1,020 research outputs found
Cool Stars and Space Weather
Stellar flares, winds and coronal mass ejections form the space weather. They
are signatures of the magnetic activity of cool stars and, since activity
varies with age, mass and rotation, the space weather that extra-solar planets
experience can be very different from the one encountered by the solar system
planets. How do stellar activity and magnetism influence the space weather of
exoplanets orbiting main-sequence stars? How do the environments surrounding
exoplanets differ from those around the planets in our own solar system? How
can the detailed knowledge acquired by the solar system community be applied in
exoplanetary systems? How does space weather affect habitability? These were
questions that were addressed in the splinter session "Cool stars and Space
Weather", that took place on 9 Jun 2014, during the Cool Stars 18 meeting. In
this paper, we present a summary of the contributions made to this session.Comment: Proceedings of the 18th Cambridge Workshop on Cool Stars, Stellar
Systems, and the Sun, Eds G. van Belle & H. Harris, 13 pages, 1 figur
FÖRSTER TRANSFER CALCULATIONS BASED ON CRYSTAL STRUCTURE DATA FROM Agmenellum quadruplicatum C-PHYCOCYANIN
Excitation energy transfer in C-phycocyanin is modeled using the Forster inductive resonance mechanism. Detailed calculations are carried out using coordinates and orientations of the chromophores derived from X-ray crystallographic studies of C-phycocyanin from two different species (Schirmer et al, J. Mol. Biol. 184, 257–277 (1985) and ibid., 188, 651-677 (1986)). Spectral overlap integrals are estimated from absorption and fluorescence spectra of C-phycocyanin of Mastigocladus laminosus and its separated subunits. Calculations are carried out for the β-subunit, αβ-monomer, (αβ)3-trimer and (αβ)0-hexamer species with the following chromophore assignments: β155 = 's’(sensitizer), β84 =‘f (fluorescer) and α84 =‘m’(intermediate):]:. The calculations show that excitation transfer relaxation occurs to 3=98% within 200 ps in nearly every case; however, the rates increase as much as 10-fold for the higher aggregates. Comparison with experimental data on fluorescence decay and depolarization kinetics from the literature shows qualitative agreement with these calculations. We conclude that Forster transfer is sufficient to account for all of the observed fluorescence properties of C-phycocyanin in aggregation states up to the hexamer and in the absence of linker polypeptides
Optical Properties of Superconducting Nanowire Single-Photon Detectors
We measured the optical absorptance of superconducting nanowire single photon
detectors. We found that 200-nm-pitch, 50%-fill-factor devices had an average
absorptance of 21% for normally-incident front-illumination of
1.55-um-wavelength light polarized parallel to the nanowires, and only 10% for
perpendicularly-polarized light. We also measured devices with lower
fill-factors and narrower wires that were five times more sensitive to
parallel-polarized photons than perpendicular-polarized photons. We developed a
numerical model that predicts the absorptance of our structures. We also used
our measurements, coupled with measurements of device detection efficiencies,
to determine the probability of photon detection after an absorption event. We
found that, remarkably, absorbed parallel-polarized photons were more likely to
result in detection events than perpendicular-polarized photons, and we present
a hypothesis that qualitatively explains this result. Finally, we also
determined the enhancement of device detection efficiency and absorptance due
to the inclusion of an integrated optical cavity over a range of wavelengths
(700-1700 nm) on a number of devices, and found good agreement with our
numerical model.Comment: will appear in optics express with minor revision
Low-energy muon-transfer reaction from hydrogen isotopes to helium isotopes
Direct muon transfer in low-energy collisions of the muonic hydrogen H
and helium (He) is considered in a three-body quantum-mechanical
framework of coordinate-space integro-differential Faddeev-Hahn-type equations
within two- and six-state close coupling approximations. The final-state
Coulomb interaction is treated without any approximation employing appropriate
Coulomb waves in the final state. The present results agree reasonably well
with previous semiclassical calculations.Comment: 4 revtex4 page
Evolution of the progenitor binary of V1309 Scorpii before merger
It was recently demonstrated that the eruption of V1309 Sco was a result of a
merger of the components of a cool contact binary. We computed a set of
evolutionary models of the detached binaries with different initial parameters
to compare it with pre-burst observations of V1309 Sco. The models are based on
our recently developed evolutionary model of the formation of cool contact
binaries. The best agreement with observations was obtained for binaries with
initial masses of 1.8-2.0 solar masses and initial periods of 2.5-3.1 d. The
evolution of these binaries consists of three phases: at first the binary is
detached and both components lose mass and angular momentum through a
magnetized wind. This takes almost two thirds of the total evolutionary
lifetime. The remaining third is spent in a semi-detached configuration of the
Algol-type, following the Roche-lobe overflow by the initially more massive
component. When the other component leaves the main sequence and moves toward
the giant branch, a contact configuration is formed for a short time, followed
by the coalescence of both components.Comment: 5 pages, 1 figure, Astronomy and Astrophysics, in prin
The Chiral Phase Transition in Dissipative Dynamics
Numerical simulations of the chiral phase transition in the (3+1)dimensional
O(4)-model are presented. The evolutions of the chiral field follow purely
dissipative dynamics, starting from random chirally symmetric initial
configurations down to the true vacuum with spontaneously broken symmetry. The
model stabilizes topological textures which are formed together with domains of
disoriented chiral condensate (DCC) during the roll-down phase. The classically
evolving field acts as source for the emission of pions and mesons.
