Stem cell mechanobiology

Stem cells are undifferentiated cells that are capable of proliferation, self-maintenance and differentiation towards specific cell phenotypes. These processes are controlled by a variety of cues including physicochemical factors associated with the specific mechanical environment in which the cells reside. The control of stem cell biology through mechanical factors remains poorly understood and is the focus of the developing field of mechanobiology. This review provides an insight into the current knowledge of the role of mechanical forces in the induction of differentiation of stem cells. While the details associated with individual studies are complex and typically associated with the stem cell type studied and model system adopted, certain key themes emerge. First, the differentiation process affects the mechanical properties of the cells and of specific subcellular components. Secondly, that stem cells are able to detect and respond to alterations in the stiffness of their surrounding microenvironment via induction of lineage-specific differentiation. Finally, the application of external mechanical forces to stem cells, transduced through a variety of mechanisms, can initiate and drive differentiation processes. The coalescence of these three key concepts permit the introduction of a new theory for the maintenance of stem cells and alternatively their differentiation via the concept of a stem cell 'mechano-niche', defined as a specific combination of cell mechanical properties, extracellular matrix stiffness and external mechanical cues conducive to the maintenance of the stem cell population.<br/

Impacts of recreation on biodiversity in wilderness

We discuss seven recreational impacts on biodiversity in wilderness areas. These include: 1) construction of trails, 2) trampling of vegetation and soils on trails and campsites, 3) collection and burning of wood in campfires, 4) water pollution associated with camping activities, 5) unintentional harassment of animals, 6) hunting, fishing, and associated management programs, and 7) grazing by processes and functions of ecosystems. The activities which have caused the greatest impact on diversity at a regional scale are fishing, hunting and associated management practices. None of these perturbations, however, have been studied in insufficient detail to assess their long-term impact

A Quarter-Century of Observations of Comet 10P/Tempel 2 at Lowell Observatory: Continued Spin-Down, Coma Morphology, Production Rates, and Numerical Modeling

We report on photometry and imaging of Comet 10P/Tempel 2 obtained at Lowell Observatory from 1983 through 2011. We measured a nucleus rotation period of 8.950 +/- 0.002 hr from 2010 September to 2011 January. This rotation period is longer than the period we previously measured in 1999, which was itself longer than the period measured in 1988. A nearly linear jet was observed which varied little during a rotation cycle in both R and CN images acquired during the 1999 and 2010 apparitions. We measured the projected direction of this jet throughout the two apparitions and, under the assumption that the source region of the jet was near the comet's pole, determined a rotational pole direction of RA/Dec = 151deg/+59deg from CN measurements and RA/Dec = 173deg/+57deg from dust measurements (we estimate a circular uncertainty of 3deg for CN and 4deg for dust). Different combinations of effects likely bias both gas and dust solutions and we elected to average these solutions for a final pole of RA/Dec = 162 +/- 11deg/+58 +/- 1deg. Photoelectric photometry was acquired in 1983, 1988, 1999/2000, and 2010/2011. The activity exhibited a steep turn-on ~3 months prior to perihelion (the exact timing of which varies) and a relatively smooth decline after perihelion. The activity during the 1999 and 2010 apparitions was similar; limited data in 1983 and 1988 were systematically higher and the difference cannot be explained entirely by the smaller perihelion distance. We measured a "typical" composition, in agreement with previous investigators. Monte Carlo numerical modeling with our pole solution best replicated the observed coma morphology for a source region located near a comet latitude of +80deg and having a radius of ~10deg. Our model reproduced the seasonal changes in activity, suggesting that the majority of Tempel 2's activity originates from a small active region located near the pole.Comment: Accepted by AJ; 29 pages of text (preprint style), 8 tables, 7 figure

Healthy Aging – Insights from Drosophila

Human life expectancy has nearly doubled in the past century due, in part, to social and economic development, and a wide range of new medical technologies and treatments. As the number of elderly increase it becomes of vital importance to understand what factors contribute to healthy aging. Human longevity is a complex process that is affected by both environmental and genetic factors and interactions between them. Unfortunately, it is currently difficult to identify the role of genetic components in human longevity. In contrast, model organisms such as C. elegans, Drosophila, and rodents have facilitated the search for specific genes that affect lifespan. Experimental evidence obtained from studies in model organisms suggests that mutations in a single gene may increase longevity and delay the onset of age-related symptoms including motor impairments, sexual and reproductive and immune dysfunction, cardiovascular disease, and cognitive decline. Furthermore, the high degree of conservation between diverse species in the genes and pathways that regulate longevity suggests that work in model organisms can both expand our theoretical knowledge of aging and perhaps provide new therapeutic targets for the treatment of age-related disorders

