Showing papers by "École Polytechnique Fédérale de Lausanne published in 1997"

Bootstrap Methods and Their Application

Abstract: This book gives a broad and up-to-date coverage of bootstrap methods, with numerous applied examples, developed in a coherent way with the necessary theoretical basis. Applications include stratified data; finite populations; censored and missing data; linear, nonlinear, and smooth regression models; classification; time series and spatial problems. Special features of the book include: extensive discussion of significance tests and confidence intervals; material on various diagnostic methods; and methods for efficient computation, including improved Monte Carlo simulation. Each chapter includes both practical and theoretical exercises. Included with the book is a disk of purpose-written S-Plus programs for implementing the methods described in the text. Computer algorithms are clearly described, and computer code is included on a 3-inch, 1.4M disk for use with IBM computers and compatible machines. Users must have the S-Plus computer application. Author resource page: http://statwww.epfl.ch/davison/BMA/

A new method for the model-independent assessment of thickness in three-dimensional images

Abstract: Three-dimensional (3-D) structural parameters derived from lower-dimensional measurements using indirect morphometric methods may be strongly biased if the measured objects deviate from the assumed structure model. With the introduction of 3-D microscopic measuring techniques it is possible to obtain a complete depiction of complex spatial structures. As a consequence, new 3-D methods have recently been developed for the estimation of morphometric parameters such as volume, surface area and connectivity by direct processing of the 3-D images. Structure thickness is an important morphometric parameter which is usually defined for specific structure models only. In this paper we propose a general thickness definition for arbitrary structures allowing us to calculate the mean structure thickness and the thickness distribution of 3-D objects in a direct way and independently of an assumed structure model. Additionally, an efficient implementation for the practical usage of the method is described using distance transformation. The new method is applied to trabecular bone structures measured with a 3-D micro-computed tomography system.

Quantification of Bone Microarchitecture with the Structure Model Index.

Abstract: The deterioration of cancellous bone structure due to aging and disease is characterized by a conversion from plate elements to rod elements. Consequently the terms “rod-like” and “plate-like” are frequently used for a subjective classification of cancellous bone. In this work a new morphometric parameter called Structure Model Index (SMI) is introduced, which makes it possible to quantify the characteristic form of a three-dimensionally described structure in terms of the amount of plates and rod composing the structure. The SMI is calculated by means of three-dimensional image analysis based on a differential analysis of the triangulated bone surface. For an ideal plate and rod structure the SMI value is 0 and 3, respectively, independent of the physical dimensions. For a structure with both plates and rods of equal thickness the value lies between 0 and 3, depending on the volume ratio of rods and plates. The SMI parameter is evaluated by examining bone biopsies from different skeletal sites. The bone ...

SU-8: a low-cost negative resist for MEMS

Abstract: This paper describes the characterization of a home-made negative photoresist developed by IBM. This resist, called SU-8, can be produced with commercially available materials. Three blends were prepared for this article and some of its optical and mechanical properties are presented. One of its numerous advantages is the broad range of thicknesses which can be obtained in one spin: from 750 nm to with a conventional spin coater. The resist is exposed with a standard UV aligner and has an outstanding aspect ratio near 15 for lines and 10 for trenches. These ratios combined with the electroplating of copper allow the fabrication of highly integrated electromagnetic coils.

Brillouin gain spectrum characterization in single-mode optical fibers

Abstract: A novel method for Brillouin gain spectrum measurements in optical fibers is presented. It is based on the pump and probe technique with the specificity to use a single laser source together with an external modulator to generate the interacting lightwaves. The high accuracy and inherent stability of the technique makes it suitable for calibration and reference measurements. Different fibers with different refractive index profiles have been tested and characterized. The problem of the evolution of the polarization of the interacting waves is addressed in the article and a polarization insensitive determination of the actual Brillouin gain coefficient is made possible through two successive measurements with different polarizations. The effects of strain and temperature on the Brillouin gain spectrum are also fully characterized.

Multilayered media Green's functions in integral equation formulations

Abstract: A compact representation is given of the electric- and magnetic-type dyadic Green's functions for plane-stratified, multilayered, uniaxial media based on the transmission-line network analog along the aids normal to the stratification. Furthermore, mixed-potential integral equations are derived within the framework of this transmission-line formalism for arbitrarily shaped, conducting or penetrable objects embedded in the multilayered medium. The development emphasizes laterally unbounded environments, but an extension to the case of a medium enclosed by a rectangular shield is also included.

