6,944 research outputs found
Competition from Cu(II), Zn(II) and Cd(II) in Pb(II) binding to Suwannee River Fulvic Acid
This is a study of trace metal competition in the complexation of Pb(II) by well-characterized humic substances, namely Suwannee River Fulvic Acid (SRFA) in model solutions. It was found that Cu(II) seems to compete with Pb(II) for strong binding sites of SRFA when present at the same concentration as Pb(II). However, Cd(II) and Zn(II) did not seem to compete with Pb(II) for strong binding sites of SRFA. These two metals did compete with Pb(II) for the weaker binding sites of SRFA. Heterogeneity of SRFA was found to play a crucial role in metal-SRFA interactions. The environmental significance of this research for freshwater is that even at relatively low Pb(II) loadings, the metals associated with lead in minerals, e.g. Cu(II), may successfully compete with Pb(II) for the same binding sites of the naturally occurring organic complexants, with the result that some of the Pb(II) may exist as free Pb2+ ions, which has been reported to be one of the toxic forms of Pb in aquatic environment
Accretion flow behaviour during the evolution of the Quasi Periodic Oscillation Frequency of XTE J1550-564 in 1998 outburst
Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought
to be due to oscillations of Comptonizing regions or hot regions embedded in
Keplerian discs. Observational evidence of evolutions of QPOs would therefore
be very important as they throw lights on the dynamics of the hotter region.
Our aim is to find systems in which there is a well-defined correlation among
the frequencies of the QPOs over a range of time so as to understand the
physical picture. In this paper, we concentrate on the archival data of XTE
J1550-564 obtained during 1998 outburst, and study the systematic drifts during
the rising phase from the 1998 September 7 to the 1998 September 19, when the
QPO frequency increased monotonically from 81mHz to 13.1Hz. Immediately after
that, QPO frequency started to decrease and on the 1998 September 26, the QPO
frequency became 2.62Hz. After that, its value remained almost constant. This
frequency drift can be modelled satisfactorily with a propagatory oscillating
shock solution where the post-shock region behaves as the Comptonized region.
Comparing with the nature of a more recent 2005 outburst of another black hole
candidate GRO 1655-40, where QPOs disappeared at the end of the rising phase,
we conjecture that this so-called `outburst' may not be a full-fledged
outburst.Comment: 15 pages, 6 figure
Evolution of the quasi-periodic oscillation frequency in GRO J1655-40 -- Implications for accretion disk dynamics
Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought
to be due to oscillations of Comptonizing regions or hot blobs embedded in
Keplerian disks. Any movement of these perturbations is expected systematically
to change the QPO frequency. Our goal is to find systems where such a
systematic drifts have been observed. We also try to find the real cause of
such drifts and whether they shed some light on the accretion disk dynamics.
Using archival data of the recent outburst of GRO J1655-40, we report the
presence of such systematic drifts not only during the rising phase from the
25th of February 2005 to the 12th March 2005, when the QPO frequency
monotonically increased from 82mHz to 17.78Hz but also in the decline phase
from the 15th September 2005 to the 5th of October 2005, when the QPO frequency
decreased from 13.14Hz to 34mHz. We fitted the frequency drifts with the
propagatory oscillating shock solution. In the shock-oscillation solution, the
frequency is inversely proportional to the infall time scale from the shock
location. We obtained the shock location and strength through such a fit. The
astonishing smoothness of the variation of the QPO frequency over a period of
weeks directly supports the view that it may due to the drift of an oscillating
shock rather than the movements of a blob inside a differentially rotating
disk.Comment: 8 pages, 3 figures, Astronomy & Astrophysics (accepted
Focused browsing: Providing topical feedback for link selection in hypertext browsing
When making decisions about whether to navigate to a linked page, users of standard browsers of hypertextual documents returned by an information retrieval search engine are entirely reliant on the content of the anchortext
associated with links and the surrounding text. This information is often insufficient for them to make reliable decisions about whether to open a linked page, and they can find themselves following many links to pages which are not helpful with subsequent return to the previous page. We describe a prototype focusing browsing application which provides feedback on the likely usefulness of each page linked from the current one, and a term cloud preview of the contents of each linked page. Results from an exploratory experiment suggest that users can find this useful in improving their search efficiency
Sensing Models and Its Impact on Network Coverage in Wireless Sensor Network
Network coverage of wireless sensor network (WSN) means how well an area of
interest is being monitored by the deployed network. It depends mainly on
