Teaching statistics to medical students using problem-based learning: the Australian experience

Background: Problem-based learning (PBL) is gaining popularity as a teaching method in UK medical schools, but statistics and research methods are not being included in this teaching. There are great disadvantages in omitting statistics and research methods from the main teaching. PBL is well established in Australian medical schools. The Australian experience in teaching statistics and research methods in curricula based on problem-based learning may provide guidance for other countries, such as the UK, where this method is being introduced. Methods: All Australian medical schools using PBL were visited, with two exceptions. Teachers of statistics and medical education specialists were interviewed. For schools which were not visited, information was obtained by email. Results: No Australian medical school taught statistics and research methods in a totally integrated way, as part of general PBL teaching. In some schools, statistical material was integrated but taught separately, using different tutors. In one school, PBL was used only for 'public health' related subjects. In some, a parallel course using more traditional techniques was given alongside the PBL teaching of other material. This model was less successful than the others. Conclusions: There are several difficulties in implementing an integrated approach. However, not integrating is detrimental to statistics and research methods teaching, which is of particular concern in the age of evidence-based medicine. Some possible ways forward are suggested

Spitzer spectral line mapping of protostellar outflows: II H2 emission in L1157

We present an analysis of Spitzer-IRS spectroscopic maps of the L1157 protostellar outflow in the H2 pure-rotational lines from S(0) to S(7). The aim of this work is to derive the physical conditions pertaining to the warm molecular gas and study their variations within the flow. The mid-IR H2 emission follows the morphology of the precessing flow, with peaks correlated with individual CO clumps and H2 2.12{\mu}m ro-vibrational emission. More diffuse emission delineating the CO cavities is detected only in the low-laying transitions, with J(lower) less or equal to 2. The H2 line images have been used to construct 2D maps of N(H2), H2 ortho-to-para ratio and temperature spectral index beta, in the assumption of a gas temperature stratification where the H2 column density varies as T^(beta). Variations of these parameters are observed along the flow. In particular, the ortho-to-para ratio ranges from 0.6 to 2.8, highlighting the presence of regions subject to recent shocks where the ortho-to-para ratio has not had time yet to reach the equilibrium value. Near-IR spectroscopic data on ro-vibrational H2 emission have been combined with the mid-IR data and used to derive additional shock parameters in the brightest blue- and red-shifted emission knots. A high abundance of atomic hydrogen (H/H2 about 0.1-0.3) is implied by the observed H2 column densities, assuming n(H2) values as derived by independent SiO observations. The presence of a high fraction of atomic hydrogen, indicates that a partially-dissociative shock component should be considered for the H2 excitation in these localized regions. However, planar shock models, either of C- or J-type, are not able to consistently reproduce all the physical parameters derived from our analysis of the H2 emission. Globally, H2 emission contributes to about 50% of the total shock radiated energy in the L1157 outflow.Comment: 31 pages, 9 figure, Accepted for publication on Ap

557 GHz Observations of Water Vapor Outflows from VY CMa and W Hydrae

We report the first detection of thermal water vapor emission in the 557 GHz, $1_{10} - 1_{01}$ ground state transition of ortho-H$_2$O toward VY Canis Majoris. In observations obtained with the Submillimeter Wave Astronomy Satellite (SWAS), we measured a flux of $\sim 450$Jy, in a spectrally resolved line centered on a velocity $v_{LSR} = 25$km s$^{-1}$ with a full width half maximum of $\sim 35$ km s$^{-1}$, somewhat dependent on the assumed line shape. We analyze the line shape in the context of three different radial outflow models for which we provide analytical expressions. We also detected a weaker 557 GHz emission line from W Hydrae. We find that these and other H$_2$O emission line strengths scale as suggested by Zubko and Elitzur (2000).Comment: Astrophysical Journal Letters, accepte

Distribution of Water Vapor in Molecular Clouds

We report the results of a large-area study of water vapor along the Orion Molecular Cloud ridge, the purpose of which was to determine the depth-dependent distribution of gas-phase water in dense molecular clouds. We find that the water vapor measured toward 77 spatial positions along the face-on Orion ridge, excluding positions surrounding the outflow associated with BN/KL and IRc2, display integrated intensities that correlate strongly with known cloud surface tracers such as CN, C2H, 13CO J =5-4, and HCN, and less well with the volume tracer N2H+. Moreover, at total column densities corresponding to Av < 15 mag., the ratio of H2O to C18O integrated intensities shows a clear rise approaching the cloud surface. We show that this behavior cannot be accounted for by either optical depth or excitation effects, but suggests that gas-phase water abundances fall at large Av. These results are important as they affect measures of the true water-vapor abundance in molecular clouds by highlighting the limitations of comparing measured water vapor column densities with such traditional cloud tracers as 13CO or C18O. These results also support cloud models that incorporate freeze-out of molecules as a critical component in determining the depth-dependent abundance of water vapor

Spitzer spectral line mapping of supernova remnants: I. Basic data and principal component analysis

We report the results of spectroscopic mapping observations carried out toward small (1 x 1 arcmin) regions within the supernova remnants W44, W28, IC443, and 3C391 using the Infrared Spectrograph of the Spitzer Space Telescope. These observations, covering the 5.2 - 37 micron spectral region, have led to the detection of a total of 15 fine structure transitions of Ne+, Ne++, Si+, P+, S, S++, Cl+, Fe+, and Fe++; the S(0) - S(7) pure rotational lines of molecular hydrogen; and the R(3) and R(4) transitions of hydrogen deuteride. In addition to these 25 spectral lines, the 6.2, 7.7, 8.6, 11.3 and 12.6 micron PAH emission bands were also observed. Most of the detected line transitions have proven strong enough to map in several sources, providing a comprehensive picture of the relative distribution of the various line emissions observable in the Spitzer/IRS bandpass. A principal component analysis of the spectral line maps reveals that the observed emission lines fall into five distinct groups, each of which may exhibit a distinct spatial distribution: (1) lines of S and H2 (J > 2); (2) the H2 S(0) line; (3) lines of ions with appearance potentials less than 13.6 eV; (4) lines of ions with appearance potentials greater than 13.6 eV, not including S++; (5) lines of S++. Lines of group (1) likely originate in molecular material subject to a slow, nondissociative shock that is driven by the overpressure within the supernova remnant, and lines in groups (3) - (5) are associated primarily with dissociative shock fronts with a range of (larger) shock velocities. The H2 S(0) line shows a low-density diffuse emission component, and - in some sources - a shock-excited component.Comment: 43 pages, including 21 figures. Accepted for publication in Ap