnetopause and ion foreshock perturbations can combine to create a highly dynamic magnetospheric ULF wave environment« less

Feasibility study of contaminant detection for food with ULF-NMR/MRI system using HTS-SQUID

NASA Astrophysics Data System (ADS)

Hatsukade, Yoshimi; Tsunaki, Shingo; Yamamoto, Masaaki; Abe, Takayuki; Hatta, Junichi; Tanaka, Saburo

2013-11-01

We have developed an ultra-low frequency (ULF) nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) system utilizing an HTS-SQUID for an application of contaminant detection in food and drink. In the system, a permanent magnet of 1.1 T was used to pre-polarize protons in a water sample. We measured NMR signals from water samples with or without various contaminants, such as stainless steel (SUS304), aluminum, and glass balls using the system. In the case that the contaminant was the SUS304 ball, the NMR signal intensity was reduced compared to that from the sample without the contaminant due to the remnant field of the contaminant. One-dimensional (1D) MRIs of the samples were also acquired to detect non-magnetic contaminants. In the 1D MRIs, changes of the MRI spectra were detected, corresponding to positions of the contaminants. These results show that the feasibility of the system to detect various contaminants in foods.

ULF foreshock under radial IMF: THEMIS observations and global kinetic simulation Vlasiator results compared

NASA Astrophysics Data System (ADS)

Palmroth, Minna; Rami, Vainio; Archer, Martin; Hietala, Heli; Afanasiev, Alexandr; Kempf, Yann; Hoilijoki, Sanni; von Alfthan, Sebastian

2015-04-01

For decades, a certain type of ultra low frequency waves with a period of about 30 seconds have been observed in the Earth's quasi-parallel foreshock. These waves, with a wavelength of about an Earth radius, are compressive and propagate with an average angle of 20 degrees with respect of the interplanetary magnetic field (IMF). The latter property has caused trouble to scientists as the growth rate for the instability causing the waves is maximized along the magnetic field. So far, these waves have been characterized by single or multi-spacecraft methods and 2-dimensional hybrid-PIC simulations, which have not fully reproduced the wave properties. Vlasiator is a newly developed, global hybrid-Vlasov simulation, which solves the six-dimensional phase space utilising the Vlasov equation for protons, while electrons are a charge-neutralising fluid. The outcome of the simulation is a global reproduction of ion-scale physics in a holistic manner where the generation of physical features can be followed in time and their consequences can be quantitatively characterised. Vlasiator produces the ion distribution functions and the related kinetic physics in unprecedented detail, in the global scale magnetospheric scale with a resolution of a couple of hundred kilometres in the ordinary space and 20 km/s in the velocity space. We run Vlasiator under a radial IMF in five dimensions consisting of the three-dimensional velocity space embedded in the ecliptic plane. We observe the generation of the 30-second ULF waves, and characterize their evolution and physical properties in time. We compare the results both to THEMIS observations and to the quasi-linear theory. We find that Vlasiator reproduces the foreshock ULF waves in all reported observational aspects, i.e., they are of the observed size in wavelength and period, they are compressive and propagate obliquely to the IMF. In particular, we discuss the issues related to the long-standing question of oblique propagation.

On the predictive potential of Pc5 ULF waves to forecast relativistic electrons based on their relationships over two solar cycles

NASA Astrophysics Data System (ADS)

Lam, Hing-Lan

2017-01-01

A statistical study of relativistic electron (>2 MeV) fluence derived from geosynchronous satellites and Pc5 ultralow frequency (ULF) wave power computed from a ground magnetic observatory data located in Canada's auroral zone has been carried out. The ground observations were made near the foot points of field lines passing through the GOESs from 1987 to 2009 (cycles 22 and 23). We determine statistical relationships between the two quantities for different phases of a solar cycle and validate these relationships in two different cycles. There is a positive linear relationship between log fluence and log Pc5 power for all solar phases; however, the power law indices vary for different phases of the cycle. High index values existed during the descending phase. The Pearson's cross correlation between electron fluence and Pc5 power indicates fluence enhancement 2-3 days after strong Pc5 wave activity for all solar phases. The lag between the two quantities is shorter for extremely high fluence (due to high Pc5 power), which tends to occur during the declining phases of both cycles. Most occurrences of extremely low fluence were observed during the extended solar minimum of cycle 23. The precursory attribute of Pc5 power with respect to fluence and the enhancement of fluence due to rising Pc5 power both support the notion of an electron acceleration mechanism by Pc5 ULF waves. This precursor behavior establishes the potential of using Pc5 power to predict relativistic electron fluence.

Application of multivariate autoregressive spectrum estimation to ULF waves

NASA Technical Reports Server (NTRS)

Ioannidis, G. A.

1975-01-01

The estimation of the power spectrum of a time series by fitting a finite autoregressive model to the data has recently found widespread application in the physical sciences. The extension of this method to the analysis of vector time series is presented here through its application to ULF waves observed in the magnetosphere by the ATS 6 synchronous satellite. Autoregressive spectral estimates of the power and cross-power spectra of these waves are computed with computer programs developed by the author and are compared with the corresponding Blackman-Tukey spectral estimates. The resulting spectral density matrices are then analyzed to determine the direction of propagation and polarization of the observed waves.

Van Allen Probes, THEMIS, GOES, and cluster observations of EMIC waves, ULF pulsations, and an electron flux dropout

DOE PAGES

Sigsbee, K.; Kletzing, C. A.; Smith, C. W.; ...

2016-03-04

We examined an electron flux dropout during the 12–14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS)-A (P5), Cluster 2, and Geostationary Operational Environmental Satellites (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at geosynchronous orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 h from 12 to 14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervalsmore » of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12–13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He + electromagnetic ion cyclotron (EMIC) waves from just inside geosynchronous orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13–14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst <–100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finally returned to near prestorm values, possibly in response to strong ultralow frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior.« less

Van Allen Probes, THEMIS, GOES, and cluster observations of EMIC waves, ULF pulsations, and an electron flux dropout

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

Sigsbee, K.; Kletzing, C. A.; Smith, C. W.

We examined an electron flux dropout during the 12–14 November 2012 geomagnetic storm using observations from seven spacecraft: the two Van Allen Probes, Time History of Events and Macroscale Interactions during Substorms (THEMIS)-A (P5), Cluster 2, and Geostationary Operational Environmental Satellites (GOES) 13, 14, and 15. The electron fluxes for energies greater than 2.0 MeV observed by GOES 13, 14, and 15 at geosynchronous orbit and by the Van Allen Probes remained at or near instrumental background levels for more than 24 h from 12 to 14 November. For energies of 0.8 MeV, the GOES satellites observed two shorter intervalsmore » of reduced electron fluxes. The first interval of reduced 0.8 MeV electron fluxes on 12–13 November was associated with an interplanetary shock and a sudden impulse. Cluster, THEMIS, and GOES observed intense He + electromagnetic ion cyclotron (EMIC) waves from just inside geosynchronous orbit out to the magnetopause across the dayside to the dusk flank. The second interval of reduced 0.8 MeV electron fluxes on 13–14 November was associated with a solar sector boundary crossing and development of a geomagnetic storm with Dst <–100 nT. At the start of the recovery phase, both the 0.8 and 2.0 MeV electron fluxes finally returned to near prestorm values, possibly in response to strong ultralow frequency (ULF) waves observed by the Van Allen Probes near dawn. A combination of adiabatic effects, losses to the magnetopause, scattering by EMIC waves, and acceleration by ULF waves can explain the observed electron behavior.« less

Evidence of low frequency waves penetration in the ionosphere observed by Chibis-M satellite

NASA Astrophysics Data System (ADS)

Pronenko, Vira; Dudkin, Fedir; Korepanov, Valery

2016-07-01

Chibis-M microsatellite (MS) was launched using ISS infrastructure to the 500 km circular orbit with inclination 52° and successfully operated during the years 2012-2014. One of the main tasks of this experiment was the study of how powerful natural and technogenic processes are reflected in the ionosphere. For this study, the magnetic wave complex (MWC) was used which measured one electrical component and three components of the magnetic vector in the frequency range 0.1 Hz-40 kHz. Due to the proximity of the magnetic sensors and the satellite control system, their high sensitivity (up to 0.02 pT/sqrt(Hz)) was not used in full because the level of magnetic noise was about 10 pT/sqrt(Hz) in the low-frequency range. Nevertheless, owing to the symmetric fixation of the electric probes relative to the satellite body, the electrical sensor provided high accuracy measurements (about 0.8-0.04 (µV/m)/sqrt(Hz)) in the frequency range of 0.1-40 000 Hz, despite the very small measurement base of 0.42 m. This allowed us to collect valuable information which revealed a number of interesting physical effects, especially in ultralow frequency (ULF) range. In ULF range the ionospheric emissions with a central frequency of 50 (60) Hz - power line emissions (PLE) and the Schumann resonance harmonics (SR) were detected, though, according to the present model of the ionosphere, they have not penetrate there. A detailed study of the obtained data revealed the features of PLE and SR. The spatial distribution of PLE and their connection with the power lines location on the ground were analyzed. It was found that the intensity of PLE depends on the load characteristics of the power line and usually has a minimum in the morning. The cases of an extra long distance of PLE propagation in the Earth's ionosphere over oceans in the equatorial region have been also observed. Further, it was detected that PLE has been recorded both in the shaded and sunlit parts of the orbits and their

Modeling of Outer Radiation Belt Electron Scattering due to Spatial and Spectral Properties of ULF Waves

NASA Astrophysics Data System (ADS)

Tornquist, Mattias

The research presented in this thesis covers wave-particle interactions for relativistic (0.5-10 MeV) electrons in Earth's outer radiation belt (r = 3-7 RE, or L-shells: L = 3-7) interacting with magnetospheric Pc-5 (ULF) waves. This dissertation focuses on ideal models for short and long term electron energy and radial position scattering caused by interactions with ULF waves. We use test particle simulations to investigate these wave-particle interactions with ideal wave and magnetic dipole fields. We demonstrate that the wave-particle phase can cause various patterns in phase space trajectories, i.e. local acceleration, and that for a global electron population, for all initial conditions accounted for, has a negligible net energy scattering. Working with GSM polar coordinates, the relevant wave field components are EL, Ephi and Bz, where we find that the maximum energy scattering is 3-10 times more effective for Ephi compared to EL in a magnetic dipole field with a realistic dayside compression amplitude. We also evaluate electron interactions with two coexisting waves for a set of small frequency separations and phases, where it is confirmed that multi-resonant transport is possible for overlapping resonances in phase space when the Chirikov criterion is met (stochasticity parameter K = 1). The electron energy scattering enhances with decreasing frequency separation, i.e. increasing K, and is also dependent on the phases of the waves. The global acceleration is non-zero, can be onset in about 1 hour and last for > 4 hours. The adiabatic wave-particle interaction discussed up to this point can be regarded as short-term scattering ( tau ˜ hours ). When the physical problem extends to longer time scales (tau ˜ days ) the process ceases to be adiabatic due to the introduction of stochastic element in the system and becomes a diffusive process. We show that any mode in a broadband spectrum can contribute to the total diffusion rate for a particular drift

Natural time analysis on the ultra-low frequency magnetic field variations prior to the 2016 Kumamoto (Japan) earthquakes

NASA Astrophysics Data System (ADS)

Potirakis, Stelios M.; Schekotov, Alexander; Asano, Tomokazu; Hayakawa, Masashi

2018-04-01

On 15 April 2016 a very strong and shallow earthquake (EQ) (MW = 7.0 , depth ∼ 10 km) occurred in Southwest Japan under the city of Kumamoto, while two very strong foreshocks (MW = 6.2 and MW = 6.0) preceded by about one day. The Kumamoto EQs being very catastrophic, have already attracted much attention among the scientific community in a quest for understanding the generation mechanism, as well as for reporting any preseismic anomalies in various observables and assessing the effectivity of the current early warning systems. In the present article we report precursory behavior of the ground-based observed ultra-low frequency (ULF) magnetic field variations before the Kumamoto EQs. By analyzing specific ULF magnetic field characteristics in terms of the recently introduced natural time (NT) analysis method, we identified that ULF magnetic field variations presented critical features from 2 weeks up to 1 month before the Kumamoto EQs. Specifically, the ULF magnetic field characteristics Fh , Fz , Dh and δDep were analyzed. The first two represent variations of the horizontal and vertical components of the geomagnetic field. The third and fourth characteristics correspond to the depression (decrease) and a relative depression of the horizontal magnetic field variations, respectively. The latter depends on the degree of ionospheric disturbance. All of them were found to reach criticality before the Kumamoto EQs; however, in different time periods for each characteristic.

Observations of a Unique Type of ULF Wave by Low-Altitude Space Technology 5 Satellites

NASA Technical Reports Server (NTRS)

Le, G.; Chi, P. J.; Strangeway, R. J.; Slavin, J. A.

2011-01-01

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three-microsatellite constellation deployed into a 300 x 4500 km dawn-dusk and Sun-synchronous polar orbit with 105.6deg inclination angle. Because of the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc2-3 frequency range. These Pc2-3 waves appear as wave packets with durations in the order of 5-10 min. As the maximum separations of the ST-5 spacecraft are in the order of 10 min, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc2-3 band; instead, the waves appear to be the common Pc4-5 waves associated with field line resonances. We suggest that these unique Pc2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-dusk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field line resonances.

Fast Room Temperature Very Low Field-Magnetic Resonance Imaging System Compatible with MagnetoEncephaloGraphy Environment

PubMed Central

Galante, Angelo; Sinibaldi, Raffaele; Conti, Allegra; De Luca, Cinzia; Catallo, Nadia; Sebastiani, Piero; Pizzella, Vittorio; Romani, Gian Luca; Sotgiu, Antonello; Della Penna, Stefania

2015-01-01

In recent years, ultra-low field (ULF)-MRI is being given more and more attention, due to the possibility of integrating ULF-MRI and Magnetoencephalography (MEG) in the same device. Despite the signal-to-noise ratio (SNR) reduction, there are several advantages to operating at ULF, including increased tissue contrast, reduced cost and weight of the scanners, the potential to image patients that are not compatible with clinical scanners, and the opportunity to integrate different imaging modalities. The majority of ULF-MRI systems are based, until now, on magnetic field pulsed techniques for increasing SNR, using SQUID based detectors with Larmor frequencies in the kHz range. Although promising results were recently obtained with such systems, it is an open question whether similar SNR and reduced acquisition time can be achieved with simpler devices. In this work a room-temperature, MEG-compatible very-low field (VLF)-MRI device working in the range of several hundred kHz without sample pre-polarization is presented. This preserves many advantages of ULF-MRI, but for equivalent imaging conditions and SNR we achieve reduced imaging time based on preliminary results using phantoms and ex-vivo rabbits heads. PMID:26630172

On the man-made contamination on ULF measurements: evidence for disturbances related to an electrified DC railway

NASA Astrophysics Data System (ADS)

Villante, U.; Piancatelli, A.; Palangio, P.

2014-09-01

An analysis of measurements performed at L'Aquila (Italy) during a deep minimum of solar and magnetospheric activity (2008-2010) allowed for the evaluation of possible contamination of the ultralow-frequency (ULF) spectrum (f ≈ 1-500 mHz) from artificial disturbances, practically in absence of natural signals. In addition, the city evacuation and the interruption of all industrial and social activities after the strong earthquake of 6 April 2009 allowed also for the examination of possible changes of the contamination level under remarkably changed environmental conditions. Our analysis reveals a persistent, season-independent, artificial signal, with the same characteristics in the H and Z components, that affects during daytime hours the entire spectrum; such contamination persists after the city evacuation. We speculate that the DC electrified railway (located ≈ 33 km from the Geomagnetic Observatory of L'Aquila, it maintained the same train traffic after the earthquake) is responsible for the observed disturbances.

Burst of ULF Electric Field Recorded by DEMETER Possibly Related to the Series of Earthquakes Occurred during the Tsunami Over the Indian Region (P19)

NASA Astrophysics Data System (ADS)

Gwal, A. K.; Shrivastava, A.

2006-11-01

ak_gwal@yahoo.co.in The scientists have found that the accumulation of tectonic energy is localized in certain places and is not universal. Taking into account this hypothesis the authors have studied the sequence of occurrence rate of the earthquakes (M≥5) in the South-East Asian region, as the chronological data related to the occurrence of earthquakes collected in that region for last five years i.e. from 2001 to 2005 have revealed that the disastrous tsunami events which took place on 26th December, 2004 as an effect of Sumatra earthquake( M=9) have increased the occurrence of earthquake frequency for a longer period (which might be due to adjustment of tectonic plates). Observing these facts i.e. sudden enhancement in occurrence rate of earthquakes, the authors have availed this opportunity to further explore the concept of seismoelectromagnetic-ionospheric phenomena, which still needs a lot of statistical evidences, comprising tremendous amount of data to establish it. In this paper the authors have tried to analyze the chain of observations made and data collected and stored month wise w.e.f. 26th December, 2004 to 31st March, 2005 in the region, using DEMETER satellite. Further, efforts have also been made to provide the statistical analysis of the ionospheric variability caused due to detected electromagnetic burst in ULF frequency ranges in the context of natural variability in order to distinguish the variability introduced by other sources. In brief, it could be concluded that there is possibility of getting the electromagnetic precursors in the ionosphere at different frequency ranges due to excess release of tectonic energy as a result of occurrence rate of the earthquakes in the region.

Cross-Linguistic Differences in Bilinguals' Fundamental Frequency Ranges

ERIC Educational Resources Information Center

Ordin, Mikhail; Mennen, Ineke

2017-01-01

Purpose: We investigated cross-linguistic differences in fundamental frequency range (FFR) in Welsh-English bilingual speech. This is the first study that reports gender-specific behavior in switching FFRs across languages in bilingual speech. Method: FFR was conceptualized as a behavioral pattern using measures of span (range of fundamental…

Ion Upwelling and Height-Resolved Electrodynamic Response of the Ionosphere to ULF Waves and Precipitation: Comparison Between Simulation and EISCAT Observations

NASA Astrophysics Data System (ADS)

Sydorenko, D.; Rankin, R.

2013-12-01

We have developed a comprehensive two-dimensional (meridional) model of coupling between the magnetosphere and ionosphere that covers an altitude range from ~100 km to few thousand km at high latitudes [Sydorenko and Rankin, 2013]. The model describes propagation of inertial scale Alfven waves, including ponderomotive forces, and has a parametric model of energetic electron precipitation; it includes vertical ion flows and chemical reactions between ions and neutrals. Model results are presented that reproduce EISCAT radar observations of electron and ion temperatures, height integrated conductivity, ion densities, and ion flows during a period of ULF activity described in [Lester, Davies, and Yeoman, 2000]. We performed simulations where the precipitation and the Alfven wave perturb the ionosphere simultaneously. By adjusting parameters of the wave and the precipitation we have achieved qualitative, and sometimes even reasonable quantitative agreement between the observations and the simulation. The model results are discussed in the context of new results anticipated from the Canadian small satellite mission ePOP "Enhanced Polar Outflow Probe", scheduled for launch on September 9, 2013. Sydorenko D. and R. Rankin, 'Simulation of O+ upflows created by electron precipitation and Alfvén waves in the ionosphere' submitted to Journal of Geophysical Research, 2013. Lester M., J. A. Davies, and T. K. Yeoman, 'The ionospheric response during an interval of PC5 ULF wave activity', Ann. Geophysicae, v.18, p.257-261 (2000).

47 CFR 15.33 - Frequency range of radiated measurements.

Code of Federal Regulations, 2014 CFR

2014-10-01

... kHz, up to at least the frequency shown in this paragraph: (1) If the intentional radiator operates... level of radiated emissions within the frequency range 9 kHz to 30 MHz, such as a CB receiver or a... used in the device, without going below 9 kHz (25 MHz for CB receivers), up to the frequency shown in...

47 CFR 15.33 - Frequency range of radiated measurements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... kHz, up to at least the frequency shown in this paragraph: (1) If the intentional radiator operates... level of radiated emissions within the frequency range 9 kHz to 30 MHz, such as a CB receiver or a... used in the device, without going below 9 kHz (25 MHz for CB receivers), up to the frequency shown in...

47 CFR 15.33 - Frequency range of radiated measurements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... kHz, up to at least the frequency shown in this paragraph: (1) If the intentional radiator operates... level of radiated emissions within the frequency range 9 kHz to 30 MHz, such as a CB receiver or a... used in the device, without going below 9 kHz (25 MHz for CB receivers), up to the frequency shown in...

47 CFR 15.33 - Frequency range of radiated measurements.

Code of Federal Regulations, 2013 CFR

2013-10-01

... kHz, up to at least the frequency shown in this paragraph: (1) If the intentional radiator operates... level of radiated emissions within the frequency range 9 kHz to 30 MHz, such as a CB receiver or a... used in the device, without going below 9 kHz (25 MHz for CB receivers), up to the frequency shown in...

Multi-dynamic range compressional wave detection using optical-frequency comb

NASA Astrophysics Data System (ADS)

Minamikawa, Takeo; Masuoka, Takashi; Oe, Ryo; Nakajima, Yoshiaki; Yamaoka, Yoshihisa; Minoshima, Kaoru; Yasui, Takeshi

2018-02-01

Compressional wave detection is useful means for health monitoring of building, detection of abnormal vibration of moving objects, defect evaluation, and biomedical imaging such as echography and photoacoustic imaging. The frequency of the compressional wave is varied from quasi-static to a few tens of megahertz depending on applications. Since the dynamic range of general compressional wave detectors is limited, we need to choose a proper compressional wave detector depending on applications. For the compressional wave detection with wide dynamic range, two or more detectors with different detection ranges is required. However, these detectors with different detection ranges generally has different accuracy and precision, disabling the seamless detection over these detection ranges. In this study, we proposed a compressional wave detector employing optical frequency comb (OFC). The compressional wave was sensed with a part of an OFC cavity, being encoded into OFC. The spectrally encoded OFC was converted to radio-frequency by the frequency link nature of OFC. The compressional wave-encoded radio-frequency can therefore be directly measured with a high-speed photodetector. To enhance the dynamic range of the compressional wave detection, we developed a cavityfeedback-based system and a phase-sensitive detection system, both of which the accuracy and precision are coherently linked to these of the OFC. We provided a proof-of-principle demonstration of the detection of compressional wave from quasi-static to ultrasound wave by using the OFC-based compressional wave sensor. Our proposed approach will serve as a unique and powerful tool for detecting compressional wave versatile applications in the future.

Statistical studies of Pc 3-5 pulsations and their relevance for possible source mechanisms of ULF waves

NASA Technical Reports Server (NTRS)

Anderson, Brian J.

1993-01-01

A number of statistical studies using spacecraft data have been made of ULF waves in the magnetosphere. These studies provide an overview of ULF pulsation activity for r = 5-15 R(E) and allow an assessment of likely source mechanisms. In this review pulsations are categorized into five general types: compressional Pc 5, poloidal Pc 4, toroidal harmonics, toroidal Pc 5 (fundamental mode), and incoherent noise. The occurrence distributions and/or distributions of wave power of the different types suggest that compressional Pc 5 and poloidal Pc 4 derive their energy locally, most likely from energetic protons. The toroidal pulsations, both harmonic and fundamental mode, appear to be driven by an energy source outside the magnetopause - directly upstream in the sheath and solar wind for harmonics and the flanks for fundamentals. Incoherent pulsations are a prominent pulsation type but from their occurrence distribution alone it is unclear what their dominant energy source may be.

Relativistic electron dynamics produced by azimuthally localized poloidal mode ULF waves: Boomerang-shaped pitch angle evolutions

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

Hao, Y. X.; Zong, Q. -G.; Zhou, X. -Z.

Here, we present an analysis of “boomerang-shaped” pitch angle evolutions of outer radiation belt relativistic electrons observed by the Van Allen Probes after the passage of an interplanetary shock on 7 June 2014. The flux at different pitch angles is modulated by Pc5 waves, with equatorially mirroring electrons reaching the satellite first. For 90° pitch angle electrons, the phase change of the flux modulations across energy exceeds 180° and increasingly tilts with time. Using estimates of the arrival time of particles of different pitch angles at the spacecraft location, a scenario is investigated in which shock-induced ULF waves interact withmore » electrons through the drift resonance mechanism in a localized region westward of the spacecraft. Numerical calculations on particle energy gain with the modified ULF wavefield reproduce the observed boomerang stripes and modulations in the electron energy spectrogram. The study of boomerang stripes and their relationship to drift resonance taking place at a location different from the observation point adds new understanding of the processes controlling the dynamics of the outer radiation belt.« less

Relativistic electron dynamics produced by azimuthally localized poloidal mode ULF waves: Boomerang-shaped pitch angle evolutions

NASA Astrophysics Data System (ADS)

Hao, Y.; Zong, Q.; Zhou, X.; Rankin, R.; Chen, X.; Liu, Y.; Fu, S.; Spence, H. E.; Blake, J. B.; Reeves, G. D.

2017-12-01

We present an analysis of "boomerang-shaped" pitch angle evolutions of outer radiation belt relativistic electrons observed by the Van Allen Probes after the passage of an interplanetary shock on June 7th, 2014. The flux at different pitch angles is modulated by Pc5 waves, with equatorially mirroring electrons reaching the satellite first. For 90º pitch angle electrons, the phase change of the flux modulations across energy exceeds 180º, and increasingly tilts with time. Using estimates of the arrival time of particles of different pitch angles at the spacecraft location, a scenario is investigated in which shock-induced ULF waves interact with electrons through the drift resonance mechanism in a localized region westward of the spacecraft. Numerical calculations on particle energy gain with the modified ULF wave field reproduce the observed boomerang stripes and modulations in the electron energy spectrogram. The study of boomerang stripes and their relationship to drift-resonance taking place at a location different from the observation point adds new understanding of the processes controlling the dynamics of the outer radiation belt.

Relativistic electron dynamics produced by azimuthally localized poloidal mode ULF waves: Boomerang-shaped pitch angle evolutions

NASA Astrophysics Data System (ADS)

Hao, Y. X.; Zong, Q.-G.; Zhou, X.-Z.; Rankin, R.; Chen, X. R.; Liu, Y.; Fu, S. Y.; Spence, H. E.; Blake, J. B.; Reeves, G. D.

2017-08-01

We present an analysis of "boomerang-shaped" pitch angle evolutions of outer radiation belt relativistic electrons observed by the Van Allen Probes after the passage of an interplanetary shock on 7 June 2014. The flux at different pitch angles is modulated by Pc5 waves, with equatorially mirroring electrons reaching the satellite first. For 90° pitch angle electrons, the phase change of the flux modulations across energy exceeds 180° and increasingly tilts with time. Using estimates of the arrival time of particles of different pitch angles at the spacecraft location, a scenario is investigated in which shock-induced ULF waves interact with electrons through the drift resonance mechanism in a localized region westward of the spacecraft. Numerical calculations on particle energy gain with the modified ULF wavefield reproduce the observed boomerang stripes and modulations in the electron energy spectrogram. The study of boomerang stripes and their relationship to drift resonance taking place at a location different from the observation point adds new understanding of the processes controlling the dynamics of the outer radiation belt.

Relativistic electron dynamics produced by azimuthally localized poloidal mode ULF waves: Boomerang-shaped pitch angle evolutions

DOE PAGES

Hao, Y. X.; Zong, Q. -G.; Zhou, X. -Z.; ...

2017-07-10

Here, we present an analysis of “boomerang-shaped” pitch angle evolutions of outer radiation belt relativistic electrons observed by the Van Allen Probes after the passage of an interplanetary shock on 7 June 2014. The flux at different pitch angles is modulated by Pc5 waves, with equatorially mirroring electrons reaching the satellite first. For 90° pitch angle electrons, the phase change of the flux modulations across energy exceeds 180° and increasingly tilts with time. Using estimates of the arrival time of particles of different pitch angles at the spacecraft location, a scenario is investigated in which shock-induced ULF waves interact withmore » electrons through the drift resonance mechanism in a localized region westward of the spacecraft. Numerical calculations on particle energy gain with the modified ULF wavefield reproduce the observed boomerang stripes and modulations in the electron energy spectrogram. The study of boomerang stripes and their relationship to drift resonance taking place at a location different from the observation point adds new understanding of the processes controlling the dynamics of the outer radiation belt.« less

Adiabatic description of long range frequency sweeping

NASA Astrophysics Data System (ADS)

Breizman, Boris; Nyqvist, Robert; Lilley, Matthew

2012-10-01

A theoretical framework is developed to describe long range frequency sweeping events in the 1D electrostatic bump-on-tail model with fast particle sources and collisions. The model includes three collision operators (Krook, drag (dynamical friction) and velocity space diffusion), and allows for a general shape of the fast particle distribution function. The behavior of phase space holes and clumps is analyzed, and the effect of particle trapping due to separatrix expansion is discussed. With a fast particle distribution function whose slope decays above the resonant phase velocity, hooked frequency sweeping is found for holes in the presence of drag collisions alone.

Long range ultra-high frequency (UHF) radio frequency identification (RFID) antenna design

NASA Astrophysics Data System (ADS)

Reynolds, Nathan D.

There is an ever-increasing demand for radio frequency identification (RFID) tags that are passive, long range, and mountable on multiple surfaces. Currently, RFID technology is utilized in numerous applications such as supply chain management, access control, and public transportation. With the combination of sensory systems in recent years, the applications of RFID technology have been extended beyond tracking and identifying. This extension includes applications such as environmental monitoring and healthcare applications. The available sensory systems usually operate in the medium or high frequency bands and have a low read range. However, the range limitations of these systems are being overcome by the development of RFID sensors focused on utilizing tags in the ultra-high frequency (UHF) band. Generally, RFID tags have to be mounted to the object that is being identified. Often the objects requiring identification are metallic. The inherent properties of metallic objects have substantial effects on nearby electromagnetic radiation; therefore, the operation of the tag antenna is affected when mounted on a metallic surface. This outlines one of the most challenging problems for RFID systems today: the optimization of tag antenna performance in a complex environment. In this research, a novel UHF RFID tag antenna, which has a low profile, long range, and is mountable on metallic surfaces, is designed analytically and simulated using a 3-D electromagnetic simulator, ANSYS HFSS. A microstrip patch antenna is selected as the antenna structure, as patch antennas are low profile and suitable for mounting on metallic surfaces. Matching and theoretical models of the microstrip patch antenna are investigated. Once matching and theory of a microstrip patch antenna is thoroughly understood, a unique design technique using electromagnetic band gap (EBG) structures is explored. This research shows that the utilization of an EBG structure in the patch antenna design yields

Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology Five Mission

NASA Technical Reports Server (NTRS)

Le, G.; Chi, P.; Strangeway, R. J.; Slavin, J. A.

2011-01-01

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6deg inclination angle. Due to the Earth s rotation and the dipole tilt effect, the spacecraft s dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Satellites

NASA Technical Reports Server (NTRS)

Le, G.; Chi, P. J.; Strangeway, R. J.; Slavin, J. A.

2011-01-01

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6deg inclination angle. Due to the Earth s rotation and the dipole tilt effect, the spacecraft s dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that this unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Mission

NASA Technical Reports Server (NTRS)

Le, Guan; Chi, P.; Strangeway, R. J.; Slavin, J. A.

2011-01-01

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6 inclination angle. Due to the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as sub auroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at sub auroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST -5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Mission

NASA Technical Reports Server (NTRS)

Le, G.; Chi, P.; Strangeway, R. J.; Slavin, J. A.

2010-01-01

We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6 degree inclination angle. Due to the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at sub auroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

Buried Object Detection Method Using Optimum Frequency Range in Extremely Shallow Underground

NASA Astrophysics Data System (ADS)

Sugimoto, Tsuneyoshi; Abe, Touma

2011-07-01

We propose a new detection method for buried objects using the optimum frequency response range of the corresponding vibration velocity. Flat speakers and a scanning laser Doppler vibrometer (SLDV) are used for noncontact acoustic imaging in the extremely shallow underground. The exploration depth depends on the sound pressure, but it is usually less than 10 cm. Styrofoam, wood (silver fir), and acrylic boards of the same size, different size styrofoam boards, a hollow toy duck, a hollow plastic container, a plastic container filled with sand, a hollow steel can and an unglazed pot are used as buried objects which are buried in sand to about 2 cm depth. The imaging procedure of buried objects using the optimum frequency range is given below. First, the standardized difference from the average vibration velocity is calculated for all scan points. Next, using this result, underground images are made using a constant frequency width to search for the frequency response range of the buried object. After choosing an approximate frequency response range, the difference between the average vibration velocity for all points and that for several points that showed a clear response is calculated for the final confirmation of the optimum frequency range. Using this optimum frequency range, we can obtain the clearest image of the buried object. From the experimental results, we confirmed the effectiveness of our proposed method. In particular, a clear image of the buried object was obtained when the SLDV image was unclear.

Adiabatic description of long range frequency sweeping

NASA Astrophysics Data System (ADS)

Nyqvist, R. M.; Lilley, M. K.; Breizman, B. N.

2012-09-01

A theoretical framework is developed to describe long range frequency sweeping events in the 1D electrostatic bump-on-tail model with fast particle sources and collisions. The model includes three collision operators (Krook, drag (dynamical friction) and velocity space diffusion), and allows for a general shape of the fast particle distribution function. The behaviour of phase space holes and clumps is analysed in the absence of diffusion, and the effect of particle trapping due to separatrix expansion is discussed. With a fast particle distribution function whose slope decays above the resonant phase velocity, hooked frequency sweeping is found for holes in the presence of drag collisions alone.

ULF waves and plasma stability in different regions of the magnetosheath

NASA Astrophysics Data System (ADS)

Soucek, Jan; Escoubet, C. Philippe; Grison, Benjamin

2016-04-01

We present a statistical study of the occurrence and properties of ultra low frequency waves in the magnetosheath and interpret the results in terms of the competition of mirror and Alfvén-ion-cyclotron (AIC) instabilities. Both mirror and AIC waves are generated in high beta plasma of the magnetosheath when ion temperature anisotropy exceeds the threshold of the respective instabilities. These waves are frequently observed in the terrestrial and planetary magnetosheaths, but their distribution within the magnetosheath is inhomogeneous and their character varies as a function of location, local and upstream plasma parameters. We studied the spatial distribution of the two wave modes in the magnetosheath together with the local plasma parameters important for the stability of ULF waves. This analysis was performed on a dataset of all magnetosheath crossings observed by Cluster spacecraft over two years. For each observation we used bow shock, magnetopause and magnetosheath flow models to identify the relative position of the spacecraft with respect to magnetosheath boundaries and local properties of the upstream shock crossing. A strong dependence of parameters characterizing plasma stability and mirror/AIC wave occurrence on upstream ΘBn and MA is identified. The occurrence of mirror and AIC modes was compared against the respective instability thresholds and it was observed that AIC waves occurred nearly exclusively under mirror stable conditions. This is interpreted in terms of the different character of non-linear saturation of the two modes.

Measurement technology for seismomagnetic signals

NASA Astrophysics Data System (ADS)

Korepanov, Valery; Dudkin, Fedir; Marusenkov, Andriy

2010-05-01

Ultra low frequency (ULF) band (0.001-3 Hz) is usually used for study of natural magnetic field variations of ionospheric and magnetospheric origin. At present this frequency range gains in importance at monitoring of lithospheric magnetic activity in seismo-hazardous areas for application to short-time earthquake (EQ) forecasting. A big number of publications confirm that ULF magnetic precursors were recorded from few weeks up to few hours before EQ. The measurement technology of these signals has several peculiarities. First, the lithospheric ULF EQ magnetic precursors as a rule are very weak and their frequency range is overlapping with signals of magnetospheric or ionospheric origin. Second, for resolution of magnetic precursors at the background of more powerful sources it is necessary to have magnetic field sensors with wide dynamics and minimum possible spectral noise density (SND) level. Additionally, monitoring of lithospheric activity should be provided in close proximity to probable EQ area and almost in real-time regime. For the study of ULF magnetic precursors the magnetometers with search-coil (SC) and fluxgate (FG) sensors are used. SC sensors for ULF band usually have length 0.8-1.2 m, diameter 10-15 cm and weight few kilograms with SND 0.1-200 pT/Hz0.5 (here and further maximum SND value relates to a lower part of frequency range). FG sensors are very compact (pencil-shaped with length ~ 4 cm) but have greater SND in this band (about 10-500 pT/Hz0.5). Next requirement, if to use SC, is that at 3-component magnetic field measurement it is necessary to provide spacing between sensors about 1-2 of their length for avoiding mutual influence between them. This requirement creates problems caused by non-rigidity of such construction and their spatial instability relatively ground surface (or horizontal plane). In addition, for such a long sensor a ratio of core length/diameter is big enough, what leads to increased SC sensor sensitivity to variety of

Investigation of a slot nanoantenna in optical frequency range

NASA Astrophysics Data System (ADS)

Dinesh kumar, V.; Asakawa, Kiyoshi

2009-11-01

Following the analogy of radio frequency slot antenna and its complementary dipole, we propose the implementation of a slot nanoantenna (SNA) in the optical frequency range. Using finite-difference time-domain (FDTD) method, we investigate the electromagnetic (EM) properties of a SNA formed in a thin gold film and compare the results with the properties of a gold dipole nanoantenna (DNA) of the same dimension as the slot. It is found that the response of the SNA is very similar to the DNA, like their counterparts in the radio frequency (RF) range. The SNA can enhance the near field intensity of incident field which strongly depends on its feedgap dimension. The resonance of the SNA is influenced by its slot length; for the increasing slot length, resonant frequency decreases whereas the sharpness of resonance increases. Besides, the resonance of the SNA is found sensitive to the thickness of metal film, when the latter is smaller than the skin depth. The effect of polarization of incident field on the EM response of the SNA was examined; the field enhancement is optimum when polarization is parallel to the feedgap. Finally, we calculate the radiation patterns of the DNA and SNA and compare them with those of the RF dipole antenna. The radiation pattern of the SNA is found to be independent of its slot length when excited at resonant frequency. To the best of our knowledge, this is the first study on a slot antenna in the optical frequency.

Numerical Analysis of Stochastic Dynamical Systems in the Medium-Frequency Range

DTIC Science & Technology

2003-02-01

frequency vibration analysis such as the statistical energy analysis (SEA), the traditional modal analysis (well-suited for high and low: frequency...that the first few structural normal modes primarily constitute the total response. In the higher frequency range, the statistical energy analysis (SEA

A test of the Hall-MHD model: Application to low-frequency upstream waves at Venus

NASA Technical Reports Server (NTRS)

Orlowski, D. S.; Russell, C. T.; Krauss-Varban, D.; Omidi, N.

1994-01-01

Early studies suggested that in the range of parameter space where the wave angular frequency is less than the proton gyrofrequency and the plasma beta, the ratio of the thermal to magnetic pressure, is less than 1 magnetohydrodynamics provides an adequate description of the propagating modes in a plasma. However, recently, Lacombe et al. (1992) have reported significant differences between basic wave characteristics of the specific propagation modes derived from linear Vlasov and Hall-magnetohydrodynamic (MHD) theories even when the waves are only weakly damped. In this paper we compare the magnetic polarization and normalization magnetic compression ratio of ultra low frequency (ULF) upstream waves at Venus with magnetic polarization and normalized magnetic compression ratio derived from both theories. We find that while the 'kinetic' approach gives magnetic polarization and normalized magnetic compression ratio consistent with the data in the analyzed range of beta (0.5 less than beta less than 5) for the fast magnetosonic mode, the same wave characteristics derived from the Hall-MHD model strongly depend on beta and are consistent with the data only at low beta for the fast mode and at high beta for the intermediate mode.

ULF waves and radiation belts: earthward penetration of Pc 4-5 waves and energetic electron flux enhancements during geospace magnetic storms

NASA Astrophysics Data System (ADS)

Georgiou, Marina; Daglis, Ioannis; Zesta, Eftyhia; Balasis, George; Tsinganos, Kanaris

2013-04-01

Energetic particle fluxes in the outer radiation belt can vary over orders of magnitude on time scales ranging from minutes, to days and years. Geospace magnetic storms when sufficiently strong to exceed key thresholds of the Dst index may either increase or decrease the fluxes of energetic electrons. We examine the responses of energetic electrons to nine moderate, intense and weak magnetic storms, which occurred at different phases of the solar cycle, and compare these with concurrent variations of ULF wave power. Pc 4-5 waves with frequencies in the range of a few mHz may be generated internally in the magnetosphere by low frequency instabilities of ring current ions and externally by shear instabilities at the magnetopause flanks, or compressive variations in the solar wind. Here, we present multipoint observations from ground-based magnetometer arrays collocated with electron drift orbits, which are complemented and measurements by conjugate multi-point satellites, such as CHAMP, Cluster, GOES and THEMIS. We discuss the excitation, growth and decay characteristics of Pc 4-5 waves during the different phases of the magnetic storms with particular emphasis on the distribution of Pc 4-5 wave power over a variety of L shells. We investigate whether Pc 4-5 wave power penetrates to lower L shell values during periods of relatively intense geomagnetic activity as compared to weak magnetic storms. Structural changes of the magnetosphere during intense geomagnetic storms can play an important role in the generation and penetration of Pc 4-5 waves deep into the inner magnetosphere, which in turn is of significance for the wave-particle interactions contributing to the acceleration, transport and loss of electrons in the outer radiation belt. We present preliminary statistics of Pc 4-5 waves observed during magnetic storms of varying intensity, which occurred over the course of the previous solar cycle. This work is supported by the European Community's Seventh Framework

Improving frequencies range measurement of vibration sensor based on Fiber Bragg Grating (FBG)

NASA Astrophysics Data System (ADS)

Qomaruddin; Setiono, A.; Afandi, M. I.

2017-04-01

This research aimed to develop a vibration sensor based on Fiber Bragg Grating (FBG). The design was mainly done by attaching FBG at the cantilever. The free-end of the cantilever was tied to a vibration source in order to increase the measurement range of vibration frequencies. The results indicated that the developed sensor was capable of detecting wide range of frequencies (i.e. 10 - 1700 Hz). The results also showed both good stability and repeatability. The measured frequency range was 566 times greater than the range obtained from the previous works.

Ultrafast optical ranging using microresonator soliton frequency combs

NASA Astrophysics Data System (ADS)

Trocha, P.; Karpov, M.; Ganin, D.; Pfeiffer, M. H. P.; Kordts, A.; Wolf, S.; Krockenberger, J.; Marin-Palomo, P.; Weimann, C.; Randel, S.; Freude, W.; Kippenberg, T. J.; Koos, C.

2018-02-01

Light detection and ranging is widely used in science and industry. Over the past decade, optical frequency combs were shown to offer advantages in optical ranging, enabling fast distance acquisition with high accuracy. Driven by emerging high-volume applications such as industrial sensing, drone navigation, or autonomous driving, there is now a growing demand for compact ranging systems. Here, we show that soliton Kerr comb generation in integrated silicon nitride microresonators provides a route to high-performance chip-scale ranging systems. We demonstrate dual-comb distance measurements with Allan deviations down to 12 nanometers at averaging times of 13 microseconds along with ultrafast ranging at acquisition rates of 100 megahertz, allowing for in-flight sampling of gun projectiles moving at 150 meters per second. Combining integrated soliton-comb ranging systems with chip-scale nanophotonic phased arrays could enable compact ultrafast ranging systems for emerging mass applications.

Ultralow-frequency Raman system down to 10 cm{sup −1} with longpass edge filters and its application to the interface coupling in t(2+2)LGs

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

Lin, M.-L.; Qiao, X.-F.; Wu, J.-B.

Ultralow-frequency (ULF) Raman spectroscopy becomes increasingly important in the area of two-dimensional (2D) layered materials; however, such measurement usually requires expensive and nonstandard equipment. Here, the measurement of ULF Raman signal down to 10 cm{sup −1} has been realized with high throughput by combining a kind of longpass edge filters with a single monochromator, which are verified by the Raman spectrum of L-cystine using three laser excitations. Fine adjustment of the angle of incident laser beam from normal of the longpass edge filters and selection of polarization geometry are demonstrated how to probe ULF Raman signal with high signal-to-noise. Davydovmore » splitting of the shear mode in twisted (2+2) layer graphenes (t(2+2)LG) has been observed by such system in both exfoliated and transferred samples. We provide a direct evidence of twist-angle dependent softening of the shear coupling in t(2+2)LG, while the layer-breathing coupling at twisted interfaces is found to be almost identical to that in bulk graphite. This suggests that the exfoliation and transferring techniques are enough good to make a good 2D heterostructures to demonstrate potential device application. This Raman system will be potentially applied to the research field of ULF Raman spectroscopy.« less

First Vlasiator results on foreshock ULF wave activity

NASA Astrophysics Data System (ADS)

Palmroth, M.; Eastwood, J. P.; Pokhotelov, D.; Hietala, H.; Kempf, Y.; Hoilijoki, S.; von Alfthan, S.; Vainio, R. O.

2013-12-01

For decades, a certain type of ultra low frequency waves with a period of about 30 seconds have been observed in the Earth's quasi-parallel foreshock. These waves, with a wavelength of about an Earth radius, are compressive and propagate obliquely with respect to the interplanetary magnetic field (IMF). The latter property has caused trouble to scientists as the growth rate for the instability causing the waves is maximized along the magnetic field. So far, these waves have been characterized by single or multi-spacecraft methods and 2-dimensional hybrid-PIC simulations, which have not fully reproduced the wave properties. Vlasiator is a newly developed, global hybrid-Vlasov simulation, which solves ions in the six-dimensional phase space using the Vlasov equation and electrons using magnetohydrodynamics (MHD). The outcome of the simulation is a global reproduction of ion-scale physics in a holistic manner where the generation of physical features can be followed in time and their consequences can be quantitatively characterized. Vlasiator produces the ion distribution functions and the related kinetic physics in unprecedented detail, in the global magnetospheric scale presently with a resolution of 0.13 RE in the ordinary space and 20 km/s in the velocity space. We run two simulations, where we use both a typical Parker-spiral and a radial IMF as an input to the code. The runs are carried out in the ecliptic 2-dimensional plane in the ordinary space, and with three dimensions in the velocity space. We observe the generation of the 30-second ULF waves, and characterize their evolution and physical properties in time, comparing to observations by Cluster spacecraft. We find that Vlasiator reproduces these waves in all reported observational aspects, i.e., they are of the observed size in wavelength and period, they are compressive and propagate obliquely to the IMF. In particular, we investigate the oblique propagation and discuss the issues related to the long

Free induction decay MR signal measurements toward ultra-low field MRI with an optically pumped atomic magnetometer.

PubMed

Oida, Takenori; Kobayashi, Tetsuo

2013-01-01

Ultra-low field magnetic resonance imaging (ULF-MRI) has attracted attention because of its low running costs and minimum patient exposure. An optically pumped atomic magnetometer (OPAM) is a magnetic sensor with high sensitivity in the low frequency range, which does not require a cryogenic cooling system. In an effort to develop a ULF-MRI, we attempted to measure the free induction decay MR signals with an OPAM. We successfully detected the MR signals by combining an OPAM and a flux transformer, demonstrating the feasibility of the proposed system.

Cross-Linguistic Differences in Bilinguals' Fundamental Frequency Ranges.

PubMed

Ordin, Mikhail; Mennen, Ineke

2017-06-10

We investigated cross-linguistic differences in fundamental frequency range (FFR) in Welsh-English bilingual speech. This is the first study that reports gender-specific behavior in switching FFRs across languages in bilingual speech. FFR was conceptualized as a behavioral pattern using measures of span (range of fundamental frequency-in semitones-covered by the speaker's voice) and level (overall height of fundamental frequency maxima, minima, and means of speaker's voice) in each language. FFR measures were taken from recordings of 30 Welsh-English bilinguals (14 women and 16 men), who read 70 semantically matched sentences, 35 in each language. Comparisons were made within speakers across languages, separately in male and female speech. Language background and language use information was elicited for qualitative analysis of extralinguistic factors that might affect the FFR. Cross-linguistic differences in FFR were found to be consistent across female bilinguals but random across male bilinguals. Most female bilinguals showed distinct FFRs for each language. Most male bilinguals, however, were found not to change their FFR when switching languages. Those who did change used different strategies than women when differentiating FFRs between languages. Detected cross-linguistic differences in FFR can be explained by sociocultural factors. Therefore, sociolinguistic factors are to be taken into account in any further study of language-specific pitch setting and cross-linguistic differences in FFR.

