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The Diderot meteorite: The second chassignite
The Diderot meteorite is a dunite discovered in Sahara. The martian origin is unambiguous and Diderot shares strong petrographical similarities with Chassigny
The relative importance of seed competition, resource competition and perturbations on community structure
While the regional climate is the primary selection pressure for whether a plant strategy can survive, however, competitive interactions strongly affect the relative abundances of plant strategies within communities. Here, we investigate the relative importance of competition and perturbations on the development of vegetation community structure. To do so, we develop DIVE (Dynamics and Interactions of VEgetation), a simple general model that links plant strategies to their competitive dynamics, using growth and reproduction characteristics that emerge from climatic constraints. The model calculates population dynamics based on establishment, mortality, invasion and exclusion in the presence of different strengths of perturbations, seed and resource competition. The highest levels of diversity were found in simulations without competition as long as mortality is not too high. However, reasonable successional dynamics were only achieved when resource competition is considered. Under high levels of competition, intermediate levels of perturbations were required to obtain coexistence. Since succession and coexistence are observed in plant communities, we conclude that the DIVE model with competition and intermediate levels of perturbation represents an adequate way to model population dynamics. Because of the simplicity and generality of DIVE, it could be used to understand vegetation structure and functioning at the global scale and the response of vegetation to global change
Dipolar Bose-Einstein condensates with dipole-dependent scattering length
We consider a Bose-Einstein condensate of polar molecules in a harmonic trap,
where the effective dipole may be tuned by an external field. We demonstrate
that taking into account the dependence of the scattering length on the dipole
moment is essential to reproducing the correct energies and for predicting the
stability of the condensate. We do this by comparing Gross-Pitaevskii
calculations with diffusion Monte Carlo calculations. We find very good
agreement between the results obtained by these two approaches once the dipole
dependence of the scattering length is taken into account. We also examine the
behavior of the condensate in non-isotropic traps
Synchronization of Sound Sources
Sound generation and -interaction is highly complex, nonlinear and
self-organized. Already 150 years ago Lord Rayleigh raised the following
problem: Two nearby organ pipes of different fundamental frequencies sound
together almost inaudibly with identical pitch. This effect is now understood
qualitatively by modern synchronization theory (M. Abel et al., J. Acoust. Soc.
Am., 119(4), 2006). For a detailed, quantitative investigation, we substituted
one pipe by an electric speaker. We observe that even minute driving signals
force the pipe to synchronization, thus yielding three decades of
synchronization -- the largest range ever measured to our knowledge.
Furthermore, a mutual silencing of the pipe is found, which can be explained by
self-organized oscillations, of use for novel methods of noise abatement.
Finally, we develop a specific nonlinear reconstruction method which yields a
perfect quantitative match of experiment and theory.Comment: 5 pages, 4 figure
Ultracold collisions of oxygen molecules
Collision cross sections and rate constants between two ground- state oxygen
molecules are investigated theoretically at translational energies below K and in zero magnetic field. We present calculations for elastic and spin-
changing inelastic collision rates for different isotopic combinations of
oxygen atoms as a prelude to understanding their collisional stability in
ultracold magnetic traps. A numerical analysis has been made in the framework
of a rigid- rotor model that accounts fully for the singlet, triplet, and
quintet potential energy surfaces in this system. The results offer insights
into the effectiveness of evaporative cooling and the properties of molecular
Bose- Einstein condensates, as well as estimates of collisional lifetimes in
magnetic traps. Specifically, looks like a good candidate for
ultracold studies, while is unlikely to survive evaporative
cooling. Since is representative of a wide class of molecules that
are paramagnetic in their ground state we conclude that many molecules can be
successfully magnetically trapped at ultralow temperatures.Comment: 15 pages, 9 figure
Measuring public opinion and acceptability of prevention policies: an integrative review and narrative synthesis of methods.
