290 research outputs found
Recent mass balance of the Purogangri Ice Cap, central Tibetan Plateau, by means of differential X-band SAR interferometry
Due to their remoteness, altitude and harsh climatic conditions, little is known about the glaciological parameters of ice caps on the Tibetan Plateau. This study presents a geodetic mass balance estimate of the Purogangri Ice Cap, Tibet's largest ice field between 2000 and 2012. We utilized data from the actual TerraSAR-X mission and its add-on for digital elevation measurements and compared it with elevation data from the Shuttle Radar Topography Mission. The employed data sets are ideal for this approach as both data sets were acquired at X-band at nearly the same time of the year and are available at a fine grid spacing. In order to derive surface elevation changes we employed two different methods. The first method is based on differential synthetic radar interferometry while the second method uses common DEM differencing. Both approaches revealed a slightly negative mass budget of â44 ± 15 and â38 ± 23 mm w.eq. a<sup>â1</sup> (millimeter water equivalent) respectively. A slightly negative trend of â0.15 ± 0.01 km<sup>2</sup> a<sup>â1</sup> in glacier extent was found for the same time period employing a time series of Landsat data. Overall, our results show an almost balanced mass budget for the studied time period. Additionally, we detected one continuously advancing glacier tongue in the eastern part of the ice cap
Exploration of a periodic GLOF in Halji, West Nepal using modeling and remote sensing
Abstract HKT-ISTP 2013
B
Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim
Multicolor (BVRI) light curves of the eclipsing classical nova V Per are
presented, and a total of twelve new eclipse timings are measured for the
system. When combined with previous eclipse timings from the literature, these
timings yield a revised ephemeris for the times of mid-eclipse given by HJD =
2,447,442.8260(1) + 0.107123474(3) E. The eclipse profiles are analyzed with a
parameter-fitting model that assumes four sources of luminosity: a white dwarf
primary star, a main-sequence secondary star, a flared accretion disk with a
rim, and a bright spot at the intersection of the mass-transfer stream and the
disk periphery. A matrix of model solutions are computed, covering an extensive
range of plausible parameter values. The solution matrix is then explored to
determine the optimum values for the fitting parameters and their associated
errors. For models that treat the accretion disk as a flat structure without a
rim, optimum fits require that the disk have a flat temperature profile.
Although models with a truncated inner disk (R_in >> R_wd) result in a steeper
temperature profile, steady-state models with a temperature profile
characterized by T(r) \propto r^{-3/4} are found only for models with a
significant disk rim. A comparison of the observed brightness and color at
mid-eclipse with the photometric properties of the best-fitting model suggests
that V Per lies at a distance of ~ 1 kpc.Comment: Accepted for publication in The Astrophysical Journal. Thirty-nine
pages, including 9 figures. V2 - updated to include additional references and
related discussion to previous work overlooked in the original version, and
to correct a typo in the ephemeris given in the abstract. V3 - Minor typos
corrected. The paper is scheduled for the 20 June 2006 issue of the ApJ. V4 -
An error in equation (9) has been corrected. The results presented in the
paper were not affected, as all computations were made using the correct
formulation of this equatio
Evolution of Purogangri Ice Cap, central Tibetan Plateau, 2000-2012 - a comparison of two glaciological methods
Abstract HKT-ISTP 2013
B
Wide-Field Infrared Imaging Polarimetry of the NGC 6334 Region: A Nest of Infrared Reflection Nebulae
We report the detection of eighteen infrared reflection nebulae (IRNe) in the
, , & linear polarimetric observations of the NGC 6334 massive
star-formation complex, of which 16 IRNe are new discoveries. Our images cover
180 square arcminutes, one of the widest near-infrared polarization data
in star-formation regions so far. These IRNe are most likely associated with
embedded young OB stars at different evolutionary phases, showing a variety of
sizes, morphologies, and polarization properties, which can be divided into
four categories. We argue the different nebula characteristics to be a possible
evolutionary sequence of circumstellar structures around young massive stars.Comment: 4 pages, 1 figur
A Mid-Infrared Study of the Class 0 Cluster in LDN 1448
We present ground-based mid-infrared observations of Class 0 protostars in
LDN 1448. Of the five known protostars in this cloud, we detected two, L1448N:A
and L1448C, at 12.5, 17.9, 20.8, and 24.5 microns, and a third, L1448 IRS 2, at
24.5 microns. We present high-resolution images of the detected sources, and
photometry or upper limits for all five Class 0 sources in this cloud. With
these data, we are able to augment existing spectral energy distributions
(SEDs) for all five objects and place them on an evolutionary status diagram.Comment: Accepted by the Astronomical Journal; 26 pages, 9 figure
9286 Stars: An Agglomeration of Stellar Polarization Catalogs
This is a revision. The revisions are minor. The new version of the catalog
should be used in preference to the old. The most serious error in the older
version was that was incorrect, being sometimes far too large,
for Reiz and Franco entries; the correct values are all zero for that
reference.
