Photoproduction of K∗+ΛK^{*+}\Lambda and K+Σ(1385)K^+\Sigma(1385) in the reaction \gamma \lowercase{p} \to K^+ \Lambda \pi^0 at Jefferson Lab

The search for missing nucleon resonances using coupled channel analysis has mostly been concentrated on $N\pi$ and $KY$ channels, while the contributions of $K^*Y$ and $KY^*$ channels have not been investigated thoroughly mostly due to the lack of data. With an integrated luminosity of about 75 $pb^{-1}$, the photoproduction data using a proton target recently collected by the CLAS Collaboration at Jefferson Lab with a photon energy range of 1.5-3.8 GeV provided large statistics for the study of light hyperon photoproduction through exclusive reactions. The reaction $\gamma p \to K^+ \Lambda \pi^0$ has been investigated. Preliminary results of the $K^{*+}\Lambda$ and $K^+\Sigma(1385)$ cross sections are not negligible compared with the $KY$ channels. The $\Lambda \pi^0$ invariant mass spectrum is dominated by the $\Sigma(1385)$ signal and no significant structure was found around the $\Sigma(1480)$ region.Comment: 4 pages, 3 figures, to be publised on the NSTAR05 proceeding

The Schrodinger-like Equation for a Nonrelativistic Electron in a Photon Field of Arbitrary Intensity

The ordinary Schrodinger equation with minimal coupling for a nonrelativistic electron interacting with a single-mode photon field is not satisfied by the nonrelativistic limit of the exact solutions to the corresponding Dirac equation. A Schrodinger-like equation valid for arbitrary photon intensity is derived from the Dirac equation without the weak-field assumption. The "eigenvalue" in the new equation is an operator in a Cartan subalgebra. An approximation consistent with the nonrelativistic energy level derived from its relativistic value replaces the "eigenvalue" operator by an ordinary number, recovering the ordinary Schrodinger eigenvalue equation used in the formal scattering formalism. The Schrodinger-like equation for the multimode case is also presented.Comment: Tex file, 13 pages, no figur

Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems

Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion

Spin singlet pairing in the superconducting state of NaxCoO2\cdot1.3H2O: evidence from a ^{59}Co Knight shift in a single crystal

We report a ^{59}Co Knight shift measurement in a single crystal of the cobalt oxide superconductor Na_{x}CoO_2\cdot1.3H_2O (T_c=4.25 K). We find that the shift due to the spin susceptibility, K^s, is substantially large and anisotropic, with the spin shift along the a-axis K^s_a being two times that along the c-axis K^s_c. The shift decreases with decreasing temperature (T) down to T\sim100 K, then becomes a constant until superconductivity sets in. Both K^s_a and K^s_c decrease below T_c. Our results indicate unambiguously that the electron pairing in the superconducting state is in the spin singlet form.Comment: 4 pages, 5 figure

Chiral Extrapolation of Lattice Data for Heavy Meson Hyperfine Splittings

We investigate the chiral extrapolation of the lattice data for the light-heavy meson hyperfine splittings D^*-D and B^*-B to the physical region for the light quark mass. The chiral loop corrections providing non-analytic behavior in m_\pi are consistent with chiral perturbation theory for heavy mesons. Since chiral loop corrections tend to decrease the already too low splittings obtained from linear extrapolation, we investigate two models to guide the form of the analytic background behavior: the constituent quark potential model, and the covariant model of QCD based on the ladder-rainbow truncation of the Dyson-Schwinger equations. The extrapolated hyperfine splittings remain clearly below the experimental values even allowing for the model dependence in the description of the analytic background.Comment: 14 pages, 4 figures, typos corrected, presentation clarifie

Magnetically-induced reconstructions of the ground state in a few-electron Si quantum dot

We report unexpected fluctuations in the positions of Coulomb blockade peaks at high magnetic fields in a small Si quantum dot. The fluctuations have a distinctive saw-tooth pattern: as a function of magnetic field, linear shifts of peak positions are compensated by abrupt jumps in the opposite direction. The linear shifts have large slopes, suggesting formation of the ground state with a non-zero angular momentum. The value of the momentum is found to be well defined, despite the absence of the rotational symmetry in the dot.Comment: 5 pages, 4 figures, accepted to PR

Topological Analysis of Emerging Bipole Clusters Producing Violent Solar Events

During the rising phase of Solar Cycle 24 tremendous activity occurred on the Sun with fast and compact emergence of magnetic flux leading to bursts of flares (C to M and even X-class). We investigate the violent events occurring in the cluster of two active regions (ARs), NOAA numbers 11121 and 11123, observed in November 2010 with instruments onboard the {\it Solar Dynamics Observatory} and from Earth. Within one day the total magnetic flux increased by $70\%$ with the emergence of new groups of bipoles in AR 11123. From all the events on 11 November, we study, in particular, the ones starting at around 07:16 UT in GOES soft X-ray data and the brightenings preceding them. A magnetic-field topological analysis indicates the presence of null points, associated separatrices and quasi-separatrix layers (QSLs) where magnetic reconnection is prone to occur. The presence of null points is confirmed by a linear and a non-linear force-free magnetic-field model. Their locations and general characteristics are similar in both modelling approaches, which supports their robustness. However, in order to explain the full extension of the analysed event brightenings, which are not restricted to the photospheric traces of the null separatrices, we compute the locations of QSLs. Based on this more complete topological analysis, we propose a scenario to explain the origin of a low-energy event preceding a filament eruption, which is accompanied by a two-ribbon flare, and a consecutive confined flare in AR 11123. The results of our topology computation can also explain the locations of flare ribbons in two other events, one preceding and one following the ones at 07:16 UT. Finally, this study provides further examples where flare-ribbon locations can be explained when compared to QSLs and only, partially, when using separatrices.Comment: 42 pages, 15 figure