Measuring the local dark matter density

We examine systematic problems in determining the local matter density from the vertical motion of stars, i.e. the 'Oort limit'. Using collisionless simulations and a Monte Carlo Markov Chain technique, we determine the data quality required to detect local dark matter at its expected density. We find that systematic errors are more important than observational errors and apply our technique to Hipparcos data to reassign realistic error bars to the local dark matter density.Comment: 3 pages, 1 figure, to be published in "Hunting for the Dark: The Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista & C.C. Popescu, AIP Conf. Se

X-ray imaging of water flow through soil

In this study a laboratory experiment on preferential flow was conducted with the aim to quantify the importance of water repellency, soil structure and irrigation rate on water infiltration into soil. To do so, the study was conducted as follows: (a) comparison between the wetting fronts of the irrigations done on the same sample; (b) the tortuosity of the wetting fronts, this was analysed calculating a tortuosity index; (c) the average infiltration velocity and (d) a visual comparison between the 3D images. The aim of the latter was to see whether there were differences in the structure before and after the irrigations, and to understand how the structure influenced the water infiltration through the soil. Furthermore, we tested whether the X-ray computed tomography is a suitable technique for this kind of studies. In order to use this technique, an irrigation device and fifteen quasi-2D boxes were specially designed to fit in the X-ray scanner. The experiments were conducted on three different kinds of soil samples: a bare mixture of soil and peat (50/50 by volume), a planted mixture of soil and peat (50/50 by volume) and garden soil samples that once collected and prepared where buried underground for four weeks. The images obtained with the x-ray machine were analysed using the computer program ImageJ. The main outcomes of this project were found to be: (a) the infiltration patterns through bare and garden soil samples remained identical throughout different irrigations runs while they changed in the sown soil samples; (b) high irrigation rates reduced the wetting front tortuosity; (c) the tortuosity of the wetting front increased with time; (d) macroporosity and initial water content strongly influenced the water infiltration velocity through the soil, the bigger they were the higher the infiltration velocity; (e) plants roots and long consolidation times exerted a stabilizing effect on the soil structure. The X-ray computed tomography, despite the setup can be improved, demonstrated to be a useful technique to investigate water infiltration through the soil as it was able to very well detect water in the soil samples. If used together with an image analysis software it has a huge potential as it can be used even for 3D infiltration experiments. During this project just a small part of the X-ray computed tomography potential was used, to estimate its potential many more similar projects are needed

Limits on the local dark matter density

We revisit systematics in determining the local dark matter density ρdm from the vertical motion of stars in the solar neighbourhood. Using a simulation of a Milky Way like galaxy, we determine the data quality required to detect ρdm at its expected local value. We introduce a new method for recovering ρdm that uses moments of the Jeans equations, combined with a Markov chain Monte Carlo technique, to marginalize over the unknown parameters. Given sufficiently good data, we show that our method can recover the correct local dark matter density even in the face of disc inhomogeneities, non-isothermal tracers and a non-separable distribution function. We illustrate the power of our technique by applying it to Hipparcos data. We first make the assumption that the A- and F-star tracer populations are isothermal. This recovers ρdm= 0.003+0.009− 0.007 M⊙ pc−3 (ρdm= 0.11+0.34− 0.27 GeV cm−3, with 90 per cent confidence), consistent with previous determinations. However, the vertical dispersion profile of these tracers is poorly known. If we assume instead a non-isothermal profile similar to that of the blue disc stars from SDSS DR-7 recently measured, we obtain a fit with a very similar χ2 value, but with ρdm= 0.033+0.008− 0.009 M⊙ pc−3 (ρdm= 1.25+0.30− 0.34 GeV cm−3 with 90 per cent confidence). This highlights that it is vital to measure the vertical dispersion profile of the tracers to recover an unbiased estimate of ρd

Limits on the local dark matter density

We revisit systematics in determining the local dark matter density (rho_dm) from the vertical motion of stars in the Solar Neighbourhood. Using a simulation of a Milky Way-like galaxy, we determine the data-quality required to detect the dark matter density at its expected local value. We introduce a new method for recovering rho_dm that uses moments of the Jeans equations, combined with a Monte Carlo Markov Chain technique to marginalise over the unknown parameters. Given sufficiently good data, we show that our method can recover the correct local dark matter density even in the face of disc inhomogeneities, non-isothermal tracers and a non-separable distribution function. We illustrate the power of our technique by applying it to Hipparcos data [Holmberg & Flynn 2000,2004]. We first make the assumption that the A and F star tracer populations are isothermal. This recovers rho_dm=0.003^{+0.009}_{-0.007}Msun/pc^3 (with 90 per cent confidence), consistent with previous determinations. However, the vertical dispersion profile of these tracers is poorly known. If we assume instead a non-isothermal profile similar to the blue disc stars from SDSS DR-7 [Abazajian et al. 2009] measured by Bond et al. (2009), we obtain a fit with a very similar chi^2 value, but with rho_dm=0.033^{+0.008}_{-0.009}Msun/pc^3 (with 90 per cent confidence). This highlights that it is vital to measure the vertical dispersion profile of the tracers to recover an unbiased estimate of the local dark matter density.Comment: 25 pages, 21 figures; accepted for publication in MNRA

pKBuS13, a KPC-2-Encoding Plasmid from Klebsiella pneumoniae Sequence Type 833, Carrying Tn4401b Inserted into an Xer Site-Specific Recombination Locus

