575 research outputs found
Survey of the plasma electron environment of Jupiter: A view from Voyager
The plasma environment within Jupiter's bow shock is considered in terms of the in situ, calibrated electron plasma measurements made between 10 eV and 5.95 keV by the Voyager plasma science experiment (PLS). Measurements were analyzed and corrected for spacecraft potential variations; the data were reduced to nearly model independent macroscopic parameters of the local electron density and temperature. It is tentatively concluded that the radial temperature profile within the plasma sheet is caused by the intermixing of two different electron populations that probably have different temporal histories and spatial paths to their local observation. The cool plasma source of the plasma sheet and spikes is probably the Io plasma torus and arrives in the plasma sheet as a result of flux tube interchange motions or other generalized transport which can be accomplished without diverting the plasma from the centrifugal equator. The hot suprathermal populations in the plasma sheet have most recently come from the sparse, hot mid-latitude "bath" of electrons which were directly observed juxtaposed to the plasma sheet
Serum anti-Müllerian hormone concentrations before and after treatment of an ovarian granulosa cell tumour in a cat
Case summary A 15-year-old female cat was presented for investigation of progressive behavioural changes, polyuria, polydipsia and periuria. An ovarian granulosa cell tumour was identified and the cat underwent therapeutic ovariohysterectomy (OHE). The cat’s clinical signs resolved, but 6 months later it was diagnosed as having an anaplastic astrocytoma and was euthanased. Serum anti-Müllerian hormone (AMH) concentration prior to OHE was increased vs a control group of entire and neutered female cats. Following OHE, serum AMH concentration decreased to <1% of the original value. Relevance and novel information Serum AMH measurement may represent a novel diagnostic and monitoring tool for functional ovarian neoplasms in cats
Interaction of the solar wind with Venus
Two topics related to the interaction of the solar wind with Venus are considered. First, a short review of the experimental evidence with particular attention to plasma measurements carried out on Mariner-5 and Mariner-10 is given. Secondly, the results of some recent theoretical work on the interaction of the solar wind with the ionosphere of Venus are summarized
Generalised-Lorentzian Thermodynamics
We extend the recently developed non-gaussian thermodynamic formalism
\cite{tre98} of a (presumably strongly turbulent) non-Markovian medium to its
most general form that allows for the formulation of a consistent thermodynamic
theory. All thermodynamic functions, including the definition of the
temperature, are shown to be meaningful. The thermodynamic potential from which
all relevant physical information in equilibrium can be extracted, is defined
consistently. The most important findings are the following two: (1) The
temperature is defined exactly in the same way as in classical statistical
mechanics as the derivative of the energy with respect to the entropy at
constant volume. (2) Observables are defined in the same way as in Boltzmannian
statistics as the linear averages of the new equilibrium distribution function.
This lets us conclude that the new state is a real thermodynamic equilibrium in
systems capable of strong turbulence with the new distribution function
replacing the Boltzmann distribution in such systems. We discuss the ideal gas,
find the equation of state, and derive the specific heat and adiabatic exponent
for such a gas. We also derive the new Gibbsian distribution of states. Finally
we discuss the physical reasons for the development of such states and the
observable properties of the new distribution function.Comment: 13 pages, 1 figur
New Insights into Dissipation in the Electron Layer During Magnetic Reconnection
Detailed comparisons are reported between laboratory observations of
electron-scale dissipation layers near a reconnecting X-line and direct
two-dimensional full-particle simulations. Many experimental features of the
electron layers, such as insensitivity to the ion mass, are reproduced by the
simulations; the layer thickness, however, is about 3-5 times larger than the
predictions. Consequently, the leading candidate 2D mechanism based on
collisionless electron nongyrotropic pressure is insufficient to explain the
observed reconnection rates. These results suggest that, in addition to the
residual collisions, 3D effects play an important role in electron-scale
dissipation during fast reconnection.Comment: 17 pages, 4 figure
MeV magnetosheath ions energized at the bow shock
A causal relationship between midlatitude magnetosheath energetic ions and bow shock magnetic geometry was previously established for ion energy up to 200 keV e−1 for the May 4, 1998, storm event. This study demonstrates that magnetosheath ions with energies above 200 keV up to 1 MeV simply extend the ion spectrum to form a power law tail. Results of cross-correlation analysis suggest that these ions also come directly from the quasi-parallel bow shock, not the magnetosphere. This is confirmed by a comparison of energetic ion fluxes simultaneously measured in the magnetosheath and at the quasi-parallel bow shock when both regions are likely connected by the magnetic field lines. We suggest that ions are accelerated at the quasi-parallel bow shock to energies as high as 1 MeV and subsequently transported into the magnetosheath during this event
Acute exercise facilitates brain function and cognition in children who need it most: An ERP study of individual differences in inhibitory control capacity
AbstractThe present study examined the effects of moderate-intensity aerobic exercise on aspects of cognitive control in two groups of children categorized by higher- and lower-task performance. Event-related brain potentials (ERPs) were collected in 40 preadolescent children during a modified flanker task following 20min of treadmill walking and seated rest on separate occasions. Participants were bifurcated into two groups based on task performance following the resting session. Findings revealed that following exercise, higher-performers maintained accuracy and exhibited no change in P3 amplitude compared to seated rest. Lower-performers demonstrated a differential effect, such that accuracy measures improved, and P3 amplitude increased following exercise. Lastly, both groups displayed smaller N2 amplitude and shorter P3 latency following exercise, suggesting an overall facilitation in response conflict and the speed of stimulus classification. The current findings replicate prior research reporting the beneficial influence of acute aerobic exercise on cognitive performance in children. However, children with lower inhibitory control capacity may benefit the most from single bouts of exercise. These data are among the first to demonstrate the differential effect of physical activity on individuals who vary in inhibitory control, and further support the role of aerobic exercise for brain health during development
Electron and proton heating by solar wind turbulence
Previous formulations of heating and transport associated with strong
magnetohydrodynamic (MHD) turbulence are generalized to incorporate separate
internal energy equations for electrons and protons. Electron heat conduction
is included. Energy is supplied by turbulent heating that affects both
electrons and protons, and is exchanged between them via collisions. Comparison
to available Ulysses data shows that a reasonable accounting for the data is
provided when (i) the energy exchange timescale is very long and (ii) the
deposition of heat due to turbulence is divided, with 60% going to proton
heating and 40% into electron heating. Heat conduction, determined here by an
empirical fit, plays a major role in describing the electron data
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