Minimum-weight design with piecewise constant specific stiffness

Much of the literature on minimum-weight design is concerned with structures with continuously varying dimensions. Structures of this kind achieve an absolute minimum of weight and thereby provide a useful standard of comparison, but their manufacturing cost is prohibitive in most applications. As a step toward the establishment of optimality conditions for more practical structures, the present paper discusses optimal design of sandwich beams and frames with segmentwise constant cross sections. Optimality is shown to require that the mean square stress in the face sheets has the same value for all segments. The use of the optimality condition is illustrated by examples.This research was supported by the Advanced Research Projects Agency, Project DEFENDER, and was monitored by the US Army Research Office-Durham, Contract No. DA-31-124-ARO-D-257.     

Study on the stevioside analogues of steviolbioside, steviol, and isosteviol 19-alkyl amide dimers: synthesis and cytotoxic and antibacterial activity

A new group of steviolbioside amide dimers 2a-g, derivatives 2h-i and their related steviol and isosteviol amide dimers 3a and 4a were prepared by reacting aliphatic alkylamine and alkyldiamines with PyBOP and DIEA. The synthesized compounds had cytotoxic effects on cancer and human embryonic lung cells. Compounds 3a, 4a, 2b and 2h were cytotoxic to cancer cells and to a lesser extent to human embryo lung cells. Compounds 2f, 2g and 4 of this series had favorable antibacterial effects, and were superior to penicillin G at inhibiting growth of Bacillus subtilis (BCRC 10029). The cytotoxicity and antibacterial effects may depend on the dimerization and derivative moieties in relation to the respective aglycons.     

Diffusion processes on graphs: stochastic differential equations,large deviation principle

Ito's rule is established for the diffusion processes on the graphs. We also consider a family of diffusions processes with small noise on a graph. Large deviation principle is proved for these diffusion processes and their local times at the vertices. Received: 12 February 1997 / Revised version: 3 March 1999     

Investigation of two plane paralleltiinven ilated jets

Measurements of mean velocity components, mean flow direction, turbulent intensities and Reynolds shear stress were made with a split film probe of hot wire anemometer to investigate the flow field generated by two identical jets of air issuing from plane parallel nozzles in a common end wall and mixing with the ambient room air. Due to the sensitivity of the split film probe to the flow direction, the reverse flow in the converging region was detected by the split film probe and observed by flow visualization. The mean velocity approaches self-preservation in both the converging and the combined regions, while the turbulent intensities and Reynolds shear stress approach self-preservation in the combined region only. The trajectory of the maximum velocity is almost unchanged by variance of nozzle spacing in the converging region. The distance of the merging point from the nozzle exit increases linearly with nozzle spacing. The spread of the converging jet increases more rapidly than that of the combined jet.     

(-)-Hydroxylindestrenolide, a new sesquiterpenoid from a gorgonian coral Menella sp. (Plexauridae)

(-)-Hydroxylindestrenolide (1), an enantiomer of the known sesquiterpenoid, (+)-hydroxylindestrenolide (2), was isolated from a gorgonian coral identified as Menella sp. The structure, including the relative stereochemistry of 1 was established by spectroscopic methods and by comparison the spectral and physical data with those of 2. Sesquiterpenoid 1 exhibited marginal cytotoxicity toward HL-60 and K562 leukemia tumor cells, and displayed a weak inhibitory effect on superoxide anion generation at a concentration of 10 μg/ml by human neutrophils.     

Cladieunicellins A-E, new eunicellins from an Indonesian soft coral Cladiella sp

Five new eunicellin-type diterpenoids, cladieunicellins A-E (1-5), were isolated from an Indonesian soft coral identified as Cladiella sp. The structures of diterpenoids 1-5 were established using spectroscopic methods. Eunicellins 2 and 5 were found to be cytotoxic against DLD-1 and HL-60 tumor cells, respectively, and 3 displayed inhibitory effects against superoxide anion generation by human neutrophils.     

Unsymmetric 1,3,4-oxa(thia)diazoles of quinoxaline–naphthalene conjugates

Two new series of unsymmetric 1,3,4-oxa(thia)diazoles 1a,b containing both quinoxaline and naphthalene moieties were prepared and their mesomorphic properties were investigated. The mesomorphic behavior of compounds 1a,b and 2 was studied by DSC analysis and polarized optical microscopy. All compounds 1a and 2 exhibited hexagonal columnar phases (Col_h), which were also confirmed by powder XRD diffractometer. N_cell and R_ar values equal to 5.23 and 22.73 Å² within a slice of 9.0 Å thick were also obtained for 1a (n=16), indicating that a more disc-like structure constructed by two molecules lying side-by-side was correlated in Col_h phases. In contrast, all compounds 1b were not mesogenic, and the lack of mesomorphic properties in 1b might be due to their unfavorable conformations. The PL spectra of all compounds 1a,b showed one intense peak at λ_max=509–512 nm, and these photoluminescent emissions originated from quinoxaline moiety.     

Study of Thin Polymeric Film Deposited by the PECVD Process for use at 193 nm

A plasma enhanced chemical vapor deposition (PECVD) reactor was used to deposit thin polymeric films with high absorption at 193 nm. The reactor is suitable to deposit uniform and pinhole free thin polymeric films with conformality over 95%. Conformal films with thickness as low as 200 Å have been deposited on silicon, glass, and quartz substrates, as well as silicon oxide, silicon nitrate, and aluminum films. Deposited films had variations in thickness of 3 to 5% over an area of 8 inches in diameter. Thin films deposited on silicon substrates under varying levels of RF power were scanned using the AFM technique. The measurements show increasing surface roughness of the scanned samples as the RF power increases.     

Catenar bimetallomesogens derived from quinoxaline–salicylaldimine conjugates

The preparation, characterization, and mesomorphic properties of two series of tridentate N-salicylidene-2-hydroxyanilines and their metal complexes were described. The crystal and molecular structure of bis[2-hydroxy-4-propyloxy-N-(2-hydroxy-3,4-dipropyloxybenzylidene) aniline]copper(II) were determined by means of X-ray analysis. It crystallizes in the monoclinic space group P2(1)/n and a Z=4. The geometry at Cu²⁺ ions is square pyramidal with a THF solvent molecule coordinated. The core structure was nearly flat, and the intramolecular Cu–Cu atoms were separated by ca. 3.0163(6) Å. All compounds 2a formed smectic C phases, and copper complexes 1a–Cu were not mesogenic. In contrast, compound 2e and complexes 1b–Cu, 1d–Cu, 1e–Cu, and 1e–Pd exhibited columnar phases. The lack of mesomorphism in 1e–Zn was attributed to a preferred tetrahedral over square planar geometry. A N_cell equal to 2.44–2.92, calculated from powder XRD data within a 9.0 Å thick indicated that an induced structure correlated by two catenar-shaped molecules was formed in Col_h phases.