Engineering tool for trapped proton flux anisotropy evaluation

At low altitudes, the high-energy trapped proton fluxes are strongly anisotropic. The proton flux is controlled by the density distribution of the Earth's atmosphere that induces a steep pitch-angle distribution and an East-West effect, the latter caused by the finite size of the proton gyration radius. We have developed a software package, ANISO, to evaluate averaged energy spectra of trapped proton unidirectional fluxes for a given spacecraft orbit and attitude by deducing the angular-dependent proton flux spectra from the AP-8 omnidirectional flux. Included in the model are both the Armstrong et al. (1990) model and a model based on the Badhwar and Konradi (1990) pitch-angle distribution.     

A note on vector flux models for radiation dose calculations

This paper reviews and extends modelling of anisotropic fluxes for radiation belt protons to provide closed-form equations for vector proton fluxes and proton flux anisotropy in terms of standard omnidirectional flux models. These equations provide a flexible alternative to the data-based vector flux models currently available. At higher energies, anisotropy of trapped proton flux in the upper atmosphere depends strongly on the variation of atmospheric density with altitude. Calculations of proton flux anisotropies using present models require specification of the average atmospheric density along trapped particle trajectories and its variation with mirror point altitude. For an isothermal atmosphere, calculations show that in a dipole magnetic field, the scale height of this trajectory-averaged density closely approximates the scale height of the atmosphere at the mirror point of the trapped particle. However, for the earth's magnetic field, the altitudes of mirror points vary for protons drifting in longitude. This results in a small increase in longitude-averaged scale heights compared to the atmospheric scale heights at minimum mirror point altitudes. The trajectory-averaged scale heights are increased by about 10-20% over scale heights from standard atmosphere models for protons mirroring at altitudes less than 500 km in the South Atlantic Anomaly. Atmospheric losses of protons in the geomagnetic field minimum in the South Atlantic Anomaly control proton flux anisotropies of interest for radiation studies in low earth orbit. Standard atmosphere models provide corrections for diurnal, seasonal and solar activity-driven variations. Thus, determination of an "equilibrium" model of trapped proton fluxes of a given energy requires using a scale height that is time-averaged over the lifetime of the protons. The trajectory-averaged atmospheric densities calculated here lead to estimates for trapped proton lifetimes. These lifetimes provide appropriate time-averaging intervals for equilibrium models of trapped proton fluxes.     

Synchrotron radiation of electrons trapped in earth's magnetosphere

Relatively large fluxes of trapped electrons with energy above several tens of MeV in the inner radiation belt, established according to low altitude satellite measurements, invoked the question of their production of synchrotron radiation in geomagnetic field. Based on experimental data on electrons, rough estimate of the spectral density of synchrotron radiation at the Equator is obtained in the region of maximum emissivity. Relatively low value of the radiation flux implies that only precise measurements at 1 GHz allowing to measure the directivity of emissions may be relevant.     

Ni2O3掺杂对新固相源顶部籽晶熔渗生长法制备单畴GdBCO超导块材超导性能的影响

本文通过在新固相源中添加Ni₂O₃的方法, 采用顶部籽晶熔渗生长工艺(TSIG)制备出组分为(1-x) (Gd₂O₃+1.2BaCuO₂)+x Ni₂O₃、直径为20 mm的单畴GdBCO 超导块材(其中x = 0, 0.02, 0.06, 0.10, 0.14, 0.18, 0.30, 0.50 wt%), 并研究了Ni₂O₃的掺杂量x对样品的表面生长形貌、微观结构、临界温度T_c、磁悬浮力以及俘获磁通密度的影响. 研究结果表明, 当Ni₂O₃的掺杂量x在0–0.50 wt%的范围内时, 均可制备出单畴性良好的样品, 且Ni₂O₃的掺杂对样品中Gd211粒子的分布和粒径没有明显的影响. 在Ni₂O₃的掺杂量x从0增加到0.50 wt%的过程中, 样品的临界温度T_c呈现下降的趋势, 从x=0时的92.5 K下降到x=0.50 wt%时的86.5 K, 这是由于Ni^{3 +}替代GdBCO晶体中Cu^{2 +}所致; 样品磁悬浮力和俘获磁通密度均呈现先增大后减小的变化规律, x=0.14 wt%时, 磁悬浮力达到最大值34.2 N, x=0.10 wt%时, 俘获磁通密度达到最大值0.354 T. 样品磁悬浮力和俘获磁通密度的变化规律与Ni₂O₃的掺杂量x有密切关系, 只有当掺杂量x合适时, Ni³⁺对Cu^{2 +}的替代既不会造成T_c的明显下降, 但又能产生适量的Ni^{3 +}/Cu²⁺ 晶格畸变, 从而达到提高样品磁通钉扎能力和超导性能的效果.     

