MAST

Most rigs are now fitted with a system whereby the drill string is rotated by a drive mechanism in the mast rather than by the rotary table at rig floor level. Thus 90 foot sections can be drilled before connections need to be made, and the drill string can be rotated while pulling out of the hole in 90 foot sections. This improved system, which speeds up the operation and allows better reaming of the hole is known as top drive. 

Synthesis. Histamine [51-45-6] 2-(4-imidazolyl)ethylarnine (1) is formed by decarboxylation of histidine by the enzyme L-histidine decarboxylase (Fig. 1). Most histamine is stored preformed in cytoplasmic granules of mast cells and basophils. In humans mast cells are found in the loose connective tissue of all organs, especially around blood and lymphatic vessels and nerves. These cells are most abundant in the organs expressing allergic diseases the skin, respiratory tract, and gastrointestinal tract. 

Histamine in the Cardiovascular System. It has been known for many years that histamine is present in sympathetic nerves and has a distribution within the heart that parallels that of norepinephrine (see Epinephrine and norepinephrine). A physiological role for cardiac histamine as a modulator of sympathetic responses is highly plausible (15). A pool of histamine in rat heart located neither in mast cells nor in sympathetic nerves has been demonstrated. The turnover of this metaboHcaHy active pool of histamine appears to be maintained by normal sympathetic activity. 

Histamine AND histamine antagonists). It is formed from histidine by the enzyme L-histidine decarboxylase. In the periphery, histamine is stored ia mast cells, basophils, cells of the gastric mucosa, and epidermal cells. In the CNS, histamine is released from nerve cells and acts as a neurotransmitter. The actions of histamine ate terrninated by methylation and subsequent oxidation via the enzymes histamine-/V-methyltransferase and monoamine oxidase. 

Elevation of cycHc AMP levels is also known to inhibit the release of inflammatory and contractile mediators from mast cells (42). The good clinical efficacy of P2" goiAsts may be related to this action because some members of this class of dmgs inhibit mediator release at the same concentrations at which they relax smooth muscle (43). In contrast to their effectiveness against immediate bronchoconstriction, P2" gonists do not inhibit the late asthmatic... 

Products can be found in every principal market area including rocket motor and shell casings, air and gas pressure tanks, aircraft wing fuel tanks, utihty poles, automotive and tmck drive shafts, sailboat masts, vaulting poles, fishing rods, golf shafts, railroad tanks cars, and pipes and tanks for oil, gas, and chemical processing. 

There are other glycosaminoglycans. Hyaluronic acid [9004-61-9] occurs both free and in noncovalent association with proteoglycan molecules. Heparin [9005-49-6] and heparan sulfate [39403-40-2] also known as heparitin sulfate [9050-30-0] occur in mast cells and in the aorta, Hver, and lungs. 

The many options available for lift trucks f l into two classes vehicle specialties, which include controls, transmissions, guards, etc. and accessories, which are devices that handle specific types of loads (Fig. 21-55). Included in this second category are high-lift masts, up to 7 m (24 ft) handhng attachments for circular products, such as drums and roll goods attachments such as carton clamps and the fork side-to-side shifting mechanism. 

Lift trucks are available to meet a variety of clearance restrictions. Noteworthy is narrow-aisle equipment. Another accessory worthy of consideration is the multilift mast, which permits lifting loads over 3.7 m (12 ft). Of special importance in specifying any mast is that it will clear the various door openings it must enter, which includes those of trucks, railcars, and buildings. To meet most conditions, the collapsed height of the mast must be 2235 mm (88 in). An ideal lift truck for chemical-plant distribution warehouses would have 2000-kg (4000-lb) capacity electric (battery) propulsion solid-state controls ... 

Solid-state controls (standard) Trilift mast, to 4800 mm (189 in) 4,500 4,500... 

Sticking of valve stems is common if solids are present in the steam. The steam mast be without sohds. (Note comments later under loss of power.) It is important that units operating on a steady load for long periods be checked for sticking stems at regular intervals. The records show that in several cases deposits have caused the stem of both the governor valve and the trip valve to stick when there was a loss of load. The effect of the loss of load was destructive overspeed. 

The toughness of wood is important in design for exactly the same reasons that that of steel is it determines whether a structure (a frame building, a pit prop, the mast of a yacht) will fail suddenly and unexpectedly by the propagation of a fast crack. In a steel structure the initial crack is that of a defective weld, or is formed by corrosion or fatigue in a wooden structure the initial defect may be a knot, or a saw cut, or cell damage caused by severe mishandling. 

Y for a definite electrode or object X (B, reference electrode Me, metal E, ground M, mast R, pipe S, rail T, tunnel)... 

A Sail, R Matsumoto, HP McNeil, M Karplus, RL Stevens. Three-dimensional models of four mouse mast cell chymases. Identification of proteoglycan-bmdmg regions and protease-specific antigenic epitopes. I Biol Chem 268 9023-9034, 1933. 

---