716 research outputs found
Hydrogen Spectroscopy with a Lamb-shift Polarimeter - An Alternative Approach Towards Anti-Hydrogen Spectroscopy Experiments
A Lamb-shift polarimeter, which has been built for a fast determination of
the polarization of protons and deuterons of an atomic-beam source and which is
frequently used in the ANKE experiment at COSY-J\"ulich, is shown to be an
excellent device for atomic-spectroscopy measurements of metastable hydrogen
isotopes. It is demonstrated that magnetic and electric dipole transitions in
hydrogen can be measured as a function of the external magnetic field, giving
access to the full Breit-Rabi diagram for the and the
states. This will allow the study of hyperfine structure, factors and the
classical Lamb shift. Although the data are not yet competitive with
state-of-the-art measurements, the potential of the method is enormous,
including a possible application to anti-hydrogen spectroscopy.Comment: 6 pages, 7 figures, accepted by European Physical Journal
Penetration Depth Scaling for Impact Into Wet Granular Packings
We present experimental measurements of penetration depths for the impact of spheres into wetted granular media. We observe that the penetration depth in the liquid saturated case scales with projectile density, size, and drop height in a fashion consistent with the scaling observed in the dry case, but with smaller penetrations. Neither viscous drag nor density effects can explain the enhancement to the stopping force. The penetration depth exhibits a complicated dependence on liquid fraction, accompanied by a change in the drop-height dependence, that must be the consequence of accompanying changes in the conformation of the liquid phase in the interstices
Monte Carlo Methods for Rough Free Energy Landscapes: Population Annealing and Parallel Tempering
Parallel tempering and population annealing are both effective methods for
simulating equilibrium systems with rough free energy landscapes. Parallel
tempering, also known as replica exchange Monte Carlo, is a Markov chain Monte
Carlo method while population annealing is a sequential Monte Carlo method.
Both methods overcome the exponential slowing associated with high free energy
barriers. The convergence properties and efficiency of the two methods are
compared. For large systems, population annealing initially converges to
equilibrium more rapidly than parallel tempering for the same amount of
computational work. However, parallel tempering converges exponentially and
population annealing inversely in the computational work so that ultimately
parallel tempering approaches equilibrium more rapidly than population
annealing.Comment: 10 pages, 3 figure
Nuclear spins, magnetic moments and quadrupole moments of Cu isotopes from N = 28 to N = 46: probes for core polarization effects
Measurements of the ground-state nuclear spins, magnetic and quadrupole
moments of the copper isotopes from 61Cu up to 75Cu are reported. The
experiments were performed at the ISOLDE facility, using the technique of
collinear laser spectroscopy. The trend in the magnetic moments between the
N=28 and N=50 shell closures is reasonably reproduced by large-scale
shell-model calculations starting from a 56Ni core. The quadrupole moments
reveal a strong polarization of the underlying Ni core when the neutron shell
is opened, which is however strongly reduced at N=40 due to the parity change
between the and orbits. No enhanced core polarization is seen beyond
N=40. Deviations between measured and calculated moments are attributed to the
softness of the 56Ni core and weakening of the Z=28 and N=28 shell gaps.Comment: 13 pagers, 19 figures, accepted by Physical Review
Antimony(III)-D, L-tartrates exhibit proton-assisted enantioselective binding in solution and in the gas phase
The global wildland–urban interface
The wildland–urban interface (WUI) is where buildings and wildland vegetation meet or intermingle1,2. It is where human–environmental conflicts and risks can be concentrated, including the loss of houses and lives to wildfire, habitat loss and fragmentation and the spread of zoonotic diseases3. However, a global analysis of the WUI has been lacking. Here, we present a global map of the 2020 WUI at 10 m resolution using a globally consistent and validated approach based on remote sensing-derived datasets of building area4 and wildland vegetation5. We show that the WUI is a global phenomenon, identify many previously undocumented WUI hotspots and highlight the wide range of population density, land cover types and biomass levels in different parts of the global WUI. The WUI covers only 4.7% of the land surface but is home to nearly half its population (3.5 billion). The WUI is especially widespread in Europe (15% of the land area) and the temperate broadleaf and mixed forests biome (18%). Of all people living near 2003–2020 wildfires (0.4 billion), two thirds have their home in the WUI, most of them in Africa (150 million). Given that wildfire activity is predicted to increase because of climate change in many regions6, there is a need to understand housing growth and vegetation patterns as drivers of WUI change
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