Showing papers by "Sapienza University of Rome published in 1994"
TL;DR: This paper showed that as U.S. manufacturing firms grow more diverse, they maintain a constant level of coherence between neighboring activities, which runs counter to the idea that firms with many activities are generally more "incoherent".
Abstract: Multiproduct firms are perceived to be coherent in their scope, yet there is no strong theoretical foundations to explain coherence in modern industrial organization theory. This paper shows that as U.S. manufacturing firms grow more diverse, they maintain a constant level of coherence between neighboring activities. This finding runs counter to the idea that firms with many activities are generally more ‘incoherent’. A framework is then presented which appeals to the nature of enterprise learning, path dependencies, and the nature of the selection environment to explain the ubiquity of coherent diversifiers.
1,480 citations
TL;DR: In this article, the authors propose spacetime uncertainty relations motivated by Heisenberg's uncertainty principle and by Einstein's theory of classical gravity, which is described by a non-commutative algebra whose commutation relations do imply our uncertainty relations.
826 citations
TL;DR: The authors presents the basic ideas and methodologies of a set of contemporary contributions which are grouped under the general heading of "evolutionary economics" and discusses some achievements, some unresolved issues and a few promising topics of research are flagged.
Abstract: This paper presents the basic ideas and methodologies of a set of contemporary contributions which are grouped under the general heading of “evolutionary economics”. Some achievements-especially with regard to the analysis of technological change and economic dynamics-are illustrated, some unresolved issues are discussed and a few promising topics of research are flagged.
772 citations
TL;DR: Evidence is presented that saccadic suppression does occur, but that it is selective for patterns modulated in luminance at low spatial frequencies, and patterns of higher spatial frequency were not suppressed during saccades, but actually enhanced.
Abstract: VISUAL scientists have long sought to explain why the world remains stable during saccades, the ballistic eye-movements that continually displace the retinal image at fast but resolvable1 velocities. An early suggestion was that vision may be actively suppressed during saccades2, but experimental support has been variable3–5. Here we present evidence that saccadic suppression does occur, but that it is selective for patterns modulated in luminance at low spatial frequencies. Patterns of higher spatial frequency, and equiluminant patterns (modulated only in colour) at all spatial frequencies were not suppressed during saccades, but actually enhanced. The selectivity of the suppression suggests that it is confined to the colour-blind magnocellular stream (which provides the dominant input to motion centres and areas involved with attention), where it could dull the otherwise disturbing sense of fast low-spatial-frequency image motion. Masking studies suggest that the suppression precedes the site of contrast masking and may therefore occur early in visual processing, possibly as early as the lateral geniculate nucleus.
666 citations
TL;DR: It is demonstrated that sex reversal results from the presence of two active copies of an Xp locus rather than from its rearrangement and that alterations at this locus constitute one of the causes of sex reversal in individuals with a normal 46,XY karyotype.
Abstract: Male to female sex reversal has been observed in individuals with duplications of the short arm of the X chromosome. Here we demonstrate that sex reversal results from the presence of two active copies of an Xp locus rather than from its rearrangement and that alterations at this locus constitute one of the causes of sex reversal in individuals with a normal 46,XY karyotype. We have named this locus DSS (Dosage Sensitive Sex reversal) and localized it to a 160 kilobase region of chromosome Xp21, adjacent to the adrenal hypoplasia congenita locus. The identification of male individuals deleted for DSS suggests that this locus is not required for testis differentiation. We propose that DSS has a role in ovarian development and/or functions as a link between ovary and testis formation.
660 citations
TL;DR: The authors found that comprehension of sentences compared with the lexical-decision task, induced extensive activation in several regions of the left hemisphere, including the prefrontal and basal frontal cortex, the middle and inferior temporal gyri and temporal pole, the parietal cortex and the precuneus.
Abstract: We investigated cerebral activity in six normal volunteers using PET to explore the hypothesis that the right hemisphere has a specific role in the interpretation of figurative aspects of language such as metaphors. We also mapped the anatomical structures involved in sentence comprehension. During regional cerebral blood flow measurement subjects were asked to perform three different linguistic tasks: (i) metaphorical comprehension; (ii) literal comprehension of sentences; and (iii) a lexical-decision task. We found that comprehension of sentences compared with the lexical-decision task, induced extensive activation in several regions of the left hemisphere, including the prefrontal and basal frontal cortex, the middle and inferior temporal gyri and temporal pole, the parietal cortex and the precuneus. Comprehension of metaphors was associated with similar activations in the left hemisphere, but in addition, a number of sites were activated in the right hemisphere: the prefrontal cortex, the middle temporal gyrus, the precuneus and the posterior cingulate. We conclude that the interpretation of language involves widespread distributed systems bilaterally with the right hemisphere having a special role in the appreciation of metaphors.
