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Showing papers by "University of Crete published in 1995"


Journal ArticleDOI
TL;DR: A general framework for the formal specification and algorithmic analysis of hybrid systems is presented, which considers symbolic model-checking and minimization procedures that are based on the reachability analysis of an infinite state space.

2,091 citations


Journal ArticleDOI
TL;DR: This paper studies the approximation and learning properties of one class of recurrent networks, known as high-order neural networks; and applies these architectures to the identification of dynamical systems.
Abstract: Several continuous-time and discrete-time recurrent neural network models have been developed and applied to various engineering problems. One of the difficulties encountered in the application of recurrent networks is the derivation of efficient learning algorithms that also guarantee the stability of the overall system. This paper studies the approximation and learning properties of one class of recurrent networks, known as high-order neural networks; and applies these architectures to the identification of dynamical systems. In recurrent high-order neural networks, the dynamic components are distributed throughout the network in the form of dynamic neurons. It is shown that if enough high-order connections are allowed then this network is capable of approximating arbitrary dynamical systems. Identification schemes based on high-order network architectures are designed and analyzed. >

761 citations


Journal ArticleDOI
TL;DR: This work determines the complexity of testing whether a finite state, sequential or concurrent probabilistic program satisfies its specification expressed in linear-time temporal logic and addresses questions for specifications described by ω-automata or formulas in extended temporal logic.
Abstract: We determine the complexity of testing whether a finite state, sequential or concurrent probabilistic program satisfies its specification expressed in linear-time temporal logic. For sequential programs, we present an algorithm that runs in time linear in the program and exponential in the specification, and also show that the problem is in PSPACE, matching the known lower bound. For concurrent programs, we show that the problem can be solved in time polynomial in the program and doubly exponential in the specification, and prove that it is complete for double exponential time. We also address these questions for specifications described by o-automata or formulas in extended temporal logic.

664 citations



Journal ArticleDOI
01 Sep 1995-Chest
TL;DR: UPAA is frequently misdiagnosed in adulthood and is often not considered in the differential diagnosis of the unilateral hyperlucent lung, so clinicians and radiologists should be aware of the possibility of undiagnosed cases in adults.

242 citations


Journal ArticleDOI
TL;DR: In this article, detailed dynamic equations for the power system and wind energy conversion system (WECS) components and their synthesis to a unified model are presented, which is the basis for creating simulation software able to perform the transient stability analysis of isolated diesel-wind turbine power systems for accurate assessment of their interaction.
Abstract: In the first part of this two-part paper, detailed dynamic equations for the power system and wind energy conversion system (WECS) components and their synthesis to a unified model are presented. This model is the basis for creating simulation software able to perform the transient stability analysis of isolated diesel-wind turbine power systems for accurate assessment of their interaction. Approximations in the various component models, when necessary, remain between limits that do not affect the accuracy of the analysis performed. A new general multimachine power system model is also developed which describes the topology and the complexity of wind-diesel power systems in a compact form which is easy to implement in the simulation software. >

212 citations


Journal ArticleDOI
TL;DR: It is suggested that YŻ functions to abstract hydrogen atoms from aquo- and hydroxy-bound managanese ions in the (Mn)4 cluster on each S-state transition, and that this hydrogen-atom abstraction process may occur either by sequential or concerted kinetic pathways.
Abstract: Recent magnetic-resonance work on YŻ suggests that this species exhibits considerable motional flexibility in its functional site and that its phenol oxygen is not involved in a well-ordered hydrogen-bond interaction (Tang et al., submitted; Tommos et al., in press). Both of these observations are inconsistent with a simple electron-transfer function for this radical in photosynthetic water oxidation. By considering the roles of catalytically active amino acid radicals in other enzymes and recent data on the water-oxidation process in Photosystem II, we rationalize these observations by suggesting that YŻ functions to abstract hydrogen atoms from aquo- and hydroxy-bound managanese ions in the (Mn)4 cluster on each S-state transition. The hydrogen-atom abstraction process may occur either by sequential or concerted kinetic pathways. Within this model, the (Mn)4/YZ center forms a single catalytic center that comprises the Oxygen Evolving Complex in Photosystem II.

