Factors influencing mechanism

The mechanical properties and the failure mechanisms of transition-metal carbides are reviewed in detail by Toth.t l Generally, large spreads in the reported values found in the literature are common. This is particularly true in older reports which were mostly performed on sintered materials. More recently, testing has been switched to single crystals or polycrystalline materials obtained from the melt or by thin-film deposition. These are believed to yield more accurate and consistent information. Yet, any test must be carefully characterized in order to be meaningful. The following factors influence mechanical testing.l H ... 

For a discussion of mechanical properties and variables see Sec. 4.1 of Ch. 4. The mechanical properties of the covalent carbides often show a large spread in the reported values mostly due to differences in the fabrication processes. In addition, the following factors influence mechanical testing ... 

Molecular orientation is another important factor influencing mechanical properties of coextruded films (11). Biaxial orientation can greatly improve film strength. However, uniaxial or highly unbalanced orientation causes poor transverse properties, which result in easy splitting of coextruded films in the machine direction. This tendency may occur even when a relatively thin layer responds to unidirectional orientation and propagates failure to thicker adjacent layers. 

Beyer G. Flame retardant properties of EVA-nanocomposites and improvements by combination of nanofiller with aluminium trihydrate. Fire Mater, 2001 25 pp. 193-197. Rothon NR. Particulate-Filled Polymer Composites. Harlow Longman Scientific 1995. Hawroth B, Raymond CL, Sutherland I. Polyethylene compounds containing mineral fillers modified by acid coatings. 2. Factors influencing mechanical properties. Polym Eng Sci, 2001 41 pp. 1345-1364. 

The theoretical yield is approached by the firefly reaction, discussed later, which is reported to have of 88% (5). In practice, however, most chemiluminescent reactions are inefficient, withQc values on the order of 1% or much less. The factors influencing yields can be discussed in terms of a generalized three-step chemiluminescent mechanism (6) ... 

All areas of the cooling water system where a specific form of damage is likely to be found are described. The corrosion or failure causes and mechanisms are also described. Especially important factors influencing the corrosion process are listed. Detailed descriptions of each failure mode are given, along with many common, and some not-so-common, case histories. Descriptions of closely related and similarly appearing damage mechanisms allow discrimination between failure modes and avoidance of common mistakes and misconceptions. 

The figures given in the table are obtained on mouldings relatively free from orientation and tested under closely controlled conditions of temperature, testing rate, and humidity. Changes in these conditions or the use of additives may profoundly affect these properties. Details of the influence of these factors on mechanical properties have been published in the trade literature but Figures 18.11-18.14 have been included to illustrate some salient features. 

The mechanism of the reaction of ethyl glyoxylate 4 with 2,3-dimethyl-l,3-hutadiene 5 leading to the ene product 7 is shown in Scheme 4.5. This brief introduction to the reaction mechanism for cycloaddition reactions of carhonyl compounds activated hy Lewis acids indicates that many factors influence the course of the reaction. 

Radiative heat transfer is perhaps the most difficult of the heat transfer mechanisms to understand because so many factors influence this heat transfer mode. Radiative heat transfer does not require a medium through which the heat is transferred, unlike both conduction and convection. The most apparent example of radiative heat transfer is the solar energy we receive from the Sun. The sunlight comes to Earth across 150,000,000 km (93,000,000 miles) through the vacuum of space. FIcat transfer by radiation is also not a linear function of temperature, as are both conduction and convection. Radiative energy emission is proportional to the fourth power of the absolute temperature of a body, and radiative heat transfer occurs in proportion to the difference between the fourth power of the absolute temperatures of the two surfaces. In equation form, q/A is defined as ... 

Column diameter for a particular service is a function of the physical properties of the vapor and liquid at the tray conditions, efficiency and capacity characteristics of the contacting mechanism (bubble trays, sieve trays, etc.) as represented by velocity effects including entrainment, and the pressure of the operation. Unfortunately the interrelationship of these is not clearly understood. Therefore, diameters are determined by relations correlated by empirical factors. The factors influencing bubble cap and similar devices, sieve tray and perforated plate columns are somewhat different. 

In Ugi four-component reactions (for mechanism, see Section 1.4.4.1.) all four components may potentially serve as the stereodifferentiating tool65. However, neither the isocyanide component nor the carboxylic acid have pronounced effects on the overall stereodiscrimination60 66. As a consequence, the factors influencing the stereochemical course of Ugi reactions arc similar to those in Strecker syntheses. The use of chiral aldehydes is commonly found in substrate-controlled syntheses whereas the asymmetric synthesis of new enantiomerically pure compounds via Ugi s method is restricted to the application of optically active amines as the chiral auxiliary group. 

In addition, it was concluded that the liquid-phase diffusion coefficient is the major factor influencing the value of the mass-transfer coefficient per unit area. Inasmuch as agitators operate poorly in gas-liquid dispersions, it is impractical to induce turbulence by mechanical means that exceeds gravitational forces. They conclude, therefore, that heat- and mass-transfer coefficients per unit area in gas dispersions are almost completely unaffected by the mechanical power dissipated in the system. Consequently, the total mass-transfer rate in agitated gas-liquid contacting is changed almost entirely in accordance with the interfacial area—a function of the power input. 

The 2 -chloro and 2 -bromo congeners of either 748 (FIAC) or 758 (FMAU) are more cytotoxic than FIAC and FMAU, suggesting that these chloro and bromo nucleosides, in contrast to the 2 -fluoro compounds, are comparatively better substrates for deoxycytidine kinase of human lymphocytes than the substrates for viral-specific thymidine kinase. The disposition of the 2 -fluoro group may also be important from the biological viewpoint. It should be noted that the structural difference between RNA and DNA is at the 2 -position. The ribo type of analog (738) of FIAC is 10 times less effective in suppression of HSV replication than is FIAC. Thus Fox, and Watanabe and coworkers concluded that the 2 - up fluorine disposition and the species of the substituent at C-5 are the two important factors influencing antiviral activity. Nevertheless, the mechanism of action of 2 -deoxy-2 -fluorocytidine (737) on certain herpes viruses, including HSV-1... 

Many factors influence the contractile activity of smooth muscle. The strength of contraction of multiunit smooth muscle may be enhanced by stimulation of a greater number of cells, or contractile units. This mechanism is directly comparable to motor-unit recruitment employed by skeletal muscle. As the number of contracting muscle cells increases, so does the strength of contraction. However, this mechanism is of no value in single-unit smooth muscle. Due to the presence of gap junctions, all of the muscle cells in the tissue are activated at once. 

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