28,088 research outputs found
Very smooth points of spaces of operators
In this paper we study very smooth points of Banach spaces with special
emphasis on spaces of operators. We show that when the space of compact
operators is an -ideal in the space of bounded operators, a very smooth
operator attains its norm at a unique vector (up to a constant
multiple) and is a very smooth point of the range space. We show that if
for every equivalent norm on a Banach space, the dual unit ball has a very
smooth point then the space has the Radon--Nikod\'{y}m property. We give an
example of a smooth Banach space without any very smooth points.Comment: 12 pages, no figures, no table
Anti-correlated time lags in the Z source GX 5-1: Possible evidence for a truncated accretion disk
We investigate the nature of the inner accretion disk in the neutron star
source GX 5-1 by making a detailed study of time lags between X-rays of
different energies. Using the cross-correlation analysis, we found
anti-correlated hard and soft time lags of the order of a few tens to a few
hundred seconds and the corresponding intensity states were mostly the
horizontal branch (HB) and upper normal branch (NB). The model independent and
dependent spectral analysis showed that during these time lags the structure of
accretion disk significantly varied. Both eastern and western approaches were
used to unfold the X-ray continuum and systematic changes were observed in soft
and hard spectral components. These changes along with a systematic shift in
the frequency of quasi-periodic oscillations (QPOs) made it substantially
evident that the geometry of the accretion disk is truncated. Simultaneous
energy spectral and power density spectral study shows that the production of
the horizontal branch oscillations (HBOs) are closely related to the
Comptonizing region rather than the disk component in the accretion disk. We
found that as the HBO frequency decreases from the hard apex to upper HB, the
disk temperature increases along with an increase in the coronal temperature
which is in sharp contrast with the changes found in black hole binaries where
the decrease in QPO frequency is accompanied by a decrease in the disk
temperature and a simultaneous increase in the coronal temperature. We discuss
the results in the context of re-condensation of coronal material in the inner
region of the disk.Comment: 40 pages, 7 figures, accepted for publication in The Astrophysical
Journal Supplement (ApJS
Novel magnetic properties of graphene: Presence of both ferromagnetic and antiferromagnetic features and other aspects
Investigations of the magnetic properties of graphenes prepared by different
methods reveal that dominant ferromagnetic interactions coexist along with
antiferromagnetic interactions in all the samples. Thus, all the graphene
samples exhibit room-temperature magnetic hysteresis. The magnetic properties
depend on the number of layers and the sample area, small values of both
favoring larger magnetization. Molecular charge-transfer affects the magnetic
properties of graphene, interaction with a donor molecule such as
tetrathiafulvalene having greater effect than an electron-withdrawing molecule
such as tetracyanoethyleneComment: 16 pges, 5 figure
Observational evidence for mass ejection during soft X-ray dips in GRS1915+105
We investigate the connection between the X-ray and radio properties of the
Galactic microquasar GRS1915+105, by analyzing the X-ray data observed with
RXTE, during the presence of a huge radio flare (~450 mJy). The X-ray
lightcurve shows two dips of ~100 second duration. Detailed time resolved
spectral analysis shows the existence of three spectral components: a
multicolor disk-blackbody, a Comptonized component due to hot plasma and a
power-law. We find that the Comptonized component is very weak during the dip.
This is further confirmed by the PHA ratio of the raw data and ratio of the
lightcurves in different energy bands. These results, combined with the fact
that the 0.5 -- 10 Hz QPO disappears during the dip and that the Comptonized
component is responsible for the QPO lead to the conclusion that during the
dips the matter emitting Comptonized spectrum is ejected away. This establishes
a direct connection between the X-ray and radio properties of the source.Comment: Replaced with some minor changes, corrected typos. Added Journal Re
Detection of a Series of X-ray Dips Associated with a Radio Flare in GRS 1915+105
We report the detection of a series of X-ray dips in the Galactic black hole
candidate GRS 1915+105 during 1999 June 6-17 from observations carried out with
the Pointed Proportional Counters of the Indian X-ray Astronomy Experiment on
board the Indian satellite IRS-P3. The observations were made after the source
made a transition from a steady low-hard state to a chaotic state which
occuered within a few hours. Dips of about 20-160 seconds duration are observed
on most of the days. The X-ray emission outside the dips shows a QPO at ~ 4 Hz
which has characteristics similar to the ubiquitous 0.5 - 10 Hz QPO seen during
the low-hard state of the source. During the onset of dips this QPO is absent
and also the energy spectrum is soft and the variability is low compared to the
non-dip periods. These features gradually re-appear as the dip recovers. The
onset of the occurrence of a large number of such dips followed the start of a
huge radio flare of strength 0.48 Jy (at 2.25 GHz). We interpret these dips as
the cause for mass ejection due to the evacuation of matter from an accretion
disk around the black hole. We propose that a super-position of a large number
of such dip events produces a huge radio jet in GRS 1915+105.Comment: 18 pages, 7 figures, Accepted for publication in Ap
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