Development of Acceleration Sensor and Acceleration Evaluation System for Super-Low-Range Frequencies

NASA Astrophysics Data System (ADS)

Asano, Shogo; Matsumoto, Hideki

2001-05-01

This paper describes the development process for acceleration sensors used on automobiles and an acceleration evaluation system designed specifically for acceleration at super-low-range frequencies. The features of the newly developed sensor are as follows. 1) Original piezo-bimorph design based on a disc-center-fixed structure achieves pyroeffect cancelling and stabilization of sensor characteristics and enables the detection of the acceleration of 0.0009 G at the super-low-range-frequency of 0.03 Hz. 2) The addition of a self-diagnostic function utilizing the characteristics of piezoceramics enables constant monitoring of sensor failure. The frequency range of acceleration for accurate vehicle motion control is considered to be from DC to about 50 Hz. However, the measurement of acceleration in the super-low-range frequency near DC has been difficult because of mechanical and electrical noise interruption. This has delayed the development of the acceleration sensor for automotive use. We have succeeded in the development of an acceleration evaluation system for super-low-range frequencies from 0.015 Hz to 2 Hz with detection of the acceleration range from 0.0002 G (0.2 gal) to 1 G, as well as the development of a piezoelectric-type acceleration sensor for automotive use.

Frequency-Modulated, Continuous-Wave Laser Ranging Using Photon-Counting Detectors

NASA Technical Reports Server (NTRS)

Erkmen, Baris I.; Barber, Zeb W.; Dahl, Jason

2014-01-01

Optical ranging is a problem of estimating the round-trip flight time of a phase- or amplitude-modulated optical beam that reflects off of a target. Frequency- modulated, continuous-wave (FMCW) ranging systems obtain this estimate by performing an interferometric measurement between a local frequency- modulated laser beam and a delayed copy returning from the target. The range estimate is formed by mixing the target-return field with the local reference field on a beamsplitter and detecting the resultant beat modulation. In conventional FMCW ranging, the source modulation is linear in instantaneous frequency, the reference-arm field has many more photons than the target-return field, and the time-of-flight estimate is generated by balanced difference- detection of the beamsplitter output, followed by a frequency-domain peak search. This work focused on determining the maximum-likelihood (ML) estimation algorithm when continuous-time photoncounting detectors are used. It is founded on a rigorous statistical characterization of the (random) photoelectron emission times as a function of the incident optical field, including the deleterious effects caused by dark current and dead time. These statistics enable derivation of the Cramér-Rao lower bound (CRB) on the accuracy of FMCW ranging, and derivation of the ML estimator, whose performance approaches this bound at high photon flux. The estimation algorithm was developed, and its optimality properties were shown in simulation. Experimental data show that it performs better than the conventional estimation algorithms used. The demonstrated improvement is a factor of 1.414 over frequency-domainbased estimation. If the target interrogating photons and the local reference field photons are costed equally, the optimal allocation of photons between these two arms is to have them equally distributed. This is different than the state of the art, in which the local field is stronger than the target return. The optimal

Multibeam single frequency synthetic aperture radar processor for imaging separate range swaths

NASA Technical Reports Server (NTRS)

Jain, A. (Inventor)

1982-01-01

A single-frequency multibeam synthetic aperture radar for large swath imaging is disclosed. Each beam illuminates a separate ""footprint'' (i.e., range and azimuth interval). The distinct azimuth intervals for the separate beams produce a distinct Doppler frequency spectrum for each beam. After range correlation of raw data, an optical processor develops image data for the different beams by spatially separating the beams to place each beam of different Doppler frequency spectrum in a different location in the frequency plane as well as the imaging plane of the optical processor. Selection of a beam for imaging may be made in the frequency plane by adjusting the position of an aperture, or in the image plane by adjusting the position of a slit. The raw data may also be processed in digital form in an analogous manner.

Modal density of rectangular structures in a wide frequency range

NASA Astrophysics Data System (ADS)

Parrinello, A.; Ghiringhelli, G. L.

2018-04-01

A novel approach to investigate the modal density of a rectangular structure in a wide frequency range is presented. First, the modal density is derived, in the whole frequency range of interest, on the basis of sound transmission through the infinite counterpart of the structure; then, it is corrected by means of the low-frequency modal behavior of the structure, taking into account actual size and boundary conditions. A statistical analysis reveals the connection between the modal density of the structure and the transmission of sound through its thickness. A transfer matrix approach is used to compute the required acoustic parameters, making it possible to deal with structures having arbitrary stratifications of different layers. A finite element method is applied on coarse grids to derive the first few eigenfrequencies required to correct the modal density. Both the transfer matrix approach and the coarse grids involved in the finite element analysis grant high efficiency. Comparison with alternative formulations demonstrates the effectiveness of the proposed methodology.

Radial energy transport by magnetospheric ULF waves: Effects of magnetic curvature and plasma pressure

NASA Technical Reports Server (NTRS)

Kouznetsov, Igor; Lotko, William

1995-01-01

The 'radial' transport of energy by internal ULF waves, stimulated by dayside magnetospheric boundary oscillations, is analyzed in the framework of one-fluid magnetohydrodynamics. (the term radial is used here to denote the direction orthogonal to geomagnetic flux surfaces.) The model for the inhomogeneous magnetospheric plasma and background magnetic field is axisymmetric and includes radial and parallel variations in the magnetic field, magnetic curvature, plasma density, and low but finite plasma pressure. The radial mode structure of the coupled fast and intermediate MHD waves is determined by numerical solution of the inhomogeneous wave equation; the parallel mode structure is characterized by a Wentzel-Kramer-Brillouin (WKB) approximation. Ionospheric dissipation is modeled by allowing the parallel wave number to be complex. For boudnary oscillations with frequencies in the range from 10 to 48 mHz, and using a dipole model for the background magnetic field, the combined effects of magnetic curvature and finite plasma pressure are shown to (1) enhance the amplitude of field line resonances by as much as a factor of 2 relative to values obtained in a cold plasma or box-model approximation for the dayside magnetosphere; (2) increase the energy flux delivered to a given resonance by a factor of 2-4; and (3) broaden the spectral width of the resonance by a factor of 2-3. The effects are attributed to the existence of an 'Alfven buoyancy oscillation,' which approaches the usual shear mode Alfven wave at resonance, but unlike the shear Alfven mode, it is dispersive at short perpendicular wavelengths. The form of dispersion is analogous to that of an internal atmospheric gravity wave, with the magnetic tension of the curved background field providing the restoring force and allowing radial propagation of the mode. For nominal dayside parameters, the propagation band of the Alfven buoyancy wave occurs between the location of its (field line) resonance and that of the

Ultralow frequency MHD waves in Jupiter's middle magnetosphere

NASA Technical Reports Server (NTRS)

Khurana, Krishan K.; Kivelson, Margaret G.

1989-01-01

Ultralow frequency (ULF) magnetohydrodynamic pulsations (periods between 10 and 20 min) were observed on July 8-11, 1979 as Voyager 2 traveled through the middle magnetosphere of Jupiter between radial distances of 10 R(J) and 35 R(J). The particle and magnetic pressure perturbations associated with the waves were anticorrelated. The electron and ion perturbations on the dayside were in phase. The pressure perturbations occurred both within and outside of the plasma sheet. Perturbations in the transverse components of the magnetic field were associated with the compressional perturbations but the transverse power peaked within the plasma sheet of Jupiter and diminished rapidly outside of it.

Widely tunable laser frequency offset lock with 30 GHz range and 5 THz offset.

PubMed

Biesheuvel, J; Noom, D W E; Salumbides, E J; Sheridan, K T; Ubachs, W; Koelemeij, J C J

2013-06-17

We demonstrate a simple and versatile method to greatly extend the tuning range of optical frequency shifting devices, such as acousto-optic modulators (AOMs). We use this method to stabilize the frequency of a tunable narrow-band continuous-wave (CW) laser to a transmission maximum of an external Fabry-Perot interferometer (FPI) with a tunable frequency offset. This is achieved through a servo loop which contains an in-loop AOM for simple radiofrequency (RF) tuning of the optical frequency over the full 30 GHz mode-hop-free tuning range of the CW laser. By stabilizing the length of the FPI to a stabilized helium-neon (HeNe) laser (at 5 THz offset from the tunable laser) we simultaneously transfer the ~ 1 MHz absolute frequency stability of the HeNe laser to the entire 30 GHz range of the tunable laser. Thus, our method allows simple, wide-range, fast and reproducible optical frequency tuning and absolute optical frequency measurements through RF electronics, which is here demonstrated by repeatedly recording a 27-GHz-wide molecular iodine spectrum at scan rates up to 500 MHz/s. General technical aspects that determine the performance of the method are discussed in detail.

Effect of upstream ULF waves on the energetic ion diffusion at the earth's foreshock: Theory, Simulation, and Observations

NASA Astrophysics Data System (ADS)

Otsuka, F.; Matsukiyo, S.; Kis, A.; Hada, T.

2017-12-01

Spatial diffusion of energetic particles is an important problem not only from a fundamental physics point of view but also for its application to particle acceleration processes at astrophysical shocks. Quasi-linear theory can provide the spatial diffusion coefficient as a function of the wave turbulence spectrum. By assuming a simple power-law spectrum for the turbulence, the theory has been successfully applied to diffusion and acceleration of cosmic rays in the interplanetary and interstellar medium. Near the earth's foreshock, however, the wave spectrum often has an intense peak, presumably corresponding to the upstream ULF waves generated by the field-aligned beam (FAB). In this presentation, we numerically and theoretically discuss how the intense ULF peak in the wave spectrum modifies the spatial parallel diffusion of energetic ions. The turbulence is given as a superposition of non-propagating transverse MHD waves in the solar wind rest frame, and its spectrum is composed of a piecewise power-law spectrum with different power-law indices. The diffusion coefficients are then estimated by using the quasi-linear theory and test particle simulations. We find that the presence of the ULF peak produces a concave shape of the diffusion coefficient when it is plotted versus the ion energy. The results above are used to discuss the Cluster observations of the diffuse ions at the Earth's foreshock. Using the density gradients of the energetic ions detected by the Cluster spacecraft, we determine the e-folding distances, equivalently, the spatial diffusion coefficients, of ions with their energies from 10 to 32 keV. The observed e-folding distances are significantly smaller than those estimated in the past statistical studies. This suggests that the particle acceleration at the foreshock can be more efficient than considered before. Our test particle simulation explains well the small estimate of the e-folding distances, by using the observed wave turbulence spectrum

MESSENGER Magnetic Field Observations of Upstream Ultra-Low Frequency Waves at Mercury

NASA Technical Reports Server (NTRS)

Le, G.; Chi, P. J.; Boardsen, S.; Blanco-Cano, X.; Anderosn, B. J.; Korth, H.

2012-01-01

The region upstream from a planetary bow shock is a natural plasma laboratory containing a variety of wave particle phenomena. The study of foreshocks other than the Earth's is important for extending our understanding of collisionless shocks and foreshock physics since the bow shock strength varies with heliocentric distance from the Sun, and the sizes of the bow shocks are different at different planets. The Mercury's bow shock is unique in our solar system as it is produced by low Mach number solar wind blowing over a small magnetized body with a predominately radial interplanetary magnetic field. Previous observations of Mercury upstream ultra-low frequency (ULF) waves came exclusively from two Mercury flybys of Mariner 10. The MESSENGER orbiter data enable us to study of upstream waves in the Mercury's foreshock in depth. This paper reports an overview of upstream ULF waves in the Mercury's foreshock using high-time resolution magnetic field data, 20 samples per second, from the MESSENGER spacecraft. The most common foreshock waves have frequencies near 2 Hz, with properties similar to the I-Hz waves in the Earth's foreshock. They are present in both the flyby data and in every orbit of the orbital data we have surveyed. The most common wave phenomenon in the Earth's foreshock is the large-amplitude 30-s waves, but similar waves at Mercury have frequencies at near 0.1 Hz and occur only sporadically with short durations (a few wave cycles). Superposed on the "30-s" waves, there are spectral peaks at near 0.6 Hz, not reported previously in Mariner 10 data. We will discuss wave properties and their occurrence characteristics in this paper.

Quantum plasmons with optical-range frequencies in doped few-layer graphene

NASA Astrophysics Data System (ADS)

Shirodkar, Sharmila N.; Mattheakis, Marios; Cazeaux, Paul; Narang, Prineha; Soljačić, Marin; Kaxiras, Efthimios

2018-05-01

Although plasmon modes exist in doped graphene, the limited range of doping achieved by gating restricts the plasmon frequencies to a range that does not include the visible and infrared. Here we show, through the use of first-principles calculations, that the high levels of doping achieved by lithium intercalation in bilayer and trilayer graphene shift the plasmon frequencies into the visible range. To obtain physically meaningful results, we introduce a correction of the effect of plasmon interaction across the vacuum separating periodic images of the doped graphene layers, consisting of transparent boundary conditions in the direction perpendicular to the layers; this represents a significant improvement over the exact Coulomb cutoff technique employed in earlier works. The resulting plasmon modes are due to local field effects and the nonlocal response of the material to external electromagnetic fields, requiring a fully quantum mechanical treatment. We describe the features of these quantum plasmons, including the dispersion relation, losses, and field localization. Our findings point to a strategy for fine-tuning the plasmon frequencies in graphene and other two-dimensional materials.

Wide tracking range, auto ranging, low jitter phase lock loop for swept and fixed frequency systems

DOEpatents

Kerner, Thomas M.

2001-01-01

The present invention provides a wide tracking range phase locked loop (PLL) circuit that achieves minimal jitter in a recovered clock signal, regardless of the source of the jitter (i.e. whether it is in the source or the transmission media). The present invention PLL has automatic harmonic lockout detection circuitry via a novel lock and seek control logic in electrical communication with a programmable frequency discriminator and a code balance detector. (The frequency discriminator enables preset of a frequency window of upper and lower frequency limits to derive a programmable range within which signal acquisition is effected. The discriminator works in combination with the code balance detector circuit to minimize the sensitivity of the PLL circuit to random data in the data stream). In addition, the combination of a differential loop integrator with the lock and seek control logic obviates a code preamble and guarantees signal acquisition without harmonic lockup. An adaptive cable equalizer is desirably used in combination with the present invention PLL to recover encoded transmissions containing a clock and/or data. The equalizer automatically adapts to equalize short haul cable lengths of coaxial and twisted pair cables or wires and provides superior jitter performance itself. The combination of the equalizer with the present invention PLL is desirable in that such combination permits the use of short haul wires without significant jitter.

Modeling of long range frequency sweeping for energetic particle modes

NASA Astrophysics Data System (ADS)

Nyqvist, R. M.; Breizman, B. N.

2013-04-01

Long range frequency sweeping events are simulated numerically within a one-dimensional, electrostatic bump-on-tail model with fast particle sources and collisions. The numerical solution accounts for fast particle trapping and detrapping in an evolving wave field with a fixed wavelength, and it includes three distinct collisions operators: Drag (dynamical friction on the background electrons), Krook-type collisions, and velocity space diffusion. The effects of particle trapping and diffusion on the evolution of holes and clumps are investigated, and the occurrence of non-monotonic (hooked) frequency sweeping and asymptotically steady holes is discussed. The presented solution constitutes a step towards predictive modeling of frequency sweeping events in more realistic geometries.

Range compensation for backscattering measurements in the difference-frequency nearfield of a parametric sonar.

PubMed

Foote, Kenneth G

2012-05-01

Measurement of acoustic backscattering properties of targets requires removal of the range dependence of echoes. This process is called range compensation. For conventional sonars making measurements in the transducer farfield, the compensation removes effects of geometrical spreading and absorption. For parametric sonars consisting of a parametric acoustic transmitter and a conventional-sonar receiver, two additional range dependences require compensation when making measurements in the nonlinearly generated difference-frequency nearfield: an apparently increasing source level and a changing beamwidth. General expressions are derived for range compensation functions in the difference-frequency nearfield of parametric sonars. These are evaluated numerically for a parametric sonar whose difference-frequency band, effectively 1-6 kHz, is being used to observe Atlantic herring (Clupea harengus) in situ. Range compensation functions for this sonar are compared with corresponding functions for conventional sonars for the cases of single and multiple scatterers. Dependences of these range compensation functions on the parametric sonar transducer shape, size, acoustic power density, and hydrography are investigated. Parametric range compensation functions, when applied with calibration data, will enable difference-frequency echoes to be expressed in physical units of volume backscattering, and backscattering spectra, including fish-swimbladder-resonances, to be analyzed.

Living Organisms Coupling to Electromagnetic Radiation Below Thermal Noise

NASA Astrophysics Data System (ADS)

Stolc, Viktor; Freund, Friedemann

2013-04-01

Ultralow frequency (ULF) and extremely low frequency (ELF) electromagnetic (EM) radiation is part of the natural environment. Prior to major earthquakes the local ULF and global ELF radiation field is often markedly perturbed. This has detrimental effects on living organisms. We are studying the mechanism of these effects on the biochemical, cellular and organismal levels. The transfer of electrons along the Electron Transfer Chain (ETC) controls the universal reduction-oxidation reactions that are essential for fundamental biochemical processes in living cells. In order for these processes to work properly, the ETC has to maintain some form of synchronization, or coherence with all biochemical reactions in the living cells, including energy production, RNA transcription, and DNA replication. As a consequence of this synchronization, harmful chemical conflict between the reductive and the oxidative partial reactions can be minimized or avoided. At the same time we note that the synchronization allows for a transfer of energy, coherent or interfering, via coupling to the natural ambient EM field. Extremely weak high frequency EM fields, well below the thermal noise level, tuned in frequency to the electron spins of certain steps in the ETC, have already been shown to cause aberrant cell growth and disorientation among plants and animals with respect to the magnetic and gravity vectors. We investigate EM fields over a much wider frequency range, including ULF known to be generated deep in the Earth prior to major earthquakes locally, and ELF known to be fed by lightning discharges, traveling around the globe in the cavity formed between the Earth's surface and the ionosphere. This ULF/ELF radiation can control the timing of the biochemical redox cycle and thereby have a universal effect on physiology of organisms. The timing can even have a detrimental influence, via increased oxidative damage, on the DNA replication, which controls heredity.

Ultra-low frequency transcutaneous electric nerve stimulation does not affect the centric relation registration.

PubMed

de Bragança, Rafaella Mariana Fontes; Rodrigues, Carolina Almeida; Melchior, Melissa Oliveira; Magri, Laís Valencise; Mazzetto, Marcelo Oliveira

2018-01-01

To evaluate the influence of ULF-TENS on the displacement of the mandibular condyle and on the repeatability of centric relation (CR) registration of three different techniques: bimanual manipulation (BM), long strip technique, and harmonic centric occlusal relationship (R.O.C.A. wires). Twenty-five participants without temporomandibular disorder (TMD) underwent two study stages conducted via electronic position analysis: (1) three CR records were made, one for each manipulation technique; (2) the ULF-TENS was applied for 30 min, and after that the same CR records were repeated. Mann-Whitney, ICC, and one-tailed F test. The ULF-TENS did not influence the condyle total displacement, regardless of CR recording technique used (p > 0.05). BM showed an improvement in repeatability after ULF-TENS. Concerning the variance, BM showed less variation at the X-axis. Long strip technique and R.O.C.A. wires varied less at the Y-axis. Long strip technique was again less variable at the Z-axis.

Experiments and error analysis of laser ranging based on frequency-sweep polarization modulation

NASA Astrophysics Data System (ADS)

Gao, Shuyuan; Ji, Rongyi; Li, Yao; Cheng, Zhi; Zhou, Weihu

2016-11-01

Frequency-sweep polarization modulation ranging uses a polarization-modulated laser beam to determine the distance to the target, the modulation frequency is swept and frequency values are measured when transmitted and received signals are in phase, thus the distance can be calculated through these values. This method gets much higher theoretical measuring accuracy than phase difference method because of the prevention of phase measurement. However, actual accuracy of the system is limited since additional phase retardation occurs in the measuring optical path when optical elements are imperfectly processed and installed. In this paper, working principle of frequency sweep polarization modulation ranging method is analyzed, transmission model of polarization state in light path is built based on the theory of Jones Matrix, additional phase retardation of λ/4 wave plate and PBS, their impact on measuring performance is analyzed. Theoretical results show that wave plate's azimuth error dominates the limitation of ranging accuracy. According to the system design index, element tolerance and error correcting method of system is proposed, ranging system is built and ranging experiment is performed. Experiential results show that with proposed tolerance, the system can satisfy the accuracy requirement. The present work has a guide value for further research about system design and error distribution.

Note: Digital laser frequency auto-locking for inter-satellite laser ranging

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

Luo, Yingxin; Yeh, Hsien-Chi, E-mail: yexianji@mail.hust.edu.cn; Li, Hongyin

2016-05-15

We present a prototype of a laser frequency auto-locking and re-locking control system designed for laser frequency stabilization in inter-satellite laser ranging system. The controller has been implemented on field programmable gate arrays and programmed with LabVIEW software. The controller allows initial frequency calibrating and lock-in of a free-running laser to a Fabry-Pérot cavity. Since it allows automatic recovery from unlocked conditions, benefit derives to automated in-orbit operations. Program design and experimental results are demonstrated.

A current drive by using the fast wave in frequency range higher than two timeslower hybrid resonance frequency on tokamaks

NASA Astrophysics Data System (ADS)

Kim, Sun Ho; Hwang, Yong Seok; Jeong, Seung Ho; Wang, Son Jong; Kwak, Jong Gu

2017-10-01

An efficient current drive scheme in central or off-axis region is required for the steady state operation of tokamak fusion reactors. The current drive by using the fast wave in frequency range higher than two times lower hybrid resonance (w>2wlh) could be such a scheme in high density, high temperature reactor-grade tokamak plasmas. First, it has relatively higher parallel electric field to the magnetic field favorable to the current generation, compared to fast waves in other frequency range. Second, it can deeply penetrate into high density plasmas compared to the slow wave in the same frequency range. Third, parasitic coupling to the slow wave can contribute also to the current drive avoiding parametric instability, thermal mode conversion and ion heating occured in the frequency range w<2wlh. In this study, the propagation boundary, accessibility, and the energy flow of the fast wave are given via cold dispersion relation and group velocity. The power absorption and current drive efficiency are discussed qualitatively through the hot dispersion relation and the polarization. Finally, those characteristics are confirmed with ray tracing code GENRAY for the KSTAR plasmas.

Optimal frequency range for medical radar measurements of human heartbeats using body-contact radar.

PubMed

Brovoll, Sverre; Aardal, Øyvind; Paichard, Yoann; Berger, Tor; Lande, Tor Sverre; Hamran, Svein-Erik

2013-01-01

In this paper the optimal frequency range for heartbeat measurements using body-contact radar is experimentally evaluated. A Body-contact radar senses electromagnetic waves that have penetrated the human body, but the range of frequencies that can be used are limited by the electric properties of the human tissue. The optimal frequency range is an important property needed for the design of body-contact radar systems for heartbeat measurements. In this study heartbeats are measured using three different antennas at discrete frequencies from 0.1 - 10 GHz, and the strength of the received heartbeat signal is calculated. To characterize the antennas, when in contact with the body, two port S-parameters(†) are measured for the antennas using a pork rib as a phantom for the human body. The results shows that frequencies up to 2.5 GHz can be used for heartbeat measurements with body-contact radar.

Multimode VCSEL model for wide frequency-range RIN simulation

NASA Astrophysics Data System (ADS)

Perchoux, Julien; Rissons, Angélique; Mollier, Jean-Claude

2008-01-01

In this paper, we present an equivalent circuit model for oxide-confined AlGaAs/GaAs VCSEL with the noise contribution adapted to optomicrowave links applications. This model is derived from the multimode rate equations. In order to understand the modal competition process, we restrain our description to a two-modes rate equations system affected by the spectral hole-burning. The relative intensity noise (RIN) measurements which were achieved on a prober in Faraday cage confirm the low frequency enhancement described by the model. We validate our model for a wide frequency-range [1 MHz-10 GHz] and high bias level up to six times the threshold current.

Identification of flexible structures by frequency-domain observability range context

NASA Astrophysics Data System (ADS)

Hopkins, M. A.

2013-04-01

The well known frequency-domain observability range space extraction (FORSE) algorithm provides a powerful multivariable system-identification tool with inherent flexibility, to create state-space models from frequency-response data (FRD). This paper presents a method of using FORSE to create "context models" of a lightly damped system, from which models of individual resonant modes can be extracted. Further, it shows how to combine the extracted models of many individual modes into one large state-space model. Using this method, the author has created very high-order state-space models that accurately match measured FRD over very broad bandwidths, i.e., resonant peaks spread across five orders-of-magnitude of frequency bandwidth.

Magnetic Earth Ionosphere Resonant Frequencies (NASA-MEIRF Project)

NASA Technical Reports Server (NTRS)

1994-01-01

During this current reporting period, the project has focused on completing Phase 1 of the field monitoring work and documenting research results. Highlights of these efforts include presentations of papers at the annual joint meeting of the American Physical Society/American Association of Physics Teachers, April 18-22, 1994, in Crystal City, Virginia, and at the International Space, Time, and Gravitation Conference and Etoiles de L'Ecole Polytechnique Symposium, May 23-28, 1994, in St. Petersburg, Russia. Field measurements of the background ultra low frequency (ULF) electromagnetic spectrum in the New Mexico and Texas regions show interesting differences. Included are papers entitled 'Triplet Solution of the Twin Paradox' and 'Classical Electron Mass and Fields, Part 3.'

Power allocation and range performance considerations for a dual-frequency EBPSK/MPPSK system

NASA Astrophysics Data System (ADS)

Yao, Yu; Wu, Lenan; Zhao, Junhui

2017-12-01

Extended binary phase shift keying/M-ary position phase shift keying (EBPSK/MPPSK)-MODEM provides radar and communication functions on a single hardware platform with a single waveform. However, its range estimation accuracy is worse than continuous-wave (CW) radar because of the imbalance of power in two carrier frequencies. In this article, the power allocation method for dual-frequency EBPSK/MPPSK modulated systems is presented. The power of two signal transmitters is adequately allocated to ensure that the power in two carrier frequencies is equal. The power allocation ratios for two types of modulation systems are obtained. Moreover, considerations regarding the range of operation of the dual-frequency system are analysed. In addition to theoretical considerations, computer simulations are provided to illustrate the performance.

Semiannual Status Report. [excitation of electromagnetic waves in the whistler frequency range

NASA Technical Reports Server (NTRS)

1994-01-01

During the last six months, we have continued our study of the excitation of electromagnetic waves in the whistler frequency range and the role that these waves will play in the acceleration of electrons and ions in the auroral region. A paper entitled 'Electron Beam Excitation of Upstream Waves in the Whistler Mode Frequency Range' was listed in the Journal of Geophysical Research. In this paper, we have shown that an anisotropic electron beam (or gyrating electron beam) is capable of generating both left-hand and right-hand polarized electromagnetic waves in the whistler frequency range. Since right-hand polarized electromagnetic waves can interact with background electrons and left-hand polarized waves can interact with background ions through cyclotron resonance, it is possible that these beam generated left-hand and right-hand polarized electromagnetic waves can accelerate either ions or electrons (or both), depending on the physical parameters under consideration. We are currently carrying out a comprehensive study of the electromagnetic whistler and lower hybrid like waves observed in the auroral zone using both wave and particle data. Our first task is to identify these wave modes and compare it with particle observations. Using both the DE-1 particle and wave measurements, we can positively identify those electromagnetics lower hybrid like waves as fast magnetosonic waves and the upper cutoff of these waves is the local lower hybrid frequency. From the upper cutoff of the frequency spectrum, one can infer the particle density and the result is in very good agreement with the particle data. Since these electromagnetic lower hybrid like waves can have frequencies extended down to the local ion cyclotron frequency, it practically confirms that they are not whistler waves.

Magnetic losses of commercial REBCO coated conductors in the low frequency range

NASA Astrophysics Data System (ADS)

De Marzi, G.; Iannone, G.; Gambardella, U.

2018-05-01

We have investigated the frequency dependence of the magnetic losses of different 2 G commercial REBCO coated-conductor tapes in the low frequency range ∼1–10 mHz of applied magnetic field at 5 and 77 K. We explored high field range, well above the penetration field, with fields applied perpendicularly to the flat surface. We found that the in-field hysteresis losses increase with increasing frequencies in all the investigated high-temperature superconductor (HTS) tapes, following a power-law dependence. An electromagnetic 2D finite element method model, based on H-formulation, has also been implemented, in which the frequency dependence of the hysteretic loss is computed taking into account the measured power-law E(J) characteristic for the electric field, and the experimental J c(B). Experimental and numerical findings are in very good agreement, so an extrapolation to higher ramp rate values is possible, thus providing a useful basis for the assessment of the hysteresis losses in fusion and accelerator HTS magnets.

Apollo experience report: Very high frequency ranging system

NASA Technical Reports Server (NTRS)

Panter, W. C.; Shores, P. W.

1972-01-01

The history of the Apollo very-high-frequency ranging system development program is presented from the program-planning stage through the final-test and flight-evaluation stages. Block diagrams of the equipment are presented, and a description of the theory of operation is outlined. A sample of the distribution of errors measured in the aircraft-flight test program is included. The report is concluded with guidelines or recommendations for the management of development programs having the same general constraints.

Controlling the angle range in acoustic low-frequency forbidden transmission in solid-fluid superlattice

NASA Astrophysics Data System (ADS)

Zhang, Sai; Xu, Bai-qiang; Cao, Wenwu

2018-03-01

We have investigated low-frequency forbidden transmission (LFT) of acoustic waves with frequency lower than the first Bragg bandgap in a solid-fluid superlattice (SFSL). LFT is formed when the acoustic planar wave impinges on the interface of a SFSL within a certain angle range. However, for the SFSL comprised of metallic material and water, the angle range of LFT is extremely narrow, which restricts its practical applications. The variation characteristics of the angle range have been comprehensively studied here by the control variable method. The results suggest that the filling ratio, layer number, wave velocity, and mass density of the constituent materials have a significant impact on the angle range. Based on our results, an effective strategy for obtaining LFT with a broad angle range is provided, which will be useful for potential applications of LFT in various devices, such as low frequency filters and subwavelength one-way diodes.

Cross-validation of independent ultra-low-frequency magnetic recording systems for active fault studies

NASA Astrophysics Data System (ADS)

Wang, Can; Bin, Chen; Christman, Lilianna E.; Glen, Jonathan M. G.; Klemperer, Simon L.; McPhee, Darcy K.; Kappler, Karl N.; Bleier, Tom E.; Dunson, J. Clark

2018-04-01

When working with ultra-low-frequency (ULF) magnetic datasets, as with most geophysical time-series data, it is important to be able to distinguish between cultural signals, internal instrument noise, and natural external signals with their induced telluric fields. This distinction is commonly attempted using simultaneously recorded data from a spatially remote reference site. Here, instead, we compared data recorded by two systems with different instrumental characteristics at the same location over the same time period. We collocated two independent ULF magnetic systems, one from the QuakeFinder network and the other from the United States Geological Survey (USGS)-Stanford network, in order to cross-compare their data, characterize data reproducibility, and characterize signal origin. In addition, we used simultaneous measurements at a remote geomagnetic observatory to distinguish global atmospheric signals from local cultural signals. We demonstrated that the QuakeFinder and USGS-Stanford systems have excellent coherence, despite their different sensors and digitizers. Rare instances of isolated signals recorded by only one system or only one sensor indicate that caution is needed when attributing specific recorded signal features to specific origins.[Figure not available: see fulltext.

Contribution of the ULF wave activity to the global recovery of the outer radiation belt during the passage of a high-speed solar wind stream observed in September 2014

NASA Astrophysics Data System (ADS)

Dal Lago, A.; Da Silva, L. A.; Alves, L. R.; Dallaqua, R.; Marchezi, J.; Medeiros, C.; Souza, V. M. C. E. S.; Koga, D.; Jauer, P. R.; Vieira, L.; Rockenbach, M.; Mendes, O., Jr.; De Nardin, C. M.; Sibeck, D. G.

2016-12-01

The interaction of the solar wind with the Earth's magnetosphere can either increase or decrease the relativistic electron population in the outer radiation belt. In order to investigate the contribution of the ULF wave activity to the global recovery of the outer radiation belt relativistic electron population, we searched the Van Allen data for a period in which we can clearly distinguish the enhancement of the fluxes from the background. The complex solar wind structure observed from September 12-24, 2014, which resulted from the interaction of two coronal mass ejections (CMEs) and a high-speed stream, presented such a scenario. The CMEs are related to the dropout of the relativistic electron population followed by several days of low fluxes. The global recovery started during the passage of the high-speed stream that was associated with the occurrence of substorms that persisted for several days. Here we estimate the contribution of ULF wave-particle interactions to the enhancement of the relativistic electron fluxes. Our approach is based on estimates of the ULF wave radial diffusion coefficients employing two models: (a) an analytic expression presented by Ozeke et al. (2014); and (b) a simplified model based on the solar wind parameters. The preliminary results, uncertainties and future steps are discussed in details.

Frequency-modulated laser ranging sensor with closed-loop control

NASA Astrophysics Data System (ADS)

Müller, Fabian M.; Böttger, Gunnar; Janeczka, Christian; Arndt-Staufenbiel, Norbert; Schröder, Henning; Schneider-Ramelow, Martin

2018-02-01

Advances in autonomous driving and robotics are creating high demand for inexpensive and mass-producible distance sensors. A laser ranging system (Lidar), based on the frequency-modulated continuous-wave (FMCW) method is built in this work. The benefits of an FMCW Lidar system are the low-cost components and the performance in comparison to conventional time-of-flight Lidar systems. The basic system consists of a DFB laser diode (λ= 1308 nm) and an asymmetric fiber-coupled Mach-Zehnder interferometer with a fixed delay line in one arm. Linear tuning of the laser optical frequency via injection current modulation creates a beat signal at the interferometer output. The frequency of the beat signal is proportional to the optical path difference in the interferometer. Since the laser frequency-to-current response is non-linear, a closed-loop feed-back system is designed to improve the tuning linearity, and consequently the measurement resolution. For fast active control, an embedded system with FPGA is used, resulting in a nearly linear frequency tuning, realizing a narrow peak in the Fourier spectrum of the beat signal. For free-space measurements, a setup with two distinct interferometers is built. The fully fiber-coupled Mach-Zehnder reference interferometer is part of the feed-back loop system, while the other - a Michelson interferometer - has a free-space arm with collimator lens and reflective target. A resolution of 2:0 mm for a 560 mm distance is achieved. The results for varying target distances show high consistency and a linear relation to the measured beat-frequency.

Storm-time fingerprints of Pc 4-5 waves on energetic electron flux at geosynchronous orbit

NASA Astrophysics Data System (ADS)

Georgiou, Marina; Daglis, Ioannis A.; Zesta, Eftyhia; Balasis, George; Mann, Ian R.; Tsinganos, Kanaris

2014-05-01

Geospace magnetic storms, associated with either coronal mass ejections (CMEs) or high speed solar streams, involve global variations of the geomagnetic field as well as acceleration of charged particles in the magnetosphere. Ultra low frequency (ULF) waves with frequencies in the range of a few mHz (Pc 4-5 waves) can be generated externally by compressive variations in the solar wind or shear flow along the magnetopause unstable to the Kelvin-Helmholtz effect. Furthermore, low frequency instabilities of ring current ions are also considered as a possible internal driver of ULF wave growth. We examine power enhancements of ULF waves during four successive magnetic storms, which occurred in July 2004 and were characterized by a decreasing minimum of the Dst index, from -76 nT down to -197 nT. During the course of the magnetic storms, ULF wave power variations have been observed nearly simultaneously at different magnetic latitudes and longitudes by the ground-based CARISMA, IMAGE, 210 MM and SAMBA magnetometer networks. Nonetheless, stronger magnetic storms were accompanied by greater ULF wave power enhancements tending to be more pronounced at magnetic stations located at lower L shells. Furthermore, the generation and penetration of ULF wave power deep into the inner magnetosphere seems to be contributing to the energization and transport of relativistic electrons. Except for the magnetic storm on 25 July 2000, the three magnetic storms on 17, 23 and 27 July 2004 were characterized by a significant increase in the flux of electrons with energies higher than 1 MeV, as measured by GOES-10 and -12 during the recovery phase of each storm. On the other hand, when looking at the magnetic storm on 17 August 2001, the initial decrease was followed by an increase six days after the commencement of the storm. The electron flux decrease was more than two orders of magnitude and remained low after the recovery of the Dst index. These observations provided us the basis for

An acoustical assessment of pitch-matching accuracy in relation to speech frequency, speech frequency range, age and gender in preschool children

NASA Astrophysics Data System (ADS)

Trollinger, Valerie L.

This study investigated the relationship between acoustical measurement of singing accuracy in relationship to speech fundamental frequency, speech fundamental frequency range, age and gender in preschool-aged children. Seventy subjects from Southeastern Pennsylvania; the San Francisco Bay Area, California; and Terre Haute, Indiana, participated in the study. Speech frequency was measured by having the subjects participate in spontaneous and guided speech activities with the researcher, with 18 diverse samples extracted from each subject's recording for acoustical analysis for fundamental frequency in Hz with the CSpeech computer program. The fundamental frequencies were averaged together to derive a mean speech frequency score for each subject. Speech range was calculated by subtracting the lowest fundamental frequency produced from the highest fundamental frequency produced, resulting in a speech range measured in increments of Hz. Singing accuracy was measured by having the subjects each echo-sing six randomized patterns using the pitches Middle C, D, E, F♯, G and A (440), using the solfege syllables of Do and Re, which were recorded by a 5-year-old female model. For each subject, 18 samples of singing were recorded. All samples were analyzed by the CSpeech for fundamental frequency. For each subject, deviation scores in Hz were derived by calculating the difference between what the model sang in Hz and what the subject sang in response in Hz. Individual scores for each child consisted of an overall mean total deviation frequency, mean frequency deviations for each pattern, and mean frequency deviation for each pitch. Pearson correlations, MANOVA and ANOVA analyses, Multiple Regressions and Discriminant Analysis revealed the following findings: (1) moderate but significant (p < .001) relationships emerged between mean speech frequency and the ability to sing the pitches E, F♯, G and A in the study; (2) mean speech frequency also emerged as the strongest

Dispersion of surface plasmon polaritons on metal wires in the terahertz frequency range.

PubMed

Wang, Kanglin; Mittleman, Daniel M

2006-04-21

We report the experimental and theoretical study of the dispersive behavior of surface plasmon polaritons (SPPs) on cylindrical metal surfaces in the terahertz frequency range. Time-domain measurements of terahertz SPPs propagating on metal wires reveal a unique structure that is inconsistent with a simple extrapolation of the high frequency portion of the dispersion diagram for SPPs on a planar metal surface, and also distinct from that of SPPs on metal nanowires observed at visible and near-infrared frequencies. The results are consistent with a numerical solution of Maxwell's equations, showing that the dispersive behavior of SPPs on a cylindrical metal surface at terahertz frequencies is quite different from that of SPPs on a flat surface. These findings indicate the increasing importance of skin effects for SPPs in the terahertz range, as well as the enhancement of such effects on curved surfaces.

ULF waves: the main periodicities and their relationships with solar wind structures and magnetospheric electron flux

NASA Astrophysics Data System (ADS)

Piersanti, M.; Alberti, T.; Lepreti, F.; Vecchio, A.; Villante, U.; Carbone, V.; Waters, C. L.

2015-12-01

We use high latitude ULF wave power in the range 2-7 mHz (Pc5 geomagnetic micropulsations), solar wind speed and dynamic pressure, and relativistic magnetospheric electron flux (E > 0.6 MeV), in the period January - September 2008, in order to detect typical periodicities and physical mechanisms involved into the solar wind-magnetosphere coupling during the declining phase of the 23th solar cycle. Using the Empirical Mode Decomposition (EMD) and applying a statistical test and cross-correlation analysis,we investigate the timescales and the physical mechanisms involved into the solar wind-magnetosphere coupling.Summarizing, we obtain the following results:1. We note the existence of two different timescales into the four datasets which are related to the short-term dynamics, with a characteristic timescale τ<3 days, and to the longer timescale dynamics, with a timescale between 7 and 80 days. The short-term variations could be related to the fluctuations around a characteristic mean value, while longer timescales dynamics can be associated with solar rotational periodicity and mechanisms regarding the occurrence of high-speed streams and corotating interaction regions but also with stream-stream interactions and synodic solar rotation.2. The cross-correlation analysis highlights the relevant role of the dynamical coupling between solar wind and magnetosphere via pressure balance and direct transfer of compressional waves into the magnetosphere. Moreover, it shows that the Kelvin-Helmholtz instability is not the primary source of geomagnetic ultra-low frequency wave activity. These results are in agreement with previous works [Engebretson et al, 1998].3. The cross-correlation coefficient between Pc5 wave power and relativistic electron flux longscale reconstructions shows that Pc5 wave activity leads enhancements in magnetospheric electron flux to relativistic energy with a characteristic time delay of about 54 hours, which is in agreement with the lag of about 2

Anomalous geomagnetic variations associated with Parkfield (Ms=6.0, 28-SEP-2004, California, USA) earthquake

NASA Astrophysics Data System (ADS)

Kotsarenko, A. A.; Pilinets, S. A.; Perez Enriquez, R.; Lopez Cruz Abeyro, J. A.

2007-05-01

Analysis of geomagnetic and telluric data, measured at the station PRK (Parkfield, ULF flux-gate 3-axial magnetometer) 1 week before (including) the day of the major EQ (EarthQuake, Ms=6.0, 28-SEP-2004, 17:15:24) near Parkfield, California, USA, are presented. Spectral analysis reveal the ULF geomagnetic disturbances observed the day before the event, Sep 27, at 15:00- 20:00 by UT, and at the day of the EQ, Sep 28, at 11:00-19:00. Filtering in the corresponding frequency band f = 0.25-0.5 Hz gives the following estimations of the amplitudes of the signals: up to 20 pT for the magnetic channels and 1.5 mkV/km for the telluric ones. Observed phenomena occurs under quiet geomagnetic conditions (|Dst|<20 nT); revision of the referent stations data situated far away from the EQ epicenter (330 km) does not reveal any similar effect. Moreover, the Quake Finder research group (http:www.quakefinder.com) received very similar results (ELF range instrument, placed about 50 km from the EQ epicenter) for the day of the EQ. Mentioned above suggests the localized character of the source, possibly of the ionosphere or tectonic origin rather than of magnetosphere. Comparative analysis of the mentioned 2 stations show that we observed the lower-frequency part of the ULF- ELF burst, localized in the frequency range 0.25-1 Hz, generated 9 hours before the earthquake. Acknowledgements. The authors are grateful to Malcolm Johnston for providing us with the geomagnetic data.

A wide-range programmable frequency synthesizer based on a finite state machine filter

NASA Astrophysics Data System (ADS)

Alser, Mohammed H.; Assaad, Maher M.; Hussin, Fawnizu A.

2013-11-01

In this article, an FPGA-based design and implementation of a fully digital wide-range programmable frequency synthesizer based on a finite state machine filter is presented. The advantages of the proposed architecture are that, it simultaneously generates a high frequency signal from a low frequency reference signal (i.e. synthesising), and synchronising the two signals (signals have the same phase, or a constant difference) without jitter accumulation issue. The architecture is portable and can be easily implemented for various platforms, such as FPGAs and integrated circuits. The frequency synthesizer circuit can be used as a part of SERDES devices in intra/inter chip communication in system-on-chip (SoC). The proposed circuit is designed using Verilog language and synthesized for the Altera DE2-70 development board, with the Cyclone II (EP2C35F672C6) device on board. Simulation and experimental results are included; they prove the synthesizing and tracking features of the proposed architecture. The generated clock signal frequency of a range from 19.8 MHz to 440 MHz is synchronized to the input reference clock with a frequency step of 0.12 MHz.

Direct imaging of neural currents using ultra-low field magnetic resonance techniques

DOEpatents

Volegov, Petr L [Los Alamos, NM; Matlashov, Andrei N [Los Alamos, NM; Mosher, John C [Los Alamos, NM; Espy, Michelle A [Los Alamos, NM; Kraus, Jr., Robert H.

2009-08-11

Using resonant interactions to directly and tomographically image neural activity in the human brain using magnetic resonance imaging (MRI) techniques at ultra-low field (ULF), the present inventors have established an approach that is sensitive to magnetic field distributions local to the spin population in cortex at the Larmor frequency of the measurement field. Because the Larmor frequency can be readily manipulated (through varying B.sub.m), one can also envision using ULF-DNI to image the frequency distribution of the local fields in cortex. Such information, taken together with simultaneous acquisition of MEG and ULF-NMR signals, enables non-invasive exploration of the correlation between local fields induced by neural activity in cortex and more `distant` measures of brain activity such as MEG and EEG.

ULF Narrowband Emissions Analysis in the Terrestrial Polar Cusps

NASA Astrophysics Data System (ADS)

Grison, B.; Pisa, D.

2013-05-01

Polar cusps are known to be a key region for transfer of mass and momentum between the adjacent magnetosheath and the magnetosphere. The 4 spacecraft of the Cluster ESA mission crossed the polar cusps in their most distant part to the Earth in the early years of the mission (2000-2004) because of their highly eccentric orbit. The ULF wave activity in the cusp region has been linked with the magnetosheath plasma penetration since HEOS observations (D'Angelo et al., 1974). Wave and particle interaction play an important role in this colisionless plasma. The observed wave activity certainly results from both distant and local generation mechanisms. From Cluster case studies we propose to focus on one aspect for each of this place of generation. Concerning the distant generation, the possibility of a wave generation at the magnetopause itself is investigated. For this purpose we compare the propagation of the emissions on each side of the magnetopasue, i.e. in the cusp and in the magnetosheath. Concerning the local generation, the presence of locally generated waves above the local proton gyrofrequency that display a left hand polarization has been reported in Polar and Cluster studies (Le et al., 2001; Nykyri et al., 2003 ). The Doppler shift was not large enough to explain the observed frequency. We propose here to combine various techniques (k-filtering analysis, WHAMP simulations) to achieve a precise wave vector estimation and to explain these observations. References: D'Angelo, N., A. Bahnsen, and H. Rosenbauer (1974), Wave and particle measurements at the polar cusp, J. Geophys. Res., 79( 22), 3129-3134, doi:10.1029/JA079i022p03129. Le, G., X. Blanco-Cano, C. T. Russell, X.-W. Zhou, F. Mozer, K. J. Trattner, S. A. Fuselier, and B. J. Anderson (2001), Electromagnetic ion cyclotron waves in the high-altitude cusp: Polar observations, J. Geophys. Res., 106(A9), 19067-19079, doi:10.1029/2000JA900163. Nykyri, K., P. J. Cargill, E. A. Lucek, T. S. Horbury, A. Balogh

Ring Current He Ion Control by Bounce Resonant ULF Waves

NASA Astrophysics Data System (ADS)

Kim, Hyomin; Gerrard, Andrew J.; Lanzerotti, Louis J.; Soto-Chavez, Rualdo; Cohen, Ross J.; Manweiler, Jerry W.

2017-12-01

Ring current energy He ion (˜65 keV to ˜520 keV) differential flux data from the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instrument aboard the Van Allan Probes spacecraft show considerable variability during quiet solar wind and geomagnetic time periods. Such variability is apparent from orbit to orbit (˜9 h) of the spacecraft and is observed to be ˜50-100% of the nominal flux. Using data from the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument, also aboard the Van Allen Probes spacecraft, we identify that a dominant source of this variability is from ULF waveforms with periods of tens of seconds. These periods correspond to the bounce resonant timescales of the ring current He ions being measured by RBSPICE. A statistical survey using the particle and field data for one full spacecraft precession period (approximately 2 years) shows that the wave and He ion flux variations are generally anticorrelated, suggesting the bounce resonant pitch angle scattering process as a major component in the scattering of He ions.

VLF Wave Local Acceleration & ULF Wave Radial Diffusion: The Importance of K-Dependent PSD Analysis for Diagnosing the cause of Radiation Belt Acceleration.

NASA Astrophysics Data System (ADS)

Ozeke, L.; Mann, I. R.; Claudepierre, S. G.; Morley, S.; Henderson, M. G.; Baker, D. N.; Kletzing, C.; Spence, H. E.

