32,534 research outputs found
Some questions of space bioengineering
Zero-gravity offers selective effect on growth and metabolic activity unicellular organisms as well as unique opportunities in purification of organic compounds. These make it possible to consider the biosynthesis and recovery of certain metabolites economically feasible in space. Design, construction and operation of systems for the above mentioned purposes requires interdisciplinary actions within the scope of a new discipline: space bioengineering. The problems and perspectives of this discipline particularly in the application of bioreactor-recovery systems in space to manufacture metabolites of high economic and scientific value. Special attention is paid to pivotal factors such as various mass transport phenomena, contamination control, automatic control of optimum environment and synchronization of the operation of the biological (biosynthesis) and the physiochemical (recovery-purification) systems
Fair Exchange in Strand Spaces
Many cryptographic protocols are intended to coordinate state changes among
principals. Exchange protocols coordinate delivery of new values to the
participants, e.g. additions to the set of values they possess. An exchange
protocol is fair if it ensures that delivery of new values is balanced: If one
participant obtains a new possession via the protocol, then all other
participants will, too. Fair exchange requires progress assumptions, unlike
some other protocol properties. The strand space model is a framework for
design and verification of cryptographic protocols. A strand is a local
behavior of a single principal in a single session of a protocol. A bundle is a
partially ordered global execution built from protocol strands and adversary
activities. The strand space model needs two additions for fair exchange
protocols. First, we regard the state as a multiset of facts, and we allow
strands to cause changes in this state via multiset rewriting. Second, progress
assumptions stipulate that some channels are resilient-and guaranteed to
deliver messages-and some principals are assumed not to stop at certain
critical steps. This method leads to proofs of correctness that cleanly
separate protocol properties, such as authentication and confidentiality, from
invariants governing state evolution. G. Wang's recent fair exchange protocol
illustrates the approach
Towards a new generation of transport services adapted to multimedia application
Une connexion d'ordre et de fiabilité partiels (POC, partial order connection) est une connexion de transport autorisée à perdre certains objets mais également à les délivrer dans un ordre éventuellement différent de celui d'émission. L'approche POC établit un lien conceptuel entre les protocoles sans connexion au mieux et les protocoles fiables avec connexion. Le concept de POC est motivé par le fait que dans les réseaux hétérogènes sans connexion tels qu'Internet, les paquets transmis sont susceptibles de se perdre et d'arriver en désordre, entraînant alors une réduction des performances des protocoles usuels. De plus, on montre qu'un protocole associé au transport d'un flux multimédia permet une réduction très sensible de l'utilisation des ressources de communication et de mémorisation ainsi qu'une diminution du temps de transit moyen. Dans cet article, une extension temporelle de POC, nommée TPOC (POC temporisé), est introduite. Elle constitue un cadre conceptuel permettant la prise en compte des exigences de qualité de service des applications multimédias réparties. Une architecture offrant un service TPOC est également introduite et évaluée dans le cadre du transport de vidéo MPEG. Il est ainsi démontré que les connexions POC comblent, non seulement le fossé conceptuel entre les protocoles sans connexion et avec connexion, mais aussi qu'ils surpassent les performances des ces derniers lorsque des données multimédias (telles que la vidéo MPEG) sont transportées
Parallelizing Deadlock Resolution in Symbolic Synthesis of Distributed Programs
Previous work has shown that there are two major complexity barriers in the
synthesis of fault-tolerant distributed programs: (1) generation of fault-span,
the set of states reachable in the presence of faults, and (2) resolving
deadlock states, from where the program has no outgoing transitions. Of these,
the former closely resembles with model checking and, hence, techniques for
efficient verification are directly applicable to it. Hence, we focus on
expediting the latter with the use of multi-core technology.
We present two approaches for parallelization by considering different design
choices. The first approach is based on the computation of equivalence classes
of program transitions (called group computation) that are needed due to the
issue of distribution (i.e., inability of processes to atomically read and
write all program variables). We show that in most cases the speedup of this
approach is close to the ideal speedup and in some cases it is superlinear. The
second approach uses traditional technique of partitioning deadlock states
among multiple threads. However, our experiments show that the speedup for this
approach is small. Consequently, our analysis demonstrates that a simple
approach of parallelizing the group computation is likely to be the effective
method for using multi-core computing in the context of deadlock resolution
Trace-level speculative multithreaded architecture
This paper presents a novel microarchitecture to exploit trace-level speculation by means of two threads working cooperatively in a speculative and non-speculative way respectively. The architecture presents two main benefits: (a) no significant penalties are introduced in the presence of a misspeculation and (b) any type of trace predictor can work together with this proposal. In this way, aggressive trace predictors can be incorporated since misspeculations do not introduce significant penalties. We describe in detail TSMA (trace-level speculative multithreaded architecture) and present initial results to show the benefits of this proposal. We show how simple trace predictors achieve significant speed-up in the majority of cases. Results of a simple trace speculation mechanism show an average speed-up of 16%.Peer ReviewedPostprint (published version
Metachronal waves in a chain of rowers with hydrodynamic interactions
Filaments on the surface of a microorganism such as Paramecium or Ophalina
beat highly synchronized and form so-called metachronal waves that travel along
the surfaces. In order to study under what principal conditions these waves
form, we introduce a chain of beads, called rowers, each periodically driven by
an external force on a straight line segment. To implement hydrodynamic
interactions between the beads, they are considered point-like. Two beads
synchronize in antiphase or in phase depending on the positive or negative
curvature of their driving-force potential. Concentrating on in-phase
synchronizing rowers, we find that they display only transient synchronization
in a bulk fluid. On the other hand, metachronal waves with wavelengths of 7-10
rower distances emerge, when we restrict the range of hydrodynamic interactions
either artificially to nearest neighbors or by the presence of a bounding
surface as in any relevant biological system.Comment: 9 pages, 10 figure
Symbol Synchronization for SDR Using a Polyphase Filterbank Based on an FPGA
This paper is devoted to the proposal of a highly efficient symbol synchronization subsystem for Software Defined Radio. The proposed feedback phase-locked loop timing synchronizer is suitable for parallel implementation on an FPGA. The polyphase FIR filter simultaneously performs matched-filtering and arbitrary interpolation between acquired samples. Determination of the proper sampling instant is achieved by selecting a suitable polyphase filterbank using a derived index. This index is determined based on the output either the Zero-Crossing or Gardner Timing Error Detector. The paper will extensively focus on simulation of the proposed synchronization system. On the basis of this simulation, a complete, fully pipelined VHDL description model is created. This model is composed of a fully parallel polyphase filterbank based on distributed arithmetic, timing error detector and interpolation control block. Finally, RTL synthesis on an Altera Cyclone IV FPGA is presented and resource utilization in comparison with a conventional model is analyzed
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