使过半数规则具有传递性的偏好断面的规模

证明了当ｎ＞３时，使过半数投票表决的结果具有传递性的个人偏好序的最大数目大于２￣（ｎ－），从而否定了Ｃｒａｖｅｎ猜想。文中给出了最大偏好序的递推公式以及确定相应约束集的三条规则。     

控制量变化率受限时的MRAS鲁棒变结构控制

本文研究了控制量变化率受限时的MRAS控制。在文献[1～3]的启发下,本文提出了控制量变化率受限时的MRAS鲁棒变结构控制问题;给出了控制器结构、控制律、自适应律,分析了系统的稳定性和渐近收敛性。     

Insulin-stimulated MAP-2 kinase phosphorylates and activates ribosomal protein S6 kinase II

Ribosomal protein S6 is a component of the eukaryotic 40S ribosomal subunit that becomes phosphorylated on multiple serine residues in response to a variety of mitogens, including insulin, growth factors, and transforming proteins of many oncogenic viruses. Recently, an activated S6 kinase (S6 K II) has been purified to homogeneity from Xenopus eggs, and characterized immunologically and at the molecular level. Purified S6 K II can be deactivated in vitro by incubation with either protein phosphatase 1 or protein phosphatase 2A. Reactivation and phosphorylation of S6 K II occurs in vitro with an insulin-stimulated microtubule-associated protein-2 (MAP-2) protein kinase which is itself a phosphoprotein that can be deactivated by protein phosphatase 2A. These studies suggest that a step in insulin signalling involves sequential activation by phosphorylation of at least two serine/threonine protein kinases.     

Expression of the gamma-delta T-cell receptor on intestinal CD8+ intraepithelial lymphocytes

The vast majority of mature T lymphocytes in the peripheral blood and lymphoid organs use the CD3-associated alpha, beta T-cell receptor (TCR) heterodimer for antigen recognition. A second class of TCRs consists of disulphide-linked gamma and delta proteins that are also CD3-associated. A subset of early CD3+ fetal and adult CD4- 8- thymocytes express gamma, delta TCRs before alpha, beta TCRs are detectable. In addition, a minor (1-5%) subpopulation of peripheral T lymphocytes, and some spleen cells from nude mice express gamma, delta TCRs. Notably, dendritic epidermal cells have also been shown to express gamma, delta TCRs. All of these populations lack CD4 and CD8 molecules. We now report that most mature T cells residing in the murine intestinal epithelium express CD3-associated TCRs composed of gamma-chains disulphide-linked to a protein resembling the delta-chain. The striking feature of these intraepithelial lymphocytes (IEL) was that they were exclusively CD4-8+. In addition, approximately half of CD3-bearing IEL lacked detectable Thy-1 on the cell surface, which is unprecedented for murine T cells. In contrast to other CD8+ peripheral T cells, freshly isolated IEL could be induced to display cytolytic activity by engaging the CD3 molecule, indicating that activation had occurred in vivo. Thus, CD8+ IEL are a phenotypically diverse and anatomically restricted population of lymphocytes that use gamma-chain containing heterodimers for antigen recognition.     

Type I phosphatidylinositol kinase makes a novel inositol phospholipid, phosphatidylinositol-3-phosphate

The generation of second messengers from the hydrolysis of phosphatidylinositol-4,5-bisphosphate (PtdInsP2) by phosphoinositidase C has been implicated in the mediation of cellular responses to a variety of growth factors and oncogene products. The first step in the production of PtdInsP2 from phosphatidylinositol (PtdIns) is catalysed by PtdIns kinase. A PtdIns kinase activity has been found to associate specifically with several oncogene products, as well as with the platelet-derived growth factor (PDGF) receptor. We have previously identified two biochemically distinct PtdIns kinases in fibroblasts, and have found that only one of these, designated type I, specifically associates with activated tyrosine kinases. We have now characterized the site on the inositol ring phosphorylated by type I PtdIns kinase, and find that this kinase specifically phosphorylates the D-3 ring position to generate a novel phospholipid, phosphatidylinositol-3-phosphate (PtdIns(3)P). In contrast, the main PtdIns kinase in fibroblasts, designated type II, specifically phosphorylates the D-4 position to produce phosphatidylinositol-4-phosphate (PtdIns(4)P), previously considered to be the only form of PtdInsP. We have also tentatively identified PtdIns(3)P as a minor component of total PtdInsP in intact fibroblasts. We propose that type I PtdIns kinase is responsible for the generation of PtdIns(3)P in intact cells, and that this novel phosphoinositide could be important in the transduction of mitogenic and oncogenic signals.     

