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Calculation Scheme (calculation + scheme)
Selected AbstractsRendering natural waters taking fluorescence into accountCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 5 2004By E. Cerezo Abstract The aim of the work presented here is to generalize a system, developed to treat general participating media, to make it capable of considering volumetric inelastic processes such as fluorescence. Our system, based on the discrete ordinates method, is adequate to treat a complex participating medium such as natural waters as it is prepared to deal with not only anisotropic but also highly peaked phase functions, as well as to consider the spectral behaviour of the medium's characteristic parameters. It is also able to generate detailed quantitative illumination information, such as the amount of light that reaches the medium boundaries or the amount of light absorbed in each of the medium voxels. First, we present an extended form of the radiative transfer equation to incorporate inelastic volumetric phenomena. Then, we discuss the necessary changes in the general calculation scheme to include inelastic scattering. We have applied all this to consider the most common inelastic effect in natural waters: fluorescence in chlorophyll-a. Copyright © 2004 John Wiley & Sons, Ltd. [source] Electronic structure calculation by monte carlo diagonalization methodINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2001Y. Shigeta We propose an electronic structure calculation scheme for ground and low-lying excited states of molecular systems by using the generalized coherent state for fermion, where the coefficients of the coherent states are determined by a stochastic approach. This method has both the advantage of the ordinary quantum Monte Carlo and that of the direct diagonalization methods and does not suffer from the negative sign problem. We demonstrate a performance of the present method. © 2001 John Wiley & Sons, Inc. Int J Quant Chem, 2001 [source] Compensation of aniseikonia in astigmatic pseudophakic eyes,OPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 6 2005Graeme E. MacKenzie Abstract Purpose:, A recently published manuscript addressed the problem of compensating for aniseikonia between pseudophakic astigmatic eyes using a least-squares calculation scheme. The purpose of this paper is to revisit this topic with the specific aim of providing explicit formulae for the determination of the intra-ocular lens required to produce a specified transverse image size at the plane of the retina and the characteristics of the contact or spectacle lens required to realize some desired refractive outcome. Methods:, The 4 × 4 ray transference is central to the development of all formulae presented in this paper. Specifically, the formula for the determination of the power of the intra-ocular lens required to achieve some transverse image size at the retina is derived directly from the disjugacy of the pseudophakic eye. Results:, The formula is applicable to both stigmatic and astigmatic systems without restriction. A detailed numerical example for an unusual eye is provided. Conclusion:, A formula for the determination of the intra-ocular lens required to produce any given transverse image size at the retina is derived. This approach does not require the application of the Moore-Penrose pseudo-inverse and one is able to work rather with the properties of the optical system directly without further modification. [source] Determination of pseudophakic accommodation with translation lenses using Purkinje image analysisOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 2 2005Achim Langenbucher Abstract Purpose:, To determine pseudophakic accommodation of an accommodating posterior chamber intraocular lens (translation lens) using Purkinje image analysis and linear matrix methods in the paraxial space. Methods:, A 2 × 2 system matrix was defined for each Purkinje image I to IV using refraction, translation and mirror matrices. Image size (m) and axial image position (z) was determined as an example for an off-axis object (a 0.2 m off-axis object located 0.5 m in front of the cornea.). First, our method was applied to the phakic relaxed (emmetropic) and accommodated (6.96 D) Le Grand eye. Secondly, for demonstration of the applicability of the calculation scheme to the pseudophakic eye, we provide a clinical example where we determine the accommodation amplitude of the translation lens (1 CU, HumanOptics, Erlangen, Germany) from photographed Purkinje images in the relaxed and accommodated state. From the biometric data: axial length 23.7 mm, corneal power 43.5, corneal thickness 550 microns, implanted intraocular lens (IOL) with a refractive power of 20.5 D (shape equi-biconvex, refractive index 1.46), and refractive indices of the cornea, aqueous and vitreous from the Le Grand model eye, we calculated the refractive state and the sizes of Purkinje images I and III initiated from two off-axis light sources. Results:, For the Le Grand model eye, Purkinje image II (z/m = 3.5850 mm/0.0064) is slightly smaller than and directly in front of image I (z/m = 3.8698 mm/0.0077). Purkinje image III (z/m = 10.6097 mm/0.0151) is nearly double the size of image I and during accommodation it moves from the vitreous into the crystalline lens. Purkinje IV (z/m = 4.3244 mm/,0.0059) is inverted, three quarters the size of image I, lies in the crystalline lens and moves slightly towards the retina. For the pseudophakic eye, pseudophakic accommodation of 1.10 D was calculated from the proportion of distances between both Purkinje images I and III in the relaxed (3.04) and accommodated (2.75) state, which is in contrast to the total subjective accommodation of 2.875 D evaluated with an accommodometer. Conclusions:, We present a straightforward mathematical strategy for calculation of the Purkinje images I,IV. Results of our model calculation resemble the values provided by Le Grand. In addition, this approach yields a simple en bloc scheme for determination of pseudophakic