Outburst Morphology in the Soft X-ray Transient Aquila X-1

We present optical and near-IR (OIR) observations of the major outbursts of the neutron star soft X-ray transient binary system Aquila X-1, from summer 1998 -- fall 2007. The major outbursts of the source over the observed timespan seem to exhibit two main types of light curve morphologies, (a) the classical Fast-Rise and Exponential-Decay (FRED) type outburst seen in many soft X-ray transients and (b) the Low-Intensity State (LIS) where the optical-to-soft-X-ray flux ratio is much higher than that seen during a FRED. Thus there is no single correlation between the optical (R-band) and soft X-ray (1.5-12 keV, as seen by the ASM onboard RXTE) fluxes even within the hard state for Aquila X-1, suggesting that LISs and FREDs have fundamentally different accretion flow properties. Time evolution of the OIR fluxes during the major LIS and FRED outbursts is compatible with thermal heating of the irradiated outer accretion disk. No signature of X-ray spectral state changes or any compact jet are seen in the OIR, showing that the OIR color-magnitude diagram (CMD) can be used as a diagnostic tool to separate thermal and non-thermal radiation from X-ray binaries where orbital and physical parameters of the system are reasonably well known. We suggest that the LIS may be caused by truncation of the inner disk in a relatively high mass accretion state, possibly due to matter being diverted into a weak outflow.Comment: Accepted for publication in ApJ. Uses aastex. 27 pages and 10 figure

On the modulation of low frequency Quasi-Periodic Oscillations in black-hole transients

We studied the properties of the low-frequency quasi-periodic oscillations detected in a sample of six black hole candidates (XTE J1550-564, H 1743-322, XTE J1859+226, 4U 1630-47,GX 339-4, XTE J1650-500) observed by the Rossi XTE satellite. We analyzed the relation between the full width half maximum and the frequency of all the narrow peaks detected in power density spectra where a type-C QPO is observed. Our goal was to understand the nature of the modulation of the signal by comparing the properties of different harmonic peaks in the power density spectrum. We find that for the sources in our sample the width of the fundamental and of the first harmonic are compatible with a frequency modulation, while that of the sub-harmonic is independent of frequency, possibly indicating the presence of an additional modulation in amplitude. We compare our results with those obtained earlier from GRS 1915+105 and XTE J1550-564.Comment: 8 pages, 3 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journa

Magnetodielectric effect in nickel nanosheet-Na-4 mica composites

Nickel nanosheets of thickness 0.6 nm were grown within the nanochannels of Na-4 mica template. The specimens show magnetodielectric effect at room temperature with a change of dielectric constant as a function of magnetic field, the electric field frequency varying from 100 to 700 kHz. A decrease of 5% in the value of dielectric constant was observed up to a field of 1.2 Tesla. This is explained by an inhomogeneous two-component composite model as theoretically proposed recently. The present approach will open up synthesis of various nanocomposites for sensor applications.Comment: 11 pages, 7 figure

Quantum time of flight distribution for cold trapped atoms

The time of flight distribution for a cloud of cold atoms falling freely under gravity is considered. We generalise the probability current density approach to calculate the quantum arrival time distribution for the mixed state describing the Maxwell-Boltzmann distribution of velocities for the falling atoms. We find an empirically testable difference between the time of flight distribution calculated using the quantum probability current and that obtained from a purely classical treatment which is usually employed in analysing time of flight measurements. The classical time of flight distribution matches with the quantum distribution in the large mass and high temperature limits.Comment: 6 pages, RevTex, 4 eps figure

Quantum teleportation using non-orthogonal entangled channels

We study quantum teleportation with the resource of non-orthogonal qubit states. We first extend the standard teleportation protocol to the case of such states. We investigate how the loss of teleportation fidelity resulting for the use of non-orthogonal states compares to a similar loss of fidelity when noisy or non-maximally entangled states as used as teleportation resource. Our analysis leads to certain interesting results on the teleportation efficiency of both pure and mixed non-orthgonal states compared to that of non-maximally entangled and mixed states.Comment: 7 pages, latex, 5 eps fig

A new window on Strange Quark Matter as the ground state of strongly interacting matter

If strange quark matter is the true ground state of matter, it must have lower energy than nuclear matter. Simultaneously, two-flavour quark matter must have higher energy than nuclear matter, for otherwise the latter would convert to the former. We show, using an effective chiral lagrangian, that the existence of a new lower energy ground state for two-flavour quark matter, the pion condensate, shrinks the window for strange quark matter to be the ground state of matter and sets new limits on the current strange quark mass

Mesons in (2+1) Dimensional Light Front QCD. II. Similarity Renormalization Approach

Recently we have studied the Bloch effective Hamiltonian approach to bound states in 2+1 dimensional gauge theories. Numerical calculations were carried out to investigate the vanishing energy denominator problem. In this work we study similarity renormalization approach to the same problem. By performing analytical calculations with a step function form for the similarity factor, we show that in addition to curing the vanishing energy denominator problem, similarity approach generates linear confining interaction for large transverse separations. However, for large longitudinal separations, the generated interaction grows only as the square root of the longitudinal separation and hence produces violations of rotational symmetry in the spectrum. We carry out numerical studies in the G{\l}azek-Wilson and Wegner formalisms and present low lying eigenvalues and wavefunctions. We investigate the sensitivity of the spectra to various parameterizations of the similarity factor and other parameters of the effective Hamiltonian, especially the scale $\sigma$. Our results illustrate the need for higher order calculations of the effective Hamiltonian in the similarity renormalization scheme.Comment: 31 pages, 4 figures, to be published in Physical Review