972,821 research outputs found
Test well exploration in the Myakka River Basin area, Florida
In recent years, difficulties encountered in obtaining ground-water supplies
with acceptable chemical characteristics in the Myakka River basin area led to
the implementation of a test drilling program. Under this program, well drilling
and data collection were executed in such a manner that all water-producing
zones of the local aquifers, together with the quality and quantity of the water
available, were effectively identified.
A step-drilling method was utilized which allowed the collection of
formation cuttings, water samples, and water-level data, from isolated zones in
the well as drilling proceeded. The step drilling procedure is described. The
driller's logs, geophysical logs, and chemical quality of water tables are
presented.(Document has 66 pages.
Break-up of shells under explosion and impact
A theoretical and experimental study of the fragmentation of closed thin
shells made of a disordered brittle material is presented. Experiments were
performed on brown and white hen egg-shells under two different loading
conditions: fragmentation due to an impact with a hard wall and explosion by a
combustion mixture giving rise to power law fragment size distributions. For
the theoretical investigations a three-dimensional discrete element model of
shells is constructed. Molecular dynamics simulations of the two loading cases
resulted in power law fragment mass distributions in satisfactory agreement
with experiments. Based on large scale simulations we give evidence that power
law distributions arise due to an underlying phase transition which proved to
be abrupt and continuous for explosion and impact, respectively. Our results
demonstrate that the fragmentation of closed shells defines a universality
class different from that of two- and three-dimensional bulk systems.Comment: 11 pages, 14 figures in eps forma
Increased resistance to stress corrosion of aluminum alloys
Stress corrosion resistance is increased by distorting surface grain-boundary structure and by interrupting the corrosion and stress corrosion. The first is accomplished by machining or shot peening and the second by removal from and later reexposure to the corrosive environment
A shortcut to the riddle of the moon
The Lunar Data Information Center which serves as a reference and lending collection is described. The Center incorporates such methods as a classification scheme for mission-oriented documentation, sample photo browse files, lunar feature index, and color coding; a computer-based Moon Literature Bibliography provides search capability
Rapid and precise analysis for calcium in blood serum
Differential absorption spectrophotometric technique, using murexide, gives a highly precise analysis of calcium in volumes of blood serum as small as 0.01 ml. The method of additions and proper timing allows compensation to be made for fading, variation in type of serum or plasma, and aging of the specimen
Enhanced domain wall velocity near a ferromagnetic instability
Assuming a Fermi liquid behavior for -conduction electrons, we rewrite the
extended Landau-Lifshitz-Gilbert (LLG) equation renormalized by interactions
through the Landau parameters () in an explicit
form to describe the dynamic of a domain wall (DW) due to spin transfer torque
phenomenon. The interaction between spins of the \textit{s}-conduction
electrons explains qualitatively the DW velocity experimental observations in
(Permalloy) recalculated by us without
defects or impurity hypothesis. Close to Stoner ferromagnetic instability point
where , the DW velocity becomes high
( ) and critical spin current density becomes
reduced ( ) when compared to that
calculated by nonadiabatic approach. At the critical point, the DW velocity
diverges while critical spin current density at the same point goes to zero.
Our theory also provides a prediction to looking for materials in which is
possible applies a smallest critical spin current density and observes higher
DW velocity.Comment: 7 pages, 5 figure
Conceptual and socio-cognitive support for collaborative learning in videoconferencing environments
Studies have shown that videoconferences are an effective medium for facilitating communication between parties who are separated by distance. Furthermore, studies reveal that videoconferences are effective when used for distance learning, particularly when learners are engaged in complex collaborative learning tasks. However, as in face-to-face communication, learners benefit most when they receive additional support for such learning tasks. This article provides an overview of three empirical studies to illustrate more general insights regarding some of the more and less effective ways of supporting collaborative learning with videoconferencing. The focus is on conceptual support, such as structural visualization and socio-cognitive support, such as scripts. Based on the results of the three studies, conclusions can be drawn about the conceptual and socio-cognitive support measures that promote learning. Conclusions can also be reached about the need for employing both conceptual and socio-cognitive support to provide learners with the most benefit
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