294 research outputs found
An observation of LHR noise with banded structure by the sounding rocket S29 Barium-GEOS
The measurement of electrostatic and obviously locally produced noise near the lower hybrid frequency made by the sounding rocket S29 Barium-GEOS is reported. The noise is strongly related to the spin of the rocket and reaches well below the local lower hybrid resonance frequency. Above the altitude of 300 km the noise shows banded structure roughly organized by the hydrogen cyclotron frequency. Simultaneously with the banded structure, a signal near the hydrogen cyclotron frequency is detected. This signal is also spin related. The characteristics of the noise suggest that it is locally generated by the rocket payload disturbing the plasma. If this interpretation is correct we expect plasma wave experiments on other spacecrafts, e.g., the space shuttle to observe similar phenomena
Uranium on uranium collisions at relativistic energies
Deformation and orientation effects on compression, elliptic flow and
particle production in uranium on uranium collisions (UU) at relativistic
energies are studied within the transport model ART. The density compression in
tip-tip UU collisions is found to be about 30% higher and lasts approximately
50% longer than in body-body or spherical UU reactions. The body-body UU
collisions have the unique feature that the nucleon elliptic flow is the
highest in the most central collisions and remain a constant throughout the
reaction. We point out that the tip-tip UU collisions are more probable to
create the QGP at AGS and SPS energies while the body-body UU collisions are
more useful for studying properties of the QGP at higher energies.Comment: 8 pages + 4 figure
Sounding rocket study of two sequential auroral poleward boundary intensifications
The Cascades-2 sounding rocket was launched on 20 March 2009 at 11:04:00 UT from the Poker Flat Research Range in Alaska, and flew across a series of poleward boundary intensifications (PBIs). The rocket initially crosses a diffuse arc, then crosses the equatorward extent of one PBI (a streamer), and finally crosses the initiation of a separate PBI before entering the polar cap. Each of the crossings have fundamentally different in situ electron energy and pitch angle structure, and different ground optics images of visible aurora. It is found that the diffuse arc has a quasi-static acceleration mechanism, and the intensification at the poleward boundary has an Alfvénic acceleration mechanism. The streamer shows characteristics of both types of acceleration. PFISR data provide ionospheric context for the rocket observations. Three THEMIS satellites in close conjunction with the rocket foot point show earthward flows and slight dipolarizations in the magnetotail associated with the in situ observations of PBI activity. An important goal of the Cascades-2 study is to bring together the different observational communities (rocket, ground cameras, ground radar, satellite) with the same case study. The Cascades-2 experiment is the first sounding rocket observation of a PBI sequence, enabling a detailed investigation of the electron signatures and optical aurora associated with various stages of a PBI sequence as it evolves from an Alfvénic to a more quasi-static structure
Dayside Field-Aligned Current Impacts on Ionospheric Irregularities
Global Navigation Satellite Systems (GNSS) are subject to disturbances caused by plasma irregularities in the ionosphere. Studies have suggested that in addition to the gradient drift and KelvinâHelmholtz instabilities, electron precipitation may be important for phase scintillations in the dayside auroral region. This study combines in situ Swarm data with ground GNSS observations to investigate the potential role of filamentary fieldâaligned currents (FACs) on phase scintillations in the dayside auroral region by analyzing 22 events with phase scintillations exceeding 0.45 radians. We observe colocation between regions of severe phase scintillations and highly filamented FACs with fluctuations measured in the spacecraft frame of the order of 20 Hz. The observations indicate that filamentary FACs are crucial drivers for irregularities responsible for creating severe phase scintillations measured in the dayside auroral region and are thus of significant importance in the context of space weather impact on satellite communication.publishedVersio
Role of isospin dependent mean field in pion production in heavy ion reactions
The importance of a isospin dependent nuclear mean field (IDMF) in regard to
the pion production mechanism is studied for the reaction at 1
GeV/nucleon using the Quantum Molecular Dynamics (QMD) model. In particular,
the effect of the IDMF on pion spectra and the charged pion ratio are analyzed.
It is found that the inclusion of a IDMF considerably suppresses the low
pions, thus, leading to a better agreement with the data on pion spectra.
Moreover, the rapidity distribution of the charged pion ratio appears to be
sensitive to the isospin dependence of the nuclear mean field.Comment: 16 pages, using RevTex, 6 PS-Figure
Electron temperature in the cusp as measured with the SCIFER-2 sounding rocket
It is expected that energy deposited by soft auroral electron precipitation in the ionosphere should result in heating of ionospheric electrons in that location, and this heating is an important step in the ion outflow process. We present coordinated observations from the SCIFER-2 sounding rocket in the cusp region overflying optical observing sites in Svalbard. The rocket payload included a sensor which is designed to measure the temperature of thermal electrons. We show that elevated electron temperatures measured in situ are correlated with electron precipitation as inferred from auroral emissions during the 60â120 s preceding the passage of the rocket. This integrated âcooking timeâ is an important factor in determining the origin and resulting flux of outflowing ions
The energy dependence of flow in Ni induced collisions from 400 to 1970A MeV
We study the energy dependence of collective (hydrodynamic-like) nuclear
matter flow in 400-1970 A MeV Ni+Au and 1000-1970 A MeV Ni+Cu reactions. The
flow increases with energy, reaches a maximum, and then gradually decreases at
higher energies. A way of comparing the energy dependence of flow values for
different projectile-target mass combinations is introduced, which demonstrates
a common scaling behaviour among flow values from different systems.Comment: 12 pages, 3 figures. Submitted to Physical Review Letter
Radial Flow in Au+Au Collisions at E=0.25-1.15 A GeV
A systematic study of energy spectra for light particles emitted at
midrapidity from Au+Au collisions at E=0.25-1.15 A GeV reveals a significant
non-thermal component consistent with a collective radial flow. This component
is evaluated as a function of bombarding energy and event centrality.
Comparisons to Quantum Molecular Dynamics (QMD) and Boltzmann-Uehling-Uhlenbeck
(BUU) models are made for different equations of state.Comment: 10 pages of text and 4 figures (all ps files in a uuencoded package)
Longitudinal Flow of Protons from 2-8 AGeV Central Au+Au Collisions
Rapidity distributions of protons from central Au + Au
collisions measured by the E895 Collaboration in the energy range from 2 to 8
AGeV at the Brookhaven AGS are presented. Longitudinal flow parameters derived
using a thermal model including collective longitudinal expansion are extracted
from these distributions. The results show an approximately linear increase in
the longitudinal flow velocity, , as a function of the
logarithm of beam energy.Comment: 5 Pages, including 3 figures, 1 tabl
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