Here, we report the first detection of a Klebsiella pneumoniae carbapenemase 2 (KPC-2)-producing Klebsiella pneumoniae strain belonging to sequence type 833 (ST833), collected in an Italian hospital from a patient coming from South America. Its bla KPC determinant was carried by a ColE1 plasmid, pKBuS13, that showed the Tn4401b::bla KPC-2 transposon inserted into the regulatory region of an Xer site-specific recombination locus. This interfered with the correct resolution of plasmid multimers into monomers, lowering plasmid stability and leading to overestimation of the number of plasmids harbored by a single host cell. Sequencing of the fragments adjacent to Tn4401b detected a region that did not have significant matches in databases other than the genome of a carbapenem-resistant Escherichia coli strain collected during the same year at a hospital in Boston. This is interesting in an epidemiologic context, as it suggests that despite the absence of tra genes and the instability under nonselective conditions, the circulation of pKBuS13 or of analogous plasmids might be wider than reported

The severity of early fluid overload assessed by bioelectrical vector impedance as an independent risk factor for longer patient care after cardiac surgery

Background and aims: Fluid overload is a common postoperative complication in patients undergoing cardiac surgery. Although this condition is notably associated with relevant adverse outcomes, assessment of hydration status in clinical practice is challenging. Bioelectrical impedance vector analysis (BIVA) has emerged as a potentially effective method to monitor hydration changes, but the available evidence in critically ill patients undergoing cardiac surgery is limited and sometimes conflicting. The aim of this study was to explore by mean of BIVA the evolution over time of hydration status and its impact on relevant outcomes. Methods: Prospective observational study enrolling 130 patients undergoing cardiac surgery. Height normalized impedance was calculated both before surgery (baseline) and in the first five postoperative days. Relevant clinical and laboratory data were collected daily close to BIVA measurements. Length of mechanical ventilation (MV), intensive care unit (ICU) and hospital stay exceeding the 75th percentile of the study population were considered as study endpoints. Results: Compared to baseline, a significant reduction in impedance was found at first postoperative day, demonstrating a relevant fluid overload. An adjusted impedance at first postoperative day shorter than the best respective threshold was associated to longer MV (7.4 times), ICU stay (4.7 times) and hospital stay (5.6 times). A significant change in impedance and phase angle was documented throughout the observation days (p < 0.001), without returning to the baseline value. The co-existence of low impedance and high plasma osmolarity increased significantly the risk of incurring the study outcomes. Conclusions: In patients with cardiac surgery-induced fluid overload, recovery to baseline conditions occurs slowly. A relevant early fluid overload should be considered predictive for longer time of MV, ICU and total hospital stay

Análise ambiental integrada da localidade de sambaqui na microbacia hidrográfica do Rio Sagrado, Morretes (PR)

A presente Pesquisa está em curso no contexto da Zona de Educação para o Ecodesenvolvimento (ZEE), localizado na APA de Guaratuba, caracterizada por vasta produção de plantas ornamentais e hortifrutigranjeiros. Valendo-se da importância do planejamento baseado no compartilhamento de sabedorias tradicionais incorporadas ao conhecimento científico, o presente estudo procurou identificar e caracterizar as unidades da paisagem através da elaboração de transectos geoambientais. Os resultados da pesquisa identificaram que a localidade de Sambaqui, situada em área morfologicamente plana e regular, é adequada ao uso e ocupação do solo. Caracterizada como uma das áreas deposicionais de materiais decorrentes das corridas de massa e detrito, Sambaqui sofre com enchentes que alteram a largura e o curso do rio. Com a postura de que é preciso prevenir muito mais do que corrigir, o processo de planejamento implementado segue com diagnóstico e prognóstico que identifica vocações e limitações para o uso do solo e dos recursos naturais. Palavras-chave: Desenvolvimento econômico - aspectos ambientais; Desenvolvimento sustentável; Impacto ambiental; Microbacia hidrográfica do Rio Sagrado – Morretes (PR)

Análise ambiental integrada da localidade de sambaqui na microbacia hidrográfica do Rio Sagrado, Morretes (PR)

A presente Pesquisa está em curso no contexto da Zona de Educação para o Ecodesenvolvimento (ZEE), localizado na APA de Guaratuba, caracterizada por vasta produção de plantas ornamentais e hortifrutigranjeiros. Valendo-se da importância do planejamento baseado no compartilhamento de sabedorias tradicionais incorporadas ao conhecimento científico, o presente estudo procurou identificar e caracterizar as unidades da paisagem através da elaboração de transectos geoambientais. Os resultados da pesquisa identificaram que a localidade de Sambaqui, situada em área morfologicamente plana e regular, é adequada ao uso e ocupação do solo. Caracterizada como uma das áreas deposicionais de materiais decorrentes das corridas de massa e detrito, Sambaqui sofre com enchentes que alteram a largura e o curso do rio. Com a postura de que é preciso prevenir muito mais do que corrigir, o processo de planejamento implementado segue com diagnóstico e prognóstico que identifica vocações e limitações para o uso do solo e dos recursos naturais. Palavras-chave: Desenvolvimento econômico - aspectos ambientais; Desenvolvimento sustentável; Impacto ambiental; Microbacia hidrográfica do Rio Sagrado – Morretes (PR)