Shi Shaohua

Mid-holocene climates and environments in China

Abstract This paper focuses mainly on the climatic and environmental variations 5 to 3 ka. B.P. with particular reference to one stable warmer and wetter millennium (7.2-6 ka B.P.). Some large-scale centennial warming was accompanied by an increase in precipitation owing to the expansion of the monsoon circulation, e.g. rapid warming during the period from 8.5 to 8.3 ka B.P. and was reflected in the high level of some inland lakes and the sudden expansion of vegetation in pollen diagrams. The growth of the Neolithic culture with agriculture and settlement in the present semi-arid area of Northwest China was undoubtedly related to the dramatic warming and wetting before 8 ka B.P. According to the proxy data of palynological studies, the deviation of annual mean temperature from todays about 7-6 ka B.P. was roughly estimated at about 1°C in South China, 2°C in the Changjiang (Yangtze) Valley, 3°C in North China and Northeast China. The strongest warming by 4–5°C was recorded in Qinghai-Xizang (Tibet) Plateau. The winter temperature rise was much greater than the annual average temperature. In the eastern half of China, the vegetation zones are mainly parallel to the latitude. During the climax of the Holocene warm period, the northern limit of the tropical monsoonal rain forest shifted less than 1° of latitude northward, the subtropical broad-leaved evergreen forest about 1° of latitude, the north subtropical deciduous and evergreen broad-leaved mixed forest about 3° of latitude in the coastal area but only 1–1.5° of latitude in mid-West China and the warm temperate deciduous forest moved 4° of latitude northward, greatly expanding its distribution. Further north, the cool temperate boreal forest withdrew from its southern boundary by about 2° of latitude. Global climatic warming in the mid-Holocene resulted in a sea-level rise. During the period from 6 to 5 ka BP. the sea-level was about 1–3 m higher than the present level. Large area of coastal lowland was submerged by sea water and frequency of occurrence of storm surges also increased during the high sea-level period.

A novel timing-delay measuring method based on PN code in telephone time service

The key problem of telephone time service by PSTN is how to synchronize user time with standard time, in other words, measuring time delay of transmission is the important problem. Now, there are two methods of measuring time delay, the first way is by transmitting character signal; the second way is through phase-detecting. The precision of measuring time delay will have a directly influence on system synchronization time precision, also, The traditional analog modulation/demodulation will highly effect the precision, but the phase error is inevitably because of the effect caused by the noise and channel characteristic when using phase-detecting. A new method, using correlation of PN code will be presented in this paper. Testing shows it can obviously improve the precision of telephone timing service.

A method of high precision time transfer based on DVB-S

A method of transferring high precise time based on the satellite digital TV broadcasting system (DVB-S) is presented in this paper. PCR (Program Clock Reference) in the signal of TV is considered as the Time Synchronization Flag, precise timestamp captured by PCR is real-time recorded in both transmitting segment and user segment, so time in both sides will be synchronized roughly. Then the period of signal from transmitting segment to user segment is calculated by Precise Satellite Ephemeris, and the time will be synchronized precisely. The experimental result showed the method is feasible, and the RMS<; 100ns.

Redundant frequency source with seamless switchover

This paper describes a redundant frequency source system with seamless switchover that produces a stable and continuous output frequency signal. This system has primary and backup frequency produce links to generate the reference frequency. It has the ability to monitor the integrity of the frequency produce links and switchover seamlessly between the primary and the backup links. By use intermediate oscillator of the measurement system as a third party criterion, the autonomous monitor integrity of frequency produce links was achieved without external reference signal. The excellent short-term stability characteristics of intermediate oscillator improves the accuracy and real-time for the monitoring of sudden failure and the degradation of performance. Seamless switchover was defined as the maintenance of both output phase and frequency continuity while and after the switcher from the primary to the backup links. It was initiated when system detects a degradation of the integrity of primary links. The experiment result has been presented showing that there were no detectable change in phase and frequency after the switchover, and the jump of frequency was less than 2e-13, the change of phase less than 100ps.

Design of multi-channel digital pulse signal generator

This paper describes a device that is multi-channel pulse signal generator based on digital. This device utilizes the computer serial port control mode and the digital technology of the electronic design automation (EDA). It is mainly implemented by the complex programmable logic device (CPLD). The experiment result shows that the pulse signal generator can generate the nine-channel pulse signal. The average relative deviation of each channel can reach to 40.7ps when the time interval is 100 microseconds. This generator can meet the requirement for the testing resolution of the multi-channels time interval measurement equipment.

A multi-channel time interval measurement for time comparison

This paper presents improvements on a multichannel time interval measurement for Time Comparison. The measurement has eight channels and measurements the time interval between nine clocks at the same tine. The measurement design is based on a commercially available GPX ASIC from acam-messelectronic gmbh provides a maximum of 86ps resolution per channel. In this measurement precision the measurement range of system is less than 10us and goes beyond the requirement of the time comparison. We extend the measurement range to endless by the internal start re-trigger and external interrupt. The architecture details of this system as shown in figure 1. We also develop a software runs on pc can control the measurement and display the measurement result in real time. We analyze the resolution variation of the measurements and the present linearity plots finally. The calculate results indicate that the precision per channel just a little decline after the measurement range was extended.