A comparative study of gamma-ray interaction and absorption in some building materials using Zeff-toolkit

The gamma-ray shielding behaviour of a material can be investigated by determining its various interaction and energy-absorption parameters (such as mass attenuation coefficients, mass energy absorption coefficients, and corresponding effective atomic numbers and electron densities). Literature review indicates that the effective atomic number (Z_eff) has been used as extensive parameters for evaluating the effects and defect in the chosen materials caused by ionising radiations (X-rays and gamma-rays). A computer program (Z_eff-toolkit) has been designed for obtaining the mean value of effective atomic number calculated by three different methods. A good agreement between the results obtained with Z_eff-toolkit, Auto_Z_eff software and experimentally measured values of Z_eff has been observed. Although the Z_eff-toolkit is capable of computing effective atomic numbers for both photon interaction (Z_eff,PI) and energy absorption (Z_eff,En) using three methods in each. No similar computer program is available in the literature which simultaneously computes these parameters simultaneously. The computed parameters have been compared and correlated in the wide energy range (0.001–20?MeV) for 10 commonly used building materials. The prominent variations in these parameters with gamma-ray photon energy have been observed due to the dominance of various absorption and scattering phenomena. The mean values of two effective atomic numbers (Z_eff,PI and Z_eff,En) are equivalent at energies below 0.002?MeV and above 0.3?MeV, indicating the dominance of gamma-ray absorption (photoelectric and pair production) over scattering (Compton) at these energies. Conversely in the energy range 0.002–0.3?MeV, the Compton scattering of gamma-rays dominates the absorption. From the 10 chosen samples of building materials, 2 soils showed better shielding behaviour than did other 8 materials.     

Difference Covering Arrays and Pseudo-Orthogonal Latin Squares

A pair of Latin squares, A and B, of order n, is said to be pseudo-orthogonal if each symbol in A is paired with every symbol in B precisely once, except for one symbol with which it is paired twice and one symbol with which it is not paired at all. A set of t Latin squares, of order n, are said to be mutually pseudo-orthogonal if they are pairwise pseudo-orthogonal. A special class of pseudo-orthogonal Latin squares are the mutually nearly orthogonal Latin squares (MNOLS) first discussed in 2002, with general constructions given in 2007. In this paper we develop row complete MNOLS from difference covering arrays. We will use this connection to settle the spectrum question for sets of 3 mutually pseudo-orthogonal Latin squares of even order, for all but the order 146.     

Structure control for fine tuning fluorescence emission from side-chain azobenzene polymers

New fluorescent azobenzene dyes and side-chain polymers have been synthesized and characterized and their photophysical properties studied. A series of azobenzene dyes having different fluorophores such as phenol (S1), phenylphenol (S2) and naphthol (S3) incorporated in them were synthesized. S2 had unusually high fluorescence with a quantum yield of phi f = 0.2 recorded in dichloromethane (DCM), whereas S1 and S3 were found to be weakly fluorescent. The azobenzene dyes were converted into methacrylate monomers having short ethyleneoxy spacers and then free radically polymerized. Phenylphenol-based azobenzene polymer (P2) continued to show fluorescence, whereas fluorescence was completely quenched in the case of phenol (P1)- and naphthol (P3)-based polymers. Phenylphenol, though twisted in the ground state is known to have a more planar geometry in the excited state--a factor that enables it to retain its fluorescence behavior even when it is incorporated as part of an azobenzene unit. In contrast, naphthol, which is a better fluorophore compared to phenylphenol, loses much of its emissive behavior upon coupling to the azobenzene unit. The extent of trans to cis photoisomerization in solution was very low (approximately 17%) for P2 after 30 min of continuous irradiation using 365 nm light, in contrast to approximately 40% for P1 under identical conditions. This is attributed to the steric repulsion brought about by the bulky phenylphenol units that restrict rotation. A 2-fold enhancement in fluorescence emission was observed for P2 upon irradiation by UV light at 360 nm, which relaxed to the original intensity in about 7 day's time. The higher emission of the cis azobenzenes is generally attributed to an inhibition of photoinduced electron transfer (PET) mechanism. The emission of P2 showed a concentration dependence which increased initially and then decreased in intensity with the formation of a new red-shifted peak at higher concentration due to aggregation. Irradiation of the fluorescence quenched highly concentrated (1 x 10(-3) M) sample of P2 showed an enhancement in emission from aggregates at 532 nm.     

Microstructural reorganization and cargo release in pyrene urethane methacrylate random copolymer hollow capsules

We report the synthesis of polymer microcapsules by direct one-pot free radical random copolymerization approach. Urethane methacrylate comb monomers having pendant pyrene (Py) and 3-pentadecyl phenol (PDP) units were copolymerized in a random manner using benzoyl peroxide (BPO) as free radical initiator in dimethylformamide (DMF) as solvent. These copolymers and corresponding homopolymers spontaneously self-organized into microspheres upon drop casting from solvents like DMF and tetrahydrofuran (THF). Stable microspheres were obtained in water by dialyzing THF solution of the polymers against water in dialysis bags with molecular weight cutoff of ～2000. The hollow nature of the spheres was confirmed by rhodamine B (RhB) encapsulation followed by F?rster resonance energy transfer (FRET) based fluorescence emission from RhB upon exciting pyrene. The microenvironment inside the capsule was probed by following the I(1)/I(3) ratio of pyrene emission as well as RhB release as a function of temperature. The RhB encapsulated in the pyrene homopolymer PIHP-100Py capsules experienced strong donor-acceptor interaction and did not undergo complete release even at high temperature (85 °C). The encapsulated RhB from the copolymers with low pyrene incorporation was released almost fully upon heating beyond 50 °C. Pyrene moieties in the PIHP-100Py were shielded from surrounding water and experienced a hydrophobic environment, whereas in the low pyrene incorporated copolymer the PDP units were better shielded from the hydrophilic environment. This work represents a simple approach to produce polymer hollow capsules, and the varying pyrene incorporation was used to trace the microenvironment inside the capsules.     

