The dusty atmosphere of the brown dwarf Gliese 229B

The brown dwarf Gliese 229B has an observable atmosphere too warm to contain ice clouds like those on Jupiter and too cool to contain silicate clouds like those on low-mass stars. These unique conditions permit visibility to higher pressures than possible in cool stars or planets. Gliese 229B's 0.85- to 1.0-micrometer spectrum indicates particulates deep in the atmosphere (10 to 50 bars) having optical properties of neither ice nor silicates. Their reddish color suggests an organic composition characteristic of aerosols in planetary stratospheres. The particles' mass fraction (10(-7)) agrees with a photochemical origin caused by incident radiation from the primary star and suggests the occurrence of processes native to planetary stratospheres.     

Serial cytological assay of micronucleus induction: a new tool to predict human cancer radiosensitivity

The role of the propeptide sequence and a disulfide bridge between sites 1 and 122 in chymotrypsin has been examined by comparing enzyme activities of wild-type and mutant enzymes. The kinetic constants of mutants devoid of the Cys1-Cys122 disulfide-linked propeptide show that this linkage is not important either for activity or substrate specificity. However this linkage appears to be the major factor in keeping the zymogen stable against non-specific activation. A comparison of zymogen stabilities showed that the trypsinogen propeptide is ten times more effective than the chymotrypsinogen propeptide in preventing non-specific zymogen activation during heterologous expression and secretion from yeast. This feature can also be transferred in trans to chymotrypsinogen; i.e. the chymotrypsin trypsin propeptide chimera forms a stable zymogen.     

Experimental fetal tracheal ligation reverses the structural and physiological effects of pulmonary hypoplasia in congenital diaphragmatic hernia

Infants with congenital diaphragmatic hernia (DH) and profound pulmonary hypoplasia are currently unsalvageable. The authors previously demonstrated that tracheal ligation (TL) accelerates fetal lung growth and reverses the pulmonary hypoplasia of fetal nephrectomy. The purpose of this study was to determine if the pulmonary hypoplasia of experimental DH could be similarly reversed and, if so, whether the resulting lungs would show better function than those of their DH counterparts. Eighteen fetal lambs were divided into three experimental groups of six animals each. In group 1, DH was created at 90 days' gestation. In group 2, DH was created at 90 days' gestation and TL performed during the same operation. Group 3 consisted of sham-operated controls. These animals were delivered near full-term, and their lungs analyzed by standard morphometric techniques. Ten additional fetal lambs were divided into two experimental groups of five animals each. In group 4, DH was created at 90 days' gestation. In group 5, DH was created at 90 days' gestation and TL performed 20 days later, at 110 days' gestation. These animals were pressure-ventilated via tracheostomy over a 2-hour period in which PaO2, PaCO2, and compliance were measured. Intratracheal pressure (ITP) was measured at the time of delivery in all groups. Upon retrieval, DH animals had abdominal viscera in the chest and small lungs; in contrast, DH/TL animals had the herniated viscera reduced from the chest by enlarged lungs. DH/TL lungs showed markedly increased growth, with significant increases in lung volume:body weight ratio (LV:BW; P = .0001), alveolar surface area (ALV.SA; P = .0001), and alveolar number (ALV#) (P = .0001) when compared with those of the DH or control group. This growth was associated with a normal maturation pattern based on histological appearance, normal airspace fraction, and normal alveolar numerical density. ITP in the DH/TL group was increased when compared with that of DH and control animals (P = .0001). Total lung DNA and protein were both elevated in the DH/TL animals (P = .0001). However, the DNA:protein ratio remained normal, suggesting lung growth had occurred through cell proliferation, not by hypertrophy. When ventilated over a range of settings, DH/TL lungs were more compliant (P = .0001) and achieved higher PaO2s (P < .003) and lower PaCO2s (P = .0001) than their DH counterparts. From these data, the authors conclude: (1) Experimental fetal DH produces hypoplastic lungs that are not capable of adequate gas exchange with conventional ventilation.(ABSTRACT TRUNCATED AT 400 WORDS)     

我国台湾省的抽水蓄能电站

我国台湾省目前有明潭和明湖两座抽水蓄能电站，其装机容量２６０２ 万ｋ Ｗ ，占台湾省电力系统总装机容量的１０１％ ， 主要用来解决峰谷差的矛盾和提高电网供电质量， 降低系统发电综合成本， 其运行和检修情况良好。台湾省电力公司对这两个直属的抽水蓄能电厂直接负责其建设与运行管理。     

An in vitro model for toxin-mediated vascular leak syndrome: ricin toxin A chain increases the permeability of human endothelial cell monolayers

Vascular leak syndrome (VLS) is the dose-limiting toxicity observed in clinical trials of immunotoxins containing ricin toxin A chain (RTA). RTA itself is thought to cause VLS by damaging vascular endothelial cells, but the exact mechanism remains unclear. This is partially due to the paucity of appropriate models. To study VLS, we developed an in vitro model in which human umbilical vein-derived endothelial cells were first grown to confluence on microporous supports and then cultured under low pressure in the presence or absence of RTA. Endothelial cell barrier function was assessed by measuring the volume of fluid that passed through each monolayer per unit time. We found that RTA significantly increased monolayer permeability at times and concentrations consistent with the onset of VLS in patients treated with RTA-based immunotoxins. Scanning electron microscopy showed that intercellular gaps formed in endothelial monolayers exposed to RTA. Intercellular gap formation followed endothelial cell death caused by the enzymatic activity of RTA. We conclude that RTA is directly toxic to endothelial cells in vitro and speculate that this contributes to VLS in vivo.     