Ultrafast Electron Injection: Implications for a Photoelectrochemical Cell Utilizing an Anthocyanin Dye-Sensitized TiO2 Nanocrystalline Electrode

Abstract: colloidal TiO2 powder, is shown to convert sunlight to electrical power at an efficiency of 0.56% under full sun. Fluorescence quenching is observed for the excited state of the TiO2-adsorbed anthocyanin dye, cyanin, and the photocurrent spectrum correlates well with the optical absorption of the cyanin-sensitized TiO 2 nanocrystalline film. The incident photon-to-current efficiency of 19% at the peak of the visible absorption band of the dye, the open-circuit voltages of 0.5-0.4 V, and short-circuit photocurrents of 1.5-2.2 mA/cm 2 are remarkable for such a simple system and suggest efficient charge carrier injection. The ultrafast excitedstate dynamics of cyanin in solution are compared with those of surface-adsorbed cyanin on TiO2 and ZrO2 colloids, as well as complexed with Al(III) ions. A transient absorption signal with a risetime of <100 fs for cyanin-sensitized TiO2 nanoparticles is assigned to electrons injected from the dye to TiO 2. This signal is fit to a double-exponential decay with time constants of 0.52 and 67 ps. The 0.52 ps component is due to trapping of conduction band electrons or to fast direct recombination with the dye cation, while the 67 ps decay is attributed to trap state mediated indirect recombination. In contrast, stimulated emission with a 2.6 ps decay time is observed for cyanin in solution, cyanin on ZrO2, and cyanin complexed with Al(III) ions. When compared to the photon-to-current efficiency measured for the solar cell, the efficiency estimated from the injection and recombination rate constants suggests that electron recapture by the redox mediator and light screening mechanisms may limit the efficiency of the cell.

Ants can colour graphs

Abstract: In the last few years researchers have shown how insect colonies can be seen as a natural model of collective problem solving. The analogy between the behaviour of ants looking for food and the well known travelling salesman problem has recently given rise to promising solution methods. We present in this paper an evolutionary search procedure for tackling assignment type problems. The algorithm repeatedly constructs feasible solutions of the problem under study by taking account of two complementary notions, namely the trace factor and the desirability factor. The use of such search principles will be illustrated for graph colouring problems. The results obtained have proven satisfactory when compared with those existing in the literature.

UV Laser Machined Polymer Substrates for the Development of Microdiagnostic Systems

Abstract: This report describes a UV laser photoablation method for the production of miniaturized liquid-handling systems on polymer substrate chips. The fabrication of fluid channel and reservoir networks is accomplished by firing 200 mJ pulses from an UV excimer laser at substrates moving in predefined computer-controlled patterns. This method was used for producing channels in polystyrene, polycarbonate, cellulose acetate, and poly(ethylene terephthalate). Efficient sealing of the resulting photoablated polymer channels was accomplished using a low-cost film lamination technique. After fabrication, the ablated structures were observed to be well defined, i.e., possessing high aspect ratios, as seen by light, scanning electron, and atomic force microscopy. Relative to the original polymer samples, photoablated surfaces showed an increase in their hydrophilicity and rugosity as a group, yet differences were noted between the polymers studied. These surface characteristics demonstrate the capability of generating electroosmotic flow in the cathodic direction, which is characterized here as a function of applied electric field, pH, and ionic strength of common electrophoretic buffer systems. These results show a correlation between the ablative changes in surface conditions and the resulting electroosmotic flow. The effect of protein coatings on ablated surfaces is also demonstrated to significantly dampen the electroosmotic flow for all polymers. All of these results are discussed in terms of developing liquid-handling capability, which is an essential part of many μ-TAS and chemical diagnostic systems.

