Search

Triplet correlations play a central role in our understanding of fluids and their properties. Of particular interest is the relationship between the pair and triplet correlations. Here we use a combination of Fluctuation Solution Theory and experimental pair radial distribution functions to investigate the accuracy of the Kirkwood Superposition Approximation (KSA), as given by integrals over the relevant pair and triplet correlation functions, at a series of state points for pure water using only experimental quantities. The KSA performs poorly, in agreement with a variety of other studies. Several additional approximate relationships between the pair and triplet correlations in fluids are also investigated and generally provide good agreement for the fluid thermodynamics for regions of the phase diagram where the compressibility is small. A simple power law relationship between the pair and triplet fluctuations is particularly successful for state points displaying low to moderately high compressibilities.

Dichlorodibutylstannane, dichlorodioctylstannane and dichlorodiphenylstannane were reacted with different amounts of sodium in liquid ammonia. At a molar ratio of R2SnCl2/Na of 1:2, polystannanes precipitated, in some cases accompanied by cyclic oligostannanes. The products resulting from mixtures with R2SnCl2/Na ratios of 1:3 to 1:10 were soluble and, hence, could be studied in-situ in liquid ammonia with 119Sn NMR spectroscopy. The compounds obtained, tin hydrides of the type R2SnH− and in certain cases distannides of the composition R4Sn22−, formed essentially independent of the R2SnCl2/Na ratio; this, in contrast to views expressed in the literature. Our experiments showed that the chemical structure of the in-situ generated species did not permit to draw conclusions about the composition of the reaction products with bromoethane and vice versa – a practice commonly described. Furthermore, we observed migration of the butyl groups both in-situ during the reaction of dichlorodibutylstannane with sodium in liquid ammonia, as well as in the final reaction product. By contrast in the case of the phenyl substituent, migration was detected not during the chemical event in liquid ammonia, but only in the compounds formed. These observations imply a different mechanism for butyl and phenyl group migration.

It has been known for over a century that the presence of cosolvents such as urea and formamide can alter the morphology of NaCl crystals grown from solution. To help understand this effect we have been developing a theoretical approach based on the Kirkwood-Buff (KB) theory of solutions, and have combined this with computer simulations of the interation of urea with different crystal faces of NaCl. In this way one can predict the effect of urea on the thermodynamic stability of different NaCl faces, with atomic level detail provided by the simulations. We observe that urea is preferentially excluded from 100 and 111 crystal faces, but is less excluded from 111 faces which present chloride ions at the surface. The results indicate that the 111 face is stabilized in urea solutions and promotes the formation of octahedral over cubic NaCl crystals. The approach is totally general and can be applied to understand a variety of interfacial properties. Furthermore, we apply KB theory to study several other issues regarding the simulation of crystal growth.

We demonstrate that blending α-quaterthiophene (4T) with high-density polyethylene (HDPE) under judiciously chosen processing conditions allows preparation of continuous thin films of insulator content as high as 90 wt% without considerably sacrificing the electronic properties of the semiconducting species, as measured in field-effect transistors (FETs). Similar behaviour was recently reported for all-polymeric crystalline–crystalline semiconducting blends such as poly(3-hexylthiophene):HDPE. However, while that previous work focussed on the sequence in which the two components crystallize, we show here that for the present small molecule:polymer binaries – in addition to the crystallization sequence – the extent of solid–solid phase separation that occurs during blend preparation strongly affects the electronic properties of the active layers.

Recent results concerning the formulation and evaluation of preferential interactions in biological systems in terms of Kirkwood–Buff (KB) integrals are presented. In particular, experimental and simulated preferential interactions of a cosolvent with a biomolecule in the presence of water are described. It is argued that the preferential interaction parameter defined in a system open to both cosolvent and solvent corresponds to the situation most relevant to the analysis of computer simulation results of cosolvent interactions with proteins and small peptides. Hence, KB theory provides a path from quantities determined from simulation data to the corresponding thermodynamic data.

