22 research outputs found
Middle atmosphere measurements of small-scale electron density irregularities and ion properties during the MAC/Epsilon campaign
Rocket payloads designed to measure small scale electron density irregularities and ion properties in the middle atmosphere were flown with each of the three main salvos of the MAC/Epsilon campaign conducted at the Andoya Rocket Range, Norway, during October to November 1987. Fixed bias, hemispheric nose tip probes measured small scale electron density irregularities, indicative of neutral air turbulence, during the rocket's ascent; and subsequently, parachute-borne Gerdien condensers measured the region's polar electrical conductivity, ion mobility and density. One rocket was launched during daylight (October 15, 1052:20 UT), and the other two launches occurred at night (October 21, 2134 UT: November 12, 0021:40 UT) under moderately disturbed conditions which enhanced the detection and measurement of turbulence structures. A preliminary analysis of the real time data displays indicates the presence of small scale electron density irregularities in the altitude range of 60 to 90 km. Ongoing data reduction will determine turbulence parameters and also the region's electrical properties below 90 km
Theoretical analysis of the mechanisms of a gender differentiation in the propensity for orthostatic intolerance after spaceflight
<p>Abstract</p> <p>Background</p> <p>A tendency to develop reentry orthostasis after a prolonged exposure to microgravity is a common problem among astronauts. The problem is 5 times more prevalent in female astronauts as compared to their male counterparts. The mechanisms responsible for this gender differentiation are poorly understood despite many detailed and complex investigations directed toward an analysis of the physiologic control systems involved.</p> <p>Methods</p> <p>In this study, a series of computer simulation studies using a mathematical model of cardiovascular functioning were performed to examine the proposed hypothesis that this phenomenon could be explained by basic physical forces acting through the simple common anatomic differences between men and women. In the computer simulations, the circulatory components and hydrostatic gradients of the model were allowed to adapt to the physical constraints of microgravity. After a simulated period of one month, the model was returned to the conditions of earth's gravity and the standard postflight tilt test protocol was performed while the model output depicting the typical vital signs was monitored.</p> <p>Conclusions</p> <p>The analysis demonstrated that a 15% lowering of the longitudinal center of gravity in the anatomic structure of the model was all that was necessary to prevent the physiologic compensatory mechanisms from overcoming the propensity for reentry orthostasis leading to syncope.</p
A multiscale model to predict current absolute risk of femoral fracture in a postmenopausal population
Osteoporotic hip fractures are a major healthcare problem. Fall severity and bone strength are important risk factors of hip fracture. This study aims to obtain a mechanistic explanation for fracture risk in dependence of these risk factors. A novel modelling approach is developed that combines models at different scales to overcome the challenge of a large spaceâtime domain of interest and considers the variability of impact forces between potential falls in a subject. The multiscale model and its component models are verified with respect to numerical approximations made therein, the propagation of measurement uncertainties of model inputs is quantified, and model predictions are validated against experimental and clinical data. The main results are model predicted absolute risk of current fracture (ARF0) that ranged from 1.93 to 81.6% (median 36.1%) for subjects in a retrospective cohort of 98 postmenopausal British women (49 fracture cases and 49 controls); ARF0 was computed up to a precision of 1.92 percentage points (pp) due to numerical approximations made in the model; ARF0 possessed an uncertainty of 4.00Â pp due to uncertainties in measuring model inputs; ARF0 classified observed fracture status in the above cohort with AUC = 0.852 (95% CI 0.753â0.918), 77.6% specificity (95% CI 63.4â86.5%) and 81.6% sensitivity (95% CI 68.3â91.1%). These results demonstrate that ARF0 can be computed using the model with sufficient precision to distinguish between subjects and that the novel mechanism of fracture risk determination based on fall dynamics, hip impact and bone strength can be considered validated
Observation of electron biteout regions below sporadic E layers at polar latitudes
The descent of a narrow sporadic E layer near 95 km altitude over Poker
Flat Research Range in Alaska was observed with electron probes on two
consecutive sounding rockets and with incoherent scatter radar during a 2 h period near magnetic midnight. A series of four trimethyl aluminum
chemical releases demonstrated that the Es layer remained just slightly
above the zonal wind node, which was slowly descending due to propagating
long-period gravity waves. The location of the layer is consistent with the
equilibrium position due to combined action of the wind shear and electric
fields. Although the horizontal electric field could not be measured
directly, we estimate that it was ~ 2 mV m<sup>â1</sup> southward, consistent with
modeling the vertical ion drift, and compatible with extremely quiet
conditions. Both electron probes observed deep biteout regions just below the
Es enhancements, which also descended with the sporadic layers. We discuss
several possibilities for the cause of these depletions; one possibility is
the presence of negatively charged, nanometer-sized mesospheric smoke
particles. Such particles have recently been detected in the upper
mesosphere, but not yet in immediate connection with sporadic E. Our
observations of electron depletions suggest a new process associated with
sporadic E
Sporadic sodium and E layers observed during the summer 2002 MaCWAVE/MIDAS rocket campaign
On 5 July 2002, a MaCWAVE (Mountain and Convective
Waves Ascending VErtically) payload launched from
Andøya Rocket Range, Norway, observed narrow enhanced layers of electron
density that were nearly coincident with sporadic sodium layers measured by
the Weber sodium lidar at the nearby ALOMAR Observatory. We investigate the
formation mechanism of these layers using the neutral wind and temperature
profiles measured directly by the lidar and the vertical motion deduced from
the sodium mixing ratio. Through comparisons of the lidar data to the
sporadic E in situ data, we find support for the concentration and downward
motion of ions to an altitude where chemical models predict the rapid
conversion of sodium ions to neutral sodium
In-situ electron and ion measurements and observed gravity wave effects in the polar mesosphere during the MaCWAVE program
Langmuir probe electron and ion measurements from four instrumented rockets
flown during the MaCWAVE (Mountain and Convective
Waves Ascending VErtically) program are reported.
