Showing papers by "University of Udine published in 1989"

Non-parallel chains in crystalline γ-isotactic polypropylene

Abstract: CRYSTALLINE synthetic polymers generally exhibit highly anisotropic arrangements of the polymer chains, which tend to lie parallel to each other. Indeed, chain-axis parallelism has become virtually an unchallenged principle of polymer crystallization, essentially for two reasons. First, it seems consistent with the requirements of the close packing of rods, which may be assumed to approximate crystallized polymer chains, and second, most polymer crystal structures have been determined from samples that are fibrous. As part of a study1–1 of crystal structures of polymer phases that do not readily form fibrous specimens, we have determined the crystal structure of the γ-form of isotactic polypropylene (γ-iPP)5-8. We show that the structure comprises layers which are two chains wide, reminiscent of the α-phase9, but with the chain-axis directions in adjacent bilayers at an angle of 80° to one another. This feature recalls the arrangement, at the same inter-helical angle, that is proposed to occur at the branching points in α-iPP crystals10-12. Similar packing at large interaxial angles between isochiral chain fragments is also often found in globular proteins13. The γ-iPP crystal structure is unusual, however, in that non-parallel chains appear in a fully ordered array. The driving force for such packing seems to be the favourable registration between helices that occurs for this tilt angle.

Constitutive equation and compatibility of the external loads for linear elastic masonry-like materials

Abstract: The first part of the paper is devoted to the motivation of the constitutive equation of the masonry-like material. It is proved that this equation is the result of three fundamental constitutive assumptions: infinitesimal elasticity, no tensile strength, and a postulate of normality. A necessary and sufficient condition for the existence of a strain energy function is also supplied.

A general purpose device simulator coupling Poisson and Monte Carlo transport with applications to deep submicron MOSFETs

Abstract: An efficient self-consistent device simulator coupling Poisson equation and Monte Carlo transport suitable for general silicon devices, including those with regions of high doping/carrier densities, is discussed. Key features include an original iteration scheme and an almost complete vectorization of the program. The simulator has been used to characterize nonequilibrium effects in deep submicron nMOSFETs. Substantial overshoot effects are noticeable at gate lengths of 0.25 mu m at room temperatures. >

Probabilistic approach for design optimization of rockfall protective barriers

Abstract: Many alpine and pre-alpine areas of northern Italy are affected by dangerous rockfall phenomena. In designing rockfall protective barriers it is necessary to estimate the reliability of the defensive structures considering the following input parameters: (i) predicted impact energy field, (ii) possible rock block trajectories and (iii) impact strength of the barrier construction material. The reliability analysis aims at predicting the probability that a rock mass may go beyond the barrier (failure or overfly) or beyond the barrier system. The paper describes a design procedure which involves the evaluation of the probability of occurrence of a specific rock body bouncing down. This moving block is characterized by a certain rock mass ( m ), translation velocity (υ t ) and rotation velocity (υ r ). The paper discusses the practical application of a computer block trajectory simulation procedure used to design optimization problems in mountain sites of Friuli which are exposed to rockslide risk.

Mechanical alloying of Fe and V powders: Intermixing and amorphous phase formation

Abstract: Mossbauer spectrometry and x-ray diffractometry were used to characterize the microstructural changes that occurred during the mechanical alloying of Fe and V powders, After 3 h of essentially no interatomic intermixing, an Fe–V alloy began to form. At first the chemical composition of this alloy was highly inhomogeneous, having large variations over distance scales of less than 100 A. After about 24 h of ball milling, the alloy homogenized and then became at least partly amorphous.

Demonstration of Phenolic Compounds in Plant Tissues by An Osmium-Iodide Postfixation Procedure

Abstract: A simple procedure to stain phenols in plant tissues is described. Postfixation with an aqueous solution prepared by mixing 2 cc of 2% osmium tetroxide and 8 cc of 3% potassium iodide yields brilliant visualization of phenol-containing vacuoles in different tissues of plants (e.g., coffee, oak, tobacco and spruce) bearing high concentration of phenolic compounds. Areas bearing phenols become dark gray to black. Chemical experiments demonstrate that osmium-potassium iodide (Os-KI) mixture reacts rapidly with several naturally occurring plant phenols, developing black solutions from which black solids precipitate. Phenols containing omicron-dihydroxy groups react with Os-KI solution more rapidly than other structurally different phenols. Therefore, omicron-dihydroxy units in an aromatic ring seem to function as primary sites of reactivity with the osmium-iodide complexes.

