Showing papers by "École Polytechnique Fédérale de Lausanne published in 1995"

A Carbon Nanotube Field-Emission Electron Source

Abstract: A high-intensity electron gun based on field emission from a film of aligned carbon nanotubes has been made. The gun consists of a nanotube film with a 1-millimeter-diameter grid about 20 micrometers above it. Field-emission current densities of about 0.1 milliampere per square centimeter were observed for applied voltages as low as 200 volts, and current densities greater than 100 milliamperes per square centimeter have been realized at 700 volts. The gun is air-stable, easy and inexpensive to fabricate, and functions stably and reliably for long times (short-term fluctuations are on the order of 10 percent). The entire gun is only about 0.2 millimeter thick and can be produced with virtually no restrictions on its area, from less than 1 square millimeter to hundreds of square centimeters, making it suitable for flat panel display applications.

Similarity of color images

Abstract: We describe two new color indexing techniques. The first one is a more robust version of the commonly used color histogram indexing. In the index we store the cumulative color histograms. The L1-, L2-, L(infinity )-distance between two cumulative color histograms can be used to define a similarity measure of these two color distributions. We show that this method produces slightly better results than color histogram methods, but it is significantly more robust with respect to the quantization parameter of the histograms. The second technique is an example of a new approach to color indexing. Instead of storing the complete color distributions, the index contains only their dominant features. We implement this approach by storing the first three moments of each color channel of an image in the index, i.e., for a HSV image we store only 9 floating point numbers per image. The similarity function which is used for the retrieval is a weighted sum of the absolute differences between corresponding moments. Our tests clearly demonstrate that a retrieval based on this technique produces better results and runs faster than the histogram-based methods.

An analytical MOS transistor model valid in all regions of operation and dedicated to low-voltage and low-current applications

Abstract: Afully analytical MOS transistor model dedicated to the design and analysis of low-voltage, low-current analog circuits is presented. All the large-and small-signal variables, namely the currents, the transconductances, the intrinsic capacitances, the non-quasi-static transadmittances and the thermal noise are continuous in all regions of operation, including weak inversion, moderate inversion, strong inversion, conduction and saturation. The same approach is used to derive all the equations of the model: the weak and strong inversion asymptotes are first derived, then the variables of interest are normalized and linked using an appropriate interpolation function. The model exploits the inherent symmetry of the device by referring all the voltages to the local substrate. It is shown that the inversion chargeQ inv is controlled by the voltage differenceV P — Vch whereV ch is the channel voltage, defined as the difference between the quasi-Fermi potentials of the carriers. The pinch-off voltageV P is defined as the particular value of Vch, such that the inversion charge is zero for a given gate voltage. It depends only on the gate voltage and can be interpreted as the equivalent effect of the gate voltage referred to the channel. The various modes of operation of the transistor are then presented in terms of voltagesV P —V S andV P —V D Using the charge sheet model with the assumption of constant doping in the channel, the drain currentIDis derived and expressed as the difference between a forward componentI F and a reverse componentI R. Each of these is proportional to a function ofV P —V S respectivelyV P —V D through a specific currentI S This function is exponential in weak inversion and quadratic in strong inversion. The current in the moderate inversion region is then modelled by using an appropriate interpolation function resulting in a continuous expression valid from weak to strong inversion. A quasi-static small-signal model including the transconductances and the intrinsic capacitances is obtained from an accurate evaluation of the total charges stored on the gate and in the channel. The transconductances and the intrinsic capacitances are modelled in moderate inversion using the same interpolation function and without any additional parameters. This small-signal model is then extended to higher frequencies by replacing the transconductances by first order transadmittances obtained from a non-quasi-static calculation. All these transadmittances have the same characteristic time constant which depends on the bias condition in a continuous manner. To complete the model, a general expression for the thermal noise valid in all regions of operation is derived. This model has been successfully implemented in several computer simulation programs and has only 9 physical parameters, 3 fine tuning fitting coefficients and 2 additional temperature parameters.

