Mulches are used for various agricultural and gardening purposes, they are applied to the soil surface. Properly used, they benefit plant growth and minimize garden labor. The main functions of mulches are the conservation of soil moisture and the moderation of soil temperature. They moderate internal soil temperatures by retaining heat from the day and radiating it to the soil at night during spring and fall; in the winter mulches moderate soil warming during the day, limiting the stress plants undergo during soil freezing and thawing cycles. They also are used to prevent frost heaving of unestablished plants in winter. During summer, they keep soil cool by blocking direct sunlight exposure of the soil surface. Mulches are used to block evaporation of water from the soil, slowing down soil drying. They also help control the growth of weeds, blocking sunlight and/or smothering weed seedlings under layers of material. Mulch also reflects sunlight back from the ground to the leaves of plants, they also provide a clean and dry surface for ground-lying fruits. They prevent soil erosion from heavy rains, prevent surface run-off of water, and prevent the direct impact of hard rains on the soil surface. Some mulches improve soil texture, adding humus. Organic mulches may add nutrients to the soil as they breakdown. Biodegradable mulches, as they decay, are incorporated into the soil where they provide air spaces and surfaces for fungi and root growth.[1]
While mulching may improve the growth of various plants by directly manipulating the plant's abiotic environment, mulch can also improve growth as an effective means of pest control. Various forms of mulch, deter herbivorous insects and increase the numbers of beneficial insects .
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Saturday, July 4, 2009
barotropic atmosphere
In meteorology, a barotropic atmosphere is one in which the pressure depends only on the density and vice versa, so that isobaric surfaces (constant pressure surfaces) are also isopycnic surfaces (constant density surfaces). The isobaric surfaces will also be isothermal surfaces, hence (from the thermal wind equation) the geostrophic wind is independent of height. Hence the motions of a rotating barotropic fluid are strongly constrained.
A barotropic flow is a generalization of the barotropic atmosphere described above: It is a flow in which the pressure is a function of the density only and vice versa. In other words, it is a flow in which isobaric surfaces are isopycnic surfaces and vice versa. One may have a barotropic flow with a non-barotropic fluid, but a barotropic fluid must always follow a barotropic flow. Examples include barotropic layers of the oceans, an isothermal ideal gas or an isentropic ideal gas.
Barotropic fluids are also important idealized fluids in astrophysics, such as in the study of stellar interiors or of the interstellar medium. One common class of barotropic model used in astrophysics is a polytropic fluid. Typically, the barotropic assumption is not very realistic.
Contrast baroclinic. In particular, for a barotropic fluid or a barotropic flow (such as a barotropic atmosphere), the baroclinic vector is always zero.
A barotropic flow is a generalization of the barotropic atmosphere described above: It is a flow in which the pressure is a function of the density only and vice versa. In other words, it is a flow in which isobaric surfaces are isopycnic surfaces and vice versa. One may have a barotropic flow with a non-barotropic fluid, but a barotropic fluid must always follow a barotropic flow. Examples include barotropic layers of the oceans, an isothermal ideal gas or an isentropic ideal gas.
Barotropic fluids are also important idealized fluids in astrophysics, such as in the study of stellar interiors or of the interstellar medium. One common class of barotropic model used in astrophysics is a polytropic fluid. Typically, the barotropic assumption is not very realistic.
Contrast baroclinic. In particular, for a barotropic fluid or a barotropic flow (such as a barotropic atmosphere), the baroclinic vector is always zero.
what is cat?
Clear air turbulence weather, sometimes colloquially referred to as "air pockets", is the erratic movement of air masses in the absence of any visual cues, such as clouds. Clear-air turbulence is caused when bodies of air moving at widely different speeds meet; at high altitudes (7,000-12,000 metres/23,000-39,000 feet) this is frequently encountered around jet streams or sometimes near mountain ranges. Clear-air turbulence is impossible to detect either with the naked eye or with conventional radar, meaning that it is difficult to avoid. However, it can be remotely detected with instruments that can measure turbulence with optical techniques, such as scintillometers or Doppler LIDARs.
This kind of turbulence creates a hazard for air navigation. Because aircraft move so quickly, they experience sudden unexpected accelerations or 'bumps' as they rapidly cross invisible bodies of air which are moving vertically at many different speeds. Cabin crew and passengers on airliners have been injured (and in a small number of cases, killed, as in the case of a United Airlines Flight 826 on December 28, 1997) when tossed around inside an aircraft cabin during extreme turbulence. BOAC Flight 911 broke-up in flight in 1966 after experiencing severe lee wave turbulence just downwind of Mount Fuji, Japan.
TURBULENCE
Turbulence causes the formation of eddies of many different length scales. Most of the kinetic energy of the turbulent motion is contained in the large scale structures. The energy "cascades" from these large scale structures to smaller scale structures by an inertial and essentially inviscid mechanism. This process continues, creating smaller and smaller structures which produces a hierarchy of eddies. Eventually this process creates structures that are small enough that molecular diffusion becomes important and viscous dissipation of energy finally takes place.
This kind of turbulence creates a hazard for air navigation. Because aircraft move so quickly, they experience sudden unexpected accelerations or 'bumps' as they rapidly cross invisible bodies of air which are moving vertically at many different speeds. Cabin crew and passengers on airliners have been injured (and in a small number of cases, killed, as in the case of a United Airlines Flight 826 on December 28, 1997) when tossed around inside an aircraft cabin during extreme turbulence. BOAC Flight 911 broke-up in flight in 1966 after experiencing severe lee wave turbulence just downwind of Mount Fuji, Japan.
TURBULENCE
Turbulence causes the formation of eddies of many different length scales. Most of the kinetic energy of the turbulent motion is contained in the large scale structures. The energy "cascades" from these large scale structures to smaller scale structures by an inertial and essentially inviscid mechanism. This process continues, creating smaller and smaller structures which produces a hierarchy of eddies. Eventually this process creates structures that are small enough that molecular diffusion becomes important and viscous dissipation of energy finally takes place.
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