Reinventing College Physics for Biologists: Explicating an epistemological curriculum

The University of Maryland Physics Education Research Group (UMd-PERG) carried out a five-year research project to rethink, observe, and reform introductory algebra-based (college) physics. This class is one of the Maryland Physics Department's large service courses, serving primarily life-science majors. After consultation with biologists, we re-focused the class on helping the students learn to think scientifically -- to build coherence, think in terms of mechanism, and to follow the implications of assumptions. We designed the course to tap into students' productive conceptual and epistemological resources, based on a theoretical framework from research on learning. The reformed class retains its traditional structure in terms of time and instructional personnel, but we modified existing best-practices curricular materials, including Peer Instruction, Interactive Lecture Demonstrations, and Tutorials. We provided class-controlled spaces for student collaboration, which allowed us to observe and record students learning directly. We also scanned all written homework and examinations, and we administered pre-post conceptual and epistemological surveys. The reformed class enhanced the strong gains on pre-post conceptual tests produced by the best-practices materials while obtaining unprecedented pre-post gains on epistemological surveys instead of the traditional losses.Comment: 35 pages including a 15 page appendix of supplementary material

Bacteria in ice cream---II

The work done in various laboratories during the last 10 to 15 years has clearly established that the ice cream ordinarily offered tor sale contains large and frequently enormous numbers of bacteria. As a result, certain health departments have begun to consider the sanitary as well as the chemical condition of the ice cream sold within their districts and have established various regulations intended to prevent the sale of a product that may contain organisms liable to set up diseased conditions in the persons consuming it. These regulations are undoubtedly of value and many of them have been of great help in improving the quality of the ice cream sold, but it is very evident to persons giving them any attention that our knowledge of the bacteria in ice cream, as well as the influence of such procedures as storage, freezing and hardening on the numbers of organisms present is insufficient to permit of the establishment of fair and consistent bacterial standards

Galaxy disks do not need to survive in the L-CDM paradigm: the galaxy merger rate out to z~1.5 from morpho-kinematic data

About two-thirds of present-day, large galaxies are spirals such as the Milky Way or Andromeda, but the way their thin rotating disks formed remains uncertain. Observations have revealed that half of their progenitors, six billion years ago, had peculiar morphologies and/or kinematics, which exclude them from the Hubble sequence. Major mergers, i.e., fusions between galaxies of similar mass, are found to be the likeliest driver for such strong peculiarities. However, thin disks are fragile and easily destroyed by such violent collisions, which creates a critical tension between the observed fraction of thin disks and their survival within the L-CDM paradigm. Here we show that the observed high occurrence of mergers amongst their progenitors is only apparent and is resolved when using morpho-kinematic observations which are sensitive to all the phases of the merging process. This provides an original way of narrowing down observational estimates of the galaxy merger rate and leads to a perfect match with predictions by state-of-the-art L-CDM semi-empirical models with no particular fine-tuning needed. These results imply that half of local thin disks do not survive but are actually rebuilt after a gas-rich major merger occurring in the past nine billion years, i.e., two-thirds of the lifetime of the Universe. This emphasizes the need to study how thin disks can form in halos with a more active merger history than previously considered, and to investigate what is the origin of the gas reservoir from which local disks would reform.Comment: 19 pages, 7 figures, 2 tables. Accepted in ApJ. V2 to match proof corrections and added reference

Chandra X-ray Observations of Galaxies in an Off-Center Region of the Coma Cluster

We have performed a pilot Chandra survey of an off-center region of the Coma cluster to explore the X-ray properties and Luminosity Function of normal galaxies. We present results on 13 Chandra-detected galaxies with optical photometric matches, including four spectroscopically-confirmed Coma-member galaxies. All seven spectroscopically confirmed giant Coma galaxies in this field have detections or limits consistent with low X-ray to optical flux ratios (fX/fR < 10^-3). We do not have sufficient numbers of X-ray detected galaxies to directly measure the galaxy X-ray Luminosity Function (XLF). However, since we have a well-measured optical LF, we take this low X-ray to optical flux ratio for the 7 spectroscopically confirmed galaxies to translate the optical LF to an XLF. We find good agreement with Finoguenov et al. (2004), indicating that the X-ray emission per unit optical flux per galaxy is suppressed in clusters of galaxies, but extends this work to a specific off-center environment in the Coma cluster. Finally, we report the discovery of a region of diffuse X-ray flux which might correspond to a small group interacting with the Coma Intra-Cluster Medium (ICM).Comment: Accepted for publication in the Astrophysical Journa