Tobacco Smoke is a Source of Toxic Reactive Glycation Products

Abstract: Smokers have a significantly higher risk for developing coronary and cerebrovascular disease than nonsmokers Advanced glycation end products (AGEs) are reactive, cross-linking moieties that form from the reaction of reducing sugars and the amino groups of proteins, lipids, and nucleic acids AGEs circulate in high concentrations in the plasma of patients with diabetes or renal insufficiency and have been linked to the accelerated vasculopathy seen in patients with these diseases Because the curing of tobacco takes place under conditions that could lead to the formation of glycation products, we examined whether tobacco and tobacco smoke could generate these reactive species that would increase AGE formation in vivo Our findings show that reactive glycation products are present in aqueous extracts of tobacco and in tobacco smoke in a form that can rapidly react with proteins to form AGEs This reaction can be inhibited by aminoguanidine, a known inhibitor of AGE formation We have named these glycation products “glycotoxins” Like other known reducing sugars and reactive glycation products, glycotoxins form smoke, react with protein, exhibit a specific fluorescence when cross-linked to proteins, and are mutagenic Glycotoxins are transferred to the serum proteins of human smokers AGE-apolipoprotein B and serum AGE levels in cigarette smokers were significantly higher than those in nonsmokers These results suggest that increased glycotoxin exposure may contribute to the increased incidence of atherosclerosis and high prevalence of cancer in smokers

Fast power cycling test of IGBT modules in traction application

Abstract: The numerous advantages of insulated gate bipolar transistor (IGBT) power modules and their ongoing development for higher voltage and current ratings make them interesting for traction applications. These applications imply high reliability requirements. One important requirement is the ability to withstand power cycles. Power cycles cause temperature changes which lead to a mechanical stress that can result in a failure. Lifting of bond wires is thereby the predominant failure mechanism. A fast power cycling test method activating the main failure mechanism has been developed which allows reproduction of millions of temperature changes in a short time. The applicability of fast testing is supported by a mechanical analysis. Test results show the number of cycles to failure as a function of temperature changes for an IGBT single switch. A descriptive model is deduced from the results.

Disruption of the mouse L1 gene leads to malformations of the nervous system

Abstract: The adhesion molecule L1 is a member of the immunoglobulin super-family1. L1 is involved in various recognition processes in the CMS and PNS2–3, and binding to L1 can activate signal transduction pathways4,5. Mutations in the human L1 gene are associated with a variable phenotype, including mental retardation and anomalous development of the nervous system, referred to as ‘CRASH’ (corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraplegia, and hydrocephalus)6. We generated an animal model of these conditions by gene targeting. Mutant mice were smaller than wild-type and were less sensitive to touch and pain, and their hind-legs appeared weak and uncoordinated. The size of the corticospinal tract was reduced and, depending on genetic background, the lateral ventricles were often enlarged. Non-myelinating Schwann cells formed processes not associated with axons and showed reduced association with axons. In vitro, neurite outgrowth on an L1 substrate and fasciculation were impaired. The mutant mouse described here will help to elucidate the functions of L1 in the nervous system and how these depend on genetic influences.

Software-based replication for fault tolerance

Abstract: Replication handled by software on off-the-shelf hardware costs less than using specialized hardware. Although an intuitive concept, replication requires sophisticated techniques for successful implementation. Group communication provides an adequate framework. We present a survey of the techniques developed since the mid-1980s to implement replicated services, emphasizing the relationship between replication techniques and group communication.

Beta limits in long-pulse tokamak discharges

Abstract: The maximum normalized beta achieved in long-pulse tokamak discharges at low collisionality falls significantly below both that observed in short pulse discharges and that predicted by the ideal MHD theory. Recent long-pulse experiments, in particular those simulating the International Thermonuclear Experimental Reactor (ITER) [M. Rosenbluth et al., Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1995), Vol. 2, p. 517] scenarios with low collisionality nu(e)*, are often limited by low-m/n nonideal magnetohydrodynamic (MHD) modes. The effect of saturated MHD modes is a reduction of the confinement time by 10%-20%, depending on the island size and location, and can lead to a disruption. Recent theories on neoclassical destabilization of tearing modes, including the effects of a perturbed helical bootstrap current, are successful in explaining the qualitative behavior of the resistive modes and recent results are consistent with the size of the saturated islands. Also, a strong correlation is observed between the onset of these low-m/n modes with sawteeth, edge localized modes (ELM), or fishbone events. consistent with the seed island required by the theory. We will focus on a quantitative comparison between both the conventional resistive and neoclassical theories, and the experimental results of several machines, which have all observed these low-min nonideal modes. This enables us to single out the key issues in projecting the long-pulse beta limits of ITER-size tokamaks and also to discuss possible plasma control methods that can increase the soft beta limit, decrease the seed perturbations, and/or diminish the effects on confinement. (C) 1997 American Institute of Physics.