Using the Stallings Observation System to Investigate Time on Task in Four Countries

This paper presents the history of the Stallings Observation System (SOS) and describes the adaptation of the SOS instrument, training for its use in international settings, and results from four countries of the World Bank International Time on Task (ITOT) project. The ITOT project had three major goals: 1) to discover how instructional time is used at different levels in certain countries, particularly in rural and low income areas; 2) to identify obstacles to optimal use of instructional time; and 3) to encourage governments to take the necessary measures to provide students with optimal time for learning . In order to address ITOT at the classroom level, a pilot study in Tunisia was conducted that targeted four related objectives: 1)adaptation of the Stallings snapshot observation instrument for use in project classrooms; 2) design and implementation of training for observers; 3) determination of reliability and validity of observation procedures; and 4) generation of a sample profile of classrooms in a Tunisian elementary school. This paper summarizes the training and findings from the initial pilot study of time usage at the classroom level conducted in Tunisia in January, 2004 and the training and results from subsequent ITOT studies in four countries: Tunisia, Morocco, Ghana, and Brazil. More specifically, sections of the paper provide an overview of the research on effective use of instructional time using the Stallings instrument, description of the adaptation of the Stallings Snapshot observation instrument for use in the project, a summary of the training and procedures developed for the pilot study and implemented in four countries, and the results and conclusions from the observational studies in four countries

Planning Coverage Campaigns for Mission Design and Analysis: CLASP for DESDynl

Mission design and analysis presents challenges in that almost all variables are in constant flux, yet the goal is to achieve an acceptable level of performance against a concept of operations, which might also be in flux. To increase responsiveness, automated planning tools are used that allow for the continual modification of spacecraft, ground system, staffing, and concept of operations, while returning metrics that are important to mission evaluation, such as area covered, peak memory usage, and peak data throughput. This approach was applied to the DESDynl mission design using the CLASP planning system, but since this adaptation, many techniques have changed under the hood for CLASP, and the DESDynl mission concept has undergone drastic changes. The software produces mission evaluation products, such as memory highwater marks, coverage percentages, given a mission design in the form of coverage targets, concept of operations, spacecraft parameters, and orbital parameters. It tries to overcome the lack of fidelity and timeliness of mission requirements coverage analysis during mission design. Previous techniques primarily use Excel in ad hoc fashion to approximate key factors in mission performance, often falling victim to overgeneralizations necessary in such an adaptation. The new program allows designers to faithfully represent their mission designs quickly, and get more accurate results just as quickly

The Increasing Rotation Period of Comet 10P/Tempel 2

We imaged comet 10P/Tempel 2 on 32 nights from 1999 April through 2000 March. R-band lightcurves were obtained on 11 of these nights from 1999 April through 1999 June, prior to both the onset of significant coma activity and perihelion. Phasing of the data yields a double-peaked lightcurve and indicates a nucleus rotational period of 8.941 +/- 0.002 hr with a peak-to-peak amplitude of ~0.75 mag. Our data are sufficient to rule out all other possible double-peaked solutions as well as the single- and triple- peaked solutions. This rotation period agrees with one of five possible solutions found in post-perihelion data from 1994 by Mueller and Ferrin (1996, Icarus, 123, 463-477), and unambiguously eliminates their remaining four solutions. We applied our same techniques to published lightcurves from 1988 which were obtained at an equivalent orbital position and viewing geometry as in 1999. We found a rotation period of 8.932 +/- 0.001 hr in 1988, consistent with the findings of previous authors and incompatible with our 1999 solution. This reveals that Tempel 2 spun-down by ~32 s between 1988 and 1999 (two intervening perihelion passages). If the spin-down is due to a systematic torque, then the rotation period prior to perihelion during the 2010 apparition is expected to be an additional 32 s longer than in 1999.Comment: Accepted by The Astronomical Journal; 22 pages of text, 3 tables, 6 figure