Microstructure dependent dynamic fracture analyses of trabecular bone based on nascent bone atomistic simulations

Trabecular bone fracture is closely related to the trabecular architecture, microdamage accumulation, and bone tissue properties. Primary constituents of trabecular tissue are hydroxyapatite (HA) mineralized type-I collagen fibers. In this research, dynamic fracture in two dimensional (2-D) micrographs of ovine (sheep) trabecular bone is modeled using the mesoscale cohesive finite element method (CFEM). The bone tissue fracture properties are obtained based on the atomistic strength analyses of a type-I collagen + HA interfacial arrangement using molecular dynamics (MD). Analyses show that the presented framework is capable of analyzing the architecture dependent fracture in 2-D micrographs of trabecular bone.     

Thermal effects on parallel resonance energy of whistler mode wave

In this short communication, we have evaluated the effect of thermal velocity of the plasma particles on the energy of resonantly interacting energetic electrons with the propagating whistler mode waves as a function of wave frequency and L-value for the normal and disturbed magnetospheric conditions. During the disturbed conditions when the magnetosphere is depleted in electron density, the resonance energy of the electron enhances by an order of magnitude at higher latitudes, whereas the effect is small at low latitudes. An attempt is made to explain the enhanced wave activity observed during magnetic storm periods.     

Melt-polymerizable bisimido-bisphthalonitriles containing silicon,fluoro, and ether groups: Synthesis,characterization, and NMR study

Various melt-polymerizable bisimido-bisphthalonitrile polymer precursors were synthesized by the reaction of 4-aminophthalonitrile (4-APN) with bis(3,4-dicarboxyphenyl) dimethylsilane dianhydride (SIDA), 4,4′-hexafluoroisopropylidene diphthalic anhydride (6FDA), bis(3,4-dicarboxyphenyl)ether dianhydride (ODPA), and 3,3′, 4,4′-tetracarboxylichenzophen+ne dianhydride (BTDA) in an aprotic solvent. The synthesized monomers showed crystalline melting at 269 and 271°C. Elemental analysis, differential thermal analysis (DTA), infrared (IR), nuclear magnetic resonance (¹H-NMR) and mass spectral studies were carried out to characterize the synthesized monomers. Thermogravimetric analysis (TGA) of the synthesized monomers showed their thermal stability at 410–400°C. A detailed study and NMR investigation of the first step of condensation reaction was carried out and indicated the formation of a transient charge transfer complex. Thermal cyclization of the formed intermediate, however, gave the required monomers. A preliminary study demonstrated that melt-polymerization of the synthesized monomers gave thermallystable, tough polymers.     

Heat-resistant polymers from melt-processable bisimido-bisphthalonitriles

Heat-resistant polymers which are processable into void-free components and suitable for composite applications have been synthesized by thermal/chemical polymerization of four newly developed bisimido-bisphthalonitriles containing silicon, ether, carbonyl, and hexafluoroisopropylidene groups. Thermal polymerization involving addition reactions was performed at 200–275°C for 2–10 h and then post-curing at 310°C for 10 h. Polymers VI, VII, VIII , and IX were obtained. The thermal polymerization was monitored using infrared spectroscopy. Thermal polymerization was also carried out in the presence of an aromatic diamine. A polyhexasocyclane ( V ) was synthesized by condensation polymerization of ether containing bisimido-bisphthalonitrile with 4,4′-diaminodiphenyl ether in solvent phenol. The synthesized polymers were evaluated for thermal stability using dynamic thermogravimetric analysis (TGA). Polymers VII, VIII, IX , and X showed thermal decomposition temperature in the range of 475–500°C in nitrogen and air atmosphere. The char yield of the polymers was in the range of 60–69% in nitrogen at 800°C. This study indicated that synthesized thermosetting polymers from ether and keto containing bisimido-bisphthalo-nitrile are potential candidates for development of graphite composites. © 1993 John Wiley & Sons, Inc.     

New polypyromellitimide films based on cyclotriphosphazene and bisaspartimide derived diamines

Three new thermally stable polypyromellitimide films were made by the thermal cyclodehydration of the corresponding polyamic acids obtained by the polymerization of pyromellitic dianhydride with 4,4′-bis{N²-[4-(4-aminobenzyl)phenyl]aspartimido} diphenylmethane, 4,4′-bis{N²-[4-(4-aminophenoxy)phenyl]aspartimido} diphenylether, and bis(4-aminophenoxy)tetrakis (4-phthalamic acid phenoxy)cyclotriphosphazene. The bis(4-aminophenoxy)tetrakis (4-phthalamic acid phenoxy)cyclotriphosphazene was obtained from hexakis(4-aminophenoxy)cyclotriphosphazene involving its reaction with phthalic anhydride. The structure of these materials and precursors were characterized by using Fourier-transform-infrared (FT–IR) and proton nuclear magnetic resonance spectroscopy. The thermal stabilities of the films were evaluated by the thermogravimetric analysis, showing char yields at 800°C ranging from 68% to 58% in a nitrogen atmosphere and 24% in air atmosphere.     

