179 research outputs found
A simple and controlled single electron transistor based on doping modulation in silicon nanowires
A simple and highly reproducible single electron transistor (SET) has been
fabricated using gated silicon nanowires. The structure is a
metal-oxide-semiconductor field-effect transistor made on silicon-on-insulator
thin films. The channel of the transistor is the Coulomb island at low
temperature. Two silicon nitride spacers deposited on each side of the gate
create a modulation of doping along the nanowire that creates tunnel barriers.
Such barriers are fixed and controlled, like in metallic SETs. The period of
the Coulomb oscillations is set by the gate capacitance of the transistor and
therefore controlled by lithography. The source and drain capacitances have
also been characterized. This design could be used to build more complex SET
devices.Comment: to be published in Applied Physics Letter
Size scaling of the addition spectra in silicon quantum dots
We investigate small artificial quantum dots obtained by geometrically
controlled resistive confinement in low mobility silicon-on-insulator
nanowires. Addition spectra were recorded at low temperature for various dot
areas fixed by lithography. We compare the standard deviation of the addition
spectra with theory in the high electron concentration regime. We find that the
standard deviation scales as the inverse area of the dot and its absolute value
is comparable to the energy spacing of the one particle spectrum.Comment: 4 pages, 5 figure
Background charges and quantum effects in quantum dots transport spectroscopy
We extend a simple model of a charge trap coupled to a single-electron box to
energy ranges and parameters such that it gives new insights and predictions
readily observable in many experimental systems. We show that a single
background charge is enough to give lines of differential conductance in the
stability diagram of the quantum dot, even within undistorted Coulomb diamonds.
It also suppresses the current near degeneracy of the impurity charge, and
yields negative differential lines far from this degeneracy. We compare this
picture to two other accepted explanations for lines in diamonds, based
respectively on the excitation spectrum of a quantum dot and on fluctuations of
the density-of-states in the contacts. In order to discriminate between these
models we emphasize the specific features related to environmental charge
traps. Finally we show that our model accounts very well for all the anomalous
features observed in silicon nanowire quantum dots.Comment: 7 pages, 6 figure
Hyaluronan: Biosynthesis and signaling
Background
Hyaluronan is a critical component of extracellular matrix with several different roles. Besides the contribution to the tissue hydration, mechanical properties and correct architecture, hyaluronan plays important biological functions interacting with different molecules and receptors.
Scope of review
The review addresses the control of hyaluronan synthesis highlighting the critical role of hyaluronan synthase 2 in this context as well as discussing the recent findings related to covalent modifications which influence the enzyme activity. Moreover, the interactions with specific receptors and hyaluronan are described focusing on the importance of polymer size in the modulation of hyaluronan signaling.
Major conclusions
Due to its biological effects on cells recently described, it is evident how hyaluronan is to be considered not only a passive component of extracellular matrix but also an actor involved in several scenarios of cell behavior.
General significance
The effects of metabolism on the control of hyaluronan synthesis both in healthy and pathologic conditions are critical and still not completely understood. The hyaluronan capacity to bind several receptors triggering specific pathways may represent a valid target for new approach in several therapeutic strategies. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties
Hyaluronan Produced by Smooth Muscle Cells Plays a Critical Role in Neointima Formation
Large body of evidence supports the idea that microenvironment plays a critical role in several pathologies including atherosclerosis and cancer. The amount of hyaluronan (HA) is involved in the microenvironment alterations and the concentration of this polymer reflects the progression of the diseases promoting neoangiogenesis, cell migration, and inflammation. The HA synthesis is regulated by several factors: UDP sugar precursors availability and the phosphorylation of synthetic enzyme HAS2 as well as specific drugs reducing the UDP precursors. The HAS2 phosphorylation is done by AMP kinase, a sensor of cell energy. When the cells have low energy, AMP kinase is activated and modifies covalently the regulatory enzymes, blocking all biosynthetic processes and activating the energy producing metabolism. It was recently reported that the hexosamine biosynthetic pathway (HBP) may increase the concentration of HA precursor UDP-N-acetylglucosamine (UDP-GlcNAc) leading to an increase of HA synthesis. We demonstrated that the increase of HA synthesis depends on the HAS2 post translational modification O-GlcNAcylation, which increases HA secretion modifying a residue different from the phosphorylation site of AMP kinase. In this report we highlighted the critical aspects of the post translational HAS2 regulation and its influence on HA synthesis
Coulomb Blockade in low mobility nanometer size Si:MOSFETs
We investigate coherent transport in Si:MOSFETs with nominal gate lengths 50
to 100nm and various widths at very low temperature. Independent of the
