High Resolution Timing of MIPs with RPCs

Proposal of abstract for RPC99, Bari, Italy, 28-29 October 1999. RPCs made with glass and metal electrodes, forming accurately spaced gaps of a few hundred micrometres, have reached timing accuracies below 70 ps with efficiencies above 95This type of detector, operating at atmospheric pressure with non-flammable gases, seems well suited for large area TOF sytems, providing performances comparable to the existing scintillator-based TOF technology but with significantly lower price per channel.In this work we describe the principles of operation and the performance of several chamber configurations

Interval tree clocks: a logical clock for dynamic systems

Lecture Notes in Computer Science 5401, 2008Causality tracking mechanisms, such as vector clocks and version vectors, rely on mappings from globally unique identifiers to integer counters. In a system with a well known set of entities these ids can be preconfigured and given distinct positions in a vector or distinct names in a mapping. Id management is more problematic in dynamic systems, with large and highly variable number of entities, being worsened when network partitions occur. Present solutions for causality tracking are not appropriate to these increasingly common scenarios. In this paper we introduce Interval Tree Clocks, a novel causality tracking mechanism that can be used in scenarios with a dynamic number of entities, allowing a completely decentralized creation of processes/replicas without need for global identifiers or global coordination. The mechanism has a variable size representation that adapts automatically to the number of existing entities, growing or shrinking appropriately. The representation is so compact that the mechanism can even be considered for scenarios with a fixed number of entities, which makes it a general substitute for vector clocks and version vectors

Version stamps-decentralized version vectors

Version vectors and their variants play a central role in update tracking in optimistic distributed systems. Existing mechanisms for a variable number of participants use a mapping from identities to integers, and rely on some form of global configuration or distributed naming protocol to assign unique identifiers to each participant. These approaches are incompatible with replica creation under arbitrary partitions, a typical mode of operation in mobile or poorly connected environments. We present an update tracking mechanism that overcomes this limitation; it departs from the traditional mapping and avoids the use of integer counters, while providing all the functionality of version vectors in what concerns version tracking

Breakdown Limit Studies in High Rate Gaseous Detectors

We report results from a systematic study of breakdown limits for novel high rate gaseous detectors: MICROMEGAS, CAT and GEM, together with more conventional devices such as thin-gap parallel-mesh chambers and high-rate wire chambers. It was found that for all these detectors, the maximum achievable gain, before breakdown appears, drops dramatically with incident flux, and is sometimes inversely proportional to it. Further, in the presence of alpha particles, typical of the backgrounds in high-energy experiments, additional gain drops of 1-2 orders of magnitude were observed for many detectors. It was found that breakdowns at high rates occur through what we have termed an "accumulative" mechanism, which does not seem to have been previously reported in the literature. Results of these studies may help in choosing the optimum detector for given experimental conditions

TOFtracker: combination of time-of-flight and high-accuracy bidimensional tracking in a single gaseous detector

A 5-gap timing RPC equipped with patterned electrodes coupled to both charge-sensitive and timing circuits yields a time accuracy of 77 ps along with a position accuracy of 38 μm. These results were obtained by calculating the straight-line fit residuals to the positions provided by a 3-layer telescope made out of identical detectors, detecting almost perpendicular cosmic-ray muons. The device may be useful for particle identification by time-of-flight, where simultaneous measurements of trajectory and time are necessary

Concise server-wide causality management for eventually consistent data stores

Large scale distributed data stores rely on optimistic replication to scale and remain highly available in the face of net work partitions. Managing data without coordination results in eventually consistent data stores that allow for concurrent data updates. These systems often use anti-entropy mechanisms (like Merkle Trees) to detect and repair divergent data versions across nodes. However, in practice hash-based data structures are too expensive for large amounts of data and create too many false conflicts. Another aspect of eventual consistency is detecting write conflicts. Logical clocks are often used to track data causality, necessary to detect causally concurrent writes on the same key. However, there is a nonnegligible metadata overhead per key, which also keeps growing with time, proportional with the node churn rate. Another challenge is deleting keys while respecting causality: while the values can be deleted, perkey metadata cannot be permanently removed without coordination. Weintroduceanewcausalitymanagementframeworkforeventuallyconsistentdatastores,thatleveragesnodelogicalclocks(BitmappedVersion Vectors) and a new key logical clock (Dotted Causal Container) to provides advantages on multiple fronts: 1) a new efficient and lightweight anti-entropy mechanism; 2) greatly reduced per-key causality metadata size; 3) accurate key deletes without permanent metadata.(undefined

DottedDB: anti-entropy without merkle trees, deletes without tombstones

To achieve high availability in the face of network partitions, many distributed databases adopt eventual consistency, allow temporary conflicts due to concurrent writes, and use some form of per-key logical clock to detect and resolve such conflicts. Furthermore, nodes synchronize periodically to ensure replica convergence in a process called anti-entropy, normally using Merkle Trees. We present the design of DottedDB, a Dynamo-like key-value store, which uses a novel node-wide logical clock framework, overcoming three fundamental limitations of the state of the art: (1) minimize the metadata per key necessary to track causality, avoiding its growth even in the face of node churn; (2) correctly and durably delete keys, with no need for tombstones; (3) offer a lightweight anti-entropy mechanism to converge replicated data, avoiding the need for Merkle Trees. We evaluate DottedDB against MerkleDB, an otherwise identical database, but using per-key logical clocks and Merkle Trees for anti-entropy, to precisely measure the impact of the novel approach. Results show that: causality metadata per object always converges rapidly to only one id-counter pair; distributed deletes are correctly achieved without global coordination and with constant metadata; divergent nodes are synchronized faster, with less memory-footprint and with less communication overhead than using Merkle Trees.This work is financed by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation - COMPETE 2020 Programme within project «POCI-01-0145-FEDER-006961», and by National Funds through the Portuguese funding agency, FCT - Fundação para a Ciência e a Tecnologia as part of project «UID/EEA/50014/2013».info:eu-repo/semantics/publishedVersio

Host Card Emulation with Tokenisation: Security Risk Assessment

Host Card Emulation (HCE) is an architecture that provides virtual representation of contactless cards, enabling transactional communication for mobile devices with Near-Field Communication (NFC) support without the need of Secure Element (SE) hardware. Performing the card emulation mainly by software, usually in wallet-like applications which store payment tokens for enabling transactions, creates several risks that need to be properly evaluated in order to be able to materialise a risk-based implementation. This paper describes the HCEt and proposes the identification and assessment of its risks through a survey conducted to specialists in the subject matter, analysing the model from the point of view of a wallet application on a mobile device that stores payment tokens to be able to perform contactless transactions. Despite the increasing complexity and specialisation of software, hardware, and the respective technical cyberattacks we conclude that the human nature remains the easiest to exploit, with greater gains

Promoting entrepreneurship among informatics engineering students: insights from a case study

Universities seek to promote entrepreneurship through effective education approaches, which need to be in permanent evolution. Nevertheless, the literature in entrepreneurship education lacks empirical evidence. This article discusses relevant issues related to promoting entrepreneurship in the software field, based on the experience of a 15-European Credit Transfer and Accumulation System course. This course seeks to instil in the students the recognition of the need to reconcile technical and business visions, organisational and commercial aspects, most of which have never been addressed previously. A series of semi-structured interviews made it possible to obtain relevant insights about the teaching–learning process underlying this course and its evolution over a seven-year period. Materials related with this course have been analysed, namely guidelines produced by the teachers and deliverables produced by the students. This article discusses the dimensions that were identified as fundamental for promoting entrepreneurship skills in the field of software, namely teamwork, project engagement, and contact with the market