Showing papers by "University of Patras published in 1994"

The CSP method for simplifying kinetics

Abstract: The Computational Singular Perturbation (CSP) method of simplified kinetics modeling is presented with emphasis on its comparative merits versus conventional methodologies. A new “refinement” procedure for the basis vectors spanning the fast reaction subspace is presented. A simple example is first worked through using the conventional partial-equilibrium and quasi-steady approximations, and is then treated in some detail using CSP.

Hemodynamic and analgesic profile after intrathecal clonidine in humans. A dose-response study.

Abstract: Background:Epidural clonidine produces effective postoperative analgesia in humans. Observed side effects include hypotension, bradycardia, sedation, and dryness of the mouth. A recent clinical study demonstrated that 150µg intrathecal clonidine administered postoperatively as the sole analgesic age

Ki-67 immunoreactivity in human central nervous system tumors: a study with MIB 1 monoclonal antibody on archival material.

Abstract: Paraffin-embedded surgical specimens from 136 primary human central nervous system (CNS) tumors, including 50 meningiomas, 24 astrocytomas, 26 anaplastic astrocytomas, 9 glioblastomas, 8 oligoden-drogliomas, 4 ependymomas, 1 anaplastic ependymoma, 2 subependymomas, 9 medulloblastomas, and 3 paragangliomas, were immunostained, following microwave processing, using a streptavidin/peroxidase method and the MIB 1 monoclonal antibody (mAb) against the Ki-67 antigen. The following mean Ki-67 labeling index (LI) values ± SD were found: meningiomas, 2.47 ± 1.83; astrocytomas, 2.03 ± 2.03; anaplastic astrocytomas, 12.80 ± 6.29; glioblastomas, 14.57 ± 6.77; oligodendrogliomas, 5.06 ± 4.78; ependymomas, 2.63 ± 2.58; anaplastic ependymoma, 6.89; subependymomas, 1.79 ± 1.54; medulloblastomas, 18.77 ± 9.65; and paragangliomas, 2.19 ± 2.51. Our findings indicate that while malignant CNS tumors always exhibited high Ki-67 LI values, and benign CNS tumors generally displayed lower values, increased immunoreactivity for Ki-67 epitopes (Ki-67 LI higher than 4) was noted in a number of meningiomas, astrocytomas, ependymomas, oligodendrogliomas and paragangliomas, contrasting with their benign histological features. Further investigations of the Ki-67 immunoreactivity in CNS tumors and systematic correlation with the postoperative follow-up of patients are necessary to determine the value of Ki-67 LI in predicting the biological behavior of CNS neoplasms.

Evidence that nitric oxide is an endogenous antiangiogenic mediator

Abstract: 1. The involvement of nitric oxide (NO) in the regulation of angiogenesis was examined in the in vivo system of the chorioallantoic membrane (CAM) of the chick embryo and in the matrigel tube formation assay. 2. Sodium nitroprusside (SNP) (0.37-28 nmol/disc), which releases NO spontaneously, caused a dose-dependent inhibition of angiogenesis in the CAM in vivo and reversed completely the angiogenic effects of alpha-thrombin (6.7 nmol/disc) and the protein kinase C (PKC) activator 4-beta-phorbol-12-myristate-13-acetate (PMA) (0.97 nmol/disc). In addition, SNP (28 x 10(-6) M) stimulated the release of guanosine 3'-5'-cyclic monophosphate (cyclic GMP) from the CAM in vitro. 3. In the matrigel tube formation assay, an in vitro assay of angiogenesis, both SNP (1-3 x 10(-6) M) and the cell permeable cyclic GMP analogue, Br-cGMP (0.3-1.0 x 10(-3) M) reduced tube formation. 4. The inhibitors of NO synthase, NG-monomethyl-L-arginine (L-NMMA) (3.8-102 nmol/disc) and NG-nitro-L-arginine methylester (L-NAME) (1.3-34.2 nmol/disc) stimulated angiogenesis in the CAM in vivo, in a dose-dependent fashion. D-NMMA and D-NAME on the other hand had no effect on angiogenesis in this system. 5. L-Arginine (10.9 nmol/disc), although it had a modest antiangiogenic effect by itself, was capable of abolishing the angiogenic effects of L-NMMA (34.2 nmol/disc) and of L-NAME (3.8 nmol/disc). 6. Dexamethasone, an inhibitor of the induction of NO synthase, at 0.2-116.1 nmol/disc, stimulated angiogenesis in the CAM, whereas at 348.4-1161 nmol/disc it inhibited this process. Combination of 38.7 nmol/disc dexamethasone with L-NAME (9.3 nmol/disc) resulted in a potentiation of the angiogenic effect of the former. It appears therefore that both the constitutive and the inducible NO synthase may contribute to the NO-mediated inhibition of angiogenesis. 7. Superoxide dismutase (SOD), which prevents the destruction of NO, at 300 i.u./disc had a modest antiangiogenic effect in the CAM, by itself. In addition, SOD, prevented alpha-thrombin (6.7 nmol/disc) and PMA (0.97 nmol/disc) from stimulating angiogenesis in the CAM.8. These results suggest that NO may be an endogenous antiangiogenic molecule of pathophysiological importance.

