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Showing papers by "University of Trento published in 1993"


Journal ArticleDOI
TL;DR: An experimental study of the luminescence time decay in porous silicon as a function of temperature, excitation, and observation energies is reported.
Abstract: An experimental study of the luminescence time decay in porous silicon as a function of temperature, excitation, and observation energies is reported. The decay line shape is well described by a stretched exponential for a variety of experimental conditions. A hierarchy of waiting times for carrier hopping, of intersite distances, and of site energies result from the analysis of our data.

223 citations


Journal ArticleDOI
TL;DR: It was inferred that EqT-II increases membrane permeability by forming oligomeric channels comprising several copies of the cytolysin monomer, indicating the formation of cation-selective channels.
Abstract: The interaction ofActinia equina equinatoxin II (EqT-II) with human red blood cells (HRBC) and with model lipid membranes was studied. It was found that HRBC hemolysis by EqT-II is the result of a colloid-osmotic shock caused by the opening of toxin-induced ionic pores. In fact, hemolysis can be prevented by osmotic protectants of adequate size. The functional radius of the lesion was estimated to be about 1.1 nm. EqT-II increased also the permeability of calcein-loaded lipid vesicles comprised of different phospholipids. The rate of permeabilization rised when sphingomyelin was introduced into the vesicles, but it was also a function of the pH of the medium, optimum activity being between pH 8 and 9; at pH 10 the toxin became markedly less potent. From the dose-dependence of the permeabilization it was inferred that EqT-II increases membrane permeability by forming oligomeric channels comprising several copies of the cytolysin monomer. The existence of such oligomers was directly demonstrated by chemical cross-linking. Addition of EqT-II to one side of a planar lipid membrane (PLM) increases the conductivity of the film in discrete steps of defined amplitude indicating the formation of cation-selective channels. The conductance of the channel is consistent with the estimated size of the lesion formed in HRBC. High pH and sphingomyelin promoted the interaction even in this system. Chemical modification of lysine residues or carboxyl groups of this protein changed the conductance, the ion selectivity and the current-voltage characteristic of the pore, suggesting that both these groups were present in its lumen.

196 citations


Journal ArticleDOI
TL;DR: The trapped biocatalyst survives experimental working-up and displays kinetic behavior excluding mass transport interference during sucrose degradation, attributed to the mechanical features of this film, which displays a tensile strength sufficient to contrast the tensile stress exerted by cell reproduction.

112 citations


Journal ArticleDOI
TL;DR: In this paper, UHMPE and HDPE composites were fabricated under various processing conditions and the tensile strength and modulus values of composite appeared to be fairly high and close to those reported for other composites reinforced with polyethylene (PE) fibers.
Abstract: Drawing on the difference in melting points of UHMPE fiber (150°C) and HDPE matrix (130°C), single-polymer composites were fabricated under various processing conditions. Because of the chemical similarity of the composite components, good bonding at the fiber-matrix interface could be expected. The matrix, the fiber, and unidirectional composite laminae were studied using TMA and DSC analyses, a hot-stage crystallization unit attached to a polarizing microscope, and an universal tensile testing machine. The TMA showed negative thermal expansion of the fiber over the complete temperature range of the experiment. Three regimes of contraction according to the values of the thermal expansion coefficient were detected. DSC analyses of either the fiber or the composite specimens did not show any appreciable changes after various thermal treatments. They also showed no evidence of fiber relaxation during manufacture, probably because of the pressure-related transverse constraint. The tensile strength and modulus values of the composite appeared to be fairly high and close to those reported for other composites reinforced with polyethylene (PE) fibers. An apparent maximum on the temperature dependencies of tensile properties was observed. A study of the matrix microstructure did not give any proof of transcrystalline growth at the fiber-matrix interface even for chemical or plasma surface-treated fibers. © 1993 John Wiley & Sons, Inc.

101 citations


Journal ArticleDOI
TL;DR: In this article, the lineshape of the Si 2p and Ti 2p peaks indicate that silicon and titanium are present as SiO2 and TiO2 oxide both for the starting and thermal-treated powders.

