Réseaux sans fil dans les pays en développement
Le livre Réseaux sans fil dans les pays en développement peut être gratuitement téléchargé au complet ou par chapitres en format PDF.
Food Insufficiency Is Associated with High-Risk Sexual Behavior among Women in Botswana and Swazilan
Background Both food insufficiency and HIV infection are major public health problems in sub-Saharan Africa, yet the impact of food insufficiency on HIV risk behavior has not been systematically investigated. We tested the hypothesis that food insufficiency is associated with HIV transmission behavior. Methods and Findings We studied the association between food insufficiency (not having enough food to eat over the previous 12 months) and inconsistent condom use, sex exchange, and other measure
Carex communis habit
Carex communis habit. For context, see: Carex communis species page and Carex Interactive Identification Key.
Symmetries and Their Properties-Part 4: Glide Reflections
A glide reflection is a symmetry transformation that consists of a translation followed by a reflection across the translation line. Of all the different symmetries, this is the hardest for students to understand and to identify. Glide reflections are very tricky to identify in a tiling or wallpaper pattern. The “footprints” image helps, but you can still expect students to have trouble. Using tracing paper over a design may also help.
Sticks and Stones Game
Students will play Sticks and Stones, a game based on the Apache game "Throw Sticks," which was played at multi-nation celebrations. Students will collect data, investigate the likelihood of various moves, and use basic ideas of expected value to determine the average number of turns needed to win a game.
X-Ray Vision, Crystallography
This site features a tutorial designed to allow students to gain an appreciation of how X-ray crystallography works. Using X-ray diffraction patterns to determine the arrangement of atoms in a molecule requires sophisticated mathematics. This activity depends only on light from an overhead projector passing through a ball-and-stick molecular model placed on the stage of the projector, making it an ideal introduction to x-ray diffraction.
Twinning, Polymorphism, Polytypism, Pseudomorphism
This site is a lecture by Dr. Stephen Nelson from Tulane University that discusses the various nonstandard forms of crystal growth that are characteristic to some minerals. Topics include twinning (contact and penetration, polysynthetic and cyclical), the origins of twinning, and twin laws in the triclinic, monoclinic, orthorhombic, tetragonal, hexagonal, and isometric systems. Various types of polymorphism in many minerals are discussed as well as polytypism, metamict minerals, mineraloids, and
The Atmosphere And Its Relation To The Crust And Hydrosphere
This site provides an illustrated lecture from a geochemistry course offered by Dr. Scott Wood at the University of Idaho. Topics include a review of the structure and formation of the Earth's crust, atmosphere, and hydrological cycle, and the composition of the atmosphere. Additional topics covered are the concept of residence time, geological and biological sources of components in the atmosphere, acid-base theory, Henry's law and the solubility of gases in water, primary and secondary air pol
Origin Of The Universe And The Abundance Of Elements
This resource features an illustrated lecture from a geochemistry course offered by Dr. Scott Wood at the University of Idaho. Topics include the Big Bang theory, the evolution of stars, the relative abundances of elements in the Universe, and some fundamental nucleosynthetic processes that explain elemental abundance patterns. The lecture presentation may be downloaded as a PDF document or a PowerPoint presentation. Reading assignments and a homework problem set with answers is also provided.
Axial Ratios, Parameters, Miller Indices
This site is a lecture about crystal structure from Dr. Stephen Nelson at Tulane University. Topics include axial ratios, intercepts of crystal faces (Weiss Parameters), determination of the Miller Index of a crystal, the modified notation of hexagonal systems, which is referred to as Miller-Bravais Indices, and using the Miller Index notation to designate crystal forms. Tables and illustrations accompany the text.
Plate Tectonic Movement Visualizations
This collection provides a wide array of visual resources and supporting material about plate tectonic movements. Visualizations include simple animations, GIS-based animated maps, paleogeographic maps and globes, and numerous illustrations and photos. This collection is not exhaustive but does represent some of the best sources for teaching. Resources can be incorporated into lectures, labs, or other activities.
Glacial Landforms Resulting from Erosion and Deposition
This site provides visual resources and supporting material about how glaciers modify the landscape. Animations and movies illustrate both depositional and erosional landforms such as moraines, outwash plains, U-shaped valleys, cirques, and hanging waterfalls. These resources may be incorporated into lectures, labs, and other activities.
This site provides visual resources that illustrate the process of chemical weathering. Animations demonstrate how temperature and precipitation affect the evolution of parent material from highly resistant primary minerals to both secondary minerals and minerals in solution, as well as showing rates of weathering of various common minerals. A collection of photographs gives examples of chemical weathering in both natural outcrops and constructed features such as tombstones and carvings. These r
Crystal Growth Movies
This site, maintained by the Department of Geology and Geophysics at the University of Wyoming, contains four QuickTime videos of actual crystal growth. To access the videos, scroll down to the bottom of the page and click on any of the downloads that are available. These videos enhance understanding of the processes involved in crystallization.
Observe River Erosion Creating Waterfalls and Chasms
This animation illustrates the processes involved in waterfall formation. Related features such as chasms and plunge pools, as well as headward erosion and migration are also portrayed. Users can stop, play, fast forward and rewind the animation at any time. This visualization is one of several animations in a series developed as a component of Exploring Earth, a website that supports the textbook Earth Science.
Animation Showing Growth of a Continent
This Flash animation illustrates continental growth. It shows a convergent boundary where a terrane on a subducting plate is fused to the edge of a continent. Users can stop, play, fast forward and rewind the animation at any time. This visualization is one of several animations in a series developed as a component of Exploring Earth, a website that supports the textbook Earth Science.
Graphical Representation of Geologic Time
This spiral graph visualization, which includes both marine and terrestrial components, represents 4.5 billion years of geologic time. Stratigraphy, paleontology, and geochronology study results provide evidence in support of this old earth. This graphical representation is from an article called Age of the Earth.
CLT: Exploring Climate Events and Human Development
This animation on the Climate TimeLine (CTL) site depicts changes in land cover due to land use over the past 100 years. Data is based on census data, tax records, land surveys, and historical geography estimates. This visualization is the work of the National Institute of Public Health and the Environment (RIVM, Netherlands) and the Center for Sustainability and the Global Environment (SAGE, USA).
Part of the supporting resources for the School of Earth Sciences dynamic earth module, the -Why Topography?- site discusses two models introduced in the 19th century that are still used to explain topographic variations. These models are the Pratt and Airy models of isostasy. In the Pratt model, high topography (relative to surroundings) is due to lower density whereas in the Airy model, high topography is due to thick crust.
Impact of the Seasons on Earth Systems
This site features Flash animations that illustrate how seasons impact various Earth systems, including surface temperature, latent heat flux, air temperature, net radiation, precipitation, runoff, and soil moisture. These resources are suitable for use in lectures, labs, or other teaching activities.