Digital Three-Dimensional Atlas of Quail Development Using High-Resolution MRI

We present an archetypal set of three-dimensional digital atlases of the quail embryo based on microscopic magnetic resonance imaging (µMRI). The atlases are composed of three modules: (1) images of fixed ex ovo quail, ranging in age from embryonic day 5 to 10 (e05 to e10); (2) a coarsely delineated anatomical atlas of the µMRI data; and (3) an organ system–based hierarchical graph linked to the anatomical delineations. The atlas is designed to be accessed using SHIVA, a free Java application. The atlas is extensible and can contain other types of information including anatomical, physiological, and functional descriptors. It can also be linked to online resources and references. This digital atlas provides a framework to place various data types, such as gene expression and cell migration data, within the normal three-dimensional anatomy of the developing quail embryo. This provides a method for the analysis and examination of the spatial relationships among the different types of information within the context of the entire embryo

Algebraic and combinatorial aspects of sandpile monoids on directed graphs

The sandpile group of a graph is a well-studied object that combines ideas from algebraic graph theory, group theory, dynamical systems, and statistical physics. A graph's sandpile group is part of a larger algebraic structure on the graph, known as its sandpile monoid. Most of the work on sandpiles so far has focused on the sandpile group rather than the sandpile monoid of a graph, and has also assumed the underlying graph to be undirected. A notable exception is the recent work of Babai and Toumpakari, which builds up the theory of sandpile monoids on directed graphs from scratch and provides many connections between the combinatorics of a graph and the algebraic aspects of its sandpile monoid. In this paper we primarily consider sandpile monoids on directed graphs, and we extend the existing theory in four main ways. First, we give a combinatorial classification of the maximal subgroups of a sandpile monoid on a directed graph in terms of the sandpile groups of certain easily-identifiable subgraphs. Second, we point out certain sandpile results for undirected graphs that are really results for sandpile monoids on directed graphs that contain exactly two idempotents. Third, we give a new algebraic constraint that sandpile monoids must satisfy and exhibit two infinite families of monoids that cannot be realized as sandpile monoids on any graph. Finally, we give an explicit combinatorial description of the sandpile group identity for every graph in a family of directed graphs which generalizes the family of (undirected) distance-regular graphs. This family includes many other graphs of interest, including iterated wheels, regular trees, and regular tournaments.Comment: v2: Cleaner presentation, new results in final section. Accepted for publication in J. Combin. Theory Ser. A. 21 pages, 5 figure

The Education System in Mexico

Over the last three decades, a significant amount of research has sought to relate educational institutions, policies, practices and reforms to social structures and agencies. A number of models have been developed that have become the basis for attempting to understand the complex relation between education and society. At the same time, national and international bodies tasked with improving educational performances seem to be writing in a void, in that there is no rigorous theory guiding their work, and their documents exhibit few references to groups, institutions and forces that can impede or promote their programmes and projects. As a result, the recommendations these bodies provide to their clients display little to no comprehension of how and under what conditions the recommendations can be put into effect. The Education System in Mexico directly addresses this problem. By combining abstract insights with the practicalities of educational reforms, policies, practices and their social antecedents, it offers a long overdue reflection of the history, effects and significance of the Mexican educational system, as well as presenting a more cogent understanding of the relationship between educational institutions and social forces in Mexico and around the world

DIRECT ESTIMATION OF ABOVEGROUND FOREST PRODUCTIVITY THROUGH HYPERSPECTRAL REMOTE SENSING OF CANOPY NITROGEN

The concentration of nitrogen in foliage has been related to rates of net photosynthesis across a wide range of plant species and functional groups and thus represents a simple and biologically meaningful link between terrestrial cycles of carbon and nitrogen. Although foliar N is used by ecosystem models to predict rates of leaf‐level photosynthesis, it has rarely been examined as a direct scalar to stand‐level carbon gain. Establishment of such relationships would greatly simplify the nature of forest C and N linkages, enhancing our ability to derive estimates of forest productivity at landscape to regional scales. Here, we report on a highly predictive relationship between whole‐canopy nitrogen concentration and aboveground forest productivity in diverse forested stands of varying age and species composition across the 360 000‐ha White Mountain National Forest, New Hampshire, USA. We also demonstrate that hyperspectral remote sensing can be used to estimate foliar N concentration, and hence forest production across a large number of contiguous images. Together these data suggest that canopy‐level N concentration is an important correlate of productivity in these forested systems, and that imaging spectrometry of canopy N can provide direct estimates of forest productivity across large landscapes

Isoprenoids determine Th1/Th2 fate in pathogenic T cells, providing a mechanism of modulation of autoimmunity by atorvastatin.

3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is a critical enzyme in the mevalonate pathway that regulates the biosynthesis of cholesterol as well as isoprenoids that mediate the membrane association of certain GTPases. Blockade of this enzyme by atorvastatin (AT) inhibits the destructive proinflammatory T helper cell (Th)1 response during experimental autoimmune encephalomyelitis and may be beneficial in the treatment of multiple sclerosis and other Th1-mediated autoimmune diseases. Here we present evidence linking specific isoprenoid intermediates of the mevalonate pathway to signaling pathways that regulate T cell autoimmunity. We demonstrate that the isoprenoid geranylgeranyl-pyrophosphate (GGPP) mediates proliferation, whereas both GGPP and its precursor, farnesyl-PP, regulate the Th1 differentiation of myelin-reactive T cells. Depletion of these isoprenoid intermediates in vivo via oral AT administration hindered these T cell responses by decreasing geranylgeranylated RhoA and farnesylated Ras at the plasma membrane. This was associated with reduced extracellular signal-regulated kinase (ERK) and p38 phosphorylation and DNA binding of their cotarget c-fos in response to T cell receptor activation. Inhibition of ERK and p38 mimicked the effects of AT and induced a Th2 cytokine shift. Thus, by connecting isoprenoid availability to regulation of Th1/Th2 fate, we have elucidated a mechanism by which AT may suppress Th1-mediated central nervous system autoimmune disease

