Design and Analysis of Transport Protocols for Reliable High-Speed Communications

The design and analysis of transport protocols for reliable communications constitutes the topic of this dissertation. These transport protocols guarantee the sequenced and complete delivery of user data over networks which may lose, duplicate and reorder packets. Reliable transport services are required by a wide range of applications such as the World-Wide Web, remote network access, and distributed computing. The design of these protocols is heavily influenced by the parameters of the underlying network infrastructure and by the assumptions about the host computers and applications. Therefore the recent advances in optical transmission and computer technologies stimulated the design of several novel transport protocols. Many of the proposed protocols use similar or at least related techniques. Our goal with this thesis is to improve the understanding of reliable communications by analyzing the protocols that implement this service and to contribute to the design of reliable transport protocols. The basis of our analysis is the formal specification and verification of the protocol mechanisms under investigation. The behavior of the protocol is captured by a state-transition system and properties are established using assertional reasoning. The framework is capable to handle unbounded and modulo-N state variables and to capture real-time aspects of the protocols which is essential for the modeling of realistic systems. Practical protocols of considerable complexity are specified and verified in the thesis. One advantage of the formal verification is that it increases our confidence in the correctness of these protocols. The formalism forces us to clarify all the details of the working of the protocol and to state explicitly every assumption about the protocol and its environment. During the process of the verification one also gains insight into the mechanisms of the protocol. But probably the most important result is that during the verication we obtain conditions for the correctness of the protocol in the form of inequalities on some protocol parameters. These conditions allow the comparison of the different protocol mechanisms and can be used to judge the suitability of a protocol for a certain environment. The functionality of transport protocols can be naturally divided into data transfer and connection management. Data transfer deals with the sequenced delivery of user data, while connection management is concerned with the orderly setup and release of connections.\ud In the thesis we study three different data transfer protocols. The usage of timestamps in data transfer protocols is analyzed in detail through the example of the PAWS mechanism which was proposed as an extension to TCP. The analysis reveals that the use of timestamps increases the functionality of the transport protocol by facilitating the simple measurement of round-trip delays, but it also reduces the maximum allowable transmission rate as compared to the plain sliding-window protocol. Another data transfer protocol called SNR is analyzed which is based on the idea of periodic state exchange. We start from an earlier specification of SNR and compare it to the plain sliding-window protocol. The analysis reveals that the maximum transmission speed achievable by that SNR specification is higher than that of the plain sliding-window protocol, but it comes with a serious limitation. In the SNR specication it is assumed that no duplicates are generated by either the network or the transport protocol itself. This assumption may seriously limit the eective performance of the protocol in case of losses in the network and demonstrates the importance of considering all the assumptions when selecting a protocol for a certain environment. The use of timestamps is also investigated in the context of connection management protocols. The detailed analysis of the connection setup protocol SCMP is presented which is based on the assumption that clocks of computers can be synchronized relatively cheaply even in a large network. In our verification it is proven that the safety of the protocol does not depend of the synchronization assumption, therefore the protocol can be used safely in cases when there are no absolute guarantees of the clocks being synchronized. Since practical clock synchronization algorithms give only probabilistic guarantees, our result provides an important theoretical support of the applicability of the protocol in practical environments. Based on earlier work by others, a family of connection management protocols is analyzed that use a cache to store information needed to shorten the connection setup latency. We contribute to this work by proposing improvements which allow to reduce considerably the memory usage of these protocols. Furthermore, we show that the correctness of the protocol can be assured without assuming an upper bound on the incarnation lifetime, i.e., the maximum duration of a connection. This result greatly improves the practical applicability of the protocol

High efficiency gaseous tracking detector for cosmic muon radiography

A tracking detector system has been constructed with an innovative approach to the classical multi-wire proportional chamber concept, using contemporary technologies. The detectors, covering an area of 0.58 square meters each, are optimized for the application of muon radiography. The main features are high (>99.5%) and uniform detection efficiency, 9 mm FWHM position resolution, filling gas consumption below 2 liters per hour for the non toxic, non flammable argon and carbon dioxide mixture. These parameters, along with the simplicity of the construction and the tolerance for mechanical effects, make the detectors to be a viable option for a large area muography observation system.Comment: 15 pages, 15 figure

Use of Transcranial Doppler in Intensive Care Unit

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Molecular surgery concept from bench to bedside: a focus on TRPV1+ pain-sensing neurons

“Molecular neurosurgery” is emerging as a new medical concept, and is the combination of two partners: (i) a molecular neurosurgery agent, and (ii) the cognate receptor whose activation results in the selective elimination of a specific subset of neurons in which this receptor is endogenously expressed. In general, a molecular surgery agent is a selective and potent ligand, and the target is a specific cell type whose elimination is desired through the molecular surgery procedure. These target cells have the highest innate sensitivity to the molecular surgery agent usually due to the highest receptor density being in their plasma membrane. The interaction between the ligand and its receptor evokes an overactivity of the receptor. If the receptor is a ligand-activated non-selective cation channel, the overactivity of receptor leads to excess Ca2+ and Na+ influx into the cell and finally cell death. One of the best known examples of such an interaction is the effect of ultrapotent vanilloids on TRPV1- expressing pain-sensing neurons. One intrathecal resiniferatoxin (RTX) dose allows for the receptor-mediated removal of TRPV1+ neurons from the peripheral nervous system. The TRPV1 receptor-mediated ion influx induces necrotic processes, but only in pain-sensing neurons, and usually within an hour. Besides that, target-specific apoptotic processes are also induced. Thus, as a nano-surgery scalpel, RTX removes the neurons responsible for generating pain and inflammation from the peripheral nervous system providing an option in clinical management for the treatment of morphine-insensitive pain conditions. In the future, the molecular surgery concept can also be exploited in cancer research for selectively targeting the specific tumor cell