Direct correlation between work function of indium-tin-oxide electrodes and solar cell performance influenced by ultraviolet irradiation and air exposure

We report on reversible changes of the work function (WF) values of indium-tin-oxide (ITO) under prolonged ultraviolet (UV) and air exposure. The WF of ITO is reduced from 4.7 eV to 4.2 eV by photon absorption in ITO under UV illumination or an air mass 1.5 solar simulator (100 mW cm(-2)). Air or oxygen exposure is found to increase the WF of ITO (UV-exposed) to a value of 4.6 eV. These changes of ITO's WF lead to reversible variations of the performance of organic photovoltaic devices where ITO acts primarily as the electron collecting or hole collecting electrode. These variations can be reflected in the disappearance (or appearance) of an S-shaped kink in the J-V characteristics upon continuous UV or solar simulator illumination (or air exposure). This reversible phenomenon is ascribed to the adsorption and desorption of oxygen on the surface and grain boundaries of ITO. The use of surface modifiers to either decrease or increase the WF of ITO in organic photovoltaic devices with inverted and conventional geometries is also shown to be an effective route to stabilize the device performance under UV illumination.     

NO-NSAIDs. Part 3: nitric oxide-releasing prodrugs of non-steroidal anti-inflammatory drugs

In continuation of our efforts to discover novel nitric oxide-releasing non-steroidal anti-inflammatory drugs (NO-NSAIDs) as potentially "Safe NSAIDs," we report herein the design, synthesis and evaluation of 21 new NO-NSAIDs of commonly used NSAIDs such as aspirin, diclofenac, naproxen, flurbiprofen, ketoprofen, sulindac, ibuprofen and indomethacin. These prodrugs have NO-releasing disulfide linker attached to a parent NSAID via linkages such as an ester (compounds 9-16), a double ester (compounds 17-24), an imide (compounds 25-30) or an amide (compounds 31-33). Among these NO-NSAIDs, the ester-containing NO-aspirin (9), NO-diclofenac (10), NO-naproxen (11), and the imide-containing NO-aspirin (25), NO-flurbiprofen (27) and NO-ketoprofen (28) have shown promising oral absorption, anti-inflammatory activity and NO-releasing property, and also protected rats from NSAID-induced gastric damage. NO-aspirin compound 25, on further co-evaluation with aspirin at equimolar doses, exhibited comparable dose-dependent pharmacokinetics, inhibition of gastric mucosal prostaglandin E(2) (PGE(2)) synthesis and analgesic properties to those of aspirin, but retained its gastric-sparing properties even after doubling its oral dose. These promising NO-NSAIDs could therefore represent a new class of potentially "Safe NSAIDs" for the treatment of arthritic pain and inflammation.     

Self assembled nanoparticle Pb1−xFexSe/single crystal Si heterojunctions

Nanoparticle Pb_1−xFe_xSe (0.00  x  0.16) thin films have been deposited on quartz, glass and silicon substrates by chemical bath deposition technique. Structural and optical properties of the films with iron concentration 0.00  x  0.16 indicate that the films grow as single-phase Pb_1−xFe_xSe ternary alloys with rocksalt structure and with direct optical band gaps (E_g) that increase with decrease in grain size and have values larger than 0.28 eV of the bulk PbSe. Average grain size in films grown at fixed bath temperature T_b of 85 °C is observed to decrease from 72 to 22 nm whereas lattice parameter is observed to increase from 6.12 to 6.14 Å with increase in Fe concentration from x = 0.00 to x = 0.16. The observed blue shift in film materials originates from quantum confinement in the nanograins. Nanoparticle Pb_1−xFe_xSe/single crystal Si heterojunctions show rectifying behavior. On illumination of heterojunctions with visible light current is observed to increase in forward and reverse bias. This increase in current in the presence of visible light is considered to be due to carrier multiplication by Auger electron emission.     

Testing of holographic optical elements for holographic gun-sight

Conventional methods of measuring the various parameters of holographic optical elements are tedious for mass production. A novel approach is described for the holographic elements used in the holographic sight, in which the parameters are defined and measured as per their intended final application. Since the holographic sight is used for accurate target acquisition along with the other features, parallax in the sight becomes a critical parameter. Besides, the maximum brightness of the reticle is another parameter of the device, which is important for the use of sight in the strong sunlight in summers. There are two holographic elements, namely holographic reticle and holographic lens in the sight. Both can be tested in a simple set-up in terms of the parallax of the sight and the brightness of the reticle. The masters for both elements are required to be benchmarked once and rest of the elements in a mass production can be tested with the reference of masters.     

Plane finite element for static and free vibration analysis of sandwich plates

Conclusions Triangular sandwich finite elements (MPLW30) with 30 DOF have been developed for the static and free vibration analysis of sandwich plates with thin faces and low core shear modules. The results of numerical examples presented here demonstrate the accuracy and suitability of the formulations for the analysis of sandwich plates with k_H > 25 and k_E > 200.Published in Mekhanika Kompozitnykh Materialov, Vol. 30, No. 2, pp 238–248, March–April, 1994.