Multiple liquid crystal phases of DNA at high concentrations

DNA packaging in vivo is very tight, with volume concentrations approaching 70% w/v in sperm heads, virus capsids and bacterial nucleoids. The packaging mechanisms adopted may be related to the natural tendency of semi-rigid polymers to form liquid crystalline phases in concentrated solutions. We find that DNA forms at least three distinct liquid crystalline phases at concentrations comparable to those in vivo, with phase transitions occurring over relatively narrow ranges of DNA concentration. A weakly birefringent, dynamic, 'precholesteric' mesophase with microscopic textures intermediate between those of a nematic and a true cholesteric phase forms at the lowest concentrations required for phase separation. At slightly higher DNA concentrations, a second mesophase forms which is a strongly birefringent, well-ordered cholesteric phase with a concentration-dependent pitch varying from 2 to 10 micron. At the highest DNA concentrations, a phase forms which is two-dimensionally ordered and resembles smectic phases of thermotropic liquid crystals observed with small molecules.     

Noradrenaline contracts arteries by activating voltage-dependent calcium channels

Noradrenaline (NA) regulates arterial smooth muscle tone and hence blood vessel diameter and blood flow. NA apparently increases tone by causing a calcium influx through the cell membrane. Two calcium influx pathways have been proposed: voltage-activated calcium channels and NA-activated calcium-permeable channels that are voltage-insensitive. Although voltage-activated calcium channels have been identified in arterial smooth muscle, voltage-insensitive calcium channels activated by NA have not. We show here that NA contractions of rabbit mesenteric arteries increase with depolarization. The increase parallels the elevation of open-state probability (P0) of single, voltage-dependent calcium channels. The action of noradrenaline can be explained by NA-activating voltage-dependent calcium channels, rather than by opening a second type of channel. We show directly that NA increases the open-state probability of single calcium channels. Thus, in the presence of NA, calcium entry through voltage-dependent calcium channels can regulate smooth muscle tone at physiological membrane potentials. These results may have relevance to pathophysiological conditions such as hypertension.     

In vitro development ofXenopus skin glands producing 5-hydroxytryptamine and caerulein

The granular glands of amphibian skin synthesize and store a large amount of bioactive amines and peptides which are structurally similar to mammalian brain-gut peptides. To investigate the development of peptide- and amine-producing cells in the granular glands, pieces of dorsal skin taken at various stages fromXenopus laevis tadpoles were cultured, and the contents of caerulein and 5-hydroxytryptamine (5-HT) were measured. When pieces of skin from tadpoles at stages 57 to 60 (Nieuwkoop and Faber stages) were cultured in a medium containing 10% fetal calf serum (FCS medium) or one containing FCS treated with charcoal (chFCS medium), the caerulein and 5-HT levels were increased for the six days of the incubation period. The caerulein content was lower in the chFCS medium than in the FCS medium. Addition of thyroxine to the chFCS medium had no significant effect on the caerulein content. These results show that the caerulein-and 5-HT-producing cells of the granular glands can develop in a culture system with FCS- or chFCS-containing media, and suggest that FCS contains substances which are absorbed by charcoal and stimulate development of the amine- and peptideproducing cells of the glands. In a preliminary search for correlation between caerulein and 5-HT synthesis, addition of 5-hydroxytryptophan (5-HTP), a precursor to 5-HT, to the FCS medium increased 5-HT content and, conversely, caused significant decrease in caerulein content, suggesting that accumulation of caerulein in the granular glands is influenced by the amount of 5-HT synthesis. These studies indicate that this culture system is a useful model for investigating the development of peptide- and amine-producing cells.     

Banach空间中的广义p正常算子

本文是在文献[4]基础上利用广义半内积空间的理论引入Banach空间上的广义p正常算子T=A+iB,AB-BA=0,其中A,B是广义p自共轭算子;同时还引入广义p正常算子的对偶算子T~*=A-iB及广义p酉算子,并就这些算子的有关谱进行了讨论。     

An AIDS-related cytotoxic autoantibody reacts with a specific antigen on stimulated CD4+ T cells

Patients with the acquired immune deficiency syndrome (AIDS) and AIDS-related conditions are known to have abnormalities of T cell subpopulations, including a decreased helper/inducer (bearing the CD4 antigen) to suppressor/cytotoxic (bearing the CD8 antigen) T cell ratio and decreased absolute numbers of T cells with the CD4+ phenotype. Infection of T cells with a retrovirus, termed human immunodeficiency virus (HIV), is thought to be important in these abnormalities. HIV infection alone does not adequately explain the CD4+ T-cell abnormalities seen in AIDS, however, and the nature of T-cell destruction in this disease remains poorly characterized. Here we describe an AIDS-related serum autoantibody that reacts with an antigen of relative molecular mass 18,000 (Mr 18K) restricted to lectin-stimulated or HIV-infected CD4+ T cells. The antibody also suppresses proliferation of CD4+ T cells in vitro and induces cytotoxicity of these cells in the presence of complement. Its role in the development of AIDS merits attention.