1,050 research outputs found
Stationary perturbations and infinitesimal rotations of static Einstein-Yang-Mills configurations with bosonic matter
Using the Kaluza-Klein structure of stationary spacetimes, a framework for
analyzing stationary perturbations of static Einstein-Yang-Mills configurations
with bosonic matter fields is presented. It is shown that the perturbations
giving rise to non-vanishing ADM angular momentum are governed by a
self-adjoint system of equations for a set of gauge invariant scalar
amplitudes. The method is illustrated for SU(2) gauge fields, coupled to a
Higgs doublet or a Higgs triplet. It is argued that slowly rotating black holes
arise generically in self-gravitating non-Abelian gauge theories with bosonic
matter, whereas, in general, soliton solutions do not have rotating
counterparts.Comment: 8 pages, revtex, no figure
The generalization of the Regge-Wheeler equation for self-gravitating matter fields
It is shown that the dynamical evolution of perturbations on a static
spacetime is governed by a standard pulsation equation for the extrinsic
curvature tensor. The centerpiece of the pulsation equation is a wave operator
whose spatial part is manifestly self-adjoint. In contrast to metric
formulations, the curvature-based approach to gravitational perturbation theory
generalizes in a natural way to self-gravitating matter fields. For a certain
relevant subspace of perturbations the pulsation operator is symmetric with
respect to a positive inner product and therefore allows spectral theory to be
applied. In particular, this is the case for odd-parity perturbations of
spherically symmetric background configurations. As an example, the pulsation
equations for self-gravitating, non-Abelian gauge fields are explicitly shown
to be symmetric in the gravitational, the Yang Mills, and the off-diagonal
sector.Comment: 4 pages, revtex, no figure
Perturbation theory for self-gravitating gauge fields I: The odd-parity sector
A gauge and coordinate invariant perturbation theory for self-gravitating
non-Abelian gauge fields is developed and used to analyze local uniqueness and
linear stability properties of non-Abelian equilibrium configurations. It is
shown that all admissible stationary odd-parity excitations of the static and
spherically symmetric Einstein-Yang-Mills soliton and black hole solutions have
total angular momentum number , and are characterized by
non-vanishing asymptotic flux integrals. Local uniqueness results with respect
to non-Abelian perturbations are also established for the Schwarzschild and the
Reissner-Nordstr\"om solutions, which, in addition, are shown to be linearly
stable under dynamical Einstein-Yang-Mills perturbations. Finally, unstable
modes with are also excluded for the static and spherically
symmetric non-Abelian solitons and black holes.Comment: 23 pages, revtex, no figure
Controlled lasing from active optomechanical resonators
Planar microcavities with distributed Bragg reflectors (DBRs) host, besides
confined optical modes, also mechanical resonances due to stop bands in the
phonon dispersion relation of the DBRs. These resonances have frequencies in
the sub-terahertz (10E10-10E11 Hz) range with quality factors exceeding 1000.
The interaction of photons and phonons in such optomechanical systems can be
drastically enhanced, opening a new route toward manipulation of light. Here we
implemented active semiconducting layers into the microcavity to obtain a
vertical-cavity surface-emitting laser (VCSEL). Thereby three resonant
excitations -photons, phonons, and electrons- can interact strongly with each
other providing control of the VCSEL laser emission: a picosecond strain pulse
injected into the VCSEL excites long-living mechanical resonances therein. As a
result, modulation of the lasing intensity at frequencies up to 40 GHz is
observed. From these findings prospective applications such as THz laser
control and stimulated phonon emission may emerge
Sequences of globally regular and black hole solutions in SU(4) Einstein-Yang-Mills theory
SU(4) Einstein-Yang-Mills theory possesses sequences of static spherically
symmetric globally regular and black hole solutions. Considering solutions with
a purely magnetic gauge field, based on the 4-dimensional embedding of
in , these solutions are labelled by the node numbers of
the three gauge field functions , and . We classify the various
types of solutions in sequences and determine their limiting solutions. The
limiting solutions of the sequences of neutral solutions carry charge, and the
limiting solutions of the sequences of charged solutions carry higher charge.
