WR 技术的发展与应用

本文介绍一种在精密时钟同步协议（PTP）的基础上发展而来的新技术——WR 技术（White Rabbit，白兔）。WR 联合同步以太网以及双混频时差法测量手段，通过对主从时钟间链路环路延迟的不间断高精度的测量，后以测量结果对从时钟的时钟信息进行动态校准，主从时钟的同步精度达到亚纳秒甚至皮秒级。文章先引出WR的发展历史，以及WR 中所包含的主要技术，并介绍目前WR 在某些科学领域所发挥的作用，最后提出WR 未来在其他领域的应用。     

Wolf–Rayet optically thick winds with Alfvén waves

The Wolf–Rayet (WR) stars are hot luminous objects which are suffering an extreme mass loss via a continuous stellar wind. The high values of mass loss rates and high terminal velocities of the WR stellar winds constitute a challenge to the theories of radiation driven winds. Several authors incorporated magnetic forces to the line driven mechanism in order to explain these characteristics of the wind. Observations indicate that the WR stellar winds may reach, at the photosphere, velocities of the order of the terminal values, which means that an important part of the wind acceleration occurs at the optically thick region. The aim of this study is to analyze a model in which the wind in a WR star begins to be accelerated in the optically thick part of the wind. We used as initial conditions stellar parameters taken from the literature and solved the energy, mass and momentum equations. We demonstrate that the acceleration only by radiative forces is prevented by the general behavior of the opacities. Combining radiative forces plus a flux of Alfvén waves, we found in the simulations a fast drop in the wind density profile which strongly reduces the extension of the optically thick region and the wind becomes optically thin too close its base. The understanding how the WR wind initiate is still an open issue.     

Radiation protection issues in galactic cosmic ray risk assessment.

Radiation protection involves the limitation of exposure to below threshold doses for direct (or deterministic) effects and a knowledge of the risk of stochastic effects after low doses. The principal stochastic risk associated with low dose rate galactic cosmic rays is the increased risk of cancer. Estimates of this risk depend on two factors (a) estimates of cancer risk for low-LET radiation and (b) values of the appropriate radiation weighting factors, WR, for the high-LET radiations of galactic cosmic rays. Both factors are subject to considerable uncertainty. The low-LET cancer risk derived from the late effects of the atomic bombs is vulnerable to a number of uncertainties including especially that from projection in time, and from extrapolation from high to low dose rate. Nevertheless, recent low dose studies of workers and others tend to confirm these estimates. WR, relies on biological effects studied mainly in non-human systems. Additional laboratory studies could reduce the uncertainties in WR and thus produce a more confident estimate of the overall risk of galactic cosmic rays.     

Role of endogenous thiols in protection.

Aminothiols represent the most important group of radioprotective compounds. The most effective compounds administered at an optimal dose and time before irradiation are able to provide a protection in mice with a dose reduction factor (DRF) of about 2-2.5. The working mechanism can partly be explained as a scavenging process of radicals induced in water and partly as a chemical repair process of injured DNA. The endogenous aminothiol which has far-out the highest intracellular concentration is glutathione (GSH). The importance of intracellular GSH in determining cellular radiosensitivity has been shown by irradiating cells that had very low GSH levels. Such cells appear to have a high radiosensitivity, especially in hypoxic conditions. On the other hand, it has been demonstrated that induction of a high GSH level (100-200% above the normal level) provides only a small protection. In vitro experiments with DNA indicate that thiols with a high positive charge condense in the vicinity of DNA and are effective protectors, whereas thiols with a negative charge are kept away from it and are poor protectors. In comparison with the most effective exogenous aminothiols like cysteamine and WR1065, GSH is not an effective radioprotector. Putative explanations for this relatively poor protective ability of GSH are presented.     

Simulation experiments of the effect of space environment on bacteriophage and DNA thin films.

The main goal of PUR experiment (phage and uracil response) is to examine and quantify the effect of specific space conditions on nucleic acid models. To achieve this an improved method was elaborated for the preparation of DNA and bacteriophage thin films. The homogeneity of the films was controlled by UV spectroscopy and microscopy. To provide experimental evidence for the hypothesis that interplanetary transfer of the genetic material is possible, phage T7 and isolated T7 DNA thin films have been exposed to selected space conditions: intense UVC radiation (lambda=254 nm) and high vacuum (10(-4) Pa). The effects of DNA hydration, conformation and packing on UV radiation damage were examined. Characteristic changes in the absorption spectrum, in the electrophoretic pattern of DNA and the decrease of the amount of PCR products have been detected indicating the photodamage of isolated and intraphage DNA.     

