Colour appearance in immersive three‐dimensional virtual environments

Technology is constantly evolving and, consequently, all the technological advances taking place are regularly integrated into the daily life of society. During recent years, there has been a trend towards virtual resources such as teleworking, telemedicine and e‐commerce. In many countries, this virtualisation process has been accelerated by the changing circumstances caused by the COVID‐19 pandemic. In any case, there is a growing demand for virtual systems, and virtual reality is a suitable field for the application of a multitude of solutions. However, advances in virtual reality occur without any regard to colour science, and there are several challenges to be overcome to improve the visual appearance and fidelity of colour reproduction in all types of related devices. This paper discusses three open issues related to the visual appearance and visual fidelity of virtual reality systems. We believe it is necessary to direct future research efforts in each of these directions to secure improvements in the visual fidelity of virtual reality systems.     

Bacteria Single-Cell and Photosensitizer Interaction Revealed by Quantitative Phase Imaging

Quantifying changes in bacteria cells in the presence of antibacterial treatment is one of the main challenges facing contemporary medicine; it is a challenge that is relevant for tackling issues pertaining to bacterial biofilm formation that substantially decreases susceptibility to biocidal agents. Three-dimensional label-free imaging and quantitative analysis of bacteria–photosensitizer interactions, crucial for antimicrobial photodynamic therapy, is still limited due to the use of conventional imaging techniques. We present a new method for investigating the alterations in living cells and quantitatively analyzing the process of bacteria photodynamic inactivation. Digital holographic tomography (DHT) was used for in situ examination of the response of Escherichia coli and Staphylococcus aureus to the accumulation of the photosensitizers immobilized in the copolymer revealed by the changes in the 3D refractive index distributions of single cells. Obtained results were confirmed by confocal microscopy and statistical analysis. We demonstrated that DHT enables real-time characterization of the subcellular structures, the biophysical processes, and the induced local changes of the intracellular density in a label-free manner and at sub-micrometer spatial resolution.     

Thermal effect of radiation on dye-doped polystyrene particles covered with a silver layer

The heating of laser-irradiated two-layer spherical particles is analyzed theoretically and numerically by solution of the heat conduction equation. The internal heat source function and temperature distributions are presented for particles composed of a dye-doped polystyrene core and a deposited silver shell. It is shown that the internal heat source function distributions inside such particles substantially depend on core radii and shell thicknesses. Therefore the same parameters also strongly influence the heating times of such particles. In particular, the increase in thickness of the surface silver layer can result both in reduction of the heating time of two-layer particles and in strong growth of the heating time.     

Highly efficient luminescence from a hybrid state found in strongly quantum confined PbS nanocrystals

We report that high quality PbS nanocrystals, synthesized in the strong quantum confinement regime, have quantum yields as high as 70% at room temperature. We use a combination of modelling and photoluminescence up-conversion to show that we obtain a nearly monodisperse size distribution. Nevertheless, the emission displays a large nonresonant Stokes shift. The magnitude of the Stokes shift is found to be directly proportional to the degree of quantum confinement, from which we establish that the emission results from the recombination of one quantum confined charge carrier with one localized or surface-trapped charge carrier. Furthermore, the surface state energy is found to lie outside the bulk bandgap so that surface-related emission only commences for strongly quantum confined nanocrystals, thus highlighting a regime where improved surface passivation becomes necessary.     

Photooxidative degradation of carboxylated poly(vinyl chloride)

Thin films of poly(vinyl chloride), PVC, and carboxylated poly(vinyl chloride), C-PVC, containing 1.8% of carboxyl groups were exposed to high energy ultraviolet radiation (λ = 254 nm) in laboratory conditions. The photochemical reactions in irradiated samples were studied by FTIR and UV–Vis spectroscopy, gel permeation chromatography and gravimetric estimation of insoluble gel. It was found that photodegradation and photocrosslinking in C-PVC is accelerated, whereas photodehydrochlorination is retarded comparing to these processes in PVC. Photooxidation investigated on the base of reaction leading to formation of hydroxyl groups is also more efficient in modified PVC. However, the total amount of carbonyl groups is much lower in UV-irradiated C-PVC than that in PVC. It indicates that competitive reactions (destruction of carboxyl groups and formation of new carbonyls) occur simultaneously in C-PVC chains. The influence of carbonyl groups on photochemical processes can be explained by an efficient Norrish I and II reactions as well as by energy transfer from absorbing species to weak chemical bonds.     