For sequences of black hole solutions with node structure and
, several distinct branches of solutions exist up to critical values
of the horizon radius. We determine the critical behaviour for these sequences
of solutions. We also consider SU(4) Einstein-Yang-Mills-dilaton theory and
show that these sequences of solutions are analogous in most respects to the
corresponding SU(4) Einstein-Yang-Mills sequences of solutions.Comment: 40 pages, 5 tables, 19 Postscript figures, use revtex.st
Influence of Vitis xylem fluid and xylem fluid plus cecropin on growth of Xylella fastidiosa
Colony growth of Xylella fastidiosa (UCLA PD and STL PD strains) was quantified after incubation for 48 h in xylem fluid of Vitis rotundifolia Michx. cv. Noble and Vitis vinifera L. cv. Chardonnay. Xylem fluid was collected from grapevines in the field (dormant and growing season) and from container-grown plants in a screen house (growing season). Colony forming units·ml-1 (cfu·ml-1) were counted 15 d after plating on periwinkle wilt (PW+) medium. Colony growth was promoted or inhibited compared to PW+ medium, and was dependent on X. fastidiosa strain, plant species and source of xylem fluid. The efficacy of cecropin A and B was tested against this bacterium. Colony growth of X. fastidiosa was greatly inhibited after a 1-h-exposure to cecropin A or B. The minimum inhibitory concentration (MIC) of cecropin A or B for 100 % inhibition of X. fastidiosa was < 1 μM. The activity of cecropin B in xylem fluid of V. rotundifolia cv. Noble was progressively reduced over time from 0.2 to 24 h. When 2 and 10 μM concentrations of cecropin A and cecropin B were mixed with xylem fluid for 24 h, a substantial amount of bacterial growth occurred after subsequent plating; shorter time intervals did not degrade the cecropins and did not prevent colony growth. Cecropin B (1 μM) added to xylem fluid of V. rotundifolia cv. Noble and V. vinifera cv. Chardonnay for 24, 48, 72 and 96 h did not prevent subsequent colony growth. Colony number tended to be higher for V. rotundifolia cv. Noble than V. vinifera cv. Chardonnay. Tricine-sodium dodecyl sulphate polyacrylamide gel electrophoresis (Tricine-SDS-PAGE) of cecropin B in xylem fluid showed that cecropin B degraded completely (V. vinifera cv. Chardonnay) or almost completely (V. rotundifolia cv. Noble) after 96 h
Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells
This work has been funded by Russian Scientific Foundation (Grant No. 14-12-01372) and State of Bavaria.We report close to circularly polarized lasing at ћω = 1.473 and 1.522 eV from an AlAs/AlGaAs Bragg microcavity, with 12 GaAs quantum wells in the active region and chirally etched upper distributed Bragg refractor under optical pump at room temperature. The advantage of using the chiral photonic crystal with a large contrast of dielectric permittivities is its giant optical activity, allowing to fabricate a very thin half-wave plate, with a thickness of the order of the emitted light wavelength, and to realize the monolithic control of circular polarization.PostprintPeer reviewe
Cosmological Sphaleron from Real Tunneling and Its Fate
We show that the cosmological sphaleron of Einstein-Yang-Mills system can be
produced from real tunneling geometries. The sphaleron will tend to roll down
to the vacuum or pure gauge field configuration, when the universe evolves in
the Lorentzian signature region with the sphaleron and the corresponding
hypersurface being the initial data for the Yang-Mills field and the universe,
respectively. However, we can also show that the sphaleron, although unstable,
can be regarded as a pseudo-stable solution because its lifetime is even much
greater than those of the universe.Comment: 20 pages, LaTex, article 12pt style, TIT/HEP-242/COSMO-3
Internal Structure of Einstein-Yang-Mills Black Holes
It is shown that a generic black hole solution of the SU(2)
Einstein-Yang-Mills equations develops a new type of an infinitely oscillating
behavior near the singularity. Only for certain discrete values of the event
horizon radius exceptional solutions exist, possessing an inner structure of
the Schwarzschild or Reissner-Nordstrom type.Comment: 4.5 LaTeX pages, 8 eps figures, uses RevTeX, boxedeps.tex. 4 more
typos fixed, a footnote adde
Electroencephalographic source imaging: a prospective study of 152 operated epileptic patients
Electroencephalography is mandatory to determine the epilepsy syndrome. However, for the precise localization of the irritative zone in patients with focal epilepsy, costly and sometimes cumbersome imaging techniques are used. Recent small studies using electric source imaging suggest that electroencephalography itself could be used to localize the focus. However, a large prospective validation study is missing. This study presents a cohort of 152 operated patients where electric source imaging was applied as part of the pre-surgical work-up allowing a comparison with the results from other methods. Patients (n = 152) with >1 year postoperative follow-up were studied prospectively. The sensitivity and specificity of each imaging method was defined by comparing the localization of the source maximum with the resected zone and surgical outcome. Electric source imaging had a sensitivity of 84% and a specificity of 88% if the electroencephalogram was recorded with a large number of electrodes (128–256 channels) and the individual magnetic resonance image was used as head model. These values compared favourably with those of structural magnetic resonance imaging (76% sensitivity, 53% specificity), positron emission tomography (69% sensitivity, 44% specificity) and ictal/interictal single-photon emission-computed tomography (58% sensitivity, 47% specificity). The sensitivity and specificity of electric source imaging decreased to 57% and 59%, respectively, with low number of electrodes (<32 channels) and a template head model. This study demonstrated the validity and clinical utility of electric source imaging in a large prospective study. Given the low cost and high flexibility of electroencephalographic systems even with high channel counts, we conclude that electric source imaging is a highly valuable tool in pre-surgical epilepsy evaluation
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