Extraordinary evanescent field confinement waveguide sensor for mid-infrared trace gas spectroscopy

Nanophotonic waveguides are at the core of a great variety of optical sensors.These structures confine light along defined paths on photonic chips and provide light-matter interaction via an evanescent field.However,waveguides still lag behind free-space optics for sensitivity-critical applications such as trace gas detection.Short optical pathlengths,low interaction strengths,and spurious etalon fringes in spectral transmission are among the main reasons why on-chip gas sensing is still in its infancy.In this work,we report on a mid-infrared integrated waveguide sensor that successfully addresses these drawbacks.This sensor operates with a 107%evanescent field confinement factor in air,which not only matches but also outperforms free-space beams in terms of the per-length optical interaction.Furthermore,negligible facet reflections result in a flat spectral background and record-low absorbance noise that can finally compete with free-space spectroscopy.The sensor performance was validated at 2.566μm,which showed a 7 ppm detection limit for acetylene with only a 2 cm long waveguide.     

Torsion problem for elastic cylinder with inserts and holes

An integral equation method to solve the classical torsion problem for an elastic cylinder with inserts and holes is treated. The bounded region outside the inserts and the holes will be termed a matrix. As is well-known the solution depends on finding plane harmonic functions in the matrix and inserts such that (a) on the outer boundary of the matrix and the boundaries of the holes the harmonic function in the matrix takes the values $\text{1}\text{2}\text{(x}{}^2\text{+y}{}^2\text{)+c}{}_{\mathrm{j}}$, and (b) on the interfaces of the matrix and the inserts relations exist between the harmonic functions and between their normal derivatives. Here (x, y) are the coordinates of the point on the boundary and c_j, are unknown constants. The usual methods are cumbersome and lengthy. In this paper a straightforward method is presented which is easily programmable. The numerical solution is obtained by evaluating a few integrals either analytically or numerically and solving a system of linear simultaneous equations. An example of a cylinder with an eccentric insert is given which substantiates the theory developed in this paper and is found to agree with known results. However, the method is general and may be applied to a variety of problems.     

Annealing effects on transition temperature of r.f. sputtered Bi-Sr-Ca-Cu-O thin films

High-T_c Bi-Sr-Ca-Cu-O thin films have been made on YSZ substrates by single-target r.f. sputtering. The target was prepared for a composition of Bi₄Sr₃Ca₃Cu₄O_x. The best film showed the onset of superconductivity at 83 K and zero resistance at 75 K. The dependence of T_c(o) of sputtered films on annealing conditions is studied in detail.     

Optimum dispersion map profile for a stable DM soliton system

This paper investigates the optimum dispersion map profile for stable DM soliton formation and propagation. Results of numerical analysis suggest that anomalous–normal–normal–anomalous (A-N-N-A) profile is the most suitable one for a dispersion map with perfect dispersion compensation. DM soliton stability and propagation behavior has been further explored for an undercompensated A-N-N-A profile which increases the distance for stable propagation but requires a positive initial chirp. The stability region has been identified for such DM links in the parametric space of residual dispersion and initial chirp. The study of DM soliton interaction and collision dynamics indicates that a DM soliton formed in such stable parametric space offers improved spectral efficiency as compared to the fundamental solitons.     

Dietary intake of metals by Mumbai adult population

Daily intake of 12 metals (Na, K, Ca, Cu, Zn, Fe, Mn, Mg, Pb, Cd, Co and Ni) by Mumbai adult population were assessed by analysing duplicate diet samples. These metals were determined by flame atomic absorption spectrophotometry (AAS) and stripping voltammetric techniques. A total of 250 diet samples containing 170 vegetarian diet and 80 non-vegetarian diet collected during April 2003 to March 2004 were analysed during this study. Daily dietary intakes of 2.4 g Na and 1.2 g K were observed for Mumbai adults. Daily dietary intakes of Ca, Cu, Zn, Fe, Mn and Mg were 367, 1.0, 6.3, 6.7, 2.0 and 304 mg, respectively. Pb, Cd, Co and Ni intakes by Mumbai adults were 32.3, 2.2, 2.2 and 108 microg/day, respectively. From this study it has been observed that the intake of toxic metals such as Pb, Cd and Ni is much lower than the tolerable daily intake derived from PTWI given by FAO/WHO and could not be considered harmful in this group of subjects. Daily intake of the studied 12 metals was found to be higher in non-vegetarian diet compared to the vegetarian diet (P<0.02, 0.01).     

