Search

We report on observation of the infrared photoresistance of twisted bilayer graphene under continuous quantum cascade laser illumination at a frequency of 57.1 THz. The photoresistance shows an intricate sign-alternating behavior under variations of temperature and back gate voltage, and exhibits giant resonance-like enhancements at certain gate voltages. The structure of the photoresponse correlates with weaker features in the dark dc resistance reflecting the complex band structure of twisted bilayer graphene. It is shown that the observed photoresistance is well captured by a bolometric model describing the electron and hole gas heating, which implies an ultrafast thermalization of the photoexcited electron-hole pairs in the whole range of studied temperatures and back gate voltages. We establish that photoresistance can serve a highly sensitive probe of the temperature variations of electronic transport in twisted bilayer graphene., 8 pages, 10 figures

The purpose of this study was to assess the adherence to therapy in patients with relapsing remitting multiple sclerosis (RR-MS) and to analyze the possible influence of factors such as hospital care and patients socioeconomic status. Two hundred eighty-five patients with RR-MS according to Mc Donald’s criteria and naïve disease-modifying drugs (DMDs) naïve were enrolled. Two self-administered questionnaires addressing the management of patients at therapy prescription and the personal perception of the daily life changes caused by DMDs were administered at months 3 and 12. Full adherence, considered as correct use of the therapy prescribed, was observed in a very high percentage of subjects (97.3% and 93.9% at 3 and 12 months). The main cause for reduced adherence was single dose forgetfulness, followed by anxiety, pain at the injection site, and tiredness of “doing all injections.” Nurses and neurologists of MS Center were identified as the major resource in coping with the disease at 3 and 12 months by patients. The neurologist was the health professional involved in MS management in 95% of cases and the nurse appeared to play a central role in patient training and drug administration management (50.3%).

Internet Service Providers can enforce a fine-grained control of Interdomain Routing by cleverly configuring the Border Gateway Protocol. However, the price to pay for the flexibility of BGP is the lack of convergence guarantees. The literature on network protocol design introduced several sufficient conditions that routing policies should satisfy to guarantee convergence. However, a methodology to systematically check BGP policies for convergence is still missing. This paper presents two fundamental contributions. First, we describe a heuristic algorithm that statically checks BGP configurations for guaranteed routing convergence. Our algorithm has several highly desirable properties: i) it exceeds state-of-the-art algorithms by correctly reporting more configurations as stable, ii) it can be implemented efficiently enough to analyze Internet-scale configurations, iii) it is free from false positives, namely never reports a potentially oscillating configuration as stable, and iv) it can help spot troublesome points in a detected oscillation. Second, we propose an architecture for a modular tool that exploits our algorithm to process native router configurations and report the presence of potential oscillations. Such a tool can effectively integrate syntactic checkers and assist operators in verifying configurations. We validate our approach using a prototype implementation and show that it scales well enough to enable Internet-scale convergence checks.

Background and Purpose— We sought to determine whether the introduction of EEG monitoring during head-up tilt testing could significantly improve the understanding of the cerebral events occurring during tilt-induced vasovagal syncope and the potential danger to the patient of this diagnostic procedure. Methods— EEG monitoring was performed during head-up tilt testing in a group of 63 consecutive patients (27 males and 36 females; mean age, 41.5 years) with a history of recurrent syncope of unknown origin despite extensive clinical and laboratory assessment. Results— Syncope occurred in 27 of 63 patients (42.8%) during head-up tilt testing and was found to be cardioinhibitory in 11 of 27 (40.7%) and vasodepressor in 16 of 27 (59.3%). All patients with a negative response to head-up tilt testing showed no significant EEG modifications. In patients with vasodepressor syncope, a generalized high-amplitude, 4- to 5-Hz (theta range) slowing of EEG activity appeared at the onset of syncope, followed by an increase of brain-wave amplitude with the reduction of frequency at 1.5 to 3 Hz (delta range). The return to the supine position was associated with brain-wave amplitude reduction and frequency increase to 4 to 5 Hz, followed by restoration of a normal EEG pattern and arousal (mean total duration of syncope, 23.2 seconds.). In patients with cardioinhibitory syncope, a generalized high-amplitude EEG slowing in the theta range was noted at the onset of syncope, followed by a brain-wave amplitude increase and slowing in the delta range. A sudden reduction of brain-wave amplitude then ensued, leading to the disappearance of electrocerebral activity (“flat” EEG). The return to the supine position did not allow either the immediate resolution of EEG abnormalities or consciousness recovery, both of which occurred after a further time interval (mean total duration of syncope, 41.4 seconds.). Conclusions— EEG monitoring during head-up tilt testing allowed recording and systematic description of electrocerebral abnormalities developing in the course of tilt-induced vasovagal syncope.

