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[en] A new class of efficient stationary phase has been investigated for use in the liquid chromatographic separation of low molecular weight analytes and high molecular weight biomolecules, based on the application of immobilised stimuli-responsive polymers (SRPs). To this end, two polymeric units, namely poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(acrylic acid) (PAA) were tethered to a triazine core. The derived poly(2-dimethyl-aminoethyl methacrylate)-block-poly(acrylic acid) (PDMAEMA-b-PAA), as a diblock co-polymer, was then immobilised onto the surface of porous silica particles. The performance of this microparticulate adsorbent was evaluated under various temperature, ionic strength and/or pH conditions in packed columns in a high-performance liquid chromatography (HPLC) format. Baseline separations of a variety of low molecular weight analytes were achieved at different temperatures with this SRP-based adsorbent using 10 mM sodium phosphate buffer, pH 6.0, as the mobile phase. Moreover, when the ionic strength of the mobile phase was increased to 40 mM sodium phosphate buffer, pH 6.0, similar temperature changes resulted in further increases in resolution for the hydrophobic analytes. In addition, changes in the pH of the mobile phase from pH 6.0 to pH 8.0 led to significant changes in selectivity of the analytes, including reversal in their elution orders. Upon increasing the temperature, the retention times of all analytes decreased but without loss of resolution. These findings can be attributed to the consequence of the immobilised copolymer undergoing a phase transition at its lower critical solution temperature (LCST), which leads to changes in its solvated structure, including how the electrostatic, hydrophilic and hydrophobic regions/domains of the copolymer are exposed to the bulk mobile phase. Thermodynamic data were indicative of a temperature-related re-organisation of the structure of the immobilised PDMAEMA-b-PAA stationary phase with exothermic binding of the analytes occurring at temperatures below the lower critical solution temperature (LCST). In this manner; changes in the system temperature could directly be used to manipulate the adsorption and desorption behaviour of these analytes with this stimuli-responsive, polymer-modified porous silica stationary phase. Additional studies with several proteins further documented the versatility of these stimuli-responsive separation materials. The results indicated that these separations could be tuned by variation of the temperature with fully aqueous mobile phases at specific ionic strength and pH values, without the need to use an organic solvent as a component in the mobile phase. - Highlights: • A new class of stimuli-responsive separation materials has been evaluated. • Changes in temperature, pH or ionic strength can be used to affect separation. • Low and high molecular weight compounds, including proteins, efficiently separated. • Separations achieved using aqueous mobile phases without organic solvents needed.
[en] Growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe)radiation detectors have been described. Alpha-particle spectroscopy measurements and time resolved current transient measurements have yielded an average charge collection efficiency approaching 100 %. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of tellurium inclusions within the detector bulk. Further, it has been shown that the role of tellurium inclusions in degrading chargecollection is reduced with increasing values of bias voltage. The electron transit time was determined from time of flight measurements. From the dependence of drift velocity on applied electric field the electron mobility was found to be n = (718 55) cm2/Vs at room temperature.
[en] Doppler-free two-photon laser spectroscopy has been employed for excited transitions between the 1S and 2S states in muonium. An unambiguous signal could be observed. The frequency interval was determined to be Δν1S-2S = 2 455 529 002(33)(46) MHz, where the first error arises from statistics and the second one is due to systematic effects which mainly are related to the properties of the high power pulsed laser system. There is agreement with a prior less accurate independent experiment at KEK and with QED theory within two standard deviations. The Lamb shift contributions are tested at the 8 · 10-3 level. The muonium-hydrogen and muonium-deuterium isotope shifts of the 1S-2S transition have a high potential for a precise mass determination of the positive muon. The experiment yields at present m1S-2Sμ = 105.658 80(29)(43) MeV/c2
[en] A new experimental search for muonium-antimuonium conversion was conducted at the Paul Scherrer Institute, Villigen, Switzerland. The preliminary analysis yielded one event fulfilling all required criteria at an expected background of 1.7(2) events due to accidental coincidences. An upper limit for the conversion probability in 0.1 T magnetic field is extracted as 8·10-11 (90% CL)
[en] Resonance line narrowing up to 1/2 of the natural linewidth has been observed for microwave magnetic-resonance transitions between Zeeman levels of ground-state muonium at a strong magnetic field of 1.7 T. The observed lines are in good agreement with predicted line shapes and are useful for a precision determination of Δν and μμ/μp
[en] High precision measurements of two Zeeman hyperfine transitions in the ground state of muonium in a strong magnetic field have been made at LAMPF using microwave magnetic resonance spectroscopy and a resonance line narrowing technique. These determine the most precise values of the ground state hyperfine structure interval of muonium Δν=4463302 765(53) Hz (12 ppb) , and of the ratio of magnetic moments μμ/μp=3.183 34513(39) (120 ppb) , representing a factor of 3 improvement. Values of the mass ratio mμ/me and the fine structure constant α are derived from these results. copyright 1999 The American Physical Society
[en] A new experiment has been set up at the Paul Scherrer Institut to search for muonium to antimuonium conversion. No event was found to fulfil the requested signature which consists of the coincident detection of both constituents of the antiatom in its decay. Assuming an effective (V-A)x(V-A) type interaction an improved upper limit is established for the conversion probability of PbarMM≤8x10-9 (90% C.L.), which is almost 2 orders of magnitude lower compared to previous results and provides a sensitive test for theoretical extensions of the standard model. copyright 1996 The American Physical Society
[en] The 1s-2s energy interval in the muonium (μ+e-) atom has been measured by Doppler free two photon laser spectroscopy. A value of 2455528941.0(9.8) MHz has been obtained in good agreement with quantum electrodynamics (QED). The muon-electron mass ratio can be extracted and is found to be 206.76838(17). The measurement may also be interpreted as a determination of the muon-electron charge ratio as -1- 1.1(2.1). 10-9. Corresponding measurements in deuterium using the same experimental setup confirmed the validity of the applied analysis procedure