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The interaction of an incoming slow neutron with a straight semi-infinite material waveguide (physically, a very lengthy one) located in vacuum (clad) in the infinite three-dimensional (3D) space is studied. The waveguide creates an attractive potential on the neutron. The physical quantum-mechanical wave phenomena are: (i) reflection and scattering of the neutron by the waveguide and (ii) its confined propagation along the latter, in specific propagation modes. The direct application of standard scattering integral equations meets several difficulties, arising mainly from the infinite length of the waveguide and (ii). New and more convenient 3D scattering integral equations are proposed and discussed, using suitable Green functions, adequate for the semi-infinite waveguide and accounting for (i) and the above difficulties. Approximate formulae for the probability amplitudes and fluxes for (i) and (ii) are given: in particular, the formulas for slow neutron confined propagation extend the ones given previously for optical waveguides. Some detailed applications and numerical computations for two-dimensional media and waveguides are presented.

Zusammenfassung Es wurden Untersuchungen uber die Besinflussung der Mikrobenpopulation des Wie-derkauerpansens durch ein Antibiotikum (”Terramycin„) durchgefuhrt. Als Unter-suchungsmethode diente das Verfahren des ”kiinstlichen Pansens„, jedoch mit natur-licher Pansenflussigkeit als Ausgangsmaterial, die von unter konstanten Haltungs-und Futterungsbedingungen lebenden Schafen gewonnen wurde. Der Ablauf der Pansenfunktion wurde an Hand der Zellulosezersetzung kontrolliert und auf den bestmoglichen Stand gebracht. Vor Beginn der Versuche und nach jeder Garungs-periode wurde die Mikrobenpopulation mikroskopisch und mikrobiologisch unter-sucht, z. B. ausgezahlt und ihren Arten nach charakterisiert. Jeder Garungsansatz wurde ohne (Kontrollen) und mit Zusatz von Terramycin und jeweils 3 Parallelen durchgefuhrt. In einer zweiten mit den gleichen Ansatzen ausgefuhrten Versuchsserie wurde von der 4. (jeweils 36stundigen) Garungsperiode ab jedem Ansatz 60 ml steri-lisierter und zentrifugierter Pansenflussigkeit (bei einem Gesamtvolumen von 350 ml) zur Unterstutzung der Widerstandskraft der Organismen hinzugegeben. Als Substrat der Garungen diente Heu. Terramycin wurde jeweils in einer Menge von 2 mg kristallisiertem Oxytetra-cyclin-hydrochlorid auf 350 ml Garungsvolumen hinzugegeben. Durch den Zusatz wurde zunachst das auch ohne ihn allmahlich vor sich gehende Verschwinden der Pro-tozoen (Ciliaten) erheblich beschleunigt, vermutlich durch Einwirkung auf die als Nahrung der Protozoen dienenden Bakterienarten. Die Variationsbreite der morphologisch differenzierten Bakterientypen gemas ihrer Fahigkeit, in der Plattenkultur Kolonien zu bilden, wurde durch Terramycin erheblich vermindert. Vollstandig unterdriickt wurden in jedem Falle, auch bei Zusatz von steriler Pansenflussigkeit, die zelluloseverdauenden Organismen, die sich sonst, wie die Kontrollen zeigten, bis zum Schlus der Versuche (324 Stunden lang) unver-mindert garungskraftig erhielten. Fur alle nach Moir und Masson klassifizierbaren Pansenbakterien wurde die Empfindlichkeit bzw. Widerstandskraft gegen Terramycin unter Versuchsbedingungen festgelegt. Im ganzen gesehen besteht eine wesentliche und wahrscheinlich weitgehend irreversible Einwirkung des Antibiotikums auf die Pansenflora, so das eine Anwendung in der Futterung von Wiederkauern, deren symbiontische Flora schon entwickelt und funktionsfahig ist, schwerwiegende Folgen haben mus. Es bedarf sicher weiterer ein-gehender Arbeiten. das genaue Ausmas dieser Einwirkungen festzustellen. Die Arbeit wurde durch Stipendien des Deutschen Akademischen Austausch-dienstes und des Consejo Superior de Investigaciones Cientificas, Madrid, ermoglicht und gefordert. Unserer besonderer Dank gilt weiterhin Herrn Prof. Dr. Richter vom Institut fur Tierernahrung der Forschungsanstalt fur Landwirtschaft, Braunschweig-Volken-rode, fur die Aufnahme in seinem Institut und die Zurverfugungstellung der Appa-rate und Einrichtungen, sowie Herrn Prof. Dr. Flaig und Herrn Dr. Kuster vom Institut fur Biochemie des Bodens der Forschungsanstalt, in dem der mikrobiologische Teil der Arbeiten durchgefuhrt wurde. Bei der Herstellung der deutschsprachigen Fassung unserer Arbeit wirkte Herr Prof. Dr. Becker vom Institut fur Tierernahrung mit.

