5,938 research outputs found
On a zero speed sensitive cellular automaton
Using an unusual, yet natural invariant measure we show that there exists a
sensitive cellular automaton whose perturbations propagate at asymptotically
null speed for almost all configurations. More specifically, we prove that
Lyapunov Exponents measuring pointwise or average linear speeds of the faster
perturbations are equal to zero. We show that this implies the nullity of the
measurable entropy. The measure m we consider gives the m-expansiveness
property to the automaton. It is constructed with respect to a factor dynamical
system based on simple "counter dynamics". As a counterpart, we prove that in
the case of positively expansive automata, the perturbations move at positive
linear speed over all the configurations
Dispersive fields in de Sitter space and event horizon thermodynamics
When Lorentz invariance is violated at high energy, the laws of black hole
thermodynamics are apparently no longer satisfied. To shed light on this
observation, we study dispersive fields in de Sitter space. We show that the
Bunch-Davies vacuum state restricted to the static patch is no longer thermal,
and that the Tolman law is violated. However we also show that, for free fields
at least, this vacuum is the only stationary stable state, as if it were in
equilibrium. We then present a precise correspondence between dispersive
effects found in de Sitter and in black hole metrics. This indicates that the
consequences of dispersion on thermodynamical laws could also be similar.Comment: 19 pages. Black and White version on Phys.Rev.D serve
Processing The Interspecies Quorum-Sensing Signal Autoinducer-2 (AI-2) Characterization Of Phospho-(S)-4,5-Dihydroxy-2,3-Pentanedione Isomerization By LsrG Protein
The molecule (S)-4,5-dihydroxy-2,3-pentanedione (DPD) is produced by many different species of bacteria and is the precursor of the signal molecule autoinducer-2 (AI-2). AI-2 mediates interspecies communication and facilitates regulation of bacterial behaviors such as biofilm formation and virulence. A variety of bacterial species have the ability to sequester and process the AI-2 present in their environment, thereby interfering with the cell-cell communication of other bacteria. This process involves the AI-2-regulated lsr operon, comprised of the Lsr transport system that facilitates uptake of the signal, a kinase that phosphorylates the signal to phospho-DPD (P-DPD), and enzymes (like LsrG) that are responsible for processing the phosphorylated signal. Because P-DPD is the intracellular inducer of the lsr operon, enzymes involved in P-DPD processing impact the levels of Lsr expression. Here we show that LsrG catalyzes isomerization of P-DPD into 3,4,4-trihydroxy-2-pentanone-5-phosphate. We present the crystal structure of LsrG, identify potential catalytic residues, and determine which of these residues affects P-DPD processing in vivo and in vitro. We also show that an lsrG deletion mutant accumulates at least 10 times more P-DPD than wild type cells. Consistent with this result, we find that the lsrG mutant has increased expression of the lsr operon and an altered profile of AI-2 accumulation and removal. Understanding of the biochemical mechanisms employed by bacteria to quench signaling of other species can be of great utility in the development of therapies to control bacterial behavior
Connections and dynamical trajectories in generalised Newton-Cartan gravity I. An intrinsic view
The "metric" structure of nonrelativistic spacetimes consists of a one-form
(the absolute clock) whose kernel is endowed with a positive-definite metric.
