Showing papers by "University of Turin published in 1986"

On Petri nets with deterministic and exponentially distributed firing times

Abstract: A class of Petri nets (DSPN) in which transitions can fire after either a deterministic or a random, exponentially distributed, firing delay is defined, and a solution technique is presented to obtain the steady-state probability distribution over markings, introducing restrictions on the use of deterministic firing delays. An example of application of this modeling technique is presented to demonstrate the impact that the use of a mix of deterministic and exponentially distributed firing delays (instead of all exponentially distributed firing delays) can have on performance and reliability estimates.

Electronic structure and stability of different crystal phases of magnesium oxide.

Abstract: Three different crystal phases of magnesium oxide [B1 (NaCl), B2 (CsCl), and B${8}_{1}$ (inverse NiAs)] are investigated theoretically. An ab initio all-electron linear combination of atomic orbitals Hartree-Fock approximation is adopted; extended basis sets are used which have been variationally optimized in each case. In ordinary conditions, the B${8}_{1}$ and B2 structures result less stable with respect to the rocksalt structure by 0.44 and 1.77 eV, respectively. With increasing pressure, the transition B1\ensuremath{\rightarrow}B2 is estimated to occur around 2.2 Mbar, while it is not excluded that a pressure interval exists around 2 Mbar where the B${8}_{1}$ phase is the most stable of the three structures. Data on the electronic properties of the three phases are provided and discussed: Mulliken populations, charge-density distribution, electron momentum distribution and anisotropy, magnesium core deformation, and band structure.

Negative binomial multiplicity distributions in high energy hadron collisions

Abstract: This paper concerns the results recently obtained by the UA5 Collaboration on charged particle multiplicity distributions at the CERN\(p\bar p\) collider\((\sqrt s = 540 GeV)\) and their comparison with lower energy data [1, 2]. Our aim is to interpret in general terms the experimental finding that the distributions are of negative binomial (NB) form both for total multiplicities and in finite pseudorapidity intervals. This can be understood in terms of partial stimulated emission of bosons, or of a simple form of cascade process, or (more artificially) with both mechanisms. The cascade interpretation appears to be the most attractive. It leads to a new concept of clustering, the empirical data imply unexpected properties for the clusters, and a novel type of high energy asymptotics seems to emerge. We briefly discuss the relation with QCD-based models for hadron production and the case ofe+e− annihilation.

Buffer management in relational database systems

Abstract: The hot-set model, characterizing the buffer requirements of relational queries, is presented. This model allows the system to determine the optimal buffer space to be allocated to a query; it can also be used by the query optimizer to derive efficient execution plans accounting for the available buffer space, and by a query scheduler to prevent thrashing. The hot-set model is compared with the working-set model. A simulation study is presented.

Fibronectin-plasma membrane interaction in the adhesion of hemopoietic cells.

Abstract: Many hemopoietic cell lines were examined for their ability to adhere to culture dishes coated with extracellular matrix proteins. Adhesion assay was performed with murine and human leukemic cell lines representative of different stages of differentiation along both erythroid and myeloid lineages. All the hemopoietic cell lines tested adhered to fibronectin but not to laminin, types I, III, and IV collagen, serum-spreading factor, and cartilage proteoglycans. In addition to immortalized cell lines, immature erythroid and myeloid mouse bone marrow cells adhered to fibronectin. To define the fibronectin region involved in hemopoietic cell adhesion, proteolytic fragments, monoclonal antibodies, and synthetic peptides were used. Among different fibronectin fragments tested, only a 110-kD polypeptide, corresponding to the fibroblast attachment domain, was active in promoting adhesion. Moreover, a monoclonal antibody to the cell binding site located within this domain prevented hemopoietic cell adhesion. Finally, the tetrapeptide Arg-Gly-Asp-Ser, which corresponds to the fibronectin sequence recognized by fibroblastic cells, specifically and competitively inhibited attachment of hemopoietic cells to this molecule. The cell surface molecule involved in the interaction of mouse hemopoietic cells with fibronectin was identified as a 145,000-D membrane glycoprotein by adhesion-blocking antibodies. This glycoprotein was found to be antigenically and functionally related to the GP135 membrane glycoprotein involved in the adhesion of fibroblasts to fibronectin (Giancotti, F. G., P. M. Comoglio, and G. Tarone, 1986, Exp. Cell Res., 163:47-62). On the basis of these data, we conclude that interaction of hemopoietic cells with fibronectin involves a specific fibronectin sequence and a 145,000-D cell surface glycoprotein. We speculate that this property might be relevant for the interaction of hemopoietic cells with the bone marrow stroma, which represents the natural site of hemopoiesis.