96 citations


Journal ArticleDOI
TL;DR: In this article, a density functional theory is used to predict the binding energy of atomic and molecular impurities (Ne, Ar, Kr, Xe, Li, Na, K, Rb, Cs, and SF$_6$) in the center of $4$He clusters, in the limit of zero temperature and for zero angular momentum states.
Abstract: A density functional theory is used to predict the binding energy of atomic and molecular impurities (Ne, Ar, Kr, Xe, Li, Na, K, Rb, Cs, and SF$_6$) in the center of $^4$He clusters, in the limit of zero temperature and for zero angular momentum states. The size dependence of the binding energy, from small clusters to the bulk liquid limit, is investigated. The behaviour of the $^4$He density near the impurity is also studied.

92 citations


Journal ArticleDOI
TL;DR: In this paper, a description of the asymptotic development of a family of minimum problems is proposed by a suitable iteration of Γ-limit procedures, and an example of the development of functionals related to phase transformations is also given.
Abstract: A description of the asymptotic development of a family of minimum problems is proposed by a suitable iteration of Γ-limit procedures. An example of asymptotic development for a family of functionals related to phase transformations is also given.

90 citations


Journal ArticleDOI
TL;DR: In this paper, a dimensionally regularized Wilson loop with light-like segments was performed in the lightlike axial gauge with the Mandelstam-Leibbrandt prescription for the gluon propagator.

82 citations


Journal ArticleDOI
TL;DR: Caulerpenyne, the major metabolite of C. taxifolia, is the most active on sea urchin eggs and may represent an ecological risk for microorganisms and the eggs of multicellular animals living close to this alga.
Abstract: Caulerpa taxifolia (Vahl) C. Agardh (Ulvophyceae, Caulerpales) is an alga of tropical origin that was accidentally introduced into the Mediterranean sea in 1984, where this species can reach an abundance that has never been described in tropical endemic regions. It is known that caulerpacean algae can develop an efficient strategy against grazers consisting of the synthesis of repulsive of toxic secondary metabolites: we report here the first study of the toxicity of purified secondary metabolites and raw extracts fromC. taxifolia from the Mediterranean. Toxicity was evaluated on three models: mice (lethality), mammalian cells in culture (cytotoxicity) and sea urchin eggs (disturbance of cell proliferation). Aqueous extracts are only active on fibroblasts and mice. In the three toxicity models a seasonal variation of toxicity is observed for the crude methanol extract as well as a decrease of this activity whenC. taxifolia from the Mediterranean is kept in aquaria. Pure compounds exhibit different toxicity depending on the assay. 10,11-epoxycaulerpenyne is the most active substance on mice and fibroblasts whereas taxifolial A and D are inactive or only weakly toxic. Among the four tested compounds caulerpenyne, the major metabolite ofC. taxifolia, is the most active on sea urchin eggs. Caulerpenyne may therefore represent an ecological risk for microorganisms and the eggs of multicellular animals living close to this alga. The ecological impact of this toxicity on marine organisms and the interaction of this alga with the herbivorous fauna are discussed.

80 citations


Journal ArticleDOI
TL;DR: In this article, a detailed analysis of infrared absorption spectra of porous silicon is performed on the basis of high spatial resolution measurements, where Si atoms of the porous silicon surface are found to bind to H, O, C atoms and to CH3 and OH groups.

78 citations


Journal ArticleDOI
TL;DR: Amorphous carbon-rich silicon carbide films Si0.45C0.55, deposited on silicon, were obtained by r.f. magnetron sputtering of sintered SiC targets in argon plasma and characterized by means of X-ray photoelectron spectroscopy, Auger electron spectroscope, Rutherford backscattering spectroscopic and elastic recoil detection analysis as discussed by the authors.

Book
05 Jun 1993
TL;DR: In this paper, the concept of hysteresis operator was introduced and the existence of a solution for a parabolic differential equation containing a hystereis operator is proven.
Abstract: The concept ofhysteresis operator is introduced. Existence of a solution is proven for a parabolic differential equation containing a hysteresis operator.

Journal ArticleDOI
TL;DR: The physics behind the fast-sound effect in liquid water is studied by a comprehensive microscopic approach and is found to be a rather extreme case of a well-known phenomenon occurring even in monatomic liquids.
Abstract: Both inelastic-neutron-scattering experiments and computer simulations have established that liquid water can support a longitudinal mode propagating with a velocity much larger than the ordinary speed of sound. The physics behind this peculiar behavior is studied by a comprehensive microscopic approach. The effect is found to be a rather extreme case of a well-known phenomenon occurring even in monatomic liquids. To make the analogies and the differences more transparent, simulation data in water and in a simple alkali metal (liquid Cs near melting) are also reported. Finally, we discuss the ultimate microscopic origin of fast-sound effect in liquid water.

