Two-color rubidium fiber frequency standard

We demonstrate an optical frequency standard based on rubidium vapor loaded within a hollow-core photonic crystal fiber. We use the 5S(1/2)→5D(5/2) two-photon transition, excited with two lasers at 780 and 776 nm. The sum-frequency of these lasers is stabilized to this transition using modulation transfer spectroscopy, demonstrating a fractional frequency stability of 9.8×10(-12) at 1 s. The current performance limitations are presented, along with a path to improving the performance by an order of magnitude. This technique will deliver a compact, robust standard with potential applications in commercial and industrial environments.C. Perrella, P. S. Light, J. D. Anstie, F. N. Baynes, F. Benabid, and A. N. Luite

PLoS Pathog

Metabolomics coupled with heavy-atom isotope-labelled glucose has been used to probe the metabolic pathways active in cultured bloodstream form trypomastigotes of Trypanosoma brucei, a parasite responsible for human African trypanosomiasis. Glucose enters many branches of metabolism beyond glycolysis, which has been widely held to be the sole route of glucose metabolism. Whilst pyruvate is the major end-product of glucose catabolism, its transamination product, alanine, is also produced in significant quantities. The oxidative branch of the pentose phosphate pathway is operative, although the non-oxidative branch is not. Ribose 5-phosphate generated through this pathway distributes widely into nucleotide synthesis and other branches of metabolism. Acetate, derived from glucose, is found associated with a range of acetylated amino acids and, to a lesser extent, fatty acids; while labelled glycerol is found in many glycerophospholipids. Glucose also enters inositol and several sugar nucleotides that serve as precursors to macromolecule biosynthesis. Although a Krebs cycle is not operative, malate, fumarate and succinate, primarily labelled in three carbons, were present, indicating an origin from phosphoenolpyruvate via oxaloacetate. Interestingly, the enzyme responsible for conversion of phosphoenolpyruvate to oxaloacetate, phosphoenolpyruvate carboxykinase, was shown to be essential to the bloodstream form trypanosomes, as demonstrated by the lethal phenotype induced by RNAi-mediated downregulation of its expression. In addition, glucose derivatives enter pyrimidine biosynthesis via oxaloacetate as a precursor to aspartate and orotate

The Athena X-ray Integral Field Unit: a consolidated design for the system requirement review of the preliminary definition phase

Instrumentatio

Author manuscript, published in "48th IEEE Conference on Decision and Control, CDC'09, Shanghai: China (2009)" Design of observer-based controllers

for LPV systems with unknown parameter

Frequency Estimation in Iterative Interference Cancellation Applied to Multibeam Satellite Systems

This paper deals with interference cancellation techniques to mitigate cochannel interference on the reverse link of multibeam satellite communication systems. The considered system takes as a starting point the DVB-RCS standard with the use of convolutional coding. The considered algorithm consists of an iterative parallel interference cancellation scheme which includes estimation of beamforming coefficients. This algorithm is first derived in the case of a symbol asynchronous channel with time-invariant carrier phases. The aim of this article is then to study possible extensions of this algorithm to the case of frequency offsets affecting user terminals. The two main approaches evaluated and discussed here are based on (1) the use of block processing for estimation of beamforming coefficients in order to follow carrier phase variations and (2) the use of single-user frequency offset estimations

X Band Downlink for CubeSat

Six years ago, CNES started R&D studies related to telemetry in X band, with the goal of providing to micro satellite platform manufacturers a low cost but high performances X band transmitter. The promising results achieved have led to the decision to develop a transmitter for ESA PROBA-V spacecraft to be launched in 2013. The first flight models have been designed in only 18 months and will be delivered to ESA in February 2012. In the same way, CNES is now studying a solution to download telemetry in X band for cube and nano satellites. The aim is to provide a high data rate subsystem for missions with high telemetry needs such as Space Spectrum Survey, Automatic Identification System by satellite, Earth Observation, etc…. In the first part, the paper presents the miniaturized transmitter in development, specially designed to cope with the restricted space and energy of very small platforms. The footprint and volume are specially designed to fit with CubeSat dimensions. The consumption is also optimized with 10W for 32 to 34 dBm RF output power. Critical or innovating functions such as flexible bit rate section, data interface, high efficiency power amplifier are described. The second part of the paper is dedicated to the antenna. The design is based on a simple patch antenna realized on standard substrate. The performances of a prototype has been measured in CNES antenna facilities and compared with simulations. Finally, link budgets are presented with 3.4 or 5 m diameter antenna ground stations and data rates up to 50 Mbps, to demonstrate the capacity of this solution to download several gigabytes per day