In order to study the post-polymerization functionalization of a poly(N-substituted pyrrole) film, the β-ferrocene ethylamine used as redox probe has been immobilized via a chemical coupling on the surface of a preformed polypyrrole film bearing activated ester groups. From the electrochemical response of the anchored ferrocene units, the post-polymerization functionalization efficiency has been evaluated to be 20–22%. This level is the same whatever the length of spacer arm (2, 5 and 12 carbons) linking the activated ester groups to the polypyrrole backbone and the hydrophilic and hydrophobic nature of this polymer. Using a similar strategy based on this chemical grafting, we have developed a new approach to the immobilization of biotin entities onto the ester activated-polypyrrole film surface. From fluorescence measurements, it appears that the anchoring of streptavidine bearing a fluorophore (streptavidin-R-phycoerythrin, SAPE) on this biotinylated polypyrrole film gives a fluorescence intensity similar to the one achieved from the immobilization of SAPE onto a film electrosynthesized from pyrrole monomers bearing biotin units. Thus, this result shows the efficiency of this new functionalization method for attaching biotinylated entities.

The electrical deposition(electropolymerization)of polypyrrole, PPy, grafted by different ODN probes is the key to construct oligonucleotides, ODN, arrays on silicon devices bearing a matrix of gold microelectrodes. The straightforward functionalization of PPy allows finalizing a more general grafting based on affinity interactions between a biotinylated polypyrrole support and the biological probe and results in a surface renewable DNA sensor. The electrical monitoring of the thickness of the PPy deposit at the nanometer range allows the real time monitoring of the biological interactions using Surface Plasmon Resonance imaging. Recently, the electroconductivity of the PPy was exploited to trigger the electrochemiluminescence of a DNA sequence labelled with a luminol derivative, ABEI.

The silicon photonic wire evanescent field (PWEF) sensor platform offers the advantages of small sensor size, high levels of function integration, and low cost manufacturing that comes with the use of established semiconductor fabrication processes. The technology should be fully compatible with existing infrastructure in molecular analysis and research and the manufactured sensor array chip cost should be low enough that the chips can be considered disposable. Furthermore, since many applications require simultaneous monitoring of many different simultaneous binding reactions, the possibility of integrating tens or even hundreds of independent molecular sensors on a single disposable sensor chip is very compelling. We present an overview of our multiplexed photonic wire sensor chip and a reader instrument that allows up to 128 independent binding reactions to be monitored simultaneously. A complete photonic wire molecular biosensor microarray chip architecture and supporting instrumentation is discussed. This microarray system is used to demonstrate a multiplexed assay for serotyping E. coli bacteria based on polyclonal antibody probe molecules. A coherent detection scheme that enables direct read-out of the optical phase and an order of magnitude enhancement of sensitivity compared to conventional detection is also discussed. Finally, we present advances in Fourier-transform interferometer arrays for spectroscopic sensing. A planar waveguide Fourier-transform spectrometer with densely arrayed Mach-Zehnder interferometers is presented. Subwavelength gratings are used to produce an optical path difference without waveguide bends. The fabricated device comprises of an array of 32 Mach-Zehnder interferometers, which produce a spatial interferogram without any moving parts, yielding a spectral resolution of 50 pm and a free-spectral range of 0.78 nm. As a result of similar propagation losses in subwavelength grating waveguides and conventional strip waveguides, loss imbalance is minimized and high interferometric extinction ratio of -25 to -30 dB is obtained. Furthermore, phase and amplitude errors arising from normal fabrication variation are compensated by the spectral retrieval process using calibration measurements., 2014 16th International Conference on Transparent Optical Networks (ICTON), 6-10 July 2014, Graz, Austria

