The Optics of the Compound Eye of the Honeybee (Apis mellifera)

The optical system of the compound eye of the worker honeybee, as a representative of the closed-rhabdom type of eye, was investigated and its function analyzed. Measurements of refractive indices of the elements of the optical system were made with an interference microscope. With the use of the resulting measurements, the optical system was analyzed by means of a ray-tracing procedure implemented for the IBM 7094 digital computer, and by means of the Gaussian thick lens formulae. The more detailed results of the ray-tracing technique were used for further analyses. Direct visual confirmation of the focal point was obtained. The rhabdom and the surrounding zone of lower refractive index act together as a wave guide, as demonstrated by the presence of several wave guide modes in the rhabdom. An admittance function was defined as the percentage of the rays reaching the rhabdom with respect to those entering the ommatidium. Good agreement with experimental results was found. The characterization of the visual field of an ommatidium by means of an admittance function permits the analysis of the influence of different stimuli on the eye.     

Slow and fast invasion waves in a model of acid-mediated tumour growth

This work is concerned with a reaction-diffusion system that has been proposed as a model to describe acid-mediated cancer invasion. More precisely, we consider the properties of travelling waves that can be supported by such a system, and show that a rich variety of wave propagation dynamics, both fast and slow, is compatible with the model. In particular, asymptotic formulae for admissible wave profiles and bounds on their wave speeds are provided.     

Studies on the relations between pressure and flow in the circulation

Simple theoretical models are proposed for the study of the interdependence between cardiac contraction, arterial pressure, and capillary drainage. The relation between pressure and flow is derived for a model of branching distensible tubes taking into account the finite pulse wave velocity. Equations are derived both for the case where the pulse wave is non-distorted and for the case where the wave is damped and distorted to a limited extent. Following the model of J. W. Remington and W. F. Hamilton (1947), the former case is applied to the larger arteries. Expressions are developed for the stroke volume, cardiac ejection, and systolic arterial storage in both the steady and non-steady states. Expressions for the percentage discrepancy involved in the computation of these quantities from a single tube model as contrasted with a multi-branched model are derived. For typical cases these discrepancies are small and thus credence is lent to the further use of the simpler single tube model which requires fewer independent parameters. It is also shown that the formulae for stroke volume and arterial storage are only slightly sensitive to changes in pulse wave velocities, and that for some purposes it would seem permissible to assume an infinite velocity. The problem of capillary drainage is discussed, and the consequences of equations developed for the case of a distorted wave are shown to compare favorably with published experimental data. An approximate boundary condition for capillary drainage is derived. Finally, A. V. Hill's velocity load equation for muscle is used to obtain a first approximation for the velocity of cardiac contraction in terms of the initial arterial pressure, the heart radius, and the parameters of the heart musculature. It is shown how methods developed for stroke volume determination from the pressure contour may be used to estimate the heart and “air chamber” parameters. Use of these parameters and those obtained by other independent measurements permits the principle variables to be determined numerically.     

Multilamellar liposomes of triamcinolone acetonide: preparation,stability, and characterization

The aim of this study was to assess and characterize the stability of multilamellar liposomes as a delivery vehicle for triamcinolone acetonide. A standardized preparation method for a liposomal delivery vehicle was developed, after varying composition and storage conditions, and assessing encapsulation efficiency and loss of active principle. The assessment of temperature as a factor in formula stability during storage showed that stability improved under refrigeration (4–6°C) (less early diffusion of active principle through the liposomal wall), in comparison with samples stored at room temperature. To improve stability, cholesterol was added to some formulae, which although resulting in a decrease in average encapsulation efficiency, mitigated subsequent losses of retained active principle (formulae 4, 5, and 6), in comparison with those without cholesterol (formulae 1, 2, and 3). This was evident both under refrigerated and room-temperature conditions. Finally, after testing the effects of adding an antioxidant and/or preservative to the formulae, a liposomal design was achieved with acceptable stability, vesicle dimensions, and encapsulation efficiency.     

