Instability map for cold and warm working of as-cast 304 stainless steel

The deformation characteristics of as-cast 304 stainless steel under compression in the temperature range 20-600 degrees C and strain rate range 0.001-100 s(-1) have been studied with a view to characterizing the flow instabilities occurring in the microstructure. Ar strain rates of less than 0.05 s(-1), as-cast 304 stainless steel exhibits flow localization in the temperature range 20-600 degrees C, whereas dynamic strain ageing occurs at intermediate temperatures and below 5 s(-1). At room temperatures and strain rates of less than 0.05 s(-1), martensite formation is observed. To avoid the above microstructural instabilities warm working should be carried out at strain rates greater than 10 s(-1) in the temperature range 400-600 degrees C and cold working could be done in the range of about 0.05-0.8 s(-1). The continuum criterion developed on the basis of the principles of maximum rate of entropy production and separability of the dissipation function, predicts accurately all of the above instability features. (C) 1997 Elsevier Science S.A.

Isolation of transforming growth factor-beta 2 cDNA from a fish, Cyprinus carpio by RT-PCR

Transforming Growth Factors-beta (TGF-beta s) have been described in many vertebrate species of amphibians, aves and mammals. In this report we demonstrate the presence of TGF-beta 2 in pisces. TGF-beta 2 has been cloned from a fish, Cyrinus carpio, by RT-PCR using degenerate oligonucleotide primers. Sequence analysis of the amplified product and alignment of the deduced amino acid sequence with the human TGF-beta 2 amino acid sequence revealed 81% and 93% identity in the precursor and the mature regions, respectively. The northern blot analysis of fish heart RNA shows a major messenger RNA species of about 8.0 kb and two messages of very low abundance of about 5.0 kb and 4.0 kb. The identification of TGF-beta 2 isoform in Pisces and it's high degree of homology with the mammalian isoform suggests that among all TGF-beta isoforms, TGF-beta 2 is the most conserved during evolution. (C) 1997 Elsevier Science B.V.

On the incoming water waves against a vertical cliff

The problems of obliquely incident surface water waves against a vertical cliff have been handled in both the cases of water of infinite as well as finite depth by straightforward uses of appropriate Havelock-type expansion theorems. The logarithmic singularity along the shore-line has been incorporated in a direct manner, by suitably representing the Dirac's delta function.

Role of two consecutive alpha,beta-dehydrophenylalanines in peptide structure: Crystal and molecular structure of Boc-Leu-Delta Phe-Delta Phe-Ala-Phe-NHMe

An N-alpha-protected model pentapeptide containing two consecutive Delta Phe residues, Boc-Leu-Delta Phe-Delta Phe-Ala-Phe-NHMe, has been synthesized by solution methods and fully characterized. H-1-nmr studies provided evidence for the occurrence of a significant population of a conformer having three consecutive, intramolecularly II-bonded beta-bends in solution. The solid state structure has been determined by x-ray diffraction methods. The crystals grown from aqueous methanol are orthorhombic, space group P2(1)2(1)2(1),, a = 11.503(2), b = 16.554(2), c = 22.107(3) Angstrom, V = 4209(1) Angstrom,(3) and Z = 4. The x-ray data were collected on a CAD4 diffractometer using CuKalpha radiation (lambda = 1.5418 Angstrom). The structure was determined using direct methods and refined by full-matrix least-squares procedure. The R factor is 5.3%. The molecule is characterized by a right handed 3(10)-helical conformation ((phi) = -68.2 degrees (psi) = -26.3 degrees), which is made up of two consecutive type III beta-bends and one type I beta-bend. In the solid state the helical molecules are aligned head-to-tail, thus forming long rod like structures. A comparison with other peptide structures containing consecutive Delta Phe residues is also provided. The present study confirms that the -Delta Phe-Delta Phe-sequence can be accommodated in helical structures. (C) 1997 John Wiley & Sons, Inc.

Translational and rotational motion in molecular liquids: A computer simulation study of Lennard-Jones ellipsoids

In order to understand the translational and rotational motion in dense molecular liquids, detailed molecular dynamics simulations of Lennard-Jones ellipsoids have been carried out for three different values of the aspect ratio kappa. For ellipsoids with an aspect ratio equal to 2, the product of the translational diffusion coefficient (D-T) and the average orientational correlation time of the l-th rank harmonics (tau(lR)), converges to a nearly constant value at high density. Surprisingly, this density independent value of D-T tau(lR) is within 5% of the hydrodynamic prediction with the slip boundary condition. This is despite the fact that both D-T and tau(lR) themselves change nearly by an order of magnitude in the density range considered, and the rotational correlation function itself is strongly nonexponential. For small aspect ratios (kappa less than or equal to 1.5), the rotational correlation function remains largely Gaussian even at a very large density, while for a large aspect ratio (kappa greater than or equal to 3), the transition to the nematic liquid-crystalline phase precludes the hydrodynamic regime. Thus, the rotational dynamics of ellipsoids show great sensitivity to the aspect ratio. At low density, tau(lR) goes through a minimum value, indicating the role of interactions in enhancing the rate of orientational relaxation. (C) 1997 American Institute of Physics. [S0021-9606(97)50142-5].

