Hair diameter

Murray (1977) uses the same formula (equation 21.18) to predict interception rates of sensory hairs on insect antennae, but provides an additional insight in its application. As long as Pe < 1 (where L is hair diameter), the odorant molecules may be assumed to strike the hair anywhere. As Pe becomes larger (Pe >1), the interception rate will differ more with downstream/upstream location on the cylinder. The same logic may be used to estimate the potential for spatially dependent interception by a filiform antenna. 

One estimate for characteristic time (t) may be obtained by dividing the hair diameter by the average air velocity through the gap (L/U), and therefore represents the time during which that air sample is passing directly between the hairs. Making this substitution results in... 

Microfiltration and UF hollow fiber membranes are different than the hollow fine fibers discussed in Chapter 4.3.4. The MF and UF membranes are thicker and not quite as flexible, resembling fine-diameter straws rather than human hair. Diameter of fibers ranges... 

Hair diameters were calculated using the equation ... 

Figure 1, Geometry of apparatus for precise measurements of hair diameter by optical diffraction H, hair fiber L, laser B, laser beam T, plane target with diffraction pattern C, central beam...

Figure 2. Increase of hair diameter as a function of relative humidity ( ) intact hair CAl bleached hair ( ) descaled hair...

Fluid flow around a hair in an array depends on the relative importance of inertial and viscous forces, as represented by the Reynolds number (Re = ulp/p), where u is velocity, 1 is hair diameter, p is fluid density, and p is the dynamic viscosity of the fluid (viscosity is the resistance of the fluid to being sheared a fluid is sheared when neighboring layers of fluid move at different velocities). We humans are big (high 1), rapidly moving (large u) organisms who experience high Re turbulent flow dominated by inertia. In contrast, very small (low 1) structures such as aesthetascs operate at low Re, where fluid motion is smooth and laminar because viscous forces damp out disturbances to the flow. 

In a study of women with idiopathic hirsutism (excessive male pattern hair growth in women with normal levels of serum androgens), involving topical application of a cream containing 1 or 2% fennel ethanol extract daily for 8 or 12 weeks, a dose-dependent reduction in hair diameter was observed. The authors of the article indicated that estrogenic activity of fennel was responsible for this reduction (Javidnia et al. 2003). 

In some fibers, very few medullary cells are present and the medullary canal appears as a well-defined air-filled space. Bnmner and Comans have classified the medulla on the basis of its absence or interruption [161]. Alternatively, in the forensic sciences, Clement et al. have classified human medullae as either intermediate or fragmental [162]. The latter used the ratio of medulla diameter to hair diameter to obtain the medullary index (MD/HD = MI). 

At the crime scene, various fibers and hairs are collected by policemen. They are immediately examined at the forensic laboratory in order to identify the suspect and help solve the crime. The examination needs to establish (1) whether it is a hair or a fiber (synthetic or plant) (2) its species if it is a hair (3) its somatic origin if it is a human hair (4) whether it is similar to the suspect or the concerned persons. Microscopic examination will resolve the first point. It will also allow discrimination between human and animal hair, as the medulla of human hair does not develop well and shows less than 0.30 of medullary index (ratio of medulla diameter to hair diameter). But determining the species of animal requires experience in animal hair examination. Almost every animal hair shows specific shape of cuticule and medulla under microscopical observation. With regard to the somatic origin of human hair, there are some basic features that usually indicate the bodily origin of the hair. For example, head hair has long length, 30-120 pm diameter, tapered tip, little diameter variation, various medullation, sometimes cut tips, and treatment. Pubic hair has a twisted... 

Human hair diameter is 100 pm, living blood cell diameter 8 pm Glass hardness is about 5 GPa 50 000 atm... 

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