Time-resolved carrier dynamics and electron-phonon coupling strength in proximized weak ferromagnet-superconductor nanobilayers

We present our femtosecond optical pump-probe studies of proximized ferromagnet-superconductor nanobilayers. The weak ferromagnetic nature of a thin NiCu film makes it possible to observe the dynamics of the nonequilibrium carriers through the near-surface optical reflectivity change measurements. The subpicosecond biexponential reflectivity decay has been identified as electron-phonon Debye and acoustic phonon relaxation times, and the decay of Debye phonons versus temperature dependence was used to evaluate the electron-phonon coupling constants for both the pure Nb and proximized Nb/NiCu heterostructures down to low temperatures. We have also demonstrated that the NiCu overlay on top of Nb dramatically reduced the slow, bolometric component of the photoresponse component, making such bilayers attractive for future radiation detector applications

Confinement and the center of the gauge group

The question of the role of the center of the gauge group in the phenomenon of confinement in Yang-Mills theory is addressed. The investigation is performed from the most general perspective of considering all possible choices for the gauge symmetry group. In this context, an interesting role is played by G(2) Yang-Mills theory: the simplest pure gauge theory with a trivial center and without 't Hooft flux vortices. Numerical simulations show the presence of a first order finite temperature deconfinement phase transition in G(2) Yang-Mills theory in (3+1) dimensions. Interestingly, the G(2) gauge symmetry can be broken to an SU(3) subgroup by the Higgs mechanism. We investigate the relation between the deconfinement phase transition in G(2) and SU(3) Yang-Mills theories by numerical simulations in the G(2) gauge-Higgs system.Comment: Plenary talk at 23rd International Symposium on Lattice Field Theory: Lattice 2005, Trinity College, Dublin, Ireland, 25-30 Jul 200

Laplacian gauge and instantons

We exhibit the connection between local gauge singularities in the Laplacian gauge and topological charge, which opens the possibility of studying instanton excitations without cooling. We describe our version of Laplacian gauge-fixing for SU(N).Comment: Lattice 2000 (Topology and Vacuum), 4 pages, 3 figures -- cosmetic change

Color Screening, Casimir Scaling, and Domain Structure in G(2) and SU(N) Gauge Theories

We argue that screening of higher-representation color charges by gluons implies a domain structure in the vacuum state of non-abelian gauge theories, with the color magnetic flux in each domain quantized in units corresponding to the gauge group center. Casimir scaling of string tensions at intermediate distances results from random spatial variations in the color magnetic flux within each domain. The exceptional G(2) gauge group is an example rather than an exception to this picture, although for G(2) there is only one type of vacuum domain, corresponding to the single element of the gauge group center. We present some numerical results for G(2) intermediate string tensions and Polyakov lines, as well as results for certain gauge-dependent projected quantities. In this context, we discuss critically the idea of projecting link variables to a subgroup of the gauge group. It is argued that such projections are useful only when the representation-dependence of the string tension, at some distance scale, is given by the representation of the subgroup.Comment: 24 pages, 14 figures; v2: references added; v3: published version containing some additional introductory discussio

Advanced Software Techniques for Data Management Systems. Volume 2: Space Shuttle Flight Executive System: Functional Design

A functional design of software executive system for the space shuttle avionics computer is presented. Three primary functions of the executive are emphasized in the design: task management, I/O management, and configuration management. The executive system organization is based on the applications software and configuration requirements established during the Phase B definition of the Space Shuttle program. Although the primary features of the executive system architecture were derived from Phase B requirements, it was specified for implementation with the IBM 4 Pi EP aerospace computer and is expected to be incorporated into a breadboard data management computer system at NASA Manned Spacecraft Center's Information system division. The executive system was structured for internal operation on the IBM 4 Pi EP system with its external configuration and applications software assumed to the characteristic of the centralized quad-redundant avionics systems defined in Phase B

