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Showing papers by "Sapienza University of Rome published in 1995"


Journal ArticleDOI
23 Jun 1995-Science
TL;DR: A gene, ATM, that is mutated in the autosomal recessive disorder ataxia telangiectasia was identified by positional cloning on chromosome 11q22-23 and encoded a putative protein that is similar to several yeast and mammalian phosphatidylinositol-3' kinases that are involved in mitogenic signal transduction, meiotic recombination, and cell cycle control.
Abstract: A gene, ATM, that is mutated in the autosomal recessive disorder ataxia telangiectasia (AT) was identified by positional cloning on chromosome 11q22-23. AT is characterized by cerebellar degeneration, immunodeficiency, chromosomal instability, cancer predisposition, radiation sensitivity, and cell cycle abnormalities. The disease is genetically heterogeneous, with four complementation groups that have been suspected to represent different genes. ATM, which has a transcript of 12 kilobases, was found to be mutated in AT patients from all complementation groups, indicating that it is probably the sole gene responsible for this disorder. A partial ATM complementary DNA clone of 5.9 kilobases encoded a putative protein that is similar to several yeast and mammalian phosphatidylinositol-3' kinases that are involved in mitogenic signal transduction, meiotic recombination, and cell cycle control. The discovery of ATM should enhance understanding of AT and related syndromes and may allow the identification of AT heterozygotes, who are at increased risk of cancer.

2,729 citations


Journal ArticleDOI
TL;DR: This presents the first test of the Ruelle principle on a many particle system far from equilibrium, and a specific prediction, obtained without the need to construct explicitly the SRB itself, is shown to be in agreement with a recent computer experiment on a strongly sheared fluid.
Abstract: Ruelle`s principle for turbulence leading to what is usually called the Sinai-Ruelle-Bowen (SRB) distribution is applied to the statistical mechanics of many particle systems in nonequilibrium stationary states. A specific prediction, obtained without the need to construct explicitly the SRB itself, is shown to be in agreement with a recent computer experiment on a strongly sheared fluid. This presents the first test of the principle on a many particle system far from equilibrium. A possible application to fluid mechanics is also discussed.

1,587 citations


Journal ArticleDOI
TL;DR: This paper deals with methodological problems related to the reconstruction of the position and orientation of the human pelvis and the lower limb bones in space during the execution of locomotion and physical exercises using a stereophotogrammetric system.

1,513 citations


Journal ArticleDOI
TL;DR: In this article, uncertainty relations for the different coordinates of spacetime events are proposed, motivated by Heisenberg's principle and by Einstein's theory of classical gravity, and a model of Quantum Spacetime is discussed where the commutation relations exactly implement our uncertainty relations.
Abstract: We propose uncertainty relations for the different coordinates of spacetime events, motivated by Heisenberg's principle and by Einstein's theory of classical gravity. A model of Quantum Spacetime is then discussed where the commutation relations exactly implement our uncertainty relations.

1,453 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed an iterative method to unfold experimental distributions in order to get the best estimates of the true ones, where the weak point of the Bayes approach, namely the need of the knowledge of the initial distribution, can be overcome by an iteration procedure.
Abstract: Bayes' theorem offers a natural way to unfold experimental distributions in order to get the best estimates of the true ones. The weak point of the Bayes approach, namely the need of the knowledge of the initial distribution, can be overcome by an iterative procedure. Since the method proposed here does not make use of continuous variables, but simply of cells in the spaces of the true and of the measured quantities, it can be applied in multidimensional problems.

