Reversal frequency

The frequency (number per second) of /transitions from all g. degenerate initial internal states and from the p. d E. initial external translational states is equal to tire reverse frequency from the g degenerate final internal states and the pyd final external translational states. The detailed balance relation between the forward and reverse frequencies is therefore... 

Cell name Mutagens Selective agents Mutating frequency Phenotype sign Reverse frequency... 

Mutagenic activity was recorded if at least one strain showed an increased reversion frequency in response to the test sample. (—) = no activity detected (-H) = at least 2x the number of colonies appeared as on a control plate situated in a ring around the sample disc (0) = an increased colony count was noted, but not 2x the control value, or not in a ring. 

S. tVDhimurium (TA 1535, TA 1538, TA 98) NRU) + No increase in reversion frequency (less than 2-fold increase) Anderson and Styles 1978... 

In summary, DMH and AOM failed to increase in vitro mutagenic frequency with or without liver extracts. However, MAM caused a dose-dependent increase in reversion frequency without hepatic enzymes as expected since MAM decomposes heterolytically to methyl-diazonium and formaldehyde (32). Methyldiazonium ions yield nitrogen and methylcarbonium, a powerful alkylating agent. Formaldehyde is oxidized to (X. In contrast to in vitro conditions, the host-mediated assay showed that intact animals converted DMH and AOM to mutagenic products. 

The analytical estimations of creeping front parameters given by eqs (1)—(5) can be used for analysis of the reactor with a long catalyst bed operated at low reversal frequency. Another simplified model describes relaxed steady operation relating to intermediate reversal frequencies. The cycle time at such frequencies is much shorter than the time needed for the reaction zone to travel through the catalyst bed, but at the same time, it is much longer than the residence time of the gas flow in the reactor. This situation is quite possible for processes performed under atmospheric pressure when the densities of the catalyst and the gas phase... 

Values (literature cf. ref. 63) determined from reversion frequencies of mutants and hence represent true error rates (to be distinguished from population numbers of mutants, i.e., so-called mutant frequencies). 

Amplicon Vector Titer = 10 - lO TU/ml Wild-type Reversion Frequency < 1 in 10 ... 

In contrast to Mutascreen, the AmesII assay utilizes fluctuation analysis for calculation of reversion frequency. Besides the standard Salmonella tester strain TA98, the AmesII assay also includes new strains each designed to revert by only one specific base pair substitution mutation.13 Thus, when mixed, all six base pair substitutions can be represented in one culture. 

It is also evident in Fig. 7.124 that the effect of frequency on the fatigue crack growth rate reverses on increasing AK above AKSCC. At a specific AK below AKSCC, the crack-growth rate increases with increase in frequency the reverse frequency dependency is observed above AKSCC. 

The recorded images of swimming cells are analyzed using the EVIOOO computerized (66) cell-tracking system to extract the time-dependent reversal frequency of the cells (Fig. 5 see for example ref. 67). 

Takahashi, T., and Kobatake, Y. (1982) Computer-linked automated method for measurement of the reversal frequency in phototaxis of Elalobacterium halobium. Cell Struct. Eunct. 7,183-192. 

Shi, W., Ngok, F. and Zusman, D.R. (1996). Cell density regulates cellular reversal frequency in Myxococcus xanthus. Proc. Natl. Acad. Sci. U.S.A. 93, 4142-4146. 

Abbreviations NT = not tested, + = significant increase in reversion frequency over control, — = no significant difiference in reversion frequencies between treated and untreated. 

The multiplicative property of the demodulation factors and the additive property of the individnal phase angles are the origin of a reversed frequency dependence of the apparent phase-shift and demodulation lifetimes and the inversion of apparent phase and moduISlion lifetimes when conpared to those of a heterogeneous sainpie. The apparent phase lifetime (x)i) calculated from the measured phase ( a) of the relaxed state is... 

The Frederiks transition near the dielectric anisotropy sign reversal frequency was initially observed by de Jeu et al. [18], but was tentatively treated as an electrohydrodynamic instability [19]. 

Experimental data confirm the main conclusion of the theory that near the sign reversal frequency of Ae there occurs the Frederiks transition. The observed modulated structure is static, and its threshold depends on neither the value of conductivity cr) nor its anisotropy experimentally measured threshold conditions... 

The considerable variation among laboratories in the reversion frequencies found with the /Salmonella test system has been ascribed largely to the variable source and method of preparation of the S-9 fraction, and experimental conditions used. ° ° Similar variation is to be expected in the results of the SCE test with S-9. For example, CP is metabolized to an SCE-inducing metabolite far more effectively by S-9 prepared from liver of rats induced with Aroclor 1254 or phenobarbital than with 3-methylcholanthrene. ° An additional factor to be considered is the inactivation of compounds by either serum or S-9 components e.g., the SCE-inducing ability of AAAF and N-hydroxyacetylaminofluorene is reduced in the presence of S-9 Mix. Thus, any compound under investigation must be tested both with and without S-9 Mix and serum. 

Less well-studied VSV mutants have been identified by their reduced cytopathogenicity, usually manifested as a small plaque. One such small-plaque mutant, first identified by Wagner et al. (1963), was found to grow to lower titer than the wild-type parent and to establish persistent infection more readily, but had a very high reversion frequency. 

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