大斜视角SAR成像的改进频率变标算法

首先给出了一种改进的频率变标算法。该算法适用于处理距离解线调后的聚束式SAR数据。对大斜視角数据,由于二次距离压缩误差的影响,偏离参考距离的散射点未能完全聚焦,且离参考距离越远聚焦性能越差。将非线性变标的方法加入频率变标算法对数据进行二次距离压缩,有效地减小了距离压缩误差。最后通过仿真实验表明,对给定的SAR参数,在斜视角为定值时,也能得到较好的成像结果。     

Lower receptor avidity required for thymic clonal deletion than for effector T-cell function.

Clonal deletion in the thymus plays a major part in T-cell tolerance to self antigens. But the mechanism of negative selection, its fine specificity and the threshold of affinity and avidity remains unknown. We have now examined these aspects of negative selection with mice expressing a transgenic T-cell receptor with specificity for lymphocytic choriomeningitis virus (LCMV) glycoprotein in association with the class I H-2Db molecule. These mice were rendered tolerant to LCMV by neonatal infection with mutant LCMVs bearing point mutations in the T-cell epitope recognized by the transgenic T-cell receptor. Variant LCMVs were also tested for their ability to elicit antiviral responses in transgenic mice in vivo and in vitro. Comparison in vivo revealed that a low-avidity receptor interaction, which was unable to induce effector T cells in the periphery, was still sufficient for clonal deletion in the thymus.     

Endothelial cells as part of a vascular oxygen-sensing system: hypoxia-induced release of autacoids

Higher developed organisms are equipped with many central and local control mechanisms, which enable an adequate blood and oxygen supply to tissues over a wide range of demands. Global adaptive responses include changes in the circulatory and ventilatory system as well as increases in the oxygen carrying capacity of the blood. At the level of the specialized organs there exist additional control systems for the regulation of local blood flow. Most systems make use of highly specialized cells which are able to sense the oxygen partial pressure of the transport medium, blood, and within the tissues. In the past years, it has been shown that the vascular endothelium lining the entire circulatory system can actively modulate the vascular tone and platelet functions by the release of autacoids, among them prostacyclin and endothelium-derived nitric oxide (EDRF). Recent experiments demonstrate that the release of EDRF is PO2-dependent, which suggests that endothelial cells may act as functional local oxygen sensors within the vascular system.     

Cloning defined regions of the human genome by microdissection of banded chromosomes and enzymatic amplification

The molecular analysis of many genetic diseases requires the isolation of probes for defined human chromosome regions. Existing techniques such as the screening of chromosome-specific libraries, subtractive DNA cloning and chromosome jumping are either tedious or not generally applicable. Microdissection and microcloning has successfully been applied to various chromosome regions in Drosophila and mouse, but conventional microtechniques are too coarse and inefficient for analysis of the human genome. Because microdissection has previously been used on unbanded chromosomes only, cell lines in which the chromosome of interest could be identified without banding had to be used. At least one hundred chromosomes were needed for dissection and lambda vectors used to achieve maximum cloning efficiency. Recombinant phage clones are, however, more difficult to characterize than plasmid clones. Here we describe the dissection of the Langer-Giedion syndrome region on chromosome 8 from GTG-banded metaphase chromosomes (G-banding with trypsin-Giemsa) and the universal enzymatic amplification of the dissected DNA. Eighty per cent of clones from this library (total yield 20,000) identify single-copy DNA sequences. Fifty per cent of clones detect deletions in two patients with Langer-Giedion syndrome. Although the other clones have not yet been mapped, this result demonstrates that thousands of region-specific probes can be isolated within ten days.     

Metallothionein induction by cadmium and zinc in rat secretory organs

Metallothionein (MT) levels were determined in four secretory organs of the rat following administration of zinc (Zn) and cadmium (Cd). The concentrations of MT in the lacrimal, parotid and adrenal glands of untreated rats were in the range of 2.2-4.9 micrograms/g wet weight tissue while in the pancreas it was shown to be 15.2 micrograms/g. Injection of zinc at total doses of 16, 32 and 80 mg/kg resulted in a 1.8-, 3.2- and 5.9-fold increase in lacrimal MT content, respectively, while a 10.2- and 13.1-fold elevation was observed following treatment with 4 and 8 mg/kg of Cd, respectively. Similar findings were found in the adrenal gland. The parotid MT was elevated 5.9 and 17 times following Zn treatment at doses of 16 and 80 mg/kg respectively, whereas 4 mg/kg of Cd increased MT 14.4 times in this gland. Pancreatic MT was elevated by 39- and 40-fold after injection of Zn at doses of 16 and 32 mg/kg respectively, whereas 4 and 8 mg/kg of Cd caused a 9.8- and 17.9-fold induction, respectively. These results may indicate that secretory organs participate in metabolism of heavy metals in the mammalian body.     

A highly divergent HIV-2-related isolate

It has been suggested that the human immunodeficiency virus type 2 (HIV-2) and the simian immunodeficiency virus from rhesus macaques (SIVmac) evolved from the sooty mangabey virus SIVsm (ref. 1). We now describe an HIV-2-related isolate, HIV-2-D205, from a healthy Ghanaian woman that is genetically equidistant to the prototypic HIV-2 strains and to SIVsm and SIVmac. Supported by the observation that HIV-2D205 differs in a step of envelope glycoprotein processing, our data indicate that it could represent an alternative HIV-2 subtype and that viruses of the HIV-2/SIVsm/SIVmac group could have already infected humans before HIV-2 and SIVsm/SIVmac diverged.     

Karyotype and chromosome banding in the reed frog Hyperolius viridiflavus ommatostictus (Amphibia, Anura, Hyperoliidae)

C-banding and mithramycin staining were used to characterize the karyotypes of 10 specimens of the African reed frog Hyperolius viridiflavus ommatostictus from Tanzania. The diploid chromosome number is 2n = 24. Although no heteromorphic sex chromosomes were present in the mitotic karyotypes, in many diakineses of male meiosis one or two bivalents exhibited an end-to-end arrangement. In the laboratory 7 out of 24 females changed sex spontaneously. This indicates that an XY/XX system of sex determination operates in H. viridiflavus ommatostictus.     

New observations in the metabolism of morphine. The formation of codeine from morphine in man

Zusammenfassung Nach Morphium-oder Heroingaben wurden im Urin normaler und heroinsüchtiger Versuchspersonen freies und gebundenes Codein als neues Morphiumstoffwechselprodukt mit Dünnschichtchromatographie und Massenspektroskopie nachgewiesen.