We present an agglomeration of stellar polarization catalogs with results for
9286 stars. We have endeavored to eliminate errors, provide accurate
(arcsecond) positions, sensibly weight multiple observations of the same star,
and provide reasonable distances. This catalog is included as an ASCII file
(catalog.txt) in the source of this submission.Comment: The most serious error in the older version was that
was incorrect, being sometimes far too large, for Reiz and Franco entries;
the correct values are all zero for that reference. 11 pages, no figures.
Accepted for Astronomical Journal. Catalog also available as an ASCII file by
anonymous FTP from ftp://vermi.berkeley.edu/pub/polcat/p14.ou
Abnormal joint torque patterns exhibited by chronic stroke subjects while walking with a prescribed physiological gait pattern
<p>Abstract</p> <p>Background</p> <p>It is well documented that individuals with chronic stroke often exhibit considerable gait impairments that significantly impact their quality of life. While stroke subjects often walk asymmetrically, we sought to investigate whether prescribing near normal physiological gait patterns with the use of the Lokomat robotic gait-orthosis could help ameliorate asymmetries in gait, specifically, promote similar ankle, knee, and hip joint torques in both lower extremities. We hypothesized that hemiparetic stroke subjects would demonstrate significant differences in total joint torques in both the frontal and sagittal planes compared to non-disabled subjects despite walking under normal gait kinematic trajectories.</p> <p>Methods</p> <p>A motion analysis system was used to track the kinematic patterns of the pelvis and legs of 10 chronic hemiparetic stroke subjects and 5 age matched controls as they walked in the Lokomat. The subject's legs were attached to the Lokomat using instrumented shank and thigh cuffs while instrumented footlifters were applied to the impaired foot of stroke subjects to aid with foot clearance during swing. With minimal body-weight support, subjects walked at 2.5 km/hr on an instrumented treadmill capable of measuring ground reaction forces. Through a custom inverse dynamics model, the ankle, knee, and hip joint torques were calculated in both the frontal and sagittal planes. A single factor ANOVA was used to investigate differences in joint torques between control, unimpaired, and impaired legs at various points in the gait cycle.</p> <p>Results</p> <p>While the kinematic patterns of the stroke subjects were quite similar to those of the control subjects, the kinetic patterns were very different. During stance phase, the unimpaired limb of stroke subjects produced greater hip extension and knee flexion torques than the control group. At pre-swing, stroke subjects inappropriately extended their impaired knee, while during swing they tended to abduct their impaired leg, both being typical abnormal torque synergy patterns common to stroke gait.</p> <p>Conclusion</p> <p>Despite the Lokomat guiding stroke subjects through physiologically symmetric kinematic gait patterns, abnormal asymmetric joint torque patterns are still generated. These differences from the control group are characteristic of the hip hike and circumduction strategy employed by stroke subjects.</p
Transient Gamma Ray Spectrometer Measurements of Gamma-Ray Lines from Novae. I. Limits on the Positron Annihilation Line in Five Individual Novae
The Transient Gamma Ray Spectrometer (TGRS) on board the WIND spacecraft has
spent most of the interval 1995-1997 in a high-altitude orbit where gamma-ray
backgrounds are low. Its high-resolution Ge spectrometer is thus able to detect
weak lines which are slightly offset from stronger background features. One
such line is predicted from nucleosynthesis in classical novae, where
beta-decays on a time-scale of a few hours in an expanding envelope produce
positrons that annihilate to generate a line which is blueshifted by a few keV
away from the background annihilation line at 511 keV. The broad TGRS field of
view contained five known Galactic novae during 1995 January - 1997 June, and
we have searched the spectra taken around the times of these events for the
blueshifted nova annihilation line. Although no definite detections were made,
the method is shown to be sensitive enough to detect novae occurring on
ONeMg-rich white dwarfs out to about 2.5 kpc.Comment: 27 pp. + 10 figs., or offprint mailed by request to
[email protected]
Can Life develop in the expanded habitable zones around Red Giant Stars?
We present some new ideas about the possibility of life developing around
sub-giant and red giant stars. Our study concerns the temporal evolution of the
habitable zone. The distance between the star and the habitable zone, as well
as its width, increases with time as a consequence of stellar evolution. The
habitable zone moves outward after the star leaves the main sequence, sweeping
a wider range of distances from the star until the star reaches the tip of the
asymptotic giant branch. If life could form and evolve over time intervals from
to years, then there could be habitable planets with
life around red giant stars. For a 1 M star at the first stages of
its post main-sequence evolution, the temporal transit of the habitable zone is
estimated to be of several 10 years at 2 AU and around 10 years at 9
AU. Under these circumstances life could develop at distances in the range 2-9
AU in the environment of sub-giant or giant stars and in the far distant future
in the environment of our own Solar System. After a star completes its first
ascent along the Red Giant Branch and the He flash takes place, there is an
additional stable period of quiescent He core burning during which there is
another opportunity for life to develop. For a 1 M star there is an
additional years with a stable habitable zone in the region from 7 to 22
AU. Space astronomy missions, such as proposed for the Terrestrial Planet
Finder (TPF) and Darwin should also consider the environments of sub-giants and
red giant stars as potentially interesting sites for understanding the
development of life
- âŠ