Showing papers by "École Polytechnique Fédérale de Lausanne published in 1985"

Second-generation image-coding techniques

Abstract: The digital representation of an image requires a very large number of bits. The goal of image coding is to reduce this number, as much as possible, and reconstruct a faithful duplicate of the original picture. Early efforts in image coding, solely guided by information theory, led to a plethora of methods. The compression ratio, starting at 1 with the first digital picture in the early 1960s, reached a saturation level around 10:1 a couple of years ago. This certainly does not mean that the upper bound given by the entropy of the source has also been reached. First, this entropy is not known and depends heavily on the model used for the source, i.e., the digital image. Second, the information theory does not take into account what the human eye sees and how it sees. Recent progress in the study of the brain mechanism of vision has opened new vistas in picture coding. Directional sensitivity of the neurones in the visual pathway combined with the separate processing of contours and textures has led to a new class of coding methods capable of achieving compression ratios as high as 70:1. Image quality, of course, remains as an important problem to be investigated. This class of methods, that we call second generation, is the subject of this paper. Two groups can be formed in this class: methods using local operators and combining their output in a suitable way and methods using contour-texture descriptions. Four methods, two in each class, are described in detail. They are applied to the same set of original pictures to allow a fair comparison of the quality in the decoded pictures. If more effort is devoted to this subject, a compression ratio of 100:1 is within reach.

Electronic and structural properties of sodium clusters

Abstract: We present an investigation of the structural and electronic properties of the sodium clusters ${\mathrm{Na}}_{\mathrm{n}}$ and ${\mathrm{Na}}_{\mathrm{n}}$${\mathrm{}}^{+}$ with n\ensuremath{\le}8 and n=13, based on self-consistent pseudopotential local-spin-density calculations. In order to obtain the equilibrium geometries without imposing any symmetry constraint, we start from randomly generated cluster geometries and let them relax under the action of the forces on the atoms, which are derived from the Hellmann-Feynman theory. We find that the clusters with up to five atoms have planar equilibrium geometries, the six-atom cluster is quasiplanar, and real three-dimensional structures only begin to occur when the number of atoms is greater than or equal to seven. We compare our results with recently obtained experimental data and find good agreement with the measured photoionization appearance potentials and the electron-spin-resonance spectra. Metallic bonding is the dominant feature of our calculated electronic structures and we show that the equilibrium geometries can be explained with a simple model having the delocalized nature of the metallic electrons and the Jahn-Teller effect as basic ingredients.

General integral equation formulation for microstrip antennas and scatterers

Abstract: The paper deals with the dynamic analysis of microstrip structures. It is shown that the mixed-potential integral equation for stratified media, which was introduced in a previous publication, provides a rigorous and powerful approach. The Green's functions belonging to the kernel of the integral equation are expressed as Sommerfeld integrals, in which surface wave effects are automatically included. A two-dimensional moment's method using subsectional basis functions has been chosen. Thus, microstrip patches of any shape can be analysed at any frequency and for any substrate. Practical numerical aspects are carefully discussed, and special numerical devices are introduced to reduce computation time without loss of accuracy. Complete results for a rectangular patch and for a slotted patch are given and compared with measured values. Radiation patterns corresponding to the ideal situation of a substrate with infinite transverse dimensions are presented for a rectangular patch.

Computer animation

Abstract: Introduction The main goal of computer animation is to synthesize the desired motion effect which is a mixing of natural phenomena, perception and imagination. The animator designs the object's dynamic behavior with his mental representation of causality. He/she imagines how it moves, gets out of shape or reacts when it is pushed, pressed, pulled, or twisted. So, the animation system has to provide the user with motion control tools able to translate his/her wishes from his/her own language. Computer animation methods may also help to understand physical laws by adding motion control to data in order to show their evolution over time. Visualization has become an important way of validating new models created by scientists. When the model evolves over time, computer simulation is generally used to obtain the evolution of time, and computer animation is a natural way of visualizing the results obtained from the simulation.

Enhanced fields on rough surfaces: dipolar interactions among particles of sizes exceeding the Rayleigh limit