1,102 citations


Journal ArticleDOI
TL;DR: In this paper, a chaotic hypothesis for reversible dissipative many-particle systems in nonequilibrium stationary states in general is proposed, which leads to the identification of a unique distribution μ describing the asymptotic properties of the system for initial data randomly chosen with respect to a uniform distribution on phase space.
Abstract: We propose, as a generalization of an idea of Ruelle's to describe turbulent fluid flow, a chaotic hypothesis for reversible dissipative many-particle systems in nonequilibrium stationary states in general. This implies an extension of the zeroth law of thermodynamics to nonequilibrium states and it leads to the identification of a unique distribution μ describing the asymptotic properties of the time evolution of the system for initial data randomly chosen with respect to a uniform distribution on phase space. For conservative systems in thermal equilibrium the chaotic hypothesis implies the ergodic hypothesis. We outline a procedure to obtain the distribution μ: it leads to a new unifying point of view for the phase space behavior of dissipative and conservative systems. The chaotic hypothesis is confirmed in a nontrivial, parameter-free, way by a recent computer experiment on the entropy production fluctuations in a shearing fluid far from equilibrium. Similar applications to other models are proposed, in particular to a model for the Kolmogorov-Obuchov theory for turbulent flow.

910 citations


Posted Content
TL;DR: In this paper, the role of capital in financial institutions is discussed and some possible unintended consequences of capital requirements are examined. But the authors focus on the problem of measuring the Modigliani-Miller (MM) risk exposure, which is difficult to measure and its measured value may be subject to manipulation by gains trading.
Abstract: This paper examines the role of capital in financial institutions. As the introductory article to a conference on the role of capital management in banking and insurance, it describes the authors' views of why capital is important, how market-generated capital requirements' differ from regulatory requirements and the form that regulatory requirements should take. It also examines the historical trends in bank capital, problems in measuring capital and some possible unintended consequences of capital requirements. According to the authors, the point of departure for all modern research on capital structure is the Modigliani-Miller (MM it is difficult to measure, and its measured value may be subject to manipulation by gains trading . The risk exposure in the denominator is also difficult to measure, corresponds only weakly to actual risk and may be subject to significant manipulation. These imprecisions worsen the social tradeoff between the externalities from bank failures and the quantity of bank intermediation. To keep bank risk to a tolerable level, capital standards must be higher on average than they otherwise would be if the capital ratios could be set more precisely, raising bank costs and reducing the amount of intermediation in the economy in the long run. Since actual capital standards are, at best, an approximation to the ideal, the authors argue that it should not be surprising that they may have had some unintended effects. They examine two unintended effects on bank portfolio risk or credit allocative inefficiencies. These two are the explosive growth of securitization and the so-called credit crunch by U.S. banks in the early 1990s. The authors show that capital requirements may give incentives for some banks to increase their risks of failure. Inaccuracies in setting capital requirements distort relative prices and may create allocative inefficiencies that divert financial resources from their most productive uses. During the 1980s, capital requirements may have created artificial incentives for banks to take off-balance sheet risk, and changes in capital requirements in the 1990s may have contributed to a credit crunch.

824 citations


Journal ArticleDOI
TL;DR: In this article, the authors examine the role of capital in financial institutions, why it is important, how market-generated capital "requiremenents" differ from regulatory requirments and the form that regulatory requirements should take.
Abstract: This introductory article examines the role of capital in financial institutions — why it is important, how market-generated capital ‘requiremenents’ differ from regulatory requirments and the form that regulatory requirements should take. Along the way, we examine historical trends in bank capital, problems in measuring capital, and some possible unintended consequences of capital requirements. Within this framework, we evaluate how the contributions to this special issue advance the literature and suggest topics for future research.

766 citations


Journal ArticleDOI
01 Feb 1995-Nature

561 citations


Journal ArticleDOI
TL;DR: In this paper, a non-perturbative method for computing the renormalization constants of generic composite operators is proposed, which is intended to reduce some systematic errors, which are present when one tries to obtain physical predictions from the matrix elements of lattice operators.

539 citations


Journal ArticleDOI
TL;DR: It is described how mice lacking C/EBP beta develop a pathology similar to mice overexpressing IL‐6 and nearly identical to multicentric Castleman's disease in human patients, with marked splenomegaly, peripheral lymphadenopathy and enhanced haemopoiesis.
Abstract: C/EBP beta is considered a key element of interleukin-6 (IL-6) signalling as well as an important transcriptional regulator of the IL-6 gene itself. We describe here how mice lacking C/EBP beta develop a pathology similar to mice overexpressing IL-6 and nearly identical to multicentric Castleman's disease in human patients, with marked splenomegaly, peripheral lymphadenopathy and enhanced haemopoiesis. Humoral, innate and cellular immunity are also profoundly distorted, as shown by the defective activation of splenic macrophages, the strong impairement of IL-12 production, the increased susceptibility to Candida albicans infection and the altered T-helper function. Our data show that C/EBP beta is crucial for the correct functional regulation and homeostatic control of haemopoietic and lymphoid compartments.