2017-12-01

We present results showing the temporal evolution of electron Phase Space Density (PSD) in the outer radiation belt during the most intense geomagnetic storm of the last decade which occurred on March 17th 2015. Based on observations of growing local PSD peaks at fixed first and second adiabatic invariants of M=1000 MeV/G and K=0.18 G1/2Re respectively, previous studies argued that the outer radiation belt flux enhancement that occurred during this storm resulted from local acceleration driven by VLF waves. Here we show that the vast majority of the outer radiation belt consisted of electrons with much lower K-values than 0.18 G1/2Re, and that at these lower K-values there is no clear evidence of growing local PSD peaks consistent with that expected from local acceleration. Contrary to prior studies we show that the outer radiation belt flux enhancement is consistent with inward radial diffusion driven by ULF waves and present evidence that the growing local PSD peaks at K=0.18 G1/2Re and M=1000 MeV/G result from pitch-angle scattering of lower-K electrons to K=0.18 G1/2Re. In addition, we also show that the observed outer radiation belt flux enhancement during this geomagnetic storm can be reproduced using a radial diffusion model driven by measured ULF waves without including any local acceleration. These results highlight the importance of careful analysis of the electron PSD profiles as a function of L* over a range of fixed first, M and second K, adiabatic invariants to correctly determine the mechanism responsible for the electron flux enhancements observed in the outer radiation belt.

An atomic magnetometer with autonomous frequency stabilization and large dynamic range

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

Pradhan, S., E-mail: spradhan@barc.gov.in, E-mail: pradhans75@gmail.com; Poornima,; Dasgupta, K.

2015-06-15

The operation of a highly sensitive atomic magnetometer using elliptically polarized resonant light is demonstrated. It is based on measurement of zero magnetic field resonance in degenerate two level systems using polarimetric detection. The transmitted light through the polarimeter is used for laser frequency stabilization, whereas reflected light is used for magnetic field measurement. Thus, the experimental geometry allows autonomous frequency stabilization of the laser frequency leading to compact operation of the overall device and has a preliminary sensitivity of <10 pT/Hz{sup 1/2} @ 1 Hz. Additionally, the dynamic range of the device is improved by feedback controlling the biasmore » magnetic field without compromising on its sensitivity.« less

Observations of ULF oscillations in the ion fluxes at small pitch angles with ATS 6. [low energy particle detection

NASA Technical Reports Server (NTRS)

Su, S.-Y.; Mcpherron, R. L.; Konradi, A.; Fritz, T. A.

1980-01-01

The ultra-low-frequency modulation of ion flux densities at small pitch angles observed by ATS 6 is examined, with particular attention given to a detailed analysis of a representative event. ULF modulation events with maximum modulation at small pitch angles were identified 14 times during the first eight months of operation of the NOAA low-energy particle detector on ATS 6. For the event of October 23, 1974, maximum flux modulation, with a maximum/minimum intensity ratio of 3.7, was observed in the 100 to 150 keV detector at an angle of 32 deg to the ambient field. Spectral analysis of magnetic field data reveals a right elliptically polarized magnetic perturbation with a 96-sec period and a 5-gamma rms amplitude, propagating in the dipole meridian at an angle of about 15 deg to the ambient field and the dipole axis. Proton flux modulation is found to lag the field by up to 180 deg for the lowest-energy channel. Observations are compared with the drift wave, MHD slow wave, and bounce resonant interaction associated with transverse wave models, and it is found that none of the wave models can adequately account for all of the correlated particle and field oscillations.

Quasi-monochromatic ULF foreshock waves as observed by the four-spacecraft Cluster mission: 2. Oblique propagation

NASA Astrophysics Data System (ADS)

Eastwood, J. P.; Balogh, A.; Lucek, E. A.; Mazelle, C.; Dandouras, I.

2005-11-01

This paper presents the results of a statistical investigation into the nature of oblique wave propagation in the foreshock. Observations have shown that foreshock ULF waves tend to propagate obliquely to the background magnetic field. This is in contrast to theoretical work, which predicts that the growth rate of the mechanism responsible for the waves is maximized for parallel propagation, at least in the linear regime in homogenous plasma. Here we use data from the Cluster mission to study in detail the oblique propagation of a particular class of foreshock ULF wave, the 30 s quasi-monochromatic wave. We find that these waves persistently propagate at oblique angles to the magnetic field. Over the whole data set, the average value of θkB was found to be 21 ± 14°. Oblique propagation is observed even when the interplanetary magnetic field (IMF) cone angle is small, such that the convective component of the solar wind velocity, vE×B, is comparable to the wave speed. In this subset of the data, the mean value of θkB was 12.9 ± 7.1°. In the subset of data for which the IMF cone angle exceeded 45°, the mean value of θkB was 19.5 ± 10.7°. When the angle between the IMF and the x geocentric solar ecliptic (GSE) direction (i.e., the solar wind vector) is large, the wave k vectors tend to be confined in the plane defined by the x GSE direction and the magnetic field and a systematic deflection is observed. The dependence of θkB on vE×B is also studied.

Ionospheric Coherence Bandwidth Measurements in the Lower VHF Frequency Range

NASA Astrophysics Data System (ADS)

Suszcynsky, D. M.; Light, M. E.; Pigue, M. J.

2015-12-01

The United States Department of Energy's Radio Frequency Propagation (RFProp) experiment consists of a satellite-based radio receiver suite to study various aspects of trans-ionospheric signal propagation and detection in four frequency bands, 2 - 55 MHz, 125 - 175 MHz, 365 - 415 MHz and 820 - 1100 MHz. In this paper, we present simultaneous ionospheric coherence bandwidth and S4 scintillation index measurements in the 32 - 44 MHz frequency range collected during the ESCINT equatorial scintillation experiment. 40-MHz continuous wave (CW) and 32 - 44 MHz swept frequency signals were transmitted simultaneously to the RFProp receiver suite from the Reagan Test Site at Kwajalein Atoll in the Marshall Islands (8.7° N, 167.7° E) in three separate campaigns during the 2014 and 2015 equinoxes. Results show coherence bandwidths as small as ~ 1 kHz for strong scintillation (S4 > 0.7) and indicate a high degree of ionospheric variability and irregularity on 10-m spatial scales. Spread-Doppler clutter effects arising from preferential ray paths to the satellite due to refraction off of isolated density irregularities are also observed and are dominant at low elevation angles. The results are compared to previous measurements and available scaling laws.

Evolution of ionospheric convection and ULFs during the 27 March 2017 storm: ERG-SuperDARN campaign

NASA Astrophysics Data System (ADS)

Hori, T.; Nishitani, N.; Shepherd, S. G.; Ruohoniemi, J. M.; Connors, M. G.; Teramoto, M.; Nakano, S.; Seki, K.; Takahashi, N.; Kasahara, S.; Yokota, S.; Mitani, T.; Takashima, T.; Higashio, N.; Matsuoka, A.; Asamura, K.; Kazama, Y.; Wang, S. Y.; Tam, S. W. Y.; Miyoshi, Y.; Shinohara, I.

2017-12-01

The Exploration of energization and Radiation in Geospace (ERG) satellite, which was nicknamed "Arase" after its launch on late December, 2016, has successfully started regular observations recently. In concert with in situ measurement made by Arase in the inner magnetosphere, campaign observations with SuperDARN radars have been conducted with a special scan mode "interleaved_normalscan" since March, 2017. Some of the radars being operated in the special mode observed the dynamic evolution of ionospheric convection including superimposed ULF-like convection fluctuations with frequencies of mHz over the North American sector during a moderate magnetic storm on March 27, 2017. The large-scale evolution provided by the radar observations in the early morning sector shows that the ionospheric convection changed direction between westward and eastward several times in the course of the storm main phase. Some meso-scale patchy structures seen on 2-D profiles of the line-of-sight (LOS) velocity propagated both westward and eastward just after a major substorm intensification. Interestingly, the velocity fluctuations were accompanied by a drifting energetic electron population as observed by particle instruments onboard Arase. A simulation of the inner magnetosphere coupled with a global MHD simulation for this event reproduces intense particle injections in the premidnight sector, consistent with the energy dispersion of the observed drifting population. A detailed interpretation of the observations including those captured by Arase is discussed and compared with the simulation results.

A machine learning approach for automated wide-range frequency tagging analysis in embedded neuromonitoring systems.

PubMed

Montagna, Fabio; Buiatti, Marco; Benatti, Simone; Rossi, Davide; Farella, Elisabetta; Benini, Luca

2017-10-01

EEG is a standard non-invasive technique used in neural disease diagnostics and neurosciences. Frequency-tagging is an increasingly popular experimental paradigm that efficiently tests brain function by measuring EEG responses to periodic stimulation. Recently, frequency-tagging paradigms have proven successful with low stimulation frequencies (0.5-6Hz), but the EEG signal is intrinsically noisy in this frequency range, requiring heavy signal processing and significant human intervention for response estimation. This limits the possibility to process the EEG on resource-constrained systems and to design smart EEG based devices for automated diagnostic. We propose an algorithm for artifact removal and automated detection of frequency tagging responses in a wide range of stimulation frequencies, which we test on a visual stimulation protocol. The algorithm is rooted on machine learning based pattern recognition techniques and it is tailored for a new generation parallel ultra low power processing platform (PULP), reaching performance of more that 90% accuracy in the frequency detection even for very low stimulation frequencies (<1Hz) with a power budget of 56mW. Copyright © 2017 Elsevier Inc. All rights reserved.

Acoustic Treatment Design Scaling Methods. Volume 2; Advanced Treatment Impedance Models for High Frequency Ranges

NASA Technical Reports Server (NTRS)

Kraft, R. E.; Yu, J.; Kwan, H. W.

1999-01-01

The primary purpose of this study is to develop improved models for the acoustic impedance of treatment panels at high frequencies, for application to subscale treatment designs. Effects that cause significant deviation of the impedance from simple geometric scaling are examined in detail, an improved high-frequency impedance model is developed, and the improved model is correlated with high-frequency impedance measurements. Only single-degree-of-freedom honeycomb sandwich resonator panels with either perforated sheet or "linear" wiremesh faceplates are considered. The objective is to understand those effects that cause the simple single-degree-of- freedom resonator panels to deviate at the higher-scaled frequency from the impedance that would be obtained at the corresponding full-scale frequency. This will allow the subscale panel to be designed to achieve a specified impedance spectrum over at least a limited range of frequencies. An advanced impedance prediction model has been developed that accounts for some of the known effects at high frequency that have previously been ignored as a small source of error for full-scale frequency ranges.

Noise in any frequency range can enhance information transmission in a sensory neuron

NASA Astrophysics Data System (ADS)

Levin, Jacob E.

1997-05-01

The effect of noise on the neural encoding of broadband signals was investigated in the cricket cercal system, a mechanosensory system sensitive to small near-field air particle disturbances. Known air current stimuli were presented to the cricket through audio speakers in a controlled environment in a variety of background noise conditions. Spike trains from the second layer of neuronal processing, the primary sensory interneurons, were recorded with intracellular Electrodes and the performance of these neurons characterized with the tools of information theory. SNR, mutual information rates, and other measures of encoding accuracy were calculated for single frequency, narrowband, and broadband signals over the entire amplitude sensitivity range of the cells, in the presence of uncorrelated noise background also spanning the cells' frequency and amplitude sensitivity range. Significant enhancements of transmitted information through the addition of external noise were observed regardless of the frequency range of either the signal or noise waveforms, provided both were within the operating range of the cell. Considerable improvements in signal encoding were observed for almost an entire order of magnitude of near-threshold signal amplitudes. This included sinusoidal signals embedded in broadband white noise, broadband signals in broadband noise, and even broadband signals presented with narrowband noise in a completely non-overlapping frequency range. The noise related increases in mutual information rate for broadband signals were as high as 150%, and up to 600% increases in SNR were observed for sinusoidal signals. Additionally, it was shown that the amount of information about the signal carried, on average, by each spike was INCREASED for small signals when presented with noise—implying that added input noise can, in certain situations, actually improve the accuracy of the encoding process itself.

Obtaining eigensolutions for multiple frequency ranges in a single NASTRAN execution

NASA Technical Reports Server (NTRS)

Pamidi, P. R.; Brown, W. K.

1990-01-01

A novel and general procedure for obtaining eigenvalues and eigenvectors for multiple frequency ranges in a single NASTRAN execution is presented. The scheme is applicable to normal modes analyzes employing the FEER and Inverse Power methods of eigenvalue extraction. The procedure is illustrated by examples.

STS 129 Return Samples: Assessment of Air Quality aboard the Shuttle (STS-129) and International Space Station (ULF3)

NASA Technical Reports Server (NTRS)

James, John T.

2010-01-01

Reports on the air quality aboard the Space Shuttle (STS-129), and the International Space station (ULF3). NASA analyzed the grab sample canisters (GSCs) and the formaldehyde badges aboard both locations for carbon monoxide levels. The three surrogates: (sup 13)C-acetone, fluorobenzene, and chlorobenzene registered 109, 101, and 109% in the space shuttle and 81, 87, and 55% in the International Space Station (ISS). From these results the atmosphere in both the Space Shuttle and the International Space Station (ISS) was found to be breathable.

Measurements of vocal fold tissue viscoelasticity: Approaching the male phonatory frequency range

NASA Astrophysics Data System (ADS)

Chan, Roger W.

2004-06-01

Viscoelastic shear properties of human vocal fold tissues have been reported previously. However, data have only been obtained at very low frequencies (<=15 Hz). This necessitates data extrapolation to the frequency range of phonation based on constitutive modeling and time-temperature superposition. This study attempted to obtain empirical measurements at higher frequencies with the use of a controlled strain torsional rheometer, with a design of directly controlling input strain that introduced significantly smaller system inertial errors compared to controlled stress rheometry. Linear viscoelastic shear properties of the vocal fold mucosa (cover) from 17 canine larynges were quantified at frequencies of up to 50 Hz. Consistent with previous data, results showed that the elastic shear modulus (G'), viscous shear modulus (G''), and damping ratio (ζ) of the vocal fold mucosa were relatively constant across 0.016-50 Hz, whereas the dynamic viscosity (ɛ') decreased monotonically with frequency. Constitutive characterization of the empirical data by a quasilinear viscoelastic model and a statistical network model demonstrated trends of viscoelastic behavior at higher frequencies generally following those observed at lower frequencies. These findings supported the use of controlled strain rheometry for future investigations of the viscoelasticity of vocal fold tissues and phonosurgical biomaterials at phonatory frequencies.

Coupling of ELF/ULF energy from lightning and MeV particles to the middle atmosphere, inosphere, and global circuit

NASA Technical Reports Server (NTRS)

Hale, Leslie C.

1994-01-01

In an attempt to explain numerous atmospheric electrical phenomena, the elements of the global electrical circuit are reexamined. In addition to being a 'quasi-static 'DC' generator' and source of radiated energy at VLF and higher, the thunderstorm is found to be a pulse generator, with most of the external energy contained in ELF and ULF pulse currents to the ionosphere (and Earth). The pulse energy is found to deposit largely in the middle atmosphere above the thunderstorm. The VLF and above components are well understood, as are the ULF components due to the conductivity gradient. However, a previously poorly understood ELF component on the millsecond timescale, or 'slow tail,' contains a large fraction of the electrical energy. This component couples strongly to the ionosphere and also launches a unipolar transverse electromagnetic (TEM) wavelet in the radial Earth-ionosphere transmission line. The increase in charge with distance associated with such wavelets, and their ensemble sum at a point, may explain some large mesospheric 'DC' fields but there are still difficulties explaining other than rare occurrences, except for antipodal reconvergence. These millisecond duration unipolar wavelets also coupled to the ionosphere and may trigger other lightning at a distance. A schema is elucidated by which the charge of MeV particles deposited in the middle atmosphere persists for much longer than the local relaxation time. This also gives rise to unipolar waves of global extent which may explain lower-latitude field perturbations associated with solar/geomagnetic events.

Frequency ranges of heart rate variability related to autonomic nerve activity in the mouse.

PubMed

Tsai, Meng-Li; Chen, Chien-Chang; Yeh, Chang-Jyi; Chou, Li-Ming; Cheng, Chiung-Hsiang

2012-01-01

Mice have gained more and more attention in recent years and been widely used in transgenic experiments. Although the number of researches on the heart rate variability (HRV) of mice has been gradually increasing, a consensus on the frequency ranges of autonomic modulation has not been established. Therefore, the main purpose of this study was to find a HRV "prototype" for conscious mice in the state of being motionless and breathing regularly (called "genuinely resting"), and to determine the frequency ranges corresponding to the autonomic modulation. Further, whether these frequencies will change when the mice move freely was studied to evaluate the feasibility of the HRV spectrum as an index of the autonomic modulation of mice. The recording sites were specially arranged to simultaneously obtain the electrocardiography and electromyography data to be provided for the use of HRV analysis and motion monitoring, respectively. The states of being motionless and breathing regularly as judged from the electromyography results were selected as a genuine resting state of a conscious mouse. The frequencies related to autonomic modulation of HRV were determined by comparing the spectrum changes before and after blockades of the autonomic tone by different pharmaceutical agents in both the genuine resting state and freely moving states. Our results showed that the HRV of mice is not suitable for indexing sympathetic modulation; however, it is possible to use the spectral power in the frequency range between 0.1 and 1 Hz as an index of parasympathetic modulation.

Complex magnetic susceptibility setup for spectroscopy in the extremely low-frequency range.

PubMed

Kuipers, B W M; Bakelaar, I A; Klokkenburg, M; Erné, B H

2008-01-01

A sensitive balanced differential transformer was built to measure complex initial parallel magnetic susceptibility spectra in the 0.01-1000 Hz range. The alternating magnetic field can be chosen sufficiently weak that the magnetic structure of the samples is only slightly perturbed and the low frequencies make it possible to study the rotational dynamics of large magnetic colloidal particles or aggregates dispersed in a liquid. The distinguishing features of the setup are the novel multilayered cylindrical coils with a large sample volume and a large number of secondary turns (55 000) to measure induced voltages with a good signal-to-noise ratio, the use of a dual channel function generator to provide an ac current to the primary coils and an amplitude- and phase-adjusted compensation voltage to the dual phase differential lock-in amplifier, and the measurement of several vector quantities at each frequency. We present the electrical impedance characteristics of the coils, and we demonstrate the performance of the setup by measurement on magnetic colloidal dispersions covering a wide range of characteristic relaxation frequencies and magnetic susceptibilities, from chi approximately -10(-5) for pure water to chi>1 for concentrated ferrofluids.

Parallel PWMs Based Fully Digital Transmitter with Wide Carrier Frequency Range

PubMed Central

Zhou, Bo; Zhang, Kun; Zhou, Wenbiao; Zhang, Yanjun; Liu, Dake

2013-01-01

The carrier-frequency (CF) and intermediate-frequency (IF) pulse-width modulators (PWMs) based on delay lines are proposed, where baseband signals are conveyed by both positions and pulse widths or densities of the carrier clock. By combining IF-PWM and precorrected CF-PWM, a fully digital transmitter with unit-delay autocalibration is implemented in 180 nm CMOS for high reconfiguration. The proposed architecture achieves wide CF range of 2 M–1 GHz, high power efficiency of 70%, and low error vector magnitude (EVM) of 3%, with spectrum purity of 20 dB optimized in comparison to the existing designs. PMID:24223503

Implementation of acoustic demultiplexing with membrane-type metasurface in low frequency range

NASA Astrophysics Data System (ADS)

Chen, Xing; Liu, Peng; Hou, Zewei; Pei, Yongmao

2017-04-01

Wavelength division multiplexing technology, adopted to increase the information density, plays a significant role in optical communication. However, in acoustics, a similar function can be hardly implemented due to the weak dispersion in natural acoustic materials. Here, an acoustic demultiplexer, based on the concept of metasurfaces, is proposed for splitting acoustic waves and propagating along different trajectories in a low frequency range. An acoustic metasurface, containing multiple resonant units, is designed with various phase profiles for different frequencies. Originating from the highly dispersive properties, the resonant units are independent and merely work in the vicinity of their resonant frequencies. Therefore, by combing multiple resonant units appropriately, the phenomena of anomalous reflection, acoustic focusing, and acoustic wave bending can occur in different frequencies. The proposed acoustic demultiplexer has advantages on the subwavelength scale and the versatility in wave control, providing a strategy for separating acoustic waves with different Fourier components.

Precision improvement of frequency-modulated continuous-wave laser ranging system with two auxiliary interferometers

NASA Astrophysics Data System (ADS)

Shi, Guang; Wang, Wen; Zhang, Fumin

2018-03-01

The measurement precision of frequency-modulated continuous-wave (FMCW) laser distance measurement should be proportional to the scanning range of the tunable laser. However, the commercial external cavity diode laser (ECDL) is not an ideal tunable laser source in practical applications. Due to the unavoidable mode hopping and scanning nonlinearity of the ECDL, the measurement precision of FMCW laser distance measurements can be substantially affected. Therefore, an FMCW laser ranging system with two auxiliary interferometers is proposed in this paper. Moreover, to eliminate the effects of ECDL, the frequency-sampling method and mode hopping influence suppression method are employed. Compared with a fringe counting interferometer, this FMCW laser ranging system has a measuring error of ± 20 μm at the distance of 5.8 m.

Research on the range side lobe suppression method for modulated stepped frequency radar signals

NASA Astrophysics Data System (ADS)

Liu, Yinkai; Shan, Tao; Feng, Yuan

2018-05-01

The magnitude of time-domain range sidelobe of modulated stepped frequency radar affects the imaging quality of inverse synthetic aperture radar (ISAR). In this paper, the cause of high sidelobe in modulated stepped frequency radar imaging is analyzed first in real environment. Then, the chaos particle swarm optimization (CPSO) is used to select the amplitude and phase compensation factors according to the minimum sidelobe criterion. Finally, the compensated one-dimensional range images are obtained. Experimental results show that the amplitude-phase compensation method based on CPSO algorithm can effectively reduce the sidelobe peak value of one-dimensional range images, which outperforms the common sidelobe suppression methods and avoids the coverage of weak scattering points by strong scattering points due to the high sidelobes.

Pulsating midmorning auroral arcs, filamentation of a mixing region in a flank boundary layer, and ULF waves observed during a Polar-Svalbard conjunction

NASA Astrophysics Data System (ADS)

Farrugia, C. J.; Sandholt, P. E.; Maynard, N. C.; Burke, W. J.; Scudder, J. D.; Ober, D. M.; Moen, J.; Russell, C. T.

2000-12-01

Magnetically conjugate observations by the HYDRA and the Magnetic Field Experiment instruments on Polar, meridian-scanning photometers and all-sky imagers at Ny-Ålesund, and International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers on November 30, 1997, illustrate aspects of magnetosphere-ionosphere coupling at 0900-1000 magnetic local times (MLT) and 70°-80° magnetic latitudes and their dependence on interplanetary parameters. Initially, Polar crossed a boundary layer on closed field lines where magnetospheric and magnetosheath plasmas are mixed. This region contains filaments where magnetospheric electron and ion fluxes are enhanced. These filaments are associated with field-aligned current structures embedded within the large-scale region 1 (R1) current. Ground auroral imagery document the presence at this time of discrete, east-west aligned arcs, which are in one-to-one correspondence with the filaments. Temporal variations present in these auroral arcs correlate with Pc 5 pulsations and are probably related to modulations in the interplanetary electric field. The auroral observations indicate that the filamented mixing region persisted for many tens of minutes, suggesting a spatial structuring. The data suggest further that the filamented, mixing region is an important source of the R1 current and the associated midmorning arcs. When the interplanetary magnetic field (IMF) turned strongly north, Polar had entered the dayside extension of the central plasma sheet/region 2 current system where it and the underlying ground magnetometers recorded a clear field line resonance of frequency ~2.4 mHz (Pc 5 range). The source of these oscillations is most likely the Kelvin-Helmholtz instability. Subsequent to the IMF northward turning, the multiple arcs were replaced by a single auroral form to the north of Ny-Ålesund (at 1000 MLT) in the vicinity of the westward edge of the cusp. ULF pulsation activity changed to the Pc 3-4 range in the regime of

Doppler imaging with dual-detection full-range frequency domain optical coherence tomography

PubMed Central

Meemon, Panomsak; Lee, Kye-Sung; Rolland, Jannick P.

2010-01-01

Most of full-range techniques for Frequency Domain Optical Coherence Tomography (FD-OCT) reported to date utilize the phase relation between consecutive axial lines to reconstruct a complex interference signal and hence may exhibit degradation in either mirror image suppression performance or detectable velocity dynamic range or both when monitoring a moving sample such as flow activity. We have previously reported a technique of mirror image removal by simultaneous detection of the quadrature components of a complex spectral interference called a Dual-Detection Frequency Domain OCT (DD-FD-OCT) [Opt. Lett. 35, 1058-1060 (2010)]. The technique enables full range imaging without any loss of acquisition speed and is intrinsically less sensitive to phase errors generated by involuntary movements of the subject. In this paper, we demonstrate the application of the DD-FD-OCT to a phase-resolved Doppler imaging without degradation in either mirror image suppression performance or detectable velocity dynamic range that were observed in other full-range Doppler methods. In order to accommodate for Doppler imaging, we have developed a fiber-based DD-FD-OCT that more efficiently utilizes the source power compared with the previous free-space DD-FD-OCT. In addition, the velocity sensitivity of the phase-resolved DD-FD-OCT was investigated, and the relation between the measured Doppler phase shift and set flow velocity of a flow phantom was verified. Finally, we demonstrate the Doppler imaging using the DD-FD-OCT in a biological sample. PMID:21258488

Direct Determination of Wavenumbers of ULF Waves Using the Cluster Multipoint and Multicomponent Measurements

NASA Astrophysics Data System (ADS)

Grison, B.; Escoubet, C.; Santolik, O.; Cornilleau-Wehrlin, N.

2013-12-01

The wavenumber is a key parameter to understand the physics of the interactions between the electromagnetic waves and the ionized particles in space plasmas. Search-coil magnetometers and electric antennas measure time series of both magnetic and electric field fluctuations, respectively. The fleet of four Cluster spacecraft made possible to determine the full wave vector and even to differentiate the waves present at the same frequency in the spacecraft frame through various techniques: k-filtering analysis, wave telescope, phase differentiating method. However the fleet configuration (inter-spacecraft separation, tetrahedron elongation and planarity) limit the possibilities to use these techniques. From single spacecraft measurements, assumptions concerning the wave mode -and thus, concerning the physical processes- are usually required to derive the corresponding wavenumber. Using three orthogonal magnetic components and two electric antennas, it is possible to estimate n/Z where n is the refractive index and Z the transfer function of the interface between the plasma and the electric antennas. For ULF waves we assume Z=1 and we thus obtain the wavenumber. We test this hypothesis on a case where the spacecraft are in a close configuration in the distant cusp region and where we are able to apply the k-filtering analysis, too. The results obtained by multispacecraft and multicomponents analysis are close to each other and permit us to precise the value of Z. We test this procedure on several events (in various regions of the magnetosphere) in order to get more precise wave number measurements from the single spacecraft analysis. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7-SPACE-2010-1) under grant agreement n. 284520 (MAARBLE).

Single frequency thermal wave radar: A next-generation dynamic thermography for quantitative non-destructive imaging over wide modulation frequency ranges.

PubMed

Melnikov, Alexander; Chen, Liangjie; Ramirez Venegas, Diego; Sivagurunathan, Koneswaran; Sun, Qiming; Mandelis, Andreas; Rodriguez, Ignacio Rojas

2018-04-01

Single-Frequency Thermal Wave Radar Imaging (SF-TWRI) was introduced and used to obtain quantitative thickness images of coatings on an aluminum block and on polyetherketone, and to image blind subsurface holes in a steel block. In SF-TWR, the starting and ending frequencies of a linear frequency modulation sweep are chosen to coincide. Using the highest available camera frame rate, SF-TWRI leads to a higher number of sampled points along the modulation waveform than conventional lock-in thermography imaging because it is not limited by conventional undersampling at high frequencies due to camera frame-rate limitations. This property leads to large reduction in measurement time, better quality of images, and higher signal-noise-ratio across wide frequency ranges. For quantitative thin-coating imaging applications, a two-layer photothermal model with lumped parameters was used to reconstruct the layer thickness from multi-frequency SF-TWR images. SF-TWRI represents a next-generation thermography method with superior features for imaging important classes of thin layers, materials, and components that require high-frequency thermal-wave probing well above today's available infrared camera technology frame rates.

Single frequency thermal wave radar: A next-generation dynamic thermography for quantitative non-destructive imaging over wide modulation frequency ranges

NASA Astrophysics Data System (ADS)

Melnikov, Alexander; Chen, Liangjie; Ramirez Venegas, Diego; Sivagurunathan, Koneswaran; Sun, Qiming; Mandelis, Andreas; Rodriguez, Ignacio Rojas

2018-04-01

Single-Frequency Thermal Wave Radar Imaging (SF-TWRI) was introduced and used to obtain quantitative thickness images of coatings on an aluminum block and on polyetherketone, and to image blind subsurface holes in a steel block. In SF-TWR, the starting and ending frequencies of a linear frequency modulation sweep are chosen to coincide. Using the highest available camera frame rate, SF-TWRI leads to a higher number of sampled points along the modulation waveform than conventional lock-in thermography imaging because it is not limited by conventional undersampling at high frequencies due to camera frame-rate limitations. This property leads to large reduction in measurement time, better quality of images, and higher signal-noise-ratio across wide frequency ranges. For quantitative thin-coating imaging applications, a two-layer photothermal model with lumped parameters was used to reconstruct the layer thickness from multi-frequency SF-TWR images. SF-TWRI represents a next-generation thermography method with superior features for imaging important classes of thin layers, materials, and components that require high-frequency thermal-wave probing well above today's available infrared camera technology frame rates.

Cluster spacecraft observations of a ULF wave enhanced by Space Plasma Exploration by Active Radar (SPEAR)

NASA Astrophysics Data System (ADS)

Badman, S. V.; Wright, D. M.; Clausen, L. B. N.; Fear, R. C.; Robinson, T. R.; Yeoman, T. K.

2009-09-01

Space Plasma Exploration by Active Radar (SPEAR) is a high-latitude ionospheric heating facility capable of exciting ULF waves on local magnetic field lines. We examine an interval from 1 February 2006 when SPEAR was transmitting a 1 Hz modulation signal with a 10 min on-off cycle. Ground magnetometer data indicated that SPEAR modulated currents in the local ionosphere at 1 Hz, and enhanced a natural field line resonance with a 10 min period. During this interval the Cluster spacecraft passed over the heater site. Signatures of the SPEAR-enhanced field line resonance were present in the magnetic field data measured by the magnetometer on-board Cluster-2. These are the first joint ground- and space-based detections of field line tagging by SPEAR.

Outdoor stocking density in free-range laying hens: radio-frequency identification of impacts on range use.

PubMed

Campbell, D L M; Hinch, G N; Dyall, T R; Warin, L; Little, B A; Lee, C

2017-01-01

The number and size of free-range laying hen (Gallus gallus domesticus) production systems are increasing within Australia in response to consumer demand for perceived improvement in hen welfare. However, variation in outdoor stocking density has generated consumer dissatisfaction leading to the development of a national information standard on free-range egg labelling by the Australian Consumer Affairs Ministers. The current Australian Model Code of Practice for Domestic Poultry states a guideline of 1500 hens/ha, but no maximum density is set. Radio-frequency identification (RFID) tracking technology was used to measure daily range usage by individual ISA Brown hens housed in six small flocks (150 hens/flock - 50% of hens tagged), each with access to one of three outdoor stocking density treatments (two replicates per treatment: 2000, 10 000, 20 000 hens/ha), from 22 to 26, 27 to 31 and 32 to 36 weeks of age. There was some variation in range usage across the sampling periods and by weeks 32 to 36 individual hens from the lowest stocking density on average used the range for longer each day (P<0.001), with fewer visits and longer maximum durations per visit (P<0.001). Individual hens within all stocking densities varied in the percentage of days they accessed the range with 2% of tagged hens in each treatment never venturing outdoors and a large proportion that accessed the range daily (2000 hens/ha: 80.5%; 10 000 hens/ha: 66.5%; 20 000 hens/ha: 71.4%). On average, 38% to 48% of hens were seen on the range simultaneously and used all available areas of all ranges. These results of experimental-sized flocks have implications for determining optimal outdoor stocking densities for commercial free-range laying hens but further research would be needed to determine the effects of increased range usage on hen welfare.

A real time index of geomagnetic background noise for the MAD (Magnetic Anomaly Detection) frequency band

NASA Astrophysics Data System (ADS)

Bernardi, A.; Fraser-Smith, A. C.; Villard, O. G.

1985-02-01

An index of geomagnetic activity in the upper part of the ultra low frequency (ULF) range (less than 4.55 Hz) has been developed. This index will be referred to as the MA index (magnetic activity index). The MA index is prepared every half hour and is a measure of the strength of the geomagnetic activity in the Pc1-Pc3 pulsation frequency range during that half hour period. Activity in the individual Pc pulsation ranges can also be measured, if desired. The index is calculated from the running average of the full-wave rectified values of the band pass filtered geomagnetic signals and thus it provides a better indication of the magnitude of these band pass filtered magnetic pulsations than does the ap index, for example. Daily variations of the band pass filtered magnetic signals are also better captured by the MA index. To test this system we used analog tape recordings of wide-band geomagnetic signals. The indices for these tapes are presented in the form of plots, together with a comparison with the ap indices of the same time intervals. The MA index shows the daily variation of the geometric signals quite clearly during times when there is strong activity, i.e., when the ap index values are large. Because impulsive signals, such as lightning discharges, tend to be suppressed in the averaging process, the MA index is insensitive to impulsive noise. It is found that the time variation of the MA index is in general markedly different from the variation of the ap index for the same time intervals.

Hematite from Natural Iron Stones as Microwave Absorbing Material on X-Band Frequency Ranges

NASA Astrophysics Data System (ADS)

Zainuri, Mochamad

2017-05-01

This study has been investigated the effect of hematite as microwave absorbing materials (RAM) on X-Band frequency ranges. Hematite was succesfully processed by coprecipitation method and calcined at 500 °C for 5 hour. It was synthesized from natural iron stones from Tanah Laut, South Kalimantan, Indonesia. The products were characterized by X-ray diffraxtion (XRD), conductivity measurement, Vibrating Sample Magnetometer (VSM), and Vector Network Analyzer (VNA). The result was shown that hematite has conductivity value on (2.5-3).10-7 S/cm and be included as dielectric materials. The hysterisis curve was shown that hematite was a super paramagnetic materials. The product was mixed on paint with procentage 10% of total weight and coated on steel grade AH36 with spray methods. Then, the maximum of reflection loss on x - band’s frequency range (8,2-12,4) GHz was -7 dB on frequency of 10.5 GHz. It mean that almost 50% electromagnetic energy was absorbed by hematite.

Analysis of ULF Waves During Substorms Observed in the Ionosphere from the Dayside Ground Magnetometer and in the Solar Wind from the Satellite

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Alimaganbetov, M.

2017-12-01

Magnetospheric substorm is one of the most interesting and complicated phenomena of solar-terrestrial interactions. Despite numerous theoretical and experimental studies conducted during last 50 years, its several important phenomena are not completely understood yet. One of them are intense, ultra-low-frequency (from 0.5 mHz to 100 mHz), electromagnetic pulsations which are always observed during the substorms with the ground-based magnetometers and radars at high latitudes. These waves have the largest amplitudes in the power spectral densities during substorms. Hence, they are the most effective drivers of such mechanisms as high-latitude ionosphere energization, ion outflow production, formation of plasma density cavities, etc. In our study, we focus on the waves with frequencies 0.5-1.0 mHz, which is the lowest part of the frequency spectra observed during the substorm. The questions of what phenomena cause these oscillations and what are their spatiotemporal properties are among the most important ones about the physics of the substorm. To answer these questions, we analyzed disturbances of the magnetic field obtained from the two sources for the period from October 2015 to November 2016 during several substorms. One source is the fluxgate magnetometer in Poker Flat, Alaska. Another is the NASA Advanced Composite Explorer satellite in the Lagrangian L1 point that detects most of the solar wind from the Sun. The goal of our project is to find correlations between the disturbances observed from these sources, which will be a strong argument that the solar wind has a strong influence on the electromagnetic coupling between the ionosphere and magnetosphere of the Earth during the substorms. We observed 48 substorms during the abovementioned period. Our findings show that 1) the dominant frequency of the large-amplitude ULF waves observed during the substorms is 1 mHz or less; and 2) the same frequencies are frequently observed in the waves detected from the both

Ultrawideband temperature-dependent dielectric properties of animal liver tissue in the microwave frequency range.

PubMed

Lazebnik, Mariya; Converse, Mark C; Booske, John H; Hagness, Susan C

2006-04-07

The development of ultrawideband (UWB) microwave diagnostic and therapeutic technologies, such as UWB microwave breast cancer detection and hyperthermia treatment, is facilitated by accurate knowledge of the temperature- and frequency-dependent dielectric properties of biological tissues. To this end, we characterize the temperature-dependent dielectric properties of a representative tissue type-animal liver-from 0.5 to 20 GHz. Since discrete-frequency linear temperature coefficients are impractical and inappropriate for applications spanning wide frequency and temperature ranges, we propose a novel and compact data representation technique. A single-pole Cole-Cole model is used to fit the dielectric properties data as a function of frequency, and a second-order polynomial is used to fit the Cole-Cole parameters as a function of temperature. This approach permits rapid estimation of tissue dielectric properties at any temperature and frequency.

Photonic chirped radio-frequency generator with ultra-fast sweeping rate and ultra-wide sweeping range.

PubMed

Wun, Jhih-Min; Wei, Chia-Chien; Chen, Jyehong; Goh, Chee Seong; Set, S Y; Shi, Jin-Wei

2013-05-06

A high-performance photonic sweeping-frequency (chirped) radio-frequency (RF) generator has been demonstrated. By use of a novel wavelength sweeping distributed-feedback (DFB) laser, which is operated based on the linewidth enhancement effect, a fixed wavelength narrow-linewidth DFB laser, and a wideband (dc to 50 GHz) photodiode module for the hetero-dyne beating RF signal generation, a very clear chirped RF waveform can be captured by a fast real-time scope. A very-high frequency sweeping rate (10.3 GHz/μs) with an ultra-wide RF frequency sweeping range (~40 GHz) have been demonstrated. The high-repeatability (~97%) in sweeping frequency has been verified by analyzing tens of repetitive chirped waveforms.

High precision spectroscopy and imaging in THz frequency range

NASA Astrophysics Data System (ADS)

Vaks, Vladimir L.

2014-03-01

Application of microwave methods for development of the THz frequency range has resulted in elaboration of high precision THz spectrometers based on nonstationary effects. The spectrometers characteristics (spectral resolution and sensitivity) meet the requirements for high precision analysis. The gas analyzers, based on the high precision spectrometers, have been successfully applied for analytical investigations of gas impurities in high pure substances. These investigations can be carried out both in absorption cell and in reactor. The devices can be used for ecological monitoring, detecting the components of chemical weapons and explosive in the atmosphere. The great field of THz investigations is the medicine application. Using the THz spectrometers developed one can detect markers for some diseases in exhaled air.

[Inefficiency of electrosmog-shielding mats. Part 2: radio frequency range].

PubMed

Leitgeb, N; Cech, R

2005-09-01

It could already be shown that electromagnetic shielding mats do not reduce but even enhance electric field exposure in daily life situations. By measurements and numerical simulations the claims of manufacturers were checked who pretend that radio frequency electromagnetic fields can be shielded to 99% and more, and transferred to earth by earth cables (if attached). It could be shown that in the radio frequency range such products do not fulfil the justified expectations of customers, but in most cases even cause the opposite. The results depend on the electric properties of the material. Good electric conductivity of shielding mats even considerably increases electromagnetic field exposure. To connect the mats with earth potential by an attached cable might increase the beliefs on a protective effect, however, this is not capable to enhance the shielding effect. The investigation demonstrates that in spite of references made to experts opinions manufacturers claims about the shielding efficiency of radio frequency fields are misleading and fool clients about the real situation. Overall, acquisition and use of electrosmog shielding mats must be discouraged. If at all, shielding can be reached by placing a shielding cover between the source and the person. However, even in this case, efficiency is much lower than promised by manufacturers and decreases even more if it is taken into account that the head naturally remains uncovered and hence unshielded.

AC electric field induced dielectrophoretic assembly behavior of gold nanoparticles in a wide frequency range

NASA Astrophysics Data System (ADS)

Liu, Weiyu; Wang, Chunhui; Ding, Haitao; Shao, Jinyou; Ding, Yucheng

2016-05-01

In this work, we focus on frequency-dependence of pearl chain formations (PCF) of gold nanoparticles driven by AC dielectrophoresis (DEP), especially in a low field-frequency range, where induced double-layer charging effect at ideally polarizable surfaces on particle DEP behavior and surrounding liquid motion need not be negligible. As field frequency varies, grown features of DEP assembly structures ranging from low-frequency non-bridged gap to high-frequency single gold nanoparticle-made nanowires bridging the electrodes are demonstrated experimentally. Specifically, at 10 kHz, a kind of novel channel-like structure with parallel opposing banks is formed at the center of interelectrode gap. In stark contrast, at 1 MHz, thin PCF with diameter of 100 nm is created along the shortest distance of the isolation spacing. Moreover, a particular conductive path of nanoparticle chains is produced at 1 MHz in a DEP device embedded with multiple floating electrodes. A theoretical framework taking into account field-induced double-layer polarization at both the particle/electrolyte and electrode/electrolyte interface is developed to correlate these experimental observations with induced-charge electrokinetic (ICEK) phenomenon. And a RC circuit model is helpful in accounting for the formation of this particular non-bridged channel-like structure induced by a low-frequency AC voltage. As compared to thin PCF formed at high field frequency that effectively short circuits the electrode pair, though it is difficult for complete PCF bridging to occur at low frequency, the non-bridged conducting microstructure has potential to further miniaturize the size of electrode gap fabricated by standard micromachining process and may find useful application in biochemical sensing.

An impedance bridge measuring the capacitance ratio in the high frequency range up to 1 MHz

NASA Astrophysics Data System (ADS)

Bee Kim, Dan; Kew Lee, Hyung; Kim, Wan-Seop

2017-02-01

This paper describes a 2-terminal-pair impedance bridge, measuring the capacitance ratio in the high frequency range up to 1 MHz. The bridge was configured with two voltage sources and a phase control unit which enabled the bridge balance by synchronizing the voltage sources with an enhanced phase resolution. Without employing the transformers such as inductive voltage divider, injection and detection transformers, etc, the bridge system is quite simple to set up, and the balance procedure is quick and easy. Using this dual-source coaxial bridge, the 1:1 and 10:1 capacitance ratios were measured with 1 pF-1 nF capacitors in the frequency range from 1 kHz to 1 MHz. The measurement values obtained by the dual-source bridge were then compared with reference values measured using a commercial precision capacitance bridge of AH2700A, the Z-matrix method developed by ourselves, and the 4-terminal-pair coaxial bridge by the Czech Metrological Institute. All the measurements agreed within the reference uncertainty range of an order of 10-6-10-5, proving the bridge ability as a trustworthy tool for measuring the capacitance ratio in the high frequency range.

Detection of Geomagnetic Pulsations of the Earth Using GPS-TEC Data

NASA Astrophysics Data System (ADS)

Koroglu, Ozan; Arikan, Feza; Köroǧlu, Meltem; Sabri Ozkazanc, Yakup

2016-07-01

The magnetosphere of the Earth is made up of both magnetic fields and plasma. In this layer, plasma waves propagate as Ultra Low Frequency (ULF) waves having mHz scale frequencies. ULF waves are produced due to complicated solar-geomagnetic interactions. In the literature, these ULF waves are defined as pulsations. The geomagnetic pulsations are classified into main two groups as continuous pulsations (Pc) and irregular pulsations (Pi). These pulsations can be determined by ionospheric parameters due to the complex lithosphere-ionosphere-magnetosphere coupling processes. Total Electron Content (TEC) is one of the most important parameters for investigating the variability of ionosphere. Global Positioning System (GPS) provides a cost-effective means for estimating TEC from GPS satellite orbital height of 20,000 km to the ground based receivers. Therefore, the time series of GPS-TEC inherently contains the above mentioned ULF waves. In this study, time series analysis of GPS-TEC is carried out by applying periodogram method to the mid-latitude annual TEC data. After the analysis of GPS-TEC data obtained for GPS stations located in Central Europe and Turkey for 2011, it is observed that some of the fundamental frequencies that are indicators of Pc waves, diurnal and semi-diurnal periodicity and earth-free oscillations can be identified. These results will be used in determination of low frequency trend structure of magnetosphere and ionosphere. Further investigation of remaining relatively low magnitude frequencies, all Pi and Pc can be identified by using time and frequency domain techniques such as wavelet analysis. This study is supported by the joint TUBITAK 115E915 and joint TUBITAK114E092 and AS CR 14/001 projects.

Opto-electronic device for frequency standard generation and terahertz-range optical demodulation based on quantum interference

DOEpatents

Georgiades, Nikos P.; Polzik, Eugene S.; Kimble, H. Jeff

1999-02-02

An opto-electronic system and technique for comparing laser frequencies with large frequency separations, establishing new frequency standards, and achieving phase-sensitive detection at ultra high frequencies. Light responsive materials with multiple energy levels suitable for multi-photon excitation are preferably used for nonlinear mixing via quantum interference of different excitation paths affecting a common energy level. Demodulation of a carrier with a demodulation frequency up to 100's THZ can be achieved for frequency comparison and phase-sensitive detection. A large number of materials can be used to cover a wide spectral range including the ultra violet, visible and near infrared regions. In particular, absolute frequency measurement in a spectrum from 1.25 .mu.m to 1.66 .mu.m for fiber optics can be accomplished with a nearly continuous frequency coverage.

Radial Diffusion Coefficients Using E and B Field Data from the Van Allen Probes: Comparison with the CRRES Study

NASA Astrophysics Data System (ADS)

Ali, A.; Elkington, S. R.; Malaspina, D.

2014-12-01

The Van Allen radiation belts contain highly energetic particles which interact with a variety of plasma and MHD waves. Waves with frequencies in the ULF range are understood to play an important role in loss and acceleration of energetic particles. We are investigating the contributions from perturbations in both the magnetic and the electric fields in driving radial diffusion of charged particles and wish to probe two unanswered questions about ULF wave driven radial transport. First, how important are the fluctuations in the magnetic field compared with the fluctuations in the electric field in driving radial diffusion? Second, how does ULF wave power distribution in azimuth affect radial diffusion? Analytic treatments of the diffusion coefficients generally assume uniform distribution of power in azimuth but in situ measurements suggest otherwise. We present results from a study using the electric and magnetic field measurements from the Van Allen Probes to estimate the radial diffusion coefficients as a function of L and Kp. During the lifetime of the RBSP mission to date, there has been a dearth of solar activity. This compels us to consider Kp as the only time and activity dependent parameter instead of solar wind velocity and pressure.

A Novel Unit Cell for Active Switches in the Millimeter-Wave Frequency Range

NASA Astrophysics Data System (ADS)

Müller, Daniel; Scherer, Gunnar; Lewark, Ulrich J.; Massler, Hermann; Wagner, Sandrine; Tessmann, Axel; Leuther, Arnulf; Zwick, Thomas; Kallfass, Ingmar

2018-02-01

This paper presents a novel transistor unit cell which is intended to realize compact active switches in the high millimeter-wave frequency range. The unit cell consists of the combination of shunt and common gate transistor within a four-finger transistor cell, achieving gain in the amplifying state as well as good isolation in the isolating state. Gate width-dependent characteristics of the unit cell as well as the design of actual switch implementations are discussed in detail. To verify the concept, two switches, a single pole double throw (SPDT) switch and single pole quadruple throw (SP4T) switch, intended for the WR3 frequency range (220-325 GHz) were manufactured and characterized. The measured gain at 250 GHz is 4.6 and 2.2 dB for the SPDT and SP4T switch, respectively. An isolation of more than 24 dB for the SPDT switch and 12.8 dB for the SP4T switch was achieved.

