Quasinormal modes and absorption of a massless scalar field for the magnetic Gauss–Bonnet black hole

We study the massless scalar quasinormal frequencies of an asymptotically flat static and spherically symmetric black hole with a nonzero magnetic charge in four-dimensional extended scalar-tensor-Gauss–Bonnet theory. The results show that the real part of the quasinormal frequency becomes larger and the imaginary part becomes smaller with increasing the magnetic charge or the angular harmonic index. The existence of magnetic charges will reduce the damping of scalar perturbation, but increase the frequency. We also study the absorption cross-section of the scalar field in this black hole. We find that its curve will become lower as the magnetic charge increases, i.e. the magnetic charge will weaken the absorption capacity of the black hole. Meanwhile, the high-frequency limit of the total absorption cross-section is just the area of black hole shadow.     

有机/聚合物白光电致发光器件

将聚合物材料作为空穴传输材料,以有机小分子蓝光染料1,1,4,4－四苯基丁二烯,绿光染料8－羟基喹啉铝和黄光染料5,6,11,12－四苯基四苯并作为产生白光所需要的三种色源,制备了有机／聚合物白光电致发光器件。这种器件的设计使聚合物的热电稳定性好的优点与有机小分子材料荧光效率高的优点相结合,拓宽了材料的选择范围,更有利于选择能带匹配的材料体系。器件的开启电压为2.5V左右,发光效率在9V时达到最大1.24lm／W,该电压下的亮度达到1600cd/m^2,器件的最大亮度超过20000cd/m^2（18V）,器件最佳色度为（0.319,0.332),这在目前国际上有报道的有机／聚合物白光发光器件中居领先水平。     

The microstructure and Ruppeiner geometry of charged anti-de Sitter black holes in Gauss–Bonnet gravity: from the critical point to the triple point

Ruppeiner geometry has been successfully applied in the study of the black hole microstructure by combining with the small–large black hole phase transition, and the potential interactions among the molecular-like constituent degrees of freedom are uncovered. In this paper, we will extend the study to the triple point, where three black hole phases coexist acting as a typical feature of black hole systems quite different from the small–large black hole phase transition. For the six-dimensional charged Gauss–Bonnet anti-de Sitter black hole, we thoroughly investigate the swallow tail behaviors of the Gibbs free energy and the equal area laws. After obtaining the black hole triple point in a complete parameter space, we exhibit its phase structures both in the pressure–temperature and temperature–horizon radius diagrams. Quite different from the liquid–vapor phase transition, a double peak behavior is present in the temperature–horizon radius phase diagram. Then we construct the Ruppeiner geometry and calculate the corresponding normalized curvature scalar. Near the triple point, we observe multiple negatively divergent behaviors. Positive curvature scalar is observed for the small black hole with high temperature, which indicates that the repulsive interaction dominates among the microstructure. Furthermore, we consider the variation of the curvature scalar along the coexisting intermediate and large black hole curves. Combining with the observation for different fluids, the result suggests that this black hole system behaves more like the argon or methane. Our study provides a first and preliminary step towards understanding black hole microstructure near the triple point, as well as uncovering the particular properties of the Gauss–Bonnet gravity.     

Exact Hawking radiation of scalars,fermions, and bosons using the tunneling method without back-reaction

Hawking radiation is studied for arbitrary scalars, fermions and spin-1 bosons, using a tunneling approach, to every order in ? but ignoring back-reaction effects. It is shown that the additional quantum terms yield no new contribution to the Hawking temperature. Indeed, it is found that the limit of small ? in the standard quantum WKB approximation is replaced by the near-horizon limit in the gravitational WKB approach.     

