275 research outputs found
Probing Lorentz and CPT violation with space-based experiments
Space-based experiments offer sensitivity to numerous unmeasured effects
involving Lorentz and CPT violation. We provide a classification of clock
sensitivities and present explicit expressions for time variations arising in
such experiments from nonzero coefficients in the Lorentz- and CPT-violating
Standard-Model Extension.Comment: 15 page
Microalgae as a biocathode and feedstock in anode chamber for a selfsustainable microbial fuel cell technology : a review
Abstract:Microbial fuel cell (MFC) technology has been investigated for over a decade now and it has been deemed as a preferred technique for energy generation since it is environmentally benign and does not produce toxic by/end products. However, this technology is characterized by low power outputs, poor microbial diversity detection, and the presence of methanogenic microorganisms, poor electrochemically active microorganisms’ enrichment techniques, and the type of electrode that is used, amongst others. Furthermore, this technology has relied mostly on refined chemicals for energy production and this practice is not sustainable for long-term application of this technology. This paper reviews the use of a microalgae-assisted MFC for a self-sustainable microbial fuel cell where a microalgae-assisted cathode is established to facilitate the oxidation/reduction reactions (ORR) while recycling the generated algal biomass to the anode compartment as a feedstock for improved energy generation. Furthermore, this review proposes for the utilization of cell disruption techniques to maximize nutrient availability for maximal power generation while also making use of molecular diagnostic tools such as metagenomics and metatranscriptomics to monitor the microbial community structure and function
Higgs production and decay: Analytic results at next-to-leading order QCD
The virtual two-loop corrections for Higgs production in gluon fusion are
calculated analytically in QCD for arbitrary Higgs and quark masses. Both
scalar and pseudo-scalar Higgs bosons are considered. The results are obtained
by expanding the known one-dimensional integral representation in terms of
m_H/m_q, and matching it with a suitably chosen ansatz of Harmonic
Polylogarithms. This ansatz is motivated by the known analytic result for the
Higgs decay rate into two photons. The method also allows us to check this
result and to extend it to the pseudo-scalar decay rate.Comment: LaTeX, 16 pages, 5 figures (8 eps-files
Quantum correlated twin atomic beams via photo-dissociation of a molecular Bose-Einstein condensate
We study the process of photo-dissociation of a molecular Bose-Einstein
condensate as a potential source of strongly correlated twin atomic beams. We
show that the two beams can possess nearly perfect quantum squeezing in their
relative numbers.Comment: Corrected LaTeX file layou
Thermodynamics and collapse of self-gravitating Brownian particles in D dimensions
We address the thermodynamics (equilibrium density profiles, phase diagram,
instability analysis...) and the collapse of a self-gravitating gas of Brownian
particles in D dimensions, in both canonical and microcanonical ensembles. In
the canonical ensemble, we derive the analytic form of the density scaling
profile which decays as f(x)=x^{-\alpha}, with alpha=2. In the microcanonical
ensemble, we show that f decays as f(x)=x^{-\alpha_{max}}, where \alpha_{max}
is a non-trivial exponent. We derive exact expansions for alpha_{max} and f in
the limit of large D. Finally, we solve the problem in D=2, which displays
rather rich and peculiar features
Phase Diagram of Bosonic Atoms in Two-Color Superlattices
We investigate the zero temperature phase diagram of a gas of bosonic atoms
in one- and two-color standing-wave lattices in the framework of the
Bose-Hubbard model. We first introduce some relevant physical quantities;
superfluid fraction, condensate fraction, quasimomentum distribution, and
matter-wave interference pattern. We then discuss the relationships between
them on the formal level and show that the superfluid fraction, which is the
relevant order parameter for the superfluid to Mott-insulator transition,
cannot be probed directly via the matter wave interference patterns. The formal
considerations are supported by exact numerical solutions of the Bose-Hubbard
model for uniform one-dimensional systems. We then map out the phase diagram of
bosons in non-uniform lattices. The emphasis is on optical two-color
superlattices which exhibit a sinusoidal modulation of the well depth and can
be easily realized experimentally. From the study of the superfluid fraction,
the energy gap, and other quantities we identify new zero-temperature phases,
including a localized and a quasi Bose-glass phase, and discuss prospects for
their experimental observation.Comment: 18 pages, 17 figures, using REVTEX
Thermodynamics of Black Holes in Two (and Higher) Dimensions
A comprehensive treatment of black hole thermodynamics in two-dimensional
dilaton gravity is presented. We derive an improved action for these theories
and construct the Euclidean path integral. An essentially unique boundary
counterterm renders the improved action finite on-shell, and its variational
properties guarantee that the path integral has a well-defined semi-classical
limit. We give a detailed discussion of the canonical ensemble described by the
Euclidean partition function, and examine various issues related to stability.