Probabilistic diversification and intensification in local search for vehicle routing

Abstract: This article presents a probabilistic technique to diversify, intensify, and parallelize a local search adapted for solving vehicle routing problems. This technique may be applied to a very wide variety of vehicle routing problems and local searches. It is shown that efficient first-level tabu searches for vehicle routing problems may be significantly improved with this technique. Moreover, the solutions produced by this technique may often be improved by a postoptimization technique presented in this article, too. The solutions of nearly forty problem instances of the literature have been improved.

Aligned carbon nanotube films: production and optical and electronic properties

Abstract: Carbon nanotube material can now be produced in macroscopic quantities. However, the raw material has a disordered structure, which restricts investigations of both the properties and applications of the nanotubes. A method has been developed to produce thin films of aligned carbon nanotubes. The tubes can be aligned either parallel or perpendicular to the surface, as verified by scanning electron microscopy. The parallel aligned surfaces are birefringent, reflecting differences in the dielectric function along and normal to the tubes. The electrical resistivities are anisotropic as well, being smaller along the tubes than perpendicular to them, because of corresponding differences in the electronic transport properties.

Urbach tail of anatase TiO2.

Abstract: The fundamental absorption edge of the anatase phase of ${\mathrm{TiO}}_{2}$ has been studied by performing polarized optical transmission measurements on single crystals at temperatures ranging from 4.2 to 300 K. An Urbach tail has been found that shows an exponential spectral dependence down to liquid-helium temperature. The optical gap of anatase has been estimated to be 3.420 eV in polarization E\ensuremath{\perp}c, and 3.460 eV in polarization E\ensuremath{\parallel}c. Our experimental results can be accounted for in terms of the theory of Toyozawa and co-workers, which ascribes the Urbach tail to the momentary localization of excitons due to phonon interaction. Comparing, in this case, the measured abosrption spectra of anatase and rutile, we conclude that the excitons in anatase are self-trapped while those in rutile are free. This opposite nature of exciton states in anatase and rutile is consistent with the results of previous photoluminescence studies.

Autoinducer-mediated regulation of rhamnolipid biosurfactant synthesis in Pseudomonas aeruginosa

Abstract: The opportunistic human pathogen Pseudomonas aeruginosa produces a variety of virulence factors, including exotoxin A, elastase, alkaline protease, alginate, phospholipases, and extracellular rhamnolipids. The previously characterized rhlABR gene cluster encodes a regulatory protein (RhlR) and a rhamnosyltransferase (RhlAB), both of which are required for rhamnolipid synthesis. Another gene, rhII, has now been identified downstream of the rhlABR gene cluster. The putative RhlI protein shares significant sequence similarity with bacterial autoinducer synthetases of the LuxI type. A P. aeruginosa rhlI mutant strain carrying a disrupted rhlI gene was unable to produce rhamnolipids and lacked rhamnosyltransferase activity. Rhamnolipid synthesis was restored by introducing a wild-type rhlI gene into such strains or, alternatively, by adding either the cell-free spent supernatant from a P. aeruginosa wild-type strain or synthetic N-acylhomoserine lactones. Half-maximal induction of rhamnolipid synthesis in the rhlI mutant strain required 0.5 microM N-butyrylhomoserine lactone or 10 microM N-(3-oxohexanoyl)homoserine lactone. The P. aeruginosa rhlA promoter was active in the heterologous host Pseudomonas putida when both the rhlR and rhlI genes were present or when the rhlR gene alone was supplied together with synthetic N-acylhomoserine lactones. The RhlR-RhlI regulatory system was found to be essential for the production of elastase as well, and cross-communication between the RhlR-RhlI rhamnolipid regulatory system and the LasR-LasI elastase regulatory system was demonstrated.

Double Description Method Revisited

Abstract: The double description method is a simple and useful algorithm for enumerating all extreme rays of a general polyhedral cone in ℝd, despite the fact that we can hardly state any interesting theorems on its time and space complexities. In this paper, we reinvestigate this method, introduce some new ideas for efficient implementations, and show some empirical results indicating its practicality in solving highly degenerate problems.