The exponents of power laws for the growth of angular correlations and for
emission rates are extracted. Fluctuations in the abundance ratios for neutral
and charged pions are compared with those for uncorrelated sources as potential
signature for the chiral phase transition after heavy-ion collisions. It is
found that the presence of stabilizing textures (baryons and antibaryons)
prevents sufficiently rapid growth of DCC-domain size, so observability of
anomalous tails in the abundance ratios is unlikely. However, the transient
formation of growing DCC domains causes sizable broadening of the distributions
as compared to the statistical widths of generic sources.Comment: 28 pages, 8 figure
Broadband mid-IR frequency comb with CSP and AGS from a Er,Tm:Ho fiber laser
We report on the generation of a 2500 nm bandwidth frequency comb at 6.5 μm central wavelength based on critically phase-matched parametric down-conversion in the nonlinear crystal
CdSiP
2
CdSiP2
(CSP), driven by a compact Er,Tm:Ho fiber laser. The generated ultra-broadband pulses show a transform-limited duration of 2.3 optical cycles and carry up to 150 pJ of energy at a 100 MHz pulse repetition rate. For comparison, the spectrum generated in
AgGaS
2
AgGaS2
(AGS) spans from 6.2 to 7.4 μm at full-width at half-maximum (FWHM) with a pulse energy of 3 pJ. A full 3D nonlinear wave propagation code is used for optimization of the noncollinear angle, propagation direction, and crystal thickness.Peer ReviewedPostprint (author's final draft
DCC Dynamics in (2+1)D-O(3) model
The dynamics of symmetry-breaking after a quench is numerically simulated on
a lattice for the (2+1)-dimensional O(3) model. In addition to the standard
sigma-model with temperature-dependent Phi^4-potential the energy functional
includes a four-derivative current-current coupling to stabilize the size of
the emerging extended topological textures. The total winding number can be
conserved by constraint. As a model for the chiral phase transition during the
cooling phase after a hadronic collision this allows to investigate the
interference of 'baryon-antibaryon' production with the developing disoriented
aligned domains. The growth of angular correlations, condensate, average
orientation is studied in dependence of texture size, quench rate, symmetry
breaking. The classical dissipative dynamics determines the rate of energy
emitted from the relaxing source for each component of the 3-vector field which
provides a possible signature for domains of Disoriented Chiral Condensate. We
find that the 'pions' are emitted in two distinct pulses; for sufficiently
small lattice size the second one carries the DCC signal, but it is strongly
suppressed as compared to simultaneous 'sigma'-meson emission. We compare the
resulting anomalies in the distributions of DCC pions with probabilities
derived within the commonly used coherent state formalism.Comment: 27 pages, 17 figures; several minor insertions in the text; two
references adde
Theories for multiple resonances
Two microscopic theories for multiple resonances in nuclei are compared,
n-particle-hole RPA and quantized Time-Dependent Hartree-Fock (TDHF). The
Lipkin-Meshkov-Glick model is used as test case. We find that quantized TDHF is
superior in many respects, except for very small systems.Comment: 14 Pages, 3 figures available upon request
Основні закономірності зародження і росту втомних тріщин в алюмінієвих пластинах із зміцненими отворами
The method of modeling stress-strain state for holes burnishing using FEM has been
analyzed. A series of fatigue tests were carried out using plates containing plain holes and cold
expanded holes in aluminium For various diameters of holes and cold expansion degree there exists
a certain correlation between the stress range or maximum stress on the edge of hole on the entrance
face of plate and lifetime of fatigue crack initiation
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