Sudden Critical Current Drops Induced in S/F Structures

In the search for new physical properties of S/F structures, we have found that the superconductor critical current can be controlled by the domain state of the neighboring ferromagnet. The superconductor is a thin wire of thickness d_{s} ~ 2 xi_{S}. Nb/Co and Nb/Py (Permalloy Ni_{80}Fe_{20}) bilayer structures were grown with a significant magnetic anisotropy. Critical current measurements of Nb/Co structures with ferromagnet thickness d_{F} > 30nm show sudden drops in two very defined steps when the measurements are made along the hard axes direction (i.e. current track parallel to hard anisotropy axes direction). These drops disappear when they are made along the easy axis direction or when the ferromagnet thickness is below 30nm. The drops are accompanied by vortex flux flow. In addition magnetorestistance measurements close to Tc show a sharp increase near saturation fields of the ferromagnet. Similar results are reproduced in Nb/Py bilayer structure with the ferromagnet thickness d_{F} ~ 50nm along the easy anisotropy axes. These results are explained as being due to spontaneous vortex formation and flow induced by Bloch domain walls of the ferromagnet underneath. We argue these Bloch domain walls produce a 2D vortex-antivortex lattice structure.Comment: 6 pages, 6 figure

The bimodal spiral galaxy surface brightness distribution

We have assessed the significance of Tully and Verheijen's (1997) bimodal Ursa Major Cluster spiral galaxy near-infrared surface brightness distribution, focussing on whether this bimodality is simply an artifact of small number statistics. A Kolmogorov-Smirnov style of significance test shows that the total distribution is fairly represented by a single-peaked distribution, but that their isolated galaxy subsample (with no significant neighbours within a projected distance of around 80 kpc) is bimodal at the 96 per cent level. We have also investigated the assumptions underlying the isolated galaxy surface brightness distribution, finding that the (often large) inclination corrections used in the construction of this distribution reduce the significance of the bimodality. We conclude that the Ursa Major Cluster dataset is insufficient to establish the presence of a bimodal near-infrared surface brightness distribution: an independent sample of around 100 isolated, low inclination galaxies is required to establish bimodality at the 99 per cent level.Comment: 5 pages LaTeX; 2 embedded figures; re-submitted to MNRAS after replying to referee's comment

Criteria for generalized macroscopic and mesoscopic quantum coherence

We consider macroscopic, mesoscopic and "S-scopic" quantum superpositions of eigenstates of an observable, and develop some signatures for their existence. We define the extent, or size $S$ of a superposition, with respect to an observable \hat{x}, as being the range of outcomes of \hat{x} predicted by that superposition. Such superpositions are referred to as generalized $S$-scopic superpositions to distinguish them from the extreme superpositions that superpose only the two states that have a difference $S$ in their prediction for the observable. We also consider generalized $S$-scopic superpositions of coherent states. We explore the constraints that are placed on the statistics if we suppose a system to be described by mixtures of superpositions that are restricted in size. In this way we arrive at experimental criteria that are sufficient to deduce the existence of a generalized $S$-scopic superposition. The signatures developed are useful where one is able to demonstrate a degree of squeezing. We also discuss how the signatures enable a new type of Einstein-Podolsky-Rosen gedanken experiment.Comment: 15 pages, accepted for publication in Phys. Rev.

SOAR (Support Office for Aerogeophysical Research) Annual Report 1995/1996

The Support Office for Aerogeophysical Research (SOAR) was a facility of the National Science Foundation's Office of Polar Programs whose mission is to make airborne geophysical observations available to the broad research community of geology, glaciology and other sciences. The central office of the SOAR facility is located in Austin, Texas within the University of Texas Institute for Geophysics. Other institutions with significant responsibilities are the Lamont­ Doherty Earth Observatory of Columbia University and the Geophysics Branch of the U.S . Geological Survey. This report summarizes the goals and accomplishments of the SOAR facility during 1995/1996 and plans for the next year.National Science Foundation's Office of Polar ProgramsInstitute for Geophysic

Unified criteria for multipartite quantum nonlocality

Wiseman and co-workers (Phys. Rev. Lett. 98, 140402, 2007) proposed a distinction between the nonlocality classes of Bell's nonlocality, steering and entanglement based on whether or not an overseer trusts each party in a bipartite scenario where they are asked to demonstrate entanglement. Here we extend that concept to the multipartite case and derive inequalities that progressively test for those classes of nonlocality, with different thresholds for each level. This framework includes the three classes of nonlocality above in special cases and introduces a family of others.Comment: V2: corrected image display; V3: substantial changes including new proofs, arguments, and result

Light Element Abundance Inhomogeneities in Globular Clusters: Probing Star Formation and Evolution in the Early Milky Way

