Bleaching Properties Research Articles

Structured illumination microscopy: artefact analysis and reduction utilizing a parameter optimization approach

Practical applications of structured illumination microscopy (SIM) often suffer from various artefacts that result from imprecise instrumental hardware and certain bleaching properties of the sample. These artefacts can be observed as residual stripe patterns originating from the illumination grating. We investigated some significant causes of these artefacts and developed a correction approach that can be applied to images after acquisition. Most of the artefacts can be attributed to changes in illumination and detection intensities during acquisition. The proposed correction algorithm has been shown to be functional on noisy image data, and produces exceptional, artefact-free results in everyday laboratory work.

Fifth-order optical nonlinearity of pseudoisocyanine solution at 529 nm

Evidence of the interference between third- and fifth-order nonlinear optical processes is shown in the studies of pseudoisocyanine (PIC) dye aqueous solution using 529 nm radiation (t = 475 fs) and the Z -scan technique. The third-order nonlinear refractive index of the PIC solution was measured to be −8 × 10 −14 cm 2 W −1 .W e have shown th at PIC solution changes from being self-defocusing to self-focusing at high laser intensity that was attributed to the influence of fifth-order nonlinearity. The fifth-order nonlinear refractive index was measured to be 4 × 10 −24 cm 4 W −2 .T he bleaching properties of PIC solution were analysed, and the imaginary part of third-order nonlinear susceptibility was measured to be Im χ (3) =− 2 × 10 −12 esu.

Bleachability of Kraft Pulps from Earlywood and Latewood of Fast‐Growing Loblolly Pine

The pulping and bleaching properties of earlywood and latewood of a fast‐growing loblolly pine were studied. Under the same pulping condition, the kappa number of the latewood kraft pulp was higher than that of the earlywood. At around the same kappa number, the yield of the latewood was higher than that of the earlywood. The bleaching results showed that the latewood kraft pulp had lower bleachability than the earlywood kraft pulp, due to its thicker cell wall and slower leaching rate.

Modeling and analysis of bleaching processes in photo-excited chlorophyll solutions

Photo-bleaching phenomena occurring in chlorophyll- a (Chl- a) during irradiation with UV spectra sources were investigated. A general mathematical formalism was developed to quantify the chromophores spatio-temporal concentration in the irradiated solutions. The measured changes of the optical transmission in photo-excited solutions were used to evaluate the chromophores bleaching reaction rate. An empirical expression for the reaction rate is sought and combined with the mathematical model to characterize the bleaching properties of the chlorophyll solutions and their optical density recovery by diffusion after the irradiation.

Experimental and theoretical study of non-volatile photorefractive holograms in doubly doped LiNbO3:Fe:Cu

We report the bleaching properties of iron and copper co-doped lithium niobate crystals that are candidates for non-volatile holographic storage. In experiment, we propose a three-step recording/fixing scheme to realize non-volatile holographic storage in LiNbO 3 :Fe:Cu, which firstly uses two coherent red beams for recording, secondly one Bragg-matched red beam together with a uniform ultraviolet light for developing and thirdly a single red beam for fixing. In theory, we have considered not only the material response to the incidence light but also the response of the light to the medium. We present a theoretical model in which the two-center band-transport equations, the coupled-wave equations and the coherent readout are considered simultaneously. The time evolution of space–charge field and the optimal conditions for both processing and material prescriptions of holographic storage are analyzed numerically in detail. Which include the dopant concentrations, the oxidation/reduction states, the intensity ratio of the two red recording beams to the UV light.

Fabrication of Nanoporous WO[sub 3] Membranes and Their Electrochromic Properties

Highly ordered WO 3 nanohole-array membranes were fabricated by a two-step molding process using highly ordered anodic porous alumina as the starting material. The size and interval of the holes were controlled by changing the geometrical structure of the original porous alumina, and the depth of the holes by the amount of electrochemically deposited WO 3 . In terms of the electrochromic properties, the WO 3 nanohole-array membranes showed faster coloration and bleaching than flat WO 3 membranes of identical thickness. These coloration and bleaching properties also depended on the porosity of the WO 3 nanohole-array membranes.

Improvement in pulping and bleaching properties of xylem from transgenic tobacco plants

AbstractIn an attempt to improve the pulping properties of xylem pieces and the bleaching properties of the resultant pulp, we compared two lines of transgenic tobacco in which the biosynthesis of lignin had been altered by suppression of the activity of 4‐coumarate: CoA ligase (4CL). The results of Kraft pulping on a laboratory scale indicated that the xylem of transgenic tobacco exhibited a higher delignification efficiency than that of corresponding controls subjected to the same conditions. This facilitated delignification was accompanied by a high pulp yield, but there was no excessive degradation of cellulose in the pulp fibres. The unbleached pulps from the 4CL‐suppressed tobacco plants were easily bleached with a lower consumption of chemicals than was required for the controls. Furthermore, the strength and optical properties of handsheets prepared from the 4CL‐suppressed tobacco plants were similar to those of handsheets prepared from the controls. Our observations suggest that modification of lignin by genetic engineering of the suppression of 4CL activity should result in both an increased pulping yield and a saving of bleaching reagent.© 2002 Society of Chemical Industry

