First detection of CF+ towards a high-mass protostar

We report the first detection of the J = 1 - 0 (102.6 GHz) rotational lines of CF+ (fluoromethylidynium ion) towards CygX-N63, a young and massive protostar of the Cygnus X region. This detection occurred as part of an unbiased spectral survey of this object in the 0.8-3 mm range, performed with the IRAM 30m telescope. The data were analyzed using a local thermodynamical equilibrium model (LTE model) and a population diagram in order to derive the column density. The line velocity (-4 km s-1) and line width (1.6 km s-1) indicate an origin from the collapsing envelope of the protostar. We obtain a CF+ column density of 4.10e11 cm-2. The CF+ ion is thought to be a good tracer for C+ and assuming a ratio of 10e-6 for CF+/C+, we derive a total number of C+ of 1.2x10e53 within the beam. There is no evidence of carbon ionization caused by an exterior source of UV photons suggesting that the protostar itself is the source of ionization. Ionization from the protostellar photosphere is not efficient enough. In contrast, X-ray ionization from the accretion shock(s) and UV ionization from outflow shocks could provide a large enough ionizing power to explain our CF+ detection. Surprisingly, CF+ has been detected towards a cold, massive protostar with no sign of an external photon dissociation region (PDR), which means that the only possibility is the existence of a significant inner source of C+. This is an important result that opens interesting perspectives to study the early development of ionized regions and to approach the issue of the evolution of the inner regions of collapsing envelopes of massive protostars. The existence of high energy radiations early in the evolution of massive protostars also has important implications for chemical evolution of dense collapsing gas and could trigger peculiar chemistry and early formation of a hot core.Comment: 6 page

Efeito do cruzamento entre linhas diploides e tetraploides de melancia na producao de sementes hibridas.

Os hibridos triploides de melancia, apesar de crescentemente preferidos nos principais mercados consumidores dos EUA, Uniao Europeia e Japao, apresentam elevado preco da semente e problemas de germinacao. Correntemente, os mesmos sao produzidos pelo cruzamento de linhas diploides como fornecedoras de polen com linhas tetraploides. Em um experimento realizado em casa de vegetacao na Embrapa Semi- Arido, amostras de 20 sementes de uma linha parcialmente endogamica e da populacao Charleston Tetra Numero 3 (CT3) foram postas para germinar utilizando substrato comercial "Plantmax"para hortalicas e posteriormente transplantadas para sacos plasticos de 20 litros de solo, 15 apos o semeio. As plantas foram tutoradas e os ramos foram amarrados com fita plastica a medida que se desenvolveram. Quando as plantas iniciaram o florescimento foram feitos cruzamentos entre a linha diploide e a cultivar CT3 nos dois sentidos. Depois da colheita as sementes foram extraidas e postas para secar a sombra. De cada cruzamento foi retirada uma amostra de dez sementes para verificar a presenca de embrioes, que uma vez encontrados foram postos para germinar em condicoes de laboratorio. Observou-se que sementes triploides podem ser obtidas em cruzamentos envolvendo linhas diploides, resistente ao oidio, com plantas da populacao tetraploide CT3, nos dois sentidos. Foi observado que existe uma capacidade especifica de combinacao entre plantas diploides e tetraploides para formacao de sementes com embrioes, bem como, para a germinacao dos embrioes formados. Esta especificidade na combinacao entre plantas diploides e tetraploides, deve ser levada em conta no programa de melhoramento de melancia para o desenvolvimento de hibridos triploides.Suplemento. Edição do 41 Congresso Brasileiro de Olericultura; 1 Encontro sobre Plantas Medicinais, Aromáticas e Condimentares, Brasília, DF, jul. 2001

On a generalised model for time-dependent variance with long-term memory

The ARCH process (R. F. Engle, 1982) constitutes a paradigmatic generator of stochastic time series with time-dependent variance like it appears on a wide broad of systems besides economics in which ARCH was born. Although the ARCH process captures the so-called "volatility clustering" and the asymptotic power-law probability density distribution of the random variable, it is not capable to reproduce further statistical properties of many of these time series such as: the strong persistence of the instantaneous variance characterised by large values of the Hurst exponent (H > 0.8), and asymptotic power-law decay of the absolute values self-correlation function. By means of considering an effective return obtained from a correlation of past returns that has a q-exponential form we are able to fix the limitations of the original model. Moreover, this improvement can be obtained through the correct choice of a sole additional parameter, $q_{m}$. The assessment of its validity and usefulness is made by mimicking daily fluctuations of SP500 financial index.Comment: 6 pages, 4 figure