A diagram is a drawing on the plane that represents a graph like structure, where nodes are represented by symbols and edges are represented by curves connecting pairs of symbols. An automatic layout facility is a tool that receives as input a graph like structure and is able to produce a diagram that nicely represents such a structure. Many systems use diagrams in the interaction with the users; thus, automatic layout facilities and algorithms for graphs layout have been extensively studied in the last years. We present a new approach in designing an automatic layout facility. Our approach is based on a modular management of a large collection of algorithms and on a strategy that, given the requirements of an application, selects a suitable algorithm for such requirements. The proposed approach has been used for designing the automatic layout facility of Diagram Server, a network server that offers to its clients several facilities for managing diagrams. >

An entity relationship oriented model, that includes the notion of class, together with different types of assertions on classes, is presented. The assertions are used to model IS-A and disjointness relations both between entities and between relationships, part-of relations between entities and relationships, mandatory participation of an entity in a relationship, and interdependencies between the projections of relationships. The semantics of the model are defined in terms of first-order logic, and a sound and complete inference algorithm for such a model is presented. The algorithm is shown to have polynomial time complexity in the case where interdependencies on the projections of relationships are not taken into account. It is suggested that the model and the associated inference capabilities provide a suitable formal basis for designing an effective environment supporting conceptual modeling. >

The data dictionary contains the description of all types of data produced, managed, exchanged, and maintained in an organization. Data descriptions (very often hundreds of schemas) should be organized in such a way to allow all the users of the information system to understand the meaning of data and their relationships. To this end, a set of structuring primitives for a dictionary of entity relationship data schemas is presented. The formal properties of such structuring primitives are investigated, and the feasibility of their usage is shown by providing a methodology for dictionary design. >

The policy-oriented nature ofBGP provides network operators with great flexibility and control over the interdomain routing, nevertheless researchers showed that these benefits come at the cost of stability and predictability. In particular, policy interactions often separate, both in time and space, the effects of network events from their causes, making it hard to assess and debug network configurations. To better understand the complexity of BGP's behavior, we developed BGPATH, a publicly available tool that analyzes user-specified prefixes and relates their routing dynamics to the global Internet activity. Namely, BGPATH records data collected by distributed vantage points, checks the reliability of data sources, and evaluates the usage of each inter-AS link, both from a single and cross-vantage point perspective. The algorithms BGPATH relies on are shown to efficiently process huge streams of BGP data. We discuss time and space performance of these algorithms, underlining the potential to evolve towards a real-time system for BGP data measurement. BGPATH also provides the user with an effective visualization of the BGP activity related to a user-specified routing change, including contextual information which makes the analysis of the change less biased by BGP path exploration and outages of data sources. We exemplify the usefulness of our tool through a real usage scenario.

Interdomain routes change over time, and it is impressive to observe up to which extent. Routes may change many times in the same day and sometimes in the same hour or minute. Such changes are caused by several types of events, e.g., a routing policy variation in an ISP, a router reboot, or a link fault. In this paper we do a step towards the identification of the cause of route changes, a problem that is attracting increasing attention from both researchers and network administrators. Namely, we propose a methodology for analyzing a given BGP route change in order to, at least partially, locate the event that triggered the change. The methodology is supported by a publicly available on-line service.

