3,665 research outputs found
Discovery of Solar Rieger Periodicities in Another Star
The Rieger periods are solar cycles with a time scale of months, which are
present in both flaring activity and sunspot occurrence. These short-term
periodicities, tentatively explained by equatorially trapped Rossby-type waves
modulating the emergence of magnetic flux at the surface, are considered a
peculiar and not yet fully understood solar phenomenon. We chose a stellar
system with solar characteristics, UX Arietis, and performed a timing analysis
of two 9-year datasets of radio and optical observations. The analysis reveals
a 294-day cycle. When the two 9-year datasets are folded with this period, a
synchronization of the peak of the optical light curve (i.e., the minimum spot
coverage) with the minimum radio flaring activity is observed. This close
relationship between two completly independent curves makes it very likely that
the 294-day cycle is real. We conclude that the process invoked for the Sun of
a periodical emergence of magnetic flux may also be applied to UX Arietis and
can explain the cyclic flaring activity triggered by interactions between
successive cyclic emergences of magnetic flux.Comment: 4 Pages, 1 table, 3 figures (quality of Fig. 1 degraded to match the
requested size), needs aa.cls, accepted to be published as a letter in
Astronomy & Astrophysic
LUNCHEON ADDRESS [on telecommunications] TO THE US COUNCIL FOR INTERNATIONAL BUSINESS by M. CARPENTIER, DIRECTOR-GENERAL INFORMATION TECHNOLOGIES AND TELECOMMUNICATIONS TASK FORCE COMMISSION OF THE EUROPEAN COMMUNITIES. Washington D.C., 15 April 1986
Stability of the Bragg glass phase in a layered geometry
We study the stability of the dislocation-free Bragg glass phase in a layered
geometry consisting of coupled parallel planes of d=1+1 vortex lines lying
within each plane, in the presence of impurity disorder. Using renormalization
group, replica variational calculations and physical arguments we show that at
temperatures the 3D Bragg glass phase is always stable for weak
disorder. It undergoes a weakly first order transition into a decoupled 2D
vortex glass upon increase of disorder.Comment: RevTeX. Submitted to EP
Dephasing due to nonstationary 1/f noise
Motivated by recent experiments with Josephson qubits we propose a new
phenomenological model for 1/f noise due to collective excitations of
interacting defects in the qubit's environment. At very low temperatures the
effective dynamics of these collective modes are very slow leading to
pronounced non-Gaussian features and nonstationarity of the noise. We analyze
the influence of this noise on the dynamics of a qubit in various regimes and
at different operation points. Remarkable predictions are absolute time
dependences of a critical coupling and of dephasing in the strong coupling
regime.Comment: 4 pages, 2 figures, to be published in the proceedings of the Vth
Rencontres de Moriond in Mesoscopic Physic
Glass phases of flux lattices in layered superconductors
We study a flux lattice which is parallel to superconducting layers, allowing
for dislocations and for disorder of both short wavelength and long wavelength.
We find that the long wavelength disorder has a significant effect on the phase
diagram -- it produces a first order transition within the Bragg glass phase
and leads to melting at strong disorder. This then allows a Friedel scenario of
2D superconductivity.Comment: 5 pages, 1 eps figure, Revte
Some algebraic properties of differential operators
First, we study the subskewfield of rational pseudodifferential operators
over a differential field K generated in the skewfield of pseudodifferential
operators over K by the subalgebra of all differential operators.
Second, we show that the Dieudonne' determinant of a matrix
pseudodifferential operator with coefficients in a differential subring A of K
lies in the integral closure of A in K, and we give an example of a 2x2 matrix
differential operator with coefficients in A whose Dieudonne' determiant does
not lie in A.Comment: 15 page
Superoxide reductase from Giardia intestinalis: structural characterization of the first sor from a eukaryotic organism shows an iron centre that is highly sensitive to photoreduction
Superoxide reductase (SOR), which is commonly found in prokaryotic organisms, affords protection from oxidative stress by reducing the superoxide anion to hydrogen peroxide. The reaction is catalyzed at the iron centre, which is highly conserved among the prokaryotic SORs structurally characterized to date. Reported here is the first structure of an SOR from a eukaryotic organism, the protozoan parasite Giardia intestinalis (GiSOR), which was solved at 2.0 Ã… resolution. By collecting several diffraction data sets at 100 K from the same flash-cooled protein crystal using synchrotron X-ray radiation, photoreduction of the iron centre was observed. Reduction was monitored using an online UV-visible microspectrophotometer, following the decay of the 647 nm absorption band characteristic of the iron site in the glutamate-bound, oxidized state. Similarly to other 1Fe-SORs structurally characterized to date, the enzyme displays a tetrameric quaternary-structure arrangement. As a distinctive feature, the N-terminal loop of the protein, containing the characteristic EKHxP motif, revealed an unusually high flexibility regardless of the iron redox state. At variance with previous evidence collected by X-ray crystallography and Fourier transform infrared spectroscopy of prokaryotic SORs, iron reduction did not lead to dissociation of glutamate from the catalytic metal or other structural changes; however, the glutamate ligand underwent X-ray-induced chemical changes, revealing high sensitivity of the GiSOR active site to X-ray radiation damage
Dephasing by a nonstationary classical intermittent noise
We consider a new phenomenological model for a classical
intermittent noise and study its effects on the dephasing of a two-level
system. Within this model, the evolution of the relative phase between the
states is described as a continuous time random walk (CTRW). Using
renewal theory, we find exact expressions for the dephasing factor and identify
the physically relevant various regimes in terms of the coupling to the noise.
In particular, we point out the consequences of the non-stationarity and
pronounced non-Gaussian features of this noise, including some new anomalous
and aging dephasing scenarii.Comment: Submitted to Phys. Rev.
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