Digital signature of color images using amplitude modulation

Abstract: Watermarking techniques, also referred to as digital signature, sign images by introducing changes that are imperceptible to the human eye but easily recoverable by a computer program. Generally, the signature is a number which identifies the owner of the image. The locations in the image where the signature is embedded are determined by a secret key. Doing so prevents possible pirates from easily removing the signature. Furthermore, it should be possible to retrieve the signature from an altered image. Possible alternations of signed images include blurring, compression and geometrical transformations such as rotation and translation. These alterations are referred to as attacks. A new method based on amplitude modulation is presented. Single signature bits are multiply embedded by modifying pixel values in the blue channel. These modifications are either additive or subtractive, depending on the value of the bit, and proportional to the luminance. This new method has shown to be resistant to both classical attacks, such as filtering, and geometrical attacks. Moreover, the signature can be extracted without the original image.

Large Improvement of the Lower Detection Limit of Ion-Selective Polymer Membrane Electrodes

Abstract: The lower detection limits of ion-selective polymeric membrane electrodes (ISEs) are in the micromolar range except when sample ion activities are adjusted by using ion buffers, which maintain low and constant activity via superimposed complexation or solubility equilibria. 1 Therefore, they are unsuitable for many important applications. In contrast, detection limits in the picomolar range have been achieved with optical sensors on the basis of similar technology and the same ionophores, 2

Transgenic rice (Oryza sativa) endosperm expressing daffodil (Narcissus pseudonarcissus) phytoene synthase accumulates phytoene, a key intermediate of provitamin A biosynthesis

Abstract: Rice (Oryza sativa L.), the major food staple for more than two billion people, contains neither beta-carotene (provitamin A) nor C40 carotenoid precursors thereof in its endosperm. To improve the nutritional value of rice, genetic engineering was chosen as a means to introduce the ability to make beta-carotene into rice endosperm tissue. Investigation of the biochemical properties of immature rice endosperm using [14C]-labelled substrates revealed the presence of geranyl geranyl diphosphate, the C20 general isoprenoid precursor necessary for C40 carotenoid biosynthesis. Phytoene synthase, which condenses two molecules of geranyl geranyl diphosphate, is the first of four specific enzymes necessary for beta-carotene biosynthesis in plants. Therefore, the Japonica rice model variety Taipei 309 was transformed by microprojectile bombardment with a cDNA coding for phytoene synthase from daffodil (Narcissus pseudonarcissus) under the control of either a constitutive or an endosperm-specific promoter. In transgenic rice plants, the daffodil enzyme is active, as measured by the in vivo accumulation of phytoene in rice endosperm. Thus, it is demonstrated for the first time that it is in principle possible to engineer a critical step in provitamin A biosynthesis in a non-photosynthetic, carotenoid-lacking plant tissue. These results have important implications for long-term prospects of overcoming worldwide vitamin A deficiency.

Overexpression of an endogenous thionin enhances resistance of Arabidopsis against Fusarium oxysporum.

Abstract: Thionins are antimicrobial proteins that are thought to be involved in plant defense. Concordant with this view, we have recently shown that the Arabidopsis thionin Thi2.1 gene is inducible by phytopathogenic fungi. Here, we demonstrate that constitutive overexpression of this thionin enhances the resistance of the susceptible ecotype Columbia (Col-2) against attack by Fusarium oxysporum f sp matthiolae. Transgenic lines had a reduced loss of chlorophyll after inoculation and supported significantly less fungal growth on the cotyledons, as evaluated by trypan blue staining. Moreover, fungi on cotyledons of transgenic lines had more hyphae with growth anomalies, including hyperbranching, than on cotyledons of the parental line. No transcripts for pathogenesis-related PR-1, PR-5, or the pathogen-inducible plant defensin Pdf1.2 could be detected in uninoculated transgenic seedlings, indicating that all of the observed effects of the overexpressing lines are most likely the result of the toxicity of the THI2.1 thionin. Our findings strongly support the view that thionins are defense proteins.

