MMIC power amplifiers as local oscillator drivers for FIRST

The Heterodyne Instrument for the Far-Infrared and Sub- millimeter Telescope requires local oscillators well into the terahertz frequency range. The mechanism to realize the local oscillators will involve synthesizers, active multiplier chains (AMC's) with output frequencies from 71 - 112.5 GHz, power amplifiers to amplify the AMC signals, and chains of Schottky diode multipliers to achieve terahertz frequencies. We will present the latest state-of-the-art results on 70 - 115 GHz Monolithic Millimeter-wave Integrated Circuit power amplifier technology

Development of 200-GHz to 2.7-THz multiplier chains for submillimeter-wave heterodyne receivers

Several astrophysics and Earth observation space missions planned for the near future will require submillimeter-wave heterodyne radiometers for spectral line observations. One of these, the Far InfraRed and Submillimeter Telescope will perform high-sensitivity, high-resolution spectroscopy in the 400 to 2700 GHz range with a seven channel super- conducting heterodyne receiver complement. The local oscillators for all these channels will be constructed around state-of-the-art GaAs power amplifiers in the 71 to 115 GHz range, followed by planar Schottky diode multiplier chains. The Jet Propulsion Laboratory is responsible for developing the multiplier chains for the 1.2, 1.7, and 2.7 THz bands. This paper will focus on the designs and technologies being developed to enhance the current state- of-the-art, which is based on discrete planar or whisker contacted GaAs Schottky diode chips mounted in waveguide blocks. We are proposing a number of new planar integrated circuit and device topologies to implement multipliers at these high frequencies. Approaches include substrateless, framed and frameless GaAs membrane circuitry with single, and multiple planar integrated Schottky diodes. Circuits discussed include 200 and 400 GHz doublers, a 1.2 THz tripler and a 2.4 THz doubler. Progress to date, with the implications of this technology development for future Earth and space science instruments, is presented

MMIC power amplifiers as local oscillator drivers for FIRST

The Heterodyne Instrument for the Far-Infrared and Sub- millimeter Telescope requires local oscillators well into the terahertz frequency range. The mechanism to realize the local oscillators will involve synthesizers, active multiplier chains (AMC's) with output frequencies from 71 - 112.5 GHz, power amplifiers to amplify the AMC signals, and chains of Schottky diode multipliers to achieve terahertz frequencies. We will present the latest state-of-the-art results on 70 - 115 GHz Monolithic Millimeter-wave Integrated Circuit power amplifier technology

The Homeodomain Derived Peptide Penetratin Induces Curvature of Fluid Membrane Domains

BACKGROUND:Protein membrane transduction domains that are able to cross the plasma membrane are present in several transcription factors, such as the homeodomain proteins and the viral proteins such as Tat of HIV-1. Their discovery resulted in both new concepts on the cell communication during development, and the conception of cell penetrating peptide vectors for internalisation of active molecules into cells. A promising cell penetrating peptide is Penetratin, which crosses the cell membranes by a receptor and metabolic energy-independent mechanism. Recent works have claimed that Penetratin and similar peptides are internalized by endocytosis, but other endocytosis-independent mechanisms have been proposed. Endosomes or plasma membranes crossing mechanisms are not well understood. Previously, we have shown that basic peptides induce membrane invaginations suggesting a new mechanism for uptake, "physical endocytosis". METHODOLOGY/PRINCIPAL FINDINGS:Herein, we investigate the role of membrane lipid phases on Penetratin induced membrane deformations (liquid ordered such as in "raft" microdomains versus disordered fluid "non-raft" domains) in membrane models. Experimental data show that zwitterionic lipid headgroups take part in the interaction with Penetratin suggesting that the external leaflet lipids of cells plasma membrane are competent for peptide interaction in the absence of net negative charges. NMR and X-ray diffraction data show that the membrane perturbations (tubulation and vesiculation) are associated with an increase in membrane negative curvature. These effects on curvature were observed in the liquid disordered but not in the liquid ordered (raft-like) membrane domains. CONCLUSIONS/SIGNIFICANCE:The better understanding of the internalisation mechanisms of protein transduction domains will help both the understanding of the mechanisms of cell communication and the development of potential therapeutic molecular vectors. Here we showed that the membrane targets for these molecules are preferentially the fluid membrane domains and that the mechanism involves the induction of membrane negative curvature. Consequences on cellular uptake are discussed

Jérémie fut-il prophète pour les nations?

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Is the solar system entering a nearby interstellar cloud

Summary: « Reading ebooks : a new reading contact ? » Since ebook reader software and hand-held dedicated ebook devices have arrived on the market in 1998, they have been heralded for opening new intellectual cognitive pathways. At the same time, alarmist voices have arisen, prophetizing the end of the printed book and of reading traditions. Is the future of reading really at stake ? Reading practices develop within implicit “reading contracts” which define minimal conditions and necessary presuppositions for establishing communication structures between texts, readers and authors. Ebooks with their “invisible” digital format could greatly upset these conventions and fragilise the central role of books in western culture and society. Do ebooks modify or change the different ways of negociating meaning through texts ? Will a new reading contract emerge with these dedicated devices that offer high readability (in the sense of legibility), portability and physical eye comfort ? These issues will be addressed through the results of a recent survey done with public library users of ebooks in the Rhone-Alps region in the first semester of 2002

Structural malleability of plasticins: Preorganized conformations in solution and relevance for antimicrobial activity

International audiencePlasticins (23 long residue glycine-leucine-rich dermaseptin-related peptides produced by the skin of South American hylids) have very similar amino acid sequences, hydrophobicities, and amphipathicities, but differ in their membrane-damaging properties and structurations (i.e. destabilized helix states, beta-hairpin, beta-sheet, and disordered states) at anionic and zwitterionic membrane interfaces. Structural malleability of plasticins in aqueous solutions together with parameters that may govern their ability to fold within beta-hairpin like structures were analyzed through circular dichroism and FTIR spectroscopic studies completed by molecular dynamics simulations in polar mimetic media. The goal of this study was to probe to which extent pre-existent peptide conformations, i.e. intrinsic ``conformational landscape'', may be responsible for variability in bioactive conformation and antimicrobial/hemolytic mechanisms of action of these peptides in relation with their various membrane disturbing properties. All plasticins present a turn region that does not always result in folding into a beta-hairpin shaped conformation. Residue at position 8 plays a major role in initiating the folding, while position 12 is not critical. Conformational stability has no major impact on antimicrobial efficacy. However, preformed beta-hairpin in solution may act as a conformational lock that prevents switch to alpha-helical structure. This lock lowers the antimicrobial efficiency and explains subtle differences in potencies of the most active antimicrobial plasticins