5,157 research outputs found
Deconfinement to Quark Matter in Neutron Stars - The Influence of Strong Magnetic Fields
We use an extended version of the hadronic SU(3) non-linear realization of
the sigma model that also includes quarks to study hybrid stars. Within this
approach, the degrees of freedom change naturally as the temperature/density
increases. Different prescriptions of charge neutrality, local and global, are
tested and the influence of strong magnetic fields and the anomalous magnetic
moment on the particle population is discussed.Comment: To appear in the proceedings of conference XII HADRON PHYSICS April,
22-27, 2012, Bento Goncalves, Wineyards Valley Region, Rio Grande do Sul,
Brazil Revised version with corrections made to the text in page
Abelian covers of surfaces and the homology of the level L mapping class group
We calculate the first homology group of the mapping class group with
coefficients in the first rational homology group of the universal abelian -cover of the surface. If the surface has one marked point, then the
answer is \Q^{\tau(L)}, where is the number of positive divisors of
. If the surface instead has one boundary component, then the answer is
\Q. We also perform the same calculation for the level subgroup of the
mapping class group. Set . If the surface has one
marked point, then the answer is \Q[H_L], the rational group ring of .
If the surface instead has one boundary component, then the answer is \Q.Comment: 32 pages, 10 figures; numerous corrections and simplifications; to
appear in J. Topol. Ana
Virtually Haken fillings and semi-bundles
Suppose that M is a fibered three-manifold whose fiber is a surface of
positive genus with one boundary component. Assume that M is not a semi-bundle.
We show that infinitely many fillings of M along dM are virtually Haken. It
follows that infinitely many Dehn-surgeries of any non-trivial knot in the
three-sphere are virtually Haken.Comment: This is the version published by Geometry & Topology on 29 November
200
Mass, radius, and composition of the outer crust of nonaccreting cold neutron stars
The properties and composition of the outer crust of nonaccreting cold
neutron stars are studied by applying the model of Baym, Pethick, and
Sutherland, which was extended by including higher order corrections of the
atomic binding, screening, exchange and zero-point energy. The most recent
experimental nuclear data from the atomic mass table of Audi, Wapstra, and
Thibault from 2003 is used. Extrapolation to the drip line is utilized by
various state-of-the-art theoretical nuclear models (finite range droplet,
relativistic nuclear field and non-relativistic Skyrme Hartree-Fock
parameterizations). The different nuclear models are compared with respect to
the mass and radius of the outer crust for different neutron star
configurations and the nuclear compositions of the outer crust.Comment: 5 pages, 2 figures, submitted to J. Phys. G, part of the proceedings
of the Nuclear Physics in Astrophysics III conference in Dresde
Dynamical Systems On Three Manifolds Part II: 3-Manifolds,Heegaard Splittings and Three-Dimensional Systems
The global behaviour of nonlinear systems is extremely important in control
and systems theory since the usual local theories will only give information
about a system in some neighbourhood of an operating point. Away from that
point, the system may have totally different behaviour and so the theory
developed for the local system will be useless for the global one.
In this paper we shall consider the analytical and topological structure of
systems on 2- and 3- manifolds and show that it is possible to obtain systems
with 'arbitrarily strange' behaviour, i.e., arbitrary numbers of chaotic
regimes which are knotted and linked in arbitrary ways. We shall do this by
considering Heegaard Splittings of these manifolds and the resulting systems
defined on the boundaries.Comment: 15 pages with 9 pictures. Accepted by Int. J. of Bifurcation and
Chao
Colour-colour diagrams and extragalactic globular cluster ages. Systematic uncertainties using the (V-K)-(V-I) diagram
(abridged) We investigate biases in cluster ages and [Fe/H] estimated from
the (V-K)-(V-I) diagram, arising from inconsistent Horizontal Branch
morphology, metal mixture, treatment of core convection between observed
clusters and the theoretical colour grid employed for age and metallicity
determinations. We also study the role played by statistical fluctuations of
the observed colours, caused by the low total mass of typical globulars.
Horizontal Branch morphology is potentially the largest source of uncertainty.