167 citations


Proceedings ArticleDOI
29 May 1995
TL;DR: This work studies the problem of uniquely identifying the initial state of a given finite-state machine from among a set of possible choices, based on the input-output behavior, and provides optimal bounds for deciding whether such games have strategies winning with probability 1.
Abstract: We study the problem of uniquely identifying the initial state of a given finite-state machine from among a set of possible choices, based on the input-output behavior. Equivalently, given a set of machines, the problem is to design a test that distinguishes among them. We consider nondeterministic machines as well as probabilistic machines. In both cases, we show that it is PsPAcE-complete to decide whether there is a preset distinguishing strategy (i.e. a sequence of inputs fixed in advance), and it is ExPTIME-complete to decide whether there is an adaptive distinguishing strategy (i.e. when the next input can be chosen based on the outputs observed so far). The probabilistic testing is closely related to probabilistic games, or Markov Decision Processes, with incomplete information. We also provide optimal bounds for deciding whether such games have strategies winning with probability 1.

157 citations


Journal ArticleDOI
TL;DR: Chitin deacetylase, the enzyme that catalyzes the hydrolysis of acetamido groups of N-acetyl-D-glucosamine in chitin, has been purified to homogeneity from the culture filtrate of the fungus Colletotrichum lindemuthianum and further characterized.

156 citations


Journal ArticleDOI
TL;DR: In this paper, band structure results for elastic waves in periodic composite materials consisting of scatterers (spheres, cubes, or rods) embedded in a homogeneous polymer matrix are presented.

130 citations


Journal ArticleDOI
01 Dec 1995
TL;DR: A direct nonlinear adaptive state regulator, for unknown dynamical systems that are modeled by dynamic neural networks is discussed, and modifications of the original control and update laws are provided, so that at least uniform ultimate boundedness is guaranteed.
Abstract: A direct nonlinear adaptive state regulator, for unknown dynamical systems that are modeled by dynamic neural networks is discussed. In the ideal case of complete model matching, convergence of the state to zero plus boundedness of all signals in the closed loop is ensured. Moreover, the behavior of the closed loop system is analyzed for cases in which the true plant differs from the dynamic neural network model in the sense that it is of higher order, or due to the presence of a modeling error term. In both cases, modifications of the original control and update laws are provided, so that at least uniform ultimate boundedness is guaranteed, even though in some cases the stability results obtained for the ideal case are retained.

Journal ArticleDOI
TL;DR: Data establish that SecY, SecE, and SecG constitute the integral membrane domain of preprotein translocase, and that all three of the proteins are strongly overexpressed and recovered in the plasma membrane fraction.

Journal ArticleDOI
TL;DR: A new assay is presented for the determination of chitin deacetylase activity employing hexa-N-acetylchitohexaose as substrate and measuring the acetate released enzymatically, as well as the pH and temperature dependence of activity and the thermostability of the enzyme.

Journal ArticleDOI
TL;DR: Adult cancer patients were prospectively studied to determine the relationship between ultrastructural and microbiologic catheter colonization and clinical catheter-related infections and the extent of biofilm formation.
Abstract: Adult cancer patients were prospectively studied to determine the relationship between ultrastructural and microbiologic catheter colonization and clinical catheter-related infections. Participants included 38 patients whose central venous catheters were removed because of suspected catheter infection (16 patients) or other noninfectious causes (22 controls). The presence of clinical infection was determined. Catheters were examined by microbiologic methods (sonication and roll-plate culture) and by scanning and transmission electron microscopy. Ultrastructural microbial colonization and biofilm formation were universal and occurred as early as one day after catheter insertion. The extent of biofilm formation was unrelated to the clinical status of patient or the catheter microbiological findings. Secondary seeding of catheters was rarely seen. Catheter microbial biofilm formation occurs early, is universal and does not necessarily represent an infectious condition.

