Nucleation of the crystalline phase of proteins in the presence of semidilute non-adsorbing polymer

Starting from a protein solution which is metastable with respect to the crystalline phase, the effect of adding semidilute non-adsorbing polymer is considered. It is found to increase the chemical potential of the protein by a few tenths of kT, which may be enough to lower the barrier to nucleation of the crystalline phase by enough to allow crystallisation. It is also shown that assuming that the polymer induces a pairwise additive attraction leads to qualitatively incorrect results.Comment: 5 pages, 1 figur

Scaling theory for the free-energy barrier to homogeneous nucleation of a non-critical phase near a critical point

Homogeneous nucleation of a new phase near an Ising-like critical point of another phase transition is studied. A scaling analysis shows that the free energy barrier to nucleation contains a singular term with the same scaling as the order parameter associated with the critical point. The total magnetisation of the nucleus scales as the response function and so it diverges. Vapour-liquid critical points are in the Ising universality class and so our results imply that near such a critical point the number of molecules in a nucleus of a another phase, such as a crystalline phase, diverges as the isothermal compressibility. The case where symmetry prevents coupling between the nucleus and the order parameter is also considered.Comment: 7 pages including 2 figures (revision adds consideration of nuclei which do not couple to the order parameter and some dynamic scaling

On Estimating the Effects of Increased Aid to Education

[Excerpt] The 1983 report, A Nation at Risk, of the National Commission on Excellence in Education decried the state of public education in the United States and suggested a number of reforms. Among their recommendations was increased federal aid for education. The view was that this would lead to desirable outcomes such as reduced class sizes and higher teacher salaries, with the latter aiding in the recruitment and retention of high-quality teachers. Somewhat surprisingly, previous research on the economics of education provides us with very few insights about what the effects of such proposals might be. For example, while there is an extensive literature on the determinants of cross-section variations in teachers\u27 salaries and teacher/student ratios, virtually nothing has been written on how changes in aid levels influence changes in salaries, teacher/student ratios, other expenditure levels, and local tax rates. Similarly, while there are many studies of how grants-in-aid affect overall expenditure levels and some studies of the determinants of cross-section variations in the share of expenditures spent on various categories (e.g., instructional and administrative), virtually nothing has been written on how changes in aid affect the various expenditure shares. To provide answers to some of these questions, our paper examines data from a panel of approximately 700 school districts in New York State over a five-year period (1978-79 to 1982-83) and tries to infer how school districts will respond to future changes in aid from how they responded to changes in state aid during the period. We focus on how past aid changes have influenced teacher salaries, tax rates, teacher/student ratios, and other staff/student ratios. The analyses exploit the fact that although school aid formulas change frequently in New York State, each district is usually guaranteed at least the same aid level as the previous year ( save harmless provisions). As a result, over any given two-year period, the percentage increase in aid varies widely across districts. This provides a convenient form of natural experiment

In-flight measurement of propeller noise on the fuselage of an airplane

In-flight measurements of propeller noise on the fuselage of an OV-10A aircraft were obtained using a horizontal and a vertical microphone array. A wide range of flight conditions were tested including changes in angle of attack, sideslip angle, power coefficient, helical tip Mach number and advance ratio, and propeller direction of rotation. Results show a dependence of the level and directivity of the tones on the angle of attack and on the sideslip angle with the propeller direction of rotation, which is similar to results obtained in wind tunnel tests with advanced propeller designs. The level of the tones at each microphone increases with increasing angle of attack for inboard-down propeller rotation and decreases for inboard-up rotation. The level also increases with increasing slideslip angle for both propeller directions of rotation. Increasing the power coefficient results in a slight increase in the level of the tones. A strong shock wave is generated by the propeller blades even at relatively low helical tip Mach numbers resulting in high harmonic levels. As the helical tip Mach number and the advance ratio are increased, the level of the higher harmonics increases much faster than the level of the blade passage frequency

Are School Superintendents Rewarded for “Performance”?

[Excerpt] This chapter presents analyses of the compensation and mobility of school superintendents in New York State during the 1978-79 to 1982-83 period. The focus is on school superintendents because they are the chief operating officers of school districts, their salaries are determined through individual negotiations with school boards, and their salary data were made available to us. In contrast, school principals\u27 salary data were not available to us. Especially in large districts, principals tend to be members of a union and their salary increases negotiated collectively, which limits the likelihood of observing individual principals\u27 salaries being related to measures of their school\u27s performance

3-Dimensional simulation of multistage depressed collectors on microcomputers.

A three-dimensional (3-D) package for simulation of asymmetric and crossed-field multistage depressed collectors for microwave tubes has been developed. This package is based upon the 3-D finite-difference code KOBRA3-INP. The main features of the package are a user-friendly input interface, postprocessors for collector analysis and calculation of secondary electron trajectories, and versatile output graphics. Both PC and. mainframe versions of the package have been developed. The results of simple benchmark tests and those of simulation and analysis of asymmetric and crossed-field collectors including the effects of secondary electrons are presented. It is found that the asymmetric hyperbolic electric field collector shows very low backstreaming. It is shown that the representation of trajectories in energy space gives a better insight into the behavior of individual trajectories than plotting in coordinate-space. The package will be useful for designing novel types of depressed collector