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1.
Large single crystals of copper with an uniform and very narrow mosaic spread between 25 seconds and 1 minute of arc are now available at I.L.L. This result is of great interest in the construction of a Laue lens for astrophysical applications for which such quality copper single crystals may be used. The X-ray diffraction properties of copper single crystals produced at I.L.L. were studied for x-ray energies ranging from 100 keV to 400 keV. Several monocrystalline plates with different thicknesses and mosaic distributions were then prepared from the as-grown crystals in order to measure their diffraction efficiency as a function of energy. As expected, the value of the peak reflectivity depends on the crystal thickness. Reflectivity measurements show the excellent properties of copper crystals for gamma-ray diffraction. A peak reflectivity of 24% was measured at 220 keV from a copper single crystal of 3.75 mm thickness having a mosaic spread of 1.5 minutes of arc. Some technical aspects on the preparation of copper single crystal plates are also discussed.  相似文献   

2.
本文讨论多通道滤光器的第三种型式——带多通道头的滤光器。在多通道头中设置较初级的滤光级次,分出各所需要的通道,使指定的工作谱线分别通过各通道,然后分别在各通道之后配置高级次的滤光级,构成整个多通道滤光器。这一结构:1)不需要将最热敏的最厚级置于滤光器最前部,避免了温敏引起的波带位置不稳定;2)各通道可根据工作需要各自选择带宽;3)有利于在其后配置众多的Fabry-Perot和Daystar等各种单通道滤光器;4)可将天文台中现存的所有滤光器,经过多通道头组合在一起,在一个镜筒中实现同时的多通道观测。 本文还讨论了与多通道滤光器相配合的多通道太阳望远镜的一些结构特点和设计方法。  相似文献   

3.
Abstract– The oxygen isotopic microdistributions within melilite measured using in situ secondary ion mass spectrometry correspond to the chemical zoning profiles in single melilite crystals of a fluffy type A Ca‐Al‐rich inclusions (CAIs) of reduced CV3 Vigarano meteorite. The melilite crystals show chemical reverse zoning within an individual single crystal from the åkermanite‐rich core to the åkermanite‐poor rim. The composition changes continuously with the crystal growth. The zoning structures suggest that the melilite grew in a hot nebular gas by condensation with decreasing pressure. The oxygen isotopic composition of melilite also changes continuously from 16O‐poor to 16O‐rich with the crystal growth. These observations suggest that the melilite condensation proceeded with change consistent with an astrophysical setting around the inner edge of a protoplanetary disk where both 16O‐rich solar coronal gas and 16O‐poor dense protoplanetary disk gas could coexist. Fluffy type A CAIs could have been formed around the inner edge of the protoplanetary disk surrounding the early sun.  相似文献   

4.
MgAl2O4 spinels from Allende and NWA 763 carbonaceous chondrites were studied by X‐ray single crystal diffraction, SEM, electron microprobe, LA‐ICP‐MS, and Raman spectroscopy. Those from Allende are almost pure, but, in one case, we found a strong FeOtot zonation. Spinels from NWA 763 show Mg‐Fe2+ substitutions. Almost pure MgAl2O4 spinels from both meteorites underwent slow cooling and reached their intracrystalline closure temperature (Tc) in the range 460–520 °C. The NWA 763 spinel with higher FeO content shows a Tc of about 720 °C. X‐ray single crystal diffraction and Raman spectroscopy suggest a slow cooling and an ordered structure with trivalent cations in M site and divalent in T site. Among the trace elements, Ti and Co are enriched with respect to the terrestrial analogs, while Mn, Ni, and Sn show intermediate values between different terrestrial occurrences. Vanadium cannot be used as a tracer of extraterrestrial origin as for Cr‐spinels, because its content is similar in extraterrestrial and terrestrial spinels. In the zoned crystal from Allende, Co show a strong zonation similar to that of FeO.  相似文献   

