Problem, nature

Gas separation Hollow-fibre for high-volume applications with low-flux, low-selectivity membranes in which concentration polarisation is easily controlled (nitrogen from air) Spiral-wound when fluxes are higher, feed gases more contaminated, and concentration polarisation a problem (natural gas separations, vapour permeation). 

Parsegian, A. (1969). Energy of an ion crossing a low dielectric membrane solutions to four relevant electrostatic problems, Nature, 221, 844-846. 

The presence of aphids, Toxoptera graminum (Rondani) and Macrosiphum granarium (Kirby), on wheat during March and April has caused considerable alarm to wheat farmers in central Mexico. It has been found, however, that in the majority of cases the aphids do not represent a serious economic problem. Naturally occurring predators are able to reduce the aphid populations rapidly. For cases in which this natural biological control is not effective it has been found that benzene hexachloride (BHC) applied as a dust gives good control of these pests. 

Nature of the problem Nature of the effect Reversibility of effects Scale of effects Impact on economy Sectoral Human health Relatively easy Local-regional Direct losses Multisectoral Human health and ecosystem Relatively difficult International-global Substantial in course of time... 

A good starting point is photoexcitation from the ground state of H. The problem naturally divides itself into two regimes below the energy of classical ionization limit, where the states are for all practical purposes stable against ionization, and above it where the spectrum is continuous. 

Spiral-wound when fluxes are higher, feed gases more contaminated and concentration polarization a problem (natural gas separations, vapor permeation)... 

This verdict is confirmed by practically all experts, who differ only in that their alternatives of global ecodynamics are sometimes controversial. Some problems naturally crop up here regarding the rational organization of society and creation of a technology that makes compromises between collective decisions about the... 

Trewavas, Anthony. 1999. Much food, many problems. Nature 402(November 18) 231-232. 

Students sometimes wonder How do I decide when to use the combined gas law and when to use the ideal gas law The answer depends on the problem, naturally. If moles are involved, the combined gas law cannot be used. 

In some low-speed combustion problems natural convection is of importance, and consequently f, is not negligible. Since the acceleration due to gravity is the same for all species, f, is the same for all i in these problems. Body forces disappear from equations (3) and (7) and remain only in the momentum equation. 

Bowie JU. Solving the membrane protein folding problem. Nature 2005 438 581-589. 

Qian B, Raman S, Das R, Bradley P, McCoy AJ, Read RJ, Baker D. High-resolution structure prediction and the crystallographic phase problem. Nature 2007 450 259-264. 

The transfer of the information described in the preceding sections of this chapter to the in vivo situation is a matter where opinions are sharply divided, even if more than 20 years have elapsed since the discovery by Vasington and Murphy [4]. One key problem, naturally, is the impossibility of reproducing the composition and the conditions of the cytosol in in vitro experiments. The above mentioned effect of Mg on the rate of Ca influx into mitochondria is but one striking example of the difficulties inherent to the extrapolation to the in situ conditions. Of interest in this respect are recent experiments [124,125] in which methods have been devised to estimate simultaneously the membrane potential across the plasma membrane and the mitochondria of nerve endings in situ. The conclusion of this work has been that the concentration of free Ca in the cytosol correlates directly to the membrane potential across the mitochondrial membrane, and is maintained at a steady-state level below 1 jaM. Simulation of the in situ conditions has also been the aim of studies [126] in which isolated liver endoplasmic reticulum has been added to media in which isolated liver mitochondria were made to take up Ca, or in which liver cells have been treated with digitonin to abolish the permeability barrier of the plasma membrane. It was found that respiring mitochondria lower the external Ca " concentration to about 0.5 /iM. The addition of endoplasmic reticulum vesicles produces a further decrease of the external Ca " to about 0.2 jaM. Thus, mitochondria... 

Carboxylation is, in the first place, a thermodynamic problem. Nature solves this problem by associating the carboxylation with some exergonic process. This may be reduction of a product (as in the case of malic enzyme and isocitrate dehydrogenase), hydrolysis of ATP (as in the case of pyruvate carboxylase), hydrolysis of phosphoenolpyruvate (as in the case of phosphoenolpyruvate carboxylase), or cleavage of a carbon-carbon bond (as in the case of ribulose-bisphosphate carboxylase). 

The careful application of this equation is necessary to most fluid-mechanics problems. Naturally we can divide by time and find... 

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