Spontaneous otoacoustic emissions, threshold microstructure, and psychophysical tuning over a wide frequency range in humansa

PubMed Central

Baiduc, Rachael R.; Lee, Jungmee; Dhar, Sumitrajit

2014-01-01

Hearing thresholds have been shown to exhibit periodic minima and maxima, a pattern known as threshold microstructure. Microstructure has previously been linked to spontaneous otoacoustic emissions (SOAEs) and normal cochlear function. However, SOAEs at high frequencies (>4 kHz) have been associated with hearing loss or cochlear pathology in some reports. Microstructure would not be expected near these high-frequency SOAEs. Psychophysical tuning curves (PTCs), the expression of frequency selectivity, may also be altered by SOAEs. Prior comparisons of tuning between ears with and without SOAEs demonstrated sharper tuning in ears with emissions. Here, threshold microstructure and PTCs were compared at SOAE frequencies ranging between 1.2 and 13.9 kHz using subjects without SOAEs as controls. Results indicate: (1) Threshold microstructure is observable in the vicinity of SOAEs of all frequencies; (2) PTCs are influenced by SOAEs, resulting in shifted tuning curve tips, multiple tips, or inversion. High frequency SOAEs show a greater effect on PTC morphology. The influence of most SOAEs at high frequencies on threshold microstructure and PTCs is consistent with those at lower frequencies, suggesting that high-frequency SOAEs reflect the same cochlear processes that lead to SOAEs at lower frequencies. PMID:24437770

Opto-electronic device for frequency standard generation and terahertz-range optical demodulation based on quantum interference

DOEpatents

Georgiades, N.P.; Polzik, E.S.; Kimble, H.J.

1999-02-02

An opto-electronic system and technique for comparing laser frequencies with large frequency separations, establishing new frequency standards, and achieving phase-sensitive detection at ultra high frequencies are disclosed. Light responsive materials with multiple energy levels suitable for multi-photon excitation are preferably used for nonlinear mixing via quantum interference of different excitation paths affecting a common energy level. Demodulation of a carrier with a demodulation frequency up to 100`s THZ can be achieved for frequency comparison and phase-sensitive detection. A large number of materials can be used to cover a wide spectral range including the ultra violet, visible and near infrared regions. In particular, absolute frequency measurement in a spectrum from 1.25 {micro}m to 1.66 {micro}m for fiber optics can be accomplished with a nearly continuous frequency coverage. 7 figs.

A method to improve the range resolution in stepped frequency continuous wave radar

NASA Astrophysics Data System (ADS)

Kaczmarek, Paweł

2018-04-01

In the paper one of high range resolution methods - Aperture Sampling - was analysed. Unlike MUSIC based techniques it proved to be very efficient in terms of achieving unambiguous synthetic range profile for ultra-wideband stepped frequency continuous wave radar. Assuming that minimal distance required to separate two targets in depth (distance) corresponds to -3 dB width of received echo, AS provided a 30,8 % improvement in range resolution in analysed scenario, when compared to results of applying IFFT. Output data is far superior in terms of both improved range resolution and reduced side lobe level than used typically in this area Inverse Fourier Transform. Furthermore it does not require prior knowledge or an estimate of number of targets to be detected in a given scan.

Magnetic Resonance Relaxometry at Low and Ultra low Fields.

PubMed

Volegov, P; Flynn, M; Kraus, R; Magnelind, P; Matlashov, A; Nath, P; Owens, T; Sandin, H; Savukov, I; Schultz, L; Urbaitis, A; Zotev, V; Espy, M

2010-01-01

Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are ubiquitous tools in science and medicine. NMR provides powerful probes of local and macromolecular chemical structure and dynamics. Recently it has become possible and practical to perform MR at very low fields (from 1 μT to 1 mT), the so-called ultra-low field (ULF) regime. Pulsed pre-polarizing fields greatly enhance the signal strength and allow flexibility in signal acquisition sequences. Improvements in SQUID sensor technology allow ultra-sensitive detection in a pulsed field environment.In this regime the proton Larmor frequencies (1 Hz - 100 kHz) of ULF MR overlap (on a time scale of 10 μs to 100 ms) with "slow" molecular dynamic processes such as diffusion, intra-molecular motion, chemical reactions, and biological processes such as protein folding, catalysis and ligand binding. The frequency dependence of relaxation at ultra-low fields may provide a probe for biomolecular dynamics on the millisecond timescale (protein folding and aggregation, conformational motions of enzymes, binding and structural fluctuations of coupled domains in allosteric mechanisms) relevant to host-pathogen interactions, biofuels, and biomediation. Also this resonance-enhanced coupling at ULF can greatly enhance contrast in medical applications of ULF-MRI resulting in better diagnostic techniques.We have developed a number of instruments and techniques to study relaxation vs. frequency at the ULF regime. Details of the techniques and results are presented.Ultra-low field methods are already being applied at LANL in brain imaging, and detection of liquid explosives at airports. However, the potential power of ultra-low field MR remains to be fully exploited.

Effective conductivity and permittivity of unsaturated porous materials in the frequency range 1 mHz–1GHz

PubMed Central

Revil, A

2013-01-01

A model combining low-frequency complex conductivity and high-frequency permittivity is developed in the frequency range from 1 mHz to 1 GHz. The low-frequency conductivity depends on pore water and surface conductivities. Surface conductivity is controlled by the electrical diffuse layer, the outer component of the electrical double layer coating the surface of the minerals. The frequency dependence of the effective quadrature conductivity shows three domains. Below a critical frequency fp, which depends on the dynamic pore throat size Λ, the quadrature conductivity is frequency dependent. Between fp and a second critical frequency fd, the quadrature conductivity is generally well described by a plateau when clay minerals are present in the material. Clay-free porous materials with a narrow grain size distribution are described by a Cole-Cole model. The characteristic frequency fd controls the transition between double layer polarization and the effect of the high-frequency permittivity of the material. The Maxwell-Wagner polarization is found to be relatively negligible. For a broad range of frequencies below 1 MHz, the effective permittivity exhibits a strong dependence with the cation exchange capacity and the specific surface area. At high frequency, above the critical frequency fd, the effective permittivity reaches a high-frequency asymptotic limit that is controlled by the two Archie's exponents m and n like the low-frequency electrical conductivity. The unified model is compared with various data sets from the literature and is able to explain fairly well a broad number of observations with a very small number of textural and electrochemical parameters. It could be therefore used to interpret induced polarization, induction-based electromagnetic methods, and ground penetrating radar data to characterize the vadose zone. PMID:23576823

A wide-frequency-range air-jet shaker

NASA Technical Reports Server (NTRS)

Herr, Robert W

1957-01-01

This paper presents a description of a simple air-jet shaker. Its force can be calibrated statically and appears to be constant with frequency. It is relatively easy to use, and it has essentially massless characteristics. This shaker is applied to define the unstable branch of a frequency-response curve obtained for a nonlinear spring with a single degree of freedom.

Modeling and performance analysis of an all-optical photonic microwave filter in the frequency range of 0.01-15 GHz

NASA Astrophysics Data System (ADS)

Aguayo-Rodríguez, Gustavo; Zaldívar-Huerta, Ignacio E.; Rodríguez-Asomoza, Jorge; García-Juárez, Alejandro; Alonso-Rubio, Paul

2010-01-01

The generation, distribution and processing of microwave signals in the optical domain is a topic of research due to many advantages such as low loss, light weight, broadband width, and immunity to electromagnetic interference. In this sense, a novel all-optical microwave photonic filter scheme is proposed and experimentally demonstrated in the frequency range of 0.01-15.0 GHz. A microwave signal generated by optical mixing drives the microwave photonic filter. Basically, photonic filter is composed by a multimode laser diode, an integrated Mach- Zehnder intensity modulator, and 28.3-Km of single-mode standard fiber. Frequency response of the microwave photonic filter depends of the emission spectral characteristics of the multimode laser diode, the physical length of the single-mode standard fiber, and the chromatic dispersion factor associated to this type of fiber. Frequency response of the photonic filter is composed of a low-pass band centered at zero frequency, and several band-pass lobes located periodically on the microwave frequency range. Experimental results are compared by means of numerical simulations in Matlab exhibiting a small deviation in the frequency range of 0.01-5.0 GHz. However, this deviation is more evident when higher frequencies are reached. In this paper, we evaluate the causes of this deviation in the range of 5.0-15.0 GHz analyzing the parameters involved in the frequency response. This analysis permits to improve the performance of the photonic microwave filter to higher frequencies.

Double Brillouin frequency spaced multiwavelength Brillouin-erbium fiber laser with 50 nm tuning range

NASA Astrophysics Data System (ADS)

Zhao, J. F.; Liao, T. Q.; Zhang, C.; Zhang, R. X.; Miao, C. Y.; Tong, Z. R.

2012-09-01

A 50 nm tuning range multiwavelength Brillouin-erbium fiber laser (MWBEFL) with double Brillouin frequency spacing is presented. Two separated gain blocks with symmetrical architecture, consisted by erbium-doped fiber amplifiers (EDFAs) and Brillouin gain media, are used to generate double Brillouin frequency spacing. The wider tuning range is realized by eliminating the self-lasing cavity modes existing in conventional MWBEFLs because of the absence of the physical mirrors at the ends of the linear cavity. The Brillouin pump (BP) is preamplified by the EDFA before entering the single-mode fiber (SMF), which leads to the reduction of threshold power and the generation enhancement of Brillouin Stokes (BS) signals. Four channels with 0.176 nm spacing are achieved at 2 mW BP power and 280 mW 980 nm pump power which can be tuned from 1525 to 1575 nm.

International Space Station United States Laboratory Module Water Recovery Management Subsystem Verification from Flight 5A to Stage ULF2

NASA Technical Reports Server (NTRS)

Williams, David E.; Labuda, Laura

2009-01-01

The International Space Station (ISS) Environmental Control and Life Support (ECLS) system comprises of seven subsystems: Atmosphere Control and Supply (ACS), Atmosphere Revitalization (AR), Fire Detection and Suppression (FDS), Temperature and Humidity Control (THC), Vacuum System (VS), Water Recovery and Management (WRM), and Waste Management (WM). This paper provides a summary of the nominal operation of the United States (U.S.) Laboratory Module WRM design and detailed element methodologies utilized during the Qualification phase of the U.S. Laboratory Module prior to launch and the Qualification of all of the modification kits added to it from Flight 5A up and including Stage ULF2.

Explaining the dynamics of the ultra-relativistic third Van Allen radiation belt

DOE PAGES

Mann, I. R.; Ozeke, L. G.; Murphy, K. R.; ...

2016-06-20

Since the discovery of the Van Allen radiation belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron radiation belt. Current theory asserts that loss in the heart of the outer belt, essential to the formation of the third belt, must be controlled by high-frequency plasma wave–particle scattering into the atmosphere, via whistler mode chorus, plasmaspheric hiss, or electromagnetic ion cyclotron waves. However, this has failed to accurately reproduce the third belt. In this paper, using a data-driven, time-dependent specification of ultra-low-frequency (ULF) waves we showmore » for the first time how the third radiation belt is established as a simple, elegant consequence of storm-time extremely fast outward ULF wave transport. High-frequency wave–particle scattering loss into the atmosphere is not needed in this case. Finally, when rapid ULF wave transport coupled to a dynamic boundary is accurately specified, the sensitive dynamics controlling the enigmatic ultra-relativistic third radiation belt are naturally explained.« less

Explaining the dynamics of the ultra-relativistic third Van Allen radiation belt

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

Mann, I. R.; Ozeke, L. G.; Murphy, K. R.

Since the discovery of the Van Allen radiation belts over 50 years ago, an explanation for their complete dynamics has remained elusive. Especially challenging is understanding the recently discovered ultra-relativistic third electron radiation belt. Current theory asserts that loss in the heart of the outer belt, essential to the formation of the third belt, must be controlled by high-frequency plasma wave–particle scattering into the atmosphere, via whistler mode chorus, plasmaspheric hiss, or electromagnetic ion cyclotron waves. However, this has failed to accurately reproduce the third belt. In this paper, using a data-driven, time-dependent specification of ultra-low-frequency (ULF) waves we showmore » for the first time how the third radiation belt is established as a simple, elegant consequence of storm-time extremely fast outward ULF wave transport. High-frequency wave–particle scattering loss into the atmosphere is not needed in this case. Finally, when rapid ULF wave transport coupled to a dynamic boundary is accurately specified, the sensitive dynamics controlling the enigmatic ultra-relativistic third radiation belt are naturally explained.« less

An Ultrasonic Multiple-Access Ranging Core Based on Frequency Shift Keying Towards Indoor Localization

PubMed Central

Segers, Laurent; Van Bavegem, David; De Winne, Sam; Braeken, An; Touhafi, Abdellah; Steenhaut, Kris

2015-01-01

This paper describes a new approach and implementation methodology for indoor ranging based on the time difference of arrival using code division multiple access with ultrasound signals. A novel implementation based on a field programmable gate array using finite impulse response filters and an optimized correlation demodulator implementation for ultrasound orthogonal signals is developed. Orthogonal codes are modulated onto ultrasound signals using frequency shift keying with carrier frequencies of 24.5 kHz and 26 kHz. This implementation enhances the possibilities for real-time, embedded and low-power tracking of several simultaneous transmitters. Due to the high degree of parallelism offered by field programmable gate arrays, up to four transmitters can be tracked simultaneously. The implementation requires at most 30% of the available logic gates of a Spartan-6 XC6SLX45 device and is evaluated on accuracy and precision through several ranging topologies. In the first topology, the distance between one transmitter and one receiver is evaluated. Afterwards, ranging analyses are applied between two simultaneous transmitters and one receiver. Ultimately, the position of the receiver against four transmitters using trilateration is also demonstrated. Results show enhanced distance measurements with distances ranging from a few centimeters up to 17 m, while keeping a centimeter-level accuracy. PMID:26263986

Cryocooled terahertz photoconductive detector system with background-limited performance in 1.5-4 THz frequency range.

PubMed

Aoki, Makoto; Hiromoto, Norihisa

2015-10-01

We describe a 4-K-cryocooled dual-band terahertz (THz) photoconductive detector system with background-limited performance. The detector system comprises two THz photoconductive detectors covering a response in a wide frequency range from 1.5 to 4 THz, low noise amplifiers, optical low-pass filters to eliminate input radiation of higher frequencies, and a mechanical 4 K Gifford-McMahon refrigerator that provides practical and convenient operation without a liquid He container. The electrical and optical performances of the THz detector system were evaluated at a detector temperature of 4 K under 300 K background radiation. We proved that the detector system can achieve background-limited noise-equivalent-power on the order of 10(-14) W/Hz(1/2) in the frequency range from 1.5 to 4 THz even if the vibration noise of the mechanical refrigerator is present.

An optimal frequency range for assessing the pressure reactivity index in patients with traumatic brain injury.

PubMed

Howells, Tim; Johnson, Ulf; McKelvey, Tomas; Enblad, Per

2015-02-01

The objective of this study was to identify the optimal frequency range for computing the pressure reactivity index (PRx). PRx is a clinical method for assessing cerebral pressure autoregulation based on the correlation of spontaneous variations of arterial blood pressure (ABP) and intracranial pressure (ICP). Our hypothesis was that optimizing the methodology for computing PRx in this way could produce a more stable, reliable and clinically useful index of autoregulation status. The patients studied were a series of 131 traumatic brain injury patients. Pressure reactivity indices were computed in various frequency bands during the first 4 days following injury using bandpass filtering of the input ABP and ICP signals. Patient outcome was assessed using the extended Glasgow Outcome Scale (GOSe). The optimization criterion was the strength of the correlation with GOSe of the mean index value over the first 4 days following injury. Stability of the indices was measured as the mean absolute deviation of the minute by minute index value from 30-min moving averages. The optimal index frequency range for prediction of outcome was identified as 0.018-0.067 Hz (oscillations with periods from 55 to 15 s). The index based on this frequency range correlated with GOSe with ρ=-0.46 compared to -0.41 for standard PRx, and reduced the 30-min variation by 23%.

A wide-range variable-frequency resonant tunneling diode oscillator using a variable resonator suitable for simple MEMS process

NASA Astrophysics Data System (ADS)

Yamashita, Takashi; Nakano, Daisuke; Mori, Masayuki; Maezawa, Koichi

2018-04-01

A resonant tunneling diode oscillator having a wide frequency variation range based on a novel MEMS resonator was proposed, which exploits the change in the signal propagation velocity on a coplanar waveguide according to a movable ground plane. First, we discussed the velocity modulation mechanism, and clarified the importance of the dielectric constant of the substrate. Then, a prototype device oscillating in a 10 to 20 GHz frequency range was fabricated to demonstrate the basic operation. A large and continuous increase in the oscillation frequency of about two times was achieved with this device. This is promising for various applications including THz spectroscopy.

Global Low Frequency Protein Motions in Long-Range Allosteric Signaling

NASA Astrophysics Data System (ADS)

McLeish, Tom; Rogers, Thomas; Townsend, Philip; Burnell, David; Pohl, Ehmke; Wilson, Mark; Cann, Martin; Richards, Shane; Jones, Matthew

2015-03-01

We present a foundational theory for how allostery can occur as a function of low frequency dynamics without a change in protein structure. Elastic inhomogeneities allow entropic ``signalling at a distance.'' Remarkably, many globular proteins display just this class of elastic structure, in particular those that support allosteric binding of substrates (long-range co-operative effects between the binding sites of small molecules). Through multi-scale modelling of global normal modes we demonstrate negative co-operativity between the two cAMP ligands without change to the mean structure. Crucially, the value of the co-operativity is itself controlled by the interactions around a set of third allosteric ``control sites.'' The theory makes key experimental predictions, validated by analysis of variant proteins by a combination of structural biology and isothermal calorimetry. A quantitative description of allostery as a free energy landscape revealed a protein ``design space'' that identified the key inter- and intramolecular regulatory parameters that frame CRP/FNR family allostery. Furthermore, by analyzing naturally occurring CAP variants from diverse species, we demonstrate an evolutionary selection pressure to conserve residues crucial for allosteric control. The methodology establishes the means to engineer allosteric mechanisms that are driven by low frequency dynamics.

A Constant Energy-Per-Cycle Ring Oscillator Over a Wide Frequency Range for Wireless Sensor Nodes

PubMed Central

Lee, Inhee; Sylvester, Dennis; Blaauw, David

2016-01-01

This paper presents an energy-efficient oscillator for wireless sensor nodes (WSNs). It avoids short-circuit current by minimizing the time spent in the input voltage range from Vthn to [Vdd − |Vthp|]. A current-feeding scheme with gate voltage control enables the oscillator to operate over a wide frequency range. A test chip is fabricated in a 0.18 μm CMOS process. The measurements show that the proposed oscillator achieves a constant energy-per-cycle (EpC) of 0.8 pJ/cycle over the 21–60 MHz frequency range and is more efficient than a conventional current-starved ring oscillator (CSRO) below 300 kHz at 1.8 V supply voltage. As an application example, the proposed oscillator is implemented in a switched-capacitor DC–DC converter. The converter is 11%–56% more efficient for load power values ranging from 583 pW to 2.9 nW than a converter using a conventional CSRO. PMID:27546899

A Constant Energy-Per-Cycle Ring Oscillator Over a Wide Frequency Range for Wireless Sensor Nodes.

PubMed

Lee, Inhee; Sylvester, Dennis; Blaauw, David

2016-03-01

This paper presents an energy-efficient oscillator for wireless sensor nodes (WSNs). It avoids short-circuit current by minimizing the time spent in the input voltage range from V thn to [ V dd - | V thp |]. A current-feeding scheme with gate voltage control enables the oscillator to operate over a wide frequency range. A test chip is fabricated in a 0.18 μm CMOS process. The measurements show that the proposed oscillator achieves a constant energy-per-cycle (EpC) of 0.8 pJ/cycle over the 21-60 MHz frequency range and is more efficient than a conventional current-starved ring oscillator (CSRO) below 300 kHz at 1.8 V supply voltage. As an application example, the proposed oscillator is implemented in a switched-capacitor DC-DC converter. The converter is 11%-56% more efficient for load power values ranging from 583 pW to 2.9 nW than a converter using a conventional CSRO.

The new geophysical observatory in Northern Caucasus (Elbrus volcanic area) and results of studies of ULF magnetic variations preceding strong geodynamic events

NASA Astrophysics Data System (ADS)

Sobissevitch, Leonid E.; Sobissevitch, Alex L.; Kanonidi, Konstantin Kh.; Filippov, Ivan N.

2010-05-01

The new geophysical observatory for fundamental scientific studies of geophysical processes in the Elbrus volcanic area (Northern Caucasus) has been organized recently as a result of merging of five geophysical laboratories positioned round the Elbrus volcano and equipped with modern geophysical instruments including broadband tri-axial seismometers, quartz tilt-meters, magnetic variometers, geo-acoustic sensors, hi-precision distributed thermal sensors, gravimeters, and network-enabled data acquisition systems with precise GPS-timing and integrated monitoring of auxiliary parameters (variations on ambient humidity, atmospheric pressure etc). Two laboratories are located in the horizontal 4.3 km deep tunnel drilled under the mount Andyrchi, about 20 km from the Elbrus volcano. Analysis of multi-parameter streams of experimental data allows one to study the structure of geophysical wave fields induced by earthquakes and regional catastrophic events (including snow avalanches). On the basis of continuous observations carried out since 2007 there have been determined anomalous wave forms in ULF geomagnetic variations preceding strong seismic events with magnitude 7 or more. Mentioned wave forms may be natively related to processes of evolution of dilatational structures in a domain of forthcoming seismic event. Specific patterns in anomalous ULF wave forms are distinguished for undersea earthquakes and for earthquakes responsible for triggering tsunami events. Thus, it is possible to consider development of a future technology to suggest the possible area and the time frame of such class of catastrophic events with additional reference to forecast information (including acoustic, hydro-acoustic and geo-acoustic) being concurrently analyzed.

Tuning the resonance frequencies and mode shapes in a large range multi-degree of freedom micromirror.

PubMed

Morrison, Jessica; Imboden, Matthias; Bishop, David J

2017-04-03

The ability to actively shift the primary resonance of a 2D scanning micromirror allows the user to set the scanning direction, set the scanning frequency, and lift otherwise degenerate modes in a symmetrically designed system. In most cases, resonant scanning micromirrors require frequency stability in order to perform imaging and projection functions properly. This paper suggests a method to tune the tip and tilt resonant frequencies in real time while actively suppressing or allowing degeneracy of the two modes in a symmetric electrothermal micromirror. We show resonant frequency tuning with a range of degeneracy separation of 470 Hz or by approximately ±15% and controllable coupling.

Nanostructured composite layers for electromagnetic shielding in the GHz frequency range

NASA Astrophysics Data System (ADS)

Suchea, M.; Tudose, I. V.; Tzagkarakis, G.; Kenanakis, G.; Katharakis, M.; Drakakis, E.; Koudoumas, E.

2015-10-01

We report on preliminary results regarding the applicability of nanostructured composite layers for electromagnetic shielding in the frequency range of 4-20 GHz. Various combinations of materials were employed including poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), polyaniline, graphene nanoplatelets, carbon nanotubes, Cu nanoparticles and Poly(vinyl alcohol). As shown, paint-like nanocomposite layers consisting of graphene nanoplatelets, polyaniline PEDOT:PSS and Poly(vinyl alcohol) can offer quite effective electromagnetic shielding, similar or even better than that of commercial products, the response strongly depending on their thickness and resistivity.

Thrombolysis using multi-frequency high intensity focused ultrasound at MHz range: an in vitro study

NASA Astrophysics Data System (ADS)

Suo, Dingjie; Guo, Sijia; Lin, Weili; Jiang, Xiaoning; Jing, Yun

2015-09-01

High intensity focused ultrasound (HIFU) based thrombolysis has emerged as a promising drug-free treatment approach for ischemic stroke. The large amount of acoustic power required by this approach, however, poses a critical challenge to the future clinical translation. In this study, multi-frequency acoustic waves at MHz range (near 1.5 MHz) were introduced as HIFU excitations to reduce the required power for treatment as well as the treatment time. In vitro bovine blood clots weighing around 150 mg were treated by single-frequency and multi-frequency HIFU. The pulse length was 2 ms for all experiments except the ones where the duty cycle was changed. It was found that dual-frequency thrombolysis efficiency was statistically better than single-frequency under the same acoustic power and excitation condition. When varying the acoustic power but fixing the duty cycle at 5%, it was found that dual-frequency ultrasound can save almost 30% power in order to achieve the same thrombolysis efficiency. In the experiment where the duty cycle was increased from 0.5% to 10%, it was shown that dual-frequency ultrasound can achieve the same thrombolysis efficiency with only half of the duty cycle of single-frequency. Dual-frequency ultrasound could also accelerate the thrombolysis by a factor of 2-4 as demonstrated in this study. No significant differences were found between dual-frequencies with different frequency differences (0.025, 0.05, and 0.1 MHz) and between dual-frequency and triple-frequency. The measured cavitation doses of dual-frequency and triple-frequency excitations were at about the same level but both were significantly higher than that of single-frequency.

Third-harmonic entanglement and Einstein-Podolsky-Rosen steering over a frequency range of more than an octave

NASA Astrophysics Data System (ADS)

Olsen, M. K.

2018-03-01

The development of quantum technologies which use quantum states of the light field interacting with other systems creates a demand for such states over wide frequency ranges. In this work we compare the bipartite entanglement and Einstein-Podolsky-Rosen (EPR) -steering properties of the two different parametric schemes which produce third-harmonic optical fields from an input field at the fundamental frequency. The first scheme uses second harmonic cascaded with sum-frequency generation, while the second uses triply degenerate four- wave mixing, also known as direct third-harmonic generation. We find that both schemes produce continuous-variable bipartite entanglement and EPR steering over a frequency range which has previously been unobtainable. The direct scheme produces a greater degree of EPR steering, while the cascaded scheme allows for greater flexibility in having three available bipartitions, thus allowing for greater flexibility in the tailoring of light matter interfaces. There are also parameter regimes in both for which classical mean-field analyses fail to predict the mean-field solutions. Both schemes may be very useful for applications in quantum communication and computation networks, as well as providing for quantum interfaces between a wider range of light and atomic ensembles than is presently practicable.

Alteration of frequency range for binaural beats in acute low-tone hearing loss.

PubMed

Karino, Shotaro; Yamasoba, Tatsuya; Ito, Ken; Kaga, Kimitaka

2005-01-01

The effect of acute low-tone sensorineural hearing loss (ALHL) on the interaural frequency difference (IFD) required for perception of binaural beats (BBs) was investigated in 12 patients with unilateral ALHL and 7 patients in whom ALHL had lessened. A continuous pure tone of 30 dB sensation level at 250 Hz was presented to the contralateral, normal-hearing ear. The presence of BBs was determined by a subjective yes-no procedure as the frequency of a loudness-balanced test tone was gradually adjusted around 250 Hz in the affected ear. The frequency range in which no BBs were perceived (FRNB) was significantly wider in the patients with ALHL than in the controls, and FRNBs became narrower in the recovered ALHL group. Specifically, detection of slow BBs with a small IFD was impaired in this limited (10 s) observation period. The significant correlation between the hearing level at 250 Hz and FRNBs suggests that FRNBs represent the degree of cochlear damage caused by ALHL.

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.

A theoretical study on directivity control of multiple-loudspeaker system with a quadrupole radiation pattern in low frequency range

NASA Astrophysics Data System (ADS)

Irwansyah, Kuse, Naoyuki; Usagawa, Tsuyoshi

2017-08-01

Directivity pattern of an ordinary loudspeaker becomes more directive at higher frequencies. However, because a single loudspeaker tends to radiate uniformly in all directions at low frequencies, reverberation from surrounding building walls may affect speech intelligibility when installing a multiple-loudspeaker system at crossroads. As an alternative, a sharply directive sound source is recommended to be used, but in many cases the directivity of an ordinary loudspeaker is less sharp at lower frequencies. Therefore, in order to overcome such a limitation, this paper discusses the possibility of using four loudspeakers under active control to realize a quadrupole radiation pattern in low frequency range. In this study, the radiation pattern of a primary loudspeaker and three secondary loudspeakers has been modelled. By placing the loudspeakers close together in the direction of 0°, 90°, 180°, and 270°, it was theoretically demonstrated that a quadrupole radiation pattern can be shaped in the target frequency range up to 600 Hz by simply controlling the directivity in three of four directions which are 45°, 135°, 225°, and 315°. Although, the radiation pattern model is far from realistic configurations and conditions, it is possible to realize a quadrupole radiation pattern in the low frequency range.

Slope-assisted BOTDA based on vector SBS and frequency-agile technique for wide-strain-range dynamic measurements.

PubMed

Zhou, Dengwang; Dong, Yongkang; Wang, Benzhang; Jiang, Taofei; Ba, Dexin; Xu, Pengbai; Zhang, Hongying; Lu, Zhiwei; Li, Hui

2017-02-06

We present a slope-assisted BOTDA system based on the vector stimulated Brillouin scattering (SBS) and frequency-agile technique (FAT) for the wide-strain-range dynamic measurement. A dimensionless coefficient K defined as the ratio of Brillouin phase-shift to gain is employed to demodulate the strain of the fiber, and it is immune to the power fluctuation of pump pulse and has a linear relation of the frequency detuning for the continuous pump and Stokes waves. For a 30ns-square pump pulse, the available frequency span of the K spectrum can reach up to 200MHz, which is larger than fourfold of 48MHz-linewidth of Brillouin gain spectrum. For a single-slope assisted BOTDA, dynamic strain measurement with the maximum strain of 2467.4με and the vibration frequency components of 10.44Hz and 20.94Hz is obtained. For a multi-slope-assisted BOTDA, dynamic measurement with the strain variation up to 5372.9με and the vibration frequency components of 5.58Hz and 11.14Hz is achieved by using FAT to extend the strain range.

LTP in Hippocampal Area CA1 Is Induced by Burst Stimulation over a Broad Frequency Range Centered around Delta

ERIC Educational Resources Information Center

Grover, Lawrence M.; Kim, Eunyoung; Cooke, Jennifer D.; Holmes, William R.

2009-01-01

Long-term potentiation (LTP) is typically studied using either continuous high-frequency stimulation or theta burst stimulation. Previous studies emphasized the physiological relevance of theta frequency; however, synchronized hippocampal activity occurs over a broader frequency range. We therefore tested burst stimulation at intervals from 100…

One palatal implant for skeletal anchorage--frequency and range of indications.

PubMed

Krieger, Elena; Yildizhan, Zeynep; Wehrbein, Heinrich

2015-04-21

Aim of this investigation was to analyze the frequency and range of indications of orthodontic treatments using one palatal implant for skeletal anchorage, in a time frame of four years. A sample was comprised by viewing retrospectively the patient collective of a specialized university clinic who started orthodontic treatment in the time frame 01/09-12/12. Inclusion criterion was the first application of a superstructure within the investigated period after successful insertion of a palatal implant (Ortho-System®, Straumann, Basel, Switzerland). Frequency and range of indications of the conducted skeletally anchored tooth movement were determined by analyzing the individual patient documentation such as medical records, radiographs and casts. From a total of 1350 patients who started orthodontic treatment in this period met 56 (=4.2%) the inclusion criterion. In 85.7% of this sample was sagittal orthodontic tooth movement conducted, most frequently mesialization of ≥1 tooth (44.6%). Vertical tooth movement was in 57.1% of the sample performed, mostly extrusion of ≥1 tooth (34%). In 33.9% of the sample was ≥1 displaced tooth orthodontically relocated. One or two upper incisors were in 16.1% of the sample permanently replaced by the superstructure, all but one even after orthodontic treatment. In 66.1% of all cases were multi-functional anchorage challenges performed. 4.2 % of all treated patients within the investigated period required orthodontic treatment with skeletal anchorage (palatal implant), mainly for performing sagittal tooth movement (mesialization). The palatal implant was primarily used for multi-functional anchorage purposes, including skeletally anchored treatment in the mandible.

Acoustic behavior of Halobacterium salinarum gas vesicles in the high frequency range: experiments and modeling

PubMed Central

Cherin, Emmanuel; Melis, Johan M.; Bourdeau, Raymond W.; Yin, Melissa; Kochmann, Dennis M.; Foster, F. Stuart; Shapiro, Mikhail G.

2017-01-01

Gas vesicles are a new and unique class of biologically derived ultrasound contrast agents with sub-micron size whose acoustic properties have not been fully elucidated. In this study, we investigated the acoustic collapse pressure and behavior of Halobacterium salinarum gas vesicles at transmit center frequencies ranging from 12.5 to 27.5 MHz. The acoustic collapse pressure was found to be above 550 kPa at all frequencies, 9 fold higher than the critical pressure observed in hydrostatic conditions. We show that gas vesicles behave non-linearly when exposed to ultrasound at incident pressure ranging from 160 kPa to the collapse pressure, and generate second harmonic amplitudes of −2 to −6 dB below the fundamental in media with viscosities ranging from 0.89 to 8 mPa.s. Simulations performed using a Rayleigh-Plesset type model accounting for buckling, and a dynamic finite element analysis, suggest that buckling is the mechanism behind the generation of harmonics. We found good agreement between the level of second harmonic relative to the fundamental measured at 20 MHz and the Rayleigh-Plesset model predictions. Finite element simulations extended these findings to a non-spherical geometry, confirmed that the acoustic buckling pressure corresponds to the critical pressure in hydrostatic conditions, and support the hypothesis of limited gas flow across the GV shell during the compression phase in the frequency range investigated. From simulations, estimates of GV bandwidth-limited scattering indicate that a single GV has a scattering cross-section comparable to that of a red blood cell. These findings will inform the development of GV-based contrast agents and pulse sequences to optimize their detection with ultrasound. PMID:28258771

A Technique for Real-Time Ionospheric Ranging Error Correction Based On Radar Dual-Frequency Detection

NASA Astrophysics Data System (ADS)

Lyu, Jiang-Tao; Zhou, Chen

2017-12-01

Ionospheric refraction is one of the principal error sources for limiting the accuracy of radar systems for space target detection. High-accuracy measurement of the ionospheric electron density along the propagation path of radar wave is the most important procedure for the ionospheric refraction correction. Traditionally, the ionospheric model and the ionospheric detection instruments, like ionosonde or GPS receivers, are employed for obtaining the electron density. However, both methods are not capable of satisfying the requirements of correction accuracy for the advanced space target radar system. In this study, we propose a novel technique for ionospheric refraction correction based on radar dual-frequency detection. Radar target range measurements at two adjacent frequencies are utilized for calculating the electron density integral exactly along the propagation path of the radar wave, which can generate accurate ionospheric range correction. The implementation of radar dual-frequency detection is validated by a P band radar located in midlatitude China. The experimental results present that the accuracy of this novel technique is more accurate than the traditional ionospheric model correction. The technique proposed in this study is very promising for the high-accuracy radar detection and tracking of objects in geospace.

The influence of flight speed on the ranging performance of bats using frequency modulated echolocation pulses

NASA Astrophysics Data System (ADS)

Boonman, Arjan M.; Parsons, Stuart; Jones, Gareth

2003-01-01

Many species of bat use ultrasonic frequency modulated (FM) pulses to measure the distance to objects by timing the emission and reception of each pulse. Echolocation is mainly used in flight. Since the flight speed of bats often exceeds 1% of the speed of sound, Doppler effects will lead to compression of the time between emission and reception as well as an elevation of the echo frequencies, resulting in a distortion of the perceived range. This paper describes the consequences of these Doppler effects on the ranging performance of bats using different pulse designs. The consequences of Doppler effects on ranging performance described in this paper assume bats to have a very accurate ranging resolution, which is feasible with a filterbank receiver. By modeling two receiver types, it was first established that the effects of Doppler compression are virtually independent of the receiver type. Then, used a cross-correlation model was used to investigate the effect of flight speed on Doppler tolerance and range-Doppler coupling separately. This paper further shows how pulse duration, bandwidth, function type, and harmonics influence Doppler tolerance and range-Doppler coupling. The influence of each signal parameter is illustrated using calls of several bat species. It is argued that range-Doppler coupling is a significant source of error in bat echolocation, and various strategies bats could employ to deal with this problem, including the use of range rate information are discussed.

PROPERTIES OF PHANTOM TISSUE-LIKE POLYMETHYLPENTENE IN THE FREQUENCY RANGE 20–70 MHZ

PubMed Central

Madsen, Ernest L; Deaner, Meagan E; Mehi, James

2011-01-01

Quantitative ultrasound (QUS) has been employed to characterize soft tissues at ordinary abdominal ultrasound frequencies (2–15 MHz) and is beginning application at high frequencies (20–70 MHz). For example, backscatter and attenuation coefficients can be estimated in vivo using a reference phantom. At high frequencies it is crucial that reverberations do not compromise the measurements. Such reverberations can occur between the phantom's scanning window and transducer components as well as within the scanning window between its surfaces. Transducers are designed to minimize reverberations between the transducer and soft tissue. Thus, the acoustic impedance of a phantom scanning window should be tissue-like; polymethylpentene (TPX) is commonly used because of its tissue-like acoustic impedance. For QUS it is also crucial to correct for the transmission coefficient of the scanning window. Computation of the latter requires knowledge of the ultrasonic properties, viz, density, speed and attenuation coefficients. This work reports values for the ultrasonic properties of two versions of TPX over the high frequency range. One form (TPX film) is used as a scanning window on high frequency phantoms, and at 40 MHz and 22°C was found to have an attenuation coefficient of 120 dB/cm and a propagation speed of 2093 m/s. PMID:21723451

Acoustic Behavior of Halobacterium salinarum Gas Vesicles in the High-Frequency Range: Experiments and Modeling.

PubMed

Cherin, Emmanuel; Melis, Johan M; Bourdeau, Raymond W; Yin, Melissa; Kochmann, Dennis M; Foster, F Stuart; Shapiro, Mikhail G

2017-05-01

Gas vesicles (GVs) are a new and unique class of biologically derived ultrasound contrast agents with sub-micron size whose acoustic properties have not been fully elucidated. In this study, we investigated the acoustic collapse pressure and behavior of Halobacterium salinarum gas vesicles at transmit center frequencies ranging from 12.5 to 27.5 MHz. The acoustic collapse pressure was found to be above 550 kPa at all frequencies, nine-fold higher than the critical pressure observed under hydrostatic conditions. We illustrate that gas vesicles behave non-linearly when exposed to ultrasound at incident pressure ranging from 160 kPa to the collapse pressure and generate second harmonic amplitudes of -2 to -6 dB below the fundamental in media with viscosities ranging from 0.89 to 8 mPa·s. Simulations performed using a Rayleigh-Plesset-type model accounting for buckling and a dynamic finite-element analysis suggest that buckling is the mechanism behind the generation of harmonics. We found good agreement between the level of second harmonic relative to the fundamental measured at 20 MHz and the Rayleigh-Plesset model predictions. Finite-element simulations extended these findings to a non-spherical geometry, confirmed that the acoustic buckling pressure corresponds to the critical pressure under hydrostatic conditions and support the hypothesis of limited gas flow across the GV shell during the compression phase in the frequency range investigated. From simulations, estimates of GV bandwidth-limited scattering indicate that a single GV has a scattering cross section comparable to that of a red blood cell. These findings will inform the development of GV-based contrast agents and pulse sequences to optimize their detection with ultrasound. Copyright © 2017 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Cryocooled terahertz photoconductive detector system with background-limited performance in 1.5–4 THz frequency range

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

Aoki, Makoto; Hiromoto, Norihisa, E-mail: dnhirom@ipc.shizuoka.ac

2015-10-15

We describe a 4-K-cryocooled dual-band terahertz (THz) photoconductive detector system with background-limited performance. The detector system comprises two THz photoconductive detectors covering a response in a wide frequency range from 1.5 to 4 THz, low noise amplifiers, optical low-pass filters to eliminate input radiation of higher frequencies, and a mechanical 4 K Gifford-McMahon refrigerator that provides practical and convenient operation without a liquid He container. The electrical and optical performances of the THz detector system were evaluated at a detector temperature of 4 K under 300 K background radiation. We proved that the detector system can achieve background-limited noise-equivalent-power onmore » the order of 10{sup −14} W/Hz{sup 1/2} in the frequency range from 1.5 to 4 THz even if the vibration noise of the mechanical refrigerator is present.« less

47 CFR 15.33 - Frequency range of radiated measurements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... radiator operates at or above 30 GHz: to the fifth harmonic of the highest fundamental frequency or to 200... kHz, up to at least the frequency shown in this paragraph: (1) If the intentional radiator operates below 10 GHz: to the tenth harmonic of the highest fundamental frequency or to 40 GHz, whichever is...

Eddy-current non-inertial displacement sensing for underwater infrasound measurements.

PubMed

Donskoy, Dimitri M; Cray, Benjamin A

2011-06-01

A non-inertial sensing approach for an Acoustic Vector Sensor (AVS), which utilizes eddy-current displacement sensors and operates well at Ultra-Low Frequencies (ULF), is described here. In the past, most ULF measurements (from mHertz to approximately 10 Hertz) have been conducted using heavy geophones or seismometers that must be installed on the seafloor; these sensors are not suitable for water column measurements. Currently, there are no readily available compact and affordable underwater AVS that operate within this frequency region. Test results have confirmed the validity of the proposed eddy-current AVS design and have demonstrated high acoustic sensitivity. © 2011 Acoustical Society of America

Satellite and Ground Signatures of Kinetic and Inertial Scale ULF Alfven Waves Propagating in Warm Plasma in Earth's Magnetosphere

NASA Astrophysics Data System (ADS)

Rankin, R.; Sydorenko, D.

2015-12-01

Results from a 3D global numerical model of Alfven wave propagation in a warm multi-species plasma in Earth's magnetosphere are presented. The model uses spherical coordinates, accounts for a non-dipole magnetic field, vertical structure of the ionosphere, and an air gap below the ionosphere. A realistic density model is used. Below the exobase altitude (2000 km) the densities and the temperatures of electrons, ions, and neutrals are obtained from the IRI and MSIS models. Above the exobase, ballistic (originating from the ionosphere and returning to ionosphere) and trapped (bouncing between two reflection points above the ionosphere) electron populations are considered similar to [Pierrard and Stegen (2008), JGR, v.113, A10209]. Plasma parameters at the exobase provided by the IRI are the boundary conditions for the ballistic electrons while the [Carpenter and Anderson (1992), JGR, v.97, p.1097] model of equatorial electron density defines parameters of the trapped electron population. In the simulations that are presented, Alfven waves with frequencies from 1 Hz to 0.01 Hz and finite azimuthal wavenumbers are excited in the magnetosphere and compared with Van Allen Probes data and ground-based observations from the CARISMA array of ground magnetometers. When short perpendicular scale waves reflect form the ionosphere, compressional Alfven waves are observed to propagate across the geomagnetic field in the ionospheric waveguide [e.g., Lysak (1999), JGR, v.104, p.10017]. Signals produced by the waves on the ground are discussed. The wave model is also applied to interpret recent Van Allen Probes observations of kinetic scale ULF waves that are associated with radiation belt electron dynamics and energetic particle injections.

Temperature and frequency characteristics of low-loss MnZn ferrite in a wide temperature range

NASA Astrophysics Data System (ADS)

Sun, Ke; Lan, Zhongwen; Yu, Zhong; Xu, Zhiyong; Jiang, Xiaona; Wang, Zihui; Liu, Zhi; Luo, Ming

2011-05-01

A low-loss Mn0.7Zn0.24Fe2.06O4 ferrite has been prepared by a solid-state reaction method. The MnZn ferrite has a high initial permeability, μi (3097), a high saturation induction, Bs (526 mT), a high Curie temperature, Tc (220 °C), and a low core loss, PL (≤ 415 kW/m3) in a wide temperature (25-120 °C) and frequency (10-100 kHz) range. As the temperature increases, an initial decrease followed by a subsequent increase of hysteresis loss, Ph, and eddy current loss, Pe is observed. Both Ph and Pe increase with increasing frequency. When f ≥ 300 kHz, a residual loss, Pr, appears. Pe increases with increasing temperature and frequency. The temperature and frequency dependence of Ph can be explained by irreversible domain wall movements, Pe by the skin effect, and Pr by domain wall resonance, respectively.

Unusual Childhood Waking as a Possible Precursor of the 1995 Kobe Earthquake

PubMed Central

Ikeya, Motoji; Whitehead, Neil E.

2013-01-01

Simple Summary The paper investigates whether young children may waken before earthquakes through a cause other than foreshocks. It concludes there is statistical evidence for this, but the mechanism best supported is anxiety produced by Ultra Low Frequency (ULF) electromagnetic waves. Abstract Nearly 1,100 young students living in Japan at a range of distances up to 500 km from the 1995 Kobe M7 earthquake were interviewed. A statistically significant abnormal rate of early wakening before the earthquake was found, having exponential decrease with distance and a half value approaching 100 km, but decreasing much slower than from a point source such as an epicentre; instead originating from an extended area of more than 100 km in diameter. Because an improbably high amount of variance is explained, this effect is unlikely to be simply psychological and must reflect another mechanism—perhaps Ultra-Low Frequency (ULF) electromagnetic waves creating anxiety—but probably not 222Rn excess. Other work reviewed suggests these conclusions may be valid for animals in general, not just children, but would be very difficult to apply for practical earthquake prediction. PMID:26487316

Frequency range selection method of trans-impedance amplifier for high sensitivity lock-in amplifier used in the optical sensors

NASA Astrophysics Data System (ADS)

Park, Chang-In; Jeon, Su-Jin; Hong, Nam-Pyo; Choi, Young-Wan

2016-03-01

Lock-in amplifier (LIA) has been proposed as a detection technique for optical sensors because it can measure low signal in high noise level. LIA uses synchronous method, so the input signal frequency is locked to a reference frequency that is used to carry out the measurements. Generally, input signal frequency of LIA used in optical sensors is determined by modulation frequency of optical signal. It is important to understand the noise characteristics of the trans-impedance amplifier (TIA) to determine the modulation frequency. The TIA has a frequency range in which noise is minimized by the capacitance of photo diode (PD) and the passive component of TIA feedback network. When the modulation frequency is determined in this range, it is possible to design a robust system to noise. In this paper, we propose a method for the determination of optical signal modulation frequency selection by using the noise characteristics of TIA. Frequency response of noise in TIA is measured by spectrum analyzer and minimum noise region is confirmed. The LIA and TIA circuit have been designed as a hybrid circuit. The optical sensor is modeled by the laser diode (LD) and photo diode (PD) and the modulation frequency was used as the input to the signal generator. The experiments were performed to compare the signal to noise ratio (SNR) of the minimum noise region and the others. The results clearly show that the SNR is enhanced in the minimum noise region of TIA.

Radial diffusion of relativistic electrons into the radiation belt slot region during the 2003 Halloween geomagnetic storms

NASA Astrophysics Data System (ADS)

Loto'Aniu, T. M.; Mann, I. R.; Ozeke, L. G.; Chan, A. A.; Dent, Z. C.; Milling, D. K.

2006-04-01

A study was undertaken to estimate the radial diffusion timescale, τLL, for relativistic electrons (2-6 MeV) to diffuse into the slot region due to drift-resonance with Pc5 ULF waves (2-10 mHz) on 29 October 2003. Large amplitude ULF waves were observed by ground-based magnetometer arrays to penetrate deep into the slot region (L ≃ 2-3) starting at 0600 UT and maximising (˜200 nT p-p) between 0930-1630 UT. Around the same time, the SAMPEX PET instrument measured an over two orders of magnitude increase in relativistic (2-6 MeV) electron flux levels in ˜24 hours within the slot region. The ground-based D-component magnetic power spectral densities (PSDδB) for 29 October were estimated for six latitudinally spaced ground stations covering L ˜ 2.3-4.3 for an observed ULF wave with central frequency ˜4 mHz. The PSDδB values were used to calculate the in situ equatorial poloidal wave electric field power spectral densities (PSDδEm) using a standing Alfvén wave model. The radial diffusion coefficients, DLL, were estimated using the PSDδEm values. The fastest τLL were 3-5 hours at L > 4, while τLL initially increased with decreasing L-value below L ≃ 4; peaking at L ≃ 3 with τLL ˜ 12-24 hours with PSDδEm estimated using a wave frequency bandwidth between Δf = 1 mHz and Δf = 2.5 mHz. The τLL over the L-range L ˜ 2.3-3.3 were consistent with the timescales observed by SAMPEX for the increase in relativistic fluxes in the slot region on 29 October. The authors believe that this is the first example of the ULF wave drift-resonance with relativistic electrons explaining a radiation belt slot region filling event.

Noise Performance of a 72 m Suspended FABRY-PÉROT Cavity

NASA Astrophysics Data System (ADS)

Dumas, Jean-Charles; Ju, Li; Barriga, Pablo; Zhao, Chunnong; Woolley, Andrew A.; Blair, David G.

