Birth, death and diffusion of interacting particles

Individual-based models of chemical or biological dynamics usually consider individual entities diffusing in space and performing a birth-death type dynamics. In this work we study the properties of a model in this class where the birth dynamics is mediated by the local, within a given distance, density of particles. Groups of individuals are formed in the system and in this paper we concentrate on the study of the properties of these clusters (lifetime, size, and collective diffusion). In particular, in the limit of the interaction distance approaching the system size, a unique cluster appears which helps to understand and characterize the clustering dynamics of the model.Comment: 15 pages, 6 figures, Iop style. To appear in Journal of Physics A: Condensed matte

Precise measurements of UV atomic lines: Hyperfine structure and isotope shifts in the 398.8 nm line of Yb

We demonstrate a technique for frequency measurements of UV transitions with sub-MHz precision. The frequency is measured using a ring-cavity resonator whose length is calibrated against a reference laser locked to the $D_2$ line of $^{87}$Rb. We have used this to measure the 398.8 nm ${^1S}_0 \leftrightarrow {^1P}_1$ line of atomic Yb. We report isotope shifts of all the seven stable isotopes, including the rarest isotope $^{168}$Yb. We have been able to resolve the overlapping $^{173}$Yb($F = 3/2$) and $^{172}$Yb transitions for the first time. We also obtain high-precision measurements of excited-state hyperfine structure in the odd isotopes, $^{171}$Yb and $^{173}$Yb. The measurements resolve several discrepancies among earlier measurements.Comment: 7 pages, 6 figure

On certain relationships between cosmological observables in the Einstein-Cartan gravity

We show that in the Einstein-Cartan gravity it is possible to obtain a relation between Hubble's expansion and the global rotation (vorticity) of the Universe. Gravitational coupling can be reduced to dimensionless quantity of order unity, fixing the scalar mass density and the resulting negative cosmological constant at spacelike infinity. Current estimates of the expansion and rotation (see also astro-ph/9703082) of the Universe favour the massive spinning particles as candidate particles for cold and hot dark matter. Nodland and Ralston vorticity (Phys. Rev. Lett. 78 (1997) 3043) overestimates the value favoured by the Einstein-Cartan gravity for three orders of magnitude.Comment: 7 pages, LaTeX styl

Student Perceptions Of The Online Classroom: An Update

In this paper, the authors compare perceptions of 2001-2002 undergraduate students toward online courses, with the attitudes of undergraduate students matriculating in 2005. Specifically, a questionnaire developed and used in a study during the period 2001-2002, in which there were eight hundred ninety-six (896) undergraduate students at two medium-sized southern universities, was again given to six hundred twenty-six (626) undergraduate students at these same two universities in 2005. The results suggest that students continue to have questions about the overall appeal of online courses, despite the fact that three to four years have elapsed. The results of this study should be of interest to university administrators, faculty members, and students who plan to offer, teach, or take online courses in the future. This information may be helpful to university administrators in deciding which types of courses at their universities might be offered online. Faculty who are considering teaching one or more online courses may find the results of this study helpful in structuring these online offerings. This research is also intended to give students a realistic expectation of what to anticipate from online courses, based upon information we have found and studies we have done

Biases in the polarization position angles in the NVSS point source catalogue

We have examined the statistics of the polarization position angles determined for point sources in the NRAO-VLA sky survey (NVSS) and find that there is a statistically significant bias toward angles which are multiples of 45 degrees. The formal probability that the polarization angles are drawn from a uniform distribution is exponentially small. When the sample of those NVSS sources with polarizations detected with a signal to noise $\geq$3 is split either around the median polarized flux density or the median fractional polarization, the effect appears to be stronger for the more highly polarized sources. Regions containing strong sources and regions at low galactic latitudes are not responsible for the non-uniform distribution of position angles. We identify CLEAN bias as the probable cause of the dominant effect, coupled with small multiplicative and additive offsets on each of the Stokes parameters. Our findings have implications for the extraction of science, such as information concerning galactic magnetic fields, from large scale polarization surveys

What Would Happen If You Ditched Your Textbook? Gettysburg Faculty Share Strategies

How much do your course materials really cost? Do your students obtain all the books you assign? How much does access to required readings affect student success? What would happen if you ditched your textbook? If you’ve ever been tempted to toss your conventional reading list out the window and start over, this session is for you. Learn how colleagues are swapping out expensive course materials for more affordable options, including freely available materials, library-licensed items, and original creations. Our panelists are: Ian Clarke – Ian recently abandoned his $150 textbook for ENG 111 (Writing through Literature) and created an open reading list instead. Sharon Birch – In 2011, Sharon dropped the classic text for SOC 203 (Population) and replaced it with a variety of library-licensed and freely available materials. More recently she has begun developing her own open textbook for this course. Chuck Kann – Chuck has written several open educational resources and posted them in The Cupola. He uses them in CS 221 (Computer Organization and Assembly Language Programming); they have also been adopted by professors teaching at other institutions and have been downloaded around the world. You’ll leave with a clear idea of how a range of simple to complex strategies could help make your course materials more affordable, too