Abundance patterns of the elements C, N, and O are sensitive probes of stellar nucleosynthesis processes and, in addition, O abundances are an important input for stellar age determinations. Understanding the nature of the observed distribution of these elements is key to constraining protogalactic star formation history. Patterns deduced from low-resolution spectroscopy of the CN, CH, NH, and CO molecules for low-mass stars in their core-hydrogen or first shell-hydrogen burning phases in the oldest ensembles known, the Galactic globular star clusters, are reviewed. New results for faint stars in NGC 104 (47 Tuc, C0021-723) reveal that the bimodal, anticorrelated pattern of CN and CH strengths found among luminous evolved stars is also present in stars nearing the end of their main-sequence lifetimes. In the absence of known mechanisms to mix newly synthesized elements from the interior to the observable surface layers of such unevolved stars, those particular inhomogeneities imply that the original material from which the stars formed some 15 billion years ago was chemically inhomogeneous in the C and N elements. However, in other clusters, observations of abundance ratios and C isotope ratios suggest that alterations to surface chemical compositions are produced as stars evolve from the main sequence through the red giant branch. Thus, the current observed distributions of C, N, and O among the brightest stars (those also observed most often) may not reflect the true distribution from which the protocluster cloud formed. The picture which is emerging of the C, N and O abundance patterns within globular clusters may be one whichComment: 12 pages in uuencoded compressed postscript (including figures), to appear in the Canadian Journal of Physics (Special Issue in Honor of G. Herzberg

From Quasars to Extraordinary N-body Problems

We outline reasoning that led to the current theory of quasars and look at George Contopoulos's place in the long history of the N-body problem. Following Newton we find new exactly soluble N-body problems with multibody forces and give a strange eternally pulsating system that in its other degrees of freedom reaches statistical equilibrium.Comment: 13 pages, LaTeX with 1 postscript figure included. To appear in Proceedings of New York Academy of Sciences, 13th Florida Workshop in Nonlinear Astronomy and Physic

Excess sub-millimetre emission from GRS 1915+105

We present the first detections of the black hole X-ray binary GRS 1915+105 at sub-millimetre wavelengths. We clearly detect the source at 350 GHz on two epochs, with significant variability over the 24 hr between epochs. Quasi-simultaneous radio monitoring indicates an approximately flat spectrum from 2 - 350 GHz, although there is marginal evidence for a minimum in the spectrum between 15 - 350 GHz. The flat spectrum and correlated variability imply that the sub-mm emission arises from the same synchrotron source as the radio emission. This source is likely to be a quasi-steady partially self-absorbed jet, in which case these sub-mm observations probe significantly closer to the base of the jet than do radio observations and may be used in future as a valuable diagnostic of the disc:jet connection in this source.Comment: 5 pages, 3 figures, accepted for publication in MNRA

Spectrum of cosmic rays, produced in supernova remnants

Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants is employed to calculate CR spectra. The magnetic field in SNRs is assumed to be significantly amplified by the efficiently accelerating nuclear CR component. It is shown that the calculated CR spectra agree in a satisfactory way with the existing measurements up to the energy $10^{17}$ eV. The power law spectrum of protons extends up to the energy $3\times 10^{15}$ eV with a subsequent exponential cutoff. It gives a natural explanation for the observed knee in the Galactic CR spectrum. The maximum energy of the accelerated nuclei is proportional to their charge number $Z$. Therefore the break in the Galactic CR spectrum is the result of the contribution of progressively heavier species in the overall CR spectrum so that at $10^{17}$ eV the CR spectrum is dominated by iron group nuclei. It is shown that this component plus a suitably chosen extragalactic CR component can give a consistent description for the entire Galactic CR spectrum.Comment: 4 pages with emulateapj, 3 figures, accepted for publication in the Astrophysical Journal Letter

Detecting Pulsars with Interstellar Scintillation in Variance Images

Pulsars are the only cosmic radio sources known to be sufficiently compact to show diffractive interstellar scintillations. Images of the variance of radio signals in both time and frequency can be used to detect pulsars in large-scale continuum surveys using the next generation of synthesis radio telescopes. This technique allows a search over the full field of view while avoiding the need for expensive pixel-by-pixel high time resolution searches. We investigate the sensitivity of detecting pulsars in variance images. We show that variance images are most sensitive to pulsars whose scintillation time-scales and bandwidths are close to the subintegration time and channel bandwidth. Therefore, in order to maximise the detection of pulsars for a given radio continuum survey, it is essential to retain a high time and frequency resolution, allowing us to make variance images sensitive to pulsars with different scintillation properties. We demonstrate the technique with Murchision Widefield Array data and show that variance images can indeed lead to the detection of pulsars by distinguishing them from other radio sources.Comment: 8 papes, 9 figures, accepted for publication in MNRA