Cross correlator

System First correlation Second correlation Cross term... 

In the case in which T l is laiger than J, one would think that the antiphase character of the cross peaks in the TPPI mode cancels partially or totally the cross peaks. Indeed, much of the intensity of the signal is lost. The loss can, however, be reduced if the cross peaks are phased in dispersion mode [48] or if the experiments are performed in magnitude mode [36] (Section 8.5). The occurrence of coherence transfer phenomena may give rise to COSY cross peaks even in the absence of scalar coupling (Section 8.8) [35]. As long as this is kept in mind, COSY cross peaks between very broad lines can be looked for, and interpreted as dipolar correlation cross peaks. 

Fig. 17. First HYSCORE data from GdDTPA at 4 K, 3502 G. The correlated cross peaks, with splittings from 0.6-1.0 MHz, may reveal 14N-Gd couplings that can be probed [92]...

This is the simple heteronuclear -X COSY (or HETCOR) pulse sequence adapted to long-range correlations simply by adjustment of the Ai and A2 delays. Small coupling constants rule out the use of broad-band proton decoupling during evolution time t by BIRD, and thus the correlation cross-peaks display the structure of proton multiplets, which reduces further the sensitivity of the experiment. 

Although the evolution intervals, t, of the IPAP-INADEQUATE experiment are optimised for nJcc couplings, the one-bond correlation cross peaks appear in the spectra with random intensities. However, by recording two spectra with setting T = 0.5/n/cc and T = 0.5/n/cc + 0-5/1/co the one-bond cross peaks will appear at least in one spectrum. The long-range correlations will appear with practically unchanged intensities in both spectra and are analysed from the spectrum which is their sum. 

Chapman, R.B. and Penman, D.R., Negatively correlated cross-resistance to a synthetic pyrethroid in organophosphorus-resistant Tetranychus urticae, Nature, 281, 298,1979. 

In Section 4.2.2 it has been shown that due to intended or natural orbital correlations, crossings may occur in the configuration correlation diagram that are avoided in the state correlation diagram. If no avoided crossing is... 

Use of compounds that display negatively-correlated cross-resistance. 

Cross Resistance. This seemingly simple term is also subject to various interpretations. It is probably best defined as resistance of an organism to two or more toxicants (with the implication that the normal population is sensitive to both). Recently the added qualifier positive or positively correlated cross resistance has been suggested, since there are instances where resistance to one toxicant is accompanied by increased sensitivity to another, which are then termed negative or negatively correlated cross resistance. (For an example, see Fujimura, Ishii, this volume.)... 

In principle, one of the most effective means to cope with resistance of plant pathogens is the use of fungicides to which resistant strains show negatively correlated cross resistance. However, until now this strategy has seen limited use in practice, principally for lack of suitably effective compounds. Herein we discuss one of the first practically useful examples of negatively correlated cross resistance, and report on its genetic and molecular basis. 

Leroux and Gredt reported that benzimidazole-resistant strains of Botrytis cinerea and Penicillium expansum exhibited negatively correlated cross resistance to herbicidal N-phenylcarbamates such as barban, chlorpropham, and chlorbufam (10, 11, 12). Based on their observation, Sumitomo scientists evaluated many examples of N-phenylcarbamates to search for compounds with potent fungitoxicity and no phytotoxicity. This effort was eventually successful, leading to new fungicides such as MDPC ( , 21 ) and diethofencarb (14, 23, 24) (Figure 2). 

We used N. crassa as a model fungus and attempted to elucidate the mechanism of negatively correlated cross resistance between benzimidazoles and N-phenylcarbamates. MBC resistant mutants were isolated from the wild type strain of N. crassa by UV treatment. Selection of the MBC resistant mutants was carried out on medium containing 50ppm MBC. MBC (carbendazim), the degradation product of benomyl and thiophanate-methyl, appears to be the active form in fungi (1). 

Genetic studies of negatively correlated cross resistance between benzimidazoles and N-phenylcarbamates. 

To elucidate the mechanism of negatively correlated cross resistance and mode of action of diethofencarb, we isolated diethofencarb resistant mutants from mutagenized F914 strain. 

However difference aspect was observed in resistance to MBC between N. crassa isolates in laboratory and B. cinerea isolates from the field. Laboratory-generated mutants of N. crassa showed various levels of resistance to MBC, and a specific one showed negatively correlated cross resistance to diethofencarb. Others showed double resistance to these chemicals. On the other hand, most of the benzimidazole resistants isolated from the field, especially in in the case of B. cinerea, were supersensitive to diethofencarb. This difference between laboratory and field strains may derive from a difference in fitness among the resistant strains of the plant pathogen. 

Considerable interest has developed in resistance management through the use of 1) compounds that are more active against fungicide-resistant biotypes than their sensitive counterparts (i.e., the resistant biotypes exhibit negatively-correlated cross resistance) and 2) compounds that interfere with the resistance mechanism (i.e., synergists). Both approaches to resistance control have been reviewed by De Waard (24,45). 

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