Effect of secondary radiation produced by 70 GeV protons on DNA of mammalian cells.

It is shown that the RBE of the 70 GeV proton secondary radiation for the induction of single-strand break is 1.6-7.6 in Chinese hamster fibroblasts and 1.04-3.8 in limphoid cells and for the lethality of Chinese hamster cells 1.14-1.7. The RBE value increases with decreasing dose of the secondary radiation. On post-irradiation incubation of mammalian cells at 37 degrees C, single-strand breaks induced by the secondary radiation are repaired with the sane time course as those induced by gamma-rays. In our earlier works we have made an attempt to estimate the biological efficiency of radiation generated by the 70 GeV protons on bacteria, phage T4 and Vicia faba beans. The obtained values of the relative biological efficiency (RBE) of this radiation varied between 1.4 and 5.5, depending on the object, criterion of estimation, times of registration and other experimental conditions. The aim of the present work is to estimate the biological efficiency of synchrotron radiation by its effect on mammalian cells.     

Host–parasite interactions in closed and open microbial cultivation system

The study addresses interaction of bacteria and phages in the host–parasite system in batch and continuous cultures. The study system consists of the auxotrophic strain of Brevibacterium – Brevibacterium sp. 22L – and the bacteriophage of Brevibacterium sp., isolated from the soil by the enrichment method.

1.

Closed system. In the investigation of the relationship between the time of bacterial lysis and multiplicity of phage infection it has been found that at a lower phage amount per cell it takes a longer time for the lysis of the culture to become discernible. Another important factor determining cytolysis in liquid medium is the physiological state of bacterial population. Specific growth rate of bacteria at the moment of phage infection has been chosen as an indicator of the physiological state of bacteria. It has been shown that the shortest latent period and the largest output of the phage are observed during the logarithmic growth phase of bacteria grown under favorable nutrient conditions. In the stationary phase, bacterial cells become “a bad host” for the phage, whose reproduction rate decreases, and the lysis either slows down significantly or does not occur at all.     

X-ray variability in V444 Cygni — Evidence for colliding winds

Phase-resolved ROSAT observations of the soft X-ray flux from V444 Cygni confirm the orbital dependence of the flux suggested by analysis of IPC observations. The X-ray behavior suggests that a region of X-ray emitting gas exists between the 2 stars, probably produced by a collision between the WR and O star winds.     

Biological UV dosimeters in simulated space conditions.

Polycrystalline uracil thin layers participate in the phage and uracil response (PUR) experiment, assigned to the biological dosimetry of the extraterrestrial solar radiation on the International Space Station (ISS). In ground based experiments (experiment verification tests), the following space parameters were simulated and studied: temperature, vacuum and short wavelength UV (UV-C, down to 200 nm) radiation. The closed uracil samples proved to be vacuum-tight for 7 days. In the tested temperature range (from -20 to +40 degrees C) the uracil samples are stable. The kinetic of dimer formation (dimerization) and reversion (monomerization) of uracil dimers due to short wavelength UV radiation was detected, the monomerization efficiency of the polychromatic deuterium lamp is higher than that of the germicidal lamp. A mathematical model describing the kinetic of monomerization-dimerization was constructed. Under the influence of UV radiation the dimerization-monomerization reactions occur simultaneously, thus the additivity law of the effect of the various wavelengths is not applicable.     

Effect of clinostat rotation on differentiation of embryonic bone in vitro.

We have investigated the effect of changes in the gravity vector on osteoblast behaviour, using the clinostat set at 8 rpm. Two sources of osteoblasts were used: secondary cultures of fetal rat bone cells, and the rat osteosarcoma line 17/2.8 (ROS). Cell number was determined by incubation with 3-(4,dimethyl-2yl)-2,3 diphenyl) tetrazolium bromide (MTT) and measurement of optical density at 570 nm (OD). Alkaline phosphatase activity was detected by standard cytochemical methods. Dividing cells were localised by labelling dividing nuclei with Bromodeoxyuridine (BrdU), detected by immunofluorescence. Cell culture was initiated at densities between 1-4x10(4) cells ml-1. Growth rates in all cultures during the first 48 hours exposure to clinostat rotation were less than in stationary controls. After 3 days, ROS cell numbers were 35% lower, and calvarial cells 39% lower than their respective controls. Alkaline phosphatase activity in calvarial control cultures was uniformly present in characteristically polygonal cells, but after culture in the clinostat the enzyme was present sporadically, and the cells were cuboid. There was also no BrdU uptake in nuclei, but it was present in cell cytoplasms. We conclude that the clinostat decreases cell numbers and cell division. Both cell shape and the distribution of alkaline phosphatase activity in calvarial cell cultures were also affected. This implies that changes in the gravity vector can affect osteoblasts directly, without interaction with other cell types.     