Research and development of particle detectors for muon tomography and the CERN ALICE experiment

The Standard Model of particle physics describes successfully the building blocks of the material and their interactions, which are confirmed by most of the experimental observations. However, there are several open questions, e. g. how the Universe was created or where the missing antimatter is? We can answer these questions by new or upgraded experiments. In these experiments, we apply particle detectors to measure the particles originated from colliders or high-energy cosmic rays. This Ph.D. thesis focuses mainly on the research and development of particle detectors. The ALICE experiment at the Large Hadron Collider (LHC) of the European Laboratory for Particle Physics (CERN), investigates the quark gluon plasma (QGP), which is produced in heavy-ion collisions. ALICE has a complex apparatus consists of tracking, identification and calorimeter detectors. To measure more precisely the properties of QPG, the increase of energy and luminosity of collisions is necessary. This implies the better understanding of the operation of subdetectors of ALICE and their upgrades. The development of the instrumentation and the methods of particle physics led to the appearance of new applications. The muon radiography or muon tomography is an imaging method which is based on cosmic muon tracking. This is applicable to image largesize and high-density bjects. With an appropriate instrument, we can measure the change of the density in volcanoes in real time and predict even their eruptions. If the imaging of low-Z materials can be realised, that led to a non-invasive medical imaging procedure

Cerebrovaszkuláris betegségek megelőzése

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Az antikoaguláció szerepe a stroke-megelőzésben: a megfelelő NOAC-dózis választása = The role of anticuagulation in stroke prevention: selection of the appropriate NOAC dose

A pitvarfibrilláció (PF) a népesség öregedésével egyre gyakoribb, s az iszkémiás stroke rizikóját ötszörösére emelve jelentősen hozzájárul a stroke-ok nagy számához. A PF okozta stroke-rizikó nagymértékben csökkenthető az antikoaguláns szerek használatával. Az elmúlt évtizedben megjelent új típusú orális antikoagulánsok (NOAC) számos előnnyel rendelkeznek a warfarinnal szemben. Bár a NOAC-ok esetében nincs szükség folyamatos dózismódosításra, az öszszes NOAC esetén döntenünk kell, hogy standard, vagy csökkentett dózist javaslunk. A valóélet-adatok azt mutatták, hogy a pitvarfibrilláló betegek sokkal gyakrabban (36-64%-ban) kapnak csökkentett adagú NOAC-ot a mindennapi gyakorlatban, mint a klinikai vizsgálatokban. Az előírásoknak megfelelő (on-label) csökkentett dózisú NOAC-ok hatásossága és biztonságossága hasonló volt a warfarinhoz, de az apixaban esetén a major vérzések, a dabigatran esetén pedig a halálozás rizikója kisebb volt a warfarinhoz képest. Az off-label NOAC-dózisok használata szintén nem elhanyagolható: az előírttól kisebb adagot a betegek kb. 20%-a, nagyobb adagot 5%-a kap. A nagy metaanalízisek eredményei szerint az on-label adagoláshoz képest az off-label aluldozírozás esetén nem csökken a major vérzés rizikója, de nő a halálozás és a tromboembóliás események száma, vagyis a dóziscsökkentés ellenére nem nő a biztonság, de romlik a hatásosság. Az off-label túldozírozás esetén nő a major vérzések és a halálozás rizikója, s a várttal ellentétben nem csökken a stroke kockázata. A közlemény a NOAC-ok off-label adagolásának a gyakoriságára, s a dozírozással kapcsolatos potenciális veszélyekre hívja fel a figyelmet

Köztér és művészet – A polisz terei

A Köztér és művészet – a polisz terei című ír ásom a kortárs köztéri művészet, szobrászat kérdéseit járja körül. Az egyéni emlékezés, a közösségi, a történeti emlékezés, a városépítészet szempontjainak, valamint az elmúlt 25 év jelleg zetes , magyar köztéri kompozícióinak elemzésével arra keresem a választ, h ogyan változnak azok a követelm ények, melyeket speciálisan a köztéri művészettel szemben támasztunk

Hexapod Design For All-Sky Sidereal Tracking

In this paper we describe a hexapod-based telescope mount system intended to provide sidereal tracking for the Fly's Eye Camera project -- an upcoming moderate, 21"/pixel resolution all-sky survey. By exploiting such a kind of meter-sized telescope mount, we get a device which is both capable of compensating for the apparent rotation of the celestial sphere and the same design can be used independently from the actual geographical location. Our construction is the sole currently operating hexapod telescope mount performing dedicated optical imaging survey with a sub-arcsecond tracking precision.Comment: Accepted for publication in PASP, 10 page