We have constructed an “expert-knowledge classification system” to categorize 309 fish taxa in the California Cooperative Oceanic Fisheries Investigations ichthyoplankton database into primary (coastal, coastal-oceanic, and oceanic) assemblages based on their principal ecological domains and subsequently, secondary assemblages according to the habitat affinities of adults. We examined effects of fishing, climate, adult habitat, and age-at-maturation on long-term variation of fish populations. We tested the hypothesis that populations of unexploited taxa track climatic trends more closely than those of exploited taxa insofar as climatic signals may be confounded by fishing effects. Most oceanic taxa (23/34) showed a significant relationship with environmental variables and followed the trend of the Pacific Decadal Oscillation. Very few coastal (3/10) and coastal-oceanic (3/23) taxa exhibited a significant relationship with environmental signals; however, several fluctuated coherently, and age-at-maturation is an important factor. The lack of close correlation between fish populations and environmental signals in the coastal and coastal-oceanic assemblages indicates that these species might show nonlinear biological responses to external forcing rather than a simple linear tracking of environmental variables. We did not find a systematic pattern indicating that fishing influenced population fluctuation of exploited species. Constrained comparisons of exploited to unexploited species living in the same habitat and reaching maturity at the same age revealed evidence of overexploitation for some species but not for all. Our results suggest that considering life history and ecological characteristics of fish species and applying a community approach are important in understanding fishing effects on fish populations in the context of a changing environment.

A thermodynamic relationship is obtained which links the effect of a cosolvent on the denaturation equilibrium of a protein to the effect of the cosolvent on the change in partial molar volume (pmv) of a protein on denaturation. The relationship uses the concept of preferential interactions and is exact for an infinitely dilute protein. Analysis of the literature data on protein volume changes suggests that many of the observed volume changes are thermodynamically inconsistent with the corresponding free energy changes, especially at low cosolvent concentrations. It is argued that the most reasonable explanation for this involves cosolvent induced changes in the degree of protein-protein association.

Fifty-year ichthyoplankton and oceanographic time series of the California Cooperative Oceanic Fisheries Investigations were used to describe changes in larval fish abundance and associated habitat features in the Southern California Bight region, extending seaward to the limits of the California Current. The ichthyoplankton data set for this analysis was based on single tows taken at all CalCOFI survey stations occupied within the current sampling pattern from 1951 to 2000 and consisted of a total of 11,917 samples from which 1,365,988 fish larvae were identified. The analysis included data on habitat temperature, macrozooplankton volumes, and 14 taxa of larval fishes, some of commercial interest (Pacific sardine, Pacific hake, Pacific and jack mackerel, and rockfishes), and a group of important mesopelagic species that represent specific habitats in the California Current region. Data are presented in a series of graphs showing changes in average abundance, triennial abundance ratios, and normalized quarterly abundance (1988–2000 only). Larval data clearly track the decline and recovery of the Pacific sardine population. Mesopelagic larvae of southern offshore species had the greatest response to the regime shift of 1976–77, increasing markedly in the Southern California Bight region after 1977. Likewise, this group of species showed the greatest response to the 1957–59 El Nino. There was no consistent response in larval abundance of Subarctic-Transitional mesopelagic species and nearshore taxa to the 1976–77 regime shift. Most of the species showed a negative shift in triennial larval abundance ratios in relation to hypothesized 1989–90 and 1998–99 regime shifts. These changes are discussed in relation to changes in temperature and macrozooplankton volumes.

Previous research shows that offshore mesoscale eddies in the Southern California Bight region are areas where sardine larval abundance is significantly increased relative to inshore, slope and surrounding offshore waters. In order for mesoscale eddies to be a mechanism linking climate and sardine population variability they must be areas of exceptional prerecruit production. Temperature and prey data from various Southern California Bight (SCB) habitats, including offshore eddies, were applied to a spatially-explicit bioenergetic model which predicts sardine prerecruit growth potential. Growth potential was similar in inshore, slope, and eddy regions (11% and 12% day −1 ), and was lower in the offshore region, 9% day −1 . To estimate production in eddy and non-eddy habitats, growth potential was multiplied by habitat-specific estimates of sardine larval biomass from at-sea surveys. A production index, a measure of potential production resulting from individual growth rate potential and local abundance, was greater in the model cyclonic eddy than in all other regions by more than an order of magnitude. In fact, the production index in the eddy was four times greater than in all other regions combined.

