Properties of the 3− first excited state in the doubly closed shell nucleus146Gd

Conversion electron measurements confirm the 3^? assignment recently proposed for the 1579 keV first excited state in¹⁴⁶Gd. Fromγγ- ande ^? γ-coincidence data the half life of that state has been determined asT _1/2=1.06±0.12 ns.     

Protonh 2 11/2 and octupole excitations in148 66Dy82 and149 66Dy83

The yrast states of¹⁴⁸Dy and¹⁴⁹Dy have been studied by γ-ray and conversion electron measurements in (α, xn) and (¹⁶O,xn) reactions on enriched¹⁵²Gd and¹³⁵Ce targets. Level schemes to above 4 MeV for the two nuclei are reported. The πh ² _11/2 spectrum identified in¹⁴⁸Dy and the πh _11/2 effective chargee _eff=1.52±0.05e, derived from the measuredE2 transition rate between the (πh ² _11/2) 10⁺ and 8⁺ states, are discussed and compared with results for other two-particle nuclei. The yrast cascades in¹⁴⁸Dy and¹⁴⁹Dy continue above the (πh ² _11/2) 10⁺ and πh ² _11/2 vf _7/2) 27/2^? states by ～ 1 MeVE1 transitions de-exciting the lowest members of octupole multiplets built on these states. The energy shifts for the observed members of the πh ² _11/2 × 3^? multiplet are analyzed in terms of twoparticle-phonon exchange coupling using an empirical coupling strength extracted from the one valence particle nucleus¹⁴⁷Tb. The dominantvf _7/2×3^? character of low-lying 13/2⁺ isomers in¹⁴⁹Dy and otherN=83 nuclei is emphasized.     

Allenic and acetylenic spiropiperidine alkaloids from the neotropical frog, Dendrobates histrionicus

Four analogs of the acetylenic alkaloid, histrionicotoxin (C₁₉H₂₅NO) and the allenic alkaloid, isodihydrohistrionicotoxin have been isolated from extracts of skins of the arrow poison frog, Dendrobates histrionicus and characterized as neodihydrohistrionicotoxin, tetrahydrohistrionicotoxin, isotetrahydrohistrionicotoxin and octahydrohistrionicotoxin. These spiropiperidine (8-hydroxy-1-azaspiro[5.5]undecane) alkaloids differ only in the degree of unsaturation in the five carbon atoms (position 2) and four carbon atoms (position 7) side chains. A fifth compound, HTX-D, corresponds in empirical formula to a tetrahydrohistrionicotoxin with a 7-(cis-1-butenyl-3-ynyl) side chain, but the major mass spectral fragmentation with loss of C₂H₅O is not characteristic of the histrionicotoxins. Reduction of histrionicotoxin with hydrogen and Lindlar catalyst affords an isomeric dihydrohistrionicotoxin with the terminal acetylene of the five carbon atoms side chain reduced, tetrahydrohistrionicotoxin and hexahydrohistrionicotoxins, while reduction with hydrogen and palladium on charcoal affords dodecahydrohistrionicotoxin which is readily methylated to the tertiary amine by methyl iodide.     

Syntheses of alpha- and beta-C-glucopyranosyl serines from a common intermediate

A versatile synthesis leading to either C-linked alpha- or beta-glucopyranosyl serines is presented from a common, advanced synthetic intermediate. Cyclization of the penultimate carbinol onto the alkene and methanolysis of the lactone yields selectively the alpha-linkage. A transposition of these last steps leads to the beta-linked isomer selectively.     

A necessary condition for Calderón-Zygmund singular integral operators

Calderón-Zygmund singular integral operators have been extensively studied for almost half a century. This paper provides a context for and proof of the following result: If a Calderón-Zygmund convolution singular integral operator is bounded on the Hardy space H¹ (Rⁿ), then the homogeneous of degree zero kernel is in the Hardy space H¹(S^n–1) on the sphere.     

Active Slip System Identification in Polycrystalline Metals by Digital Image Correlation (DIC)

In this paper, a novel approach was proposed to increase the confidence of active slip system identification in polycrystalline metals. The approach takes advantage of microscale deformation tracking via Digital Image Correlation (DIC) combined with scanning electron microscopy (SEM). The experimentally-obtained high-resolution deformation fields were mapped to an undeformed configuration, which gives slip traces suitable for comparison with undeformed crystal orientation data. A metric, named herein as the ‘relative displacement ratio’ (RDR), is calculated from the displacement fields near slip traces to characterize the localized deformation due to slip. In validation cases, the experimentally-measured RDRs matched well with RDRs theoretically-calculated from active slip systems. In test cases, active slip system identification by incorporating RDR as an additional constraint was demonstrated to be preferable to using Schmid factor alone as a constraint. The proposed approach supplements existing techniques for slip system identification with increased confidence.     

