5,936 research outputs found
On Dirac-like Monopoles in a Lorentz- and CPT-violating Electrodynamics
We study magnetic monopoles in a Lorentz- and CPT-odd electrodynamical
framework in (3+1) dimensions. This is the standard Maxwell model extended by
means of a Chern-Simons-like term, (
constant), which respects gauge invariance but violates both Lorentz and CPT
symmetries (as a consequence, duality is also lost). Our main interest concerns
the analysis of the model in the presence of Dirac monopoles, so that the
Bianchi identity no longer holds, which naively yields the non-conservation of
electric charge. Since gauge symmetry is respected, the issue of charge
conservation is more involved. Actually, the inconsistency may be circumvented,
if we assume that the appearance of a monopole induces an extra electric
current. The reduction of the model to (2+1) dimensions in the presence of both
the magnetic sources and Lorentz-violating terms is presented. There, a
quantization condition involving the scalar remnant of , say, the mass
parameter, is obtained. We also point out that the breaking of duality may be
associated with an asymmetry between electric and magnetic sources in this
background, so that the electromagnetic force experienced by a magnetic pole is
supplemented by an extra term proportional to , whenever compared to the
one acting on an electric charge.Comment: 10 pages, no figures, typed in te
COMPARATIVE ANALYSIS OF THE IAPWS-IF97 FORMULATION PERFORMANCE FOR THERMODYNAMIC PROPERTIES OF WATER ON A RANKINE CYCLE
The present paper presents the computational implementation of the industrial
formulation of the thermodynamic properties of water at liquid and
steam phases, proposed by the International Association for the Properties
of Water and Steam, known as IAPWS-IF97. The validity field extends over
to temperatures T between 0ºC and 800°C, for pressures p up to 100 MPa.
Temperature T, specific volume v, specific enthalpy h, specific entropy s,
specific heat at constant pressure cp and constant volume cv, besides saturation
pressure ps, are calculated having a pair of known input values (p,T),
(p,h) or (p,s). A comparative analysis between the IAPWS-IF97 routines
and others, based on foregoing propositions, from an application on Rankine
cycle, is made. IAPWS-IF97 has proved to be more precise, mainly because
it accounts for the region of compressed liquid, besides requiring less processing
time. The development is carried out as FORTRAN90 subroutines
and functions and is available for public use according to a General Public
License
Benthic macro-invertebrates as indicators of ecological fragility of small rivers ('igarapés') in a bauxite mining region of Brazilian Amazonia
Benthic macroinvertebrate communities were studied in the igarapés Saracá, Caranã and Água Fria near Porto Trombetas, Municipality of Oriximiná, State of Pará, Brazil (1°25' to 1°35'S and 56°15' to 56°W). The main objective was to investigate the potential use of the benthic macroinvertebrates community as indicators of the ecological fragility of the igarapés located in an area of the Amazon basin influenced by bauxite mining. These aquatic ecosystems have low pH (< 4.5); low electrical conductivity (< 90 µS cm-1); low or undetectable total alkalinity; low nutrient concentrations in the sediment, which implies low primary productivity; low species richness; low secondary productivity; and low rates of organic matter decomposition. The benthic macroinvertebrates utilize mainly allochthonous organic matter. Some areas of the ecosystems investigated have been modified by bauxite tailings (especially in their sediment granulometry), by a dam formed by railroad construction (which altered the hydrodynamics and eliminated the terra firma vegetation), and by accidental discharges of various minerals from the railroad traffic and bauxite mining. These factors have drastically modified the local benthic macroinvertebrate communities. The value of benthic macroinvertebrates as indicators of ecological fragility, the health of the ecosystem investigated, and water quality is evaluated
Trinucleon photonuclear reactions with Δ-isobar excitation: Processes below pion-production threshold