We have analyzed a 1.2-ns molecular dynamics simulation of 51 mM d(CG.G)7 with 21 Na+ counter-ions and 1 M NaCl in water. Via the dipole fluctuations, the dielectric constant for the DNA is found to be around 16, whereas that for the bases and sugars combined is only 3. The dielectric constant for water in this system is 41, which is much smaller than 71 for pure SPC/E water, because of the strong restriction imposed on the motion of water molecules by the DNA and the ions. Also addressed in the present work are several technical issues related to the calculation of the dipole moment of an ionic solution from molecular dynamics simulations using periodic boundary conditions.

A method is described which improves the efficiency of Ewald simulations of large condensed phase systems. This is achieved by partitioning the real space sum into a short and long range component. The long range component is calculated every time the pair list is generated and included in subsequent steps using a multiple time step algorithm. The corresponding increase in the effective cutoff distance results in an algorithm which is only slightly more expensive than a traditional cutoff simulation, but with fewer artifacts than obtained using a cutoff. The method is tested on a 1.0 M solution of sodium chloride.

The application of molecular dynamics computer simulation methods to study the dynamics of proteins is reviewed with an eye to its possibilities and limitations. Examples are given, mainly using nanosecond trajectories of the proteins bovine pancreatic trypsin inhibitor and lysozyme, of the different protein properties, of which the dynamics can be or cannot be sampled on a nanosecond time scale. It is concluded that the major asset of the simulation technique is that the different factors contributing to the dynamics of a particular process can be analyzed at atomic detail, as long as one has sampled the appropriate time scale.

Order parameters as well as longitudinal and transverse relaxation rates are calculated for the backbone 15N and 13C alpha nuclei of the basic pancreatic trypsin inhibitor (BPTI) from a 1000 ps molecular dynamics trajectory in explicit water at 277 K using the "model free" approach of Lipari and Szabo. New NMR relaxation data at 277 K are presented, and a comparison is made between NMR relaxation measurements and molecular dynamics relaxation data. It is found that the relaxation processes determining the longitudinal (T1) relaxation rates are inadequately sampled even during this length of simulation. In effect, the calculated relaxation rates are determined almost solely by the order parameters and the overall rotational correlation time of the protein, which appears to be in clear contrast to experimental relaxation rates.

Extensive data sets on the bioenergetics of the northern anchovy, Engraulis mordax, and the patchy food distribution in its natural habitat allow its foraging dynamics to be inferred by modeling using techniques from population biology and behavioral ecology. The behavioral model consistently predicts that E. mordax grows much more slowly than would be expected with a pure, net-energy intake rate maximization strategy. The reduced growth rates could result from the fish avoiding zooplankton patches, where they are under increased predation risk, by swimming slowly in the waters between zooplankton patches. The combinations of growth rates and daily instantaneous mortality rates generated by the behavioral model are internally consistent with a Lefkovitch matrix population model, which includes an early juvenile stage of a stable and stationary population. Several novel and testable predictions are made by the behavioral model, including: (1) anchovies swim very slowly between zooplankton patch encounters; (2) within a patch fish swim very rapidly while searching for prey; and (3) fish often leave zooplankton patches before totally filling their stomachs. Given these encouraging initial results, the behavioral modeling approach appears to be a valuable technique for examining how potential habitat changes due to global warming may affect fish behavior and populations. Several such scenarios are proposed and discussed.

The shear viscosity of the SPC and SPC/E water models at 277 and 300 K has been determined using equilibrium molecular dynamics. Good agreement with experiment was obtained for the SPC/E model at both temperatures. The viscosity of the SPC model was lower than the experimental value at both temperatures and displayed only a small temperature dependence. The effect of using a reaction field treatment for the long-range electrostatic interaction was also investigated and found to be negligible.

