Using “Student Technology” in introductory physics: a comparison of three tools to study falling objects

Being able to facilitate effective hands‐on laboratory experiences in introductory physics courses is a challenging task, even when contemporary laboratory facilities, equipment, and new technologies for data collection and analysis are available. At institutions without adequate resources, especially those in developing countries, we have found that the problem of providing effective laboratory experiences is especially daunting for at least two reasons: 1) the lack of equipment and contemporary measuring devices; and 2) even at institutions that have some laboratory equipment, students who have access to cell phones with digital timing and video capabilities or inexpensive digital cameras are bored with trying to use “old‐fashioned” apparatus for measurements.Fil: Saraiva Da Rocha, Fábio. Universidade Federal do Pampa; BrasilFil: Fajardo, Fabio. Universidad Nacional de Colombia; ColombiaFil: Grisolía, Maricarmen. Universidad de Los Andes; VenezuelaFil: Benegas, Julio Ciro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Matemática Aplicada de San Luis "Prof. Ezio Marchi". Universidad Nacional de San Luis. Facultad de Ciencias Físico, Matemáticas y Naturales. Instituto de Matemática Aplicada de San Luis ; ArgentinaFil: Tchitnga, Robert. University of Dschang; CamerúnFil: Laws, Priscilla. Dickinson College; Estados Unido

Spatio-temporal variability of precipitation in the venezuelan Amazon.

A região amazônica desempenha um papel fundamental no balanço hídrico global. Assim, a análise espaço-temporal da precipitação é essencial para a avaliação dos impactos das mudanças climáticas. No entanto, ainda existe uma lacuna de informação na Amazônia venezuelana. O objetivo deste trabalho é analisar o padrão espaço-temporal de 12 anos da precipitação na Amazônia venezuelana a partir de dados de superfície da região. Foram utilizados dados diários de precipitação pluvial para um período de 12 anos (2000-2011) de 10 localidades da Amazônia venezuelana. As estruturas temporais e espaciais da variabilidade interanual da precipitação foram avaliadas. Foi utilizado o teste não paramétrico de Mann-Kendall para determinar se as tendências anuais de precipitação em cada local podem ser identificadas em uma série temporal que inclua um componente sazonal. Para avaliar a autocorrelação espacial da precipitação entre as observações com base no Era-Interim, o índice global de Moran foi usado. Foram distinguidos dois grupos homogêneos de precipitação, quando as localidades são separadas por médias anuais. Com relação à precipitação mensal por localidade, as variáveis (meses) que definem os grupos homogêneos de precipitação. Os resultados mostram que nesta região da Amazônia prevalece um padrão unimodal de precipitação nas diferentes localidades, com um longo período de chuva e um período menos chuvoso entre dezembro e março. Esse padrão é explicado pela Zona de Convergência Intertropical que nesses meses se encontra deslocado para latitudes mais ao sul, modulando a dinâmica das chuvas na Amazônia. Outra das principais consequências no padrão de precipitação na Amazônia é a influência da Zona de Convergência do Atlântico Sul com a ocorrência dos altos índices pluviais. Ao avaliar a associação espacial local pelo ERA-Interim, observa-se que os grupos de precipitação (índice de Moran) expressam a variabilidade existente em função do nível de significância dos valores de seus índices locais

Planck Intermediate Results II: Comparison of Sunyaev-Zeldovich measurements from Planck and from the Arcminute Microkelvin Imager for 11 galaxy clusters

A comparison is presented of Sunyaev-Zeldovich measurements for 11 galaxy clusters as obtained by Planck and by the ground-based interferometer, the Arcminute Microkelvin Imager. Assuming a universal spherically-symmetric Generalised Navarro, Frenk & White (GNFW) model for the cluster gas pressure profile, we jointly constrain the integrated Compton-Y parameter (Y_500) and the scale radius (theta_500) of each cluster. Our resulting constraints in the Y_500-theta_500 2D parameter space derived from the two instruments overlap significantly for eight of the clusters, although, overall, there is a tendency for AMI to find the Sunyaev-Zeldovich signal to be smaller in angular size and fainter than Planck. Significant discrepancies exist for the three remaining clusters in the sample, namely A1413, A1914, and the newly-discovered Planck cluster PLCKESZ G139.59+24.18. The robustness of the analysis of both the Planck and AMI data is demonstrated through the use of detailed simulations, which also discount confusion from residual point (radio) sources and from diffuse astrophysical foregrounds as possible explanations for the discrepancies found. For a subset of our cluster sample, we have investigated the dependence of our results on the assumed pressure profile by repeating the analysis adopting the best-fitting GNFW profile shape which best matches X-ray observations. Adopting the best-fitting profile shape from the X-ray data does not, in general, resolve the discrepancies found in this subset of five clusters. Though based on a small sample, our results suggest that the adopted GNFW model may not be sufficiently flexible to describe clusters universally.Comment: update to metadata author list onl