5.
Abstract– Alloys of the refractory metals Re, Os, W, Ir, Ru, Mo, Pt, and Rh with small amounts of Fe and Ni are predicted to be one of the very first high‐temperature condensates in a cooling gas of solar composition. Recently, such alloy grains were found in acid‐resistant residues of the Murchison CM2 chondrite. We used focused ion beam (FIB) preparation to obtain electron‐transparent sections of 15 submicrometer‐sized refractory metal nuggets (RMNs) from the original Murchison residue. We studied their crystallography, microstructures, and internal compositional variations using transmission electron microscopy (TEM). Our results show that all RMNs studied have hexagonal close‐packed (hcp) crystal structures despite considerable variations of their bulk compositions. Crystallographic superstructures or signs of spinodal decomposition are absent and defect microstructures are scarce. Internally, RMNs are compositionally homogeneous, with no evidence for zoning patterns or heterogeneities due to exsolution. Many RMNs show well‐defined euhedral crystal shapes and all are nearly perfect single crystal. Our findings are consistent with a direct (near‐) equilibrium condensation of refractory metals into a single alloy at high temperature in the solar nebula as predicted by current condensation models. We suggest that this alloy is generally hcp structured due to an extended ε‐phase field in the relevant multicomponent alloy system. The high degree of structural perfection and compositional homogeneity is attributed to high defect energies, high formation temperatures, slow cooling rates, small grain sizes, and rapid internal diffusion.  相似文献   

6.
基于单片机和GPS信号的校频系统   总被引：5，自引：0，他引：5  
介绍一种基于INTEL 80C196KC单片机的校频系统,包括系统的设计原理、硬件组成和软件实现。该系统通过利用GPS接收机得到的1PPS秒脉冲信号,实现对晶体振荡器频率的校准,从而获得一个短期及长期稳定度都比较优良的时间频率标准。该系统采用了量化时延原理进行短时间间隔比对,对测量数据进行卡尔曼滤波处理。  相似文献   

7.
Gan  W. Q.  Watanabe  T. 《Solar physics》1997,174(1-2):403-412
Using the observational data of a Bragg crystal spectrometer on Yohkoh for the period from October 1991 to the end of 1995, we have made a statistical study of flares which consist of a single loop or are dominated by a single loop in SXT images. A total of 158 flares are sampled. With a temporal resolution of three seconds, we conclude that although the blue asymmetry is very common during the impulsive phase, the number of events with total blue shift is rather small, and only a very small number have a large total blue shift, contrasting with the predictions of some hydrodynamic models. It is also found that the blue shift for most flares appears at the early impulsive phase and is temporally correlated with the broadening of the line. These results demonstrate the necessity for checking whether chromospheric evaporation always occurs in solar flares.  相似文献   

8.
The rate of formation of molecular hydrogen from hydrogen atoms adsorbed on grains is analyzed, assuming that the grains are single crystals, polycrystalline or amorphous. On polycrystalline grains, and on graphite platelets, this rate could be orders of magnitude lower than on single crystal grains. The same is true for amorphous grains because there, at low temperatures, only atoms absorbed on neighboring sites can form molecules. Suitable formulae are derived and compared with the classical results for single crystal grains. Quantitative results are given for crystalline and amorphous ice, but with small changes these should also be valid for other solids. The rates for amorphous grains can approximate, within a factor of 10 or so, those for crystalline grains if the density of H atoms is high and the density of H2 molecules is low and only when the temperature of the grains satisfies a relation which for ice and graphite leads to a value in the proximity of 15–17 K. This maximum rate occurs only a degree or so above the temperature at which the grains are totally covered by an H2 layer and the reaction ceases. Furthermore, for a constant number density of grains, the rates on amorphous grains are second order while those on crystalline grains are first order. Both these circumstances predict amorphous grains to lead to H2 clouds with irregular and sharply delineated features in contrast to more uniform clouds formed on crystalline grains.  相似文献   

9.
怀柔观测基地的多通道太阳望远镜是通过数十个电机调节晶体偏转角度实现多波带同时观测的自动控制。原有的计算机是通过一个串行接口控制若干个调波带的电机,响应时间长,速度慢且技术比较落后。本文利用当今流行的USB2.0芯片CYPRESS EZ-USB改造原有的串口通信控制系统,大大提高了响应的速度,同时,为解决一个USB应用程序控制多个电机转动的问题,提出了一种"编号"的方法。这样每个USB设备不论其插入顺序,PC主机都能通过识别其固定编号而加以区分,PC主机可以通过4个USB接口(16个电机)控制多通道太阳望远镜滤光嚣的调制角度,实现自动控制。这为大规模改造其他计算机接口提供了研制基础。  相似文献   