By using a suitably functionalized acid to protonate the base form of polyaniline, the counter ion can induce processibility of the resulting PANI complex. Thus, polyaniline can be processed in its conducting form from the melt and/or from a wide variety of common organic solvents, such as decalin, xylene, chloroform and m-cresol, etc. The resulting conducting polyaniline can be processed neat or in blends with common, insulating bulk polymers to enable the fabrication of thin films, sheets, fibers, transparent conductive films, bulk parts, etc. These materials exhibit relatively high levels of electrical conductivity at low volume fractions of the polyaniline complex, while maintaining excellent mechanical properties, essentially equivalent to those of the host bulk polymer.

By using a suitably functionalized protonic acid to protonate polyaniline, the counter ion can induce processibility of the resulting PANI complex. Our results demonstrate the feasibility of processing, in the conducting form , polyaniline and a variety of polyblends made from polyaniline. The resulting conducting polymer materials can be melt-processed or processed from solution to enable the fabrication of thin films, sheets, fibers, transparent conductive films, bulk parts, etc. These materials exhibit relatively high levels of electrical conductivity at low volume fractions of the polyaniline complex, while maintaining excellent mechanical properties, essentially equivalent to those of the host bulk polymer.

Pseudoobstruction of the colon is a specific variety of adynamic ileus. Its characteristic clinical presentation is severe cramping lower abdominal pain, a massively distended abdomen, and a characteristic x-ray picture. Thirty-five patients with this disease complex have been reviewed, and their surgical and medical therapy is discussed. Guidelines for continued medical versus surgical intervention are suggested. Two patients underwent decompression with the colonoscope. Its use and a possible hazard of the procedure are discussed. For those patients who develop pseudoobstruction after trauma or surgery, a pathophysiologic explanation is offered. The possible role of prostaglandin abnormality in the genesis of pseudoobstruction is also discussed.

This paper investigates the empirical significance of the real-balance effect (RBE) via a small scale econometric model with real balances included in both the investment and the consumption functions. Both the method of analysis and the results differ from previous work on the RBE which investigated its impact on consumption alone. The main conclusion is that the RBE may have a significantly stronger stabilizing effect than previous empirical work would suggest. The results also suggest that policy-induced wealth effects may play a significant role in monetary policy.

This paper is concerned with the Blinder-Solow contention that negative government expenditures multipliers are trivial inasmuch as the resulting equilibrium is unstable in a conventional IS-LM model with constant prices. An aggregate supply side, which features progressive taxation of labor income and a real balances effect in the labor supply equation, is added to the model, and it is shown that negative multipliers are not necessarily inconsistent with local asympototic stability.

1. 1. An electronic heart sound meter has been devised to convert the complex pattern of low-frequency cardiac vibrations picked up at the chest wall into a simple “resultant frequency.” 2. 2. The “resultant frequency” varies during each heart cycle in a manner similar to the ventricular volume curve. 3. 3. Simultaneous records of the high-frequency ballistocardiograph and the heart sound meter made on rested, supine subjects show a close correlation between the cardiac output as calculated by Starr's formula, 11(I+J) C32 A and an “output” calculated from the formula, S=f12−f22 in which f1 is the maximum “resultant frequency” occurring at commencement of systole, and f2 is the minimum “resultant frequency” at the end of systole. 4. 4. Records of the ballistocardiograph and the heart sound meter taken immediately after exercise do not give comparable calculations of cardiac output. However, heart sound meter data after moderate exercise, after anoxia produced by breathing nitrogen, and after the Flack Test show qualitative and quantitative trends comparable to data obtained by other procedures.

A method was devised to prevent stimulation of the nasal chemoreceptors when flavors are presented to the tongue. This was accomplished by bucking the otherwise normal movement of odorous molecules from mouth to nose through the nasopharynx with a stream of air flowing in the opposite direction.