Efficacy of an ototoxic aminoglycoside (gentamicin) on the differentiation of the inner ear of cichlid fish.

Previous investigations revealed that the growth of fish inner ear otoliths depends on the amplitude and the direction of gravity, thus suggesting the existence of a (negative) feedback mechanism. In the course of these experiments, it was shown that altered gravity both affected otolith size (and thus the provision of the proteinacious matrix) as well as the incorporation of calcium. It is hitherto unknown, as of whether sensory hair cells are involved either in the regulation of otolith growth or in the provision of otolithic material (such as protein or inorganic components) or even both. The ototoxic aminoglycoside gentamicin (GM) damages hair cells in many vertebrates (and is therefore used for the treatment of Meniere's disease in humans). The present study was thus designed to determine as of whether vestibular sensory cells are needed for otolith growth by applying GM in order to induce a (functionally relevant) loss of these cells. Developing cichlid fish Oreochromis mossambicus were therefore immersed in 120 mg/l GM for 10 or 21 days. At the beginning and at the end of the experimental periods, the fish were incubated in the calcium-tracer alizarin complexone (AC). After the experiment, otoliths were dissected and the area grown during GM-exposure (i.e., the area enclosed by the two AC labellings) was determined planimetrically. The results showed that incubating the animals in a GM-solution had no effect on otolith growth, but the development of otolith asymmetry was affected. Ultrastructural examinations of the sensory hair cells revealed that they had obviously not been affected by GM-treatment (no degenerative morphological features observed). Overall, the present results suggest that hair cells are not affected by GM concerning their possible role in (general) otolith growth, but that these cells indeed might have transitionally been impaired by GM resulting in a decreased capacity of regulating otolith symmetry.     

Tumor suppressor function of Betaig-h3 gene in radiation carcinogenesis.

Interaction between cell and extracellular matrix (ECM) plays a crucial role in tumor invasiveness and metastasis. Using an immortalized human bronchial epithelial (BEP2D) cell model, we showed previously that expression of a list of genes including Betaig-h3 (induced by transforming growth factor-beta), DCC (deleted in colorectal cancer), p21(cipl), c-fos, Heat shock protein (HSP27) and cytokeratin 14 were differentially expressed in several independently generated, radiation-induced tumor cell lines (TL1-TL5) relative to parental BEP2D cells. Our previous data further demonstrated that loss of tumor suppressor gene(s) as a likely mechanism of radiation carcinogenesis. In the present study, we chose Betaig-h3 and DCC that were downregulated in tumorigenic cells for further study. Restored expression of Betaig-h3 gene, not DCC gene, by transfecting cDNA into tumor cells resulted in a significant reduction in tumor growth. While integrin receptor alpha 5 beta 1 was overexpressed in tumor cells, its expression was corrected to the level found in control BEP2D cells after Betaig-h3 transfection. These data suggest that Betaig-h3 gene is involved in tumor progression by regulating integrin alpha 5 beta 1 receptor. Furthermore, exogenous TGF- beta 1 induced expression of Betaig-h3 gene and inhibited the growth of both control and tumorigenic BEP2D cells. Therefore, downregulation of Betaig-h3 gene may results from the decreased expression of upstream mediators such as TGF-beta. The findings provide strong evidence that the Betaig-h3 gene has tumor suppressor function in radiation-induced tumorigenic human bronchial epithelial cells and suggest a potential target for interventional therapy.     

Induction of chromosome aberrations in mammalian cells after heavy ion exposure.

