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PubMed2006

Theoretical realization of holey fiber with flat chromatic dispersion and large mode area: an intriguing defected approach.

We present a novel design approach for realizing holey fibers (HFs) with flat dispersion characteristics and large mode area based on the existence of an artificially defected air-hole ring in the cladding, and on the inclusion of additional defected air holes in the core of the fiber. This unique type of HF can be used for achieving remarkable flat dispersion characteristics as well as a large mode area, which are particularly useful for high-speed data transmission. The validation of the proposed design is done by adopting an efficient full-vectorial finite element method for optical characterization of HFs. The proposed fiber can be employed in reconfigurable optical transmission systems for performing wavelength division multiplexing operation. Typical characteristics of the proposed HF are a flattened dispersion of 6.3 +/- 0.5 ps/km/nm from 1.45 to 1.65 microm and an effective mode area as large as 100 microm2 in the same frequency range.

Journal Article↗
PubMed2006

Chromatic properties of horizontal and ganglion cell responses follow a dual gradient in cone opsin expression.

In guinea pig retina, immunostaining reveals a dual gradient of opsins: cones expressing opsin sensitive to medium wavelengths (M) predominate in the upper retina, whereas cones expressing opsin sensitive to shorter wavelengths (S) predominate in the lower retina. Whether these gradients correspond to functional gradients in postreceptoral neurons is essentially unknown. Using monochromatic flashes, we measured the relative weights with which M, S, and rod signals contribute to horizontal cell responses. For a background that produced 4.76 log10 photoisomerizations per rod per second (Rh*/rod/s), mean weights in superior retina were 52% (M), 2% (S), and 46% (rod). Mean weights in inferior retina were 9% (M), 50% (S), and 41% (rod). In superior retina, cone opsin weights agreed quantitatively with relative pigment density estimates from immunostaining. In inferior retina, cone opsin weights agreed qualitatively with relative pigment density estimates, but quantitative comparison was impossible because individual cones coexpress both opsins to varying and unquantifiable degrees. We further characterized the functional gradients in horizontal and brisk-transient ganglion cells using flickering stimuli produced by various mixtures of blue and green primary lights. Cone weights for both cell types resembled those obtained for horizontal cells using monochromatic flashes. Because the brisk-transient ganglion cell is thought to mediate behavioral detection of luminance contrast, our results are consistent with the hypothesis that the dual gradient of cone opsins assists achromatic contrast detection against different spectral backgrounds. In our preparation, rod responses did not completely saturate, even at background light levels typical of outdoor sunlight (5.14 log10 Rh*/rod/s).

Animals↗
PubMed1989

Neural mechanisms of chromatic adaptation in L-type cone horizontal cells of the carp retina.

When a background light is delivered, the responsiveness of horizontal cells to light stimulus initially lowers but subsequently recovers gradually as shown by the increase in response amplitude to test light. These changes of responsiveness are observed when white or close wavelengths are used for both the background and test lights. However, the response amplitude to blue-green test light was initially enhanced but decreased and reached a steady state after the onset of red background illumination. The mechanism causing such a change of test responses was studied in the luminosity-type cone horizontal cells. The initial response enhancement was accompanied by an increase of the slope of hyperpolarizing phase, while the subsequent decrease of response amplitude was caused by the advancement of the recovery phase. The advancement of the recovery phase was eliminated by gamma-aminobutyric acid (GABA) or Co2+ (50 microM), which blocks GABA-induced currents in cone terminals. Dopamine, which inhibits GABA release from horizontal cells, stimulated the advancement of the recovery phase. The time course of the hyperpolarizing phase was not affected by these agents. The enhancement and the subsequent decrease of test responses were also observed in 6-hydroxydopamine-treated retinae. The results suggest that the GABAergic feedback pathway from horizontal cells to cones advances the recovery phase of response to test light. It appears, therefore, that the feedback modifies the responsiveness of horizontal cells to light stimulus under a red background illumination. The mechanism enhancing response amplitude will be also discussed.

Adaptation, Physiological↗
PubMed1989

[Chromatic research on the spectral radiance factors of teeth. Maxillary anterior teeth].

This research used the spectroradiometer (Pritchard Model 1980 B) to measure the spectral radiance factors of women's maxillary anterior teeth. The following conclusions were reached: 1. The spectral distributions of the anterior teeth were all similar at the cervical, middle, and incisal areas respectively. Their spectral distributions ran in parallel at an almost equal distance, with the curves for the central incisor at the top, below which were those for the lateral incisor and the canine, respectively. 2. The spectral distribution of each area of the central incisor, lateral incisor, and the canine showed their respective distribution curves. The trends of these curves were almost the same for all areas of each tooth. 3. The spectral distribution of each measured portion for women resembled the corresponding portion for men. However, with the central incisor, the spectral distribution curves for women were in a higher position than those for men. With the lateral incisor and the canine, the spectral distribution curves for men were in a higher position than those for women. 4. The spectral distribution of the cervical area showed some absorptional bands, which were identical to those of hemoglobin. 5. Research of the spectral distribution of natural teeth is judged to be helpful in resolving the problem of metamerism.

Color↗
PubMed2004

[Chromatic study of all-ceramic crown--IPS Empress: difference of color by manufacturing technique and cements].

