The paper examines the stability of the uniform flow which approaches a two-dimensional stagnation region formed when a cylinder or a two-dimensional blunt body of finite curvature is immersed in a crossflow. It is shown that such a flow is unstable with respect to three-dimensional disturbances. This conclusion is reached on the basis of a mathematical analysis of a simplified form of the disturbance equation for the stream-wise component of the vorticity vector. The ultimate, or stable, flow pattern is governed by a singular Sturm–Liouville problem whose solution possesses a single eigenvalue. The resulting flow is one in which a regularly distributed system of counter-rotating vortices is super-imposed on the basic, Hiemenz-like pattern of streamlines. The spacing of the vortices is a unique function of the characteristics of the flow, and a theoretical estimate for it agrees well with experimental results. The analysis is extended heuristically to include the effect of free-stream turbulence on the spacing.The problem is similar to the classical Görtler–Hämmerlin study of the stability of stagnation flow against an infinite flat plate, which revealed the existence of a spectrum of eigenvalues for the disturbance equation. The present analysis yields the same result when an infinite radius of curvature is assumed for the blunt body.

The β-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with β-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region N≳126. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the β-decay strength distribution. This provides important constraints on global theoretical models currently used in r-process nucleosynthesis.

This paper describes new local mass-transfer measurements from two cylinders, coated with a layer of paradichlorobenzene (p-C6H4Cl2), to air. The cylinders were placed in cross flow, and measurements were performed at three nominal values of the Reynolds number (75, 100, 125 × 103) as well as at varying levels of turbulence intensity. In the range where the boundary layer is laminar, the effect of turbulence intensity is always to increase the transfer rate, approximately by a constant factor φ which depends on the turbulence intensity as well as the Reynolds number. Across the turbulent boundary layer and wake the influence is not systematic, as both increases and decreases are observed. The data for the stagnation line are compared with other measurements. They can all be correlated against the single parameter TuRe1/2, as suggested by a semiempirical theory due to Smith and Kuethe. However, the global correlation equation (a second-degree polynomial) differs from the originally proposed linear relationship, and the uncertainty is one of ±8 percent.

Background: There have been measurements on roughly 230 nuclei that are β-delayed neutron emitters. They range from 8 He up to 150 La. Apart from 210 Tl, with a branching ratio of only 0.007%, no other neutron emitter has been measured beyond A = 150. Therefore, new data are needed, particularly in the region of heavy nuclei around N = 126, in order to guide theoretical models and help understand the formation of the third r-process peak at A ∼ 195. Purpose: To measure both β-decay half-lives and neutron branching ratios of several neutron-rich Au, Hg, Tl, Pb, and Bi isotopes beyond N = 126. Method: Ions of interest were produced by fragmentation of a 238 U beam, selected and identified via the GSI-FRS fragment separator. A stack of segmented silicon detectors (SIMBA) was used to measure ion implants and β decays. An array of 30 3 He tubes embedded in a polyethylene matrix (BELEN) was used to detect neutrons with high efficiency and selectivity. A self-triggered digital system is employed to acquire data and to enable time correlations. The latter were analyzed with an analytical model and results for the half-lives and neutron-branching ratios were derived by using the binned maximum-likelihood method. Results: Twenty new β-decay half-lives are reported for [204][205][206][208][209][210][211][211][212][213][214][215][216][215][216][217][218][218][219][220] Bi, nine of them for the first time. Neutron emission probabilities are reported for 210,211 Hg and 211-216 Tl. 2469-9985/2017/95(6)/064322(16) 064322-1 Published by the American Physical Society R. CABALLERO-FOLCH et al. PHYSICAL REVIEW C 95, 064322 (2017) Conclusions:The new β-decay half-lives are in good agreement with previous measurements on nuclei in this region. The measured neutron emission probabilities are comparable to or smaller than values predicted by global models such as relativistic Hartree Bogoliubov plus the relativistic quasi-particle random phase approximation (RHB + RQRPA).