We report on a seismic isolator with a relatively compact 3 m stack, combining new passive isolation techniques. It consists of three cascaded passive 3D isolator stages suspended from an Ultra Low Frequency (ULF) horizontal Robert linkage stage which itself is suspended from a ULF 3D pre-isolator. The 3D isolators use self-damping pendulums and Euler springs for the horizontal and vertical stages respectively, while the 3D pre-isolator is the combination of an inverse pendulum which provides low frequency horizontal pre-isolation, and a LaCoste linkage for low frequency vertical pre-isolation. Two isolators suspending mirror test masses have been built to form a 72 m optical cavity in order to test their performance. We report results which demonstrate residual motion at nanometer level at frequencies above 1 Hz.

Characterization of a Prototype Radio Frequency Space Environment Path Emulator for Evaluating Spacecraft Ranging Hardware

NASA Technical Reports Server (NTRS)

Mitchell, Jason W.; Baldwin, Philip J.; Kurichh, Rishi; Naasz, Bo J.; Luquette, Richard J.

2007-01-01

The Formation Flying Testbed (FFTB) at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) provides a hardware-in-the-loop test environment for formation navigation and control. The facility is evolving as a modular, hybrid, dynamic simulation facility for end-to-end guidance, navigation and control (GN&C) design and analysis of formation flying spacecraft. The core capabilities of the FFTB, as a platform for testing critical hardware and software algorithms in-the-loop, have expanded to include S-band Radio Frequency (RF) modems for interspacecraft communication and ranging. To enable realistic simulations that require RF ranging sensors for relative navigation, a mechanism is needed to buffer the RF signals exchanged between spacecraft that accurately emulates the dynamic environment through which the RF signals travel, including the effects of the medium, moving platforms, and radiated power. The Path Emulator for Radio Frequency Signals (PERFS), currently under development at NASA GSFC, provides this capability. The function and performance of a prototype device are presented.

High-sensitivity operation of single-beam optically pumped magnetometer in a kHz frequency range

DOE PAGES

Savukov, Igor Mykhaylovich; Kim, Y. J.; Shah, V.; ...

2017-02-02

Here, optically pumped magnetometers (OPM) can be used in various applications, from magnetoencephalography to magnetic resonance imaging and nuclear quadrupole resonance (NQR). OPMs provide high sensitivity and have the significant advantage of non-cryogenic operation. To date, many magnetometers have been demonstrated with sensitivity close to 1 fT, but most devices are not commercialized. Most recently, QuSpin developed a model of OPM that is low cost, high sensitivity, and convenient for users, which operates in a single-beam configuration. Here we developed a theory of single-beam (or parallel two-beam) magnetometers and showed that it is possible to achieve good sensitivity beyond theirmore » usual frequency range by tuning the magnetic field. Experimentally we have tested and optimized a QuSpin OPM for operation in the frequency range from DC to 1.7 kHz, and found that the performance was only slightly inferior despite the expected decrease due to deviation from the spin-exchange relaxation-free regime.« less

High-sensitivity operation of single-beam optically pumped magnetometer in a kHz frequency range

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

Savukov, Igor Mykhaylovich; Kim, Y. J.; Shah, V.

Here, optically pumped magnetometers (OPM) can be used in various applications, from magnetoencephalography to magnetic resonance imaging and nuclear quadrupole resonance (NQR). OPMs provide high sensitivity and have the significant advantage of non-cryogenic operation. To date, many magnetometers have been demonstrated with sensitivity close to 1 fT, but most devices are not commercialized. Most recently, QuSpin developed a model of OPM that is low cost, high sensitivity, and convenient for users, which operates in a single-beam configuration. Here we developed a theory of single-beam (or parallel two-beam) magnetometers and showed that it is possible to achieve good sensitivity beyond theirmore » usual frequency range by tuning the magnetic field. Experimentally we have tested and optimized a QuSpin OPM for operation in the frequency range from DC to 1.7 kHz, and found that the performance was only slightly inferior despite the expected decrease due to deviation from the spin-exchange relaxation-free regime.« less

Pulsed Artificial Electrojet Generation

NASA Astrophysics Data System (ADS)

Papadopoulos, K.

2008-12-01

Traditional techniques for generating low frequency signals in the ULF/ELF range (.1-100 Hz) and rely on ground based Horizontal Electric Dipole (HED) antennas. It is, furthermore, well known that a Vertical Electric Dipole (VED) is by more than 50 dB more efficient than a HED with the same dipole current moment. However, the prohibitively long length of VED antennas in the ELF/ULF range coupled with voltage limitations due to corona discharge in the atmosphere make them totally impracticable. In this paper we discuss a novel concept, inspired by the physics of the equatorial electrojet, that allows for the conversion of a ground based HED to a VED in the E-region of the equatorial ionosphere with current moment comparable to the driving HED. The paper focuses in locations near the dip-equator, where the earth's magnetic is in predominantly in the horizontal direction. The horizontal electric field associated with a pulsed HED drives a large Hall current in the ionospheric E-region, resulting in a vertical current. It is shown that the pulsed vertical current in the altitude range 80-130 km, driven by a horizontal electric field of, approximately, .1 mV/m at 100 km altitude, is of the order of kA. This results in a pulsed VED larger than 106 A-m. Such a pulsed VED will drive ELF/ULF pulses with amplitude in excess of .1 nT at a lateral range larger than few hundred kilometers. This is by three orders of magnitude larger than the one expected by a HED with comparable current moment. The paper will conclude with the description of a sneak-through technique that allows for creating pulsed electric fields in the ionosphere much larger than expected from steady state oscillatory HED antennas.

Study of interaction of ELF-ULF range (0.1-200 Hz) electromagnetic waves with the earth's crust and the ionosphere in the field of industrial power transmission lines (FENICS experiment)

NASA Astrophysics Data System (ADS)

Zhamaletdinov, A. A.; Shevtsov, A. N.; Velikhov, E. P.; Skorokhodov, A. A.; Kolesnikov, V. E.; Korotkova, T. G.; Ryazantsev, P. A.; Efimov, B. V.; Kolobov, V. V.; Barannik, M. B.; Prokopchuk, P. I.; Selivanov, V. N.; Kopytenko, Yu. A.; Kopytenko, E. A.; Ismagilov, V. S.; Petrishchev, M. S.; Sergushin, P. A.; Tereshchenko, P. E.; Samsonov, B. V.; Birulya, M. A.; Smirnov, M. Yu.; Korja, T.; Yampolski, Yu. M.; Koloskov, A. V.; Baru, N. A.; Poljakov, S. V.; Shchennikov, A. V.; Druzhin, G. I.; Jozwiak, W.; Reda, J.; Shchors, Yu. G.

2015-12-01

This article is devoted to describing the theory, technique, and first experimental results of a control source electromagnetic (CSEM) study of the Earth's crust and ionosphere with the use of two mutually orthogonal industrial transmission lines 109 and 120 km in length in the frame of FENICS (Fennoscandian Electrical Conductivity from Natural and Induction Control Source Soundings) experiment. The main part of the measurements is executed on the territory of the Fennoscandian shield at distances from the first hundreds kilometers up to 856 km from the source with the purpose of the deep electromagnetic sounding of the Earth's crust and upper mantle. According to the results of these studies clarifying the parameters of "normal" (standard) geoelectric section of the lithosphere to a depth of 60-70 km, the anisotropy parameters are evaluated and a geothermal and rheological interpretation in conjunction with the analysis of the seismic data is executed. Furthermore, to study the propagation of ELF-LLF waves (0.1-200 Hz) in an "Earth-Ionosphere" waveguide, the measurements are carried out apart from Fennoscandian shield at distances up to 5600 km from the source (in Ukraine, Spitsbergen, Poland, Kamchatka, and other areas). According to the results of these studies, the experimental estimates of the influence of the ionosphere and of the displacement currents on the propagation of ELF-ULF waves in the upper half-space at the different azimuths generation of the primary field are obtained.

Absolute backscatter coefficient estimates of tissue-mimicking phantoms in the 5–50 MHz frequency range

PubMed Central

McCormick, Matthew M.; Madsen, Ernest L.; Deaner, Meagan E.; Varghese, Tomy

2011-01-01

Absolute backscatter coefficients in tissue-mimicking phantoms were experimentally determined in the 5–50 MHz frequency range using a broadband technique. A focused broadband transducer from a commercial research system, the VisualSonics Vevo 770, was used with two tissue-mimicking phantoms. The phantoms differed regarding the thin layers covering their surfaces to prevent desiccation and regarding glass bead concentrations and diameter distributions. Ultrasound scanning of these phantoms was performed through the thin layer. To avoid signal saturation, the power spectra obtained from the backscattered radio frequency signals were calibrated by using the signal from a liquid planar reflector, a water-brominated hydrocarbon interface with acoustic impedance close to that of water. Experimental values of absolute backscatter coefficients were compared with those predicted by the Faran scattering model over the frequency range 5–50 MHz. The mean percent difference and standard deviation was 54% ± 45% for the phantom with a mean glass bead diameter of 5.40 μm and was 47% ± 28% for the phantom with 5.16 μm mean diameter beads. PMID:21877789

The Influence of Fundamental Frequency and Sound Pressure Level Range on Breathing Patterns in Female Classical Singing

ERIC Educational Resources Information Center

Collyer, Sally; Thorpe, C. William; Callaghan, Jean; Davis, Pamela J.

2008-01-01

Purpose: This study investigated the influence of fundamental frequency (F0) and sound pressure level (SPL) range on respiratory behavior in classical singing. Method: Five trained female singers performed an 8-s messa di voce (a crescendo and decrescendo on one F0) across their musical F0 range. Lung volume (LV) change was estimated, and…

A MEMS Interface IC With Low-Power and Wide-Range Frequency-to-Voltage Converter for Biomedical Applications.

PubMed

Arefin, Md Shamsul; Redouté, Jean-Michel; Yuce, Mehmet Rasit

2016-04-01

This paper presents an interface circuit for capacitive and inductive MEMS biosensors using an oscillator and a charge pump based frequency-to-voltage converter. Frequency modulation using a differential crossed coupled oscillator is adopted to sense capacitive and inductive changes. The frequency-to-voltage converter is designed with a negative feedback system and external controlling parameters to adjust the sensitivity, dynamic range, and nominal point for the measurement. The sensitivity of the frequency-to-voltage converter is from 13.28 to 35.96 mV/MHz depending on external voltage and charging current. The sensitivity ranges of the capacitive and inductive interface circuit are 17.08 to 54.4 mV/pF and 32.11 to 82.88 mV/mH, respectively. A capacitive MEMS based pH sensor is also connected with the interface circuit to measure the high acidic gastric acid throughout the digestive tract. The sensitivity for pH from 1 to 3 is 191.4 mV/pH with 550 μV(pp) noise. The readout circuit is designed and fabricated using the UMC 0.18 μm CMOS technology. It occupies an area of 0.18 mm (2) and consumes 11.8 mW.

Relationships between range access as monitored by radio frequency identification technology, fearfulness, and plumage damage in free-range laying hens.

PubMed

Hartcher, K M; Hickey, K A; Hemsworth, P H; Cronin, G M; Wilkinson, S J; Singh, M

2016-05-01

Severe feather-pecking (SFP), a particularly injurious behaviour in laying hens (Gallus gallus domesticus), is thought to be negatively correlated with range use in free-range systems. In turn, range use is thought to be inversely associated with fearfulness, where fearful birds may be less likely to venture outside. However, very few experiments have investigated the proposed association between range use and fearfulness. This experiment investigated associations between range use (time spent outside), fearfulness, plumage damage, and BW. Two pens of 50 ISA Brown laying hens (n=100) were fitted with radio frequency identification (RFID) transponders (contained within silicone leg rings) at 26 weeks of age. Data were then collected over 13 days. A total of 95% of birds accessed the outdoor run more than once per day. Birds spent an average duration of 6.1 h outside each day over 11 visits per bird per day (51.5 min per visit). The top 15 and bottom 15 range users (n=30), as determined by the total time spent on the range over 13 days, were selected for study. These birds were tonic immobility (TI) tested at the end of the trial and were feather-scored and weighed after TI testing. Birds with longer TI durations spent less time outside (P=0.01). Plumage damage was not associated with range use (P=0.68). The small group sizes used in this experiment may have been conducive to the high numbers of birds utilising the outdoor range area. The RFID technology collected a large amount of data on range access in the tagged birds, and provides a potential means for quantitatively assessing range access in laying hens. The present findings indicate a negative association between fearfulness and range use. However, the proposed negative association between plumage damage and range use was not supported. The relationships between range use, fearfulness, and SFP warrant further research.

Multi-year high-frequency hydrothermal monitoring of selected high-threat Cascade Range volcanoes

NASA Astrophysics Data System (ADS)

Crankshaw, I. M.; Archfield, S. A.; Newman, A. C.; Bergfeld, D.; Clor, L. E.; Spicer, K. R.; Kelly, P. J.; Evans, W. C.; Ingebritsen, S. E.

2018-05-01

From 2009 to 2015 the U.S. Geological Survey (USGS) systematically monitored hydrothermal behavior at selected Cascade Range volcanoes in order to define baseline hydrothermal and geochemical conditions. Gas and water data were collected regularly at 25 sites on 10 of the highest-risk volcanoes in the Cascade Range. These sites include near-summit fumarole groups and springs/streams that show clear evidence of magmatic influence (high 3He/4He ratios and/or large fluxes of magmatic CO2 or heat). Site records consist mainly of hourly temperature and hydrothermal-flux data. Having established baseline conditions during a multiyear quiescent period, the USGS reduced monitoring frequency from 2015 to present. The archived monitoring data are housed at (doi:10.5066/F72N5088). These data (1) are suitable for retrospective comparison with other continuous geophysical monitoring data and (2) will provide context during future episodes of volcanic unrest, such that unrest-related variations at these thoroughly characterized sites will be more clearly recognizable. Relatively high-frequency year-round data are essential to achieve these objectives, because many of the time series reveal significant diurnal, seasonal, and inter-annual variability that would tend to mask unrest signals in the absence of baseline data. Here we characterize normal variability for each site, suggest strategies to detect future volcanic unrest, and explore deviations from background associated with recent unrest.

Experimental demonstrations in audible frequency range of band gap tunability and negative refraction in two-dimensional sonic crystal.

PubMed

Pichard, Hélène; Richoux, Olivier; Groby, Jean-Philippe

2012-10-01

The propagation of audible acoustic waves in two-dimensional square lattice tunable sonic crystals (SC) made of square cross-section infinitely rigid rods embedded in air is investigated experimentally. The band structure is calculated with the plane wave expansion (PWE) method and compared with experimental measurements carried out on a finite extend structure of 200 cm width, 70 cm depth and 15 cm height. The structure is made of square inclusions of 5 cm side with a periodicity of L = 7.5 cm placed inbetween two rigid plates. The existence of tunable complete band gaps in the audible frequency range is demonstrated experimentally by rotating the scatterers around their vertical axis. Negative refraction is then analyzed by use of the anisotropy of the equi-frequency surface (EFS) in the first band and of a finite difference time domain (FDTD) method. Experimental results finally show negative refraction in the audible frequency range.

Sources of anomalous transient electric signals (ATESs) in the ULF band in the Lamia region (central Greece): electrochemical mechanisms for their generation

NASA Astrophysics Data System (ADS)

Pham, V.-N.; Boyer, D.; Chouliaras, G.; Savvaidis, A.; Stavrakakis, G.; Le Mouël, J.-L.

2002-04-01

Anomalous transient electric signals (ATESs) in the ultra low frequency (ULF) band have been often observed during magnetotelluric (MT) investigations [Nature 319 (1986) 310; Phys. Earth Planet. Int. 114 (1999) 141; Geophys. J. Int. 142 (2000) 948], but their origin was unknown until now. They have the same characteristics as the so-called seismic electric signals (SES) claimed to be earthquake precursors by the VAN group (e.g. [Tectonophysics 110 (1984) 73] and later works by this group). Our analysis suggests that the so-called SES could be of anthropic origin. Following the devastating 7 September 1999 Athens earthquake, the VAN group claimed that a SES had been recorded at LAM station (Lamia, central Greece) some days prior to the main shock and that a second SES, which might correspond to an impending even larger earthquake, had been observed after the main shock. In the 2 years after the Athens main shock, no subsequent large earthquakes have occurred near Athens. We conducted a campaign of measurement in the Lamia region in May and June 2001. The results show that ATESs, which look like SES, have several different sources: pump-stations for ground-water, high power electric lines, and factories located to the SE of Lamia city. The ATESs can be generated by two electrochemical mechanisms of metallic electrode polarization: the "galvanic cell" and the "ac electrolytic cell" which are studied by simulated field experiments and discussed in detail in Appendix A. These two mechanisms can occur over a wide range of length scales in the field. Any isolation failure in buried metallic conductors, such as electrical and telecommunication networks, oil, water and gas pipes, railways, high power electric lines, factories and so on, can produce a galvanic cell or an ac electrolytic cell, or both, which could generate, under some circumstances, an "overvoltage", the ATES. Finally, the absence of a magnetic signal has been observed during ATES and does not constitute a

Joint Bearing and Range Estimation of Multiple Objects from Time-Frequency Analysis.

PubMed

Liu, Jeng-Cheng; Cheng, Yuang-Tung; Hung, Hsien-Sen

2018-01-19

Direction-of-arrival (DOA) and range estimation is an important issue of sonar signal processing. In this paper, a novel approach using Hilbert-Huang transform (HHT) is proposed for joint bearing and range estimation of multiple targets based on a uniform linear array (ULA) of hydrophones. The structure of this ULA based on micro-electro-mechanical systems (MEMS) technology, and thus has attractive features of small size, high sensitivity and low cost, and is suitable for Autonomous Underwater Vehicle (AUV) operations. This proposed target localization method has the following advantages: only a single snapshot of data is needed and real-time processing is feasible. The proposed algorithm transforms a very complicated nonlinear estimation problem to a simple nearly linear one via time-frequency distribution (TFD) theory and is verified with HHT. Theoretical discussions of resolution issue are also provided to facilitate the design of a MEMS sensor with high sensitivity. Simulation results are shown to verify the effectiveness of the proposed method.

Effects of the gaseous and liquid water content of the atmosphere on range delay and Doppler frequency

NASA Technical Reports Server (NTRS)

Flock, W. L.

1981-01-01

When high precision is required for range measurement on Earth space paths, it is necessary to correct as accurately as possible for excess range delays due to the dry air, water vapor, and liquid water content of the atmosphere. Calculations based on representative values of atmospheric parameters are useful for illustrating the order of magnitude of the expected delays. Range delay, time delay, and phase delay are simply and directly related. Doppler frequency variations or noise are proportional to the time rate of change of excess range delay. Tropospheric effects were examined as part of an overall consideration of the capability of precision two way ranging and Doppler systems.

Characterization of Different Cable Ferrite Materials to Reduce the Electromagnetic Noise in the 2-150 kHz Frequency Range.

PubMed

Suarez, Adrian; Victoria, Jorge; Alcarria, Antonio; Torres, Jose; Martinez, Pedro A; Martos, Julio; Soret, Jesus; Garcia-Olcina, Raimundo; Muetsch, Steffen

2018-01-23

The gap of standardization for conducted and field coupled electromagnetic interferences (EMI) in the 2-150 kHz frequency range can lead to Electromagnetic Compatibility (EMC) problems. This is caused by power systems such as Pulse Width Modulation (PWM) controlled rectifiers, photovoltaic inverters or charging battery units in electric vehicles. This is a very important frequency spectral due to interferences generated in a wide range of devices and, specifically, communication problems in the new technologies and devices incorporated to the traditional grid to convert it into a Smart Grid. Consequently, it is necessary to provide new solutions to attenuate this kind of interference, which involves finding new materials that are able to filter the electromagnetic noise. This contribution is focused on characterizing the performance of a novel material based on nanocrystalline and comparing it to most common material compositions such as MnZn and NiZn. This research is carried out from the point of view of the manufacturing process, magnetic properties and EMI suppression ability. This last item is carried out through two analysis procedures: a theoretical method by determining the attenuation ratio by measuring impedance parameter and proposing a new empirical technique based on measuring directly the insertion loss parameter. Therefore, the main aim of this characterization process is to determine the performance of nanocrystalline compared to traditional cable ferrite compositions to reduce the interferences in this controversial frequency range. From the results obtained, it is possible to deduce that nanocrystalline cable ferrite provides the best performance to filter the electromagnetic noise in the 2-150 kHz frequency range.

Dielectric Properties of Marsh Vegetation in a Frequency Range of 0.1-18 GHz Under Variation of Temperature and Moisture

NASA Astrophysics Data System (ADS)

Romanov, A. N.; Kochetkova, T. D.; Suslyaev, V. I.; Shcheglova, A. S.

2017-09-01

Dielectric characteristics of some species of marsh vegetation: lichen Cladonia stellaris (Opiz) Pouzar, moss Sphagnum, and a representative of Bryidae mosses - Dicranum polysetum are studied in the frequency range from 100 MHz to 18 GHz. At a frequency of 1.41 GHz, the influence of temperature in the range from -12 to +20°C on the behavior of dielectric characteristics of mosses, lichens, and peat is studied. The dependences of the dielectric characteristics of vegetation on the volumetric wetness are established.

Ultralow-field and spin-locking relaxation dispersion in postmortem pig brain.

PubMed

Dong, Hui; Hwang, Seong-Min; Wendland, Michael; You, Lixing; Clarke, John; Inglis, Ben

2017-12-01

To investigate tissue-specific differences, a quantitative comparison was made between relaxation dispersion in postmortem pig brain measured at ultralow fields (ULF) and spin locking at 7 tesla (T). The goal was to determine whether ULF-MRI has potential advantages for in vivo human brain imaging. Separate specimens of gray matter and white matter were investigated using an ULF-MRI system with superconducting quantum interference device (SQUID) signal detection to measure T1ULF at fields from 58.7 to 235.0 μT and using a commercial MRI scanner to measure T1ρ7T at spin-locking fields from 5.0 to 235.0 μT. At matched field strengths, T1ρ7T is 50 to 100% longer than T1ULF. Furthermore, dispersion in T1ULF is close to linear between 58.7 and 235 µT, whereas dispersion in T1ρ7T is highly nonlinear over the same range. A subtle elbow in the T1ULF dispersion at approximately 140 µT is tentatively attributed to the local dipolar field of macromolecules. It is suggested that different relaxation mechanisms dominate each method and that ULF-MRI has a fundamentally different sensitivity to the macromolecular structure of neural tissue. Ultralow-field MRI may offer distinct, quantitative advantages for human brain imaging, while simultaneously avoiding the severe heating limitation imposed on high-field spin locking. Magn Reson Med 78:2342-2351, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Novel Waveguide Structures in the Terahertz Frequency Range

NASA Astrophysics Data System (ADS)

Mbonye, Marx

Over the last decade, considerable research interest has peaked in realizing an efficient Terahertz (THz) waveguide for potential applications in imaging, sensing, and communications applications. Two of the promising candidates are the two-wire waveguide and the parallel-plate waveguide (PPWG). I present theoretical and experimental evidence that show that the two-wire waveguide supports low loss terahertz pulse propagation, and illustrate that the mode pattern at the end of the waveguide resembles that of a dipole. In comparison to the weakly guided Sommerfeld wave of a single wire waveguide, this two-wire structure exhibits much lower bending losses. I also observe that a commercial 300-Ohm two-wire TVantenna cable can be used for guiding frequency components of up to 0.2 THz, although these cables are generally designed to operate only up to about 800 MHz. The parallel-plate waveguide is another promising candidate that would make an efficient THz waveguide, since it has relatively low Ohmic losses. The transverse electromagnetic mode (TEM) of this waveguide has been generally preferred since it has no cutoff frequency, and therefore no group velocity dispersion. Utilizing this TEM mode, I study the reflection of THz radiation at the end of a PPWG, due to the impedance mismatch between the propagating transverse-electromagnetic mode and the free-space background. I find that for a PPWG with uniformly spaced plates, the reflection coefficient at the output face increases as the plate separation decreases, consistent with predictions by early low frequency ray optical theory. I observe this same trend in tapered PPWGs, when the input separation is fixed, and the output separation is varied. In another study, I investigate how to minimize diffraction losses in PPWGs by using plates with slightly concave surfaces. Using a simple "bouncing plane wave" analysis, I demonstrate how to determine an ideal radius of curvature for a waveguide operating at a given THz

Range-gated field disturbance sensor with range-sensitivity compensation

DOEpatents

McEwan, T.E.

1996-05-28

A field disturbance sensor operates with relatively low power, provides an adjustable operating range, is not hypersensitive at close range, allows co-location of multiple sensors, and is inexpensive to manufacture. The sensor includes a transmitter that transmits a sequence of transmitted bursts of electromagnetic energy. The transmitter frequency is modulated at an intermediate frequency. The sequence of bursts has a burst repetition rate, and each burst has a burst width and comprises a number of cycles at a transmitter frequency. The sensor includes a receiver which receives electromagnetic energy at the transmitter frequency, and includes a mixer which mixes a transmitted burst with reflections of the same transmitted burst to produce an intermediate frequency signal. Circuitry, responsive to the intermediate frequency signal indicates disturbances in the sensor field. Because the mixer mixes the transmitted burst with reflections of the transmitted burst, the burst width defines the sensor range. The burst repetition rate is randomly or pseudorandomly modulated so that bursts in the sequence of bursts have a phase which varies. 8 figs.

Range-gated field disturbance sensor with range-sensitivity compensation

DOEpatents

McEwan, Thomas E.

1996-01-01

A field disturbance sensor operates with relatively low power, provides an adjustable operating range, is not hypersensitive at close range, allows co-location of multiple sensors, and is inexpensive to manufacture. The sensor includes a transmitter that transmits a sequence of transmitted bursts of electromagnetic energy. The transmitter frequency is modulated at an intermediate frequency. The sequence of bursts has a burst repetition rate, and each burst has a burst width and comprises a number of cycles at a transmitter frequency. The sensor includes a receiver which receives electromagnetic energy at the transmitter frequency, and includes a mixer which mixes a transmitted burst with reflections of the same transmitted burst to produce an intermediate frequency signal. Circuitry, responsive to the intermediate frequency signal indicates disturbances in the sensor field. Because the mixer mixes the transmitted burst with reflections of the transmitted burst, the burst width defines the sensor range. The burst repetition rate is randomly or pseudorandomly modulated so that bursts in the sequence of bursts have a phase which varies.

High-resolution frequency measurement method with a wide-frequency range based on a quantized phase step law.

PubMed

Du, Baoqiang; Dong, Shaofeng; Wang, Yanfeng; Guo, Shuting; Cao, Lingzhi; Zhou, Wei; Zuo, Yandi; Liu, Dan

2013-11-01

A wide-frequency and high-resolution frequency measurement method based on the quantized phase step law is presented in this paper. Utilizing a variation law of the phase differences, the direct different frequency phase processing, and the phase group synchronization phenomenon, combining an A/D converter and the adaptive phase shifting principle, a counter gate is established in the phase coincidences at one-group intervals, which eliminates the ±1 counter error in the traditional frequency measurement method. More importantly, the direct phase comparison, the measurement, and the control between any periodic signals have been realized without frequency normalization in this method. Experimental results show that sub-picosecond resolution can be easily obtained in the frequency measurement, the frequency standard comparison, and the phase-locked control based on the phase quantization processing technique. The method may be widely used in navigation positioning, space techniques, communication, radar, astronomy, atomic frequency standards, and other high-tech fields.

Range and Frequency of Africanized Honey Bees in California (USA)

PubMed Central

Kono, Yoshiaki; Kohn, Joshua R.

2015-01-01

Africanized honey bees entered California in 1994 but few accounts of their northward expansion or their frequency relative to European honey bees have been published. We used mitochondrial markers and morphometric analyses to determine the prevalence of Africanized honeybees in San Diego County and their current northward progress in California west of the Sierra Nevada crest. The northernmost African mitotypes detected were approximately 40 km south of Sacramento in California’s central valley. In San Diego County, 65% of foraging honey bee workers carry African mitochondria and the estimated percentage of Africanized workers using morphological measurements is similar (61%). There was no correlation between mitotype and morphology in San Diego County suggesting Africanized bees result from bidirectional hybridization. Seventy percent of feral hives, but only 13% of managed hives, sampled in San Diego County carried the African mitotype indicating that a large fraction of foraging workers in both urban and rural San Diego County are feral. We also found a single nucleotide polymorphism at the DNA barcode locus COI that distinguishes European and African mitotypes. The utility of this marker was confirmed using 401 georeferenced honey bee sequences from the worldwide Barcode of Life Database. Future censuses can determine whether the current range of the Africanized form is stable, patterns of introgression at nuclear loci, and the environmental factors that may limit the northern range of the Africanized honey bee. PMID:26361047

In vitro Neurons in Mammalian Cortical Layer 4 Exhibit Intrinsic Oscillatory Activity in the 10- to 50-Hz Frequency Range

NASA Astrophysics Data System (ADS)

Llinas, Rodolfo R.; Grace, Anthony A.; Yarom, Yosef

1991-02-01

We report here the presence of fast subthreshold oscillatory potentials recorded in vitro from neurons within layer 4 of the guinea pig frontal cortex. Two types of oscillatory neurons were recorded: (i) One type exhibited subthreshold oscillations whose frequency increased with membrane depolarization and encompassed a range of 10-45 Hz. Action potentials in this type of neuron demonstrated clear after-hyperpolarizations. (ii) The second type of neuron was characterized by narrow-frequency oscillations near 35-50 Hz. These oscillations often outlasted the initiating depolarizing stimulus. No calcium component could be identified in their action potential. In both types of cell the subthreshold oscillations were tetrodotoxin-sensitive, indicating that the depolarizing phase of the oscillation was generated by a voltage-dependent sodium conductance. The initial depolarizing phase was followed by a potassium conductance responsible for the falling phase of the oscillatory wave. In both types of cell, the subthreshold oscillation could trigger spikes at the oscillatory frequency, if the membrane was sufficiently depolarized. Combining intracellular recordings with Lucifer yellow staining showed that the narrow-frequency oscillatory activity was produced by a sparsely spinous interneuron located in layer 4 of the cortex. This neuron has extensive local axonal collaterals that ramify in layers 3 and 4 such that they may contribute to the columnar synchronization of activity in the 40- to 50-Hz range. Cortical activity in this frequency range has been proposed as the basis for the "conjunctive properties" of central nervous system networks.

A reconfigurable multi-mode multi-band transmitter with integrated frequency synthesizer for short-range wireless communication

NASA Astrophysics Data System (ADS)

Nan, Qi; Fan, Chen; Lingwei, Zhang; Xiaoman, Wang; Baoyong, Chi

2013-09-01

A reconfigurable multi-mode direct-conversion transmitter (TX) with integrated frequency synthesizer (FS) is presented. The TX as well as the FS is designed with a flexible architecture and frequency plan, which helps to support all the 433/868/915 MHz ISM band signals, with the reconfigurable bandwidth from 250 kHz to 2 MHz. In order to save power and chip area, only one 1.8 GHz VCO is adopted to cover the whole frequency range. All the operation modes can be regulated in real time by configuring the integrated register-bank through an SPI interface. Implemented in 180 nm CMOS, the FS achieves a frequency coverage of 320-460 MHz and 620-920 MHz. The lowest phase noise can be -107 dBc/Hz at a 100 kHz offset and -126 dBc/Hz at a 1 MHz offset. The transmitter features a + 10.2 dBm peak output power with a +9.5 dBm 1-dB-compression point and 250 kHz/500 kHz/1 MHz/2 MHz reconfigurable signal bandwidth.

EMI shielding performance of lead hexaferrite/polyaniline composite in 8-18 GHz frequency range

NASA Astrophysics Data System (ADS)

Choudhary, Harish Kumar; Pawar, Shital Patangrao; Bose, Suryasarathi; Sahoo, Balaram

2018-05-01

EMI shielding properties of nanocomposite containing lead hexaferrite (PFO) and polyaniline (PANI), a conducting polymer, was studied in X and Ku band frequencies. The nanocomposite shows enhanced EMI shielding properties than that of the pure PANI. Incorporation of PFO particles in the PANI enhances the total shielding effectiveness (SET) up to -24 dB at 18 GHz. This means that these nanocomposites can shield ˜99 % of the incoming EM radiation. The PFO/PANI shows much higher attenuation constant values over the measured frequency range. By adding the PFO in the PANI we have created more interfaces between Wax-PFO, Wax-PANI, PANI-PFO and PFO-PANI. These enhanced interfaces lead to Maxwell-Wagner polarization which results in a higher dielectric loss than only PANI.

Dynamic stiffness of chemically and physically ageing rubber vibration isolators in the audible frequency range: Part 2—waveguide solution

NASA Astrophysics Data System (ADS)

Kari, Leif

2017-09-01

The dynamic stiffness of a chemically and physically ageing rubber vibration isolator in the audible frequency range is modelled as a function of ageing temperature, ageing time, actual temperature, time, frequency and isolator dimension. In particular, the dynamic stiffness for an axially symmetric, homogeneously aged rubber vibration isolator is derived by waveguides where the eigenmodes given by the dispersion relation for an infinite cylinder satisfying traction free radial surface boundary condition are matched to satisfy the displacement boundary conditions at the lateral surface ends of the finite rubber cylinder. The constitutive equations are derived in a companion paper (Part 1). The dynamic stiffness is calculated over the whole audible frequency range 20-20,000 Hz at several physical ageing times for a temperature history starting at thermodynamic equilibrium at +25°C and exposed by a sudden temperature step down to -60°C and at several chemical ageing times at temperature +25°C with simultaneous molecular network scission and reformation. The dynamic stiffness results are displaying a strong frequency dependence at a short physical ageing time, showing stiffness magnitude peaks and troughs, and a strong physical ageing time dependence, showing a large stiffness magnitude increase with the increased physical ageing time, while the peaks and troughs are smoothed out. Likewise, stiffness magnitude peaks and troughs are frequency-shifted with increased chemical ageing time. The developed model is possible to apply for dynamic stiffness prediction of rubber vibration isolator over a broad audible frequency range under realistic environmental condition of chemical ageing, mainly attributed to oxygen exposure from outside and of physical ageing, primarily perceived at low-temperature steps.

Complex-Spectrum Magnetic Environment enhances and/or modifies Bioeffects of Hypokinetic Stress Condition: an Animal Study

NASA Astrophysics Data System (ADS)

Temuriantz, N. A.; Martinyuk, V. S.; Ptitsyna, N. G.; Villoresi, G.; Iucci, N.; Tyasto, M. I.; Dorman, L. I.

During last decades it was shown by many authors that ultra-low and extremely low frequency electric and magnetic fields ULF 0-10 Hz ELF 10-1000 Hz may produce biological effects and consequently may be a possible source for health problems Spaceflight electric and magnetic environments are characterized by complex combination of static and time-varying components in ULF-ELF range and by high variability The objective of this study was to investigate the possible influence of such magnetic fields on rats to understand the pathway regarding functional state of cardiovascular system Magnetic field MF pattern with variable complex spectra in 0-150 Hz frequency range was simulated using 3-axial Helmholtz coils and special computer-based equipment The effect of the real world MF exposure on rats was also tested in combination with hypokinetic stress condition which is typical for spaceflights It was revealed that variable complex-spectrum MF acts as a weak or moderate stress-like factor which amplifies and or modifies the functional shifts caused by other stress-factors The value and direction of the functional shifts caused by MF exposure significantly depend on gender individual-typological constitutional features and also on the physiological state norm stress of organism Our results support the idea that variable complex-spectrum MF action involves sympathetic activation overload in cholesterol transport in blood and also secretor activation of tissue basophyls mast cells that can influence the regional haemodynamics These

Fabrication and characterization of biotissue-mimicking phantoms in the THz frequency range

NASA Astrophysics Data System (ADS)

Liakhov, E.; Smolyanskaya, O.; Popov, A.; Odlyanitskiy, E.; Balbekin, N.; Khodzitsky, M.

2016-08-01

The study revealed the most promising candidates for phantoms mimicking different biological tissues in the terahertz frequency range. Closest to biological tissues in terms of the refractive index appeared to be gelatin-based gels; in terms of the absorption coefficient they were agar-based gels. Gelatin is more stable in time, but requires special storage conditions to limit water evaporation. The dense structure of the agar-based phantom allows its use without mold and risk of damage. However, agar is a nutrient medium for bacteria and its parameters degrade even when the phantom form and water content are retained. Use of liquid suspensions of lecithin and milk powder are found to be extremely limited.

Physics of the Brain. Prevention of the Epileptic Seizures by the Multi-photon Pulsed-operated Fiber Lasers in the Ultraviolet Range of Frequencies.

NASA Astrophysics Data System (ADS)

Stefan, V. Alexander; IAPS Team

The novel study of the epileptogenesis mechanisms is proposed. It is based on the pulsed-operated (amplitude modulation) multi-photon (frequency modulation) fiber-laser interaction with the brain epilepsy-topion (the epilepsy onset area), so as to prevent the excessive electrical discharge (epileptic seizure) in the brain. The repetition frequency, Ω, matches the low frequency (epileptic) phonon waves in the brain. The laser repetition frequency (5-100 pulses per second) enables the resonance-scanning of the wide range of the phonon (possible epileptic-to-be) activity in the brain. The tunable fiber laser frequencies, Δω (multi photon operation), are in the ultraviolet frequency range, thus enabling monitoring of the electrical charge imbalance (within the 10s of milliseconds), and the DNA-corruption in the epilepsy-topion, as the possible cause of the disease. Supported by Nikola Tesla Labs., Stefan University.

Dynamic stiffness of chemically and physically ageing rubber vibration isolators in the audible frequency range. Part 1: constitutive equations

NASA Astrophysics Data System (ADS)

Kari, Leif

2017-09-01

The constitutive equations of chemically and physically ageing rubber in the audible frequency range are modelled as a function of ageing temperature, ageing time, actual temperature, time and frequency. The constitutive equations are derived by assuming nearly incompressible material with elastic spherical response and viscoelastic deviatoric response, using Mittag-Leffler relaxation function of fractional derivative type, the main advantage being the minimum material parameters needed to successfully fit experimental data over a broad frequency range. The material is furthermore assumed essentially entropic and thermo-mechanically simple while using a modified William-Landel-Ferry shift function to take into account temperature dependence and physical ageing, with fractional free volume evolution modelled by a nonlinear, fractional differential equation with relaxation time identical to that of the stress response and related to the fractional free volume by Doolittle equation. Physical ageing is a reversible ageing process, including trapping and freeing of polymer chain ends, polymer chain reorganizations and free volume changes. In contrast, chemical ageing is an irreversible process, mainly attributed to oxygen reaction with polymer network either damaging the network by scission or reformation of new polymer links. The chemical ageing is modelled by inner variables that are determined by inner fractional evolution equations. Finally, the model parameters are fitted to measurements results of natural rubber over a broad audible frequency range, and various parameter studies are performed including comparison with results obtained by ordinary, non-fractional ageing evolution differential equations.

Frequency-Range Distribution of Boulders Around Cone Crater: Relevance to Landing Site Hazard Avoidance

NASA Technical Reports Server (NTRS)

Clegg-Watkins, R. N.; Jolliff, B. L.; Lawrence, S. J.

2016-01-01

Boulders represent a landing hazard that must be addressed in the planning of future landings on the Moon. A boulder under a landing leg can contribute to deck tilt and boulders can damage spacecraft during landing. Using orbital data to characterize boulder populations at locations where landers have safely touched down (Apollo, Luna, Surveyor, and Chang'e-3 sites) is important for determining landing hazard criteria for future missions. Additionally, assessing the distribution of boulders can address broader science issues, e.g., how far craters distribute boulders and how this distribution varies as a function of crater size and age. The availability of new Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) images [1] enables the use of boulder size- and range frequency distributions for a variety of purposes [2-6]. Boulders degrade over time and primarily occur around young or fresh craters that are large enough to excavate bedrock. Here we use NAC images to analyze boulder distributions around Cone crater (340 m diameter) at the Apollo 14 site. Cone crater (CC) was selected because it is the largest crater where astronaut surface photography is available for a radial traverse to the rim. Cone crater is young (approximately 29 Ma [7]) relative to the time required to break down boulders [3,8], giving us a data point for boulder range-frequency distributions (BRFDs) as a function of crater age.

1.55-μm mode-locked quantum-dot lasers with 300 MHz frequency tuning range

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

Sadeev, T., E-mail: tagir@mailbox.tu-berlin.de; Arsenijević, D.; Bimberg, D.

2015-01-19

Passive mode-locking of two-section quantum-dot mode-locked lasers grown by metalorganic vapor phase epitaxy on InP is reported. 1250-μm long lasers exhibit a wide tuning range of 300 MHz around the fundamental mode-locking frequency of 33.48 GHz. The frequency tuning is achieved by varying the reverse bias of the saturable absorber from 0 to −2.2 V and the gain section current from 90 to 280 mA. 3 dB optical spectra width of 6–7 nm leads to ex-facet optical pulses with full-width half-maximum down to 3.7 ps. Single-section quantum-dot mode-locked lasers show 0.8 ps broad optical pulses after external fiber-based compression. Injection current tuning from 70 tomore » 300 mA leads to 30 MHz frequency tuning.« less

[The algorithm based on wavelet for canceling muscle electricity and wide range frequency of power line hum in ECG].

PubMed

Zhao, Jie; Hua, Mei

2004-06-01

To develop a wavelet noise canceller that cancels muscle electricity and power line hum in wide range of frequency. According to the feature that the QRS complex has higher frequency components, and the T, P wave have lower frequency components, the biorthogonal wavelet was selected to decompose the original signals. An interference-eliminated signal ECG was formed by reconstruction from the changed coefficients of wavelet. By using the canceller, muscle electricity and power line interference between 49 Hz and 61 Hz were eliminated from the ECG signals. This canceller works well in canceling muscle electricity, and basic and harmonic frequencies of power line hum. The canceller is also insensitive to the frequency change of power line, the same procedure is good for both 50 and 60 Hz power line hum.

Numerical Exposure Assessment Method for Low Frequency Range and Application to Wireless Power Transfer.

PubMed

Park, SangWook; Kim, Minhyuk

2016-01-01

In this paper, a numerical exposure assessment method is presented for a quasi-static analysis by the use of finite-difference time-domain (FDTD) algorithm. The proposed method is composed of scattered field FDTD method and quasi-static approximation for analyzing of the low frequency band electromagnetic problems. The proposed method provides an effective tool to compute induced electric fields in an anatomically realistic human voxel model exposed to an arbitrary non-uniform field source in the low frequency ranges. The method is verified, and excellent agreement with theoretical solutions is found for a dielectric sphere model exposed to a magnetic dipole source. The assessment method serves a practical example of the electric fields, current densities, and specific absorption rates induced in a human head and body in close proximity to a 150-kHz wireless power transfer system for cell phone charging. The results are compared to the limits recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the IEEE standard guidelines.

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

Yukhimuk, V.; Roussel-Dupre, R.

In this paper the evolution of nonlinear scattering of whistler mode waves by kinetic Alfven waves (KAW) in time and two spatial dimensions is studied analytically. The authors suggest this nonlinear process as a mechanism of kinetic Alfven wave generation in space plasmas. This mechanism can explain the dependence of Alfven wave generation on whistler waves observed in magnetospheric and ionospheric plasmas. The observational data show a dependence for the generation of long periodic pulsations Pc5 on whistler wave excitation in the auroral and subauroral zone of the magnetosphere. This dependence was first observed by Ondoh T.I. For 79 casesmore » of VLF wave excitation registered by Ondoh at College Observatory (L=64.6 N), 52 of them were followed by Pc5 geomagnetic pulsation generation. Similar results were obtained at the Loparskaia Observatory (L=64 N) for auroral and subauroral zone of the magnetosphere. Thus, in 95% of the cases when VLF wave excitation occurred the generation of long periodic geomagnetic pulsations Pc5 were observed. The observations also show that geomagnetic pulsations Pc5 are excited simultaneously or insignificantly later than VLF waves. In fact these two phenomena are associated genetically: the excitation of VLF waves leads to the generation of geomagnetic pulsations Pc5. The observations show intensive generation of geomagnetic pulsations during thunderstorms. Using an electromagnetic noise monitoring system covering the ULF range (0.01-10 Hz) A.S. Fraser-Smith observed intensive ULF electromagnetic wave during a large thunderstorm near the San-Francisco Bay area on September 23, 1990. According to this data the most significant amplification in ULF wave activity was observed for waves with a frequency of 0.01 Hz and it is entirely possible that stronger enhancements would have been measured at lower frequencies.« less

Ranging Behaviour of Commercial Free-Range Broiler Chickens 2: Individual Variation

PubMed Central

Groves, Peter J.; Rault, Jean-Loup

2017-01-01

Simple Summary Although the consumption of free-range chicken meat has increased, little is known about the ranging behaviour of meat chickens on commercial farms. Studies suggest range use is low and not all chickens access the range when given the opportunity. Whether ranging behaviour differs between individuals within a flock remains largely unknown and may have consequences for animal welfare and management. We monitored individual chicken ranging behaviour from four mixed sex flocks on a commercial farm across two seasons. Not all chickens accessed the range. We identified groups of chickens that differed in ranging behaviour (classified by frequency of range visits): chickens that accessed the range only once, low frequency ranging chickens and high frequency ranging chickens, the latter accounting for one-third to one half of all range visits. Sex was not predictive of whether a chicken would access the range or the number of range visits, but males spent more time on the range in winter. We found evidence that free-range chicken ranging varies between individuals within the same flock on a commercial farm. Whether such variation in ranging behaviour relates to variation in chicken welfare remains to be investigated. Abstract Little is known about broiler chicken ranging behaviour. Previous studies have monitored ranging behaviour at flock level but whether individual ranging behaviour varies within a flock is unknown. Using Radio Frequency Identification technology, we tracked 1200 individual ROSS 308 broiler chickens across four mixed sex flocks in two seasons on one commercial farm. Ranging behaviour was tracked from first day of range access (21 days of age) until 35 days of age in winter flocks and 44 days of age in summer flocks. We identified groups of chickens that differed in frequency of range visits: chickens that never accessed the range (13 to 67% of tagged chickens), low ranging chickens (15 to 44% of tagged chickens) that accounted for <15

Characterization of air-coupled ultrasound transducers in the frequency range 40 kHz-2 mHz using light diffraction tomography.

PubMed

Almqvist, M; Holm, A; Persson, H W; Lindström, K

2000-01-01

The aim of this work was to show the applicability of light diffraction tomography on airborne ultrasound in the frequency range 40 kHz-2 MHz. Seven different air-coupled transducers were measured to show the method's performance regarding linearity, absolute pressure measurements, phase measurements, frequency response, S/N ratio and spatial resolution. A calibrated microphone and the pulse-echo method were used to evaluate the results. The absolute measurements agreed within the calibrated microphone's uncertainty range. Pulse waveforms and corresponding FFT diagrams show the method's higher bandwidth compared with the microphone. Further, the method offers non-perturbing measurements with high spatial resolution, which was especially advantageous for measurements close to the transducer surfaces. The S/N ratio was higher than or in the same range as that of the two comparison methods.

Energy deposition processes in biological tissue: nonthermal biohazards seem unlikely in the ultra-high frequency range.

PubMed

Pickard, W F; Moros, E G

2001-02-01

The prospects of ultra high frequency (UHF, 300--3000 MHz) irradiation producing a nonthermal bioeffect are considered theoretically and found to be small. First, a general formula is derived within the framework of macroscopic electrodynamics for the specific absorption rate of microwaves in a biological tissue; this involves the complex Poynting vector, the mass density of the medium, the angular frequency of the electromagnetic field, and the three complex electromagnetic constitutive parameters of the medium. In the frequency ranges used for cellular telephony and personal communication systems, this model predicts that the chief physical loss mechanism will be ionic conduction, with increasingly important contributions from dielectric relaxation as the frequency rises. However, even in a magnetite unit cell within a magnetosome the deposition rate should not exceed 1/10 k(B)T per second. This supports previous arguments for the improbability of biological effects at UHF frequencies unless a mechanism can be found for accumulating energy over time and space and focussing it. Second, three possible nonthermal accumulation mechanisms are then considered and shown to be unlikely: (i) multiphoton absorption processes; (ii) direct electric field effects on ions; (iii) cooperative effects and/or coherent excitations. Finally, it is concluded that the rate of energy deposition from a typical field and within a typical tissue is so small as to make unlikely any significant nonthermal biological effect. Copyright 2001 Wiley-Liss, Inc.

Long-term monitoring of ULF electromagnetic fields at Parkfield, CA

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

Kappler, K.N.; Morrison, H.F.; Egbert, G.D.