Selenium content of Spanish infant formulae and human milk: Influence of protein matrix, interactions with other trace elements and estimation of dietary intake by infants

The selenium content of infant formulae varies as a result of differences in the amount of intrinsic selenium compounds. Manufacturers have been gradually changing the protein profile of infant formulae to reflect human milk contents more closely. Because of these variations in infant formula composition and their potential impact on selenium content, this trace element was analysed with regard to the different protein sources.

The aims of this study were to determine the selenium content in infant formulae sold commercially in Spain, to estimate a daily dietary intake for infants fed on formulae and to compare with the selenium provided by Spanish breast milk samples used as a reference. We have also identified certain trace elements added to formulae which interact with selenium according to the type and protein matrix of the infant formulae.

Selenium concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES) with a hydride generator.

The selenium concentrations in human milk and infant formulae determined in this study are similar to those found by other researchers in different countries. The daily selenium intake from the formulae studied was estimated according to the recommended doses from the manufacturers. The theoretical selenium intake of nursed infants has been studied in relation to the Recommended Dietary Allowance (RDA: 10 μg Se/day) and the specific recommendations for infant formula nutrient contents (10–35 μg Se/L) set by the Expert Panel of Life Sciences Research Office (LSRO) of the American Society for Nutritional Sciences.

According to our results, on an overall view, infants fed on the studied infant formulae have an intake between basal and normative requirements. This might be considered as providing an adequate selenium supply. However, the intake of selenium provided by several formulae included in this research did not reach the RDA for the first month of neonate life.     

Substrate-dependent modulation of the enzymatic catalytic activity: Reduction of nitrate, chlorate and perchlorate by respiratory nitrate reductase from Marinobacter hydrocarbonoclasticus 617

The respiratory nitrate reductase complex (NarGHI) from Marinobacter hydrocarbonoclasticus 617 (Mh, formerly Pseudomonas nautica 617) catalyzes the reduction of nitrate to nitrite. This reaction is the first step of the denitrification pathway and is coupled to the quinone pool oxidation and proton translocation to the periplasm, which generates the proton motive force needed for ATP synthesis. The Mh NarGH water-soluble heterodimer has been purified and the kinetic and redox properties have been studied through in-solution enzyme kinetics, protein film voltammetry and spectropotentiometric redox titration. The kinetic parameters of Mh NarGH toward substrates and inhibitors are consistent with those reported for other respiratory nitrate reductases. Protein film voltammetry showed that at least two catalytically distinct forms of the enzyme, which depend on the applied potential, are responsible for substrate reduction. These two forms are affected differentially by the oxidizing substrate, as well as by pH and inhibitors. A new model for the potential dependence of the catalytic efficiency of Nars is proposed.     

Surface Plasmon Polariton Propagation at the Interface of a Metal and an Ambichiral Nanostructured Medium

The propagation of a surface plasmon polariton wave at the interface of a metal and an ambichiral nanostructured medium was theoretically investigated in the Kretschmann configuration using transfer matrix method. The dependence of optical absorption linear polarization on structural parameters was reported. The results were compared with those obtained from the interface of a metal and a chiral dielectric medium as a reference structure. We found that multiple plasmon modes are excited at the interface of metal and ambichiral dielectric medium. Our calculations revealed that there exist five plasmon modes for chiral, trigonal, and tetragonal structures; three plasmon modes for pentagonal structure; two plasmon modes for hexagonal structure; and one plasmon mode for dodecagonal structure that propagate with different phase speeds. The obtained results showed that only one plasmon mode occurs at all pitches, while other modes exist at some of the pitches of anisotropic chiral and ambichiral dielectric mediums. The time-averaged Poynting vector versus the thickness of metal film confirmed that the energy of photons of incident light is transferred to surface plasmon polariton quasiparticles and the surface plasmon polariton wave is localized at the interface of metal and ambichiral dielectric medium.     