Anomalous contents of heavy metals in soils and vegetation of a mine area in S.W. Sardinia, Italy

Abstract: Samples of soils and vegetation from the mining area of South-West Sardinia (Italy) were analyzed for Pb, Zn, Cd, and Cu content. The area (more than 100 km2) is inhabited by many thousands of people; land utilization includes mainly grapes on some small plains and permanent sheep pasture on the hills. The levels of Pb, Zn, and Cd were found to be exceptionally high in most samples. Lead concentration was up to 71000 μg g−1 in the soils and 4000 jig g−1 in vegetation; Cd concentration was found up to 665 μg g−1 in soils and 26.5 μg g−1 in vegetation. The heavy metal content of some soil samples was highly variable. Data show that Pb is easily absorbed by plant roots and translocated to foliage. In spite of the high heavy metal level, no signs of toxicity were apparent in vegetation.

Natural Continuous Extensions of Runge-Kutta Methods for Volterra Integral Equations of the Second-Kind and Their Applications

Abstract: We consider a very general class of Runge-Kutta methods for the numerical solution of Volterra integral equations of the second kind, which includes as special cases all the more important methods which have been considered in the literature. The main purpose of this paper is to define and prove the existence of the Natural Continuous Extensions (NCE's) of Runge-Kutta methods, i.e., piecewise polynomial functions which extend the approximation at the grid points to the whole interval of integration. The particular properties required of the NCE's allow us to construct the tail approximations, which are quite efficient in terms of kernel evaluations.

Snap-back softening instability in high strength concrete beams

Abstract: Three-point bending tests on pre-cracked slabs of high-strength concrete are interpreted on the basis of a virtual crack propagation model. As theoretically shown by the model, a snap-back softening instability appears only for initial crack lengths smaller than 0.3 times the beam depth. As a limit-case, when the material is sufficiently brittle or the specimen size is sufficiently large, such an instability can be predicted by the LEFM condition K1=KIC.

Non-markovian behavior in low-temperature damping: An application of the averaging method

Abstract: We give a description of the reduced dynamics of an open quantum system whose initial state is (in general) correlated with the surroundings. The averaging method (whose mathematical theory was developed in another paper) is used to construct a series expansion of the reduced dynamics in powers of the ratio τ 1 /τ 0 of the characteristic relaxation times τ 1 and τ 0 of the surroundings and of the system respectively. To first order in τ 1 /τ 0 we obtain the well-known Markovian approximation which corresponds to the weak coupling limit. Starting from second order in τ 1 /τ 0 there appear various kinds of non-Markovian effects including initial slips which have attracted much attention in the recent literature. The relevance of these higher-order corrections stems from the fact that the characteristic time τ 1 cannot be much smaller than h kT for quantum surroundings at temperature T .

Quantum Poisson processes and dilations of dynamical semigroups

Abstract: The notion of a quantum Poisson process over a quantum measure space is introduced. This process is used to construct new quantum Markov processes on the matrix algebraM n with stationary faithful state π. If (ℳ, μ) is the quantum measure space in question (ℳ a von Neumann algebra and μ a faithful normal weight), then the semigroupe tL of transition operators on (M n , π) has generator whereu is an arbitrary unitary element of the centraliser of (M n ⊗ℳ,φ⊗μ).

Building Expert Systems: From Life Cycle to Development Methodology

Abstract: Publisher Summary This chapter describes the development methodology of building expert systems. Expert system technology is still largely relying at present on empirical methods and is not supported by the sound and general methodologies. It is therefore more like handicraft than engineering, and it lacks several of the desirable features, such as reliability, repeatability, work sharing, cost estimableness, and quality assurance of an industrial process. The transition of expert system technology from handicraft to engineering is widely recognized at present as a much-needed step aimed at overcoming some of the major bottlenecks, which currently hamper the large-scale application of expert systems in business and industry. This transition may be grounded on the concept of life cycle, which can serve as a basis for designing full development methodologies specific to each individual organization and application domain. Expert systems are developed manually and their production process should be organized and disciplined according to a very detailed methodology based on a very specific life cycle concept. However, this does not exclude the use of dedicated support tools during the execution of some steps of the methodology. The quality of the results obtained so far by research in the expert system field and the consideration of the current trends in tool development allow hypothesizing that the type of expert system production environment outlined will be superseded by a major advancement in the technology.

