53,770 research outputs found
Evolving wormhole geometries within nonlinear electrodynamics
In this work, we explore the possibility of evolving (2+1) and
(3+1)-dimensional wormhole spacetimes, conformally related to the respective
static geometries, within the context of nonlinear electrodynamics. For the
(3+1)-dimensional spacetime, it is found that the Einstein field equation
imposes a contracting wormhole solution and the obedience of the weak energy
condition. Nevertheless, in the presence of an electric field, the latter
presents a singularity at the throat, however, for a pure magnetic field the
solution is regular. For the (2+1)-dimensional case, it is also found that the
physical fields are singular at the throat. Thus, taking into account the
principle of finiteness, which states that a satisfactory theory should avoid
physical quantities becoming infinite, one may rule out evolving
(3+1)-dimensional wormhole solutions, in the presence of an electric field, and
the (2+1)-dimensional case coupled to nonlinear electrodynamics.Comment: 17 pages, 1 figure; to appear in Classical and Quantum Gravity. V2:
minor corrections, including a referenc
On the Interpretation of the Atmospheric Neutrino Data in Terms of Flavor Changing Neutrino Interactions
Flavour changing (FC) neutrino-matter interactions have been proposed as a
solution to the atmospheric neutrino anomaly. Here we perform the analysis of
the full set of the recent 52 kTy Super-Kamiokande atmospheric neutrino data,
including the zenith angle distribution of the contained events as well as the
higher energy upward-going stopping and through-going muon events. Our results
show that the FC mechanism can describe the full data sample with a
chi^2_{min}=44/(33 d.o.f) which is acceptable at the 90% confidence level. The
combined analysis confines the amount of FC to be either close to maximal or to
the level of about (10-50)%.Comment: 15 pages, 4 Postscript figures, uses ReVTeX. Updated analysis to 52
kTy Super-Kamiokande data. A new figure for the up-down asymmetry is
included. Some comments and references are adde
Subtraction of temperature induced phase noise in the LISA frequency band
Temperature fluctuations are expected to be one of the limiting factors for
gravitational wave detectors in the very low frequency range. Here we report
the characterisation of this noise source in the LISA Pathfinder optical bench
and propose a method to remove its contribution from the data. Our results show
that temperature fluctuations are indeed limiting our measurement below one
millihertz, and that their subtraction leads to a factor 5.6 (15 dB) reduction
in the noise level at the lower end of the LISA measurement band 10^{-4} Hz,
which increases to 20.2 (26 dB) at even lower frequencies, i.e., 1.5x10^{-5}
Hz. The method presented here can be applied to the subtraction of other noise
sources in gravitational wave detectors in the general situation where multiple
sensors are used to characterise the noise source.Comment: 8 pages, 6 figure
Manipulation and Generation of Supercurrent in Out-of-Equilibrium Josephson Tunnel Nanojunctions
We demonstrate experimentally manipulation of supercurrent in Al-AlO_x-Ti
Josephson tunnel junctions by injecting quasiparticles in a Ti island from two
additional tunnel-coupled Al superconducting reservoirs. Both supercurrent
enhancement and quenching with respect to equilibrium are achieved. We
demonstrate cooling of the Ti line by quasiparticle injection from the normal
state deep into the superconducting phase. A model based on heat transport and
non-monotonic current-voltage characteristic of a Josephson junction
satisfactorily accounts for our findings.Comment: 4 pages, 4 colour figures, published versio
A proposal of sensitive indicators of the rehabilitation nursing care of people in the surgical process, to be included in the ontology of aging
Given the complex surgical scenario observed today, it is necessary to change the urgent definition of a specific ontology, especially in terms of aging. The interventions of the Specialist Nurse in Rehabilitation Nursing to the person in the surgical process are primordial for the maintenance of the functional capacities, prevention of complications and impediment of incapacities. However, it is necessary to provide individualized and fostered care in a practice of excellence, and the consequent organized reading of records of an aging ontology for decision making on rehabilitation indicators. Method: a systematic review of the literature was carried out using the EBSCO host (MEDLINE with Full Text, CINAHL Plus with Full Text and MedicLatina), using the PI [C] O method, and 11 articles were selected. Results: 41 indicators were identified to be included in the ontology classes of aging: pain control, patient and family education, support and communication, reduction of postoperative complications, gain of functionality, restoration of physical function, mobility, multidisciplinary intervention and the frequency of interventions. Conclusion: it is considered that it was imperative to identify sensitive indicators for rehabilitation nursing care, based on scientific evidence and thus provide an opportunity for nurses to reflect on their daily practices and conduct their actions towards excellence in care, to propose a set of 41 classes internationally on the ontology of aging
Traversable wormholes coupled to nonlinear electrodynamics
In this work we explore the possible existence of static, spherically
symmetric and stationary, axisymmetric traversable wormholes coupled to
nonlinear electrodynamics. Considering static and spherically symmetric (2+1)
and (3+1)-dimensional wormhole spacetimes, we verify the presence of an event
horizon and the non-violation of the null energy condition at the throat. For
the former spacetime, the principle of finiteness is imposed, in order to
obtain regular physical fields at the throat. Next, we analyze the
(2+1)-dimensional stationary and axisymmetric wormhole, and also verify the
presence of an event horizon, rendering the geometry non-traversable.
Relatively to the (3+1)-dimensional stationary and axisymmetric wormhole
geometry, we find that the field equations impose specific conditions that are
incompatible with the properties of wormholes. Thus, we prove the non-existence
of the general class of traversable wormhole solutions, outlined above, within
the context of nonlinear electrodynamics.Comment: 9 pages, Revtex4. V2: major change in title; considerable additions
in the Introduction and in the rotating solution, no physics changes;
correction of a reference, one reference added; now 10 pages. This version to
appear in Classical and Quantum Gravit
Resonances in a trapped 3D Bose-Einstein condensate under periodically varying atomic scattering length
Nonlinear oscillations of a 3D radial symmetric Bose-Einstein condensate
under periodic variation in time of the atomic scattering length have been
studied analytically and numerically. The time-dependent variational approach
is used for the analysis of the characteristics of nonlinear resonances in the
oscillations of the condensate. The bistability in oscillations of the BEC
width is invistigated. The dependence of the BEC collapse threshold on the
drive amplitude and parameters of the condensate and trap is found. Predictions
of the theory are confirmed by numerical simulations of the full
Gross-Pitaevski equation.Comment: 17 pages, 10 figures, submitted to Journal of Physics
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