Behavior of a rhombus frame of nonlinear elastic material under large deflection

The large-deflection spring behavior of an inextensible thin rhombus frame is studied in this work. The frame has a rectangular cross-section and supports two equal and opposite diagonal forces that act on its two opposite corners with a given apex angle γ. Both geometrical and material nonlinearities have been considered in the study. The beam was assumed to be made of a material having a nonlinear stress-strain relationship of the Ludwick type.A semi-analytical solution has been formulated for the relation between the large displacement at the corners of the frame and the applied forces. The deformed shapes and the nonlinear secant stiffnesses of the rhombus frame were plotted against applied loads. The frame behavior was fully investigated for different apex angles and nonlinear elastic material constants, n.In order to check the accuracy and efficiency of the proposed analytical solution, a large-displacement finite-element analysis utilizing the multi-purpose computer program ADINA was performed. Each side of the rhombus frame was divided into 10 moment-curvature beam elements. Results obtained using the analytical solution were identical to the results obtained using the software ADINA.     

A Rapid and Highly Efficient Microwave-Promoted Four-Component Domino Reaction for the Synthesis of Novel Spiro[benzo[a]chromeno[2,3-c]phenazine] Derivatives Under Solvent-Free Conditions

p-Toluenesulfonic acid was applied as an efficient, non-toxic and solid acid catalyst for the one-pot, four-component condensation between 2-hydroxy-1,4-naphthoquinone, benzene-1,2-diamine, cyclic 1,3-dicarbonyl compounds and isatin or ninhydrin to afford the corresponding novel spiro[benzo[a]chromeno[2,3-c]phenazine] derivatives via a new two-step domino protocol under conventional heating and microwave irradiation. This solvent-free process produces biologically considerable heterocycles with the formation of five new bonds (two C–C, two C?N, and one C–O) and two new rings in a single operation and this effective green process provides considerable advantages such as: operational simplicity, very short reaction time, high yields, absence of any tedious process or purification, and it avoids hazardous reagents/solvents.     

Reclamation and additional alloying of 18Ni(350) maraging steel

The possibility of gainfully utilizing grade 18Ni(350) maraging steel scrap has been investigated, along with the effect of additional alloying with niobium. A vacuum induction melting and casting furnace was used for melting and additional alloying. The cast ingots were hot forged and their properties compared with those of the stock material. The composition of the reprocessed material was found to be within the prescribed range for 18Ni(350) steel, except for some loss in titanium content. The hardness and tensile strength of the recycled steel were similar to those of the stock material. A slight decrease in hardness in the aged condition could be attributed to loss of titanium during remelting. Charpy V- notch impact test-ing indicated significantly higher toughness in the remelted material; this has been attributed to a homo-geneous, refined microstructure and a lower level of inclusions. Additional alloying with 2% Nb not only improved the mechanical properties but also affected the amount of reverted austenite obtained after ag-ing.     

Studies with inorganic precipitate membranes—XI: Evaluation of the thermodynamically effective fixed charge density by various methods

Thermodynamically effective fixed charge densities of parchment supported membranes were estimated by methods of (a) Teorell—Meyer—Sievers, (b) Altug and Hair, and (c) the most recent one of Kobatake based on the thermodynamics of irreversible processes. The two limiting forms of Kobatake's equation for dilute and concentrated ranges gave identical values of charge densities. It is interesting to note that these two values of limiting cases are closer to the Teorell—Meyer—Sievers and Altug and Hair values. The theoretical prediction for membrane potential by the Kobatake's equation were borne out quite satisfactorily by experimental results obtained with both the membranes.     

Studies with inorganic precipitate membranes—XII: Consideration of membrane field strength and energetics of permeation

Electrolytic transfort processes occuring across parchment supported membranes have been described by Nernst Planck flux equation taking into account the membrane resistance R_m, membrane potential E_metc.E_m values for various electrolytes display very interesting phenomena. In the case of 1:1 electrolyte the E_m values are all positive, while in the case of (2:1) and (3:1) electrolytes surface charge reversal takes place. The diffusion rate sequence and selectivity of the membrane for different uni- bi- and trivalent cations was found to be primarily dependent on the difference in the hydration energies of counter ions in the external solution. On the basis of Eisenman-Sherry theory the diffusion rate sequence of alkali metal cations point towards the weak field strength of the fixed charge groups. Various thermodynamic parameters, ΔH^≠, ΔF^≠ and ΔS^≠ were evaluated by applying the theory of absolute reactions rates to the diffusion process through parchment supported membranes. The values of ΔS^≠ were found to be negative, indicating that diffusion takes place with partial immobilization in the membrane phase. The relative partial immobility was found to increase with increase in the valence of the ions constituting the electrolyte. A formal relation between ΔH_hydration, ΔF_hydration and ΔS_hydration of cations with the corresponding values of ΔH^≠, ΔF^≠ and ΔS^≠ for diffusion, was also found to exist for these membranes.     

Fabrication and characterization of in situ synthesized iron oxide‐modified polyimide nanoweb by needleless electrospinning

A series of poly(amic acid) (PAA) solutions were prepared by sol–gel condensation of 4,4′‐oxydianiline (ODA) and 4,4′‐oxydiphthalic anhydride (ODPA), containing various wt % (5, 10, 15) of an iron oxide precursor, that is, tris(acetylacetonato)iron(III) complex. The resulting PAA solutions were electrospun at 78 kV and collected as webs of nonwoven nanofibers of diameter ～60–70 nm and subsequently converted to iron oxide‐modified polyimide (PI) nanofibers by slow thermal imidization. Aminopropyl triethoxysilane (APTES) and tetraethoxyorthosilicate (TEOS) were used as coupling agent and silica precursor, respectively, to enhance the compatibility between organic polymer matrix and inorganic moieties. SEM images reveal smooth and defect‐free surface morphologies of the nanofibers. Superparamagnetic properties of the nanofibers were revealed by vibrating sample magnetometer (VSM). FT‐infrared spectroscopy (IR), powder XRD, thermogravimetric analysis, and differential scanning calorimetry were employed to systematically characterize material structural properties, thermal stabilities, etc. Nanowebs showed excellent thermal stability around 446°C, with a glass transition temperature around 270°C. The above study demonstrates a good example for fabrication of highly thermally stable bead‐free nanofiber webs by needleless electrospinning. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40432.     

Longitudinal splitting of boron nitride nanotubes for the facile synthesis of high quality boron nitride nanoribbons

Boron nitride nanoribbons (BNNRs), the boron nitride structural equivalent of graphene nanoribbons (GNRs), are predicted to possess unique electronic and magnetic properties. We report the synthesis of BNNRs through the potassium-intercalation-induced longitudinal splitting of boron nitride nanotubes (BNNTs). This facile, scalable synthesis results in narrow (down to 20 nm), few sheet (typically 2-10), high crystallinity BNNRs with very uniform widths. The BNNRs are at least 1 μm in length with minimal defects within the ribbon plane and along the ribbon edges.