Showing papers by "Sapienza University of Rome published in 1988"

Algorithms for drawing graphs: an annotated bibliography

Abstract: Several data presentation problems involve drawing graphs so that they are easy to read and understand. Examples include circuit schematics and diagrams for information systems analysis and design. In this paper we present a bibliographic survey on algorithms whose goal is to produce aesthetically pleasing drawings of graphs. Research on this topic is spread over the broad spectrum of computer science. This bibliography constitutes a first attempt to encompass both theoretical and application-oriented papers from disparate areas.

Innovation, Diversity and Diffusion: A Self-Organisation Model

Abstract: A number of features of innovation diffusion are identified: appropriability, diversity, expectations, selection, learning, and spillover externalities. A dynamic model is formul ated to embed the diffusion question into a more general framework of disequilibrium competition. The model incorporates distinct vintage structures reflecting a change in technological trajectory, learning-by-using, a nd expectations-driven investment rules of thumb. Simulation studies reveal robust quasi-logistic curves, but a complicated pattern of net market share gains and losses. Uncertainty regarding the rationality of early or late adoption, it is argued, ensures that the requisite behavioral variety is present to generate these diffusion patterns. Copyright 1988 by Royal Economic Society.

Application of the Green's functions method to the study of the optical properties of semiconductors

Abstract: 75 APPENDIX E. 77 APPENDIX F. 79 APPENDIX G. 82 APPENDIX H. Introduction. Generalized Green's functions. Equations of motion for the generalized single-particle Green's function. Bethe-Salpeter equation for the two-particle Green's function. Connection with linear-response theory. Conserving approximations. Gauge invariance, current conservation, and the Ward identities. Optical properties of semiconductors. Single-particle energy levels. Screening of static impurities. Excitonic states. A functional derivative identity. Dyson's equation. Reducible vs. irreducible parts of the correlation functions. Elimination of the spin variables and transformation to the energy-momentum representation. The Thomas-Reiche-Kuhn sum rule. The Clausius-Mossotti relation. The particle-hole Green's function. The Haken potential.

Knot theory and quantum gravity.

Abstract: A new representation for quantum general relativity is described, which is defined in terms of functionals of sets of loops in three-space. In this representation exact solutions of the quantum constraints may be obtained. This result is related to the simplification of the constraints in Ashtekar's new formalism. We give in closed form the general solution of the diffeomorphism constraints and a large class of solutions of the full set of constraints. These are classified by the knot and link classes of the spatial three-manifold.

Moduli Spaces of Curves and Representation Theory

Abstract: We establish a canonical isomorphism between the second coho- mology of the Lie algebra of regular differential operators on (Cx of degree ^ 1, and the second singular cohomology of the moduli space &g-γ of quintuples (C, p, z, L, (_φ~\\ where C is a smooth genus g Riemann surface, p a point on C, z a local parameter at /?, L a degree g— 1 line bundle on C, and (φ) a class of local trivializations of L at p which differ by a non-zero factor. The construction uses an interplay between various infinite-dimensional manifolds based on the topological space H of germs of holomorphic functions in a neighborhood of 0 in (C x and related topological spaces. The basic tool is a canonical map from #0_! to the infinite-dimensional Grassmannian of subspaces off/, which is the orbit of the subspace H_ of holomorphic functions on (Cx vanishing at oo, under the group AutH. As an application, we give a Lie-algebraic proof of the Mumford formula: λn = (6n2 — 6n + ί)λu where λn is the determinant line bundle of the vector bundle on the moduli space of curves of genus g, whose fiber over C is the space of differentials of degree n on C.

Parental smoking enhances bronchial responsiveness in nine-year-old children.

