1,540 research outputs found
Magnetic Field Reconstruction for a Realistic Multi-Point, Multi-Scale Spacecraft Observatory
Future in situ space plasma investigations will likely involve spatially distributed observatories comprised of multiple spacecraft, beyond the four and five spacecraft configurations currently in operation. Inferring the magnetic field structure across the observatory, and not simply at the observation points, is a necessary step towards characterizing fundamental plasma processes using these unique multi-point, multi-scale data sets. We propose improvements upon the classic first-order reconstruction method, as well as a second-order method, utilizing magnetometer measurements from a realistic nine-spacecraft observatory. The improved first-order method, which averages over select ensembles of four spacecraft, reconstructs the magnetic field associated with simple current sheets and numerical simulations of turbulence accurately over larger volumes compared to second-order methods or first-order methods using a single regular tetrahedron. Using this averaging method on data sets with fewer than nine measurement points, the volume of accurate reconstruction compared to a known magnetic vector field improves approximately linearly with the number of measurement points
Stochastic proton heating by kinetic-Alfvén-wave turbulence in moderately high-β plasmas
Stochastic heating refers to an increase in the average magnetic moment of charged
particles interacting with electromagnetic fluctuations whose frequencies are smaller than
the particles’ cyclotron frequencies. This type of heating arises when the amplitude of
the gyroscale fluctuations exceeds a certain threshold, causing particle orbits in the plane
perpendicular to the magnetic field to become stochastic rather than nearly periodic. We
consider the stochastic heating of protons by Alfv´en-wave (AW) and kinetic-Alfv´en-wave
(KAW) turbulence, which may make an important contribution to the heating of the
solar wind. Using phenomenological arguments, we derive the stochastic-proton-heating
rate in plasmas in which βp ∼ 1 − 30, where βp is the ratio of the proton pressure to
the magnetic pressure. (We do not consider the βp & 30 regime, in which KAWs at
the proton gyroscale become non-propagating.) We test our formula for the stochasticheating
rate by numerically tracking test-particle protons interacting with a spectrum
of randomly phased AWs and KAWs. Previous studies have demonstrated that at
βp . 1, particles are energized primarily by time variations in the electrostatic potential
and thermal-proton gyro-orbits are stochasticized primarily by gyroscale fluctuations
in the electrostatic potential. In contrast, at βp & 1, particles are energized primarily
by the solenoidal component of the electric field and thermal-proton gyro-orbits are
stochasticized primarily by gyroscale fluctuations in the magnetic field
The Near-Sun Streamer Belt Solar Wind: Turbulence and Solar Wind Acceleration
The fourth orbit of Parker Solar Probe (PSP) reached heliocentric distances
down to 27.9 Rs, allowing solar wind turbulence and acceleration mechanisms to
be studied in situ closer to the Sun than previously possible. The turbulence
properties were found to be significantly different in the inbound and outbound
portions of PSP's fourth solar encounter, likely due to the proximity to the
heliospheric current sheet (HCS) in the outbound period. Near the HCS, in the
streamer belt wind, the turbulence was found to have lower amplitudes, higher
magnetic compressibility, a steeper magnetic field spectrum (with spectral
index close to -5/3 rather than -3/2), a lower Alfv\'enicity, and a "1/f" break
at much lower frequencies. These are also features of slow wind at 1 au,
suggesting the near-Sun streamer belt wind to be the prototypical slow solar
wind. The transition in properties occurs at a predicted angular distance of
~4{\deg} from the HCS, suggesting ~8{\deg} as the full-width of the streamer
belt wind at these distances. While the majority of the Alfv\'enic turbulence
energy fluxes measured by PSP are consistent with those required for
reflection-driven turbulence models of solar wind acceleration, the fluxes in
the streamer belt are significantly lower than the model predictions,
suggesting that additional mechanisms are necessary to explain the acceleration
of the streamer belt solar wind
ALPS: the Arbitrary Linear Plasma Solver
The Arbitrary Linear Plasma Solver (ALPS) is a parallelised numerical code that
solves the dispersion relation in a hot (even relativistic) magnetised plasma with an
arbitrary number of particle species with arbitrary gyrotropic equilibrium distribution
functions for any direction of wave propagation with respect to the background
field. ALPS reads the background momentum distributions as tables of values on
a (p⊥, pk) grid, where p⊥ and pk are the momentum coordinates in the directions
perpendicular and parallel to the background magnetic field, respectively. We present
the mathematical and numerical approach used by ALPS and introduce our algorithms
for the handling of poles and the analytic continuation for the Landau contour
integral. We then show test calculations of dispersion relations for a selection of
stable and unstable configurations in Maxwellian, bi-Maxwellian, κ-distributed and
Jüttner-distributed plasmas. These tests demonstrate that ALPS derives reliable plasma
dispersion relations. ALPS will make it possible to determine the properties of waves
and instabilities in the non-equilibrium plasmas that are frequently found in space,
laboratory experiments and numerical simulations
Absence of diabetic retinopathy in a patient who has had diabetes mellitus for 69 years, and inadequate glycemic control: case presentation
