Small momentum transfer measurements of S(k) in 4He at T = 4.27 K as function of density

We report the first measurements of S(k) in ⁴He at a fixed temperature of T = 4.27 K for 126 < p < 164 kg/m³ for the momentum transfer range $\text{0.18 < k < 1.03}\text{A}\text{?}{}^{\mathrm{?1}}$. Our results are consistent with expectations at zero momentum transfer based on thermodynamics.     

A digital integrator for controlled-potential coulometry

Accurate electrolysis current integration is required in controlled-potential coulometry. Analog integrators have been shown to deviate from ideal response by as much as —0.1%. A digital integrator was designed to optimize the linearity of the voltage-to-frequency converter used, minimize the effects of temperature, eliminate integration errors caused by small polarity changes and signal noise, and allow interchangeability with an analog integrator in a state-of-the-art coulometer widely used throughout the nuclear field for controlled-potential coulometry. Evaluation of the digital integrator, calibrated versus the Faraday, showed bias-free determinations of plutonium with a relative standard deviation of approximately 0.02%. The integrator was designed specifically for use in the controlled-potential coulometric determination of plutonium, but many of the features incorporated can be adopted to digital integrators for other uses where accurate integration over long periods of time is required.     

Limits of chromatic zeros of some families of maps

Two families of maps are considered, one consisting of maps with two pentagons separated by n 5-rings, the other of maps with two n-gons separated by two n-rings. For each family, a homogeneous linear recursion is derived for the corresponding family of chromatic polynomials. It is shown that B₅, B₇, and B₁₀ are limits of sequences of zeros from one or another of the families, where $\text{B}{}_{\mathrm{n}}\text{= 2(1+}\text{cos}\text{2π}\text{n}\text{)}$.     

Pressure-dependent diffusion in velocity sedimentation

We have calculated approximate profiles for the concentration gradient in velocity sedimentation of a homogeneous solute when both the diffusion and the sedimentation coefficient depend on pressure. Pressure dependence of the diffusion coefficient narrows the peak but does not seem to shift the maximum appreciably.