Journal ArticleDOI
TL;DR: The simulation findings for the dynamic structure factor are found to be in excellent agreement with the inelastic-neutron-scattering data recently reported, and to a very good approximation the same for all the alkali metals.
Abstract: In this paper we report the results of a comprehensive simulation study of the structural and dynamical properties of liquid Na, K, Rb, and Cs near the melting point. An important consequence of this investigation is that both the equilibrium and the time-dependent correlations can be cast in a properly scaled form, which is to a very good approximation the same for all the alkali metals. In particular, for liquid Cs the simulation findings for the dynamic structure factor are found to be in excellent agreement with the inelastic-neutron-scattering data recently reported. Finally, the analysis is extended to the two main transport properties, the diffusion and the shear-viscosity coefficients. The simulation results compare satisfactorily with the actual experimental findings and confirm the validity of the simplified mode-coupling approaches recently proposed for these two quantities.

Journal ArticleDOI
TL;DR: In this article, a general covariant quantum field theory with an infinite number of degrees of freedom was defined by combining the Husain-Kuchař model, the Loop Representation, the idea of defining diffeomorphism invariant observables in terms of material reference systems, and the Ashtekar-Isham C∗-algebra representation theory.

Journal ArticleDOI
15 Jan 1993-Cancer
TL;DR: The cost‐effectiveness ratio of a health campaign for the early diagnosis of cutaneous melanoma (CM), currently the only means to reduce mortality from this melanoma, was calculated for the Trentino region in Italy.
Abstract: Background. The cost-effectiveness ratio of a health campaign for the early diagnosis of cutaneous melanoma (CM), currently the only means to reduce mortality from this melanoma, was calculated for the Trentino region in Italy. Methods. Health campaigns in Trentino were carried out, and comparisons were made with neighboring regions where there had been no campaigns. To do this, the trend of the mortality rates calculated according to sex and age using the direct standardized method and data provided by ISTAT (the Central Italian Institute of Statistics) was considered. Results. It was determined that 22.3 lives were saved by early diagnosis during the period 1977–1985, resulting in a savings of $494,636 to the Italian National Health Service in avoided treatments. The total cost to the Health Service of the campaign was $70,800. The cost per year of lives saved was calculated to be $400. Conclusions. The outcome of this campaign was a recommendation for the use of such programs in other countries and regions.

Journal ArticleDOI
TL;DR: In this article, an algebraic model of coupled anharmonic benders capable of describing the complete spectrum and intensities of bending vibrations of medium size and large polyatomic molecules was introduced.

Journal ArticleDOI
TL;DR: In this paper, the role of the carbon fiber matrix transcrystalline interphase in a single pitch-based carbon fiber reinforced J-polymer is investigated. But the authors assume that the Weibull statistics are controlled by Weibell statistics.

Journal ArticleDOI
TL;DR: The method described seems to provide a dynamic index of the sympatho-vagal balance at the ventricle that can be useful for a deeper understanding of ventricular repolarisation duration variability.
Abstract: This study assesses the feasibility of beat-to-beat measurement of the R-T interval in Holter ECG recordings. The low sampling rate of the Holter system was increased by a specific interpolating filter, and the precision and accuracy of two T-wave fiducial point (T-wave maximum: Tm, T-wave end: Te) detection algorithms were compared. The results of the validation tests show better performance of the Tm measurement procedure in the presence of high noise levels. The overall process for the beat-to-beat R-T interval measurement was then tested on ECG Holter recordings collected during free and controlled respiration. Finally, the R-Tm and the corresponding R-R intervals were measured on 24 h ECG recordings of healthy subjects and the spectral analysis was applied to the constructed series. Both R-R and R-Tm spectra show two main frequency components (low-frequency approximately 0.1 Hz, high-frequency approximately 0.25 Hz) changing in their power ratios continuously throughout the 24 h period. The method described seems to provide a dynamic index of the sympatho-vagal balance at the ventricle that can be useful for a deeper understanding of ventricular repolarisation duration variability.

