Skin thickness

It is interesting to generalise this solution for any core skin density ratio. Fig. 2.20 shows how the optimum skin thickness varies with D. This is independent of the solid material density or modulus but is based on a weight... 

Fig. 2.20 Variation of optimum skin thickness with core skin density ratio...

A composite of gfrp skin and foamed core is to have a fixed weight of 200 g/m. If its width is 15 mm investigate how the stiffness of the composite varies with skin thickness. The density of the skin material is 1450 kg/m and the density of the core material is 450 kg/m. State tte value of skin thickness which would be best and for this thickness calculate the ratio of the weight of the skin to the total composite weight. 

The basics observed in molded products are always the same only the extent of the features varies depending on the process variables, material properties, and cavity contour. That is the inherent hydrodynamic skin-core structure characteristic of all IM products. However, the ratio of skin thickness to core thickness will vary basically with process conditions and material characteristics, flow rate, and melt-mold temperature difference. These inherent features have given rise to an increase in novel commercial products and applications via coinjection, gas-assisted, low pressure, fusible-core, in-mold decorating, etc. 

Topical corticosteroids vary in potency, depending on tiie concentration of the drug (percentage), the vehicle in which the drug is suspended (lotion, cream, aerosol spray), and the area to which the drug is applied (open or denuded skin, unbroken skin, thickness of the skin over tiie treated area). 

Patients with photodamage can apply a lotion containing 25% glycolic acid for 6 months. In such cases an increase in total skin thickness of approximately 25% was reported, accompanied by an increased thickness of viable epidermis and dermis, an increased content of acid mucopolysaccharides, a greater collagen density and an improved quality of the elastic fibers. This could be defined as self-treatment. 

It is important to obtain details regarding isotretinoin (Accutane, Roacutane) treatment and history of keloid or hypertrophic scar formation. Isotretinoin use necessitates a delay period of 6-12 months (depending on the skin thickness and oiliness) until chemical peel is performed. Active acne is not a contraindication for chemical peel. In these cases the peel is combined with systemic antibiotics for 2-3 weeks. It is always advisable to consider isotretinoin treatment after the peel to avoid acne flare and scar reappearance. 

Assess phototype, degree of sebaceous activity, skin thickness, and pigmentary abnormalities (Wood s light). 

G. The sex of the test animals can also alter study results, because both regional skin thickness and surface blood flow vary between males and females. 

Figure 5. Neutron skin thickness versus <24 for 208Pb for a variety of mean field models (from [20]). The circles correspond to results for the Skyrme force, the squares to RMF models with mesons, and the triangles to RMF with point couplings the shaded area indicates the range of NR values consistent with the present empirical information for 208Pb.

In recent years, several pilot clinical trials, assessing the elfects of GH administration to ageing adults, have been carried out. Typically, trial duration is 4-6 months. A 7% increase in lean body mass and skin thickness, along with a 14% drop in body fat, was observed in one trial, although results recorded in other trials were less striking. More detailed clinical trials and cost benefit analysis must be carried out in order to fully assess the potential of GH to counteract some of the elfects of ageing in the elderly population. 

Prednicarbate is a topical glucocorticoid that seems to have an improved benefit-harm balance, as has been shown in 24 healthy volunteers (7 men, 17 women, aged 25-49 years) in a double-blind, randomized, placebo-con-trolled study of the effects of prednicarbate, mometasone furoate, and betamethasone 17-valerate on total skin thickness over 6 weeks (175). On day 36, total skin thickness was reduced by a mean of 1% in test fields treated with vehicle the relative reductions were 13,17, and 24% for prednicarbate, mometasone furoate, and betamethasone 17-valerate respectively. There were visible signs of atrophy or telangiectasia in two subjects each with betamethasone 17-valerate and mometasone furoate, but not with prednicarbate or its vehicle. 

The intercellular pathway is now accepted as the major pathway for absorption. Recall that the rate of penetration is often correlated with the partition coefficient. In fact this is a very tortuous pathway, and the h (skin thickness) in Fick s first law of diffusion is really 10 x the measured distance. By placing a solvent (e.g., ether, acetone) on the surface or tape stripping the surface, the stratum comeum (SC) is removed, and absorption can be significantly increased by removing this outer barrier. This may not be the case for very lipophilic chemical. This is because the viable epidermis and dermis are regarded as aqueous layers compared to the SC. Note that the more lipophilic the drug, the more likely it will form a depot in the SC and be slowly absorbed over time and thus have a prolonged half-life. 

These observations have several practical consequences for membrane processes where the selective layers are as thin as or even thinner than the low end of the range studied here. First, it is clear that use of thick film data to design or select membrane materials only gives a rough approximation of the performance that might be realized in practice. Second, because the absolute permeability of a thin film may be severalfold different than the bulk permeability, use of the latter type of data to estimate skin thickness from flux observations on asymmetric or composite membranes structures is also a very approximate method. Finally, these data indicate that one could expect... 

Fig. 13.32 Schematic comparison of the skin thickness distributions in co- and gas-assisted injection molded parts due to the negligible gas viscosity.

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