118651169
CASIMIR EFFECT WITH A HELIX TORUS BOUNDARY CONDITION
We use the generalized Chowla–Selberg formula to consider the Casimir effect of a scalar field with a helix torus boundary condition in the flat (D + 1)-dimensional spacetime. We obtain the exact results of the Casimir energy density and pressure for any D for both massless and massive scalar fields. The numerical calculation indicates that once the topology of spacetime is fixed, the ratio of the sizes of the helix will be a decisive factor. There is a critical value rc of the ratio r of the lengths at which the pressure vanishes. The pressure changes from negative to positive as the ratio r passes through rc increasingly. In the massive case, we find the pressure tends to the result of massless field when the mass approaches zero. Furthermore, there is another critical ratio of the lengths and the pressure is independent of the mass at in the D = 3 case.
119228196
Latest observational constraints to the ghost dark energy model by using the Markov chain Monte Carlo approach
Recently, the vacuum energy of the QCD ghost field in a time-dependent background was proposed as a kind of dark energy candidate called the ghost dark energy model (GDE) to explain the acceleration of the Universe. In this model, the energy density of the dark energy is proportional to the Hubble parameter $H$, which is also regarded as the Hawking temperature on the Hubble horizon of the Friedmann-Robertson-Walker Universe. In this paper, the statefinder and $Om$ diagnostics are applied to the GDE models, and the differences among them are significant during the time of transition. And at that time, the viscosity plays an important role. Furthermore, we find that once the viscosity is taken into account, the age problem of Universe could be alleviated. We also perform a constraint on the GDE models with and without bulk viscosity by using the Markov Chain Monte Carlo method and the combined latest observational data from the type Ia supernova compilations including Union2.1(580) and Union2(557), cosmic microwave background, baryon acoustic oscillation, and the observational Hubble parameter data.
15618257
Reheating and Cosmic String Production
Abstract We compute the string production rate at the end of inflation, using the string spectrum obtained in [M. Li, W. Song, Y. Song, Quantizing strings in de Sitter space, JHEP 0704 (2007) 042, hep-th/0701258 ] in a near-de Sitter space. Our result shows that highly excited strings are hardly produced, thus the simple slow-roll inflation alone does not offer a cosmic string production mechanism.
137255349
Electronics of BESIII TOF Monitor System
This paper describes the control electronics for the time of flight (TOF) monitor system of BESIII. A 9U VME module is designed as the interface between the TOF monitor laser box and BESIII data acquisition system. It takes charge of enabling the laser source, sending trigger signals to the laser driver, controlling the optic path, and measuring the charge and arrival time of pulses from two reference phototubes. The module also sends a Level 1 trigger to the TOF readout system, after each trigger pulse to the laser source. The interface and control logic are implemented in one Altera field-programmable gate array, and signals from the reference PMTs of the laser system are digitized with the CERN HPTDC technique. A series of experimental tests show that the time resolution of the monitor electronics is better than 25 ps, and the relative methodical error of the charge measurement is less than 0.5% after quadratic fitting. The TOF monitor system was installed at the end of 2007 and has been operating continuously since then. A total time resolution of about 70 ps and a charge resolution of about 4% of the TOF counters have been obtained during field monitor tests.
204935814
A new method of waveform digitization based on time-interleaved A/D conversion
Time interleaved analog-to-digital conversion (TIADC) based on parallelism is an effective way to meet the requirement of the ultra-fast waveform digitizer beyond Gsps. Different methods to correct the mismatch errors among different analog-to-digital conversion channels have been developed previously. To overcome the speed limitation in hardware design and to implement the mismatch correction algorithm in real time, this paper proposes a fully parallel correction algorithm. A 12-bit 1-Gsps waveform digitizer with ENOB around 10.5 bit from 5 MHz to 200 MHz is implemented based on the real-time correction algorithm.
33505335
Design of the readout electronics for the Qualification Model of DAMPE BGO calorimeter
The DAMPE (DArk Matter Particle Explorer) is a scientific satellite aimed at cosmic ray study, gamma ray astronomy, and searching for the clue of dark matter particles, with a planned mission period of more than 3 years. The calorimeter, which is composed of 308 BGO (Bismuth Germanate Oxid) crystal bars, is a critical sub-detector for measuring the energy of cosmic particles from 5 GeV to 10TeV, distinguishing positrons/electrons and gamma rays from hadron background, and providing trigger information to the whole payload. In the calorimeter each BGO crystal bar is coupled by two Hamamatsu R5610A PMTs (photomultiplier tubes) from both ends respectively, while each PMT send out signals from three dynodes (2, 5, 8) to cover a large dynamic range from about 11 MeV to 2 TeV for each crystal unit. Thus 616 PMTs and 1848 signal channels are used in the BGO calorimeter. The large amount of detector components and signal channels, as well as large dynamic range requirement, greatly challenge the design of readout electronics, because of the confined area for PCB (Printed Circuit Board) layout and cable layout, the potential crosstalk between high density signal channels especially from dynode 8 to dynode 2, and limited power budget. Besides there are other particular requirements derived from hash space environment, such as good radiation tolerance, high reliability, etc. To conquer above challenges, a serial of methods are taken into the design. Two ASICs with low power consumption, low noise, high dynamic range and high integrity, named VA160 and VATA160, are chosen as the front end chips to read out the charge signal from PMT dynodes, and to provide fast trigger information. The Flash-based FPGA (Field Programmable Gate Array) from Actel ProASIC Plus family is applied, which is considered to be less sensitive to SEU (Single Event Upset) and more power-saving, compared to regular SRAM-based FPGAs. In order to estimate the performances of the ASICs and FPGA chips in radiative space environment, both single event effect (SEE) and total ionizing dose (TID) tests are conducted, and SEU and SEL (Single Event Latch-up) protecting measures are adopted, based on the test results. Right now the DAMPE mission is in QM (Qualification Model) stage, all the readout electronics for the qualification model of BGO calorimeter were successfully designed and produced in the end of year 2013. The DAMPE BGO calorimeter was later integrated at the beginning of 2014 and right now the environmental tests, such as vibration test, thermal cycling and thermal-vacuum test, have been performed. Currently the BGO calorimeter is under integration tests with other sub-detectors, and a beam test will be carried out at CERN, in the autumn of 2014.
120054500
The non-gated charge-to-time converter for TOF detector in BES III
Abstract The TOF (Time-Of-Flight) detector in BES (Beijing Spectrometer) III experiment requires a total time resolution of better than 90 ps (for the barrel part) and 110 ps (for the endcap part). With the requirement of such a high precision time measurement, it is essential to measure the amplitude or charge of the PMT (photomultiplier tube) signals, in order to correct the amplitude dependent time-walk. A method of using non-gated QTC (Charge-to-Time Converter) to measure the input signal charge was developed for BES III TOF readout electronics. The non-gated QTC with differential inputs was designed to measure the input charge covering a dynamic range of about 30–927 pC. Test results showed that the rms resolution is better than 10 bit and the relative error is less than 0.5% after quadratic fitting. The designed converter is simple, stable and suitable for multi-channel systems. A total of 448 channels of QTCs have been developed for BES III TOF readout electronics, which help the TOF system achieve the expected time resolution after the time-walk correction.