Journal ArticleDOI
TL;DR: The structure determination of glutamate dehydrogenase from P. furiosus contains a striking series of ion-pair networks on the surface of the protein subunits and buried at both interdomain and intersubunit interfaces, which suggest that the formation of such extended networks may represent a major stabilizing feature associated with the adaptation of enzymes to extreme temperatures.

Journal ArticleDOI
TL;DR: In this paper, the transport and electrochemical properties of gel-type ionic conducting membranes formed by immobilizing liquid solutions of lithium salts in a poly(methylmethacrylate) matrix have been determined.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the prescription of the asymptotic behavior for such connections is controlled by the geometry of a suitable modification of C ~ in which the union of the polar hyperplanes is replaced by a divisor with normal crossings.
Abstract: The motivation stems from our attempt to understand Drinfeld's construction (el. [Dr2]) of special solutions of the Khniznik-Zamolodchikov equation (of. [K-Z]) with some prescribed asymptotic behavior and its consequences for some universal constructions associated to braiding: universal unipotent monodromy representations of braid groups, the construction of a universal Vassiliev invariant for knots, braided categories etc. The K-Z connection is a special flat meromorphic connection on C ~ with simple poles on a family of hyperplanes. It turns out that the prescription of the asymptotic behavior for such connections is controlled by the geometry of a suitable modification of C ~ in which the union of the polar hyperplanes is replaced by a divisor with normal crossings. In the process of developing this geometry we realized that our constructions could be developed more generally for subspace arrangements and became aware of the paper of Fulton-MaePherson [F-M] in which a Hironaka model is described for the complement of the big diagonal in the power of a smooth variety X. It became clear to us that our techniques were quite similar to theirs and so we adopted their notation of nested set in the appropriate general form. Although we work in a linear subspaces setting it is clear that the methods are essentially local and one can recover their results from our analysis applied to certain special configurations of subspaces. In fact the theory can be applied whenever we have a subvariety of a smooth variety which locally (in the gtale topology) appears as a union of subspaces.

Journal ArticleDOI
TL;DR: It is proposed that the superior parietal lobule (Brodmann area 5) might represent a substrate for a body-centered positional code and could be a neural correlate of the psychophysical observation that these spatial parameters are processed in parallel and largely independent of each other in man.
Abstract: How is spatial information for limb movement encoded in the brain? Computational and psychophysical studies suggest that beginning hand position, via-points, and target are specified relative to the body to afford a comparison between the sensory (e.g., kinesthetic) reafferences and the commands that generate limb movement. Here we propose that the superior parietal lobule (Brodmann area 5) might represent a substrate for a body-centered positional code. Monkeys made arm movements in different parts of 3D space in a reaction-time task. We found that the activity of area 5 neurons can be related to either the starting point, or the final point, or combinations of the two. Neural activity is monotonically tuned in a body-centered frame of reference, whose coordinates define the azimuth, elevation, and distance of the hand. Each spatial coordinate tends to be encoded in a different subpopulation of neurons. This parcellation could be a neural correlate of the psychophysical observation that these spatial parameters are processed in parallel and largely independent of each other in man.

Journal ArticleDOI
TL;DR: Within the infinite-U Hubbard-Holstein model in the slave-boson large-N technique it is found that the dynamic scattering amplitude is strongly singular at zero momentum transfer close to the phase separation instability and it has the same form provided by gauge-field theories.
Abstract: We analyze the dynamic scattering amplitude between quasiparticles at the Fermi surface in the proximity of a charge instability, which may occur in the high temperature superconductors. Within the infinite-$U$ Hubbard-Holstein model we find that in the absence of long-range Coulomb forces the scattering amplitude is strongly singular at zero momentum transfer close to the phase separation instability. In the presence of long-range Coulomb forces the singularity occurs at finite wave vectors. In both cases we show how normal state properties are largely affected by this scattering.