Axonal regrowth after spinal cord transection in adult zebrafish

Abstract: Using axonal tracers, we characterized the neurons projecting from the brain to the spinal cord as well as the terminal fields of ascending spinal projections in the brain of adult zebrafish with unlesioned or transected spinal cords. Twenty distinct brain nuclei were found to project to the spinal cord. These nuclei were similar to those found in the closely related goldfish, except that additionally the parvocellular preoptic nucleus, the medial octavolateralis nucleus, and the nucleus tangentialis, but not the facial lobe, projected to the spinal cord in zebrafish. Terminal fields of axons, visualized by anterograde tracing, were seen in the telencephalon, the diencephalon, the torus semicircularis, the optic tectum, the eminentia granularis, and throughout the ventral brainstem in unlesioned animals. Following spinal cord transection at a level approximately 3.5 mm caudal to the brainstem/spinal cord transition zone, neurons in most brain nuclei grew axons beyond the transection site into the distal spinal cord to the level of retrograde tracer application within 6 weeks. However, the individually identifiable Mauthner cells were never seen to do so up to 15 weeks after spinal cord transection. Nearly all neurons survived axotomy, and the vast majority of axons that had grown beyond the transection site belonged to previously axotomized neurons as shown by double tracing. Terminal fields were not re-established in the torus semicircularis and the eminentia granularis following spinal cord transection.

Structural Abnormalities and Deficient Maintenance of Peripheral Nerve Myelin in Mice Lacking the Gap Junction Protein Connexin 32

Abstract: Mutations affecting the connexin 32 (Cx32) gene are associated with the X-linked form of the hereditary peripheral neuropathy Charcot–Marie–Tooth disease (CMTX). We show that Cx32-deficient mice develop a late-onset progressive peripheral neuropathy with abnormalities comparable to those associated with CMTX, thus providing proof of the critical role of Cx32 in the maintenance of peripheral nerve myelin and an animal model for CMTX. Frequently observed features include abnormally thin myelin sheaths, cellular onion bulb formation reflecting myelin degeneration-induced Schwann cell proliferation, and enlarged periaxonal collars while nerve conductance properties are altered only slightly. These observations are consistent with earlier hypotheses suggesting a function of Cx32 as a channel-forming protein that facilitates the communication between the abaxonal and adaxonal aspects of Schwann cell cytoplasm.

Fluorometric assessments of mitochondrial function and viability in cryopreserved bovine spermatozoa.

Abstract: Mitochondrial function and sperm viability were quantified in samples of cryopreserved bovine spermatozoa from 12 bulls using fluorometric techniques. The active mitochondria of the spermatozoa were fluorescently stained using three different fluorophores: rhodamine 123 (R123), 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolyl-carbocyan ine iodide (JC-1) or MitoTracker Green FM (MITO). The stained spermatozoa, and companion aliquots that had been stained with SYBR-14 (a living-cell nucleic acid stain) and propidium iodide to assess viability, were quantified using flow cytometry. The resulting fluorescent measurements of mitochondrial function were compared with microscopic assessments of progressive sperm motility immediately after thawing, with motility after 3-h incubation at 37 degrees C, and with the fluorescent assessment of sperm viability. Staining with either R123 or MITO resulted in a single green population. In contrast, the JC-1 staining of mitochondria produced both green and red-orange populations of spermatozoa and sometimes a progressive gradient between the two populations. The ability of JC-1 to discriminate between mitochondria exhibiting high membrane potential from those having low to medium membrane potential provided a more rigorous estimate of metabolic function than the other two fluorescent stains. Overall, the three fluorometric measurements of mitochondrial function were highly correlated with each other, with the SYBR-14 assessment of viability, and with the microscopic estimates of motility.

Maize Phenylalanine Ammonia-Lyase Has Tyrosine Ammonia-Lyase Activity

Abstract: A full-length cDNA encoding phenylalanine ammonia-lyase (PAL) from Zea mays L. was isolated and the coding region was expressed in Escherichia coli as a C-terminal fusion to glutathione S-transferase. After purification by glutathione-Sepharose chromatography, the glutathione S-transferase moiety was cleaved off and the resulting PAL enzyme analyzed. In contrast to PAL from dicots, this maize PAL isozyme catalyzed the deamination of both L-phenylalanine (PAL activity) and L-tyrosine (tyrosine ammonialyase activity). These results provide unequivocal proof that PAL and tyrosine ammonia-lyase activities reside in the same polypeptide. In spite of large differences in the Michaelis constant and turnover number of the two activities, their catalytic efficiencies are very similar. Also, both activities have the same pH and temperature optima. These results imply that maize can produce p-coumaric acid from both phenylalanine and tyrosine.