A scintillation counter for the measurement of extremely low specific beta activities has been developed which achieves its high sensitivity through the application of large amounts of radioactive substance, and the use of an efficient liquid scintillation phosphor. The counter can be used in two different ways; as a volume counter and as a multiple-sample counter. In the first type of counter the solid radioactive sample is mixed with the liquid phosphor to form a transparent paste; in the second type a smaller amount of solid sample is spread out on a large surface of cellophane and immersed in the scintillating fluid. Experiments have been made with K⁴⁰ , C¹⁴ , and S³⁵ to determine the range of application, sensitivity, and efficiency of the counters. The volume counter can be used to assay a wide variety of material and is especially suited for biological problems. Its sensitivity was found to be better than 10⁻¹¹ curies/gm., while that of the multiple-sample counter is of the order of 10⁻¹⁰ curies/gm.. These sensitivities can be measured with a good degree of reproducibility and are superior to the conventional methods, with the exception of the elaborate screen-wall counter method. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

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Thesis (M.S.)--University of Wisconsin--Madison, 1984. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 81-86).

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Metallo-beta-lactamases (MBLs) are members of the metallohydrolases family and constitute a very effective resistance mechanism employed by bacteria to escape the action of most beta-lactam antibiotics. Emergence of acquired MBLs among pathogenic species represents a major clinical threat, especially since no efficient inhibitors are available. On the basis of their primary structures, these enzymes have been subdivided in three subclasses (B1, B2 and B3). The enzyme studied in this work, termed BcII, is produced by Bacillus cereus, strain 569/H/9, and is the most studied MBL so far (class B1 ; 227 a.a. ; M.W. 24960 Da). It displays a binuclear active site centre, which can bind various metal ions (e.g. Co2+ and Cd2+), although Zn2+ is the natural cofactor used for beta-lactams hydrolysis. The first part of this work was dedicated to the characterization of the equilibrium folding properties of both the apo and holo forms of BcII. We used a variety of biophysical techniques, including absorbance, circular dichroism and intrinsic fluorescence spectroscopy, nuclear magnetic resonance (NMR), and mass spectrometry (MS). Interestingly, optical measurements revealed that although the apo and dizinc species exhibit undistinguishable tertiary structural organizations, the metal-depleted enzyme shows a significant decrease in its α-helical content, presumably associated with enhanced flexibility. The holoenzyme was found to be much more stable than the zinc-depleted form. Whereas the latter unfold according to a simple two-state mechanism, unfolding of the holoenzyme was found to be non-cooperative, with the population of intermediate species showing 3D structures very similar to the native species. Besides folding studies, we investigated the process of metal binding to BcII. Zinc binding was monitored using complementary techniques, including circular dichroism in the far UV, enzymatic activity measurements, competition with a chromophoric chelator, MS and NMR. Most noticeably, MS and NMR experiments, together with catalytic activity measurements demonstrated that two zinc ions bind cooperatively to the enzyme active site (with K1/K2 ≥ 5, indicating positive cooperativity) and hence that catalysis is associated with the dizinc enzyme species only. Furthermore, competitive experiments with the chromophoric chelator Mag-Fura-2 indicated K2 < 80 nM.

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This paper surveys the method of beta decomposition and the evolution of different type betas in Taiwan stock market. We break the unexpected market return into two different types of news term, which are the discount-rate news about the expected change of discount rate and the cash-flow news about the expected change of future cash dividends, and then, estimate the relationship between these two market news and the return of different cross-section industries. The traditional beta used in financial market is broken into two different betas with different risk price. Our study finds out some evidence about the change in the attitude of investors for our two news term that affect market return.