sensing model of nodes. In this paper, we present three types of sensing models
viz. Boolean sensing model, shadow-fading sensing model and Elfes sensing
model. We investigate the impact of sensing models on network coverage. We also
investigate network coverage based on Poisson node distribution. A comparative
study between regular and random node placement has also been presented in this
paper. This study will be useful for coverage analysis of WSN.Comment: 5 pages, 5 figures, IEEE Region 10 Colloquium and the Third ICIIS,
Kharagpur, INDIA December 8-10, 200
Open computation tree logic for formal verification of modules
Modules of large VLSI circuits are often designed by different designers spread across the globe. One of the main challenges of the designer is to guarantee that the module he/she designs will work correctly in the global design, the details of which, is often unknown to him/her. Modules are open systems whose behavior is subject to the inputs it receives from its environment. It has been shown that verification of open systems (modules) is computationally very hard (EXPTIME complete, 1996) when we consider all possible environments. On the other hand we show that integrating the specification of the properties to be verified with the specification of only the valid input patterns (under which the module is expected to function correctly) gives us a powerful syntax which can be verified in polynomial time. We call the proposed logic Open-CTL (CTL for open systems). The convenience of being able to specify the property and the environment in a unified way in Open-CTL is demonstrated through a study of the PCI Bus properties. We present a symbolic BDD-based verification scheme for checking Open-CTL formulas, and present experimental results on modules from the Texas-97 Verification Benchmark circuits
QPO Evolution in 2005 Outburst of the Galactic Nano Quasar GRO J1655-40
GRO J1655-40 showed significant X-ray activity in the last week of February,
2005 and remained active for the next 260 days. The rising and the decline
phases of this particular outburst show evidence for systematic movements of
the Comptonizing region, assumed to be a CENBOL, which causes the
Quasi-periodic Oscillations or QPOs. We present both the spectral and the
timing results of the RXTE/PCA data taken from these two hard spectral states.
Assuming that the QPOs originate from an oscillating shock CENBOL, we show how
the shock slowly moves in through the accretion flow during the rising phase at
a constant velocity and accelerate away outward during the later part of the
decline phase. By fitting the observed frequencies with our solution, we
extract time variation of various disk parameters such as the shock locations,
velocity etc.Comment: 5 Pages, 2 Figures, Proceeding of the 2nd Kolkata Conference on
"Observational Evidence for the Black Holes in the Universe", Published in
AIP, 200
RTT relations, a modified braid equation and noncommutative planes
With the known group relations for the elements of a quantum
matrix as input a general solution of the relations is sought without
imposing the Yang - Baxter constraint for or the braid equation for
. For three biparametric deformatios, and , the standard,the nonstandard and the
hybrid one respectively, or is found to depend, apart from the
two parameters defining the deformation in question, on an extra free parameter
,such that only for two values of , given explicitly for each case, one
has the braid equation. Arbitray corresponds to a class (conserving the
group relations independent of ) of the MQYBE or modified quantum YB
equations studied by Gerstenhaber, Giaquinto and Schak. Various properties of
the triparametric , and are
studied. In the larger space of the modified braid equation (MBE) even
can satisfy outside braid equation (BE)
subspace. A generalized, - dependent, Hecke condition is satisfied by each
3-parameter . The role of in noncommutative geometries of the
, and deformed planes is studied. K is found to
introduce a "soft symmetry breaking", preserving most interesting properties
and leading to new interesting ones. Further aspects to be explored are
indicated.Comment: Latex, 17 pages, minor change
Satellite observations of thought experiments close to a black hole
Since black holes are `black', methods of their identification must
necessarily be indirect. Due to very special boundary condition on the horizon,
the advective flow behaves in a particular way, which includes formation of
centrifugal pressure dominated boundary layer or CENBOL where much of the
infall energy is released and outflows are generated. The observational aspects
of black holes must depend on the steady and time-dependent properties of this
boundary layer. Several observational results are written down in this review
which seem to support the predictions of thought experiments based on this
advective accretion/outflow model. In future, when gravitational waves are
detected, some other predictions of this model could be tested as well.Comment: Published in Classical and Quantum Gravity, v. 17, No. 12, p. 2427,
200
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