2009-08-01

Electric and magnetic fields in the (10{sup -4}-1.0) Hz band were monitored at two sites adjacent to the San Andreas Fault near Parkfield and Hollister, California from 1995 to present. A data window [2002-2005], enclosing the September 28, 2004 M6 Parkfield earthquake, was analyzed to determine if anomalous electric or magnetic fields, or changes in ground conductivity, occurred before the earthquake. The data were edited, removing intervals of instrument malfunction leaving 875 days in the four-year period. Frequent, spike-like disturbances were common, but were not more frequent around the time of the earthquake; these were removed before subsequent processing. Signalmore » to noise amplitude spectra, estimated via magnetotelluric processing showed the behavior of the ULF fields to be remarkably constant over the period of analysis. These first-order plots make clear that most of the recorded energy is coherent over the spatial extent of the array. Three main statistical techniques were employed to separate local anomalous electrical or magnetic fields from the dominant coherent natural fields: transfer function estimates between components at each site were employed to subtract the dominant field, and look deeper at the 'residual' fields; the data were decomposed into principal components to identify the dominant coherent array modes; and the technique of canonical coherences was employed to distinguish anomalous fields which are spatially broad from anomalies which occur at a single site only, and furthermore to distinguish anomalies which are present in both the electric and magnetic fields from those which are present in only one field type. Standard remote reference apparent resistivity estimates were generated daily at Parkfield. A significant seasonal component of variability was observed suggesting local distortion due to variations in near surface resistance. In all cases, high levels of sensitivity to subtle electromagnetic effects were demonstrated

Characterization of Different Cable Ferrite Materials to Reduce the Electromagnetic Noise in the 2–150 kHz Frequency Range

PubMed Central

Suarez, Adrian; Victoria, Jorge; Alcarria, Antonio; Torres, Jose; Martinez, Pedro A.; Muetsch, Steffen

2018-01-01

The gap of standardization for conducted and field coupled electromagnetic interferences (EMI) in the 2–150 kHz frequency range can lead to Electromagnetic Compatibility (EMC) problems. This is caused by power systems such as Pulse Width Modulation (PWM) controlled rectifiers, photovoltaic inverters or charging battery units in electric vehicles. This is a very important frequency spectral due to interferences generated in a wide range of devices and, specifically, communication problems in the new technologies and devices incorporated to the traditional grid to convert it into a Smart Grid. Consequently, it is necessary to provide new solutions to attenuate this kind of interference, which involves finding new materials that are able to filter the electromagnetic noise. This contribution is focused on characterizing the performance of a novel material based on nanocrystalline and comparing it to most common material compositions such as MnZn and NiZn. This research is carried out from the point of view of the manufacturing process, magnetic properties and EMI suppression ability. This last item is carried out through two analysis procedures: a theoretical method by determining the attenuation ratio by measuring impedance parameter and proposing a new empirical technique based on measuring directly the insertion loss parameter. Therefore, the main aim of this characterization process is to determine the performance of nanocrystalline compared to traditional cable ferrite compositions to reduce the interferences in this controversial frequency range. From the results obtained, it is possible to deduce that nanocrystalline cable ferrite provides the best performance to filter the electromagnetic noise in the 2–150 kHz frequency range. PMID:29360754

ULF waves associated with enhanced subauroral proton precipitation

NASA Astrophysics Data System (ADS)

Immel, Thomas J.; Mende, S. B.; Frey, H. U.; Patel, J.; Bonnell, J. W.; Engebretson, M. J.; Fuselier, S. A.

Several types of sub-auroral proton precipitation events have been identified using the Spectrographic Imager (SI) onboard the NASA-IMAGE satellite, including dayside subauroral proton flashes and detached proton arcs in the dusk sector. These have been observed at various levels of geomagnetic activity and solar wind conditions and the mechanism driving the precipitation has often been assumed to be scattering of protons into the loss cone by enhancement of ion-cyclotron waves in the interaction of the thermal plasmaspheric populations and more energetic ring current particles. Indeed, recent investigation of the detached arcs using the MPA instruments aboard the LANL geosynchronous satellites has shown there are nearly always heightened densities of cold plasma on high-altitude field lines which map down directly to the sub-auroral precipitation. If the ion-cyclotron instability is a causative mechanism, the enhancement of wave activity at ion-cyclotron frequencies should be measurable. It is here reported that magnetic pulsations in the Pc1 range occur in the vicinity of each of 4 detached arcs observed in 2000-2002, though with widely varying signatures. Additionally, longer period pulsations in the Pc5 ranges are also observed in the vicinity of the arcs, leading to the conclusion that a bounce-resonance of ring-current protons with the azimuthal Pc5 wave structure may also contribute to the detached precipitation.

Rapid estimation of frequency response functions by close-range photogrammetry

NASA Technical Reports Server (NTRS)

Tripp, J. S.

1985-01-01

The accuracy of a rapid method which estimates the frequency response function from stereoscopic dynamic data is computed. It is shown that reversal of the order of the operations of coordinate transformation and Fourier transformation, which provides a significant increase in computational speed, introduces error. A portion of the error, proportional to the perturbation components normal to the camera focal planes, cannot be eliminated. The remaining error may be eliminated by proper scaling of frequency data prior to coordinate transformation. Methods are developed for least squares estimation of the full 3x3 frequency response matrix for a three dimensional structure.

Laser-Bioplasma Interaction: Excitation and Suppression of the Brain Waves by the Multi-photon Pulsed-operated Fiber Lasers in the Ultraviolet Range of Frequencies

NASA Astrophysics Data System (ADS)

Stefan, V. Alexander; IAPS-team Team

2017-10-01

The novel study of the laser excitation-suppression of the brain waves is proposed. It is based on the pulsed-operated multi-photon fiber-laser interaction with the brain parvalbumin (PV) neurons. The repetition frequency matches the low frequency brain waves (5-100 Hz); enabling the resonance-scanning of the wide range of the PV neurons (the generators of the brain wave activity). The tunable fiber laser frequencies are in the ultraviolet frequency range, thus enabling the monitoring of the PV neuron-DNA, within the 10s of milliseconds. In medicine, the method can be used as an ``instantaneous-on-off anesthetic.'' Supported by Nikola Tesla Labs, Stefan University.

Waves from the Sun: to the 100th anniversary of V.A. Troitskaya's birth

NASA Astrophysics Data System (ADS)

Guglielmi, Anatol; Potapov, Alexander

2017-09-01

It has been one hundred years since the birth of the outstanding scientist Professor V.A. Troitskaya. Her remarkable achievements in solar-terrestrial physics are widely known. For many years, Valeria A. Troitskaya was the President of the International Association of Geomagnetism and Aeronomy. This article deals with only one aspect of the multifaceted creative activity of V.A. Troitskaya. It relates to the problem of sources of ultra-low frequency (ULF) electromagnetic oscillations and waves outside Earth’s magnetosphere. We were fortunate to work under the leadership of V.A. Troitskaya on this problem. In this paper, we briefly describe the history from the emergence of the idea of the extramagnetospheric origin of dayside permanent ULF oscillations in the late 1960s to the modern quest made by ground and satellite means for ULF waves excited by solar surface oscillations propagating in the interplanetary medium and reaching Earth.

Ion cyclotron range of frequencies heating of plasma with small impurity production

DOEpatents

Ohkawa, Tihiro

1987-01-01

Plasma including plasma ions is magnetically confined by a magnetic field. The plasma has a defined outer surface and is intersected by resonance surfaces of respective common ion cyclotron frequency of a predetermined species of plasma ions moving in the magnetic field. A radio frequency source provides radio frequency power at a radio frequency corresponding to the ion cyclotron frequency of the predetermined species of plasma ions moving in the field at a respective said resonance surface. RF launchers coupled to the radio frequency source radiate radio frequency energy at the resonance frequency onto the respective resonance surface within the plasma from a plurality of locations located outside the plasma at such respective distances from the intersections of the respective resonance surface and the defined outer surface and at such relative phases that the resulting interference pattern provides substantially null net radio frequency energy over regions near and including substantial portions of the intersections relative to the radio frequency energy provided thereby at other portions of the respective resonance surface within the plasma.

Broadband classification and statistics of echoes from aggregations of fish measured by long-range, mid-frequency sonar.

PubMed

Jones, Benjamin A; Stanton, Timothy K; Colosi, John A; Gauss, Roger C; Fialkowski, Joseph M; Michael Jech, J

2017-06-01

For horizontal-looking sonar systems operating at mid-frequencies (1-10 kHz), scattering by fish with resonant gas-filled swimbladders can dominate seafloor and surface reverberation at long-ranges (i.e., distances much greater than the water depth). This source of scattering, which can be difficult to distinguish from other sources of scattering in the water column or at the boundaries, can add spatio-temporal variability to an already complex acoustic record. Sparsely distributed, spatially compact fish aggregations were measured in the Gulf of Maine using a long-range broadband sonar with continuous spectral coverage from 1.5 to 5 kHz. Observed echoes, that are at least 15 decibels above background levels in the horizontal-looking sonar data, are classified spectrally by the resonance features as due to swimbladder-bearing fish. Contemporaneous multi-frequency echosounder measurements (18, 38, and 120 kHz) and net samples are used in conjunction with physics-based acoustic models to validate this approach. Furthermore, the fish aggregations are statistically characterized in the long-range data by highly non-Rayleigh distributions of the echo magnitudes. These distributions are accurately predicted by a computationally efficient, physics-based model. The model accounts for beam-pattern and waveguide effects as well as the scattering response of aggregations of fish.

Three dimensional ray tracing Jovian magnetosphere in the low frequency range

NASA Technical Reports Server (NTRS)

Menietti, J. D.

1982-01-01

Ray tracing of the Jovian magnetosphere in the low frequency range (1+40 MHz) has resulted in a new understanding of the source mechanism for Io dependent decametric radiation (DAM). Our three dimensional ray tracing computer code has provided model DAM arcs at 10 deg. intervals of Io longitude source positions for the full 360 deg of Jovian system III longitude. In addition, particularly interesting arcs were singled out for detailed study and modelling. Dependent decametric radiation arcs are categorized according to curvature--the higher curvature arcs are apparently due to wave stimulation at a nonconstant wave normal angle, psi. The psi(f) relationship has a signature that is common to most of the higher curvature arcs. The low curvature arcs, on the other hand, are adequately modelled with a constant wave normal angle of close to 90 deg. These results imply that for higher curvature arcs observed for from Jupiter (to diminish spacecraft motion effects) the electrons providing the gyroemission are relativistically beamed.

Noise and range considerations for close-range radar sensing of life signs underwater.

PubMed

Hafner, Noah; Lubecke, Victor

2011-01-01

Close-range underwater sensing of motion-based life signs can be performed with low power Doppler radar and ultrasound techniques. Corresponding noise and range performance trade-offs are examined here, with regard to choice of frequency and technology. The frequency range examined includes part of the UHF and microwave spectrum. Underwater detection of motion by radar in freshwater and saltwater are demonstrated. Radar measurements exhibited reduced susceptibility to noise as compared to ultrasound. While higher frequency radar exhibited better signal to noise ratio, propagation was superior for lower frequencies. Radar detection of motion through saltwater was also demonstrated at restricted ranges (1-2 cm) with low power transmission (10 dBm). The results facilitate the establishment of guidelines for optimal choice in technology for the underwater measurement motion-based life signs, with respect to trade offs involving range and noise.

SQUIDs vs. Induction Coils for Ultra-Low Field Nuclear Magnetic Resonance: Experimental and Simulation Comparison

PubMed Central

Matlashov, Andrei N.; Schultz, Larry J.; Espy, Michelle A.; Kraus, Robert H.; Savukov, Igor M.; Volegov, Petr L.; Wurden, Caroline J.

2011-01-01

Nuclear magnetic resonance (NMR) is widely used in medicine, chemistry and industry. One application area is magnetic resonance imaging (MRI). Recently it has become possible to perform NMR and MRI in the ultra-low field (ULF) regime requiring measurement field strengths of the order of only 1 Gauss. This technique exploits the advantages offered by superconducting quantum interference devices or SQUIDs. Our group has built SQUID based MRI systems for brain imaging and for liquid explosives detection at airport security checkpoints. The requirement for liquid helium cooling limits potential applications of ULF MRI for liquid identification and security purposes. Our experimental comparative investigation shows that room temperature inductive magnetometers may provide enough sensitivity in the 3–10 kHz range and can be used for fast liquid explosives detection based on ULF NMR technique. We describe experimental and computer-simulation results comparing multichannel SQUID based and induction coils based instruments that are capable of performing ULF MRI for liquid identification. PMID:21747638

Simulation of electron transport in GaAs/AlAs superlattices with a small number of periods for the THz frequency range

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

Pavelyev, D. G., E-mail: pavelev@rf.unn.ru, E-mail: obolensk@rf.unn.ru; Vasilev, A. P., E-mail: vasiljev@mail.ioffe.ru; Kozlov, V. A., E-mail: kozlov@ipm.sci-nnov.ru

2016-11-15

The electron transport in superlattices based on GaAs/AlAs heterostructures with a small number of periods (6 periods) is calculated by the Monte Carlo method. These superlattices are used in terahertz diodes for the frequency stabilization of quantum cascade lasers in the range up to 4.7 THz. The band structure of superlattices with different numbers of AlAs monolayers is considered and their current–voltage characteristics are calculated. The calculated current–voltage characteristics are compared with the experimental data. The possibility of the efficient application of these superlattices in the THz frequency range is established both theoretically and experimentally.

Ultra-low field T1 vs. T1rho at 3T and 7T: study of rotationally immobilized protein gels and animal brain tissues

NASA Astrophysics Data System (ADS)

Dong, Hui; Inglis, Ben; Barr, Ian; Clarke, John

2015-03-01

Clinical magnetic resonance imaging (MRI) machines operating in static fields of typically 1.5 T or 3 T can capture information on slow molecular dynamics utilizing the so-called T1rho technique. This technique, in which a radiofrequency (RF) spin-lock field is applied with microtesla amplitude, has been used, for example, to determine the onset time of stroke in studies on rats. The long RF pulse, however, may exceed the specific absorption rate (SAR) limit, putting subjects at risk. Ultra-low-field (ULF) MRI, based on Superconducting Quantum Interference Devices (SQUIDs), directly detects proton signals at a static magnetic field of typically 50-250 μT. Using our ULF MRI system with adjustable static field of typically 55 to 240 μT, we systematically measured the T1 and T2 dispersion profiles of rotationally immobilized protein gels (bovine serum albumin), ex vivo pig brains, and ex vivo rat brains with induced stroke. Comparing the ULF results with T1rho dispersion obtained at 3 T and 7 T, we find that the degree of protein immobilization determines the frequency-dependence of both T1 and T1rho. Furthermore, T1rho and ULF T1 show similar results for stroke, suggesting that ULF MRI may be used to image traumatic brain injury with negligible SAR. This research was supported by the Henry H. Wheeler, Jr. Brain Imaging Center and the Donaldson Trust.

Numerical Exposure Assessment Method for Low Frequency Range and Application to Wireless Power Transfer

PubMed Central

Kim, Minhyuk

2016-01-01

In this paper, a numerical exposure assessment method is presented for a quasi-static analysis by the use of finite-difference time-domain (FDTD) algorithm. The proposed method is composed of scattered field FDTD method and quasi-static approximation for analyzing of the low frequency band electromagnetic problems. The proposed method provides an effective tool to compute induced electric fields in an anatomically realistic human voxel model exposed to an arbitrary non-uniform field source in the low frequency ranges. The method is verified, and excellent agreement with theoretical solutions is found for a dielectric sphere model exposed to a magnetic dipole source. The assessment method serves a practical example of the electric fields, current densities, and specific absorption rates induced in a human head and body in close proximity to a 150-kHz wireless power transfer system for cell phone charging. The results are compared to the limits recommended by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and the IEEE standard guidelines. PMID:27898688

Modulation of auroral electron fluxes in the frequency range 50 kHz to 10 MHz

NASA Technical Reports Server (NTRS)

Spiger, R. J.; Murphree, J. S.; Anderson, H. R.; Loewenstein, R. F.

1976-01-01

A sounding rocket-borne electron detector of high time resolution is used to search for modulation of auroral electron fluxes in the frequency range 50 kHz to 10 MHz and energy range 5-7 keV. Data were telemetered to ground via a 93-kHz subcarrier. A cross-correlation analysis of the data collected indicates low-level modulation near the detection threshold of the instrument. Two U-1 events are observed which are interpreted as indications of modulation. The two modulation events occur during a period of increasing flux for a region marking the boundary between two current sheets detected by the payload magnetometer. The strongest argument against interference contamination is the lack of any observable modulation at times other than those mentioned in the study.

Development of a Radio Frequency Space Environment Path Emulator for Evaluating Spacecraft Ranging Hardware

NASA Technical Reports Server (NTRS)

Mitchell, Jason W.; Baldwin, Philip J.; Kurichh, Rishi; Naasz, Bo J.; Luquette, Richard J.

2007-01-01

The Formation Flying Testbed (FFTB) at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) provides a hardware-in-the-loop test environment for formation navigation and control. The facility is evolving as a modular, hybrid, dynamic simulation facility for end-to-end guidance, navigation and. control (GN&C) design and analysis of formation flying spacecraft. The core capabilities of the FFTB, as a platform for testing critical hardware and software algorithms in-the-loop, have expanded to include S-band Radio Frequency (RF) modems for inter-spacecraft communication and ranging. To enable realistic simulations that require RF ranging sensors for relative navigation, a mechanism is needed to buffer the RF signals exchanged between spacecraft that accurately emulates the dynamic environment through which the RF signals travel, including the effects of medium, moving platforms, and radiated power. The Path Emulator for RF Signals (PERFS), currently under development at NASA GSFC, provides this capability. The function and performance of a prototype device are presented.

Programmable Thermostats for MPLM Shell Heater Control ULF1. 1; Thermal Performances

NASA Technical Reports Server (NTRS)

Glasgow, Shaun; Clark, Dallas; Trichilo, Michele; Trichilo, Michele

2007-01-01

The Multi-Purpose Logistics Module (MPLM) is the primary carrier for "pressurized" logistics to and from the International Space Station (ISS). The MPLM is transported in the payload bay of the Space Shuttle and is docked to the ISS for unloading, and reloading, of contents within the ISS shirt sleeve environment. Foil heaters, controlled originally with bi-metallic thermostats, are distributed across the outside of the MPLM structure and are utilized to provide energy to the structure to avoid exposure to cold temperatures and prevent condensation. The existing bi-metallic, fixed temperature set point thermostats have been replaced with Programmable Thermostats Modules (PTMs) in the Passive Thermal Control Subsystem (PTCS) 28Vdc shell heater circuits. The goal of using the PTM thermostat is to improve operational efficiency of the MPLM on-orbit shell heaters by providing better shell temperature control via feedback control capability. Each heater circuit contains a programmable thermostat connected to an external temperature sensor, a Resistive Temperature Device (RTD), which is used to provide continuous temperature monitoring capability. Each thermostat has programmable temperature set points and control spans. The data acquisition system uses a standard RS-485 serial interface communications cable to provide digital control capability. The PTM system was designed by MSFC, relying upon ALTEC support for their integration within the MPLM system design, while KSC performed the installation and ground checkout testing of the thermostat and RS-485 communication cable on the MPLM FM1 flight module. The PTMs were used for the first time during the STS-121/ULF1.1 mission. This paper will describe the design, development and verification of the PTM system, as well as the PTM flight performance and comparisons with SINDA thermal model predictions.

Diversity, Frequency, and Persistence of Escherichia coli O157 Strains from Range Cattle Environments†

PubMed Central

Renter, David G.; Sargeant, Jan M.; Oberst, Richard D.; Samadpour, Mansour

2003-01-01

Genetic diversity, isolation frequency, and persistence were determined for Escherichia coli O157 strains from range cattle production environments. Over the 11-month study, analysis of 9,122 cattle fecal samples, 4,083 water source samples, and 521 wildlife fecal samples resulted in 263 isolates from 107 samples presumptively considered E. coli O157 as determined by culture and latex agglutination. Most isolates (90.1%) were confirmed to be E. coli O157 by PCR detection of intimin and Shiga toxin genes. Pulsed-field gel electrophoresis (PFGE) of XbaI-digested preparations revealed 79 unique patterns (XbaI-PFGE subtypes) from 235 typeable isolates confirmed to be E. coli O157. By analyzing up to three isolates per positive sample, we detected an average of 1.80 XbaI-PFGE subtypes per sample. Most XbaI-PFGE subtypes (54 subtypes) were identified only once, yet the seven most frequently isolated subtypes represented over one-half of the E. coli O157 isolates (124 of 235 isolates). Recurring XbaI-PFGE subtypes were recovered from samples on up to 10 sampling occasions and up to 10 months apart. Seven XbaI-PFGE subtypes were isolated from both cattle feces and water sources, and one of these also was isolated from the feces of a wild opossum (Didelphis sp.). The number of XbaI-PFGE subtypes, the variable frequency and persistence of subtypes, and the presence of identical subtypes in cattle feces, free-flowing water sources, and wildlife feces indicate that the complex molecular epidemiology of E. coli O157 previously described for confined cattle operations is also evident in extensively managed range cattle environments. PMID:12514039

Active stabilization of error field penetration via control field and bifurcation of its stable frequency range

NASA Astrophysics Data System (ADS)

Inoue, S.; Shiraishi, J.; Takechi, M.; Matsunaga, G.; Isayama, A.; Hayashi, N.; Ide, S.

2017-11-01

An active stabilization effect of a rotating control field against an error field penetration is numerically studied. We have developed a resistive magnetohydrodynamic code ‘AEOLUS-IT’, which can simulate plasma responses to rotating/static external magnetic field. Adopting non-uniform flux coordinates system, the AEOLUS-IT simulation can employ high magnetic Reynolds number condition relevant to present tokamaks. By AEOLUS-IT, we successfully clarified the stabilization mechanism of the control field against the error field penetration. Physical processes of a plasma rotation drive via the control field are demonstrated by the nonlinear simulation, which reveals that the rotation amplitude at a resonant surface is not a monotonic function of the control field frequency, but has an extremum. Consequently, two ‘bifurcated’ frequency ranges of the control field are found for the stabilization of the error field penetration.

Investigation of Multiple Frequency Ranges Using Discrete Wavelet Decomposition of Resting-State Functional Connectivity in Mild Traumatic Brain Injury Patients

PubMed Central

Chen, Haoxing; Roys, Steven; Zhuo, Jiachen; Varshney, Amitabh; Gullapalli, Rao P.

2015-01-01

Abstract The aim of this study was to investigate if discrete wavelet decomposition provides additional insight into resting-state processes through the analysis of functional connectivity within specific frequency ranges within the default mode network (DMN) that may be affected by mild traumatic brain injury (mTBI). Participants included 32 mTBI patients (15 with postconcussive syndrome [PCS+] and 17 without [PCS−]). mTBI patients received resting-state functional magnetic resonance imaging (rs-fMRI) at acute (within 10 days of injury) and chronic (6 months postinjury) time points and were compared with 31 controls (healthy control [HC]). The wavelet decomposition divides the time series into multiple frequency ranges based on four scaling factors (SF1: 0.125–0.250 Hz, SF2: 0.060–0.125 Hz, SF3: 0.030–0.060 Hz, SF4: 0.015–0.030 Hz). Within each SF, wavelet connectivity matrices for nodes of the DMN were created for each group (HC, PCS+, PCS−), and bivariate measures of strength and diversity were calculated. The results demonstrate reduced strength of connectivity in PCS+ patients compared with PCS− patients within SF1 during both the acute and chronic stages of injury, as well as recovery of connectivity within SF1 across the two time points. Furthermore, the PCS− group demonstrated greater network strength compared with controls at both time points, suggesting a potential compensatory or protective mechanism in these patients. These findings stress the importance of investigating resting-state connectivity within multiple frequency ranges; however, many of our findings are within SF1, which may overlap with frequencies associated with cardiac and respiratory activities. PMID:25808612

Investigation of Multiple Frequency Ranges Using Discrete Wavelet Decomposition of Resting-State Functional Connectivity in Mild Traumatic Brain Injury Patients.

PubMed

Sours, Chandler; Chen, Haoxing; Roys, Steven; Zhuo, Jiachen; Varshney, Amitabh; Gullapalli, Rao P

2015-09-01

The aim of this study was to investigate if discrete wavelet decomposition provides additional insight into resting-state processes through the analysis of functional connectivity within specific frequency ranges within the default mode network (DMN) that may be affected by mild traumatic brain injury (mTBI). Participants included 32 mTBI patients (15 with postconcussive syndrome [PCS+] and 17 without [PCS-]). mTBI patients received resting-state functional magnetic resonance imaging (rs-fMRI) at acute (within 10 days of injury) and chronic (6 months postinjury) time points and were compared with 31 controls (healthy control [HC]). The wavelet decomposition divides the time series into multiple frequency ranges based on four scaling factors (SF1: 0.125-0.250 Hz, SF2: 0.060-0.125 Hz, SF3: 0.030-0.060 Hz, SF4: 0.015-0.030 Hz). Within each SF, wavelet connectivity matrices for nodes of the DMN were created for each group (HC, PCS+, PCS-), and bivariate measures of strength and diversity were calculated. The results demonstrate reduced strength of connectivity in PCS+ patients compared with PCS- patients within SF1 during both the acute and chronic stages of injury, as well as recovery of connectivity within SF1 across the two time points. Furthermore, the PCS- group demonstrated greater network strength compared with controls at both time points, suggesting a potential compensatory or protective mechanism in these patients. These findings stress the importance of investigating resting-state connectivity within multiple frequency ranges; however, many of our findings are within SF1, which may overlap with frequencies associated with cardiac and respiratory activities.

New sample cell configuration for wide-frequency dielectric spectroscopy: DC to radio frequencies.

PubMed

Nakanishi, Masahiro; Sasaki, Yasutaka; Nozaki, Ryusuke

2010-12-01

A new configuration for the sample cell to be used in broadband dielectric spectroscopy is presented. A coaxial structure with a parallel plate capacitor (outward parallel plate cell: OPPC) has made it possible to extend the frequency range significantly in comparison with the frequency range of the conventional configuration. In the proposed configuration, stray inductance is significantly decreased; consequently, the upper bound of the frequency range is improved by two orders of magnitude from the upper limit of conventional parallel plate capacitor (1 MHz). Furthermore, the value of capacitance is kept high by using a parallel plate configuration. Therefore, the precision of the capacitance measurement in the lower frequency range remains sufficiently high. Finally, OPPC can cover a wide frequency range (100 Hz-1 GHz) with an appropriate admittance measuring apparatus such as an impedance or network analyzer. The OPPC and the conventional dielectric cell are compared by examining the frequency dependence of the complex permittivity for several polar liquids and polymeric films.

Application of AWE Along with a Combined FEM/MoM Technique to Compute RCS of a Cavity-Backed Aperture in an Infinite Ground Plane Over a Frequency Range

NASA Technical Reports Server (NTRS)

Reddy, C.J.; Deshpande, M.D.

1997-01-01

A hybrid Finite Element Method (FEM)/Method of Moments (MoM) technique in conjunction with the Asymptotic Waveform Evaluation (AWE) technique is applied to obtain radar cross section (RCS) of a cavity-backed aperture in an infinite ground plane over a frequency range. The hybrid FEM/MoM technique when applied to the cavity-backed aperture results in an integro-differential equation with electric field as the unknown variable, the electric field obtained from the solution of the integro-differential equation is expanded in Taylor series. The coefficients of the Taylor series are obtained using the frequency derivatives of the integro-differential equation formed by the hybrid FEM/MoM technique. The series is then matched via the Pade approximation to a rational polynomial, which can be used to extrapolate the electric field over a frequency range. The RCS of the cavity-backed aperture is calculated using the electric field at different frequencies. Numerical results for a rectangular cavity, a circular cavity, and a material filled cavity are presented over a frequency range. Good agreement between AWE and the exact solution over the frequency range is obtained.

Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector

DOE PAGES

Min, Kyungguk; Takahashi, Kazue; Ukhorskiy, Aleksandr Y.; ...

2017-02-24

This paper presents observations of ultralow-frequency (ULF) waves from Van Allen Probes. The event that generated the ULF waves occurred 2 days after a minor geomagnetic storm during a geomagnetically quiet time. Narrowband pulsations with a frequency of about 7 mHz with moderate amplitudes were registered in the premidnight sector when Probe A was passing through an enhanced density region near geosynchronous orbit. Probe B, which passed through the region earlier, did not detect the narrowband pulsations but only broadband noise. Despite the single-spacecraft measurements, we were able to determine various wave properties. We find that the observed waves aremore » a second harmonic poloidal mode propagating westward with an azimuthal wave number estimated to be ~100; the magnetic field fluctuations have a finite compressional component due to small but finite plasma beta (~0.1); the energetic proton fluxes in the energy ranging from above 10 keV to about 100 keV exhibit pulsations with the same frequency as the poloidal mode and energy-dependent phase delays relative to the azimuthal component of the electric field, providing evidence for drift-bounce resonance; and the second harmonic poloidal mode may have been excited via the drift-bounce resonance mechanism with free energy fed by the inward radial gradient of ~80 keV protons. Here, we show that the wave active region is where the plume overlaps the outer edge of ring current and suggest that this region can have a wide longitudinal extent near geosynchronous orbit.« less

Second harmonic poloidal waves observed by Van Allen Probes in the dusk-midnight sector

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

Min, Kyungguk; Takahashi, Kazue; Ukhorskiy, Aleksandr Y.

This paper presents observations of ultralow-frequency (ULF) waves from Van Allen Probes. The event that generated the ULF waves occurred 2 days after a minor geomagnetic storm during a geomagnetically quiet time. Narrowband pulsations with a frequency of about 7 mHz with moderate amplitudes were registered in the premidnight sector when Probe A was passing through an enhanced density region near geosynchronous orbit. Probe B, which passed through the region earlier, did not detect the narrowband pulsations but only broadband noise. Despite the single-spacecraft measurements, we were able to determine various wave properties. We find that the observed waves aremore » a second harmonic poloidal mode propagating westward with an azimuthal wave number estimated to be ~100; the magnetic field fluctuations have a finite compressional component due to small but finite plasma beta (~0.1); the energetic proton fluxes in the energy ranging from above 10 keV to about 100 keV exhibit pulsations with the same frequency as the poloidal mode and energy-dependent phase delays relative to the azimuthal component of the electric field, providing evidence for drift-bounce resonance; and the second harmonic poloidal mode may have been excited via the drift-bounce resonance mechanism with free energy fed by the inward radial gradient of ~80 keV protons. Here, we show that the wave active region is where the plume overlaps the outer edge of ring current and suggest that this region can have a wide longitudinal extent near geosynchronous orbit.« less

Possible link of sudden onset and short-time periodic pulsation of polar mesosphere summer echoes to ULF Pc5 geomagnetic pulsations and solar wind dynamic pressure enhancement

NASA Astrophysics Data System (ADS)

Lee, Y.; Kirkwood, S.; Kwak, Y. S.

2016-12-01

The EISCAT VHF incoherent scatter radar in Tromsö, Norway, makes occasional observations of electron densities and Polar Mesosphere Summer Echoes, in the summer polar D-region ionosphere. In one of those datasets, pulsating polar mesospheric summer echoes (PMSE) are observed, with periodicities in the ultra-low frequency (ULF) Pc5 band (1.6-6.7 mHz), following an abrupt increase of the radar reflectivity when a geomagnetic field excursion is started, in turn linked to dynamic pressure (Pdyn) enhancement in the solar wind. At the excursion of the magnetic field, at auroral altitudes of 90 km and above, electron density is abruptly enhanced, followed by a series of short-lived peaks, superimposed on an enhanced level. The short-lived peaks are likely a signature of transient Pc5 geomagnetic pulsations and associated energetic electron precipitation from pitch-angle scattering into the loss cone in the magnetosphere. At the same time, at altitudes around 80-90 km, a sharp increase of PMSE reflectivity occurs, 100 times greater than the increase of electron density, and is followed by pulsating PMSE reflectivity with periodicities in the Pc5 band, increasing and decreasing in magnitude during the course of the next hour. The increase of the pulsation magnitude may be attributed to an increase of high-energy electron precipitation flux ( >30 keV) penetrating to at least the height of maximum PMSE reflectivity. This study suggests that Pc5 pulsation bursts in both magnetic field and high energy electron precipitation could play a crucial role in producing PMSE fluctuations on minute-to-minute time scales.

SQUIDs vs. Faraday coils for ultlra-low field nuclear magnetic resonance: experimental and simulation comparison

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

Matlashov, Andrei N; Espy, Michelle A; Kraus, Robert H

2010-01-01

Nuclear magnetic resonance (NMR) methods are widely used in medicine, chemistry and industry. One application area is magnetic resonance imaging or MRI. Recently it has become possible to perform NMR and MRI in ultra-low field (ULF) regime that requires measurement field strengths only of the order of 1 Gauss. These techniques exploit the advantages offered by superconducting quantum interference devices or SQUIDs. Our group at LANL has built SQUID based MRI systems for brain imaging and for liquid explosives detection at airports security checkpoints. The requirement for liquid helium cooling limits potential applications of ULF MRI for liquid identification andmore » security purposes. Our experimental comparative investigation shows that room temperature inductive magnetometers provide enough sensitivity in the 3-10 kHz range and can be used for fast liquid explosives detection based on ULF NMR/MRI technique. We describe an experimental and computer simulation comparison of the world's first multichannel SQUID based and Faraday coils based instruments that are capable of performing ULF MRI for liquids identification.« less

Brain states recognition during visual perception by means of artificial neural network in the different EEG frequency ranges

NASA Astrophysics Data System (ADS)

Musatov, V. Yu.; Runnova, A. E.; Andreev, A. V.; Zhuravlev, M. O.

2018-04-01

In the present paper, the possibility of classification by artificial neural networks of a certain architecture of ambiguous images is investigated using the example of the Necker cube from the experimentally obtained EEG recording data of several operators. The possibilities of artificial neural network classification of ambiguous images are investigated in the different frequency ranges of EEG recording signals.

Magnetosheath plasma stability and ULF wave occurrence as a function of location in the magnetosheath and upstream bow shock parameters

NASA Astrophysics Data System (ADS)

Soucek, Jan; Escoubet, C. Philippe; Grison, Benjamin

2015-04-01

We present the results of a statistical study of the distribution of mirror and Alfvén-ion cyclotron (AIC) waves in the magnetosheath together with plasma parameters important for the stability of ULF waves, specifically ion temperature anisotropy and ion beta. Magnetosheath crossings registered by Cluster spacecraft over the course of 2 years served as a basis for the statistics. For each observation we used bow shock, magnetopause, and magnetosheath flow models to identify the relative position of the spacecraft with respect to magnetosheath boundaries and local properties of the upstream shock crossing. A strong dependence of both plasma parameters and mirror/AIC wave occurrence on upstream ΘBn and MA is identified. We analyzed a joint dependence of the same parameters on ΘBn and fractional distance between shock and magnetopause, zenith angle, and length of the flow line. Finally, the occurrence of mirror and AIC modes was compared against the respective instability thresholds. We noted that AIC waves occurred nearly exclusively under mirror stable conditions. This is interpreted in terms of different characters of nonlinear saturation of the two modes.

Time-frequency analysis of acoustic signals in the audio-frequency range generated during Hadfield's steel friction

NASA Astrophysics Data System (ADS)

Dobrynin, S. A.; Kolubaev, E. A.; Smolin, A. Yu.; Dmitriev, A. I.; Psakhie, S. G.

2010-07-01

Time-frequency analysis of sound waves detected by a microphone during the friction of Hadfield’s steel has been performed using wavelet transform and window Fourier transform methods. This approach reveals a relationship between the appearance of quasi-periodic intensity outbursts in the acoustic response signals and the processes responsible for the formation of wear products. It is shown that the time-frequency analysis of acoustic emission in a tribosystem can be applied, along with traditional approaches, to studying features in the wear and friction process.

A crossover trial comparing wide dynamic range compression and frequency compression in hearing aids for tinnitus therapy.

PubMed

Hodgson, Shirley-Anne; Herdering, Regina; Singh Shekhawat, Giriraj; Searchfield, Grant D

2017-01-01

It has been suggested that frequency lowering may be a superior tinnitus reducing digital signal processing (DSP) strategy in hearing aids than conventional amplification. A crossover trial was undertaken to determine if frequency compression (FC) was superior to wide dynamic range compression (WDRC) in reducing tinnitus. A 6-8-week crossover trial of two digital signal-processing techniques (WDRC and 2 WDRC with FC) was undertaken in 16 persons with high-frequency sensorineural hearing loss and chronic tinnitus. WDRC resulted in larger improvements in Tinnitus Functional Index and rating scale scores than WDRC with FC. The tinnitus improvements obtained with both processing types appear to be due to reduced hearing handicap and possibly decreased tinnitus audibility. Hearing aids are useful assistive devices in the rehabilitation of tinnitus. FC was very successful in a few individuals but was not superior to WDRC across the sample. It is recommended that WDRC remain as the default first choice tinnitus hearing aid processing strategy for tinnitus. FC should be considered as one of the many other options for selection based on individual hearing needs. Implications of Rehabilitation Hearing aids can significantly reduce the effects of tinnitus after 6-8 weeks of use. Addition of frequency compression digital signal processing does not appear superior to standard amplitude compression alone. Improvements in tinnitus were correlated with reductions in hearing handicap.

Large allele frequency differences between human continental groups are more likely to have occurred by drift during range expansions than by selection.

PubMed

Hofer, T; Ray, N; Wegmann, D; Excoffier, L

2009-01-01

Several studies have found strikingly different allele frequencies between continents. This has been mainly interpreted as being due to local adaptation. However, demographic factors can generate similar patterns. Namely, allelic surfing during a population range expansion may increase the frequency of alleles in newly colonised areas. In this study, we examined 772 STRs, 210 diallelic indels, and 2834 SNPs typed in 53 human populations worldwide under the HGDP-CEPH Diversity Panel to determine to which extent allele frequency differs among four regions (Africa, Eurasia, East Asia, and America). We find that large allele frequency differences between continents are surprisingly common, and that Africa and America show the largest number of loci with extreme frequency differences. Moreover, more STR alleles have increased rather than decreased in frequency outside Africa, as expected under allelic surfing. Finally, there is no relationship between the extent of allele frequency differences and proximity to genes, as would be expected under selection. We therefore conclude that most of the observed large allele frequency differences between continents result from demography rather than from positive selection.

Individual Ranging Behaviour Patterns in Commercial Free-Range Layers as Observed through RFID Tracking.

PubMed

Larsen, Hannah; Cronin, Greg M; Gebhardt-Henrich, Sabine G; Smith, Carolynn L; Hemsworth, Paul H; Rault, Jean-Loup

2017-03-09

In this exploratory study, we tracked free-range laying hens on two commercial flocks with Radio Frequency Identification (RFID) technology with the aim to examine individual hen variation in range use. Three distinct outdoor zones were identified at increasing distances from the shed; the veranda [0-2.4 m], close range [2.4-11.4 m], and far range [>11.4 m]. Hens' movements between these areas were tracked using radio frequency identification technology. Most of the hens in both flocks (68.6% in Flock A, and 82.2% in Flock B) accessed the range every day during the study. Of the hens that accessed the range, most hens accessed all three zones (73.7% in Flock A, and 84.5% in Flock B). Hens spent half of their time outdoors in the veranda area. Within-individual consistency of range use (daily duration and frequency) varied considerably, and hens which were more consistent in their daily range use spent more time on the range overall ( p < 0.001). Understanding variation within and between individuals in ranging behaviour may help elucidate the implications of ranging for laying hens.

Are the initial frequency-modulated components of the mustached bat's biosonar pulses important for ranging?

PubMed

Fitzpatrick, D C; Suga, N; Misawa, H

1991-12-01

1. FM-FM neurons in the auditory cortex of the mustached bat, Pteronotus parnellii, are specialized to process target range. They respond when the terminal frequency-modulated component (TFM) of a biosonar pulse is paired with the TFM of the echo at a particular echo delay. Recently, it has been suggested that the initial FM components (IFMs) of biosonar signals may also be important for target ranging. To examine the possible role of IFMs in target ranging, we characterized the properties of IFMs and TFMs in biosonar pulses emitted by bats swung on a pendulum. We then studied responses of FM-FM neurons to synthesized biosonar signals containing IFMs and TFMs. 2. The mustached bat's biosonar signal consists of four harmonics, of which the second (H2) is the most intense. Each harmonic has an IFM in addition to a constant-frequency component (CF) and a TFM. Therefore each pulse potentially consists of 12 components, IFM1-4, CF1-4, and TFM1-4. The IFM sweeps up while the TFM sweeps down. 3. The IFM2 and TFM2 depths (i.e., bandwidths) were measured in 217 pulses from four animals. The mean IFM2 depth was much smaller than the mean TFM2 depth, 2.87 +/- 1.52 (SD) kHz compared with 16.27 +/- 1.08 kHz, respectively. The amplitude of the IFM2 continuously increased throughout its duration and was always less than the CF2 amplitude, whereas the TFM2 was relatively constant in amplitude over approximately three-quarters of its duration and was often the most intense part of the pulse. The maximum amplitude of the IFM2 was, on average, 11 dB smaller than that of the TFM2. Because range resolution increases with depth and the maximum detectable range increases with signal amplitude, the IFMs are poorly suited for ranging compared with the TFMs. 4. FM-FM neurons (n = 77) did not respond or responded very poorly to IFMs with depths and intensities similar to those emitted on the pendulum. The mean IFM2 depth at which a just-noticeable response appeared was 4.48 +/- 1.98 k

Dielectric spectroscopy in aqueous solutions of paracetamol over the frequency range of 20 Hz to 2 MHz at 293.15 K temperature

NASA Astrophysics Data System (ADS)

Pandit, T. R.; Rana, V. A.

2018-05-01

Frequency domain dielectric relaxation spectroscopy plays an important role in the study of pharmaceutical drug molecules. The complex relative dielectric permittivity ɛ*(ω) = ɛ' - j ɛ" of aqueous solutions of paracetamol in the frequency range of 20 Hz to 2 MHz at a temperature range of 293.15 K are measured with the help of Agilent precision LCR meter E4980A along with four terminal liquid test fixture Agilent 16452A. Data of complex relative permittivity are used to calculate loss tangent for all concentrations of paracetamol in distilled water. Electrode polarization relaxation time has been calculated for all solutions. Effect of variation of concentrations of paracetamol in distilled water on these dielectric parameters is discussed.

Microwave soft x-ray microscopy for nanoscale magnetization dynamics in the 5–10 GHz frequency range

DOE PAGES

Bonetti, Stefano; Kukreja, Roopali; Chen, Zhao; ...

2015-09-10

In this study, we present a scanning transmission x-ray microscopy setup combined with a novel microwave synchronization scheme in order to study high frequency magnetization dynamics at synchrotron light sources. The sensitivity necessary to detect small changes of the magnetization on short time scales and nanometer spatial dimensions is achieved by combination of the developed excitation mechanism with a single photon counting electronics that is locked to the synchrotron operation frequency. The required mechanical stability is achieved by a compact design of the microscope. Our instrument is capable of creating direct images of dynamical phenomena in the 5-10 GHz range,more » with 35 nm resolution. When used together with circularly polarized x-rays, the above capabilities can be combined to study magnetic phenomena at microwave frequencies, such as ferromagnetic resonance (FMR) and spin waves. We demonstrate the capabilities of our technique by presenting phase resolved images of a –6 GHz nanoscale spin wave generated by a spin torque oscillator, as well as the uniform ferromagnetic precession with ~0.1° amplitude at –9 GHz in a micrometer-sized cobalt strip.« less

Magnetohydrodynamic modeling of three Van Allen Probes storms in 2012 and 2013

NASA Astrophysics Data System (ADS)

Paral, J.; Hudson, M. K.; Kress, B. T.; Wiltberger, M. J.; Wygant, J. R.; Singer, H. J.

2015-08-01

Coronal mass ejection (CME)-shock compression of the dayside magnetopause has been observed to cause both prompt enhancement of radiation belt electron flux due to inward radial transport of electrons conserving their first adiabatic invariant and prompt losses which at times entirely eliminate the outer zone. Recent numerical studies suggest that enhanced ultra-low frequency (ULF) wave activity is necessary to explain electron losses deeper inside the magnetosphere than magnetopause incursion following CME-shock arrival. A combination of radial transport and magnetopause shadowing can account for losses observed at radial distances into L = 4.5, well within the computed magnetopause location. We compare ULF wave power from the Electric Field and Waves (EFW) electric field instrument on the Van Allen Probes for the 8 October 2013 storm with ULF wave power simulated using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic (MHD) magnetospheric simulation code coupled to the Rice Convection Model (RCM). Two other storms with strong magnetopause compression, 8-9 October 2012 and 17-18 March 2013, are also examined. We show that the global MHD model captures the azimuthal magnetosonic impulse propagation speed and amplitude observed by the Van Allen Probes which is responsible for prompt acceleration at MeV energies reported for the 8 October 2013 storm. The simulation also captures the ULF wave power in the azimuthal component of the electric field, responsible for acceleration and radial transport of electrons, at frequencies comparable to the electron drift period. This electric field impulse has been shown to explain observations in related studies (Foster et al., 2015) of electron acceleration and drift phase bunching by the Energetic Particle, Composition, and Thermal Plasma Suite (ECT) instrument on the Van Allen Probes.

Frequency comb swept lasers.

PubMed

Tsai, Tsung-Han; Zhou, Chao; Adler, Desmond C; Fujimoto, James G

2009-11-09

We demonstrate a frequency comb (FC) swept laser and a frequency comb Fourier domain mode locked (FC-FDML) laser for applications in optical coherence tomography (OCT). The fiber-based FC swept lasers operate at a sweep rate of 1kHz and 120kHz, respectively over a 135nm tuning range centered at 1310nm with average output powers of 50mW. A 25GHz free spectral range frequency comb filter in the swept lasers causes the lasers to generate a series of well defined frequency steps. The narrow bandwidth (0.015nm) of the frequency comb filter enables a approximately -1.2dB sensitivity roll off over approximately 3mm range, compared to conventional swept source and FDML lasers which have -10dB and -5dB roll offs, respectively. Measurements at very long ranges are possible with minimal sensitivity loss, however reflections from outside the principal measurement range of 0-3mm appear aliased back into the principal range. In addition, the frequency comb output from the lasers are equally spaced in frequency (linear in k-space). The filtered laser output can be used to self-clock the OCT interference signal sampling, enabling direct fast Fourier transformation of the fringe signals, without the need for fringe recalibration procedures. The design and operation principles of FC swept lasers are discussed and designs for short cavity lasers for OCT and interferometric measurement applications are proposed.

Frequency comb swept lasers

PubMed Central

Tsai, Tsung-Han; Zhou, Chao; Adler, Desmond C.; Fujimoto, James G.

2010-01-01

We demonstrate a frequency comb (FC) swept laser and a frequency comb Fourier domain mode locked (FC-FDML) laser for applications in optical coherence tomography (OCT). The fiber-based FC swept lasers operate at a sweep rate of 1kHz and 120kHz, respectively over a 135nm tuning range centered at 1310nm with average output powers of 50mW. A 25GHz free spectral range frequency comb filter in the swept lasers causes the lasers to generate a series of well defined frequency steps. The narrow bandwidth (0.015nm) of the frequency comb filter enables a ~−1.2dB sensitivity roll off over ~3mm range, compared to conventional swept source and FDML lasers which have −10dB and −5dB roll offs, respectively. Measurements at very long ranges are possible with minimal sensitivity loss, however reflections from outside the principal measurement range of 0–3mm appear aliased back into the principal range. In addition, the frequency comb output from the lasers are equally spaced in frequency (linear in k-space). The filtered laser output can be used to self-clock the OCT interference signal sampling, enabling direct fast Fourier transformation of the fringe signals, without the need for fringe recalibration procedures. The design and operation principles of FC swept lasers are discussed and designs for short cavity lasers for OCT and interferometric measurement applications are proposed. PMID:19997365

Ranging Behaviour of Commercial Free-Range Broiler Chickens 2: Individual Variation.

