Subdwarf B stars from the common envelope ejection channel

From the canonical binary scenario, the majority of sdBs are produced from low-mass stars with degenerate cores where helium is ignited in a way of flashes. Due to numerical difficulties, the models of produced sdBs are generally constructed from more massive stars with non-degenerate cores, leaving several uncertainties on the exact characteristics of sdB stars. Employing MESA, we systematically studied the characteristics of sdBs produced from the common envelope (CE) ejection channel, and found that the sdB stars produced from the CE ejection channel appear to form two distinct groups on the effective temperature-gravity diagram. One group (the flash-mixing model) almost has no H-rich envelope and crows at the hottest temperature end of the extremely horizontal branch (EHB), while the other group has significant H-rich envelope and spreads over the whole canonical EHB region. The key factor for the dichotomy of the sdB properties is the development of convection during the first helium flash, which is determined by the interior structure of the star after the CE ejection. For a given initial stellar mass and a given core mass at the onset of the CE, if the CE ejection stops early, the star has a relatively massive H-rich envelope, resulting in a canonical sdB generally. The fact of only a few short-orbital-period sdB binaries being in the flash-mixing sdB region and the lack of He-rich sdBs in short-orbital-period binaries indicate that the flash mixing is not very often in the products of the CE ejection. A falling back process after the CE ejection, similar to that happened in nova, is an appropriate way of increasing the envelope mass, then prevents the flash mixing.Comment: accepted by A&A 12 pages, 11 figure

Exchange Field-Mediated Magnetoresistance in the Correlated Insulator Phase of Be Films

We present a study of the proximity effect between a ferromagnet and a paramagnetic metal of varying disorder. Thin beryllium films are deposited onto a 5 nm-thick layer of the ferromagnetic insulator EuS. This bilayer arrangement induces an exchange field, $H_{ex}$, of a few tesla in low resistance Be films with sheet resistance $R\ll R_Q$, where $R_Q=h/e^2$ is the quantum resistance. We show that $H_{ex}$ survives in very high resistance films and, in fact, appears to be relatively insensitive to the Be disorder. We exploit this fact to produce a giant low-field magnetoresistance in the correlated insulator phase of Be films with $R\gg R_Q$.Comment: To be published in Physical Review Letter

Mystery of Excess Low Energy States in a Disordered Superconductor in a Zeeman Field

Tunneling density of states measurements of disordered superconducting (SC) Al films in high Zeeman fields reveal a significant population of subgap states which cannot be explained by standard BCS theory. We provide a natural explanation of these excess states in terms of a novel disordered Larkin-Ovchinnikov (dLO) phase that occurs near the spin-paramagnetic transition at the Chandrasekhar-Clogston critical field. The dLO superconductor is characterized by a pairing amplitude that changes sign at domain walls. These domain walls carry magnetization and support Andreev bound states, which lead to distinct spectral signatures at low energy.Comment: 5 pages, 4 figures, plus supplementary section describing methods (2 pages

Study on vibration of offshore wind turbine supporting system under the wind-wave coupling effect

For offshore wind turbines, the wind and wave loads are the main actions exerted on the offshore structures during the operational process. In order to reasonably simulate the wind-wave coupling effect and the dynamic characteristics of the structure under the coupling effect, the Davenport horizontal fluctuating wind speed spectrum is processed according to the Fourier transform and the harmonic superposition method, thus the fluctuating wind spectrum which coincided well with the target power spectrum is acquired. On the basis of the random wave theory, the calculation equation of wave load for offshore wind turbine structures are put forward. Besides, the wind and wave coupling mechanism analysis is carried out by Turkstra method. In numerical analysis, the integrated finite element model of the offshore wind turbine structure is established considering the interaction between the wind turbine foundation and the soil. Meanwhile, based on the frequency domain method, the in-site measured acceleration signals of an offshore wind turbine are processed and analyzed and the dynamic characteristics of each part of the wind turbine supporting system are obtained. Comparing the measured values with the numerical simulation results, it shows that the calculation method of the wind-wave coupling effect has a preferable accuracy as well as a certain amount of safety coefficient, which can ensure the safety of the structure in actual operation process

Intrinsic electron glassiness in strongly localized Be films

We present results of out-of-equilibrium transport measurements made on strongly localized Beryllium films and demonstrate that these films exhibit all the earmarks of intrinsic electron glasses. These include slow (logarithmic) relaxation, memory effects, and more importantly, the observation of a memory dip that has a characteristic width compatible with the carrier concentration of beryllium. The latter is an empirical signature of the electron glass. Comparing various nonequilibrium attributes of the beryllium films with other systems that exhibit intrinsic electron-glasses behavior reveals that high carrier concentration is their only common feature rather than the specifics of the disorder that rendered them insulating. It is suggested that this should be taken as an important hint for any theory that attempts to account for the surprisingly slow relaxation times observed in these systems. © 2010 The American Physical Society

Saturation of the anomalous hall effect in critically disordered ultrathin CNi3 films

We demonstrate that a distinct high-disorder anomalous Hall effect phase emerges at the correlated insulator threshold of ultrathin, amorphous, ferromagnetic CNi3 films. In the weak-localization regime, where the sheet conductance G e2/h, the anomalous Hall resistance of the films increases with increasing disorder and the Hall conductance scales as Gxy Gφ with φ=1.6. However, at sufficiently high disorder the system begins to enter the 2D correlated insulator regime, at which point the Hall resistance Rxy abruptly saturates and the scaling exponent becomes φ=2. Tunneling measurements show that the saturation behavior is commensurate with the emergence of the 2D Coulomb gap, suggesting that e-e interactions mediate the high-disorder phase. © 2010 The American Physical Society