Superelastic shape memory alloy cables: Part II – Subcomponent isothermal responses

This paper constitutes the second part of our experimental study of the thermo-mechanical behavior of superelastic NiTi shape memory alloy cables. Part I introduced the fundamental, room temperature, tensile responses of two cable designs (7 × 7 right regular lay, and 1 × 27 alternating lay). In Part II, each cable behavior is studied further by breaking down the response into the contributions of its hierarchical subcomponents. Selected wire strands were extracted from the two cable constructions, and their quasi-static tension responses were measured using the same experimental setup of Part I. Consistent with the shallow wire helix angles in the 7 × 7 construction, the force–elongation responses of the core wire, 1 × 7 core strand and full 7 × 7 cable were similar on a normalized basis, with only a slight decrease in transformation force plateaus and slight increase in plateau strains in this specimen sequence. By contrast, each successive 1 × 27 component (1 × 6 core strand, 1 × 15 strand, and full cable) included an additional outer layer of wires with a larger number of wires, greater helix radius, and deeper helix angle, so the normalized axial load responses became significantly more compliant. Each specimen in the sequence also exhibited progressively larger strains at failure, reaching 40% strain in the full 1 × 27 cable.Stress-induced phase transformations involved localized strain/temperature and front propagation in all of the tested 7 × 7 components but none of the 1 × 27 components aside from the 1 × 27 core wire. Stereo digital image correlation measurements revealed finer features within a global transformation front of the 1 × 7 core strand than the 7 × 7 cable, consisting of an staggered pattern of individual wire fronts that moved in lock-step during elongation. Although the 1 × 27 multi-layer strands exhibited temperature/strain localizations in a distributed pattern during transformations, the localizations did not propagate and their cause was traced back to contact indentations (stress concentrations) arising from the cable’s fabrication. The normalized axial torque responses of the multi-layer 1 × 27 components during transformation were distinctly non-monotonic and complex, due to the alternating handedness of the layers. Force and torque contributions of individual wire layers were deduced by subtracting 1 × 27 component responses, which helped to clarify the transformation kinetics within each layer and explain the unusual force and torque undulations seen in the 1 × 27 cable response of Part I.     

Solid energy calibration standards for P K‐edge XANES: electronic structure analysis of PPh4Br

P K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy is a powerful method for analyzing the electronic structure of organic and inorganic phosphorus compounds. Like all XANES experiments, P K‐edge XANES requires well defined and readily accessible calibration standards for energy referencing so that spectra collected at different beamlines or under different conditions can be compared. This is especially true for ligand K‐edge X‐ray absorption spectroscopy, which has well established energy calibration standards for Cl (Cs₂CuCl₄) and S (Na₂S₂O₃·5H₂O), but not neighboring P. This paper presents a review of common P K‐edge XANES energy calibration standards and analysis of PPh₄Br as a potential alternative. The P K‐edge XANES region of commercially available PPh₄Br revealed a single, highly resolved pre‐edge feature with a maximum at 2146.96 eV. PPh₄Br also showed no evidence of photodecomposition when repeatedly scanned over the course of several days. In contrast, we found that PPh₃ rapidly decomposes under identical conditions. Density functional theory calculations performed on PPh₃ and PPh₄⁺ revealed large differences in the molecular orbital energies that were ascribed to differences in the phosphorus oxidation state (III versus V) and molecular charge (neutral versus +1). Time‐dependent density functional theory calculations corroborated the experimental data and allowed the spectral features to be assigned. The first pre‐edge feature in the P K‐edge XANES spectrum of PPh₄Br was assigned to P 1s → P‐C π* transitions, whereas those at higher energy were P 1s → P‐C σ*. Overall, the analysis suggests that PPh₄Br is an excellent alternative to other solid energy calibration standards commonly used in P K‐edge XANES experiments.     

Synthesis and structural diversity of barium (N,N-dimethylamino)diboranates

The reaction of a slurry of BaBr(2) in a minimal amount of tetrahydrofuran (THF) with 2 equiv of Na(H(3)BNMe(2)BH(3)) in diethyl ether followed by crystallization from diethyl ether at -20 °C yields crystals of Ba(H(3)BNMe(2)BH(3))(2)(Et(2)O)(2) (1). Drying 1 at room temperature under vacuum gives the partially desolvated analogue Ba(H(3)BNMe(2)BH(3))(2)(Et(2)O)(x) (1') as a free-flowing white solid, where the value of x varies from <0.1 to about 0.4 depending on whether desolvation is carried out with or without heating. The reaction of 1 or 1' with Lewis bases that bind more strongly to barium than diethyl ether results in the formation of new complexes Ba(H(3)BNMe(2)BH(3))(2)(L), where L = 1,2-dimethoxyethane (2), N,N,N',N'-tetramethylethylenediamine (3), 12-crown-4 (4), 18-crown-6 (5), N,N,N',N'-tetraethylethylenediamine (6), and N,N,N',N",N"-pentamethylethylenetriamine (7). Recrystallization of 4 and 5 from THF affords the related compounds Ba(H(3)BNMe(2)BH(3))(2)(12-crown-4)(THF)·THF (4') and Ba(H(3)BNMe(2)BH(3))(2)(18-crown-6)·2THF (5'). In addition, the reaction of BaBr(2) with 2 equiv of Na(H(3)BNMe(2)BH(3)) in the presence of diglyme yields Ba(H(3)BNMe(2)BH(3))(2)(diglyme)(2) (8), and the reaction of 1 with 15-crown-5 affords the diadduct [Ba(15-crown-5)(2)][H(3)BNMe(2)BH(3)](2) (9). Finally, the reaction of BaBr(2) with Na(H(3)BNMe(2)BH(3)) in THF, followed by the addition of 12-crown-4, affords the unusual salt [Na(12-crown-4)(2)][Ba(H(3)BNMe(2)BH(3))(3)(THF)(2)] (10). All of these complexes have been characterized by IR and (1)H and (11)B NMR spectroscopy, and the structures of compounds 1-3, 4', 5', and 6-10 have been determined by single-crystal X-ray diffraction. As the steric demand of the Lewis bases increases, the structure changes from polymers to dimers to monomers and then to charge-separated species. Despite the fact that several of the barium complexes are monomeric in the solid state, none is appreciably volatile up to 200 °C at 10(-2) Torr.