PubMed

Taylor, Peta S; Hemsworth, Paul H; Groves, Peter J; Gebhardt-Henrich, Sabine G; Rault, Jean-Loup

2017-07-20

Little is known about broiler chicken ranging behaviour. Previous studies have monitored ranging behaviour at flock level but whether individual ranging behaviour varies within a flock is unknown. Using Radio Frequency Identification technology, we tracked 1200 individual ROSS 308 broiler chickens across four mixed sex flocks in two seasons on one commercial farm. Ranging behaviour was tracked from first day of range access (21 days of age) until 35 days of age in winter flocks and 44 days of age in summer flocks. We identified groups of chickens that differed in frequency of range visits: chickens that never accessed the range (13 to 67% of tagged chickens), low ranging chickens (15 to 44% of tagged chickens) that accounted for <15% of all range visits and included chickens that used the range only once (6 to 12% of tagged chickens), and high ranging chickens (3 to 9% of tagged chickens) that accounted for 33 to 50% of all range visits. Males spent longer on the range than females in winter ( p < 0.05). Identifying the causes of inter-individual variation in ranging behaviour may help optimise ranging opportunities in free-range systems and is important to elucidate the potential welfare implications of ranging.

Expanding Hardware-in-the-Loop Formation Navigation and Control with Radio Frequency Crosslink Ranging

NASA Technical Reports Server (NTRS)

Mitchell, Jason W.; Barbee, Brent W.; Baldwin, Philip J.; Luquette, Richard J.

2007-01-01

The Formation Flying Testbed (FFTB) at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) provides a hardware-in-the-loop test environment for formation navigation and control. The facility continues to evolve as a modular, hybrid, dynamic simulation facility for end-to-end guidance, navigation, and control (GN&C) design and analysis of formation flying spacecraft. The core capabilities of the FFTB, as a platform for testing critical hardware and software algorithms in-the-loop, are reviewed with a focus on recent improvements. With the most recent improvement, in support of Technology Readiness Level (TRL) 6 testing of the Inter-spacecraft Ranging and Alarm System (IRAS) for the Magnetospheric Multiscale (MMS) mission, the FFTB has significantly expanded its ability to perform realistic simulations that require Radio Frequency (RF) ranging sensors for relative navigation with the Path Emulator for RF Signals (PERFS). The PERFS, currently under development at NASA GSFC, modulates RF signals exchanged between spacecraft. The RF signals are modified to accurately reflect the dynamic environment through which they travel, including the effects of medium, moving platforms, and radiated power.

Studies of Lower Hybrid Range of Frequencies Actuators in the ARC Device

NASA Astrophysics Data System (ADS)

Bonoli, P. T.; Lin, Y.; Shiraiwa, S.; Wallace, G. M.; Wright, J. C.; Wukitch, S. J.

2017-10-01

High field side (HFS) placement of lower hybrid range of frequencies (LHRF) actuators is attractive from both the standpoint of a more quiescent scrape off layer (SOL) and from the improved LH wave accessibility and penetration to higher electron temperature that results from the higher magnetic field on the HFS. The resulting profiles of LH current drive (LHCD) are also more suitable for advanced tokamak (AT) operation where it is most desirable to provide a significant ( 20-30%) contribution to the total current density with a broad profile extending from r/a 0.5-0.85. Here we re-assess HFS LHCD in the ARC device using a hierarchy of LHCD models that include a combined adjoint plus ray tracing calculation, a ray tracing plus 3D Fokker Planck calculation, and a full-wave plus Fokker Planck simulation. Work supported by the U.S. DoE, Office of Science, Office of Fusion Energy Sciences, User Facility Alcator C-Mod under DE-FC02-99ER54512 and a PSFC Theory Grant under DE-FG02-91-ER54109.

Effects of diffraction by ionospheric electron density irregularities on the range error in GNSS dual-frequency positioning and phase decorrelation

NASA Astrophysics Data System (ADS)

Gherm, Vadim E.; Zernov, Nikolay N.; Strangeways, Hal J.

2011-06-01

It can be important to determine the correlation of different frequency signals in L band that have followed transionospheric paths. In the future, both GPS and the new Galileo satellite system will broadcast three frequencies enabling more advanced three frequency correction schemes so that knowledge of correlations of different frequency pairs for scintillation conditions is desirable. Even at present, it would be helpful to know how dual-frequency Global Navigation Satellite Systems positioning can be affected by lack of correlation between the L1 and L2 signals. To treat this problem of signal correlation for the case of strong scintillation, a previously constructed simulator program, based on the hybrid method, has been further modified to simulate the fields for both frequencies on the ground, taking account of their cross correlation. Then, the errors in the two-frequency range finding method caused by scintillation have been estimated for particular ionospheric conditions and for a realistic fully three-dimensional model of the ionospheric turbulence. The results which are presented for five different frequency pairs (L1/L2, L1/L3, L1/L5, L2/L3, and L2/L5) show the dependence of diffractional errors on the scintillation index S4 and that the errors diverge from a linear relationship, the stronger are scintillation effects, and may reach up to ten centimeters, or more. The correlation of the phases at spaced frequencies has also been studied and found that the correlation coefficients for different pairs of frequencies depend on the procedure of phase retrieval, and reduce slowly as both the variance of the electron density fluctuations and cycle slips increase.

Modulation of electromagnetic and absorption properties in 18-26.5 GHz frequency range of strontium hexaferrites with doping of cobalt-zirconium

NASA Astrophysics Data System (ADS)

Pubby, Kunal; Narang, Sukhleen Bindra; Kaur, Prabhjyot; Chawla, S. K.

2017-05-01

Hexaferrite nano-particles of stoichiometric composition {{Sr}}{({{CoZr}})_x}{{F}}{{{e}}_{12 - 2x}}{{{O}}_{19}}, with x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0 were prepared using sol-gel auto-combustion route owing to its advantages such as low sintering temperature requirement, homogeneity and uniformity of grains. Tartaric acid as a fuel was utilized to complete the chemical reaction. The goal of this study is to analyse the effect of co-substitution of cobalt and zirconium on the electromagnetic and absorption properties of pure {{SrF}}{{{e}}_{12}}{{{O}}_{19}} hexaferrite. The properties were measured on the rectangular pellets of thickness 2.5 mm for K-frequency band using Vector Network Analyzer. The doping of Co-Zr has resulted in increase in real as well as imaginary parts of permittivity. The values of real permittivity lie in the range 3.6-7.0 for all the composition. The real part of permeability remains in range 0.7-1.6 in the studied frequency band for all the samples and shows slightly increasing trend with frequency. The maximum values of dielectric loss tangent peak (3.04) and magnetic loss tangent peak (2.34), among all the prepared compositions, have been observed for composition x = 0.2. Compositions with x = 0.6 and x = 0.0 also have high dielectric and magnetic loss peaks. Dielectric loss peaks are attributed to dielectric resonance and magnetic loss peaks are attributed to natural resonance. Experimentally determined reflection loss results show that all six compositions of prepared series have high values of absorption to propose them as single-layer absorbers in 18-26.5 GHz frequency range. The composition with x = 0.2 has maximum absorption capacity with reflection loss peak of -37.2 dB at 24.3 GHz frequency. The undoped composition also has high absorption peak (-25.46 dB), but -10 dB absorption bandwidth is minimum (2.2 GHz) out of the present series. Maximum absorption bandwidth is obtained for x = 1.0 (4.1 GHz). Other doped compositions also

Nonlinear optical response of a gold surface in the visible range: A study by two-color sum-frequency generation spectroscopy. I. Experimental determination

NASA Astrophysics Data System (ADS)

Dalstein, L.; Revel, A.; Humbert, C.; Busson, B.

2018-04-01

We experimentally determine the effective nonlinear second-order susceptibility of gold over the visible spectral range. To reach that goal, we probe by vibrational two-color sum-frequency generation spectroscopy the methyl stretching region of a dodecanethiol self-assembled monolayer adsorbed on a gold film. The sum-frequency generation spectra show a remarkable shape reversal when the visible probe wavelength is tuned from 435 to 705 nm. After correcting from Fresnel effects, the methyl stretching vibrations serve as an internal reference, allowing to extract the dispersion of the absolute phase and relative amplitude of the effective nonlinear optical response of gold in the visible range.

Paternal kin recognition in the high frequency / ultrasonic range in a solitary foraging mammal

PubMed Central

2012-01-01

Background Kin selection is a driving force in the evolution of mammalian social complexity. Recognition of paternal kin using vocalizations occurs in taxa with cohesive, complex social groups. This is the first investigation of paternal kin recognition via vocalizations in a small-brained, solitary foraging mammal, the grey mouse lemur (Microcebus murinus), a frequent model for ancestral primates. We analyzed the high frequency/ultrasonic male advertisement (courtship) call and alarm call. Results Multi-parametric analyses of the calls’ acoustic parameters and discriminant function analyses showed that advertisement calls, but not alarm calls, contain patrilineal signatures. Playback experiments controlling for familiarity showed that females paid more attention to advertisement calls from unrelated males than from their fathers. Reactions to alarm calls from unrelated males and fathers did not differ. Conclusions 1) Findings provide the first evidence of paternal kin recognition via vocalizations in a small-brained, solitarily foraging mammal. 2) High predation, small body size, and dispersed social systems may select for acoustic paternal kin recognition in the high frequency/ultrasonic ranges, thus limiting risks of inbreeding and eavesdropping by predators or conspecific competitors. 3) Paternal kin recognition via vocalizations in mammals is not dependent upon a large brain and high social complexity, but may already have been an integral part of the dispersed social networks from which more complex, kin-based sociality emerged. PMID:23198727

The effects of sampling frequency on the climate statistics of the European Centre for Medium-Range Weather Forecasts

NASA Astrophysics Data System (ADS)

Phillips, Thomas J.; Gates, W. Lawrence; Arpe, Klaus

1992-12-01

The effects of sampling frequency on the first- and second-moment statistics of selected European Centre for Medium-Range Weather Forecasts (ECMWF) model variables are investigated in a simulation of "perpetual July" with a diurnal cycle included and with surface and atmospheric fields saved at hourly intervals. The shortest characteristic time scales (as determined by the e-folding time of lagged autocorrelation functions) are those of ground heat fluxes and temperatures, precipitation and runoff, convective processes, cloud properties, and atmospheric vertical motion, while the longest time scales are exhibited by soil temperature and moisture, surface pressure, and atmospheric specific humidity, temperature, and wind. The time scales of surface heat and momentum fluxes and of convective processes are substantially shorter over land than over oceans. An appropriate sampling frequency for each model variable is obtained by comparing the estimates of first- and second-moment statistics determined at intervals ranging from 2 to 24 hours with the "best" estimates obtained from hourly sampling. Relatively accurate estimation of first- and second-moment climate statistics (10% errors in means, 20% errors in variances) can be achieved by sampling a model variable at intervals that usually are longer than the bandwidth of its time series but that often are shorter than its characteristic time scale. For the surface variables, sampling at intervals that are nonintegral divisors of a 24-hour day yields relatively more accurate time-mean statistics because of a reduction in errors associated with aliasing of the diurnal cycle and higher-frequency harmonics. The superior estimates of first-moment statistics are accompanied by inferior estimates of the variance of the daily means due to the presence of systematic biases, but these probably can be avoided by defining a different measure of low-frequency variability. Estimates of the intradiurnal variance of accumulated

Blood optical properties at various glucose level values in THz frequency range

NASA Astrophysics Data System (ADS)

Gusev, S. I.; Borovkova, M. A.; Strepitov, M. A.; Khodzitsky, M. K.

2015-07-01

the patients. Most biomolecules have characteristic signature frequencies in the terahertz (THz) range, which can reveal their presence and determine the concentration. Therefore, this paper is intended to study the blood optical properties in the THz frequency range in order to determine THz radiation effect on blood. The main aim of this investigation is to determine the effect of blood glucose concentration on the blood optical properties. In the case if blood optical properties vary at different glucose concentrations having a proportional relationship between them, these results will confirm the possibility of development of non-invasive procedures for blood glucose level diagnostics.

High-Resolution 2D Lg and Pg Attenuation Models in the Basin and Range Region with Implications for Frequency-Dependent Q

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

Pyle, Moira L.; Walter, William R.; Pasyanos, Michael E.

Here, we develop high–resolution, laterally varying attenuation models for the regional crustal phases of Pg and Lg in the area surrounding the Basin and Range Province in the western United States. The models are part of the characterization effort for the Source Physics Experiment (SPE), a series of chemical explosions at the Nevada National Security Site designed to improve our understanding of explosion source phenomenology. To aid in SPE modeling efforts, we focus on improving our ability to accurately predict amplitudes in a set of narrow frequency bands ranging from 0.5 to 16.0 Hz. To explore constraints at higher frequenciesmore » where data become more sparse, we test the robustness of the empirically observed power–law relationship between quality factor Q and frequency (Q=Q 0f γ). Our methodology uses a staged approach to consider attenuation, physics–based source terms, site terms, and geometrical spreading contributions to amplitude measurements. Tomographic inversion results indicate that the frequency dependence is a reasonable assumption as attenuation varies laterally for this region through all frequency bands considered. Our 2D Pg and Lg attenuation models correlate with underlying physiographic provinces, with the highest Q located in the Sierra Nevada Mountains and the Colorado plateau. Compared to a best–fitting 1D model for the region, the 2D model provides an 81% variance reduction overall for Lg residuals and a 75% reduction for Pg. These detailed attenuation maps at high frequencies will facilitate further study of local and regional distance P/S amplitude discriminants that are typically used to distinguish between earthquakes and underground explosions.« less

High-Resolution 2D Lg and Pg Attenuation Models in the Basin and Range Region with Implications for Frequency-Dependent Q

DOE PAGES

Pyle, Moira L.; Walter, William R.; Pasyanos, Michael E.

2017-10-24

Here, we develop high–resolution, laterally varying attenuation models for the regional crustal phases of Pg and Lg in the area surrounding the Basin and Range Province in the western United States. The models are part of the characterization effort for the Source Physics Experiment (SPE), a series of chemical explosions at the Nevada National Security Site designed to improve our understanding of explosion source phenomenology. To aid in SPE modeling efforts, we focus on improving our ability to accurately predict amplitudes in a set of narrow frequency bands ranging from 0.5 to 16.0 Hz. To explore constraints at higher frequenciesmore » where data become more sparse, we test the robustness of the empirically observed power–law relationship between quality factor Q and frequency (Q=Q 0f γ). Our methodology uses a staged approach to consider attenuation, physics–based source terms, site terms, and geometrical spreading contributions to amplitude measurements. Tomographic inversion results indicate that the frequency dependence is a reasonable assumption as attenuation varies laterally for this region through all frequency bands considered. Our 2D Pg and Lg attenuation models correlate with underlying physiographic provinces, with the highest Q located in the Sierra Nevada Mountains and the Colorado plateau. Compared to a best–fitting 1D model for the region, the 2D model provides an 81% variance reduction overall for Lg residuals and a 75% reduction for Pg. These detailed attenuation maps at high frequencies will facilitate further study of local and regional distance P/S amplitude discriminants that are typically used to distinguish between earthquakes and underground explosions.« less

In-Situ Ultra Low Frequency Poroelastic Response of a Natural Macro-Fracture

NASA Astrophysics Data System (ADS)

Guglielmi, Y.; Cappa, F.; Rutqvist, J.; Tsang, C.; Gaffet, S.

2008-12-01

The seismic visibility of macro-fractures filled with fluids is a central problem in the exploration of thermo- hydro-mechanical and chemical processes that occur in Earth' s subsurface. Most studies have been concerned (1) with cracks of a small size relative to the seismic wavelength (2) with "core-sized" samples of single macro-fractures. In comparison, in-situ studies of macro-fractures are very rare and no real estimate is made of the relevance of this convenient "core-sized" data to in-situ reservoirs in general. In this study, we present a new experimental approach to in-situ characterize mechanical and hydraulic properties of fractures using the innovative HPPP protocol. This protocol allows simultaneous high-frequency (120.2 Hz) sampling of normal displacement and fluid pressure in a borehole intersecting the fracture. We show preliminary results conducted in a single fracture vertically embedded in a carbonate reservoir that contains 3 sets of macro-fractures with an average 2m spacing. Two HPPP probes were set, spaced one meter vertically in the fracture. Two types of ULF seismic sources are applied: a fluid pressure pulse injected in the fracture and a hammer hit at a point located 5m far from the fracture plane. There is a highly non-linear variation of fracture normal displacement-versus- fluid pressure as a function of frequency, the higher the frequency, the lower the displacement spectral amplitude is. The pressure pulse and the hammer hit allow exploring the fracture poroelastic response in the [0 - 3Hz] frequency range. The fracture plays the role of a "low-pass" filter for fluid pressure waves; only a quasi-static pressure signal being registered at the receiver. The displacement wave propagation is more complex resulting in uncoupled quasi-static-pressure-2Hz-deformation signals at the receiver. For low magnitude seismic sources (low amplitude pulse and seismic wave), the fracture natural resonance is amplified resulting in separate signals

Dynamic train-turnout interaction in an extended frequency range using a detailed model of track dynamics

NASA Astrophysics Data System (ADS)

Kassa, Elias; Nielsen, Jens C. O.

2009-03-01

A time domain solution method for general three-dimensional dynamic interaction of train and turnout (switch and crossing) that accounts for excitation in an extended frequency range (up to several hundred Hz) is proposed. Based on a finite element (FE) model of a standard turnout design, a complex-valued modal superposition of track dynamics is applied using the first 500 eigenmodes of the turnout model. The three-dimensional model includes the distribution of structural flexibility along the turnout, such as bending and torsion of rails and sleepers, and the variations in rail cross-section and sleeper length. Convergence of simulation results is studied while using an increasing number of eigenmodes. It is shown that modes with eigenfrequencies up to at least 200 Hz have a significant influence on the magnitudes of the wheel-rail contact forces. Results from using a simplified track model with a commercial computer program for low-frequency vehicle dynamics are compared with the results from using the detailed FE model in conjunction with the proposed method.

Ubiquity of Kelvin–Helmholtz waves at Earth's magnetopause

PubMed Central

Kavosi, Shiva; Raeder, Joachim

2015-01-01

Magnetic reconnection is believed to be the dominant process by which solar wind plasma enters the magnetosphere. However, for periods of northward interplanetary magnetic field (IMF) reconnection is less likely at the dayside magnetopause, and Kelvin–Helmholtz waves (KHWs) may be important agents for plasma entry and for the excitation of ultra-low-frequency (ULF) waves. The relative importance of KHWs is controversial because no statistical data on their occurrence frequency exist. Here we survey 7 years of in situ data from the NASA THEMIS (Time History of Events and Macro scale Interactions during Substorms) mission and find that KHWs occur at the magnetopause ∼19% of the time. The rate increases with solar wind speed, Alfven Mach number and number density, but is mostly independent of IMF magnitude. KHWs may thus be more important for plasma transport across the magnetopause than previously thought, and frequently drive magnetospheric ULF waves. PMID:25960122

Synthetic range profiling in ground penetrating radar

NASA Astrophysics Data System (ADS)

Kaczmarek, Pawel; Lapiński, Marian; Silko, Dariusz

2009-06-01

The paper describes stepped frequency continuous wave (SFCW) ground penetrating radar (GPR), where signal's frequency is discretely increased in N linear steps, each separated by a fixed ▵f increment from the previous one. SFCW radar determines distance from phase shift in a reflected signal, by constructing synthetic range profile in spatial time domain using the IFFT. Each quadrature sample is termed a range bin, as it represents the signal from a range window of length cτ/2, where τ is duration of single frequency segment. IFFT of those data samples resolves the range bin in into fine range bins of c/2N▵f width, thus creating the synthetic range profile in a GPR - a time domain approximation of the frequency response of a combination of the medium through which electromagnetic waves propagates (soil) and any targets or dielectric interfaces (water, air, other types of soil) present in the beam width of the radar. In the paper, certain practical measurements done by a monostatic SFCW GPR were presented. Due to complex nature of signal source, E5062A VNA made by Agilent was used as a signal generator, allowing number of frequency steps N to go as high as 1601, with generated frequency ranging from 300kHz to 3 GHz.

Development of calibration techniques for ultrasonic hydrophone probes in the frequency range from 1 to 100 MHz

PubMed Central

Umchid, S.; Gopinath, R.; Srinivasan, K.; Lewin, P. A.; Daryoush, A. S.; Bansal, L.; El-Sherif, M.

2009-01-01

The primary objective of this work was to develop and optimize the calibration techniques for ultrasonic hydrophone probes used in acoustic field measurements up to 100 MHz. A dependable, 100 MHz calibration method was necessary to examine the behavior of a sub-millimeter spatial resolution fiber optic (FO) sensor and assess the need for such a sensor as an alternative tool for high frequency characterization of ultrasound fields. Also, it was of interest to investigate the feasibility of using FO probes in high intensity fields such as those employed in HIFU (High Intensity Focused Ultrasound) applications. In addition to the development and validation of a novel, 100 MHz calibration technique the innovative elements of this research include implementation and testing of a prototype FO sensor with an active diameter of about 10 μm that exhibits uniform sensitivity over the considered frequency range and does not require any spatial averaging corrections up to about 75 MHz. The results of the calibration measurements are presented and it is shown that the optimized calibration technique allows the sensitivity of the hydrophone probes to be determined as a virtually continuous function of frequency and is also well suited to verify the uniformity of the FO sensor frequency response. As anticipated, the overall uncertainty of the calibration was dependent on frequency and determined to be about ±12% (±1 dB) up to 40 MHz, ±20% (±1.5 dB) from 40 to 60 MHz and ±25% (±2 dB) from 60 to 100 MHz. The outcome of this research indicates that once fully developed and calibrated, the combined acousto-optic system will constitute a universal reference tool in the wide, 100 MHz bandwidth. PMID:19110289

Vibroacoustics of the piano soundboard: (Non)linearity and modal properties in the low- and mid-frequency ranges

NASA Astrophysics Data System (ADS)

Ege, Kerem; Boutillon, Xavier; Rébillat, Marc

2013-03-01

The piano soundboard transforms the string vibration into sound and therefore, its vibrations are of primary importance for the sound characteristics of the instrument. An original vibro-acoustical method is presented to isolate the soundboard nonlinearity from that of the exciting device (here: a loudspeaker) and to measure it. The nonlinear part of the soundboard response to an external excitation is quantitatively estimated for the first time, at ≈-40 dB below the linear part at the ff nuance. Given this essentially linear response, a modal identification is performed up to 3 kHz by means of a novel high resolution modal analysis technique [K. Ege, X. Boutillon, B. David, High-resolution modal analysis, Journal of Sound and Vibration 325 (4-5) (2009) 852-869]. Modal dampings (which, so far, were unknown for the piano in this frequency range) are determined in the mid-frequency domain where FFT-based methods fail to evaluate them with an acceptable precision. They turn out to be close to those imposed by wood. A finite-element modelling of the soundboard is also presented. The low-order modal shapes and the comparison between the corresponding experimental and numerical modal frequencies suggest that the boundary conditions can be considered as blocked, except at very low frequencies. The frequency-dependency of the estimated modal densities and the observation of modal shapes reveal two well-separated regimes. Below ≈1 kHz, the soundboard vibrates more or less like a homogeneous plate. Above that limit, the structural waves are confined by ribs, as already noticed by several authors, and localised in restricted areas (one or a few inter-rib spaces), presumably due to a slightly irregular spacing of the ribs across the soundboard.

Verification of the effects of Schumann frequency range electromagnetic fields on the human cardiovascular system

NASA Astrophysics Data System (ADS)

Tuzhilkin, D. A.; Borodin, A. S.

2017-11-01

The results of the study of variations in the electromagnetic background parameters of the Schumann resonator frequency range and the variability indices of the human heart period during its free activity are presented on the basis of 24-hour synchronous monitoring data. It is shown that the integral evaluation of the conjugacy of the heart rate variability indices from the Schumann resonance parameters is extremely weak. In this case, the differential evaluation of this dependence with separation into characteristic time intervals of the day, characterized by different motor activity of the subjects, becomes significantly higher. The number of volunteers whose conjugacy is characterized by a strong correlation in some cases reaches 35 percent of the sample.

A Short Range, High Accuracy Radar Ranging System,

DTIC Science & Technology

1984-12-01

may be of any type and can perform the same functions as any other type of radar (pulsed or continuous wave (CW), coherent or noncoherent , etc.). The...use of an optical carrier frequency 4 enables laser radars to take advantage of the benefits inherent in higher frequencies: higher bandwidths allow...results that are inaccurate or incorrect. Also, directing a laser beam at an aircraft cockpit from a range of 25 feet would pose a serious safety

High-frequency transducers for point-of-care ultrasound applications: what is the optimal frequency range?

PubMed

Adhikari, Srikar

2014-06-01

To compare images obtained using two linear transducers with a different range of frequencies, and to determine if there is a significant difference in the quality of images between the two transducers for medical decision-making. This was a single-blinded, cross-sectional study at an academic medical center. Twenty-five emergency medicine clinical scenarios with ultrasound images (using both 10-5 and 14-5 MHz transducers) covering a variety of point-of-care ultrasound applications were presented to four emergency physician sonographers. They were blinded to the study hypothesis and type of the transducer used to obtain the images. On a scale of 1-10, the mean image quality rating for 10-5 MHz transducer was 7.09 (95 % CI 6.73-7.45) and 6.49 (95 % CI 5.99-6.99) for 14-5 MHz transducer. In the majority of cases (84 %, 95 % CI 75.7-92.3 %), sonographers indicated that images obtained with a 10-5 MHz transducer were satisfactory for medical decision-making. They preferred images obtained with a 10-5 MHz transducer over 14-5 MHz transducer in 39 % (95 % CI 30-50 %) of cases. The images obtained with a 14-5 MHz transducer were preferred over 10-5 MHz transducer in only 16 % (95 % CI 7.7-24.3 %) of the cases. The 14-5 MHz transducer has a slight advantage over 10-5 MHz transducer for ocular, upper airway, and musculoskeletal (tendon) ultrasound applications. A 10-5 MHz linear transducer is adequate to obtain images that can be used for medical decision-making for a variety of point-of-care ultrasound applications.

The magnetic field investigation on the ARASE (ERG) mission: Data characteristics and initial scientific results

NASA Astrophysics Data System (ADS)

Matsuoka, A.; Teramoto, M.; Nomura, R.; Nose, M.; Fujimoto, A.; Tanaka, Y.; Shinohara, M.; Nagatsuma, T.; Shiokawa, K.; Obana, Y.; Miyoshi, Y.; Takashima, T.; Shinohara, I.

2017-12-01

The ARASE (ERG) satellite was successfully launched on December 20 2016. A fluxgate magnetometer (MGF) was built for the ARASE satellite to measure DC and low-frequency magnetic field. The requirements to the magnetic field measurements by ARASE was defined as (1) accuracy of the absolute field intensity is within 5 nT (2) angular accuracy of the field direction is within 1 degree (3) measurement frequency range is from DC to 60Hz or wider. MGF measures the vector magnetic field with the original sampling frequency of 256 Hz. The dynamic range is switched between +/-8000nT and +/- 60000nT according to the background field intensity. The MGF initial checkout was carried on January 10th 2017, when the MGF normal performance and downlinked data were confirmed. The 5-m length MAST for the sensor was deployed on 17th January. The nominal operation of MGF started in March 2017. The MGF data are calibrated based on the results from the ground experiments and in-orbit data analysis. The MGF CDF files are distributed by the ARASE Science Center and available by Space Physics Environment Data Analysis Software (SPEDAS). The acceleration process of the charged particles in the inner magnetosphere is considered to be closely related to the deformation and perturbation of the magnetic field. Accurate measurement of the magnetic field is required to understand the acceleration mechanism of the charged particles, which is one of the major scientific objectives of the ARASE mission. We designed a fluxgate magnetometer which is optimized to investigate following topics; (1) accurate measurement of the background magnetic field - the deformation of the magnetic field and its relationship with the particle acceleration. (2) MHD waves - measurement of the ULF electromagnetic waves of frequencies about 1mHz (Pc4-5), and investigation of the radiation-belt electrons radially diffused by the resonance with the ULF waves. (3) EMIC waves - measurement of the electromagnetic ion

Low-frequency sound speed and attenuation in sandy seabottom from long-range broadband acoustic measurements.

PubMed

Wan, Lin; Zhou, Ji-Xun; Rogers, Peter H

2010-08-01

A joint China-U.S. underwater acoustics experiment was conducted in the Yellow Sea with a very flat bottom and a strong and sharp thermocline. Broadband explosive sources were deployed both above and below the thermocline along two radial lines up to 57.2 km and a quarter circle with a radius of 34 km. Two inversion schemes are used to obtain the seabottom sound speed. One is based on extracting normal mode depth functions from the cross-spectral density matrix. The other is based on the best match between the calculated and measured modal arrival times for different frequencies. The inverted seabottom sound speed is used as a constraint condition to extract the seabottom sound attenuation by three methods. The first method involves measuring the attenuation coefficients of normal modes. In the second method, the seabottom sound attenuation is estimated by minimizing the difference between the theoretical and measured modal amplitude ratios. The third method is based on finding the best match between the measured and modeled transmission losses (TLs). The resultant seabottom attenuation, averaged over three independent methods, can be expressed as alpha=(0.33+/-0.02)f(1.86+/-0.04)(dB/m kHz) over a frequency range of 80-1000 Hz.

Design, performance, and grounding aspects of the International Thermonuclear Experimental Reactor ion cyclotron range of frequencies antenna

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

Durodié, F., E-mail: frederic.durodie@rma.ac.be; Dumortier, P.; Vrancken, M.

2014-06-15

ITER's Ion Cyclotron Range of Frequencies (ICRF) system [Lamalle et al., Fusion Eng. Des. 88, 517–520 (2013)] comprises two antenna launchers designed by CYCLE (a consortium of European associations listed in the author affiliations above) on behalf of ITER Organisation (IO), each inserted as a Port Plug (PP) into one of ITER's Vacuum Vessel (VV) ports. Each launcher is an array of 4 toroidal by 6 poloidal RF current straps specified to couple up to 20 MW in total to the plasma in the frequency range of 40 to 55 MHz but limited to a maximum system voltage of 45 kV andmore » limits on RF electric fields depending on their location and direction with respect to, respectively, the torus vacuum and the toroidal magnetic field. A crucial aspect of coupling ICRF power to plasmas is the knowledge of the plasma density profiles in the Scrape-Off Layer (SOL) and the location of the RF current straps with respect to the SOL. The launcher layout and details were optimized and its performance estimated for a worst case SOL provided by the IO. The paper summarizes the estimated performance obtained within the operational parameter space specified by IO. Aspects of the RF grounding of the whole antenna PP to the VV port and the effect of the voids between the PP and the Blanket Shielding Modules (BSM) surrounding the antenna front are discussed. These blanket modules, whose dimensions are of the order of the ICRF wavelengths, together with the clearance gaps between them will constitute a corrugated structure which will interact with the electromagnetic waves launched by ICRF antennas. The conditions in which the grooves constituted by the clearance gaps between the blanket modules can become resonant are studied. Simple analytical models and numerical simulations show that mushroom type structures (with larger gaps at the back than at the front) can bring down the resonance frequencies, which could lead to large voltages in the gaps between the blanket modules and

Soliton microcomb range measurement

NASA Astrophysics Data System (ADS)

Suh, Myoung-Gyun; Vahala, Kerry J.

2018-02-01

Laser-based range measurement systems are important in many application areas, including autonomous vehicles, robotics, manufacturing, formation flying of satellites, and basic science. Coherent laser ranging systems using dual-frequency combs provide an unprecedented combination of long range, high precision, and fast update rate. We report dual-comb distance measurement using chip-based soliton microcombs. A single pump laser was used to generate dual-frequency combs within a single microresonator as counterpropagating solitons. We demonstrated time-of-flight measurement with 200-nanometer precision at an averaging time of 500 milliseconds within a range ambiguity of 16 millimeters. Measurements at distances up to 25 meters with much lower precision were also performed. Our chip-based source is an important step toward miniature dual-comb laser ranging systems that are suitable for photonic integration.

On the determination of the dynamic properties of a transformer oil based ferrofluid in the frequency range 0.1-20 GHz

NASA Astrophysics Data System (ADS)

Fannin, P. C.; Vekas, L.; Marin, C. N.; Malaescu, I.

2017-02-01

Complex susceptibility measurements provide a unique and efficient means for the investigation and determination of the dynamic properties of magnetic fluids. In particular, measurement of the frequency, f(Hz), and field, H(kA/m), dependent, complex susceptibility, χ(ω, Η)= χ‧(ω, Η)-iχ″(ω, Η), of magnetic fluids has proven to be a valuable and reliable technique for investigating such properties. The experimental data presented here was obtained from measurements of a transformer oil based ferrofluid, with measurements being performed over the frequency range 0.1-20 GHz and polarising fields 0-168 kA/m. In the case of transformer oil magnetic fluids, the normal measurement emphasis has been on the investigation of their dielectric properties, including the effects which lightning may have on these properties. Little has been reported on the measurement of the corresponding magnetic susceptibility, χ(ω), of such fluids and in this paper we address this fact. Thus we consider it worthwhile, in the case of a transformer with magnetic fluid transformer oil, being affected as a result of a lightening occurrence, to have knowledge of the fluids dynamic properties, at the microwave frequencies. In the process of determining the sample susceptibility profiles, it was found that the peak value of the χ″(ω) component, was approximately constant over the frequency range 2.4-6.3 GHz. From this it was determined that the fluid was effectively operating as a wideband absorber over a bandwidth of 3.9 GHz.

Measurement of a free spectral range of a Fabry-Perot cavity using frequency modulation and null method under off-resonance conditions

NASA Astrophysics Data System (ADS)

Aketagawa, Masato; Kimura, Shohei; Yashiki, Takuya; Iwata, Hiroshi; Banh, Tuan Quoc; Hirata, Kenji

2011-02-01

In this paper, we discuss a method to measure the free spectral range (FSR) of a Fabry-Perot cavity (FP-cavity) using frequency modulation with one electric optical modulator (EOM) and the null method. A laser beam modulated by the EOM, to which a sine wave signal is supplied from a radio frequency (RF) oscillator, is incident on the FP-cavity. The transmitted or reflected light from the FP-cavity is observed and converted to an RF signal by a high-speed photodetector, and the RF signal is synchronously demodulated with a lock-in amplifier by referring to a cosine wave signal from the oscillator. We theoretically and experimentally demonstrate that the lock-in amplifier signal for the transmitted or reflected light becomes null with a steep slope when the modulation frequency is equal to the FSR under the condition that the carrier frequency of the laser is slightly detuned from the resonance of the FP-cavity. To reduce the measurement uncertainty for the FSR, we also discuss a selection method for laser power, a modulation index and the detuning shift of the carrier frequency, respectively.

Structural partitioning of complex structures in the medium-frequency range. An application to an automotive vehicle

NASA Astrophysics Data System (ADS)

Kassem, M.; Soize, C.; Gagliardini, L.

2011-02-01

In a recent work [ Journal of Sound and Vibration 323 (2009) 849-863] the authors presented an energy-density field approach for the vibroacoustic analysis of complex structures in the low and medium frequency ranges. In this approach, a local vibroacoustic energy model as well as a simplification of this model were constructed. In this paper, firstly an extension of the previous theory is performed in order to include the case of general input forces and secondly, a structural partitioning methodology is presented along with a set of tools used for the construction of a partitioning. Finally, an application is presented for an automotive vehicle.

Intensity autocorrelation measurements of frequency combs in the terahertz range

NASA Astrophysics Data System (ADS)

Benea-Chelmus, Ileana-Cristina; Rösch, Markus; Scalari, Giacomo; Beck, Mattias; Faist, Jérôme

2017-09-01

We report on direct measurements of the emission character of quantum cascade laser based frequency combs, using intensity autocorrelation. Our implementation is based on fast electro-optic sampling, with a detection spectral bandwidth matching the emission bandwidth of the comb laser, around 2.5 THz. We find the output of these frequency combs to be continuous even in the locked regime, but accompanied by a strong intensity modulation. Moreover, with our record temporal resolution of only few hundreds of femtoseconds, we can resolve correlated intensity modulation occurring on time scales as short as the gain recovery time, about 4 ps. By direct comparison with pulsed terahertz light originating from a photoconductive emitter, we demonstrate the peculiar emission pattern of these lasers. The measurement technique is self-referenced and ultrafast, and requires no reconstruction. It will be of significant importance in future measurements of ultrashort pulses from quantum cascade lasers.

Variable frequency iteration MPPT for resonant power converters

DOEpatents

Zhang, Qian; Bataresh, Issa; Chen, Lin

2015-06-30

A method of maximum power point tracking (MPPT) uses an MPPT algorithm to determine a switching frequency for a resonant power converter, including initializing by setting an initial boundary frequency range that is divided into initial frequency sub-ranges bounded by initial frequencies including an initial center frequency and first and second initial bounding frequencies. A first iteration includes measuring initial powers at the initial frequencies to determine a maximum power initial frequency that is used to set a first reduced frequency search range centered or bounded by the maximum power initial frequency including at least a first additional bounding frequency. A second iteration includes calculating first and second center frequencies by averaging adjacent frequent values in the first reduced frequency search range and measuring second power values at the first and second center frequencies. The switching frequency is determined from measured power values including the second power values.

Intermediate frequency band digitized high dynamic range radiometer system for plasma diagnostics and real-time Tokamak control

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

Bongers, W. A.; Beveren, V. van; Westerhof, E.

2011-06-15

An intermediate frequency (IF) band digitizing radiometer system in the 100-200 GHz frequency range has been developed for Tokamak diagnostics and control, and other fields of research which require a high flexibility in frequency resolution combined with a large bandwidth and the retrieval of the full wave information of the mm-wave signals under investigation. The system is based on directly digitizing the IF band after down conversion. The enabling technology consists of a fast multi-giga sample analog to digital converter that has recently become available. Field programmable gate arrays (FPGA) are implemented to accomplish versatile real-time data analysis. A prototypemore » system has been developed and tested and its performance has been compared with conventional electron cyclotron emission (ECE) spectrometer systems. On the TEXTOR Tokamak a proof of principle shows that ECE, together with high power injected and scattered radiation, becomes amenable to measurement by this device. In particular, its capability to measure the phase of coherent signals in the spectrum offers important advantages in diagnostics and control. One case developed in detail employs the FPGA in real-time fast Fourier transform (FFT) and additional signal processing. The major benefit of such a FFT-based system is the real-time trade-off that can be made between frequency and time resolution. For ECE diagnostics this corresponds to a flexible spatial resolution in the plasma, with potential application in smart sensing of plasma instabilities such as the neoclassical tearing mode (NTM) and sawtooth instabilities. The flexible resolution would allow for the measurement of the full mode content of plasma instabilities contained within the system bandwidth.« less

A New Microwave Shield Preparation for Super High Frequency Range: Occupational Approach to Radiation Protection.

PubMed

Zaroushani, Vida; Khavanin, Ali; Jonidi Jafari, Ahmad; Mortazavi, Seyed Bagher

2016-01-01

Widespread use of X-band frequency (a part of the super high frequency microwave) in the various workplaces would contribute to occupational exposure with potential of adverse health effects.  According to limited study on microwave shielding for the workplace, this study tried to prepare a new microwave shielding for this purpose. We used EI-403 epoxy thermosetting resin as a matrix and nickel oxide nanoparticle with the diameter of 15-35 nm as filler. The Epoxy/ Nickel oxide composites with 5, 7, 9 and 11 wt% were made in three different thicknesses (2, 4 and 6 mm). According to transmission / reflection method, shielding effectiveness (SE) in the X-band frequency range (8-12.5 GHz) was measured by scattering parameters directly given by the 2-port Vector Network Analyzer. The fabricated composites characterized by X-ray Diffraction and Field Emission Scanning Electron Microscope. The best average of shielding effectiveness in each thickness of fabricated composites obtained by 11%-2 mm, 7%-4 mm and 7%-6 mm composites with SE values of 46.80%, 66.72% and 64.52%, respectively. In addition, the 11%-6 mm, 5%-6 mm and 11%-4 mm-fabricated composites were able to attenuate extremely the incident microwave energy at 8.01, 8.51 and 8.53 GHz by SE of 84.14%, 83.57 and 81.30%, respectively. The 7%-4mm composite could be introduced as a suitable alternative microwave shield in radiation protection topics in order to its proper SE and other preferable properties such as low cost and weight, resistance to corrosion etc. It is necessary to develop and investigate the efficacy of the fabricated composites in the fields by future studies.

Occurrence and characteristics of nighttime ULF waves at low latitude: The results of a comprehensive analysis

NASA Astrophysics Data System (ADS)

Villante, Umberto; Tiberi, Pietro

2016-05-01

The occurrence and characteristics of ULF events (f ≈ 10-100 mHz) detected during the night at low latitude (L'Aquila, Italy, λ ≈ 36.3°), during quiet and moderately perturbed magnetospheric conditions, have been examined by means of a long-term analysis between 1996 and 2012. Clearly defined events (≈8000 on each component) are typically more energetic in H than in D and basically consist of penetrating upstream waves, resonances of local field lines, and Pi2 waves. The global event occurrence shows a strong asymmetry about midnight, with a much higher wave activity before dawn than after dusk: it mostly comes from the intense penetration of upstream waves through the dawn flank of the magnetopause. D events are more frequent in summer and H events more frequent in winter, suggesting a different influence of the ionospheric modification of the downgoing signals. Between f ≈ 30 and 45 mHz, the reversal of the dominant polarization across midnight reveals tailward propagation of penetrating waves. Below f ≈ 25 mHz, intermingled with continuous Pc3 and Pc4 waves, a large fraction of events exhibit Pi2 characteristics: the dominant left-handed polarization and the switch of the tilt angle of the major axis of the polarization ellipses are consistent with the pattern expected for waves related to the substorm current wedge. A relevant percentage of the power spectra shows a second enhancement above f ≈ 55 mHz, revealing resonance of local field lines also during the night.

Detection of g modes in the asymptotic frequency range: evidence for a rapidly rotating core

NASA Astrophysics Data System (ADS)

Ulrich, Roger K.; Fossat, Eric; Boumier, Patrick; Corbard, Thierry; Provost, Janine; Salabert, David; Schmider, François-Xavier; Gabriel, Alan; Grec, Gerard; Renaud, Catherine; Robillot, Jean-Maurice; Roca Cortés, Teodoro; Turck-Chièze, Sylvaine

2017-08-01

We present the identification of very low frequency g modes, in the asymptotic regime, and two important parameters: the core rotation rate and the asymptotic equidistant period spacing of these g modes. The GOLF instrument on the SOHO space observatory has provided two decades of full disk helioseismic data. The search for g modes in GOLF measurements has been extremely difficult, due to solar and instrumental noise. In the present study, the p modes of the GOLF signal are analyzed differently, searching for possible collective frequency modulations produced by periodic changes in the deep solar structure. Such modulations provide access to only very low frequency g modes, thus allowing statistical methods to take advantage of their asymptotic properties. For oscillatory periods in the range between 9 and nearly 48 hours, almost 100 g modes of spherical harmonic degree 1 and more than 100 g modes of degree 2 are predicted. They are not observed individually, but when combined, they unambiguously provide their asymptotic period equidistance and rotational splittings, in excellent agreement with the requirements of the asymptotic approximations. P0, the g-mode period equidistance parameter, is measured to be 34 min 01 s, with a 1 s uncertainty. The previously unknown g-mode splittings have now been measured from a non synodic reference with a very high accuracy, and they imply a mean weighted rotation of 1277 ± 10 nHz (9-day period) of their kernels, resulting in a rapid rotation frequency of 1644 ± 23 nHz (period of one week) of the solar core itself, which is a factor 3:8 ± 0:1 faster than the rotation of the radiative envelope.Acknowledgements. Ulrich is first author on this abstract due to AAS rules, Fossat is the actual first author. SOHO is a project of international collaboration between ESA and NASA. We would like to acknowledge the support received continuously during more than 3 decades from CNES. DS acknowledges the financial support from the CNES GOLF

Dawn- Dusk Auroral Oval Oscillations Associated with High- Speed Solar Wind

NASA Technical Reports Server (NTRS)

Liou, Kan; Sibeck, David G.

2018-01-01

We report evidence of global-scale auroral oval oscillations in the millihertz range, using global auroral images acquired from the Ultraviolet Imager on board the decommissioned Polar satellite and concurrent solar wind measurements. On the basis of two events (15 January 1999 and 6 January 2000) studied, it is found that (1) quasi-periodic auroral oval oscillations (approximately 3 megahertz) can occur when solar wind speeds are high at northward or southward interplanetary magnetic field turning, (2) the oscillation amplitudes range from a few to more than 10 degrees in latitudes, (3) the oscillation frequency is the same for each event irrespective of local time and without any azimuthal phase shift (i.e., propagation), (4) the auroral oscillations occur in phase within both the dawn and dusk sectors but 180 degrees out of phase between the dawn and dusk sectors, and (5) no micropulsations on the ground match the auroral oscillation periods. While solar wind conditions favor the growth of the Kelvin-Helmholtz (K-H) instability on the magnetopause as often suggested, the observed wave characteristics are not consistent with predictions for K-H waves. The in-phase and out-of-phase features found in the dawn-dusk auroral oval oscillations suggest that wiggling motions of the magnetotail associated with fast solar winds might be the direct cause of the global-scale millihertz auroral oval oscillations. Plain Language Summary: We utilize global auroral image data to infer the motion of the magnetosphere and show, for the first time, the entire magnetospheric tail can move east-west in harmony like a windsock flapping in wind. The characteristic period of the flapping motion may be a major source of global long-period ULF (Ultra Low Frequency) waves, adding an extra source of the global mode ULF waves.

How did the urban land in floodplains distribute and expand in China from 1992-2015?

NASA Astrophysics Data System (ADS)

Du, Shiqiang; He, Chunyang; Huang, Qingxu; Shi, Peijun

2018-03-01

Urban land in floodplains (ULF) is a vital component of flood exposure and its variations can cause changes in flood risk. In the context of rapid urbanization, ULF is expanding rapidly in China and imperiling societal sustainability. However, a national-scale analysis of ULF patterns and dynamics has yet to be conducted. Therefore, this study aims to investigate the spatiotemporal changes in China’s ULF at different spatial scales (the country, region, basin, and sub-basin scales) from 1992-2015. We found that ULF accounted for 44.41% of the total urban land in China in 2015, which was 3.68 times greater than the proportion of floodplains relative to the total land area in China (12.06%). From 1992-2015, the ULF area increased by 26.43 × 103 km2, or 542.21%. Moreover, the ULF area is expected to grow by 16.89 × 103 km2 (53.38%) between 2015 and 2050. ULF growth was strongly associated with the flood occurrence in China, and continued growth will pose a considerable challenge to urban sustainability, particularly in basins with poor flood defenses. Greater attention should thus be paid to ULF dynamics in China.

Sound propagation in water containing large tethered spherical encapsulated gas bubbles with resonance frequencies in the 50 Hz to 100 Hz range.

PubMed

Lee, Kevin M; Hinojosa, Kevin T; Wochner, Mark S; Argo, Theodore F; Wilson, Preston S; Mercier, Richard S

2011-11-01

The efficacy of large tethered encapsulated gas bubbles for the mitigation of low frequency underwater noise was investigated with an acoustic resonator technique. Tethered latex balloons were used as the bubbles, which had radii of approximately 5 cm. Phase speeds were inferred from the resonances of a water and balloon-filled waveguide approximately 1.8 m in length. The Commander and Prosperetti effective-medium model [J. Acoust. Soc. Am. 85, 732-746 (1989)] quantitatively described the observed dispersion from well below to just below the individual bubble resonance frequency, and it qualitatively predicted the frequency range of high attenuation for void fractions between 2% and 5% for collections of stationary balloons within the waveguide. A finite-element model was used to investigate the sensitivity of the waveguide resonance frequencies, and hence the inferred phase speeds, to changes in individual bubble size and position. The results indicate that large tethered encapsulated bubbles could be used mitigate low frequency underwater noise and that the Commander and Prosperetti model would be useful in the design of such a system.

Cosmic ray scintillations in the frequency range from 0.00001 to 0.01 Hz

NASA Technical Reports Server (NTRS)

Gehrels, N.; Lheureux, J.

1978-01-01

Power spectra of the flux variations in cosmic rays of energy greater than a few GeV are presented. The data were obtained at balloon altitudes (40-45 km) from two scintillation-type detectors flown for six hours from Palestine, Texas, on November 4, 1972. The large area detectors had effective count rates up to 2000 cps setting the Poisson noise level in the power spectra of the relative fluctuations at 0.001/Hz. The analysis was made on the singles rate of each of the counters as well as on the coincidence rates between them. In all cases, the spectra between 0.0001 and 0.002 Hz are power laws in frequency of the form f to the exponent negative gamma, where gamma is between 1.5 and 2.0. No significant peaks in the range 0.0001 to 0.01 Hz are observed.

