Showing papers by "University of Crete published in 1993"

Hybrid Automata: An Algorithmic Approach to the Specification and Verification of Hybrid Systems

Abstract: We introduce the framework of hybrid automata as a model and specification language for hybrid systems. Hybrid automata can be viewed as a generalization of timed automata, in which the behavior of variables is governed in each state by a set of differential equations. We show that many of the examples considered in the workshop can be defined by hybrid automata. While the reachability problem is undecidable even for very restricted classes of hybrid automata, we present two semidecision procedures for verifying safety properties of piecewiselinear hybrid automata, in which all variables change at constant rates. The two procedures are based, respectively, on minimizing and computing fixpoints on generally infinite state spaces. We show that if the procedures terminate, then they give correct answers. We then demonstrate that for many of the typical workshop examples, the procedures do terminate and thus provide an automatic way for verifying their properties.

Prospective evaluation of effects of broad-spectrum antibiotics on gastrointestinal yeast colonization of humans.

Abstract: This study evaluated the effects of broad-spectrum antibiotics on the gastrointestinal (G.I.) yeast flora of humans and correlated the findings with those obtained from a mouse model of G.I. colonization by Candida albicans. We prospectively studied 46 adult cancer patients who received one of five broad-spectrum antibiotics (ceftriaxone, ceftazidime, ticarcillin-clavulanic acid, imipenem-cilastatin, and aztreonam) as therapy for infections. Quantitative examination of yeast colonization of stools was conducted at the baseline, at the end of antibiotic treatment, and 1 week after discontinuation of therapy. Antibiotics with anaerobic activity (ticarcillin-clavulanic acid) or high G.I. concentrations (ceftriaxone) caused a higher and more sustained increase in G.I. colonization by yeasts than did antibiotics with poor anaerobic activity (ceftazidime and aztreonam) or a low G.I. concentration (imipenem-cilastatin). These results were similar to those obtained with a mouse model of G.I. colonization by C. albicans that involved the same antibiotics. Hence, the mouse model may be useful for evaluation of yeast colonization of the human G.I. tract.

Polyamines in the photosynthetic apparatus : Photosystem II highly resolved subcomplexes are enriched in spermine.

Abstract: The three main polyamines putrescine (Put), spermidine (Spd) and spermine (Spm) were characterized by HPLC in intact spinach leaf cells, intact chloroplasts, thylakoid membranes, Photosystem II membranes, the light-harvesting complex and the PS II complex. All contain the three polyamines in various ratios; the HPLC polyamine profiles of highly resolved PS II species (a Photosystem II core and the rection center) suggest an enrichment in the polyamine Spm.

A detailed genetic map for the X chromosome of the malaria vector, Anopheles gambiae.

Abstract: Anopheles gambiae, the primary vector of human malaria in Africa, is responsible for approximately a million deaths per year, mostly of children. Despite its significance in disease transmission, this mosquito has not been studied extensively by genetic or molecular techniques. To facilitate studies on this vector, a genetic map has been developed that covers the X chromosome at an average resolution of 2 centimorgans. This map has been integrated with the chromosome banding pattern and used to localize a recessive, sex-linked mutation (white eye) to within 1 centimorgan of flanking markers.

Computing Accumulated Delays in Real-time Systems

Abstract: We present a verification algorithm for duration properties of real-time systems. While simple real-time properties constrain the total elapsed time between events, duration properties constrain the accumulated satisfaction time of state predicates. We formalize the concept of durations by introducing duration measures for timed automata. A duration measure assigns to each finite run of a timed automaton a real number —the duration of the run— which may be the accumulated satisfaction time of a state predicate along the run. Given a timed automaton with a duration measure, an initial and a final state, and an arithmetic constraint, the duration-bounded reachability problem asks if there is a run of the automaton from the initial state to the final state such that the duration of the run satisfies the constraint. Our main result is an (optimal) PSPACE decision procedure for the duration-bounded reachability problem.

Structural properties and energetics of amorphous forms of carbon.

