Superluminous supernovae: no threat from eta Carinae

Recently, Supernova 2006gy was noted as the most luminous ever recorded, with a total radiated energy of approximately 10(44) Joules. It was proposed that the progenitor may have been a massive evolved star similar to eta Carinae, which resides in our own Galaxy at a distance of about 2.3 kpc. eta Carinae appears ready to detonate. Although it is too distant to pose a serious threat as a normal supernova, and given that its rotation axis is unlikely to produce a gamma-ray burst oriented toward Earth, eta Carinae is about 30,000 times nearer than 2006gy, and we re-evaluate it as a potential superluminous supernova. We have found that, given the large ratio of emission in the optical to the X-ray, atmospheric effects are negligible. Ionization of the atmosphere and concomitant ozone depletion are unlikely to be important. Any cosmic ray effects should be spread out over approximately 10(4) y and similarly unlikely to produce any serious perturbation to the biosphere. We also discuss a new possible effect of supernovae-e-ndocrine disruption induced by blue light near the peak of the optical spectrum. This is a possibility for nearby supernovae at distances too large to be considered "dangerous" for other reasons. However, due to reddening and extinction by the interstellar medium, eta Carinae is unlikely to trigger such effects to any significant degree.     

The Dynamic Albedo of Neutrons (DAN) experiment for NASA's 2009 Mars Science Laboratory

We present a summary of the physical principles and design of the Dynamic Albedo of Neutrons (DAN) instrument onboard NASA's 2009 Mars Science Laboratory (MSL) mission. The DAN instrument will use the method of neutron-neutron activation analysis in a space application to study the abundance and depth distribution of water in the martian subsurface along the path of the MSL rover.     

With a grain of salt: what halite has to offer to discussions on the origin of life

This experimental study investigated how the dynamics of the crystallization of the evaporite mineral halite could affect the accumulation and preservation of organic macromolecules present in the crystallizing solution. Halite was grown under controlled conditions in the presence of polymer nanoparticles that acted as an analog to protocellular material. Optical microscopy, atomic force microscopy, and laser scanning confocal fluorescence microscopy were used to trace the localization of the nanoparticles during and after growth of halite crystals. The present study revealed that the organic nanoparticles were not regularly incorporated within the halite, but were very concentrated on its surfaces. Their distribution was controlled dominantly by the morphologic surface features of the mineral rather than by specific molecular interactions with an atomic plane of the mineral. This means that the distribution of organic molecules was controlled by surfaces like those of halite's evaporitic growth forms. The experiments with halite also demonstrated that a mineral need not continuously incorporate organic molecules during its crystallization to preserve those molecules: After rejection by (non-incorporation into) the crystallizing halite, the organic nanoparticles increased in concentration in the evaporating brine. They ultimately either adsorbed in rectilinear patterns onto the hopper-enhanced surfaces and along discontinuities within the crystals, or they were encapsulated within fluid inclusions. Of additional importance in origin-of-life considerations is the fact that halite in the natural environment rapidly can change its role from that of a protective repository (in the absence of water) to that of a source of organic particles (as soon as water is present) when the mineral dissolves.     

仿生硬件及其进展

文章详细介绍了仿生硬件的概念、主要特征及用途 ,阐述了仿生硬件的进化原理及实现思想 ,重点分析了仿生硬件的关键技术———可进化硬件电路、硬件进化方法 ,并总结了研究状况与最新进展 ,讨论了需要解决的核心难点问题及其解决思路 ,最后指出了仿生硬件的研究方向及发展前景。     

Transport modeling of energetic electrons in the inner magnetosphere with synchrotron energy losses

The resulting L-distributions and energy spectra of energetic magnetospheric electrons obtained from numerical solution of the radiation belt transport equation with and without accounting for electron synchrotron energy losses are compared. It is demonstrated that synchrotron losses play an important role in formation of the space and energetic distributions of electrons in the inner magnetosphere.     

