Synthesis of novel spiro[2.3]hexane carbocyclic nucleosides via enzymatic resolution

[reaction: see text] Novel R- and S-spiro[2.3]hexane nucleosides have been synthesized. The key step involved the Pseudomonas cepacia lipase catalyzed resolution of racemic compound 2, synthesized in seven steps starting from diethoxyketene and diethyl fumarate, to give (+)-acetate 3 and (-)-alcohol 13. (+)-Acetate 3 and (-)-acetate 14 were converted to R- and S-9-(6-hydroxymethylspiro[2.3]hexane)-4-adenine, respectively.     

Positive values of non-homogeneous indefinite quadratic forms of type (1,4)

Let Γ _r,n-r denote the infimum of all numbers Γ>0 such that for any real indefinite quadraticQ inn variables of type (r, n?r), determinantD≠0 and real numbersc ₁,…,c _n there exist (x ₁,…,x _n )≡(c ₁,…,c _n ) (mod 1) satisfying $$0< Q(x_1 ,...,x_n ) \leqslant (\Gamma \left| D \right|)^{1/n} .$$ . All the values of Γ _r,3 are known except Γ_1,4. It is shown that $$8 \leqslant \Gamma _{1,4} \leqslant 16.$$ .     

Determination of uranium isotopes in urine samples from radiation workers using 232U tracer, anion-exchange resin and alpha-spectrometry

Bioassay technique is used for the estimation of actinides present in the body based on the excretion rate of body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha-spectrometry requires pre-concentration of large volumes of urine. This paper deals with standardization of analytical method for the determination of U-isotopes in urine samples using anion-exchange resin and ²³²U tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of uranium along with calcium phosphate. Separation of U was carried out by Amberlite, IRA-400, anion-exchange resin. U-fraction was electrodeposited and activity estimated using tracer recovery by alpha-spectrometer. Eight routine urine samples of radiation workers were analyzed and consistent radiochemical tracer recovery was obtained in the range of 51% to 67% with a mean and standard deviation of 60% and 5.4%, respectively.     

Separation and determination of <Superscript>241</Superscript>Am in urine samples from radiation workers using PC88-A and alpha spectrometry

Bioassay technique is used for the estimation of actinides present in the body based on their excretion rate through body fluids. For occupational radiation workers urine assay is the preferred method for monitoring of chronic internal exposure. Determination of low concentrations of actinides such as plutonium, americium and uranium at low level of mBq in urine by alpha spectrometry requires pre-concentration of large volumes of urine. This article deals with standardization of analytical method for the determination of ²⁴¹Am isotope in urine samples using Extraction Chromatography (EC) and ²⁴³Am tracer for radiochemical recovery. The method involves oxidation of urine followed by co-precipitation of americium along with calcium phosphate. This precipitate after treatment is further subjected to calcium oxalate co-precipitation. Separation of Am was carried out by EC column prepared by PC88-A (2-ethyl hexyl phosphonic acid 2-ethyl hexyl monoester) adsorbed on microporous resin XAD-7 (PC88A-XAD7). Am-fraction was electro-deposited and activity estimated using tracer recovery by alpha spectrometer. Ten routine urine samples of radiation workers were analyzed and consistent radiochemical recovery was obtained in the range 44–60% with a mean and standard deviation of 51 and 4.7% respectively.     

Generation and detection of optical vortices using all fiber-optic system

We demonstrate simultaneous generation, propagation and detection of optical vortices using all fiber-optic system. A fiber-optic Y-coupler was used for generating spherical and doughnut beams, simultaneously. Gaussian (TEM₀₀) beam emitted from CW red He-Ne laser is coupled into the fiber coupler and is converted into vortex beam via second arm of fiber which propagates with azimuthal phase dependence having well defined orbital angular momentum. The phase structure of vortex beam was detected by interfering both the beams using simple fiber-optic interferometer. The present all fiber-optic system might find application for detecting, sensing physical parameters and is simple and cost effective for generating and detecting optical vortices.