10.
The search for fast radio bursts(FRBs) is a hot topic in current radio astronomy studies. In this work, we carry out a single pulse search with a very long baseline interferometry(VLBI) pulsar observation data set using both auto spectrum and cross spectrum search methods. The cross spectrum method,first proposed in Liu et al., maximizes the signal power by fully utilizing the fringe phase information of the baseline cross spectrum. The auto spectrum search method is based on the popular pulsar software package PRESTO, which extracts single pulses from the auto spectrum of each station. According to our comparison, the cross spectrum method is able to enhance the signal power and therefore extract single pulses from data contaminated by high levels of radio frequency interference(RFI), which makes it possible to carry out a search for FRBs in regular VLBI observations when RFI is present.  相似文献   

11.
Abstract— Quantitative textural data for Northwest Africa (NWA) 032 and the LaPaz (LAP) mare basalt meteorites (LAP 02205, LAP 02224, LAP 02226, and LAP 02436) prvide constraints on their crystallization and mineral growth histories. In conjunction with whole‐rock and mineral chemistry, textural analysis provides powerful evidence for meteorite pairing. Petrographic observations and crystal size distribution (CSD) measurements of NWA 032 indicate a mixed population of slowly cooled phenocrysts and faster cooled matrix. LaPaz basalt crystal populations are consistent with a single phase of nucleation and growth. Spatial distribution patterns (SDP) of minerals in the meteorites highlight the importance of clumping and formation of clustered crystal frameworks in their melts, succeeded by continued nucleation and growth of crystals. This process resulted in increasingly poor sorting, during competition for growth, as the melt crystallized. Based on CSD and SDP data, we suggest a potential lava flow geometry model to explain the different crystal populations for NWA 032 and the LaPaz basalts. This model involves crystallization of early formed phenocrysts at hypabyssal depths in the lunar crust, followed by eruption and flow differentiation on the lunar surface. Lava flow differentiation would allow for formation of a cumulate base and facilitate variable cooling within the stratigraphy, explaining the varied textures and modal mineralogies of mare basalt meteorites. The model may also provide insight into the relative relationships of some Apollo mare basalt suites, shallow‐level crystal fractionation processes, and the nature of mare basalt volcanism over lunar history.  相似文献   

12.
In this paper we study the effect of the channeling of ions recoiling from collisions with weakly interacting massive particles (WIMPs) in single crystal detectors. In particular we investigate the possibility that channeling may give rise to diurnal modulations of the counting rate as the Earth rotates relative to the direction of the WIMP wind, and the effect that channeling has on the “quenching factor” of a detector.  相似文献   

13.
We describe the channel-to-energy calibration of the Spectroscopy Detectors of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (GRO). These detectors consist of NaI(Tl) crystals viewed by photomultiplier tubes whose output in turn is measured by a pulse height analyzer. The calibration of these detectors has been complicated by frequent gain changes and by nonlinearities specific to the BATSE detectors. Nonlinearities in the light output from the NaI crystal and in the pulse height analyzer are shifted relative to each other by changes in the gain of the photomultiplier tube. We present the analytical model which is the basis of our calibration methodology, and outline how the empirical coefficients in this approach were determined. We also describe the complications peculiar to the Spectroscopy Detectors, and how our understanding of the detectors' operation led us to a solution to these problems.  相似文献   

14.
波前相位差法是利用焦面像和离焦面像通过一个相位多样性算法来拟合相位或对目标复原,这就要求采集两个图像,一个是焦面像,另一个是离焦面像。本文的设计是根据晶体的偏振原理分像,并将焦面像和离焦像同时采集到同一个CCD(Charge Coupled Device)上,这种方法保证了两个图像的同步、实时,而且光学系统简单。文中具体给出了一种新型波前相位差法探测器的设计方案、像差分析,并且模拟了波前相位差法探测器对模拟结果的影响。  相似文献   