Physico-chemical properties of 3-methoxy-2-nitrobenzoates of some rare earth elements（Ⅲ）

The complexes of 3-methoxy-2-nitrobenzoates of Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Er(III) and Tm(III) with the formula: Ln(C8H6NO5)3·2H2O, where Ln=lanthanides(III), were synthesized and characterized by elemental analysis, Forier transform irtrared (FTIR) spectroscopy, magnetic and thermogravimetric studies and also by X-ray diffraction (XRD) measurements. The complexes had col- ours typical for Ln(III) ions. The carboxylate groups bound as bidentate chelating. On heating to 1173 K in air they decomposed in the same way, at first, dehydrated in one step to anhydrous salts, and then decomposed to the oxides of respective metals with intermediate formation of the oxycarbonates. The enthalpy values of the dehydration process changed from 133.72 to 44.50 kJ/mol. Their solubility in water at 293 K was of the order of 10-4 mol/dm3. The magnetic moments of analysed complexes were determined by Gouy’s method in the range of 76-303 K.     

The Antioxidant Activity and Oxidative Stability of Cold-Pressed Oils

In our study, we characterized the antioxidant activity and oxidative stability of cold-pressed macadamia, avocado, sesame, safflower, pumpkin, rose hip, Linola, flaxseed, walnut, hempseed, poppy, and milk thistle oils. The radical scavenging activity of the non-fractionated fresh oil, as well as the lipophilic and hydrophilic fractions of the oil was determined using a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay. The fatty acid composition of the fresh and stored oils was analyzed by gas chromatography. The acid value, peroxide value, p-anisidine value and conjugated diene and triene contents in the fresh oils, as well as in those stored throughout the whole period of their shelf life, were measured by CEN ISO methods. The antioxidant activity of the oils expressed as Trolox equivalent antioxidant capacity (TEAC), ranged from 0.17 to 2.32 mM. The lipophilic fractions of the oils were characterized by much higher antioxidant activity than the hydrophilic ones. There were no significant changes in fatty acid composition and only slight changes in the oxidative stability parameters of the oils during their shelf life. Through the assessment of the relationship between antiradical activity and the oxidative stability of oils, it is proposed that a DPPH assay predicts the formation of oxidation products in cold-pressed oils—however, the correlations differ in fractionated and nonfractionated oils.     

Effect of ripening stage on thiamin and riboflavin levels in lupin, pea and faba bean seeds

 Seeds of yellow pea lupin (Lupinus luteus L., cv. Juno), pea (Pisum sativum L., cv. Ergo) and faba bean (Vicia faba sp. minor Harz., cv. Tibo) were harvested at different stages of seed maturity. Changes in thiamin and riboflavin levels during growth and maturation were studied. The results obtained showed that thiamin and riboflavin were found in high abundance early in the development of lupins and peas, but that their content decreased during maturation. The thiamin content of faba bean seeds increased from 33 to 47 days after flowering (DAF), then a decrease was observed until 61 DAF; however, no significant differences between these levels in faba bean seeds harvested from 61 to 89 DAF were found. The riboflavin content of faba beans increased after 54 DAF, and no significant changes were observed between then and 89 DAF. The thiamin and riboflavin contents in lupin, pea and faba bean seeds during development were fitted to modelling curves in order to predict the vitamin content at different stages of maturity. Received: 17 July 1997     

Investigation on the Use of the Weakly Basic Polyacrylate AnionExchanger Amberlite IRA-68 for Sorption and Separation of Iminodiacetate Complexes of Rare Earth Elements

Based on the determined affinity series of rare earth element complexes with IMDA for the anion-exchangers, purification of macroquantities of Nd^3 from Y^3 , Sm^3 from Ho^3 , La^3 from Nd^3 and La^3 from Pr^3 on the weakly basic gel anion-exchanger Amberlite IRA-68 was studied. Using the presented method on 1 L of Amberlite IRA-68 in the acetate form, it is possible to obtain about 240 g Nd2O3 purified from Y2O3. Great difference in affinity of La^3 and Nd^3 as well as Pr^3 complexes for this anion-exchanger in the acetate form indicates the possibility of applying this process for purification of lanthanum on the increased scale. On 1 L of Amberihe IRA-68 in the acetate form it is possible to obtain about 1125 g La2O3 purified from Nd2O3. On the basis of these results it can be assumed that unique properties of polyacrylate anion-exchangers enable their application for separation of rare earth elements.     

Effect of high-fat cholesterol enriched diets on hypolipemic action of Oenothera paradoxa oil in rats. Part 2. Blood serum and liver fatty acids

The effect of Oenothera paradoxa oil on blood serum and liver fatty acids composition in rats was studied. Rats were fed high-fat diets containing 15% of lard or sunflower oil with or without 0.5% of cholesterol. Soybean protein isolate (27%) was the source of proteins. Intake of Oe. paradoxa oil resulted in increase of levels of gamma-linolenic acid (GLA) and linoleic acid (LA) in blood serum and liver of experimental animals. The effect of Oe. paradoxa oil on blood serum and liver fatty acids composition depended mainly on the type and to the lower degree on the amount of fat in a diet. The addition of cholesterol did not change the influence of examined oil on the composition of fatty acids.