1,302 research outputs found
The Effects of Turbulence on Three-Dimensional Magnetic Reconnection at the Magnetopause
Two- and three-dimensional particle-in-cell simulations of a recent encounter
of the Magnetospheric Multiscale Mission (MMS) with an electron diffusion
region at the magnetopause are presented. While the two-dimensional simulation
is laminar, turbulence develops at both the x-line and along the magnetic
separatrices in the three-dimensional simulation. The turbulence is strong
enough to make the magnetic field around the reconnection island chaotic and
produces both anomalous resistivity and anomalous viscosity. Each contribute
significantly to breaking the frozen-in condition in the electron diffusion
region. A surprise is that the crescent-shaped features in velocity space seen
both in MMS observations and in two-dimensional simulations survive, even in
the turbulent environment of the three-dimensional system. This suggests that
MMS's measurements of crescent distributions do not exclude the possibility
that turbulence plays an important role in magnetopause reconnection.Comment: Revised version accepted by GR
Dependence of CMI Growth Rates on Electron Velocity Distributions and Perturbation by Solitary Waves
We calculate growth rates and corresponding gains for RX and LO mode
radiation associated with the cyclotron maser instability for parameterized
horseshoe electron velocity distributions. The velocity distribution function
was modeled to closely fit the electron distribution functions observed in the
auroral cavity. We systematically varied the model parameters as well as the
propagation direction to study the dependence of growth rates on model
parameters. The growth rate depends strongly on loss cone opening angle, which
must be less than for significant CMI growth. The growth rate is
sharply peaked for perpendicular radiation (), with a
full-width at half-maximum , in good agreement with observed k-vector
orientations and numerical simulations. The fractional bandwidth varied between
10 and 10, depending most strongly on propagation direction. This
range encompasses nearly all observed fractional AKR burst bandwidths. We find
excellent agreement between the computed RX mode emergent intensities and
observed AKR intensities assuming convective growth length 20-40 km
and group speed 0.15. The only computed LO mode growth rates compatible
observed LO mode radiation levels occurred for number densities more than 100
times the average energetic electron densities measured in auroral cavities.
This implies that LO mode radiation is not produced directly by the CMI
mechanism but more likely results from mode conversion of RX mode radiation. We
find that perturbation of the model velocity distribution by large ion solitary
waves (ion holes) can enhance the growth rate by a factor of 2-4. This will
result in a gain enhancement more than 40 dB depending on the convective growth
length within the structure. Similar enhancements may be caused by EMIC waves.Comment: 21 pages, 11 figures. J. Geophys. Res. 2007 (accepted
Stage III Xanthogranulomatous Pyelonephritis treated with antibiotherapy and percutaneous drainage
Xanthogranulomatous pyelonephritis (XPN) is a rare inflammatory condition usually secondary to chronic obstruction caused by nephrolithiasis and resulting in infection and irreversible destruction of the renal parenchyma. Its standard therapy consists of total or partial nephrectomy. A case of stage III xanthogranulomatous pyelonephritis treated with antibiotherapy and percutaneous drainage is presented in this paper
325 MHz VLA Observations of Ultracool Dwarfs TVLM 513-46546 and 2MASS J0036+1821104
We present 325 MHz (90 cm wavelength) radio observations of ultracool dwarfs
TVLM 513-46546 and 2MASS J0036+1821104 using the Very Large Array (VLA) in June
2007. Ultracool dwarfs are expected to be undetectable at radio frequencies,
yet observations at 8.5 GHz (3.5 cm) and 4.9 GHz (6 cm) of have revealed
sources with > 100 {\mu}Jy quiescent radio flux and > 1 mJy pulses coincident
with stellar rotation. The anomalous emission is likely a combination of
gyrosynchrotron and cyclotron maser processes in a long-duration, large-scale
magnetic field. Since the characteristic frequency for each process scales
directly with the magnetic field magnitude, emission at lower frequencies may
be detectable from regions with weaker field strength. We detect no significant
radio emission at 325 MHz from TVLM 513-46546 or 2MASS J0036+1821104 over
multiple stellar rotations, establishing 2.5{\sigma} total flux limits of 795
{\mu}Jy and 942 {\mu}Jy respectively. Analysis of an archival VLA 1.4 GHz
observation of 2MASS J0036+1821104 from January 2005 also yields a
non-detection at the level of < 130 {\mu}Jy . The combined radio observation
history (0.3 GHz to 8.5 GHz) for these sources suggests a continuum emission
spectrum for ultracool dwarfs which is either flat or inverted below 2-3 GHz.