The exact cause of Alzheimer's disease and the part played in it by aluminum is still speculative. We have studied serum aluminum in 356 healthy people, and we have observed that serum aluminum concentration is increased in aging people in relation to age. We suggest that this could be associated with an enhanced gastric permeability or by an increase in metal accumulation proportional to age. We have measured serum aluminum levels in patients with probable Alzheimer's disease, patients with other senile dementias, and age-matched group. Patients with probable Alzheimer's disease have statistically significant higher serum aluminum levels than patients with other types of senile dementias (alcoholic, vascular, multi-infart) and an age-matched control group. When we compare serum aluminum of patients with senile dementias from other causes with the age-matched control group, we do not find significant differences.

The authors present a mathematical formalism for studying the behaviour of the total kernel of the Fresnel integral describing the diffraction of light by a cascaded linear system. The optical system is formed by an arbitrary number of optical devices with small aperture pupils and small axial thicknesses. The total diffracted field is formulated in the Fresnel regime. The boundary value problem and the convergence behaviour of the kernel are analysed. Numerical results are given for the spectrum of the kernel of certain systems of interest, namely, circular aperture, slit aperture, apodizing aperture pupil and grid aperture. The possibilities for a quantum representation in terms of Lie algebra operators are explored.

The aetiology and clinical features of peroxisomal diseases vary widely. An altered very-long-chain fatty acid (VLCFA) profile is commonly found in many of these diseases, and this makes it easier to point the diagnosis in the right direction.We review our experience in the diagnosis of cases of peroxisomal diseases with an altered VLCFA pattern; these were determined in serum only when there was a strong clinical suspicion up to the end of 1998, when their quantification by chromatography was introduced into our laboratory.The neuropaediatric database included 10,239 cases between May 1990 and 1st October 2007. Ten cases of peroxisomal disease with an altered VLCFA pattern were identified, all of them males. There were two cases of Zellweger syndrome spectrum, one unclassified peroxisomal oxidation defect and seven X-linked adrenoleukodystrophies (four with neurological compromise and three with no neurological damage; two were identified in siblings of patients and the other due to the presence of Addison's syndrome).In our 10 cases, the diagnosis was guided by the clinical or familial features that led to the determination of VLCFA. Being able to determine VLCFA makes early systematic diagnosis of patients possible. At present, VLCFA determination is performed when there is a clinical suspicion of Zellweger spectrum, suspected X-linked adrenoleukodystrophy/adrenomyeloneuropathy of unclear causation, Addison's disease, both in males and females, and above all in cases of chronic encephalopathy of unknown causation, with or without prenatal onset.

A programmable digital circuit typically consists of a microprocessor, a memory device, an input data device and an output data device, with its corresponding communication busses. These devices work following a program which is stored in the memory device, as codified instructions. An opto-electronic system that emulates a programmable digital circuit is proposed and described in this work. This circuit is commanded by a sequential program stored as a spatial distribution of Fourier Holograms into a photorefractive crystal. The sequential program is conformed by instructions, which have been codified as binary pixels maps. To read and decode each instruction, the spatial position of the photorefractive crystal must change; and then a CCD camera captures the output image of the Fourier Hologram. Our LabVIEW software decodes the instruction from the captured output image and it commands the circuit to realize the decoded instruction. This software controls the CCD camera and an electromechanical system which moves the spatial position of the photorefractive crystal. The electromechanical system is continuously in communication with a PC through our software. This is because the electronic circuit of the electromechanical system, moves three stepper motors; depending on the position in which the crystal needs to be to read the next instruction. The experimental results and the complete description of the practical advantages and disadvantages of the complete engineering system and the emulation of the opto-electronic programmable digital circuit will be described in this work.