geometry, localized states appear when G=e^{2}/h and transport is dominated by
resonant tunnelling through a single quantum dot formed by an impurity
potential. We find that the typical size of the relevant impurity quantum dot
is comparable to the channel length and that the periodicity of the observed
Coulomb blockade oscillations is roughly inversely proportional to the channel
length. The spectrum of resonances and the nonlinear I-V curves allow to
measure the charging energy and the mean level energy spacing for electrons in
the localized state. Furthermore, we find that in the dielectric regime, the
variance var(lng) of the logarithmic conductance lng is proportional to its
average value consistent with one-electron scaling models.Comment: 4 pages, 4 figure
Oxidized low density lipoprotein (LDL) affects hyaluronan synthesis in human aortic smooth muscle cells
Thickening of the vessel in response to high low density lipoprotein(s) (LDL) levels is a hallmark of atherosclerosis, characterized by increased hyaluronan (HA) deposition in the neointima. Human native LDL trapped within the arterial wall undergoes modifications such as oxidation (oxLDL). The aim of our study is to elucidate the link between internalization of oxLDL and HA production in vitro, using human aortic smooth muscle cells. LDL were used at an effective protein concentration of 20-50 \u3bcg/ml, which allowed 80% cell viability. HA content in the medium of untreated cells was 28.9 \ub1 3.7 nmol HA-disaccharide/cell and increased after oxLDL treatment to 53.9 \ub1 5.6. OxLDL treatments doubled the transcripts of HA synthase HAS2 and HAS3. Accumulated HA stimulated migration of aortic smooth muscle cells and monocyte adhesiveness to extracellular matrix. The effects induced by oxLDL were inhibited by blocking LOX-1 scavenger receptor with a specific antibody (10 \u3bcg/ml). The cholesterol moiety of LDL has an important role in HA accumulation because cholesterol-free oxLDL failed to induce HA synthesis. Nevertheless, cholesterol-free oxLDL and unmodified cholesterol (20 \u3bcg/ml) induce only HAS3 transcription, whereas 22,oxysterol affects both HAS2 and HAS3. Moreover, HA deposition was associated with higher expression of endoplasmic reticulum stress markers (CHOP and GRP78). Our data suggest that HA synthesis can be induced in response to specific oxidized sterol-related species delivered through oxLDL
Barth Syndrome: Exploring Cardiac Metabolism With Induced Pluripotent Stem Cell-Derived Cardiomyocytes
© 2019 by the authors. Licensee MDPI, Basel, Switzerland. Barth syndrome (BTHS) is an X-linked recessive multisystem disorder caused by mutations in the TAZ gene (TAZ, G 4.5, OMIM 300394) that encodes for the acyltransferase tafazzin. This protein is highly expressed in the heart and plays a significant role in cardiolipin biosynthesis. Heart disease is the major clinical manifestation of BTHS with a high incidence in early life. Although the genetic basis of BTHS and tetralinoleoyl cardiolipin deficiency in BTHS-affected individuals are well-established, downstream metabolic changes in cardiac metabolism are still uncovered. Our study aimed to characterize TAZ-induced metabolic perturbations in the heart. Control (PGP1-TAZWT) and TAZ mutant (PGP1-TAZ517delG) iPS-CM were incubated with13C6-glucose and13C5-glutamine and incorporation of13C into downstream Krebs cycle intermediates was traced. Our data reveal that TAZ517delG induces accumulation of cellular long chain acylcarnitines and overexpression of fatty acid binding protein (FABP4). We also demonstrate that TAZ517delG induces metabolic alterations in pathways related to energy production as reflected by high glucose uptake, an increase in glycolytic lactate production and a decrease in palmitate uptake. Moreover, despite mitochondrial dysfunction, in the absence of glucose and fatty acids, TAZ517delG-iPS-CM can use glutamine as a carbon source to replenish the Krebs cycle
Individual charge traps in silicon nanowires: Measurements of location, spin and occupation number by Coulomb blockade spectroscopy
We study anomalies in the Coulomb blockade spectrum of a quantum dot formed
in a silicon nanowire. These anomalies are attributed to electrostatic
interaction with charge traps in the device. A simple model reproduces these
anomalies accurately and we show how the capacitance matrices of the traps can
be obtained from the shape of the anomalies. From these capacitance matrices we
deduce that the traps are located near or inside the wire. Based on the
occurrence of the anomalies in wires with different doping levels we infer that
most of the traps are arsenic dopant states. In some cases the anomalies are
accompanied by a random telegraph signal which allows time resolved monitoring
of the occupation of the trap. The spin of the trap states is determined via
the Zeeman shift.Comment: 9 pages, 8 figures, v2: section on RTS measurements added, many
improvement
Advances, Challenges and Opportunities in 3D CMOS Sequential Integration
3D sequential integration enables the full use of the third dimension thanks to its high alignment performance. In this paper, we address the major challenges of 3D sequential integration: in particular, the control of molecular bonding allows us to obtain pristine quality top active layer. With the help of Solid Phase Epitaxy, we can match the performance of top FET, processed at low temperature (600°C), with the bottom FET devices. Finally, the development of a stable salicide enables to retain bottom performance after top FET processing. Overcoming these major technological issues offers a wide range of applications
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