Abstract: We have made a comparative theoretical study of the most common forms of unhydrogenated amorphous carbon (\ensuremath{\alpha}-C), namely, of the dense, diamondlike phase and the low-density evaporated \ensuremath{\alpha}-C (e-C). Emphasis is given to the connection among the structure, energetics, and stability of these phases. To make the simulations of the amorphous structures (formed by quenching the liquid) tractable, we used the Monte Carlo method, combined with the empirical-potential approach. Our analysis employs a powerful total-energy-partitioning scheme, which is proved very useful in treating the energetics of disordered systems. It is found that threefold ${\mathit{sp}}^{2}$ sites are the energetically favorable geometries in e-C, and thus they are by far more numerous. The nonplanar character of ${\mathit{sp}}^{2}$ sites and the absence of sixfold rings indicate that medium-range order is rather not significant in e-C. The increasing graphitic character of e-C, as the temperature is raised, is explained by resorting to the effective temperatures ${\mathit{T}}^{\mathrm{*}}$, at which the atoms freeze in their lattice positions. For diamondlike \ensuremath{\alpha}-C, the simulations show that there exist two distinctly different dense structures. The ``as-quenched'' one (i-C) is mostly ${\mathit{sp}}^{3}$ bonded, but it is metastable. Upon annealing, it converts into a second phase (i-${\mathrm{C}}^{\mathrm{*}}$), mostly ${\mathit{sp}}^{2}$ bonded, with a significant energy gain. A specific mechanism is proposed for this transition. The insensitivity of density to annealing is explained if we use the concept of the ``glass transition temperature'' ${\mathit{T}}^{\mathrm{*}}$. Finally, by introducing an isotropic bulk modulus for the amorphous phase, it is found that e-C has a much lower compressibility than i-${\mathrm{C}}^{\mathrm{*}}$, enhancing the distinguishability among the two low-coordinated forms of \ensuremath{\alpha}-C.

Manipulation of the line shape and final products of autoionization through the phase of the electric fields.

Abstract: We show that the autoionization line shape can be modified by the choice of two laser intensities and the relative phase Under well specified conditions, proper choice of the phase can lead to selective cancellation of the transition to the discrete or the continuum part of the state Application of the idea to a multichannel problem in the rare gases also provides significant effects

Anal manometry in patients with fissure-in-ano before and after internal sphincterotomy

Abstract: The motility pattern of the internal anal sphincter was estimated manometrically in 42 patients with fissure-in-ano before and after left lateral internal sphincterotomy (LAS). Resting anal pressure and anal pressure during straining were significantly higher in patients than in controls (132 +/- 21 SD cmH2O vs 81 +/- 14 SD cmH2O P < 0.0002 and 46 +/- 16 SD cmH2O vs 13 +/- 4 SD cmH2O P < 0.0005), but were normal after LAS. Slow waves were more common in fissure patients (86 +/- 6 SD% of total recording time vs 68 +/- 11 SD% of total recording time, P < 0.0002), but also became normal after successful treatment. The presence of ultra slow waves was also more common in fissure patients (P < 0.0001), and although it was significantly reduced postoperatively (P < 0.0001), it did not return to normal. Sampling was less frequent in fissure patients (P < 0.0001) and improved significantly after successful treatment (P < 0.0002). Rectal distension produced significantly less reduction in anal pressure in fissure patients as compared to controls (P < 0.01), but successful treatment returned the response to normal. There were 2 patients with anal fissure who did not heal after left LAS. Those patients and a further 5 patients with non healed fissures after left LAS showed the same pathological manometric features as before surgery. Their fissures were successfully treated by additional right lateral internal sphincterotomy. In conclusion, increased internal sphincter activity is probably an aetiological factor in fissure-in-ano, while successful LAS improves anal sphincter function.(ABSTRACT TRUNCATED AT 250 WORDS)

An indirect negative autoregulatory mechanism involved in hepatocyte nuclear factor-1 gene expression

Abstract: Recent studies have revealed that hepatocyte nuclear factor 4 (HNF-4) is an essential positive regulator of another liver enriched transcription factor HNF-1, defining a transcriptional hierarchy between the two factors operating in hepatocytes. To assess the possible autoregulation of the HNF-1 gene we have examined the effect of HNF-1 on its own transcription. In transient transfection assays, HNF-1 strongly down-regulated transcription driven by its own promoter in HepG2 cells. In addition HNF-1 also repressed the activity of HNF-4 dependent ApoCIII and ApoAI promoters. The same effect was observed using vHNF-1, a distinct but highly related protein to HNF-1. Both HNF-1 and vHNF-1 downregulated HNF-4 activated transcription from intact and chimeric promoter constructs carrying various HNF-4 binding sites implying that they act by impeding HNF-4 binding or activity. DNA binding and cell free transcription experiments however failed to demonstrate any direct or indirect interaction of HNF-1 and vHNF-1 with the above regulatory regions. Both factors repressed HNF-4 induced transcription of the ApoCIII and HNF-1 genes in HeLa cells, arguing against the requirement of a hepatocyte specific function. These findings define an indirect negative autoregulatory mechanism involved in HNF-1 gene expression, which in turn may affect HNF-4 dependent transcription of other liver specific genes.

