Polarizabilities of the 87Sr Clock Transition

In this paper, we propose an in-depth review of the vector and tensor polarizabilities of the two energy levels of the 87Sr clock transition whose measurement was reported in [P. G. Westergaard et al., Phys. Rev. Lett. 106, 210801 (2011)]. We conduct a theoretical calculation that reproduces the measured coefficients. In addition, we detail the experimental conditions used for their measurement in two Sr optical lattice clocks, and exhibit the quadratic behaviour of the vector and tensor shifts with the depth of the trapping potential and evaluate their impact on the accuracy of the clock

Analysis and calibration of absorptive images of Bose-Einstein condensate at non-zero temperatures

We describe the method allowing quantitative interpretation of absorptive images of mixtures of BEC and thermal atoms which reduces possible systematic errors associated with evaluation of the contribution of each fraction. By using known temperature dependence of the BEC fraction, the analysis allows precise calibration of the fitting results. The developed method is verified in two different measurements and compares well with theoretical calculations and with measurements performed by another group.Comment: 17 pages, 8 figure

Procjena povratka investicija za predloženo rabljenje solarnih sustava u Poljskoj

This paper focuses on the assessment of possibilities to subsidize the purchase and installation of solar collectors in Poland by government or local government grants and special funds designed for this purpose. It analysis of costs and profits resulting from the application of solar installations in the process of heat generation for household requirements, by calculating the payback time, with taking into account prices of other energy carriers and the above mentioned subsidies. Collectors at present are manufactured solely from metals (copper, aluminium, Al-Mg alloys). The use of these materials is tied to considerable energy demand and the production technology is complex. This affects the economy of running a solar device.Članak je usmjeren na procjenu mogućnosti novčane potpore nabavke instalacija solarnih kolektora u Poljskoj od vlade ili lokalnih pokrovitelja te posebni fondovi utemeljeni u tu svrhu. Analizirani su troškovi i dobit kao rezultat primjene solarnih instalacija u procesima zagrijavanja po zahtjevima, proračuna povratka investicije, uzimajući u obzir cijene računa ostalih, tj. više drugih usporednih energija. Sadašnji kolektori ustrojeni su od metala (bakra, aluminija, Al-Mg legure). Rabljenje ovih materijala je u svezi energetskim zahtjevima i proizvodnom tehnologijom. Utjecaji ekonomije ovisni su o solarnim uređajima

Probe spectroscopy in an operating magneto-optical trap: the role of Raman transitions between discrete and continuum atomic states

We report on cw measurements of probe beam absorption and four-wave-mixing spectra in a $^{85}$Rb magneto-optical trap taken while the trap is in operation. The trapping beams are used as pump light. We concentrate on the central feature of the spectra at small pump-probe detuning and attribute its narrow resonant structures to the superposition of Raman transitions between light-shifted sublevels of the ground atomic state and to atomic recoil processes. These two contributions have different dependencies on trap parameters and we show that the former is inhomogeneously broadened. The strong dependence of the spectra on the probe-beam polarization indicates the existence of large optical anisotropy of the cold-atom sample, which is attributed to the recoil effects. We point out that the recoil-induced resonances can be isolated from other contributions, making pump-probe spectroscopy a highly sensitive diagnostic tool for atoms in a working MOT.Comment: 9 pages, 8 figure

Forage Production and Grazing Behaviour of Beef Cattle in Agrosilvopastoral Systems in Brazil during the Dry Season

We aimed at evaluating the microclimate, canopy structure, and grazing behaviour of cattle on Brachiaria sp. pastures within continuous pasture (CON), integrated crop-livestock (ICL), and crop-livestock-forestry (ICLF) systems in Brazilian dry season. Forage accumulation was monthly assessed in four paddocks per system from May to August 2019. To characterize the microclimate, air temperature and relative humidity were measured every hour and temperature-humidity index calculated. Grazing behaviour of 12 Nellore heifers per system (mean bodyweight 355 standard deviation±32.6 kg) was recorded by chewing sensors on nine continuous days (1 d adaptation + 8 d measurement) of three 15-d periods. Four animals per system were evaluated per period (n=3 systems x 3 animals x 3 periods x 8 d). Data were analysed by mixed model using SAS v9.4. Statistical significances were tested at P\u3c 0.05. Across the whole dry season, heifers were exposed to 343 hours of moderate heat stress and 76 hours of severe heat stress in CON and ICL. Instead, 342 hours of moderate heat stress but no severe heat stress conditions were observed in ICLF. Forage accumulation rate was greater in CON than ICLF, with no differences between ICLF and ICL. There were no differences between the systems for proportions of green leaf and dead plant material, although dead material accounted for 73% of total forage biomass on dry matter basis. Pasture in ICL was taller and had greater stem proportion than CON and ICLF. Forage canopy structure likely reduced bite mass in CON and ICL. As a compensatory mechanism, heifers in CON and ICL increased their number of grazing bites and prolonged their daily grazing time (in CON) as compared to animals in ICLF. In summary, under conditions of Brazilian dry season, grazing behaviour of Nellore heifers seems to be more influenced by canopy structure than by microclimatic factors

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

Experimenting an optical second with strontium lattice clocks

Progress in realizing the SI second had multiple technological impacts and enabled to further constraint theoretical models in fundamental physics. Caesium microwave fountains, realizing best the second according to its current definition with a relative uncertainty of 2-4x10^(-16), have already been superseded by atomic clocks referenced to an optical transition, both more stable and more accurate. Are we ready for a new definition of the second? Here we present an important step in this direction: our system of five clocks connects with an unprecedented consistency the optical and the microwave worlds. For the first time, two state-of-the-art strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.6x10^(-16). Their comparison with three independent caesium fountains shows a degree of reproducibility henceforth solely limited at the level of 3.1x10^(-16) by the best realizations of the microwave-defined second.Comment: 9 pages, 4 figures, 2 table

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

Free-fall expansion of finite-temperature Bose-Einstein condensed gas in the non Thomas-Fermi regime

We report on our study of the free-fall expansion of a finite-temperature Bose-Einstein condensed cloud of 87Rb. The experiments are performed with a variable total number of atoms while keeping constant the number of atoms in the condensate. The results provide evidence that the BEC dynamics depends on the interaction with thermal fraction. In particular, they provide experimental evidence that thermal cloud compresses the condensate.Comment: 8 pages, 4 figure