A 2-d ionospheric model for low latitude area – Hong Kong

The ionosphere is an important part of the atmosphere and it is the largest error source of GNSS positioning for single-frequency users. So establishing a precise ionosphere model is one of the critical steps for satellite navigation and also for ionospheric research.     

Key ecological challenges for closed systems facilities

Closed ecological systems are desirable for a number of purposes. In space life support systems, material closure allows precious life-supporting resources to be kept inside and recycled. Closure in small biospheric systems facilitates detailed measurement of global ecological processes and biogeochemical cycles. Closed testbeds facilitate research topics which require isolation from the outside (e.g. genetically modified organisms; radioisotopes) so their ecological interactions and fluxes can be studied separate from interactions with the outside environment. But to achieve and maintain closure entails solving complex ecological challenges. These challenges include being able to handle faster cycling rates and accentuated daily and seasonal fluxes of critical life elements such as carbon dioxide, oxygen, water, macro- and mico-nutrients. The problems of achieving sustainability in closed systems for life support include how to handle atmospheric dynamics including trace gases, producing a complete human diet, recycling nutrients and maintaining soil fertility, the maintenance of healthy air and water and preventing the loss of critical elements from active circulation. In biospheric facilities, the challenge is also to produce analogues to natural biomes and ecosystems, studying processes of self-organization and adaptation in systems that allow specification or determination of state variables and cycles which may be followed through all interactions from atmosphere to soils. Other challenges include the dynamics and genetics of small populations, the psychological challenges for small isolated human groups and backup technologies and strategic options which may be necessary to ensure long-term operation of closed ecological systems.     

Latitudinal variation of F2-region response to geomagnetic disturbance

The effect of geomagnetic storms on the F2 region was studied by calculating the deviation, ΔfoF2, of foF2 during 40 magnetic storms, ranging from moderate (Dst < −50 nT) to very intense (Dst < −200 nT) of the 21st solar cycle. In order to study the variation of storm-time foF2 with latitude, season and storm strength, ionosonde data were obtained from eight stations spanning a latitudinal range of +60–−60°. The stations chosen lay in a narrow longitudinal range of 140–151°, so that local time difference between the stations is practically negligible. The features exhibited by positive and negative phases were essentially different. The storm time ΔfoF2 clearly exhibited a latitudinal variation and this variation were found to be coupled with the seasonal variation. As for the variation with storm intensity, though ΔfoF2 was found to vary even between two storms of almost equal intensity, the amplitude of a positive or negative phase, |ΔfoF2max| showed a distinct upper limit for each intensity category of storms.     

ATS矩阵开关自检研究

矩阵开关作为一种最灵活的开关拓扑结构,在ATS系统中得到了广泛的应用,也是ATS自检的关键部件之一.受限于自身结构特性,矩阵开关可靠性相对较低,且一般不自带自检功能.依据ATS中矩阵开关的特性、常见故障及其自检目的,研究和分析了矩阵开关自检的内容,并针对某型ATS中的双线矩阵,设计了不同的自检方法,通过分析和对比,可为其他ATS矩阵开关自检方法设计提供参考.     

γ-H2AX as a biomarker of DNA damage induced by ionizing radiation in human peripheral blood lymphocytes and artificial skin

Ionizing radiation (IR) exposure is inevitable in our modern society and can lead to a variety of deleterious effects including cancer and birth defects. A reliable, reproducible and sensitive assessment of exposure to IR and the individual response to that exposure would provide much needed information for the optimal treatment of each donor examined. We have developed a diagnostic test for IR exposure based on detection of the phosphorylated form of variant histone H2AX (γ-H2AX), which occurs specifically at sites of DNA double-strand breaks (DSBs). The cell responds to a nascent DSB through the phosphorylation of thousands of H2AX molecules flanking the damaged site. This highly amplified response can be visualized as a γ-H2AX focus in the chromatin that can be detected in situ with the appropriate antibody. Here we assess the usability of γ-H2AX focus formation as a possible biodosimeter for human exposure to IR using peripheral blood lymphocytes irradiated ex vivo and three-dimensional artificial models of human skin biopsies. In both systems, the tissues were exposed to 0.2–5 Gy, doses of IR that might be realistically encountered in various scenarios such as cancer radiotherapies or accidental exposure to radiation. Since the γ-H2AX response is maximal 30 min after exposure and declines over a period of hours as the cells repair the damage, we examined the time limitations of the useful detectability of γ-H2AX foci. We report that a linear response proportional to the initial radiation dose was obtained 48 and 24 h after exposure in blood samples and skin cells respectively. Thus, detection of γ-H2AX formation to monitor DNA damage in minimally invasive blood and skin tests could be useful tools to determine radiation dose exposure and analyze its effects on humans.     