Features of the Mechanism of Formation of the Radiation Belt of High-Energy Electrons and Positrons

New results of the PAMELA experiment revealed significant difference in the electron and positrons flux and fraction between trapped particles of the radiation belt and quasitrapped particles. A decrease in the ratio of the electron-to-positron fluxes both with increasing altitude and with decreasing energy was observed for the inner radiation belt, but this does not fit in currently used models. The residual atmosphere density in the trapping region for L ~ 1.15?1.2 is estimated on the basis of calculations of trapped-particle trajectories in the Earth’s magnetosphere. It is shown that processes leading to the energy loss for trapped electrons and positrons in the interactions with residual-atmosphere atoms play an important role in the formation of fluxes of these particles, but these processes cannot cause the reduction of the positron fraction in the total flux at energies below some 100 MeV. The role of the process of δ-electron production in the formation of the belt of trapped electrons and positrons is considered. Allowance for this process makes it possible to explain the above reduction at least partly.     

Observations of the low Earth orbit radiation environment from Mir

Recent measurements of the high-energy charged particle environment with the Radiation Environment Monitor (REM) aboard the Russian Mir space station are presented. Ionizing dose rates in a silicon detector have been measured with two shieldings. The dose is mainly accumulated in two distinct areas, the South Atlantic Anomaly (SAA) and the region of closest approach to the magnetic poles. Whereas the radiation in the South Atlantic Anomaly varied little during 1995, large changes of the daily absorbed doses in the polar regions are observed. A comparison of REM doses with the NASA AP-8 and AE-8 radiation models revealed major differences. AP-8 tends to underestimate the average REM doses, whereas AE-8 overestimates REM doses, and rather describes the worst case.     

高空核爆炸注入辐射带电子的大气扩散损失

利用辐射带电子大气倾角扩散的福克-普朗克方程,通过推导与拟合处理扩散系数表征式,构造二阶精度有限差分格式,给出辐射带捕获电子大气扩散损失的数值计算方法.计算高空核爆炸裂变β谱电子注入辐射带后在不同L壳上的通量损失和能谱变化,结果表明,当L < 1.3时,大气作用引起的扩散损失效应明显,低能电子比高能电子消失要快,电子通量初始阶段衰减很快,随后逐渐近似成时间指数函数形式衰减.     

Topological Lifshitz transition and novel edge states induced by non-Abelian SU(2) gauge field on bilayer honeycomb lattice

We investigate the SU(2) gauge effects on bilayer honeycomb lattice thoroughly. We discover a topological Lifshitz transition induced by the non-Abelian gauge potential. Topological Lifshitz transitions are determined by topologies of Fermi surfaces in the momentum space. Fermi surface consists of N = 8 Dirac points at π-flux point instead of N = 4 in the trivial Abelian regimes. A local winding number is defined to classify the universality class of the gapless excitations. We also obtain the phase diagram of gauge fluxes by solving the secular equation. Furthermore, the novel edge states of biased bilayer nanoribbon with gauge fluxes are also investigated.     

