9,386 research outputs found
Effects of dark energy on the efficiency of charged AdS black holes as heat engine
In this paper, we study the heat engine where charged AdS black holes
surrounded by dark energy is the working substance and the mechanical work is
done via term in the first law of black hole thermodynamics in the
extended phase space. We first investigate the effects of a kind of dark energy
(quintessence field in this paper) on the efficiency of the RN-AdS black holes
as heat engine defined as a rectangle closed path in the plane. We get
the exact efficiency formula and find that quintessence field can improve the
heat engine efficiency which will increase as the field density grows.
At some fixed parameters, we find that bigger volume difference between the
smaller black holes() and the bigger black holes( ) will lead to a
lower efficiency, while the bigger pressure difference will make the
efficiency higher but it is always smaller than 1 and will never be beyond
Carnot efficiency which is the maximum value of the efficiency constrained by
thermodynamics laws, this is consistent to the heat engine in traditional
thermodynamics. After making some special choices for thermodynamical
quantities, we find that the increase of electric charge and normalization
factor can also promote heat engine efficiency which would infinitely
approach the Carnot limit when or goes to infinity.Comment: 28 pages, 16 figures, refernces added, discussion and computation
improve
Angular Momentum Independence of the Entropy Sum and Entropy Product for AdS Rotating Black Holes In All Dimensions
In this paper, we investigate the angular momentum independence of the
entropy sum and product for AdS rotating black holes based on the first law of
thermodynamics and a mathematical lemma related to Vandermonde determinant. The
advantage of this method is that the explicit forms of the spacetime metric,
black hole mass and charge are not needed but the Hawking temperature and
entropy formula on the horizons are necessary for static black holes, while our
calculations require the expressions of metric and angular velocity formula. We
find that the entropy sum is always independent of angular momentum for all
dimensions and the angular momentum-independence of entropy product only holds
for the dimensions with at least one rotation parameter , while
the mass-free of entropy sum and entropy product for rotating black holes only
stand for higher dimensions () and for all dimensions, respectively. On
the other hand, we find that the introduction of a negative cosmological
constant does not affect the angular momentum-free of entropy sum and product
but the criterion for angular momentum-independence of entropy product will be
affected.Comment: 14 pages, 0 figures,accepted for publication in Physics Letters
On K_2 of certain families of curves
We construct families of smooth, proper, algebraic curves in characteristic
0, of arbitrary genus g, together with g elements in the kernel of the tame
symbol. We show that those elements are in general independent by a limit
calculation of the regulator. Working over a number field, we show that in some
of those families the elements are integral. We determine when those curves are
hyperelliptic, finding, in particular, that over any number field we have
non-hyperelliptic curves of all composite genera g with g independent integral
elements in the kernel of the tame symbol.Comment: Revised version: improved exposition. some sections spli
Canonical simulations of supersymmetric SU(N) Yang-Mills quantum mechanics
The fermion loop formulation naturally separates partition functions into
their canonical sectors. Here we discuss various strategies to make use of this
for supersymmetric SU(N) Yang-Mills quantum mechanics obtained from dimensional
reduction in various dimensions and present numerical results for the separate
canonical sectors with fixed fermion numbers. We comment on potential problems
due to the sign of the contributions from the fermions and due to flat
directions.Comment: 7 pages, 3 figure
Production in High Energy Nuclear Collisions
We investigate the production of baryon in high energy nuclear
collisions via quark coalescence mechanism. The wave function of
is solved from the Schr\"odinger equation for the bound state of three charm
quarks by using the hyperspherical method. The production cross section of
per binary collision in a central Pb+Pb collision at
TeV reaches 9 nb, which is at least two orders of
magnitude larger than that in a p+p collision at the same energy. Therefore, it
is most probable to discover in heavy ion collisions at LHC, and
the observation will be a clear signature of the quark-gluon plasma formation.Comment: 6 pages, 5 figure
- …