300 research outputs found
Optical cooling and trapping of highly magnetic atoms: The benefits of a spontaneous spin polarization
From the study of long-range-interacting systems to the simulation of gauge
fields, open-shell Lanthanide atoms with their large magnetic moment and narrow
optical transitions open novel directions in the field of ultracold quantum
gases. As for other atomic species, the magneto-optical trap (MOT) is the
working horse of experiments but its operation is challenging, due to the large
electronic spin of the atoms. Here we present an experimental study of
narrow-line Dysprosium MOTs. We show that the combination of radiation pressure
and gravitational forces leads to a spontaneous polarization of the electronic
spin. The spin composition is measured using a Stern-Gerlach separation of spin
levels, revealing that the gas becomes almost fully spin-polarized for large
laser frequency detunings. In this regime, we reach the optimal operation of
the MOT, with samples of typically atoms at a temperature of
15\,K. The spin polarization reduces the complexity of the radiative
cooling description, which allows for a simple model accounting for our
measurements. We also measure the rate of density-dependent atom losses,
finding good agreement with a model based on light-induced Van der Waals
forces. A minimal two-body loss rate cm/s is
reached in the spin-polarized regime. Our results constitute a benchmark for
the experimental study of ultracold gases of magnetic Lanthanide atoms.Comment: 21 pages, 9 figure
Fossiliferous Cretaceous Amber from Myanmar (Burma): Its Rediscovery, Biotic Diversity, and Paleontological Significance
The termites of Early Eocene Cambay amber, with the earliest record of the Termitidae (Isoptera)
This is the publisher's version, also available electronically from http://www.pensoft.net.The fauna of termites (Isoptera) preserved in Early Eocene amber from the Cambay Basin (Gujarat, India) are described and figured. Three new genera and four new species are recognized, all of them Neoisoptera â Parastylotermes krishnai Engel & Grimaldi, sp. n. (Stylotermitidae); Prostylotermes kamboja Engel & Grimaldi, gen. et sp. n. (Stylotermitidae?); Zophotermes Engel, gen. n., with Zophotermes ashoki Engel & Singh, sp. n. (Rhinotermitidae: Prorhinotermitinae); and Nanotermes isaacae Engel & Grimaldi, gen. et sp. n. (Termitidae: Termitinae?). Together these species represent the earliest Tertiary records of the Neoisoptera and the oldest definitive record of Termitidae, a family that comprises >75% of the living species of Isoptera. Interestingly, the affinities of the Cambay amber termites are with largely Laurasian lineages, in this regard paralleling relationships seen between the fauna of bees and some flies. Diversity of Neoisoptera in Indian amber may reflect origin of the amber deposit in Dipterocarpaceae forests formed at or near the paleoequator
Revealing the Superfluid Lambda Transition in the Universal Thermodynamics of a Unitary Fermi Gas
We have observed the superfluid phase transition in a strongly interacting
Fermi gas via high-precision measurements of the local compressibility, density
and pressure down to near-zero entropy. Our data completely determine the
universal thermodynamics of strongly interacting fermions without any fit or
external thermometer. The onset of superfluidity is observed in the
compressibility, the chemical potential, the entropy, and the heat capacity. In
particular, the heat capacity displays a characteristic lambda-like feature at
the critical temperature of . This is the first clear
thermodynamic signature of the superfluid transition in a spin-balanced atomic
Fermi gas. Our measurements provide a benchmark for many-body theories on
strongly interacting fermions, relevant for problems ranging from
high-temperature superconductivity to the equation of state of neutron stars.Comment: 11 pages, 8 figure
Topography of the Dolomites modulates range dynamics of narrow endemic plants under climate change
open9noClimate change is expected to threaten endemic plants in the Alps. In this context, the factors that may modulate species responses are rarely investigated at a local scale. We analyzed eight alpine narrow endemics of the Dolomites (southeastern Alps) under different predicted climate change scenarios at fine spatial resolutions. We tested possible differences in elevation, topographic heterogeneity and velocity of climate change among areas of gained, lost, or stable climatic habitat. The negative impact of climate change ranged from moderate to severe, depending on scenario and species. Generally, range loss occurred at the lowest elevations, while gained and stable areas were located at highest elevations. For six of the species, climate change velocity had higher values in stable and gained areas than in lost ones. Our findings support the role of topographic heterogeneity in maintaining climatic microrefugia, however, the peculiar topography of the Dolomites, characterized by high altitude plateaus, resulted in high climate change velocity in areas of projected future climatic suitability. Our study supports the usefulness of multiple predictors of spatio-temporal range dynamics for regional climate-adapted management and eventual assisted colonization planning to not overlook or overestimate the potential impact of climate change locally.openRota F.; Casazza G.; Genova G.; Midolo G.; Prosser F.; Bertolli A.; Wilhalm T.; Nascimbene J.; Wellstein C.Rota, F.; Casazza, G.; Genova, G.; Midolo, G.; Prosser, F.; Bertolli, A.; Wilhalm, T.; Nascimbene, J.; Wellstein, C
Exploring patterns of beta-diversity to test the consistency of biogeographical boundaries: A case study across forest plant communities of Italy
