9,592 research outputs found
Fast and secure key distribution using mesoscopic coherent states of light
This work shows how two parties A and B can securely share sequences of
random bits at optical speeds. A and B possess true-random physical sources and
exchange random bits by using a random sequence received to cipher the
following one to be sent. A starting shared secret key is used and the method
can be described as an unlimited one-time-pad extender. It is demonstrated that
the minimum probability of error in signal determination by the eavesdropper
can be set arbitrarily close to the pure guessing level. Being based on the
-ry encryption protocol this method also allows for optical amplification
without security degradation, offering practical advantages over the BB84
protocol for key distribution.Comment: 11 pages and 4 figures. This version updates the one published in PRA
68, 052307 (2003). Minor changes were made in the text and one section on
Mutual Information was adde
The Stellar Content of Obscured Galactic Giant HII Regions. VI: W51A
We present K-band spectra of newly born OB stars in the obscured Galactic
giant H II region W51A and ~ 0.8'' angular resolution images in the J, H and
K_S-bands. Four objects have been spectroscopically classified as O-type stars.
The mean spectroscopic parallax of the four stars gives a distance of 2.0 \pm
0.3 kpc (error in the mean), significantly smaller than the radio recombination
line kinematic value of 5.5 kpc or the values derived from maser propermotion
observations (6--8 kpc). The number of Lyman continuum photons from the
contribution of all massive stars (NLyc ~ 1.5 x 10^{50} s^{-1}) is in good
agreement with that inferred from radio recombination lines (NLyc = 1.3 x
10^{50} s^{-1}) after accounting for the smaller distance derived here.
We present analysis of archival high angular resolution images (NAOS CONICA
at VLT and T-ReCS at Gemini) of the compact region W51 IRS2. The K_S--band
images resolve the infrared source IRS~2 indicating that it is a very young
compact HII region. Sources IRS2E was resolved into compact cluster (within 660
AU of projected distance) of 3 objects, but one of them is just bright extended
emission. W51d1 and W51d2 were identified with compact clusters of 3 objects
(maybe 4 in the case of W51d1) each one. Although IRS~2E is the brightest
source in the K-band and at 12.6 \micron, it is not clearly associated with a
radio continuum source. Our spectrum of IRS~2E shows, similar to previous work,
strong emission in Br and HeI, as well as three forbidden emission
lines of FeIII and emission lines of molecular hydrogen (H_2) marking it as a
massive young stellar object.Comment: 31 pages and 9 figures, submitted to A
Identificação de fungos em mudas de mangueiras apresentando morte súbita.
Suplemento. Edição dos Resumos do 44 Congresso Brasileiro de Fitopatologia, Bento Gonçalves, ago. 2011
Seca-da-mangueira detecção, sintomatologia e controle.
O cultivo da mangueira È uma das principais atividades agrícolas do polo de fruticultura Petrolina-PE/Juazeiro-BA, contribuindo com mais de 90% da exportação nacional de manga. Apesar do bom desempenho desse polo agrícola em relação as demais áreas produtoras do país, as ocorrências de doenças como antracnose, malformação floral e vegetativa e podridões causadas por diferentes patógenos vem se tornando cada vez mais relevantes, apesar de o clima semi-árido ser, na maior parte do ano, desfavorável alta incidência de doenças, quando comparado as outras regiões produtoras do país. Para que essa regi„o continue sendo o principal polo produtor/exportador no cenário nacional, é imprescindível que a qualidade fitossanitária do pomar seja resguardada
Network conduciveness with application to the graph-coloring and independent-set optimization transitions
We introduce the notion of a network's conduciveness, a probabilistically
interpretable measure of how the network's structure allows it to be conducive
to roaming agents, in certain conditions, from one portion of the network to
another. We exemplify its use through an application to the two problems in
combinatorial optimization that, given an undirected graph, ask that its
so-called chromatic and independence numbers be found. Though NP-hard, when
solved on sequences of expanding random graphs there appear marked transitions
at which optimal solutions can be obtained substantially more easily than right
before them. We demonstrate that these phenomena can be understood by resorting
to the network that represents the solution space of the problems for each
graph and examining its conduciveness between the non-optimal solutions and the
optimal ones. At the said transitions, this network becomes strikingly more
conducive in the direction of the optimal solutions than it was just before
them, while at the same time becoming less conducive in the opposite direction.
