Collapse of square and rectangular tubes in transverse loading

Summary Analysis of the in plane lateral collapse of square and rectangular cross-section tubes is presented by considering the out-of-straightness of horizontal and vertical arms, corner radius, friction between the platens and the deforming specimen and instability of vertical arms. Results of collapse load for tubes of aluminium and mild steel, thus computed, are presented for some typical tube geometrics, and influence thereon of various parameters considered is discussed. Experiments were conducted wherein tubes of square and rectangular cross-sections of both the materials were laterally compressed between two parallel platens in an Instron machine. The observed collapse loads compare very well with the corresponding computed values.

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Kollaps von vertikal belasteten Rohren mit quadratischem und rechteckigem Querschmitt

Übersicht Der Kollaps von Rohren mit quadratischem und rechteckigem Querschnitt, welche senkrecht zur Achse belastet werden, wird untersucht, wobei schiefe Vertikal- und Horizontalstege, gerundete Profilecken, Reibung zwischen Belastungsplatten und Rohr sowie die Stabilität der Vertikalstege brücksichtigt werden. Die Kollapslast wird für Aluminium und Weichstahl und einige typische Rohrgeometrien ermittelt und der Einfluß verschiedener Parameter wird untersucht. Die Experimente wurden auf einer Instron-Maschine durchgeführt, wobei Rohre mit quadratischem und rechteckigem Querschnitt aus beiden Werkstoffen zwischen zwei parallelen Platten quer zur Achse komprimiert wurden. Es konnte eine gute Übereinstimmung zwischen den Resultaten aus Experiment und Rechnung festgestellt werden.

     

(1-Adamantanethio)pyridines and tetrahydropyridines from the reaction of 1-adamantanethiol with pyridine I-oxide in acetic anhydride

The reaction of pyridine 1-oxide with 1-adamantanethiol in acetic anhydride produced a mixture of 2- and 3-(1-adamantanethio)pyridines, 1-aeetyl-2-(1-adamantanethio)-3-hydroxy-4-acetoxy-1,2,3,4-telrahydropyridine and the corresponding 3-acetoxyderivative. Pure substances were separated by means of column chromatography on alumina. The tetrahydropyridines were identified by means of their proton magnetic and mass spectra. 4-(1-Adamantanethio)pyridine was synthesized from 4-chloropyridinc and 1-adamantanethiol. The three isomeric (1-adamantanethio)-pyridines were, each, cleaved by concentrated hydrochloric acid to give 1-chloroadamantane and the corresponding pyridinethiol.     

Stereoselective synthesis of trans-3-functionalized-4-pyrazolo[5,1-b]thiazole-3-carboxylate substituted β-lactams: Potential synthons for diverse biologically active agents

Abstract

An efficient protocol for the stereoselective synthesis of pyrazolo[5,1-b]thiazole-3-carboxylate tethered β-lactam conjugates 8a–j from novel pyrazolo [5,1-b]thiazole-3-carboxylate substituted Schiff’s bases 6a–f is reported here. The reaction between various ketene precursors and novel Schiff’s bases 6a–f afforded exclusive formation of trans-β-lactams 8a–j. The substrate scope of this approach was investigated extensively by varying different groups (R, Z). All the novel compounds were characterized using various spectroscopic techniques, such as FT-IR, ¹H NMR, ¹³C NMR, elemental analysis, ¹³C NMR (DEPT-135), and mass spectrometry in representative cases. Single crystal X-ray crystallographic study of trans-ethyl 7-(1-(4-methoxyphenyl)-4-oxo-3-phenoxyazetidin-2-yl)-6-methyl-2-(methylthio)pyrazolo[5,1-b]thiazole-3-carboxylate 8a has confirmed the molecular structure and the stereochemical outcome. To the best of our knowledge, the synthesis of such types of Schiff’s bases and β-lactam conjugates has not been reported so far.     

Dynamic evolution of topological defects around drops and bubbles rising in a nematic liquid crystal

We report observations of topological defects around drops and bubbles that rise through a vertically aligned nematic liquid crystal. We provide direct evidence for downstream convection of the Saturn-ring defect and its transformation to a hyperbolic point defect. The point defect is convected further in the wake of the drop or bubble as the rising velocity increases. In equilibrium, both defect configurations may persist for long times in the narrow cell. But the point defect sometimes spontaneously opens into a Saturn ring, indicating the latter as the globally stable configuration in the presence of tight wall confinement.     

Spontaneous emission and spectral properties of radiation by relativistic electrons in a gyro‐klystron and optical‐klystron undulator

In this paper spontaneous emission of radiation by relativistic electrons in a gyro‐klystron is studied. The scheme consists of two solenoid sections separated by a dispersive section. In the dispersive section the electrons are made non‐resonant with the radiation. The dispersive section transforms a small change of the velocity into changes of the phases of the electrons. This leads to enhanced radiation due to klystron‐type modulation as compared with a conventional gyrotron‐type device driven by cyclotron maser interaction. It is shown that the klystron‐modulated spectrum depends on the dispersive field strength, finite perpendicular velocity component and length of the solenoids but is independent of the axial magnetic field strength. A simple scheme to design a gyro‐klystron is discussed.     

