Synchronisation in

The G2-phase of the cell cycle is perhaps the most difficult to study as it is the most difficult phase in which to obtain a synchronised cell population. This is because, if cells are synchronised by selection at mitosis or accumulation at the Gl/S boundary, by the time they reach G2 much of the synchrony has been lost. This is because of the dispersion forces arising from the different rates at which individual cells in a population traverse the cycle. G2 populations are always contaminated with cells in other phases of the cycle and the maximum fractions of Chinese hamster (CHO) cells obtainable in G2 are 0.7 by double thymidine block and 0.4 by mitotic selection (Enger et al., 1968). 

Although most cultured cell populations come to rest in Gl, i.e. between cell division and DNA synthesis, a proportion of mouse ear epidermal cells are thought to be arrested in G2 (Gelfant, 1959, 1963), although recent evidence casts doubt on these conclusions (Sauerbom et al., 1978). There is some evidence that human embryonic fibroblasts maintained in culture for 48 passages (i.e. in the terminal phase) may arrest in G2 (Maciero-Coelho et al., 1966) but these are so abnormal as to be of no value in studies of G2. As mentioned in 11.6, some tumour cells arrest in G2 on medium exhaustion, but again many metabolic processes are affected and the cells cannot be considered as typical of G2-phase cells. 

One way of obtaining a population of G2-cells is to have a mutant with a temperature sensitive stage in G2-phase, and Basilico (1978) has described a procedure which should select for such temperature sensitive mutants. 

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Although such a definition is seemingly quite clear and unique, the practical exploitation of the above criterion is complicated by the fact that the scission and formation of bonds is a microscopic process, inaccessible to direct experimental observation. This, of course, suggests the necessity of searching other, more easily exploitable, criteria of concert. One such criterion is the remarkable stereospecificity accompanying the formation of products in allowed pericyclic reactions [60,61]. The fact that the origin of the synchronisation in the process of scission and the formation of the bonds was always intuitively related to a certain energetic stabilisation led to another widespread opinion that all allowed reactions are automatically concerted. On the other hand nonconcertedness, advocated by frequently observed stereo-randomization [60] was practically always expected in forbidden reactions. 

Loop-based introduction is more suitable for inserting small sample volumes because the analytical repeatability tends to be preserved when the loop dimensions are reduced. For very small inserted sample volumes and the use of pulsed flows, pumping and injection should be synchronised in order to avoid sample insertion under different instantaneous flow rates (see also 5.23.2). 

Synchronisation of cell growth was shown to be dependent on the technical set-up of the growth experiments. It took more than twenty years to stabilise synchronisation in high yield chemostats (Munch et al. [12,13]) and to reproduce changes in a cell population from the birth to the death of cells. 

Redundancy is a term often confused with resilience. In effect, redundancy is a strategy one may choose to implement in pursuit of a resilient system. It can be defined as the Provision of multiple components or mechanisms to achieve the same function such that failure of one or more of the components or mechanisms does not prevent the performance of the function [3]. In other words redundancy represents the inclusion of additional hardware or functionality which might not be critically required during normal operation but is seamlessly available should it be called upon in situations of failure. For example, one might choose to operate a system with not one but two databases hosted in different geographical locations and synchronised in real time. Should one fail the system can be designed to automatically revert to the alternative without any obvious impact on the user. 

R. Alur, C. Courcoubetics D.L. Dill (1990), Model Checking for Real-Time Systems, in Proceedings of the Fifth Annual Symposium on Logic in Computer Science , IEEE Computer Society Press, Washington, D.C., pp. 414-425. Rajkumar, R. (1989), Task synchronisation in real-time systems, PhD thesis, Carnegie Mellon University. 

In our simulations we made the assumption that the clocks on our different machines were synchronised but we made no effort to guarantee that the assumption was met. We considered three implementation choices for ensuring that our clocks are synchronised in any further development of our distributed system ... 

The flow of main steam entering the high-pressure turbine is controlled by four control valves. The turbine control valves are adjusted automatically by electrohydraulic servo actuators. These actuators control the turbine speed when it is starting up, and for load control after the turbine-generator unit is synchronised. In series with each control valve is a stop valve, whose function is to shut off and isolate the steam flow to the turbine when required. 

Rieckhof, R, Seifert, M., Aszmann, U. Ontology-based model synchronisation. In Proceedings of TWOMDE Workshop (2010)... 

Losche, T Paland, E.-G. Poll, G. Wear Behaviour of Synchronisers in Relation to a Duty Parameter Tribology for Energy Conservation, Tribology Series, 34 (ISBN 0-444-50033-2, Vol. 34), ed. Dowson, D., Elsevier Science, Amsterdam (1998)... 

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