271 research outputs found
Spectroscopic signature of phosphate crystallization in Erbium-doped optical fibre preforms
In rare-earth-doped silica optical fibres, the homogeneous distribution of
amplifying ions and part of their spectroscopic properties are usually improved
by adding selected elements, such as phosphorus or aluminum, as structural
modifier. In erbium ion (Er3+) doped fibres, phosphorus preferentially
coordinates to Er3+ ions to form regular cages around it. However, the
crystalline structures described in literature never gave particular
spectroscopic signature. In this article, we report emission and excitation
spectra of Er3+ in a transparent phosphorus-doped silica fibre preform. The
observed line features observed at room and low temperature are attributed to
ErPO4 crystallites
Tension term, interchange symmetry, and the analogy of energy and tension laws of the AdS soliton solution
In this paper, we reconsider the energy and tension laws of the Ricci flat
black hole by taking the contribution of the tension term into account. After
this considering and inspired by the interchange symmetry between the Ricci
flat black hole and the AdS soliton solution which arises from the double
analytic continuation of the time and compact spatial direction, we find out
the analogy of the energy and tension laws of the AdS soliton solution.
Moreover, we also investigate the energy and tension laws of the boosted Ricci
flat black hole, and discuss the boosted AdS soliton solution. However,
although there is the same interchange symmetry between the boosted Ricci flat
black hole and boosted AdS soliton, the analogy of laws of the boosted AdS
soliton solution may be of no sense for the existence of the closed timelike
curves and conical singularity. In spite of that, the conserved charges such as
the energy and momentum of the boosted AdS soliton are well-defined, and an
interesting result is that its energy is lower than that of the static AdS
soliton. On the other hand, note that although the laws obtained above are the
same as those of the asymptotically flat case, the underlying deduced contents
are different. Thus, our results could also be considered as a simple
generalization to the asymptotically AdS case. Moreover, during the
calculation, we find that there may be a new way to define the gravitational
tension which can come from the quasi-local stress tensor of the counter-term
method.Comment: V4: 15 pages, no figure, version to appear in JHE
Low-Temperature Thermodynamics of and su(3)-invariant Spin Chains
We formulate the thermodynamic Bethe Ansatz (TBA) equations for the closed
(periodic boundary conditions) quantum spin chain in an external
magnetic field, in the (noncritical) regime where the anisotropy parameter
is real. In the limit , we recover the TBA equations of the
antiferromagnetic su(3)-invariant chain in the fundamental representation. We
solve these equations for low temperature and small field, and calculate the
specific heat and magnetic susceptibility.Comment: 31 pages, UMTG-16
Bosonization and Duality in Arbitrary Dimensions: New Results
A generic massive Thirring Model in three space-time dimensions exhibits a
correspondence with a topologically massive bosonized gauge action associated
to a self-duality constraint, and we write down a general expression for this
relationship.
We also generalize this structure to dimensions, by adopting the
so-called doublet approach, recently introduced. In particular, a non-
conventional formulation of the bosonization technique in higher dimensions (in
the spirit of ), is proposed and, as an application, we show how fermionic
(Thirring-like) representations for bosonic topologically massive models in
four dimensions may be built up.Comment: Revised version, to appear in Phys. Rev.
How to Stop (Worrying and Love) the Bubble: Boundary Changing Solutions
We discover that a class of bubbles of nothing are embedded as time dependent
scaling limits of previous spacelike-brane solutions. With the right initial
conditions, a near-bubble solution can relax its expansion and open the compact
circle. Thermodynamics of the new class of solutions is discussed and the
relationships between brane/flux transitions, tachyon condensation and
imaginary D-branes are outlined. Finally, a related class of simultaneous
connected S-branes are also examined.Comment: 47 pages; v2 introduction to Weyl cards added, comments added,
references added, typos corrected, matches JHEP versio
Mapping the Potential Risk of Mycetoma Infection in Sudan and South Sudan Using Ecological Niche Modeling
In 2013, the World Health Organization (WHO) recognized mycetoma as one of the neglected tropical conditions due to the efforts of the mycetoma consortium. This same consortium formulated knowledge gaps that require further research. On
De Sitter Holography and the Cosmic Microwave Background
We interpret cosmological evolution holographically as a renormalisation
group flow in a dual Euclidean field theory, as suggested by the conjectured
dS/CFT correspondence. Inflation is described by perturbing around the
infra-red fixed point of the dual field theory. The spectrum of the cosmic
microwave background radiation is determined in terms of scaling violations in
the field theory. The dark energy allows similar, albeit less predictive,
considerations. We discuss the cosmological fine-tuning problems from the
holographic perspective.Comment: 17 pages, 2 figures, uses JHEP style files; corrected and added
reference
Local well-posedness for membranes in the light cone gauge
In this paper we consider the classical initial value problem for the bosonic
membrane in light cone gauge. A Hamiltonian reduction gives a system with one
constraint, the area preserving constraint. The Hamiltonian evolution equations
corresponding to this system, however, fail to be hyperbolic. Making use of the
area preserving constraint, an equivalent system of evolution equations is
found, which is hyperbolic and has a well-posed initial value problem. We are
thus able to solve the initial value problem for the Hamiltonian evolution
equations by means of this equivalent system. We furthermore obtain a blowup
criterion for the membrane evolution equations, and show, making use of the
constraint, that one may achieve improved regularity estimates.Comment: 29 page
Introduction to M Theory and AdS/CFT Duality
An introductory survey of some of the developments that have taken place in
superstring theory in the past few years is presented. The main focus is on
three particular dualities. The first one is the appearance of an 11th
dimension in the strong coupling limit of the type IIA theory, which give rise
to M theory. The second one is the duality between the type IIB theory
compactified on a circle and M theory on a two-torus. The final topic is an
introduction to the recently proposed duality between superstring theory or M
theory on certain anti de Sitter space backgrounds and conformally invariant
quantum field theories.Comment: 26 pages; To be published in the Proceedings of a conference held in
Corfu, Greece in September 1998. v2: reference adde
Accretion, Outflows, and Winds of Magnetized Stars
Many types of stars have strong magnetic fields that can dynamically
influence the flow of circumstellar matter. In stars with accretion disks, the
stellar magnetic field can truncate the inner disk and determine the paths that
matter can take to flow onto the star. These paths are different in stars with
different magnetospheres and periods of rotation. External field lines of the
magnetosphere may inflate and produce favorable conditions for outflows from
the disk-magnetosphere boundary. Outflows can be particularly strong in the
propeller regime, wherein a star rotates more rapidly than the inner disk.
Outflows may also form at the disk-magnetosphere boundary of slowly rotating
stars, if the magnetosphere is compressed by the accreting matter. In isolated,
strongly magnetized stars, the magnetic field can influence formation and/or
propagation of stellar wind outflows. Winds from low-mass, solar-type stars may
be either thermally or magnetically driven, while winds from massive, luminous
O and B type stars are radiatively driven. In all of these cases, the magnetic
field influences matter flow from the stars and determines many observational
properties. In this chapter we review recent studies of accretion, outflows,
and winds of magnetized stars with a focus on three main topics: (1) accretion
onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and
(3) winds from isolated massive magnetized stars. We show results obtained from
global magnetohydrodynamic simulations and, in a number of cases compare global
simulations with observations.Comment: 60 pages, 44 figure
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