Estrogen- and Tamoxifen-induced Rearrangement of Cytoskeletal and Adhesion Structures in Breast Cancer MCF-7 Cells

Abstract: The cytoskeleton, the shape, and the adhesion complexes of MCF-7 breast carcinoma cells have been studied by fluorescence, phase contrast, and interference reflection microscopy. Cells have been grown in media containing different concentrations of estrogen and with or without the addition of the antiestrogen tamoxifen. The pattern of actin microfilaments and keratin intermediate filaments (tonofilaments) and the distribution of adhesion areas change as a function of the estrogen concentration. When cells are cultured in estrogen-deprived medium, they appear roundish and flattened and adhere firmly to the substratum, with multiple vinculin-positive adhesion plaques at their ventral surface. Upon stimulation with estrogen, these cells display pseudopodial cytoplasmic protrusions and ruffling membranes; in interference reflection microscopy the adhesion areas are mostly localized in these projections. A rearrangement of microfilaments and of tonofilaments in the cell projections and the formation of a dense network of keratin fibers takes place. Tamoxifen affects cellular shape and cytoskeletal arrangement in a way similar to that induced by estrogen. An effect of estrogen-receptor stimulation on the adhesion structures and on the rearrangement of intermediate and actin filaments (and accordingly of the shape and internal structure of breast cancer cells) can be suggested. Such an effect might be direct or mediated through unknown mechanisms; it seems, however, to be independent of the well known estrogenic effect on cell proliferation.

The squalene-2,3-epoxide cyclase as a model for the development of new drugs

Abstract: The 2,3-oxido squalene (SO) cyclases represent a group of enzymes which convert SO into polycyclic triterpenoids such as lanosterol, cycloartenol, cucurbitadienol and beta-amyrin Taking into account the postulated model of the enzymatic cyclization of SO, we have investigated the possibility of designing compounds that would be selective and potent inhibitors of SO cyclases Due to the fundamental role of sterols in animal, higher plant and fungal tissues, these inhibitors might behave as very selective (ipocholesterolemic, antifungal or phytotoxic) drugs Our first approach was the synthesis and biological evaluation of 2-aza-2,3-dihydrosqualene and its derivatives which, being protonated at physiological pH, would present some similarities to the C-2 carbon ion generated by the opening of the oxirane ring of SO Microsomes from different sources (germinated pea cotyledons, maize seedlings, rat liver and yeasts) were utilized to determine the inhibition values (I50: concentration of inhibitor producing 50% inhibition at a given substrate concentration) From the results obtained so far we conclude that 2-aza-2-dihydrosqualene and its derivatives strongly inhibited the cyclases, the site of the enzyme responsible for binding to the inhibitor is quite sensitive to the steric hindrance, and the degree of the inhibitory activity is greater in higher plants than in rat liver or fungi

Receptor for bombesin with associated tyrosine kinase activity.

