Discovery of two new bright magnetic B stars: i Car and Atlas

The BRITE (BRIght Target Explorer) constellation of nano-satellites performs seismology of bright stars via high precision photometry. In this context, we initiated a high resolution, high signal-to-noise, high sensitivity, spectropolarimetric survey of all stars brighter than V=4. The goal of this survey is to detect new bright magnetic stars and provide prime targets for both detailed magnetic studies and asteroseismology with BRITE. Circularly polarised spectra were acquired with Narval at TBL (France) and HarpsPol at ESO in La Silla (Chile). We discovered two new magnetic B stars: the B3V star i Car and the B8V component of the binary star Atlas. Each star was observed twice to confirm the magnetic detections and check for variability. These bright magnetic B stars are prime targets for asteroseismology and for flux-demanding techniques, such as interferometry.Comment: accepted in MNRAS Letters, 5 pages, 3 figure

A 300-800MHz Tunable Filter and Linearized LNA applied in a Low-Noise Harmonic-Rejection RF-Sampling Receiver

A multiband flexible RF-sampling receiver aimed at software-defined radio is presented. The wideband RF sampling function is enabled by a recently proposed discrete-time mixing downconverter. This work exploits a voltage-sensing LNA preceded by a tunable LC pre-filter with one external coil to demonstrate an RF-sampling receiver with low noise figure (NF) and high harmonic rejection (HR). The second-order LC filter provides voltage pre-gain and attenuates the source noise aliasing, and it also improves the HR ratio of the sampling downconverter. The LNA consists of a simple amplifier topology built from inverters and resistors to improve the third-order nonlinearity via an enhanced voltage mirror technique. The RF-sampling receiver employs 8 times oversampling covering 300 to 800 MHz in two RF sub-bands. The chip is realized in 65 nm CMOS and the measured gain across the band is between 22 and 28 dB, while achieving a NF between 0.8 to 4.3 dB. The IIP2 varies between +38 and +49 dBm and the IIP3 between -14 dBm and -9 dBm, and the third and fifth order HR ratios are more than 60 dB. The LNA and downconverter consumes 6 mW, and the clock generator takes 12 mW at 800 MHz RF.\ud \u

Nucleation threshold and deactivation mechanisms of nanoscopic cavitation nuclei

The acoustic nucleation threshold for bubbles trapped in cavities has theoretically been predicted within the crevice theory by Atchley and Prosperetti [“The crevice model of bubble nucleation,” J. Acoust. Soc. Am. 86, 1065 (1989)]. Here, we determine this threshold experimentally, by applying\ud a single pressure pulse to bubbles trapped in cylindrical nanoscopic pits (“artificial crevices”) with radii down to 50 nm. By decreasing the minimum pressure stepwise, we observe the threshold for which the bubbles start to nucleate. The experimental results are quantitatively in good agreement with the theoretical predictions of Atchley and Prosperetti. In addition, we provide the mechanism which explains the deactivation of cavitation nuclei: gas diffusion together with an aspherical bubble collapse. Finally, we present superhydrophobic nuclei which cannot be deactivated, unless with a high-speed liquid jet directed into the pit

Phased-Array antenna beam squinting related to frequency dependency of delay circuits

Abstract-Practical time delay circuits do not have a perfectly linear phase-frequency characteristic. When these delay circuits are applied in a phased-array system, this frequency dependency shows up as a frequency dependent beam direction (“beam squinting”). This paper quantifies beam squinting for a linear one-dimensional phased array with equally spaced antenna elements. The analysis is based on a (frequency-dependent) linear approximation of the phase transfer function of the delay circuit. The resulting relation turns out to be invariant for cascaded cells. Also a method is presented to design time-delay circuits to meet a maximum phased-array beam squinting requirement

Integrating Human Health into Environmental Impact Assessment: Case Studies of Canada’s Northern Mining Resource Sector

