Высшее образование в Китае и России: сходство и отличие

В статье дана сравнительная характеристика высшего образования в странах Китай и Россия.The article gives a comparative description of higher education in China and Russia

LOFF Pairing vs. Breached Pairing in Asymmetric Fermion Superfluids

A general analysis for the competition between breached pairing (BP) and LOFF pairing mechanisms in asymmetric fermion superfluids is presented in the frame of a four fermion interaction model. Two physical conditions which can induce mismatched Fermi surfaces are considered: (1) fixed chemical potential asymmetry $\delta\mu$ and (2) fixed fermion number asymmetry $\alpha$. In case (1), the BP state is ruled out because of Sarma instability and LOFF state is thermodynamically stable in a narrow window of $\delta\mu$. In case (2), while the Sarma instability can be avoided and both the BP and LOFF states can survive provided $\alpha$ is less than the corresponding critical value, the BP state suffers magnetic instability and the LOFF state is always thermodynamically stable. While the LOFF window in case (2) is much larger than the one in the conventional case (1), for small $\alpha$ the longitudinal superfluid density of the LOFF state is negative and it suffers also magnetic instability.Comment: 12 pages, 13 figures, published in Physical Review B. Notice: an algebra error in Equation (39) correcte

Geometric Mean Neutrino Mass Relation

Present experimental data from neutrino oscillations have provided much information about the neutrino mixing angles. Since neutrino oscillations only determine the mass squared differences $\Delta m^2_{ij} = m^2_i - m^2_j$, the absolute values for neutrino masses $m_i$ can not be determined using data just from oscillations. In this work we study implications on neutrino masses from a geometric mean mass relation $m_2=\sqrt{m_1 m_3}$ which enables one to determined the absolute masses of the neutrinos. We find that the central values of the three neutrino masses and their $2\sigma$ errors to be $m_1 = (1.58\pm 0.18){meV}$, $m_2 = (9.04\pm 0.42){meV}$, and $m_3 = (51.8\pm 3.5){meV}$. Implications for cosmological observation, beta decay and neutrinoless double beta decays are discussed.Comment: 7 pages. Talk given at COSPA06. A reference adde

Mitigation of Side-Effect Modulation in Optical OFDM VLC Systems

Side-effect modulation (SEM) has the potential to be a significant source of interference in future visible light communication (VLC) systems. SEM is a variation in the intensity of the light emitted by a luminaire and is usually a side-effect caused by the power supply used to drive the luminaires. For LED luminaires powered by a switched mode power supply, the SEM can be at much higher frequencies than that emitted by conventional incandescent or fluorescent lighting. It has been shown that the SEM caused by commercially available LED luminaires is often periodic and of low power. In this paper, we investigate the impact of typical forms of SEM on the performance of optical OFDM VLC systems; both ACO-OFDM and DCO-OFDM are considered. Our results show that even low levels of SEM power can significantly degrade the bit-error-rate performance. To solve this problem, an SEM mitigation scheme is described. The mitigation scheme is decision-directed and is based on estimating and subtracting the fundamental component of the SEM from the received signal. We describe two forms of the algorithm; one uses blind estimation while the other uses pilot-assisted estimation based on a training sequence. Decision errors, resulting in decision noise, limit the performance of the blind estimator even when estimation is based on very long signals. However, the pilot system can achieve more accurate estimations, thus better performance. Results are first presented for typical SEM waveforms for the case where the fundamental frequency of the SEM is known. The algorithms are then extended to include a frequency estimation step and the mitigation algorithm is shown also to be effective in this case

Intrinsic Anomalous Hall Effect in Magneto-Chiral States

We show that a finite Hall effect in zero applied magnetic field occurs for partially filled bands in certain time-reversal violating states with zero net flux per unit-cell. These states are the Magneto-chiral states with parameters in the effective one-particle Hamiltonian such that they do not satisfy the Haldane-type constraints for topological electronic states. The results extend an earlier discussion of the Kerr effect observed in the cuprates but may be applicable to other experimental situations.Comment: published versio

