Biomedical subjects

K Uchikawa

Publications and source records attributed to K Uchikawa.

52 records · Page 3Linked to original sources

PubMed1986

Accuracy of memory for brightness of colored lights measured with successive comparison method.

Successive and simultaneous brightness comparisons between test colors and a comparison white were performed to study how accurately the brightness of colored lights was maintained in memory. The test colors were monochromatic lights chosen from 410 to 670 nm and a white light. The stimulus duration was 1 sec, and test-comparison stimulus-onset asynchronies in successive comparisons were more than 11 sec depending on the experiments. The results show that the variability of successive brightness comparisons was 1.5-2.0 times greater than that of simultaneous brightness comparison. This degree of deterioration of brightness discrimination is reasonably consistent with those of hue and saturation discrimination previously reported. Brightness shifts in the darker direction were found for most colors.

Color Perception↗

PubMed1986

Temporal integration of chromatic double pulses for detection of equal-luminance wavelength changes.

Detection probabilities for wavelength changes were measured as functions of stimulus onset asynchrony (SOA) with the chromatic double-pulse method. Two test stimuli of a wavelength lambda t were successively exchanged with a reference stimulus of a wavelength lambda r in equal luminance for a short duration with a SOA. Durations were 5 and 50 msec, and the SOA varied between 5 or 50 and 2000 msec. Lambda r's were 571 and 518 nm, chosen from wavelengths near unique yellow and unique green so that wavelength difference delta lambda = lambda t - lambda r was perceived mainly as redness and greeness for lambda r = 571 nm and yellowness and blueness for lambda r = 518 nm. The results showed that temporal integration characteristics for these equal-luminance wavelength changes were quite consistent: complete integration with SOA up to 20 msec, partial integration with SOA between 20 and 200 msec, and probability integration with SOA greater than 200 msec. They did not show any inhibitory integration that was found for luminance changes.

Adult↗

PubMed1985

Structural study on teichoic acids of Listeria monocytogenes types 4a and 4d.

The chemical compositions of the cell walls obtained from 10 strains (serotypes 1a, 3a, 4a, 4b, 4c, 4d, 4e, 4e, 4f, 6, and 7) of Listeria monocytogenes were analyzed. These cell walls were shown to be mainly composed of peptidoglycan and ribitol teichoic acids. Considerable variations in the composition of neutral sugars were observed among these cell walls. Chemical and NMR analyses indicated that the teichoic acids from L. monocytogenes serotypes 4a and 4d are composed of the following repeating units: Formula: See Text.

Carbohydrate Conformation↗

PubMed1985

A common linkage saccharide unit between teichoic acids and peptidoglycan in cell walls of Bacillus coagulans.

Teichoic acid-glycopeptide complexes were isolated from lysozyme digests of the cell walls of Bacillus coagulans AHU 1631, AHU 1634, and AHU 1638, and the structure of the teichoic acid moieties and their linkage regions was studied. On treatment with hydrogen fluoride, each of the complexes gave a hexosamine-containing disaccharide, which was identified to be glucosyl(beta 1----4)N-acetylglucosamine, in addition to dephosphorylated repeating units of the teichoic acids, namely, galactosyl(alpha 1----2)glycerol and either galactosyl(alpha 1----2)[glucosyl(alpha 1----1/3)]glycerol (AHU 1638) or galactosyl(alpha 1----2)[glucosyl(beta 1----1/3)]glycerol (AHU 1631 and AHU 1634). From the results of Smith degradation, methylation analysis, and partial acid hydrolysis, the teichoic acids from these strains seem to have the same backbone chains composed of galactosyl(alpha 1----2)glycerol phosphate units joined by phosphodiester bonds at C-6 of the galactose residues. The presence of the disaccharide, glucosyl(beta 1----4)N-acetylglucosamine, in the linkage regions between teichoic acids and peptidoglycan was confirmed by the isolation of a disaccharide-linked glycopeptide fragment from each complex after treatment with mild alkali and of a teichoic acid-linked saccharide from each cell wall preparation after treatment with mild acid. Thus, it is concluded that despite structural differences in the glycosidic branches, the teichoic acids in the cell walls of the three strains are linked to peptidoglycan through a common linkage saccharide, glucosyl (beta 1----4) N-acetylglucosamine.

Bacillus↗

PubMed1985

Structure of acidic polysaccharide from cell wall of Propionibacterium acnes strain C7.

The structure of polysaccharide prepared by lysozyme digestion from the cell wall of Propionibacterium acnes strain C7 was examined. The polysaccharide fraction was composed of glucose, galactose, mannose, galactosamine, and diaminomannuronic acid in a molar ratio of 1:1:0.3:1:2. By Smith degradation of the polysaccharide, diaminouronic acid-containing fractions were obtained, and the configuration of diaminouronic acid was identified as 2,3-diacetamido-2,3-dideoxymannuronic acid [Man(NAc)2A] by means of 1H-NMR and 13C-NMR spectroscopic analyses. The results of analyses involving methylation and partial acid hydrolysis led to the conclusion that the polysaccharide has the repeating unit----6)Gal(alpha 1----4)Man(NAc)2A(beta 1----6)Glc(alpha 1----4)Man(NAc)2A (beta 1----3)GalNAc(beta 1--. In addition, a portion of the galactose residues were substituted at C-4 by alpha 1----2 linked mannotriose.

Cell Wall↗

PubMed1983

Purity discrimination: successive vs simultaneous comparison method.

Purity discrimination thresholds (delta p) were measured with successive (SOA = 3 sec) and simultaneous (SOA = 0 sec) comparison methods for seven dominant wavelengths; 410, 480, 500, 530, 570, 600 and 650 nm. The stimulus duration was 1 sec. The delta p values with the successive comparison method were found to be about 1.5-2.0 times larger than those obtained in the simultaneous case. The degree of purity discrimination deterioration shown in this study is similar to that of wavelength discrimination deterioration previously reported (Uchikawa and Ikeda, 1981, Vision Res. 21, 591-595). Saturation shifts of stimuli with the successive comparison method were also observed; these were toward increased saturation direction for most dominant wavelengths.

Adult↗

PubMed1982

Equating colors for saturation and brightness: the relationship to luminance.

With a modified step-by-step brightness-matching procedure, a series of colors, with dominant wavelengths from 400 to 670 nm, was adjusted so that the saturations and brightnesses of the colors appeared equal to those of the reference, which was a mixture of 570-nm and white light. The results show that equally bright and equally saturated colors are not equal in luminance. We also report a saturation function of spectral lights derived by utilizing these equally bright and equally saturated colors. Finally, our equally saturated colors do not plot as a circle in the 1976 CIE u', v' space, which indicates some limitations of this uniform chromaticity diagram.

Color↗

PubMed1982