Abstract: Amplified electromagnetic fields generated by a surface of finitely sized metal or dielectric particles are calculated. Regular arrays of particles produced by lithographic techniques and stochastic particle distributions that occur, e.g., in island films, are discussed. Retarded dipolar interactions between the particles are explicitly taken into account. Particles of finite size are considered for which dynamic depolarization and radiation damping effects are important. Limits of validity of the present approach are indicated. The total electromagnetic field from the surface is calculated by superposition: Scalar potentials characterizing a single particle are convoluted with a distribution function describing the particle positions. The surface Hertz vector is obtained from the single-particle Hertz vector by convolution with a two-dimensional Shah function representing the array or with the autocorrelation function of the stochastic surface. A plane-wave description of the dipolar fields is used, whereby the convolution is transformed into a simple multiplication in Fourier space. Cylindrical, general spheroidal, and spherical shapes are considered for the individual particle. Particle dipole moments are obtained by a self-consistent procedure. Dipolar interactions result in shifts and broadening of the particle plasmon resonances, which are responsible for the local intensity enhancement. A set of universal curves is given from which shift and broadening can be calculated for particles of all sizes and shapes. Extrema in the dipolar interactions arise when grating orders change from radiative to evanescent character. The strong variation of the Raman enhancement with angle and wavelength in the vicinity of these extrema is clearly predicted from the Hertz-vector calculation. The formalism described permits one to calculate electromagnetic properties of the surface and enhancement factors for any electromagnetic process occurring at or near the surface. As examples, the calculation of reflectivities for s-and p-polarized excitation and surface-enhanced Raman-scattering cross sections are discussed.

Effects of different energy intakes before and after calving on food intake, performance and blood hormones and metabolites in dairy cows

Abstract: An experiment with 25 dairy cows was performed to investigate the effects of different energy intakes on food intake, performance and blood hormone and metabolite levels during the last 70 days of pregnancy and the first 125 days after parturition. Compared with animals fed ad libitum before parturition, cows fed only according to requirements during the same time showed no decrease of food intake at calving. Cows fed at a restricted level also showed a faster increase in food intake, a smaller energy deficiency at the onset of lactation and a smaller weight loss after parturition. Peak milk yield was also lower, but the peak was maintained for a longer period, and during the first 2 months of lactation these cows had higher concentrations of glucose and lactic acid, and lower concentrations of non-esterified fatty acids and ketone bodies in the blood. Weight losses, and decrease of milk production during the 1st weeks of lactation were higher in cows fed only 0·75 of requirements during the first 60 days of lactation than in animals whose energy intake was planned to cover energy requirements, and during the first 2 months of lactation levels of unesterified fatty acids, ketone bodies and urea were higher, whereas levels of insulin, thyroxine and triiodothyronine were lower. Endocrine and metabolic changes seen during early lactation suggested improved glucose homeostasis, diminished fat mobilization and ketogenesis in cows given reduced amounts of energy during the dry period compared to animals fed ad libitum. To prevent the development of acetonaemia an adequate energy supply during the first part of lactation is, however, of greater importance.

Catalytic Synthesis of Higher Aliphatic Amines from the Corresponding Alcohols

Abstract: Aliphatic amines are of considerable industrial importance and find application in almost every field of modern technology, agriculture, and medicine [1], Lower aliphatic amines (C1 to C6) are important intermediates for the chemical and pharmaceutical industries. A large number of drugs, herbicides, pesticides, dyes, and other chemicals contain amino pups which originate from reactions with such intermediates, Many important applications of higher aliphatic amines (fatty amines) and their derivatives (most important derivatives are quarternary ammonium compounds) are based on their cationic surface activity. Relatively small amounts of such compounds are usually required to achieve the desired changes in surface and colloidal properties. Thus, not surprising, one of the first applications of fatty amines was in the flotation separation of nonmetallic materials such as potash, feldspar, phosphate, and mica. Today, probably the biggest demand for fatty amines lies in the production of fabric softe...

Reduced and compensatory growth: endocrine and metabolic changes during food restriction and refeeding in steers.

Abstract: Effects of food restriction, followed by refeeding, on energy and nitrogen metabolism, growth rates and blood levels of hormones and metabolites were studied in steers. During the restriction period, which lasted for almost 5 mo, allowance for energy and nitrogen were close to maintenance requirements. Heat production and growth rates were markedly lowered. In response to reduced food intake concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3), insulin (IRI), glucose and alpha-amino-acid nitrogen (AAN) were reduced, those of growth hormone (GH) and nonesterified fatty acids (NEFA) were elevated, whereas 3,3',5'-triiodothyronine (rT3) and albumin were not different from levels measured in nonrestricted animals. During refeeding heat production and energy balances increased, nitrogen balances were transiently elevated and the animals exhibited compensatory growth. In response to refeeding, concentrations of T4, T3 and IRI increased within days. In contrast, GH decreased whereas rT3 did not change. Within 2 d of refeeding there was a rapid fall of NEFA, and an increase of glucose, and beta-hydroxybutyrate within 2 and 12 d, respectively. The data demonstrate the ability of growing ruminants to adapt rapidly to variations in food intake by closely linked metabolic and endocrine changes, which are associated with shifts in energy and nitrogen metabolism and, finally, by reduced or compensatory growth.

