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A Flexible and Efficient Protocol for Multi-Scope Service Registry Replication
Service registries play an important role in service discovery systems by accepting service registrations and answering service queries; they can serve a wide range of purposes, such as membership services, lookup services, and search services. To provide fault tolerant, and enhance scalability, availability and performance, service registries often need to be replicated. In this paper, we present Swift (Selective anti-entropy WIth FasT update propagation), a flexible and efficient protocol for multi-scope service registry replication. As consistency is a less of concern compared with availability in service registry replication, we choose to build Swift on top of anti-entropy to support high availability replication. Swift makes two contributions as follows. First, it defines a more general and flexible form of anti-entropy called selective anti-entropy, which extends the applicability of anti-entropy from full replication to partial replication by selectively reconciling inconsistent states between two replicas, and improves anti-entropy efficiency by fine controlling update propagation within each subset. Selective anti-entropy is the first that we are aware of in using anti-entropy to support generic partial replication. Secondly, Swift integrates service registry overlay networks with selective anti-entropy. Different topologies, such as full mesh and spanning tree, can be used for constructing service registry overlay networks. These overlay networks are used to propagate new updates quickly so as to minimize inconsistency among replicas. We have implemented Swift for replicating multi-scope Directory Agents in the Service Location Protocol. Our experience shows that Swift is flexible, efficient, and lightweight
Squeezed thermal reservoirs as a resource for a nano-mechanical engine beyond the Carnot limit
The efficient conversion of thermal energy to mechanical work by a heat
engine is an ongoing technological challenge. Since the pioneering work of
Carnot, it is known that the efficiency of heat engines is bounded by a
fundamental upper limit, the Carnot limit. Theoretical studies suggest that
heat engines may be operated beyond the Carnot limit by exploiting stationary,
non-equilibrium reservoirs that are characterized by a temperature as well as
further parameters. In a proof-of-principle experiment, we demonstrate that the
efficiency of a nano-beam heat engine coupled to squeezed thermal noise is not
bounded by the standard Carnot limit. Remarkably, we also show that it is
possible to design a cyclic process that allows for extraction of mechanical
work from a single squeezed thermal reservoir. Our results demonstrate a
qualitatively new regime of non-equilibrium thermodynamics at small scales and
provide a new perspective on the design of efficient, highly miniaturized
engines.Comment: 5 pages, 3 figure
Optimized sympathetic cooling of atomic mixtures via fast adiabatic strategies
We discuss fast frictionless cooling techniques in the framework of
sympathetic cooling of cold atomic mixtures. It is argued that optimal cooling
of an atomic species - in which the deepest quantum degeneracy regime is
achieved - may be obtained by means of sympathetic cooling with another species
whose trapping frequency is dynamically changed to maintain constancy of the
Lewis-Riesenfeld adiabatic invariant. Advantages and limitations of this
cooling strategy are discussed, with particular regard to the possibility of
cooling Fermi gases to a deeper degenerate regime.Comment: 5 pages, 3 figure
Enhanced magnetocaloric effect due to selective dilution in a triangular Ising antiferromagnet
We employ an effective-field theory with correlations in order to study a
magnetocaloric effect on a triangular Ising antiferromagnet, which is
selectively diluted by non-magnetic impurities on one of the three sublattices.
