5,431 research outputs found
The energy partitioning of non-thermal particles in a plasma: or the Coulomb logarithm revisited
The charged particle stopping power in a highly ionized and weakly to
moderately coupled plasma has been calculated to leading and next-to-leading
order by Brown, Preston, and Singleton (BPS). After reviewing the main ideas
behind this calculation, we use a Fokker-Planck equation derived by BPS to
compute the electron-ion energy partitioning of a charged particle traversing a
plasma. The motivation for this application is ignition for inertial
confinement fusion -- more energy delivered to the ions means a better chance
of ignition, and conversely. It is therefore important to calculate the
fractional energy loss to electrons and ions as accurately as possible, as this
could have implications for the Laser Megajoule (LMJ) facility in France and
the National Ignition Facility (NIF) in the United States. The traditional
method by which one calculates the electron-ion energy splitting of a charged
particle traversing a plasma involves integrating the stopping power dE/dx.
However, as the charged particle slows down and becomes thermalized into the
background plasma, this method of calculating the electron-ion energy splitting
breaks down. As a result, the method suffers a systematic error of order T/E0,
where T is the plasma temperature and E0 is the initial energy of the charged
particle. In the case of DT fusion, for example, this can lead to uncertainties
as high as 10% or so. The formalism presented here is designed to account for
the thermalization process, and in contrast, it provides results that are
near-exact.Comment: 10 pages, 3 figures, invited talk at the 35th European Physical
Society meeting on plasma physic
Effective 't Hooft-Polyakov monopoles from pure SU(3) gauge theory
The well known topological monopoles originally investigated by 't Hooft and
Polyakov are known to arise in classical Yang-Mills-Higgs theory. With a pure
gauge theory it is known that the classical Yang-Mills field equation do not
have such finite energy configurations. Here we argue that such configurations
may arise in a semi-quantized Yang-Mills theory, where the original gauge
group, SU(3), is reduced to a smaller gauge group, SU(2), and with some
combination of the coset fields of the SU(3) to SU(2) reduction acting as
effective scalar fields. The procedure is called semi-quantized since some of
the original gauge fields are treated as quantum degrees of freedom, while
others are postulated to be effectively described as classical degrees of
freedom. Some speculation is offer on a possible connection between these
monopole configurations and the confinement problem, and the nucleon spin
puzzle.Comment: one error is correcte
Hawking radiation, Unruh radiation and the equivalence principle
We compare the response function of an Unruh-DeWitt detector for different
space-times and different vacua and show that there is a {\it detailed}
violation of the equivalence principle. In particular comparing the response of
an accelerating detector to a detector at rest in a Schwarzschild space-time we
find that both detectors register thermal radiation, but for a given,
equivalent acceleration the fixed detector in the Schwarzschild space-time
measures a higher temperature. This allows one to locally distinguish the two
cases. As one approaches the horizon the two temperatures have the same limit
so that the equivalence principle is restored at the horizon.Comment: 9 pages. Added references and added discussion. To be published in
PR
Persistence to high temperatures of interlayer coherence in an organic superconductor
The interlayer magnetoresistance of the organic metal \cuscn is
studied in fields of up to 45 T and at temperatures from 0.5 K to 30 K. The
peak in seen in in-plane fields, a definitive signature of
interlayer coherence, remains to s exceeding the Anderson criterion for
incoherent transport by a factor . Angle-dependent magnetoresistance
oscillations are modeled using an approach based on field-induced quasiparticle
paths on a 3D Fermi surface, to yield the dependence of the scattering rate
. The results suggest that does not vary strongly over
the Fermi surface, and that it has a dependence due to electron-electron
scattering
Opening of DNA double strands by helicases. Active versus passive opening
Helicase opening of double-stranded nucleic acids may be "active" (the
helicase directly destabilizes the dsNA to promote opening) or "passive" (the
helicase binds ssNA available due to a thermal fluctuation which opens part of
the dsNA). We describe helicase opening of dsNA, based on helicases which bind
single NA strands and move towards the double-stranded region, using a discrete
``hopping'' model. The interaction between the helicase and the junction where
the double strand opens is characterized by an interaction potential. The form
of the potential determines whether the opening is active or passive. We
calculate the rate of passive opening for the helicase PcrA, and show that the
rate increases when the opening is active. Finally, we examine how to choose
the interaction potential to optimize the rate of strand separation. One
important result is our finding that active opening can increase the unwinding
rate by 7 fold compared to passive opening.Comment: 13 pages, 3 figure
Wormholes and Flux Tubes in 5D Kaluza-Klein Theory
In this paper spherically symmetric solutions to 5D Kaluza-Klein theory, with
``electric'' and/or ``magnetic'' fields are investigated. It is shown that the
global structure of the spacetime depends on the relation between the
``electrical'' and ``magnetic'' Kaluza-Klein fields. For small ``magnetic''
field we find a wormhole-like solution. As the strength of the ``magnetic''
field is increased relative to the strength of the ``electrical'' field, the
wormhole-like solution evolves into a finite or infinite flux tube depending on
the strengths of the two fields. For the large ``electric'' field case we
conjecture that this solution can be considered as the mouth of a wormhole,
with the , and components of the metric acting as
the source of the exotic matter necessary for the formation of the wormhole's
mouth. For the large ``magnetic'' field case a 5D flux tube forms, which is
similar to the flux tube between two monopoles in Type-II superconductors, or
the hypothesized color field flux tube between two quarks in the QCD vacuum.Comment: 12 pages, 5 eps.figures, REVTEX, Discussion about null surfaces
ammended. References added. To be published in PR
Small animal disease surveillance: respiratory disease 2017
This report focuses on surveillance for respiratory disease in companion animals. It begins with an analysis of data from 392 veterinary practices contributing to the Small Animal Veterinary Surveillance Network (SAVSNET) between January and December 2017.
The following section describes canine respiratory coronavirus infections in dogs, presenting results from laboratory-confirmed cases across the country between January 2010 and December 2017. This is followed by an update on the temporal trends of three important syndromes in companion animals, namely gastroenteritis, pruritus and respiratory disease, from 2014 to 2017.
A fourth section presents a brief update on Streptococcus equi subspecies zooepidemicus in companion animals. The final section summarises some recent developments pertinent to companion animal health, namely eyeworm (Thelazzia callipaeda) infestations in dogs imported to the UK and canine influenza virus in the USA and Canada
Electrons as quasi-bosons in magnetic white dwarfs
A white dwarf star achieves its equilibrium from the balancing of the
gravitational compression against the Fermi degeneracy pressure of the electron
gas. In field theory there are examples (e.g. the monopole-charge system) where
a strong magnetic field can transform a boson into a fermion or a fermion into
a boson. In some condensed matter systems (e.g. fractional quantum Hall
systems) a strong magnetic field can transform electrons into effective
fermions, or effective anyons. Based on these examples we investigate the
possibility that the strong magnetic fields of some white dwarfs may transform
some fraction of the electrons into effective bosons. This could have
consequences for the structure of highly magnetized white dwarfs. It would
alter the mass-radius relationship, and in certain instances one could envision
a scenario where a white dwarf below the Chandrasekhar limit could nevertheless
collapse into a neutron star due to a weakening of the electron degeneracy
pressure. In addition the transformation of electrons into effective bosons
could result in the electrons Bose condensing, which could speed up the cooling
rate of white dwarfs.Comment: 10 pages. To be published IJMP
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