Chemical, Biological and Antitumor Properties of Ruthenium(II) Complexes with Dimethylsulfoxide

Abstract: Two ruthenium(II)-dimethylsulfoxide complexes, cis- and trans-RuCl2(DMSO)4 are shown to possess antitumor and, in particular, antimetastatic activity against several murine tumor models. The complexes interact both in vitro and in vivo with DNA, which seems to be their most likely target. The synthesis and chemical behavior of the two complexes are dscribed and related to their interactions with DNA and their antitumor properties. A tentative scheme of the mechanism of action of the two isomers is also reported.

An explanation for the presentation-order effect in the method of constant stimuli.

Abstract: The point of subjective equality obtained by the method of constant stimuli depends to a great extent on whether the standard (S) or the variable (V) stimulus occurs first, This presentation­ order effect was studied using lines as stimuli. Successive S,V pairs were presented, with inter­ stimulus and interpair intervals equal. Observers, who were not told which was S or V, reported whether a given line was longer or shorter than the immediately preceding line. Although the observers' subjective experience was of a train of lines that was not organized into pairs, the presentation-order effect still occurred. This implies that the effect does not depend on the order of presentation of the stimuli in an experienced pair. It was also shori that the observers could categorize line lengths, since they could identify stochastically the most frequent stimulus (S). We propose that the presentation-order effect depends on a decision process based on response probabilities inferred from length categories. In the method of constant stimuli (MCS) for the deter­ mination of the point of subjective equality (PSE), the standard (S) stimulus is paired with a variable (V) stimu­ lus. The observer's task is to report whether one of the two stimuli is greater or less than the other with respect to a given attribute. The S, usually physically equal to one ofthe Vs, is chosen so that the probability of detect­ ing a difference between the S and a V is greater than o and less than 1. The version of the MCS in which the S and the V in a pair are presented successively is known to produce a time error whose magnitude depends on a variety of fac­ tors (Guilford, 1954; Hellstrom, 1985; Woodworth & Schlosberg, 1954). One such factor is the presentation order of S and V in a pair (Fechner, 1860; Masin, 1987; Woodruff, Jennings, & Rico, 1975; see Needham, 1934, for a review of early studies). The PSE tends to be dis­ placed away from (toward) the center of the range of Vs when S appears second (first) in a pair. The effect occurs for different kinds of stimuli, including lines (Masin, 1988). However, the presentation-order effect may be indepen­ dent of the order of presentation in an experienced pair. As far as we know, in all studies on the MCS, the inter­ stimulus interval was different from the interpair inter­ val. This procedure assumes that the difference between the two intervals has no effect on the PSE. If this were true, then it should also be true that the order of presenThis researchwas supportedby a grant from the Italian Research Coun­ cil (CNR). We thank M. Teghtsoonian for helpful comments on the manuscript. Correspondence may be addressed to S. C. Masin. Insti­ tute of Philosophy. Pedagogics, and Teaching of Modem Languages, Via Antonini 8, 33100 Udine, Italy.

Artificial intelligence techniques in seismic signal interpretation

Abstract: SUMMARY We show that system architectures based on artificial intelligence (AI) techniques can be applied to the automation of seismic signal interpretation. In particular, blackboard systems appear to provide flexible and efficient ways to model the strategy a human expert adopts for the analysis. We also present the design of the Seismic Network Analyser, (SNA), a blackboard system applied to the interpretation of signals from a local seismometric network. Results, examples and performances of a prototype implementation of SNA are reported and extensively discussed.

Parameter extraction from I-V characteristics of single MOSFETs

Abstract: A method is presented to extract the bias-dependent series resistances and intrinsic conductance factor of individual MOS transistors from measured I-V characteristics. If applied to groups of scaled channel length devices, it also allows determination of the effective channel length together with the transversal field dependence of the carrier mobility. The method is exactly derived from conventional MOS theory based on the gradual channel approximation, and the deviations from such an ideal case are studied by means of two-dimensional device simulations. Experimental results obtained with n- and p-channel transistors of conventional as well as LDD type are presented to show the correctness of the proposed extraction procedure. >