691 research outputs found
Arp 65 interaction debris: massive HI displacement and star formation
Context: Pre-merger interactions between galaxies can induce significant
changes in the morphologies and kinematics of the stellar and ISM components.
Large amounts of gas and stars are often found to be disturbed or displaced as
tidal debris. This debris then evolves, sometimes forming stars and
occasionally tidal dwarf galaxies. Here we present results from our HI study of
Arp 65, an interacting pair hosting extended HI tidal debris. Aims: In an
effort to understand the evolution of tidal debris produced by interacting
pairs of galaxies, including in situ star and tidal dwarf galaxy formation, we
are mapping HI in a sample of interacting galaxy pairs. The Arp 65 pair is one
of them. Methods: Our resolved HI 21 cm line survey is being carried out using
the Giant Metrewave Radio Telescope (GMRT). We used our HI survey data as well
as available SDSS optical, Spitzer infra-red and GALEX UV data to study the
evolution of the tidal debris and the correlation of HI with the star-forming
regions within it. Results: In Arp 65 we see a high impact pre-merger
interaction involving a pair of massive galaxies (NGC 90 and NGC 93) that have
a stellar mass ratio of ~ 1:3. The interaction, which probably occurred ~ 1.0
-- 2.5 10 yr ago, appears to have displaced a large fraction of
the HI in NGC 90 (including the highest column density HI) beyond its optical
disk. We also find extended ongoing star formation in the outer disk of NGC 90.
In the major star-forming regions, we find the HI column densities to be ~ 4.7
10 cm or lower. But no signature of star formation was
found in the highest column density HI debris, SE of NGC 90. This indicates
conditions within the highest column density HI debris remain hostile to star
formation and it reaffirms that high HI column densities may be a necessary but
not sufficient criterion for star formation.Comment: Accepted in A&
6-[(Dimethylamino)methyleneamino]-1,3-dimethylpyrimidine-2,4(1H,3H)-dione dihydrate
Uracil, the pyrimidine nucleobase, which combined with adenine forms one of the major motifs present in the biopolymer RNA, is also involved in the self-assembly of RNA. In the title compound, C9H14N4O2·2H2O, the asymmetric unit contains one dimethylaminouracil group and two water molecules. The plane of the N=C—NMe2 side chain is inclined at 27.6 (5)° to the plane of the uracil ring. Both water molecules form O—H⋯O hydrogen bonds with the carbonyl O atoms of the uracil group. Additional water–water hydrogen-bond interactions are also observed in the crystal structure. The O—H⋯O hydrogen bonds lead to the formation of a two-dimensional hydrogen-bonded network cage consisting of two dimethylaminouracil groups and six water molecules
Regional waveform calibration in the Pamir-Hindu Kush region
Twelve moderate-magnitude earthquakes (m_b 4–5.5) in the Pamir-Hindu Kush region are investigated to determine their focal mechanisms and to relocate them using their regional waveform records at two broadband arrays, the Kyrgyzstan Regional Network (KNET), and the 1992 Pakistan Himalayas seismic experiment array (PAKH) in northern Pakistan. We use the “cut-and-paste” source estimation technique to invert the whole broadband waveforms for mechanisms and depths, assuming a one-dimensional velocity model developed for the adjacent Tibetan plateau. For several large events the source mechanisms obtained agree with those available from the Harvard centroid moment tensor (CMT) solutions. An advantage of using regional broadband waveforms is that focal depths can be better constrained either from amplitude ratios of Pnl to surface waves for crustal events or from time separation between the direct P and the shear-coupled P wave (sPn + sPmP) for mantle events. All the crustal events are relocated at shallower depths compared with their International Seismological Centre bulletin or Harvard CMT depths. After the focal depths are established, the events are then relocated horizontally using their first-arrival times. Only minor offsets in epicentral location are found for all mantle events and the bigger crustal events, while rather large offsets (up to 30 km) occur for the smaller crustal events. We also tested the performance of waveform inversion using only two broadband stations, one from the KNET array in the north of the region and one from the PAKH array in the south. We found that this geometry is adequate for determining focal depths and mechanisms of moderate size earthquakes in the Pamir-Hindu Kush region
Magnetized Plasma Sheath in the Presence of Negative Ions
The sheath formation in a weakly magnetized collisionless electronegative
plasma consisting of electrons, negative and positive ions has been numerically
investigated using the hydrodynamic equations. The electrons and negative ions
are assumed to follow Boltzmann relation. A sheath formation criterion has been
analytically derived. The paper focuses on studying the sheath structure by
varying the electronegativity. It has been observed that the presence of
negative ions has a substantial effect on the sheath structure. The
observations made in the present work have profound significance on processing
plasmas, especially in the semiconductor industry as well as in fusion studies
XRD and FT-IR investigations of sub-bituminous Assam coals
Two coal samples collected from Makum coal field,
Assam, India were studied by XRD and FT-IR techniques.