Journal ArticleDOI
TL;DR: It is concluded that, in spite of free migration of swordfish across the Straits of Gibraltar, little genetic exchange occurs between the populations inhabiting the Mediterranean Sea and the tropical Atlantic ocean.
Abstract: Restriction analysis of mitochondrial DNA (mtDNA) from 204 individuals of swordfish (Xiphias gladius) revealed no differentiation among samples from three sites in the Mediterranean Sea (Greece, Italy, Spain), but a high degree of differentiation between Mediterranean samples and a sample from the Gulf of Guinea. A fifth sample from the Atlantic side of the Straits of Gibraltar (Tarifa) consisted mostly of mitotypes that are common in the Mediterranean, but contained several of mtDNA types of the Guinea sample not found in the Mediterranean. We conclude that, in spite of free migration of swordfish across the Straits of Gibraltar, little genetic exchange occurs between the populations inhabiting the Mediterranean Sea and the tropical Atlantic ocean. This is the first evidence of genetic differentiation among geographic populations of this highly mobile species that supports a world‐wide fishery.

Journal ArticleDOI
TL;DR: The best developed the external ear, the better developed the middle ear in patients with congenital aural atresia is found.
Abstract: Objective: To correlate the appearance of the external ear with the development of the middle ear in patients with congenital aural atresia. Design: Retrospective analysis of patients with congenital aural atresia. Obtain the microtia grades assigned to affected ears and correlate them with atresia scores that describe the degree of the middle ear malformation. Setting: University of Texas—Houston Otolaryngology Clinic (1988 to 1992). Patients: A total of 199 ears with congenital microtia and aural atresia and 25 ears with canal stenosis without microtia were identified, all of which had been previously evaluated by high-resolution computed tomography of the temporal bone, and then assigned an atresia score. Patients with Treacher Collins syndrome were not included in our study. Results: The average atresia score in cases with grade I microtia was 8.5; grade II microtia, 7.2; and grade III microtia, 5.9. In cases with canal stenosis without microtia, the average atresia score was 8.3. Conclusion: The better developed the external ear, the better developed the middle ear. (Arch Otolaryngol Head Neck Surg. 1995;121:885-886)

Journal ArticleDOI
TL;DR: In this article, a general algorithm to simulate and assess the dynamic behavior of any isolated diesel-wind turbine power system is analyzed and implemented, which can be used to determine the wind energy penetration level at any disturbed operation conditions.
Abstract: In the second part of this two-part paper, a general algorithm to simulate and assess the dynamic behavior of any isolated diesel-wind turbine power system is analyzed and implemented. It is presented how the various power system and wind energy conversion system (WECS) component models described in detail in Part I of the paper can be implemented in order to create integrated simulation software. Case studies for the small size isolated power system on the French island of Desirade are given and analyzed. The algorithm is validated and its usefulness to determine the wind energy penetration level at any disturbed operation conditions is demonstrated. >

Journal ArticleDOI
TL;DR: It is suggested that CRF may be involved in the local increase of capillary permeability seen in implantation sites, and that its production by stromal cells may be the consequence of a paracrine action of epithelial prostaglandin, released under the effect of PAF and IL-1, derived from or produced by blastocysts in endometrial cells.
Abstract: This review summarizes the information available on the involvement of prostaglandins in blastocyst implantation, and examines their interactions with three other inflammatory mediators, platelet-activating factor (PAF), interleukin (IL-1) and corticotrophin-releasing factor (CRF). Essential elements of this information, consistent with the assumption that prostaglandins play an important role in implantation, appear to be: (i) the burst of endometrial prostaglandin production, following the blastocyst signal(s) or an artificial stimulus; (ii) the main localization of this production at the luminal epithelium and release towards the stroma; and (iii) the presence at the stromal level of specific progesterone-dependent binding sites for prostaglandin E2. In addition, accumulated data indicate a paracrine interaction at the endometrial level between PAF and prostaglandin E2, which could serve, among others, to amplify the embryonic signal(s). Pro-inflammatory cytokines IL-1 alpha and IL-1 beta may also play a significant role in endometrial response via the modulation of prostaglandin E2 production. Prostaglandins and IL-1 induce the expression of CRF, which acts as an autocrine/paracrine inflammatory regulator. CRF exhibits a strong vasoactivity in skin tests, inducing a local increase of capillary permeability at a concentrations of 10(-10) M. Levels of CRF and its mRNA were found to be higher in rat implantation sites compared with those in the interimplantation regions. Stromal cells were found to be positive for immunoreactive CRF at the implantation sites only. It is suggested that CRF may be involved in the local increase of capillary permeability seen in implantation sites, and that its production by stromal cells may be the consequence of a paracrine action of epithelial prostaglandin, released under the effect of PAF and IL-1, derived from or produced by blastocysts in endometrial cells.