Radiative nucleon-deuteron capture and two- and three-body photodisintegration of the three-nucleon bound state are described. The description uses the purely nucleonic charge-dependent CD-Bonn potential and its coupled-channel extension CD Bonn +Δ. The Δ-isobar excitation yields an effective three-nucleon force and effective two- and three-nucleon currents beside other Δ-isobar effects; they are mutually consistent. Exact solutions of three-particle equations are employed for the initial and final states of the reactions. The current has one-baryon and two-baryon contributions and couples nucleonic with Δ-isobar channels. Δ-isobar effects on the observables are isolated. Shortcomings of the theoretical description are discussed and their consequence for the calculation of observables is estimated
One-to-one full scale simulations of laser wakefield acceleration using QuickPIC
We use the quasi-static particle-in-cell code QuickPIC to perform full-scale,
one-to-one LWFA numerical experiments, with parameters that closely follow
current experimental conditions. The propagation of state-of-the-art laser
pulses in both preformed and uniform plasma channels is examined. We show that
the presence of the channel is important whenever the laser self-modulations do
not dominate the propagation. We examine the acceleration of an externally
injected electron beam in the wake generated by 10 J laser pulses, showing that
by using ten-centimeter-scale plasma channels it is possible to accelerate
electrons to more than 4 GeV. A comparison between QuickPIC and 2D OSIRIS is
provided. Good qualitative agreement between the two codes is found, but the 2D
full PIC simulations fail to predict the correct laser and wakefield
amplitudes.Comment: 5 pages, 5 figures, accepted for publication IEEE TPS, Special Issue
- Laser & Plasma Accelerators - 8/200
Antiangiogenic Drugs in Age Related Macular Degeneration: evidence based medicine and off-label use
Direct approach to the problem of strong local minima in Calculus of Variations
The paper introduces a general strategy for identifying strong local
minimizers of variational functionals. It is based on the idea that any
variation of the integral functional can be evaluated directly in terms of the
appropriate parameterized measures. We demonstrate our approach on a problem of
W^{1,infinity} weak-* local minima--a slight weakening of the classical notion
of strong local minima. We obtain the first quasiconvexity-based set of
sufficient conditions for W^{1,infinity} weak-* local minima.Comment: 26 pages, no figure
Tillering Dynamics of \u3ci\u3ePanicum maximum\u3c/i\u3e Jacq. cv. Tanzania-1 After Grazing
Tillering dynamics and tiller dry matter weight from Tanzania grass (Panicum maximum cv. Tanzania-1) were evaluated in two post-grazing stubbles (High Post-grazing Stubble – HPS-3.6 t of DM/ha and Low Post-grazing Stubble – LPS-2.3 t of DM/ha). There was no difference between post-grazing stubbles for decapitated axillary and basal remainder and new axillary tillers. The LPS presented greater number of new basal tillers. The rate of appearance of new basal and axillary tillers decreased with time after grazing. There were differences between the treatments on tiller dry matter weight, and greater values were found in the high post-graze stubble
Treatment of exudative age-related macular degeneration with intravitreal ranibizumab in clinical practice: a 3-year follow-up
PURPOSE:
To evaluate the 36-month efficacy of intravitreal ranibizumab injections for choroidal neovascularization secondary to age-related macular degeneration (AMD) in real world clinical practice.
METHODS:
Retrospective study involving 84 eyes of 77 patients; 52 eyes completed 3 years of follow-up. Subjects were observed initially on a monthly basis and with extended follow-up intervals if signs of quiescence were detected, according to an established protocol. A comprehensive ophthalmologic examination was performed, including best-corrected visual acuity (BCVA) determined with Early Treatment Diabetic Retinopathy Study charts, stereoscopic macular biomicroscopy and optical coherence tomography (OCT) with fluorescein angiography and indocyanine green angiography if considered necessary. Treatment was given if signs of active lesions were present.
RESULTS:
The mean baseline BCVA was 49.33 and 49.52 letters at the 36-month visit. The average of treatments was 8.6 at 3 years. At this time point, 77% of treated eyes stabilized or improved their vision (VA loss ≤ 5 letters). A predictive value for better VA was found for younger age, better baseline VA, good response on OCT and more frequent treatments.
CONCLUSION:
At 3 years, intravitreal ranibizumab is able to maintain baseline VA in exudative AMD patients, with a reduced number of injections, but not to show VA improvement, in clinical practice.info:eu-repo/semantics/publishedVersio
- …