PURPOSE: In recent years,aesthetic appearance and function are called for and all-ceramic crowns are spreading. By choosing an all-ceramic crown the problem of metal ceramics is avoided. There are difficulties of color tone reproducibility of cervical margin and darkness of gingival margin. We examined IPS Empress also in various all-ceramic crowns. IPS Empress has high permeability a ceramic ingot of various color tones and excellent color tone reproducibility of natural teeth. Generally a layering technique is used for an anterior tooth and the staining technique is used for a molar. However the details are unknown We examined how differences of manufacturing method and cement affect the color tone of all ceramics clinically. METHODS: Two kinds of Empress crown were fabricated for a 27 year-old woman's upper left-side central incisors:the staining technique of IPS Empress and the layering technique of IPS Empress II. Various try-in pastes(transparent opaque white white and yellow) of VariolinkII of the IPS Empress System were used for cementing. Color was measured using a spectrophotometer CMS 35FS. The L*a*b* color system was used for showing a color. The right-side central incisors on the opposite side of the same name teeth were used for comparison. RESULTS: We analyzed the color difference (DeltaE* ab)with a natural tooth. Consequently when it had no cement of staining technique and was tranceparent small values were obtained. CONCLUSIONS: It is considered that the color tone can be adjusted by color cement. It is effective to use the staining technique for an anterior tooth crown depending on the case. The crown manufactured using the layering technique is not easily influenced by cement. The crown manufactured by the staining technique tends to be influenced by cement.

English Abstract↗
PubMed2006

[Chromatic study of all-ceramic restorations--influence of abutment tooth color on color tone of copings].

PURPOSE: Recently, the use of all-ceramic crowns has spread widely in clinical applications to meet the demand for both functional and esthetically-pleasing restorations. In making all-ceramic crowns, it is necessary to reproduce the shape and color near to those of the natural teeth. However, the color shades of abutments might influence the color of the copings which are made of material with high transparency. This study examined the influence of the color shades of the abutments on the final color of copings for three kinds of all-ceramic core materials: Empress, Empress 2 (IVOCLAR VIVADENT), and Procera AllCeram (Nobel Biocare). METHODS: Copings with 0.5 mm in thickness were fabricated by using Empress (TC1), Empress 2 (100), and Procera AllCeram (white) core materials for an upper-right central incisor. Abutments were made by using six kinds of die materials of the Empress system (ST1, ST2, ST3, ST5, ST8, ST9), gold-silver-palladium alloy, gold alloy, and experimental black body. Copings were inserted in each abutment and the final color of the central part of the buccal surface was measured using a spectrophotometer according to the L*a*b* color system. RESULTS: Regardless of the color shades of the abutments, the chroma values of the copings rose in the order of Empress, Empress 2, and Procera, and the values of lightness rose in the order of Empress, Procera, and Empress 2. When the final color of each coping measured under the wet and dry conditions were compared, the difference in chroma was great. CONCLUSIONS: Within the limitations of this study, the results suggest that the influence of the color shades of the abutments on the final color of the three kinds of copings is small in the order of Empress, Procera, and Empress 2. In clinical and dental laboratory operations, it is hoped to observe and measure the color of copings and restorations under the wet condition.

Ceramics↗
PubMed2005

Explanation for neon color effect in achromatic line segments on chromatic inducers based on the multiple interpretation hypothesis.

In van Tuijl's neon configurations, an achromatic line segment on a blue inducer produces yellowish illusory color in the illusory area. This illusion has been explained based on the idea of the complementary color induced by the blue inducer. However, it is proposed here that this illusion can be also explained by introducing the assumption that the visual system unconsciously interprets an achromatic color as information that is constituted by transparent and nontransparent colors. If this explanation is correct, not only this illusion, but also the simultaneous color contrast illusion can be explained without using the idea of the complementary color induction.

Adult↗
PubMed1980

Effects of multi-chromatic and achromatic targets and darts on throwing.

This study determined the effects of achromatic and multichromatic targets and darts on throwing. Subjects were 56 college men assigned to one of four dart-and-target throwing conditions as follows: white target--white darts, white target--multi-colored darts, multi-colored target--white darts, and multi-colored target--multi-colored darts. Subjects threw from 20 ft. using an overhand throwing pattern. The main effect of target color and the interaction of target color and dart color were significant. The results indicated that white backgrounds are superior to colored backgrounds. Also, the interactions of colored darts against a white background produced the best combination for performance. In target tasks which depend upon response-produced feedback, color of figures and background interact apparently to affect motor performance.

Adolescent↗
PubMed2004

Explanation for neon color effect of chromatic configurations on the basis of perceptual ambiguity in form and color.

Under reflected light conditions, we observed a neon color effect in a van Tuijl-type pattern for 30 combinations by pairing CMY inks. The results cannot be fully explained by Bressan's proposal as follows: (1) the illusory colors for the six configurations contradicted her predictions, (2) strong effects were not presented for complementary color pairs, and (3) for four configurations, the colors of line segments assimilated into those of the inducing patterns. Thus, the author proposes an hypothesis that the visual system treats neon color displays as ambiguous figures in form and color. This proposal can explain both illusory colors of the illusory area and those of the line segments themselves.

Color Perception↗