Such a dilution generally relieves massive degeneracy in our system and
therefore the ground-state entropy diminishes and the magnetocaloric effect
weakens at low temperatures. However, at relatively higher temperatures we can
observe significantly enhanced negative isothermal entropy changes for the
sublattice concentration .Comment: 3 pages, 5 figures, CSMAG'16 conferenc
Extreme genetic fragility of the HIV-1 capsid
Genetic robustness, or fragility, is defined as the ability, or lack thereof, of a biological entity to maintain function in the face of mutations. Viruses that replicate via RNA intermediates exhibit high mutation rates, and robustness should be particularly advantageous to them. The capsid (CA) domain of the HIV-1 Gag protein is under strong pressure to conserve functional roles in viral assembly, maturation, uncoating, and nuclear import. However, CA is also under strong immunological pressure to diversify. Therefore, it would be particularly advantageous for CA to evolve genetic robustness. To measure the genetic robustness of HIV-1 CA, we generated a library of single amino acid substitution mutants, encompassing almost half the residues in CA. Strikingly, we found HIV-1 CA to be the most genetically fragile protein that has been analyzed using such an approach, with 70% of mutations yielding replication-defective viruses. Although CA participates in several steps in HIV-1 replication, analysis of conditionally (temperature sensitive) and constitutively non-viable mutants revealed that the biological basis for its genetic fragility was primarily the need to coordinate the accurate and efficient assembly of mature virions. All mutations that exist in naturally occurring HIV-1 subtype B populations at a frequency >3%, and were also present in the mutant library, had fitness levels that were >40% of WT. However, a substantial fraction of mutations with high fitness did not occur in natural populations, suggesting another form of selection pressure limiting variation in vivo. Additionally, known protective CTL epitopes occurred preferentially in domains of the HIV-1 CA that were even more genetically fragile than HIV-1 CA as a whole. The extreme genetic fragility of HIV-1 CA may be one reason why cell-mediated immune responses to Gag correlate with better prognosis in HIV-1 infection, and suggests that CA is a good target for therapy and vaccination strategies
Error threshold in optimal coding, numerical criteria and classes of universalities for complexity
The free energy of the Random Energy Model at the transition point between
ferromagnetic and spin glass phases is calculated. At this point, equivalent to
the decoding error threshold in optimal codes, free energy has finite size
corrections proportional to the square root of the number of degrees. The
response of the magnetization to the ferromagnetic couplings is maximal at the
values of magnetization equal to half. We give several criteria of complexity
and define different universality classes. According to our classification, at
the lowest class of complexity are random graph, Markov Models and Hidden
Markov Models. At the next level is Sherrington-Kirkpatrick spin glass,
connected with neuron-network models. On a higher level are critical theories,
spin glass phase of Random Energy Model, percolation, self organized
criticality (SOC). The top level class involves HOT design, error threshold in
optimal coding, language, and, maybe, financial market. Alive systems are also
related with the last class. A concept of anti-resonance is suggested for the
complex systems.Comment: 17 page
Stochastic thermodynamics of quantum maps with and without equilibrium
We study stochastic thermodynamics for a quantum system of interest whose
dynamics are described by a completely positive trace-preserving (CPTP) map as
a result of its interaction with a thermal bath. We define CPTP maps with
equilibrium as CPTP maps with an invariant state such that the entropy
production due to the action of the map on the invariant state vanishes.
Thermal maps are a subgroup of CPTP maps with equilibrium. In general, for CPTP
maps, the thermodynamic quantities, such as the entropy production or work
performed on the system, depend on the combined state of the system plus its
environment. We show that these quantities can be written in terms of system
properties for maps with equilibrium. The relations that we obtain are valid
for arbitrary coupling strengths between the system and the thermal bath. The
fluctuations of thermodynamic quantities are considered in the framework of a
two-point measurement scheme. We derive the entropy production fluctuation
theorem for general maps and a fluctuation relation for the stochastic work on
a system that starts in the Gibbs state. Some simplifications for the
probability distributions in the case of maps with equilibrium are presented.
We illustrate our results by considering spin 1/2 systems under thermal maps,
non-thermal maps with equilibrium, maps with non-equilibrium steady states and
concatenations of them. Finally, we consider a particular limit in which the
concatenation of maps generates a continuous time evolution in Lindblad form
for the system of interest, and we show that the concept of maps with and
without equilibrium translates into Lindblad equations with and without quantum
detailed balance, respectively. The consequences for the thermodynamic
quantities in this limit are discussed.Comment: 17 pages, 4 figures; new section added, typos correcte
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