We believe that, besides becoming useful also in other areas in which network
theory has a role to play, network conduciveness may become instrumental in
helping clarify further issues related to NP-hardness that remain poorly
understood
Localizing gravity on thick branes: a solution for massive KK modes of the Schroedinger equation
We generate scalar thick brane configurations in a 5D Riemannian space time
which describes gravity coupled to a self-interacting scalar field. We also
show that 4D gravity can be localized on a thick brane which does not
necessarily respect Z_2-symmetry, generalizing several previous models based on
the Randall-Sundrum system and avoiding the restriction to orbifold geometries
as well as the introduction of the branes in the action by hand. We begin by
obtaining a smooth brane configuration that preserves 4D Poincar'e invariance
and violates reflection symmetry along the fifth dimension. The extra dimension
can have either compact or extended topology, depending on the values of the
parameters of the solution. In the non-compact case, our field configuration
represents a thick brane with positive energy density centered at y=c_2,
whereas in the compact case we get pairs of thick branes. We recast as well the
wave equations of the transverse traceless modes of the linear fluctuations of
the classical solution into a Schroedinger's equation form with a volcano
potential of finite bottom. We solve Schroedinger equation for the massless
zero mode m^2=0 and obtain a single bound wave function which represents a
stable 4D graviton and is free of tachyonic modes with m^2<0. We also get a
continuum spectrum of Kaluza-Klein (KK) states with m^2>0 that are suppressed
at y=c_2 and turn asymptotically into plane waves. We found a particular case
in which the Schroedinger equation can be solved for all m^2>0, giving us the
opportunity of studying analytically the massive modes of the spectrum of KK
excitations, a rare fact when considering thick brane configurations.Comment: 8 pages in latex. We corrected signs in the field equations, the
expressions for the scalar field and the self-interacting potential. Due to
the fact that no changes are introduced in the warp factor, the physics of
the system remains the sam
Can Virialization Shocks be Detected Around Galaxy Clusters Through the Sunyaev-Zel'dovich Effect?
In cosmological structure formation models, massive non-linear objects in the
process of formation, such as galaxy clusters, are surrounded by large-scale
shocks at or around the expected virial radius. Direct observational evidence
for such virial shocks is currently lacking, but we show here that their
presence can be inferred from future, high resolution, high-sensitivity
observations of the Sunyaev-Zel'dovich (SZ) effect in galaxy clusters. We study
the detectability of virial shocks in mock SZ maps, using simple models of
cluster structure (gas density and temperature distributions) and noise
(background and foreground galaxy clusters projected along the line of sight,
as well as the cosmic microwave background anisotropies). We find that at an
angular resolution of 2'' and sensitivity of 10 micro K, expected to be reached
at ~ 100 GHz frequencies in a ~ 20 hr integration with the forthcoming ALMA
instrument, virial shocks associated with massive M ~ 10^15 M_Sun clusters will
stand out from the noise, and can be detected at high significance. More
generally, our results imply that the projected SZ surface brightness profile
in future, high-resolution experiments will provide sensitive constraints on
the density profile of cluster gas.Comment: 15 pages, submitted to Ap
Efeito da temperatura no crescimento micelial de Fusicoccum aesculis isolado de mangueira.
Fusicoccum aesculis é um dos principais patógenos causadores de podridão em frutas de climas tropical e temperado. No Submédio do Vale do São Francisco, esse fungo, juntamente com outros, vem causando perdas em pós-colheita da manga. Objetivou-se, nesse trabalho, avaliar a influência da temperatura no crescimento desse fungo. Para tanto, o fungo foi cultivado em câmara de crescimento sob as temperaturas de 20 °C, 25 °C, 30 °C e 35 °C e fotoperíodo de 12 horas. O meio de cultivo utilizado foi o batata-dextrose-ágar (BDA), e o experimento instalado em delineamento experimental inteiramente casualizado com cinco repetições. Avaliou-se, a cada 24 horas, o crescimento das colônias em dois sentidos perpendiculares, com régua milimetrada, até que o crescimento micelial atingisse o bordo da placa em uma das temperaturas. Concluiu-se que temperaturas entre 20 °C e 25 °C são favoráveis ao crescimento de F. aesculis, mas temperaturas superiores a 25 °C afetam drasticamente o seu crescimento micelial
Lattice Model for water-solute mixtures
A lattice model for the study of mixtures of associating liquids is proposed.
Solvent and solute are modeled by adapting the associating lattice gas (ALG)
model. The nature of interaction solute/solvent is controlled by tuning the
energy interactions between the patches of ALG model. We have studied three set
of parameters, resulting on, hydrophilic, inert and hydrophobic interactions.
Extensive Monte Carlo simulations were carried out and the behavior of pure
components and the excess properties of the mixtures have been studied. The
pure components: water (solvent) and solute, have quite similar phase diagrams,
presenting: gas, low density liquid, and high density liquid phases. In the
case of solute, the regions of coexistence are substantially reduced when
compared with both the water and the standard ALG models. A numerical procedure
has been developed in order to attain series of results at constant pressure
from simulations of the lattice gas model in the grand canonical ensemble. The
excess properties of the mixtures: volume and enthalpy as the function of the
solute fraction have been studied for different interaction parameters of the
model. Our model is able to reproduce qualitatively well the excess volume and
enthalpy for different aqueous solutions. For the hydrophilic case, we show
that the model is able to reproduce the excess volume and enthalpy of mixtures
of small alcohols and amines. The inert case reproduces the behavior of large
alcohols such as, propanol, butanol and pentanol. For last case (hydrophobic),
the excess properties reproduce the behavior of ionic liquids in aqueous
solution.Comment: 28 pages, 13 figure
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