Analysis of Test Method to Extract Material Properties From Candu Fuel Channel Spacers Made of Helical Springs

In a particular nuclear application, separation between two concentric tubes is supported by helical springs installed in the annular space. Evaluation of material degradation due to the unique operating environment requires testing of ex-service spring material. Testing is done by compressing short segments of the spring material between two surfaces as per the loading mode in operation. Nominally, the specimen behaves like multiple rings loaded uniformly in parallel, but analysis of test results based on this approximation neglects significant end effects. A detailed analysis addresses the transition from the free end boundary condition through to where the coils become confined by friction to behave like rings. The thin ring solution is compared with finite element results as well as test results. Trends from the detailed thin ring solution correspond closely to the finite element and test results. A more precise relationship between the total applied load and the maximum stress in the material is determined.

The first law of heterotic stringy black hole mechanics at zeroth order in α′

We prove the first law of black hole mechanics in the context of the Heterotic Superstring effective action compactified on a torus to leading order in α′, using Wald’s formalism, covariant Lie derivatives and momentum maps. The Kalb-Ramond field strength of this theory has Abelian Chern-Simons terms which induce Nicolai-Townsend transformations of the Kalb-Ramond field. We show how to deal with all these gauge symmetries deriving the first law in terms of manifestly gauge-invariant quantities. In presence of Chern-Simons terms, several definitions of the conserved charges exist, but the formalism picks up only one of them to play a role in the first law. We study explicitly a non-extremal, charged, black ring solution of pure $$ \mathcal{N} $$ N = 1, d = 5 supergravity embedded in the Heterotic Superstring effective field theory.This work is a first step towards the derivation of the first law at first order in α′ where, more complicated, non-Abelian, Lorentz (“gravitational”) and Yang-Mills Chern-Simons terms are included in the Kalb-Ramond field strength. The derivation of a first law is a necessary step towards the derivation of a manifestly gauge-invariant entropy formula which is still lacking in the literature. In its turn, this entropy formula is needed to compare unambiguously macroscopic and microscopic black hole entropies.

Role Of Computational Simulations In The Design Of Piston Rings

The paper presents computational approaches using modern strategies for a dynamic piston ring solution as a fluid structural problem. Computational model outputs can be used to understand design parameter influences on defined results of a primarily integral character. Piston ring dynamics incorporates mixed lubrication conditions, the influence of surface roughness on oil film lubrication, the influence of ring movement on gas dynamics, oil film formulation on a cylinder liner and other significant influences. The solution results are presented for several parameters of SI engine piston rings.

Structure, mechanism and ensemble formation of the alkylhydroperoxide reductase subunits AhpC and AhpF fromEscherichia coli

Hydroperoxides are reactive oxygen species (ROS) that are toxic to all cells and must be converted into the corresponding alcohols to alleviate oxidative stress. InEscherichia coli, the enzyme primarily responsible for this reaction is alkylhydroperoxide reductase (AhpR). Here, the crystal structures of both of the subunits ofEcAhpR,EcAhpF (57 kDa) andEcAhpC (21 kDa), have been solved. TheEcAhpF structures (2.0 and 2.65 Å resolution) reveal an open and elongated conformation, while that ofEcAhpC (3.3 Å resolution) forms a decameric ring. Solution X-ray scattering analysis ofEcAhpF unravels the flexibility of its N-terminal domain, and its binding toEcAhpC was demonstrated by isothermal titration calorimetry. These studies suggest a novel overall mechanistic model of AhpR as a hydroperoxide scavenger, in which the dimeric, extended AhpF prefers complex formation with the AhpC ring to accelerate the catalytic activity and thus to increase the chance of rescuing the cell from ROS.

Three-dimensional coating and rimming flow: a ring of fluid on a rotating horizontal cylinder

The steady three-dimensional flow of a thin, slowly varying ring of Newtonian fluid on either the outside or the inside of a uniformly rotating large horizontal cylinder is investigated. Specifically, we study ‘full-ring’ solutions, corresponding to a ring of continuous, finite and non-zero thickness that extends all of the way around the cylinder. In particular, it is found that there is a critical solution corresponding to either a critical load above which no full-ring solution exists (if the rotation speed is prescribed) or a critical rotation speed below which no full-ring solution exists (if the load is prescribed). We describe the behaviour of the critical solution and, in particular, show that the critical flux, the critical load, the critical semi-width and the critical ring profile are all increasing functions of the rotation speed. In the limit of small rotation speed, the critical flux is small and the critical ring is narrow and thin, leading to a small critical load. In the limit of large rotation speed, the critical flux is large and the critical ring is wide on the upper half of the cylinder and thick on the lower half of the cylinder, leading to a large critical load. We also describe the behaviour of the non-critical full-ring solution and, in particular, show that the semi-width and the ring profile are increasing functions of the load but, in general, non-monotonic functions of the rotation speed. In the limit of large rotation speed, the ring approaches a limiting non-uniform shape, whereas in the limit of small load, the ring is narrow and thin with a uniform parabolic profile. Finally, we show that, while for most values of the rotation speed and the load the azimuthal velocity is in the same direction as the rotation of the cylinder, there is a region of parameter space close to the critical solution for sufficiently small rotation speed in which backflow occurs in a small region on the upward-moving side of the cylinder.