Probable values of the cosmological constant in a holographic theory

We point out that for a large class of universes, holography implies that the most probable value for the cosmological constant is zero. In four space-time dimensions, the probability distribution takes the Baum-Hawking form, dP approximately exp(cM(2)(p)/Lambda)dLambda.

The use of a response surface methodology on HPLC analysis of methyldopa, amiloride and hydrochlorothiazide in tablets.

A multifactor optimisation technique is successfully applied to develop a new HPLC method in which methyldopa, hydrochlorothiazide and amiloride were analysed and determined on a C18 column with detection at 286 nm. The optimal conditions of HPLC separation were determined with the aid of the response surface diagram -- 'window diagram'. The effect of simultaneously varying the pH, proportion aqueous acetic acidum and methanol in the mobile phase were studied to optimise the separation. The mobile phase composition that provides an acceptable resolution methyldopa, hydrochlorothiazide and amiloride in a short elution time is water--methanol (75:25) and pH 3.60. The k' values for methyldopa, hydrochlorothiazide and amiloride after optimisation were 1.40, 2.50 and 5.33, respectively. Relative retention (alpha) for ratio hydrochlorothiazide/methyldopa and amiloride/hydrochlorothiazide were 1.767 and 2.159, respectively. Correlation coefficients of the calibration curves for all analytes were greater than 0.995 and the R.S.D. values for the slope and the intercept with respect to the linearity were less than 2%. A method is applied for the quantitative analysis of Alatan tablets (Lek-Ljubljana). The powdered tablets are extracted with methanol, containing caffeine as the internal standard and assayed by comparison of peak areas after liquid chromatography. The high recovery (for all analytes about 100%) and the low R.S.D. (<2%) confirm good precision and reproducibility of the chromatographic method.

Application of experimental design to the development of an HPLC method for the analysis of ochratoxin A in Triticum aestivum grain.

Ochratoxin A is a mycotoxin, a natural product of Aspergillus and Penicillium species. It can be present in grain from Triticum aestivum, (Graminae) and other starch-abundant cereals. This paper describes the investigation of ochratoxin A in grain from Triticum aestivum using a statistically optimized HPLC method. The assay was developed using two mathematical statistical models: factorial design and response surface mapping. The final step was to optimize the values of variables by response surface design. The analysis of variance 'ANOVA' method was applied to the analytical results in order to construct an adequate model. The optimal experimental conditions obtained by the response surface diagram method were: pH = 2.5, composition of the mobile phase acetonitrile: water 55:45 v/v and flow rate 1.0 ml/min. with a C18 column. Retention time and capacity factor for ochratotoxin A were 7.46 min. and 1.19, respectively.