Abstract: We studied the relationship between parental smoking habits and atopy and bronchial responsiveness (BR) in 9-year-old, non-selected schoolchildren. A questionnaire on respiratory disease and maternal and paternal smoking habits was administered to one parent. Skin prick tests using the most common allergens present in central Italy, a flow-volume spirometric test, and a bronchial provocation test using carbachol in increasing doses were performed. Male children with smoking parents had significantly increased BR when compared to those whose parents did not smoke (Odds Ratio (OR) = 4.3, p = 0.009). No such significant increase in BR was found in female children of smoking parents (OR = 1.5, p = 0.4). The relationship between BR in children and smoking in parents was stronger in asthmatics (p = 0.02), but was still significant after controlling for asthma and atopy. Bronchial responsiveness was significantly correlated with atopy (p = 0.001). This was also true for nonasthmatic children and for both males a...

Interaction between vision and language in category-specific semantic impairment

Abstract: A category-specific semantic disorder, selectively affecting Living things and food and sparing inanimate objects, was observed in a patient (LA) who had made a partial recovery from herpes simplex encephalitis. This impairment was observed to have similar characteristics both with verbal and pictorial material, and a significant degree of consistency was observed between repeated presentations and across various modalities of administration of the same stimuli. In order to study the possible role of interactions between verbal-semantic and visual-semantic impairment, we constructed a test of “naming animals by definitions”, in which two sorts of definitions were contrasted: (1) those stressing visual perceptual features; and (2) those using verbal metaphorical expressions, or a description of the function accomplished by that animal for man, to allow identification. LA performed much better in the second than in the first condition. On the grounds of these results, the following hypotheses were ...

Spectral Transform and Solitons: How to Solve and Investigate Nonlinear Evolution Equations

Abstract: The soliton was discovered (and named) in 1965 by Zabusky and Kruskal,(1) who were experimenting with the numerical solution by computer of the Korteweg-de Vries (KdV) equation. This nonlinear partial differential equation had been introduced at the end of the last century to describe wave motion in shallow canals.(2) Zabusky and Kruskal studied the equation because of its relevance to plasma physics, as well as to the Fermi-Pasta-Ulam puzzle(3) (for a fascinating account of the motivations that led to the “birth of the soliton,” see Kruskal.(4)) The first scientific description of the soliton as a natural phenomenon, however, goes back to the first half of the nineteenth century, and was reported by J. Scott-Russell in the following prose:(5) I was observing the motion of a boat which was rapidly drawn along a narrow channel by a pair of horses, when the boat suddenly stopped—not so the mass of water in the channel which it had put in motion; it accumulated round the prow of the vessel in a state of violent agitation, then suddenly leaving it behind, rolled forward with great velocity, assuming the form of a large solitary elevation, a rounded, smooth and well defined heap of water, which continued its course along the channel apparently without change of form or diminution of speed. I followed it on horseback, and overtook it still rolling on at a rate of some eight or nine miles an hour, preserving its original figure some thirty feet long and a foot to a foot and a half in height. Its height gradually diminished, and after a chase of one or two miles I lost it in the windings of the channel. Such, in the month of August 1834, was my first chance interview with that singular and beautiful phenomenon....

Immunofluorescent staining of kinetochores in micronuclei: a new assay for the detection of aneuploidy

Abstract: The immunofluorescent staining of kinetochores in micronuclei with antikinetochore antibodies was used to develop an in vitro assay for aneuploidy-inducing agents. The results show that about 80% of micronuclei induced by either colchicine or chloral hydrate contained kinetochores; only 9% of X-ray-induced micronuclei reacted positively to the antibody. These findings indicate that the in vitro micronucleus assay coupled with immunofluorescent staining of kinetochores can be a useful method for assessing the ability of chemicals to induce aneuploidy and/or chromosome aberrations.

On a non linear partial differential equation having natural growth terms and unbounded solution

Abstract: We prove the existence of a solution of the nonlinear elliptic equation: A(u) + g(x, u, Du) = h(x), where A is a Leray-Lions operator from W 0 1 , p ( Ω ) into W−1, p′(Ω) and g is a nonlinear term with “natural” growth with respect to Du [i.e. such that |g(x, u, ξ)| ≦ b(|u|) (|ξ|p + c(x))], satisfying the sign condition g(x, u, ξ)u ≧ 0 but no growth condition with respect to u. Here h belongs to W−1, p′(Ω), thus the solution u of the problem does not in general be more smooth than W 0 1 , p ( Ω ) . The existence of a solution is also proved for the corresponding obstacle problem.

