Dispersal[ edit ] Biofilm Dispersal Dispersal of cells from the biofilm colony is an essential stage of the biofilm life cycle. Dispersal enables biofilms to spread and colonize new surfaces. Enzymes that degrade the biofilm extracellular matrixsuch as dispersin B and deoxyribonucleasemay contribute to biofilm dispersal. Secreted by Pseudomonas aeruginosathis compound induces cyclo heteromorphic cells in several species of bacteria and the yeast Candida albicans.
Fertility in developing countries: Farooq and George B. Theories of fertility, including macrolevel theories, microeconomic theories, and the more recent structural and community-level approaches are described and compared.
A theory consists of a series of statements about the relationship between clearly defined variables. Fertility theories seek to describe the major influences affecting fertility. The theories are abstract, and no theory is capable of explaining fertility behavior in all societies throughout time.
Some empirical observations can be explained by several theories. Criteria for selecting the most appropriate theory in these situations are: Major macrolevel approaches include the population theories of Malthus and of Marx and the demographic transition theory.
According to Malthus, population growth reduces income. As income declines, couples begin to marry later. Subsequently, fertility declines and continues to decline until population size is once again consistent with the resource base.
Resource scarcity is a central theme of the theory. If the government provides assistance for the poor, the natural process is interrupted, and population growth continues unabated. The theory assumes that technology is static, land resources are fixed, class structure is rigid, and marital fertility is equivalent to natural fertility.
These assumptions do not accord with empirical evidence. In contrast, Neomalthusian theory is more concerned with limited resources at the family level.
According to this theory, high fertility depresses a family's living standard and fertility can be controlled by contraception as well as by late marriage.
This theory ignores the economic value of children and treats children as consumption units. It ignores the investment aspects of having children.
The demographic transition theory states that fertility reduction occurs when a decline in the mortality rate leads to population pressure. Another common response is migration. Furthermore, empirical evidence indicates that fertility sometimes declines before there is a decline in mortality.
Microeconomic theories seek to explain differences in fertility at the household level. The fertility decisions made by a couple are conceptualized in terms of market choices.
The new home-economic approach, the social determinants approach, and several other approaches are discussed. The home economic model, as initially formulated by Becker, stresses the demand for children and treats children as consumption goods.
Couples have lifetime income restraints, and within this context, they seek to maximize their utility in regard to the number and quality of children they have and the quantity of other goods they consume.
According to this model, if a couple's income increases, they will increase the number and quality of their children. Empirical evidence does not lend much support to this hypothesis. Becker and others later expanded the model to recognize the stochastic component of fertility and the impact of external factors on fertility.
The social determinants model recognizes that couples vary in regard to the value they place on children and that there are biological constraints on fertility. In addition, social determinants models use control variables such as religion and education. The models proposed by Leibenstein, Easterlin, and Turchi are described.
In general, the microeconomic models have produced only minimal empirical explanations of fertility and tend to have a low predictive capacity. New theorectical approaches which seek to overcome the problems inherent in previous approaches are beginning to emerge.
These approaches focus attention on how social institutions and community level variables influence the fertility of couples. These approaches provide a complete theory of fertility by combining microlevel and macrolevel analysis.
The formal structures of several economic models are provided in the appendix.Power market participants have encountered a growing number of challenges due to competition and other pertinent factors. For most markets at present, electricity is a non-storable commodity and its price is extremely sensitive to changes in supply and demand.
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These studies provided the basic background information needed to formulate.