Thorium and uranium isotopes in a manganese nodule from the Peru basin determined by alpha spectrometry and thermal ionization mass spectrometry (TIMS): Are manganese supply and growth related to climate?

Thorium- and uranium isotopes were measured in a diagenetic manganese nodule from the Peru basin applying alpha- and thermal ionization mass spectrometry (TIMS). Alpha-counting of 62 samples was carried out with a depth resolution of 0.4 mm to gain a high-resolution230Thexcess profile. In addition, 17 samples were measured with TIMS to obtain precise isotope concentrations and isotope ratios. We got values of 0.06–0.59 ppb (230Th), 0.43–1.40 ppm (232Th), 0.09–0.49 ppb (234U) and 1.66–8.24 ppm (238U). The uranium activity ratio in the uppermost samples (1–6 mm) and in two further sections in the nodule at 12.5±1.0 mm and 27.3–33.5 mm comes close to the present ocean water value of 1.144±0.004. In two other sections of the nodule, this ratio is significantly higher, probably reflecting incorporation of diagenetic uranium. The upper 25 mm section of the Mn nodule shows a relatively smooth exponential decrease in the230Thexcess concentration (TIMS). The slope of the best fit yields a growth rate of 110 mm/Ma up to 24.5 mm depth. The section from 25 to 30.3 mm depth shows constant230Thexcess concentrations probably due to growth rates even faster than those in the top section of the nodule. From 33 to 50 mm depth, the growth rate is approximately 60 mm/Ma. Two layers in the nodule with distinct laminations (11–15 and 28–33 mm depth) probably formed during the transition from isotopic stage 8 to 7 and in stage 5e, respectively. The Mn/Fe ratio shows higher values during interglacials 5 and 7, and lower ones during glacials 4 and 6. A comparison of our data with data from adjacent sediment cores suggests (a) a variable supply of hydrothermal Mn to sediments and Mn nodules of the Peru basin or (b) suboxic conditions at the water sediment interface during periods with lower Mn/Fe ratios

The relationship between accruals, earnings, and cash flows: evidence from latin america

The relationships between earnings, accruals, and cash flows for selected Latin American countries (Mexico, Chile, and Argentina) are investigated in this study from 1990 to 2009. We find a negative relationship between accruals and cash flow across decile portfolios. More importantly, firms reporting the highest level of accruals, have the worst level of cash flows, but not the worst level of earnings. This relationship is of economic importance given that investors are very oriented towards firms yielding high earnings and might fail to realize that earnings are not always accompanied by strong levels of cash flows. Results are disaggregated by years and countries, and compared to previous results for U.S. firms.ITESO, A.C.UPSoutheastern Louisiana UniversityUniversity of Florid

The portafolio as an instrument for evaluating a teaching training programme

Este trabajo presenta los resultados de un estudio que utilizó el portafolio como instrumento para la evaluación de profesores que participaron en un programa de formación docente en el sureste de México. Los resultados del estudio indican que la metodología utilizada fue valiosa para evaluar el desempeño de los docentes e identificar áreas de mejora. La investigación es parte del proyecto Modelo para el desarrollo y evaluación de competencias académicas de la Red de Desarrollo y Evaluación de Competencias Académicas (PROMEP).Este trabalho apresenta os resultados de um estudo que usado o portfólio como uma ferramenta para a avaliação de professores que participou de um programa de formação de professores de Sudeste do México. Os resultados do estudo indicam que a metodologia foi valiosa para avaliar o desempenho dos professores e identificar áreas para melhoria. A pesquisa é parte do projeto modelo para o desenvolvimento e a avaliação das competências académicas da rede de desenvolvimento e avaliação das competências académicas (PROMEP).This paper presents the findings of a study that used a teacher portfolio as instrument for evaluating faculty members who participated in a preparation program in Southeast Mexico. Findings of the study indicate that portfolios were valuable both for evaluation and for improvement purposes. The study is part of a larger research endeavor: Model fro the development and assessment of academic competencies developed by the Red de Desarrollo y Evaluación de Competencias Académicas (PROMEP)

The Gould's Belt Very Large Array Survey III. The Orion region

We present results from a high-sensitivity (60 $\mu$Jy), large-scale (2.26 square degree) survey obtained with the Karl G. Jansky Very Large Array as part of the Gould's Belt Survey program. We detected 374 and 354 sources at 4.5 and 7.5 GHz, respectively. Of these, 148 are associated with previously known Young Stellar Objects (YSOs). Another 86 sources previously unclassified at either optical or infrared wavelengths exhibit radio properties that are consistent with those of young stars. The overall properties of our sources at radio wavelengths such as their variability and radio to X-ray luminosity relation are consistent with previous results from the Gould's Belt Survey. Our detections provide target lists for followup VLBA radio observations to determine their distances as YSOs are located in regions of high nebulosity and extinction, making it difficult to measure optical parallaxes.Comment: Accepted for publication in ApJ; 51 pages, 15 figures, 5 table