The induction of chromosome aberrations by heavy charged particles was studied in V79 Chinese hamster cells over a wide range of energies (3-100 MeV/u) and LET (20-16000 keV/micrometer). For comparison, X-ray experiments were performed. Our data indicate quantitative and qualitative differences in the response of cells to particle and x-ray irradiation. For the same level of cell survival the amount of damaged cells which can be observed is smaller in heavy ion (11.4 MeV/u Ar) irradiated samples. The highest yield of damaged cells is found 8 to 12 hours after particle irradiation and 4 hours after x-irradiation. Differences in the amount of damaged cells are attributed to cell cycle perturbations which interfere with the expression of damage. After heavy ion exposure the amount of cells reaching mitosis (mitotic index) decreases drastically and not all damaged cells reach mitosis within 48 hours after exposure. A portion of cells die in interphase. Cell cycle delays induced by x-ray irradiation are less pronounced and all cells reach the first post-irradiation mitosis within 24 hours after irradiation. Additionally, the damage produced by charged particles seems to be more severe. The disintegration of chromosomes was only observed after high LET radiation: an indication of the high and local energy deposition in the particle track. Only cross sections for the induction of chromosome aberrations in mitotic cells were reported in this paper because of the problems arising from the drastic cell cycle perturbations. In this case, cells were irradiated in mitosis and assayed immediately.     

Effects of prolonged exposure of lettuce seeds to HZE particles on orbital stations.

In a study of the biological effects of cosmic HZE particles, lettuce (Lactuca sativa) seeds were flown on the orbital stations Salyut 6 and 7 for varying periods of time (from 40 to 457 days). The dependence of the biological damage on flight duration, physical parameters and the fact of passage of an HZE particle through the seed was estimated using the criterion of the frequency of aberrant cells. The arrangement of the flight biological container Biobloc made it possible to trace the location of tracks of individual HZE particles with Z > or = 6 and LET 200 keV/um. In seeds hit by HZE particles, for all exposure times, a statistically significant much higher yield of aberrant cells and also of cells containing multiple chromosome aberrations was observed than in the control material. The frequency of aberrant cells is markedly higher (by a factor of 1,5) in seeds hit than in non-hit ones. The changes of the yield of aberrant cells as a function of the absorbed dose (3.2-63.4 mGy) and the fluence (4.8-44.2 particles/cm2) are linear for the exposure duration ranging from 40 to 457 days.     

Influence of gravity on the photomorphism of secondary moss protonemata

In dark-grown plantlets of the moss, Pottia intermedia, negatively gravitropic secondary protonemata differentiate from the superficial cells of leafy shoots. When transferred to the light, distal parts of the protonemata nearest to the apical cells begin to ramify and the apical cells of the side branches as well as of the main protonemal filaments often differentiate as buds. Dark-grown protonemata were oriented horizontally and illuminated from below with white light of different intensities. Only light with an intensity of 4.5 μmol·m⁻²·s⁻¹ was sufficient to induce: (a) phototropism in the apical cells, (b) light-directed initiation of branch primordia, and (c) directed growth of side branches and bud differentiation. Apical cells illuminated with light of lower (0.03–0.37 μmol·m⁻²·s⁻¹) intensity grew upwards (i.e., away from the light). It was shown that this upward growth was determined by the action of gravity. Although initiation of branch primordia was only slightly affected, their growth was strongly stimulated on the upper side of the protonemata.     

Gravitaxis and graviperception in Euglena gracilis.

Gravitactic orientation in the flagellate Euglena gracilis is mediated by an active physiological receptor rather than a passive alignment of the cells. During a recent space flight on the American shuttle Columbia the cells were subjected to different accelerations between 0 and 1.5 x g and tracked by computerized real-time image analysis. The dependence of orientation on acceleration followed a sigmoidal curve with a threshold at < or = 0.16 x g and a saturation at about 0.32 x g. No adaptation of the cells to the conditions of weightlessness was observed over the duration of the space mission (12 days). Under terrestrial conditions graviorientation was eliminated when the cells were suspended in a medium the density of which (Ficoll) equaled that of the cell body (1.04 g/ml) and was reversed at higher densities indicating that the whole cytoplasm exerts a pressure on the respective lower membrane. There it probably activates stretch-sensitive calcium specific ion channels since gravitaxis can be affected by gadolinium which is a specific inhibitor of calcium transport in these structures. The sensory transduction chain could involve modulation of the membrane potential since ion channel blockers, ionophores and ATPase inhibitors impair graviperception.     

