Laser-induced thermal stresses on steel surface

In laser heat treatment of steels, a thin surface layer of austenite forms during heating and subsequent phase change process in the cooling period. However, thermal stress develops due to high-temperature gradient attainment in the surface vicinity which in turn results in microcrack development at the surface. The present study is carried out to compute the temperature profiles due to step input pulse laser radiation and determine the resulting thermal stresses. The study is extended to include three-step input pulses having the same energy content. This provides the comparison for the influence of the pulse length on the resulting thermal stresses. To validate the theoretical predictions, an experiment is conducted to irradiate the AISI 4142 steel surface by an Nd–YAG laser. Microphotography and EDS analysis of the heated regions are carried out. It is found that considerable thermal stress is eveloped at the workpiece surface due to attainment of high-temperature gradient in this region. In addition, microcracks are observed at the surface of the irradiated spot.     

Natural radioactivity in Zambian building materials collected from Lusaka

Samples of natural and manufactures building materials collected around Lusaka have been analyzed for natural radionuclides using -spectrometry. A simple comparison of the specific radioactivities of primordial radionuclides in these materials to the world averages for soil (25 Bq kg^{–1 238}U, 25 Bg kg^{–1 232}Th, 370 Bq kg^{–1 40}K and 89 Bq kg^–1 Ra_eq) shows that, of the nine types of samples analyzed, only burnt clay bricks (for²³⁸U,²³²Th and⁴⁰K), cement roofing tiles (for²³⁸U), building and river sands (for²³²Th and⁴⁰K) have greater activities than does soil. Radiological evaluation of specific radioactivities in these materials indicates that all materials meet the external -ray dose limitation of 1.5 mSv y^–1, that is, all samples have a radium equivalent activity of less than 370 Bq kg^–1.     

A direct route to six and seven membered lactones via γ-C(sp3)–H activation: a simple protocol to build molecular complexity

Lactones comprise a class of valuable compounds having biological as well as industrial importance. Development of a methodology to synthesize such molecules directly from readily available materials such as aliphatic carboxylic acid is highly desirable. Herein, we have reported synthesis of δ-lactones and ε-lactones via selective γ-C(sp³)–H activation. The γ-C–H bond containing aliphatic carboxylic acids provide six or seven membered lactones depending on the olefin partner in the presence of a palladium catalyst. A mechanistic investigation suggests that C–H activation is the rate-determining step. Further transformations of the lactones have been carried out to showcase the applicability of the present strategy.

Six and seven membered lactones have been synthesized directly from readily available aliphatic acids.     

Elemental analysis in solutions by radioisotope excited X-ray fluorescence

The problem of spectrochemical analysis of elements in solutions has been investigated for a number of elements across the periodic table using radioisotope-induced energy dispersive X-ray fluorescence method. In this study a low intensity¹⁰⁹Cd X-ray source was used for characteristic X-ray excitation. Experimental parameters such as saturation thickness and critical thickness have been studied to evaluate their role in this method. Minimum detection limits, sensitivities and the nature of concentration calibration at critical thickness have been obtained as a function of Z to find the limits of the method. Results obtained have been discussed in the light of theories and potential areas of applicability of the method have been indicated.     

Comparative structural and fungicidal studies of Mono-methyl phthalate and its Tin(IV) derivatives

The results of an investigation into the fungicidal properties of some organotin(IV) compounds with Mono-methyl phthalate are reported. The compounds were characterized by various spectroscopic techniques including ¹H-¹³C-¹¹⁹Sn-NMR, FT-IR, and ¹¹⁹Sn Mössbauer studies. On the basis of these techniques, all the complexes show penta coordination with a trigonal bipyramidal environment around the tin. The synthesized compounds were tested against a number of plant pathogenic fungi. The fungicidal data reveal that the tri-phenyltin(IV) compound proves to be a powerful fungicide. Comparison between the fungicidal activity of the trialkyltin(IV) compounds shows that the tri-phenyl tin(IV) complex is most active against all plant pathogens; the rest of the complexes also exhibit significant antifungal activity but less than the former one.     

Circularly Symmetric Static Metric in Three Dimensions and Its Killing Symmetry

In this note we consider a general three-dimensional circularly symmetric static metric and investigate possible Killing symmetries it possesses.We then summarize the work by addressing Einstein equations and briefly discuss their implications on the energy momentum content of some of the metrics that arise in the process.     

Diffraction of SH-waves across a mixed boundary in a plate

The diffraction of SH-waves in an infinite elastic plate is studied under general boundary conditions using the Wiener-Hopf technique. A mixed interface boundary value problem is solved as an illustration.     

Injectable Supramolecular Hydrogel/Microgel Composites for Therapeutic Delivery

Shear‐thinning hydrogels are useful for biomedical applications, from 3D bioprinting to injectable biomaterials. Although they have the appropriate properties for injection, it may be advantageous to decouple injectability from the controlled release of encapsulated therapeutics. Toward this, composites of hydrogels and encapsulated microgels are introduced with microgels that are fabricated via microfluidics. The microgel cross‐linker controls degradation and entrapped molecule release, and the concentration of microgels alters composite hydrogel rheological properties. For the treatment of myocardial infarction (MI), interleukin‐10 (IL‐10) is encapsulated in microgels and released from composites. In a rat model of MI, composites with IL‐10 reduce macrophage density after 1 week and improve scar thickness, ejection fraction, cardiac output, and the size of vascular structures after 4 weeks when compared to saline injection. Improvements are also observed with the composite without IL‐10 over saline, emphasizing the role of injectable hydrogels alone on tissue repair.     

Stability techniques in SIR epidemic models

In biological communities interaction among different species affect their stability. In this paper, we consider a nonlinear SIR model, which describes the dynamics of the interaction between susceptible and infected individuals in population. We establish stability techniques to find out the equilibria for the model and their numerical results are given. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)