605 citations
Purdue University1, University of Granada2, Simón Bolívar University3, University of Valencia4, University of Murcia5, Autonomous University of Madrid6, Technical University of Madrid7, University of Nottingham8, University of Basel9, University of Rouen10, University College London11, Sapienza University of Rome12, University of Cincinnati13
TL;DR: An overview of the subject of robust Bayesian analysis is provided, one that is accessible to statisticians outside the field, and recent developments in the area are reviewed.
Abstract: Robust Bayesian analysis is the study of the sensitivity of Bayesian answers to uncertain inputs. This paper seeks to provide an overview of the subject, one that is accessible to statisticians outside the field. Recent developments in the area are also reviewed, though with very uneven emphasis.
587 citations
TL;DR: It is reported here that hepatitis B virus isolates derived from two chronically infected patients display variant epitopes that act as natural TCR antagonists with the capacity to inhibit the CTL response to the wild-type epitope.
Abstract: IT has been suggested that mutations within immunodominant cytotoxic T-lymphocyte (CTL) epitopes may be exploited by viruses to evade protective immune responses critical for clearance1–4. Viral escape could originate from passive mechanisms, such as mutations within crucial CTL epitopes, either affecting major histocompatibility complex binding or T-cell antigen receptor (TCR) recognition. Additionally, it has recently been shown that substitutions of TCR contact sites can yield analogue peptides that can still interact with the T-cell receptor but be unable to deliver a full stimulatory signal, thus inducing anergy5 or acting as an antagonist for the TCR6–8. We report here that hepatitis B virus isolates derived from two chronically infected patients display variant epitopes that act as natural TCR antagonists with the capacity to inhibit the CTL response to the wild-type epitope. During natural infection, TCR antagonist mutations of CTL epitopes could contribute to the development of viral persistence, especially if the antiviral CTL response is monospecific or the epitope is strongly immunodominant.
543 citations
TL;DR: In this article, a model of electric residential end-use is proposed for establishing the load diagram of an area by a process of synthesis, following a bottom-up approach, allowing construction of the relative load shape of the area, starting from knowledge of its most relevant socioeconomic and demographic characteristics, unitary energy consumption and the load profiles of individual household appliances.
Abstract: A model of electric residential end-use is proposed for establishing the load diagram of an area by a process of synthesis. The model follows a "bottom-up" approach, allowing construction of the relative load shape of the area, starting from knowledge of its most relevant socioeconomic and demographic characteristics, unitary energy consumption and the load profiles of individual household appliances. Several probability functions have been introduced in order to cover the close relationship existing between the demand of residential customers and the psychological and behavioral factors typical of the household; the model makes frequent use of the latter through a Monte Carlo extraction process. The model has been applied for the simulation of a residential area where field measurements of power demand had been made at 15-minute intervals and a combined mail survey had been conducted to investigate household energy usage. The paper reports the results of a comparison between recorded and predicted load profiles. >
528 citations
TL;DR: In this paper, the authors describe the properties of the anode, cathode and electrolyte materials which presently seem to be the most promising for the development of these batteries, and evaluate the impact that the rockingchair concept may ultimately have on the progress of rechargeable lithium battery technology.
451 citations
TL;DR: Testi et al. as discussed by the authors showed that the broad expression of CD69 and its conserved ability to generate intracellular signals suggests a general role for the CD69 receptor in the biology of hematopoietic cells.
TL;DR: In this paper, the authors derived analytical results for the long-time relaxation of the Sherrington-Kirkpatrick model, starting from a random configuration, and showed that the system never achieves local equilibrium in any fixed sector of phase space, but remains in an asymptotic out-of-equilibrium regime.
Abstract: Starting from a set of assumptions on the long-time limit behaviour of the nonequilibrium relaxation of mean-field models in the thermodynamic limit, we derive analytical results for the long-time relaxation of the Sherrington-Kirkpatrick model, starting from a random configuration. The system never achieves local equilibrium in any fixed sector of phase space, but remains in an asymptotic out-of-equilibrium regime. We clearly state and motivate the assumptions made. For the study of the out-of-equilibrium dynamics of spin-glass models, we propose as a tool, both numerical and analytical, the use of 'triangle relations' which describe the geometry of the configurations at three (long) different times.