Aim: To date, despite their great potential biogeographical regionalization models have been mostly developed on descriptive and empirical bases. This paper aims at applying the beta-diversity framework on a statistically representative data set to analytically test the consistency of the biogeographical regionalization of Italian forests. Location: Italy. Taxon: Vascular plants. Methods: Forest plant communities were surveyed in 804 plots made in a statistically representative sample of forest communities made by 201 sites of Italian forests across the three biogeographical regions of the country: Alpine, Continental, and Mediterranean. We conducted an ordination analysis and an analysis of beta-diversity, decomposing it into its turnover and nestedness components. Results: Our results provide only partial support to the consistency of the biogeographical regionalization of Italy. While the differences in forest plant communities support the distinction between the Alpine and the other two regions, differences between Continental and Mediterranean regions had lower statistical support. Pairwise beta-diversity and its turnover component are higher between- than within-biogeographical regions. This suggests that different regional species pools contribute to assembly of local communities and that spatial distance between-regions has a stronger effect than that within-regions. Main conclusions: Our findings confirm a biogeographical structure of the species pools that is captured by the biogeographical regionalization. However, nonsignificant differences between the Mediterranean and Continental biogeographical regions suggest that this biogeographical regionalization is not consistent for forest plant communities. Our results demonstrate that an analytical evaluation of species composition differences among regions using beta-diversity analysis is a promising approach for testing the consistency of biogeographical regionalization models. This approach is recommended to provide support to the biogeographical regionalization used in some environmental conservation polices adopted by EU
Epiphytic lichens of the sacred natural site "Bosco di Sant'Antonio" (Majella National Park - Abruzzo)
Sacred Natural Sites are relevant for biodiversity conservation, as in the case of forest sites that, across centuries, developed old growth structures and are now crucial for the conservation of epiphytic lichens and other specialized forest organisms. In this study, we investigated the epiphytic lichen flora of a small forest patch included in the Majella National Park (Abruzzo), whose old growth features and naturalness reflect its long lasting spiritual role that perfectly fits with the concept of Sacred Natural Site. Results revealed that the "Bosco di Sant'Antonio" hosts a rich and interesting epiphytic lichen flora, thus indicating the potential of this Sacred Natural Site for lichen conservation. Fifty-six species were found including two species newly recorded in Abruzzo, two red-listed species, and the sensitive species Lobaria pulmonaria. This study corroborates the hypothesis that sacred forest sites are relevant for the conservation of specialized epiphytic lichens. In particular, in the Italian forest landscape where old-growth stands are practically absent, sacred forest sites may provide unique old-growth structures and buffer anthropogenic disturbance
Factors influencing epiphytic bryophyte and lichen species richness at different spatial scales in managed temperate forests
The effect of management related factors on species richness of epiphytic
bryophytes and lichens was studied in managed deciduous-coniferous mixed
forests in Western-Hungary. At the stand level, the potential explanatory
variables were tree species composition, stand structure, microclimate and
light conditions, landscape and historical variables; while at tree level host
tree species, tree size and light were studied. Species richness of the two
epiphyte groups was positively correlated. Both for lichen and bryophyte plot
level richness, the composition and diversity of tree species and the abundance of shrub layer were the most influential positive factors. Besides, for
bryophytes the presence of large trees, while for lichens amount and
heterogeneity of light were important. Tree level richness was mainly
determined by host tree species for both groups. For bryophytes oaks, while for lichens oaks and hornbeam turned out the most favourable hosts. Tree size
generally increased tree level species richness, except on pine for bryophytes
and on hornbeam for lichens.
The key variables for epiphytic diversity of the region were directly
influenced by recent forest management; historical and landscape variables
were not influential. Forest management oriented to the conservation of
epiphyte s should focus on: (i) the maintenance of tree species diversity in
mixed stands; (ii) increment the proportion of deciduous trees (mainly oaks);
(iii) conserving large trees within the stands; (iv) providing the presence of
shrub and regeneration layer; (v) creating heterogeneous light conditions. For
these purposes tree selection and selective cutting management seem more
appropriate than shelterwood system
Exploring the Thermodynamics of a Universal Fermi Gas
From sand piles to electrons in metals, one of the greatest challenges in
modern physics is to understand the behavior of an ensemble of strongly
interacting particles. A class of quantum many-body systems such as neutron
matter and cold Fermi gases share the same universal thermodynamic properties
when interactions reach the maximum effective value allowed by quantum
mechanics, the so-called unitary limit [1,2]. It is then possible to simulate
some astrophysical phenomena inside the highly controlled environment of an
atomic physics laboratory. Previous work on the thermodynamics of a
two-component Fermi gas led to thermodynamic quantities averaged over the trap
[3-5], making it difficult to compare with many-body theories developed for
uniform gases. Here we develop a general method that provides for the first
time the equation of state of a uniform gas, as well as a detailed comparison
with existing theories [6,14]. The precision of our equation of state leads to
new physical insights on the unitary gas. For the unpolarized gas, we prove
that the low-temperature thermodynamics of the strongly interacting normal
phase is well described by Fermi liquid theory and we localize the superfluid
transition. For a spin-polarized system, our equation of state at zero
temperature has a 2% accuracy and it extends the work of [15] on the phase
diagram to a new regime of precision. We show in particular that, despite
strong correlations, the normal phase behaves as a mixture of two ideal gases:
a Fermi gas of bare majority atoms and a non-interacting gas of dressed
quasi-particles, the fermionic polarons [10,16-18].Comment: 8 pages, 5 figure
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