Laminar flow in rectangular channels. Part I: Entry analysis. Part II: Numerical solution for a square channel?

Laminar incompressible flow in rectangular channels is considered. In Part I, the entry region is evaluated by a boundary layer/potential core analysis. It is shown that the three-dimensional displacement induced potential flow can be described with a pair of two-dimensional potential functions. Second-order boundary layer solutions, with and without surface mass transfer, are determined; an interesting secondary flow reversal is predicted. In Part II, numerical solutions are obtained for the viscous channel equations, which are derived from the asymptotic theory of Part I. A two stream function, velocity, vorticity system, independent of the Reynolds Number, is solved with a combined iterative ADI/point-relaxation numerical procedure. A single calculation applied for all Reynolds numbers, which appears only in the coordinate scaling. The axial flow behavior of Parts I and II are in good agreement in the asymptotic entry region where both analysis apply. Secondary flow reversal is calculated; however, the grid is too crude for quantitative comparisons. Numerical solutions are obtained until fully developed conditions are achieved. Agreement with experimental data is good.     

Urinary response toin vivo lipid peroxidation induced by vitamin E deficiency

Experiments were carried out to measure the urinary excretion of free and conjugated malonaldehyde (MDA) and other thiobarbituric acid reactive substances (TBARS) in vitamin E deficient and vitamin E supplemented rats. From both dietary groups, six TBA positive fractions were isolated, in addition to that containing free MDA, by high-performance liquid chromatography (HPLC) on a TSK-GEL G-1000PW column. Three of the fractions isolated were found to be significantly increased in vitamin E deficiency. After acid hydrolysis, only one of the above compounds produced free MDA which indicated the presence of derivatized MDA. Only this fraction exhibited fluorescence at excitation 370 nm and emission 450 nm. The five other fractions formed 2,4-dinitrophenylhydrazones (2,4-DNPH), indicating the presence of carbonyl groups, but the derivatized MDA fraction did not. No significant differences were found in free MDA levels between the vitamin E deficient and the vitamin E supplemented groups.     

Indigenous marine diatoms as novel sources of bioactive peptides with antihypertensive and antioxidant properties

Several bioactive compounds from microalgae have demonstrated diverse biological activities with positive effects on human health. However, the potential of bioactive peptides as functional foods is still undervalued. Therefore, the exploration of microalgae strains as sources of bioactive peptides could reveal strong and unique bioactivities, especially when these marine sources have never been explored before. For this aim, protein extracts from six indigenous marine diatoms were subjected to enzymatic hydrolysis using four proteases (flavourzyme, pepsin, papain and trypsin). The hydrolysates were then tested for angiotensin converting enzyme (ACE)-inhibitory, antioxidant and antihypertensive properties. Results showed that papain hydrolysates from all microalgae strains exhibited strong ACE-inhibitory activities and antioxidant properties. In particular, protein hydrolysates from Bellerochea malleus were found to reduce blood pressure properties of 17 mmHg after 5 days of oral administration to SHR animals. These results revealed the potential of bioactive peptides from indigenous marine diatoms for use as functional foods or nutraceuticals.     

The particulate Be/Pbxs and Th/Pbxs activity ratios as tracers for tidal-to-seasonal particle dynamics in the Gironde estuary (France): Implications for the budget of particle-associated contaminants

The short-lived natural radionuclides ⁷Be (T_1/2 = 53 days), ²³⁴Th_xs (T_1/2 = 24.1 days) and ²¹⁰Pb_xs (T_1/2 = 22.3 years), i.e. ²³⁴Th and ²¹⁰Pb in excesses of that supported within particles by the decay of their parent isotopes, were analysed in suspended particulate matter (SPM) to study the particle dynamics in the Gironde fluvial estuarine system (France), strongly impacted by heavy metal pollution. From surveys of this land-ocean interface in 2006 and 2007, we established a times series of these radioisotopes and of their activity ratios (⁷Be/²¹⁰Pb_xs and ²³⁴Th/²¹⁰Pb_xs ARs) in particles sampled under different hydrological conditions.The particulate ⁷Be/²¹⁰Pb_xs AR varies along the fluvial estuarine system mainly due to variations in ⁷Be activities, controlled by riverine, oceanic and atmospheric inputs and by resuspension of old ⁷Be-deficient sediments. These processes vary with river discharge, tidal cycle and season. Therefore, seasonal particle transport processes can be described using variations of the SPM ⁷Be/²¹⁰Pb_xs ARs.During high river discharge, the SPM ⁷Be/²¹⁰Pb_x ARs decrease from river to the ocean. The turbidity maximum zone (TMZ) is dispersed and the particles, and the associated contaminants, are rapidly transported from river to coastal waters, without significant retention within the TMZ. During low river discharge, the TMZ intrudes into the fluvial estuary, and the lowest ⁷Be/²¹⁰Pb_x ARs are observed there due to resuspension of ⁷Be-deficient sediments. Away from the TMZ, from the middle to lower estuary, SPM ⁷Be/²¹⁰Pb_x ARs increase, indicating that the particles have been recently tagged with ⁷Be. We explain this trend as being caused by marine input of dissolved radionuclides, as traced by SPM ²³⁴Th/²¹⁰Pb_xs ARs, followed by scavenging in the estuary. This result indicates that particle transport models based on ⁷Be and trace-metal budgets must consider oceanic dissolved inputs as an additional source of ⁷Be and, possibly, of contaminants to estuaries.     

