53 research outputs found
Study of nonlinear ion- and electron-acoustic waves in multi-component space plasmas
Large amplitude ion-acoustic and electron-acoustic waves in an unmagnetized multi-component plasma system consisting of cold background electrons and ions, a hot electron beam and a hot ion beam are studied using Sagdeev pseudo-potential technique. Three types of solitary waves, namely, slow ion-acoustic, ion-acoustic and electron-acoustic solitons are found provided the Mach numbers exceed the critical values. The slow ion-acoustic solitons have the smallest critical Mach numbers, whereas the electron-acoustic solitons have the largest critical Mach numbers. For the plasma parameters considered here, both type of ion-acoustic solitons have positive potential whereas the electron-acoustic solitons can have either positive or negative potential depending on the fractional number density of the cold electrons relative to that of the ions (or total electrons) number density. For a fixed Mach number, increases in the beam speeds of either hot electrons or hot ions can lead to reduction in the amplitudes of the ion-and electron-acoustic solitons. However, the presence of hot electron and hot ion beams have no effect on the amplitudes of slow ion-acoustic modes. Possible application of this model to the electrostatic solitary waves (ESWs) observed in the plasma sheet boundary layer is discussed
Simultaneous observations of ESF irregularities over Indian region using radar and GPS
In this paper, we present simultaneous observations of temporal and spatial variability of total electron content (TEC) and GPS amplitude scintillations on L1 frequency (1.575 GHz) during the time of equatorial spread F (ESF) while the MST radar (53 MHz) located at Gadanki (13.5° N, 79.2° E, Dip latitude 6.3° N), a low latitude station, made simultaneous observations. In particular, the latitudinal and longitudinal extent of TEC and L-band scintillations was studied in the Indian region for different types of ESF structures observed using the MST radar during the low solar activity period of 2004 and 2005. Simultaneous radar and GPS observations during severe ESF events in the pre-midnight hour reveal that significant GPS L band scintillations, depletions in TEC, and the double derivative of the TEC index (DROTI), which is a measure of fluctuations in TEC, obtained at low latitudes coincide with the appearance of radar echoes at Gadanki. As expected, when the irregularities reach higher altitudes as seen in the radar map during pre-midnight periods, strong scintillations on an L-band signal are observed at higher latitudes. Conversely, when radar echoes are confined to only lower altitudes, weak scintillations are found and their latitudinal extent is small. During magnetically quiet periods, we have recorded plume type radar echoes during a post-midnight period that is devoid of L-band scintillations. Using spectral slopes and cross-correlation index of the VHF scintillation observations, we suggest that these irregularities could be "dead" or "fossil" bubbles which are just drifting in from west. This scenario is consistent with the observations where suppression of pre-reversal enhancement (PRE) in the eastward electric field is indicated by ionosonde observations of the height of equatorial F layer and also occurrence of low spectral width in the radar observations relative to pre-midnight period. However, absence of L-band scintillations during post-midnight event, when radar observed plume like structures and scintillations were recorded on VHF band, raises questions about the process of evolution of the irregularities. A possible explanation is that whereas small scale (∼3 m) irregularities are generated through secondary waves that grow on the walls of km scale size irregularities, in this case evolution of the Rayleigh-Taylor instability itself did not extend to irregularities of scale sizes of a few hundred meters that produce scintillation on a L-band signal
Baseline observations from the POSSIBLE EU® study: characteristics of postmenopausal women receiving bone loss medications
Summary: Prospective Observational Scientific Study Investigating Bone Loss Experience in Europe (POSSIBLE
EU®) is an ongoing longitudinal cohort study that utilises
physician- and patient-reported measures to describe the
characteristics and management of postmenopausal women
on bone loss therapies. We report the study design and
baseline characteristics of 3,402 women recruited from
general practice across five European countries.
Purpose The POSSIBLE EU® is a study describing the
characteristics and management of postmenopausal women
receiving bone loss medications.
Methods: Between 2005 and 2008, general practitioners
enrolled postmenopausal women initiating, switching or
continuing treatment with bone loss treatment in France,
Germany, Italy, Spain and the UK. Patients and physicians
completed questionnaires at study entry and at 3-month
intervals, for 1 year.
Results: Of 3,402 women enrolled (mean age 68.2 years
[SD] 9.83), 96% were diagnosed with low bone mass; 55%
of these using dual energy X-ray absorptiometry. Most
women (92%) had comorbidities. Mean minimum T score
(hip or spine) at diagnosis was −2.7 (SD 0.89; median −2.7
[interquartile range, −3.2, −2.2]) indicating low bone
mineral density. Almost 40% of the women had prior
fractures in adulthood, mostly non-vertebral, non-hip in
nature, 30% of whom had at least two fractures and more
than half experienced moderate/severe pain or fatigue.
Bisphosphonates were the most common type of bone loss
treatment prescribed in the 12 months preceding the study.
Conclusions POSSIBLE EU® characterises postmenopausal
women with low bone mass, exhibiting a high rate of
prevalent fracture, substantial bone fragility and overall
comorbidity burden. Clinical strategies for managing
osteoporosis in this population varied across the five
participating European countries, reflecting their different
guidelines, regulations and standards of care
A Bayesian Analysis of the Correlations Among Sunspot Cycles
Sunspot numbers form a comprehensive, long-duration proxy of solar activity
and have been used numerous times to empirically investigate the properties of
the solar cycle. A number of correlations have been discovered over the 24
cycles for which observational records are available. Here we carry out a
sophisticated statistical analysis of the sunspot record that reaffirms these
correlations, and sets up an empirical predictive framework for future cycles.
An advantage of our approach is that it allows for rigorous assessment of both
the statistical significance of various cycle features and the uncertainty
associated with predictions. We summarize the data into three sequential
relations that estimate the amplitude, duration, and time of rise to maximum
for any cycle, given the values from the previous cycle. We find that there is
no indication of a persistence in predictive power beyond one cycle, and
conclude that the dynamo does not retain memory beyond one cycle. Based on
sunspot records up to October 2011, we obtain, for Cycle 24, an estimated
maximum smoothed monthly sunspot number of 97 +- 15, to occur in
January--February 2014 +- 6 months.Comment: Accepted for publication in Solar Physic
Power spectral characteristics of ESF irregularities during magnetically quiet and disturbed days
Amplitude scintillations on 251 MHz signal recorded by spaced receivers at Tirunelveli (8.7°N, 77.8°E, dip latitude 0.6°N) for eight months during 1995–2005 are utilized in present work. Power spectral analysis of weak scintillations (0.15≤S4≤0.5) is carried out and spectral index, m of ESF irregularities, is computed for quiet and disturbed days. Maximum cross-correlation, CI(x0,t<sub>m</sub>), of intensity variations between two receivers is used to identify the fresh generation of EPBs resulted from magnetic activity. Increase in F-region height is seen prior to the generation of these fresh EPBs and associated ESF irregularities found to possess shallower power spectrum
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