The X-ray diffractogram shows the existence of some
crystalline carbons in Assam coals as proven by the
appearance of peaks. The radial distribution functional
(RDF) method was applied for the determination of
structural aspects of the coals. The study indicates that
the coals are lignite in type and there is no evidence of
graphite-like structures. The maximum in the G(r) plots
of function of radial distribution of atoms (FRDA) relates
to different distances between carbon atoms of aliphatic
chains. The first significant maximum relates to the C-C
bond (type C-CH=CH-C), the second maximum relates
to the distance between carbon atoms of aliphatic chains
that are located across one carbon atom. The curve
intensity profiles obtained from FRDA show quite regular
molecular packets for this coal. The coals were found to
be lignite in nature. FT-IR study shows the presence of
aliphatic carbon, C=O and C-O stretching associated with
-OH and -NH stretching vibrations. Kaolinite and quartz
were also found to be major minerals in Assam coals by
FTIR spectroscopy. The difference in intensities of
carbonyl groups of the coal samples is likely to relate
with the rank. © Indian Academy of Sciences
Seismic source and structure estimation in the western Mediterranean using a sparse broadband network
We present a study of regional earthquakes in the western Mediterranean geared toward the development of methodologies and path calibrations for source characterization using regional broadband stations. The results of this study are useful for the monitoring and discrimination of seismic events under a comprehensive test ban treaty, as well as the routine analysis of seismicity and seismic hazard using a sparse array of stations. The area consists of several contrasting geological provinces with distinct seismic properties, which complicates the modeling of seismic wave propagation. We started by analyzing surface wave group velocities throughout the region and developed a preliminary model for each of the major geological provinces. We found variations of crustal thickness ranging from 45 km under the Atlas and Betic mountains and 37 km under the Saharan shield, to 20 km for the oceanic crust of the western Mediterranean Sea, which is consistent with earlier works. Throughout most of the region, the upper mantle velocities are low which is typical for tectonically active regions. The most complex areas in terms of wave propagation are the Betic Cordillera in southern Spain and its north African counterparts, the Rif and Tell Atlas mountains, as well as the Alboran Sea, between Spain and Morocco. The complexity of the wave propagation in these regions is probably due to the sharp velocity contrasts between the oceanic and continental regions as well as the the existence of deep sedimentary basins that have a very strong influence on the surface wave dispersion. We used this preliminary regionalized velocity model to correct the surface wave source spectra for propagation effects which we then inverted for source mechanism. We found that this method, which is in use in many parts of the world, works very well, provided that data from several stations are available. In order to study the events in the region using very few broadband stations or even a single station, we developed a hybrid inversion method which combines P_(nl) waveforms synthesized with the traditional body wave methods, with surface waves that are computed using normal modes. This procedure facilitates the inclusion of laterally varying structure in the Green's functions for the surface waves and allows us to determine source mechanisms for many of the larger earthquakes (M > 4) throughout the region with just one station. We compared our results with those available from other methods and found that they agree quite well. The epicentral depths that we have obtained from regional waveforms are consistent with observed teleseismic depth phases, as far as they are available. We also show that the particular upper mantle structure under the region causes the various P_n and S_n phases to be impulsive, which makes them a useful tool for depth determination as well. Thus we conclude that with proper calibration of the seismic structure in the region and high-quality broadband data, it is now possible to characterize and study events in this region, both with respect to mechanism and depth, with a limited distribution of regional broadband stations
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