We introduce the gyrator transform which produces a rotation of two‐dimensional signal in phase space. Main properties of this transform are considered. The flexible optical set up for gyrator transform experimental implementation is discussed. The applications of the gyrator transform to image processing such as filtering, noise reduction, encryption are demonstrated.

The electrochemiluminescence (ECL) of a luminol derivate (ABEI) generated both by a carbon electrode and a polypyrrole-coated carbon electrode was examined. It was found that the polypyrrole film (ppy) did not inhibit the ECL. After that, ABEI anchored on a single stranded DNA target (ODNt) has been used for the ECL detection of the hybridization between a complementary single stranded DNA probe (ODNp) covalently linked to a polypyrrole support and the ODNt. The ECL detection has been performed using a DNA sensor having a low surface concentration of ODNp probes, constituted of a polypyrrole copolymer electrosynthesized from a pyrrole-ODNp/pyrrole monomer ratio of 1/20,000.

The effects of aluminum on growth have been studied in rats chronically poisoned with aluminum hydroxide (80 mg/kg b.w.-i.p.-three times a week, during 6 months) and in control rats, between 3 and 26 weeks of age. The growth data was evaluated according to Parks 'theory of feeding an growth. At the end of the poisoning period, the calcium metabolism was studied through a balance of calcium and the determination of bone Ca++ accretion and resorption rates with the aid of 45Ca++. The parathyroid glands function was studied using an indirect method. Treated rats showed a significant decrease in asymptotic weights and in the initial efficiency of food conversion into biomass regarding controls. No differences were observed in food intake between both group. Aluminum affected neither the peak growth rate nor the time necessary to attain maturity. The calcium balance in treated rats was significantly less than in the control group. This was accompanied by a significant increase in the calcium excreted by faces, caused perhaps by a less intestinal absorption. An important amount of aluminum on the surface of the trabecular bone and a reduction in the skeletal Ca++ mass, was observed in all treated rats. Nevertheless there are no differences in the latter when expressed for 100 g of body weight. The rate of skeletal Ca++ accretion was found to be significantly decreased in treated group with respect to controls, without any changes in the bone Ca resorption rate. The reduction in bone turnover revealed by the decrease of Vo+/Vo- was accompanied by less recovery velocity of calcemia in the aluminum treated group, being indirectly related to the parathyroid gland response to calcium depletion. In the model that we studied the decreased bone turnover could have been caused by deposits of aluminum in bone; however there could exist associated factors such as dysfunction in the secretion of PTH, or less affinity between its receptors at the bone level.

In the Spanish Autonomous Community of Aragon, with about 1.200.000 inhabitants, there are currently 314 patients suffering from chronic renal failure (CRF). They are undergoing hemodialysis in 7 public hospitals. These centers centralize their controls of the aluminum (Al) levels in the patients’ sera and in the fluids used for dialysis in the “Unidad de Metales del Servicio de Bioquimica” of the Miguel Servet Hospital.

Rats and mice were inoculated by oral route with T. cruzi from: 1. Infected mice blood, 2. Experimentally infected triatomines feces, 3. Experimentally infected alive triatomines, and 4. Free cell cultures. Mice showed to be more susceptible to the infection than rats. Mice exhibited to be infected: 30% with blood forms, 85% with triatomines feces, 75% with alive triatomines and 35% with culture forms. Rats exhibited to be infected: 10%, with blood forms, 45% with triatomines feces, 60% with alive triatomines and 25% with culture forms. In both species we observed that metacyclic trypomastigotes originated higher infection percentage than blood and culture forms. With these results we confirm that oral route is a probable way of transmission of T. cruzi and under standardized conditions, it represents a better experimental inoculation route than intraperitoneal route.