accommodation in pseudophakic eyes with accommodative lenses (translation lenses) using Purkinje image photography. [source] Computerized calculation scheme for bitoric eikonic intraocular lensesOPHTHALMIC AND PHYSIOLOGICAL OPTICS, Issue 3 2003Achim Langenbucher Abstract Despite full correction of the corneal astigmatism with toric intraocular lenses, the retinal image is distorted and the lateral image-object magnification is different in different meridians. The purpose of this study is to describe an iteration strategy for tracing an axial pencil of rays through the ,optical system eye' containing astigmatic refractive surfaces with their axes at random to calculate a thick bitoric lens implant which eliminates image distortion. The capabilities of this computing scheme are demonstrated with two clinical examples. We present a mathematically straightforward computer-based strategy for the calculation of thick bitoric eikonic lens implants. The iteration algorithm is initialized with a spherical front and a toric back surface and stepwise decreases the image distortion by adding cylinder lenses to the front lens surface corrected by the toric lens back surface. Total magnification can be modulated by varying the front-to-back surface power of the thick lens. [source] Accurate bond-valence parameters for the Bi3+/Br, ion pairACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2006Vasyl Sidey Using a new calculation scheme, reliable and physically meaningful values of the bond-valence parameters (r0 = 2.567,Å and b = 0.421,Å) have been deduced for the Bi3+/Br, ion pair from the molecular geometry and from the crystal structure of BiBr3. [source] Zur Diskussion des Böenreaktionsfaktors G nach DIN 1055-4:2005BAUTECHNIK, Issue 10 2009BayIKBau Robert Hertle Dr.-Ing., Beratender Ingenieur VBI, Prüfingenieur für Standsicherheit vpi Allgemeines; Baumechanik; General Topics; Structural Mechanics Abstract Mit Einführung der DIN 1055-4:2005 fand ein Paradigmenwechsel bei der Beschreibung der Windlasten statt. Das bisherige, deterministische Konzept zur Definition der Windeinwirkung wurde verlassen und durch ein auf stochastischen Überlegungen fußendes ersetzt. Für Konstruktionen und Bauwerke, die nicht schwingungsanfällig unter böigen Windeinwirkungen sind, ergeben sich daraus keine nennenswerten Änderungen bei der rechnerischen Untersuchung. Für die Analyse von schwingungsanfälligen Konstruktionen hat diese Neukonzeption tiefgreifende Konsequenzen. Die bekannte und einfach zu handhabende Ermittlung des Böenreaktionsfaktors auf Grundlage der Normen der achtziger und neunziger Jahre des vergangenen Jahrhunderts wurde durch ein komplexes, unübersichtliches und mit einfachen Ingenieurmethoden nicht mehr zu überprüfendes Berechnungsschema abgelöst. In diesem Beitrag wird dieses Schema diskutiert, und es wird ein einfaches Näherungsverfahren zur Ermittlung der Böenreaktion einer Konstruktion vorgeschlagen, welches, insbesondere vor dem Hintergrund der sonstigen Unschärfen und Unsicherheiten einer Berechnung, ausreichende Genauigkeit zeigt. On the discussion of the gust reaction factor acc. DIN 1055-4:2005. With the introduction of DIN 1055-4:2005 a change of paradigm concerning the description of wind loads took place. The previous concept, based on a deterministic view, was replaced by an approach using stochastic considerations. For constructions and buildings deemed to be not susceptible to gust action, no significant changes within the structural analysis arise. Enormous consequences, on the other hand, have to be faced when analyzing structures susceptible to gust action. The well known and easy to handle method for calculating the gust reaction factor using the standards of the 80th and 90th of the last century, was redeemed by a complex, partly confused calculation scheme which is not checkable with usual engineering tools. In the following paper this calculation scheme is discussed. Following to this discussion, a simplified method for calculating the gust reaction factor is presented. The accuracy of this method lies, having the usual uncertainties and deficits of structural analyses in mind, in an acceptable range. [source] Computerized calculation scheme for retinal image size after implantation of toric intraocular lensesACTA OPHTHALMOLOGICA, Issue 1 2007Achim Langenbucher Abstract. Purpose., To describe a paraxial computing scheme for tracing an axial pencil of rays through the ,optical system eye' containing astigmatic surfaces with their axes at random. Methods., Two rays (,10 prism diopters from vertical and horizontal) are traced through the uncorrected and corrected eye. In the uncorrected eye one specific ray is selected from the pencil of rays, which passes through the pupil center. In the corrected eye any ray can be traced through the eye. From the slope angle, the intersection of the ray with the refractive surface and the refraction the slope angle of the exiting ray is determined and the ray is traced to the subsequent surface. From both rays traced through the eye an ellipse is fitted to the image to characterize the image distortion of an circular object. Example., Assumptions: target refraction ,0.5,1.0D/A = 90° at 14 mm, corneal refraction 42.5 + 3.5D/A = 15°, axial length 23.6 mm, IOL position 4.6 mm, central lens thickness 0.8 mm, refractive index 1.42, front/back surface of the toric IOL 10.0 D/7.14 + 6.47D/A = 101.8°. The vertical incident ray was imaged to (x, y) = (0.0055 mm, ,1.6470 mm)/(0.0067 mm, ,1.6531 mm) in the uncorrected/corrected eye. The horizontal incident ray was imaged to (x, y) = (1.6266 mm, ,0.0055 mm)/(1.6001 mm, ,0.0067 mm) in the uncorrected/corrected eye. The ellipse (semi-major/semi-minor meridian) fitted to the conjugate image of a circle sized 1.648 mm/1.625 mm in an orientation 14.2° in the uncorrected and 1.654 mm/1.599 mm in an orientation 7.1° in the corrected eye. Conclusion., This concept may be relevant for the assessment of aniseikonia after implantation of toric intraocular lenses for correction of high corneal astigmatism. [source] | |||||||||||||