Pinning model derived from resistive measurements on melt processed Bi2Sr2CaCu2O8

On melt processed samples of the 86 K superconductor Bi₂Sr₂CaCu₂O₈ we have performed resistive measurements in the low field limit B0.13 T and 40 KT77 K. The voltage drop is found to rise exponentially with current E ∝exp j/j₀, which is interpreted in terms of thermal activation of pinned flux lines. An activation energy U₀(T)90 meV is derived from the transition width j₀(T) and is related to a plausible core pinning interaction of flux lines with normal conducting precipitates. This reproduces the measured j_c(B, T) values in the whole regime investigated. We conclude that pinning centers must have a minimum size in order to control flux creep. Finally we demonstrate that conventional summation of the single site pinning forces cannot account for the observed macroscopic depinning current density.     

Solar cycle variations of MIR radiation environment as observed by the LIULIN dosimeter.

Measurements on board the MIR space station by the Bulgarian-Russian dosimeter LIULIN have been used to study the solar cycle variations of the radiation environment. The fixed locations of the instrument in the MIR manned compartment behind 6-15 g/cm2 of shielding have given homogeneous series of particle fluxes and doses measurements to be collected during the declining phase of 22nd solar cycle between September 1989 and April 1994. During the declining phase of 22nd solar cycle the GCR (Galactic Cosmic Rays) flux observed at L>4 (where L is the McIlwain parameter) has enhanced from 0.6-0.7 cm-2 s-1 up to 1.4-1.6 cm-2 s-1. The long-term observations of the trapped radiation can be summarized as follows: the main maximum of the flux and dose rate is located at the southeast side of the geomagnetic field minimum of South Atlantic Anomaly (SAA) at L=1.3-1.4. Protons depositing few (nGy cm2)/particle in the detector predominantly populate this region. At practically the same spatial location and for similar conditions the dose rate rises up from 480 to 1470 microGy/h dose in silicon in the 1990-1994 time interval, during the declining phase of the solar cycle. On the other hand the flux rises from 35 up to 115 cm-2 s-1 for the same period of time. A power law dependence was extracted which predicts that when the total neutral density at the altitude of the station decreases from 8x10(-15) to 6x10(-16) g/cm3 the dose increase from about 200 microGy/h up to 1200 microGy/h. At the same time the flux increase from about 30 cm-2 s-1 up to 120 cm-2 s-1. The AP8 model predictions give only 5.8% increase of the flux for the same conditions.     

Estimation of daytime radiative and soil heat fluxes at Trombay, Bombay (19.1° N, 72.8° E) using routine weather data

Summary This note presents estimates of hourly averages of insolation, net radiation and soil heat flux during daytime from solar-elevation angle and routine weather data on cloud cover and screen level air temperature using a formulation procedure generally adopted in surface layer parametrisation schemes. The estimation procedure employs commonly used forms of empirical relationships and the estimates are compared with the concurrent field observations at Trombay site in Bombay (19.1° N, 72.8° E) India. Wherever possible site-specific empirical coefficients are derived. Using the observed insolation, the net radiation and soil heat flux are respectively estimated within ±18% and ±14% of their observed values. Estimated insolation was found to be within ±37% of the observed values and, when used to derive the fluxes, the uncertainty increases to ±25% and ±27%, respectively.     

Heavy ion results from different locations on LDEF

Heavy ions (Z = 8–26) with energies far below the geomagnetic cutoff energy were measured in three different plastic nuclear track detector experiments on the 28.5° inclination orbit of the NASA satellite Long Duration Exposure Facility (LDEF) at 460 km mean altitude. The results of the three experiments M0002 (Kiel University, Germany), A0015 (Deutsche Gesellschaft für Luft- und Raumfahrt (= DLR) Köln, Germany) and HIIS (Naval Research Laboratory (= NRL) Washington, DC, U.S.A.), which were exposed at different satellite locations, agree with each other. At E ≤ 70 MeV/nuc all particle groups showed a steeply falling energy spectrum and an anisotropic arrival direction distribution. The results were consistent with magnetically trapped particles registered in the South Atlantic. The detected particles originated from the anomalous cosmic rays (O, Ne, Ar) and from an unknown source (Mg, Si, Fe). At E ≥ 70 MeV/nuc measured particles of the Fe-group showed a flattening energy spectrum.     