A new reagent for the cleavage of fully protected peptides synthesised on 2-chlorotrityl chloride resin

Abstract: A mixture of hexafluoroisopropanol–dichloromethane (1:4 v/v) acts as a fast, effective and convenient reagent for cleaving protected peptide fragments with a minimal amount of racemization from 2-chlorotrityl chloride resin.

Methane to ethylene with 85 percent yield in a gas recycle electrocatalytic reactor-separator.

Abstract: Methane was oxidatively coupled to ethylene with an ethylene yield up to 85 percent and a total C(2) hydrocarbon yield up to 88 percent in a gas recycle high-temperature (800 degrees C) electrocatalytic or catalytic reactor where the recycled gas passes continuously through a molecular sieve trap in the recycle loop. Oxygen is supplied either electrocatalytically by means of the solid electrolyte support of the silver-based catalyst or in the gas phase. The C(2) products are obtained by subsequent heating of the molecular sieve trap. The selectivity to ethylene is up to 88 percent for methane conversion up to 97 percent.

Electrochemical enhancement of a catalytic reaction in aqueous solution

Abstract: THE rates of many heterogeneous catalytic reactions between gaseous adsorbates on metal surfaces supported on solid electrolytes can be increased by applying a potential to the metal1–8 This phenomenon, which has been reported previously at temperatures of 250–750°C, has been shown9 to be due to the electrochemically induced spillover of ions from the support onto the catalyst surface; the ions then act as promoters for the catalytic reaction Here we report that a similar effect can be observed in aqueous solution at ambient temperatures We studied the oxidation of H2 on a platinum/graphite electrode immersed in aqueous KOH Application of a positive potential of 1–2 V to the Pt electrode increased the rate of H2 oxidation by up to 500% We deduce that hydroxide ions are acting as promoters, and find that each ion supplied to the catalyst causes the oxidation of up to 20 hydrogen atoms This kind of rate enhancement for heterogeneous catalytic reactions in solution may be of considerable technological value, for example in the electrochemical treatment of toxic organics10 or the generation of useful industrial chemicals4

On the Role of the Viscosity Ratio during Low-Capillary-Number Forced Imbibition in Porous Media

Abstract: The role of the viscosity ratio κ during forced imbibition in porous media is investigated theoretically using a new simulator, and experimentally based on displacements in model pore networks. Both theory and experiment show that κ is an important parameter of microdisplacement in porous media, not only for intermediate and large capillary number values, but also for small values, say Ca -6 . In the latter region the residual nonwetting saturation S or is virtually independent of Ca for κ 1. The unexpected result is that, even for very small values of Ca, S or decreases appreciably as κ decreases, especially in the case of very good wettability. Simulations indicate that the effect of κ on S or for low Ca values is enhanced as the contact angle decreases. The phenomenon is attributed to a synergistic effect between capillary microfingering and localized viscous forces. It must be emphasized that the velocity gradients which are created locally by the advance of a single meniscus, or of a wetting film, are sufficiently large to make viscous stresses important, even when the Ca value of the macroscopic flow is very low (say, of order 10 -8 ). A favorable viscosity ratio reduces the extent of capillary microfingering and thus increases the efficiency of microdisplacement, despite the fact that for Ca -6 the viscous stresses are negligible on a macroscopic scale. Further work is needed to analyze the synergism between κ and θ e at low Ca values.

Quantitative determination of the cubic, tetragonal and monoclinic phases in partially stabilized zirconias by Raman spectroscopy

Abstract: Vibrational Raman spectroscopy was employed successfully for the simultaneous quantitative determination of the cubic, tetragonal and monoclinic phases of partially stabilized zirconia. Pressed pellets with known composition were prepared and used as standard mixtures. From the standard pellets, a calibration curve was obtained which was found to be a straight line if (I 640−0.47I 260)/I 177 is plotted against the inverse monoclinic molar fraction.I 260,I 177 are the Raman intensities for the tetragonal and monoclinic peaks at 260 and 177 cm−1, respectively, and were calculated by subtracting the “background”. In contrast,I 640 represents the intensity for the 640 cm−1 band, which is attributed to all three phases, and was measured including the “background”.