Journal ArticleDOI
TL;DR: By injecting sperm into the cytoplasm of an oocyte, it is now possible to achieve fertilization and pregnancy in cases of obstructive azoospermia or severe oligozoospermia and asthenospermies after obtaining sperm directly from the epididymis or testis.
Abstract: To the Editor: By injecting sperm into the cytoplasm of an oocyte1 it is now possible to achieve fertilization and pregnancy in cases of obstructive azoospermia or severe oligozoospermia and asthen...

Journal ArticleDOI
TL;DR: In this paper, the authors report some preliminary results on evolutionary modeling of the links between the microeconomics of innovation, the patterns of industrial change and some observable invariances in industrial structures.
Abstract: Industrial economics is a rich source of ‘puzzles’ for economic theory. One of them — certainly the most discussed — regards the co-existence of firms (and plants) of different sizes, displaying rather invariant skewed distributions. Other ‘puzzles’, however, concern the sectoral specificities in industrial structures, the persistence of asymmetric corporate performances and the dynamics of entry and exit. The paper reports some preliminary results on evolutionary modeling of the links between the microeconomics of innovation, the patterns of industrial change and some observable invariances in industrial structures.

Journal ArticleDOI
TL;DR: The distribution of 11 different transposable elements on Drosophila melanogaster mitotic chromosomes is determined by using high-resolution fluorescent in situ hybridization (FISH) coupled with charge-coupled device camera analysis to change the current views on the role of transposables elements in host genome evolution.
Abstract: We determined the distribution of 11 different transposable elements on Drosophila melanogaster mitotic chromosomes by using high-resolution fluorescent in situ hybridization (FISH) coupled with charge-coupled device camera analysis. Nine of these transposable elements (copia, gypsy, mdg-1, blood, Doc, I, F, G, and Bari-1) are preferentially clustered into one or more discrete heterochromatic regions in chromosomes of the Oregon-R laboratory stock. Moreover, FISH analysis of geographically distant strains revealed that the locations of these heterochromatic transposable element clusters are highly conserved. The P and hobo elements, which are likely to have invaded the D. melanogaster genome at the beginning of this century, are absent from Oregon-R heterochromatin but clearly exhibit heterochromatic clusters in certain natural populations. Together these data indicate that transposable elements are major structural components of Drosophila heterochromatin, and they change the current views on the role of transposable elements in host genome evolution.

Journal ArticleDOI
TL;DR: To investigate the existence of an association between the frequency of chromosome aberrations in non-target tissues and cancer risk, a historical cohort study was carried out in a group of 1455 subjects screened for CA over the last 20 years in Italy.

Journal ArticleDOI
TL;DR: In this paper, the heat equation with a random potential that is a white noise in space and time was studied in one space dimension and the statistical properties of the solution were investigated.
Abstract: We study, in one space dimension, the heat equation with a random potential that is a white noise in space and time. This equation is a linearized model for the evolution of a scalar field in a space-time-dependent random medium. It has also been related to the distribution of two-dimensional directed polymers in a random environment, to the KPZ model of growing interfaces, and to the Burgers equation with conservative noise. We show how the solution can be expressed via a generalized Feynman-Kac formula. We then investigate the statistical properties: the two-point correlation function is explicitly computed and the intermittence of the solution is proven. This analysis is carried out showing how the statistical moments can be expressed through local times of independent Brownian motions.

Journal ArticleDOI
TL;DR: In this article, three temporal logics are introduced that induce on labeled transition systems the same identifications as branching bisimulation, a behavioral equivalence that aims at ignoring invisible transitions while preserving the branching structure of systems.
Abstract: Three temporal logics are introduced that induce on labeled transition systems the same identifications as branching bisimulation, a behavioral equivalence that aims at ignoring invisible transitions while preserving the branching structure of systems. The first logic is an extension of Hennessy-Milner Logic with an “until” operator. The second one is another extension of Hennessy-Milner Logic, which exploits the power of backward modalities. The third logic is CTL* without the next-time operator. A relevant side-effect of the last characterization is that it sets a bridge between the state- and action-based approaches to the semantics of concurrent systems.

