The dynamic evolution of the kepler supernova remnant

been analyzed in detail. The effects ofm icroscopic energy transfer from

The Droplet Group Micro-Explosions, Viscosity and Atomization Characteristics of W/O Emulsions

The spray of emulsified fuel, composed of diesel fuel, water and methanol can make micro-explosion under high temperature conditions, and the viscosity and the atomization characteristics of emulsion have significant effects on the micro- explosion of emulsions. To clarify the combustion mechanism of water-in-oil emulsion sprays, combustion bomb experiments were carried out, and the droplet group micro- explosions in W/O fuel emulsion sprays in a high-pressure, high-temperature bomb were observed clearly by a multi-pulsed, off-axis, image-plane ruby laser holocamera and continuously by a high-speed CCD camera.The viscosity and atomization characteristics of emulsions were also studied experimentally. The experimental results show that the higher concentration of the aqueous phase (water-methanol) (<50%) increases the viscosity of the emulsions, especially for higher agent concentration, and higher aqueous phase concentration and higher viscosity results in lager Sauter Mean Diameter (SMD). The experiment results also show that the different kinds of emulsifying agents, with different Hydrophile-Lipophile Balance (HLB) values, have significant influence on the viscosity of the emulsions.

Pure Coulomb explosions of highly charged methane clusters investigated by a simple electrostatic model

The pure Coulomb explosions of the methane clusters (CA(4))(n), (light atom A = H or D) have been investigated by a simplified electrostatic model for both a single cluster and an ensemble of clusters with a given cluster size distribution. The dependence of the energy of ions produced from the explosions on cluster size and the charge state of the carbon ions has been analysed. It is found that, unlike the average proton energy which increases with the charge q of the carbon ions, the average deuteron energy tends to saturate as q becomes larger than 4. This implies that when the laser intensity is sufficiently high for the (CD4)(n) to be ionized to a charge state of (C4+D4+)(n), the neutron yield from a table-top laser-driven Coulomb explosion of deuterated methane clusters (CD4)(n) could be increased significantly by increasing the interaction volume rather than by increasing the laser intensity to produce the higher charge state (C6+D4+)(n). The flight-time spectra of the carbon ions and the light ions have also been studied.

Nuclear fusion from Coulomb explosions of deuterated methane clusters subjected to ultraintense femtosecond laser pulses

This paper reports that Coulomb explosions taken place in the experiment of heteronuclear deuterated methane clusters ((CD4)(n)) in a gas jet subjected to intense femtosecond laser pulses (170 mJ, 70 fs) have led to table-top laser driven DD nuclear fusion. The clusters produced in supersonic expansion had an average energies of deuterons produced in the laser-cluster interaction were 60 and 1.5 KeV, respectively. From DD collisons of energetic deuterons, a yield of 2.5(+/-0.4)x10(4) fusion neutrons of 2.45 MeV per shot was realized, giving rise to a neutron production efficiency of about 1.5 x 10(5) per joule of incident laser pulse energy. Theoretical calculations were performed and a fairly good agreement of the calculated neutron yield with that obtained from the present experiment was found.

Effects on the proton production from explosions of hydrogen clusters subjected to intense femtosecond laser fields

The dependence of the maximum and average energies of protons, which were produced in the interaction of an intense laser pulse (similar to 1 x 10(16) W cm(-2), 65 fs) with hydrogen clusters in a gas jet backed up to 80 bar at liquid nitrogen temperature (similar to 80 K), on the backing pressure has been studied. The general trend of the proton energy dependence on the square of the average cluster radius, which is determined by a calibrated Rayleigh scattering measurement, is similar to that described by theory under the single size approximation. Calculations are made to fit the experimental results under a simplified model by taking into account both a log-normal cluster size distribution and the laser intensity attenuation in the interaction volume. A very good agreement between the experimental proton energy spectra and the calculations is obtained in the high- energy part of the proton energy distributions, but a discrepancy of the fits is revealed in the low-energy part at higher backing pressures which are associated with denser flows. A possible mechanism which would be responsible for this discrepancy is discussed. Finally, from the fits, a variation of the cluster size distributions was revealed to be dependent on the gas backing pressure as well as on the evolving time of the gas flow of clusters.

柴油、甲醇和水三组元乳化液滴微爆过程的研究

分别采用激光全息摄影技术和高速数字摄影技术观察了柴油、甲醇和水乳化液喷雾在高温高压(773K,3.1MPa)环境中发生微爆现象的瞬间和全过程,证实了微爆现象的存在.由于微爆机理的复杂性,尚难以用数学方法准确描述该过程.实验分析表明:若环境温度处于"最佳温度"范围内,乳化液滴表面首先形成"无水层",液滴内部形成一个水滴的概率很小,可能形成几个相对较大的水滴,只要其中一个较大水滴的蒸汽压力大于液滴的表面张力和环境压力之和,液滴就有可能发生微爆,微爆不仅与液滴直径、组分的质量分数和组分间的沸点差等乳化液的本身特性有关,而且环境温度和压力的影响也不容忽视.该研究可以为乳化液喷雾微爆过程的数学模拟提供参考.

