1,536 research outputs found

    Response of a spaceborne gravitational wave antenna to solar oscillations

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    We investigate the possibility of observing very small amplitude low frequency solar oscillations with the proposed laser interferometer space antenna (LISA). For frequencies ν\nu below 3×104Hz3\times 10^{-4} {\rm Hz} the dominant contribution is from the near zone time dependent gravitational quadrupole moments associated with the normal modes of oscillation. For frequencies ν\nu above 3×104Hz 3\times 10^{-4} {\rm Hz} the dominant contribution is from gravitational radiation generated by the quadrupole oscillations which is larger than the Newtonian signal by a factor of the order (2πrν/c)4(2 \pi r \nu/ c)^4, where rr is the distance to the Sun, and cc is the velocity of light. The low order solar quadrupole pressure and gravity oscillation modes have not yet been detected above the solar background by helioseismic velocity and intensity measurements. We show that for frequencies ν2×104Hz\nu \lesssim 2\times 10^{-4} {\rm Hz}, the signal due to solar oscillations will have a higher signal to noise ratio in a LISA type space interferometer than in helioseismology measurements. Our estimates of the amplitudes needed to give a detectable signal on a LISA type space laser interferometer imply surface velocity amplitudes on the sun of the order of 1-10 mm/sec in the frequency range 1×1045×104Hz1\times 10^{-4} -5\times 10^{-4} {\rm Hz}. If such modes exist with frequencies and amplitudes in this range they could be detected with a LISA type laser interferometer.Comment: 16 pages, 6 figures, 1 table. A reworked and considerably improved version of ArXiv:astro-ph/0103472, Published in PR

    RVB gauge theory and the Topological degeneracy in the Honeycomb Kitaev model

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    We relate the Z2_2 gauge theory formalism of the Kitaev model to the SU(2) gauge theory of the resonating valence bond (RVB) physics. Further, we reformulate a known Jordan-Wigner transformation of Kitaev model on a torus in a general way that shows that it can be thought of as a Z2_2 gauge fixing procedure. The conserved quantities simplify in terms of the gauge invariant Jordan-Wigner fermions, enabling us to construct exact eigen states and calculate physical quantities. We calculate the fermionic spectrum for flux free sector for different gauge field configurations and show that the ground state is four-fold degenerate on a torus in thermodynamic limit. Further on a torus we construct four mutually anti-commuting operators which enable us to prove that all eigenstates of this model are four fold degenerate in thermodynamic limit.Comment: 12 pages, 3 figures. Added affiliation and a new section, 'Acknowledgements'.Typos correcte

    Superconducting Gap Nodal Surface and Fermi Surface: their partial overlap in cuprates

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    Electron correlation in cuprates leads to a global constraint kΔk=0\sum_{\bf k} \Delta_{\bf k} = 0 on the gap function Δk\Delta_{\bf k} resulting in a gap nodal surface. We give physical arguments supported by numerical results and discuss some experimental results to argue that correlations also lead to a local constraint on charge fluctuations in k{\bf k}-space close to the Fermi surface, which may result in a substantial overlap of the Fermi surface with the gap nodal surface.Comment: RevTeX 3.0, 4 Pages, 6 PostScript Figures

    Depositional characteristics of \u3csup\u3e7\u3c/sup\u3eBe and \u3csup\u3e210\u3c/sup\u3ePb in southeastern Michigan

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    The depositional fluxes in the bulk and dry fallout as well as the concentrations of 7Be and 210Pb in aerosols were measured for a period of 17 months at Detroit, Michigan. The bulk depositional fluxes of 7Be and 210Pb varied between 3.11 and 63.0 dpm cm−2 yr−1 (mean of 11.4 dpm cm−2 yr−1) and 0.35 and 10.3 dpm cm−2 yr−1 (mean of 1.41 dpm cm−2 yr−1), respectively, and this variability in the depositional fluxes is attributed to the frequency and amount of precipitation and seasonal variations in the depositional fluxes. The dry depositional fluxes of 7Be and 210Pb contributed 2.1–19.8% and 3.6–48.6% of the bulk depositional fluxes, respectively. The higher precipitation-normalized enrichment factor for 7Be during spring is attributed to the stratosphere-troposphere exchange of air masses during spring and large-scale atmospheric mixing during summer. We report that snow is more efficient than rain in removing 210Pb from the atmosphere, and this is likely due to higher surface area of snow flurries compared to the rain droplets. The volume-weighted concentrations of 7Be and 210Pb are the highest reported in literature so far. The concentration of 7Be in the air showed a seasonal increase during the spring and summer months, and no seasonal variation was observed for 210Pb. The mean deposition velocities of aerosols calculated using concentrations of 7Be and 210Pb in air and precipitation are 1.6 and 1.1 cm s−1, respectively, and the corresponding washout ratios are 948 and 637. There is no significant correlation between the aerosol mass and depositional velocities of 7Be and 210Pb in the air masses. We propose that a relatively minor portion of the aerosols actively participate in the removal of these nuclides from the air masses


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    Objective: Thymoquinone (TQ), the main active ingredient of the volatile oil isolated from the Nigella sativa seeds has been shown to possess a widearray of pharmacological effects. Recently, we have reported the anticancer potential of TQ in 7, 12-dimethylbenz (a) anthracene (DMBA) inducedrats. DMBA acts as a potent site and organ-specific carcinogen by generating various reactive metabolic intermediates leading to oxidative stress. Thepresent study was hypothesized to explore the protective effect of TQ against DMBA induced liver injury in rats.Methods: DMBA was used to induce breast cancer in rats. Oral treatment of TQ (25 mg/kg body weight) to DMBA induced rats daily for 4 weeks wasfound to be effective against DMBA induced mammary gland carcinogenesis in female Wistar rats. The levels of nucleic acids, oxidative stress markand antioxidants were determined. The activities of Phase I and Phase II enzymes, tricarboxylic acid (TCA) cycle enzymes were assayed.Results: The increased levels of DNA and RNA were found to be decreased on treatment with TQ. The altered activities of Phase I and Phase IIbiotransformation enzymes were found to be regulated on treatment with thymoqionone. The hepatoprotective nature of TQ was assessed byanalyzing the markers of oxidative stress, and antioxidant competence in DMBA induced rats. Treatment with TQ revealed a significant decline in thelevels of lipid peroxides, and a significant improvement in the levels of enzymatic and non-enzymatic antioxidants in the liver tissue. In addition, TQmodulated the activities of TCA cycle enzymes.Conclusion: The results of the present study clearly indicate that TQ protects the tissues from oxidative stress-mediated damage which is evidentfrom improved antioxidant status.Keywords: 7, 12-dimethylbenz (a) anthracene, Thymoquinone, Oxidative stress, Liver tissues, Antioxidant potential

    Effect of salinity stress on neurosecretory cells, protein and free amino acid content and rate of ammonia excretion of the prawn Penaeus indicus H Milne Edwards

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    Stress induced changes resulting from salinity exposure are sought in the neurosecretory cells of different neuroendocrine centres, in protein and free amino acid content in haemolymph, muscle. and hepatopancreas, and in rale of ammonia excretion in the prawn Penaeusindicus. Prawns acclimated to low saline medium (S . 10%0) when uansferred to rugh saline medium (5 .. 4Q%.o) showed liule change in their neurosecrelOry cell histologY'. However, protein and free amino acid content in haemolymph. muscle. and hepatopancreas increased considerably. Simultaneously, the rate of ammonia excretion was reduced. Prawns acclimated 10 high salinity medium when transferred 10 low salinity exhibited changes in the above parameters in reverse to those findings in the former experiment. The probable reasons for such changes are discussed