30,703 research outputs found
Regularization of Vertical-Cavity Surface-Emitting Lasers emission by periodic non-Hermitian potentials
We propose a novel physical mechanism based on periodic non-Hermitian
potentials to efficiently control the complex spatial dynamics of broad-area
lasers, particularly in Vertical-Cavity Surface-Emitting Lasers (VCSELs),
achieving a stable emission of maximum brightness. Radially dephased periodic
refractive index and gain-loss modulations accumulate the generated light from
the entire active layer and concentrate it around the structure axis to emit
narrow, bright beams. The effect is due to asymmetric-inward radial coupling
between transverse modes, for particular phase differences of the refractive
index and gain-loss modulations. Light is confined into a central beam with
large intensity opening the path to design compact, bright and efficient
broad-area light sources. We perform a comprehensive analysis to explore the
maximum central intensity enhancement and concentration regimes. The study
reveals that the optimum schemes are those holding unidirectional inward
coupling but not fulfilling a perfect local PT-symmetry.Comment: 4 pages, 4 figure
Fourth-generation SM imprints in B -> K^*l^+l^- decays with polarized K^*
The implication of the fourth-generation quarks in the B -> K^*l^+l^-
(l=mu,tau) decays, when K^* meson is longitudinally or transversely polarized,
is presented. In this context, the dependence of the branching ratio with
polarized K^* and the helicity fractions (f_{L,T}) of K^* meson are studied. It
is observed that the polarized branching ratios as well as helicity fractions
are sensitive to the NP parameters, especially when the final state leptons are
tauons. Hence the measurements of these observables at LHC can serve as a good
tool to investigate the indirect searches of new physics beyond the Standard
Model.Comment: 13 pages, 10 figures, V2: some of the graphs are modified according
to the new data from recent experiments. arXiv admin note: substantial text
overlap with arXiv:1107.569
Practical Broad-Band Tuning of Dye Lasers by Solvent Shifting
We have operated a dye laser over a broad wavelength range (593.8-667.0nm) by shifting the dye emission profile with incremental changes of solvent composition. This was accomplished with the laser operating continuously, and only minor adjustment of the laser optics was required. Solvent tuning was facilitated by the critical dependence of the optimum laser wavelength on concentration of the second solvent. Using the known solvent-sensitive laser dye 9-diethylaminobenzo[a]phenoxaz-5-one (DBP), 87% of the tuning range from pure xylenes to pure methanol was covered by cumulative addition of 24 vol. % methanol to the starting xylenes solution. The optimum dye concentration was found to be independent of solvent composition, so that maximum laser power could be maintained by mixing equimolar dye solutions in the two solvents. These results establish the practicality of solvent-tuning as a method of conducting laser experiments over a broad wavelength range
Formal Availability Analysis using Theorem Proving
Availability analysis is used to assess the possible failures and their
restoration process for a given system. This analysis involves the calculation
of instantaneous and steady-state availabilities of the individual system
components and the usage of this information along with the commonly used
availability modeling techniques, such as Availability Block Diagrams (ABD) and
Fault Trees (FTs) to determine the system-level availability. Traditionally,
availability analyses are conducted using paper-and-pencil methods and
simulation tools but they cannot ascertain absolute correctness due to their
inaccuracy limitations. As a complementary approach, we propose to use the
higher-order-logic theorem prover HOL4 to conduct the availability analysis of
safety-critical systems. For this purpose, we present a higher-order-logic
formalization of instantaneous and steady-state availability, ABD
configurations and generic unavailability FT gates. For illustration purposes,
these formalizations are utilized to conduct formal availability analysis of a
satellite solar array, which is used as the main source of power for the Dong
Fang Hong-3 (DFH-3) satellite.Comment: 16 pages. arXiv admin note: text overlap with arXiv:1505.0264
South and South-East Asian coastal fisheries: their status and directions for improved management: conference synopsis and recommendations
As a step to address the problems of coastal fisheries in Asia, the WorldFish Center joined forces with fisheries agencies from eight developing Asian countries (Bangladesh, India, Indonesia, Malaysia, The Philippines, Sri Lanka, Thailand and Vietnam) and the Asian Development Bank, to implement a project entitled “Sustainable Management of Coastal Fish Stocks in Asia” (also known as the “TrawlBase” project). The project was implemented between 1998 and 2001. The main achievements of this partnership were: (a) Development of a database called “Fisheries Resource Information System and Tools” (FiRST), which contains trawl research survey data and socioeconomic information for selected fisheries, and facilitates its analysis; (b) Evaluation of the extent of resource decline and over-fishing, both biological and economic, in the region; (c) Identification of the measures needed to manage coastal fisheries in the participating countries, resulting in draft strategies and action plans; and (d) Strengthening of national capacity in coastal fisheries assessment, planning and management
Hawking Radiation of Dirac Particles in a Variable-mass Kerr Space-time
Hawking effect of Dirac particles in a variable-mass Kerr space-time is
investigated by using a method called as the generalized tortoise coordinate
transformation. The location and the temperature of the event horizon of the
non-stationary Kerr black hole are derived. It is shown that the temperature
and the shape of the event horizon depend not only on the time but also on the
angle. However, the Fermi-Dirac spectrum displays a residual term which is
absent from that of Bose-Einstein distribution.Comment: 12 pages in 12pt Revtex, no figure, to appear in Gen. Rel. Grav.
Vol.33, No.7 (2001
Entropy of Rotating Misner String Spacetimes
Using a boundary counterterm prescription motivated by the AdS/CFT
conjecture, I evaluate the energy, entropy and angular momentum of the class of
Kerr-NUT/bolt-AdS spacetimes. As in the non-rotating case, when the NUT charge
is nonzero the entropy is no longer equal to one-quarter of the area due to the
presence of the Misner string. When the cosmological constant is also non-zero,
the entropy is bounded from above.Comment: Revtex, 9 pages, 3 figure
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