Magneto-optical and ODEPR investigations of native defects in substrate-free LT-MBE grown GaAs

As-grown substrate-free LT-GaAs (200°C) and annealed samples (up to 660°C) have been investigated with magnetic circular dichroism of absorption (MCDA) and optically detected electron paramagnetic resonance (MCDA-EPR) in K- and W-bands. MCDA-EPR spectra of all samples reveal several As Ga-related defects with different excitation spectra, that indicate their different structures in as-grown and annealed material. A strong change occurs in samples annealed above 400°C. The ODEPR spectra show another yet unknown defect which we attribute to a Ga vacancy-related defect. Samples annealed at 500°C exhibit EL2-like MCDA spectra. From the above band gap MCDA spectra of the EL2-like defects evidence is found for their low symmetry. The bleaching properties and spin-lattice relaxation times of the different As Ga-related defects were investigated and compared with the properties of the EL2 defect in bulk semi-insulating GaAs.

Depigmenting and bleaching agents: coping with hyperpigmentation

Since the introduction of hydroquinone as a skinlightening agent in 1961, several products with bleaching properties have been used for the treatment of pigmentary disorders of the skin.1 The most important medical indications for the use of these agents are melasma and postinflammatory hyperpigmentation, although they have also been used as alternative options for the treatment of ephelides, solar lentigenes, nevi, and lentigo maligna. This article reviews the most commonly used bleaching agents, discusses their mechanism of action, and focuses on their efficacy and safety in treating unwanted skin pigmentation. Based on our current knowledge, the ideal bleaching agent has to fulfill certain pharmacologic criteria. It should have a potent bleaching effect with a rapid time of onset (less than 2 to 3 months), carry no short- or long-term side effects, and lead to a permanent removal of undesired pigment. Most of the currently available bleaching or depigmenting agents cause a temporary removal of hyperpigmentation, which usually recurs after discontinuation of therapy. Presently, there are three categories of bleaching agents (Table 1): phenolic compounds, nonphenolic compounds, and combination formulas.

Bleaching Properties of Alumina-Pillared Acid-Activated Montmorillonite

AbstractThe bleaching of cottonseed oil by alumina-pillared (Al-pillared) acid-activated clays was investigated. Acid activation of a Ca-rich montmorillonite (CMS STx-1) following treatment with 1, 4, and 8 eq/L sulfuric-acid solutions, as well as subsequent pillaring with alumina, produces new materials. These materials have bleaching properties dependent upon the extent of activation of the clay prior to pillaring. The pillared acid-activated montmorillonites possessed higher bleaching efficiency compared to pillared products of the untreated clay. Mild activation of the montmorillonite matrix, pillaring with the Keggin ion [Al13O4(OH)24(H2O)12]7+, and calcination temperatures to 500°C produced materials with the best fractional degree of bleaching. Direct comparison to the performance of a commercial bleaching earth (Tonsil Optimum 214, Sud-Chemie AG. Moosburg, Germany) shows that the efficiency of the Al-pillared acid-activated montmorillonite may be improved. The optimization of the bleaching process is achieved via a judicious utilization of intermediate surface area, relatively high acidity, and enhanced pore volume.

Radioluminescence dating: the IR emission of feldspar

A new luminescence reader for radioluminescence (RL) measurements is presented. The system allows detection of RL emissions in the near infrared region (IR). Basic bleaching properties of the IR-RL emission of feldspars are investigated. Sunlight-bleaching experiments as a test for sensitivity changes are presented. IR-bleaching experiments were carried out to obtain information about the underlying physical processes of the IR-RL emission.

Kraft Pulping Properties ofAcacia mearnsiiandEucalyptus grandisGrown in Zimbabwe

SYNOPSIS Pulpwood samples from 8-year old Acacia mearnsii and Eucalyptus grandis plantations grown in Zimbabwe were evaluated for kraft pulping, bleaching and papermaking properties. The possibility of co-pulping the two species was also investigated. A. mearnsii had higher chip basic density than E. grandis, and required more active alkali to produce less pulp. At about the same Kappa number, the A. mearnsii pulp had lower strength properties but higher opacity. Pulps of both species could be bleached to an acceptable brightness. The results demonstrated that the conventional prejudice against the use of A. mearnsii as pulpwood in Zimbabwe may be undeserved. The species has superior pulpwood productivity and can be successfully co-pulped with E. grandis, the preferred hardwood pulpwood species in Zimbabwe.

