Axisymmetric free vibration of thick annular plates

Free vibrationo f annularp latesh asb eens tudiedu singt he methodo f initial functionsN. umericalr esultso f the naturalf requencieasr e obtainedfo r two typicals upportc onditionsT. he presenrt esultsd epartf rom the classicapll atet heoryf or higherm odesa s wella sf or thickerp latesb, ut is in gooda greemenwt ith Mindlin's improve,pdl ateth eory.

Crystal state conformation of three model monomer units for the beta-bend ribbon structure

The molecular and crystal structures of three compounds, representing the repeating units of the -bend ribbon (an approximate 310-helix, with an intramolecular hydrogen-bonding donor every two residues), have been determined by x-ray diffraction. They are Boc-Aib-Hib-NHBzl, Z-Aib-Hib-NHBzl, and Z-L-Hyp-Aib-NHMe (Aib, -aminoisobutyric acid; Bzl, benzyl; Boc, t-butyloxycarbonyl; Hyp, hydroxyproline Hib, -hydroxyisobutyric acid; Z, benzyloxycarbonyl). The two former compounds are folded in a -bend conformation: type III (III) for Boc-Aib-Hib-NHBzl, while type II (II) for the Z analogue. Conversely, the structure of Z-L-Hyp-Aib-NHMe, although not far from a type II -bend, is partially open.

Grain boundary sliding during diffusion and dislocation creep in a Mg-0.7 pct Al alloy

Early studies on grain boundary sliding (GBS) in Mg alloys have suggested frequently that the contribution of GBS to creep is high even under conditions corresponding to dislocation creep. The role of creep strain and grain size in influencing the experimental measurements has not been clearly identified. Grain boundary sliding measurements were conducted in detail over experimental conditions corresponding to diffusion creep as well as dislocation creep in a single-phase Mg-0.7 wt pet Al alloy. The results indicated clearly that the GBS contribution to creep was Very high during,, diffusion creep at low stresses (similar to 75 pct) and substantially reduced during dislocation creep at high stresses (similar to 15 pct). These measurements were consistent with the observation of significant intragranular slip band activity observed in most grains at high stresses and very little slip band activity at low stresses. The experimental measurements and analysis indicated also that the GBS contribution to creep was high during the initial stages of creep and decreased to a steady-state value at large strains.

Studies in terpenoids-XIII. Magnetic anisotropy2 in and stereochemistry of some gem-dimethylcyclobutanoids related to pinonic acid

The chemical shifts of “axial” vs “equatorial” Me protons of some gem-dimethylcyclobutanoids derived from α-pinene, arising from magnetic anisotropy of the ring and as influenced by vicinal substituents, are discussed. Conformational aspects of some cis- and trans-pinonic, pinononic and pinic acids have been elucidated on the basis of NMR evidence.

New triquinane-based host molecules : binding with diamines

Synthesis of several shape-specific hosts through heteroaromatic annulation on cis,syn,cis-triquinanedione 1 and X-ray crystal structure determination of one of them, 4a, is reported. Preliminary results of complexation between cleft 5a and diamines are reported.

A total synthesis of 11-O-methyldebenzoyltashironin

A concise total synthesis of 11-O-methyldebenzoyltashironin is reported in which oxidative dearomatization-IMDA-RCM triad constitutes the key ring forming steps, while an unorthodox DIBAL-H mediated stereo- and regioselective reductive epoxide openings and implementation of the vinyl bromide-carbonyl equivalency concept were pivotal to the success of this endeavor. (C) 2011 Elsevier Ltd. All rights reserved.

Evolution of microstructure and texture during deformation and recrystallization of heavily rolled Cu-Cu multilayer

A Cu-Cu multilayer processed by accumulative roll bonding was deformed to large strains and further annealed. The texture of the deformed Cu-Cu multilayer differs from the conventional fcc rolling textures in terms of higher fractions of Bs and RD-rotated cube components, compared with the volume fraction of Cu component. The elongated grain shape significantly affects the deformation characteristics. Characteristic microstructural features of both continuous dynamic recrystallization and discontinuous dynamic recrystallization were observed in the microtexture measurements. X-ray texture measurements of annealing of heavily deformed multilayer demonstrate constrained recrystallization and resulted in a bimodal grain size distribution in the annealed material at higher strains. The presence of cube- and BR-oriented grains in the deformed material confirms the oriented nucleation as the major influence on texture change during recrystallization. Persistence of cube component throughout the deformation is attributed to dynamic recrystallization. Evolution of RD-rotated cube is attributed to the deformation of cube components that evolve from dynamic recrystallization. The relaxation of strain components leads to Bs at larger strains. Further, the Bs component is found to recover rather than recrystallize during deformation. The presence of predominantly Cu and Bs orientations surrounding the interface layer suggests constrained annealing behavior.

Rotating beams and non-rotating beams with shared eigenpair for pinned-free boundary condition

In this paper we look for a rotating beam, with pinned-free boundary conditions, whose eigenpair (frequency and mode-shape) is same as that of a uniform non-rotating beam for a particular mode. It is seen that for any given mode, there exists a flexural stiffness function (FSF) for which the ith mode eigenpair of a rotating beam with uniform mass distribution, is identical to that of a corresponding non-rotating beam with same length and mass distribution. Inserting these derived FSF's in a finite element code for a rotating pinned-free beam, the frequencies and mode shapes of a non-rotating pinned-free beam are obtained. For the first mode, a physically realistic equivalent rotating beam is possible, but for higher modes, the FSF has internal singularities. Strategies for addressing these singularities in the FSF for finite element analysis are provided. The proposed functions can be used as test functions for rotating beam codes and also for targeted destiffening of rotating beams.

Urea-Functionalized Self-Assembled Molecular Prism for Heterogeneous Catalysis in Water

Reaction of a ditopic urea ``strut'' (L-1) with cis-(tmen)Pd(NO3)(2) yielded a 3+3] self-assembled molecular triangle (T)L-1 = 1,4-di(4-pyridylureido)benzene; tmen = N,N,N',N'-tetrame-thylethane-1,2-diamine]. Replacing cis-(tmen)Pd(NO3)(2) in the above reaction with an equimolar mixture of Pd(NO3)(2) and a clip-type donor (L-2) yielded a template-free multicomponent 3D trigonal prism (P) decorated with multiple urea moieties L-2 = 3,3'-(1H-1,2,4-triazole-3,5-diyl)dipyridine]. This prism (P) was characterized by NMR. spectroscopy, and the structure was confirmed by X-ray crystallography. The P was employed as an effective hydrogen-bond-donor catalyst for Michael reactions of a series of water-insoluble nitro-olefins in an aqueous medium. The P showed better catalytic activity compared to the urea based ligand L-1 and the triangle T. Moreover, the confined nanospace of P in addition to large product outlet windows makes this 3D architecture a perfect molecular vessel to catalyze Diels-Alder reactions of 9-hydroxymethylanthracene with N-substituted maleimide in the aqueous medium. The present results demonstrate new observations on catalytic aqueous Diels-Alder and Michael reactions in heterogeneous fashion employing a discrete 3D architecture of Pd(II). The prism was recycled by simple filtration and reused several tithes without significant loss of activity.