Equivalent dose measurements on board an Armenian Airline flight and Concorde (correction of Concord) (9-17 km)

The results of investigations of the neutron component (E=1–10 MeV) of cosmic radiation on board the “Armenian Airlines” aircrafts using nuclear photoemulsion are presented. The emulsions were exposed on the flights from Yerevan to Moscow, St.-Petersburg, Beirut, Athens, Frankfurt, Amsterdam, Paris and Sofia, and on Concord supersonic flights from Paris to New York.

The dependence of the neutron fluxes, and on absorbed and equivalent doses on the flight parameters were investigated. On the flights of the supersonic Concord, with an altitude of 17 km, the neutron fluxes were essentially higher in comparison to those measured on Armenian airliners. It is interesting to note, that the neutron flux and equivalent dose rate decrease with altitude up to 470 km in space, for example, on board the STS-57.

The shape of the differential energy spectrum for fast neutrons is the same on all Armenian airlines flights, but significantly different at 17 km altitude, where the flux in the energy region above 3 MeV is increasing.     

基于六角形和球形冰晶模型的卷云辐射特征研究

卷云中冰晶粒子的单次光散射计算是卷云辐射传输及云微物理参数反演的重要基础。近年,利用高观测频率的静止气象卫星数据来反演水云和卷云的光学和微物理参数,进而计算地表光通量的研究倍受重视。然而,很多研究中卷云的冰晶用球形模型来模拟。由于不同形状和尺度大小的冰晶对电磁波的散射特征的不同,导致不同冰晶模型计算的卷云环境下卫星观测的辐射值及地表光通量的不同。利用不同尺度大小和电磁波波长的球形和六角形冰晶的单次散射数据,结合RSTAR辐射传输模式来定量分析了卷云环境下不同形状的冰晶模型对计算卫星观测的辐射和地表光通量中的影响。结果显示利用不同形状的冰晶模块来计算的卫星观测的辐射,地表向下辐射通量明显不同。波长在0.4～1.0 μm之间的大气窗口部分的光谱辐射通量的差距最大。总辐射通量受云粒子形状的影响显著。研究证实了正确选择冰晶模型对卫星反演卷云微物理和光学参数的反演及计算地表光通量的重要性。该结果对于云微物理参数的反演及地表向下辐射通量的模拟具有参考价值。     

Z箍缩动态黑腔动力学及辐射特性初步实验研究

在“强光一号”装置进行的Z箍缩动态黑腔实验中, 初步系统研究了动态黑腔的内爆动力学特性及辐射特性的一般规律. 通过高空间分辨图像, 对丝阵与泡沫黑腔碰撞前后泡沫辐射场的变化, 泡沫对不稳定性发展的抑制开展了细致研究. 实验结果显示, 动态黑腔负载内爆的辐射功率波形呈现双峰结构, 首峰和主峰分别对应于碰撞和滞止过程. 8 mm负载的内爆速度高于12 mm负载, 但其他内爆动力学参数和辐射参数均无明显差异. 实验使用的泡沫黑腔能够很好地抑制不稳定性的发展, 但在泡沫内部未能实现对辐射的均匀控制, 滞止泡沫等离子体柱上仍能轻易区分辐射较强和辐射较弱的区域. 关键词： Z箍缩动态黑腔 泡沫黑腔 动力学特性 辐射特性     

