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The Cylindrical GEM Inner Tracker of the BESIII experiment: Prototype test beam results
No full textA cylindrical GEM detector is under development, to serve as an upgraded inner tracker at the BESIII spectrometer. It will consist of three layers of cylindrically-shaped triple GEMs surrounding the interaction point. The experiment is taking data at the e+ e− collider BEPCII in Beijing (China) and the GEM tracker will be installed in 2018. Tests on the performances of triple GEMs in strong magnetic field have been run by means of the muon beam available in the H4 line of SPS (CERN) with both planar chambers and the first cylindrical prototype. Efficiencies and resolutions have been evaluated using different gains, gas mixtures, with and without magnetic field. The obtained efficiency is 97−98% on single coordinate view, in many operational arrangements. The spatial resolution for planar GEMs has been evaluated with two different algorithms for the position determination: the charge centroid and the micro time projection chamber (μ-TPC) methods. The two modes are complementary and are able to cope with the asymmetry of the electron avalanche when running in magnetic field, and with non-orthogonal incident tracks. With the charge centroid, a resolution lower than 100 μm has been reached without magnetic field and lower than 200 μm with a magnetic field up to 1T. The μ-TPC mode showed to be able to improve those results. In the first beam test with the cylindrical prototype, the detector had a very good stability under different voltage configurations and particle intensities. The resolution evaluation is in progress
A GIS-Statistical Approach for Assessing Built Environment Energy Use at Urban Scale
No full textEnergy consumption modelling at the urban scale is crucial for supporting a transition towards the low-carbon city. Unfortunately, there are not many robust examples or standardised approaches available in the literature for delivering effective low-carbon urban energy planning. In particular, there is a lack of appropriate frameworks or systems which allow an effective and reliable assessment of energy use in the built environment at district-urban scale. This paper illustrates the development of a geospatial bottom-up statistical model to estimate the energy consumption of a large number of residential building stocks for heating space, considering a wide range of variables. The proposed methodology is based on a 2D/3D- Geographic Information System (GIS) and Multiple Linear Regression (MLR), which provides location-based information for each single dwelling to identify correlations and assess the demand-side consumption at the urban scale. This framework was tested on a mediumsized Italian city, including around 3600 residential buildings. The results provided by the model are validated using residual analysis and cross-validation. Moreover, the spatial results provided by this study represent a useful tool to aid decision-makers in the urban planning process. These results can help to create future energy transition strategies, implementing energy efficiency and renewable energy technologies in the context of sustainable cities. This work is part of a national Smart City & Communities project, named "EEB- Zero Energy Buildings in Smart Urban Districts"; nonetheless, the methodology illustrated in this paper can be generalised and applied to other European urban contexts
Efficiency and effectiveness in the urban public transport sector: A critical review with directions for future research
No full textThis paper proposes a self-contained reference for both policy makers and scholars who want to address the problem of efficiency and effectiveness of Local Public Transport (LPT), with special emphasis on urban transit, in a sound empirical way. Framing economic efficiency studies into a transport planning perspective, it offers a critical discussion of the existing empirical studies, relating them to the main methodological approaches used. The connection between such perspectives and Operations Research studies dealing with scheduling and tactical design of public transport services is also developed. The comprehensive classification of selected relevant dimensions of the empirical literature, namely inputs, outputs, kind of data analysed, methods adopted and policy relevant questions addressed, and the systematic investigation of their interrelationships allows us to summarize the existing literature and to propose desirable developments and extensions for future studies in the fiel
Comparing reuse practices in two large software-producing companies
No full textContext Reuse can improve productivity and maintainability in software development. Research has proposed a wide range of methods and techniques. Are these successfully adopted in practice? Objective We propose a preliminary answer by integrating two in-depth empirical studies on software reuse at two large software-producing companies. Method We compare and interpret the study results with a focus on reuse practices, effects, and context. Results Both companies perform pragmatic reuse of code produced within the company, not leveraging other available artefacts. Reusable entities are retrieved from a central repository, if present. Otherwise, direct communication with trusted colleagues is crucial for access. Reuse processes remain implicit and reflect the development style. In a homogeneous infrastructure-supported context, participants strongly agreed on higher development pace and less maintenance effort as reuse benefits. In a heterogeneous context with fragmented infrastructure, these benefits did not materialize. Neither case reports statistically significant evidence of negative side effects of reuse nor inhibitors. In both cases, a lack of reuse led to duplicate implementations. Conclusion Technological advances have improved the way reuse concepts can be applied in practice. Homogeneity in development process and tool support seem necessary preconditions. Developing and adopting adequate reuse strategies in heterogeneous contexts remains challengin
A study of the impact of DNS resolvers on CDN performance using a causal approach
No full textResources such as Web pages or videos that are published in the Internet are referred to by their Uniform Resource Locator (URL). If a user accesses a resource via its URL, the host name part of the URL needs to be translated into a routable IP address. This translation is performed by the Domain Name System service (DNS). DNS also plays an important role when Content Distribution Networks (CDNs) are used to host replicas of popular objects on multiple servers that are located in geographically different areas. A CDN makes use of the DNS service to infer client location and direct the client request to the optimal server. While most Internet Service Providers (ISPs) offer a DNS service to their customers, clients may instead use a public DNS service. The choice of the DNS service can impact the performance of clients when retrieving a resource from a given CDN. In this paper we study the impact on download performance for clients using either the DNS service of their ISP or the public DNS service provided by Google DNS. We adopt a causal approach that exposes the structural dependencies of the different parameters impacted by the DNS service used and we show how to model these dependencies with a Bayesian network. The Bayesian network allows us to explain and quantify the performance benefits seen by clients when using the DNS service of their ISP. We also discuss how the further improve client performanc
