Thresholds, concept

The threshold line concept was proposed by Macheret and Rich and used to develop a continuum model for dissociation that provides reaction rates as functions of the temperatures associated with the various energy modes. For use in the DSMC technique, Boyd employed the threshold concept to develop a nonequilibrium dissociation model in terms of a dissociation probability based on the translational collision energy and the rotational and vibrational energies of the dissociating molecule. 

Johnson DE, Smith DA, Park BK. Safety/toxicity threshold concepts in drug discovery and development. Curr Opin Drug Disc Devel 2005 8(l) 24-6. 

The no-threshold concept for carcinogens is one of these assnmptions, which has inflnenced pnblic policy and resnlted in carcinogens being singled ont for special treatment. 

Finally, the linear low-dose extrapolation obviates de facto the concept of a threshold in the dose-response curve. The threshold concept is universally accepted for most other, noncancer toxicity and for many other biological phenomena (e.g., taste thresholds), and many scientists would argue that such thresholds (or practical thresholds ) should apply to the cancer or mutation response due to the undo-lying complexities in toxicokinetics and in the dynamics of DNA damage and repair, immune surveillance, and the variation in the progression of clinical diseases. ... 

Mumford, J.D. and Knight, J.D. (1997) Injury, damage and threshold concepts. In Methods in Ecological and Agricultural Entomology, D.R. Dent and M.P. Walton (eds), CAB International, Wallingford, 203-220. 

In terms of PDT dosimetry, an important conclusion arises from this threshold concept, independent of the particular T value. In the simplest case of surface irradiation of a uniform tissue volume, the depth of necrosis, d, can be written as... 

There is another complicating threshold concept. The cytotoxic threshold is considered to be the result of the finite capacity of the cell to tolerate injury to the multiplicity of cellular components other than critical parts of the genome before the cell itself sustains injury. Recurring... 

Carstensen, A.-K., Bernhard, J. (2008). Threshold concepts emd keys to the portal of understanding Some examples from electrical engineering. In R. Land, E. Meyer, J. Smith (Eds.), Threshold concepts within the disciplines (pp. 143-154). Rotterdam Sense Publishers. 

Control strategies for known or suspected carcinogens. No threshold concept. Definitions of suspected carcinogens. Strategies for typical important carcinogens asbestos, tar, vinyl chloride monomer, MBOCA. Main features of Regulations and Codes of Practice for these substances. 

On 12 October 1993, the FDA published a proposal for a Threshold Concept, the final rule of which was published on 17 July 1995. FDA The Threshold of Regulation for substances used in food contact articles in covered under Par. 17().39ofCFR21.It provides that ... 

Liminal space is a term borrowed from my engineering education colleagues studying threshold concepts — it describes the intellectual confusion experienced by students as they attempt to accommodate concepts that are transformative and, once mastered, enable them to achieve a new level of intellectual capability. 

While thresholds are accepted for acute toxicity measmements, there is some controversy around the concept of thresholds for chronic toxicity measurements, especially for carcinogenicity detection. Many scientists believe there is no safe level for carcinogens but other scientists believe there are thresholds for carcinogens just as there are for acute effects. We will present below the complications in applying this threshold concept to chronic toxicants. Another phrase to describe this threshold is the No Observed Adverse Effect Level , or NOAEL. A closer examination of this simple concept reveals many underlying complexities. 

Boltze U. and de Freitas M. H. (1996) Changes in atmospheric pressure associated with dangerous emissions from gas generating disposal sites. The explosion risk threshold concept. Proceedings of the Institution of Civil Engineers-Geotechnical Engineering, 119,177-181. 

This work draws on the emerging framework of threshold concepts originated by Erik Meyer and... 

Meyer, R., Land, R. (2003). Threshold concepts and troublesome knowledge Linkages to ways of thinking and practising. In C. Rust (Ed.), Improving student learning Theory and practice ten years on (pp. 412-424). Oxford Oxford Centre for Staff and Learning Development. 

In order to shed light on tacit ways of thinking we focused on threshold concepts which might appear from within the social science disciplines or between the social and natural sciences and which might prove troublesome for engineering students to understand - to pass through the threshold. 

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