Oxidation resistance of ODS alloy PM2000 from 880°C to 1400°C

Oxidation resistance of ODS alloy PM2000 from 880°C to 1400°

A simple laser system for atom interferometry

We present here a simple laser system for a laser cooled atom interferometer, where all functions (laser cooling, interferometry and detection) are realized using only two extended cavity laser diodes, amplified by a common tapered amplifier. One laser is locked by frequency modulation transfer spectroscopy, the other being phase locked with an offset frequency determined by an Field-Programmable Gate Array (FPGA) controlled Direct Digital Synthesizer (DDS), which allows for efficient and versatile tuning of the laser frequency. Raman lasers are obtained with a double pass acousto-optic modulator. We demonstrate a gravimeter using this laser system, with performances close to the state of the art

Evolution of microstructure and impact-strength energy in thermally and thermomechanically aged 15-5 PH

Due to its outstanding mechanical resistance and resistance to corrosion, alloy 15-5 PH can be beneficially used for manufacturing aerospace structural parts. Following exposure to intermediate temperature, from300◦–400 ◦C, the alloy embrittles through the decomposition of the martensite into iron-rich and chromium-rich domains.Depending on the ageing time, these domains are either interconnected or unconnected with each other. The embrittlement results in a drastic drop of the impact strength-energy and an increase of the ductile-to-brittle transition temperature. The initial microstructure and mechanical properties can be recovered through a re-homogenization of the distribution of chromium and iron atoms in the material in the case where the decomposition of the matrix is not too pronounced. The application of a stress higher than 60 per cent of the yield strength further enhances the ageing kinetics in the case where the combined effect of temperature and time results in the spinodal decomposition of the martensite

A compact micro-wave synthesizer for transportable cold-atom interferometers

We present the realization of a compact micro-wave frequency synthesizer for an atom interferometer based on stimulated Raman transitions, applied to transportable inertial sensing. Our set-up is intended to address the hyperfine transitions of Rubidium 87 atoms at 6.8 GHz. The prototype is evaluated both in the time and the frequency domain by comparison with state-of-the-art frequency references developed at LNE-SYRTE. In free-running mode, it features a residual phase noise level of -65 dBrad$^2.Hz^{-1} at 10-Hz offset frequency and a white phase noise level in the order of -120 dBrad^2.Hz^{-1} for Fourier frequencies above 10 kHz. The phase noise effect on the sensitivity of the atomic interferometer is evaluated for diverse values of cycling time, interrogation time and Raman pulse duration. To our knowledge, the resulting contribution is well below the sensitivity of any demonstrated cold atom inertial sensors based on stimulated Raman transitions. The drastic improvement in terms of size, simplicity and power consumption paves the way towards field and mobile operations.Comment: accepted for publication in Review of Scientific Instruments, 6 pages, 4 figure

Dick effect in a pulsed atomic clock using Coherent Population Trapping

The Dick effect can be a limitation of the achievable frequency stability of a passive atomic frequency standard when the ancillary frequency source is only periodically sampled. Here we analyze the Dick effect for a pulsed vapor cell clock using coherent population trapping (CPT). Due to its specific interrogation process without atomic preparation nor detection outside of the Ramsey pulses, it exhibits an original shape of the sensitivity function to phase noise of the oscillator. Numerical calculations using a three-level atom model are successfully compared with measurements; an approximate formula of the sensitivity function is given as an easy-to-use tool. A comparison of our CPT clock sensitivity to phase noise with a clock of the same duty cycle using a two-level system reveals a higher sensitivity in the CPT case. The influence of a free-evolution time variation and of a detection duration lengthening on this sensitivity is studied. Finally this study permitted to choose an adapted quartz oscillator and allowed an improvement of the clock fractional frequency stability at the level of 3.2x10-13 at 1

Reinforced sol–gel thermal barrier coatings and their cyclic oxidation life

Cyclic oxidation life enhancement of sol–gel thermal barrier coatings is obtained via the reinforcement of the controlled micro-crack network that forms during the initial sintering of the deposit. Two different sol–gel methods are used to fill in the process-induced cracks, namely dipcoating and spray-coating. Filling parameters, for instance the number of passes or the viscosity of the sol are adjusted, using various techniques such as profilometry and microstructural analysis, to optimise crack filling. Cyclic oxidation tests are implemented at both 1100C and 1150C to investigate the efficiency of the various reinforcement procedures developed and address the influence of the specific microstructure on the oxidation behaviour

Sub-100 attoseconds optics-to-microwave synchronization

We use two fiber-based femtosecond frequency combs and a low-noise carrier suppression phase detection system to characterize the optical to microwave synchronization achievable with such frequency divider systems. By applying specific noise reduction strategies, a residual phase noise as low as -120 dBc/Hz at 1 Hz offset frequency from a 11.55 GHz carrier is measured. The fractional frequency instability from a single optical-to-frequency divider is 1.1E-16 at 1 s averaging down to below 2E-19 after only 1000 s. The corresponding rms time deviation is lower than 100 attoseconds up to 1000 s averaging duration.Comment: 4 pages, 3 figure

Hybridizing matter-wave and classical accelerometers

We demonstrate a hybrid accelerometer that benefits from the advantages of both conventional and atomic sensors in terms of bandwidth (DC to 430 Hz) and long term stability. First, the use of a real time correction of the atom interferometer phase by the signal from the classical accelerometer enables to run it at best performances without any isolation platform. Second, a servo-lock of the DC component of the conventional sensor output signal by the atomic one realizes a hybrid sensor. This method paves the way for applications in geophysics and in inertial navigation as it overcomes the main limitation of atomic accelerometers, namely the dead times between consecutive measurements

Interfacial toughness of the nickel-nickel oxide system

International audienc

Conflicto lingüístico y separatismo en Canadá

Este artículo analiza la historia del conflicto lingüístico entre el pueblo francófono y el pueblo anglófono dentro de la doble realidad cultural de Canadá y muestra el imperialismo inglés hacia el pueblo québécois a lo largo de su historia. Con respecto a la posible independencia de Quebec, el artículo habla a favor de un Canadá unido sin miedo de ofender a los québécois. Y se desprenden dos conclusiones: una emocional y otra racional. La emocional nos recuerda las palabras del profesor Russell: “Amo a Canadá”, “Canadá es un gran país”. En la racional se nos recuerda las trágicas consecuencias de la desintegración de imperios y naciones. Y se afirma que los québécois no van a vivir mejor si se separan del resto de Canadá. Lo que se necesita verdaderamente es un federalismo más interactivo y más económicamente independiente de los Estados Unidos. This article examines the history of the linguistic conflict between Francophones and Anglophones within the double cultural reality of Canada and shows the English imperialism towards the Quebecois throughout their history. With regard to the possible independence of Quebec, the article discusses Canadian unity without fear of offending the Quebecois. Two conclusions stand out: one emotional and another rational. The emotional one reminds us of Professor Russell’s words: “I love Canada”, “Canada is a great place”. The rational conclusion reminds us of the tragic consequences of the disintegration of empires and nations. It is asserted that the Quebecois will not live better if they separate from the rest of Canada. What the country really needs is a federalism, more interactive and more economically independent from the United States