Dynamic stability of functionally graded cantilever cylindrical shells under distributed axial follower forces

In this paper, flutter of functionally graded material (FGM) cylindrical shells under distributed axial follower forces is addressed. The first-order shear deformation theory is used to model the shell, and the material properties are assumed to be graded in the thickness direction according to a power law distribution using the properties of two base material phases. The solution is obtained by using the extended Galerkin's method, which accounts for the natural boundary conditions that are not satisfied by the assumed displacement functions. The effect of changing the concentrated (Beck's) follower force into the uniform (Leipholz's) and linear (Hauger's) distributed follower loads on the critical circumferential mode number and the minimum flutter load is investigated. As expected, the flutter load increases as the follower force changes from the so-called Beck's load into the so-called Leipholz's and Hauger's loadings. The increased flutter load was calculated for homogeneous shell with different mechanical properties, and it was found that the difference in elasticity moduli bears the most significant effect on the flutter load increase in short, thick shells. Also, for an FGM shell, the increase in the flutter load was calculated directly, and it was found that it can be derived from the simple power law when the corresponding increase for the two base phases are known.     

Differential Single-Capture Cross Sections for Fast Alpha–Helium Collisions

A four-body theoretical study of the single charge transfer process in collision of energetic alpha ions with helium atoms in their ground states is presented. The model utilizes the Coulomb–Born distorted wave approximation with correct boundary conditions to calculate the single-electron capture differential and integral cross sections. The influence of the dynamic and static electron correlations on the capture probability is investigated. The results of the calculations are compared with the recent experimental measurements for differential cross sections and with the other theoretical manipulations. The results for scattering at extreme forward angles are in good agreement with the experimental measurements, but in other scattering angles the agreement is poor. However, the present four-body results for integral cross sections are in excellent agreement with the experimental data.     

Four-body treatment of the K-shell positronium formation from multi-electron atoms

The four-body Coulomb-Born distorted-wave approximation with correct boundary conditions (CBDW-4B) is applied to the K-shell positronium formation from multi-electron atoms at intermediate and high impact energies. In the present approach, both K-shell electrons are treated as active electrons. For collisions of positrons with helium, carbon, and neon atoms, both the post and prior forms of the transition amplitude are calculated and the corresponding differential and integral cross sections are compared with the results of the three-body version of the formalism (CBDW-3B). In order to investigate the effects of the static electronic correlations on the process, initial bound states of the active electrons in helium atoms are described by Hylleraas and Silverman wave functions. Also for positronium formation from helium atoms the obtained cross sections are compared with the available experimental data and also with the results of the other theories.     

Flows over time in time-varying networks: Optimality conditions and strong duality

There has been much research on network flows over time due to their important role in real world applications. This has led to many results, but the more challenging continuous time model still lacks some of the key concepts and techniques that are the cornerstones of static network flows. The aim of this paper is to advance the state of the art for dynamic network flows by developing the continuous time analogues of the theory for static network flows. Specifically, we make use of ideas from the static case to establish a reduced cost optimality condition, a negative cycle optimality condition, and a strong duality result for a very general class of network flows over time.     

Uncertainty from sampling in measurements of aflatoxins in animal feedingstuffs: application of the Eurachem/CITAC guidelines

The duplicate method for estimating uncertainty from measurement including sampling is presented in the Eurachem/CITAC guide. The applicability of this method as a tool for verifying sampling plans for mycotoxins was assessed in three case studies with aflatoxin B(1) in animal feedingstuffs. Aspects considered included strategies for obtaining samples from contaminated lots, assumptions about distributions, approaches for statistical analysis, log(10)-transformation of test data and applicability of uncertainty estimates. The results showed that when duplicate aggregate samples are formed by interpenetrating sampling, repeated measurements from a lot can be assumed to approximately follow a normal or lognormal distribution. Due to the large variation in toxin concentration between sampling targets and sometimes very large uncertainty arising from sampling and sample preparation (U(rel) ≥ 50%), estimation of uncertainty from log(10)-transformed data was found to be a more generally applicable approach than application of robust ANOVA.     

Non-phosgene route to unsymmetrical ureas from N-Cbz-α-amino acid amides

A convenient method toward the synthesis of α-amino acid-derived unsymmetrical ureas 2 is described herein. This route involves an interesting rearrangement of amides of N-Cbz-α-amino acids 1, which presumably entails the intermediacy of hydantoins that is followed by hydrolysis to afford unsymmetrical ureas 2 in quantitative yields and high purity.     

Unusual octalactones from Corynespora cassiicola, an endophyte of Laguncularia racemosa

Chemical investigation of the EtOAc extract of the mangrove-derived endophyte Corynespora cassiicola, isolated from Laguncularia racemosa (Combretaceae), afforded five new secondary metabolites, named coryoctalactones A–E (1–5). The structures of the new compounds were determined on the basis of 1D- and 2D-NMR spectroscopy as well as high-resolution mass spectrometry. The absolute configuration of the side chain in 1–3 and 5 were tentatively deduced based on biogenetic consideration in comparison with xestodecalactones, previously isolated from C. cassiicola. All isolated compounds were evaluated for their antimicrobial, cytotoxic, and antitrypanosomal activities.