TL;DR: In this paper, an extension of the van der Waals equation was proposed to incorporate the effects of the network of hydrogen bonds that exist in liquid water, and the resulting model qualitatively predicts the unique thermodynamic properties of water, including those of deeply supercooled states.
Abstract: We propose an extension of the van der Waals equation which is designed to incorporate, in an approximate fashion, the effects of the network of hydrogen bonds that exist in liquid water. The resulting model qualitatively predicts the unique thermodynamic properties of water, including those of the deeply supercooled states. It also reconciles two proposals for the phase behavior of supercooled and stretched water and provides a thermodynamic origin for the observed polymorphism of the amorphous solid form of water.
TL;DR: In this paper, a metric topology on the space of Dirichlet forms is introduced and compactness and closure properties of families of local and non-local forms are studied.
TL;DR: It is shown that the temporoparietal cortex, the insula, the putamen, and the anterior cingulate cortex are the cerebral projections of the Vestibular system in man and that the spatial disorientation caused by unilateral vestibular stimulation is associated with their asymmetric activation.
Abstract: The cerebral representation of space depends on the integration of many different sensory inputs. The vestibular system provides one such input and its dysfunction can cause profound spatial disorientation. Using positron emission tomography (PET), we measured regional cerebral perfusion with various vestibular stimulations to map central vestibular projections and to investigate the cerebral basis of spatial disorientation. We showed that the temporoparietal cortex, the insula, the putamen, and the anterior cingulate cortex are the cerebral projections of the vestibular system in man and that the spatial disorientation caused by unilateral vestibular stimulation is associated with their asymmetric activation.
TL;DR: Rearrangement of the bcl-6 gene correlated with a favorable clinical outcome in DLLC and may thus serve as a prognostic marker in patients with this form of malignant lymphoma.
Abstract: Background About 40 percent of non-Hodgkin's lymphomas are diffuse lymphomas with a large-cell component (DLLC). Current therapy can induce a long-term remission in half the patients with DLLC, but more intensive treatment has the potential to improve outcome, particularly in patients at high risk for treatment failure. Clinical and cytogenetic markers can identify subgroups at high or low risk. Rearrangement of a novel candidate proto-oncogene, bcl-6, is a possible prognostic indicator in DLLC. Methods We performed Southern blot hybridization to detect bcl-6 and bcl-2 gene rearrangement in samples of lymphoma from 102 patients with B-cell DLLC. The results were correlated with the patients' histologic features, age, disease stage, tumor sites and bulk of disease, serum lactate dehydrogenase level, and treatment outcome. Results Rearranged bcl-6 was found in 23 cases, and rearranged bcl-2 in 21 cases. Nineteen of the patients with rearranged bcl-6 had extranodal DLLC, two had primary splenic lymphomas, an...
TL;DR: Dopaminergic drugs modulate the duration of the cortical silent periods in patients and in normal subjects, through mechanisms acting mainly at basal ganglia and possibly also directly at cortical level.
Abstract: The silent period after contralateral and ipsilateral transcranial magnetic brain stimulation was studied in patients with Parkinson's disease before and after dopaminergic and anticholinergic therapy; in normal subjects before and after L-dopa administration and in patients with drug-induced parkinsonism. In patients and normal subjects the silent period was also studied after peripheral nerve stimulation. The silent period after transcranial cortical stimulation was shorter in Parkinson's disease patients than in normal subjects. In patients with Parkinson's disease L-dopa prolonged the silent period after transcranial brain stimulation and after ipsilateral cortical stimulation. Biperiden prolonged the silent period after transcranial brain stimulation. In normal subjects, L-dopa produced similar but smaller changes. In the patients with drug-induced parkinsonism the silent period after transcranial magnetic stimulation was shorter than normal subjects. The peripheral silent period was similar in normal subjects and in patients and did not change after drug administration. In conclusion cortical silent period is abnormal in patients with Parkinson's disease and drug-induced parkinsonism. Dopaminergic drugs modulate the duration of the cortical silent periods in patients and in normal subjects, through mechanisms acting mainly at basal ganglia and possibly also directly at cortical level.
TL;DR: RBAT is established as a cystinuria gene, which involves the defective transepithelial transport of cystine and dibasic amino acids in the kidney and intestine and nearly abolished the amino acid transport activity induced by rBAT in Xenopus oocytes.
