Resonantly pumped continuous wave Er:YAP laser

A continuous wave Er:YAP laser pumped by Mgo:PPLN laser locked at 1535 nm was reported. 170 mW of 1609 nm output was achieved under total incident pump power of 7 W at 77 K. The slope efficiency were 5.0 and 3.1% with the cavity length 75 and 140 mm.     

On the nuclear curvature energy

The curvature energy coefficient of the nuclear mass formulaa _c is first calculated for the model case of a Fermi gas bounded by an external Woods-Saxon potential. The semiclassical theory of Wigner and Kirkwood is used anda _c is found to be close to zero. It is, however, shown that this low value is due to the lack of selfconsistency of the potential. When available, the results of the model compare very well with quantal values and the extrapolation to the spherical cavity (billiard) checks with the value fora _c known from the Balian-Bloch theory. Second, the selfconsistent case is generalised to finite range forces. No indication is found that this modifies the fact that all theoretical values for a _c are larger than about 7 MeV which is an order of magnitude above the empirical value.     

Dark pulse generation in a dispersion-managed fiber laser

We report an experimental observation of dark pulse generation in a dispersion-managed erbium-doped fiber laser with net anomalous cavity group-velocity dispersion. It is found that apart from the bright soliton pulses, dark pulses with spectral sidebands could be obtained in the laser under appropriate operating conditions. The generation of dark pulses may be attributed to soliton shaping in the cavity.     

Completeness in Supergravity Constructions

We prove that the supergravity r- and c-maps preserve completeness. As a consequence, any component \({\mathcal{H}}\) of a hypersurface {h = 1} defined by a homogeneous cubic polynomial h such that \({-\partial^2h}\) is a complete Riemannian metric on \({\mathcal{H}}\) defines a complete projective special Kähler manifold and any complete projective special Kähler manifold defines a complete quaternionic Kähler manifold of negative scalar curvature. We classify all complete quaternionic Kähler manifolds of dimension less or equal to 12 which are obtained in this way and describe some complete examples in 16 dimensions.     

Interaction between graphene and the surface of SiO2

The interaction between graphene and a SiO(2) surface has been analyzed with first-principles DFT calculations by constructing the different configurations based on α-quartz and cristobalite structures. The fact that single-layer graphene can stay stably on a SiO(2) surface is explained based on a general consideration of the configuration structures of the SiO(2) surface. It is found that the oxygen defect in a SiO(2) surface can shift the Fermi level of graphene down which opens up the mechanism of the hole-doping effect of graphene adsorbed on a SiO(2) surface observed in a lot of experiments.     

简并四波混频实现全光信号幅度整形的系统设计

对光纤中简并四波混频(DFWM)耦合波方程进行数值求解,通过分析发现:泵浦光功率的增大会导致泵浦光与反斯托克斯光之间能量交换周期减小。阐述了优化光纤中DFWM实现全光信号幅度整形的机理。在此基础上设计了一个优化的全光信号幅度整形系统,并进行了系统仿真,结果表明:通过再生系统后,信号的消光比从9.46 dB提升到30.40 dB,品质因子从15.95提升到了180.40。     

Uncertainty-based experimental validation of nonlinear reduced order models

This paper presents the first results of a combined experimental–computational investigation focused on the validation of reduced order models of geometrically nonlinear structures in the presence of uncertainty. The validation approach considered here is based on the premise that the model is valid if the experimental results can be considered as random sample responses of the stochastic system of which the reduced order model is the mean. For the situation considered here, the power spectra of the experiments should lie within the 2nd and 98th percentiles of the response (forming the uncertainty band) of the stochastic model. Nominally clamped–clamped beams are considered to demonstrate the entire process. The construction of two mean reduced order models and their stochastic counterparts are first performed. Then, the validation effort is carried out by comparing experimentally obtained power spectra and their corresponding computational uncertainty bands. This process leads, for both reduced order models, to a very good representation of the important upper envelope (98th percentile) of the experimental data but a less good fit of the lower envelope (2nd percentile).     

Temperature independent leakage current in Au/TbMnO3/Y Ba2Cu3O7−x capacitors

Au/TbMnO₃/Y Ba₂Cu₃O_7?x capacitors were fabricated on LaAlO₃ substrates and electrical characteristics were studied in the temperature range from 300 to 25 K. When temperature is higher than 225 K, Ohmic conduction is observed in the capacitors. Non-linear current–voltage characteristics are exhibited at low temperatures. Moreover, temperature-independent leakage currents are found at temperatures lower than 150 K. These electrical characteristics can be explained in terms of conduction transition originated from a thermal activation between 225 and 150 K, and the temperature-independent leakage currents are governed by the Poole–Frenkel emission and minor trap ionization energies.     

Low‐temperature photoluminescence of oxide‐covered single‐layer MoS2

We present a photoluminescence study of single‐layer MoS₂ flakes on SiO₂ surfaces. We demonstrate that the luminescence peak position of flakes prepared from natural MoS₂, which varies by up to 25 meV between individual flakes, can be homogenized by annealing in vacuum. We use HfO₂ and Al₂O₃ layers prepared by atomic layer deposition to cover some of our flakes. In these flakes, we observe a suppression of the low‐energy luminescence peak which appears in asprepared flakes at low temperatures. We infer that this peak originates from excitons bound to surface adsorbates. We also observe different temperature‐induced shifts of the luminescence peaks for the oxide‐covered flakes. This effect stems from the different thermal expansion coefficients of the oxide layers and the MoS₂ flakes. It indicates that the single‐layer MoS₂ flakes strongly adhere to the oxide layers and are therefore strained. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)