激光诱发间隙气体放电的试验研究

通过模拟试验的方法,对影响激光触发放电电压的主要因素进行研究,结果表明,与正极性比较,激光更易于触发负极性电压气隙放电,空气湿度亦对激光触发放电电压有影响;空气湿度在９５％,相对湿度下较４０％相对湿度下,相同激光能量触发的放电电压提高５％。     

Core formation in planetesimals triggered by permeable flow

The tungsten isotope composition of meteorites indicates that core formation in planetesimals occurred within a few million years of Solar System formation. But core formation requires a mechanism for segregating metal, and the 'wetting' properties of molten iron alloy in an olivine-rich matrix is thought to preclude segregation by permeable flow unless the silicate itself is partially molten. Excess liquid metal over a percolation threshold, however, can potentially create permeability in a solid matrix, thereby permitting segregation. Here we report the percolation threshold for molten iron-sulphur compounds of approximately 5 vol.% in solid olivine, based on electrical conductivity measurements made in situ at high pressure and temperature. We conclude that heating within planetesimals by decay of short-lived radionuclides can increase temperature sufficiently above the iron-sulphur melting point (approximately 1,000 degrees C) to trigger segregation of iron alloy by permeable flow within the short timeframe indicated by tungsten isotopes. We infer that planetesimals with radii greater than about 30 km and larger planetary embryos are expected to have formed cores very early, and these objects would have contained much of the mass in the terrestrial region of the protoplanetary nebula. The Earth and other terrestrial planets are likely therefore to have formed by accretion of previously differentiated planetesimals, and Earth's core may accordingly be viewed as a blended composite of pre-formed cores.     

洪水诱发储罐失效的定量风险评估方法

为了解决自然灾害诱发的事故灾难(又称Natech事件)的风险评估问题,提出了针对Natech事件进行定量风险评估的流程框架和方法,并应用于洪水诱发储罐失效的概率和后果的风险分析中。该方法首先确定自然灾害的频率和强度,对在此灾害中可能遭受破坏的设备进行风险辨识;然后确定灾害情景的分类和特征,计算洪水触发储罐失效的概率;最后根据事件树分析的方法,对可能发生的灾害情景和后果进行分析。该文假设某化工厂储罐区域因洪水导致储罐失效,进而引发氨气泄漏的案例。应用该方法计算个人风险分布情况,并在地理信息系统(GIS)上进行了可视化展示。研究结果表明:该方法在定量化洪水诱发储罐失效的风险评估中具有可行性;同时给出了相关风险管理的措施和建议。     

Chloroplast to nucleus communication triggered by accumulation of Mg-protoporphyrinIX

Plant cells coordinately regulate the expression of nuclear and plastid genes that encode components of the photosynthetic apparatus. Nuclear genes that regulate chloroplast development and chloroplast gene expression provide part of this coordinate control. There is evidence that information also flows in the opposite direction, from chloroplasts to the nucleus. Until now, at least three different signalling pathways have been identified that originate in the plastid and control nuclear gene expression but the molecular nature of these signals has remained unknown. Here we show that the tetrapyrrole intermediate Mg-protoporphyrin (Mg-ProtoIX) acts as a signalling molecule in one of the signalling pathways between the chloroplast and nucleus. Accumulation of Mg-ProtoIX is both necessary and sufficient to regulate the expression of many nuclear genes encoding chloroplastic proteins associated with photosynthesis.     

The T-cell repertoire is heavily influenced by tolerance to polymorphic self-antigens

T cells with V beta 3+ alpha beta receptors are deleted by self-tolerance in mice with particular major histocompatibility complex/self-antigen combinations. This also occurs for other V beta elements. Polymorphism in the major histocompatibility complex and/or the self-antigens that cause massive deletion of T cells using particular V beta elements may be maintained by the need to balance the advantage of a diverse T-cell repertoire against the potential involvement of those elements in autoimmune disease.     

Human basophil degranulation triggered by very dilute antiserum against IgE

When human polymorphonuclear basophils, a type of white blood cell with antibodies of the immunoglobulin E (IgE) type on its surface, are exposed to anti-IgE antibodies, they release histamine from their intracellular granules and change their staining properties. The latter can be demonstrated at dilutions of anti-IgE that range from 1 x 10(2) to 1 x 10(120); over that range, there are successive peaks of degranulation from 40 to 60% of the basophils, despite the calculated absence of any anti-IgE molecules at the highest dilutions. Since dilutions need to be accompanied by vigorous shaking for the effects to be observed, transmission of the biological information could be related to the molecular organization of water.     