Several anthropometrical, immunological and biochemical parameters have been utilized for the detection of chronic undernourishment and inflammation. The present work proposes a comparative study between a control group and other of 24 cardiac patients, with the intention of valuating their nutritional and inflammatory state. We have used the index proposed by Ingenbleek (PINI = prognostic inflammatory and nutritional index) in which nutritional scoreboards and biochemical inflammatories correlate. We find some statistically significant differences between cases and controls, both with regard to the value of the PINI, and with regard to each of this variables. In the same way, we do not find any important correlations within each group among the nutritional biochemical, inflammatory and anthropometrical parameters. The clinical impression shows that the classification by groups of risk obtained according to the value of the PINI is very near to reality. We consider that the PINI index is useful as a predictive and evolutive parameter, and it can be used in children with a chronic illness.

Introduccion. Las enfermedades peroxisomales tienen una gran heterogeneidad etiologica y clinica. Un perfil alterado de acidos grasos de cadena muy larga (AGCML) es comun a muchas de ellas, lo que facilita su orientacion diagnostica. Pacientes y metodos. Se revisa nuestra experiencia diagnostica en los casos de enfermedad peroxisomal con patron alterado de AGCML, que se determinaban en suero solo ante fuerte sospecha clinica hasta finales de 1998, fecha en que se introdujo en nuestro laboratorio su cuantificacion por cromatografia. Resultados. En la base de datos de neuropediatria de mayo de 1990 a 1 de octubre de 2007 figuran 10.239 casos. Se han identificado 10 casos de enfermedad peroxisomal con patron alterado de AGCML, todos varones: dos casos de espectro de sindrome de Zellweger, un defecto de la beta-oxidacion peroxisomal sin tipificar y siete adrenoleucodistrofias ligadas a X (cuatro con afectacion neurologica y tres sin dano neurologico; dos identificados por ser hermanos de enfermos y el otro por presentar un sindrome de Addison). Conclusiones. En nuestros 10 casos, el diagnostico se oriento por el cuadro clinico o familiar que llevo a la determinacion de AGCML. La disponibilidad de la determinacion de AGCML permite el diagnostico sistematico de pacientes de forma precoz. Actualmente, la realizamos ante sospecha clinica del espectro Zellweger, sospecha de adrenoleucodistrofia/adrenomieloneuropatia ligada a X, leucoencefalopatias de causa no aclarada, enfermedad de Addison, tanto en varones como mujeres, y ante toda encefalopatia cronica de causa no aclarada de inicio prenatal o no.

The following study has been carried out in order to assess the repercussion of surgery on fibronectin (F) levels and its course, whether or not septic complications are presented. The F, albumin (ALB), prealbumin (PREALB), retinol binding protein (RBP) and alpha-1-glycoprotein (GLYCO) levels were controlled in 37 patients (29 undergoing scheduled digestive tract surgery and 8 undergoing heart surgery), through preoperative and postoperative tests every three days. A group of 40 healthy controls was taken as reference. Group I contained 19 patients free of septic complications, statistically significant changes were observed in PREALB and RBP levels but not in F, although a decrease was observed which return to normal by the third test. Group II contained 18 patients which were subdivided into: a) 12 patients suffering from brief septic complication without known focus of infection and, b) 6 patients suffering from more severe septic complication with known focus of infection. The IIA subgroup showed a significant decrease in all protein levels, returning to normal levels by the sixth or seventh day. Subgroup IIB showed lower F levels, which did not return to normal before the ninth day. CONCLUSION. Preoperative controls were similar in I and IIa, while IIB showed significantly lower values. Although F decreased in the first preoperative control, it was not statistically significant. Patients not suffering from complications showed F recuperation within the first week, which was not the case of septic patients. Due to the wide number of functions of F and of the factors that influence it, we believe it should not be interpreted on a single basis a nutritional parameters.

In a few earlier communications, spatial-transverse-impulse response (STIR) associated with the initial field transversely distributed across the entrance pupil of an inhomogeneous optical wave guide (photoreceptor) has been investigated. In the present work, effects of indetermination in the location of the origin on an arbitrarily defined refractive index profile, representing the degree of inhomogeity at the aperture pupil of a single receptor, have been studied. Some consequences related to a few possible technical applications have been discussed.

