23,295 research outputs found
A Number-Theoretic Error-Correcting Code
In this paper we describe a new error-correcting code (ECC) inspired by the
Naccache-Stern cryptosystem. While by far less efficient than Turbo codes, the
proposed ECC happens to be more efficient than some established ECCs for
certain sets of parameters. The new ECC adds an appendix to the message. The
appendix is the modular product of small primes representing the message bits.
The receiver recomputes the product and detects transmission errors using
modular division and lattice reduction
Asymptotically Universal Crossover in Perturbation Theory with a Field Cutoff
We discuss the crossover between the small and large field cutoff (denoted
x_{max}) limits of the perturbative coefficients for a simple integral and the
anharmonic oscillator. We show that in the limit where the order k of the
perturbative coefficient a_k(x_{max}) becomes large and for x_{max} in the
crossover region, a_k(x_{max}) is proportional to the integral from -infinity
to x_{max} of e^{-A(x-x_0(k))^2}dx. The constant A and the function x_0(k) are
determined empirically and compared with exact (for the integral) and
approximate (for the anharmonic oscillator) calculations. We discuss how this
approach could be relevant for the question of interpolation between
renormalization group fixed points.Comment: 15 pages, 11 figs., improved and expanded version of hep-th/050304
Germination and Growth of Native and Invasive Plants on Soil Associated with Biological Control of Tamarisk (Tamarix spp.)
Introductions of biocontrol beetles (tamarisk beetles) are causing dieback of exotic tamarisk in riparian zones across the western United States, yet factors that determine plant communities that follow tamarisk dieback are poorly understood. Tamarisk-dominated soils are generally higher in nutrients, organic matter, and salts than nearby soils, and these soil attributes might influence the trajectory of community change. To assess physical and chemical drivers of plant colonization after beetle-induced tamarisk dieback, we conducted separate germination and growth experiments using soil and litter collected beneath defoliated tamarisk trees. Focal species were two common native (red threeawn, sand dropseed) and two common invasive exotic plants (Russian knapweed, downy brome), planted alone and in combination. Nutrient, salinity, wood chip, and litter manipulations examined how tamarisk litter affects the growth of other species in a context of riparian zone management. Tamarisk litter, tamarisk litter leachate, and fertilization with inorganic nutrients increased growth in all species, but the effect was larger on the exotic plants. Salinity of 4 dS m 1 benefitted Russian knapweed, which also showed the largest positive responses to added nutrients. Litter and wood chips generally delayed and decreased germination; however, a thinner layer of wood chips increased growth slightly. Time to germination was lengthened by most treatments for natives, was not affected in exotic Russian knapweed, and was sometimes decreased in downy brome. Because natives showed only small positive responses to litter and fertilization and large negative responses to competition, Russian knapweed and downy brome are likely to perform better than these two native species following tamarisk dieback
Quantum cosmology of scalar-tensor theories and self-adjointness
In this paper, the problem of the self-adjointness for the case of a quantum
minisuperspace Hamiltonian retrieved from a Brans-Dicke (BD) action is
investigated. Our matter content is presented in terms of a perfect fluid, onto
which the Schutz's formalism will be applied. We use the von Neumann theorem
and the similarity with the Laplacian operator in one of the variables to
determine the cases where the Hamiltonian is self-adjoint and if it admits
self-adjoint extensions. For the latter, we study which extension is physically
more suitable.Comment: Latex file, 12 pages. Small changes made in the paper, and a a new
appendix adde
Modeling Bitcoin Contracts by Timed Automata
Bitcoin is a peer-to-peer cryptographic currency system. Since its
introduction in 2008, Bitcoin has gained noticeable popularity, mostly due to
its following properties: (1) the transaction fees are very low, and (2) it is
not controlled by any central authority, which in particular means that nobody
can "print" the money to generate inflation. Moreover, the transaction syntax
allows to create the so-called contracts, where a number of
mutually-distrusting parties engage in a protocol to jointly perform some
financial task, and the fairness of this process is guaranteed by the
properties of Bitcoin. Although the Bitcoin contracts have several potential
applications in the digital economy, so far they have not been widely used in
real life. This is partly due to the fact that they are cumbersome to create
and analyze, and hence risky to use.