Microwave preparation of oxide bronzes

Several vanadium, tungsten, and molybdenum oxide bronzes have been prepared using microwave irradiation. Metal oxides and alkali metal iodides were used as starting materials, Intermittent grinding and inert atmosphere were found to be necessary for the synthesis of most of the bronzes, The reaction temperatures are remarkably lower than those employed for conventional synthetic techniques and the microwave assisted reactions proceed at extremely fast rates. The microwave synthesized bronzes consist of particles having long, rectangular rod-like morphology. (C) 1999 Academic Press.

Rapid method of consolidation testing

The determination of consolidation characteristics forms an important aspect in the design of foundations and other earth-retaining structures. The conventional consolidation test as originally proposed by Teaaghi takes considerable time (more than 15 days in highly compressible soils with low coefficient of consolidation) and effort. Any effort to reduce the duration of testing will be desirable from several considerations. In this paper, an attempt has been made to propose a rapid method of consolidation testing. In the proposed method, the next load increment is applied as soon as the necessary time required to identify the percent consolidation is reached and to evaluate the coefficient of consolidation by one of the popular curve-fitting procedures. The rectangular hyperbola method has been used to identify the percent consolidation reached after any load increment, and to determine the coefficient of consolidation, before making the next load increment. The time required to complete the test using the rapid consolidation method could be as low as 4-5 h compared with 1 or 2 weeks in the case of the conventional consolidation test.

Synthesis and structure of a novel terminal imido complex of titanium

The reaction of eta(5)-Cp*TiCl3 and (LiNHBu)-Bu-t in hexanes yields a novel [eta(5)-Cp*Ti(=(NBu)-Bu-t)((NHBu)-Bu-t)(2)]Li . (NH2Bu)-Bu-t complex with a terminal tert-butylimido moiety. The synthesis and X-ray structural characterization are described. (C) 1999 Elsevier Science S.A. All rights reserved.

Embrittlement of a bulk metallic glass due to low-temperature annealing

Embrittlement of a bulk La-based metallic glass due to isothermal and isochronal annealing below the T-g was investigated. Results show that the impact toughness decreases with increasing annealing time or temperature, accompanied by a change in fracture morphology. Reasons for this are discussed in terms of structural relaxation. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.

Longwave radiative forcing of Indian Ocean tropospheric aerosol

A spectrally resolved discrete-ordinates radiative transfer model is used to calculate the change in downwelling surface and top-of-the-atmosphere (TOA) outgoing longwave (3.9-500 mum) radiative fluxes induced by tropospheric aerosols of the type observed over the Indian Ocean during the Indian Ocean Experiment (INDOEX). Both external and internal aerosol mixtures were considered. Throughout the longwave, the aerosol volume extinction depends more strongly on relative humidity than in most of the shortwave (0.28-3.9 mum), implying that particle growth factors and realistic relative humidity profiles must be taken into account when modeling the longwave radiative effects of aerosols. A typical boundary layer aerosol loading, with a 500-nm optical depth of 0.3, will increase the downwelling longwave flux at the surface by 7.7 W m(-2) over the clean air case while decreasing the outgoing longwave radiation by 1.3 W m(-2). A more vertically extended aerosol loading, exhibiting a high opacity plume between 2 and 3 km above the surface and having a typical 500-nm optical depth of 0.7, will increase the downwelling longwave flux at the surface by 11.2 W m(-2) over the clean air case while decreasing the outgoing longwave radiation by 2.7 W m(-2). For a vertically extended aerosol profile, approximately 30% of the TOA radiative forcing comes from sea salt and approximately 60% of the forcing comes from the combination of sea salt and dust. The remaining forcing is from anthropogenic constituents. These results are for the external mixture. For an internal mixture, TOA longwave forcings can be up to a factor of two larger. Therefore, to complete our understanding of this region's longwave aerosol radiative properties, more detailed information is needed about aerosol mixing states. These longwave radiative effects partially offset the large shortwave aerosol radiative forcing and should be included in regional and global climate modeling simulations.

Synthesis of acicular hydrogoethite (alpha-FeOOH center dot xH(2)O; 0.1 < x < 0.22) particles using morphology controlling cationic additives and magnetic properties of maghemite derived from hydrogoethite