The interaction between center monopoles in SU(2) Yang-Mills

We study the potential between a static center monopole and antimonopole in 4d SU(2) Yang-Mills theory. Using a new numerical method, we show that the 't Hooft loop is a dual order parameter with respect to the Wilson loop, for the deconfinement phase transition. We observe a 3d Ising-like critical behaviour for the dual string tension related to the spatial 't Hooft loop as a function of the temperature.Comment: Lattice2000(Topology and Vacuum), 4 pages, 3 figure

WAVE-CUSUM: Improving CUSUM performance in network anomaly detection by means of wavelet analysis

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TW Hydrae: evidence of stellar spots instead of a Hot Jupiter

TW Hydrae shows significant radial-velocity variations in the optical regime. They have been attributed to a 10 Jupiter Mass planet orbiting the star at 0.04 AU. In this work, we have tested whether the observed RV variations can be caused by stellar spots. We have also analyzed new optical and infrared data to confirm the signal of the planet companion. We fitted the RV variations of TW Hya using a cool spot model. Our model shows that a cold spot covering 7% of the stellar surface and located at a latitude of 54 deg can reproduce the reported RV variations. The model also predicts a bisector semi-amplitude variation <10 m/s, which is less than the errors of the RV measurements discussed in an earlier publication. The analysis of new optical RV data, with typical errors of 10 m/s, shows a larger RV amplitude that varies depending on the correlation mask used. A slight correlation between the RV variation and the bisector is also observed, although not at a very significant level. The infrared H-band RV curve is almost flat, showing a small variation (<35 m/s) that is not consistent with the optical orbit. All these results support the spot scenario rather than the presence of a hot Jupiter around TW Hya.Comment: accepted for publication in A&

A study of the 't Hooft loop in SU(2) Yang-Mills theory

We study the behaviour of the spatial and temporal 't Hooft loop at zero and finite temperature in the 4D SU(2) Yang-Mills theory, using a new numerical method. In the deconfined phase $T>T_c$, the spatial 't Hooft loop exhibits a dual string tension, which vanishes at $T_c$ with 3D Ising-like critical exponent.Comment: 4 pages, 5 figures. Version accepted for publication in Phys. Rev. Let

Strong HI Lyman-α\alpha variations from the 11 Gyr-old host star Kepler-444: a planetary origin ?

Kepler-444 provides a unique opportunity to probe the atmospheric composition and evolution of a compact system of exoplanets smaller than the Earth. Five planets transit this bright K star at close orbital distances, but they are too small for their putative lower atmosphere to be probed at optical/infrared wavelengths. We used the Space Telescope Imaging Spectrograph instrument onboard the Hubble Space Telescope to search for the signature of the planet's upper atmospheres at six independent epochs in the Ly-$\alpha$ line. We detect significant flux variations during the transits of both Kepler-444e and f (~20%), and also at a time when none of the known planets was transiting (~40%). Variability in the transition region and corona of the host star might be the source of these variations. Yet, their amplitude over short time scales (~2-3 hours) is surprisingly strong for this old (11.2+-1.0Gyr) and apparently quiet main-sequence star. Alternatively, we show that the in-transits variations could be explained by absorption from neutral hydrogen exospheres trailing the two outer planets (Kepler-444e and f). They would have to contain substantial amounts of water to replenish such hydrogen exospheres, which would reveal them as the first confirmed ocean-planets. The out-of-transit variations, however, would require the presence of a yet-undetected Kepler-444g at larger orbital distance, casting doubt on the planetary origin scenario. Using HARPS-N observations in the sodium doublet, we derived the properties of two Interstellar Medium clouds along the line-of-sight toward Kepler-444. This allowed us to reconstruct the stellar Ly-$\alpha$ line profile and to estimate the XUV irradiation from the star, which would still allow for a moderate mass loss from the outer planets after 11.2Gyr. Follow-up of the system at XUV wavelengths will be required to assess this tantalizing possibility.Comment: Accepted for publication in A&A Name of the system added to the title in most recent versio