In this paper we propose to remedy this problem by using the methods
originally developed for the computer-aided analysis for hardware and software
systems, in particular those based on the timed automata. More concretely, we
propose a framework for modeling the Bitcoin contracts using the timed automata
in the UPPAAL model checker. Our method is general and can be used to model
several contracts. As a proof-of-concept we use this framework to model some of
the Bitcoin contracts from our recent previous work. We then automatically
verify their security in UPPAAL, finding (and correcting) some subtle errors
that were difficult to spot by the manual analysis. We hope that our work can
draw the attention of the researchers working on formal modeling to the problem
of the Bitcoin contract verification, and spark off more research on this
topic
Parasitism, Adult Emergence, Sex Ratio, and Size of \u3ci\u3eAphidius Colemani\u3c/i\u3e (Hymenoptera: Aphidiidae) on Several Aphid Species
Aphidius colemani Viereck parasitizes several economically important aphid pests of small grain crops including the greenbug, Schizaphis graminum and the Russian wheat aphid, Diuraphis noxia. The ability of A. colemani to switch from S. graminum to several species of aphids common to agricultural and associated non-agricultural ecosystems in the Great Plains, and the effects of host-change on several biological parameters that influence population growth rate were determined. Female A. colemani parasitized and developed to adulthood in nine of 14 aphid species to which they were exposed in the laboratory. All small grain feeding aphids except Sipha flava were parasiÂtized. Two sunflower feeding species (Aphis nerii and A. helianthi) and two crucifer feeding species (Lipaphis erysimi and Brevicoryne brassicae) were parasitized, as was the cotton aphid. Aphis gossypii. The average percentage of aphids parasitized differed significantly among host aphid species. as did the percentage of parasitoids surviving from the mummy to the adult stage and the time required for immature development. The sex ratio of adults that enclosed from the various hosts did not differ significantly among species. Dry weights of adult parasitoids differed significantly among host species. Adults from S. graminum weighed most (0.054 mg) while those emerging from A. helianthi weighed least (0.020 mg). Results are discussed in terms of strategies for classical biological control of aphid pests of cereals
Exact solution of the Schrodinger equation with the spin-boson Hamiltonian
We address the problem of obtaining the exact reduced dynamics of the
spin-half (qubit) immersed within the bosonic bath (enviroment). An exact
solution of the Schrodinger equation with the paradigmatic spin-boson
Hamiltonian is obtained. We believe that this result is a major step ahead and
may ultimately contribute to the complete resolution of the problem in
question. We also construct the constant of motion for the spin-boson system.
In contrast to the standard techniques available within the framework of the
open quantum systems theory, our analysis is based on the theory of block
operator matrices.Comment: 9 pages, LaTeX, to appear in Journal of Physics A: Mathematical and
Theoretica
Wave operator bounds for 1-dimensional Schr\"odinger operators with singular potentials and applications
Boundedness of wave operators for Schr\"odinger operators in one space
dimension for a class of singular potentials, admitting finitely many Dirac
delta distributions, is proved. Applications are presented to, for example,
dispersive estimates and commutator bounds.Comment: 16 pages, 0 figure
Classical artificial two-dimensional atoms: the Thomson model
The ring configurations for classical two-dimensional atoms are calculated
within the Thomson model and compared with the results from `exact' numerical
simulations. The influence of the functional form of the confinement potential
and the repulsive interaction potential between the particles on the
configurations is investigated. We also give exact results on those eigenmodes
of the system whose frequency does not depend on the number of particles in the
system.Comment: 9 pages, RevTeX, 4 figure
Exchange bias and interface electronic structure in Ni/Co3O4(011)
A detailed study of the exchange bias effect and the interfacial electronic
structure in Ni/Co3O4(011) is reported. Large exchange anisotropies are
observed at low temperatures, and the exchange bias effect persists to
temperatures well above the Neel temperature of bulk Co3O4, of about 40 K: to
~80 K for Ni films deposited on well ordered oxide surfaces, and ~150 K for Ni
films deposited on rougher Co3O4 surfaces. Photoelectron spectroscopy
measurements as a function of Ni thickness show that Co reduction and Ni
oxidation occur over an extended interfacial region. We conclude that the
exchange bias observed in Ni/Co3O4, and in similar ferromagnetic metallic/Co3O4
systems, is not intrinsic to Co3O4 but rather due to the formation of CoO at
the interface.Comment: 8 pages, 6 figures. Accepted for publication in Physical Review B
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