Journal ArticleDOI
TL;DR: In this paper, the structural properties of Si-Ge-C alloys were studied using Monte Carlo simulations, and the large size mismatch among the constituents was overcome by introducing atom-identity switches accompanied with neighbor-atom relaxations.
Abstract: The structural properties of Si-Ge-C alloys are studied using Monte Carlo simulations. The large size mismatch among the constituents is overcome by introducing atom-identity switches accompanied with neighbor-atom relaxations. A repulsive interaction between carbon atoms is found, so no clustering is observed. No formation of Ge-C bonds is foreseen. The lattice structural parameters show strong deviations from linear behavior.

Journal ArticleDOI
TL;DR: In this paper, the authors study the Asharp-interface model for phase transitions, which incorporates the interaction of the phase boundaries with the walls of a container, and prove that if the transition-layer solutions converge to the sharp-interface solutions as the thickness of the layer tends to zero.
Abstract: We study asharpinterface model for phase transitions which incorporates the interaction of the phase boundaries with the walls of a container Ω. In this model, the interfaces move by their mean curvature and are normal to δΩ. We first establish local-in-time existence and uniqueness of smooth solutions for the mean curvature equation with a normal contact angle condition. We then discuss global solutions by interpreting the equation and the boundary condition in a weak (viscosity) sense. Finally, we investigate the relation of the aforementioned model with atransitionlayer model. We prove that if Ω isconvex, the transition-layer solutions converge to the sharp-interface solutions as the thickness of the layer tends to zero. We conclude with a discussion of the difficulties that arise in establishing this result in nonconvex domains.

Journal ArticleDOI
TL;DR: The findings suggest that CRH may play an important role in the physiological events taking place within the uterine cavity, since CRH seems to be present in nonpregnant as well as pregnant uteri.
Abstract: CRH is produced by several intrauterine sites, including placenta and desidua, during pregnancy. However, no data are available regarding the presence of CRH in the nonpregnant uterus. We now report that CRH is produced in the epithelial cells of normally cycling human uterus and in an endometrial epithelial cell-derived tumor. Specifically, we have found that: 1) Northern blot hybridization analysis of normal glandular endometrium as well as of Ishikawa human endometrial adenocarcinoma cells showed the presence of the CRH messenger RNA; the size of the transcript seemed to be identical to that present in human placenta and rat hypothalamus; 2) immunoreactive CRH (ir-CRH) was detectable in normal dispersed glandular endometrial cells as well as in the Ishikawa adenocarcinoma cells; 3) gel filtration chromatography of normal glandular endometrial and Ishikawa cell extracts and their culture media showed that most ir-CRH present had the mol wt of the authentic CRH peptide; in addition, a larger form of ir-CRH was also present in both normal and tumoral endometrial epithelial cell extracts; the latter most probably correspondents to CRH precursor molecules; and 4) immunofluorescence staining of CRH in normal glandular endometrial and Ishikawa cells revealed a cytoplasm rich in granules positive for ir-CRH. Our findings suggest that CRH may play an important role in the physiological events taking place within the uterine cavity, since CRH seems to be present in nonpregnant as well as pregnant uteri. Since CRH is expressed in normal endometrial epithelial cells and in an epithelial tumoral cell line, we propose the use of the Ishikawa cell line as a convenient model for the in vitro study of endometrial CRH.