Journal ArticleDOI
TL;DR: In this article, the effect of the degree of crystallinity on the mechanical properties is examined at two crystallinity levels of the as-received composites and of quenched composites.

Journal ArticleDOI
TL;DR: In this article, it was shown that the resulting gas-dynamic processes depend on γ, the heat capacity ratio, as well as on whether particles backscattered to the effusing surface are subject to recondensation or reflection.
Abstract: When gases are released from a pulsed nozzle or when solids are sputtered with intense laser pulses, effusion-like expansions take place which terminate abruptly. The resulting gas-dynamic processes depend on γ, the heat capacity ratio, as well as on whether particles backscattered to the effusing surface are subject to recondensation or reflection. Certain aspects of these terminating expansions have already been treated but we consider it appropriate to examine the problem further. In particular the following topics are emphasized. (a) Following previous work, the expansions are shown to consist of a series of regions separated by lines of contact, i.e. abrupt changes of slope. (b) For conditions of recondensation, there are two regions separated by one line of contact, the first region lying in part behind the effusing surface. For conditions of reflection, there are three regions, the first of which begins at the surface. Both types of expansion terminate with a region which is a remanent of the release process. (c) The nearsurface region under conditions of reflection permits an analytical approximation valid for all γ in which the sound speed is invariant with distance and the flow velocity is linear with distance. (d) The surface itself under conditions of recondensation permits an analytical approximation valid for all γ for the sound speed. More generally the near-surface region can be resolved by the method of Stanyukovich. (e) The various analytical solutions and approximations are shown to compare favorably with numerical results. (f) Plots of density and flow velocity versus distance are found to be roughly independent of γ, thence of the nature of the sputtered particles. (g) Tabulated results are presented to enable a more general use of gas-dynamic ideas.

Journal ArticleDOI
TL;DR: The tropical green seaweed Caulerpa taxifolia (VAHL) C. AGARDH (Caulerpales) which is invading the Mediterranean is shown to contain trace amounts of two further novel terpenes, 7,7-C-didehydro-6-hydroxy-6,7dihydrocaulerpenyne as discussed by the authors.
Abstract: The tropical green seaweed Caulerpa taxifolia (VAHL) C. AGARDH (Caulerpales) which is invading the Mediterranean is shown to contain trace amounts of two further novel terpenes, 7,7-C-didehydro-6-hydroxy-6,7-dihydrocaulerpenyne (= (4S, 6S,1E)-3-[(Z)-acetoxymethylidene]-6-hydroxy-11-methyl-7-methylidenedodeca-1,10-dien-8-yne-1,4-diyl diacetate; 3a) and taxifolione (= 6-methylhept-5-en-3-yn-2-one; 4). The former is the most active of the toxins so far isolated from this seaweed, both as an in vitro inhibitor of the growth of marine bacteria and as a cytotoxic agent toward marine ciliate protists. This suggests a central ecotoxicological role for triacetate 3a as an adjuvant factor in the invasion of the Mediterranean by this seaweed. Moreover, the almost equally toxic 10,11 -epoxycaulerpenyne (2) which is scarcely available from Nature for bioassays can now be obtained by peroxy-acid epoxidation of caulerpenyne (1), along with the 6,7-epoxycaulerpenynes 6b and 6a. The latter are very labile, 6a giving triacetate 3a, suggesting epoxides to be late biogenetic intermediates in C. taxifolia.

