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At least 415 records · Page 23Linked to original sources
PubMed2000

Step-along vergence procedures in stigmatic and astigmatic systems.

The traditional step-along vergence procedure applies to stigmatic systems, that is, systems that are not astigmatic. Computation is disrupted when a focus coincides with a thin lens or refracting surface. A small change to the procedure results in a modified procedure which overcomes the computational problems. The modified procedure is easier to execute than the traditional procedure and allows one to write down useful equations directly. Among the formulae are those for back-vertex power. A step-along vergence procedure also exists for astigmatic systems. It makes use of the dioptric power matrix and the reduced vergence matrix. Computational problems arise when a point or line focus coincides with a thin lens or refracting surface; however they are not overcome by an analogous modification to the procedure. Nevertheless the modified procedure has some advantages including the fact that, as for stigmatic systems, it allows one to write down useful formulae directly. Stepwise calculations of vergence are sometimes performed backward through a system; the advantages and disadvantages described for step-along procedures holds for such step-back procedures as well.

Astigmatism↗
PubMed1998

[Recombinant growth hormone increasus callus maturation time in distraction osteogenesis--a histomorphometric study].

Purpose of the present study was, to proof whether homologous recombinant GH has an stimulating effect on bone healing in distraction osteogenesis. Therefore the left tibiae of 20 micropigs were osteotomized and distracted over an external fixator 2 mm daily on each of ten consecutive days. Animals were sacrificed after a healing time of another ten days. The treatment group received 100 micrograms r-pGH per kg bodyweight per day. After sacrifice, the regenerates were embedded undecalcified and cut into 6 microns thick sagittal oriented slices. Callus area, bone area, cartilagee area and bone perimeter in the regenerates were measured using an image analysis system. The results revealed, that GH promotes bone formation and maturation of the regenerate without disturbing the callus structure.

Animals↗
PubMed1992

Conformational regions of Boc-Ala-Aib-Ala-OMe. Sampling with molecular dynamics simulations using time averaging of distance restraints.

The method of time averaging of distance restraints in molecular dynamics simulations is applied to Boc-Ala-Aib-Ala-OMe in order to demonstrate the improved sampling properties of this method compared to conventional distance restraining. Two conformational regions, beta-turn type II and gamma-turn, are seen during MD runs at a simulation temperature of 500 K, while in simulations with conventional distance restraining, no conformational transitions could be observed for temperatures up to 1000 K.

Amino Acid Sequence↗
PubMed2005

Normalization for two-channel microarray data.

OBJECTIVES: In two-channel microarray experiments the measured gene expression levels are affected by many sources of systematic variation. Normalization refers to the process of removing such systematic sources of variation, to make measured intensities within and between slides comparable. Some commonly used normalization methods removing intensity-dependent dye bias and adjusting differences in variability between slides will be reviewed with the main focus on intensity-dependent normalization methods. METHODS: This article describes different intensity-dependent within-slide normalization methods for the log ratios of red and green channel intensities but also refers to single channel normalization methods incorporating all single channels of the slides at once. RESULTS: The described procedures provide a useful approach to remove systematic sources of variation like intensity-dependent dye bias and variability between slides in cDNA microarray experiments. This is illustrated by an experimental data set. CONCLUSIONS: Several reasonable normalization procedures for two-channel microarray data have recently been proposed. Deciding on which method would perform well for a concrete experiment is difficult. Designed spike-in experiments or dilution series with known differences for some selected genes would be helpful to assess the different methods, but may be impractical for most laboratories due to the high costs.

Algorithms↗
PubMed1991

Dimensional oscillation. A fast variation of energy embedding gives good results with the AMBER potential energy function.

The structure of the AMBER potential energy surface of the cyclic tetrapeptide cyclotetrasarcosyl is analyzed as a function of the dimensionality of coordinate space. It is found that the number of local energy minima decreases as the dimensionality of the space increases until some limit at which point equipotential subspaces appear. The applicability of energy embedding methods to finding global energy minima in this type of energy-conformation space is explored. Dimensional oscillation, a computationally fast variant of energy embedding is introduced and found to sample conformation space widely and to do a good job of finding global and near-global energy minima.

Computer Simulation↗
PubMed1991

Problem area formation as an element of computer aided diagnosis: a comparison of two strategies within quick medical reference (QMR).

INTERNIST-I's use of "partitioning" to group related diagnoses into problem areas (for competitive consideration and elimination during case analysis) is felt to be the source of many of its strengths as well as some of its weaknesses. QMR, INTERNIST-I's successor program, embodies a homology function which can act as an alternative to the partitioner for problem area formation. This study undertakes a comparison of the problem areas generated by the INTERNIST-I partitioning algorithm, the QMR homology function, and expert clinicians; it finds the correlation to be poor. The authors then discuss another method of problem area formation which might better mimic a human clinician and provide an alternative approach in diagnostic computer-aided decision making.

Algorithms↗
PubMed1989

Computer system and software of POSITOLOGICA II: a whole body positron emission tomograph.

Since a whole body PET-scanner POSITOLOGICA II was installed at the National Institute of Radiological Sciences (NIRS) in 1982, improvements of the computer system and developments of new software have been continuously made to correspond to clinical requirements. As the result, POSITOLOGICA II possesses one of the most powerful systems and sophisticated software in Japan. This report describes the present status of the computer system and software of POSITOLOGICA II. It also discusses problems which still exist and proposes a future computer system for the PET study.

Brain↗
PubMed1989

Reliability of the Cobb angle index derived by traditional and computer assisted methods.

The reliability of the traditional Cobb angle index, which at present exhibits a wide range of reported values, was determined in this study and amounted to a within subject error of +/-4.3 degrees and a between subject error of +/-4.9 degrees. An attempt to pinpoint the source of this variability by investigating the influence of choice of end vertebrae proved inconclusive. The reliability of a computer assisted Cobb angle index, developed to improve measurement accuracy, was also examined and an estimated within subject error of +/-1.5 degrees and a between subject error of +/-1.6 degrees obtained. A comparison of the traditional and computer assisted methods indicates a high correlation between the Cobb angle derived using the two methods when measuring like curves and an improved reliability obtained by the computer method. Such an improvement is worth implementing clinically but of course the availability of a computer and digitizer and a little extra time for an operator to input the X-ray coordinates may be a barrier to its general use.

Diagnostic Errors↗