Proposal of the Readout Electronics for the WCDA in LHAASO Experiment

The LHAASO (Large High Altitude Air Shower Observatory) experiment is proposed for very high energy gamma ray source survey, in which the WCDA (Water Cherenkov Detector Array) is the one of the major components. In the WCDA, a total of 3600 PMTs are placed under water in four ponds, each with a size of 150 m x 150 m. Precise time and charge measurement is required for the PMT signals, over a large signal amplitude range from single P.E. (photo electron) to 4000 P.E. To fulfill the high requirement of signal measurement in so many front end nodes scattered in a large area, special techniques are developed, such as multiple gain readout, hybrid transmission of clocks, commands, and data, precise clock phase alignment, and new trigger electronics. We present the readout electronics architecture for the WCDA and several prototype modules, which are now under test in the laboratory.Comment: 8 pages, 8 figure

Observation of sub-Doppler absorption in the /Lambda-type three-level Doppler-broadened cesium system

Thanks to the atomic coherence in coupling laser driven atomic system, sub-Doppler absorption has been observed in Doppler-broadened cesium vapor cell via the /Lambda-type three-level scheme. The linewidth of the sub-Doppler absorption peak become narrower while the frequency detuning of coupling laser increases. The results are in agreement with the theoretical prediction by G. Vemuri et al.[PRA,Vol.53(1996) p.2842].Comment: 12 pages, 5 figures, to appear on Applied Physics

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.Comment: 11 pages, 15 figure

Steric effect: A quantitative description from density functional theory

The concepts of steric energy, steric potential, and steric charge are introduced within the density functional theory framework. The steric energy, representing a hypothetical state with all electrons packed into the lowest orbital and other effects entirely excluded, is a measure of the intrinsic space occupied by an electronic system. It is exclusive, repulsive, and extensive, and it vanishes for homogeneous electron gas. When Bader's zero-flux boundary condition is adopted, atoms in molecules are found to achieve balanced steric repulsion among one another with vanished steric energy density interfaces. A few molecular systems involving conformation changes and chemical reactions have been investigated to examine the relative contribution of the steric and other effects, providing insights for a few controversial topics from a different perspective