Neutron Monitor Design Improvements

The original design by J. A. Simpson of the neutron monitor enabled continuous monitoring of the primary cosmic-ray flux by ground-based recordings of the nucleonic component with only a rather simple correction for atmospheric effects. Simpson (1957) extended the original pile to the 12 counter IGY neutron monitor which was deployed in a world wide network during the International Geophysical Year 1957/8. The desirability for monitors with higher counting rates became evident soon afterwards. Subsequently the NM64 super neutron monitor was designed by H. Carmichael for deployment in time for the International Quiet Sun Year 1964. Using unusually large ¹⁰BF₃ proportional counters made at Chalk River, Hatton and Carmichael (1964) studied comprehensively the experimental design of the NM64. Consequently the efficiency of neutron counters to record evaporation neutrons produced in the lead of a monitor increased from 1.9% for the IGY to 5.7% for the NM64, an increase of 3.3 times the counting rate per unit area of lead producer. During the years much attention was given to the neutron multiplicity spectrum in neutron monitors. This spectrum is related to the energy spectrum of the nucleonic component incident on the neutron monitor, but is only weakly dependent on the spectrum of galactic cosmic rays at the top of the atmosphere. Contrary to galactic cosmic rays, solar flare protons and neutrons are observed predominantly as single counts per interaction, in multiplicity 1, because of the softness of solar flare particle energy spectra. Neutron monitors have also been specially designed to record solar neutrons with increased sensitivity. Newly developed ³He counters with a largely reduced thermal neutron absorption mean free path should lead to improved efficiency in recording primary cosmic radiation. Design criteria are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Neutron Monitor Response Functions

The neutron monitor provides continuous ground-based recording of the hadronic component in atmospheric secondary radiation which is related to primary cosmic rays. Simpson (1948) discovered that the latitude variation of the secondary hadronic component was considerably larger than the muon component suggesting the response of a neutron monitor is more sensitive to lower energies in the primary spectrum. The different methods of determining the neutron monitor response function of primary cosmic rays are reviewed and discussed including early and recent results. The authors also provide results from a new calculation (Clem, 1999) including angle dependent yield functions for different neutron monitor types which are calculated using a simulation of cosmic ray air showers combined with a detection efficiency simulation for different secondary particle species. Results are shown for IGY and NM64 configurations using the standard ¹⁰BF₃ detectors and the new ³He detectors to be used in the Spaceship Earth Project (Bieber et al., 1995). The method of calculation is described in detail and the results are compared with measurements and previous calculations. A summary of future goals is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Design and co-Ordination of Multi-Station International Neutron Monitor Networks

The world's neutron monitor network was initiated about 50 years ago. It grew to a peak of almost 100 stations towards the end of the 1960s and at present about half of these are still active. Many of the original questions about the production of atmospheric secondaries, geomagnetic effects, and neutron monitor response in general, have been settled satisfactorily. Due to their long- term reliability and automated data acquisition, the remaining neutron monitors in the network are well suited for important future contributions in several areas. Amongst these are (a) spectral measurements, which require an optimal distribution along cutoff rigidities; (b) anisotropy studies, which require a set of neutron monitors with well-defined, narrow cones of acceptance for charged particles, covering all directions as evenly as possible; and (c) solar neutron measurements, which primarily require an even distribution in longitude, at high altitude and near the equator. Steps have already been taken to improve the network with these goals in mind, and to standardize methods. This contribution describes some of these steps and suggests further strategies to achieve the most optimal network. This revised version was published online in August 2006 with corrections to the Cover Date.     

Integration of Neutron Monitor Data with Spacecraft Observations: a Historical Perspective

Beginning in the early 1950s, data from neutron monitors placed the taxonomy of cosmic ray temporal variations on a firm footing, extended the observations of the Sun as a transient source of high energy particles and laid the foundation of our early concepts of a heliosphere. The first major impact of the arrival of the Space Age in 1957 on our understanding of cosmic rays came from spacecraft operating beyond the confines of our magnetosphere. These new observations showed that Forbush decreases were caused by interplanetary disturbances and not by changes in the geomagnetic field; the existence of both the predicted solar wind and interplanetary magnetic field was confirmed; the Sun was revealed as a frequent source of energetic ions and electrons in the 10–100 MeV range; and a number of new, low-energy particle populations was discovered. Neutron monitor data were of great value in interpreting many of these new results. With the launch of IMP 6 in 1971, followed by a number of other spacecraft, long-term monitoring of low and medium energy galactic and anomalous cosmic rays and solar and interplanetary energetic particles, and the interplanetary medium were available on a continuous basis. Many synoptic studies have been carried out using both neutron monitor and space observations. The data from the Pioneer 10/11 and Voyagers 1/2 deep space missions and the journey of Ulysses over the region of the solar poles have significantly extended our knowledge of the heliosphere and have provided enhanced understanding of many effects that were first identified in the neutron monitor data. Solar observations are a special area of space studies that has had great impact on interpreting results from neutron monitors, in particular the identification of coronal holes as the source of high-speed solar wind streams and the recognition of the importance of coronal mass ejections in producing interplanetary disturbances and accelerating solar energetic particles. In the future, with the new emphasis on carefully intercalibrated networks of neutron monitors and the improved instrumentation for space studies, these symbionic relations should prove to be even more productive in extending our understanding of the acceleration and transport of energetic particles in our heliosphere. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cosmogenic Radionuclides as an Extension of the Neutron Monitor Era into the Past: Potential and Limitations