The clinical significance of serum C reactive protein levels in Crohn's disease. Results of a prospective longitudinal study.

Abstract: We measured the serum C reactive protein (CRP) levels by a sensitive immunochemistry method in 101 outpatients with Crohn's disease enrolled in a prospective longitudinal study. At entry, 51 of the 101 patients had raised CRP levels, which showed good correlation with the clinical score. However, one-third of the patients with clinically active disease had normal CRP while one-third of the patients in clinical remission had a raised CRP. The longitudinal study showed that (a) in patients with active disease, CRP levels tended to decrease as the disease went into remission; (b) in patients who achieved remission, the likelihood of clinical relapse after 2 years of entry was higher in those with persistently raised CRP than in those with persistently normal CRP; and (c) in patients with quiescent disease at entry who remained in remission throughout the first year of the study, the likelihood of clinical relapse during the second year of the study was higher for those with persistently raised CRP than for the others. This study confirms that serum CRP is a useful laboratory index for supplementing clinical scores in patients with Crohn's disease, in monitoring the response to treatment, in helping to predict the course of the disease, and in contributing to defining subgroups of patients.

Competitive inhibition of the auxin‐induced elongation by α‐D‐oligogalacturonides in pea stem segments

Abstract: Branca, C, De Lorenzo, G. and Cervone, F. 1988. Competitive inhibition of the auxin-induced elongation by α-D-oligogalacturonides in pea stem segments. - Physiol. Plant. 72: 499–504. α-D-galacturonide oligomers (OG) were prepared by partial hydrolysis of sodium polypectate with an homogeneous Aspergillus niger endopolygalacturonase (EC 3.2.1.15). OG, obtained after digestion for 10, 20, 30, 60, 120 min and 24 h, were assayed for their ability to interfere with the IAA-induced elongation of pea (Pisum sativum L. cv. Alaska) stems. Maximum inhibiting activity was exhibited by oligomers with an approximate degree of polymerization higher than 8. Inhibition by longer OG was much lower, and the products of the 24 h digestion and the unhydrolysed polypectate were ineffective. The addition of OG to pea stems caused a parallel shift to the right of the IAA dose-effect curve. The shift depended on the amount of OG used, showing that oligogalacturonides behave as competitive antagonists of IAA. The presence of OG caused the disappearance of the second maximum of the elongation rate and reduced the first maximum. OG were also tested for their ability to inhibit IAA-induced ethylene evolution of pea stem segments. Maximal inhibition was obtained with OG of the same size as those that interfered with IAA-induced elongation. Inhibition of the auxin action seemed to be specific as OG did not interfere with the activity of gibberellic acid (GA3) or kinetin. It was concluded that oligogalacturonides strongly interfere with the activity of IAA, although they are by themselves incapable to influence the elongation of pea stem segments directly.

Parton Densities from Deep Inelastic Scattering to Hadronic Processes at Super Collider Energies

Abstract: We give several sets of parton densities derived from recent measurements of structure functions in deep inelastic scattering. The difference among these densities reflects the uncertainties from deep inelastic data of different experiments, allowing an estimate of the error band for the predictions one may obtain for any given hadronic process at higher energy. The densities are available at any scaleQ2≦5.109 GeV2 andx≧5.10−5 and include next-to-leading corrections as well as threshold effects due to heavy flavours. A comparison with a large set of data in a wide range of scales (Drell-Yan,W andZ production, etc.) is also presented.

On the nonlinear equivalent of the notion of transmission zeros

Abstract: The purpose of this paper is to show that three possible characterizations of the notion of "transmission zero", namely "pole" of the inverse system, zero-output-constrained dynamics and unobservable dynamics under certain state-feedback, which are equivalent for any invertible linear system, may have different analogues for nonlinear input-affine systems. It is also shown that some nonlinear versions of the so-called structure algorithm, proposed by Hirschorn and Singh, may be successfully used in this framework.

