Some open questions

The excitatory signal transduction, as reviewed in the preceding paragraphs, appears to be relatively well worked out. However, there are a number of components and processes that have been shown to be involved in this transduction but whose function and site of action are not yet known. In addition, there are several intriguing questions with respect to major signal transduction processes. A few examples follow. 

Other questions that I have mentioned in different sections are How are the sensory signals transduced across the membrane by the chemotaxis receptors How do differently abundant receptors generate signals of similar strength How is the signal propagated within the switch subsequent to CheY P binding  

Adaptation—the process of recovery from a stimulated behavior when the stimulus is still present—is essential for every behavioral system. It allows detection of small changes in the stimulus level on top of existing, constant level of stimulation. In the case of bacterial chemotaxis, adaptation enables bacteria to respond to new stimuli in the presence of constant levels of chemoattractants and/or chemorepellents. 

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Nevertheless, despite all these remarkable achievements, some open questions still remain. Among them is the influence of the molecular transport properties, in particular Lewis number effects, on the structure of turbulent premixed flames. Additional work is also needed to quantify the flame-generated turbulence phenomena and its relationship with the Darrieus-Landau instability. Another question is what are exactly the conditions for turbulent scalar transport to occur in a coimter-gradient mode Finally, is it realistic to expect that a turbulent premixed flame reaches an asymptotic steady-state of propagation, and if so, is it possible, in the future, to devise an experiment demonstrating it ... 

These reactions take place very slowly under the extreme ultra-high vacuum conditions present in outer space, so that the chemistry is different to that observed in the laboratory. Thus there are still some open questions regarding the mysterious interstellar ion H3+, particularly with respect to its occurrence in diffuse clouds and its rate of decomposition (Suzor-Weiner and Schneider, 2001 Kokoruline et al., 2001). 

Hutzinger, O. Fiedler, H. (1993). From source to exposure some open questions. Chemosphere, 27, 121-129. 

Here we briefly describe the first two approaches with the aim of contrasting them to simultaneous methods presented in Section V. In that section, the advantages of simultaneous methods also lead us to consider some open questions and concentrate on current work in this area. 

These include the Rayleigh quotient method" and variational transition state theory (VTST).46 9 xhg 0 called PGH turnover theory and its semiclassical analog/ which presents an explicit expression for the rate of reaction for almost arbitrary values of the friction function is reviewed in Section IV. Quantum rate theories are discussed in Section V and the review ends with a Discussion of some open questions and problems. 

Pyrimidines. The pyrimidines react with eaq at practically diffusion-controlled rates (Table 10.6). The ensuing reactions of the radical anions of Ura and Thy are very well understood, while with that of Cyt some open questions still remain. 

Hutzinger O, Fiedler H. 1993. Form source to exposure Some open questions. Chemosphere 27(ISS 1-3) 121-129. 

Although some open questions still remain, the experiments of Ref. 18 may be used to predict the heat transfer to a number of liquids under constant-heat-flux conditions. The empirical correlations obtained were ... 

Whether you manage to get an open atmosphere depends on how strongly you try to stmcture the interview (Figure N4-11). If you determine the sequence and all questions in detail beforehand, as is often done with marketing enquiries, you leave no room for the interviewed. You only get answers to the question that you ask, but no other information. This is alright if you know exactly what you want, but then you could just as well let the interviewed fill in a list, which takes a lot less time. If you want to get information that you have not thought about before, at least part of the interview must be unstmctured, and you should have some open questions to keep this going. 

Although there is a consensus that encainide and flecainide were associated with an increase in the rate of mortality in CAST, there are stiU some open questions. First, all the patients recruited to CAST had asymptomatic ventricular dysrhjdhmias after myocardial infarction, and it is not clear whether the results can be extrapolated to other patients. Secondly, the reasons for the increased mortality in the treated patients are not clear ventricular dysrhythmias and worsening of left ventricular function are both possible. Thirdly, it is not clear whether the results of CAST in patients with asymptomatic ventricular dysrhythmias after myocardial infarction can also be applied to other Class I antidysrhythmic drugs. 

All reported experiments so far indicate that the experimental limits of molecule interferometry are still far out. And M. Arndt el al. discuss some open questions in the quest for quantum experiments with macromolecules. 

At this point, we can suggest some open questions ... 

Some Open Questions, both Formal and Practical... 

Numerous results from kinetic and mechanistic studies using photo-reactors have been obtained which have contributed significantly to an increase in our knowledge on atmospheric chemistry, in particularly in the gas phase. Some open questions still remain, e.g. the mechanisms of the photooxidation of aromatic hydrocarbons and the process of gas-to-particle conversion. More recently also aerosol studies are being carried out in chambers. Some very recent work has led now to a much better understanding of the photochemieal wall effects in chambers which produce OH radicals (Rohrer et al., 2005). 

Summarizing, promising activity improvements could be achieved in model gas experiments with Pd-only catalysts, even though some open questions regarding sulfur poisoning or the formation of secondary emissions have to answered. 

There still remain some open questions which could be mentioned partially only in this paper. One is to deal with the number of imknown parameters. The number of parameters in geochemical and biogeochemical models is often very high, so that even modem parameter estimation tools, like PEST, have problems to handle the problem. There are problems with the execution time of these models and with their convergence towards an optimal solution in the parameter space ... 

It would be tempting to conclude, from the RR results, that Pgso consists of a monomeric Chi a. Within this interpretation, one of the two histidine residues found in the primary sequences of D1 and D2 could bind a Chi a molecule whose role might be analogous to that of the accessory BChl of bacterial RC. However, some open questions remain about the localization of the P state in PS II. Indeed, triplet state orientation, with respect to the membrane plane, in various PSIl preparations, is perpendicular to the orientation observed In bacterial RCs (9). These observations led Rutherford (9) to hypothesize that a specialized Chi a molecule, located near Peso- could trap the triplet state of the primary electron donor after charge recombination. The RR difference spectrum displayed in fig 2 could arise, according to this hypothesis, from the neutral, ground state of this Chi a. 

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