Long-range structural changes in proteinase K triggered by calcium ion removal

The X-ray crystal structure of the subtilisin-type enzyme proteinase K at 1.5 A resolution shows that is has two binding sites for Ca2+. Scatchard analysis indicates that one Ca2+ binds tightly, with pK 7.6 x 10(-8) M-1, and the other only weakly. Although Ca2+ is not directly involved in the catalytic mechanism and is 16.6 A away from the alpha-carbon atoms of the catalytic triad Asp 39-His 69-Ser 224, the activity of proteinase K towards the synthetic substrate succinyl-Ala-Ala-Ala-p-nitroanilide drops slowly to approximately 20% of its original value when it is depleted of Ca2+. This is not due to autolysis of the enzyme. The X-ray crystal structure of Ca2+-free proteinase K shows that removal of Ca2+ from the tight binding site triggers a concerted domino-like movement of five peripheral loops and of two alpha-helices. At a distance of 25 A from this calcium-binding site, the geometry of both the secondary substrate binding site and of the catalytic triad is affected by this movement thereby reducing the activity of the enzyme.     

Fast neurotransmitter release triggered by Ca influx through AMPA-type glutamate receptors

Feedback inhibition at reciprocal synapses between A17 amacrine cells and rod bipolar cells (RBCs) shapes light-evoked responses in the retina. Glutamate-mediated excitation of A17 cells elicits GABA (gamma-aminobutyric acid)-mediated inhibitory feedback onto RBCs, but the mechanisms that underlie GABA release from the dendrites of A17 cells are unknown. If, as observed at all other synapses studied, voltage-gated calcium channels (VGCCs) couple membrane depolarization to neurotransmitter release, feedforward excitatory postsynaptic potentials could spread through A17 dendrites to elicit 'surround' feedback inhibitory transmission at neighbouring synapses. Here we show, however, that GABA release from A17 cells in the rat retina does not depend on VGCCs or membrane depolarization. Instead, calcium-permeable AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) receptors (AMPARs), activated by glutamate released from RBCs, provide the calcium influx necessary to trigger GABA release from A17 cells. The AMPAR-mediated calcium signal is amplified by calcium-induced calcium release (CICR) from intracellular calcium stores. These results describe a fast synapse that operates independently of VGCCs and membrane depolarization and reveal a previously unknown form of feedback inhibition within a neural circuit.     

Cretaceous oceanic anoxic event 2 triggered by a massive magmatic episode

Oceanic anoxic events (OAEs) were episodes of widespread marine anoxia during which large amounts of organic carbon were buried on the ocean floor under oxygen-deficient bottom waters. OAE2, occurring at the Cenomanian/Turonian boundary (about 93.5 Myr ago), is the most widespread and best defined OAE of the mid-Cretaceous. Although the enhanced burial of organic matter can be explained either through increased primary productivity or enhanced preservation scenarios, the actual trigger mechanism, corresponding closely to the onset of these episodes of increased carbon sequestration, has not been clearly identified. It has been postulated that large-scale magmatic activity initially triggered OAE2 (refs 4, 5), but a direct proxy of magmatism preserved in the sedimentary record coinciding closely with the onset of OAE2 has not yet been found. Here we report seawater osmium isotope ratios in organic-rich sediments from two distant sites. We find that at both study sites the marine osmium isotope record changes abruptly just at or before the onset of OAE2. Using a simple two-component mixing equation, we calculate that over 97 per cent of the total osmium content in contemporaneous seawater at both sites is magmatic in origin, a approximately 30-50-fold increase relative to pre-OAE conditions. Furthermore, the magmatic osmium isotope signal appears slightly before the OAE2-as indicated by carbon isotope ratios-suggesting a time-lag of up to approximately 23 kyr between magmatism and the onset of significant organic carbon burial, which may reflect the reaction time of the global ocean system. Our marine osmium isotope data are indicative of a widespread magmatic pulse at the onset of OAE2, which may have triggered the subsequent deposition of large amounts of organic matter.     

Oncogene-induced senescence is a DNA damage response triggered by DNA hyper-replication

Early tumorigenesis is associated with the engagement of the DNA-damage checkpoint response (DDR). Cell proliferation and transformation induced by oncogene activation are restrained by cellular senescence. It is unclear whether DDR activation and oncogene-induced senescence (OIS) are causally linked. Here we show that senescence, triggered by the expression of an activated oncogene (H-RasV12) in normal human cells, is a consequence of the activation of a robust DDR. Experimental inactivation of DDR abrogates OIS and promotes cell transformation. DDR and OIS are established after a hyper-replicative phase occurring immediately after oncogene expression. Senescent cells arrest with partly replicated DNA and with DNA replication origins having fired multiple times. In vivo DNA labelling and molecular DNA combing reveal that oncogene activation leads to augmented numbers of active replicons and to alterations in DNA replication fork progression. We also show that oncogene expression does not trigger a DDR in the absence of DNA replication. Last, we show that oncogene activation is associated with DDR activation in a mouse model in vivo. We propose that OIS results from the enforcement of a DDR triggered by oncogene-induced DNA hyper-replication.     

The chemical repertoire of natural ribozymes

Although RNA is generally thought to be a passive genetic blueprint, some RNA molecules, called ribozymes, have intrinsic enzyme-like activity--they can catalyse chemical reactions in the complete absence of protein cofactors. In addition to the well-known small ribozymes that cleave phosphodiester bonds, we now know that RNA catalysts probably effect a number of key cellular reactions. This versatility has lent credence to the idea that RNA molecules may have been central to the early stages of life on Earth.     