Radio plasma imager simulations and measurements

The Radio Plasma Imager (RPI) will be the first-of-its kind instrument designed to use radio wave sounding techniques to perform repetitive remote sensing measurements of electron number density (N _e) structures and the dynamics of the magnetosphere and plasmasphere. RPI will fly on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) mission to be launched early in the year 2000. The design of the RPI is based on recent advances in radio transmitter and receiver design and modern digital processing techniques perfected for ground-based ionospheric sounding over the last two decades. Free-space electromagnetic waves transmitted by the RPI located in the low-density magnetospheric cavity will be reflected at distant plasma cutoffs. The location and characteristics of the plasma at those remote reflection points can then be derived from measurements of the echo amplitude, phase, delay time, frequency, polarization, Doppler shift, and echo direction. The 500 m tip-to-tip X and Y (spin plane) antennas and 20 m Z axis antenna on RPI will be used to measures echoes coming from distances of several R _E. RPI will operate at frequencies between 3 kHz to 3 MHz and will provide quantitative N _e values from 10^–1 to 10⁵ cm^–3. Ray tracing calculations, combined with specific radio imager instrument characteristics, enables simulations of RPI measurements. These simulations have been performed throughout an IMAGE orbit and under different model magnetospheric conditions. They dramatically show that radio sounding can be used quite successfully to measure a wealth of magnetospheric phenomena such as magnetopause boundary motions and plasmapause dynamics. The radio imaging technique will provide a truly exciting opportunity to study global magnetospheric dynamics in a way that was never before possible.     

The Radio Plasma Imager investigation on the IMAGE spacecraft

Radio plasma imaging uses total reflection of electromagnetic waves from plasmas whose plasma frequencies equal the radio sounding frequency and whose electron density gradients are parallel to the wave normals. The Radio Plasma Imager (RPI) has two orthogonal 500-m long dipole antennas in the spin plane for near omni-directional transmission. The third antenna is a 20-m dipole along the spin axis. Echoes from the magnetopause, plasmasphere and cusp will be received with the three orthogonal antennas, allowing the determination of their angle-of-arrival. Thus it will be possible to create image fragments of the reflecting density structures. The instrument can execute a large variety of programmable measuring options at frequencies between 3 kHz and 3 MHz. Tuning of the transmit antennas provides optimum power transfer from the 10 W transmitter to the antennas. The instrument can operate in three active sounding modes: (1) remote sounding to probe magnetospheric boundaries, (2) local (relaxation) sounding to probe the local plasma frequency and scalar magnetic field, and (3) whistler stimulation sounding. In addition, there is a passive mode to record natural emissions, and to determine the local electron density, the scalar magnetic field, and temperature by using a thermal noise spectroscopy technique.     

基于排队模型的航天器环模设备负载能力分析

一般真空热试验对于空间环境模拟设备的占用时间长达7～30天。随着发射任务量的增加,试件排队等待进行试验的情况时有发生。文章针对这种情况,以一组中型环模设备为对象,统计分析了其近5年的试验任务量,结果显示：试件的到达间隔时间近似服从负指数分布,试验持续时间近似服从Gamma分布。基于此,建立了描述试件进行真空热试验的M/G/k排队模型,通过蒙特卡罗方法给出了不同试验持续时间分布、不同任务量下的平均排队长度、平均排队时间等关键指标,可为未来相应设备的建设与规划提供参考。     

Structure of the Program of Short-term Prediction of Powerful Solar Flares

Input data of the system are two-dimensional images and one-dimensional distributions of total and polarized solar emission at 5.2 cm wavelength obtained with SSRT. Together with photoheliograms, magnetograms, Hα-filtergrams and characteristics of active regions received from other sources, they form the initial database. The first stage includes superimposing the images, identifying microwave sources with active regions, assigning NOAA numbers to the sources, and determining for each active region the heliolatitude, extent, and inclination angle of the group's axis to the equator. These data are used to calculate the boundaries of longitude zones for each active region. A next stage involves determining the brightness temperatures of microwave sources less than the polarization distribution, the degree of polarization, and microwave emission flux, as well as calculating the parameters of microwave sources. Each parameter is assigned its own value of the weight factor, and the sum of values is used to draw the conclusion about the flare occurrence probability in each active region and on the Sun in general.     

基于无线传感器网络的低功耗目标探测系统设计与实现

基于无线传感器网络的目标探测系统利用磁场、振动、声音等环境参数的变化实现对移动目标的探测。针对无线传感器网络的能量受限问题,从传感器节点硬件选型、节点休眠设计、网络拓扑结构设计和数据传输协议设计等方面出发,进行系统低功耗设计优化。实验结果表明,该探测系统在传感器节点采用容量4 A·h锂电池,采样率10 Hz情况下,平均工作电流仅为3.78 mA,连续工作时长可达33天。