Multiple-Wavelength Focusing and Demultiplexing Plasmonic Lens Based on Asymmetric Nanoslit Arrays

A multiple-wavelength focusing and demultiplexing plasmonic lens based on asymmetric nanoslit arrays is designed. The nanoslit arrays are perforated in a gold film and act as metal–insulator–metal plasmonic waveguides. By manipulating the widths of the slit arrays, the plasmonic lens can concentrate two incident plane wave beams to two separated focal points corresponding to their wavelengths. The full wave simulation is performed to verify the designed lens. This work provides a way to design more compact and integrated wavelength-division multiplexing plasmonic devices for nanophotonic communication and spectral imaging.     

A thin-film electrochemical study of the "blue" copper proteins,auracyanin A and auracyanin B,from the photosynthetic bacterium <Emphasis Type="Italic">Chloroflexus</Emphasis><Emphasis Type="Italic">aurantiacus</Emphasis>: the reduction potential as a function of pH

The reversible formal potentials of auracyanin A and auracyanin B, two closely related "blue" copper proteins from the photosynthetic bacterium Chloroflexus aurantiacus, have been determined by protein film voltammetry in the range 4相似文献   

Electrochemical analysis of the interactions and reactivity of ferrocene-based drugs with a lipid environment: A qualitative overview

Transport, reactivity and interactions of anti-tumor ferrocene-based compounds within lipid environments have been investigated electrochemically at a glassy carbon electrode (GCE) modified with a lipid bilayer film. Cyclic voltammetry performed in the presence of an adsorbed bilipid film in a H₂O/EtOH (8/2) mixture, clearly showed that the affinity of the starting neutral ferrocifen derivatives towards the lipidic bilayer depends on both their size and their polarity. Likewise, the electrogenerated ferrocenium derivatives were expulsed reversibly from the bilayer in agreement with their positive charge. The reactivity of ferrocifen compounds was also investigated under the same conditions and in the presence of a base in order to trigger an intramolecular ferrocene-mediated (−2e −2H⁺) process within the lipidic film. Under these conditions, two distinct sequential electrochemical behaviors were observed depending on the base availability in the lipid layer, the magnitude of the corresponding two electrons wave being limited by the base concentration in the film. A full two-electron oxidation process, was observed as long as the amount of base present into the lipid layer was high enough to titrate the two protons released in the two-electron process. When this was sub-stoichiometric a second wave was observed at higher potential values representing the one electron oxidation of the ferrocifen excess.     

Differentiating the orientations of photosynthetic reaction centers on Au electrodes linked by different bifunctional reagents

The photosynthetic reaction center (RC) composite film was fabricated by self-assembled monolayers (SAMs) on the Au electrode with two different bifunctional reagents, 4-aminothiophenol (ATP) and 2-mercaptoethylamine (MEA), respectively. The square wave voltametry (SWV), bulk electrolysis and photocurrent test were employed for characterizing the composite film. The dramatic different electrochemical characteristics were observed for the two types of films, which strongly suggested an orientational difference for RC arising from the structural difference between the two bifunctional reagents. For RC-MEA film, three redox peaks which implying electron transfer (ET) between the primary donor (P) and the bacteriopheophytin (Bphe) were observed. While for RC-ATP film, two redox peaks implying ET between the nonheme iron and the primary quinone (Q(A)) were observed. The ET behavior driven by electric field also supported the result that the RC could be linked to the electrode at different sites. The site-specific immobilization approach reported here supplies a method to differentiate the protein orientation.     