Fire- and heat-resistant matrix resins based on ethynyl-substituted aromatic cyclotriphosphazenes

A novel class of fire- and heat-resistant matrix resins has been synthesized by thermal polymerization of ethynyl-substituted aromatic cyclotriphosphazenes. Thermal polymerization of new tris[4-(4′-ethynylbenzanilido)phenoxy]tris(phenoxy) cyclotriphosphazene ( III ) and tris[4-(4′-ethynylphthalimido)phenoxy]tris(phenoxy)cyclotriphosphazene ( VII ) at 250°C for 1–1.5 h gave tough polymers. The thermal stabilities of the polymers were evaluated in nitrogen and in air by thermogravimetric analysis (TGA). The synthesised polymers were stable to 400–410°C and showed char yield of 78–65% at 800°C in nitrogen and of 78–69% at 700°C in air. The ethynyl-substituted polymer precursor ( III ) was synthesised by the reaction of tris(4-aminophenoxy)tris(phenoxy)cyclotriphosphazene ( I ) with 4-ethynylbenzoyl chloride. The polymer precursor ( VII ) was synthesised by a solution condensation of I with 4-ethynylphthalic anhydride followed by in situ thermal cyclodehydration at 150°C. The structure of polymer precursors was characterized using proton nuclear magnetic resonance (¹H-NMR), infrared (IR) spectroscopy, and elemental analysis. The curing of polymer precursors was monitored by differential scanning calorimetery (DSC) and IR spectroscopy. The synthesised matrix resins are potential candidates for the development of heat- and fire-resistant fiber-reinforced composites. © 1993 John Wiley & Sons, Inc.     

Heat-resistant thermosetting polymers based on a novel tetrakisaminophenoxycyclotriphosphazene

Two heat-resistant thermosetting polymers ( IX and X ) have been developed based on a new cyclotriphosphazene containing tetrakisamine. These polymers were synthesized by the reaction of tetrakisamine ( IV ) with maleic anhydride followed by in situ cyclodehydration and polymerization of the maleimides ( VII and VIII ) at 235–240°C for 1.5 h and 290°C for 0.5 h. The thermogravimetric analyses (TGA) of the developed cyclotriphosphazene containing cyclomatrix polymers showed their thermal stability up to 350°C and char yield of 71% in nitrogen at 800°C and 65% in air at 700°C. The monomer, 2,2,4,4-tetrakis(4′-aminophenoxy) -6,6-diphenylcyclotriphosphazene ( IV ), useful for producing a variety of heat- and fire-resistant polymers, has been synthesized in good yield. Its syntheses involve Friedel-Crafts reaction of hexachlorocyclotriphosphazene ( I ) with benzene followed by the reaction of 2,2,4,4-tetrachloro-6,6-diphenylcyclotriphosphazene ( II ) with potassium 4-nitrophenoxide. The reduction of the obtained 2,2,4,4-tetrakis(4′-nitrophenoxy)-6,6-diphenylcyclotriphosphazene ( III ) with molecular hydrogen in presence of PtO₂ gave the tetrakisamine ( IV ). The structure of the synthesized monomer and intermediates were characterized by FT-IR, ¹H-NMR, ³¹P-NMR, mass spectroscopy, differential scanning calorimetry (DSC), and elemental analysis. These resins are potential candidates for the development of heat- and fire-resistant composites, laminates, and adhesives, useful for space, aerospace, and electronic application. © 1993 John Wiley & Sons, Inc.     

Protein extraction and cytotoxicity abilities of colloidal gold-coated silica hybrid nanoparticles

Monodisperse non-hybrid silica and hybrid colloidal silica of ≤?200 nm decorated with small Au nanoparticles (NPs) were synthesized in a simple single-step method. Non-hybrid silica NPs were synthesized in the absence and presence of different twin tail cationic surfactants, while tiny Au NPs were grown under in situ reaction conditions on non-hybrid silica synthesized previously by using cationic dextran. Bio-applicability and cytotoxicity of both hybrid as well as non-hybrid silica NPs were tested by using them for the extraction of protein fractions from complex aqueous protein solutions and treating them with blood cells, respectively. Both non-hybrid and hybrid silica NPs demonstrate excellent ability to extract proteins fractions predominantly of relatively low molecular masses, i.e., ~ 80 kDa. Extraction preferences between both kinds of silica became prominent when predominantly hydrophobic proteins such zein and rice proteins were used rather than mainly polar protein like BSA. Applicability for more complex biological fluid like serum indicated the competitive extractions among strongly versus weakly bound proteins. With significant bearing in in vivo conditions, hybrid silica was potentially toxic towards the blood cells in comparison to non-hybrid silica. It stems from the collective interactions of silica as well as nanometallic surfaces of Au NPs to interact with the blood cells causing hemolysis and hence may not be the suitable vehicles for drug release in systemic circulation.

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Investigation of factors influencing the performance of nanofluid-based direct absorption solar collector using Taguchi method

Journal of Thermal Analysis and Calorimetry - The performance of nanofluid-based solar collector depends on different factors like nanoparticle material, base fluid, mass fraction of nanoparticles,...