46,589 research outputs found
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
Negative Specific Heat in a Quasi-2D Generalized Vorticity Model
Negative specific heat is a dramatic phenomenon where processes decrease in
temperature when adding energy. It has been observed in gravo-thermal collapse
of globular clusters. We now report finding this phenomenon in bundles of
nearly parallel, periodic, single-sign generalized vortex filaments in the
electron magnetohydrodynamic (EMH) model for the unbounded plane under strong
magnetic confinement. We derive the specific heat using a steepest descent
method and a mean field property. Our derivations show that as temperature
increases, the overall size of the system increases exponentially and the
energy drops. The implication of negative specific heat is a runaway reaction,
resulting in a collapsing inner core surrounded by an expanding halo of
filaments.Comment: 12 pages, 3 figures; updated with revision
Quantum Theory from Quantum Gravity
We provide a mechanism by which, from a background independent model with no
quantum mechanics, quantum theory arises in the same limit in which spatial
properties appear. Starting with an arbitrary abstract graph as the microscopic
model of spacetime, our ansatz is that the microscopic dynamics can be chosen
so that 1) the model has a low low energy limit which reproduces the
non-relativistic classical dynamics of a system of N particles in flat
spacetime, 2) there is a minimum length, and 3) some of the particles are in a
thermal bath or otherwise evolve stochastically. We then construct simple
functions of the degrees of freedom of the theory and show that their
probability distributions evolve according to the Schroedinger equation. The
non-local hidden variables required to satisfy the conditions of Bell's theorem
are the links in the fundamental graph that connect nodes adjacent in the graph
but distant in the approximate metric of the low energy limit. In the presence
of these links, distant stochastic fluctuations are transferred into universal
quantum fluctuations.Comment: 17 pages, 2 eps figure
Investigations of electron emission characteristics of low work function surfaces Quarterly report no. 5, 1 Oct. - 31 Dec. 1965
Electron emission characteristics of low work function surfaces from magnetic deflection probe measurements of cesium adsorption on tungste
Investigations of electron emission characteristics of low work function surfaces Quarterly report no. 2, 1 Jan. - 31 Mar. 1966
Formation and electron emission characteristics of low work function surface
Environmental dependence of AGN activity in the supercluster A901/2
We present XMM data for the supercluster A901/2, at z ~ 0.17, which is
combined with deep imaging and 17-band photometric redshifts (from the COMBO-17
survey), 2dF spectra and Spitzer 24um data, to identify AGN in the
supercluster. The 90ksec XMM image contains 139 point sources, of which 11 are
identified as supercluster AGN with L_X(0.5-7.5keV) > 1.7x10^41 erg/cm2/s. The
host galaxies have M_R < -20 and only 2 of 8 sources with spectra could have
been identified as AGN by the detected optical emission lines. Using a large
sample of 795 supercluster galaxies we define control samples of massive
galaxies with no detected AGN. The local environments of the AGN and control
samples differ at >98 per cent significance. The AGN host galaxies lie
predominantly in areas of moderate projected galaxy density and with more local
blue galaxies than the control sample, with the exception of one very bright
Type I AGN very near the centre of a cluster. These environments are similar
to, but not limited to, cluster outskirts and blue groups. Despite the large
number of potential host galaxies, no AGN are found in regions with the highest
galaxy density (excluding some cluster cores where emission from the ICM
obscures moderate luminosity AGN). AGN are also absent from the areas with
lowest galaxy density. We conclude that the prevalence of cluster AGN is linked
to their environment.Comment: 20 pages, 15 figures. MNRAS accepted. Version with full resolution
figures, including Figure 14, is available at
http://www.sc.eso.org/~rgilmour
Investigations of electron emission characteristics of low work function surfaces Final report, 27 Sep. 1964 - 28 Sep. 1966
Electron emission characteristics of low work function surface
Vibration effects on heat transfer in cryogenic systems Quarterly progress report no. 1, Jun. 1 - Aug. 31, 1966
Vibration effects on natural convection and fluid transport properties in cryogenic system
Investigations of electron emission characteristics of low work function surfaces Quarterly report, 28 Sep. - 27 Dec. 1966
Coadsorption of cesium and fluorine on tungsten, and analysis of mechanisms leading to decay of field emission current from low work function zirconium/oxygen coated tungsten emitte
Argyrin B a non-competitive inhibitor of the human immunoproteasome exhibiting preference for β1i
Inhibitors of the proteasome have found broad therapeutic applications however, they show severe toxicity due to the abundance of proteasomes in healthy cells. In contrast, inhibitors of the immunoproteasome, which is upregulated during disease states, are less toxic and have increased therapeutic potential including against autoimmune disorders. In this project, we report argyrin B, a natural product cyclic peptide to be a reversible, non-competitive inhibitor of the immunoproteasome. Argyrin B showed selective inhibition of the β5i and β1i sites of the immunoproteasome over the β5c and β1c sites of the constitutive proteasome with nearly 20-fold selective inhibition of β1i over the homologous β1c. Molecular modelling attributes the β1i over β1c selectivity to the small hydrophobic S1 pocket of β1i and β5i over β5c to site-specific amino acid variations that enable additional bonding interactions and stabilization of the binding conformation. These findings facilitate the design of immunoproteasome selective and reversible inhibitors that may have a greater therapeutic potential and lower toxicity
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