Heavy ion induced double strand breaks in bacteria and bacteriophages.

DNA damage induced by heavy ions in bacterial cells and bacteriophages such as Bacillus subtilis, E. coli and Bacteriophage T1 were investigated by analyzing the double strand breaks in the chromosomal DNA. This kind of lesion is considered as one of the main reasons for lethal events. To analyze double strand breaks in long molecules of DNA--up to some Mbp in length--the technique of pulse field agarose gel electrophoresis has been used. This allows the detection of one double strand break per genome. Cell lysis and DNA isolation were performed in small agarose blocks directly. This procedure secured minimum DNA destruction by shearing forces. After running a gel, the DNA was stained with ethidium bromide. The light intensity of ethidium bromide fluorescence for both the outcoming (running) DNA and the remaining intact DNA were measured by scanning. The mean number of double strand breaks was calculated by determining the quotient of these intensities. Strand break induction after heavy ion and X-ray irradiation was compared.     

Direct radiation action of heavy ions on DNA as studied by ESR-spectroscopy.

The effects of heavy ions on the mechanisms of free radical formation in DNA-constituents as compared to low-LET irradiation are investigated by means of Electron Spin Resonance (ESR) spectroscopy. Dose-yield curves were measured at low (T < 100 K) and ambient temperatures in order to obtain the G-value, that is number of radicals formed per 100 eV absorbed energy. These G-values show a characteristic LET-dependence and are one to two orders of magnitude lower than for low-LET irradiation. Measurements on 2'Deoxycytidine at 300 K using combined heavy ion and X-ray irradiation methods suggested that this effect can be partially explained by a destruction of radicals during the irradiation.     

Fractionation of SI, NE, and MG Isotopes in the Solar Wind as Measured by Soho/Celias/MTOF

Using the high-resolution mass spectrometer CELIAS/MTOF on board SOHO we have measured the solar wind isotope abundance ratios of Si, Ne, and Mg and their variations in different solar wind regimes with bulk velocities ranging from 330 km/s to 650 km/s. Data indicate a small systematic depletion of the heavier isotopes in the slow solar wind on the order of (1.4±1.3)% per amu (2σ-error) compared to their abundances in the fast solar wind from coronal holes. These variations in the solar wind isotopic composition represent a pure mass-dependent effect because the different isotopes of an element pass the inner corona with the same charge state distribution. The influence of particle mass on the acceleration of minor solar wind ions is discussed in the context of theoretical models and recent optical observations with other SOHO instruments. This revised version was published online in June 2006 with corrections to the Cover Date.     

应用级信息安全解决方案的研究与设计

计算机网络的发展向信息安全提出了新的挑战,在电子商务给人们带来巨大便利的同时,也产生了很多的安全隐患。信息安全是一个不容忽视的问题,而且也越来越得到人们的重视。本文结合开发远程教材管理信息系统的实例,对应用级信息安全需求进行研究分析,根据应用系统的实际业务流程,构建其信息安全解决方案并加以实现。信息安全方案的实施保障了系统的安全性、远程数据传输的完整性和保密性。     

Corotating Particle Events

The corotating particle events give us a unique opportunity to probe the three-dimensional structures of the heliosphere. This is especially true if we have observations over a period of extreme stability of the CIRs, such as existed over the recent solar minimum. We discuss how the observations fit into the context of current heliospheric magnetic field models. The energetic particle signatures of CIRs throughout the regions of the heliosphere covered by the deep-space missions are reviewed. The CIRs accelerate these particles and at the same time modulate both the high energy galactic cosmic rays and the anomalous cosmic rays.     

The Solar Energetic Particle Ionic Charge Analyzer (SEPICA) and the Data Processing Unit (S3DPU) for SWICS,SWIMS and SEPICA

The Solar Energetic Particle Ionic Charge Analyzer (SEPICA) is the main instrument on the Advanced Composition Explorer (ACE) to determine the ionic charge states of solar and interplanetary energetic particles in the energy range from ≈0.2 MeV nucl−1 to ≈5 MeV charge−1. The charge state of energetic ions contains key information to unravel source temperatures, acceleration, fractionation and transport processes for these particle populations. SEPICA will have the ability to resolve individual charge states and have a substantially larger geometric factor than its predecessor ULEZEQ on ISEE-1 and -3, on which SEPICA is based. To achieve these two requirements at the same time, SEPICA is composed of one high-charge resolution sensor section and two low- charge resolution, but large geometric factor sections. The charge resolution is achieved by the focusing of the incoming ions, through a multi-slit mechanical collimator, deflection in an electrostatic analyzer with a voltage up to 30 kV, and measurement of the impact position in the detector system. To determine the nuclear charge (element) and energy of the incoming ions, the combination of thin-window flow-through proportional counters with isobutane as counter gas and ion-implanted solid state detectors provide for 3 independent ΔE (energy loss) versus E (residual energy) telescopes. The multi-wire proportional counter simultaneously determines the energy loss ΔE and the impact position of the ions. Suppression of background from penetrating cosmic radiation is provided by an anti-coincidence system with a CsI scintillator and Si-photodiodes. The data are compressed and formatted in a data processing unit (S3DPU) that also handles the commanding and various automatted functions of the instrument. The S3DPU is shared with the Solar Wind Ion Charge Spectrometer (SWICS) and the Solar Wind Ion Mass Spectrometer (SWIMS) and thus provides the same services for three of the ACE instruments. It has evolved out of a long family of data processing units for particle spectrometers. This revised version was published online in June 2006 with corrections to the Cover Date.