Search results for "insulator"
showing 10 items of 228 documents
High Resolution Time Domain Reflectometry for Dielectric State Monitoring in High Voltage Cables
2017
A high resolution Time Domain Reflectometry system has been designed in order to investigate the possibility of measuring with good accuracy the dielectric properties of high voltage cables insulator materials by means of Time-of-Flight measures. The system employs a dedicated Time-To-Digital Converter in order to achieve a time resolution of 90 ps. By exploiting averaging techniques the resolution has been further increased. Experimental results showed the possibility of measuring the dielectric constant with a resolution of 0.03%.
Promoter activity of the sea urchin (Paracentrotus lividus) nucleosomal H3 and H2A and linker H1 a-histone genes is modulated by enhancer and chromat…
2009
Core promoters and chromatin insulators are key regulatory elements that may direct a transcriptional enhancer to prefer a specific promoter in complex genetic loci. Enhancer and insulator flank the sea urchin (Paracentrotus lividus) alpha-histone H2A transcription unit in a tandem repeated cluster containing the five histone genes. This article deals with the specificity of interaction between the H2A enhancer-bound MBF-1 activator and histone gene promoters, and with the mechanism that leads the H1 transcripts to peak at about one-third of the value for nucleosomal H3 and H2A mRNAs. To this end, in vivo competition assays of enhancer and insulator functions were performed. Our evidence su…
The modulator is a constitutive enhancer of a developmentally regulated sea urchin histone H2A gene.
2002
Going back to the late 1970s and early 1980s, we trace the Xenopus oocyte microinjection experiments that led to the emergence of the concept of “modulator”. The finding that the modulator could transactivate transcription from far upstream and in either orientation suggested that a new genetic element, different from the classical prokaryotic promoter sequences, had been discovered. This particular enhancer transactivates transcription of the sea urchin early (α) histone H2A gene which is regulated in early sea urchin development. We summarise the data from sea urchin microinjection experiments that confirm and extend the results obtained with Xenopus oocytes. We conclude that the H2A enha…
Inverse nonlinear design in silicon waveguides
2014
La tecnologia fotònica basada en silici és objecte d'intensa investigació tant al món acadèmic com a la indústria. Un dels seus principals atractius rau en la seua elevada compatibilitat amb tècniques ja desenvolupades per a la integració de circuits electrònics, cosa que podria reduir el seu cost. A més, el silici ofereix una gran diversitat d'efectes no lineals que poden ser aprofitats per processar senyals òptics en xips compactes a velocitats superiors als dispositius electrònics actuals. En particular, l'objectiu d'aquesta tesi ha estat dissenyar una guia integrada en una plataforma híbrida de silici i sílice per generar espectres supercontinus. Aquest projecte presentava diferents rep…
Ferromagnetic kinetic exchange interaction in magnetic insulators
2020
The superexchange theory predicts dominant antiferromagnetic kinetic interaction when the orbitals accommodating magnetic electrons are covalently bonded through diamagnetic bridging atoms/groups. Here we show that explicit consideration of magnetic and (leading) bridging orbitals, together with the electron transfer between the former, reveals a strong ferromagnetic kinetic exchange contribution. First principle calculations show that it is comparable in strength with antiferromagnetic superexchange in a number of magnetic materials with diamagnetic metal bridges. In particular, it is responsible for a very large ferromagnetic coupling ($-10$ meV) between the iron ions in a Fe$^{3+}$-Co$^{…
Single-mode room-temperature emission with a silicon rod lattice
2006
The authors experimentally evidence an increase of light emission efficiency at room temperature in a silicon-on-insulator photonic crystal. The photonic crystal is made of a triangular lattice of silicon rods and operates as a single-mode light extractor. It exhibits a luminescence intensity two orders of magnitude higher than silicon-on-insulator substrate. In light of photoluminescence experiments, emission diagram measurements, and finite difference time domain calculations, they identify the different optical properties of the photonic crystal and they demonstrate the existence of at least a fivefold emission efficiency enhancement per surface unit.
Nanobox array for silicon-on-insulator luminescence enhancement at room temperature
2006
We report the light extraction enhancement obtained at room temperature from a square lattice of crystalline silicon nanoboxes etched in a silicon-on-insulator substrate. Luminescence spectra recorded under optical pumping show a 125 times emission enhancement as compared with the reference unpatterned silicon-on-insulator emission. In light of band diagram calculations, it is demonstrated that the emission enhancement partially results from the coupling between electron-hole recombination inside the silicon boxes and low group velocity optical modes of the array. Moreover, it is observed that these modes present different decoupling lengths and that a complete extraction of luminescence ca…
Bloch mode coupling investigation in silicon-on-insulator W1 photonic crystal waveguide
2004
We report in this paper the study of a W1 photonic crystal waveguide which supports two Bloch modes having different parity. A monomode ridge waveguide etched in a Silicon-On-Insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, evidence the even mode propagation along the defect line and experimental spectrum is discussed in light of band diagram and FDTD calculations. Then spectrally resolved near-field patterns obtained by using a scanning near field optical microscope in collection mode for wavelengths inside and outside the multimode region of the photonic crystal wav…
Generic nature of long-range repulsion mechanism on a bulk insulator?
2017
Dynamic atomic force microscopy measurements are reported that provide evidence for the presence of long-range repulsion in molecular self-assembly on a bulk insulator surface. We present the structures formed from four different benzoic acid derivatives on the (10.4) cleavage plane of calcite kept in ultra-high vacuum. These molecules have in common that they self-assemble into molecular stripes when deposited onto the surface held at room temperature. For all molecules tested, a detailed analysis of the stripe-to-stripe distance distribution reveals a clear deviation from what would be expected for randomly placed, non-interacting stripes (i.e., geometric distribution). When excluding kin…
Molecular semiconductor-doped insulator (MSDI) heterojunctions as new transducers for chemical sensors
2011
International audience; This article describes a new principle of transduction involving an heterojunction between a Molecular Semiconductor and a Doped Insulator (MSDI). Herein, we report on an MSDI-based sensor featuring an heterojunction between a lutetium bisphthalocyanine (LuPc), which acts as Molecular Semiconductor (MS) and a thin film of Doped Insulator (DI) made of substituted or fluorinated copper phthalocyanine (CuFPc, where = 0, 8, 16). Previously, we reported the peculiar effect of the heterojunction on the MSDI's electronic behavior, suggesting this device as a new kind of transducer for gas chemosensing. Indeed, of particular significance was the key role of modulator played …