428 research outputs found
Star formation around mid-infrared bubble N37: Evidence of cloud-cloud collision
We have performed a multi-wavelength analysis of a mid-infrared (MIR) bubble
N37 and its surrounding environment. The selected 1515 area around
the bubble contains two molecular clouds (N37 cloud; V37-43 km
s, and C25.29+0.31; V43-48 km s) along the line of
sight. A total of seven OB stars are identified towards the bubble N37 using
photometric criteria, and two of them are spectroscopically confirmed as O9V
and B0V stars. Spectro-photometric distances of these two sources confirm their
physical association with the bubble. The O9V star is appeared to be the
primary ionizing source of the region, which is also in agreement with the
desired Lyman continuum flux analysis estimated from the 20 cm data. The
presence of the expanding HII region is revealed in the N37 cloud which could
be responsible for the MIR bubble. Using the CO line data and
photometric data, several cold molecular condensations as well as clusters of
young stellar objects (YSOs) are identified in the N37 cloud, revealing ongoing
star formation (SF) activities. However, the analysis of ages of YSOs and the
dynamical age of the HII region do not support the origin of SF due to the
influence of OB stars. The position-velocity analysis of CO data reveals
that two molecular clouds are inter-connected by a bridge-like structure,
favoring the onset of a cloud-cloud collision process. The SF activities (i.e.
the formation of YSOs clusters and OB stars) in the N37 cloud are possibly
influenced by the cloud-cloud collision.Comment: 18 pages, 13 figures, 2 tables, Accepted for publication in the Ap
Microgrid cost optimization: a case study on Abu Dhabi
This paper presents a microgrid cost optimization study specifically focused on the United Arab Emirates (UAE) based on the Genetic and Ant-Bee Colony algorithms. The main objective of the paper is to identify size and amount of power supply sources in Microgrids that result in minimum cost. Specific parameters pertaining to the UAE were employed within the new objective function and constraints. Two different scenarios were tested, and their results have been discussed. During this study, it was evident that solar-PV systems were the second most cost-effective way to reduce cost of microgrids preceded by micro-turbines
A multi-wavelength study of star formation activity in the S235 complex
We have carried out an extensive multi-wavelength study to investigate the
star formation process in the S235 complex. The S235 complex has a sphere-like
shell appearance at wavelengths longer than 2 m and harbors an O9.5V type
star approximately at its center. Near-infrared extinction map traces eight
subregions (having A 8 mag), and five of them appear to be
distributed in an almost regularly spaced manner along the sphere-like shell
surrounding the ionized emission. This picture is also supported by the
integrated CO and CO intensity maps and by Bolocam 1.1 mm
continuum emission. The position-velocity analysis of CO reveals an almost
semi-ring like structure, suggesting an expanding H\,{\sc ii} region. We find
that the Bolocam clump masses increase as we move away from the location of the
ionizing star. This correlation is seen only for those clumps which are
distributed near the edges of the shell. Photometric analysis reveals 435 young
stellar objects (YSOs), 59\% of which are found in clusters. Six subregions
(including five located near the edges of the shell) are very well correlated
with the dust clumps, CO gas, and YSOs. The average values of Mach numbers
derived using NH data for three (East~1, East~2, and Central~E) out of
these six subregions are 2.9, 2.3, and 2.9, indicating these subregions are
supersonic. The molecular outflows are detected in these three subregions,
further confirming the on-going star formation activity. Together, all these
results are interpreted as observational evidence of positive feedback of a
massive star.Comment: 28 pages, 15 figures, 3 tables, Accepted for publication in The
Astrophysical Journa
Posttransplant Thrombopoiesis Predicts Survival in Patients Undergoing Autologous Hematopoietic Progenitor Cell Transplantation