Numerous examples are provided, including black hole backgrounds that appear in
two dimensional solutions of string theory. We show that the Exact String Black
Hole is one of the rare cases that admits a consistent thermodynamics without
the need for an external thermal reservoir. Our approach can also be applied to
certain higher-dimensional black holes, such as Schwarzschild-AdS,
Reissner-Nordstrom, and BTZ.Comment: 63 pages, 3 pdf figures, v2: added reference
Very-high energy gamma-ray astronomy: A 23-year success story in high-energy astroparticle physics
Very-high energy (VHE) gamma quanta contribute only a minuscule fraction -
below one per million - to the flux of cosmic rays. Nevertheless, being neutral
particles they are currently the best "messengers" of processes from the
relativistic/ultra-relativistic Universe because they can be extrapolated back
to their origin. The window of VHE gamma rays was opened only in 1989 by the
Whipple collaboration, reporting the observation of TeV gamma rays from the
Crab nebula. After a slow start, this new field of research is now rapidly
expanding with the discovery of more than 150 VHE gamma-ray emitting sources.
Progress is intimately related with the steady improvement of detectors and
rapidly increasing computing power. We give an overview of the early attempts
before and around 1989 and the progress after the pioneering work of the
Whipple collaboration. The main focus of this article is on the development of
experimental techniques for Earth-bound gamma-ray detectors; consequently, more
emphasis is given to those experiments that made an initial breakthrough rather
than to the successors which often had and have a similar (sometimes even
higher) scientific output as the pioneering experiments. The considered energy
threshold is about 30 GeV. At lower energies, observations can presently only
be performed with balloon or satellite-borne detectors. Irrespective of the
stormy experimental progress, the success story could not have been called a
success story without a broad scientific output. Therefore we conclude this
article with a summary of the scientific rationales and main results achieved
over the last two decades.Comment: 45 pages, 38 figures, review prepared for EPJ-H special issue "Cosmic
rays, gamma rays and neutrinos: A survey of 100 years of research
Classical Stabilization of Homogeneous Extra Dimensions
If spacetime possesses extra dimensions of size and curvature radii much
larger than the Planck or string scales, the dynamics of these extra dimensions
should be governed by classical general relativity. We argue that in general
relativity, it is highly nontrivial to obtain solutions where the extra
dimensions are static and are dynamically stable to small perturbations. We
also illustrate that intuition on equilibrium and stability built up from
non-gravitational physics can be highly misleading. For all static, homogeneous
solutions satisfying the null energy condition, we show that the Ricci
curvature of space must be nonnegative in all directions. Much of our analysis
focuses on a class of spacetime models where space consists of a product of
homogeneous and isotropic geometries. A dimensional reduction of these models
is performed, and their stability to perturbations that preserve the spatial
symmetries is analyzed. We conclude that the only physically realistic examples
of classically stabilized large extra dimensions are those in which the
extra-dimensional manifold is positively curved.Comment: 25 pages; minor changes, improved reference
Towards the Theory of Cosmological Phase Transitions
We discuss recent progress (and controversies) in the theory of finite
temperature phase transitions. This includes the structure of the effective
potential at a finite temperature, the infrared problem in quantum statistics
of gauge fields, the theory of formation of critical and subcritical bubbles
and the theory of bubble wall propagation.Comment: 50 p
- …