Pentylenetetrazol-induced seizures decrease gamma-aminobutyric acid-mediated recurrent inhibition and enhance adenosine-mediated depression.

Abstract: To elucidate the consequences of convulsions, we examined biochemically and electrophysiologically the brains of mice that had sustained two complete tonic-clonic convulsions after administration of pentylenetetrazol (PTZ 50 mg/kg intraperitoneally, i.p.), 48 and 24 h before decapitation. Control mice were injected with saline. Input/output curves of the extracellular synaptic responses in the CA1 area of hippocampal slices showed that PTZ-induced seizures do not establish the persistent change in hippocampal excitability itself that can be detected in vitro. However, use of the paired-pulse stimulation paradigm showed that gamma-aminobutyric acid A (GABAA)-mediated recurrent inhibition was significantly weaker (by 19-25%) in the CA1 area of slices from PTZ-treated mice (PTZ slices) as compared with slices from control mice (control slices). The density of GABAA receptors (high-affinity component) was also lower in hippocampus (by 19%) and cortex (by 14%) of PTZ-treated mice. A GABA-related disinhibitory mechanism underlying PTZ seizures may thus persist for 1 day after the seizure, predisposing the brain to subsequent seizures. On the other hand, the depressant effect of a single dose of adenosine 10 microM on the CA1 synaptic response was stronger (by 35% on population spikes) and longer lasting in PTZ slices as compared with controls. This could be attributed to significantly higher adenosine A1 receptor density in hippocampus (Bmax of [3H]CHA was higher by 34%) as well as cortex and cerebellum of these animals. The phenomenon may reflect an adenosine A1-mediated adaptive mechanism that offers protection from subsequent seizures.

Flexural vibrations of poroelastic plates

Abstract: The governing equations of flexural vibrations of thin, fluid-saturated poroelastic plates are derived in detail. The plate material obeys Biot's theory of poroelasticity with one degree of porosity, while the plate theory employed is the one due to Kirchhoff. These governing equations are compared with the corresponding ones for thermoelastic plates and a poroelastic-thermoelastic analogy for flexural plate dynamics is established in the frequency domain. The dynamic response of a rectangular, simply supported, poroelastic plate to harmonic load is obtained analytically-numerically and the effects of inertia as well as of porosity and permeability on the response is assessed.

Age at Onset in Subtypes of Schizophrenic Disorders

Abstract: Age at onset and sex differences in the age at onset were investigated in the schizophrenic subtypes of 200 patients. Significant differences in the age at onset were observed among these subtypes; the disorganized subtype demonstrated the earliest and the paranoid the latest onset. The mean age at onset of all female patients was significantly greater than that of the male. Specifically, in the paranoid subtype the onset for men occurred earlier than for women. Conversely, in the disorganized subtype the disorder appeared earlier in women. There was no significant sex difference in the age at onset in the undifferentiated and the residual subtypes. In the paranoid subtype most men developed the disease before age 30 (72%), whereas women had an even distribution of the onset before and after 30. Ninety-six patients admitted for the first time demonstrated findings similar to those of the total sample. The data provide additional information on the phenotypic expression of the subtypes of schizophrenic disorders and indicate the necessity for further demographic and genetic studies to delineate the underlying defect.

Dexamethasone therapy for bacterial meningitis in children: 2-versus 4-day regimen.

Abstract: Four-day dexamethasone therapy has been used to treat bacterial meningitis. This prospective, randomized study compared the effect of a 2-day versus a 4-day regimen. Children (n = 118, ages 2.5 months to 15 years) were evaluated; 50% of the cases were due to Neisseria meningitidis and 40% to Haemophilus influenzae type b. Patients were treated intravenously (iv) mainly with conventional antimicrobial therapy and were randomly assigned to receive dexamethasone, 0.15 mg/kg iv every 6 h for 2 or 4 days. The clinical response was similar for both dexamethasone regimens. The meningococcal meningitis patients survived without neurologic or audiologic sequelae. On long-term follow-up, neurologic sequelae or moderate or more severe unilateral or bilateral hearing impairment (or both) were found in 1.8% and 3.8% of patients treated with dexamethasone for 2 and 4 days, respectively. The 2-day regimen appears appropriate for the treatment of H. influenzae and meningococcal meningitis.