For an Internet Service Provider (ISP), the knowledge of which interdomain paths could be traversed by its BGP announcements - and thus traffic flows - is essential to predict the impact of network faults, to develop effective traffic engineering and peering strategies, and to assess the quality of upstream providers. However, current methodologies do not provide this information. We present methodologies to discover how the BGP announcements for an ISP’s prefix are propagated through the Internet using withdrawals and specially crafted AS-sets. The techniques allow an ISP to determine which paths could be traversed in the presence of network faults or different routing policies on the ISP’s part and to deduce the routing policies of other ISPs with respect to its network. We validate our techniques through experimentation in the IPv6 and IPv4 Internet, showing that they can be safely and effectively applied in real-world situations.

This paper is devoted to study the combinatorial properties of Local Minimum Spanning Trees (LMSTs), a geometric structure that is attracting increasing research interest in the wireless sensor networks community. Namely, we study which topologies are allowed for a sensor network that uses, for supporting connectivity, a local minimum spanning tree approach. First, we refine the current definition of LMST realizability, focusing on the role of the power of transmission (i.e., of the radius of the covered area). Second, we show simple planar, connected, and triangle-free graphs with maximum degree 3 that cannot be represented as an LMST. Third, we present several families of graphs that can be represented as LMSTs. Then, we show a relationship between planar graphs and their representability as LMSTs based on homeomorphism. Finally, we show that the general problem of determining whether a graph is LMST representable is NP-hard.

Tunnels are widely used to improve security and to expand networks without having to deploy native infrastructure, and play an important role in the migration to IPv6. In this paper we introduce a number of techniques to detect, and collect information about, IPv6-in-IPv4 tunnels. We also show how, once a tunnel has been discovered, it can be used as a "vantage point" to launch third-party tunnel-discovery explorations, scaling up the discovery process. We describe the Tunneltrace tool which implements the proposed techniques, and validate them by means of a wide experimentation on the 6bone tunneled network, on the Italian Academic and Research network, and through the test boxes deployed worldwide by the RIPE NCC as part of the Test Traffic Measurements Service. We assess to what extent 6bone registry information is coherent with the actual network topology, and we provide the first experimental results on the current distribution of IPv6-in-IPv4 tunnels in the Internet, showing that tunnels are very common: even the "native" networks we tested reach more than 60% of all IPv6 prefixes through tunnels.

The problem of computing the types of the relationships between Internet autonomous systems is investigated. We refer to the model introduced in (ref.1), (ref.2) that bases the discovery of such relationships on the analysis of the AS paths extracted from the BGP routing tables. We characterize the time complexity of the above problem, showing both NP-completeness results and efficient algorithms for solving specific cases. Motivated by the hardness of the general problem, we propose heuristics based on a novel paradigm and show their effectiveness against publicly available data sets. The experiments put in evidence that our heuristics performs significantly better than state of the art heuristics.

An automatic layout facility is a tool that receives as input a graph-like structure and is able to produce a diagram that nicely represents such a structure. Due to the increasing number of systems that manage diagrams, the automatic layout facilities and the algorithms for graphs layout have been extensively studied. The authors present a new approach in building an automatic layout facility. The approach is based on a modular management of a collection of algorithms and on a tool that is able to 'synthesize' the best algorithm for a given application. Such an approach has been used for devising the automatic layout facility of Diagram Server, a network server that offers to its clients an effective set of facilities for managing diagrams. >

A polynomial-time algorithm for testing if a triconnected directed graph has an upward drkwing is presented. An upward drkwing is a planar drkwing such that all the edges flow in a common direction (e.g., from bottom to top). The problem arises in the fields of automatic graph drkwing and ordered sets, and has been open for several years. The proposed algorithm is based on a new combinatorial characterization that maps the problem into a max-flow problem on a sparse network; the time complexity isO(n+r 2) , wheren is the number of vertices andr is the number of sources and sinks of the directed graph. If the directed graph has an upward drkwing, the algorithm allows us to construct one easily.

In this paper we give a model for dynamic graph algorithms, based on performing queries and updates on an implicit representation of the drawing. We present dynamic algorithms for drawing planar graphs that use a variety of drawing standards (such as polyline, straight-line, orthogonal, grid, upward, and visibility drawings), and address aesthetic criteria that are important for readability, such as the display of planarity, symmetry, and reachability. Also, we provide techniques that are especially tailored for important subclasses of planar graphs such as trees and series-parallel digraphs. Our dynamic drawing algorithms have the important property of performing “smooth updates” of the drawing. Of special geometric interest is the possibility of performing point-location and window queries on the implicit representation of the drawing.