3,4-Dicyano-5-aminopyrazole complexes of anhydrous divalent transition metal chlorides and their triphenylphosphine derivatives

Summary 3,4-Dicyano-5-aminopyrazole, H3,4(CN)₂5NH₂pz (L) reacts either with anhydrous MCl₂ or with [M(PPh₃)₂Cl₂] to yield ML₄Cl₂ complexes (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd or Hg), whose monomeric and covalent natures have been confirmed by their solubility in most non-polar solvents and their low electrical conductivities. The bonding mode of substituted pyrazole is inferred from the position of the (C-N) band in the i.r. spectra. The electronic spectra and the magnetic moments of these compounds were recorded.     

Dimeric tetrahedral complexes of manganese(II) and iron(II) with benzoyl hydrazones

Summary Dimeric manganese(II)and iron(II)complexes, (ML)₂, derived from benzoyl hydrazones ofo-hydroxyaryl aldehydes and ketones arc described and characterised by elemental analyses and by conductance, molecular weight, magnetic, electronic and i.r. spectral measurements. The dimeric nature of the complexes is revealed by i.r. spectra which show bands atca. 885 Mn²⁺ and 820 cm^–1 Fe²⁺, characteristic of ring vibrations. The i.r. spectra reveal the terdentate nature of the ligands. The electronic spectra in dimethylformamide are consistent with the tetrahedral nature of the complexes. The appreciable lowering in _eff is attributed to the presence of exchange interactions between two paramagnetic atomsvia oxygen bridges.Reprints of this article are not available.     

Structure of aromatic polyimides

With a view to understanding the structure of aromatic polyimide backbone, model compound N,N-bis(4-phenoxyphenyl)-1,2:4,5-benzenetetracarboxdiimide was synthesized by the condensation of pyromellitic dianhydride and 4-aminodiphenyl ether in solvent N,N-dimethylacetamide or N,N-dimethylformamide. Various side products formed during the reaction were isolated and identified by spectroscopical methods. This study reveals that the polymer backbone contains nearly 85% imide rings. The uncyclizable residues in the backbone are those derived by the chemical interaction of polymerization solvent or by the modification of intermediate orthoamido acid. The uncyclizable nature of the latter was explained in mass and infrared (IR) spectral studies. The role of the dipolar solvent appears to be vital to imidization.     

A family of oxorhenium(v) complexes incorporating chelated monoanionic ONN reduced Schiff base and dianionic ONNO tetradentate ligands: synthesis, spectroscopic and electrochemical studies

The green colored complexes of the type Re(V)O(L(SB))Cl(2), 1, have been synthesised by reacting NBu(4)[ReOCl(4)] with HL(SB) in dry ethanol. Here, L(SB)(-) are the deprotonated forms of N-(2-hydroxybenzyl)-2-picolylamine (HL(SB)(1)); N-(2-hydroxybenzyl)-N',N'-dimethylethylenediamine (HL(SB)(2)) and N-(2-hydroxybenzyl)-N',N'-diethylethylenediamine (HL(SB)(3)). Similarly, NBu(4)[ReOCl(4)] reacted with N,N-bis(2-hydroxybenzyl)-2-picolylamine (H(2)L(1)); N,N-bis(2-hydroxybenzyl)-N',N'-dimethylethylenediamine (H(2)L(2)); N,N-bis(2-hydroxybenzyl)-N',N'-diethylethylenediamine (H(2)L(3)); [N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)]-2-aminoethanol (H(2)L(4)); [N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)]-2-methyl-2-amino-1-propanol (H(2)L(5)); N,N-bis(1-hydroxyethyl)-2-picolylamine (H(2)L(6)), to give the monochloro complexes Re(V)O(L)Cl, 2. The X-ray structures of the complexes are reported. The molecular structures observed in the solid state are preserved in solution ((1)H NMR). In acetonitrile solution the Re(V)O(L)Cl, 2, display a one-electron couple, Re(VI)O(L)Cl(+)-Re(V)O(L)Cl, near 1.0 V vs SCE. The electrogenerated hexavalent complexes [Re(VI)O(L)Cl]ClO(4), 3, are paramagnetic and display sextet EPR spectra in solution at room temperature (A(av) approximately 417 (G), g approximately 1.914).     

Rheological characteristics of CeO2, Al2O3 and their hybrid mixture in ethylene glycol base fluid in the wide range of temperature and concentration

Journal of Thermal Analysis and Calorimetry - In the present work, the rheological behaviour of three different categories of nanofluid samples, 25 nm CeO2/EG, 13 nm Al2O3/EG and...