Planck Intermediate Results. IV. The XMM-Newton validation programme for new Planck galaxy clusters

We present the final results from the XMM-Newton validation follow-up of new Planck galaxy cluster candidates. We observed 15 new candidates, detected with signal-to-noise ratios between 4.0 and 6.1 in the 15.5-month nominal Planck survey. The candidates were selected using ancillary data flags derived from the ROSAT All Sky Survey (RASS) and Digitized Sky Survey all-sky maps, with the aim of pushing into the low SZ flux, high-z regime and testing RASS flags as indicators of candidate reliability. 14 new clusters were detected by XMM, including 2 double systems. Redshifts lie in the range 0.2 to 0.9, with 6 clusters at z>0.5. Estimated M500 range from 2.5 10^14 to 8 10^14 Msun. We discuss our results in the context of the full XMM validation programme, in which 51 new clusters have been detected. This includes 4 double and 2 triple systems, some of which are chance projections on the sky of clusters at different z. We find that association with a RASS-BSC source is a robust indicator of the reliability of a candidate, whereas association with a FSC source does not guarantee that the SZ candidate is a bona fide cluster. Nevertheless, most Planck clusters appear in RASS maps, with a significance greater than 2 sigma being a good indication that the candidate is a real cluster. The full sample gives a Planck sensitivity threshold of Y500 ~ 4 10^-4 arcmin^2, with indication for Malmquist bias in the YX-Y500 relation below this level. The corresponding mass threshold depends on z. Systems with M500 > 5 10^14 Msun at z > 0.5 are easily detectable with Planck. The newly-detected clusters follow the YX-Y500 relation derived from X-ray selected samples. Compared to X-ray selected clusters, the new SZ clusters have a lower X-ray luminosity on average for their mass. There is no indication of departure from standard self-similar evolution in the X-ray versus SZ scaling properties. (abridged)Comment: accepted by A&

Risk factors for hepatitis B virus infection in Rio de Janeiro, Brazil

BACKGROUND: Despite international efforts to prevent hepatitis B virus (HBV) infection through global vaccination programs, new cases are still being reported throughout the world. METHODS: To supply data that might assist in improving preventive measures and national surveillance for HBV infection, a cross-sectional study was conducted among individuals referred to the Brazilian National Reference Center for Viral Hepatitis (Rio de Janeiro) during a two-year period. Reported risk factors among infected subjects ("HBV-positive") were compared to those of subjects never exposed ("HBV-negative") to HBV. Two subgroups were further identified within the HBV-positive group, "acute" infection and "non-acute" infection. RESULTS: A total of 1,539 subjects were tested for HBV, of which 616 were HBV-positive (79 acute infection and 537 non-acute infection). HBV-positive subjects were more likely to be of male gender (63% versus 47%); and to report multiple sexual partners (12% versus 6%) and illicit drug use (IDU and/or intranasal cocaine use) (6% versus 3%). Among the HBV-positive subgroups, age differed significantly, with 48% being under 30 years of age in subjects acutely infected compared to 17% in those with non-acute infection. CONCLUSIONS: The association of multiple sexual partners with past HBV infection and the age distribution of currently infected subjects suggest that sexual transmission played a major role in the transmission of HBV in this study population. Thus, vaccination during adolescence should be considered

Planck intermediate results. III. The relation between galaxy cluster mass and Sunyaev-Zeldovich signal

We examine the relation between the galaxy cluster mass M and Sunyaev-Zeldovich (SZ) effect signal D_A^2 Y for a sample of 19 objects for which weak lensing (WL) mass measurements obtained from Subaru Telescope data are available in the literature. Hydrostatic X-ray masses are derived from XMM-Newton archive data and the SZ effect signal is measured from Planck all-sky survey data. We find an M_WL-D_A^2 Y relation that is consistent in slope and normalisation with previous determinations using weak lensing masses; however, there is a normalisation offset with respect to previous measures based on hydrostatic X-ray mass-proxy relations. We verify that our SZ effect measurements are in excellent agreement with previous determinations from Planck data. For the present sample, the hydrostatic X-ray masses at R_500 are on average ~ 20 per cent larger than the corresponding weak lensing masses, at odds with expectations. We show that the mass discrepancy is driven by a difference in mass concentration as measured by the two methods, and, for the present sample, the mass discrepancy and difference in mass concentration is especially large for disturbed systems. The mass discrepancy is also linked to the offset in centres used by the X-ray and weak lensing analyses, which again is most important in disturbed systems. We outline several approaches that are needed to help achieve convergence in cluster mass measurement with X-ray and weak lensing observations.Comment: 19 pages, 9 figures, matches accepted versio