Accruals for latin american firms

The relationships among earnings, accruals, and cash flows for selected Latin American countries (Mexico, Chile, and Argentina) are investigated in this study from 1990 to 2009. We find a negative relationship between accruals and cash flow across decile portfolios. More importantly, firms in decile portfolio 10 reporting relative high level of earnings relative to assets, 6.5%, have the worst level of cash flows (negative 9.7%). Results are compared to previous results for U.S. firms. Given the level of sophistication of these capital markets, results for Latin American firms are less stable than for the U.S.Results disaggregated by years show that high-accruals portfolios consistently report relative high levels of earnings but low levels of cash flow. Further, the gap between earnings and cash flow is higher after 2000. This relationship is of economic importance given that investors are very oriented towards firms yielding high earnings and might fail to realize that earnings are not always accompanied by strong levels of cash flows.ITESO, A.C.UPSoutheastern Louisiana UniversityUniversity of Florid

Detection of ultra-high energy cosmic ray showers with a single-pixel fluorescence telescope

We present a concept for large-area, low-cost detection of ultra-high energy cosmic rays (UHECRs) with a Fluorescence detector Array of Single-pixel Telescopes (FAST), addressing the requirements for the next generation of UHECR experiments. In the FAST design, a large field of view is covered by a few pixels at the focal plane of a mirror or Fresnel lens. We report first results of a FAST prototype installed at the Telescope Array site, consisting of a single 200 mm photomultiplier tube at the focal plane of a 1 m$^2$ Fresnel lens system taken from the prototype of the JEM-EUSO experiment. The FAST prototype took data for 19 nights, demonstrating remarkable operational stability. We detected laser shots at distances of several kilometres as well as 16 highly significant UHECR shower candidates.Comment: Accepted for publication in Astroparticle Physic

The Gould's Belt Very Large Array Survey II: The Serpens region

We present deep ($\sim 17~\mu$Jy) radio continuum observations of the Serpens molecular cloud, the Serpens south cluster, and the W40 region obtained using the Very Large Array in its A configuration. We detect a total of 146 sources, 29 of which are young stellar objects (YSOs), 2 are BV stars and 5 more are associated with phenomena related to YSOs. Based on their radio variability and spectral index, we propose that about 16 of the remaining 110 unclassified sources are also YSOs. For approximately 65% of the known YSOs detected here as radio sources, the emission is most likely non-thermal, and related to stellar coronal activity. As also recently observed in Ophiuchus, our sample of YSOs with X-ray counterparts lies below the fiducial G\"udel & Benz relation. Finally, we analyze the proper motions of 9 sources in the W40 region. This allows us to better constrain the membership of the radio sources in the region.Comment: Accepted in The Astrophysical Journa

Critical Behavior of the Three-Dimensional Ising Spin Glass

We have simulated, using parallel tempering, the three dimensional Ising spin glass model with binary couplings in a helicoidal geometry. The largest lattice (L=20) has been studied using a dedicated computer (the SUE machine). We have obtained, measuring the correlation length in the critical region, a strong evidence for a second-order finite temperature phase transition ruling out other possible scenarios like a Kosterlitz-Thouless phase transition. Precise values for the $\nu$ and $\eta$ critical exponents are also presented.Comment: RevTex; 12 pages plus 5 ps figures. Final version to be published in PR

Astroclimatic Characterization of Vallecitos: A candidate site for the Cherenkov Telescope Array at San Pedro Martir

We conducted an 18 month long study of the weather conditions of the Vallecitos, a proposed site in Mexico to harbor the northern array of the Cherenkov Telescope Array (CTA). It is located in Sierra de San Pedro Martir (SPM) a few kilometers away from Observatorio Astron\'omico Nacional. The study is based on data collected by the ATMOSCOPE, a multi-sensor instrument measuring the weather and sky conditions, which was commissioned and built by the CTA Consortium. Additionally, we compare the weather conditions of the optical observatory at SPM to the Vallecitos regarding temperature, humidity, and wind distributions. It appears that the excellent conditions at the optical observatory benefit from the presence of microclimate established in the Vallecitos.Comment: 16 pages, 16 figures, Publication of the Astronomical Society of the Pacific, accepte