AbstractThe frequency and clinical significance of secondary thrombocytopenia following initial engraftment in autologous hematopoietic progenitor cell transplantation (HPCT) is unknown. An institutional review board approved retrospective study of thrombopoiesis was performed in 359 patients transplanted with autologous blood (97%) or marrow (3%) who achieved platelet engraftment to >50,000/μL. Idiopathic secondary posttransplant thrombocytopenia (ISPT) was defined as >50% decline in blood platelets to <100,000/μL in the absence of relapse or sepsis. ISPT occurred at a median of day +35 posttransplant in 17% of patients. Patients with ISPT had similar initial platelet engraftment (median 17 days) versus non-ISPT patients (18 days; P = NS) and recovered platelet counts (median 123,00 K/μL) by day 110 posttransplant. Four factors were independently associated with post-transplant death in a multivariate model: disease status at transplant; the number of prior chemotherapy regimens, failure to achieve a platelet count of >150,000/μL posttransplant, and the occurrence of ISPT. A prognostic score was developed based upon the occurrence of ISPT and posttransplant platelet counts of <150,000/μL. Survival of patients with both factors (n = 25) was poor (15% alive at 5 years); patients with 1 factor (n = 145) had 49% 5-year survival; patients with 0 factors (n = 189) had 72% 5-year survival. Patients who failed to achieve a platelet count of >150,000/μL received significantly fewer CD34+ cells/kg (P < .001), whereas patients with ISPT received fewer CD34+CD38− cells/kg (P = .0006). The kinetics of posttransplant thrombopoiesis is an independent prognostic factor for long-term survival following autologous HPC. ISPT and lower initial posttransplant platelet counts reflect poor engraftment with long-term and short-term repopulating CD34+ hematopoietic stem cells, respectively, and are associated with an increased risk of death from disease relapse
Performance Evaluation and Experimental Studies on Metallised Gel Propellants
Metallised gel propellants offer higher specific impulse and volumetric loading, reduced vaporisation loss, spillage and slosh problems and easy storage in comparison to the conventional liquid propellants. Theoretical performance analysis of gel propellant containing Al in unsymmetrical dimethyl hydrazine-dinitrogen tetroxide (UDMH-N/sub 2/O/sub 4} system shows peak Isp (vacuum condition) of 316.7 s and 318.3 s at oxidiser/fuel (O/f) ratios of 1.5 and 1.0, respectively for 30 per cent and 40 per cent UDMH-Al gel propellants, under standard conditions. The effect of other parameters like area ratio and chamber pressure on performance has been brought out in view of mission oriented applications. Aluminium has been found to be a better choice over magnesium in metallised gel propellants. Experimental studies on UDMH gellation using propellant grade (15 micrometer)and pyrotechnic grade (1.5 micrometer)Al in 500g batch level show that gellant(methyl cellulose) concentration could be reduced by 50 percent using pyrotechnic grade Al. The pseudoplastic-thixotropic behaviour, flow rate through die holes, burst pressure tests and bulk density are studied. UDMH -25 to 30 per cent Al gels with both grades of Al are found to be stable, pseudoplastic (shear thinning) and thixotropic (time-dependent shear thinning), but their flow pattern through die holes differ in nature
TIRSPEC : TIFR Near Infrared Spectrometer and Imager
We describe the TIFR Near Infrared Spectrometer and Imager (TIRSPEC) designed
and built in collaboration with M/s. Mauna Kea Infrared LLC, Hawaii, USA, now
in operation on the side port of the 2-m Himalayan Chandra Telescope (HCT),
Hanle (Ladakh), India at an altitude of 4500 meters above mean sea level. The
TIRSPEC provides for various modes of operation which include photometry with
broad and narrow band filters, spectrometry in single order mode with long
slits of 300" length and different widths, with order sorter filters in the Y,
J, H and K bands and a grism as the dispersing element as well as a cross
dispersed mode to give a coverage of 1.0 to 2.5 microns at a resolving power R
of ~1200. The TIRSPEC uses a Teledyne 1024 x 1024 pixel Hawaii-1 PACE array
detector with a cutoff wavelength of 2.5 microns and on HCT, provides a field
of view of 307" x 307" with a plate scale of 0.3"/pixel. The TIRSPEC was
successfully commissioned in June 2013 and the subsequent characterization and
astronomical observations are presented here. The TIRSPEC has been made
available to the worldwide astronomical community for science observations from
May 2014.Comment: 20 pages, 21 figures, 2 tables. Accepted for publication in Journal
of Astronomical Instrumentatio
Developmental Studies on Metallised UDMH and Kerosene Gels
The influence of particulate and hydrocolloid gellants and different surfactants on gellation of metallised stable gels of unsymmetrical dimethyl hydrazine (UDMH) and kerosene containing 30 per cent 15 micron Aluminium was studied. Metallised UDMH and kerosene gels were characterised with respect to pseudoplasticity, thixotropy, consistency and yield stress using Contrave's rheometer. The effect of shear rate and temperature on the viscosity of these gels was determined. Thermal stability, hypergolicity tests and flow rate studies were also conducted. Metallised UDMH and kerosene gels are found to be stable, thixotropic and pseudoplastic and easily flowing like a liquid under shear force
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