Critical dose

The critical dose of microorganisms which will irritiate an infection is largely uirknown and varies not only between species but also within a speeies. Animal and human volunteer studies have indicated that the infecting dose m be reduced significantly in the presence of trauma or foreign bodies or if aecompanied by a dmg having a local vasoconstrictive action. 

B. F. Banahan 3rd and E. M. Kolassa, A physician survey on generic drugs and substitution of critical dose medications, Arch. Intern. Med, 18, 2080 (1997). 

In aquatic environments, Spear (1981) spotlights three research needs (1) development of analytical procedures for measurement of individual dissolved zinc species, notably the aquo ion and zinc chloride, and for nondissolved species that occur in natural waters (2) separation of natural from anthropogenic influences of sediment-water interactions on flux rates, with emphasis on anoxic conditions, the role of microorganisms, and the stability of organozinc complexes and (3) establishment of toxicity thresholds for aquatic organisms based on bioaccumulation and survival to determine the critical dose and the critical dose rate, with emphasis on aquatic communities inhabiting locales where zinc is deposited in sediments. These research needs are still valid. 

ATSDR has derived a chronic oral MRL of 0.0003 mg/kg/day based on a laboratory animal study showing neurotoxic effects in dogs (Kettering Lab 1969). The EPA reference dose for endrin is 3xl0 4 mg/kg/day, and the critical dose is 0.025 mg/kg/day (IRIS 1995). Critical effects were occasional convulsions and mild histological lesions in the liver (Kettering Lab 1969). No EPA reference concentration exists for the compound. 

Sensitivity and contrast are conveniently measured experimentally by exposing areas of resist of known size to varying radiation doses and measuring the film thickness remaining after development for each area. In the case of negative resists, gel is not formed until a critical dose, denoted as the interface gel dose Dp, has been reached. At this dose no lithographi-... 

For a positive resist, the film thickness of the irradiated region after development decreases until eventually a critical dose Dp is reached which results in complete removal of the film 8,9). The sensitivity and contrast (7p) are evaluated in a manner similar to that for a negative resist. After they have been spin-coated and prebaked, a series of pads of known area are exposed to varying doses. The substrate is developed in a solvent that does not attack the unexposed film and the thickness of the film remaining in the exposed areas measured. The film thickness is normalized to the original thickness, and this value is plotted as function of log dose, as shown in Figure 5 where Dp represents the sensitivity of the positive resist. Contrast (7p) is determined from the extrapolated slope of the linear portion of the response curve as... 

This fraction displayed the greatest killing power however, the most interesting features of tjhis toxin(s) were its fast-acting and "all-or-none nature. All mice deaths, regardless of dose, occurred within one hour. In fact, it appeared that there was a critical dose-dependent time to death, after which, surviving mice recovered completely. Although Yasumoto and coworkers (14, 23) also have... 

In both cases, the replacement product is usually reported as having a distinctly fibrous or prismatic morphology. The higher level of radiation damage in metaloparite (lucasite ) could be due to a difference in the critical amorphization dose of loparite and the alteration product, provided that the alteration event occurred soon after crystallization of the loparite. For example, Smith et al. (1998) and Lumpkin et al. (1998) have shown that the critical amorphization dose of perovskite structure types may be as much as a factor of five greater than the critical dose of other Nb-Ta-Ti minerals (e.g., pyrochlore and zirconolite). 

GaudetM, CamartJ-C, BuchaUlot L, Arscott S (2005) Variation of absorption coefficient and determination of critical dose of su-8 at 365 nm. Appl Phys Lett 88 24107... 

For an un-cross-linked material that undergoes predominantly cross-linking when exposed to ionizing radiation, solvent extraction experiments reveal that at certain absorbed dose (the critical dose), a percentage of the material, is converted into insoluble gel. Beyond that point, the percentage of gel increases as a function of irradiation dose. In general, both the degrees of... 

It gives the critical dose rate (irradiation intensity) pc as a function of the elastic interaction between similar defects and the temperature ... 

The critical dose rate pc necessary for initiating the aggregation process is the smaller, the lower the temperature, the stronger elastic attraction of similar particles and the slower the diffusion (greater the activation energy for hopping). This conclusion is in a complete qualitive agreement with the results obtained recently in terms of a quite different mesoscopic approach [63-65],... 

All these findings are in agreement with both experimental data for NaCl crystals and the recent mesoscopic studies [65, 68] where the critical dose rate was found to be... 

On the other hand, the present microscopic approach leads to the critical dose rate arising from equation (7.2.13) ... 

Both equations (7.2.16) and (7.2.18) have the same dependence on the relative diffusion coefficient, D — D + D, but different dependence on the elastic interaction between defects. However, in both cases the stronger similar defect attraction, the lower is the critical dose rate. In the mesoscopic approach this effect is less pronounced (logarithmic vs. linear dependence) and here pc is considerably higher. It seems that this approach is able to detect only those mesoscopic-size aggregates which are already well-developed - unlike the microscopic formalism able to detect even the marginal aggregation effects. 

Critical Doses and Temperatures to initiate Explosives by Pulsed High-Energy Electrons (Ref 201)... 

In 1955, the International Commission on Radiological Protection set a maximum permissible occupational concentration of 3.7 x 103 Bq m-3 (10-10 Ci l-1), for continuous exposure, equivalent to 1.1 x 104 Bq m-3 (3 x 10-10 pCi P1) for a 40-h working week. Subsequently, when it was realised that the critical dose to the lung was from inhalation of decay products, not radon itself, the permissible concentration was defined in terms of the concentration of decay products. The current recommended limit (ICRP, 1986) for a working period of 2000 h per year is 1.5 x 103 Bq m 3 equilibrium equivalent radon concentration (a term defined in Section 1.8 below). 

Data have been collected in recent years on the effects of He implantation in metals109-11 Gas re-emission measurements have shown that, at low doses, essentially all of the helium is retained in the lattice. At a critical dose, which depends on a number of variables (energy, temperature and material) the surface deforms and... 

Comparison of the experiments carried out in glass and metallic cuvettes did not show any appreciable effect of the substrate material on the characteristics of the autowave processes in solid-state conversions. The critical doses required for realization of the self-sustained regimes of conversion in films turned out to be noticeably greater than in massive samples. 

Figure 14. Velocity of BC + Cl2-reaction wave-front propagation as a function of y irradiation dose at 77 K for massive cylindrical samples of diameter 5-6 nm (circles) and thin-film samples 100/an thick (triangles). Critical doses of y irradiation for massive (1) and film (2) samples are shown by dashed lines.

Swenberg, J.A., Fryar-Tita, E., Jeong, Y.C., Boysen, G., Starr, T. (2008) Biomarkers in toxicology and risk assessment informing critical dose-response relationships. Chemical Research in Toxicology 21 253-225. 

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