A single-age system harbouring a large fraction of clusters with an HB
morphology systematically bluer than the one accounted for in the theoretical
colour grid, can simulate a bimodal population with an age difference as large
as 8 Gyr. When only the redder clusters are considered, this uncertainty is
almost negligible, unless there is an extreme mass loss along the Red Giant
Branch phase. The metal mixture affects mainly the redder clusters; the effect
of colour fluctuations becomes negligible for the redder clusters, or when the
integrated Mv is brighter than -8.5 mag. The treatment of core convection is
relevant for ages below ~4 Gyr. The retrieved [Fe/H] distributions are overall
only mildly affected. Colour fluctuations and convective core extension have
the largest effect. When 1sigma photometric errors reach 0.10 mag, all biases
found in our analysis are erased, and bimodal age populations with age
differences of up to ~8 Gyr go undetected. The use of both (U-I)-(V-K) and
(V-I)-(V-K) diagrams may help disclosing the presence of blue HB stars
unaccounted for in the theoretical colour calibration.Comment: 20 pages, including 26 figures. A&A in pres
Experimental quantum verification in the presence of temporally correlated noise
Growth in the complexity and capabilities of quantum information hardware
mandates access to practical techniques for performance verification that
function under realistic laboratory conditions. Here we experimentally
characterise the impact of common temporally correlated noise processes on both
randomised benchmarking (RB) and gate-set tomography (GST). We study these
using an analytic toolkit based on a formalism mapping noise to errors for
arbitrary sequences of unitary operations. This analysis highlights the role of
sequence structure in enhancing or suppressing the sensitivity of quantum
verification protocols to either slowly or rapidly varying noise, which we
treat in the limiting cases of quasi-DC miscalibration and white noise power
spectra. We perform experiments with a single trapped Yb ion as a
qubit and inject engineered noise () to probe protocol
performance. Experiments on RB validate predictions that the distribution of
measured fidelities over sequences is described by a gamma distribution varying
between approximately Gaussian for rapidly varying noise, and a broad, highly
skewed distribution for the slowly varying case. Similarly we find a strong
gate set dependence of GST in the presence of correlated errors, leading to
significant deviations between estimated and calculated diamond distances in
the presence of correlated errors. Numerical simulations demonstrate
that expansion of the gate set to include negative rotations can suppress these
discrepancies and increase reported diamond distances by orders of magnitude
for the same error processes. Similar effects do not occur for correlated
or errors or rapidly varying noise processes,
highlighting the critical interplay of selected gate set and the gauge
optimisation process on the meaning of the reported diamond norm in correlated
noise environments.Comment: Expanded and updated analysis of GST, including detailed examination
of the role of gauge optimization in GST. Full GST data sets and
supplementary information available on request from the authors. Related
results available from
http://www.physics.usyd.edu.au/~mbiercuk/Publications.htm
Investigation of a direction sensitive sapphire detector stack at the 5 GeV electron beam at DESY-II
Extremely radiation hard sensors are needed in particle physics experiments
to instrument the region near the beam pipe. Examples are beam halo and beam
loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial
diamond sensors are widely used. In this paper single crystal sapphire sensors
are considered as a promising alternative. Industrially grown sapphire wafers
are available in large sizes, are of low cost and, like diamond sensors, can be
operated without cooling. Here we present results of an irradiation study done
with sapphire sensors in a high intensity low energy electron beam. Then, a
multichannel direction-sensitive sapphire detector stack is described. It
comprises 8 sapphire plates of 1 cm^2 size and 525 micro m thickness,
metallized on both sides, and apposed to form a stack. Each second metal layer
is supplied with a bias voltage, and the layers in between are connected to
charge-sensitive preamplifiers. The performance of the detector was studied in
a 5 GeV electron beam. The charge collection efficiency measured as a function
of the bias voltage rises with the voltage, reaching about 10 % at 950 V. The
signal size obtained from electrons crossing the stack at this voltage is about
22000 e, where e is the unit charge.
The signal size is measured as a function of the hit position, showing
variations of up to 20 % in the direction perpendicular to the beam and to the
electric field. The measurement of the signal size as a function of the
coordinate parallel to the electric field confirms the prediction that mainly
electrons contribute to the signal. Also evidence for the presence of a
polarisation field was observed.Comment: 13 pages, 7 figures, 3 table
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