7,871 research outputs found
Quantum-Mechanical Detection of Non-Newtonian Gravity
In this work the possibility of detecting the presence of a Yukawa term, as
an additional contribution to the usual Newtonian gravitational potential, is
introduced. The central idea is to analyze the effects at quantum level
employing interference patterns (at this respect the present proposal resembles
the Colella, Overhauser and Werner experiment), and deduce from it the possible
effects that this Yukawa term could have. We will prove that the corresponding
interference pattern depends on the phenomenological parameters that define
this kind of terms. Afterwards, using the so called restricted path integral
formalism, the case of a particle whose position is being continuously
monitored, is analyzed, and the effects that this Yukawa potential could have
on the measurement outputs are obtained. This allows us to obtain another
scheme that could lead to the detection of these terms. This last part also
renders new theoretical predictions that could enable us to confront the
restricted path integral formalism against some future experiments.Comment: 17 pages, accepted in International Journal of Modern Physics
Fluid--Gravity Correspondence under the presence of viscosity
The present work addresses the analogy between the speed of sound of a
viscous, barotropic, and irrotational fluid and the equation of motion for a
non--massive field in a curved manifold. It will be shown that the presence of
viscosity implies the introduction, into the equation of motion of the
gravitational analogue, of a source term which entails the flow of energy from
the non--massive field to the curvature of the spacetime manifold. The
stress-energy tensor is also computed and it is found not to be constant, which
is consistent with such energy interchange
Ultra-broadband photon pair preparation by spontaneous four wave mixing in dispersion-engineered optical fiber
We present a study of the spectral properties of photon pairs generated
through the process of spontaneous four wave mixing (SFWM) in single mode
fiber. Our analysis assumes narrowband pumps, which are allowed to be
frequency-degenerate or non-degenerate. Based on this analysis, we derive
conditions on the pump frequencies and on the fiber dispersion parameters which
guarantee the generation of ultra-broadband photon pairs. Such photon pairs are
characterized by: i) a very large degree of entanglement, and ii) a very high
degree of temporal synchronization between the signal and idler photons.
Through a numerical exercise, we find that the use of photonic crystal fiber
(PCF) facilitates the fulfilment of the conditions for ultra-broadband photon
pair generation; in particular, the spectral region in which emission occurs
can be adjusted to particular needs through an appropriate choice of the PCF
parameters. In addition, we present a novel quantum interference effect,
resulting from indistinguishable pathways to the same outcome, which can occur
when pumping a SFWM source with multiple spectral lines.Comment: 15 pages, 10 figures. To be published in Phys. Rev.
Mean Area of Self-Avoiding Loops
The mean area of two-dimensional unpressurised vesicles, or self-avoiding
loops of fixed length , behaves for large as , while their
mean square radius of gyration behaves as . The amplitude ratio
is computed exactly and found to equal . The physics of the
pressurised case, both in the inflated and collapsed phases, may be usefully
related to that of a complex O(n) field theory coupled to a U(1) gauge field,
in the limit .Comment: 12 pages, plain TeX, (one TeX macro omission corrected
Entropic Barriers, Frustration and Order: Basic Ingredients in Protein Folding
We solve a model that takes into account entropic barriers, frustration, and
the organization of a protein-like molecule. For a chain of size , there is
an effective folding transition to an ordered structure. Without frustration,
this state is reached in a time that scales as , with
. This scaling is limited by the amount of frustration which
leads to the dynamical selectivity of proteins: foldable proteins are limited
to monomers; and they are stable in {\it one} range of temperatures,
independent of size and structure. These predictions explain generic properties
of {\it in vivo} proteins.Comment: 4 pages, 4 Figures appended as postscript fil
Bogoliubov space of a Bose--Einstein condensate and quantum spacetime fluctuations
In the present work we consider the role that metric fluctuations could have
upon the properties of a Bose--Einstein condensate. In particular we consider
the Bogoliubov space associated to it and show that there are, at least, two
independent ways in which the average size of these metric fluctuations could
be, experimentally, determined. Indeed, we prove that the pressure and the
speed of sound of the ground state define an expression allowing us to
determine the average size of these fluctuations. Afterwards, an
interferometric experiment involving Bogoliubov excitations of the condensate
and the pressure (or the speed of sound of the ground state) provides a second
and independent way in which this average size could be determined,
experimentally
GPCR-OKB: the G protein coupled receptor oligomer knowledge base
Rapid expansion of available data about G Protein Coupled Receptor (GPCR) dimers/oligomers over the past few years requires an effective system to organize this information electronically. Based on an ontology derived from a community dialog involving colleagues using experimental and computational methodologies, we developed the GPCR-Oligomerization Knowledge Base (GPCR-OKB). GPCR-OKB is a system that supports browsing and searching for GPCR oligomer data. Such data were manually derived from the literature. While focused on GPCR oligomers, GPCR-OKB is seamlessly connected to GPCRDB, facilitating the correlation of information about GPCR protomers and oligomers
Synthesis and characterization of nanocrystalline cellulose derived from Pineapple peel residues
Pineapple peel biomass was used as raw material for nanocellulose extraction. The raw material is a residue from the Costa Rican fruit industry. The nanocellulose was obtained by a two-step hydrolysis process. Firstly, the cellulose was hydrolyzed with HCl to obtain microcrystalline cellulose. In the second step, the hydrolysis was carried out using H2SO4 to obtain smaller fragments and decrease the lignin content. A time-dependent study was carried out to determine the particle size decrease depending on the contact time with the H2SO4. The chemical, thermal and morphological properties were analyzed by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), zeta potential, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The nanofiber-like cellulose was obtained after 60 minutes of exposure to 65 wt% H2SO4
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