Influence of Physical Structure

Influence of Physical Structure. The hydrolytic behavior of cellulose is much influenced by its physical structure and lateral order [121-132]. Wood cellulose was hydrolyzed twice as fast as cotton [125]. Hydrolysis rate was significantly increased by physical or chemical pretreatment, with the effect depending on the source of cellulose. Hill and coworkers [127,128] reported that mercerization increased the hydrolysis rate of cotton (by 40%) and of ramie (7%), whereas the opposite effect was observed for linen and a-cellulose samples showing an approximately 30% reduction. Based on kinetic analysis, they concluded that the end-attach model proposed by Sharpies [121] can only be applied to the cellulose II structure and not to the cellulose I crystallite. Thus, the conformation of cellulose is also a significant factor affecting its reactivity and possibly the hydrolytic mechanism as well. 

Dillon GP, Yu X, Sridharan A, Ranieri JP, Bellamkonda RV. The influence of physical structure and charge on neurite extension in a 3D hydrogel scaffold. / Biomater Sci Polym Ed 1998 9 1049-69. 

The present discussion of physical structure and properties is intended to serve merely as a basis for appraising the characteristics of various polymers here surveyed. The nature of the semicrystalline state in polymers and its influence on their physical properties will be dealt with in greater detail in a later chapter. 

The Influence of DNA Structure and Environment on the Intercalation of Hydrocarbon Metabolites and Metabolite Model Compounds. The physical binding of hydrocarbon metabolites to DNA is very sensitive to DNA structure and environment. This is demonstrated by the data in Figures 4 and 5, which show how heat denaturation of DNA inhibits hydrocarbon quenching. These results are consistent with early studies which indicate that the ability of native DNA to solubilize pyrene and BP is much greater than that of denatured DNA (40). 

Nucleic Acids and Proteins, Electronic Structure Nucleic Acids and Proteins, Influence of Physical Agents 7 3... 

Proteins, Solid, Adsorption of Water on (Eley Leslie). Proteins and Nucleic Acids, Electronic Structure Proteins and Nucleic Acids, Influence of Physical Agents on Purine-Pyrimidine Pairs, Steroids, and Polycyclic Aromatic Carcinogens (Pullman). ... 

The thermal cross-linking as well as the influence of internal structural stress may give rise to some limitation of the LODP concept if hydrolytic media of different swelling powers are compared or if the range of temperatures considered exceeds 100°C. In those cases, as well as after mechanical strain on the sample, the LODP obviously is not unambiguously determined by the physical structure of the sample but depends to some extent on the conditions of hydrolysis. 

In general, a medical device is defined as follows a medical device is an implant and equipment to be used either to achieve disease diagnosis, medical treatment, or disease prevention for human and animals, or to influence the physical structure and function of human and animals. Medical devices for humans may also be classified based on whether and how long the device is in contact with tissue or cells and on the degree of disjunction induced by the device when in a disabling situation. The term covers various categories, such as scissors and tweezers, with small risk to human function, to central venous catheters, artificial dialysis (human kidney), and pacemakers, with high risk to human function. 

Figure 10.9 The relative influence of the molecular (mol) and macromolecu-lar (macro) scale, i.e., essentially crosslinking, on physical properties. The arrows indicate an increasing influence of the structural scale.

For a given material, there are generally several possible mechanisms of yielding and fracture, each characterized by the influence of temperature, loading rate, hydrostatic pressure, time (physical aging). A vast literature deals with the influence of network structure on yielding or on fracture properties, but we have to be very careful with the results obtained because of the different types of networks used in these experiments. 

The yielding of networks will be described first, beginning with the analysis of deformation mechanisms and the influence of physical aging. The effect of hydrostatic pressure will be treated with yielding criteria. The influence of physical (T, e) and structural parameters on yielding will then be described for ideal and nonideal networks. 

Hedrick JC, Arnold CA, Zumbrum MA, Ward TC, McGrath JE (1990) Poly(arylene ether ketone)/poly(aryl imide) homo- and polydimethylsiloxane segmented copolymer blends influence of chemical structure on miscibility and physical property behavior. 35th International SAMPE Symposium, pp 82-96... 

Bums, R. G. (1991) Mixed valency minerals influences of crystal structures on optical and Mossbauer spectra. In Mixed Valence Systems Applications in Chemistry, Physics and Biology. (K. Prassides, ed. Plenum Press, New York), NATO ASI-C Series, Math. Phys. Sci., C343,175-200. 

Here we outline an approach that has been taken to develop Poly(dimethylsiloxane) (PDMS) systems, which have property changes that are easier to predict. The problems associated with the inclusion of a filler phase that is required for PDMS systems to have many useful physical properties have been addressed by producing nano filled equivalents. It is shown that such systems offer easier control over the materials produced whilst also resulting in a simplification of physical properties. The production of foamed systems, which introduces an additional variable, is also discussed. The influence of foam structure upon the measured properties of a material is outlined and implications for sample production and the development of predictive ageing models are explored. 

The discussion of the essential features in the experimental and theoretical approaches to the free radical degradation of polymers is thus completed. We introduce the next section with a summary table which is subdivided according to the two extremes of degradation unzipping and random scission. The first part of Table III describes the influence of basic structure and the second deals with secondary factors for a given structure. When a polymer is processed at elevated temperatures, volatilization and deterioration of physical properties during short time intervals are a matter of concern hence initial rates are important. 

Although the preceding observations seem to indicate definite mineral matter influences on kerogen decomposition, extrapolation of the results to actual oil shale processing is tenuous because a physical mixture of kerogen and mineral matter, such as was used in most of the previous work, is not likely to reproduce the exact forms of physical structure or chemical bonding that exist in indigenous oil shale ... 

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