PubMed · 9064360
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R O West. 1997. Warm stethoscope.. https://pubmed.ncbi.nlm.nih.gov/9064360/
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A miniature broadband light source is a critical element in a spectrophotometric microsystem. The design, fabrication, and characterization of a highly stable, miniature broadband light source that comprises filaments of single-crystal silicon are presented. Electrical current versus voltage and radiant emittance spectra under constant voltage bias are measured and related to filament dimensions. A maximum stable operating temperature for these filaments is estimated to be 1200 K. Resistance drift is demonstrated to be less than 0.5% over a 10-h period of continuous operation with visible incandescence. Emittance spectra of a multifilament array, measured at three different electrical biases, are presented and shown to compare well with theoretical blackbody radiation spectra. A continuous, total radiated power of 10.7 mW was achieved with a 1 mm x 1 mm filament array with peak emittance at lambda=2.7 micrometers.
The effect of hydrostatic pressure on the secondary structure of recombinant human interferon-gamma (rhIFN-gamma) and its biologically inactive truncated form rhIFN-Delta C15 has been studied using Fourier-transform IR (FTIR) spectroscopy. In situ observation of the pressure-induced changes using the diamond anvil cell shows that the alpha-helical structure is mainly transformed into disordered structure at high pressure. Increasing pressure also induces the formation of a gel. Addition of 0.5 M MgCl(2) significantly reduces the pressure stability. Releasing the pressure below 300 MPa results in the formation of intermolecular antiparallel beta-sheets, which is seldom observed. This suggests that the intermolecular beta-sheet of rhIFN-gamma is stabilized by electrostatic interactions that are disrupted at high pressure. For comparison we also studied the effect of temperature. Temperature-induced changes reflect extensive transformation of alpha-helical structure into intermolecular antiparallel beta-sheet, as is usually observed for most proteins.
A comparison of the results obtained by applying three spectrophotometric methods (at fixed wavelength, second-derivative and multicomponent analysis) to the determination of gamma-oryzanol in rice bran oil is reported. At fixed wavelength the results are more accurate when using isopropyl alcohol, rather than n-heptane, to dilute the oil samples, because the absorption bands of gamma-oryzanol are red-shifted and the absorbance, measured at lambda(max)=327 nm, is less affected by the interference of the oil "matrix" (lambda(max)=314 nm in n-heptane).However, to obtain accurate results also in oils with a low content of gamma-oryzanol, it is necessary to perform the analysis using second-derivative ((2)D330.365) or multicomponent (lambda=310-360 nm) methods. The first one fully removes the interference of oil matrix whilst the second, which needs a specific computational program to process the spectrophotometric data, furnishes evidence the presence of some unexpected interference in the analysis and/or standards which are not representative of the analysed samples, from the square root of the sum of the squared differences at each point between the linear combination of the standards and the unknown spectra (RMS error).Finally, some aspects of the chemical, spectroscopic (UV, IR) and thermoanalytical (TG, DSC) behaviour of gamma-oryzanol and the values of the parameters which enable "computation" of its UV spectra are reported.