地空导弹系统可测试性设计

针对地空导弹武器系统检测维修困难的现状，利用可测性设计技术，提出了地空导弹武器系统可测性设计的方法。阐述了地空导弹武器中测试性设计的必要性，论述了可测性设计的基本理论，分析了地空导弹武器系统可测性设计涉及的相关问题。     

Characterization of Si implants in p-type GaN

Si ion implantation into p-type GaN followed by rapid thermal annealing (RTA) in N/sub 2/ has been performed. X-ray diffraction analyses indicate that ion-implanted damage remains even with 1050/spl deg/C, 60 s RTA. By varying implantation and postimplantation annealing conditions, we could convert carrier concentration from p-type 3 /spl times/ 10/sup 17/ cm/sup -3/ into n-type 2 /spl times/ 10/sup 17/ cm/sup -3/ /spl sim/2 /spl times/ 10/sup 19/ cm/sup -3/. It was found that typical activation energies of Si implants in p-GaN are lower than 10 meV. Such activation energies are smaller than those observed from epitaxially grown Si-doped GaN films. A deep donor level with activation energy of 60 meV was also found from some samples. Photoluminescence studies show that the peak appears at 372 nm might be related to implantation-induced defects. It was also found that a green emission band could be observed from Si-implanted GaN. It was shown that such a green emission is related to the yellow band observed from epitaxially grown Si-doped GaN. The transport properties of these Si-implanted samples were also studied.     

某框架—剪力墙结构的鉴定与加固设计

通过对某停建多年建筑物的安全性鉴定，发现已建楼层的部分梁、柱、剪力墙等构件存在结构安全问题，并对该部分构件分别采用几种可行的加固措施进行处理,同时，还对续建楼层的钢筋连接提出了解决的方法。     

Robustness of periodic trajectories

A robustness problem for periodic trajectories is considered. A nonautonomous system with a periodic solution is given. The problem is to decide whether a stable periodic solution remains in a neighborhood of the nominal periodic solution when the dynamics of the system is perturbed. The case with a structured dynamic perturbation is considered. This makes the problem a nontrivial generalization of a classical problem in the theory of dynamical systems. A solution to the robustness problem will be obtained by using a variational system obtained by linearizing the system dynamics along a trajectory, which is uncertain but within the prespecified neighborhood of the nominal trajectory. This gives rise to robustness conditions that can be solved using integral quadratic constraints for linear time periodic systems.     

Correction of MR kappa-space data corrupted by spike noise

Magnetic resonance images are reconstructed from digitized raw data, which are collected in the spatial-frequency domain (also called kappa-space). Occasionally, single or multiple data points in the k-space data are corrupted by spike noise, causing striation artifacts in images. Thresholding methods for detecting corrupted data points can fail because of small alterations, especially for data points in the low spatial frequency area where the k-space variation is large. Restoration of corrupted data points using interpolations of neighboring pixels can give incorrect results. We propose a Fourier transform method for detecting and restoring corrupted data points using a window filter derived from the striation-artifact structure in an image or an intermediate domain. The method provides an analytical solution for the alteration at each corrupted data point. It can effectively restore corrupted kappa-space data, removing striation artifacts in images, provided that the following three conditions are satisfied. First, a region of known signal distribution (for example, air background) is visible in either the image or the intermediate domain so that it can be selected using a window filter. Second, multiple spikes are separated by the full-width at half-maximum of the point spread function for the window filter. Third, the magnitude of a spike is larger than the minimum detectable value determined by the window filter and the standard deviation of kappa-space random noise.     

Anomalous Pr Ordering and Structural Analysis for Oxygenated Tetragonal 1212 Compound Pr1.5Ba1.5Cu3O7.2

Magnetic measurement and powder X-ray Rietveld analysis are performed on oxygenated Pr _1.5 Ba _1.5 Cu ₃ O _7.2 cuprate. This tetragonal compound with lattice parameters a = 0.38916 nm and c = 1.16177 nm is found to form the TlBa ₂ CaCu ₂ O ₇ 1212-type structure when written as Cu[Ba _1.5 Pr _0.5 ]PrCu ₂ O _7.2. Low temperature magnetic data indicate that anomalous Pr order temperature T _N (Pr) decreases from 18 K for orthorhombic PrBa ₂ Cu ₃ O _6.9 to 10.5 K for Pr _1.5 Ba _1.5 Cu ₃ O _7.2. The increasing Pr-O bond length with decreasing T _N indicates that Pr ordering is closely correlated with the wave function overlap between Pr-4f orbital and O-2p orbital in the CuO ₂ bi-layers.     