胶州湾海域Landsat8/OLI数据处理中多种大气校正方法的评价

海洋水色遥感研究中,精确的水体遥感反射比R_rs(λ)光谱数据是应用海洋光学卫星数据反演海洋生物地球物理参数的关键。实际工作中,遥感反射比是根据遥感仪器接收到的辐亮度经大气吸收和散射校正、太阳距离以及太阳高度角校正后计算出来的。因此对卫星传感器数据进行大气校正是我们得到精确的水体遥感反射比光谱数据的关键因素之一,也是海洋水色遥感研究中的一个重要问题。胶州湾是黄海西部的一个半封闭海湾,是北温带海湾生态系统的重要代表,该海域内规划了大范围的海洋牧场养殖区域,水体生物光学性质复杂。Landsat是美国NASA的陆地卫星计划,最初是为了观测陆地而研发,但是其高空间分辨率(30 m)的优势在海洋遥感监测中表现突出,使得其成为卫星遥感监测河流、湖泊、内陆环湾等水体不可忽略的数据源之一。基于QA(quality assurance) Score光谱质量评价体系对Landsat8/OLI数据处理中五种大气校正算法在胶州湾海域的大气校正结果进行了评价分析。五种大气校正算法分别是NASA(National Aeronautics and Space Administration)标准近红外大气校正算法(Seadas采用为默认大气校正算法,记为Seadas Default);Acolite 默认大气校正算法—暗光谱拟合算法（dark spectrum fitting,记为Acolite DSF）;以及Acolite指数外推算法（exponential extrapolation）,根据算法中所使用波段的不同,分别记为Acolite SWIR, Acolite Red/NIR, Acolite NIR/SWIR。分析结果表明在胶州湾海域Seadas Default的大气校正算法得到的R_rs(λ)数据QA得分为1的概率（83.95%）要远大于Acolite DSF（49.66%）,Acolite SWIR（4.13%）,Acolite Red/NIR（7.25%）,Acolite NIR/SWIR（1.38%）四种大气校正算法。Acolite DSF大气校正算法优于Acolite SWIR,Acolite Red/NIR,Acolite NIR/SWIR。应用MODIS/Aqua卫星数据对Seadas Default大气校正算法和Acolite DSF大气校正算法处理Landsat8/OLI卫星数据得到的R_rs(λ)在443,483,561和655 nm的数据进行了对比分析,结果表明在各个波段的Seadas Default算法所得的大气校正结果都要优于Acolite DSF算法。据此,建议在胶州湾及其附近海域应用Landsat8/OLI数据进行遥感应用研究时以NASA标准近红外大气校正算法为首选。     

Trapped Positrons and Electrons in the Inner Radiation Belt According to Data of the PAMELA Experiment

Measurements of secondary-electron and secondary-positron fluxes below the geomagnetic cutoff in near-Earth space were performed by means of the PAMELA magnetic spectrometer installed on board the Resurs-DK1 satellite launched on June 15, 2006, in an elliptical orbit of inclination 70° and altitude 350 to 600 km. This spectrometer permits measuring the fluxes of electrons and positrons over a wide energy range, as well as determining their spatial distributions to a precision of about 2°. A calculation of particle trajectories in the geomagnetic field makes it possible to separate electrons and positrons originating from cosmic-ray interactions in the Earth’s magnetosphere. The spatial distributions of quasitrapped, trapped, and short-lived albedo positrons and electrons of energy above 70 MeV in the radiation belt were analyzed. The ratio of the electron-to-positron fluxes and the energy spectra of the electrons and positrons in question are indicative of different productionmechanisms for stably trapped and quasitrapped secondary particles.     

Measurements of the linear energy transfer spectra on the Mir orbital station and comparison with radiation transport models

A tissue equivalent proportional counter designed to measure the linear energy transfer spectra (LET) in the range 0.2-1250 keV/micrometer was flown in the Kvant module on the Mir orbital station during September 1994. The spacecraft was in a 51.65 degrees inclination, elliptical (390 x 402 km) orbit. This is nearly the lower limit of its flight altitude. The total absorbed dose rate measured was 411.3 +/- 4.41 microGy/day with an average quality factor of 2.44. The galactic cosmic radiation (GCR) dose rate was 133.6 microGy/day with a quality factor of 3.35. The trapped radiation belt dose rate was 277.7 microGy/day with an average quality factor of 1.94. The peak rate through the South Atlantic Anomaly was approximately 12 microGy/min and nearly constant from one pass to another. A detailed comparison of the measured LET spectra has been made with radiation transport models. The GCR results are in good agreement with model calculations; however, this is not the case for radiation belt particles and again points to the need for improving the AP8 omni-directional trapped proton models.