Factors affecting the errors in the estimation of evolutionary distances between sequences

Phylogenetic methods that use matrices of pairwise distances between sequences (e.g., neighbor joining) will only give accurate results when the initial estimates of the pairwise distances are accurate. For many different models of sequence evolution, analytical formulae are known that give estimates of the distance between two sequences as a function of the observed numbers of substitutions of various classes. These are often of a form that we call "log transform formulae". Errors in these distance estimates become larger as the time t since divergence of the two sequences increases. For long times, the log transform formulae can sometimes give divergent distance estimates when applied to finite sequences. We show that these errors become significant when t approximately 1/2 |lambda(max)|(-1) logN, where lambda(max) is the eigenvalue of the substitution rate matrix with the largest absolute value and N is the sequence length. Various likelihood-based methods have been proposed to estimate the values of parameters in rate matrices. If rate matrix parameters are known with reasonable accuracy, it is possible to use the maximum likelihood method to estimate evolutionary distances while keeping the rate parameters fixed. We show that errors in distances estimated in this way only become significant when t approximately 1/2 |lambda(1)|(-1) logN, where lambda(1) is the eigenvalue of the substitution rate matrix with the smallest nonzero absolute value. The accuracy of likelihood-based distance estimates is therefore much higher than those based on log transform formulae, particularly in cases where there is a large range of timescales involved in the rate matrix (e.g., when the ratio of transition to transversion rates is large). We discuss several practical ways of estimating the rate matrix parameters before distance calculation and hence of increasing the accuracy of distance estimates.     

Three-Dimensional Manipulations of Surface Plasmon Polariton Wave Propagation

The plasmonic integrated circuit, a potential application of surface plasmon polaritons (SPPs), can manipulate an SPP wave propagating on a metal surface in a way similar to electronic circuits. Here, we propose the concept of three-dimensional (3D) SPP wave manipulation: control of an SPP wave propagating in both the horizontal direction and the vertical direction. A hole set in the film can guide an SPP wave in the vertical direction. In the horizontal direction, two holographic groove patterns are used to focus an incident SPP wave on one surface of the film to the hole and control the divergent SPP waves transmitted from the hole on the other metal surface, respectively. The holographic groove patterns are designed via the methodology of surface electromagnetic wave holography. 3D finite-difference time-domain method simulations show a good performance of the 3D manipulation via these designed holographic groove patterns.

     

Generalization of the variance-covariance method for microdosimetric measurements

Numerical simulations in terms of microdosimetric data for 5-MeV neutrons are utilized to test the twin detector method of microdosimetric measurements in its new, extended form. Three different conditions of measurement are considered: (I) constant dose increments per measurement, (II) fluctuating dose increments per measurement, and (III) fluctuating dose increments combined with slow changes of the dose-rate ratio for the two detectors. Under each of the conditions, large numbers of measurement series are simulated, and the estimation formulae for the mean and the two subsequent moments of the dose-weighted single-event distribution, d(y), are applied. The estimation formulae exist in three different forms: uncorrected formulae that apply to condition I, corrected formulae that are valid also for condition II, and fully corrected formulae that remain applicable under condition III. The results of the simulations indicate the acceptable ranges of doses per measurement interval. It can be seen that all three parameters are obtainable through the twin detector method, and that the fully corrected formulae for the two lower moments are generally applicable. The determination of the third moment is possible only under limited conditions, and the fully corrected formula is not useful in this case, while the corrected formula has some applicability even under condition III. Received: 10 January 1996 / Accepted in revised form: 27 May 1996     

Ecological aspects of the surface microlayer. I. ATP,ADP, AMP contents,and energy charge ratios of microplanktonic communities

Forty samples of both the surface microlayer (60 to 100 μm) and underlying waters (0.5 m), were collected in a neritic area (Gulf of Marseilles, France) and their microplanktonic composition studied by adenosine, pigment, and organic carbon content. In the surface film, the accumulation of the living fraction was weaker than for inert organic matter; this phenomenon was more marked in the hydrological structures which are named “slicks”. The relationship between nucleotides and chlorophyll provided evidence for a substantial participation of heterotrophic organisms, such as bacteria, in the living biomass of the surface film. In this layer, lower values of the energy charge, as compared with those of water from 0.5 m may indicate the presence of stressed microorganisms. Nevertheless, as was shown by ATP data, part of hyponeustonic microbiomass was alive, and not killed by severe ecological conditions of this biotope. High AMP concentrations may be partially explained by a contribution of non-living organic matter, as was proved by the high enrichment factor for this adenosine form, higher than those of ATP and ADP, closer to those of phaeophytins, degrading products from chlorophylls. Adenylic nucleotide measurements in the paniculate matter of the surface microlayer, as their ratios and relations with chlorophyll, seem to be a practical tool for investigating the sea-air interface, from an ecological point of view.     

