Upgraded experiments with super neutrino beams: Reach versus Exposure

We introduce exposure as a means to making balanced comparisons of the sensitivities of long-baseline neutrino experiments to a nonzero \theta_{13}, to CP violation and to the neutrino mass hierarchy. We illustrate its use by comparing the sensitivities of possible upgrades of superbeam experiments, namely NOvA*, T2KK and experiments with wide band beams. For the proposed exposures, we find the best nominal CP violation performance for T2KK. For equal exposures, a wide band beam experiment has the best mass hierarchy performance. The physics concept on which NOvA* is based has the best potential for discovering CP violation only for exposures above a threshold value.Comment: 4 pages, 2 figures, 1 table. Version to appear as a Rapid Communication in PR

Particles held by springs in a linear shear flow exhibit oscillatory motion

The dynamics of small spheres, which are held by linear springs in a low Reynolds number shear flow at neighboring locations is investigated. The flow elongates the beads and the interplay of the shear gradient with the nonlinear behavior of the hydrodynamic interaction among the spheres causes in a large range of parameters a bifurcation to a surprising oscillatory bead motion. The parameter ranges, wherein this bifurcation is either super- or subcritical, are determined.Comment: 4 pages, 5 figure

Future of superheavy element research: Which nuclei could be synthesized within the next few years?

Low values of the fusion cross sections and very short half-lives of nuclei with Z$>$120 put obstacles in synthesis of new elements. Different nuclear reactions (fusion of stable and radioactive nuclei, multi-nucleon transfers and neutron capture), which could be used for the production of new isotopes of superheavy (SH) elements, are discussed in the paper. The gap of unknown SH nuclei, located between the isotopes which were produced earlier in the cold and hot fusion reactions, can be filled in fusion reactions of $^{48}$Ca with available lighter isotopes of Pu, Am, and Cm. Cross sections for the production of these nuclei are predicted to be rather large, and the corresponding experiments can be easily performed at existing facilities. For the first time, a narrow pathway is found to the middle of the island of stability owing to possible $\beta^+$-decay of SH isotopes which can be formed in ordinary fusion reactions of stable nuclei. Multi-nucleon transfer processes at near barrier collisions of heavy (and very heavy, U-like) ions are shown to be quite realistic reaction mechanism allowing us to produce new neutron enriched heavy nuclei located in the unexplored upper part of the nuclear map. Neutron capture reactions can be also used for the production of the long-living neutron rich SH nuclei. Strong neutron fluxes might be provided by pulsed nuclear reactors and by nuclear explosions in laboratory conditions and by supernova explosions in nature. All these possibilities are discussed in the paper.Comment: An Invited Plenary Talk given by Valeriy I. Zagrebaev at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. To appear in the NN2012 Proceedings in Journal of Physics: Conference Series (JPCS

A Multi-Cloud Warm-Absorber Model for NGC 4051

A multi-cloud model is presented which explains the soft X-ray excess in NGC 4051 and, consistently, the optical line spectrum and the SED of the continuum. The clouds are heated and ionized by the photoionizing flux from the active center and by shocks. Diffuse radiation, partly absorbed throughout the clouds, nicely fits the bump in the soft X-ray domain, while bremsstrahlung radiation from the gaseous clouds contribute to the fit of the continuum SED. Debris of high density fragmented clouds are necessary to explain the absorption oxygen throats observed at 0.87 keV and 0.74 keV. The debris are heated by shocks of about 200-300 km/s. Low velocity (100 km/s)-density (100 cm-3) clouds contribute to the line and continuum spectra, as well as high velocity (1000 km/s)-density (8000 cm-3) clouds which are revealed by the FWHM of the line profiles. The SED in the IR is explained by reradiation of dust, however, the dust-to-gas ratio is not particularly high. Radio emission is well fitted by synchrotron radiation created at the shock front by Fermi mechanism.Comment: 19 pages + 3 figures PostScrip

X-ray variability of AGNs in the soft and the hard X-ray bands

We investigate the X-ray variability characteristics of hard X-ray selected AGNs (based on Swift/BAT data) in the soft X-ray band using the RXTE/ASM data. The uncertainties involved in the individual dwell measurements of ASM are critically examined and a method is developed to combine a large number of dwells with appropriate error propagation to derive long duration flux measurements (greater than 10 days). We also provide a general prescription to estimate the errors in variability derived from rms values from unequally spaced data. Though the derived variability for individual sources are not of very high significance, we find that, in general, the soft X-ray variability is higher than those in hard X-rays and the variability strengths decrease with energy for the diverse classes of AGN. We also examine the strength of variability as a function of the break time scale in the power density spectrum (derived from the estimated mass and bolometric luminosity of the sources) and find that the data are consistent with the idea of higher variability at time scales longer than the break time scale.Comment: 17 pages, 15 Postscript figures, 3 tables, accepted for publication in Ap

Chandra observations of the accretion-driven millisecond X-ray pulsars XTE J0929-314 and XTE J1751-305 in quiescence

(Abridge) We observed the accreting millisecond X-ray pulsars XTE J0929-314 and XTE J1751-305 in their quiescent states using Chandra. From XTE J0929-314 we detected 22 photons (0.3-8 keV) in 24.4 ksec, resulting in a count rate of 9 x 10^{-4} c/s. The small number of photons detected did not allow for a detailed spectral analysis, but we can demonstrate that the spectrum is harder than simple thermal emission which is what is usually presumed to arise from a cooling neutron star that has been heated during the outbursts. Assuming a power-law model for the spectrum, we obtain a power-law index of ~1.8 and an unabsorbed flux of 6 x 10^{-15} ergs/s/cm^2 (0.5-10 keV), resulting in a luminosity of 7 x 10^{31} (d/10 kpc)^2 ergs/s, with d in kpc. No thermal component could be detected; such a component contributed at most 30% to the 0.5-10 keV flux. Variability in the count rate of XTE J0929-314 was observed at the 95% confidence level. We did not conclusively detect XTE J1751-305 in our 43 ksec observation, with 0.5-10 keV flux upper limits between 0.2 and 2.7 x 10^{-14} ergs/s/cm^2 depending on assumed spectral shape, resulting in luminosity upper limits of 0.2 - 2 x 10^{32} (d/8 kpc)^2 ergs/s. We compare our results with those obtained for other neutron-star X-ray transients in their quiescent state. Using simple accretion disk physics in combination with our measured quiescent luminosity of XTE J0929-314 and the luminosity upper limits of XTE J1751-305, and the known spin frequency of the neutron stars, we could constrain the magnetic field of the neutron stars in XTE J0929-314 and XTE J1751-305 to be less than 3 x 10^9 (d/10 kpc) and 3 - 7 x 10^8 (d/8 kpc) Gauss (depending on assumed spectral shape of the quiescent spectrum), respectively.Comment: Accepted for publication in ApJ, 29 September 2004. Added spectral variability search for the data of XTE J0929-314 and added the non-detection with Chandra of XTE J1751-30