Initial stages of cavitation damage and erosion on copper and brass tested in a rotating disk device

In view of the differences in flow and experimental conditions, there has been a continuing debate as to whether or not the ultrasonic method of producing cavitation damage is similar to the damage occurring in cavitating flow systems, namely, venturi and rotating disk devices. In this paper, the progress of cavitation damage during incubation periods on polycrystalline copper and brass tested in a rotating disk device is presented. The results indicate several similarities and differences in the damage mechanism encountered in a rotating disk device (which simulates field rotary devices) and a magnetostriction apparatus. The macroscopic erosion appears similar to that in the vibratory device except for nonuniform erosion and apparent plastic flow during the initial damage phase

X-ray properties of the microquasar GRS 1915+105 during a variability class transition

We present a detailed X-ray study of the microquasar GRS 1915+105 during a variability class transition observed in 2000 June with the PPCs of the Indian X-ray Astronomy Experiment. We supplement this observation with data from the RXTE archives. The source made a transition from a steady low-hard state to a regular oscillatory behaviour in the light curve known as bursts or class `rho' (Belloni et al. 2000) between 2000 May 11 and 17 and reverted back to the low-hard state on 2000 June 27. A gradual change in the burst recurrence time from about 75 s to about 40 s was observed which then increased to about 120 s during the ~ 40 days of class `rho'. The regular bursts disappeared from the X-ray light curves and the class transition was observed to occur within 1.5 hours on 2000 June 27 with the PPCs. A correlation is found between the observed QPO frequency at 5-8 Hz in the quiescent phase and the average X-ray intensity of the source during the class `rho'. We notice a strong similarity between the properties of the source during the class `rho' and those during the oscillatory phase of the observations of class `alpha'. From the timing and spectral analysis, it is found that the observed properties of the source over tens of days during the class `rho' are identical to those over a time scale of a few hundreds of seconds in the class `alpha'. Examining the light curves from the beginning of the RXTE/PCA and RXTE/ASM observations, it is found that the change of state from radio-quiet low-hard state to high state occurs through the X-ray classes `rho' and `alpha' which appear together during the state transition. It is further inferred that the source switches from low-hard state to the class `rho' through the intermediate class `alpha'.Comment: 10 pages with 9 figures, LaTex. To be appeared in MNRA

Different types of X-ray bursts from GRS 1915+105 and their origin

We report the X-ray observations of the Galactic X-ray transient source GRS 1915+105 with the PPCs of the Indian X-ray Astronomy Experiment(IXAE) onboard the Indian satellite IRS-P3 during 1997 June - August, which have revealed the presence of four types of intense X-ray bursts. All the observed bursts have a slow exponential rise, a sharp linear decay, and they can broadly be put in two classes: irregular and quasi-regular bursts in one class, and regular bursts in another class. The regular bursts are found to have two distinct time scales and they persist over extended durations. There is a strong correlation between the preceding quiescent time and the burst duration for the quasi-regular and irregular bursts. No such correlation is found for the regular bursts. The ratio of average flux during the burst time to the average flux during the quiescent phase is high and variable for the quasi- regular and irregular bursts while it is low and constant for the regular bursts. We suggest that the peculiar bursts that we have seen are charact- eristic of the change of state of the source. The source can switch back and forth between the low-hard state and the high-soft state near critical accretion rates in a very short time scale. A test of the model is presented using the publicly available 13-60 keV RXTE/PCA data for irregular and regular bursts concurrent with our observations.Comment: 13 pages, 12 figures, Accepted in APJ, emulateapj style use

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

Anomalous microwave response of high-temperature superconducting thin-film microstrip resonator in weak dc magnetic fields

We have studied an anomalous microwave (mw) response of superconducting YBa_{2}Cu_{3}O_{7-delta} (YBCO) microstrip resonators in the presence of a weak dc magnetic field, H_{dc}. The surface resistance (R_{s}) and reactance (X_{s}) show a correlated non-monotonic behaviour as a function of H_{dc}. R_{s} and X_{s} were found to initially decrease with elevated H_{dc} and then increase after H_{dc} reaches a crossover field, H_{c}, which is independent of the amplitude and frequency of the input mw signal within the measurements. The frequency dependence of R_{s} is almost linear at fixed H_{dc} with different magnitudes (H_{c}). The impedance plane analysis demonstrates that r_{H}, which is defined as the ratio of the change in R_{s}(H_{dc}) and that in X_{s}(H_{dc}), is about 0.6 at H_{dc}<H_{c} and 0.1 at H_{dc}>H_{c}. The H_{dc} dependence of the surface impedance is qualitatively independent of the orientation of H_{dc}.Comment: REVTex 3.1, 5 pages, 6 EPS figures, submitted to Physica

Relaxation dynamics of maximally clustered networks

We study the relaxation dynamics of fully clustered networks (maximal number of triangles) to an unclustered state under two different edge dynamics---the double-edge swap, corresponding to degree-preserving randomization of the configuration model, and single edge replacement, corresponding to full randomization of the Erd\H{o}s--R\'enyi random graph. We derive expressions for the time evolution of the degree distribution, edge multiplicity distribution and clustering coefficient. We show that under both dynamics networks undergo a continuous phase transition in which a giant connected component is formed. We calculate the position of the phase transition analytically using the Erd\H{o}s--R\'enyi phenomenology

Shear flow induced isotropic to nematic transition in a suspension of active filaments

We study the effects of externally applied shear flow on a model of suspensions of motors and filaments, via the equations of active hydrodynamics [PRL {\bf 89} (2002) 058101; {\bf 92} (2004) 118101]. In the absence of shear, the orientationally ordered phase of {\it both} polar and apolar active particles is always unstable at zero-wavenumber. An imposed steady shear large enough to overcome the active stresses stabilises both apolar and moving polar phases. Our work is relevant to {\it in vitro} studies of active filaments, the reorientation of endothelial cells subject to shear flow and shear-induced motility of attached cells.Comment: 8 pages, 4 figures submitted to Europhysics Letter

Efficacy of Gravity Separation as an Alternative to Froth Flotation for Treating Jharia group Coal fines

In general, the Indian coals are difficult-to-wash due to their drift origin. Recovery of clean coal from coal fines is continue to he cost in-effective. Even though several advanced flotation technologies have been commercialized to treat fines, the results are not comparable with the washability data of fines. The Jharia group of coal fines are treated at Tata Steel presently in froth flotation. Keeping merit of gravity separation in view, the test results with water-only cyclone as an alternative gravity method to froth flotation for treating Jamadoba coal fines have been presented in this paper

Comment on ''the controlled charge ordering and evidence of the metallic state in Pr0.65_{0.65}Ca0.35_{0.35}MnO3_{3} films''

In a recent paper (2000 \QTR{it}{J. Phys.: Condens. Matter} \QTR{bf}{12} L133) Lee \QTR{it}{et al.} have studied the transport properties of Pr$_{0.65}$Ca$_{0.35}$MnO$_{3}$ thin films. They claimed that they are able to controlled the charge-ordered (CO) state by the lattice strains. We propose herein another alternative since another indexation of the orientation of the film can be found leading to almost no distortion of the cell, as compared to the bulk compound.Comment: 2 page