碳纤维复合材料表面形貌测量中频谱法的应用

针对现实中用户依据自身经验选择采样条件的不确定性,提出了一种能够客观判定最佳采样条件的方法.基于二维功率频谱分析,考虑奈奎斯特采样定理与混叠效应,提出一个归一近似因子来确定合适采样条件.经实验验证其适用于碳纤维复合材料表面形貌测量,研究证明用较大采样间距多次测量加工后工件的表面形貌,取粗糙度值的平均值或最大值来评定其表面质量更合理.     

Comparisons of foF2 with IRI model and equatorial vertical drifts

Measurements of the critical frequency, foF2 recorded over Ibadan: 7.4°N, 3.9°E (geographic), 6°S (dip angle) have been compared with the International Reference Ionosphere (IRI-2007) model for solar maximum geomagnetically quiet conditions, with a view to determining what modifications might bring about better predictions for the model. Our results reveal that the present version of IRI essentially reproduces diurnal trends and the general features of the experimental observations for all seasons, except for nighttime June solstice periods, which the model seriously overestimated. The model errors ranging from 50% to 125% over the four seasons considered in this study. It is also indicated that the percentage relative deviations between the observed and the modeled values vary approximately from −11% to 12% (March), −34% to 11% (June), −16% to 12% (September), and −10% to 13% (December). An unexpected feature of foF2 is obvious and remarkable reduction in values during nighttime June solstice periods compared to that in other seasons. Relationship between equatorial vertical drift and foF2 is also investigated. However, cross correlation analysis reveals strong anti-correlation between vertical drift and critical frequency during the daytime hours, but exceptionally opposite is the case for the nighttime sector. The discrepancies which are noted, particularly during June solstice season are attributed to processes most likely within the thermosphere and from meteorological influences during quiet magnetic conditions.     

压力对有序Li1/2TiS2光学性质的影响

采用第一性原理的平面波赝势方法和局域密度近似（LDA），计算了压力对Li1/2TiS2的形成能和光学性质的影响。研究发现，Li1/2TiS2体系在压强为3GPa时形成能最小，体系最稳定，之后体系的形成能随压力的增大而单调增大；随着压力的增大，导带向高能移动而价带向低能方向移动，体系费米能级上的态密度增大，各个态密度峰值降低且数目增多；光学参量峰值的位置与介电函数虚部的峰值位置很接近，随着压力增大，均向高能方向移动（蓝移），且峰值升高。     

Equatorial total electron content (TEC) at low and high solar activity

Total electron content (TEC) derived from ionosonde data recorded at the station of Korhogo (Lat = 9.33°N, Long = 5.43°W, Dip = 0.67°S) are compared to the International Reference Ionosphere (IRI) model predicted TEC for high (1999) and low (1994) solar activity conditions. The results show that the model represents the diurnal variation of the TEC as well as a solar activity and seasonal dependence. This variation is closer to that of the ionosonde-inferred TEC at high solar activity. However, at low solar activity the IRI overestimates the ionosonde-inferred TEC. The relative deviation ΔTEC is more prominent in the equinoctial seasons during nighttime hours where it is as high as 70%. At daytime hours, the relative deviation is estimated to 0–30%.     

Progress towards a new global foF2 model for the International Reference Ionosphere (IRI)

A new neural network (NN) based global empirical model for the foF2 parameter, which represents the peak electron density has been developed using extended temporal and spatial geophysical relevant inputs. The first results from this new model were presented at the International Reference Ionosphere (IRI) 2006 workshop in Buenos Aires, Argentina, and showed that this new model would be a suitable replacement for the URSI and CCIR maps currently used within the IRI model for the purpose of F2 peak electron density predictions. Measured ground based ionosonde data, from 85 global stations, spanning the period 1995–2005 and, for a few stations from 1976 to 1986, obtained from various resources of the World Data Centre (WDC) archives (Space Physics Interactive Data Resource SPIDR, the Digital Ionogram Database, DIDBase, and IPS Radio and Space Services) have been used for training a NN.