A psychometric analysis of the Statistics Concept Inventory.

A clearer picture of student understanding emerges when the item analyses are combined with analyses obtained using IRT methods. In particular, the nominal response model appears to be able to shed light on persistent misconceptions versus those that seem to diminish with instruction. Additionally, IRT methods can be utilized during the revision process to compare question versions, help make decisions which increase reliability, and make the revision process more efficient. Item characteristic curves for each question and for each response are presented. Results indicate that these methods should be very useful for revising and interpreting concept inventories, as well as having pedagogical implications.The Statistics Concept Inventory (SCI) is one of several concept inventories currently being developed in a variety of engineering disciplines following the success of the Force Concept Inventory (FCI). The direction of the current reform movement in statistics education (as well as other science, engineering, and mathematics fields) is toward an emphasis on conceptual learning instead of focusing on procedural and computational skills. These new curricular goals have given rise to new assessment needs. The SCI is a multiple choice instrument modeled after the FCI which aims to assess conceptual understanding of fundamental statistics concepts. Development of the SCI began in 2002. An overview of the development process is presented here along with baseline performance data from a variety of university level statistics courses. SCI data is analyzed from a classical test theory perspective and from an item response theory (IRT) perspective using the two parameter logistic model and the nominal response model.Posttest SCI results have been consistently low, between 40% and 50% correct; pretest to posttest gains have been minimal. These outcomes are consistent with concept inventory findings in other disciplines. As part of the ongoing development process, individual item analysis has been conducted including item discrimination, distribution of answers, and item correlation with the total score. Comments from student focus groups have also been used during the revision process. These detailed findings are presented as an annotated version of the SCI. Potential areas of confusion or possible misconceptions can be identified

Classification of Quantum Hall Universality Classes by $\ W_{1+\infty}\ $ symmetry

We show how two-dimensional incompressible quantum fluids and their excitations can be viewed as $\ W_{1+\infty}\$ edge conformal field theories, thereby providing an algebraic characterization of incompressibility. The Kac-Radul representation theory of the $\ W_{1+\infty}\$ algebra leads then to a purely algebraic complete classification of hierarchical quantum Hall states, which encompasses all measured fractions. Spin-polarized electrons in single-layer devices can only have Abelian anyon excitations.Comment: 11 pages, RevTeX 3.0, MPI-Ph/93-75 DFTT 65/9

MaNGA galaxy properties -- II. A detailed comparison of observed and simulated spiral galaxy scaling relations

We present a catalogue of dynamical properties for 2368 late-type galaxies from the MaNGA survey. The latter complements the catalogue of photometric properties for the same sample based on deep optical DESI photometry processed with AutoProf. Rotation curves (RCs), extracted by model fitting H$\alpha$ velocity maps from the MaNGA Data Analysis Pipeline, extend out to 1.4 (1.9) R$_{e}$ for the primary (secondary) MaNGA samples. The RCs and ancillary MaNGA Pipe3D data products were used to construct various fundamental galaxy scaling relations that are also compared uniformly with similar relations from NIHAO zoom-in simulations. Simulated NIHAO galaxies were found to broadly reproduce the observed MaNGA galaxy population for $\log (M_*/{\rm M_{\odot}) > 8.5}$. Some discrepancies remain, such as those pertaining to central stellar densities and the diversity of RCs due to strong feedback schemes. Also presented are spatially-resolved scatters for the velocity-size-stellar mass (VRM$_*$) structural relations using MaNGA and NIHAO samples. The scatter for these relations in the galaxian interiors is a consequence of the diversity of inner RC shapes, while scatter in the outskirts is dictated by the large range of stellar surface densities which itself is driven by sporadic star formation. The detailed spatially-resolved scatter analysis highlights the complex interplay between local and global astrophysical processes and provides a strong constraint to numerical simulations.Comment: 21 pages, 13 Figures, Accepted for publication in MNRA

A pilot investigation into the effect of maca supplementation on physical activity and sexual desire in sportsmen