Motion estimation techniques for digital TV: a review and a new contribution

Abstract: The key to high performance in image sequence coding lies in an efficient reduction of the temporal redundancies. For this purpose, motion estimation and compensation techniques have been successfully applied. This paper studies motion estimation algorithms in the context of first generation coding techniques commonly used in digital TV. In this framework, estimating the motion in the scene is not an intrinsic goal. Motion estimation should indeed provide good temporal prediction and simultaneously require low overhead information. More specifically the aim is to minimize globally the bandwidth corresponding to both the prediction error information and the motion parameters. This paper first clarifies the notion of motion, reviews classical motion estimation techniques, and outlines new perspectives. Block matching techniques are shown to be the most appropriate in the framework of first generation coding. To overcome the drawbacks characteristic of most block matching techniques, this paper proposes a new locally adaptive multigrid block matching motion estimation technique. This algorithm has been designed taking into account the above aims. It leads to a robust motion field estimation precise prediction along moving edges and a decreased amount of side information in uniform areas. Furthermore, the algorithm controls the accuracy of the motion estimation procedure in order to optimally balance the amount of information corresponding to the prediction error and to the motion parameters. Experimental results show that the technique results in greatly enhanced visual quality and significant saving in terms of bit rate when compared to classical block matching techniques. >

Anodic oxidation of phenol in the presence of NaCl for wastewater treatment

Abstract: The electrochemical oxidation of phenol in the presence of NaCl for wastewater treatment was studied at Ti/SnO2 and Ti/IrO2 anodes. The experimental results have shown that the presence of NaCl catalyses the anodic oxidation of phenol only at Ti/IrO2 anodes due to the participation of electro-generated ClO− in the oxidation. Analysis of the oxidation products has shown that initially organo-chlorinated compounds are formed in the electrolyte which are further oxidized to volatile organics (CHCl3).

Rocking Chair Lithium Battery Based on Nanocrystalline TiO2 (Anatase)

Abstract: Reference LPI-ARTICLE-1995-007View record in Web of Science Record created on 2006-02-21, modified on 2017-05-12

Hypermyelination and demyelinating peripheral neuropathy in Pmp22 -deficient mice

Abstract: Peripheral myelin protein PMP22 has been suggested to have a role in peripheral nerve myelination and cell proliferation. Defects at the PMP22 locus are associated with peripheral neuropathies such as Charcot-Marie-Tooth disease type 1A. We now demonstrate that mice devoid of Pmp22 are retarded in the onset of myelination and develop abundant sausage-like hypermyelination structures (tomacula) at a young age followed by severe demyelination, axonal loss and functional impairment. Mice carrying one functional copy of Pmp22 are less affected but they also exhibit focal tomacula comparable to the morphological features in hereditary neuropathy with liability to pressure palsies (HNPP). We conclude that Pmp22 is required for the correct development of peripheral nerves, the maintenance of axons and the determination of myelin thickness and stability.

Regulation of nitric oxide synthase activity in human immunodeficiency virus type 1 (HIV-1)-infected monocytes: implications for HIV-associated neurological disease.

Abstract: Mononuclear phagocytes (monocytes, macrophages, and dendritic cells) play major roles in human immunodeficiency virus (HIV) persistence and disease pathogenesis. Macrophage antigen presentation and effector cell functions are impaired by HIV-1 infection. Abnormalities of macrophage effector cell function in bone marrow, lung, and brain likely result as a direct consequence of cellular activation and HIV replication. To further elucidate the extent of macrophage dysfunction in HIV-1 disease, a critical activation-specific regulatory molecule, nitric oxide (NO.), which may contribute to diverse pathology, was studied. Little, if any, NO. is produced by uninfected human monocytes. In contrast, infection with HIV-1 increases NO. production to modest, but significant levels (2-5 microM). Monocyte activation (with lipopolysaccharide, tumor necrosis factor alpha, or through interactions with astroglial cells) further enhances NO. production in HIV-infected cells, whereas its levels are diminished by interleukin 4. These results suggest a possible role for NO. in HIV-associated pathology where virus-infected macrophages are found. In support of this hypothesis, RNA encoding the inducible NO synthase (iNOS) was detected in postmortem brain tissue from one pediatric AIDS patient with advanced HIV encephalitis. Corresponding iNOS mRNA was not detected in brain tissue from five AIDS patients who died with less significant brain disease. These results demonstrate that HIV-1 can influence the expression of NOS in both cultured human monocytes and brain tissue. This newly described feature of HIV-macrophage interactions suggests previously unappreciated mechanisms of tissue pathology that result from productive viral replication.

