STEM CELL GROWTH AND DIFFERENTIATION IN HYDRA ATTENUATA

The differentiation of nerve cells and nematocytes from interstitial stem cells in Hydra has been investigated under conditions of changing stem cell density. Interstitial stem cells were cultured in a feeder layer system consisting of aggregates of nitrogen mustard-inactivated tissue. The aggregates were seeded with varying numbers of stem cells from 10 to 400 per aggregate; between 4 and 7 days later the rates of nerve and nematocyte differentiation were measured. Nerve differentiation was scored by labelling the stem cell population with [3H]-thymidine and counting nests of 4 proliferating nematoblasts. In both cases the numbers of differentiating cells were normalized to the size of the stem cell population. The results indicate that the rate of nematocyte differentiation increases as the concentration of stem cells increases in aggregates; under the same conditions the rate of nerve differentiation remains essentially constant. To calculate the numbers of stem cells entering each pathway per generation, a computer was programmed to simulate the growth and differentiation of interstitial stem cells. Standard curves were prepared from the simulations relating the rates of nerve and nematocyte differentiation to the fraction of stem cells committed to each pathway per generation. The rates of nerve and nematocyte commitment were then estimated from the experimentally observed rates of differentiation using the standard curves. The results indicate that nerve commitment remains constant at about 0.13 stem cells per generation over a wide range of stem cell concentration. Nematocyte commitment, by comparison, increases from 0.15 to 0.21 stem cells per generation as stem cell concentration increases in aggregates. The fact that the ratio of nerve to nematocyte commitment changes under our conditions suggests that stem cell commitment is not a stochastic process but subject to control by environmental stimuli

Preliminary Results on the Structure and Functioning of a Taiga Watershed

Comprehensive research in ecosystem functioning may logically be undertaken in the conceptual and physical context of complete drainage basins (watersheds or catchments). The watershed forms a fundamental, cohesive landscape unit in terms of water movement following initial receipt of precipitation. Water itself is a fundamental agent in energy flux, nutrient transport, and in plant and animal life. The Caribou-Poker Creeks Research Watershed is an interagency endeavor aimed at understanding hydrologic and, ultimately, ecological functioning in the subarctic taiga, the discontinuous permafrost uplands of central Alaska. Initial work includes acquisition and analysis of data on soils, vegetation, local climate, hydrology, and stream quality. Information acquired in the research watershed is summarized here, and implications for future data acquisition and research are considered

The Potential Applications of Optical Dating to the Sandy Uplands of East Texas and Northwest Louisiana

The fine, sandy soils of East Texas and Northwest Louisiana have been the source of archaeological debate for some time. This discourse concerns the mode of burial of cultural material in the easily eroded soils and the mechanics of recent (Holocene) landform evolution. Because these deposits are typically well-drained, organic matter does not preserve well, thus hindering the dating of the geomorphic events that figure prominently in their development and the prehistoric occupations which lie buried throughout uplands of this region. A relatively new dating technique, optical dating, has much to offer this region and the archaeological community as it measures the period of time that has elapsed since sand grains were last exposed to sunlight. Hence, it directly dates the time of sediment transportation and deposition. This method is therefore applicable to a number of archaeological and geomorphic processes which may not be dated by traditional methods, owing to the lack of organic matter suitable for radiocarbon dating. In geomorphic contexts, optical dating may be preferred over radiocarbon as it directly dates the time of sedimentation rather than the age of organic matter in features such as buried soils that may be significantly different from the geomorphic event which fossilized the soil

Event-Cloud Platform to Support Decision- Making in Emergency Management

The challenge of this paper is to underline the capability of an Event-Cloud Platform to support efficiently an emergency situation. We chose to focus on a nuclear crisis use case. The proposed approach consists in modeling the business processes of crisis response on the one hand, and in supporting the orchestration and execution of these processes by using an Event-Cloud Platform on the other hand. This paper shows how the use of Event-Cloud techniques can support crisis management stakeholders by automatizing non-value added tasks and by directing decision- makers on what really requires their capabilities of choice. If Event-Cloud technology is a very interesting and topical subject, very few research works have considered this to improve emergency management. This paper tries to fill this gap by considering and applying these technologies on a nuclear crisis use-case

An analysis of the activities under Public Law 480 : the Food for Peace program

It has been my purpose in this research to unveil a clear picture of the historical activities of our Food For Peace Program, commonly know as Public Law 480, with the hope of\u27 being able to establish a basis for .future understanding. I have examined certain problems arising in both normal and abnormal situations in the activities under Public Law 480, and have presented views as to how they might be corrected or avoided

Floating potential curves

A new method for molecular calculations was applied to the hydrogen molecule ion. Energies were calculated at different internuclear separations and simple energy differences were found. The method used was an approximate one which included two basic approximations: the use of Gaussian wave functions and the one-center method. The one-center method gives a good approximation for the electronic energies but does not give near-atomic electron densities. The title Floating Potential Curves comes from the fact that the Gaussian wave functions give good potential curves over a restricted region, but these curves are not oriented correctly with respect to the minimum energy. This is an indication that calculated energy differences would be more accurate than calculated energies. This was seen to be true in a prior calculation

Sex differences in the proportion of cortex and medulla in the chicken suprarenal

Thesis (M.A.)--University of Kansas, Anatomy, 1931

The Ursinus Weekly, April 20, 1914

Varsity wins from Allentown • Scrubs win from Phoenixville • Society notes • F. & M. loses to varsity, 9-2 • Schaff prize debate • Wharton Hall needs a recreation room • An item worth while reading • Gleanings from other colleges • Personalshttps://digitalcommons.ursinus.edu/weekly/2696/thumbnail.jp