Anéis de Ferrara: - 4 Anos Depois

Os anéis intraestromais, nomeadamente o anel de Ferrara, constitui uma importante opção terapêutica das doenças ectásicas da córnea, de origem não inflamatória como o Queratocone. Os autores analisaram os primeiros 30 casos operados no Serviço de Oftalmologia do CHLC relativamente à eficácia, estabilidade e segurança deste procedimento ao longo dos 4 anos. Verificaram estabilidade refractiva, diminuição queratométrica e do equivalente esférico e boa tolerância ao material implantado. Os autores concluem que esta opção terapêutica para o queratocone é segura, reversível, com resultados estáveis que permitem adiar ou evitar a queratoplastia

Cross-sections for nuclide production in 56Fe target irradiated by 300, 500,750, 1000, 1500, and 2600 MeV protons compared with data on hydrogen target irradiation by 300, 500, 750, 1000, and 1500 MeV/nucleon 56Fe ions

Cross-sections for radioactive nuclide production in 56Fe(p,x) reactions at 300, 500, 750, 1000, 1500, and 2600 MeV were measured using the ITEP U-10 proton accelerator. In total, 221 independent and cumulative yields of products of half-lives from 6.6 min to 312 days have been obtained via the direct-spectrometry method. The measured data have been compared with the experimental data obtained elsewhere by the direct and inverse kinematics methods and with calculations by 15 codes, namely: MCNPX (INCL, CEM2k, BERTINI, ISABEL), LAHET (BERTINI, ISABEL), CEM03 (.01, .G1, .S1), LAQGSM03 (.01, .G1, >.S1), CASCADE-2004, LAHETO, and BRIEFF. Most of our data are in a good agreement with the inverse kinematics results and disprove the results of some earlier activation measurements that were quite different from the inverse kinematics measurements. The most significant calculation-to-experiment differences are observed in the yields of the A<30 light nuclei, indicating that further improvements in nuclear reaction models are needed, and pointing out as well to a necessity of more complete measurements of such reactions.Comment: 53 pages, 9 figures, 6 tables, only pdf file, submitted to Phys. Rev.

The physical and dynamical structure of Serpens - Two very different sub-(proto)clusters

Context. The Serpens North cluster is a nearby low mass star forming region which is part of the Gould belt. It contains a range of young stars thought to correspond to two different bursts of star formation and provides the opportunity to study different stages of cluster formation. Aims. This work aims to study the molecular gas in the Serpens North cluster to probe the origin of the most recent burst of star formation in Serpens. Methods. Transitions of the C17O and C18O observed with the IRAM 30 m telescope and JCMT are used to study the mass and velocity structure of the region while the physical properties of the gas are derived using LTE and non-LTE analyses of the three lowest transitions of C18O. Results. The molecular emission traces the two centres of star formation which are seen in submillimetre dust continuum emission. In the ~40 NW sub-cluster the gas and dust emission trace the same structures although there is evidence of some depletion of the gas phase C18O. The gas has a very uniform temperature (~10 K) and velocity (~8.5 km s-1) throughout the region. This is in marked contrast to the SE sub-cluster. In this region the dust and the gas trace different features, with the temperature peaking between the submillimetre continuum sources, reaching up to ~14 K. The gas in this region has double peaked line profiles which reveal the presence of a second cloud in the line of sight. The submillimetre dust continuum sources predominantly appear located in the interface region between the two clouds. Conclusions. Even though they are at a similar stage of evolution, the two Serpens sub-clusters have very different characteristics. We propose that these differences are linked to the initial trigger of the collapse in the regions and suggest that a cloud-cloud collision could explain the observed properties

On exact time-averages of a massive Poisson particle

In this work we study, under the Stratonovich definition, the problem of the damped oscillatory massive particle subject to a heterogeneous Poisson noise characterised by a rate of events, \lambda (t), and a magnitude, \Phi, following an exponential distribution. We tackle the problem by performing exact time-averages over the noise in a similar way to previous works analysing the problem of the Brownian particle. From this procedure we obtain the long-term equilibrium distributions of position and velocity as well as analytical asymptotic expressions for the injection and dissipation of energy terms. Considerations on the emergence of stochastic resonance in this type of system are also set forth.Comment: 21 pages, 5 figures. To be published in Journal of Statistical Mechanics: Theory and Experimen