应用于DSMC方法的二维Voronoi网格技术

研究了Voronoi网格技术并将其应用于直接模拟蒙特卡洛DSMC(Direct Simulation Monte Carlo)计算.基于Dirichlet镶嵌与Voronoi图理论,Voronoi网格利用特征点表征网格单元,具有建立粒子与网格单元之间映射关系的独特算法,适合于DSMC方法的统计特点.在剔除过于靠近边界的特征点以及必要情况下边界细化的基础上,通过区分由边界节点表征的非完整Voronoi网格单元以及由计算区域内镶嵌点表征的完整Voronoi网格单元,解决了Voronoi网格的二维边界匹配问题.Voronoi网格技术支持自适应DSMC计算.映射效率对比表明,Voronoi网格的DSMC计算效率高于三角形网格,低于多级直角网格.通过MEMS微喷管流动数值模拟,验证了Voronoi网格技术在DSMC方法中的有效性.      

Signs of Müller cell gliotic response found in the retina of newts exposed to real and simulated microgravity

The effects of real and simulated microgravity on the eye tissue regeneration of newts were investigated. For the first time changes in Müller glial cells in the retina of eyes regenerating after retinal detachment were detected in newts exposed to clinorotation. The cells divided, were hypertrophied, and their processes were thickened. Such changes suggested reactive gliosis and were more significant in animals exposed to rotation when compared with desk-top controls. Later experiments onboard the Russian biosatellite Bion-11 showed similar changes in the retinas that were regenerating in a two-week spaceflight. In the Bion-11 animals, GFAP, the major structural protein of retinal macroglial cells, was found to be upregulated. In a more recent experiment onboard Foton-M3 (2007), GFAP expression in retinas of space-flown, ground control (kept at 1 g), and basal control (sacrificed on launch day) newts was quantified, using microscopy, immunohistochemistry, and digital image analysis. A low level of immunoreactivity was observed in basal controls. In contrast, retinas of space-flown animals showed greater GFAP immunoreactivity associated with both an increased cell number and a higher thickness of intermediate filaments. This, in turn, was accompanied by up-regulation of stress protein (HSP90) and growth factor (FGF2) expressions. It can be postulated that such a response of Müller cells was to mitigate the retinal stress in newts exposed to microgravity. Taken together, the data suggest that the retinal population of macroglial cells could be sensitive to gravity changes and that in space it can react by enhancing its neuroprotective function.     

基于SIMP法的周期性传热材料拓扑优化

为了实现基于宏观热传导条件的周期性材料微结构设计,建立了基于固体各向同性材料惩罚法的周期性结构拓扑优化模型.模型以体积比为约束,散热弱度最小为优化目标.为了满足周期性约束,将设计域划分为若干相同子区域,并重新分配散热弱度.基于偏微分方程的图像处理方式可以有效地消除棋盘格和网格依赖性现象.讨论并分析了不同子区域个数及不同载荷工况对拓扑优化构型的影响.数值实验结果表明:周期性结构的建模方式可以实现基于宏观稳态热传导条件的周期性材料微结构设计.子区域个数不同时,优化得到不同的微结构构型,这反映了尺寸效应对材料设计的影响.当子区域个数不断增加时,优化结果逐渐趋向收敛于均匀化方法对应的极限值.      

Focal contacts organization in osteoblastic cells under microgravity and cyclic deformation conditions.

We compared quantitatively vinculin-related adhesion parameters in osteoblastic cells submitted to opposite mechanical stresses, i.e., low deformation and frequency strain regimens (stretch condition) and microgravity exposure (relaxed condition). Cyclic deformation induced a biphasic response comprising new focal contacts formation followed by their clustering in ROS cells. Microgravity exposure induced a reduction in focal contact number and clustering in ROS cells. We previously demonstrated that 1% cyclic deformations at 0.05 Hz during a daily 10 min episode over 7 days stimulated ROS 17/2.8 growth as compared to static culture whereas relaxed ROS proliferated similarly to static culture (BC). To evaluate whether the proliferation (stretch) or the survival (relaxed) status of ROS cells influences focal contact organization, we inhibited ERKs proliferative-dependent pathway. Inhibition of proliferation by PD98059 was overcome although not fully restored by stretch. Furthermore stretch-induced clustering of vinculin-positive contacts still occurs in the presence of ERKs inhibitor, whereas the increase in focal contact number is abolished. In conclusion, we showed that focal contacts are mechanoeffectors and that hyper-mechanical stimulation could up regulate focal contacts size as compared to hypo-mechanical that down regulate clusterization.