2,779 research outputs found
Chaos in computer performance
Modern computer microprocessors are composed of hundreds of millions of
transistors that interact through intricate protocols. Their performance during
program execution may be highly variable and present aperiodic oscillations. In
this paper, we apply current nonlinear time series analysis techniques to the
performances of modern microprocessors during the execution of prototypical
programs. Our results present pieces of evidence strongly supporting that the
high variability of the performance dynamics during the execution of several
programs display low-dimensional deterministic chaos, with sensitivity to
initial conditions comparable to textbook models. Taken together, these results
show that the instantaneous performances of modern microprocessors constitute a
complex (or at least complicated) system and would benefit from analysis with
modern tools of nonlinear and complexity science
The uses of Connes and Kreimer's algebraic formulation of renormalization theory
We show how, modulo the distinction between the antipode and the "twisted" or
"renormalized" antipode, Connes and Kreimer's algebraic paradigm trivializes
the proofs of equivalence of the (corrected) Dyson-Salam,
Bogoliubov-Parasiuk-Hepp and Zimmermann procedures for renormalizing Feynman
amplitudes. We discuss the outlook for a parallel simplification of
computations in quantum field theory, stemming from the same algebraic
approach.Comment: 15 pages, Latex. Minor changes, typos fixed, 2 references adde
Anomalies and Schwinger terms in NCG field theory models
We study the quantization of chiral fermions coupled to generalized Dirac
operators arising in NCG Yang-Mills theory. The cocycles describing chiral
symmetry breaking are calculated. In particular, we introduce a generalized
locality principle for the cocycles. Local cocycles are by definition
expressions which can be written as generalized traces of operator commutators.
In the case of pseudodifferential operators, these traces lead in fact to
integrals of ordinary local de Rham forms. As an application of the general
ideas we discuss the case of noncommutative tori. We also develop a gerbe
theoretic approach to the chiral anomaly in hamiltonian quantization of NCG
field theory.Comment: 30 page
Local covariant quantum field theory over spectral geometries
A framework which combines ideas from Connes' noncommutative geometry, or
spectral geometry, with recent ideas on generally covariant quantum field
theory, is proposed in the present work. A certain type of spectral geometries
modelling (possibly noncommutative) globally hyperbolic spacetimes is
introduced in terms of so-called globally hyperbolic spectral triples. The
concept is further generalized to a category of globally hyperbolic spectral
geometries whose morphisms describe the generalization of isometric embeddings.
Then a local generally covariant quantum field theory is introduced as a
covariant functor between such a category of globally hyperbolic spectral
geometries and the category of involutive algebras (or *-algebras). Thus, a
local covariant quantum field theory over spectral geometries assigns quantum
fields not just to a single noncommutative geometry (or noncommutative
spacetime), but simultaneously to ``all'' spectral geometries, while respecting
the covariance principle demanding that quantum field theories over isomorphic
spectral geometries should also be isomorphic. It is suggested that in a
quantum theory of gravity a particular class of globally hyperbolic spectral
geometries is selected through a dynamical coupling of geometry and matter
compatible with the covariance principle.Comment: 21 pages, 2 figure
Non-commutative geometry and the standard model vacuum
The space of Dirac operators for the Connes-Chamseddine spectral action for
the standard model of particle physics coupled to gravity is studied. The model
is extended by including right-handed neutrino states, and the S0-reality axiom
is not assumed. The possibility of allowing more general fluctuations than the
inner fluctuations of the vacuum is proposed. The maximal case of all possible
fluctuations is studied by considering the equations of motion for the vacuum.
