5,810 research outputs found
Rod-like Polyelectrolytes in Presence of Monovalent Salt
We investigate the properties of rigid polyelectrolyte solutions in presence
of monovalent salt. The free energy within the Debye-H\"uckel-Bjerrum (DHBj)
theory [M. E.
Fisher and Y. Levin, {\it Phys. Rev. Lett.} 71, 3826 (1993)] is constructed.
It is found that at thermodynamic equilibrium the polyelectrolyte solution
consists of clusters composed of one polyion and various counterions. The
distribution of the cluster densities is determined by finding the minimum of
the Helmholtz free energy. The osmotic pressure and the average charge of the
cluster are found and their dependence on Manning parameter is
elucidated. A good agreement with the experimental results is obtained.Comment: 11 pages, Revtex (using twocolumn style), 15 figures and postscript
file. Submitted to Macromomelecule
Coparenting in Fragile Families
Nonmarital childbearing has increased dramatically in the U.S. since the early 1960s, rising from 6% of all births in 1960 to fully 40% in 2007 (Hamilton, Martin, & Ventura, 2009). Whereas similar trends have occurred in many developed nations, the U.S. stands out in the extent to which such births are associated with socioeconomic disadvantage and relationship instability. This has given rise to a new term ‘fragile families,’ which we define as unmarried couples who have a child together. The increase in fragile families reflects changes not only in the initial context of births but also in the fundamental nature and patterns of childrearing.Fragile families, childbearing, nonmarital childbearing
Fathers in Fragile Families
Nonmarital childbearing has increased dramatically in the U.S. since the early 1960s, rising from 6% of all births in 1960 to fully 40% in 2007 (Hamilton, Martin, & Ventura, 2009; Ventura & Bachrach, 2000). Whereas similar trends have occurred in many developed nations, the U.S. stands out in the extent to which such births are associated with socioeconomic disadvantage and relationship instability, giving rise to a new term ‘fragile families.’ The increase in fragile families reflects changes not only in the context of births but also in the fundamental nature and patterns of childrearing, particularly with respect to fathers’ roles and involvement with children.Fragile families, childbearing, nonmarital childbearing, fartherhood, fathers
Liquid Polymorphism and Density Anomaly in a Lattice Gas Model
We present a simple model for an associating liquid in which polymorphism and
density anomaly are connected. Our model combines a two dimensional lattice gas
with particles interacting through a soft core potential and orientational
degrees of freedom represented through thermal \char`\"{}ice
variables\char`\"{} . The competition between the directional attractive forces
and the soft core potential leads to a phase diagram in which two liquid phases
and a density anomaly are present. The coexistence line between the low density
liquid and the high density liquid has a positive slope contradicting the
surmise that the presence of a density anomaly implies that the high density
liquid is more entropic than the low density liquid
Amphiphile Adsorption on Rigid Polyelectrolytes
A theory is presented which quantitatively accounts for the cooperative
adsorption of cationic surfactants to anionic polyelectrolytes. For high salt
concentration we find that the critical adsorption concentration (CAC) is a
bilinear function of the polyion monomer and salt concentrations, with the
coefficients dependent only on the type of surfactant used. The results
presented in the paper might be useful for designing more efficient gene
delivery systems
The Human Ecology Dialectic: Culture as a Behavioral Adaptation
Contrary to popular thought, which implicated the disengagement of Marx from anthropological theory, his dialectical concept will be applied to explain human ecology in a Boasian historical particularism milieu. Environmental conditions will be the common denominator for the Darwinian biogeography theory, intertwined with the cultural adaptation theory of Boas within the Human Ecology Dialectic (Taylor, 2014). Anthropologically, in a biological context the theories will explain the behavioral adaptation process demonstrated culturally by the prehistoric ancestors of the Inuit of the Canadian Central Arctic in their development and essential engagement in the creation of art; a pursuit that became a cultural tradition in historic and contemporary Inuit life. Art will be defined as objects of various forms and functions with aesthetic qualities made from raw organic resources such as bone, ivory, and stone
MCD and magnetization studies on nifB/nifZ minus molybdenum iron protein from Azotobacter vinelandii
This study reports a characterization of the iron-sulfur clusters of the MoFe protein expressed by the nifBnifZ deletion strain of A. vinelandii. VT-MCD spectroscopic and magnetization analysis of as-isolated ΔnifBΔnifZ MoFe protein were undertaken. VT-MCD spectra of as-isolated ΔnifBΔnifZ MoFe protein contains bands remarkably similar to those seen in as-isolated ΔnifH MoFe protein, assigned to arise from an [4Fe-4S]+ cluster. The low-temperature magnetization curve of as-isolated ΔnifBΔnifZ MoFe protein reveals the MCD spectra bands stem from an S = ½ spin system with diamagnetic contributions of some other species. As-isolated ΔnifBΔnifZ MoFe protein is compared with as-isolated ΔnifH MoFe protein, which contains a P-cluster precursor, and the as-isolated ΔnifB MoFe protein, which contains a fully assembled P-cluster ([8Fe-7S)]. Using nonlinear regression, the experimental magnetization curve of as-isolated ΔnifBΔnifZ MoFe protein is compared and factored to contributions from as-isolated ΔnifH MoFe protein and as-isolated ΔnifB MoFe protein. The simulation suggests a 1:1 ratio of ΔnifH MoFe protein to ΔnifB MoFe protein. These results suggests the as-isolated ΔnifBΔnifZ MoFe protein has an αβ subunit pair that contains a P-cluster and the other αβ subunit pair contains a latent (defined as immature, or potential) P-cluster (two [4Fe-4S] or P-cluster precursor)
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