3,757 research outputs found
General relativistic treatment of LISA optical links
LISA is a joint space mission of the NASA and the ESA for detecting low
frequency gravitational waves in the band Hz. In order to attain
the requisite sensitivity for LISA, the laser frequency noise must be
suppressed below the other secondary noises such as the optical path noise,
acceleration noise etc. This is achieved by combining time-delayed data for
which precise knowledge of time-delays is required. The gravitational field,
mainly that of the Sun and the motion of LISA affect the time-delays and the
optical links. Further, the effect of the gravitational field of the Earth on
the orbits of spacecraft is included. This leads to additional flexing over and
above that of the Sun. We have written a numerical code which computes the
optical links, that is, the time-delays with great accuracy
metres - more than what is required for time delay interferometry (TDI) - for
most of the orbit and with sufficient accuracy within metres for an
integrated time window of about six days, when one of the arms tends to be
tangent to the orbit. Our analysis of the optical links is fully general
relativistic and the numerical code takes into account effects such as the
Sagnac, Shapiro delay, etc.. We show that with the deemed parameters in the
design of LISA, there are symmetries inherent in the configuration of LISA and
in the physics, which may be used effectively to suppress the residual laser
noise in the modified first generation TDI. We demonstrate our results for some
important TDI variables
Optimising the directional sensitivity of LISA
It was shown in a previous work that the data combinations canceling laser
frequency noise constitute a module - the module of syzygies. The cancellation
of laser frequency noise is crucial for obtaining the requisite sensitivity for
LISA. In this work we show how the sensitivity of LISA can be optimised for a
monochromatic source - a compact binary - whose direction is known, by using
appropriate data combinations in the module. A stationary source in the
barycentric frame appears to move in the LISA frame and our strategy consists
of "coherently tracking" the source by appropriately "switching" the data
combinations so that they remain optimal at all times. Assuming that the
polarisation of the source is not known, we average the signal over the
polarisations. We find that the best statistic is the `network' statistic, in
which case LISA can be construed of as two independent detectors. We compare
our results with the Michelson combination, which has been used for obtaining
the standard sensitivity curve for LISA, and with the observable obtained by
optimally switching the three Michelson combinations. We find that for sources
lying in the ecliptic plane the improvement in SNR increases from 34% at low
frequencies to nearly 90% at around 20 mHz. Finally we present the
signal-to-noise ratios for some known binaries in our galaxy. We also show
that, if at low frequencies SNRs of both polarisations can be measured, the
inclination angle of the plane of the orbit of the binary can be estimated.Comment: 16 pages, 8 figures, submitted to Phys Rev
Time Delay Interferometry for LISA with one arm dysfunctional
In order to attain the requisite sensitivity for LISA - a joint space mission
of the ESA and NASA- the laser frequency noise must be suppressed below the
secondary noises such as the optical path noise, acceleration noise etc. By
combining six appropriately time-delayed data streams containing fractional
Doppler shifts - a technique called time delay interferometry (TDI) - the laser
frequency noise may be adequately suppressed. We consider the general model of
LISA where the armlengths vary with time, so that second generation TDI are
relevant. However, we must envisage the possibility, that not all the optical
links of LISA will be operating at all times, and therefore, we here consider
the case of LISA operating with two arms only. As shown earlier in the
literature, obtaining even approximate solutions of TDI to the general problem
is very difficult. Since here only four optical links are relevant, the
algebraic problem simplifies considerably. We are then able to exhibit a large
number of solutions (from mathematical point of view an infinite number) and
further present an algorithm to generate these solutions
Exact Tagged Particle Correlations in the Random Average Process
We study analytically the correlations between the positions of tagged
particles in the random average process, an interacting particle system in one
dimension. We show that in the steady state the mean squared auto-fluctuation
of a tracer particle grows subdiffusively as for large
time t in the absence of external bias, but grows diffusively
in the presence of a nonzero bias. The prefactors of the subdiffusive and
diffusive growths as well as the universal scaling function describing the
crossover between them are computed exactly. We also compute ,
the mean squared fluctuation in the position difference of two tagged particles
separated by a fixed tag shift r in the steady state and show that the external
bias has a dramatic effect in the time dependence of . For fixed
r, increases monotonically with t in absence of bias but has a
non-monotonic dependence on t in presence of bias. Similarities and differences
with the simple exclusion process are also discussed.Comment: 10 pages, 2 figures, revte
Effect of spatial bias on the nonequilibrium phase transition in a system of coagulating and fragmenting particles
We examine the effect of spatial bias on a nonequilibrium system in which
masses on a lattice evolve through the elementary moves of diffusion,
coagulation and fragmentation. When there is no preferred directionality in the
motion of the masses, the model is known to exhibit a nonequilibrium phase
transition between two different types of steady states, in all dimensions. We
show analytically that introducing a preferred direction in the motion of the
masses inhibits the occurrence of the phase transition in one dimension, in the
thermodynamic limit. A finite size system, however, continues to show a
signature of the original transition, and we characterize the finite size
scaling implications of this. Our analysis is supported by numerical
simulations. In two dimensions, bias is shown to be irrelevant.Comment: 7 pages, 7 figures, revte
Drug utilization pattern and selected biochemical parameters in pre- and post-hemodialysis state in the end stage renal disease patients: a cross sectional study at a tertiary care hospital
Background: Chronic kidney disease can progress to end-stage kidney failure (ESRD), which is fatal without artificial filtering (dialysis) or a kidney transplant.Methods: The ESRD patients of either gender age >18 years who were diagnosed by nephrologist as ESRD and are on haemodialysis regularly included for the study.Results: The blood urea, serum creatinine, phosphorous, potassium levels were reduced significantly in post – haemodialysis condition, but, there was not much weight reduction after haemodialysis. Serum albumin, serum sodium and blood haemoglobin levels were almost unchanged in post – haemodialysis state. There was no significant difference between the pre and post haemodialysis parameters- serum Na+ serum albumin and blood hemoglobulin. Out of 75 ESRD patients, almost all patients 74 (98.7%) prescribed tablet Livogen, 73 (97.3%) patients given Inj. EPO, 55 (73.3%) tab Nicardia, 54 (76%) tab Sodamint, 43 (57.3%) capsule Alpha D3, 40 (53.3%) tab Shelcal. While between 12 (16%) to 20 (26%) patients prescribed tab Nodosis, tab Metoprolol, tab Febuget, tab Ecosprin, and tab Rantac. Only 1 (1.3%) to 9 (12%) patients received tablet Augmentin, tab Arkamine, tab Carvedilol, tab Para 500, tab Atorvas, Human mixtard, tab Calcicard, tab Minipress XL, tab Dytor, and tab Clopilet.Conclusions: The available two models of treatment, i.e., haemodialysis and poly pharmacy at hospital setup to face the challenges associated with the ESRD, and even outcome after application of both these two models of therapies did not provide optimal normal healthy life status to ESRD patients
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