Strontium optical lattice clocks for practical realization of the metre and secondary representation of the second

We present a system of two independent strontium optical lattice standards probed with a single shared ultra-narrow laser. The absolute frequency of the clocks can be verified by the use of Er:fiber optical frequency comb with the GPS-disciplined Rb frequency standard. We report hertz-level spectroscopy of the clock line and measurements of frequency stability of the two strontium optical lattice clocks.Comment: This is an author-created, un-copyedited version of an article accepted for publication in Meas. Sci. Technol. The publisher is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at doi:10.1088/0957-0233/26/7/07520

Fibre-optic delivery of time and frequency to VLBI station

The quality of Very Long Baseline Interferometry (VLBI) radio observations predominantly relies on precise and ultra-stable time and frequency (T&F) standards, usually hydrogen masers (HM), maintained locally at each VLBI station. Here, we present an operational solution in which the VLBI observations are routinely carried out without use of a local HM, but using remote synchronization via a stabilized, long-distance fibre-optic link. The T&F reference signals, traceable to international atomic timescale (TAI), are delivered to the VLBI station from a dedicated timekeeping laboratory. Moreover, we describe a proof-of-concept experiment where the VLBI station is synchronized to a remote strontium optical lattice clock during the observation.Comment: 8 pages, 8 figures, matches the version published in A&A, section Astronomical instrumentatio

Line shape measurements of rubidium 5S-7S two-photon transition

We report the use of a digital lock to measure the line profile and center frequency of rubidium 5S-7S two-photon transitions with a cw laser referenced to an optical frequency comb. The narrow, two-photon transition, 5S-7S (760 nm), insensitive to first-order in a magnetic field, is a promising candidate for frequency reference

Fast Approximated POD for a Flat Plate Benchmark with a Time Varying Angle of Attack

An approximate POD algorithm provides an empirical Galerkin approximation with guaranteed a priori lower bound on the required resolution. The snapshot ensemble is partitioned into several sub-ensembles. Cross correlations between these sub-ensembles are approximated in terms of a far smaller correlation matrix. Computational speedup is nearly linear in the number of partitions, up to a saturation that can be estimated a priori. The algorithm is particularly suitable for analyzing long transient trajectories of high dimensional simulations, but can be applied also for spatial partitioning and parallel processing of very high spatial dimension data. The algorithm is demonstrated using transient data from two simulations. First, a two dimensional simulation of the flow over a flat plate, as it transitions from AOA = 30° to a horizontal position and back. Second, a three dimensional simulation of a flat plate with aspect ratio two as it transitions from a horizontal position to AOA = 30°

Active Noise Reduction Algorithm Based on NOTCH Filter and Genetic Algorithm

Application of active noise reduction (ANR) systems in hearing protectors requires the use of control algorithms to ensure stability of the ANR system and at the same time highly effective active noise reduction. A control algorithm based on NOTCH filters is an example of solutions that meet these criteria. Their disadvantage is operation over a narrow frequency band and a need for prior determination of frequencies to be reduced. This paper presents a solution of the ANR system for hearing protectors which is controlled with the use of modified NOTCH filters with parameters determined by a genetic algorithm. Application of a genetic algorithm allows to change the NOTCH filter reference signal frequency, and thus, adapt the filter to the reduced signal frequency

An active hearing protector with an external power supply system

W artykule przedstawiono opis aktywnego ochronnika słuchu przystosowanego do stosowania na stacjonarnych stanowiskach pracy oraz Bazę stacjonarnych stanowisk pracy. Konstrukcje aktywnego ochronnika słuchu zmodyfikowano wykonując moduł umożliwiaj1cy wykorzystanie dostępnego źródła zasilania na stanowisku pracy. Do modułu przeniesiono części elementów elektronicznych z nauszników aktywnego ochronnika słuchu.This paper describes an active hearing protector (adapted to stationary work stations) end a Database of stationary workstations. The active hearing protector has been modified by adding a new module, which has made the use of a current generator at a workstation possible. Some electronic elements have been transferred from the muffs of an active hearing protector to the module

Internet service of aided prevention against noise and vibration in occupational environment

W artykule przedstawiono system wspomagania profilaktyki narażenia na hałas i drgania mechaniczne w środowisku pracy oparty na serwisie internetowym umieszczonym pod adresem http://www.serwis.wypadek.pl. W serwisie tym zawarto zestaw poradników i materiałów informacyjnych profilowanych pod kątem działów gospodarki o wysokim ryzyku zawodowym, jak również użyteczne narzędzia, które mogą służyć jako pomoc w planowaniu działań profilaktycznych w zakładach pracy.This paper presents the internet system for prevention against noise and vibration based on internet service http://serwis.wypadek.pl. It includes a set of manuals and information papers designed for high occupational risk economy sectors as well as other useful tools which can be used to bail out prevention planning processes at workplaces

Cautionary device in preferential vehicles integrated with active noise reduction system

Sygnał akustyczny generowany przez pojazd uprzywilejowany musi być dostatecznie głośny, aby w warunkach ruchu drogowego był dobrze rozpoznawany przez pozostałych uczestników ruchu. Wysoki poziom ciśnienia akustycznego sygnału ostrzegawczego powoduje, że dla załogi pojazdu uprzywilejowanego stanowi on uciążliwy i szkodliwy hałas. W artykule przedstawiono najważniejsze informacje na temat sygnalizacji akustycznej w pojazdach uprzywilejowanych jak również koncepcję ograniczenia niekorzystnego wpływu sygnału ostrzegawczego na załogę pojazdu uprzywilejowanego poprzez zastosowanie systemów aktywnej redukcji hałasu.Acoustic warning signal generated by privileged vehicles should be loud enough to be well recognized in the road traffic. The high pressure level of the warning signal makes it a harmful noise for the crew of the privileged vehicle. This paper presents basic information about acoustic signalization in privileged vehicles as well as a method for limitation of influence of the noise generated by the acoustic warning device on vehicle crew

Internet assisted prevention against noise and vibration in the working environment

W artykule przedstawiono założenia systemu wspomagania profilaktyki narażenia na hałas i drgania mechaniczne w środowisku pracy, którego głównym elementem będzie serwis internetowy. Uzasadniając podjęcie tego zagadnienia, przedstawiono dane statystyczne dotyczące zagrożeń hałasem i drganiami mechanicznymi w środowisku pracy oraz chorób zawodowych wynikających z narażenia na te czynniki. Przedstawione w artykule informacje o zawartości istniejących już witryn internetowych dotyczących hałasu i drgań mechanicznych oraz dane dotyczące wykorzystania przez pracowników zasobów Internetu zadecydowały o przyjęciu przedstawionej w artykule formy serwisu.The article presents ideas and basic parameters of an Internet system for prevention against noise and vibration. The proposed system is based on a dedicated Internet portal. The concept of the system is based on the results of exposure to noise and vibration and an analysis of occupational diseases. Detailed data about Internet sources of information related to noise and vibration are presented