Excretion and metabolism of di(2-ethylhexyl)-phthalate in man

Abstract: 1. Di-(2-ethylhexyl)phthalate (DEHP) taken orally by two volunteers (30 mg each) was excreted in the urine to the extent of 11 and 15% of dose.2. After enzymic hydrolysis the urinary metabolites (derivatives of mono (2-ethylhexyl) phthalate) were methylated and identified by g.l.c.-mass spectrometry (C.I.), and the quantitative distribution of conjugated and free metabolites determined.3. DEHP taken by the same volunteers over a period of four days at doses of 10 mg daily gave no evidence of accumulation; 15 and 25% of the total dose was recovered in the urine.

Le beton numerique

Abstract: Tout d'abord, nous avons expose le fait que les differents mecanismes qui sont a l'origine du comportement du beton sont si complexes et si dependants les uns des autres qu'il est impossible de les etudier exclusivement par voie experimentale.

Fast 2-D discrete cosine transform

Abstract: A fast radix-2 two dimensional discrete cosine transform (DCT) is presented. First, the mapping into a 2-D discrete Fourier transform (DFT) of a real signal is improved. Then an usual polynomial transform approach is used in order to map the 2-D DFT into a reduced size 2-D DFT and one dimensional odd DFT's. Finally, optimized odd DFT algorithms for real signals are developped. All together, a reduction of more than 50% in the number of multiplications and a comparable amount of additions is obtained in comparison to other algorithm.

Localization and Function of M-Line-Bound Creatine Kinase

Abstract: The electron-opaque M line or M band that transverses the center of the A band is one of the striking features of cross-striated muscle myofibrils seen with the electron microscope (Figs. 1–5). It appears to be the only myofibrillar structure that connects thick filaments directly to each other. After in situ fixation of skeletal muscle, dehydration, and standard embedding for electron microscopic examination, the M-band structure appears as a complex structure made up of several transverse elements connecting the thick filaments through the bare zone region and giving rise to the typical hexagonal thick-filament lattice (Franzini-Armstrong and Porter, 1964; Knappeis and Carlsen, 1968; Pepe, 1971) (see Fig. 1). High-resolution electron microscopy in combination with image analysis of ultrathin transverse sections of muscle fiber bundles shows a hexagonal lattice of thick filaments interconnected by primary m-bridge structures (nomenclature according to Sjostrom and Squire, 1977a,b) (Fig. 1, M4) often seen to have a circular thickening in the middle (Luther and Squire, 1978; Luther et al, 1981). At a different level in transverse sections, Y-shaped secondary m bridges (M3) connecting the nodular enlargements (MF) are observed as well (Luther and Squire, 1978; Luther et al., 1981) (Fig.1). Open image in new window

Time-optimal motions of robots in assembly tasks

Abstract: For a cylindrical, and a spherical robot, and a robot with a horizontal articulated arm with two links time-optimal unconstrained trajectories for arbitrary fixed initial and final positions are calculated. The exact equations of motion are utilized. The controls (torques and forces) are limited. The general structure of the optimal solution is discussed and explained physically for each robot. The importance of such analyses during the mechanical design of a robot is pointed out. The reduction of the duration of an optimal motion, compared to more straight-forward and natural ones, and hence the increase of the productivity of the robot in an assembly cycle can be considerable. The numerical examples include the "Automelec ACR" and the "IBM 7535 B04" robots.

Palaeoclimatic and tectonic implications of Neogene microflora from the Northwestern Ethiopian highlands

Abstract: Climatic changes in East Africa have been well documented although the record is far from complete Palaeoclimatic data for both the Holocene and Pleistocene1–7 and the Pliocene1–8 are available through fossil pollen studies However, these data extend in a continuous manner only as far back as 37 Myr BP (ref 11) largely because of the emphasis on studies related to human origins Fragmentary data from macrofossils also exist for older periods from Eastern14–20, Central and Southern Africa21,22 although the scarcity of material and the lack of isotopic dates makes it difficult to define continuity in the patterns of climatic fluctuations in East Africa The late Miocene pollen/spore flora described here represents the first data from East Africa for this time period and provides new information on the pre-Pliocene flora and climate of the continent The pollen flora comes from a post-8-Myr lacustrine deposit in the heart of the Northwestern Ethiopian Plateau (12° 35′ N, 37° 06′ E) and contains ‘exotic’ taxa that are now extinct The pollen diagram is characterized by abundant wet lowland rainforest taxa and pteridophytes, a very weak representation of grasses and the total absence of conifers, indicating warm and humid climates towards the close of the Miocene Post-depositional uplift of the Chilga area (∼1,000m) is also implied from the fossil pollen/spore assemblage

Irrigation Agrosystems in Eastern Spain: Roman or Islamic Origins?

