Reduction of error in spectrophotometry of scattering media using polarization techniques

Scattering can result in erroneous determination of the concentrations of constituent absorbers in spectrophotometry. This is due to the relationship between attenuation and absorption coefficient becoming nonlinear; hence, the use of the Lambert-Beer law becomes invalid. It has previously been shown that application of polarization techniques can reduce these effects, resulting in a more linear relationship. Here we quantify the impact of this improvement on measurement of the ratio of concentrations for two general absorbing species and show that measurement using polarization-maintaining light is more accurate. This is performed using a generalized version of theory previously dependent on selection of isosbestic wavelengths. For the absorbing species and geometries considered here, the mean error on the estimation of absorber concentration ratio is 18.2% for the case of detection without polarization discrimination. When polarization-maintaining light is extracted, mean errors of 1.2% and 5.1% are achieved for linear and circular polarizations, respectively. The improvement provided by the polarization techniques is observed regardless of the illuminating wavelengths but is achieved at the expense of a reduced signal-to-noise ratio. Taking this into account, for the detection scheme considered with a detector well capacity of 4 x 10(5) electrons the improvement provided by linear polarization-maintaining light is reduced to a factor of 3.6 and for circular polarizations a factor of 2.2.     

Procedures to check the adjoint equations when using the method of steepest ascent

The method of steepest ascent is well documented in the literature [1]. However, its application to problems of high order (over 20) is not straightforward [2]. One problem that arises in the application of the method of steepest ascent, particularly to problems of high order and generally to problems of any order, is the pinpointing of errors in programming or in deriving the adjoint equations. This correspondence presents a systematic method for pinpointing such errors. First, a derivation of equations pertinent to the method of steepest ascent as developed by Bryson et al. [1] is presented. Then checks on the adjoints are followed by an illustrative example of the use of these checks.     

Help–A Computer System for Medical Decision Making

The medical record is maintained for the express purpose of enabling the physician to deliver better care to the patient. But its usefulness in achieving that purpose has often been hampered by its inflation with voluminous, unorganized notes, and test results. The medical profession has begun to recognize this, and work has recently been done in reviewing the structure of the medical record with hopes of making improvements.1 Based on what has been learned so far, it appears that the most effective record is one containing a broad data base including many investigative procedures, while at the same time focusing the physician's attention on problems or diagnoses derived from the data base.2 These problems express only the essential information derived from the data base–that information which forms the basis for the treatment regimen.     

IQ technology: an automated, high-throughput screening assay for kinase, phosphatase, and protease targets

IQ^® Technology, a homogeneous, universal-detection platform, originally designed for high-throughput screening (HTS) of kinases and phosphatases, has now been applied to protease screening. Representative enzymes from the major classes of proteases have been assayed in the IQ^® format. Enzyme activity and compound inhibition data are presented for such enzymes as Trypsin, Matrix Metalloproteinase 3 (MMP-3) and Calpain 1. The technology has been tested in 96- to 384- to 1536-well microplate formats and is universally suited for automated screening. IQ^® Technology is a direct, noncompetitive assay that does not require antibodies or radioisotopes. Fluorophore-labeled peptides are used as enzyme substrates. Kinase or phosphatase activity is quantified by direct measurement of the phosphorylation state of the substrate. For protease activity, cleavage is quantified with a peptide substrate containing a phospho-residue distal to the fluorphore. Cleavage of the substrate liberates the fluorphore-labeled terminus from the terminus containing the phospho-residue. Protease activity is measured by the change in fluorescence intensity that occurs when a proprietary compound binds specifically to phosphoryl groups on peptides and quenches the fluorescence. IQ^® Technology can be used with any peptide sequence and is insensitive to high concentrations of ATP and substrate. The IQ^® Technology has been validated against a large number of detergents, organics, and other reagents found in reaction mixtures and has been optimized for HTS applications exhibiting representative Z' values of 0.7.     

The heat storage potential of ethylenediammonium ditetramethoxyborate

The heat storage potential of ethylenediammonium ditetramethoxyborate, a white crystalline compound with a melting point of 82°C and a density of 0.86 g/cm³, has been examined. Experimental data give a value of 344 J/g for the heat of transition from solid to liquid. The potential of this compound as a heat storage material is discussed.     

Ionized serum calcium levels following combined treatment for cancer of the head and neck

Thyroid function may be reduced after treatment of cancer of the head and neck, and hypothyroidism is much more common after combination therapy. Whether hypoparathyroidism and subsequent hypocalcemia also occur after such treatment is unknown. Few related studies have been published in which changes in total serum calcium have been studied after cancer treatment with radioactive iodine or external radiation. Twenty-two disease-free head and neck cancer patients were studied, 1 to 3 years after multimodal treatment, to determine if changes in serum ionized calcium levels or thyroid function were present. Our results suggest that parathyroid function, as represented by ionized calcium levels remains normal after multimodality (surgery, radiation and/or chemotherapy) combined treatment.     

The programming language standards scene, ten years on Paper 16: C++

This paper, one of a simultaneously published set, describes the establishment in 1990 of the standards project for the object-oriented programming language C++, and the progress of the project to the end of 1993. C++ (pronounced ‘C-plus-plus’) is undoubtedly the most dynamically evolving high level programming language of the 1990s. From a handful of users in the early 1980s, usage was estimated at 400,000 in October 1991. Today it can only be guessed at, but extrapolation based on exponential growth suggests between three and five million in late 1993. Its approaching submission for ISO standardization (Draft International Standard in September 1994), and the provision of reasonably priced C/C++ compilers suggest that it will eventually supersede C as the most widely used general purpose programming language.