Journal ArticleDOI
TL;DR: Natural antimicrobial peptides isolated from amphibian skin could provide lead structures for either the chemical, or rDNA synthesis of novel antimicrobials.

Journal ArticleDOI
TL;DR: In this article, the authors studied the relationship between local minima of the potential and metastable states in spm glasses and showed a correspondence between the two sets of minima.
Abstract: In this paper we develop further a metl~od recently introduced by one of us to study metastable states in spm glasses. We consider a 'potential function', defined as the free energy of a system at a given temperature T constrained to have a fixed overlap with a reference configuration of equilibrium ai temperature T'. We apply the method to the spl~encal p-spin glass, and to some generahzation, ofthis model m the range of temperatures between the dynamic and the static transition. The analysis suggests a correspondence among local minima of the potential and metastable states. Tl~is correspondence is confirmed studying the relaxation dynamics at temperature T of a system starting from an initial configuration equilibrated at a diiferent temperature T'- Recently a partial comprehension of these phenomena in mean field has been achieved (3-5). The phenomenon of aging is described in the mean field theory as an asymptotic stationary state, where time translation invanance and the fluctuation dissipation relation do not hold. This regime turns ont to be dosely related to the nature of the static glassy transition. The models studied up to now can be divided into two classes according to their pattem of replica symmetry breaking IRSB) (6). If the RSB is "continuons", i e. if the Parisi order parameter function qi~) is continuous, then tl~e static and the dynamic transitions occur at the same temperature. The asymptotic state is sucl~ tl~at expected values of quantities which depend only on tl~e configuration of tl~e system at a smgle time ie.g. the energy or tl~e distribution of tl~e magnetizations) tend to their Boltzmal~n-Gibbs values. If instead tl~e Pansi function is discontinuous, e-g- a single step function, the dynamic transition occurs at a temperature higher than the static one, and the quantities mentioned above tend to limits different from their canonical averages. However, a careful analysis m the spherical p-spin mortel (3) has shown how this hmiting values can be related to the values of the same observable m a particular

Journal ArticleDOI
01 Sep 1995-Memory
TL;DR: The hypothesis that different categories of knowledge may be closely intertwined with different sources of sensory-motor information, was substantially confirmed and the hypothesis that action schemata may critically contribute to the development of the semantic representation of verbs was supported.
Abstract: Previous studies of category-specific semantic disturbances have focused their attention on the intrinsic cognitive structure of these disorders. The present survey aims to evaluate the relationships between disrupted semantic category and localisation of the underlying brain damage, in order to establish whether the injured brain areas house just those neurophysiological mechanisms that should have critically contributed to the acquisition of the disrupted semantic categories. We took into account in our review two double dissociations concerning respectively: (1) the impairment of a specific linguistic category--we contrast those disorders selectively affecting verbs (action names) with those selectively affecting nouns (object names); (2) the impairment of a specific conceptual/semantic domain--we contrast disorders selectively affecting living beings with those preferentially affecting man-made artefacts. The hypothesis that different categories of knowledge may be closely intertwined with different sources of sensory-motor information, was substantially confirmed. The lesion preferentially encroached on the left frontal lobe when the category "verbs" was selectively affected; it involved the left temporal lobe and the posterior association areas when the category "nouns" was preferentially disrupted; it involved bilateral temporo-limbic structures and inferior temporal lobes when the category "living beings" was selectively disrupted; it usually encroached on the left fronto-parietal areas when man-made artefacts and body parts were preferentially affected. These data support the hypothesis that: (a) action schemata may critically contribute to the development of the semantic representation of verbs, (b) mechanisms of sensory integration may play an important role in establishing the semantic representation of nouns; (c) high-level visual processing and multi-modal sensory convergency may critically contribute to organising the semantic representation of living beings; (d) motor-kinaesthetic integration may play a leading role in developing the semantic representation of man-made artefacts.

Journal ArticleDOI
TL;DR: This study unequivocally demonstrates that Mog-specific autoimmune responses are alone sufficient to induce a demyelinating disease of the CNS and supports the proposal that MOG may play an important role in the immunopathogenesis of multiple sclerosis.

