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ABSTRACT Chloride induced reinforcement corrosion in concrete is a serious durability problem. Different sources of chloride, i.e. chloride introduced at the fresh stage of concrete (i.e. internal chloride) and chloride [...]

ABSTRACT The presence of chloride ions in reinforced concrete (RC) plays a major role in reinforcement corrosion and hence for the durability and service life of RC structures. With growing [...]

In this study, compressive strength and flow behavior of fly ash incorporated cement paste and mortar were investigated. For this purpose, four water to binder ratios (w/(c+f)) such as 0.25, 0.35, 0.45 and 0.55 with three curing ages and five wide range of fly ash replacement levels (f/cratio) namely 0, 0.1, 0.2, 0.3 and 0.4 were introduced in the experimental scheme. The workability of the mixture was ensured through Marsh cone and flow table tests for fly ash blended cement paste and mortar, respectively. The test result showed that compressive strength increases with age as expected in all cases and an empirical relationship for compressive strength of blended cement paste and mortar with mix factors such as w/(c+f) ratio, f/cratio and age is also proposed. The estimated compressive strength versus w/(c+f) ratio curves for different curing ages and f/cratios resembles the nature of Abrams’ strength versus w/cratio curves.

Chemical techniques were employed to synthesize CdS nanoparticles embedded in polymer (PEG 300) and sol-gel silica matrices. Systematic growth of particles (radius 3–9 nm) was obtained by adjusting post-deposition annealing temperature and time to examine the dependence of surface-state–related luminescence on particle size. Photoluminescence (PL) peak energy showed a linear dependence with a gentle slope in the weak confinement region and a steep slope in the strong confinement region, the divergence being observed near the excitonic Bohr radius for CdS. The empirical relation proposed for the weak confinement region could be used for estimating chemically prepared CdS nanoparticle size with a high degree of reliability from PL peak energy.

Cd_1−xZn_xS nanoparticles with different compositions (0≤x≤1) embedded in silica matrix were prepared in thin film form by the sol–gel technique. The film texture and structural transformation with increasing x value were studied from transmission electron micrographs and electron diffraction patterns. Optical study indicated increase in optical bandgap and decrease in refractive index with increasing zinc content (x value). Photoluminescence studies showed emission from surface states with emission energy blue shifted with increasing zinc content in the films. Annealing behaviour of the films with increasing annealing temperature and time was studied.

Abstract: Synthesis and characterization of undoped and Mn2+ doped ZnS nanocrystallites (radius 2–3 nm) embedded in a partially densified silica gel matrix are presented. Optical transmittance, photoluminescence (PL), ellipsometric and electron spin resonance measurements revealed manifestation of quantum size effect. PL spectra recorded at room temperature revealed broad blue emission signal centred at ∼ 420 nm and Mn2+ related yellow-orange band centred at ∼ 590 nm while ESR indicated that Mn in ZnS was present as dispersed impurity rather than Mn cluster.

A simple method for synthesis of well dispersed cadmium sulphide (CdS) nanoparticles embedded in a polyethylene glycol matrix (PEG 300) in thin film form is presented. The molar ratio of PEG and CdS was varied within the range 70 : 30 to as high as 50 : 50. Films with controllable sizes (r∼ 3 –8 nm) of nanocrystals could be obtained by adjusting post-deposition annealing temperature (T) and time (t). The obtained films showed systematic variation in optical properties with decreasing crystal size due to quantum confinement. Transmission electron micrographs (TEM) indicated well resolved nanoparticles for films annealed at lower temperature (T= 373 K) and time (t< 45 min). Photoluminescence (PL) studies indicated blue shift with decreasing particle size. The films did not degrade with aging in a humid atmosphere (relative humidity 40%) for several weeks.

The combustion, oxidation, and pyrolysis chemistry of even simple light hydrocarbons can be extremely complex, involving hundreds or thousands of kinetically significant species. Even relatively minor species can play an important role in the formation of undesirable emissions and byproducts, and their properties and reactions need to be modeled in some detail in order to make accurate predictions. In many technologically important applications, the reaction chemistry is closely coupled with the mixing and heat flow, dramatically increasing the computational difficulty. The most reasonable way to deal with this complexity is to use a computer not only to solve the simulation numerically, but also to construct the model in the first place. We are developing the methods needed to make this sort of computer-aided kinetic modeling feasible for real systems. The computer is used to calculate most of the molecular properties and rate parameters in the model by a variety of quantum- and group-additivity-based techniques. We summarize our new computer methods for modeling the pressure dependence (falloff and chemical activation) of gas-phase reactions. Our approach to determining the optimal reduced kinetic models for various reaction conditions is discussed. Adaptive-chemistry methods that allow one to solve detailed macroscopic reacting flow simulations involving hundreds of species are outlined.

X-ray diffraction studies on oriented samples of 4-cyanophenyl-4'-n-heptylbenzoate in the nematic phase are reported at different temperatures. The orientational distribution function f(β) has been calculated from the angular distribution of the X-ray intensities. The orientational order parameters [image omitted]2 and [image omitted]4 have been determined from f(β). [image omitted]2 is found to be slightly greater than the value predicted by the Maier-Saupe molecular field theory, whereas the [image omitted]4 values are much smaller than those given by theory. An approximate expression for the potential of the molecular field is obtained from the temperature variation of the distribution function. The value of l and the intermolecular distance D have been determined from X-ray photograph. l, which is often close to the molecular length is found to be 28 Å. The length as measured from a model in a completely extended form is found to be 21 Å. If we assume antiparallel associations of molecules as in most cyano compounds this difference can be explained.

Large amplitude flexural vibrations of clamped as well as simply supported isotropic elastic rhombic plates (skew plates having unity aspect ratio) are investigated, the effects of shear deformation and rotatory inertia being included. Banerjee’s hypothesis [1, 2] is employed to obtain the required differential equations in oblique co-ordinates. The governing equations for plates of transversely isotropic material are solved by the well-known Galerkin procedure. A number of numerical results are presented for different edge conditions of the rhombic plates, indicating the significant influences of skew angle, transverse shear deformation and rotatory inertia.

An arrangement for the in-situ measurement of the corrosion current density, i.e. corrosion rate, of rebar embedded in concrete through a linear polarisation technique is described. It incorporates a simple experimental method being suggested for determination of the ohmic resistance of concrete, which enables the ohmic drop to be eliminated mathematically from the polarisation data. The error due to non-uniform distribution of the applied electric signal through a small size counter electrode to the working electrode (rebar) is removed by using the transmission line model. A calculation procedure for estimating Tafel slopes has also been suggested for precise estimation of the Stern--Geary constant. The utility of the arrangement and the experimental procedure suggested for in-situ corrosion rate measurement is demonstrated through a carefully planned experimental scheme.

It is argued that the Schwarzschild black hole solution follows as a unique limit of the Brans-Dicke Class I solutions, provided the correct iterated limit is taken. Such a uniqueness is essential for the validity of a recent version of the no-hair conjecture. A non-trivial modification to this version is proposed in order to exclude Brans-Dicke Class IV solutions which appear to represent scalar hair black holes in general.