The goal of this paper is to investigate the area requirements for upward grid drawings of binary trees. First, we show that there is a family of binary trees with n vertices that require ω(n log n) area; this bound is tight to within a constant factor, i.e. any binary tree with n vertices can be drawn in O(n log n) area. Then we present an algorithm for constructing an upward drawing of a complete binary tree with n vertices in O(n) area, and, finally, we extend this result to the drawings of Fibonacci trees.

A sixty-year-old patient developed a bilateral symmetrical inferior altitudinal hemianopia in the span of an hour.

The aim of the paper is to present a methodology for documentation and maintenance of conceptual data schemas. It is a common practice in conceptual data design to follow a mixed top-down and bottom-up approach, in which refinement activities are followed by integration of partial design products. Documenting the conceptual activity consists of making as clear as possible the process of generation of the conceptual schema from requirements. In this phase a pure top-down procedurality is suggested, that allows the user to understand by progressive independent steps the whole generation process. A second fundamental advantage of this approach is the simplification that is guaranteed for all subsequent maintenance activities; if requirements change, top-down documentation can be used again, and the new design can proceed by simply modifying previous top-down expansions, adapting them to new requirements.

The state of the art in automatic graph drawing is reviewed, with special attention to the readability of information system diagrams. Existing results in the literature are compared, and a comprehensive algorithmic approach to the problem is proposed. The algorithm presented draws graphs on a grid and is suitable for both undirected graphs and mixed graphs that contain as subgraphs hierarchic structures. Several applications of GIOTTO, a graphic tool that embodies the aforementioned facility, are shown. >

In diagrammatic representations of hierarchies the minimization of the number of crossings between edges is a well-known criterion for improving readability. An efficient algorithm for testing if a hierarchy is planar (i.e. if it can be drawn without edge crossings) is proposed. A complete combinatorial characterization of the class of planar hierarchies is also given. >

The Authors underline the importance of the laparoscopy in the Obstetrical and Gyneacological emergencies. For this purpose, 74 consecutive laparoscopies, performed as emergencies at the Department of Obstetrics and Gynaecology of the University of Pavia, are considered and analyzed. The Authors stress that the celioscopy has allowed a precise diagnosis in all the cases examined, and, even thanks to percelioscopic surgery, has avoided some useless laparotomies. Even more, when it was necessary to perform a major surgical act, the right laparoscopic diagnosis has addressed the therapy in several cases to conservative surgery.

The incremental planarity testing problem consists of performing the following operations on a planar graph G with n vertices: (1) testing whether a new edge can be added to G so that the resulting graph is itself planar; (2) adding vertices and edges such that planarity is preserved. An efficient technique for incremental planarity testing that uses O(n) space and supports tests and insertion of vertices and edges in O(log n) time is presented. The bounds for queries and vertex insertions are worst case, and the bound for edge insertions is amortized. >

An algorithm for k-line planarity testing of hierarchical graphs is described. If the graph is k-line planar the algorithm produces the corresponding embedding. The algorithm has time complexity O(∣V∣). Furthermore some forbidden patterns are identified, whose existence is necessary and sufficient for a hierarchical graph to be not k-line planar.

IUDs have assumed increasing importance as contraceptives. Better design and use of new materials has increased their safety and reduced their side effects. However, pathological problems are constantly reported in literature. They include menstrual alterations (menometrorrhagia), pelvic infection, ectopic pregnancies, and perforation of the uterus. Results of research conducted at the Gynecology and Obstetrics Clinic at the University of Pavia are reported. The pathogenesis and etiology of cervico-vaginitis, actinomyces infections, PID and septic abortion in patients using IUDs were examined. It is concluded that the use of the spiral IUD is contraindicated for women affected by immunodeficiency and for patients with diseases that require therapy with anti-inflammatory agents. Special attention should be given to nulliparous patients with cardiovalvular problems and to patients during the immediate postpartum period. The importance of performing a bacteriological cervico-vaginal examination before the insertion of the IUD is stressed. Aside from common aerobic germs, the patient should be examined for anaerobic germs and agents of sexually transmitted diseases. Any form of cervico-vaginitis should be treated prior to insertion. A bacteriological checkup should be performed continually in order to prevent possible phlogistic as well as asymptomatic or minor symptomatic complications. The IUD should be replaced within 2 years of insertion. If infections occur, the device must be removed and an antibiotic therapy initiated.