Simultaneous Determination of Chlorophylls, Pheophytins, β-Carotene, Tocopherols, and Tocotrienols in Olive and Soybean Oils by High-performance Liquid Chromatography

A high‐performance liquid chromatographic method is described for the simultaneous measurement of chlorophylls, pheophytins, β‐carotene, tocopherols, and tocotrienols in vegetable oils using 2 spectrophotometers in series and 1 normal‐phase silica column. Oil samples were diluted in the mobile phase, isopropanol‐hexane (1.5:98.5 vol/vol), and injected directly onto the column. A programmable UV/Vis spectrophotometer was used to measure chlorophylls a and b, pheophytins a and b, and β‐carotene at their appropriate absorption maxima (430, 452, 409, 433, and 452 nm, respectively). α‐, γ‐, and δ‐tocopherols and α‐, γ‐, and δ‐tocotrienols were measured by fluorescence at 295‐nm excitation and 330‐nm emission. Samples of virgin olive oil, soybean oil, and palm oil were analyzed.     

Erosion Testing of Coatings for Aero Engine Compressor Components

The results from a comparative study of erosion resistance of various coatings and some material modification treatments for protecting compressor airfoils made of 17-4 PH stainless steel against sand erosion, are presented. Coatings based on either aluminum, nickel or titanium nitride and material modifications by ion implantation and cryogenic treatment were evaluated by dry particle erosion testing in accordance with the ASTM G76-83 Standard Practice, at different angles of impingement (30°, 60° and 90°). The TiN coatings applied by PVD techniques, were found to be the most erosion resistant. All the PVD deposition techniques appeared capable of producing durable coatings, but in degrees that varied with the deposition method and vendor. All the TiN coatings investigated proved more resistant to erosion at a 30° impingement angle. The implications for compressor airfoil applications are discussed.     

Reduction of all-trans-retinal limits regeneration of visual pigment in mice

Absorption of photons by pigments in photoreceptor cells results in photoisomerization of the chromophore, 11-cis-retinal, to all-trans-retinal and activation of opsin. Photolysed chromophore is converted back to the 11-cis-configuration via several enzymatic steps in photoreceptor and retinal pigment epithelial cells. We investigated the levels of retinoids in mouse retina during constant illumination and regeneration in the dark as a means of obtaining more information about the rate-limiting step of the visual cycle and about cycle intermediates that could be responsible for desensitization of the visual system. All-trans-retinal accumulated in the retinas during constant illumination and following flash illumination. Decay of all-trans-retinal in the dark following constant illumination occurred without substantial accumulation of all-trans-retinal, generated by constant approximately equal to visual pigment regeneration (t1/2 approximately 5 and t1/2 approximately 7 min, respectively). All-trans-retinal, generated by constant illumination, decayed approximately 3 times more rapidly than that generated by a flash and, as shown previously, the rate of rhodopsin regeneration following a flash was approximately 4 times slower than after constant illumination. The retinyl ester pool (> 95% all-trans-retinyl ester) did not show a statistically significant change in size or composition during illumination. In addition, constant illumination increased the amount of photoreceptor membrane-associated arrestin. The results suggest that the rate-limiting step of the visual cycle is the reduction of all-trans-retinal to all-trans-retinol by all-trans-retinol dehydrogenase. The accumulation of all-trans-retinal during illumination may be responsible, in part, for the reduction in sensitivity of the visual system that accompanies photobleaching and may contribute to the development of retinal pathology associated with light damage and aging.     

Mechanisms of opsin activation

Rhodopsin is constrained in an inactive conformation by interactions with 11-cis-retinal including formation of a protonated Schiff base with Lys296. Upon photoisomerization, major structural rearrangements that involve protonation of the active site Glu113 and cytoplasmic acidic residues, including Glu134, lead to the formation of the active form of the receptor, metarhodopsin II b, which decays to opsin. However, an activated receptor may be generated without illumination by addition of all-trans-retinal or its analogues to opsin, as measured in this study by the increased phosphorylation of opsin by rhodopsin kinase. The potency of stimulation depended on the chemical and isomeric nature of the analogues and the length of the polyene chain with all-trans-C17 aldehyde and all-trans-retinal being the most active and trans-C12 aldehyde being the least active. Certain cis-isomers, 11-cis-13-demethyl-retinal and 9-cis-C17 aldehyde, were also active. Most of the retinal analogues tested did not regenerate a spectrally identifiable pigment, and many were incapable of Schiff base formation (ketone, stable oximes, and Schiff base-derivatives of retinal). Thus, receptor activation resulted from formation of non-covalent complexes with opsin. pH titrations suggested that an equilibrium exists between partially active (protonated) and inactive (deprotonated) forms of opsin. These findings are consistent with a model in which protonation of one or more cytoplasmic carboxyl groups of opsin is essential for activity. Upon addition of retinoids, the partially active conformation of opsin is converted to a more active intermediate similar to metarhodopsin II b. The model provides an understanding of the structural requirements for opsin activation and an interpretation of the observed activities of natural and experimental opsin mutants.     

Role of minor constituents in the photooxidation of virgin olive oil

Virgin olive oil was photooxidized at 2 and 40°C and at fluorescent light intensities of 0, 620, 2710, and 5340 lux. As expected, higher fluorescent light intensities induced higher peroxide formation in the oil. The thiobarbituric acid reactive substances (TBARS) were found to be good indicators of photooxidation during the early stage of the reaction. Pheophytin A and β-carotene were light- and temperature-sensitive, whereas α-tocopherol and total polyphenols were mostly affected by light. Pheophytin A functioned as a photosensitizer, resulting in rapid oxidation of the oil. β-Carotene was a strong natural inhibitor of photooxidation for all light intensities at 2°C, suggesting quenching properties for singlet oxygen. However, β-carotene antioxidant activity was reduced at 40°C because of its rapid destruction.