Study of complex permittivity spectra of binary mixtures of 2-chloroaniline and methanol in frequency range 10 KHz to 2 MHz at different temperatures

NASA Astrophysics Data System (ADS)

Shah, N. S.; Vankar, H. P.; Rana, V. A.

2017-05-01

The complex relative dielectric function ɛ*(ω)=ɛ'-jɛ″ of the binary mixture of 2-chloroaniline(2-CA) and methanol (MeOH) were measured using precision LCR meter in the frequency range of 10 KHz to 2 MHz The measurements were carried out at eight different temperatures and five different concentrations of 2-CA and MeOH. The loss tangent peaks were observed in the studied frequency range for all the binary mixtures. From the loss tangent peaks electrode polarization relaxation time were evaluated. In the plot of real part of complex permittivity against frequency, at different temperatures for 2-CA (54.54%) + MeOH (45.45%) and 2-CA (27.27%) + MeOH (72.72%)and 100% MeOH systems permittivity inversion effect was observed.

Individual Ranging Behaviour Patterns in Commercial Free-Range Layers as Observed through RFID Tracking

PubMed Central

Larsen, Hannah; Cronin, Greg M.; Gebhardt-Henrich, Sabine G.; Smith, Carolynn L.; Hemsworth, Paul H.; Rault, Jean-Loup

2017-01-01

Simple Summary Understanding of how free-range laying hens on commercial farms utilize the outdoor space provided is limited. In order to optimise use of the range, it is important to understand whether hens vary in their ranging behaviour, both between and within individual hens. In our study, we used individual tracking technology to assess how hens in two commercial free-range flocks used the range and whether they varied in their use of the range. We assessed use of three areas at increasing distance from the shed; the veranda [0–2.4 m], close range [2.4–11.4 m], and far range [>11.4 m]. Most hens accessed the range every day (68.6% in Flock A, and 82.2% in Flock B), and most hens that ranged accessed all three areas (73.7% in Flock A, and 84.5% in Flock B). Hens spent half of their time outside in the veranda adjacent to the shed. We found that some hens within the flocks would range consistently (similar duration and frequency) daily, whereas others would range inconsistently. Hens that were more consistent in their ranging behaviour spent more time on the range overall than those that were inconsistent. These different patterns of range use should be taken into account to assess the implications of ranging for laying hens. Abstract In this exploratory study, we tracked free-range laying hens on two commercial flocks with Radio Frequency Identification (RFID) technology with the aim to examine individual hen variation in range use. Three distinct outdoor zones were identified at increasing distances from the shed; the veranda [0–2.4 m], close range [2.4–11.4 m], and far range [>11.4 m]. Hens’ movements between these areas were tracked using radio frequency identification technology. Most of the hens in both flocks (68.6% in Flock A, and 82.2% in Flock B) accessed the range every day during the study. Of the hens that accessed the range, most hens accessed all three zones (73.7% in Flock A, and 84.5% in Flock B). Hens spent half of their time

A real-time 3D range image sensor based on a novel tip-tilt-piston micromirror and dual frequency phase shifting

NASA Astrophysics Data System (ADS)

Skotheim, Øystein; Schumann-Olsen, Henrik; Thorstensen, Jostein; Kim, Anna N.; Lacolle, Matthieu; Haugholt, Karl-Henrik; Bakke, Thor

2015-03-01

Structured light is a robust and accurate method for 3D range imaging in which one or more light patterns are projected onto the scene and observed with an off-axis camera. Commercial sensors typically utilize DMD- or LCD-based LED projectors, which produce good results but have a number of drawbacks, e.g. limited speed, limited depth of focus, large sensitivity to ambient light and somewhat low light efficiency. We present a 3D imaging system based on a laser light source and a novel tip-tilt-piston micro-mirror. Optical interference is utilized to create sinusoidal fringe patterns. The setup allows fast and easy control of both the frequency and the phase of the fringe patterns by altering the axes of the micro-mirror. For 3D reconstruction we have adapted a Dual Frequency Phase Shifting method which gives robust range measurements with sub-millimeter accuracy. The use of interference for generating sine patterns provides high light efficiency and good focusing properties. The use of a laser and a bandpass filter allows easy removal of ambient light. The fast response of the micro-mirror in combination with a high-speed camera and real-time processing on the GPU allows highly accurate 3D range image acquisition at video rates.

The contribution of microbunching instability to solar flare emission in the GHz to THz range of frequencies

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

Klopf, J. Michael; Kaufmann, Pierre; Raulin, Jean-Pierre

2014-07-01

Recent solar flare observations in the sub-terahertz range have provided evidence of a new spectral component with fluxes increasing for larger frequencies, separated from the well-known microwave emission that maximizes in the gigahertz range. Suggested interpretations explain the terahertz spectral component but do not account for the simultaneous microwave component. We present a mechanism for producing the observed "double spectra." Based on coherent enhancement of synchrotron emission at long wavelengths in laboratory accelerators, we consider how similar processes may occur within a solar flare. The instability known as microbunching arises from perturbations that produce electron beam density modulations, giving risemore » to broadband coherent synchrotron emission at wavelengths comparable to the characteristic size of the microbunch structure. The spectral intensity of this coherent synchrotron radiation (CSR) can far exceed that of the incoherent synchrotron radiation (ISR), which peaks at a higher frequency, thus producing a double-peaked spectrum. Successful CSR simulations are shown to fit actual burst spectral observations, using typical flaring physical parameters and power-law energy distributions for the accelerated electrons. The simulations consider an energy threshold below which microbunching is not possible because of Coulomb repulsion. Only a small fraction of the radiating charges accelerated to energies above the threshold is required to produce the microwave component observed for several events. The ISR/CSR mechanism can occur together with other emission processes producing the microwave component. It may bring an important contribution to microwaves, at least for certain events where physical conditions for the occurrence of the ISR/CSR microbunching mechanism are possible.« less

Method for ambiguity resolution in range-Doppler measurements

NASA Technical Reports Server (NTRS)

Heymsfield, Gerald M. (Inventor); Miller, Lee S. (Inventor)

1994-01-01

A method for resolving range and Doppler target ambiguities when the target has substantial range or has a high relative velocity in which a first signal is generated and a second signal is also generated which is coherent with the first signal but at a slightly different frequency such that there exists a difference in frequency between these two signals of Delta f(sub t). The first and second signals are converted into a dual-frequency pulsed signal, amplified, and the dual-frequency pulsed signal is transmitted towards a target. A reflected dual-frequency signal is received from the target, amplified, and changed to an intermediate dual-frequency signal. The intermediate dual-frequency signal is amplified, with extracting of a shifted difference frequency Delta f(sub r) from the amplified intermediate dual-frequency signal done by a nonlinear detector. The final step is generating two quadrature signals from the difference frequency Delta f(sub t) and the shifted difference frequency Delta f(sub r) and processing the two quadrature signals to determine range and Doppler information of the target.

Low Frequency Acoustic Detection Research in Support of Human Detection Range Prediction

DTIC Science & Technology

1979-10-01

beat at narrow separations and hence made estimates of bandwidth difficult. In addition, Zwicker’s and Green’s data show large discrepancies, the...already known that this spurious low frequency noise can profoundly influence psychoacoustic results. For some years a binaural phenomenon known as the...tend to be uncorrelated in the two ears) and thus preserved the binaural advantage for the low frequency signals. Green et al. (Reference 21) used a

Generation of Shear Alfvén Waves by Repetitive High Power Microwave Pulses Near the Electron Plasma Frequency - A laboratory study of a ``Virtual Antenna''

NASA Astrophysics Data System (ADS)

Wang, Yuhou; Gekelman, Walter; Pribyl, Patrick; van Compernolle, Bart; Papadopoulos, Konstantinos

2015-11-01

ELF / ULF waves are important in terrestrial radio communications but difficult to launch using ground-based structures due to their enormous wavelengths. In spite of this generation of such waves by field-aligned ionospheric heating modulation was first demonstrated using the HAARP facility. In the future heaters near the equator will be constructed and laboratory experiments on cross-field wave propagation could be key to the program's success. Here we report a detailed laboratory study conducted on the Large Plasma Device (LaPD) at UCLA. In this experiment, ten rapid pulses of high power microwaves (250 kW X-band) near the plasma frequency were launched transverse to the background field, and were modulated at a variable fraction (0.1-1.0) of fci. Along with bulk electron heating and density modification, the microwave pulses generated a population of fast electrons. The field-aligned current carried by the fast electrons acted as an antenna that radiated shear Alfvén waves. It was demonstrated that a controllable arbitrary frequency (f frequency variation and power dependence of the virtual antenna is also presented. This work is supported by an AFOSR MURI award, and conducted at the Basic Plasma Science Facility at UCLA funded by DoE and NSF.

Intrinsic vs. spurious long-range memory in high-frequency records of environmental radioactivity - Critical re-assessment and application to indoor 222Rn concentrations from Coimbra, Portugal

NASA Astrophysics Data System (ADS)

Donner, Reik V.; Potirakis, Stelios M.; Barbosa, Susana M.; Matos, Jose A. O.

2015-04-01

The presence or absence of long-range correlations in environmental radioactivity fluctuations has recently attracted considerable interest. Among a multiplicity of practically relevant applications, identifying and disentangling the environmental factors controlling the variable concentrations of the radioactive noble gas Radon is important for estimating its effect on human health and the efficiency of possible measures for reducing the corresponding exposition. In this work, we present a critical re-assessment of a multiplicity of complementary methods that have been previously applied for evaluating the presence of long-range correlations and fractal scaling in environmental Radon variations with a particular focus on the specific properties of the underlying time series. As an illustrative case study, we subsequently re-analyze two high-frequency records of indoor Radon concentrations from Coimbra, Portugal, each of which spans several months of continuous measurements at a high temporal resolution of five minutes. Our results reveal that at the study site, Radon concentrations exhibit complex multi-scale dynamics with qualitatively different properties at different time-scales: (i) essentially white noise in the high-frequency part (up to time-scales of about one hour), (ii) spurious indications of a non-stationary, apparently long-range correlated process (at time scales between hours and one day) arising from marked periodic components probably related to tidal frequencies, and (iii) low-frequency variability indicating a true long-range dependent process, which might be dominated by a response to meteorological drivers. In the presence of such multi-scale variability, common estimators of long-range memory in time series are necessarily prone to fail if applied to the raw data without previous separation of time-scales with qualitatively different dynamics. We emphasize that similar properties can be found in other types of geophysical time series (for

Airborne Gravity Gradiometry Resolves a Full Range of Gravity Frequencies

NASA Astrophysics Data System (ADS)

Mataragio, J.; Brewster, J.; Mims, J.

2007-12-01

Airborne Full Tensor Gradiometry (Air\\-FTGR) was flown at high altitude coincident with Airborne Gravity (AG) flown in 2003 in West Arnhem Land, Australia. A preliminary analysis of two data sets indicates that the Air\\-FTGR system has the capability of resolving intermediate to long wavelengths features that may be associated with relatively deeper geological structures. A comparison of frequency filtered slices and power spectral density (PSD) for both data sets using the short (> 5 km), intermediate (10 km) and long (20 km) wavelengths reveals that high altitude Air\\-FTGR data show greater response in high frequency anomalies than a conventional Airborne Gravity and matches well with the AG even at the longest wavelengths anomalies. The effect of line spacing and target resolution was examined between the two data sets. Reprocessed gradient and AG data at 2, 4 and 6 km line spacing suggest that Air\\-FTGR could be effectively flown at a comparatively wider line spacing to resolve similar targets the AG would resolve with tighter line spacing. Introduction Airborne Full Tensor Gradiometry (Air\\-FTGR) data have been available to the mining industry since 2002 and their use for geologic applications is well established. However, Air\\-FTGR data has been mostly considered and used in mapping and delineation of near surface geological targets. This is due to the fact that gravity gradiometer measurements are well suited to capture the high frequency signal associated with near\\-surface targets ( Li, 2001). This is possible because the gradiometer signal strength falls off with the cube of the distance to the target. Nonetheless, in recent years there has been an increasing demand from the mining, oil, and gas industry in utilizing Full Tensor Gravity Gradiometer as a mapping tool for both regional and prospect level surveys. Air\\-FTGR as a Regional Mapping Tool Several, relatively low altitude surveys have been successfully flown in Brazil, Canada and Australia

Power and efficiency scaling of diode pumped Cr:LiSAF lasers: 770-1110 nm tuning range and frequency doubling to 387-463 nm.

PubMed

Demirbas, Umit; Baali, Ilyes

2015-10-15

We report significant average power and efficiency scaling of diode-pumped Cr:LiSAF lasers in continuous-wave (cw), cw frequency-doubled, and mode-locked regimes. Four single-emitter broad-area laser diodes around 660 nm were used as the pump source, which provided a total pump power of 7.2 W. To minimize thermal effects, a 20 mm long Cr:LiSAF sample with a relatively low Cr-concentration (0.8%) was used as the gain medium. In cw laser experiments, 2.4 W of output power, a slope efficiency of 50%, and a tuning range covering the 770-1110 nm region were achieved. Intracavity frequency doubling with beta-barium borate (BBO) crystals generated up to 1160 mW of blue power and a record tuning range in the 387-463 nm region. When mode locked with a saturable absorber mirror, the laser produced 195 fs pulses with 580 mW of average power around 820 nm at a 100.3 MHz repetition rate. The optical-to-optical conversion efficiency of the system was 33% in cw, 16% in cw frequency-doubled, and 8% in cw mode-locked regimes.

On the dispersion management of fluorite whispering-gallery mode resonators for Kerr optical frequency comb generation in the telecom and mid-infrared range.

PubMed

Lin, Guoping; Chembo, Yanne K

2015-01-26

Optical whispering gallery mode (WGM) resonators have been very attracting platforms for versatile Kerr frequency comb generations. We report a systematic study on the material dispersion of various optical materials that are capable of supporting quality factors above 10⁹. Using an analytical approximation of WGM resonant frequencies in disk resonators, we investigate the effect of the geometry and transverse mode order on the total group-velocity dispersion (GVD). We demonstrate that the major radii and the radial mode indices play an important role in tailoring the GVD of WGM resonators. In particular, our study shows that in WGM disk-resonators, the polar families of modes have very similar GVD, while the radial families of modes feature dispersion values that can differ by up to several orders of magnitude. The effect of these giant dispersion shifts are experimentally evidenced in Kerr comb generation with magnesium fluoride. From a more general perspective, this critical feature enables to push the zero-dispersion wavelength of fluorite crystals towards the mid-infrared (mid-IR) range, thereby allowing for efficient Kerr comb generation in that spectral range. We show that barium fluoride is the most interesting crystal in this regard, due to its zero dispersion wavelength (ZDW) at 1.93 μm and an optimal dispersion profile in the mid-IR regime. We expect our results to facilitate the design of different platforms for Kerr frequency comb generations in both telecommunication and mid-IR spectral ranges.

SSVEP-BCI implementation for 37-40 Hz frequency range.

PubMed

Müller, Sandra Mara Torres; Diez, Pablo F; Bastos-Filho, Teodiano Freire; Sarcinelli-Filho, Mário; Mut, Vicente; Laciar, Eric

2011-01-01

This work presents a Brain-Computer Interface (BCI) based on Steady State Visual Evoked Potentials (SSVEP), using higher stimulus frequencies (>30 Hz). Using a statistical test and a decision tree, the real-time EEG registers of six volunteers are analyzed, with the classification result updated each second. The BCI developed does not need any kind of settings or adjustments, which makes it more general. Offline results are presented, which corresponds to a correct classification rate of up to 99% and a Information Transfer Rate (ITR) of up to 114.2 bits/min.

Theoretical and practical aspects of application of a low-energy electromagnetic radiation of the extremely high-frequency range in medicine

NASA Astrophysics Data System (ADS)

Lyapina, Elena P.; Chesnokov, Igor A.; Bushuev, Nikolay A.; Kuzyutkina, Svetlana E.; Shuldjakov, Andrey A.

2006-02-01

The questions concerning the mechanism of action of a low-energy electromagnetic radiation of the extremely high frequency range (EMR EHF) are considered. Also the features of biological effects are considered in their application as therapeutic actions. As an example the advantages of EHF treatment of patients with chronic brucellosis are shown, the algorithm of a choice of the scheme of treatment using EMR EHF is offered.

High-range resolution spectral analysis of precipitation through range imaging of the Chung-Li VHF radar

NASA Astrophysics Data System (ADS)

Tsai, Shih-Chiao; Chen, Jenn-Shyong; Chu, Yen-Hsyang; Su, Ching-Lun; Chen, Jui-Hsiang

2018-01-01

Multi-frequency range imaging (RIM) has been operated in the Chung-Li very high-frequency (VHF) radar, located on the campus of National Central University, Taiwan, since 2008. RIM processes the echo signals with a group of closely spaced transmitting frequencies through appropriate inversion methods to obtain high-resolution distribution of echo power in the range direction. This is beneficial to the investigation of the small-scale structure embedded in dynamic atmosphere. Five transmitting frequencies were employed in the radar experiment for observation of the precipitating atmosphere during the period between 21 and 23 August 2013. Using the Capon and Fourier methods, the radar echoes were synthesized to retrieve the temporal signals at a smaller range step than the original range resolution defined by the pulse width, and such retrieved temporal signals were then processed in the Doppler frequency domain to identify the atmosphere and precipitation echoes. An analysis called conditional averaging was further executed for echo power, Doppler velocity, and spectral width to verify the potential capabilities of the retrieval processing in resolving small-scale precipitation and atmosphere structures. Point-by-point correction of range delay combined with compensation of range-weighting function effect has been performed during the retrieval of temporal signals to improve the continuity of power spectra at gate boundaries, making the small-scale structures in the power spectra more natural and reasonable. We examined stratiform and convective precipitation and demonstrated their different structured characteristics by means of the Capon-processed results. The new element in this study is the implementation of RIM on spectral analysis, especially for precipitation echoes.

Soliton microcomb range measurement.

PubMed

Suh, Myoung-Gyun; Vahala, Kerry J

2018-02-23

Laser-based range measurement systems are important in many application areas, including autonomous vehicles, robotics, manufacturing, formation flying of satellites, and basic science. Coherent laser ranging systems using dual-frequency combs provide an unprecedented combination of long range, high precision, and fast update rate. We report dual-comb distance measurement using chip-based soliton microcombs. A single pump laser was used to generate dual-frequency combs within a single microresonator as counterpropagating solitons. We demonstrated time-of-flight measurement with 200-nanometer precision at an averaging time of 500 milliseconds within a range ambiguity of 16 millimeters. Measurements at distances up to 25 meters with much lower precision were also performed. Our chip-based source is an important step toward miniature dual-comb laser ranging systems that are suitable for photonic integration. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

The asymmetry of the entrainment range induced by the difference in intrinsic frequencies between two subgroups within the suprachiasmatic nucleus

NASA Astrophysics Data System (ADS)

Gu, Changgui; Yang, Huijie

2017-06-01

The rhythms of physiological and behavioral activities in mammals, which are regulated by the main clock suprachiasmatic nucleus (SCN) in the brain, can not be only synchronized to the natural 24 h light-dark cycle, but also to cycles with artificial periods. The range of the artificial periods that the animal can be synchronized to is called entrainment range. In the absence of the light-dark cycle, the animal can also maintain the circadian rhythm with an endogenous period close to 24 h. Experiments found that the entrainment range is not symmetrical with respect to the endogenous period. In the present study, an explanation is given for the asymmetry based on a Kuramoto model which describes the neuronal network of the SCN. Our numerical simulations and theoretical analysis show that the asymmetry results from the difference in the intrinsic frequencies between two subgroups of the SCN, as well as the entrainment range is affected by the difference.

Quasi-Static Alfv{é}n Dynamics and Scale-Dependent Energy Deposition in Magnetosphere-Ionosphere Coupling

NASA Astrophysics Data System (ADS)

Lotko, W.; Lysak, R. L.; Streltsov, A. V.

2002-12-01

Alfv{é}n wave dynamics become quasi-static in the ionosphere and low-altitude magnetosphere in the ULF regime below 10 mHz and at altitudes less than a few RE when the following two conditions are met: ω L RE << vA (l) and ω l << 1 / μ 0 Σ P. L is the dipole shell parameter, ω is the wave frequency in radians, l represents field-aligned distance above the ionosphere, vA (l) is the local Alfv{é}n speed, and Σ P is the ionospheric Pedersen conductance. In this limit, reactive power stored in Alfv{é}nic fluctuations at high altitude flows quasi-statically into ionospheric Joule heating and low-altitude collisionless dissipation. The combined dissipative effects are described by the electrostatic model of Chiu-Cornwall-Lyons [1980] which captures the transverse wavelength dependence of low-altitude Alfv{é}nic energy deposition. The analysis and results described here 1) correspond to the low-altitude, low-frequency limit of theories for the interaction of an Alfv{é}n wave with the ionosphere [Knudsen et al., 1992], including effects of a low-altitude collisionless dissipation layer [Vogt and Haerendel, 1998], and field line eigenmodes with allowance for finite ionospheric conductivity and realistic parallel inhomogeneity [Allan and Knox, 1979]; 2) reconcile the interpretation of inverted-V precipitation regions as electrostatic potential structures with electromagnetic energy deposition via Alfv{é}n waves at frequencies below 10 mHz; 3) provide criteria for the validity of the Knight current-voltage relation in the ULF regime and its use in global MHD simulations; 4) relate low-altitude satellite measurements of both ``static'' and ULF electric and magnetic fields directly to the ionospheric Pedersen conductivity; and 5) offer a resolution to debates about high-altitude closure of auroral potential structures as O-, U-, or S-potential forms.

The effects of slight pressure oscillations in the far infrasound frequency range on the pars flaccida in gerbil and rabbit ears.

PubMed

Didyk, L A; Bogdanov, V B; Lysenko, V A; Didyk, N P; Gorgo, Yu P; Dirckx, J J J

2007-01-01

This study was designed to clarify whether the pars flaccida (PF) as a flexible part of the tympanic membrane is capable of reacting to pressure oscillations (PO) with amplitudes and frequencies typical for natural atmospheric pressure fluctuations in the far infrasound frequency range (APF). If so, the PF mechanical reactions to APF might be involved in the overall physiologic regulation processes, which make organisms susceptible to APF. The displacements of the PF in response to PO were measured in vitro in ears of gerbils and rabbits by means of laser Doppler vibrometry. The index of the PF reactivity (R(a)) was determined as the ratio of the amplitude of the PF oscillations (PFO) to the amplitude of the PO. All kinds of PO applied caused PFO. The amplitude of the PFO increased when the amplitude of the PO was increased. In gerbils, a decrease in R(a) with the increase in amplitude of the PO was observed. In the range of PO lowest amplitudes (4-20 Pa) R(a) proved to be 1.4 times higher than in the range of highest amplitudes (90-105 Pa). Considering that the natural APF are usually within the range of +/-20 Pa, this fact points to an important contribution of the PF to the pressure dynamics in the middle ear (ME) of gerbils. In rabbit ears, R(a) was lower and recovery from plastic deformation was slower than in gerbils. Our findings are in line with the suggestion that the PF might play an important role in respect of adaptation to natural APF.

Frequency multiplexed long range swept source optical coherence tomography

PubMed Central

Zurauskas, Mantas; Bradu, Adrian; Podoleanu, Adrian Gh.

2013-01-01

We present a novel swept source optical coherence tomography configuration, equipped with acousto-optic deflectors that can be used to simultaneously acquire multiple B-scans originating from different depths. The sensitivity range of the configuration is evaluated while acquiring five simultaneous B-scans. Then the configuration is employed to demonstrate long range B-scan imaging by combining two simultaneous B-scans from a mouse head sample. PMID:23760762

Prominent facilitation at beta and gamma frequency range revealed with physiological calcium concentration in adult mouse piriform cortex in vitro

PubMed Central

Gleizes, Marie; Perrier, Simon P.; Fonta, Caroline

2017-01-01

Neuronal activity is characterized by a diversity of oscillatory phenomena that are associated with multiple behavioral and cognitive processes, yet the functional consequences of these oscillations are not fully understood. Our aim was to determine whether and how these different oscillatory activities affect short-term synaptic plasticity (STP), using the olfactory system as a model. In response to odorant stimuli, the olfactory bulb displays a slow breathing rhythm as well as beta and gamma oscillations. Since the firing of olfactory bulb projecting neurons is phase-locked with beta and gamma oscillations, structures downstream from the olfactory bulb should be driven preferentially at these frequencies. We examined STP exhibited by olfactory bulb inputs in slices of adult mouse piriform cortex maintained in vitro in an in vivo-like ACSF (calcium concentration: 1.1 mM). We replaced the presynaptic neuronal firing rate by repeated electrical stimulation (frequency between 3.125 and 100 Hz) applied to the lateral olfactory tract. Our results revealed a considerable enhancement of postsynaptic response amplitude for stimulation frequencies in the beta and gamma range. A phenomenological model of STP fitted to the data suggests that the experimental results can be explained by the interplay between three mechanisms: a short-term facilitation mechanism (time constant ≈160 msec), and two short-term depression mechanisms (recovery time constants <20 msec and ≈140 msec). Increasing calcium concentration (2.2 mM) resulted in an increase in the time constant of facilitation and in a strengthening of the slowest depression mechanism. As a result, response enhancement was reduced and its peak shifted toward the low beta and alpha ranges while depression became predominant in the gamma band. Using environmental conditions corresponding to those that prevail in vivo, our study shows that STP in the lateral olfactory tract to layer Ia synapse allows amplification of

The frequency hopping pattern design for random hopping frequency signal based on stationary phase principle

NASA Astrophysics Data System (ADS)

Liao, Zhikun; Lu, Dawei; Hu, Jiemin; Zhang, Jun

2018-04-01

For the random hopping frequency signal, the modulated frequencies are randomly distributed over given bandwidth. The randomness of modulated frequency not only improves the electronic counter countermeasure capability for radar systems, but also determines its performance of range compression. In this paper, the range ambiguity function of RHF signal is firstly derived. Then, a design method of frequency hopping pattern based on stationary phase principle to improve the peak to side-lobe ratio is proposed. Finally, the simulated experiments show a good effectiveness of the presented design method.

The STAFF-DWP wave instrument on the DSP equatorial spacecraft: description and first results

NASA Astrophysics Data System (ADS)

Cornilleau-Wehrlin, N.; Alleyne, H. St. C.; Yearby, K. H.; de La Porte de Vaux, B.; Meyer, A.; Santolík, O.; Parrot, M.; Belmont, G.; Rezeau, L.; Le Contel, O.; Roux, A.; Attié, D.; Robert, P.; Bouzid, V.; Herment, D.; Cao, J.

2005-11-01

The STAFF-DWP wave instrument on board the equatorial spacecraft (TC1) of the Double Star Project consists of a combination of 2 instruments which are a heritage of the Cluster mission: the Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment and the Digital Wave-Processing experiment (DWP). On DSP-TC1 STAFF consists of a three-axis search coil magnetometer, used to measure magnetic fluctuations at frequencies up to 4 kHz and a waveform unit, up to 10 Hz, plus snapshots up to 180 Hz. DWP provides several onboard analysis tools: a complex FFT to fully characterise electromagnetic waves in the frequency range 10 Hz-4 kHz, a particle correlator linked to the PEACE electron experiment, and compression of the STAFF waveform data. The complementary Cluster and TC1 orbits, together with the similarity of the instruments, permits new multi-point studies. The first results show the capabilities of the experiment, with examples in the different regions of the magnetosphere-solar wind system that have been encountered by DSP-TC1 at the beginning of its operational phase. An overview of the different kinds of electromagnetic waves observed on the dayside from perigee to apogee is given, including the different whistler mode waves (hiss, chorus, lion roars) and broad-band ULF emissions. The polarisation and propagation characteristics of intense waves in the vicinity of a bow shock crossing are analysed using the dedicated PRASSADCO tool, giving results compatible with previous studies: the broad-band ULF waves consist of a superimposition of different wave modes, whereas the magnetosheath lion roars are right-handed and propagate close to the magnetic field. An example of a combined Cluster DSP-TC1 magnetopause crossing is given. This first case study shows that the ULF wave power intensity is higher at low latitude (DSP) than at high latitude (Cluster). On the nightside in the tail, a first wave event comparison - in a rather quiet time interval - is shown. It

Intrinsic vs. spurious long-range memory in high-frequency records of environmental radioactivity. Critical re-assessment and application to indoor 222Rn concentrations from Coimbra, Portugal

NASA Astrophysics Data System (ADS)

Donner, R. V.; Potirakis, S. M.; Barbosa, S. M.; Matos, J. A. O.; Pereira, A. J. S. C.; Neves, L. J. P. F.

2015-05-01

The presence or absence of long-range correlations in the environmental radioactivity fluctuations has recently attracted considerable interest. Among a multiplicity of practically relevant applications, identifying and disentangling the environmental factors controlling the variable concentrations of the radioactive noble gas radon is important for estimating its effect on human health and the efficiency of possible measures for reducing the corresponding exposition. In this work, we present a critical re-assessment of a multiplicity of complementary methods that have been previously applied for evaluating the presence of long-range correlations and fractal scaling in environmental radon variations with a particular focus on the specific properties of the underlying time series. As an illustrative case study, we subsequently re-analyze two high-frequency records of indoor radon concentrations from Coimbra, Portugal, each of which spans several weeks of continuous measurements at a high temporal resolution of five minutes.Our results reveal that at the study site, radon concentrations exhibit complex multi-scale dynamics with qualitatively different properties at different time-scales: (i) essentially white noise in the high-frequency part (up to time-scales of about one hour), (ii) spurious indications of a non-stationary, apparently long-range correlated process (at time scales between some hours and one day) arising from marked periodic components, and (iii) low-frequency variability indicating a true long-range dependent process. In the presence of such multi-scale variability, common estimators of long-range memory in time series are prone to fail if applied to the raw data without previous separation of time-scales with qualitatively different dynamics.

Method and apparatus for coherent burst ranging

DOEpatents

Wachter, Eric A.; Fisher, Walter G.

1998-01-01

A high resolution ranging method is described utilizing a novel modulated waveform, hereafter referred to as coherent burst modulation. In the coherent burst method, high frequency modulation of an acoustic or electromagnetic transmitter, such as a laser, is performed at a modulation frequency. This modulation frequency is transmitted quasi-continuously in the form of interrupted bursts of radiation. Energy from the transmitter is directed onto a target, interacts with the target, and the returning energy is collected. The encoded burst pattern contained in the collected return signal is detected coherently by a receiver that is tuned so as to be principally sensitive to the modulation frequency. The receiver signal is processed to determine target range using both time-of-flight of the burst envelope and phase shift of the high frequency modulation. This approach effectively decouples the maximum unambiguous range and range resolution relationship of earlier methods, thereby allowing high precision ranging to be conducted at arbitrarily long distances using at least one burst of encoded energy. The use of a receiver tuned to the high frequency modulation contained within the coherent burst vastly improves both sensitivity in the detection of the target return signal and rejection of background interferences, such as ambient acoustic or electromagnetic noise. Simultaneous transmission at several energies (or wavelengths) is possible by encoding each energy with a separate modulation frequency or pattern; electronic demodulation at the receiver allows the return pattern for each energy to be monitored independently. Radial velocity of a target can also be determined by monitoring change in phase shift of the return signal as a function of time.

Method and apparatus for coherent burst ranging

DOEpatents

Wachter, E.A.; Fisher, W.G.

1998-04-28

A high resolution ranging method is described utilizing a novel modulated waveform, hereafter referred to as coherent burst modulation. In the coherent burst method, high frequency modulation of an acoustic or electromagnetic transmitter, such as a laser, is performed at a modulation frequency. This modulation frequency is transmitted quasi-continuously in the form of interrupted bursts of radiation. Energy from the transmitter is directed onto a target, interacts with the target, and the returning energy is collected. The encoded burst pattern contained in the collected return signal is detected coherently by a receiver that is tuned so as to be principally sensitive to the modulation frequency. The receiver signal is processed to determine target range using both time-of-flight of the burst envelope and phase shift of the high frequency modulation. This approach effectively decouples the maximum unambiguous range and range resolution relationship of earlier methods, thereby allowing high precision ranging to be conducted at arbitrarily long distances using at least one burst of encoded energy. The use of a receiver tuned to the high frequency modulation contained within the coherent burst vastly improves both sensitivity in the detection of the target return signal and rejection of background interferences, such as ambient acoustic or electromagnetic noise. Simultaneous transmission at several energies (or wavelengths) is possible by encoding each energy with a separate modulation frequency or pattern; electronic demodulation at the receiver allows the return pattern for each energy to be monitored independently. Radial velocity of a target can also be determined by monitoring change in phase shift of the return signal as a function of time. 12 figs.

Modulating action of low frequency oscillations on high frequency instabilities in Hall thrusters

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

Liqiu, Wei, E-mail: weiliqiu@gmail.com, E-mail: weiliqiu@hit.edu.cn; Liang, Han; Ziyi, Yang

2015-02-07

It is found that the low frequency oscillations have modulating action on high frequency instabilities in Hall thrusters. The physical mechanism of this modulation is discussed and verified by numerical simulations. Theoretical analyses indicate that the wide-range fluctuations of plasma density and electric field associated with the low frequency oscillations affect the electron drift velocity and anomalous electron transport across the magnetic field. The amplitude and frequency of high frequency oscillations are modulated by low frequency oscillations, which show the periodic variation in the time scale of low frequency oscillations.

Prediction of rain effects on earth-space communication links operating in the 10 to 35 GHz frequency range

NASA Technical Reports Server (NTRS)

Stutzman, Warren L.

1989-01-01

This paper reviews the effects of precipitation on earth-space communication links operating the 10 to 35 GHz frequency range. Emphasis is on the quantitative prediction of rain attenuation and depolarization. Discussions center on the models developed at Virginia Tech. Comments on other models are included as well as literature references to key works. Also included is the system level modeling for dual polarized communication systems with techniques for calculating antenna and propagation medium effects. Simple models for the calculation of average annual attenuation and cross-polarization discrimination (XPD) are presented. Calculation of worst month statistics are also presented.

Investigation of electrostatic waves in the ion cyclotron range of frequencies in L-4 and ACT-1

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

Ono, Masayuki

Electrostatic waves in the ion cyclotron range of frequencies (ICRF) were studied in the Princeton L-4 and ACT-1 devices for approximately ten years, from 1975 to 1985. The investigation began in the L-4 linear device, looking for the parametric excitation of electrostatic ion cyclotron waves in multi-ion-species plasmas. In addition, this investigation verified multi-ion-species effects on the electrostatic ion cyclotron wave dispersion religion including the ion-ion hybrid resonance. Finite-Larmor-radius modification of the wave dispersion relation was also observed, even for ion temperatures of T{sub i} {approx} 1/40 eV. Taking advantage of the relatively high field and long device length ofmore » L-4, the existence of the cold electrostatic ion cyclotron wave (CES ICW) was verified. With the arrival of the ACT-1 toroidal device, finite-Larmor-radius (FLR) waves were studied in a relatively collisionless warm-ion hydrogen plasma. Detailed investigations of ion Bernstein waves (IBW) included the verification of mode-transformation in their launching, their wave propagation characteristics, their absorption, and the resulting ion heating. This basic physics activity played a crucial role in developing a new reactor heating concept termed ion Bernstein wave heating. Experimental research in the lower hybrid frequency range confirmed the existence of FLR effects near the lower hybrid resonance, predicted by Stix in 1965. In a neon plasma with a carefully placed phased wave exciter, the neutralized ion Bernstein wave was observed for the first time. Using a fastwave ICRF antenna, two parasitic excitation processes for IBW -- parametric instability and density-gradient-driven excitation -- were also discovered. In the concluding section of this paper, a possible application of externally launched electrostatic waves is suggested for helium ash removal from fusion reactor plasmas.« less

Investigation of electrostatic waves in the ion cyclotron range of frequencies in L-4 and ACT-1

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

Ono, Masayuki.

Electrostatic waves in the ion cyclotron range of frequencies (ICRF) were studied in the Princeton L-4 and ACT-1 devices for approximately ten years, from 1975 to 1985. The investigation began in the L-4 linear device, looking for the parametric excitation of electrostatic ion cyclotron waves in multi-ion-species plasmas. In addition, this investigation verified multi-ion-species effects on the electrostatic ion cyclotron wave dispersion religion including the ion-ion hybrid resonance. Finite-Larmor-radius modification of the wave dispersion relation was also observed, even for ion temperatures of T[sub i] [approx] 1/40 eV. Taking advantage of the relatively high field and long device length ofmore » L-4, the existence of the cold electrostatic ion cyclotron wave (CES ICW) was verified. With the arrival of the ACT-1 toroidal device, finite-Larmor-radius (FLR) waves were studied in a relatively collisionless warm-ion hydrogen plasma. Detailed investigations of ion Bernstein waves (IBW) included the verification of mode-transformation in their launching, their wave propagation characteristics, their absorption, and the resulting ion heating. This basic physics activity played a crucial role in developing a new reactor heating concept termed ion Bernstein wave heating. Experimental research in the lower hybrid frequency range confirmed the existence of FLR effects near the lower hybrid resonance, predicted by Stix in 1965. In a neon plasma with a carefully placed phased wave exciter, the neutralized ion Bernstein wave was observed for the first time. Using a fastwave ICRF antenna, two parasitic excitation processes for IBW -- parametric instability and density-gradient-driven excitation -- were also discovered. In the concluding section of this paper, a possible application of externally launched electrostatic waves is suggested for helium ash removal from fusion reactor plasmas.« less

Novel Reactor Relevant RF Actuator Schemes for the Lower Hybrid and the Ion Cyclotron Range of Frequencies

NASA Astrophysics Data System (ADS)

Bonoli, Paul

2014-10-01

This paper presents a fresh physics perspective on the onerous problem of coupling and successfully utilizing ion cyclotron range of frequencies (ICRF) and lower hybrid range of frequencies (LHRF) actuators in the harsh environment of a nuclear fusion reactor. The ICRF and LH launchers are essentially first wall components in a fusion reactor and as such will be subjected to high heat fluxes. The high field side (HFS) of the plasma offers a region of reduced heat flux together with a quiescent scrape off layer (SOL). Placement of the ICRF and LHRF launchers on the tokamak HFS also offers distinct physics advantages: The higher toroidal magnetic field makes it possible to couple faster phase velocity LH waves that can penetrate farther into the plasma core and be absorbed by higher energy electrons, thereby increasing the current drive efficiency. In addition, re-location of the LH launcher off the mid-plane (i.e., poloidal ``steering'') allows further control of the deposition location. Also ICRF waves coupled from the HFS couple strongly to mode converted ion Bernstein waves and ion cyclotron waves waves as the minority density is increased, thus opening the possibility of using this scheme for flow drive and pressure control. Finally the quiescent nature of the HFS scrape off layer should minimize the effects of RF wave scattering from density fluctuations. Ray tracing / Fokker Planck simulations will be presented for LHRF applications in devices such as the proposed Advanced Divertor Experiment (ADX) and extending to ITER and beyond. Full-wave simulations will also be presented which demonstrate the possible combinations of electron and ion heating via ICRF mode conversion. Work supported by the US DoE under Contract Numbers DE-FC02-01ER54648 and DE-FC02-99ER54512.

Frequency Selection for Multi-frequency Acoustic Measurement of Suspended Sediment

NASA Astrophysics Data System (ADS)

Chen, X.; HO, H.; Fu, X.

2017-12-01

Multi-frequency acoustic measurement of suspended sediment has found successful applications in marine and fluvial environments. Difficult challenges remain in regard to improving its effectiveness and efficiency when applied to high concentrations and wide size distributions in rivers. We performed a multi-frequency acoustic scattering experiment in a cylindrical tank with a suspension of natural sands. The sands range from 50 to 600 μm in diameter with a lognormal size distribution. The bulk concentration of suspended sediment varied from 1.0 to 12.0 g/L. We found that the commonly used linear relationship between the intensity of acoustic backscatter and suspended sediment concentration holds only at sufficiently low concentrations, for instance below 3.0 g/L. It fails at a critical value of concentration that depends on measurement frequency and the distance between the transducer and the target point. Instead, an exponential relationship was found to work satisfactorily throughout the entire range of concentration. The coefficient and exponent of the exponential function changed, however, with the measuring frequency and distance. Considering the increased complexity of inverting the concentration values when an exponential relationship prevails, we further analyzed the relationship between measurement error and measuring frequency. It was also found that the inversion error may be effectively controlled within 5% if the frequency is properly set. Compared with concentration, grain size was found to heavily affect the selection of optimum frequency. A regression relationship for optimum frequency versus grain size was developed based on the experimental results.

Ranging Behaviour of Commercial Free-Range Broiler Chickens 1: Factors Related to Flock Variability

PubMed Central

Hemsworth, Paul H.; Groves, Peter J.; Rault, Jean-Loup

2017-01-01

Simple Summary Free-range chicken meat consumption has increased. However, little is known about how meat chickens use the outdoor range. Understanding ranging behaviour could help improve management and shed and range design to ensure optimal ranging opportunities. We tracked 1200 individual broiler chickens in four mixed sex flocks on one commercial farm across two seasons. More chickens accessed the range in summer than winter. Chickens that accessed the range in winter did so less frequently and for a shorter period of time daily than chickens ranging in summer. The number of chickens ranging and the frequency and duration of range visits increased over the first two weeks of range access and stabilised thereafter. More chickens entered and exited the range through particular doors in the shed. More chickens ranged in the morning and evening compared to the middle of the day. Ranging behaviour decreased with increased rainfall and shed dew point. This study provides knowledge regarding ranging behaviour in commercial conditions that may guide improvements on farm to provide chickens with optimal ranging opportunities. Abstract Little is known about the ranging behaviour of chickens. Understanding ranging behaviour is required to improve management and shed and range design to ensure optimal ranging opportunities. Using Radio Frequency Identification technology, we tracked 300 individual broiler chickens in each of four mixed sex ROSS 308 flocks on one commercial farm across two seasons. Ranging behaviour was tracked from the first day of range access (21 days of age) until 35 days of age in winter and 44 days of age in summer. Range use was higher than previously reported from scan sampling studies. More chickens accessed the range in summer (81%) than winter (32%; p < 0.05). On average, daily frequency and duration of range use was greater in summer flocks (4.4 ± 0.1 visits for a total of 26.3 ± 0.8 min/day) than winter flocks (3.2 ± 0.2 visits for a total

Tailoring single-cycle electromagnetic pulses in the 2-9 THz frequency range using DAST/SiO₂ multilayer structures pumped at Ti:sapphire wavelength.

PubMed

Stepanov, Andrei G; Rogov, Andrii; Bonacina, Luigi; Wolf, Jean-Pierre; Hauri, Christoph P

2014-09-08

We present a numerical parametric study of single-cycle electromagnetic pulse generation in a DAST/SiO₂multilayer structure via collinear optical rectification of 800 nm femtosecond laser pulses. It is shown that modifications of the thicknesses of the DAST and SiO₂layers allow tuning of the average frequency of the generated THz pulses in the frequency range from 3 to 6 THz. The laser-to-THz energy conversion efficiency in the proposed structures is compared with that in a bulk DAST crystal and a quasi-phase-matching periodically poled DAST crystal and shows significant enhancement.

Digital frequency control of satellite frequency standards. [Defense Navigation Satellites

NASA Technical Reports Server (NTRS)

Nichols, S. A.

1973-01-01

In the Frequency and Time Standard Development Program of the TIMATION System, a new miniaturized rubidium vapor frequency standard has been tested and analyzed for possible use on the TIMATION 3A launch, as part of the Defense Navigation Satellite Development Program. The design and construction of a digital frequency control was required to remotely control this rubidium vapor frequency standard as well as the quartz oscillator in current use. This control must be capable of accepting commands from a satellite telemetry system, verify that the correct commands have been sent and control the frequency to the requirements of the system. Several modifications must be performed to the rubidium vapor frequency standard to allow it to be compatible with the digital frequency control. These include the addition of a varactor to voltage tune the coarse range of the flywheel oscillator, and a modification to supply the C field current externally. The digital frequency control for the rubidium vapor frequency standard has been successfully tested in prototype form.

Study of blood plasma optical properties in mice grafted with Ehrlich carcinoma in the frequency range 0.1-1.0 THz

NASA Astrophysics Data System (ADS)

Smolyanskaya, O. A.; Kravtsenyuk, O. V.; Panchenko, A. V.; Odlyanitskiy, E. L.; Guillet, J. P.; Cherkasova, O. P.; Khodzitsky, M. K.

2017-12-01

In the course of in vitro studies of blood of laboratory animals with progressing Ehrlich carcinoma, we have revealed the change of the blood plasma optical properties in the THz range, which can be used for developing the express diagnostics of the presence of oncological diseases. An applied software package is elaborated that allows the phantoms of biological samples having a complex structure to be numerically simulated and the parameters of the electromagnetic wave reflected from these samples in the THz frequency range to be calculated. Presented at the Fundamentals of Laser Micro- and Nanotechnologies (FLAMN-16) International Symposium (Pushkin, Leningrad oblast, 27 June to 1 July 2016).

Frequency response of portable PEF meters.

PubMed

Hankinson, J L; Das, M K

1995-08-01

Peak expiratory flow (PEF) is a dynamic parameter and therefore requires a measuring device with a high-frequency response. This study evaluated the frequency-response characteristics of eight commercially available PEF meters, using simulated forced-expiratory maneuvers with a computer-controlled mechanical pump. Three different PEF levels were used (200, 400, and 600 L/min) at six levels of harmonic-frequency content similar to those observed in human subjects. For waveforms with higher frequency content (at the high end or above the physiologic range), the Assess, Vitalograph, Pocket Peak, and Spir-O-Flow PEF meters all overread PEF (greater than 15% difference from target values) at all three PEF levels. These results suggest that the frequency response of PEF meters is an important consideration in the selection of such meters and should be included in device requirements. The current practice of using various levels of American Thoracic Society (ATS) waveform 24 with its low-frequency content may not adequately evaluate the frequency characteristics of PEF meters. An upper range (5% of the fundamental frequency) of 12 Hz, within the range observed in normal subjects, appears to be more practical than an upper limit of 20 Hz.

Removing the depth-degeneracy in optical frequency domain imaging with frequency shifting

PubMed Central

Yun, S. H.; Tearney, G. J.; de Boer, J. F.; Bouma, B. E.

2009-01-01

A novel technique using an acousto-optic frequency shifter in optical frequency domain imaging (OFDI) is presented. The frequency shift eliminates the ambiguity between positive and negative differential delays, effectively doubling the interferometric ranging depth while avoiding image cross-talk. A signal processing algorithm is demonstrated to accommodate nonlinearity in the tuning slope of the wavelength-swept OFDI laser source. PMID:19484034

The South American Meridional B-field Array (SAMBA) and Pc4-5 Wave Studies

NASA Astrophysics Data System (ADS)

Sterner, Lt. Nathan; Zesta, Eftyhia; Boudouridis, Athanasios; Moldwin, Mark; Yizengaw, Endawoke; Chi, Peter

The Antarctic continent, the only landmass in the southern polar region, offers the unique opportunity for observations that geomagnetically range from polar latitudes to well into the inner magnetosphere, thus enabling conjugate observations in a wide range of geomagnetic lat-itudes. The SAMBA (South American Meridional B-field Array) chain is a meridional chain of 12 magnetometers, 11 of them at L=1.1 to L=2.5 along the coast of Chile and in the Antarc-tica peninsula, and one auroral station along the same meridian. SAMBA is conjugate to the northern hemisphere MEASURE and McMAC chains, offering unique opportunities for inter-hemispheric studies. In particular, we study asymmetries in the power of ULF waves and the role of the ionosphere in such observed asymmetries. Utilizing conjugate magnetometer stations at L=1.7 and L=2.3, we previously demonstrated that the northern hemisphere consistently shows higher ULF wave power. One possible reason for the asymmetry is solar zenith angles differences with the northern hemisphere station being closer to the ecliptic plain and having a higher power ratio. These hemispheric differences were also observed with TEC measurements indicating that the north and south conjugate ionospheres are similarly asymmetric. The initial study was done with Pc3 waves, which include the resonance frequencies for the flux tubes of our conjugate stations. We now extend the study to Pc4 and Pc5 waves that reach the lower latitudes via different mechanisms and compare these waves to the resonant Pc3 waves.