Biological movement and the encoding of its motion and orientation

Are you walking at me? Biological movement and the encoding of its motion and orientation. A person's motion conveys a wealth of information that ranges from the complex, such as intention or emotional state, to the simple, such as direction of locomotion. How we recognise and recover people's motion is addressed by models of biological motion processing. Single channel models propose that this occurs through the operation of form template neurons which respond to viewpoint dependent snapshots of posture. More controversially, a dual channel approach proposes a second stream containing motion template neurons sensitive to view dependent snapshots of biological movement's characteristic local velocity field. We used behavioural adaptation to look for the co-encoding of viewpoint and walker motion, a hallmark of motion template analysis. We show that opposite viewpoint aftereffects can simultaneously be induced for forwards and reversed walkers. This demonstrates that distinct populations of neurons encode forwards and reversed walking. To account for such aftereffects, these units must either be able to inhibit viewpoint-encoding neurons, or they must encode viewpoint directly. Whereas current single channel models would need extending to incorporate these characteristics, the idea that walker motion is encoded directly, such that viewpoint and motion are intrinsically interlinked, is a fundamental component of the dual channel model

Compactness of the space of causal curves

We prove that the space of causal curves between compact subsets of a separable globally hyperbolic poset is itself compact in the Vietoris topology. Although this result implies the usual result in general relativity, its proof does not require the use of geometry or differentiable structure.Comment: 15 page

The Use of Aerial Radiometrics for Epidemiological Studies of Leukaemia: a Preliminary Investigation in SW England

The report presents the results and conclusions of a pilot study designed to evaluate the potential use of aerial gamma ray measurements in epidemiological investigations of leukaemia. The sources of natural radiation were reviewed and associations between U, Th and K and dose to the human population noted. The association between leukaemia and radiation exposure was also noted, in particular the clear evidence from high dose studies, the potential importance of radium and radon, and the difficulties of achieving statistical significance in case-control studies at environmental dose rates due to the need for large area surveys covering large populations. Aerial surveys were conducted in three disjoint grids selected by the Leukaemia Research Fund Clinical epidemiology unit at Leeds University. The areas covered some 2,500 km, and were surveyed in a 50 hour fieldwork period in September 1989. Over 4800 gamma spectra were recorded, representing between 200 and 400 times the number of measurements per unit area of the NRPB national maps, and an area sampling density some 106 times greater. The data were used to estimate specific activities of potassium, uranium and thorium. Environmental infinite matrix alpha and beta dose rates were calculated using equilibrium assumptions and gamma ray dose rates were estimated directly from the spectra. Mean values for gamma dose rates were compatible with NRPB estimates for the counties. The detailed gamma ray maps demonstrate that both radiation levels, and quality show local variations within each survey grid of a magnitude comparable with that observed in whole of the UK in national maps. Considerable caution is thus needed in using national data for epidemiological studies. Local variations, which can be clearly associated with underlying geological and geomorphological structures should be taken into account in such work. No significant enhancements were noted due to activities at the Devonport Dockyard, in keeping with published ground based monitoring. The main enhancement in the vicinity of Hinkley Point was due to the authorised discharge of 41Ar, which was clearly detected in the survey. Two methods for associating the radiometric results with epidemiological data were developed and applied. A case-control study was performed by matching case and control locations to individual spatially averaged radiometric results and comparing the associated radiation levels. The second method evaluated radiation stratified incidence rates by combining stratified case radiometric data with similar information estimated from a population density surface constructed for the grids. Weighted regression analysis was used to assess any associations. The results are in general limited by the low number of leukaemia cases within the study area, resulting in statistically weak or insignificant links. However positive associations between equivalent uranium and leukaemia, particularly in the grid including the rivers Tavy and Tamar, were observed in both case-control and incidence rate analyses. A negative association with equivalent Thorium observed in the incidence rate analysis was not reproduced in case-control comparisons. This approach could be extended to larger area studies to increase statistical power. In parallel investigations of the relationship between environmental and individual radiation exposure, and investigation of the potential association between radium, or radon and leukaemia following the trends observed here would be appropriate

A disk census for the nearest group of young stars: Mid-infrared observations of the TW Hydrae Association

A group of young, active stars in the vicinity of TW Hydrae has recently been identified as a possible physical association with a common origin. Given its proximity ($\sim$50 pc), age ($\sim$10 Myr) and abundance of binary systems, the TW Hya Association is ideally suited to studies of diversity and evolution of circumstellar disks. Here we present mid-infrared observations of 15 candidate members of the group, 11 of which have no previous flux measurements at wavelengths longer than 2$\mu$m. We report the discovery of a possible 10$\mu$m excess in CD -33$^{\circ}$7795, which may be due to a circumstellar disk or a faint, as yet undetected binary companion. Of the other stars, only TW Hya, HD 98800, Hen 3-600A, and HR 4796A -- all of which were detected by IRAS -- show excess thermal emission. Our 10$\mu$m flux measurements for the remaining members of the Association are consistent with photospheric emission, allowing us to rule out dusty inner disks. In light of these findings, we discuss the origin and age of the TW Hya Association as well as implications for disk evolution timescales.Comment: 10 pages and 1 PostScript figure, accepted for publication in The Astrophysical Journal Letter