Optimal Spreading Sequences for Chaos-Based Communication Systems

As a continuation from [2], some higherorder statistical dependency aspects of chaotic spreading sequences used in communication systems are presented. The autocorrelation function (ACF) of the mean-adjusted squares, termed the quadratic autocorrelation function, forms the building block of nonlinear dependence assessment of the family of spreading sequences under investigation. Explicit results are provided for the theoretical lower bound, the so-called Fr´echet lower bound, of the quadratic ACF of that family. A method for producing a spreading sequence which attains the Fr´echet bound is introduced

A Computer Model for Laser Photopolymerization

A computer model for a laser induced photopolymerization process has been established which simulates stereolithography. The model couples irradiation, chemical reaction, and heat transfer equations to provide insights into rate processes occurring in the volume element contacted by the laser beam. Quantities predicted include the spatial variation in conversion of monomer to polymer, depletion of photoinitiator, and local variations in temperature in and around the spot contacted by the laser. This allows predictions to be made about the laser dwell time, depth penetration and uniformity of the photopolymer formed in the process.Mechanical Engineerin

A novel scene-recording spectroradiometer

In this paper we describe an innovative approach to providing both a synthesised dual-beam capability and a permanent photographic record of the precise area sensed by a spectroradiometer. These advances have been achieved without modifying the spectroradiometer and may be used with a wide range of commercially-available spectroradiometers

Higher order Dependency of Chaotic Maps

Some higher-order statistical dependency aspects of chaotic maps are presented. The autocorrelation function (ACF) of the mean-adjusted squares, termed the quadratic autocorrelation function, is used to access nonlinear dependence of the maps under consideration. A simple analytical expression for the quadratic ACF has been found in the case of fully stretching piece-wise linear maps. A minimum bit energy criterion from chaos communications is used to motivate choosing maps with strong negative quadratic autocorrelation. A particular map in this class, a so-called deformed circular map, is derived which performs better than other well-known chaotic maps when used for spreading sequences in chaotic shift-key communication systems

Material and Process Parameters that Affect Accuracy in Stereolithography

Experimental real time linear shrinkage rate measurements simulating stereolithography are used in an analysis of shrinkage during line drawing in stereolithography. While the amount of shrinkage depends on the polymerization kinetics, shrinkage kinetics and overall degree of cure, it also depends on the length of time to draw a line of plastic. A line drawn slowly will exhibit less apparent shrinkage than one drawn very quickly because much of the shrinkage is compensated for as the line is drawn. The data also indicates that a typical stereolithography resin in the green state may shrink to only 65% of its maximum, thus retaining considerable potential for shrinkage during post-cure. This infonnation can be used to predict the amount of shrinkage to be expected under certain exposure conditions and to fonnulate overall strategies to reduce shrinkage and subsequent warpage that causes shape distortion.Mechanical Engineerin

No difference in variability of unique hue selections and binary hue selections

If unique hues have special status in phenomenological experience as perceptually pure, it seems reasonable to assume that they are represented more precisely by the visual system than are other colors. Following the method of Malkoc et al. (J. Opt. Soc. Am. A22, 2154 [2005]), we gathered unique and binary hue selections from 50 subjects. For these subjects we repeated the measurements in two separate sessions, allowing us to measure test-retest reliabilities (0.52≤ρ≤0.78; p≪0.01). We quantified the within-individual variability for selections of each hue. Adjusting for the differences in variability intrinsic to different regions of chromaticity space, we compared the within-individual variability for unique hues to that for binary hues. Surprisingly, we found that selections of unique hues did not show consistently lower variability than selections of binary hues. We repeated hue measurements in a single session for an independent sample of 58 subjects, using a different relative scaling of the cardinal axes of MacLeod-Boynton chromaticity space. Again, we found no consistent difference in adjusted within-individual variability for selections of unique and binary hues. Our finding does not depend on the particular scaling chosen for the Y axis of MacLeod-Boynton chromaticity space

Binary time series generated by chaotic logistic maps

This paper examines stochastic pairwise dependence structures in binary time series obtained from discretised versions of standard chaotic logistic maps. It is motivated by applications in communications modelling which make use of so-called chaotic binary sequences. The strength of non-linear stochastic dependence of the binary sequences is explored. In contrast to the original chaotic sequence, the binary version is non-chaotic with non-Markovian non-linear dependence, except in a special case. Marginal and joint probability distributions, and autocorrelation functions are elicited. Multivariate binary and more discretised time series from a single realisation of the logistic map are developed from the binary paradigm. Proposals for extension of the methodology to other cases of the general logistic map are developed. Finally, a brief illustration of the place of chaos-based binary processes in chaos communications is given.Binary sequence; chaos; chaos communications; dependence; discretisation; invariant distribution; logistic map; randomness

Alfonso de Cartagena on the affair of the Canaries (1436–37): humanist rhetoric and the idea of the nation-state in fifteenth–century Castile

This paper examines the political and juridical theories expounded in Allegationes super conquesta insularum Canarie contra Portugalenses, a brief prepared in 1436 or 1437 by Alfonso de Cartagena, bishop of Burgos and Castilian legate to the Council of Basel, to present to Pope Eugenius IV the Castilian case for the colonization of the Canary Islands, and to refute Prince Henrique of Portugal’s claim to their conquest. It sets the dispute in the context of medieval theories about Just War and the papal or imperial power to authorize such conquests for the purposes of evangelization or trade, and points to its place within the broader perspective of later disputes on the legality of the Spanish conquest of America; but then shows that Cartagena deliberately sought to remove the question from the ambit of these discussions and to construct instead an argument that the Canaries belonged by right to the ancient Vizigothic province of Tingitania (Roman North Africa), and hence to the Vizigothic monarchy’s heirs, the kings of Castile. In order to dispose of the inconvenient fact that the last Vizigothic king, Roderick, was separated from the reigning Castilian monarch, Juan II, by some seven centuries of Islamic occupation of the Iberian Peninsula, Cartagena developed a theory that the ‘right of rule’ (ius principandi) of a nation resides not in the person of its monarch, but in the transfer to him of that right by its ‘people’. In doing so, the paper argues that Cartagena made an important theoretical step towards the early-modern concept of the ‘state’ as, in Quentin Skinner’s words, ‘the sole source of law and legitimate force within its own territ¬ory and [...] sole appropriate object of its citizens’ allegiances’. The paper seeks further to show how, in developing his argument, Cartagena drew not only upon the resources of Roman law but also upon the civic ideals and rhetoric of early Italian Renaissance humanism

A new dual-beam technique for precise measurements of spectral reflectance in the field

Field spectral measurements made using the single - beam method often include errors due to variation in illumination between measurement of the target and the reference (panel or cosine -corrected receptor). Although the dual-beam method avoids these errors, it introduces greater complexity due to the need to intercalibrate the two sensor heads used, and it is significantly more expensive. This paper describes an alternative dual-beam method which uses a neural network to estimate the complete irradiance spectrum from measurements made in 7 narrow bands. These narrow band measurements of irradiance may be made with a simple filter-based radiometer, thus avoiding the expense and complexity of a second spectroradiometer. The new technique has been tested using irradiance spectra from both continental and maritime locations