岩石爆炸增渗模型实验及DEM数值模拟研究

岩体中爆炸提高矿石的渗透性可以极大地提高采矿效率，是碎裂岩型矿床预裂浸出法的关键技术。混凝土与岩体都具有脆性材料的特性，因此用浇筑于铁桶中的混凝土试件进行模型实验研究岩体的爆炸增渗效果。铁桶可以提高实验效率，使边界条件更为简单和易于操作，但是，实验和原型的差异需要论证。用自主开发的基于连续介质力学模型的离散元方法，模拟了有铁桶边界的模型实验，验证了数值模拟方法的可行性及有效性，给出了有弹性侧限边界约束的混凝土和较大尺度无反射边界条件的岩石中的爆炸差别。在此基础上，分析了岩石中爆炸造成的岩石破坏规律。计算结果表明：岩石破坏面总面积和破坏区的最大裂缝宽度受药量和岩石的抗拉强度影响，破坏面总面积和裂缝宽度随药量增加而增大，随抗拉强度增大而减小；在药量相同的条件下，实际岩石环境下的岩块破坏程度比铁桶约束的大。模型实验和数值模拟相结合的办法可以对混凝土和岩石的爆炸破坏给出较为合理的结果。

Studies of ion energy and yield from argon clusters heated by intense femtosecond laser pulses

Using time-of-flight spectrometry, the interaction of intense femtosecond laser pulses with argon clusters has been studied by measuring the energy and yield of emitted ions. With two different supersonic nozzles, the dependence of average ion energy (E) over bar on cluster size (n) over bar in a large range of (n) over bar approximate to 3 x 10(3) similar to 3 x 10(6) has been measured. The experimental results indicate that when the cluster size (n) over bar <= 3 x 10(5), the average ion energy (E) over bar proportional to (n) over bar (0.5), Coulomb explosion is the dominant expansion mechanism. Beyond this size, the average ion energy gets saturated gradually, the clusters exhibit a mixed Coulomb-hydrodynamic expansion behavior. We also find that with the increasing gas backing pressure, there is a maximum ion yield, the ion yield decreases as the gas backing pressure is further increased.

Neutron source from thin foil confined by two laser pulses

Neutron production from a thin deuterium-tritium (D-T) foil irradiated by two intense femtosecond laser pulses from opposite sides with zero phase difference is studied analytically and numerically. For the interaction of a laser pulse of amplitude a = 7, focal area 100 mu m(2) and areal density 4.4 x 10(18) cm(-2) with a D-T plasma foil, about 1.17 x 10(21) neutron s(-1) can be obtained, much more than from other methods. The profiles of the ion and electron densities are also calculated.

A plasma channel scheme for the interaction of an intense femtosecond laser pulse with a deuterium cluster jet

We propose a plasma channel scheme to obtain an improved table-top laser driven fusion neutron yield as a result of explosions of large deuterium clusters irradiated by an intense laser pulse. A cylindrical plasma channel is created by two moderate intensity laser prepulses at the edge of a deuterium cluster jet along which an intense main laser pulse propagates several nanoseconds later. With the aid of this plasma channel, the main laser pulse will be allowed to deposit its energy into the central region of the deuterium gas jet where the cluster sizes are larger and the atomic density is higher. The plasma channel formation and its impact on the deuterium ion energy spectrum and the consequent fusion neutron yield have been investigated. The calculated results show that a remarkable increase of the table-top laser driven fusion neutron yield would be expected.

Effect of laser spot size on fusion neutron yield in laser-deuterium cluster interactions

The effect of the laser spot size on the neutron yield of table-top nuclear fusion from explosions of a femtosecond intense laser pulse heated deuterium clusters is investigated by using a simplified model, in which the cluster size distribution and the energy attenuation of the laser as it propagates through the cluster jet are taken into account. It has been found that there exists a proper laser spot size for the maximum fusion neutron yield for a given laser pulse and a specific deuterium gas cluster jet. The proper spot size, which is dependent on the laser parameters and the cluster jet parameters, has been calculated and compared with the available experimental data. A reasonable agreement between the calculated results and the published experimental results is found.

甲烷团簇纯库仑爆炸的离子平均动能

利用一简单的经典静电模型研究了甲烷团簇纯库仑爆炸情况下产生的离子平均动能。研究表明，甲烷团簇爆炸后离子获得的平均动能和离子的初始平均静电势能的比值，与团簇的尺寸大小无关。这意味着在甲烷团簇纯库仑爆炸近似下，不必使用分子动力学模拟，离子获得的动能可以通过这一比值以及离子的初始静电势能进行估算。给出了不同碳离子价态下的离子平均动能和其初始平均静电势能的比值。

The Yangtze River dolphin or baiji (Lipotes vexillifer): population status and conservation issues in the Yangtze River, China

1. Baiji were sighted 17 times during three recent simultaneous multi-vessel surveys in the Yangtze River, China (November 4-10, 1997; December 4-9, 1998; October 31-November 5, 1999). There were 11 sightings in 1997 (consisting of 17 animals), five in 1998 (seven animals), and two in 1999 (four animals). It was concluded that 13 individuals Could be considered as a minimum number of the baiji currently in the Yangtze River. 2. An annual rate of population decrease was roughly estimated as 10%. From the body sizes observed, the proportions of old, adult and immature individuals were approximately estimated at 57, 26, and 17% respectively. 3. Baiji showed a significant attraction to confluences and sand bars with large eddies. The present distribution range of the baiji is less than 1400 km in length in the Yangtze main river. Distances between the two nearest groups of baiji appear to be increasing. 4. Two typical sightings are described, in which surfacing and movements of baiji were recorded. Baiji were often found swimming together with finless porpoise. In the surveys they occurred in the same group in 63% of occurrences. Interactions between baiji and finless porpoise are described and discussed. 5. Human activities are the main threats to the baiji. Illegal electrical fishing accounted for 40% of known mortalities during the 1990s. Engineering explosions for maintaining navigation channels have become another main cause of baiji deaths. The last hope of saving the species may be to translocate the remaining baiji into a semi-captive reserve. known as the 'Baiji Semi-natural Reserve'. Copyright (C) 2003 John Wiley Sons, Ltd.