01 Jan 1995
TL;DR: In this paper, the structural properties of recurrent high-order neural networks (RHONN) whose weights are restricted to satisfy the symmetry property, are investigated and it is shown that these networks are gradient and stable dynamical systems and moreover they remain stable when either bounded deterministic or multiplicative stochastic disturbances concatenate their dynamics.
Abstract: The structural properties of Recurrent High-Order Neural Networks (RHONN) whose weights are restricted to satisfy the symmetry property, are investigated. First, it is shown that these networks are gradient and stable dynamical systems and moreover, they remain stable when either bounded deterministic or multiplicative stochastic disturbances concatenate their dynamics. Then, we prove that such networks are capable of approximating arbitrarily close, a large class of dynamical systems of the form χ = F(χ). Appropriate learning laws, that make these neural networks able to approximate (identify) unknown dynamical systems are also proposed. The learning laws are based on Lyapunov stability theory, and they ensure error stability and robustness.

Journal ArticleDOI
TL;DR: In this paper, the structural properties of recurrent high-order neural networks (RHONN) whose weights are restricted to satisfy the symmetry property, are investigated and it is shown that these networks are gradient and stable dynamical systems and moreover, they remain stable when either bounded deterministic or multiplicative stochastic disturbances concatenate their dynamics.
Abstract: The structural properties of Recurrent High-Order Neural Networks (RHONN) whose weights are restricted to satisfy the symmetry property, are investigated. First, it is shown that these networks are gradient and stable dynamical systems and moreover, they remain stable when either bounded deterministic or multiplicative stochastic disturbances concatenate their dynamics. Then, we prove that such networks are capable of approximating arbitrarily close, a large class of dynamical systems of the form /spl chi//spl dot/=F(/spl chi/). Appropriate learning laws, that make these neural networks able to approximate (identify) unknown dynamical systems are also proposed. The learning laws are based on Lyapunov stability theory, and they ensure error stability and robustness. >

Journal ArticleDOI
TL;DR: In this article, the Pigouvian fees are imposed on emissions revealed by the polluting firms in exchange for a lower ambient tax, and the non-point source case can be gradually transformed into a point source case.

Journal ArticleDOI
TL;DR: It is concluded, that GER patients with hiatal hernia present with an increased amount of reflux and more severe esophagitis, which results in more severely impaired esophageal peristalsis as compared to patients without hernia.
Abstract: An increased frequency of reflux events and a prolonged acid clearance have been shown in gastroesophageal reflux (GER) patients with a hiatal hernia as compared to those without. The objective of the present study was to further investigate esophageal motility and patterns of reflux in GER patients, in relation to the presence or absence of hiatal hernia. Esophageal manometry and ambulatory 24-hr esophageal pH-metry were used in 42 patients with GER and 18 controls. Eighteen of the patients were considered to have a nonreducing hiatal hernia on endoscopy. Hiatal hernia patients showed a higher extent of reflux (total composite score, P = 0.016; total reflux time, P = 0.008, reflux time in supine position, P = 0.024; reflux time in upright position, P = 0.008), a lower frequency of reflux events (P = 0.005), a more severe esophagitis on endoscopy (P < 0.01) and a lower amplitude of peristalsis at 5 cm proximal to LES (P = 0.0009) as compared to patients without hiatal hernia. The amplitude of peristalsis at the distal esophagus was inversely related to the extent of reflux (P = 0.024). Acid clearance was also significantly prolonged in the hernia subgroup (P = 0.011). Although LES resting pressure did not differ significantly between the two subgroups of patients, it was inversely related to the extent of reflux in the patients with hiatal hernia (P = 0.0005). It is concluded, that GER patients with hiatal hernia present with an increased amount of reflux and more severe esophagitis, which results in more severely impaired esophageal peristalsis as compared to patients without hernia. Prolonged acid clearance and impaired esophageal emptying observed in patients with hiatal hernia could be the result of both the presence of the hernia itself and the reduced peristaltic activity of the esophagus.