Herringbone fracture of a polycarbonate/ABS blend

Tensile fracture mechanisms in single edge notched injection-moulded specimens of a polycarbonate/ABS 30/70 wt% blend have been studied by fractography. When the tensile force was applied parallel to the injection direction, a herringbone pattern could be observed on the fracture surface, while for the perpendicular case, a reverse herringbone pattern was seen. At the same testing condition, the former was tougher than the latter. Fracture images and two-dimensional temperature profiles in the thickness direction were used to locate the crack initiation sites. Herringbone fracture occurred when the main crack repeatedly interacted with secondary cracks initiated along the centreline. Reverse herringbone fracture was formed in a similar mechanism but secondary cracks initiated near the edge. Anisotropy of the fracture modes was attributed to the processing-induced orientation of the polycarbonate phase near the edge.     

Thermodynamic and base-pairing studies of matched and mismatched DNA dodecamer duplexes containing cis-syn, (6-4) and Dewar photoproducts of TT

Cis-syn dimers, (6-4) products and their Dewar valence isomers are the major photoproducts of DNA and have different mutagenic properties and rates of repair. To begin to understand the physical basis for these differences, the thermal stability and base pairing properties of the corresponding photoproducts of the TT site in d(GAGTATTATGAG) were investigated. The (6-4) and Dewar products destabilize the duplex form by approximately 6 kcal/mol of free energy at 37 degreesC relative to the parent, whereas a cis-syn dimer only destabilizes the duplex form by 1.5 kcal/mol. Duplexes with G opposite the 3'-T of the (6-4) and Dewar products are more stable than those with A by approximately 0.4 kcal/mol, whereas the cis-syn dimer prefers A over G by 0.7 kcal/mol. Proton NMR suggests that wobble base pairing takes place between the 3'-T of the cis-syn dimer and an opposed G, whereas there is no evidence of significant H-bonding between these two bases in the (6-4) product. The thermodynamic and H-bonding data for the (6-4) product are consistent with a 4 nt interior loop structure which may facilitate flipping of the photoproduct in and out of the helix.     

A deoxyribonucleic acid-replication intermediate in the growing mosquito

The arrangement of 18-S rRNA and 28-S rRNA within their 40-S common precursor molecule (pre-rRNA) of Xenopus laevis was investigated by electron microscopic analysis of secondary structure of nascent pre-rRNA chains of oocytes, and by 5'-end analysis of 18-S rRNA and 28-S rRNA hybridized to the EcoRI fragment of rDNA cloned as plasmid pCD42. Secondary structure mapping of phenol-extracted RNA from nucleolar cores revealed complete pre-rRNA chains or molecules at various stages of processing and pre-rRNA molecules apparently lacking one end. In this latter group, which was regarded as representing nascent chains, more than 90% of the molecules had no 28-S rRNA REGION. This shows that the 28-S rRNA sequence is transcribed after the 18-S rRNA region and hence must be located nearer to the 3' end of the pre-rRNA molecule. For 5' end-group determination [3H]uridine-labelled 18-S rRNA and 28-S rRNA were hybridized, as fragments of about 200 nucleotides, to the plasmid pCD42 containing coding sequences for four-fifths of the 18-S rRNA sequence, the external transcribed spacer, the non-transcribed spacer and a tenth of the 28-S rRNA sequence. The RNA was recovered from the hybrids and analyzed for uridine 3',5'-bisphosphate (pUp) after alkaline hydrolysis. The pUp content of the hybridized 18-S rRNA fragments was 20-fold higher than in those of 28-S rRNA, THUS DEMONSTRATING THAT THE 5' END OF THE 18-S rRNA is located next to the external spacer region. From these results it is concluded that the 18-S rRNA is located close to the 5' end of the 40-S pre-rRNA molecule.     

Economics of occupational cotton dust control in cottonseed oil mills

An economic analysis of the total cost for various dust control systems for a 500 ton/day model cottonseed oil mill has been performed. All cost data have been adjusted to reflect May 1981 prices. Cost data are presented for the dust collection system, cyclone(s), baghouse(s) and prime air mover(s) for each major processing area at 3 different air-to-cloth ratios. Data were obtained for equipment and installation costs from mills using the various devices and/or complete systems wherever possible. In cases where these data were not available, estimates were obtained from several firms that manufacture and install similar equipment. At the recommended air-to-cloth ratio of 20:1, the initial capital cost was estimated as $707,900, the annual operating expenses as $226,490 and the life cycle cost as $607,510.