Opacity, definition

Toxicology. The acute oral and dermal toxicity of naphthalene is low with LD q values for rats from 1780—2500 mg/kg orally (41) and greater than 2000 mg/kg dermally. The inhalation of naphthalene vapors may cause headache, nausea, confusion, and profuse perspiration, and if exposure is severe, vomiting, optic neuritis, and hematuria may occur (28). Chronic exposure studies conducted by the NTP ia mice for two years showed that naphthalene caused irritation to the nasal passages, but no other overt toxicity was noted. Rabbits that received 1—2 g/d of naphthalene either orally or hypodermically developed changes ia the lens of the eye after a few days, foUowed by definite opacity of the lens after several days (41). Rare cases of such corneal epithelium damage ia humans have been reported (28). Naphthalene can be irritating to the skin, and hypersensitivity does occur. 

In astrophysics, particle sizes in protoplanetary disks are usually described in the context of a distribution, dn = f(a)da, where a is the particle radius and (in is the number density of particles with radii between a and a + da. Note that in cosmochemistry, grain size usually refers to the largest diameter of a monomer. The description is often associated with two assumptions. First, it is often assumed that the distribution function, /(a), is close to being a power law in the ISM, except at very large or very small sizes (Weingartner Draine 2001), and power laws are therefore often used in protoplanetary disk studies. Second, the definition of a particle radius assumes that the particles are spherical - a convenience for converting the size distribution to an opacity law. 

Opacity. Defined in ASTM - C286 as The property of reflecting light diffusely and non-selectively. For a definition relating specifically to vitreous enamel... 

Opacity or transparency are important when the amount of light to be transmitted is a consideration. These properties are usually measured as haze and luminous transmittance. Haze is here defined as the percentage of transmitted light through a test specimen that is scattered more than 2.5° from the incident beam. Luminous transmittance is the ratio of transmitted light to incident light. Table 2-24 provides the optical and various other properties of different transparent plastics. Some definitions of key terms used in identifying optical conditions follow ... 

---