15.
Abstract— This study examines the effects of shock metamorphism on fluid inclusions in crystalline basement target rocks from the Ries crater, Germany. The occurrence of two‐phase fluid inclusions decreases from shock stage 0 to shock stage 1, while single‐phase inclusions increase, likely as a result of re‐equilibration. In shock stages 2 and 3, both two‐phase and single‐phase inclusions decrease with increasing shock stage, indicating that fluid inclusion vesicles are destroyed due to plastic deformation and phase changes in the host minerals. However, quartz clasts entrained in shock stage 4 melts contain both single‐phase and two‐phase inclusions, demonstrating the rapid quenching of the melt and the heterogeneous nature of impact deformation. Inclusions in naturally shocked polycrystalline samples survive at higher shock pressures than those in single crystal shock experiments. However, fluid inclusions in both experimental and natural samples follow a similar trend in re‐equilibration at low to moderate shock pressures leading to destruction of inclusion vesicles in higher shock stages. This suggests that shock processing may lead to the destruction of fluid inclusions in many planetary materials and likely contributed to shock devolatilization of early planetesimals.  相似文献   

16.
Here we report in situ structural and chemical analyses of four presolar grains and the matrices of the Meteorite Hills (MET) 00526 L3.05 and Queen Alexandra Range (QUE) 97008 L3.05 unequilibrated ordinary chondrites (UOCs). The presolar grains in MET 00526 include one Fe-rich single crystal olivine, and one olivine grain that contains both amorphous and polycrystalline material. The single crystal olivine likely has origins in the circumstellar envelope (CSE) of a red giant branch (RGB) or asymptotic giant branch (AGB) star, and the amorphous/polycrystalline olivine has an O-isotopic composition consistent with origins in a type II supernova. The presolar grains from QUE 97008 are Fe rich and include one crystalline, stoichiometric olivine that contains a Ca-rich core and one crystalline, stoichiometric pyroxene grain, both of which have O-isotopic compositions consistent with origins in the CSEs of low-mass AGB/RGB stars. The matrices of both UOCs are mineralogically diverse with evidence for unaltered material in the form of amorphous silicates and a C-rich nanoglobule and altered material in the form of Ni-rich sulfides, abundant Fe-rich olivine, and Fe-Mg zoning in matrix silicates. No phyllosilicates were observed. The Fe-rich olivine grains are the dominant alteration phase in both UOCs and likely replaced primary amorphous silicates in the presence of an Fe-rich fluid during parent body alteration. Our work suggests that the ordinary and carbonaceous chondrites received a similar inventory of dust with comparable structures and chemistries.  相似文献   

17.
Perspectives for the Radio-Optical Telescope 54/32/2.6 are given for scientific research in radioastronomy. Its characteristics and potential scientific fields are summarized in the frame of the present French-Armenian collaboration. A 3-phase upgrade plan including a detailed technical evaluation of the antenna is presented.Published in Astrofizika, Vol. 38, No. 4, pp. 645–648, October–December, 1995.  相似文献   

18.
The problem of motion of a dynamically symmetric gyrostat acted upon by non-symmetric potential forces admitting a cyclic integral is considered. This problem is brought into equivalence with another one concerning the motion of a similar gyrostat under the action of axisymmetric potential forces. Using this analogy, new integrable cases of each of the two problems are obtained from the known cases of the other. The equations of motion are reduced to a single equation of the second order.  相似文献   

19.
Large mode area (LMA), single-mode photonic crystal fibres (PCFs) have the potential to provide significant instrumental advantages in fibre stellar interferometry, due to their broad-band attenuation spectrum, endlessly single-moded performance and very large core size. We investigate the theoretical performance of coupling the telescope point spread function directly into LMA PCFs. We find that a single LMA fibre can replace as many as three step-index fibres for atmospheric seeing characterized by   D T/ r o≥ 2  with approximately the same coupling performance and a slower feed from the telescope. This could lead to considerable simplification of broad-band fibre interferometers.  相似文献   

20.
Abstract— A shock experiment has been devised to produce large shear in a single crystal sample of olivine. The recovered sample exhibits macroscopic shear faults resembling shock veins in ordinary chondrites. Examination with transmission electron microscopy reveals a high density of dislocations in the bulk olivine. The shear faults appear as thin veins containing small grains of olivine and pockets of glass. The microstructure and composition of the material in the veins point to fractional crystallization of a melt. An order of magnitude calculation is consistent with the idea that the veins were produced by shear melting. These results support the view that shock veins in meteorites are the result of shear heating rather than of pressure heterogeneities.  相似文献   

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