Symmetry of the 3d9 ligand hole induced by doping in YBa2Cu

Abstract: Polarized Cu L/sub 3/-edge x-ray absorption spectra of a single crystal of YBa/sub 2/Cu/sub 3/O/sub 6.8/ have been measured to determine the symmetry of the orbital of the electronic holes induced by doping. The states induced by doping in YBa/sub 2/Cu/sub 3/O/sub 7-//sub delta/ (0

Morphogenesis and Auxin Sensitivity of Transgenic Tobacco with Different Complements of Ri T-DNA.

Abstract: Leaf explants of hairy root tobacco (Nicotiana tabacum) regenerants characteristically differentiate roots from the wound margins on hormonefree medium. The same response can be elicited on normal tobacco by culturing the explants in the presence of auxin. We show here that the spontaneous rooting of transformed plants is neither due to the activity of right T-DNA-borne auxin genes nor to a substantially altered balance of endogenous hormones. Rather, an increased sensitivity to auxin is conferred to transformed cells by the left T-DNA (TL-DNA). Analysis of the morphogenetic behavior of transgenic tobacco plants obtained by transferring segments of TL-DNA cloned in a binary vector system allowed us to pinpoint TL-DNA genes responsible for this increased auxin sensitivity of hairy root tissues. Three genes (open reading frames 10, 11, 12) are responsible for the spontaneous rooting of leaf explants and confer to transgenic plants an exaggerated response to auxin.

Admittance matrix formulation of waveguide discontinuity problems: computer-aided design of branch guide directional couplers

Abstract: A computational scheme is proposed that can be applied to the analysis of cascaded waveguide discontinuities of alternating boundary-enlargement and boundary-reduction type. Based on the mode-matching technique, the proposed procedure makes use of the admittance matrix characterization of waveguide stubs. With respect to the conventional S-matrix formulation, it leads to a notable reduction of the computational effort, particularly for lossless structures. At the same time, the criterion for avoiding relative convergence problems can be satisfied. The procedure has been used to set up a very accurate and efficiency computer-aided design tool of branch guide couplers (BGCs). These are key elements of beam-forming networks for multicontoured beam satellite antennas and have to be designed with very high accuracy so as to eliminate the necessity for tuning the components realized. Design accuracies better than 0.1 dB in Ka-band are demonstrated by experimental results. >

Changing prognosis of primary intracerebral hemorrhage: results of a clinical and computed tomographic follow-up study of 104 patients.

Abstract: One hundred four consecutive cases of primary intracerebral hemorrhage hospitalized at the time of stroke were followed until death or for 1 year. All were treated nonsurgically. The 30-day mortality rate was 30%. Good clinical outcome and complete resolution of the lesion on computed tomography were observed in 49 and 13% of patients, respectively. Age, state of consciousness, and size of the hemorrhage on computed tomography scan were reliable prognostic indicators. The long-term survival rate, 66%, was higher than that previously reported and should be considered in future trials evaluating medical and surgical treatment of intracerebral hemorrhage.

Alkaline phosphatase positive precursors of adipocytes in the human bone marrow.

Abstract: Developing fat cells in the bone marrow of leukaemic patients treated with chemotherapy were found to be endowed with membrane-bound alkaline phosphatase. Since alkaline phosphatase is a cytochemical marker of 'reticular' cells, this observation provides cytochemical evidence that reticular cells may convert to adipocytes when marrow cellularity abruptly decreases.

Alkaline phosphatase is a marker for myoid cells in cultures of rat peritubular and tubular tissue.

Abstract: We have studied the distribution of histochemically detectable alkaline phosphatase in cultures of seminiferous tubule fragments and of peritubular cells from prepubertal rats. The same material also was immunohistochemically evaluated for the presence of desmin-containing intermediate filaments. The comparative analysis of alkaline phosphatase and desmin positivity shows that alkaline phosphatase histochemistry selectively detects desmin-containing contractile cells in tubular and peritubular cell cultures. We propose alkaline phosphatase as a novel marker for myoid cells that can be of help in screening, defining, and eventually standardizing the exact composition of peritubular cell cultures, a model that is of increasing interest in the study of cellular interactions in the testis.