226 research outputs found
Isotope shifts of the (3s3p)P - (3s4s)S Mg I transitions
We report measurements of the isotope shifts of the (3s3p)P -
(3s4s)S Mg I transitions for the stable isotopes Mg (I=0),
Mg (I=5/2) and Mg (I=0). Furthermore the Mg S
hyperfine coefficient A(S) = (-321.6 1.5) MHz is extracted and
found to be in excellent agreement with state-of-the-art theoretical
predictions giving A(S) = -325 MHz and B(S)
MHz. Compared to previous measurements, the data presented in this work is
improved up to a factor of ten.Comment: 4 pages, 4 figures submitted to PR
Measurement of the Spin-forbidden Decay rate (3s3d)D (3s3p)P in Mg
We have measured the spin-forbidden decay rate from (3s3d)D
(3s3p)P in Mg atoms trapped in a magneto-optical trap. The
total decay rate, summing up both exit channels (3s3p)P and
(3s3p)P, yields (196 10) s in excellent agreement with
resent relativistic many-body calculations of [S.G. Porsev et al., Phys. Rev.
A. \textbf{64}, 012508 (2001)]. The characterization of this decay channel is
important as it may limit the performance of quantum optics experiments carried
out with this ladder system as well as two-photon cooling experiments currently
explored in several groups.Comment: 9 pages, 4 figure
Transportable laser system for atom interferometry
Soumis à Optics LettersWe describe an optical bench in which we lock the relative frequencies or phases of a set of three lasers in order to use them in a cold atoms interferometry experiment. As a new feature, the same two lasers serve alternately to cool atoms and to realize the atomic interferometer. This requires a fast change of the optical frequencies over a few GHz. The number of required independent laser sources is then only 3, which enables the construction of the whole laser system on a single transportable optical bench. Recent results obtained with this optical setup are also presented
Measurement of the 3s3p 3P1 lifetime in magnesium using a magneto-optical trap
We demonstrate an accurate method for measuring the lifetime of
long-lived metastable magnetic states using a magneto-optical trap
(MOT). Through optical pumping, the metastable (3s3p) (3)P(1) level is
populated in a standard MOT. During the optical pumping process, a
fraction of the population is captured in the magnetic quadrupole field
of the MOT. When the metastable atoms decay to the (3s(2)) (1)S(0)
ground state they are recaptured into the MOT. In this system no
alternative cascading transition is possible. The lifetime of the
metastable level is measured directly as an exponential load time of the
MOT. We have experimentally tested our method by measuring the lifetime
of the (3s3p) (3)P(1) of (24)Mg. This lifetime has been measured
numerous times previously, but with quite different results. Using our
method we find the (3s3p) (3)P(1) lifetime to be (4.4 +/- 0.2) ms.
Theoretical values point toward a lower value for the lifetime
Lead concentrations in blood from incubating common eiders (Somateria mollissima) in the Baltic Sea
Here we investigate if lead may be a contributing factor to the observed population decline in a Baltic colony of incubating eiders (Somateria mollissima). Body mass and blood samples were obtained from 50 incubating female eiders at the Baltic breeding colony on Christianso during spring 2017 (n = 27) and 2018 (n = 23). All the females were sampled twice during early (day 4) and late (day 24) incubation. The full blood was analysed for lead to investigate if the concentrations exceeded toxic thresholds or changed over the incubation period due to remobilisation from bones and liver tissue. Body mass, hatch date and number of chicks were also analysed with respect to lead concentrations. The body mass (mean +/- SD g) increased significantly in the order: day 24 in 2018 (1561 +/- 154 g) < day 24 in 2017 (1618 +/- 156 g) < day 4 in 2018 (2183 +/- 140 g) < day 4 in 2017 (2359 +/- 167 g) (all p < 0.001). The lead concentrations increased significantly in the opposite order i.e. day 4 in 2017 (41.7 +/- 67.1 mu g/L) < day 24 in 2017 (55.4 +/- 66.8 mu g/L) < day 4 in 2018 (177 +/- 196 mu g/L) < day 24 in 2018 (258 +/- 243) (all p < 0.001). From day 4 to 24, the eider females had a 1.33-fold increase in blood lead concentrations in 2017 and a 1.46-fold increase in 2018. Three of the birds (13%) sampled in 2018 had lead concentrations that exceeded concentrations of clinical poisoning (500 mu g/L) and eleven (48%) had concentrations that exceeded the threshold for subclinical poisoning (200 mu g/L). In 2017, none of the birds exceeded the high toxic threshold of clinical poisoning while only one (4%) exceeded the lower threshold for subclinical poisoning. Three of the birds (6%) sampled in 2018 had lead concentrations that exceeded those of clinical poisoning while 12 birds (24%) resampled in both years exceeded the threshold for subclinical poisoning. In addition, lead concentrations and body mass on day 4 affected hatch date positively in 2018 (both p < 0.03) but not in 2017. These results show that bioavailable lead in bone and liver tissue pose a threat to the health of about 25% of the incubating eiders sampled. This is particularly critical because eiders are largely capital breeding which means that incubating eiders are in an energetically stressed state. The origin of lead in incubating eiders in the Christianso colony is unknown and it remains an urgent priority to establish the source, prevalence and mechanism for uptake. The increase in lead from day 4 to day 24 is due to bone and liver remobilization; however, the additional lead source(s) on the breeding grounds needs to be identified. Continued investigations should determine the origin, uptake mechanisms and degree of exposure to lead for individual birds. Such research should include necropsies, x-ray, lead isotope and stable C and N isotope analyses to find the lead sources(s) in the course of the annual cycle and how it may affect the population dynamics of the Christianso colony which reflects the ecology of the Baltic eiders being suitable for biomonitoring the overall flyway
Boundary work: becoming middle class in suburban Dar es Salaam
Suburban space provides a useful window onto contemporary class practices in Africa, where it is difficult to identify social classes on the basis of income or occupation. In this article I argue that the middle classes and the suburbs are mutually constitutive in the Tanzanian city of Dar es Salaam. Using interviews with residents and local government officials in the city's northern suburbs, I discuss the material and representational practices of middle-class boundary work in relation to land and landscape. If the middle classes do not presently constitute a coherent political-economic force, they are nevertheless transforming the city's former northern peri-urban zones into desirable suburban residential neighbourhoods
- …