A method for the preparation of acicular hydrogoethite (alpha -FeOOH.xH(2)O, 0.1 < x < 0.22) particles of 0.3-1 mm length has been optimized by air oxidation of Fe( II) hydroxide gel precipitated from aqueous (NH4)(2)Fe(SO4)(2) solutions containing 0.005-0.02 atom% of cationic Pt, Pd or Rh additives as morphology controlling agents. Hydrogoethite particles are evolved from the amorphous ferrous hydroxide gel by heterogeneous nucleation and growth. Preferential adsorption of additives on certain crystallographic planes thereby retarding the growth in the perpendicular direction, allows the particles to acquire acicular shapes with high aspect ratios of 8-15. Synthetic hydrogoethite showed a mass loss of about 14% at similar to 280 degreesC, revealing the presence of strongly coordinated water of hydration in the interior of the goethite crystallites. As evident from IR spectra, excess H2O molecules (0.1- 0.22 per formula unit) are located in the strands of channels formed in between the double ribbons of FeO6 octahedra running parallel to the c- axis. Hydrogoethite particles constituted of multicrystallites are formed with Pt as additive, whereas single crystallite particles are obtained with Pd (or Rh). For both dehydroxylation as well as H-2 reduction, a lower reaction temperature (similar to 220 degreesC) was observed for the former (Pt treated) compared to the latter (Pd or Rh) (similar to 260 degreesC). Acicular magnetite (Fe3O4) was prepared either by reducing hydrogoethite (magnetite route) or dehydroxylating hydrogoethite to hematite and then reducing it to magnetite (hematite- magnetite route). According to TEM studies, preferential dehydroxylation of hydrogoethite along < 010 > leads to microporous hematite. Maghemite (gamma -Fe2O3 (-) (delta), 0 < < 0.25) was obtained by reoxidation of magnetite. The micropores are retained during the topotactic transformation to magnetite and finally to maghemite, whereas cylindrical mesopores are formed due to rearrangement of the oxygen sublattice from hexagonal to cubic close packing during the conversion of hydrogoethite to magnetite and then to maghemite. Accordingly, three different types of maghemite particles are realized: strongly oriented multicrystalline particles, single crystalline acicular particles with micropores or crystallites having mesopores. Higher values of saturation magnetization ((s) = 74 emu g(-1)) and coercivity (H-c = 320 Oe) are obtained for single crystalline mesoporous particles. In the other cases, the smaller size of particles and larger distribution of micropores decreases sigma (s) considerably ( < 60 emu g(-1)) due to relaxation effects of spins on the surface atoms as revealed by Mossbauer spectroscopy.

Dynamics of bound dyes in a nonpolymeric aqueous gel derived from a tripodal bile salt

Rotational dynamics of polarity sensitive fluorescent dyes (ANS and DPH) in a nonpolymertic aqueous gel derived from tripodal cholamide I was studied using ultrafast time-resolved fluorescence technique. Results were compared with that of naturally occurring di- and trihydroxy bile salts. ANS in the gel showed two rotational correlation time (phi) components, 13.2 ns (bound to the hydrophobic region of the gel) and 1.0 ns (free aqueous ANS), whereas DPH showed only one component (4.8 ns). In the sol state, faster rotational motion was observed, both for ANS and DPH. Our data revealed that dyes get encapsulated more tightly in the gel network when compared to the micellar aggregates. ANS has more restrained rotation compared to DPH. This was attributed to the interaction of the sulfonate group of ANS with water molecules and hydrophilic parts of the gelator molecule. No restricted rotation was observed for DPH in the gel state unlike when it is in the gel phase of lipid bilayer.

Grafting of m-isopropenyl-alpha, alpha-dimethylbenzyl-isocyanate (m-TMI) onto isotactic polypropylene: Synthesis and characterization

A novel vinyl monomer with an isocyanate functional group, m-isopropenyl-alpha,alpha-dimethylbenzyl-isocyanate (m-TMI), was grafted onto isotactic polypropylene (i-PP) using dicumyl peroxide (DCP) as the initiator. This would open up the possibility of using the grafted polymer with the reactive isocyanate group as compatibilizer for blending carbohydrates such as cellulose with. polypropylene. The grafting was carried out in a Brabender Plasticoder at 180degreesC. The effects of monomer and initiator concentrations on the yield of grafting were investigated by performing statistical analysis. While the grafting yield increased with the concentration of DCP at any given concentration of m-TMI, the variation of the grafting yield with m-TMI concentration, for a given concentration of DCP, went through a maximum, the optimum yield of 7.8% (w/w) being obtained at 10 wt.% concentration of both DCP and m-TMI. The grafting reaction is. accompanied by considerable chain scission of I-PP, resulting in a decrease in the molecular weight of the grafted polymer. While the molecular weight drops sharply even at a low concentration of DCP, there occurs no further significant change in the molecular weight even at much higher concentrations of the initiator.

Phase transitions in the anchored organic bilayers of long-chain alkylammonium lead iodides (CnH2n+1NH3)(2)PbI4; n=12, 16, 18

The single perovskite slab alkylammonium lead iodides (CnH2n+1NH3)(2)PbI4, n = 12, 16, 18, display two phase transitions, just above room temperature, associated with changes in the alkylammonium chains. We have followed these two phase transitions using scanning calorimetry, X-ray powder diffraction, and IR and Raman spectroscopies. We find the first phase transition to be associated with symmetry changes arising from a dynamic rotational disordering of the ammonium headgroup of the chain whereas the second transition, the melting of the chains in two dimensions, is characterized by an increased conformational disorder of the methylene units of the alkyl chains. We examine these phase transitions in light of the interesting optical properties of these materials, as well as the relevance of these systems as models for phase transitions in lipid bilayers.