Abstract: The neuropeptide bombesin is known for its potent mitogenic activity on murine 3T3 fibroblasts and other cells. Recently it has been implicated in the pathogenesis of small cell lung carcinoma, in which it acts through an autocrine loop of growth stimulation. Phosphotyrosine (P-Tyr) antibodies have been successfully used to recognize the autophosphorylated receptors for known growth factors. In Swiss 3T3 fibroblasts, phosphotyrosine antibodies identified a 115,000-Mr cell surface protein (p115) that became phosphorylated on tyrosine as a specific response to bombesin stimulation of quiescent cells. The extent of phosphorylation was dose dependent and correlated with the mitogenic effect induced by bombesin, measured by [3H]thymidine incorporation. Tyrosine phosphorylation of p115 was detectable minutes after the addition of bombesin, and its time course paralleled that described for the binding of bombesin to its receptor. Immunocomplexes of phosphorylated p115 and phosphotyrosine antibodies bound 125I-labeled [Tyr4]bombesin in a specific and saturable manner and displayed an associated tyrosine kinase activity enhanced by bombesin. Furthermore, the 125I-labeled bombesin analog gastrin-releasing peptide, bound to intact live cells, was coprecipitated with p115. These data strongly suggest that p115 participates in the structure and function of the surface receptor for bombesin, a new member of the family of growth factor receptors with associated tyrosine kinase activity.

Immunohistochemical demonstration of vimentin in human cerebral tumors.

Abstract: The distribution of vimentin (VIM) has been histochemically investigated in 53 cerebral tumors and compared in gliomas to that of glial fibrillary acidic protein (GFAP). In gliomas VIM is less positive than GFAP, but shows the same distribution. It cannot be considered as indicating immaturity of glial tumor cells. VIM is also positive in glial processes of cerebellar pilocytic astrocytomas, in Schwann cells of neurinomas and in endothelial cells of all oncotypes. In medulloblastomas, VIM decorates reactive glia cells. A diffuse positive reaction has been observed in meningiomas. In hemangioblastomas, besides intervascular and endothelial cells, groups of polygonal cells are intensely positive for both VIM and GFAP. The interpretatien of VIM in cerebral tumors is largely based on the distribution patterns of this intermediate filament in the developing CNS of rodents.

Phosphotyrosine antibodies identify the p210c-abl tyrosine kinase and proteins phosphorylated on tyrosine in human chronic myelogenous leukemia cells.

Abstract: Antibodies against phosphotyrosine are a powerful tool with which to identify proteins phosphorylated on tyrosine residues, such as viral oncogene-encoded transforming proteins and their cellular protein substrates. Probed on human leukemia cell lines, phosphotyrosine antibodies recognized a 210,000-molecular-weight protein (p210) in K562 cells, a cell line derived from a Philadelphia (Ph)'-positive chronic myelogenous leukemia (CML), but recognized no protein in control Ph'-negative non-CML leukemia cells. The p210 protein was also recognized by antisera against v-abl-encoded polypeptides and displayed kinase activity, phosphorylating itself on tyrosine, in an immunocomplex kinase assay. These data are consistent with reported findings of the expression of a recombined bcr-abl gene in Ph'-positive CML cells, leading to the synthesis of an altered p210c-abl protein endowed with tyrosine kinase activity. Phosphotyrosine antibodies also detected the expression of the p210c-abl protein in fresh bone marrow cells harvested from CML patients in blast crisis. Besides the p210c-abl protein kinase, phosphotyrosine antibodies recognized other proteins with molecular weights of 110,000, 68,000, and 36,000 (p110, p68, and p36) in K562 cells. When [gamma-32P]ATP was added to nonionic detergent-extracted cells, these proteins became phosphorylated on tyrosine, as confirmed by phosphoamino acid analysis. A comparison with fibroblasts transformed by the v-abl, v-src, and v-fps oncogenes suggested the identity of the p36 protein with the common 36-kilodalton protein substrate of viral oncogene-encoded tyrosine kinases. Enhanced tyrosine phosphorylation of cellular proteins is thus a feature shared by cells transformed by v-abl and cells expressing a rearranged bcr-abl gene.

