Phases of massive scalar field collapse

We study critical behavior in the collapse of massive spherically symmetric scalar fields. We observe two distinct types of phase transition at the threshold of black hole formation. Type II phase transitions occur when the radial extent $(\lambda)$ of the initial pulse is less than the Compton wavelength ($\mu^{-1}$) of the scalar field. The critical solution is that found by Choptuik in the collapse of massless scalar fields. Type I phase transitions, where the black hole formation turns on at finite mass, occur when $\lambda \mu \gg 1$. The critical solutions are unstable soliton stars with masses \alt 0.6 \mu^{-1}. Our results in combination with those obtained for the collapse of a Yang-Mills field~{[M.~W. Choptuik, T. Chmaj, and P. Bizon, Phys. Rev. Lett. 77, 424 (1996)]} suggest that unstable, confined solutions to the Einstein-matter equations may be relevant to the critical point of other matter models.Comment: 5 pages, RevTex, 4 postscript figures included using psfi

Strong curvature singularities in quasispherical asymptotically de Sitter dust collapse

We study the occurrence, visibility, and curvature strength of singularities in dust-containing Szekeres spacetimes (which possess no Killing vectors) with a positive cosmological constant. We find that such singularities can be locally naked, Tipler strong, and develop from a non-zero-measure set of regular initial data. When examined along timelike geodesics, the singularity's curvature strength is found to be independent of the initial data.Comment: 16 pages, LaTeX, uses IOP package, 2 eps figures; accepted for publication in Class. Quantum Gra

Expressão de genes de resistência em resposta à infecção por nematóides.

A identificação de genes relacionados com a resistência de plantas a pragas e doenças é de grande importância para o entendimento dos mecanismos de defesa envolvidos durante o ataque de patógenos. Atualmente, vários desses genes, identificados em diferentes espécies vegetais, já foram caracterizados ao nível molecular e suas seqüências estão disponíveis em Bancos de Dados. Atualmente, com a conclusão do sequenciamento do Genoma Café, homólogos de genes de defesa tiveram suas seqüências estabelecidas. No entanto, estudos de genômica funcional são necessários para que o papel destes genes no mecanismo de resistência aos patógenos do café seja conhecido. Este trabalho tem como objetivo inicial caracterizar os mecanismos de defesa em café, através da identificação e avaliação da expressão de genes relacionados com a resistência a nematóides. Foram realizadas buscas de seqüências homólogas a genes de defesa no Banco de Dados do Genoma Café através do programa BLAST e foram identificados genes pertencentes a 12 categorias de genes de defesa. Em experimentos de infecção controlada, raízes de cafeeiros suscetíveis e resistentes foram infectadas pelo nematóide Meloidogyne exigua. Amostras de RNA extraído destas raízes serviram como molde para amplificação de transcritos correspondentes a 6 genes de resistência. Os resultados mostram que os genes avaliados neste estudo apresentam uma expressão basal em raízes infectadas pelo nematóide, sugerindo que a ativação da resposta de defesa é controlada por outras famílias de genes não testadas neste estudo

Training deep neural density estimators to identify mechanistic models of neural dynamics

Mechanistic modeling in neuroscience aims to explain observed phenomena in terms of underlying causes. However, determining which model parameters agree with complex and stochastic neural data presents a significant challenge. We address this challenge with a machine learning tool which uses deep neural density estimators-- trained using model simulations-- to carry out Bayesian inference and retrieve the full space of parameters compatible with raw data or selected data features. Our method is scalable in parameters and data features, and can rapidly analyze new data after initial training. We demonstrate the power and flexibility of our approach on receptive fields, ion channels, and Hodgkin-Huxley models. We also characterize the space of circuit configurations giving rise to rhythmic activity in the crustacean stomatogastric ganglion, and use these results to derive hypotheses for underlying compensation mechanisms. Our approach will help close the gap between data-driven and theory-driven models of neural dynamics

Black hole formation from massive scalar fields

It is shown that there exists a range of parameters in which gravitational collapse with a spherically symmetric massive scalar field can be treated as if it were collapsing dust. This implies a criterion for the formation of black holes depending on the size and mass of the initial field configuration and the mass of the scalar field.Comment: 11 pages, RevTeX, 3 eps figures. Submitted to Class. Quantum Gra

Electronic effects on C-O-C ether bonds in 3-aryloxy derivatives of benzisothiazole 1,1-dioxides: rapid ethanolysis of 3-(4-nitrophenoxy)-1,2-benzisothiazole 1,1-dioxide, (1), to give 3-ethoxy-1,2-benzisothiazole 1,1-dioxide, (2)

The bond lengths in the central C-O-C ether linkage of title compound (1), C13H8N2O5S, are comparable with those found in earlier work on similar compounds. However, (1) was found to undergo very easy solvolysis with ethanol to give (2), C9H9NO3S, for which a structure was also determined, but 3-(4-methoxyphenoxy)-1,2-benzisothiazole 1,1-dioxide, (3), did not hydrolyse under the same conditions. If ground-state structures are important for solvolysis, these results suggest that there should be a difference in the corresponding C-O bond lengths for the ethers (1) and (3). Such differences are not observed. The results can be rationalized by supposing that transition-state energies for ethanolysis are more important factors than those of the ground state.info:eu-repo/semantics/publishedVersio

Relativistic shells: Dynamics, horizons, and shell crossing

We consider the dynamics of timelike spherical thin matter shells in vacuum. A general formalism for thin shells matching two arbitrary spherical spacetimes is derived, and subsequently specialized to the vacuum case. We first examine the relative motion of two dust shells by focusing on the dynamics of the exterior shell, whereby the problem is reduced to that of a single shell with different active Schwarzschild masses on each side. We then examine the dynamics of shells with non-vanishing tangential pressure $p$, and show that there are no stable--stationary, or otherwise--solutions for configurations with a strictly linear barotropic equation of state, $p=\alpha\sigma$, where $\sigma$ is the proper surface energy density and $\alpha\in(-1,1)$. For {\em arbitrary} equations of state, we show that, provided the weak energy condition holds, the strong energy condition is necessary and sufficient for stability. We examine in detail the formation of trapped surfaces, and show explicitly that a thin boundary layer causes the apparent horizon to evolve discontinuously. Finally, we derive an analytical (necessary and sufficient) condition for neighboring shells to cross, and compare the discrete shell model with the well-known continuous Lema\^{\i}tre-Tolman-Bondi dust case.Comment: 25 pages, revtex4, 4 eps figs; published in Phys. Rev.

Flexor digitorum brevis tendon transfer to the flexor digitorum longus tendon according to Valtin in posttraumatic flexible claw toe deformity due to extrinsic toe flexor shortening

AbstractClaw toe deformity after posterior leg compartment syndrome is rare but incapacitating. When the mechanism is flexor digitorum longus (FDL) shortening due to ischemic contracture of the muscle after posterior leg syndrome, a good treatment option is the Valtin procedure in which the flexor digitorum brevis (FDB) is transferred to the FDL after FDL tenotomy. The Valtin procedure reduces the deformity by lengthening and reactivating the FDL. Here, we report the outcomes of FDB to FDL transfer according to Valtin in 10 patients with posttraumatic claw toe deformity treated a mean of 34 months after the injury. Toe flexion was restored in all 10 patients, with no claw toe deformity even during dorsiflexion of the ankle