Human cytogenetic biomonitoring of occupational exposure to 1,3-butadiene

Abstract: The association of occupational exposure to 1,3-butadiene and chromosomal damage in peripheral blood lymphocytes was studied in 40 workers from two production facilities. Control persons, 30 in all, were chosen from other departments of the same plants, and they were roughly matched for age and smoking habits. The exposure levels to ambient butadiene were measured both by personal sampling using diffuse monitors and by stationary sampling at production and handling sites. Chromosome aberrations (CA) micronuclei (MN) and sister-chromatid exchanges (SCE) in peripheral lymphocytes were analyzed as markers of exposure. Smoking had a slight effect on the frequency of MN, and the mean frequency of SCEs was also higher in smokers than in non-smokers. No effect of smoking, however, was seen in relation to chromosomal aberrations. No exposure related effects were seen in any of the three cytogenetic endpoints in either of the butadiene production plants, representing typical low (below 3 ppm) exposure levels of the butadiene manufacturing industry.

Area-time efficient modulo 2/sup n/-1 adder design

Abstract: In this paper the design of modulo 2/sup n/-1 adders is discussed. Two new design procedures are given, based on the one-level and the two-level carry look-ahead addition algorithms. The adders designed according to the procedures proposed in this paper are significantly more efficient, with respect to speed and the cost function area-time product, than the corresponding adders already known from open literature. >

Rapid prenatal diagnosis of aneuploidy from uncultured amniotic fluid cells using five-colour fluorescence in situ hybridization.

Abstract: In this paper we describe the use of five-colour fluorescence in situ hybridization for prenatal diagnosis of aneuploidy using uncultured amniotic fluid cells. The analysis is based on ratio mixing of dual-labelled probes and digital imaging for the detection and visualization of five different probes specific for the five target chromosomes, 13, 18, 21, X, and Y. A retrospective blind analysis of 30 coded uncultured amniotic fluid samples correctly detected fetal sex and five trisomy 21 cases. Multicolour fluorescence in situ hybridization used in this way allows rapid and simultaneous detection of the most frequent aneuploidies.

Steady-state two-phase flow through planar and nonplanar model porous media

Abstract: A comparative experimental study of ‘steady-state’ two-phase flow in two types of model porous media is made to determine the effects of nonplanarity on the flow mechanisms and the mesoscopic flow behavior. The two model porous media have virtually the same pore geometry, but one has a planar network skeleton, whereas the other has a nonplanar (two-layer) skeleton. The latter is a new type of model porous medium that permits detailed visual observation and quantitative measurements without sacrificing the 3D character of the pore network topology. The capillary number and the flowrate ratio are changed systematically, whereas the viscosity ratio and the wettability (contact angle) are kept constant. Conventional relative permeabilities are determined and correlated with the porescale flow phenomena. In the range of parameter values investigated, the flow mechanism observed was ganglion dynamics (intrinsically unsteady, but giving a time-averaged steady-state). The nonplanarity is shown to have small qualitative but significant quantitative effects. In the nonplanar porous medium, the ganglion size distribution is wider, the mean ganglion size larger, and the stranded ganglia are fewer than those in the planar one, under the same flow conditions.

The fast Newton transversal filter: an efficient scheme for acoustic echo cancellation in mobile radio

Abstract: The authors investigate the recently suggested fast Newton family for adaptive filtering in the context of acoustic echo cancellation, with emphasis on the mobile radio case. A distinctive advantage of the fast Newton transversal filter (FNTF) is that it can offer high performance with speech inputs at low computational cost. They discuss possible implementations and compare the FNTF with classical schemes in terms of complexity. A complete numerically stabilized version is presented, and additional features for proper real-time operation with speech are discussed. Experimental comparisons using various signals and real situations show that in all cases, the FNTF behaves similarly to the standard fast RLS transversal filter (FTF) algorithm, whereas its complexity is only slightly higher than that of the normalized LMS (NLMS). Compared with the NLMS, the experiments show that in the context investigated, the latter exhibits inferior performance with respect to convergence and tracking. Thus, they demonstrate that the FNTF is an efficient scheme for acoustic echo cancellation in mobile radio. >

Intracontinental wedging and post-orogenic collapse in the Mesohellenic Trough

Abstract: The Mesohellenic Trough is a 130 km long and about 30 km wide subsiding area which contains a thick sequence of well exposed Late Cenozoic post-orogenic sediments. This intermontane basin, located at the contact between the Apulian and Pelagonian collided margins, provides a good example of the characteristics needed to study the chronology of late orogenic intracontinental structures.