Photo bleaching in Sm 2+ selectively doped epitaxial CaF 2 films

We present a study on the bleaching properties of Sm 2+ doped epitaxial CaF 2 films. Previously, the Sm 2+ emission in these films has been found to bleach partially under optical excitation. For a detailed investigation of the bleaching mechanism, single crystal CaF 2 films were grown on Si(111) surfaces by molecular beam epitaxy (MBE) and were selectively doped with Sm 2+ ions at various distances from the semiconductor/insulator interface. A correlation between the bleaching rate and the distance from the insulator-semiconductor interface could not been found. In addition, we find that the bleaching rate depends linearly on the intensity of the optical excitation and that the shape of the emission line is not altered during the bleaching process. Our results are discussed in the framework of photoionization due to excited-state absorption, tunneling of excited electrons into the semiconductor substrate, and the role of lattice defects.

The pathways of light measured in fundus reflectometry.

We measured the spectral reflectance of the fovea of ten normal subjects in four conditions, i.e. under dark-adapted and bleached conditions and at two retinal angles of incidence. The objective was to study optical pathways through the photoreceptor layer, resulting in a model that simultaneously explains spectral, directional and bleaching properties of the fovea. On theoretical grounds, we propose that small reflections from the stack of discs in the cone outer segments are the origin of the directional component of foveal reflection. Non-directional reflection occurs at the inner limiting membrane and at all layers posterior to the outer segments. With four reflectance spectra as input, the model allows determination of the density of the photostable absorbers, the lens, macular pigment, melanin and blood. Because of the simplified modeling of the layers posterior to the photoreceptor layer, the values for the density of melanin and blood are not necessarily comparable to physiological data. The density of the visual pigment calculated with this model is consistent with psychophysical data, with estimates for the ten subjects ranging from 0.41 to 0.80. The long wavelength sensitive cone fraction is calculated as 0.56.

Correlation structure-activity in the bleaching properties of peracetylated carbohydrates

Low temperature bleaching systems involving sodium perborate and an activator such as tetra acetyl ethylene diamine (TAED), with peracetic acid formation, are commonly used in Europe. Environmentally friendly bleaching agents such as carbohydrate derivatives (mono, oligo, anhydro saccharides, polyols and amino sugar acetates) could also be good products with bleaching activator properties. Correlation structure-reactivity was established; active acetyl groups were identified for each type of molecule in order to understand the effect of their nature and configuration, and to determine the role of neighbouring groups.

Bleaching kraft pulps with in-situ generated dioxiranes

The catalytic properties of aliphatic ketones to promote bleaching reactions of peroxymonosulfate with kraft softwood pulp was studied. The in-situ generation of substituted dioxiranes from keto compounds and peroxymonosulfate was demonstrated to be an effective bleaching technology. This bleaching system was shown to be very sensitive to the nature of the alkyl groups attached to the carbonyl group. Studies reported in this paper suggest that acetone may have the optimal structural features for catalyzing the bleaching properties of peroxymonosulfate

Comparison of stabilisers for wool bleaching with hydrogen peroxide

The physico‐chemical, environmental and bleaching properties of three different stabilisers for use in wool bleaching with hydrogen peroxide have been compared. The various factors influencing stabiliser choice are discussed.

Optical bleaching studies of quartz

The bleaching properties of a hydrothermal, Arkansas quartz are studied in detail. The thermoluminescence (TL) and phototransferred TL (PTTL) signals are examined as a function of wavelength, illumination time and temperature at which the sample is illuminated. We have also briefly studied the effects of pre-irradiation annealing on the sample. The results of these experiments are described and their relevance to the models for TL is discussed.

Optical Bleaching and Phototransfer of BeO TL Detector by Simulated Solar UV Light

Abstract The PTTL and optical bleaching properties of BeO detectors have been investigated as a possible technique for the epidemiological studies of solar UV radiation-induced skin cancer. BeO Thermalox 995 chips irradiated with 241Am alpha particles were exposed to UV light from a high pressure mercury lamp. The UV spectrum of the lamp was corrected approximately to the solar UV spectrum by means of an appropriate optical filter combination. The UV-induced bleaching of the TL glow signal as well as the phototransfer of second readout have been investigated as a function of UV exposure.

High-exposure dosimetry with LiF (TLD-100) by photo-acoustic spectrometry

Optical absorption of LiF:Mg, Ti (TLD-100) as-received and annealed powders was investigated in the 300-700 nm range by photo-acoustic spectrometry (PAS). Near-logarithmic behaviour was found between 3 kGy and 1 MGy for the observed absorption peaks at 380, 444 and 547 nm. Optical bleaching properties were studied with white light and monochromatic irradiations at 254 and 366 nm. Fading characteristics were determined. It is shown that PAS is an appropriate tool for measuring doses on powders, especially in the high-dose range. Suggestions are made for extending the dose range to lower levels. In this way LiF TLD-100 powder may be used continuously from the mu Gy (by thermoluminescent methods) to the MGy (by PAS) range.