Exact correlations in a single file system with a driven tracer

We study the effect of a single driven tracer particle in a bath of other particles performing the random average process on an infinite line using a stochastic hydrodynamics approach. We consider arbitrary fixed as well as random initial conditions and compute the two-point correlations. For quenched uniform and annealed steady state initial conditions we show that in the large time $T$ limit the fluctuations and the correlations of the positions of the particles grow subdiffusively as $\sqrt{T}$ and have well defined scaling forms under proper rescaling of the labels. We compute the corresponding scaling functions exactly for these specific initial configurations and verify them numerically. We also consider a non translationally invariant initial condition with linearly increasing gaps where we show that the fluctuations and correlations grow superdiffusively as $T^{3/2}$ at large times.Comment: 7 pages, 4 figures, supplementary material appended. To appear in EP

The Height Structure of the Solar Atmosphere from the EUV Perspective

We investigate the structure of the solar chromosphere and transition region using full Sun images obtained with the Extreme Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO) spacecraft. The limb seen in the EIT coronal images (taken in lines of Fe IX/X at 171 \AA, Fe XII at 195 \AA and Fe XV at 284 \AA) is an absorption limb predicted by models to occur at the top of the chromosphere where the density of neutral hydrogen becomes significant ($\sim10^{10}$ cm$^{-3}$). The transition-region limb seen in He II 304 \AA images is an emission limb. We find: (1) the limb is higher at the poles than at the equator both in the coronal images (by 1300 $\pm$ 650 km) and the 304 \AA images (by 3500 $\pm$ 120 0 km); and (2) the 304 \AA limb is significantly higher than the limb in the coronal images. The height difference is 3100 $\pm$ 1200 km at the equator, and 6600 $\pm$ 1200 km at the poles. We suggest that the elevation of the 304 \AA limb above the limb in the coronal images may be due to the upper surface of the chromosphere being bumpy, possibly because of the presence of spicules. The polar extension is consistent with a reduced heat input to the chromosphere in the polar coronal holes compared with the quiet--Sun atmosphere at the equator.Comment: 6 pages, 2 figure

A Variable Black Hole X-Ray Source in a NGC 1399 Globular Cluster

We have discovered an accreting black hole (BH) in a spectroscopically confirmed globular cluster (GC) in NGC 1399 through monitoring of its X-ray activity. The source, with a peak luminosity of L_x=2x10^39 ergs/s, reveals an order of magnitude change in the count rate within ~10 ks in a Chandra observation. The BH resides in a metal-rich [Fe/H]~0.2 globular cluster. After RZ2109 in NGC 4472 this is only the second black-hole X-ray source in a GC confirmed via rapid X-ray variability. Unlike RZ2109, the X-ray spectrum of this BH source did not change during the period of rapid variability. In addition to the short-term variability the source also exhibits long-term variability. After being bright for at least a decade since 1993 within a span of 2 years it became progressively fainter, and eventually undetectable, or marginally detectable, in deep Chandra and XMM observations. The source also became harder as it faded. The characteristics of the long term variability in itself provide sufficient evidence to identify the source as a BH. The long term decline in the luminosity of this object was likely not recognized in previous studies because the rapid variability within the bright epoch suppressed the average luminosity in that integration. The hardening of the spectrum accompanying the fading would also make this black hole source indistinguishable from an accreting neutron star in some epochs. Therefore some low mass X-ray binaries identified as NS accretors in snapshot studies of nearby galaxies may also be BHs. Thus the discovery of the second confirmed BH in an extragalactic GC through rapid variability at the very least suggests that accreting BHs in GCs are not exceedingly rare occurences.Comment: 8 pages, 2 figs. Accepted for publication in Ap

Estimate of the Collins function in a chiral invariant approach

We estimate the Collins function at a low energy scale by calculating the fragmentation of a quark into a pion at the one-loop level in the chiral invariant model of Manohar and Georgi. We give a useful parametrization of our results and we briefly discuss different spin and/or azimuthal asymmetries containing the Collins function and measurable in semi-inclusive DIS and e+ e- annihilationComment: 5 pages, 4 figures, to appear in Proceedings of 10th International Workshop on Deep Inelastic Scattering (DIS 2002), Cracow, Poland, 30 Apr-4 May 200

Meterwave observations of a coronal hole

Meter-wave maps are presented showing a coronal hole at 30.9, 50.0, and 73.8 MHz using the Clark Lake Radioheliograph in October 1984. The coronal hole seen against the disk at all three frequencies shows interesting similarities to, and significant differences from its optical signatures in HeI lambda10830 spectroheliograms. The 73.8 MHz coronal hole, when seen near disk center, appears to coincide with the HeI footprint of the hole. At the lower frequencies, the emission comes from higher levels of the corona, and the hole appears to be displaced, probably due to the non-radial structure of the coronal hole. The contrast of the hole relative to the quiet Sun is much greater than reported previously for a coronal hole observed at 80 MHz. The higher contrast is certainly real, due to the superior dynamic range, sensitivity, and calibration of the Clark Lake instrument. Using a coronal hole model, the electron density is derived from radio observations of the brightness temperature. A very large discrepancy is found between the derived density and that determined from Skylab EUV observations of coronal holes. This discrepancy suggests that much of the physics of coronal holes has yet to be elucidated

Effect of realistic interatomic interactions and two-body correlation on the heat capacity of a trapped BEC

An approximate many-body theory has been used to calculate the heat capacity and the condensate fraction of a BEC with effective repulsive interaction. The effect of interactions has been analyzed and compared with the non-interacting case. It has been found that the repulsive interaction lowers the critical temperature from the value found in the non-interacting case. The difference between the critical temperatures increases with the increase in the total number of atoms in the trap.Comment: 15 pages, 5 figure

Stability of a horizontal viscous fluid layer in a vertical time periodic electric field

The stability of a horizontal interface between two viscous fluids, one of which is conducting and the other is dielectric, acted upon by a vertical time-periodic electric field is considered. The two fluids are bounded by electrodes separated by a finite distance. By means of Floquet theory, the marginal stability curves are obtained, thereby elucidating the dependency of the critical voltage and wavenumber upon the fluid viscosities. The limit of vanishing viscosities is shown to be in excellent agreement with the marginal stability curves predicted by means of a Mathieu equation. The methodology to obtain the marginal stability curves developed here is applicable to any arbitrary but time periodic-signal, as demonstrated for the case of a signal with two different frequencies. As a special case, the marginal stability curves for an applied ac voltage biased by a dc voltage are depicted. It is shown that the mode coupling caused by the normal stress at the interface due to the electric field leads to appearance of harmonic modes and subharmonic modes. This is in contrast to the application of a voltage with a single frequency which always leads to a harmonic mode. Whether a harmonic or subharmonic mode is the most unstable one depends on details of the excitation signal. It is also shown that the electrode spacing has a distinct effect on the stability bahavior of the system