Flat rank of automorphism groups of buildings

The flat rank of a totally disconnected locally compact group G, denoted flat-rk(G), is an invariant of the topological group structure of G. It is defined thanks to a natural distance on the space of compact open subgroups of G. For a topological Kac-Moody group G with Weyl group W, we derive the inequalities: alg-rk(W)\le flat-rk(G)\le rk(|W|\_0). Here, alg-rk(W) is the maximal $\mathbb{Z}$-rank of abelian subgroups of W, and rk(|W|\_0) is the maximal dimension of isometrically embedded flats in the CAT0-realization |W|\_0. We can prove these inequalities under weaker assumptions. We also show that for any integer n \geq 1 there is a topologically simple, compactly generated, locally compact, totally disconnected group G, with flat-rk(G)=n and which is not linear

Linking engagement and performance: The social network analysis perspective

Theories developed by Tinto and Nora identify academic performance, learning gains, and involvement in learning communities as significant facets of student engagement that, in turn, support student persistence. Collaborative learning environments, such as those employed in the Modeling Instruction introductory physics course, provide structure for student engagement by encouraging peer-to-peer interactions. Because of the inherently social nature of collaborative learning, we examine student interactions in the classroom using network analysis. We use centrality---a family of measures that quantify how connected or "central" a particular student is within the classroom network---to study student engagement longitudinally. Bootstrapped linear regression modeling shows that students' centrality predicts future academic performance over and above prior GPA for three out of four centrality measures tested. In particular, we find that closeness centrality explains 28 % more of the variance than prior GPA alone. These results confirm that student engagement in the classroom is critical to supporting academic performance. Furthermore, we find that this relationship for social interactions does not emerge until the second half of the semester, suggesting that classroom community develops over time in a meaningful way

Nanoparticle Induced Cell Magneto-Rotation for the Multiplexed Monitoring of Morphology, Stress and Drug Sensitivity of Suspended Single Cancer Cells.

The metastatic process of a cancer relies on the transformation of some of the primary tumor cells into cells capable of migrating through the Extra-Cellular Matrix (ECM), surrounding the tumor, into the bloodstream and the lymph nodes, and then settle in distant tissue, growing new secondary tumors. By identifying, characterizing and quantifying these cells, the progression of cancer in a patient during therapy can be more accurately assessed. Here we describe the development of a new method for quantitative real time monitoring of cell size and morphology, on single live suspended cancer cells, unconfined in three dimensions. The enabling cell magnetorotation (CM) method is made possible by nanoparticle induced cell magnetization. Using a rotating magnetic field, the magnetically labeled cells are actively rotated, then imaged, using a high definition CCD camera. Under proper conditions, the rotation period of a magnetic object is proportional to its shape factor. We demonstrate first that the rotational period, when measured in real-time, can serve to track cellular response to drugs, cytotoxic agents and other chemical stimuli. In addition, while cells are rotated, they exhibit very specific morphological activities, even without a chemical stimulus. Described also is how to multiplex the CM method, to image several dozens to several thousands of cells simultaneously, and using morphology to classify cells into different phenotypic categories, with each phenotype being correlated with malignancy level. The intrinsic tumor heterogeneity, at the cellular level, can be visualized with relationship graphs. Shown is the ability to monitor cell morphological changes over long periods of time, in real time, in order to detect the metastatic potential for heterogeneous populations of cancer cells, using tools from statistical analysis methods. The method relies on unsupervised Machine Learning algorithms which do not require human inputs. Overall it is demonstrated that the CM method can be used as a diagnostic tool to evaluate the phenotypical heterogeneity in a cell population in general, and in a cancer cell population in particular. This fast and high throughput method promises to efficiently assess the efficacy of personalized therapeutic strategies.PHDApplied PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111434/1/relbez_1.pd

Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A grid of 200,000 YSO model SEDs

We present a grid of radiation transfer models of axisymmetric young stellar objects (YSOs), covering a wide range of stellar masses (from 0.1Msun to 50Msun) and evolutionary stages (from the early envelope infall stage to the late disk-only stage). The grid consists of 20,000 YSO models, with spectral energy distributions (SEDs) and polarization spectra computed at ten viewing angles for each model, resulting in a total of 200,000 SEDs. [...]. These models are publicly available on a dedicated WWW server: http://www.astro.wisc.edu/protostars/ . In this paper we summarize the main features of our models, as well as the range of parameters explored. [...]. We examine the dependence of the spectral indices of the model SEDs on envelope accretion rate and disk mass. In addition, we show variations of spectral indices with stellar temperature, disk inner radius, and disk flaring power for a subset of disk-only models. We also examine how changing the wavelength range of data used to calculate spectral indices affects their values. We show sample color-color plots of the entire grid as well as simulated clusters at various distances with typical {\it Spitzer Space Telescope} sensitivities. We find that young embedded sources generally occupy a large region of color-color space due to inclination and stellar temperature effects. Disk sources occupy a smaller region of color-color space, but overlap substantially with the region occupied by embedded sources, especially in the near- and mid-IR. We identify regions in color-color space where our models indicate that only sources at a given evolutionary stage should lie. [...].Comment: 69 pages, 28 figures, Accepted for publication in ApJS. Preprint with full resolution figures available at http://www.astro.wisc.edu/protostars