Acceptability of and public support for prevention are an important part of facilitating policy implementation. This review aims to identify, summarize and synthesize the methods and study designs used to measure and understand public opinion, community attitudes and acceptability of strategies to prevent chronic noncommunicable disease (NCDs) in order to allow for examination of imbalances in methodological approaches and gaps in content areas. We searched four scientific databases (CINAHL, Embase, Ovid/MEDLINE and Scopus) for peer-reviewed, English-language studies published between January 2011 and March 2020 in high-income, democratic countries across North America, Europe and the Asia-Pacific region. Studies were included if they focused on opinions, attitudes and acceptability of primary prevention strategies and interventions addressing the key NCD risk factors of alcohol use, unhealthy diet, overweight/obesity, tobacco use and smoking, and physical inactivity. A total of 293 studies were included. Two thirds of studies (n = 194, 66%) used quantitative methods such as cross-sectional studies involving surveys of representative (n = 129, 44%) or convenience (n = 42, 14%) samples. A smaller number of studies used qualitative methods (n = 60, 20%) such as focus groups (n = 21, 7%) and interviews (n = 21, 7%). Thirty-nine studies (13%) used mixed methods such as content analysis of news media (n = 17, 6%). Tobacco control remains the dominant topic of public opinion literature about prevention (n = 124, 42%). Few studies looked solely at physical inactivity (n = 17, 6%). The results of this review suggest that public opinion and acceptability of prevention in the peer-reviewed literature is investigated primarily through cross-sectional surveys. Qualitative and mixed methods may provide more nuanced insights which can be used to facilitate policy implementation of more upstream strategies and policies to prevent NCDs
Influence of local surface albedo variability and ice crystal shape on passive remote sensing of thin cirrus
Airborne measurements of solar spectral radiance reflected by cirrus are
performed with the HALO-Solar Radiation (HALO-SR) instrument onboard the High
Altitude and Long Range Research Aircraft (HALO) in November 2010. The data
are used to quantify the influence of surface albedo variability on the
retrieval of cirrus optical thickness and crystal effective radius. The
applied retrieval of cirrus optical properties is based on a standard two-wavelength approach utilizing measured and simulated reflected radiance in
the visible and near-infrared spectral region. Frequency distributions of the
surface albedos from Moderate resolution Imaging Spectroradiometer (MODIS)
satellite observations are used to compile surface-albedo-dependent lookup
tables of reflected radiance. For each assumed surface albedo the cirrus
optical thickness and effective crystal radius are retrieved as a function of
the assumed surface albedo. The results for the cirrus optical thickness are
compared to measurements from the High Spectral Resolution Lidar (HSRL). The
uncertainty in cirrus optical thickness due to local variability of surface
albedo in the specific case study investigated here is below 0.1 and thus
less than that caused by the measurement uncertainty of both instruments. It
is concluded that for the retrieval of cirrus optical thickness the surface
albedo variability is negligible. However, for the retrieval of crystal effective
radius, the surface albedo variability is of major importance,
introducing uncertainties up to 50%. Furthermore, the influence of the
bidirectional reflectance distribution function (BRDF) on the retrieval of
crystal effective radius was investigated and quantified with uncertainties
below 10%, which ranges below the uncertainty caused by the surface albedo
variability. The comparison with the independent lidar data allowed for
investigation of the role of the crystal shape in the retrieval. It is found that
if assuming aggregate ice crystals, the HSRL observations fit best with the
retrieved optical thickness from HALO-SR
Resonant control of elastic collisions in an optically trapped Fermi gas of atoms
We have loaded an ultracold gas of fermionic atoms into a far off resonance
optical dipole trap and precisely controlled the spin composition of the
trapped gas. We have measured a magnetic-field Feshbach resonance between atoms
in the two lowest energy spin-states, |9/2, -9/2> and |9/2, -7/2>. The
resonance peaks at a magnetic field of 201.5 plus or minus 1.4 G and has a
width of 8.0 plus or minus 1.1 G. Using this resonance we have changed the
elastic collision cross section in the gas by nearly 3 orders of magnitude.Comment: 4 pages, 3 figure
Autler-Townes splitting in two-color photoassociation of 6Li
We report on high-resolution two-color photoassociation spectroscopy in the
triplet system of magneto-optically trapped 6Li. The absolute transition
frequencies have been measured. Strong optical coupling of the bound molecular
states has been observed as Autler-Townes splitting in the photoassociation
signal. The spontaneous bound-bound transition rate is determined and the
molecule formation rate is estimated. The observed lineshapes are in good
agreement with the theoretical model.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. A (Rapid
Communication
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