35,875 research outputs found
Polyelectrolyte Solutions with Multivalent Salts
We investigate the thermodynamic properties of a polyelectrolyte solution in
a presence of {\it multivalent} salts. The polyions are modeled as rigid
cylinders with the charge distributed uniformly along the major axis. The
solution, besides the polyions, contain monovalent and divalent counterions as
well as monovalent coions. The strong electrostatic attraction existing between
the polyions and the counterions results in formation of clusters consisting of
one polyion and a number of associated monovalent and divalent counterions. The
theory presented in the paper allows us to explicitly construct the Helmholtz
free energy of a polyelectrolyte solution. The characteristic cluster size, as
well as any other thermodynamic property can then be determined by an
appropriate operation on the free energy
The performance of forecast-based monetary policy rules under model uncertainty
We investigate the performance of forecast-based monetary policy rules using five macroeconomic models that reflect a wide range of views on aggregate dynamics. We identify the key characteristics of rules that are robust to model uncertainty: such rules respond to the one-year-ahead inflation forecast and to the current output gap and incorporate a substantial degree of policy inertia. In contrast, rules with longer forecast horizons are less robust and are prone to generating indeterminacy. Finally, we identify a robust benchmark rule that performs very well in all five models over a wide range of policy preferences
Complex Formation Between Polyelectrolytes and Ionic Surfactants
The interaction between polyelectrolyte and ionic surfactant is of great
importance in different areas of chemistry and biology. In this paper we
present a theory of polyelectrolyte ionic-surfactant solutions. The new theory
successfully explains the cooperative transition observed experimentally, in
which the condensed counterions are replaced by ionic-surfactants. The
transition is found to occur at surfactant densities much lower than those for
a similar transition in non-ionic polymer-surfactant solutions. Possible
application of DNA surfactant complex formation to polynucleotide delivery
systems is also mentioned.Comment: 5 pages, latex, 3 figure
Improved magnesia for thermal control coatings
Formation of radiation-generated color centers using single crystals of magnesium oxide is discussed. Crystal structure of magnesium oxide is described. Chemical processes used to produce magnesium oxide with desired color center kinetics are presented. Proton irradiation of magnesium oxide crystals was conducted to determine lattice defects
Variation in a host-epiphyte relationship along a wave exposure gradient
The red alga Polysiphonia lanosa (L ) Tandy is an obligate epiphyte that primarily occurs on the fucoid brown algal basiphyte Ascophyllum nodosum (L) Le Jolis In the present study we examine how epiphytic interactions between P lanosa and A nodosum vary along a wave exposure gradient within the southern Gulf of Maine, USA P lanosa was most dense on protected shores, however because the stature of P lanosa was greater on exposed than on sheltered shores, greater biomass occurred In exposed habitats Epiphytlc P lanosa pnmanly attached to inlured vegetative bssue at exposed sites, while ~ t osc currence was primarily receptacular at sheltered sites A significantly stronger correlation was found between host receptacle abundance and epiphyte abundance at a protected low than an exposed site As a result, the distribution of epiphytes along the host S stlpe vanes at different sites We suggest that changes in the distribution and abundance of P lanosa across this wave exposure gradient are highly influenced by vanations in the distribution and persistence of suitable attachment sites on the host plant Because both the quantity and quality of attachment sites vanes w t h exposure, we hypothesize that d~fferenpt rocesses limit or de t e rm~neP lanosa populations in different locations In protected sites P lanosa may be limited by the presence of adequate substrata (inlured bssue and lateral pits) where successful recruitment may occur By contrast at exposed sites the supply of P lanosa sporelings, rather than quantity of appropnate substrata, may limlt population size
Cost-Reducing and Demand-Creating R&D With Spillovers
This paper analyzes R&D policies when the returns to cost-reducing and demand-creating R&D are imperfectly appropriable and market structure is endogenous. Previous characterizations of appropriability are generalized to permit the possibility that own and rival R&D are imperfect substitutes. We also describe how. equilibrium expenditures on process and product R&D, as well as equilibrium market structure, depend on technological opportunities and spillovers. In contrast to previous work, diminished appropriability does not necessarily reduce R&D expenditures. For example, under some conditions, an increase in the extent of process (product) spillovers will lead to an increase in product (process) R&D. We estimate several variants of the model using manufacturing line of business data and data from a survey of R&D executives.
Microscopic Approach to Shear Viscosities in Superfluid Gases: From BCS to BEC
We compute the shear viscosity, , at general temperatures , in a
BCS-BEC crossover scheme which is demonstrably consistent with conservation
laws. The study of is important because it constrains microscopic
theories by revealing the excitation spectra. The onset of a normal state
pairing gap and the contribution from pair degrees of freedom imply that
at low becomes small, rather than exhibiting the upturn predicted by most
others. Using the local density approximation, we find quite reasonable
agreement with just-published experiments.Comment: 4 pages, 2 figure
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