The cosmogenic radionuclides, ¹⁰Be, ¹⁴C and others, provide a record of the paleo-cosmic radiation that extends >10,000 years into the past. They are the only quantitative means at our disposal to study the heliosphere prior to the commencement of routine sunspot observations in the 17th century. The cosmogenic radionuclides are primarily produced by secondary neutrons generated by the galactic cosmic radiation, and can be regarded, in a sense, as providing an extrapolation of the neutron monitor era into the past. However, their characteristics are quite different from the man-made neutron monitor in several important respects: (1) they are sensitive to somewhat lower cosmic ray energies; (2) their temporal resolution is ～1 to 2 years, being determined by the rapidity with which they are sequestered in ice, biological, or other archives; (3) the statistical precision for annual data is very poor (～19%); however it is quite adequate (～5% for 22-year averages) to study the large variations (±40%) that have occurred in the paleo-cosmic ray record in the past between grand solar minima and maxima. The data contains “noise” caused by local meteorological effects, and longer-term climate effects, and the use of principal component analysis to separate these “system” effects from production effects is outlined. The concentrations of ¹⁰Be decreased by a factor of two at the commencement of Holocene, the present-day “interglacial”, due to a 100% increase in the ice accumulation rates in polar regions. The use of the ¹⁰Be flux to study heliospheric properties during the last glacial is discussed briefly.     

Civil Access to NAVSTAR GPS

US government policy is established and procedures are being formulated to direct the implementation of techniques providing limited civil access to full GPS accuracy. The results of these efforts balance the conflicting needs of civil GPS navigation and positioning against national security requirements. Granting this access will require sufficient and demonstrable user need, must clearly provide for both national and security interests, and may lead to the imposition of a user service charge. This access will only apply to Precise Positioning Service configured, code-tracking GPS receivers.     

发动机短期租赁市场被看好

2006年9月,威利斯租赁融资公司宣布建立新的北美备用发动机共享库,使得发动机可以真正地进行短期租赁,而且这些发动机都有完整的数据记录和最终的合同文件.     

Neutron measurements in space

The experimental measurements of the neutron flux and energy spectrum in space since 1964 are reviewed and related to the theoretical predictions. A discussion of the neutron sources is presented. The difficulties associated with neutron measurements of both the atmospheric neutron leakage flux and solar neutrons are included. Particular emphasis is placed upon the neutron leakage flux and energy measurements at energies greater than about 1 MeV. The possibilities of CRAND as a source for the energetic trapped protons are discussed in light of recent measurements of the 10–100 MeV neutron flux. The current status of the solar neutron flux observations is also presented.The primary purposes of neutron measurements in space have been to determine the neutron leakage flux from the atmosphere of the Earth and the solar neutron flux. As a consequence of the inefficient methods for neutron detection and the difficulties of conducting the measurements in the presence of the galactic and solar cosmic-ray backgrounds, the experimental results are very conflicting. It is the purpose of this review to interpret and discuss recent neutron measurements. In order to understand these results the theoretical predictions of the neutron fluxes and energy spectra from possible neutron sources will be briefly presented. Since comparisons of the different neutron measurements depend critically upon the experimental techniques, we will briefly discuss neutron detection methods applicable to space measurements. The emphasis will be upon measurements since 1964 made outside the Earth's atmosphere, but considerable reference will be made to high energy neutron experiments conducted within the Earth's atmosphere at < 10g cm^-2 altitude. A review of earlier neutron measurements of terrestrial and solar neutrons has been made by Haymes (1965).     

ENOVIA VPLM简化协同与数据访问

庞巴迪航空公司是公务机、支线飞机和水陆两栖飞机最主要的供应商.通过在过去16年中完成的16个主要的新型或派生飞机项目,宠巴迪航空公司在商用和公务喷气机行业确立了领先的地位.     

中子及中子散射特征

中子以它特有的性质,使它成为继X射线和电子衍射之后的又一研究微观物质结构的有效方法。由于中子散射技术的发展,人们才得以在声子色散曲线和同位素效应的研究等方面有所收获。中子散射可以说是对X射线衍射和电子衍射的一个重要的和不可缺少的补充。中子散射技术利用中子不带电、穿透力极强、能直接鉴别核素、较之X射线对轻元素灵敏、具有磁矩和波粒二象性等特点,使之成为一种独特的,从原子和分子尺度上研究各种物质结构和微观世界运动规律的高新技术。     

The IBEX Background Monitor

The IBEX Background Monitor (IBaM) provides a small and lightweight method for independently measuring IBEX’s high-energy proton background by integrating the flux of >～14 keV protons over a ～7° conical FOV. The IBaM is part of the IBEX-Hi sensor and has a co-aligned look direction. This paper describes the principle of the IBaM and details its design and responses. In particular, we show the response of major components to both ions and ultraviolet (UV) light background. We also provide the geometric factor and calculate expected count rates.     