The reaction 13C(alpha,n)16O: a background for the observation of geo-neutrinos

The absolute cross section of the $^{13}$C($\alpha$,n)$^{16}$O reaction has been measured at E$_{\alpha}$ = 0.8 to 8.0 MeV with an overall accuracy of 4%. The precision is needed to subtract reliably a background in the observation of geo-neutrinos, e.g. in the KamLAND detector.Comment: LaTex file, 13 pages including 3 ps figures. Any request to [email protected]. Phys. Rev . C, to appea

Symbolic Manipulators Affect Mathematical Mindsets

Symbolic calculators like Mathematica are becoming more commonplace among upper level physics students. The presence of such a powerful calculator can couple strongly to the type of mathematical reasoning students employ. It does not merely offer a convenient way to perform the computations students would have otherwise wanted to do by hand. This paper presents examples from the work of upper level physics majors where Mathematica plays an active role in focusing and sustaining their thought around calculation. These students still engage in powerful mathematical reasoning while they calculate but struggle because of the narrowed breadth of their thinking. Their reasoning is drawn into local attractors where they look to calculation schemes to resolve questions instead of, for example, mapping the mathematics to the physical system at hand. We model the influence of Mathematica as an integral part of the constant feedback that occurs in how students frame, and hence focus, their work

The Formation of Large Galactic Disks: Revival or Survival?

Using the deepest and the most complete set of observations of distant galaxies, we investigate how extended disks could have formed. Observations include spatially-resolved kinematics, detailed morphologies and photometry from UV to mid-IR. Six billion years ago, half of the present-day spiral progenitors had anomalous kinematics and morphologies, as well as relatively high gas fractions. We argue that gas-rich major mergers, i.e., fusions between gas-rich disk galaxies of similar mass, can be the likeliest driver for such strong peculiarities. This suggests a new channel of disk formation, e.g. many disks could be reformed after gas-rich mergers. This is found to be in perfect agreement with predictions from the state-of-the-art LCDM semi-empirical models: due to our sensitivity in detecting mergers at all phases, from pairs to relaxed post-mergers, we find a more accurate merger rate. The scenario can be finally confronted to properties of nearby galaxies, including M31 and galaxies showing ultra-faint, gigantic structures in their haloes.Comment: Proceedings of the annual meeting of the French Astronomical Society, 2011, 6 pages, 1 Figur

Slow acid production by butter cultures

Butter cultures sometimes fail to develop acid at a normal rate, and such slow growth has probably been encountered wherever butter cultures are used. One characteristic of certain types of abnormally slow growth in butter cultures is the sudden manner in which the defect often occurs. A culture may appear satisfactory at the time it is used for inoculation and then fail to bring about the desired changes in the product being manufactured. Such an occurrence greatly interferes with general plant routine. If additional time is allowed for the formation of acid, a defective product may result. Sometimes acid development is so slow and the defects in the product being manufactured so serious that the finished material is unsalable. There are various causes of slow acid production by butter cultures. Some of these are easily determined by investigation of the methods used in propagation or by direct microscopic examination of the cultures. In other cases such methods fail to disclose the cause or causes of the abnormally slow growth, and the rather unusual aspects of such cases have motivated the work herein reported

Generalized Swiss-cheese cosmologies: Mass scales

We generalize the Swiss-cheese cosmologies so as to include nonzero linear momenta of the associated boundary surfaces. The evolution of mass scales in these generalized cosmologies is studied for a variety of models for the background without having to specify any details within the local inhomogeneities. We find that the final effective gravitational mass and size of the evolving inhomogeneities depends on their linear momenta but these properties are essentially unaffected by the details of the background model.Comment: 10 pages, 14 figures, 1 table, revtex4, Published form (with minor corrections