2-D and 3-D Radiation Transfer Models of High-Mass Star Formation

2-D and 3-D radiation transfer models of forming stars generally produce bluer 1-10 micron colors than 1-D models of the same evolutionary state and envelope mass. Therefore, 1-D models of the shortwave radiation will generally estimate a lower envelope mass and later evolutionary state than multidimensional models. 1-D models are probably reasonable for very young sources, or longwave analysis (wavelengths > 100 microns). In our 3-D models of high-mass stars in clumpy molecular clouds, we find no correlation between the depth of the 10 micron silicate feature and the longwave (> 100 micron) SED (which sets the envelope mass), even when the average optical extinction of the envelope is >100 magnitudes. This is in agreement with the observations of Faison et al. (1998) of several UltraCompact HII (UCHII) regions, suggesting that many of these sources are more evolved than embedded protostars. We have calculated a large grid of 2-D models and find substantial overlap between different evolutionary states in the mid-IR color-color diagrams. We have developed a model fitter to work in conjunction with the grid to analyze large datasets. This grid and fitter will be expanded and tested in 2005 and released to the public in 2006.Comment: 10 pages, 8 figures, to appear in the proceedings of IAU Symp 227, Massive Star Birth: A Crossroads of Astrophysics, (Cesaroni R., Churchwell E., Felli M., Walmsley C. editors

Influence of coating on the thermal resistance of a Ni-Based superalloy

In this paper, the influence of M-CrAlY polycrystalline coating on the thermal fatigue behavior of a Nickel-base superalloy has been investigated. A special device using a rotating bending machine and two thermal sources has been used to perform thermo-mechanical tests. The two thermal sources have been set to obtain temperature variations between 750 and 1120 °C in the central part of the specimens, with a frequency of 0.1 Hz. The results showed a deleterious effect of the coating on the fatigue resistance. Numerical simulations have been carried out on SAMCEF to determine the thermo-mechanical field of the so-tested specimens. Calculated thermo-mechanical cycles of critical sites are associated with microstructure evolution and damage by cracking observed on the specimens. Damage mechanisms related to the presence of coating are discussed

Utilisation d'un «indice de réflexion» pour l'analyse rapide des sédiments lacustres

L'indice de réflexion ou réflectance donne une mesure de la teinte du sédiment entre le blanc (100 %) et le noir (0 %). Sa valeur est directement liée à la teneur en matières organiques.Les relations entre l'indice de réflexion et les teneurs en carbone organique, en azote Kjeldahl et en carbonates sont données pour les sédiments de dix lacs différents.Une étude particulière de prélèvements superficiels et de prélèvements profonds montre qu'une simple mesure de la réflectance donne une valeur approchée de la composition chimique.Thorough studies on many lakes in Franche-Comté, especially chemical and physical investigations concerning sediments, have been carried out for several years. Seventy-one sediment samples have been extracted at different points and depths of ten lakes in Franche-Comté. The upper stratum between 0 and - 2,5 cm were isolated and studied.A comparison of visual observations and results of chemical analysis have shown that the darkest sediments are those which contain the greatest amount of organic matter. This finds its origin in a particularity of Franche-Comté lake sediments, which are often composed of dark black organic matter in different evolutionary states, and clear mineral compounds such as calcium carbonate and detrital particles.Differences in colouration were particularly difficult to determine, so colours were defined by the reflexion factor of the sediment surfaces, after the sediments had been well dried and homogeneized.The reflectance index was measured with a reftectometer, which is generally used for determinations of dark smokes in air pollution. The reflectance index was defined between the values 0 and 100. The value 0 was obtained with a standard black glass and the value 100 with a white filter paper.Comparing reflectance indices and ignition loss has shown that there is an exponential relationship between these two parameters. These relationships were found to exist between the reflectance index and organic carbon, Kjeldahl nitrogen and carbonates.Ignition loss, organic carbon and Kjeldahl nitrogen proportions increase, but, on the contrary, carbonate proportions decrease when the reflexion index increases.The values calculated and observed were then compared and generally the difference does not appear to be too great. Once, relationships have been established, it becomes possible to use them, after measuring reflexion indices, to obtain quickly and easily a good approximation of the composition.Special relationships may also be calculated for an individual lake, as shown for St-Point Lake. If one mineral constituent prevails in the composition, it is possible to obtain a good estimation of this component.For this lake twenty-eight sediment samples were extracted and for each sample three strata were separated. The reflectance index was again defined between the values 0 and 100, but the value 100 was now obtained by using a flat calcium carbonate surface, as the principal mineral part of St-Point Lake consists of calcium carbonate.Recent results obtained from two lake sediments of the Massif Central indicate that such relationships also exist for these lakes and that this method of estimating the chemical composition can be generalised.The calculated composition may often be sufficient to estimate values required for others studies on the same lakes, especially biological studies, thus avoiding laborious and extensive chemical determinations