Contrarily to the relativistic case, the metric structure and the torsion do
not determine a unique Galilean (i.e. compatible) connection. This subtlety is
intimately related to the fact that the timelike part of the torsion is
proportional to the exterior derivative of the absolute clock. When the latter
is not closed, torsionfreeness and metric-compatibility are thus mutually
exclusive. We will explore generalisations of Galilean connections along the
two corresponding alternative roads in a series of papers. In the present one,
we focus on compatible connections and investigate the equivalence problem
(i.e. the search for the necessary data allowing to uniquely determine
connections) in the torsionfree and torsional cases. More precisely, we
characterise the affine structure of the spaces of such connections and display
the associated model vector spaces. In contrast with the relativistic case, the
metric structure does not single out a privileged origin for the space of
metric-compatible connections. In our construction, the role of the Levi-Civita
connection is played by a whole class of privileged origins, the so-called
torsional Newton-Cartan (TNC) geometries recently investigated in the
literature. Finally, we discuss a generalisation of Newtonian connections to
the torsional case.Comment: 79 pages, 7 figures; v2: added material on affine structure of
connection space, former Section 4 postponed to 3rd paper of the serie
Conformal invariance studies of the Baxter-Wu model and a related site-colouring problem
The partition function of the Baxter-Wu model is exactly related to the
generating function of a site-colouring problem on a hexagonal lattice. We
extend the original Bethe ansatz solution of these models in order to obtain
the eigenspectra of their transfer matrices in finite geometries and general
toroidal boundary conditions. The operator content of these models are studied
by solving numerically the Bethe-ansatz equations and by exploring conformal
invariance. Since the eigenspectra are calculated for large lattices, the
corrections to finite-size scaling are also calculated.Comment: 12 pages, latex, to appear in J. Phys. A: Gen. Mat
Biomassa vegetal, estoques de carbono e macronutrientes de adubos verdes usados na produção orgânica de abacaxi na Chapada Diamantina, BA.
A adubação verde pode ser uma alternativa ao preparo inicial do solo para o cultivo orgânico do abacaxizeiro. O objetivo deste estudo foi avaliar a produção de biomassa vegetal e os estoques de carbono e macronutrientes na matéria seca de diferentes espécies de adubos verdes, em cultivos solteiro ou consorciado, em área destinada ao cultivo orgânico de abacaxi na região da Chapada Diamantina, Estado da Bahia. Os tratamentos avaliados foram os cultivos das seguintes espécies: crotalária (Crotalaria ochroleuca G.Don), feijão-de-porco (Canavalia ensiformis (L.) DC.), milheto (Pennisetum glaucum R.Br), mucuna (Mucuna pruriens (L.) DC), sorgo forrageiro (Sorghum bicolor (L.) Moench), e a combinação mucuna + sorgo (50%). Foram determinados a produção de biomassa vegetal, os estoques de C e macronutrientes na matéria seca e os teores de C orgânico total do solo. A produção de matéria seca variou de 3.23 a 6.56 t ha-1. Os estoques de C na matéria seca (Figura 2) foram relativamente semelhantes entre os tratamentos e variaram de 1,34 a 2,84 t ha-1. Os tratamentos envolvendo gramíneas (Milheto e Sorgo) apresentaram um incremento médio de 0,9 t C ha-1 em relação às leguminosas. O milheto mostrou-se uma importante recicladora de P e K e com elevado potencial para manter a cobertura do solo. O feijão-de-porco pode ser considerada uma importante recicladora de Ca, Mg e S. A combinação 50% mucuna+sorgo é uma estratégia de manejo mais desejável em comparação ao cultivo solteiro de mucuna ou sorgo
Disk-Loss and Disk Renewal Phases in Classical Be Stars II. Detailed Analysis of Spectropolarimetric Data
In Wisniewski et al. 2010, paper I, we analyzed 15 years of spectroscopic and
spectropolarimetric data from the Ritter and Pine Bluff Observatories of 2 Be
stars, 60 Cygni and {\pi} Aquarii, when a transition from Be to B star
occurred. Here we anaylize the intrinsic polarization, where we observe
loop-like structures caused by the rise and fall of the polarization Balmer
Jump and continuum V-band polarization being mismatched temporally with
polarimetric outbursts. We also see polarization angle deviations from the
mean, reported in paper I, which may be indicative of warps in the disk, blobs
injected at an inclined orbit, or spiral density waves. We show our ongoing
efforts to model time dependent behavior of the disk to constrain the
phenomena, using 3D Monte Carlo radiative transfer codes.Comment: 2 pages, 6 figures, IAU Symposium 27
Características relativas ao crescimento em meio de cultura e a morfologia de colônias de "rizóbio".
Caracterização morfológica dos isolados. Tempo de crescimento. Alteração no pH do meio de cultura. Diâmetro das colônias. Transparência e forma das colônias. Superfície das colônias. Produção, consistência e aparência do muco.bitstream/CNPAB-2010/27144/1/cot019.pd
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