The main risk factors for the development and progression of diabetic retinopathy (DR) are chronic hyperglycemia, disease duration and systemic blood pressure. So far chronic hyperglycemia is the strongest evidence concerning the risk of developing DR. However there are some patients with poor metabolic control who never develop this diabetic complication. We present a case of a 73-year-old woman with type 1 diabetes mellitus, diagnosed 69 years ago. The patient is 73 years old, with no evidence of DR, despite poor glycemic control and several risk factors for DR. This case suggests the presence of a possible protection factor, which could be genetic
A Tunable Two-impurity Kondo system in an atomic point contact
Two magnetic atoms, one attached to the tip of a Scanning Tunneling
Microscope (STM) and one adsorbed on a metal surface, each constituting a Kondo
system, have been proposed as one of the simplest conceivable systems
potentially exhibiting quantum critical behaviour. We have succeeded in
implementing this concept experimentally for cobalt dimers clamped between an
STM tip and a gold surface. Control of the tip-sample distance with
sub-picometer resolution allows us to tune the interaction between the two
cobalt atoms with unprecedented precision. Electronic transport measurements on
this two-impurity Kondo system reveal a rich physical scenario which is
governed by a crossover from local Kondo screening to non-local singlet
formation due to antiferromagnetic coupling as a function of separation of the
cobalt atoms.Comment: 22 pages, 5 figure
Overexpression of Full-Length ETV1 Transcripts in Clinical Prostate Cancer Due to Gene Translocation
ETV1 is overexpressed in a subset of clinical prostate cancers as a fusion transcript with many different partners. However, ETV1 can also be overexpressed as a full-length transcript. Full-length ETV1 protein functions differently from truncated ETV1 produced by fusion genes. In this study we describe the genetic background of full-length ETV1 overexpression and the biological properties of different full-length ETV1 isoforms in prostate cancer. Break-apart FISH showed in five out of six patient samples with overexpression of full-length ETV1 a genomic rearrangement of the gene, indicating frequent translocation. We were able to study the rearrangements in more detail in two tumors. In the first tumor 5′-RACE on cDNA showed linkage of the complete ETV1 transcript to the first exon of a prostate-specific two exon ncRNA gene that maps on chromosome 14 (EST14). This resulted in the expression of both full-length ETV1 transcripts and EST14-ETV1 fusion transcripts. In chromosome spreads of a xenograft derived from the second prostate cancer we observed a complex ETV1 translocation involving a chromosome 7 fragment that harbors ETV1 and fragments of chromosomes 4 and 10. Further studies revealed the overexpression of several different full-length transcripts, giving rise to four protein isoforms with different N-terminal regions. Even the shortest isoform synthesized by full-length ETV1 stimulated in vitro anchorage-independent growth of PNT2C2 prostate cells. This contrasts the lack of activity of even shorter N-truncated ETV1 produced by fusion transcripts. Our findings that in clinical prostate cancer overexpression of full-length ETV1 is due to genomic rearrangements involving different chromosomes and the identification of a shortened biologically active ETV1 isoform are highly relevant for understanding the mechanism of ETV1 function in prostate cancer
Organizational commitment, organization-based self-esteem, emotional exhaustion and turnover: A conservation of resources perspective
We examined the relationship of four commitment dimensions (affective, normative, continuance-perceived sacrifices and continuance-lack of alternatives) to emotional exhaustion over time under the lens of conservation of resources theory. Using data from 260 employees, Time 1 lack of alternatives and normative commitment contributed positively to Time 2 emotional exhaustion, controlling for Time 1 emotional exhaustion. Organization-based self-esteem (OBSE) moderated the relationship of lack of alternatives commitment to emotional exhaustion such that the relationship was stronger when OBSE was high. We further theorized that the resource drain engendered by emotional exhaustion would cause the latter to be positively related to turnover, controlling for commitment dimensions. Results supported this prediction. The implications of these findings for future research on commitment, emotional exhaustion and turnover are discussed
Abnormal ECG Findings in Athletes: Clinical Evaluation and Considerations.
PURPOSE OF REVIEW: Pre-participation cardiovascular evaluation with electrocardiography is normal practice for most sporting bodies. Awareness about sudden cardiac death in athletes and recognizing how screening can help identify vulnerable athletes have empowered different sporting disciplines to invest in the wellbeing of their athletes. RECENT FINDINGS: Discerning physiological electrical alterations due to athletic training from those representing cardiac pathology may be challenging. The mode of investigation of affected athletes is dependent on the electrical anomaly and the disease(s) in question. This review will highlight specific pathological ECG patterns that warrant assessment and surveillance, together with an in-depth review of the recommended algorithm for evaluation
Kinetic-scale Spectral Features of Cross Helicity and Residual Energy in the Inner Heliosphere
In this work, we present the first results from the flux angle (FA) operation mode of the Faraday Cup instrument on board the Parker Solar Probe (PSP). The FA mode allows rapid measurements of phase space density fluctuations close to the peak of the proton velocity distribution function with a cadence of 293 Hz. This approach provides an invaluable tool for understanding kinetic-scale turbulence in the solar wind and solar corona. We describe a technique to convert the phase space density fluctuations into vector velocity components and compute several turbulence parameters, such as spectral index, residual energy, and cross helicity during two intervals when the FA mode was used in PSP's first encounter at 0.174 au distance from the Sun
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