Whilst there are interesting non-trivial vacua with Majorana-like mass terms
for the leptons, the conclusion is that the equations are too restrictive to
allow solutions with the standard model mass matrix.Comment: 21 pages. v2: some comments improve
Entrainment response of bed sediment to time-varying flows
Unsteady flows are ubiquitous in nature. In order to understand the behavior of sediment when subjected to unsteady flows, a set of experiments was performed in a rectangular duct with a mobile bed. A computer-operated vale governed the velocity of the water in the duct, and the flow velocity, wall shear stress, and vertical distribution of suspended sediment were simultaneously measured. Beds composed of 120 um and 580 um diameter sand were investigated. Both quasi-steady flows and pulse flows were investigated. Both quasi-steady flows and pulse flows were simulated in the duct. For the pulse flows the water was accelerated at a constant rate to a peak velocity and then decelerated at a constant rate to zero velocity. Phase lags were observed between the bed shear stress and the upward flux (entertainment) of sand from the bed. The phase lags were larger for tests with fine sand than for tests with coarse sand. Differences were attributed to differences in the bed roughness and flow Reynolds numbers. Relations based on flow acceleration and sediment size were developed for predicting the entertainment phase lag. Large phase lags can have a considerable impact on the amount of sediment transported by boat wakes, and other unsteady flows
Entrainment response of bed sediment to time-varying flows
Unsteady flows are ubiquitous in nature. In order to understand the behavior of sediment when subjected to unsteady flows, a set of experiments was performed in a rectangular duct with a mobile bed. A computer-operated vale governed the velocity of the water in the duct, and the flow velocity, wall shear stress, and vertical distribution of suspended sediment were simultaneously measured. Beds composed of 120 um and 580 um diameter sand were investigated. Both quasi-steady flows and pulse flows were investigated. Both quasi-steady flows and pulse flows were simulated in the duct. For the pulse flows the water was accelerated at a constant rate to a peak velocity and then decelerated at a constant rate to zero velocity. Phase lags were observed between the bed shear stress and the upward flux (entertainment) of sand from the bed. The phase lags were larger for tests with fine sand than for tests with coarse sand. Differences were attributed to differences in the bed roughness and flow Reynolds numbers. Relations based on flow acceleration and sediment size were developed for predicting the entertainment phase lag. Large phase lags can have a considerable impact on the amount of sediment transported by boat wakes, and other unsteady flows
Recent Development in Palladium-Catalyzed Domino Reactions: Access to Materials and Biologically Important Carbo- and Heterocycles
The chemistry of palladium complexes has no limits. Many domino processes (even multicomponent) are continuously appearing in the literature. Carbocyclic and heterocyclic molecules are efficiently prepared under the atom-economy principle using the smallest amount of the catalyst. The importance of the applications in many scientific areas of all of these cyclic skeletons made this general methodology much more attractive.We gratefully acknowledge financial support from the Spanish Ministerio de EconomĂa y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC), the Spanish Ministerio de EconomĂa, Industria y Competitividad, Agencia Estatal de InvestigaciĂłn (AEI), and Fondo Europeo de Desarrollo Regional (FEDER, EU) (projects CTQ2016-76782-P and CTQ2016-81797-REDC), the Generalitat Valenciana (PROMETEOII/2014/017), University of Alicante and Mersin University (Project. MEU-2017-COL-01007-M150D)
Comparison of efficacy and modes of action of two high-potential biocontrol Bacillus strains and commercial biocontrol products against Botrytis cinerea in table grapes
In table grapes (cv. Thomson Seedless), the antifungal activity against Botrytis cinerea was further analysed and compared between two high potential bacterial biological control agent (BCA) strains, Bacillus velezensis BUZ-14 and B. ginsengihumi S38. Two commercial biocontrol products (BPs), served as standards of comparison, Amylo-X (R) and Serenade Max (R), also based on Bacillus BCA strains. The main mode of action quantified for all the strains was antibiosis due to hydrosoluble and volatile metabolites and their combinations. The BUZ-14 strain was the most active BCA strain, demonstrating significant disease reduction exceeding 60 % when used in the culture form grown in 863 medium, including living cells (LCs) and cell-free supernatant (CFS). Both BPs exhibited significantly reduced efficacy of their CFS fraction (< 10 %) compared with that of the two BCA strains, confirming their high antibiosis potential. The novel methodology allowed us to demonstrate the significant effect of the BCA culture medium on volatilome (VOC) antagonist efficacy. The S38 strain achieved the highest disease reduction (90 %) owing to the greatest production of VOCs in the richest MOLP (Medium Optimum Lipopetide Production) culture medium, whereas grape juice was the least favourable medium for VOC efficacy for both bacterial strains (BUZ14 and S38). The overall poor activity of living Bacillus cells in all the BCA and BPs tested is discussed based on the low capacity of the BCA strains to grow in the berry. Then, the presence of living cells is also discussed with the possibility that these cells are not required in field applications of such BCA strains in this genus. Moreover, different environmental suboptimal conditions, including temperature (22 and 27 degrees C) and relative humidity (RH) (100 and 85-95 %), were tested, and BUZ-14 exhibited the highest Botrytis reduction at both temperatures and RH values. However, no significant differences were observed between temperatures or RH values for the same BCA. Further studies in vineyard conditions and applications, such as biofumigation or active packaging, will be performed to confirm the new findings reported in this investigation
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