Rigorous approximation techniques for the scattering of a classical electromagnetic wave by fixed obstacles are studied. For that purpose, a new Green's function G^T is introduced, which is divergenceless throughout all space and, hence, less singular at short distances than the one commonly used Γ. The two scattering integral equations for the total electric field with G^T and Γ respectively, as well as their iterations, are studied comparatively. It is concluded that the iterations of the integral equation containing G^T converge under more general conditions than those for the one containing Γ, so that G^T is, for rigorous studies, more suitable than Γ.

The scattering of electromagnetic waves by an infinite dielectric cylinder with variable dielectric permeability presents, in general, certain mathematical difficulties regarding the construction of rigorous solutions. We give a new divergenceless tensorGreen’s function, specially appropriate for cylindrical symmetry, and, in terms of it, present new scattering integral equations. We prove that the series for med by all successive iterations of those scattering integral equations converge under certain conditions. Suitable transformations lead to new integral equations with Hilbert–Schmidt kernels, which imply further rigorous results.

The interaction and diffraction of a classical electromagnetic wave by a thin slab characterised by a periodic dielectric permeability is studied rigorously, thereby completing previously existing studies. New integral equations for the induction vector in terms of a suitable Green function, are presented, and a condition which ensures the convergence of their iterations is obtained. A bound for the error of the usual Debye-Born-Rayleigh-Gans approximation to the diffraction amplitudes is given.

The coupling in the Holocoupler-Selfoc fiber system is studied using a new matrix method, which may be applied to arbitrary x,y,z - varying structures. The properties of the spatial transfer function for invariant linear system are used.

An exact treatment of the initial field falling on the entrance face of a photoreceptor, so that the scattered field far from the latter vanishes, is presented. Its physical interest and some consequences are discussed. By establishing certain similarities between the behaviour of the photoreceptor as light penetrates into and propagates along, and an optical linear system, it is possible to define a spatial transverse impulse response containing information on the diffraction capability of each individual receptor. The distribution of this function across a transverse plane depends upon the particular form of the refractive index in the photoreceptor. Thus, certain differences are seen to occur between the case of an homogeneous receptor and an inhomogeneous one, for particular values in the degree of inhomogeneity. This fact allows to interpret the presence of inhomogeneities in the photoreceptor structure.

Neurological complications of dissecting aneurysm of the aorta are not frequently described in the literature. A case of infarction of the spinal cord secondary to aortic aneurysm is presented. The ischemic zone extended from D5-D6 to L2-L3, showing the typical double-funnel-like configuration. Such localization is explained by the blood circulation in the spinal cord. The rupture of a dissecting aortic aneurysm in the toracic and abdominal tract, by occluding the segmental branches to the spinal cord, causes a decrease in blood flow which is responsible for the neurological manifestations. In the present case ischemia is mainly due to the involvement of the artery of Adamkiewicz, while the relative sparing found at the inferior lumbar level is justified by the existence of vessels which take origin below the aneurysm and are tributary to the cauda equina. The histological findings are in agreement with previous observations of a selective necrosis of the gray matter.

The Optical Transfer Function of a flexible conventional fibroscope to be used for "in vivo" image transmission has been calculated and numerically analized through available experimental data. The results are derived from an earlier generalized study for gradient index optical media. A criterion to determine the image quality is established and discussed

We present here numerical estimates of the density and flux of energy based on physical parameters associated with the absorption properties of certain types of absorbing optical waveguides. These results are based on a theoretical formalism established previously for the initial field incident upon the entrance pupil of an absorbing optical waveguide. Based on these results, the mechanisms of confined energy transmission and possible cross talk between neighboring waveguides are discussed. Some comments on the behavior of Bessel functions with complex arguments are also included in the discussion.