Layered representation of motion video using robust maximum-likelihood estimation of mixture models and MDL encoding

Abstract: Representing and modeling the motion and spatial support of multiple objects and surfaces from motion video sequences is an important intermediate step towards dynamic image understanding. One such representation, called layered representation, has recently been proposed. Although a number of algorithms have been developed for computing these representations, there has not been a consolidated effort into developing a precise mathematical formulation of the problem. This paper presents one such formulation based on maximum likelihood estimation (MLE) of mixture models and the minimum description length (MDL) encoding principle. The three major issues in layered motion representation are: (i) how many motion models adequately describe image motion, (ii) what are the motion model parameters, and (iii) what is the spatial support layer for each motion model. >

Integrated optical chemical and direct biochemical sensors

Abstract: An overview is given on work by the author's group on integrated optical (IO) sensors. The sensors make use of guided waves or modes in optical waveguides, in particular of the orthogonally polarized TE 0 and TM 0 modes in very thin planar waveguides of high refractive index. The principle of all direct (bio)chemical waveguide or IO sensors is as follows. A chemically selective coating on the waveguide surface binds the analyte molecules contained in the gaseous or liquid sample. Thus, the refractive index of the medium near the waveguide surface (more precisely, within the penetration depth Δz of the evanescent field of the guided wave) is changed. This effect in turn induces changes ΔN TE 0 and ΔN TM 0 of the effective refractive indices N TE 0 and N TM 0 of the guided modes. for example, in biochemical affinity sensors the chemically selective coating contains receptor molecules that specifically or selectively bind certain ligands as analyte molecules; in particular, in immunosensors or immunoassays the receptors are antibodies (or antigens, respectively) and the analyte molecules are the corresponding antigens (or antibodies). These ‘direct’ affinity of immunosensors eliminate the use of (e.g., fluorescently) labelled reagents. Effective refractive-index changes ΔN can also be induced by two other effects; namely by unspecific adsorption of molecules on the (uncoated) waveguide surface (or in pores of a waveguiding film F itself if it is microporous) and by refractive-index changes Δn C of the liquid sample. In the latter case the IO sensors work as refractometers. The effective refractive indices N give the phase velocity ν ph = c / N of the guided modes, where c is the velocity of light in vacuum. This means that the effective refractive-index changes ΔN can be measured by various optical means. Consequently, a number of different types of IO sensors can be used, in particular, grating couplers and interferometers. In the paper, I report on our own work on IO sensors including: the discovery of the basic sensor effect with grating couplers as sensors for relative-humidity changes, the theory of the sensor sensitivities, and experimental results obtained with three different types of IO sensors developed in our laboratory, namely input grating couplers, output grating couplers and the difference or polarimetric interferometer. The experiments have been performed with dip-coated SiO 2 TiO 2 waveguiding films of refractive index n F ≈ 1.75–1.88, on glass, silica and silicon wafers with oxidized buffer layers as substrates. The sensors working as refractometers are tested, for example, with glucose solutions of different concentrations. The adsorption of proteins (h-IgG, BSA, protein A, avidin) is monitored in real time. Not only the surface concentration Γ, with a resolution of a few pg mm −2 , but also the thickness d F′ and the refractive index n F′ of the adsorbing (mono)layers are determined as functions of time. Also immunoreactions (e.g., between h-IgG and anti-h-IgG, and between IgGs and protein A) and affinity reactions (between avidin and biotinylated proteins, such as biotin BSA) are observed in real time. The feasibility of IO immunosensors or affinity sensors or immunoassays with sub-nanomolar detection limits is demonstrated.

Protein zero (P0)-deficient mice show myelin degeneration in peripheral nerves characteristic of inherited human neuropathies

Abstract: Mutations in the human gene for the myelin recognition molecule protein zero (P0) give rise to severe and progressive forms of dominantly inherited peripheral neuropathies. We have previously reported that mice homozygous for a null mutation in P0 have severely hypomyelinated nerves ten weeks after birth. Here we show hypomyelination already exists at day four with subsequent demyelination and impaired nerve conduction. Furthermore, heterozygous mutants show normal myelination, but develop progressive demyelination after four months of age. Thus, the pathology of homo- and heterozygous P0 mutants resembles that of the severely affected Dejerine-Sottas and the more mildly affected Charcot-Marie-Tooth type 1B patients, respectively.