Journal ArticleDOI
TL;DR: Early stroke deterioration is still an event that is difficult to predict; it is largely determined by cerebral edema following an arterial occlusion, as indicated by an early focal hypodensity and initial mass effect on the baseline CT scan.
Abstract: Objectives: To identify predictors and possible pathogenetic mechanisms of early neurological deterioration in patients with acute ischemic strokes and to evaluate their impact on clinical outcome. Design: Case series. Setting: University hospital's stroke unit. Patients: A continuous series of 152 patients with firstever ischemic hemispheric strokes were hospitalized within 5 hours of onset, evaluated with the Canadian Neurological Scale, and underwent a computed tomographic (CT) scan. The initial subset of 80 patients also underwent angiography. A repeated CT scan or autopsy was performed within 5 to 9 days of a patient's stroke. Progressing neurological deficit was defined as a decrease of one point or more in the global neurological scale score during hospitalization, when compared with that at entry. Results: The conditions of 39 patients (26%) deteriorated during the initial 4 days; 20 patients (51%) had an impaired level of consciousness, and 19 patients (49%) had impaired limb strength and/or speech. They had been hospitalized earlier and had higher serum glucose levels at admission; the baseline CT scans of these patients showed an early focal hypodensity and initial mass effect more frequently. On the repeated CT scan (144 patients) or at autopsy (eight patients), patients with a progressing course more frequently had large infarcts, severe mass effect, and hemorrhagic infarction. We found no differences with regard to demographic data, medical history, and treatments that were given; only subcutaneous heparin calcium was more frequently administered to patients with a progressing course. Twenty-two (27%) of the 80 patients who underwent angiography had a progressing course, of whom 20 (91%) had an intracranial and/or extracranial arterial occlusion, with collateral blood supply in seven patients (35%). Logistic regression analysis showed that the independent predictors of progression were the serum glucose levels at admission and the early focal hypodensity with cortical and corticosubcortical locations, with the positive predictive values of the latter being 34% (95% confidence interval [CI], 26% to 42%) and 57% (95% CI, 47% to 67%), respectively. Among patients who underwent angiography, logistic regression analysis showed a significant correlation between carotid siphon occlusion and a progressing course. The 30-day case-fatality ratio and disability (Barthel index, Conclusions: Early stroke deterioration is still an event that is difficult to predict; it is largely determined by cerebral edema following an arterial occlusion, as indicated by an early focal hypodensity and initial mass effect on the baseline CT scan. Since early deterioration anticipates a bad outcome in 90% of patients, it might be used as an early surrogate end point in therapeutic trials.

Book ChapterDOI
TL;DR: This article presented an evolutionary microeconomic theory of innovation and production and discussed its implications for development theory using the notions of technological paradigm and trajectory, and developed an alternative view of firm behavior and learning.
Abstract: This paper presents an evolutionary microeconomic theory of innovation and production and discusses its implications for development theory Using the notions of technological paradigm and trajectory, it develops an alternative view of firm behavior and learning It is shown then how these are embedded in broader national systems of innovation which account for persistent differences in technological cappacities between countries Finally, this “bottom-up” evolutionary analysis is linked with an institutional “top-down” approach, and the potential fruitfulness of this dialogue is demonstrated

Journal ArticleDOI
TL;DR: It is demonstrated that the natural history of gallstones is less benign than is generally considered and associated with an increased risk of developing biliary colic.

Book
22 Jun 1995
TL;DR: In this article, the origin and the origins of environmental psychology are discussed, as well as the origins and origins of present-day environmental psychology, and a characterisation of the field main research topics Paradigms and Psycho-social constructs.
Abstract: PART ONE: THE ORIGIN AND THEORETICAL ROOTS OF ENVIRONMENTAL PSYCHOLOGY The Origin of Environmental Psychology Environmental Psychology and Psychological Tradition PART TWO: DIRECTIONS OF PRESENT-DAY ENVIRONMENTAL PSYCHOLOGY Characterization of the Field Main Research Topics Paradigms and Psycho-social Constructs in Present-Day Environmental Psychology