Conceptual modelling is a fundamental phase in the design of information systems in which knowledge about the Universe of Discourse (UoD) is collected and represented in a conceptual schema. Conceptual modelling has been experienced to be a difficult and time consuming process. The reason for difficulties is in the abstraction and organization of large amounts of knowledge. In order to support the modelling process computerized tools have been developed for constructing a conceptual schema. A conceptual schema can also be stored for later use. This opens a possibility to develop a library of conceptual schemata in which partial or complete conceptual schemata are stored. The schemata in the library are either factually empty patterns of structures, or predefined, meaningful conceptual schemata. In this work the idea of concept definition libraries is introduced, the units of knowledge in a library are described, and the creation and maintenance of the library is discussed together with the system required to support the concept definition library.

An integrated graphic computer system is presented that supports the whole life cycle of a statistical data base. The system provides design and documentation tools for creating and mantaining a statistical data base, and a user friendly interface for the interactive retrieval of statistical data.

In statistical applications, data are described at different levels of aggregation, from elementary facts of the reality to complex aggregations such as classifications, time series, indexes. This paper describes a methodology for conceptual design of statistical databases that provides the designer suitable strategies for defining such different levels of aggregation starting from user requirements, and checking the completness, coherence and minimality of the conceptual schema at the different levels.

The data dictionary of an organization is the integrated repository of all types of data produced, managed, exchanged, and maintained in the organization, represented in such a way as to allow all users of the information system to understand their meaning. Since the way in which data are represented is usually dependent on the application domain, that is, the DBMS used, the role of the responsible organization unit, that is, designing and maintaining a dictionary, is a challenging task. A methodology is discussed for data dictionary design; several structuring mechanisms are proposed for use in the representation of data in the dictionary. A strategy is provided to produce the dictionary according to such mechanisms. >

Given a graph G with n vertices and m edges, a k-connectivity query for vertices v' and v" of G asks whether there exist k disjoint paths between v' and v". The authors consider the problem of performing k-connectivity queries for k >

A support tool for systems that manage a diagrammatic interface, called the Diagram Server, is discussed. It offers a tailorable interface independent from the system that uses it, and can manage objects through their diagrammatic representations. It supports multiple representations of the same object, and is largely independent from the graphic environment. The architecture of the Diagram Server is described, with an emphasis on the fundamental role played by its automatic layout facility. >

Electroencephalographic (EEG) monitoring was performed during head-up tilt testing (HUT) in a group of 63 consecutive patients (27 males, 36 females, mean age 41.5 years) with a history of recurrent syncope of unknown origin despite extensive clinical and laboratory evaluation. Syncope occurred in 27/63 patients (42.8%) during HUT and was cardioinhibitory in 11/27 (40.7%) and vasodepressor in 16/27 (59.3%). All patients with a negative response to HUT had no significant EEG modifications. In patients with vasodepressor syncope a generalized high amplitude 4-5 Hz (theta range) slowing of EEG activity appeared at the onset of syncope, followed by an increase in brain wave amplitude with a reduction of frequency at 1.5-3 Hz (delta range). The return to the supine position was associated with brain wave amplitude reduction and frequency increase to 4-5 Hz, followed by restoration of a normal EEG pattern and arousal (mean total duration of syncope 23.2 s). In patients with cardioinhibitory syncope, a generalized high amplitude EEG slowing in the theta range was noted at the onset of syncope, followed by a brain wave amplitude increase and slowing in the delta range. A sudden reduction of brain wave amplitude ensued leading to the disappearance of electroencephalographic activity ("flat" EEG). The return to the supine position was not followed by immediate resolution of EEG abnormalities or consciousness recovery, both occurring after a longer time interval (mean total duration of syncope 41.4 s). EEG monitoring during HUT allowed the recording and systematic description of electroencephalographic abnormalities developing in the course of tilt induced vasovagal syncope.