Rotating elliptic analysers for the automatic analysis of polarised light- Part I

An elliptic analyser, consisting of a birefringent element and a linear element, can be converted into a rotating elliptic analyser by rotating one or both the elements. The Poincaré sphere could be scanned, with such a device, along a meridian, a latitude circle, a great circle of any arbitrary inclination to the equator or any oblique path. Continuous analysis of polarised light can be accomplished by using such an analyser. The principles of some of the possible methods of analysis are presented. The problem of analysis of partially polarised light is also briefly discussed. The speed of analysis is important in analysing changing states of polarisation and depends on the speed of rotation of the elliptic analyser. It is pointed out here that fast rates of scanning are possible by using an electro-optic cell as a birefringent element and rotating the field that causes birefringence

Rotating elliptic analysers and automatic analysis of polarised light- Part II

The various main arrangements leading to a few typical rotating elliptie analysers are discussed. Simple devices for the determination of I, M, C, S of completely and partially polarised light beams are given. The possibility of using a rotating elliptic analyser having an electro-optic cell, for the determination of the Stokes parameters of light beams whose state of polarisation is rapidly changing is pointed out. The accuracy of the Stokes parameter method is analysed and it is found that this method leads to λ ρ and ω ρ values which are subject to an error smaller than one minute of arc (intensity measurement accurate to one in ten thousand). Some of the other methods of using the rotating elliptic analysers are also discussed. It is pointed out that the Stokes parameter method and the interference method, using the concept that orthogonal states do not interfere, are the most promising methods for the analyses of polarised light

New processes for black coatings useful in harnessing solar energy. I - A room temperature black chromium plating bath

The fundamental requirements for a solar selective absorber are reviewed and various methods of obtaining selectivity together with high absorptivity are discussed. Conventional black chromium plating process is briefly surveyed. It is pointed out that its major limitation to industrial application arises from the necessity of using high current densities (75 to 150 amp/sq dm) and low temperatures (10-15 C), which demands refrigeration. Black chromium plating has now been achieved at current densities as low as 7.5 am/sq dm (i.e., same as that used for normal chromium plating) and at room temperature or even higher (up to 60 C). The optical properties and corrosion resistance of the coatings produced using this new process are discussed

Photoelastic behaviour of ionic crystals

A theory of photoelasticity in ionic crystals is proposed wherein the overlap of the electronic atmospheres of adjacent ions and the effect of strain on the ionic'polarisabilities are considered the dominant factors. The sign of the stress optical constant predicted by this theory is found to be in agreement with the experimental result. The change in the sign of the stress optical constant atlower wavelengths exhibited by some of the alkali halides is also explained. The pure temperature effect observed in the thermo-optic behaviour of crystals turns out to be a natural consequence of the proposed theory

Evaluation of the nanostructure of cervical third cementum in health and chronic periodontitis: An in vitro study

Background: During the progression of periodontal disease, the cementum undergoes alterations in its structure and composition. Understanding the nanostructure of cementum, in terms of its mechanical properties, will provide an insight into the milieu that periodontal ligament cells encounter in health and chronic periodontitis. This study aims to analyze the nanomechanical properties of the cervical third of the cementum (transverse section) in health and chronic periodontitis. Materials and Methods: Twenty teeth (10 healthy and 10 periodontally diseased) were collected and the nanomechanical properties of the transverse section of the cervical third cementum were evaluated with depth-sensing nanoindentation technique under dry conditions. A total of 100 nanoindentations were performed to analyze the modulus of elasticity and hardness of cervical third of the cementum. Results: The nanomechanical properties of the healthy cervical third cementum sections were significantly higher (P < 0.05) (hardness: 0.720 ± 0.305 GPa; modulus: 15.420 ± 3.902 GPa) than the diseased cementum section (hardness: 0.422 ± 0.157 GPa; modulus: 11.056 ± 3.434 GPa). Conclusion: The results of our study indicate that the hardness and modulus of elasticity of the cervical third cementum decreases significantly in chronic periodontitis

Piezo-absorption coefficients of weakly and strongly absorbing crystals

The effect of stress on a crystal is to distort not only the index ellipsoid but also the absorption ellipsoid. The piezo-absorption tensor like the photoelastic tensor is a fourth rank polar tensor. The methods of obtaining the components of the piezo-absorption tensor in weakly absorbing crystals are given. It is shown that by measuring the coefficients of reflection at normal and oblique incidence in stressed and unstressed metals it is possible to obtain changes in refractive and absorption indices. From this the piezo-optic and the piezo-absorption coefficients of metals may be obtained

Highly Durable Antimicrobial Tantalum Nitride/Copper Coatings on Stainless Steel Deposited by Pulsed Magnetron Sputtering

Highly durable and antimicrobial tantalum nitride/copper (TaN/Cu) nanocomposite coatings were deposited on D-9 stainless steel substrates by pulsed magnetron sputtering. The Cu content in the coating was varied in the range of 1.42–35.42 atomic % (at.%). The coatings were characterized by electron probe microanalyzer, X-ray diffraction, scanning electron microscope and atomic force microscope. The antibacterial properties of the TaN/Cu coatings against gram-negative Pseudomonas aeruginosa were evaluated using a cell culture test. The peak hardness and Young’s modulus of TaN/Cu with 10.46 at.% Cu were 24 and 295 GPa, respectively, which amounted to 15 and 41.67% higher than Cu-free TaN. Among all, TaN/Cu with 10.46 at.% exhibited the lowest friction coefficient. The TaN/Cu coatings exhibited significantly higher antibacterial activity than Cu-free TaN against Pseudomonas aeruginosa. On TaN, the bacterial count was about 4 × 106 CFU, whereas it was dropped to 1.2 × 102 CFU in case of TaN/Cu with 10.46 at.% Cu. The bacterial count was decreased from 9 to 6 when the Cu content increased from 25.54 to 30.04 at.%. Live bacterial cells were observed in the SEM images of TaN, and dead cells were found on TaN/Cu. Overall, TaN/Cu with 10.46 at.% Cu was found to be a potential coating composition in terms of higher antimicrobial activity and mechanical durability