Characterization of a Photosystem II core and its three-dimensional crystals.

Abstract: A photosystem II core from spinach containing the chlorophyll-binding proteins 47 kDa, 43 kDa, the reaction center proteins D1, D2 and cytochromeb 559 and three low molecular weight polypeptides (MW < 10 kDa) was isolated, its three-dimensional crystals were prepared, and both core and crystals were studied by spectroscopic techniques and electron microscopy. The absorption spectra of the crystallized form of the core indicate a specific orientation of the various pigments within the crystal.

Comparison of the Efficacy of Polyenes and Triazoles against Hematogenous Candida krusei Infection in Neutropenic Mice

Abstract: Candida krusei is reported to cause serious infections in immunocompromised patients, particularly those receiving prophylaxis with antifungal azoles. Treatment of this infection can be very challenging. The efficacy of amphotericin B, liposomal amphotericin B (three dosages), fluconazole, and D0870 (a new experimental oral bis-triazole) was assessed in a CF1 mouse model of hematogenous C. krusei infection. Increased survival time and reduced kidney fungal burden were achieved with treatment with amphotericin B at 2 mg/kg/day and liposomal amphotericin B at 8 and 15 mg/kg/day. D0870 at 25 mg/kg/day increased survival time but had no effect on clearance from organs, while the survival and clearance from organs of mice treated with fluconazole at a dose of 100 mg/kg/day did not differ from those of untreated animals. These findings suggest that deoxycholate and liposome-encapsulated amphotericin B are active against disseminated C. krusei infection in neutropenic mice and confirm the in vitro and in vivo resistance of this species to fluconazole.

Trace bounds on the covariances of continuous-time systems with multiplicative noise

Abstract: Matrix equations such as AP+PA/sup T/+FPF/sup T/+ Omega =0 and AQ+QA/sup T/+-QVQ+FPF/sup T/+ Omega =0, which arise in the estimation problem of systems with both additive and multiplicative noise, are treated. Trace bounds on the steady-state and error covariances P and Q are established, under complete and incomplete noise information. An example illustrates the usefulness of these bounds in determining the size of the estimation error. >

Rickettsia conorii in Greece: comparison of a microimmunofluorescence assay and western blotting for seroepidemiology.

Abstract: Since 1972, there have been no reports of Mediterranean spotted fever (MSF) in Greece. In 1991, a seroepidemiologic survey was conducted in three rural villages in the Province of Fokida in central Greece, using both an immunofluorescence assay (IFA) and Western blot to evaluate the prevalence of specific IgG and IgM antibodies to Rickettsia conorii, and to compare these two techniques. Of 254 sera tested by IFA, 148 (58.3%) were positive for IgG at a titer > or = 32 and 117 (46.1%) at a titer > or = 64. Two sera were positive for IgM at a titer > or = 32. Among the IFA-positive sera, 115 reacted against the specific protein antigen (SPA) using Western blotting and were considered as confirmed positive results, indicating a seroprevalence of 45.3%. Using the SPA reaction as a reference, the IFA diagnostic value of a single serum is poor in such an endemic area, suggesting the need for more specific tests. The results of this study have led us to conclude that for seroepidemiologic use, the IFA is not specific for MSF. Thus, the IFA is useful for sero-epidemiologic analysis only in areas where the true prevalence of MSF has been estimated using Western blotting.

Stochastic differential calculus, the Moyal *-product, and noncommutative geometry

Abstract: A reformulation of the Ito calculus of stochastic differentials is presented in terms of a differential calculus in the sense of noncommutative geometry (with an exterior derivative operator d satisfying d2 = 0 and the Leibniz rule). In this calculus, differentials do not commute with functions. The relation between both types of differential calculi is mediated by a generalized Moyal *-product. In contrast to the Ito calculus, the new framework naturally incorporates analogues of higher-order differential forms. A first step is made towards an understanding of their stochastic meaning.