Forced response of rotating bladed disks: Blade Tip-Timing measurements
No full textThe Blade Tip-Timing is a well-known non-contact measurement technique currently employed for the identification of the dynamic behaviours of rotating bladed disks. Although the measurement system has become a typical industry equipment for bladed disks vibration surveys, the type of sensors, the positioning of the sensors around the bladed disk and the used algorithm for data post-processing are still not standard techniques, and their reliability has to be proved for different operation conditions by the comparison with other well-established measurement techniques used as reference like strain gauges. This paper aims at evaluating the accuracy of a latest generation Tip-Timing system on two dummy blisks characterized by different geometrical, structural and dynamical properties. Both disks are tested into a spin-rig where a fixed number of permanent magnets excite synchronous vibrations with respect to the rotor speed. A new positioning for the Blade Tip-Timing optical sensors is tested in the case of a shrouded bladed disk. Due to the presence of shrouds, the sensors cannot be positioned at the outer radius of the disk pointing radially toward the rotation axis as in the most common applications, since the displacements at the tips are very small and cannot be detected. For this reason a particular placement of optical laser sensors is studied in order to point at the leading and trailing edges' locations where the blades experience the largest vibration amplitudes with the aim of not interfering with the flow path. Besides the typical Blade Tip-Timing application aimed at identifying the dynamical properties of each blade, an original method is here proposed to identify the operative deflection shape of a bladed disk through the experimental determination of the nodal diameters. The method is applicable when a small mistuning pattern perturbs the ideal cyclic symmetry of the bladed dis
Synchronous vibration parameters identification by tip timing measurements
No full textThe Blade Tip Timing (BTT) measurement system is a technique to measure vibration parameters of a rotating bladed disk. In particular for synchronous vibrations the BTT provides signals versus the rotation speed of the disk starting from the measurement of the time of arrival (TOA) of each blade under the tip timing probes. The signals must be post processed in order to obtain the interesting parameters of each blade vibration. The paper presents a method to extract the main parameters (amplitude and frequency) in resonance condition from the tip timing measurements. The proposed method is a revision of the already existing well known Two-Parameter Plot (2PP) method which requires a minimum of two probes. Improvements to the existing 2PP method are here suggested mainly in the part of engine order identification. The proposed method is then applied to the BTT measured signals coming from a rotating bladed disk excited at different engine orders. At the same time on the disk the vibration of one blade was detected by strain gauges. The strain gauges were calibrated and they provide the reference values of the vibration parameters. The vibration parameters derived by the proposed method are in agreement with those obtained by the strain gages methodolog
MAGMA network behavior classifier for malware traffic
No full textMalware is a major threat to security and privacy of network users. A large variety of malware is typically spread over the Internet, hiding in benign traffic. New types of malware appear every day, challenging both the research community and security companies to improve malware identification techniques. In this paper we present MAGMA, MultilAyer Graphs for MAlware detection, a novel malware behavioral classifier. Our system is based on a Big Data methodology, driven by real-world data obtained from traffic traces collected in an operational network. The methodology we propose automatically extracts patterns related to a specific input event, i.e., a seed, from the enormous amount of events the network carries. By correlating such activities over (i) time, (ii) space, and (iii) network protocols, we build a Network Connectivity Graph that captures the overall "network behavior" of the seed. We next extract features from the Connectivity Graph and design a supervised classifier. We run MAGMA on a large dataset collected from a commercial Internet Provider where 20,000 Internet users generated more than 330 million events. Only 42,000 are flagged as malicious by a commercial IDS, which we consider as an oracle. Using this dataset, we experimentally evaluate MAGMA accuracy and robustness to parameter settings. Results indicate that MAGMA reaches 95% accuracy, with limited false positives. Furthermore, MAGMA proves able to identify suspicious network events that the IDS ignored
Rank two aCM bundles on the del Pezzo fourfold of degree 6 and its general hyperplane section
No full textEfficient Caching through Stateful SDN in Named Data Networking
No full textNamed Data Networking (NDN) is an innovative paradigm to provide content based services in future networks. As compared to legacy networks, naming of network packets and in-network caching of content make NDN more feasible for content dissemination. However, the implementation of NDN requires drastic changes to the existing network infrastructure. One feasible approach is to use Software Defined Networking (SDN), according to which the control of the network is delegated to a centralized controller, which configures the forwarding data plane. This approach leads to large signaling overhead as well as large end-to-end (e2e) delays. In order to overcome these issues, we propose to enable NDN using a stateful data plane in the SDN network. In particular, we realize the functionality of an NDN node using a stateful SDN switch attached with a local cache for content storage, and use OpenState to implement such an approach. In our solution, no involvement of the controller is required once the OpenState switch has been configured. We benchmark the performance of our solution against the traditional SDN approach considering several relevant metrics. Experimental results highlight the benefits of a stateful approach and of our implementation, which avoids signaling overhead and significantly reduces e2e delays