Journal ArticleDOI
TL;DR: The lowest threshold found in the VP was slightly higher than that usually obtained for the most rewarding brain areas (VTA, dorsal raphé, LH, amygdala), which suggests that the VP represents an important structure for reward.

Journal ArticleDOI
TL;DR: A higher content of immunoreactive (IR)-CRH and CRH mRNA in the implantation sites of early pregnant rat uterus compared to the inter-implantation regions is demonstrated, suggesting that endometrial CRH may play a role in the implants of blastocyst.

Journal ArticleDOI
TL;DR: The band-structure results for elastic and acoustic waves propagating in a composite (consisting of periodically placed spheres in a host material) are analyzed by employing the frequency dependence of the scattering cross section from a single sphere.
Abstract: The band-structure results for elastic and acoustic waves propagating in a composite (consisting of periodically placed spheres in a host material) are analyzed by employing the frequency dependence of the scattering cross section from a single sphere. Two limiting modes of propagation can be visualized. According to the first the wave propagates mainly through the host material; according to the second the wave hops coherently from a sphere to its neighbors using the resonances in the single-sphere scattering cross section. This second mode is the analog of the linear combination of atomic orbitals in electronic propagation, with the atomic orbitals replaced by the resonances.

Proceedings ArticleDOI
09 May 1995
TL;DR: This work proposes a constrained estimation technique for Gaussian mixture densities, and combines it with Bayesian techniques to improve its asymptotic properties, and evaluates the algorithms on the large-vocabulary Wall Street Journal corpus for nonnative speakers of American English.
Abstract: The performance and robustness of a speech recognition system can be improved by adapting the speech models to the speaker, the channel and the task. In continuous mixture-density hidden Markov models the number of component densities is typically very large, and it may not be feasible to acquire a large amount of adaptation data for robust maximum-likelihood estimates. To solve this problem, we propose a constrained estimation technique for Gaussian mixture densities, and combine it with Bayesian techniques to improve its asymptotic properties. We evaluate our algorithms on the large-vocabulary Wall Street Journal corpus for nonnative speakers of American English. The recognition error rate is comparable to the speaker-independent accuracy achieved for native speakers.

Journal Article
TL;DR: It is found that [125I]Tyr11-somatostatin binds with high affinity to T47D cells, and analysis indicated that mu-acting opioids interact with the SSTR2 receptor subtype.
Abstract: In a previous study, we found that morphine decreases, in a dose-dependent manner, the cell growth of T47D human breast cancer cells, despite the lack of mu opioid receptors and an interaction of morphine with other opioid sites. We have therefore examined a possible interaction of morphine with other membrane receptor systems of the cell. The present study describes for the first time an interaction between mu-acting opioid drugs and the somatostatinergic system. We have found that [125I]Tyr11-somatostatin binds with high affinity to T47D cells. Analysis of the binding data showed the presence of two components: one with high affinity but low capacity (Kd, 0.145 nM; 1450 sites/cell), and another of lower affinity but higher capacity (Kd, 1.192 nM; 11920 sites/cell). Somatostatin-14 and somatostatin-28 showed multiphasic displacement curves, indicating heterogeneity of binding sites. The latter was confirmed by reverse transcription-PCR, which revealed the existence of the somatostatin receptor subtypes 2 and 3 (SSTR2 and SSTR3), with a relative mRNA concentration of 85 and 15%, respectively. Morphine and the morphinomimetic peptide morphiceptine (Tyr-Pro-Phe-Pro-NH2) displace somatostatin from its binding sites. Further analysis indicated that mu-acting opioids interact with the SSTR2 receptor subtype.