令牌多环网性能—可靠性综合评价

网络的性能与可靠性已分别得到广泛的研究,然而,怎样分析具有容错机制的环网的性能仍属有待开拓的研究领域,本文提出了一种分析具有自修复机制的多环网络系统的方法,并给出了报文传输时间分布的拉氏变换式,平均等待时间及平均队列长度公式,分析结果可用于评估故障与修复过程对实时令牌环网的实时响应特性的影响,对基于LAN的分布式实时系统设计具有指导意义。     

Identification and activity of cytosol creatine phosphokinase enzymes in normal and diseased skin

Phosphocreatine molecules (PCR) in skin regenerate adenosine triphosphate and help cutaneous tissue survive ischemia associated with skin flaps, grafts, and hair transplantation procedures. In addition, PCR concentration in psoriasis is elevated many times above normal, indicating either overproduction of PCR by mitochondrial creatine phosphokinase (CPK) enzymes or a defect in cytosol CPK enzymatic activity. Skin CPK isoenzymes, before this study, have not been identified. Herein, for the first time, cytosol CPK enzymatic activity was measured in normal and psoriatic, involved and uninvolved skin, skin tumors, and mouse skin and keratinocyte cell cultures. Creatine phosphokinase MM is the major isoenzyme in normal, uninvolved psoriatic and mouse skin. Total CPK enzymatic activity was increased in psoriasis and skin tumors. These data clearly indicate that increased PCR concentration in a psoriatic skin is not a result of decreased cytosol CPK enzymatic activity.     

Determinants of genital human papillomavirus infection among cytologically normal women attending the University of New Mexico student health center

OBJECTIVES: To confirm the risk factors for genital human papillomavirus (HPV) infection. GOAL OF THIS STUDY: To investigate risk factors for HPV detection apart from the correlated risk factors for cervical neoplasia. STUDY DESIGN: Cervical human papillomavirus (HPV) DNA was assessed in 357 cytologically normal women attending the University of New Mexico student health center. Cervical swab samples were obtained for HPV DNA detection and typing using a PCR-based DNA amplification system. Possible determinants of cervical HPV were examined including age, ethnicity, history of sexually transmitted disease, oral contraceptive use, smoking, age at first intercourse, lifetime number of sex partners, marital status, and history of pregnancy. RESULTS: A 44.3% overall prevalence of cervical HPV was observed. On univariate analysis, factors associated with increasing HPV prevalence included higher lifetime number of sex partners and single marital status. After adjustment for potential confounding variables, we found that HPV prevalence increased with higher lifetime number of sexual partners. CONCLUSION: These findings, along with those from the companion reports in this issue of the journal, support the sexual route of transmission of the virus.     

Dexamethasone inhibition of interferon-alpha 2-induced stimulation of cortisol and growth hormone secretion in chronic myeloproliferative syndrome

This study investigated the acute effects of interferon-alpha 2 (IFN-alpha 2) on hormonal secretion in adult patients affected by a chronic myeloproliferative syndrome and tried to shed some light on the mechanism by which IFN-alpha 2 stimulates cortisol and GH secretion in humans. We compared the pattern of IFN-alpha 2-induced cortisol and GH release with that elicited after the same challenge given subsequent to pretreatment with dexamethasone (Dex). We studied eight patients affected by a chronic myeloproliferative syndrome (thrombocythemia) who had been selected for treatment with IFN-alpha 2. Four sets of experiments were performed: 1) 2 mL iv saline was given at 0800 h in eight cases; 2) 3 x 10(6) IU iv IFN-alpha 2 was given at 0800 h in eight cases; 3) 3 x 10(6) IU iv IFN-alpha 2 was given at 0800 h after pretreatment with 1.5 mg Dex (1 mg at midnight the previous night and 0.5 mg at 0700 h on the day of the test) in six cases; and 4) 2 mL iv saline was given at 0800 h after the same Dex pretreatment in four cases. Cortisol and GH were measured in plasma samples drawn at 30-min intervals between 0800 and 1300 h. Acute iv administration of IFN-alpha 2 stimulated the release of both cortisol and GH in each patient with a significant increment vs. control values, as assessed by areas under the curve. The administration of Dex significantly decreased basal plasma cortisol secretion and abolished cortisol response to IFN-alpha 2 administration. These data suggest that the stimulatory action of IFN-alpha 2 on cortisol release is mediated via a modulation of the activity of the hypothalamic-pituitary axis rather than through a direct effect at the level of the adrenal cortex. After Dex plus saline administration, no significant effect was observed on plasma GH levels, which remained low. Dex administration significantly decreased GH response to IFN-alpha 2. These data suggest that a hypothalamic or pituitary stimulation (or both) is involved in the mechanism of IFN-alpha 2-induced GH secretion. It remains to be established whether IFN-alpha 2 directly stimulates pituitary somatotropic cells or whether the cytokine exerts a stimulatory action on GH secretion by indirectly modulating the hypothalamic or pituitary activity. In conclusion, acute iv administration of IFN-alpha 2 represents a potent stimulus for cortisol and GH secretion in adult human subjects.(ABSTRACT TRUNCATED AT 400 WORDS)