Colorimetry for the Stain Technologist. III. The Specification of Color Difference

This paper illustrates the calculation of color differences, involving luminance as well as chromaticity components. Color differences have been calculated for a large number of stained histological objects. Four different color difference formulae have been used, namely, those associated with the FMC 2, U*V*W*, L*u*v* and L^*a^*b^* systems. Comparison has first been made between various hematological substrates after staining with two different azure B-eosin Y stains. Next, comparison is made for the same substrates after staining with one of the azure B stains and a methylene blue-eosin Y stain. Pairwise comparison is also made of various substrates from the epithelium of the uterine cervix after Papanicolaou staining. Finally, pairwise comparison documents color differences accompanying maturation for the erythroid and myeloid cell lines in azure B-eosin Y stained bone marrow. The limitations of current color difference formulae are discussed.     

Surface behavior,microheterogeneity and adsorption equilibrium of myelin at the air-water interface

Interfacial films of whole myelin membrane adsorb at the air-water interface from myelin vesicles. The films show a liquid state and their equilibrium spreading pressure is equal to the collapse pressure (about 47 mN/m). The films appear microheterogeneous as seen by epifluorescence microscopy, consisting in two liquid phases over all the adsorption isotherm, starting with rounded liquid expanded domains (low surface pressure) immersed in a cholesterol enriched phase and reaching a fractal pattern at high surface pressure similar to those previously observed by compressing the film. Vesicles adsorb to the interfacial film mainly at the lateral interfaces. The high surface pressure at equilibrium (almost equal to the collapse pressure) indicates the formation of surface multilayers, also shown by fluorescence microscopy.     

Clades, clans, and reciprocal monophyly under neutral evolutionary models

The Yule model and the coalescent model are two neutral stochastic models for generating trees in phylogenetics and population genetics, respectively. Although these models are quite different, they lead to identical distributions concerning the probability that pre-specified groups of taxa form monophyletic groups (clades) in the tree. We extend earlier work to derive exact formulae for the probability of finding one or more groups of taxa as clades in a rooted tree, or as ‘clans’ in an unrooted tree. Our findings are relevant for calculating the statistical significance of observed monophyly and reciprocal monophyly in phylogenetics.     

Effects of elevation, wave exposure, and year on the proportion of gametophytes and tetrasporophytes in Mazzaella parksii (Rhodophyta, Gigartinaceae) populations

We investigated the effects of elevation, wave exposure, and year on the proportion of gametophytes and tetrasporophytes in populations of the intertidal red seaweed Mazzaella parksii (= M. cornucopiae, Gigartinaceae) from the Pacific coast of Canada. In July 2002, we determined the life-history phase of 864 frond samples from four populations from Barkley Sound, using the resorcinol-acetal test. For these populations, gametophytes were significantly more numerous than tetrasporophytes, and the proportion of gametophytes was significantly higher at higher elevations. The proportion of gametophytes varied directly (although less markedly) with the degree of wave exposure, but significance could not be assessed for this factor. All of these patterns were spatially consistent, as they held for two different rocky points with similar physical characteristics. One of these points had also been surveyed in 1994-1995, which allows us to conclude that the population-wise gametophyte predominance and the positive relationship between elevation and the proportion of gametophytes are stable features of this species in this area. However, the average proportion of gametophytes was similar between the studied levels of wave exposure in 1994–1995; such a difference revealed as non-significant when data were combined with those for 2002. This suggests that wave exposure is not important in determining the proportion of life-history phases for this species. Comparisons with other species are done in search of general patterns for the Gigartinaceae.