Further, if the cyclotron maser instability is responsible for the pulsed radio
emission observed on some ultracool dwarfs, our low-frequency non-detections
suggest that the active region responsible for the high-frequency bursts is
confined within 2 stellar radii and driven by electron beams with energies less
than 5 keV.Comment: 11 pages, 5 figures, submitted to A
Observations of whistler mode waves with nonlinear parallel electric fields near the dayside magnetic reconnection separatrix by the Magnetospheric Multiscale mission
We show observations from the Magnetospheric Multiscale (MMS) mission of whistler mode waves in the Earth's low-latitude boundary layer (LLBL) during a magnetic reconnection event. The waves propagated obliquely to the magnetic field toward the X line and were confined to the edge of a southward jet in the LLBL. Bipolar parallel electric fields interpreted as electrostatic solitary waves (ESW) are observed intermittently and appear to be in phase with the parallel component of the whistler oscillations. The polarity of the ESWs suggests that if they propagate with the waves, they are electron enhancements as opposed to electron holes. The reduced electron distribution shows a shoulder in the distribution for parallel velocities between 17,000 and 22,000 km/s, which persisted during the interval when ESWs were observed, and is near the phase velocity of the whistlers. This shoulder can drive Langmuir waves, which were observed in the high-frequency parallel electric field data
Electron-acoustic plasma waves: oblique modulation and envelope solitons
Theoretical and numerical studies are presented of the amplitude modulation
of electron-acoustic waves (EAWs) propagating in space plasmas whose
constituents are inertial cold electrons, Boltzmann distributed hot electrons
and stationary ions. Perturbations oblique to the carrier EAW propagation
direction have been considered. The stability analysis, based on a nonlinear
Schroedinger equation (NLSE), reveals that the EAW may become unstable; the
stability criteria depend on the angle between the modulation and
propagation directions. Different types of localized EA excitations are shown
to exist.Comment: 10 pages, 5 figures; to appear in Phys. Rev.
Prevalence and distribuion of staphylococcal enterotoxin genes among Staphylococcus aureus isolates from chicken and turkey carcasses in Algeria
ΔΕΝ ΔΙΑΤΙΘΕΤΑΙ ΠΕΡΙΛΗΨΗThis study is aimed to determine the prevalence of staphylococcus aureus (S.aureus) by biochemical tests in poultry carcasses. It is also intend to detect the distribution of genes for classical staphylococcal enterotoxins A, B, C, D and E (sea, seb, sec, sed and see) and for gene femA, specific for S.aureus species, using multiplex PCR. A total of 385 samples of neck skins from fresh poultry carcasses were collected during the period 2012-2013 from 16 different slaughterhouses located in the region of Algiers, Algeria. The overall prevalence of S.aureus in freshly slaughtered poultry carcasses was 41.56%, with an individual prevalence of 40.63% and 45.71% for chicken and turkey respectively. From the 95 strains of S.aureus identified by biochemical tests, 82 (86.32%) isolates were femA positive using multiplex PCR. The investigation has also revealed the presence of both enterotoxins B and D, with a predominance of seb (13.33%) followed by sed (1.67%), in the chicken carcasses while in turkey only sed was detected (4.55%) It has been found that strains of S.aureus of poultry origin can be enterotoxigenic with the predominance of genes encoding for enterotoxins seb in chicken and sed in turkey. As enterotoxins can be produced in adequate amounts to induce foodborne illnesses, these potential dangers must be considered in terms of a real risk to public health
The Effects Of Turbulence On Three-Dimensional Magnetic Reconnection At The Magnetopause
Two- and three-dimensional particle-in-cell simulations of a recent encounter of the Magnetospheric Multiscale Mission (MMS) with an electron diffusion region at the magnetopause are presented. While the two-dimensional simulation is laminar, turbulence develops at both the x-line and along the magnetic separatrices in the three-dimensional simulation. The turbulence is strong enough to make the magnetic field around the reconnection island chaotic and produces both anomalous resistivity and anomalous viscosity. Each contribute significantly to breaking the frozen-in condition in the electron diffusion region. A surprise is that the crescent-shaped features in velocity space seen both in MMS observations and in two-dimensional simulations survive, even in the turbulent environment of the three-dimensional system. This suggests that MMS\u27s measurements of crescent distributions do not exclude the possibility that turbulence plays an important role in magnetopause reconnection
EMIC Waves in the Outer Magnetosphere: Observations of an Off-Equator Source Region.
Electromagnetic ion cyclotron (EMIC) waves at large L shells were observed away from the magnetic equator by the Magnetospheric MultiScale (MMS) mission nearly continuously for over four hours on 28 October 2015. During this event, the wave Poynting vector direction systematically changed from parallel to the magnetic field (toward the equator), to bidirectional, to antiparallel (away from the equator). These changes coincide with the shift in the location of the minimum in the magnetic field in the southern hemisphere from poleward to equatorward of MMS. The local plasma conditions measured with the EMIC waves also suggest that the outer magnetospheric region sampled during this event was generally unstable to EMIC wave growth. Together, these observations indicate that the bidirectionally propagating wave packets were not a result of reflection at high latitudes but that MMS passed through an off-equator EMIC wave source region associated with the local minimum in the magnetic field
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