Constraints on the phase γ\gamma and new physics from B→KπB\to K\pi Decays

Recent results from CLEO on $B\to K\pi$ indicate that the phase $\gamma$ may be substantially different from that obtained from other fit to the KM matrix elements in the Standard Model. We show that $\gamma$ extracted using $B\to K\pi, \pi\pi$ is sensitive to new physics occurring at loop level. It provides a powerful method to probe new physics in electroweak penguin interactions. Using effects due to anomalous gauge couplings as an example, we show that within the allowed ranges for these couplings information about $\gamma$ obtained from $B\to K \pi, \pi\pi$ can be very different from the Standard Model prediction.Comment: Revised version with analysis done using new data from CLEO. RevTex, 11 Pages with two figure

Revisiting f(R) gravity models that reproduce Λ\LambdaCDM expansion

We reconstruct an $f(R)$ gravity model that gives rise to the particular $\Lambda$CDM background evolution of the universe. We find well-defined, real-valued analytical forms for the $f(R)$ model to describe the universe both in the early epoch from the radiation to matter dominated eras and the late time acceleration period. We further examine the viability of the derived $f(R)$ model and find that it is viable to describe the evolution of the universe in the past and there does not exist the future singularity in the Lagrangian.Comment: 7 pages, 2 figures, revised version, accepted for publication in PR

Bˉ0→π+X\bar B^0 \to \pi^+ X in the Standard Model

In this paper we investigate the possibility of studying $B\to \pi$ form factor using the semi-inclusive decays $\bar B^0 \to \pi^+ + X_q$. In general $B\to PX$ semi-inclusive decays involve several hadronic parameters. But for $\bar B^0 \to \pi^+ X_q$ decays we find that in the factorization approximation, the only unknown hadronic parameters are the form factors $F^{B\to \pi}_{0,1}$. Therefore these form factors can be studied in $\bar B^0 \to \pi^+ X_q$ decays. Using theoretical model calculations for the form factors the branching ratios for $\bar B^0 \to \pi^+ X_d(\Delta S = 0)$ and $\bar B^0 \to \pi^+ X_s (\Delta S = -1)$, with the cut $E_{\pi} > 2.1$ GeV, are estimated to be in the ranges of $(3.1\sim 4.9) \times 10^{-5}(F^{B\to \pi}_1(0)/0.33)^2$ and $(2.5\sim 4.2)\times 10^{-5}(F_1^{B\to \pi}(0)/0.33)^2$, respectively, depending on the value of $\gamma$. The combined branching ratio for $\bar B^0 \to \pi^+ (X_d+ X_s)$ is about $7.4\times 10^{-5} (F^{B\to \pi}_1(0)/0.33)^2$ and is insensitive to $\gamma$. We also discuss CP asymmetries in these decay modes.Comment: RevTex 8 pages and two figure

(13)C NMR investigation of the superconductor MgCNi_3 up to 800K

We report (13)C NMR characterization of the new superconductor MgCNi_3 (He et al., Nature (411), 54 (2001)). We found that both the uniform spin susceptibility and the spin fluctuations show a strong enhancement with decreasing temperature, and saturate below ~50K and ~20K respectively. The nuclear spin-lattice relaxation rate 1/(13)T_1T exhibits typical behaviour for isotropic s-wave superconductivity with a coherence peak below Tc=7.0K that grows with decreasing magnetic field.Comment: Accepted for publication in Physical Review Letter

Spin relaxation and coherence times for electrons at the Si/SiO2 interface

While electron spins in silicon heterostructures make attractive qubits, little is known about the coherence of electrons at the Si/SiO2 interface. We report spin relaxation (T1) and coherence (T2) times for mobile electrons and natural quantum dots at a 28Si/SiO2 interface. Mobile electrons have short T1 and T2 of 0.3 us at 5 K. In line with predictions, confining electrons and cooling increases T1 to 0.8 ms at 350 mK. In contrast, T2 for quantum dots is around 10 us at 350 mK, increasing to 30 us when the dot density is reduced by a factor of two. The quantum dot T2 is shorter than T1, indicating that T2 is not controlled by T1 at 350 mK but is instead limited by an extrinsic mechanism. The evidence suggests that this extrinsic mechanism is an exchange interaction between electrons in neighboring dots.Comment: Extended with more experiments and rewritten. 6 pages, 5 figures, to be submitted to Phys. Rev.