飞机结构健康监控中的信息获取技术

简要概述了飞机结构健康监控系统的概念和作用法,包括lamb波、智能夹层、光纤Bragg光栅传感器、电位后展望了健康监控系统关键技术的发展。重点阐述和讨论了结构健康监控系统的技术原理和方声发射、天线传感器、机电阻抗、应变和应力等,最     

涡轮增压器监控系统与PIC单片机的串行通讯

依托Borland C 5.0集成开发环境和MPLAB IDE（PIC集成开发环境）,使用Windows应用程序接口（API）函数和PIC单片机14位的精简指令（RISC）系统,开发了涡轮增压器监控系统和PIC单片机民控单元。监控系统采用C语言模块化程度设计;电控单元采用PIC精简指令系统汇编语言编程。简要介绍了涡轮增压器控制系统的组成,并给出了监控系统同PIC电控单元的双机通讯软件设计实例。     

The MESSENGER Gamma-Ray and Neutron Spectrometer

A Gamma-Ray and Neutron Spectrometer (GRNS) instrument has been developed as part of the science payload for NASA’s Discovery Program mission to the planet Mercury. Mercury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) launched successfully in 2004 and will journey more than six years before entering Mercury orbit to begin a one-year investigation. The GRNS instrument forms part of the geochemistry investigation and will yield maps of the elemental composition of the planet surface. Major elements include H, O, Na, Mg, Si, Ca, Ti, Fe, K, and Th. The Gamma-Ray Spectrometer (GRS) portion detects gamma-ray emissions in the 0.1- to 10-MeV energy range and achieves an energy resolution of 3.5 keV full-width at half-maximum for ⁶⁰Co (1332 keV). It is the first interplanetary use of a mechanically cooled Ge detector. Special construction techniques provide the necessary thermal isolation to maintain the sensor’s encapsulated detector at cryogenic temperatures (90 K) despite the intense thermal environment. Given the mission constraints, the GRS sensor is necessarily body-mounted to the spacecraft, but the outer housing is equipped with an anticoincidence shield to reduce the background from charged particles. The Neutron Spectrometer (NS) sensor consists of a sandwich of three scintillation detectors working in concert to measure the flux of ejected neutrons in three energy ranges from thermal to ∼7 MeV. The NS is particularly sensitive to H content and will help resolve the composition of Mercury’s polar deposits. This paper provides an overview of the Gamma-Ray and Neutron Spectrometer and describes its science and measurement objectives, the design and operation of the instrument, the ground calibration effort, and a look at some early in-flight data.     

我国高职教育的类型特征与提高教学质量的途径

在分析近几年我国高等职业教育蓬勃发展的大背景下,总结和概括了我国高等职业教育的内涵特征,提出了教学改革模式要实现由知识型学科倾向向素质型能力本位转变,教学改革的目标是建立能力为本位的课程体系的观点。同时,提出了深化教育教学改革,提高教育质量的思路、途径和方法。     

宽带无线接入技术

介绍了两种宽带无线接入技术：本地多点分配业务(LMDS)和自由空间光通信(FSOC)。它们各具特色。前者将新兴的LMDS技术引入无线接入网,而后者是实现无线宽带接入的另一种途径。     

Neutron star formation by collapse of white dwarfs

Mass-accreting carbon-oxygen white dwarfs become thermally and dynamically unstable when they reach high enough central densities. Carbon ignition at the star's center likely propagates subsonically and, in the case of an initially solid core, leads to collapse if the rate of increase of the core's mass is sufficiently fast. Recent results indicate, however, that solidification of the core induces carbon-oxygen separation. The central regions are then made of pure oxygen while carbon is rejected to lower-density layers. Carbon ignition happens only after neutronization of the central (oxygen) regions. Collapse to a neutron star is then independent from the rate of mass increase and the only possible restrictions are set by the behaviour of the outer, accreted layers. X-ray sources, pulsars and Type I supernovae are likely outcomes of this process.     

ROMAP: Rosetta Magnetometer and Plasma Monitor

The scientific objectives, design and capabilities of the Rosetta Lander’s ROMAP instrument are presented. ROMAP’s main scientific goals are longterm magnetic field and plasma measurements of the surface of Comet 67P/Churyumov-Gerasimenko in order to study cometary activity as a function of heliocentric distance, and measurements during the Lander’s descent to investigate the structure of the comet’s remanent magnetisation. The ROMAP fluxgate magnetometer, electrostatic analyser and Faraday cup measure the magnetic field from 0 to 32 Hz, ions of up to 8000 keV and electrons of up to 4200 keV. Additional two types of pressure sensors – Penning and Minipirani – cover a pressure range from 10⁻⁸ to 10¹ mbar. ROMAP’s sensors and electronics are highly integrated, as required by a combined field/plasma instrument with less than 1 W power consumption and 1 kg mass.