Suppressed absolute negative conductance and generation of high-frequency radiation in semiconductor superlattices

We show that space-charge instabilities (electric field domains) in semiconductor superlattices are the attribute of absolute negative conductance induced by small constant and large alternating electric fields. We propose the efficient method for suppression of this destructive phenomenon in order to obtain a generation at microwave and THz frequencies in devices operating at room temperature. We theoretically proved that an unbiased superlattice with a moderate doping subjected to a microwave pump field provides a strong gain at third, fifth, seventh, etc. harmonics of the pump frequency in the conditions of suppressed domains.Comment: 8 pages. Development of cond-mat/0503216 . Version 2: Final version, erratum is include

An innovative application of super-paramagnetic iron oxide nanoparticles for magnetic separation

© 2017, AIDIC Servizi S.r.l. In the last decades, iron oxide nanoparticle application has taken root in several technological fields, such as magnetic separation of biomolecules, biosensors, bio-fuel production, nano-devices and nano-adsorption. Various approaches can be found for the magnetic nanoparticle manufacturing. Among them a new technology to manufacture core-cell super-paramagnetic iron oxide nanoparticles (SPIONs), based on a vapour composition using single ion precursors, like cyclodextrines, has been recently developed. In this paper, we present the synthesis of functionalized SPIONs as well as the modelling for an innovative application of this magnetic nanotechnology. It consists on the use of SPIONs to trap target organic or inorganic molecules in a continuous-flow apparatus. SPIONs with proper ligands are immobilized on a magnetic surface. On that surface, the solution containing target molecules is circulated. We modelled the magnetic properties of the magnetic surface and SPIONs as well as the velocity of liquid needed in order to avoid removal of nanoparticles by the solution flow

Nonequilibrium phenomena in high Landau levels

Developments in the physics of 2D electron systems during the last decade have revealed a new class of nonequilibrium phenomena in the presence of a moderately strong magnetic field. The hallmark of these phenomena is magnetoresistance oscillations generated by the external forces that drive the electron system out of equilibrium. The rich set of dramatic phenomena of this kind, discovered in high mobility semiconductor nanostructures, includes, in particular, microwave radiation-induced resistance oscillations and zero-resistance states, as well as Hall field-induced resistance oscillations and associated zero-differential resistance states. We review the experimental manifestations of these phenomena and the unified theoretical framework for describing them in terms of a quantum kinetic equation. The survey contains also a thorough discussion of the magnetotransport properties of 2D electrons in the linear response regime, as well as an outlook on future directions, including related nonequilibrium phenomena in other 2D electron systems.Comment: 60 pages, 41 figure

Mycobacterium tuberculosis Glucosyl-3-Phosphoglycerate Synthase: Structure of a Key Enzyme in Methylglucose Lipopolysaccharide Biosynthesis

Tuberculosis constitutes today a serious threat to human health worldwide, aggravated by the increasing number of identified multi-resistant strains of Mycobacterium tuberculosis, its causative agent, as well as by the lack of development of novel mycobactericidal compounds for the last few decades. The increased resilience of this pathogen is due, to a great extent, to its complex, polysaccharide-rich, and unusually impermeable cell wall. The synthesis of this essential structure is still poorly understood despite the fact that enzymes involved in glycosidic bond synthesis represent more than 1% of all M. tuberculosis ORFs identified to date. One of them is GpgS, a retaining glycosyltransferase (GT) with low sequence homology to any other GTs of known structure, which has been identified in two species of mycobacteria and shown to be essential for the survival of M. tuberculosis. To further understand the biochemical properties of M. tuberculosis GpgS, we determined the three-dimensional structure of the apo enzyme, as well as of its ternary complex with UDP and 3-phosphoglycerate, by X-ray crystallography, to a resolution of 2.5 and 2.7 Å, respectively. GpgS, the first enzyme from the newly established GT-81 family to be structurally characterized, displays a dimeric architecture with an overall fold similar to that of other GT-A-type glycosyltransferases. These three-dimensional structures provide a molecular explanation for the enzyme's preference for UDP-containing donor substrates, as well as for its glucose versus mannose discrimination, and uncover the structural determinants for acceptor substrate selectivity. Glycosyltransferases constitute a growing family of enzymes for which structural and mechanistic data urges. The three-dimensional structures of M. tuberculosis GpgS now determined provide such data for a novel enzyme family, clearly establishing the molecular determinants for substrate recognition and catalysis, while providing an experimental scaffold for the structure-based rational design of specific inhibitors, which lay the foundation for the development of novel anti-tuberculosis therapies