Two of the rockets were launched from Andøya Rocket Range, Norway, in the
summer of 2002. Electron scavenging by ice particulates produced reductions
of the electron density in both sharp narrow (≈1–2 km) layers and
as a broad (≈13 km) depletion. Small-scale irregularities were
observed in the altitude regions of both types of electron depletion. The
scale of the irregularities extended to wavelengths comparable to those used
by ground-based radars in observing PMSE. In regions where ice particles
were not present, analysis of the spectral signatures provided reasonable
estimates of the energy deposition from breaking gravity waves.
Two more instrumented rockets were flown from Esrange, Sweden, in January 2003.
Little turbulence or energy deposition was observed during one flight,
but relatively large values were observed during the other flight. The
altitude distribution of the observed turbulence was consistent with
observations of a semidiurnal tide and gravity wave instability effects as
determined by ground-based lidar and radar measurements and by falling
sphere measurements of the winds and temperatures (Goldberg et al., 2006; Williams et al., 2006)
In-situ electron and ion measurements and observed gravity wave effects in the polar mesosphere during the MaCWAVE program
Subsonic Probe Measurements of Middle-Atmosphere Electrical Parameters J. D. Mitchell, D. C. Schroder, K. J. Ho, K. Domagalski and R. 0. Olsens
The MaCWAVE program to study gravity wave influences on the polar mesosphere
MaCWAVE (Mountain and Convective Waves
Ascending VErtically) was a highly coordinated rocket,
ground-based, and satellite program designed to address gravity wave forcing
of the mesosphere and lower thermosphere (MLT). The MaCWAVE program was
conducted at the Norwegian Andøya Rocket Range (ARR, 69.3° N) in
July 2002, and continued at the Swedish Rocket Range (Esrange, 67.9° N) during
January 2003. Correlative instrumentation included the ALOMAR MF and MST
radars and RMR and Na lidars, Esrange MST and meteor radars and RMR lidar,
radiosondes, and TIMED (Thermosphere Ionosphere Mesosphere
Energetics and Dynamics) satellite measurements of thermal structures. The
data have been used to define both the mean fields and the wave field
structures and turbulence generation leading to forcing of the large-scale
flow. In summer, launch sequences coupled with ground-based measurements at
ARR addressed the forcing of the summer mesopause environment by anticipated
convective and shear generated gravity waves. These motions were measured
with two 12-h rocket sequences, each involving one Terrier-Orion payload
accompanied by a mix of MET rockets, all at ARR in Norway. The MET rockets
were used to define the temperature and wind structure of the stratosphere
and mesosphere. The Terrier-Orions were designed to measure small-scale
plasma fluctuations and turbulence that might be induced by wave breaking in
the mesosphere. For the summer series, three European MIDAS (Middle
Atmosphere Dynamics and Structure) rockets were also launched from ARR in
coordination with the MaCWAVE payloads. These were designed to measure
plasma and neutral turbulence within the MLT. The summer program exhibited a
number of indications of significant departures of the mean wind and
temperature structures from ``normal" polar summer conditions, including an
unusually warm mesopause and a slowing of the formation of polar mesospheric
summer echoes (PMSE) and noctilucent clouds (NLC). This was suggested to be
due to enhanced planetary wave activity in the Southern Hemisphere and a
surprising degree of inter-hemispheric coupling. The winter program was
designed to study the upward propagation and penetration of mountain waves
from northern Scandinavia into the MLT at a site favored for such
penetration. As the major response was expected to be downstream (east) of
Norway, these motions were measured with similar rocket sequences to those
used in the summer campaign, but this time at Esrange. However, a major
polar stratospheric warming just prior to the rocket launch window induced
small or reversed stratospheric zonal winds, which prevented mountain wave
penetration into the mesosphere. Instead, mountain waves encountered
critical levels at lower altitudes and the observed wave structure in the
mesosphere originated from other sources. For example, a large-amplitude
semidiurnal tide was observed in the mesosphere on 28 and 29 January, and
appears to have contributed to significant instability and small-scale
structures at higher altitudes. The resulting energy deposition was found to
be competitive with summertime values. Hence, our MaCWAVE measurements as a
whole are the first to characterize influences in the MLT region of
planetary wave activity and related stratospheric warmings during both winter
and summer