Evaluation of methods for estimation of total arterial compliance

Abstract: Seven classic and recently proposed methods used for the estimation of total arterial compliance have been evaluated for their accuracy and applicability in different physiological conditions. The pressure and flow data are taken from a computer model that provides realistic simulations of the nonlinear-distributed systemic arterial tree. Besides the great flexibility in simulating different physiological or pathological cases, the major advantage of the computer model is that it allows precise knowledge of the pressure-dependent total arterial compliance, which is the variable of interest. The results show that the methods based on the two-element windkessel (WK) model are more accurate than those based on the three-element WK model. The classic exponential decay and the diastolic area method yield essentially similar results, and their compliance estimates are accurate within 10% except at high heart rates. The later part of diastole, i.e., from the time that the systolic pressure wave has reached all peripheral beds, gives the best results. The newly proposed two-area and pulse pressure methods, both based on the two-element WK model, are accurate (errors in general or = 25%). The errors in the methods based on the three-element WK model arise from the fact that the input impedance in that model deviates significantly from the true input impedance at low frequencies. The strong dependence of compliance on pressure (elastic nonlinearity) does not invalidate the compliance estimates.(ABSTRACT TRUNCATED AT 250 WORDS)

An Arabidopsis thaliana Thionin Gene Is Inducible via a Signal Transduction Pathway Different from That for Pathogenesis-Related Proteins

Abstract: Two cDNAs encoding thionin preproproteins have been isolated from Arabidopsis thaliana. The corresponding genes have been designated Thi2.1 and Thi2.2. Southern blot analysis suggests that A. thaliana most probably contains single genes for both thionins. Thi2.2 transcripts have a low basal level in seedlings and show circadian variation. Thi2.2 transcripts were also detected in rosette leaves. No potent elicitors have been found for the Thi2.2 gene. Transcripts of the Thi2.1 gene are not detectable in seedlings but are present in rosette leaves and at a very high level in flowers and in siliques. The expression of the Thi2.1 gene is highly inducible in seedlings by pathogens, silver nitrate, and methyl jasmonate, but not by salicylate, indicating that the gene is induced by a signal transduction pathway that is at least partly different from that for the pathogenesis-related proteins.

Scanning near-field optical probe with ultrasmall spot size

Abstract: A novel light-emitting probe for scanning near-field optical microscopy is investigated theoretically. The three-dimensional vectorial Helmholtz equation is solved for the new probe geometry by using the multiple multipole method. The novel probe consists of a dielectric tip that is entirely metal coated. It provides a single near-field spot that can be smaller than 20 nm (FWHM). The dependence on tip radius, taper angle, and metal thickness in front of the tip is investigated for the power transmission through the probe as well as for the spot size.

Tracer Characteristics of Brilliant Blue FCF

Abstract: Dyes are widely used to stain the travel paths of water and solutes in soils. Brilliant Blue FCF (C.I. Food Blue 2) is a valuable dye tracer for visualizing water flow patterns. Because this dye is nontoxic, it is particularly suited for field use. Depending on pH, the dye is either neutral or dissociates to a mono- or bivalent anion. The water solubility is 200 kg m -3 . In this study, properties of the dye that characterize the adsorbing behavior in soil were determined. Batch adsorption experiments were carried out in the laboratory, and a field experiment was conducted to compare the mobility of Brilliant Blue FCF with that of I - and Br - . The batch studies gave distribution coefficients K d of 0.19, 3.00, and 5.78 dm 3 kg -1 for three different soils. The results of the batch studies suggest that the dye forms ion pairs with Ca 2+ . The field experiment showed that the dye is retarded compared with the conservative tracer Br - . A comparison between Brilliant Blue FCF and I - analyzed with the iodide-starch method resulted in a relative retardation of 1.2 Brilliant Blue FCF compared with I -