Abstract: The long-standing controversy concerning Islamic diffusion of cultivars and irrigation technology to Spain is approached by comparing Roman and Islamic agrosystems at the general, regional, and local levels. We describe the Roman intensification of the older Mediterranean agrosystem and then examine the subsequent agricultural and demographic decline between A.D. 250 and 800. The operation, organization, and evolution of large, intermediate, and small-scale irrigation are analyzed in seven case studies from the Valencia region of eastern Spain. The largest systems were refurbished in Islamic times, but during a period when Berber and Arab settlement was thin and acculturation of the indigenous population incomplete. As a result the Roman agrosystem and irrigation networks remained largely unchanged, despite the presence of new technologic features and cultivars. Later transfer of irrigation agriculture to the adjacent mountain valleys followed the Roman model, but with more Islamic elements appar...

The age and origin of some Norwegian eclogites: A UPb zircon and REE study

Abstract: UPb zircon data from five different eclogites and one amphibolite, all occurring as boudinaged lenses within the 1.7-Ga old Basal Gneisses of western Norway, are reported along with eleven REE patterns on eclogites, amphibolite and country rocks. Based on the size, morphology and zoning patterns of zircon as well as the degree of UPb discordance, protoliths of both basaltic or gabbroic origin can be distinguished. Whereas zircons from eclogites formed from tholeftic and talc-alkaline basaltic protoliths allow dating of the Caledonian eclogite-facies event at ∼ 400 Ma, no precise information on their primary magmatic age is possible. On the other hand, eclogites formed from gabbroic precursors allowed the dating of both the primary magmatic age at ∼ 1.5 Ga, and in one case at more than 1.76 Ga, as well as a Caledonian eclogitization. One amphibolite sample, probably of prograde metamorphic origin, yielded a Sveconorwegian primary age (∼ 950 Ma) and a Caledonian age of metamorphism. REE analyses of the dated amphibolite and eclogites along with REE data on further eclogites within the Basal Gneisses, but also within the younger 1.5-Ma old mangeritic gneisses, are not in agreement with a pre-dominantly continental origin of the respective protoliths. The latter must be postulated if a simple in situ hypothesis for the origin of eclogites is correct. Instead, the observed REE patterns, ranging from LREE-depleted via flat to LREE-enriched patterns with both unfractionated and fractionated HREE, best fit an back arc—island are setting. Major- and trace-element data as well as initial ϵNd-values are in agreement with this hypothesis. Consequently, a tectonic interdigitation of 1.5-Ga old rocks, formed at various depths in a suboceanic mantle, into the Svecofennian grey gneiss basement is suggested. Based on the UPb systematics of some of the analysed zircon fractions together with published age results from the country rocks, a Sveconorwegian tectonometamorphic collisional event is most probable. In the course of such an event not only part of the non-metamorphic precursors of the eclogites but also some ultramafic mantle material, mangerites and other 1.5-Ga old island-arc-derived rocks could have been sub- and/or ob-ducted at various P-T conditions, resulting in a tectonic interdigitation of rocks of different metamorphic and magmatic history and origin. The non-thrusted part of the island arc, however, is thought to be welded to the continental margin of the Baltic Shield. Sveconorwegian gabbroic rocks (∼950 Ma) are transformed into amphibolites in the course of the Caledonian continent-continent collision. However, with the present amount of information on these rocks, it is only possible to say that they probably did not originate in a subcontinental mantle. After closure of the Iapetus Ocean in the Caledonian period, crustal thickening occurred due to subduction of the island-arc system and parts of the attached Baltic Shield underneath the North American-Greenland plate. This led to increasingly higher pressure metamorphism in the subducted rocks. Due to the relative eastward movement of the overriding plate, lithospheric plate thrusting, starting from the lowest eclogitefacies part of the subducted island-arc system, brought eclogites, and probably also ultramafic mantle material as well as other island-arc and continental rocks, from various depths into the crustal level where we observe them today. Similarly, also eclogites derived from older protoliths (> 1.76 Ga) which were already part of the Svecofennian continental crust were involved in such a scenario.

A microbial culture with oxygen‐sensitive product distribution as a potential tool for characterizing bioreactor oxygen transport

Abstract: The dissolved oxygen (DO) level has been shown to have a profound effect on the product distribution of a Bacillus subtilis culture, with acetoin being excreted with DO above 100 parts per billion (ppb) and butanediol below 100 ppb. The product concentration ratio changed rapidly in the 80–90 ppb range. Switching from one oxygen level to another caused one already accumulated product to be converted to the other in a reversible manner. Rates of change of 0.5–1 g/L h enabled detection within 10 min. Detection sensitivity is enhanced because the ratio of two concentrations can be measured. Remarkably sensitive to mixing rates, the culture responded to changes in stirring speed during experiments in which the dissolved oxygen was controlled at a constant level with a novel control system. Thus, the culture is capable of detecting dead zones in relatively well-mixed reactors and oxygen gradients in column and tubular reactors. High-viscosity effects can also be investigated since the culture grows well in xanthan gum solutions. Preliminary kinetic model development indicates that a useful model for simulating reactor mixing and transport effects can be developed to aid in the planning of experiments.