Staat van de ambtelijke dienst 2015 De overheid in tijden van verandering

bookHervorming Sociale Regelgevin

A Study on Magnetic Removal of Hexavalent Chromium from Aqueous Solutions Using Magnetite/Zeolite-X Composite Particles as Adsorbing Material

Toxic and heavy metals are considered harmful derivatives of industrial activities; they are not biodegradable and their accumulation in living organisms can become lethal. Among other heavy and toxic metals, chromium is considered hazardous, especially in the hexavalent (Cr6+) form. Numerous established studies show that exposure to Cr6+ via drinking water leads to elevated chromium levels in tissues, which may result in various forms of cancer. The purpose of this research is to synthesize magnetite/zeolite-X composite particles for the adsorption and magnetic removal of Cr6+ ions from aqueous solutions. Synthesis and characterization of such composite nanomaterials, along with an initial experimental evaluation of Cr6+ removal from water-based solution, are presented. Results show that zeolite-X is a very promising zeolite form, that when bound to magnetic nanoparticles can be used to trap and magnetically remove toxic ions from aqueous solutions

An innovative application of super-paramagnetic iron oxide nanoparticles for magnetic separation

© 2017, AIDIC Servizi S.r.l. In the last decades, iron oxide nanoparticle application has taken root in several technological fields, such as magnetic separation of biomolecules, biosensors, bio-fuel production, nano-devices and nano-adsorption. Various approaches can be found for the magnetic nanoparticle manufacturing. Among them a new technology to manufacture core-cell super-paramagnetic iron oxide nanoparticles (SPIONs), based on a vapour composition using single ion precursors, like cyclodextrines, has been recently developed. In this paper, we present the synthesis of functionalized SPIONs as well as the modelling for an innovative application of this magnetic nanotechnology. It consists on the use of SPIONs to trap target organic or inorganic molecules in a continuous-flow apparatus. SPIONs with proper ligands are immobilized on a magnetic surface. On that surface, the solution containing target molecules is circulated. We modelled the magnetic properties of the magnetic surface and SPIONs as well as the velocity of liquid needed in order to avoid removal of nanoparticles by the solution flow

Production of magnetic modified microalgae using iron oxide nanoparticles and electroporation technique

Immobilization of living cells is a useful technique that allows to enhance the biotechnological properties of many organisms. Currently, cell-immobilization is obtained via carrier adsorption, self-aggregation and entrapment. We are currently investigating the possibility to immobilize microalgae cells using magnetic nanoparticles on a magnetic surface. The principle is based on the introduction, inside the cell-body of microalgae, superparamagnetic nanoparticles through electroporation. Once microalgae have absorbed enough magnetic nanoparticles they will be responding to an external magnetic field. By using a flat magnetic surface, it will be possible to trap them in a specific position by means of magnetic force. Importantly, immobilized cells will be covered with a thin layer of water and during cell division only one of the daughter cells will keep the magnetic nanoparticles since they will face permanently the magnetic surface. The first step towards this goal is the introduction of magnetic nanoparticles in the microalgae cells. This work will present preliminary results of magnetic cells preparation. Magnetic nanoparticles covered with lipid, to make them biocompatible, and electroporation method to inset nanoparticles in the cells have been used. The protocol to obtain magnetic cells and viability assay that proved the feasibility of the method will be described