A three-dimensional analysis of bending losses in dielectric optical waveguides is presented. It constitutes a nontrivial generalization of previous two- and three-dimensional studies by other authors. Our analysis is based on homogeneous integral equations for the total radiation field and suitable asymptotic approximations for Green’s functions. A key role is played by a new three-dimensional approximation for a relevant Bessel function with large order and argument (the former being larger than the latter). A nontrivial check of the consistency of all those approximations is given. General formulas are presented for the radiated field and the energy flow and for a bending-loss coefficient in three dimensions. Numerical results are also given, in order to assess the difference between the results of other authors and ours. Such a difference is rather small for monomode behavior near cutoff, increases as the behavior of the waveguide changes from monomode to multimode, and decreases as the parameter V increases for a given core radius and propagation mode.

The authors present a mathematically exact formulation of the initial field striking the aperture of an absorbing optical waveguide, via an integral equation description. An analysis of the residual scattering by the waveguide is presented. Because of the presence of the non-negligible absorption coefficient, the solution for the fraction of the confined power is obtained by performing non-trivial integrations of Bessel and Hankel functions with complex arguments. In order to carry out a numerical analysis a specific computational method is applied by using an approximated polynomial expansion whose validity is also discussed.

We outline ,a systematic procedure for formulating the general transfer function of a compound optical system working in the Fresnel regime.

For pt.I see ibid., vol.17, p.475 (1984). The possible confined propagation of slow (thermal) neutrons along cladded waveguides of small cross section (fibres) is studied, in order to improve a previously published analysis. Quite suitable possibilities for the core of the waveguide could be either Al or Si (or vacuum), so as to allow for confined propagation of neutrons along reasonable lengths, without large scattering and absorption losses. Tentative possibilities for the cladding could be either Ni or Fe. The bending losses are analysed for a curved neutron fibre in two spatial dimensions. Such bending losses turn out to be completely negligible, except in the case of a small radius of curvature Rc. To quote some typical values, for any fibre diameter between 0.1 and 1 mu m and reasonable lengths for it (between 5 and 10 cm), bending losses can be neglected other than for Rc

The mathematical treatment involving Fresnel diffraction in compound linear optical systems presents difficulties due to the high degree of oscillations of the Fresnel integral kernel. Also, it is necessary to impose small pupil dimensions on the elements forming the compound system. A revised formulation for the general system having an arbitrary number of elements and generalized pupil functions allows one to represent the kernel in terms of convolution operations. This leads to a compact representation using Lie algebra operators.

It is known that the cones and rods of the retina have directional sensitivity. For a normal observer, in the absence of aberrations like myopia, astigmatism, etc. the light entering the pupil of the eye is directly focussed on the retinal plane by the optical system of the eye. There, in the retina, the cones and the rods are regularly distributed in different retinal regions forming a mosaic structure. It is very well established from the earlier works of Enoch, (1), that both types of optical photoreceptors act as optical waveguides. This behaviour can be accounted for due to their special optical properties allowing conditions for total internal reflections inside its structure. At the time of the confinement of the energy inside each single receptor an important phenomenon of orientation takes place as well. In this work, we wish to establish that the various effects arising out of this phenomenon can be interpreted in terms of a possible apodising action of the eye.It will be shown that an improvement in the resolution of the retinal image detection is possible by comparing the human visual system with an apodised optical system. For that purpose we have established a linear array model for a section of the fovea, ( all receptors having the same geometry and optical properties ), then, we have calculated the distribution of the density of energy captured in this particular section of the retina, by assuming that the receptors are acting as monomode optical waveguides.The orientation mechanism is also considered, by including an inclination factor affecting each single receptor. We have compared the so obtained distribution to the one associated to a single receptor© (1987) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An exact formulation of the electromagnetic field striking an optical waveguide is presented and compared with the decomposition relationship used in the literature. The expression for the critical angle is derived as a natural consequence of this formulation. Equations for the total fraction of power confined within a waveguide are derived and analyzed for the special case of absorbing waveguides. An explicit expression is derived for the fraction of energy confined within a waveguide supporting two sets of modes.