Abstract: Cystinuria is a classic heritable aminoaciduria that involves the defective transepithelial transport of cystine and dibasic amino acids in the kidney and intestine. Six missense mutations in the human rBAT gene, which is involved in high–affinity transport of cystine and dibasic amino acids in kidney and intestine, segregate with cystinuria. These mutations account for 30% of the cystinuria chromosomes studied. Homozygosity for the most common mutation (M467T) was detected in three cystinuric siblings. Mutation M467T nearly abolished the amino acid transport activity induced by rBAT in Xenopus oocytes. These results establish rBAT as a cystinuria gene.
TL;DR: In this article, the ΔS = 1 effective weak hamiltonian including next-to-leading order QCD and QED corrections is calculated at a scale μ of the order of a few GeV, the Wilson coefficients of the operators are given in terms of the renormalization group evolution matrix and of the coefficients computed at a large scale ∼ MW.
TL;DR: In this paper, a simple propagation law is found for light beams of various orders and their field distribution across the waist plane is similar to that produced by an ordinary gaussian beam except that the central region is flattened.
University of Barcelona1, Free University of Berlin2, Charles University in Prague3, Istituto Giannina Gaslini4, University of Turin5, University of Montpellier6, University of Copenhagen7, Boston Children's Hospital8, Sapienza University of Rome9, Trinity College, Dublin10, Semmelweis University11, Children's Hospital Oakland12, University of Helsinki13, Karolinska Institutet14, Uppsala University15
TL;DR: Haplotype data demonstrate that ΔF508 occurred more than 52,000 years ago, in a population genetically distinct from any present European group, and spread throughout Europe in chronologically distinct expansions, which are responsible for the different frequencies of ΔF50 in Europe.
Abstract: delta F508 is the most frequent cystic fibrosis (CF) mutation and accounts for approximately 70% of CF chromosomes worldwide. Three highly polymorphic microsatellite markers have been used to study the origin and evolution of delta F508 chromosomes in Europe. Haplotype data demonstrate that delta F508 occurred more than 52,000 years ago, in a population genetically distinct from any present European group, and spread throughout Europe in chronologically distinct expansions, which are responsible for the different frequencies of delta F508 in Europe.
TL;DR: Toward a Practice of Autonomous Systems --Proc.
Abstract: Toward a Practice of Autonomous Systems --Proc. of the First European Conference on Artificial Life, edited by F. Varela and P. Bourgine, The MIT Press, 1992, ISBN 0 262 72019 1, 515 pp.
Book•
01 Apr 1994TL;DR: 1. Mathematical Preliminaries, Elements of Computability Theory, and Space-Complexity Classes: Algorithms and Complexity Classes.
Abstract: 1. Mathematical Preliminaries. 2. Elements of Computability Theory. 4. The Class P. 5. The Glass NP. 6. The Complexity of Optiimzation Problems. 7. Beyond NP. 8. Space-Complexity Classes. 9. Probabiillistic. 10. Algorithms and Complexity Classes. 11. Interactivite Proof. 12. Systems. 13. Models of Parallel Computer. 14. Parallel Algorithms.
TL;DR: It is shown that a network with synapses that have two stable states can dynamically learn with optimal storage efficiency, be a palimpsest, and maintain its (associative) memory for an indefinitely long time provided the coding level is low and depression is equilibrated against potentiation.
Abstract: We discuss the long term maintenance of acquired memory in synaptic connections of a perpetually learning electronic device. This is affected by ascribing each synapse a finite number of stable states in which it can maintain for indefinitely long periods. Learning uncorrelated stimuli is expressed as a stochastic process produced by the neural activities on the synapses. In several interesting cases the stochastic process can be analyzed in detail, leading to a clarification of the performance of the network, as an associative memory, during the process of uninterrupted learning. The stochastic nature of the process and the existence of an asymptotic distribution for the synaptic values in the network imply generically that the memory is a palimpsest but capacity is as low as log N for a network of N neurons. The only way we find for avoiding this tight constraint is to allow the parameters governing the learning process (the coding level of the stimuli; the transition probabilities for potentiation and depression and the number of stable synaptic levels) to depend on the number of neurons. It is shown that a network with synapses that have two stable states can dynamically learn with optimal storage efficiency, be a palimpsest, and maintain its (associative) memory for an indefinitely long time provided the coding level is low and depression is equilibrated against potentiation. We suggest that an option so easily implementable in material devices would not have been overlooked by biology. Finally we discuss the stochastic learning on synapses with variable number of stable synaptic states.