Journal ArticleDOI
TL;DR: In this article, a retrospective investigation was made to compare the occupational risk of tuberculosis in personnel assisting human immunodeficiency virus (HIV)-infected and uninfected subjects with active tuberculosis.
Abstract: Objective:A retrospective investigation was made to compare the occupational risk of tuberculosis in personnel assisting human immunodeficiency virus (HIV)-infected and uninfected subjects with active tuberculosis.Design:We retrospectively reviewed 6 years of hospital activity in 3 units where HIV-infected patients with tuberculosis are hospitalized and in 2 units where non-HIV-infected tuberculosis patients are hospitalized. The risk of occupational tuberculosis in healthcare workers who assisted HIV-infected and non-HIV-infected patients with tuberculosis was investigated.Participants:The risk of occupational tuberculosis in healthcare workers was studied by considering the numbers of potential source cases (hospitalized patients with tuberculosis) in the two conditions investigated (HIV-positive and HIV-negative). Both potential source cases and cases of tuberculosis in healthcare workers had to be microbiologically proven in order to be considered..Results:Seven cases of tuberculosis occurred in persons who cared for 85 HIV-infected subjects with tuberculosis, while only 2 cases occurred in staff members who took care of 1,079 HIV-negative tuberculosis patients over the same period (relative risk=44.4; 95% confidence interval = 8.5-438).Conclusions:Tuberculosis seems no longer to be a neglectable risk in healthcare workers assisting patients with HIV infection. Further study is urgently needed to see whether such unexpectedly high dissemination of tuberculosis also is demonstrable in the community.


Journal ArticleDOI
TL;DR: In this paper, the authors used Electrochemical Impedance Spectroscopy (EIS) to study the electrochemical behavior properties both of undamaged fluoropolymer coatings and of samples with an artificial defect.

Journal ArticleDOI
TL;DR: In this paper, a systematic study of the recording process, followed by X-ray diffraction and differential scanning calorimetry, of a Ni3Al based alloy, previously disordered by high energy ball-milling, is reported.
Abstract: A systematic study of the kinetics of the recording process, followed by X-ray diffraction and differential scanning calorimetry, of a Ni3Al based alloy, previously disordered by high energy ball-milling, is reported. X-ray diffraction analysis of isothermally annealed samples gives apparent activation energies of 1.57 ± 0.20 eV for reordering and 1.61 ± 0.07 eV for ordered domain growth. Good agreement is found between these values and that obtained from the calorimetric analysis of the continuous heating transformation, which gives a value for the apparent activation energy of 1.64 ± 0.21 eV. However, in order to correctly reproduce the calorimetric results upon isothermal annealing, an increasing value for the activation energy of the process is needed. As the experimental results suggest that point defect diffusion has an active role in the reordering process, a vacancy trapping mechanism via impurity is put forward to account for the slowing down of the kinetics of reordering.

Journal ArticleDOI
TL;DR: In this article, a semi-empirical fitting procedure was used to reproduce the experimental data for both gases from 50 to 4000 eV, and the fit allowed them to extrapolate total cross sections into high energies.


Journal ArticleDOI
TL;DR: These substances were not found, at the sensitivity level of HPLC-UV, in the cell-free culture medium (recovered from 3-day-starved mass cultures) where they, despite insolubility in neat, were found in the liquid chromatography medium.
Abstract: Dipartimento di Scienze dell 'Ambiente e del Territorio, Sezione di Protistologia, Universith di Pisa, 1-56100 Pisa Istituto di Chimica, Universit~ di Trento, 1-38050 Povo-Trento tures by centrifugation, EtOH-extracted, and subjected to CN HPLC (7 ~m, 20×1 cm, 98:2 hexane/isopropanol, 5 ml/min) giving euplotin A 1 (I) and 132 (2) (Fig. 1) in 4.1/1 weight ratio. These substances were not found, at the sensitivity level of HPLC-UV, in the cell-free culture medium (recovered from 3-day-starved mass cultures) where they, despite insolubility in neat

Journal ArticleDOI
TL;DR: In this article, a pyrolysis process under flowing ammonia at 1000 C was performed to characterize the conversion process of the polymeric precursor fibers into the ceramic product, and the tensile strength was measured at various stages of the process and related to the corresponding structural evolution.
Abstract: Polymeric fibers were produced from a polyaluminocarbosilane obtained by reacting polycarbosilane and an aluminum alkoxide modified with a [beta]-ceto ester. The pre-ceramic fibers were converted into amorphous Si-Al-O-N ceramic fibers after a pyrolysis process under flowing ammonia at 1000 C. [sup 29]Si and [sup 27]Al magic-angle spinning nuclear magnetic resonance investigations were performed to characterize the conversion process of the polymeric precursor fibers into the ceramic product. However, because of the amount of matter required for the MAS-NMR experiments, the heat treatment applied for fibers was done on powders assuming identical evolution for both materials. Tensile strength was measured at various stages of the pyrolysis process and related to the corresponding structural evolution.