Nuclear isotope thermometry

We discuss different aspects which could influence temperatures deduced from experimental isotopic yields in the multifragmentation process. It is shown that fluctuations due to the finite size of the system and distortions due to the decay of hot primary fragments conspire to blur the temperature determination in multifragmentation reactions. These facts suggest that caloric curves obtained through isotope thermometers, which were taken as evidence for a first-order phase transition in nuclear matter, should be investigated very carefully.Comment: 9 pages, 7 figure

Apparent horizons in the quasi-spherical Szekeres models

The notion of an apparent horizon (AH) in a collapsing object can be carried over from the Lema\^{\i}tre -- Tolman (L--T) to the quasispherical Szekeres models in three ways: 1. Literally by the definition -- the AH is the boundary of the region, in which every bundle of null geodesics has negative expansion scalar. 2. As the locus, at which null lines that are as nearly radial as possible are turned toward decreasing areal radius $R$. These lines are in general nongeodesic. The name "absolute apparent horizon" (AAH) is proposed for this locus. 3. As the boundary of a region, where null \textit{geodesics} are turned toward decreasing $R$. The name "light collapse region" (LCR) is proposed for this region (which is 3-dimensional in every space of constant $t$); its boundary coincides with the AAH. The AH and AAH coincide in the L--T models. In the quasispherical Szekeres models, the AH is different from (but not disjoint with) the AAH. Properties of the AAH and LCR are investigated, and the relations between the AAH and the AH are illustrated with diagrams using an explicit example of a Szekeres metric. It turns out that an observer who is already within the AH is, for some time, not yet within the AAH. Nevertheless, no light signal can be sent through the AH from the inside. The analogue of the AAH for massive particles is also considered.Comment: 14 pages, 9 figures, includes little extensions and style corrections made after referee's comments, the text matches the published versio

Geometry of the quasi-hyperbolic Szekeres models

Geometric properties of the quasi-hyperbolic Szekeres models are discussed and related to the quasi-spherical Szekeres models. Typical examples of shapes of various classes of 2-dimensional coordinate surfaces are shown in graphs; for the hyperbolically symmetric subcase and for the general quasi-hyperbolic case. An analysis of the mass function $M(z)$ is carried out in parallel to an analogous analysis for the quasi-spherical models. This leads to the conclusion that $M(z)$ determines the density of rest mass averaged over the whole space of constant time.Comment: 19 pages, 13 figures. This version matches the published tex

Isotopic Scaling in Nuclear Reactions

A three parameter scaling relationship between isotopic distributions for elements with Z$\leq 8$ has been observed that allows a simple description of the dependence of such distributions on the overall isospin of the system. This scaling law (termed iso-scaling) applies for a variety of reaction mechanisms that are dominated by phase space, including evaporation, multifragmentation and deeply inelastic scattering. The origins of this scaling behavior for the various reaction mechanisms are explained. For multifragmentation processes, the systematics is influenced by the density dependence of the asymmetry term of the equation of state.Comment: 10 Pages, 2 Figure

Caracterização físico-química e funcional de diferentes genótipos de camu-camu (Myrciaria dubia (H.B.K.) Mc Vaugh).

O camu-camu é um fruto nativo da região Amazônica, sendo reconhecido como uma das maiores fontes de vitamina C na atualidade. Além dessa excepcional característica, apresenta em sua composição compostos bioativos que fazem deste fruto uma matéria-prima potencial para a indústria de alimentos. A Embrapa Amazônia Oriental possui um Banco Ativo de Germoplasma de camu-camu e a identificação de genótipos quanto às características físico-químicas e funcionais é importante no apoio ao melhoramento genético da espécie. Neste estudo, avaliaram-se oito genótipos (polpa e casca separadamente), sendo que dois foram ainda submetidos a um processamento, onde a casca foi incorporada a polpa. Os resultados quanto à caracterização físico-química mostraram que os genótipos indicaram médias de sólidos solúveis de 6,76 a 9,96ºBrix e pH de 2,53 a 3,13, caracterizando a forte acidez dos frutos (teores entre 2,13 a 3,24%). Quanto aos compostos bioativos, observou-se na polpa teores de vitamina C entre 11,73 a 36,17 g/100g e antocianinas totais de 12,66 a 131,64 mg/100g. A casca do camu-camu concentra a maior parte das antocianinas do fruto, com teores variando entre 16,07 a 174,74 mg/100g. Observou-se diferença significativa (Tukey p≤0,05) entre a maioria dos genótipos estudados e que o processamento proporcionou um aumento de antocianinas na polpa. Dessa forma, conclui-se que identificação de genótipos é importante para o lançamento de cultivares em potencial

A comparative study of model ingredients: fragmentation in heavy-ion collisions using quantum molecular dynamics model

We aim to understand the role of NN cross-sections, equation of state as well as different model ingredients such as width of Gaussian, clusterisation range and different clusterisation algorithms in multifragmentation using quantum molecular dynamics model. We notice that all model ingredients have sizable effect on the fragment pattern.Comment: 12 Pages, 4 Figure

Intersubband decay of 1-D exciton resonances in carbon nanotubes

We have studied intersubband decay of E22 excitons in semiconducting carbon nanotubes experimentally and theoretically. Photoluminescence excitation line widths of semiconducting nanotubes with chiral indicess (n, m) can be mapped onto a connectivity grid with curves of constant (n-m) and (2n+m). Moreover, the global behavior of E22 linewidths is best characterized by a strong increase with energy irrespective of their (n-m) mod(3)= \pm 1 family affiliation. Solution of the Bethe-Salpeter equations shows that the E22 linewidths are dominated by phonon assisted coupling to higher momentum states of the E11 and E12 exciton bands. The calculations also suggest that the branching ratio for decay into exciton bands vs free carrier bands, respectively is about 10:1.Comment: 4 pages, 4 figure