A 'snowball Earth' climate triggered by continental break-up through changes in runoff

Geological and palaeomagnetic studies indicate that ice sheets may have reached the Equator at the end of the Proterozoic eon, 800 to 550 million years ago, leading to the suggestion of a fully ice-covered 'snowball Earth'. Climate model simulations indicate that such a snowball state for the Earth depends on anomalously low atmospheric carbon dioxide concentrations, in addition to the Sun being 6 per cent fainter than it is today. However, the mechanisms producing such low carbon dioxide concentrations remain controversial. Here we assess the effect of the palaeogeographic changes preceding the Sturtian glacial period, 750 million years ago, on the long-term evolution of atmospheric carbon dioxide levels using the coupled climate-geochemical model GEOCLIM. In our simulation, the continental break-up of Rodinia leads to an increase in runoff and hence consumption of carbon dioxide through continental weathering that decreases atmospheric carbon dioxide concentrations by 1,320 p.p.m. This indicates that tectonic changes could have triggered a progressive transition from a 'greenhouse' to an 'icehouse' climate during the Neoproterozoic era. When we combine these results with the concomitant weathering effect of the voluminous basaltic traps erupted throughout the break-up of Rodinia, our simulation results in a snowball glaciation.     

离散事件触发NCS的容错与容侵协同设计方法

针对执行器失效故障和网络攻击,在离散事件触发通讯机制(DETCS)下研究了NCS故障容错与攻击容侵的协同设计问题.首先,给出了DETCS下NCS故障容错与攻击容侵的架构,并以此为基础建立了集触发条件、执行器故障与网络攻击于一体的闭环NCS故障/攻击并存模型;其次,通过构造Lyapunov-Krasovskii泛函,综合应用时滞系统理论、改进的Wirtinger不等式及互反凸组合引理等,推证出了NCS可容错故障/容侵攻击的完整性充分条件,进而给出了鲁棒H_∞容错/容侵控制器与事件触发矩阵的协同设计方法,达到了容错/容侵控制与网络通讯间的协同设计目标;最后,通过仿真算例验证了所得理论结果的有效性与可行性.     

通过调节免疫系统功能治疗癌症

摘要: 目前,对癌症的治疗除采取手术和化疗方法外,还没有发现可靠的治疗方法。科学研究表明,CTLA－4 和 PD－1是体内的两种蛋白,他们能抑制免疫系统发挥免疫攻击能力,从而导致肿瘤的形成。通过针对这两种蛋白制 备的单克隆抗体,可以破坏他们的抑制作用从而激活免疫系统,发挥抗肿瘤生长作用。此外,通过对 T 细胞进行基 因修饰可以使其将肿瘤细胞作为靶细胞。这种免疫疗法可被用于癌症的治疗并且已经取得了初步的成功。本文对以上两种方法的基本情况作了简要论述。为该领域的研究实践提供一定的参考。     

DNA疫苗经基因枪介导的免疫研究

将基因枪介导的DNA疫苗用于小鼠腹部免疫,并用免疫组化法检测gD抗原在接种部位的表达,利用ELISA检测血清中的抗gD抗体,并采用病毒攻击检测DNA疫苗对动物的保护效果。结果表明,基因枪可有效地将DNA质粒运送至小鼠皮肤组织,DNA疫苗携带的抗原保护基因gD2糖蛋白能在真皮和肌肉组织中高效表达。同时,免疫小鼠体内产生高滴度的中和抗体,能有效抵抗HSV2病毒的攻击。     

“4·20”芦山地震次生地质灾害预测评价

利用汶川地震次生地质敏感性评价模型,以距发震断层的距离、地形坡度、地层岩性、距离水系的距离、海拔高度、PGA为评价因子,对"4.20"芦山地震地质灾害的空间分布进行了快速预测,为野外调查工作提供参考。预测结果显示芦山地震次生地质灾害敏感性高的区域主要是芦山、宝兴、天全、雅安、荥经等县市的山区,并主要集中分布于发震断层附近的芦山县大川镇、宝盛乡、太平镇、双石镇、宝兴县灵关镇、天全县小河乡等区域。     

白血病间接免疫荧光法免疫表型分析

目的:研究白血病免疫表型的不同,明确诊断。方法:回顾性分析本院56例白血病患者免疫表型资料。结果:30例急性髓系白血病(AML)均表达髓系抗原,部分伴有淋巴抗原,但其阳性率明显低于急性淋巴细胞白血病(ALL)。7例M3的CD9抗原阳性率为100%,明显高于AML的其它亚型白血病。形态学诊断为ALL的12例白血病中,2例免疫表型为T-ALL,10例B-ALL。4例为杂合性急性白血病,它的诊断标准主要靠免疫分型。在10例慢性粒细胞性白血病(CML)中,4例发生急粒变,且急变期CD34抗原阳性率高于慢性期。结论:免疫表型分析与形态学、细胞化学三者结合为白血病的诊断提供了更可靠、更有价值的依据。