EDOT‐diketopyrrolopyrrole copolymers for high bulk hole mobility and near infrared absorption

To obtain novel low‐bandgap materials with tailored hole‐transport properties and extended absorption, electron rich 3,4‐ethylenedioxythiophene is introduced as a comonomer in diketopyrrolo[3,4‐c]pyrrole copolymers with different aryl flanking units. The polymers are characterized by absorption and photoluminescence spectroscopy, dynamic scanning calorimetry, cyclic voltammetry, and X‐ray diffraction. The charge transport properties of these new materials are studied carefully using an organic field effect transistor geometry where the charge carriers are transported over a narrow channel at the semiconductor/dielectric interface. These results are compared to bulk charge carrier mobilities using space‐charge limited current (SCLC) measurements, in which the charge carrier is transported through the complete film thickness of several hundred nanometers. Finally, charge carrier mobilities are correlated with the electronic structure of the compounds. We find that in particular the thiophene‐flanked copolymer PDPP[T]₂‐EDOT is a very promising candidate for organic photovoltaics, showing an absorption response in the near infrared region with an optical bandgap of 1.15 eV and a very high bulk hole mobility of 2.9 × 10^?4 cm² V^?1 s^?1 as measured by SCLC. This value is two orders of magnitudes higher than SCLC mobilities reported for other polydiketopyrrolopyrroles and is in the range of the well‐known hole transporting polymer poly(3‐hexylthiophene). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 639–648     

Schwarzschild black hole as moving puncture in isotropic coordinates

The success of the moving puncture method for the numerical simulation of black hole systems can be partially explained by the properties of stationary solutions of the 1 + log coordinate condition. We compute stationary 1 + log slices of the Schwarzschild spacetime in isotropic coordinates in order to investigate the coordinate singularity that the numerical methods have to handle at the puncture. We present an alternative integration method to obtain isotropic coordinates that simplifies numerical integration and that gives direct access to a local expansion in the isotropic radius near the puncture. Numerical results have shown that certain quantities are well approximated by a function linear in the isotropic radius near the puncture, while here we show that in some cases the isotropic radius appears with an exponent that is close to but unequal to one. This paper is dedicated to the memory of Jürgen Ehlers. I have known JE for a number of years, in particular during his time as founding director of the Albert Einstein Institute in Potsdam. JE was the mentor of my habilitation thesis in 1996, and I am deeply thankful for many insightful discussions. JE combined great breadth and physical intuition with sharp analytical thought. His example inspired me to look beyond the numerical methods and results of numerical relativity to the analytic foundations. For example, while at the AEI, S. Brandt and I introduced “puncture initial data” for the numerical construction of general multiple black hole spacetimes [3]. While the puncture construction starts with an analytic trick of the sort that numerical relativists may devise, it is fair to say that the keen interest in analytical relativity created by JE at the AEI induced us to push our analysis one step further. As a result [3] connects to [26] for an existence and uniqueness proof for such black hole initial data, using weighted Sobolev spaces (see also [4–6]). The present work and its predecessors [9–12] represent an example where numerical experiments led to the discovery of an analytic solution for the 1 + log gauge for the Schwarzschild solution, and the present result, although modest, is of the type which I believe JE would have appreciated.     

Quantum black hole and the modified uncertainty principle

Recently Ali et al. (2009) [13] proposed a Generalized Uncertainty Principle (or GUP) with a linear term in momentum (accompanied by Planck length). Inspired by this idea we examine the Wheeler-DeWitt equation for a Schwarzschild black hole with a modified Heisenberg algebra which has a linear term in momentum. We found that the leading contribution to mass comes from the square root of the quantum number n which coincides with Bekenstein?s proposal. We also found that the mass of the black hole is directly proportional to the quantum number n when quantum gravity effects are taken into consideration via the modified uncertainty relation but it reduces the value of mass for a particular value of the quantum number.     

Tunnelling effect of the non-stationary Kerr black hole

Extending Parikh and Wilczek＇s work to the non-stationary black hole, we study the Hawking radiation of the non-stationary Kerr black hole by the Hamilto-Jacobi method. The result shows that the radiation spectrum is not purely thermal and the tunnelling probability is related to the change of Bekenstein Hawking entropy, which gives a correction to the Hawking thermal radiation of the black hole.