Associative overdominance: evaluating the effects of inbreeding and linkage disequilibrium

Abstract: Expressions are obtained for the expected phenotypic values of homozygous and heterozygous genotypes for a neutral marker locus linked to a locus segregating for a recessive deleterious gene. The phenotypic values are functions of the allele frequencies at the marker locus, the inbreeding coefficient and the degree of association of the deleterious gene with the marker alleles. The analysis is extended to more than two alleles at the marker locus. Either linkage disequilibrium or inbreeding alone can produce an apparent superiority of heterozygotes for the marker locus (unless specified otherwise, the terms ‘homozygote’ and ‘heterozygote’ will refer to the marker locus). The effect of linkage disequilibrium on the difference between the heterozygote and homozygote values can be positive (associative overdominance) or negative (associative underdominance),depending on the frequencies of the marker alleles and the degree of their association with the deleterious gene. Inbreeding has always a positive effect. Inthe presence of both, the possibility of associative overdominance due to linkage disequilibrium is higher. In general, the expected value of a homozygote is a positive function of its allele frequency. When the various homozygous genotypes are combined into one class and the various heterozygous genotypes into another, the phenotypic difference of the two classes is a function of the evenness of the allelic frequency distribution. Inbreeding is a more likely explanation of associative overdominance if the frequency of the deleterious gene is low, but its effect on the character high. Conversely, linkage disequilibrium is more likely if the frequency is high and the effect low. The degrees of association between marker alleles and the deleterious gene can, in principle, be estimated from the observed phenotypic scores and used to calculate expected multi-locus genotype scores. This could provide the basis for statistical tests of the associative overdominance hypothesis as an explanation of observed correlations between multi-locus heterozygosity and phenotypic traits.

Spermicidal and antiviral properties of cholic acid: contraceptive efficacy of a new vaginal sponge (Protectaid) containing sodium cholate.

Abstract: Cholic acid (sodium cholate) exhibits a strong spermicidal and antiviral [anti-human immunodeficiency virus (HIV)-1] activity. The same effects are observed for F-5 Gel, the active mixture of a new contraceptive sponge (Protectaid), which contains sodium cholate in association with low concentrations (0.5%) of nonoxynol-9 and benzalkonium chloride. Both cholic acid and the F-5 Gel exert a dose-dependent, in-vitro inhibitory effect (i) on the activity of HIV-1 associated reverse transcriptase in an acellular system and (ii) on the potential of HIV-1 efficiently to infect human lymphocytes. During 12 months use, the contraceptive efficacy of the 'Protectaid' sponge was 100% in 20 young women who had chosen this method for reasons of both contraception and anti-sexually transmitted disease. No side-effects were recorded throughout this period. Cervical cultures at 6-month intervals showed the presence of Mycoplasma hominis and Candida albicans in one or two cases. The combined spermicidal and anti-HIV properties of cholic acid reported in this paper and used in the 'Protectaid' sponge offer a new and modern protective method of contraception.

Gender and computing in schools in Japan: the “we can, I can't” paradox

Abstract: This study examined gender differences in perception of computer self-efficacy and equality in computer competence, and the factors that might influence these perceptions among 15-yr-old Japanese students. The study replicated the “we can, I can't” phenomenon, a tendency for females to be unsure of their own individual ability to use computers, but to feel that women as a group are as able as men in this domain. Results from a series of regression analyses indicated that computer usefulness and occupational aspirations jointly accounted for significant variance in explaining self-efficacy and that computer usefulness, but not occupational aspirations, accounted for significant variance in the “we can, I can't” expectations. Results are discussed as they relate to previous research, Japanese culture and policy implications and needed areas for future research.

Similarity for Analogical Software Reuse: A Conceptual Modelling Approach

Abstract: We present our approach to defining similarity between software artifacts and discuss its potential exploitation in software reuse by analogy. We first establish properties of similarity which support its role in retrieving and mapping software descriptions. Then we develop a systematic basis for comparison within a fairly general conceptual modelling framework, whereby comparable elements of the descriptions of software objects and corresponding similarity criteria are identified. Finally, a general form of distance metrics for the computation of similarity measures is defined.

Attenuation of white gene expression in transgenic Drosophila melanogaster: possible role of a catalytic antisense RNA.

Abstract: We have transformed Drosophila melanogaster with a DNA construct encoding a catalytic antisense RNA directed against the primary white gene RNA transcript. Total RNA isolated from transformed flies was shown to catalyze the specific cleavage of in vitro transcribed substrate RNA, indicating the expression of a functional ribozyme. Moreover, transgenic lines carrying homozygous copies of this construct depict a further clear-cut reduction in eye pigmentation when present in a genetic background that has a priori reduced levels of white gene expression.