38766511
BESIII luminosity readout design based on embedded system
Zero-Degree Detector (ZDD) is a new Detector of Beijing Electron Spectrometer III (BESIII) for both double gamma event detection and luminosity monitoring to substitute the old luminosity monitor. A new luminosity readout is described in this paper which is designed in double width AMC/MTCA form factor with a large Xilinx Virtex5 FPGA in addition to normal electronic signal formation. A FPGA embedded PowerPC is used for data reading, accumulation and data transmission over a gigabit Ethernet. The setting of parameters like the discriminator threshold in Front End electronics is done via a special serial link under control of firmware in the same FPGA. This readout system has been put in operation since fall of 2012.
34447410
A prototype of self-triggering front-end unit for radio detection of ultra high energy neutrinos
Since the Tianshan Radio Experiment for Neutrino Detection (TREND) has successfully announced its first result, the Giant Radio Array for Neutrino Detection (GRAND) prototype is proposed to validate the concept of extensive air shower detection with a very high background rejection. High speed digitizing (1GHz), 12bits dynamic range and less than 10ns timing precision based on GPS are expected in the GRAND prototype experiment. This paper describes the overall structure of the data acquisition for GRAND prototype, concentrating on the development of the front-end electronics. The self-triggering front-end unit is a key part of the electronics system. It generally consists of two trigger boards (FTRIG), one digitizing board (DFADC), and one timestamp board (GPSTIM). Its main function is to get the amplitude and time stamp information of the input signal from the antenna. FTRIG board is for fast hardware trigger; GPSTIM board is for time stamp based on GPS (RMS <; 10ns); DFADC board is for dual 12bits 1GHz digitizing and fiber transmission. A prototype of the self-triggering front-end unit was built and a field test confirmed the full functionality of the prototype. The new prototype is considered to be evaluated on the speed and reliability as the ultimate design.
119207380
GAMMA-RAY BURST POLARIZATION VIA COMPTON SCATTERING PROCESS
Synchrotron radiation and Compton scattering are widely accepted as the most likely emission mechanisms of some astrophysical phenomena, such as gamma-ray bursts (GRBs) and active galactic nuclei. The measurement of the polarization of photons provides a useful tool to distinguish different emission mechanisms and structures of the emission region. Based on the differential cross section of a polarized photon scattered by an unpolarized electron of any initial momentum, we derive an analytical formula of polarization for beamed photons scattered by isotropic electrons with a power-law distribution. Numerical calculations are carried out in four special cases: electrons at rest, Thomson limit, head-on collision, and monochromatic electrons. It is found that the maximum polarization can be as high as 100% for low energy photons, if the electrons are at rest. Although polarization is highly suppressed due to the isotropic electrons, a maximum value of similar to 10%-20% can still be achieved. The Compton scattering process can be used to explain the polarization of GRB 041219A and GRB 100826A.
119183324
ON EXOTIC SPHERE FIBRATIONS, TOPOLOGICAL PHASES, AND EDGE STATES IN PHYSICAL SYSTEMS
We suggest that exotic sphere fibrations can be mapped to band topologies in condensed matter systems. These fibrations can correspond to geometric phases of two double bands or state vector bases with second Chern numbers m+n and -n, respectively. They can be related to topological insulators, magnetoelectric effects, and photonic crystals with special edge states. We also consider time-reversal symmetry breaking perturbations of topological insulator, and heterostructures of topological insulators with normal insulators and with superconductors. We consider periodic TI/NI/TI/NI′ heterostructures, and periodic TI/SC/TI/SC′ heterostructures. They also give rise to models of Weyl semimetals which have thermal and electrical transports.
18903410
Generalized Painlevé–Gullstrand descriptions of Kerr–Newman black holes
Generalized Painlevé–Gullstrand metrics are explicitly constructed for the Kerr–Newman family of charged rotating black holes. These descriptions are free of all coordinate singularities; moreover, unlike the Doran and other proposed metrics, an extra tunable function is introduced to ensure all variables in the metrics remain real for all values of the mass $$M$$, charge $$Q$$, angular momentum $$aM$$, and cosmological constant $${\Lambda } > -\frac{3}{a^2}$$. To describe fermions in Kerr–Newman spacetimes, the stronger requirement of non-singular vierbein one-forms at the horizon(s) is imposed and coordinate singularities are eliminated by local Lorentz boosts. Other known vierbein fields of Kerr–Newman black holes are analysed and discussed; and it is revealed that some of these descriptions are actually not related by physical Lorentz transformations to the original Kerr–Newman expression in Boyer–Lindquist coordinates—which is the reason complex components appear (for certain ranges of the radial coordinate) in these metrics. As an application of our constructions the correct effective Hawking temperature for Kerr black holes is derived with the method of Parikh and Wilczek.
15191903
Bubbling AdS space and 1/2 BPS geometries
We consider all 1/2 BPS excitations of AdS × S configurations in both type-IIB string theory and M-theory. In the dual field theories these excitations are described by free fermions. Configurations which are dual to arbitrary droplets of free fermions in phase space correspond to smooth geometries with no horizons. In fact, the ten dimensional geometry contains a special two dimensional plane which can be identified with the phase space of the free fermion system. The topology of the resulting geometries depends only on the topology of the collection of droplets on this plane. These solutions also give a very explicit realization of the geometric transitions between branes and fluxes. We also describe all 1/2 BPS excitations of plane wave geometries. The problem of finding the explicit geometries is reduced to solving a Laplace (or Toda) equation with simple boundary conditions. We present a large class of explicit solutions. In addition, we are led to a rather general class of AdS5 compactifications of M-theory preserving = 2 superconformal symmetry. We also find smooth geometries that correspond to various vacua of the maximally supersymmetric mass-deformed M2 brane theory. Finally, we present a smooth 1/2 BPS solution of seven dimensional gauged supergravity corresponding to a condensate of one of the charged scalars.
55602833
A new platform for topological quantum phenomena : Topological Insulator states in thermoelectric Heusler-related ternary compounds
Topological insulators (TI) realize a novel state of quantum matter that are distinguished by topological invariants of bulk band structure rather than spontaneously broken symmetries. A number of exotic quantum phenomena have been predicted to exist in multiply-connected geometries which require an enormous amount of materials flexibility. We have extended our previous search for TI materials from binary (Bi2X3 series) to the thermoelectric ternary compounds. We discover that the distorted LuPtSb is the first ternary compound harboring a 3D topological insulator state. We also show that the half-Heusler LuPtSb-type series is a natural platform that hosts a range of candidate compounds, alloys and artificial heterostructures (quantum-wells). We also discovered several different paradigms of trivial and non-trivial topological ordering in this class, including a metallic nontrivial topological state in YAuPb. Some of these materials are grown (results will be reported separately).