AIMS OF THE STUDY: Maca (Lepidium meyenii Walp) is consumed both as a sports supplement by strength and endurance athletes, and as a natural stimulant to enhance sexual drive. However, whether or not the postulated benefits of maca consumption are of scientific merit is not yet known. The aim of the study was therefore to investigate the effect of 14 days maca supplementation on endurance performance and sexual desire in trained male cyclists. MATERIALS AND METHODS: Eight participants each completed a 40 km cycling time trial before and after 14 days supplementation with both maca extract (ME) and placebo, in a randomised cross-over design. Subjects also completed a sexual desire inventory during each visit. RESULTS: ME administration significantly improved 40 km cycling time performance compared to the baseline test (P=0.01), but not compared to the placebo trial after supplementation (P>0.05). ME administration significantly improved the self-rated sexual desire score compared to the baseline test (P=0.01), and compared to the placebo trial after supplementation (P=0.03). CONCLUSIONS: 14 days ME supplementation improved 40 km cycling time trial performance and sexual desire in trained male cyclists. These promising results encourage long-term clinical studies involving more volunteers, to further evaluate the efficacy of ME in athletes and normal individuals and also to explore its possible mechanisms of action

Conformal Symmetry and Universal Properties of Quantum Hall States

The low-lying excitations of a quantum Hall state on a disk geometry are edge excitations. Their dynamics is governed by a conformal field theory on the cylinder defined by the disk boundary and the time variable. We give a simple and detailed derivation of this conformal field theory for integer filling, starting from the microscopic dynamics of $(2+1)$-dimensional non-relativistic electrons in Landau levels. This construction can be generalized to describe Laughlin's fractional Hall states via chiral bosonization, thereby making contact with the effective Chern-Simons theory approach. The conformal field theory dictates the finite-size effects in the energy spectrum. An experimental or numerical verification of these universal effects would provide a further confirmation of Laughlin's theory of incompressible quantum fluids.Comment: 39 pages, 7 figures (not included, they are mailed on request), harvmac CERN-TH 6702/9

Energy Dissipation in Interstellar Cloud Collisions

We present a study of the kinetic energy dissipation in interstellar cloud collisions. The main aim is to understand the dependence of the elasticity (defined as the ratio of the final to the initial kinetic energy of the clouds) on the velocity and mass ratio of the colliding clouds, magnetic field strength, and gas metallicity for head-on collisions. The problem has been studied both analytically and via numerical simulations. We have derived handy analytical relationships that well approximate the analogous numerical results. The main findings of this work are: (i) the kinetic energy dissipation in cloud collisions is minimum (i.e. the collision elasticity is maximum) for a cloud relative velocity $v_r \simeq 30 km s^{-1}$; (ii) the above minimum value is proportional $Z L_c^2$, where $Z$ is the metallicity and $L_c$ is the cloud size: the larger is $Z L_c^2$ the more dissipative (i.e. inelastic) the collision will be; (iii) in general, we find that the energy dissipation decreases when the magnetic field strength, and mass ratio of the clouds are increased and the metallicity is decreased, respectively. We briefly discuss the relevance of this study to the global structure of the interstellar medium and to galaxy formation and evolution.Comment: 16 pages, aasms LaTeX, 7 figures. ApJ, accepte

Elite handcycling: A qualitative analysis of recumbent handbike configuration for optimal sports performance

Our understanding of handbike configuration is limited, yet it can be a key determinant of performance in handcycling. This study explored how fourteen handcycling experts (elite handcyclists, coaches, support staff and manufacturers) perceived aspects of recumbent handbike configuration to impact upon endurance performance via semi-structured interviews. Optimising the handbike for comfort, stability and power production were identified as key themes. Comfort and stability were identified to be the foundations of endurance performance and were primarily influenced by the seat, backrest, headrest and their associated padding. Power production was determined by the relationship between the athletes’ shoulder and abdomen and the trajectories of the handgrips, which were determined by the crank axis position, crank arm length and handgrip width. Future studies should focus on quantifying the configuration of recumbent handbikes before determining the effects that crank arm length, handgrip width and crank position have on endurance performance