Microwave studies of the superconducting state in Rb3C60

Methods of electron-spin resonance (ESR) and direct, non-linear field-modulated microwave absorption (FMMA) were applied for the measurements in low- and high-purity samples of rubidium-doped fullerene, Rb₃C₆₀. The coexistence of the normal strong ESR signals and regular series of weak absorption lines similar to those seen in systems of Josephson junctions was observed in the high-purity sample. The possible influence of the vortex lattice on the ESR signals was also studied. We determined from FMMA investigations using the Portis model the critical field μ₀H^* = 40 μT, the depinning current density J_c^*(μ₀H₀ = 1 mT) 4 × 10⁸ A/m² in low magnetic field and J_c^*(μ₀H₀ > 100 mT) 1.6 × 10⁸ A/m² in higher fields. These values were generally one order of magnitude higher than the highest corresponding values previously observed in high-temperature superconductors (HTS's).     

Palladium island growth on Ni(111) Stochastic classical trajectory — ghost atom calculations

We generalize previous stochastic classical trajectory-ghost atom calculations for describing palladium deposition onto the Ni(111) surface between 0.1 and 0.5 monolayers. The growth evolves through two-dimensional islands. The islands are formed following the downward funneling mechanism. Surface temperature does not affect the island growth.     

Separation of nonstationary sound fields in the time-wavenumber domain

A number of sound field separation techniques have been proposed for different purposes. However, these techniques just consider the separation of sound fields in the space domain and are restricted to stationary sound fields. When the sound fields are nonstationary, it is also necessary to perform the separation in the time domain. Therefore, on the basis of the propagation principle of sound pressure in the time-wavenumber domain, a nonstationary sound field separation technique with two closely spaced parallel measurement surfaces is proposed. It can separate the nonstationary signals generated by the primary sources in both time and space domains when the disturbing sources exist on the other side of the measurement plane. The signals in time and space domains are separated by using the spatial Fourier transform method and the time domain deconvolution method. A simulation involving two monopoles driven by nonstationary signals demonstrates that the method proposed can remove the influence of disturbing sources in both time and space domains. The feasibility of this method is also demonstrated by an experiment with two loudspeakers located on two sides of measurement planes. Additionally, to comment more objectively on the separation results, some indicators are computed in both the simulation and experiment.     

A measurement of the neutral current electroweak parameters using the fermilab narrow band neutrino beam

We report a measurement of the electroweak parameters sin₂θ ^w and ? based on the ratios of neutral current to charged current events measured in the Fermilab narrow-band neutrino beam at energies of 30–240 GeV. The data are fully corrected for radiative effects, heavy-quark production, and other effects. The best value for sin₂θ ^w obtained, sin₂θ ^w =0.239±0.011, is consistent with the most recent values fromW andZ production, as well as from other neutrino experiments.     

Hilbert's Nullstellensatz Is in the Polynomial Hierarchy

We show that if the Generalized Riemann Hypothesis is true, the problem of deciding whether a system of polynomial equations in several complex variables has a solution is in the second level of the polynomial hierarchy (in fact, this problem is in RP^NP). The best previous bound was PSPACE.     

He-Ne激光诱变黑曲霉Sx的原生质体

对生淀粉糖化菌黑曲霉Sx用混和酶制取原生质体进行了探索.在GM培养基中加入一定量的Cu²⁺、Mn²⁺,原生质体产量较高;采用pH4～5的蜗牛酶、纤维素酶、溶菌酶的混合酶,最佳浓度比为:1.5:3.5:1.5(mg/mL).取在GM培养基中培养17～18h的菌丝,在32℃酶解3h,原生质体产量最高,达到2.4×10⁵个/mL;在加入β-巯基乙醇及二硫苏糖醇处理菌丝时,原生质体产量提高近3倍.在再生培养基中,加入终浓度为30mmol/LMgSO₄时,原生质体再生率由16.7%提高到25.6%.用He-Ne激光照射原生质体时,功率9mW照射30min时致死率为50%,随着时间的延长,原生质体存活率降低.采用波长632.5nm、功率9mW、光斑直径5mm的He-Ne激光多次照射诱变,筛选出一株酶活力最高菌株黑曲霉Sy,活力提高51%,经连续传代5次,酶活力稳定.     

Influence of phonon dispersion and exciton spectrum on the energy spectrum of magnetopolarons in a quantum well

An analysis is made of the influence of the spatial dispersion of LO phonons and the exciton effect on the energy spectrum of magnetopolarons in a quantum well. It is shown that in optical experiments where light is incident normally on the plane of the quantum well, a discrete spectrum of magnetopolarons is observed. Both the phonon dispersion and the Coulomb attraction of an electron and a hole may lead to a shift of the discrete magnetopolaron energy levels and additional contributions to the broadening of various levels.