Occupational radiation exposure due to norm in a rare-earth compounds production facility

In India, rare-earth compounds are produced from the beach sand mineral monazite. Caustic digestion of the mineral followed by selective acid extraction is the method used to separate composite rare-earth fraction. The composite rare-earth chloride contains low levels of natural radionuclides and is the starting material for individual rare-earth compounds which have wide applications. Activity concentrations in composite rare-earth compounds such as chlorides, fluorides, carbonates and oxides of Ce, Nd, Pr, Sm, Gd, etc. are presented in this paper. The external gamma exposure rates and airborne activity due to thorium and thoron progeny in the occupational environment are studied. The activity levels in liquid effluent are presented. The potential individual occupational dose is estimated to be 1.9 mSv per annum.     

Thorium in ilmenite and its radiological implications in the production of titanium dioxide

This study gives the results of measurements of (232)Th and (228)Ra in the titanium mineral ilmenite and its derived products and an assessment of related radiological issues in mineral separation and titanium dioxide production plants in India. The concentrations of (232)Th and (228)Ra in ilmenite, synthetic rutile and TiO2 are presented along with percent distribution of the radionuclides in different stages of process. External gamma exposure rates and airborne thorium levels in plants processing such minerals are studied. The study estimated a potential external gamma exposure of 1 mSv and an inhalation dose of 0.7 mSv annually to the occupational worker due to the presence of naturally occurring radioactive material in these industries. The concentrations of the nuclides in liquid effluent and solid wastes are analysed, and disequilibria with respect to (228)Ra are observed.     

Effect of aerosol carriers on ultrasonically prepared nanocrystalline ZnO powders

Nanocrystalline ZnO powders were synthesized using ultrasonic spraying and decomposition technique. The compressed air and pure oxygen were used as aerosol carriers. Effect of aerosol carriers on ultrasonically atomized nanocrystalline ZnO powders was studied. The powders were characterized using X-ray diffraction, transmission electron microscopy (TEM), electron diffraction, absorption spectroscopy and photoluminescence. The influence of air and oxygen on crystallite morphology was studied using TEM. It was confirmed from TEM analysis that the crystallites were nearly spherical in powder prepared in the presence of compressed air. In the presence of pure oxygen, the crystallites could acquire regular hexagonal shape. Complete hexagonal shapes may be due to sufficient (100%) supply of pure oxygen during the process of formation of ZnO nanocrystallite. The powder with regular shaped crystallites could be highly pure and also stoichiometric in nature. Pure oxygen could therefore be more advantageous as carrier than air for production of nanocrystalline ZnO powder. The effect of aerosol carriers (compressed air and pure oxygen) on crystallite morphology of nanocrystalline ZnO powders is reported in this article.     

Synthesis and Biological Studies of Dodecameric Cationic Antimicrobial Peptides Containing Tetrahydrofuran Amino Acids

We report here a concise route to synthesize various stereoisomers of tetrahydrofuran amino acids (TAAs) and the synthesis of TAA-containing linear cationic dodecapeptides. Some of these linear peptides show slightly better antimicrobial activities than their tetra- and octameric congeners, but no activity against Mycobacterium tuberculosis, for which octapeptides exhibited by far the best results; this implies that antibacterial activity is dependent on the length of these linear peptides. All the dodecapeptides described here were found to be toxic in nature against Vero cells. The study helps to delineate the optimal length of this series of linear peptides and select potential leads in the development of novel cationic peptide-based antibiotics.