This paper examines the integration of human health considerations into environmental impact assessment (EIA) in the Canadian North. Emphasis is placed on the northern mining sector, where more land has been staked in the past decade than in the previous 50 years combined. Using information from interviews with northern EIA and health practitioners and reviews of selected project documents, we examined three principal mining case studies, northern Saskatchewan uranium mining operations, the Ekati diamond project, and the Voisey’s Bay mine/mill project, to determine whether and how health considerations in EIA have evolved and the current nature and scope of health integration. Results suggest that despite the recognized link between environment and health and the number of high-profile megaprojects in Canada’s North, human health, particularly social health, has not been given adequate treatment in northern EIA. Health considerations in EIA have typically been limited to physical health impacts triggered directly by project-induced environmental change, while social and other health determinants have been either not considered at all, or limited to those aspects of health and well-being that the project proponent directly controlled, namely employment opportunities and worker health and safety. In recent years, we have been seeing improvements in the scope of health in EIA to reflect a broader range of health determinants, including traditional land use and culture. However, there is still a need to adopt impact mitigation and enhancement measures that are sensitive to northern society, to monitor and follow up actual health impacts after project approval, and to ensure that mitigation and enhancement measures are effective.Dans cet article, on se penche sur l’intégration des considérations en matière de santé humaine dans le cadre de l’évaluation des incidences environnementales dans le Nord canadien. On met l’accent sur le secteur minier du Nord, où plus de terres ont été jalonnées ces dix dernières années que pendant les 50 années précédentes. À la lumière des commentaires obtenus en entrevues avec des spécialistes des évaluations environnementales et de la santé du Nord ainsi que de l’examen de certains documents de projets, on a examiné trois études de cas principales portant sur l’exploitation minière – soit les exploitations d’uranium du nord de la Saskatchewan, le projet de diamants Ekati, et le projet de mine et d’usine de la baie Voisey – afin de déterminer si et comment les considérations en matière de santé dans le cadre de l’évaluation des incidences environnementales ont évolué ainsi que la nature et l’étendue actuelle de l’intégration de la santé. Les résultats indiquent que malgré le lien manifeste entre l’environnement et la santé ainsi que le nombre de mégaprojets de haut calibre entrepris dans le Nord canadien, la santé humaine, et plus particulièrement la santé sociale, n’est pas traitée adéquatement dans le cadre de l’évaluation des incidences environnementales du Nord. Généralement, les considérations de santé dans le cadre de l’évaluation des incidences environnementales se limitent aux incidences d’ordre physique directement attribuables aux changements environnementaux découlant du projet, alors que les déterminants d’ordre social ou autre n’ont pas été considérés du tout ou se sont limités aux aspects de la santé et du bien-être que les promoteurs du projet contrôlaient directement, notamment les occasions d’emploi, de même que la santé et la sécurité des travailleurs. Ces dernières années, on a enregistré des améliorations sur le plan de la santé dans le cadre de l’évaluation des incidences environnementales afin de tenir compte d’une gamme plus vaste de déterminants en matière de santé, ce qui comprend l’utilisation traditionnelle de la terre et la culture. Cela dit, le besoin d’adopter des mesures de mise en valeur et d’atténuation des incidences qui respectent la société du Nord se fait toujours sentir, de même que des mesures qui permettent de surveiller et de suivre les incidences réelles sur la santé une fois les projets approuvés. Il y a aussi lieu de s’assurer que les mesures de mise en valeur et d’atténuation portent fruits

Automatic tuning of quality factors for VHF CMOS filters

A VHF transconductance-C filter technique with automatic tuning of the quality factors and the cutoff frequency, based on a voltage controlled oscillator (VCO), is presented. The Q-tuning circuit is very simple and contains no signal carrying nodes, resulting in a well-controlled Q up to very high frequencies (100 MHz). A breadboard realization of the Q-tuning circuit gave good result

Control and tuning of a suspended Fabry-Perot cavity using digitally-enhanced heterodyne interferometry

We present the first demonstration of real-time closed-loop control and deterministic tuning of an independently suspended Fabry-Perot optical cavity using digitally-enhanced heterodyne interferometry, realising a peak sensitivity of $\sim$10 pm$/\sqrt{\mathrm{Hz}}$ over the 10-1000 Hz frequency band. The methods presented are readily extensible to multiple coupled cavities. As such, we anticipate that refinements of this technique may find application in future interferometric gravitational-wave detectors