External control growth

Phase behavior in complex fluids such as polymer blends and block copolymers has been a rich area of the chemical sciences. Near-critical and other transitional phenomena are frequently prominent. Since molecular movement in viscous systems such as these is comparatively slow, phase transitions can be studied more easily in time, and manipulated by quenching and other external influences. Processes for controlled growth of ordered materials are often readily influenced by diffusion, a variety of external fields, and the influence of interacting boundaries, or flow. 

In addition to the built-in protection and control mechanisms, the cell is also subject to a number of external controls, which ensure that cell division occurs in balance with the overall development of the organism and with external growth conditions. This is a kind of social control of cell division that regulates the progress of the cell cycle, with the help of circulating signal molecules or via cell-cell interactions. 

Cell division activities are controlled to a high degree by externally determined growth conditions such as nutrient supply. A cell may stop cell division if the physiological conditions are unfavorable. 

When mitosis has been completed, the cell requires signals in the form of growth factors to direct towards a new roimd of division. The signals become effective in the first two-thirds of Gi phase. In this time window, the cell is programmed to begin a new cell cycle or to enter Go phase. After a particular point, the restriction point R, no further signals are needed to continue the cell cycle. The cell cycle apparatus is self-contained from this point onwards. S, G2 and M phase occur without external control. The cell cycle may still be halted after crossing the restriction point, however, if the cell detects, via internal control mechanisms or checkpoints, that defects have occurred in the correct course of the phases. 

The Co content of most plants is around 1 pg g 1 and since this element is not normally considered to be essential for plant growth, its concentrations in plants tend to be externally controlled and reflect the Co content of the substrate to a better degree than does Cu. Despite the supposed non-essentiality of Co for plant growth, there... 

As discussed in Section 9.2.2., the introduction of feedback can lead to oscillations in a system. As pointed out by Randolph and Larson (1988) and as illustrated in Figure 9.24, a crystallizer has an inherent feedback structure because of the interrelationship between the growth rate, the nucleation rate, and the CSD. This feedback is responsible for observed instabilities of an open-loop crystallizer (i.e., a crystallizer that is not externally controlled). 

The quality, productivity, and batch-to-batch consistency of the final crystal product can be affected by the conditions of the batch crystallizer. Several factors considered here include batch cycle time, supersaturation profile, external seeding, fouling control, CSD control, growth rate dispersions, and mixing. 

Beyond the immediate problem of reproduction we are interested in the consumption of substrates by cells, the formation of new cellular material, and the release of metabolic by-products to the environment. One cannot ignore these questions it is the growth of single cells that determines what the environmental conditions will be (apart from external controls applied), and the environmental conditions determine in turn what the growth and reproductive characteristics of the culture will be. 

Asada S, Choi Y, Yamada M, et al. External control of Her2 expression and cancer cell growth by targeting a Ras-linked coactivator. Proc Natl Acad Sci USA 2002 99 12747-12752. 

The oxide at the external surface of the composite is predominantly a thin (0.1 pm) layer of MgO with an intermittent, underlying spinel layer The microstructure is discussed below. It could be argued that the entire process of incubation and reinitiation is caused by excess magnesium, and that a starting composition near the three-phase equilibrium should trigger immediate growth of alumina. However, controlled growth of a DM0 composite has never been reported from a bulk... 

External controls to drive the nucleation in confined areas. The external control can be any external driving force promoting the growth of MOFs (e.g., electrochemical approach) or controlling/depositing the amount of MOF precursors in precise locations (e.g., microcontact printing and evaporation-induced growth). 

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