Microbialcrusts are present on surfaces of soils throughout the world. A key feature of these crusts in arid zones is the abundance of filamentous sheath-forming and polysaccharide-excreting cyanobacteria. Several isolates of cyanobacteria were prepared from crust samples (Nizzana sand dunes, north-western Negev Desert, Israel). Optimal growth conditions for two such isolates of Microcoleus sp. were defined, and the role of the excreted polysaccharides in affecting the hydrological properties of crust-covered sand dunes was studied. Experiments with the native crust microbial population demonstrated the possibility of net primary productivity at both high relative air humidities and low moisture content.

A complete set of macroscopic equations, the solution of which describes fluid and solid stresses, displacements and temperatures, evolving from an excitation of a saturated porous medium domain in the form of an abrupt pressure and temperature changes applied at the domain's boundary is presented. The tluid is a compressible Newtonian one and the solid is thermoelastic. Nonisothermal conditions prevail. The set of equations includes mass, momentum and energy balance equations, constitutive relations and definitions. A simple example indicates that the tluid and solid displacements are described by two coupled wave equations.

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Reviews about many of the most important aerodynamic research topics in the field of wind energy are shown in the report of a different study [ ] Wind turbine aerodynamics concerns the modeling and prediction of aerodynamic forces, such as performance predictions of wind farms, as well as the design of specific parts of wind turbines, such as rotor-blade geometry. The basics of blade-element momentum theory were presented along with guidelines for the construction of airfoil data. Various theories for aerodynamically optimum rotors were discussed, and recent results on classical models were presented. State-of-the-art advanced numerical simulation tools for wind turbine rotors and wakes were reviewed, including rotor predictions as well as models for simulating wind turbine wakes and flows in wind farms [ ]. . . Wind power densityConcerning power density and its relation to wind speed, the report given in [ ] presented the features of wind power distributions that were analytically obtained from wind distribution functions. Simple equations establishing a relationship between mean power density and wind speed have been obtained for a given location and wind turbine. Different concepts relating to wind power distribution functions were shown among them the power transported by the wind and the theoretical maximum convertible power from wind, according to the "etz' law. Maximum convertible power from the wind was explained within more realistic limits, including an approximate limit to the maximum power from a wind turbine, was obtained. In addition, different equations were obtained establishing relationships between mean power density and mean wind speed. These equations are simple and useful when discarding locations for wind turbine installation [ ]. . . Wind power applicationsThe range of wind power usage is scarce. One of the most important usages is electricity. Hubbard and Shepherd [ ] considered wind turbine generators, ranging in size from a few kilowatts to several megawatts, for producing electricity both singly and in wind power stations that encompass hundreds of machines. "ccording to the researchers' claims, there are many installations in uninhabited areas far from established residences, and therefore there are no apparent environmental impacts in terms of noise. The researchers do point out, however, situations in which radiated noise can be heard by residents of adjacent neighborhoods, particularly those who live in neighborhoods with low ambient noise levels [ ].Wind power is used worldwide, not only in developed countries. Specific studies [ , ] presented a detailed study of a Manchegan windmill while considering the technological conditions of the original Manchegan windmills. In addition, a wind evaluation of the region was carried out, the power and momentum of the windmills were calculated, and the results obtained were discussed, along with a comparison with the type of Advances in Wind Power 4Southern Spanish windmill. These windmills were important for wheat milling and had been an i...

The effect of surface roughness on the transition form regualr (RR) to Mach reflection (MR) over straight wedges in pseudo-steady flows was investigated both experimentally and analytically. A model for predicting the RR \rightleftarrows$ MR transition in the (Mi, θw)-plane was developed (Mi is the incident shock wave Mach number and θw is the reflecting wedge angle). Its valdity was checked agnainst experimental results. Since the experimental results are limited to the ranges 1 < Mi < 2 and surface roughness heights of 0 < ε [les ] 0.2 cm, the proposed model is applicalbe to these ranges only. In the proposed model (the boundary-layer displacement-thickness model), the RR \rightleftarrows$ MR transition is related to the boundary - layer thickness which in turn depneds on the surface roughness.