Equine t lymphocytes express mhc class ii antigens

Abstract: SUMMARY Six anti-HLA class II mouse monoclonal antibodies (mAbs) were used in conjunction with a rat monoclonal antibody raised against horse lymphocytes to define class II major histocompatibility complex (MHC) molecules in the horse. By utilizing an ELISA assay and complement dependent lymphocytotoxicity assay, five out of the six anti-HLA class II antibodies and the rat anti-horse monoclonal antibody were found to react with a high percentage of peripheral blood lymphocytes. Flow cytometry demonstrated a variable antigen density on peripheral blood lymphocytes and clear evidence for expression by lymphocytes that carried no detectable surface immunoglobulin. None of the antibodies reacted with equine platelets. The mAbs immunoprecipitated an antigenic complex of M, 29,000-33,000 from horse lymphocytes. It appears that the distribution of MHC class II antigens in the horse is different from that in man but is similar to that in the dog, since MHC class II antigens are expressed on resting peripheral blood lymphocytes which lack membrane-bound immunoglobulins. Correlations between the distribution of MHC class II antigens on lymphocyte subpopulations and their role in immunological phenomena may contribute to our understanding of the functional properties of these molecules.

Fc receptor triggering induces expression of surface activation antigens and release of platelet-activating factor in large granular lymphocytes

Abstract: Triggering of large granular lymphocyte (LGL) Fc receptor with a specific monoclonal antibody (AB8.28) linked to an insoluble matrix induces cell activation, as witnessed by expression of HLA class II (DR and DQ) molecules and interleukin 2 receptor. Moreover, this event is accompanied by a concomitant release of platelet-activating factor by LGL. We conclude that the Fc receptor molecule identified by mAb AB8.28 represents a trigger for LGL activation.

Immunohistochemical markers of sweat gland tumors.

Abstract: Using immunoperoxidase methods, normal sweat glands, 44 benign and 4 malignant sweat gland tumors were tested for the presence of carcinoembryonic antigen (CEA), pregnancy-specific-B1-glycoprotein (SP1) and actin (ACT). CEA and SP1 stained the secretory and duct-lining cells of normal eccrine glands. Among benign tumors, 74% were positive for CEA and 44% for SP1. The staining reaction was found mainly in luminal secretions and surrounding cells. Staining by SP1 was reduced, but not suppressed, after absorption with the purified antigen. ACT was found in myoepithelial cells of the secretory tract of normal glands and in basal cells of all cases of hidradenoma papilliferum. Only 3 sweat gland carcinomas reacted for CEA. In a malignant chondroid syringoma, no ACT-positive cells were seen in the myxochondroid stroma. The potential value of CEA, SP1 and ACT in the diagnosis of sweat gland tumors is discussed.

Platelet-activating factor contracts human myometrium in vitro.

Abstract: The myometrial contractile responses to synthetic 1-0-octadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (platelet-activating factor, PAF) and to oxytocin were evaluated in vitro on uterine (lower segment) strips obtained from pregnant women at term (39th week), undergoing elective cesarean section. Contractility was measured isometrically in an isolated organ bath using a superfusion technique. PAF in a concentration range between 5 and 100 nM as well as oxytocin (0.1–10 mU/ml) induced a dose-dependent contraction which could be categorized in two patterns, depending on whether spontaneous activity was present. In resting strips, oxytocin induced a prompt (0.5–1 min) development of active tension, followed by a prolonged (6–18 min), slow contraction and a final relaxation. However, at variance with oxytocin, PAF-induced contractions were rhythmic (3–8/hr), and characterized by a prompt (0.5–2 min) development of tension, followed by a brief (0.5–2 min) plateau, and a final, rapid relaxation. In s...

The Bose-Einstein correlations in deep inelastic μ p interactions at 280 GeV

Abstract: The Bose-Einstein correlation has been observed for pions in deep inelastic μp interactions at 280 GeV. The importance of non-interference correlations in the sample of like charge pion pairs and in the sample used for reference is discussed. The pion emission region is found to be roughly spherical in the pair rest frame with a radius of 0.46–0.84 fm and the chaos factor λ is 0.60–1.08.