TL;DR: It is shown that a linear Fabry-P\'erot cavity with an oscillating end mirror can be used for quantum noise reduction and the output quantum fluctuations of the monochromatic light beam can be significantly squeezed at a frequency very close to that of the impinging light.
Abstract: We show that a linear Fabry-P\'erot cavity with an oscillating end mirror can be used for quantum noise reduction. For a high-quality factor of the mechanical oscillator the output quantum fluctuations of the monochromatic light beam can be significantly squeezed at a frequency very close to that of the impinging light. The analysis is performed by taking into account the coupling of the system with the external world.
TL;DR: In this paper, it is shown that the theory of complete analyticity and its dynamical counterpart due to Stroock and Zegarlinski cannot be applied, in general, to the whole one phase region since it requires mixing properties for regions of arbitrary shape.
Abstract: Various finite volume mixing conditions in classical statistical mechanics are reviewed and critically analyzed. In particular somefinite size conditions are discussed, together with their implications for the Gibbs measures and for the approach to equilibrium of Glauber dynamics inarbitrarily large volumes. It is shown that Dobrushin-Shlosman's theory ofcomplete analyticity and its dynamical counterpart due to Stroock and Zegarlinski, cannot be applied, in general, to the whole one phase region since it requires mixing properties for regions ofarbitrary shape. An alternative approach, based on previous ideas of Oliveri, and Picco, is developed, which allows to establish results on rapid approach to equilibrium deeply inside the one phase region. In particular, in the ferromagnetic case, we considerably improve some previous results by Holley and Aizenman and Holley. Our results are optimal in the sene that, for example, they show for the first time fast convergence of the dynamicsfor any temperature above the critical one for thed-dimensional Ising model with or without an external field. In part II we extensively consider the general case (not necessarily attractive) and we develop a new method, based on renormalizations group ideas and on an assumption of strong mixing in a finite cube, to prove hypercontractivity of the Markov semigroup of the Glauber dynamics.
01 Jan 1994
TL;DR: Ohanian and Ruffini's Gravitation and Spacetime, Second Edition, the authors is the best book on the market today of 500 pages or less on gravitation and general relativity.
Abstract: Now more than ever, Gravitation and Spacetime, Second Edition, by Hans C. Ohanian and new coauthor Remo Ruffini, deserves John Wheeler's praise as "the best book on the market today of 500 pages or less on gravitation and general relativity." Gravitation and Spacetime has been thoroughly updated with the most exciting finds and hottest theoretical topics in general relativity and cosmology. Highlights of the revision include the rise and fall of the fifth force, principles and applications of gravitational lensing, COBE's spectacular confirmation of the blackbody spectrum of the cosmic thermal radiation, theories of dark matter and inflation, and the early universe as a testing ground for particle physicists' unification theories, and much, much more. The ideal choice for a graduate-level introduction to general relativity, Gravitation and Spacetime is also suitable for an advanced undergaduate course.
TL;DR: In this paper, the electrochemical properties of gel electrolytes formed by the immobilization in a poly(acrylonitrile) matrix of solutions of common lithium salts (eg LiClO4, LiAsF6 and LiN(CF3SO2)2) in organic solvents (eg the propylene carbonate) were determined.
TL;DR: The relative contribution of potential mechanisms in leading to infection in patients with diabetes, including genetic susceptibility to infection; altered cellular and humoral immune defence mechanisms; local factors including poor blood supply and nerve damage, and alterations in metabolism associated with diabetes are assessed.
Abstract: Infections remain a serious hazard for the diabetic patient. Good metabolic control is a major factor in limiting the development and spread of infections and, most importantly, the development of diabetic complications which predispose to infections. In some patients recurrent infections can pose a problem, particularly if there is evidence of secondary immunodeficiency. In these patients adjuvant therapies, including Biological Response Modifiers (BRMS) should be considered. Several factors could predispose diabetic patients to infections. These factors include: genetic susceptibility to infection; altered cellular and humoral immune defence mechanisms; local factors including poor blood supply and nerve damage, and alterations in metabolism associated with diabetes. In the context of a diabetic patient all or some of these factors may operate. The purpose of this review is to assess the relative contribution of these potential mechanisms in leading to infection in patients with diabetes.
TL;DR: Ten new peptides, ranging in size from 24 to 46 residues, all possessing an intramolecular disulfide bridge located at the carboxyl-terminal end, were isolated from skin secretions of R. esculenta and it is demonstrated that esculentin-1 also inhibits the growth of Pseudomonas aeruginosa, Candida albicans, and Saccharomyces cerevisiae.