1,226 research outputs found
Nuclear wastewater decontamination by 3D-Printed hierarchical zeolite monoliths
3D-printed monoliths of zeolites chabazite and 4A were made, characterized, and shown effective for removing strontium and caesium from water
Rolling of asymmetric disks on an inclined plane
In a recent papers, Turner and Turner (2010 {\em Am. J. Phys.} {\bf 78}
905-7) and Jensen (2011 {\em Eur. J. Phys.} {\bf 32} 389-397) analysed the
motion of asymmetric rolling rigid bodies on a horizontal plane. These papers
addressed the common misconception that the instantaneous point of contact of
the rolling body with the plane can be used to evaluate the angular momentum
and the torque in the equation of motion
. To obtain the correct equation of motion,
the "phantom torque" or various rules that depend on the motion of the point
about which and are evaluated were discussed. In
this paper, I consider asymmetric disks rolling down an inclined plane and
describe the most basic way of obtaining the correct equation of motion; that
is, to choose the point about which and are
evaluated that is stationary in an inertial frame
What is stopping you? The falling employment-to-employment mobility in the UK
What contributed to the decline in employment-to-employment (EE) transition rate in the UK in recent decades? This paper empirically examines potential channels that caused the sluggish EE mobility from 2000-2019. First, I break down the observed fall in EE mobility relative to unemployed-to-employment (UE) transition into changes in relative search intensity and worker’s acceptance rate. I find the vast majority of the persistent decline after 2010 was due to fall in job acceptance. Second, I estimate a dynamic job ladder model using UK survey data to examine the relative importance of changes in employment and job offer distribution in reducing job acceptance. Results reveal that the falling job acceptance in the 2000s was attributed to workers moving up the job ladder; while acceptance remained low in the 2010s as a result of deterioration in offer qualities. Counterfactual exercise shows that if the attractiveness of poaching offers did not deteriorate after 2010, the EE mobility would have returned to levels in early 2000s. Finally, I test the contribution of composition changes to the fall in EE rate by implementing a between-within decomposition using a structural framework, which accounts for both worker heterogeneity and sectoral compositions. Results rule out demographic changes or structural transformation as main drivers of the fall in EE rates
Assessing and Improving the Reliability of Volunteered Land Cover Reference Data
Volunteered geographic data are being used increasingly to support land cover mapping and validation, yet the reliability of the volunteered data still requires further research. This study proposes data-based guidelines to help design the data collection by assessing the reliability of volunteered data collected using the Geo-Wiki tool. We summarized the interpretation difficulties of the volunteers at a global scale, including those areas and land cover types that generate the most confusion. We also examined the factors affecting the reliability of majority opinion and individual classification. The results showed that the highest interpretation inconsistency of the volunteers occurred in the ecoregions of tropical and boreal forests (areas with relatively poor coverage of very high resolution images), the tundra (a unique region that the volunteers are unacquainted with), and savannas (transitional zones). The volunteers are good at identifying forests, snow/ice and croplands, but not grasslands and wetlands. The most confusing pairs of land cover types are also captured in this study and they vary greatly with different biomes. The reliability can be improved by providing more high resolution ancillary data, more interpretation keys in tutorials, and tools that assist in coverage estimation for those areas and land cover types that are most prone to confusion. We found that the reliability of the majority opinion was positively correlated with the percentage of volunteers selecting this choice and negatively related to their self-evaluated uncertainty when very high resolution images were available. Factors influencing the reliability of individual classifications were also compared and the results indicated that the interpretation difficulty of the target sample played a more important role than the knowledge base of the volunteers. The professional background and local knowledge had an influence on the interpretation performance, especially in identifying vegetation land cover types other than croplands. These findings can help in building a better filtering system to improve the reliability of volunteered data used in land cover validation and other applications
Nambu-Goldstone Dark Matter and Cosmic Ray Electron and Positron Excess
We propose a model of dark matter identified with a pseudo-Nambu-Goldstone
boson in the dynamical supersymmetry breaking sector in a gauge mediation
scenario. The dark matter particles annihilate via a below-threshold narrow
resonance into a pair of R-axions each of which subsequently decays into a pair
of light leptons. The Breit-Wigner enhancement explains the excess electron and
positron fluxes reported in the recent cosmic ray experiments PAMELA, ATIC and
PPB-BETS without postulating an overdensity in halo, and the limit on
anti-proton flux from PAMELA is naturally evaded.Comment: 3 figure
Ultra-High Energy Neutrino Fluxes: New Constraints and Implications
We apply new upper limits on neutrino fluxes and the diffuse extragalactic
component of the GeV gamma-ray flux to various scenarios for ultra high energy
cosmic rays and neutrinos. As a result we find that extra-galactic top-down
sources can not contribute significantly to the observed flux of highest energy
cosmic rays. The Z-burst mechanism where ultra-high energy neutrinos produce
cosmic rays via interactions with relic neutrinos is practically ruled out if
cosmological limits on neutrino mass and clustering apply.Comment: 10 revtex pages, 9 postscript figure
Small-x QCD studies with CMS at the LHC
The capabilities of the CMS experiment to study the low-x parton structure
and QCD evolution in the proton and the nucleus at LHC energies are presented
through four different measurements, to be carried out in Pb-Pb at sqrt(s_NN) =
5.5 TeV: (i) the charged hadron rapidity density and (ii) the
ultraperipheral (photo)production of Upsilon; and in p-p at sqrt(s) = 14 TeV:
(iii) inclusive forward jets and (iv) Mueller-Navelet dijets (separated by
8).Comment: Quark Matter'06 Proceedings. To appear in J.Phys.
How fast is the wave function collapse?
Using complex quantum Hamilton-Jacobi formulation, a new kind of non-linear
equations is proposed that have almost classical structure and extend the
Schroedinger equation to describe the collapse of the wave function as a
finite-time process. Experimental bounds on the collapse time are reported (of
order 0.1 ms to 0.1 ps) and its convenient dimensionless measure is introduced.
This parameter helps to identify the areas where sensitive probes of the
possible collapse dynamics can be done. Examples are experiments with
Bose-Einstein condensates, ultracold neutrons or ultrafast optics.Comment: 9 pages; v2: a shorter version to suit the 4 page limit of
Proceedings of International Conference on Mathematical Modelling in Physical
Sciences, 3-7 September 2012, Budapest, Hungary (IC-MSQUARE 2012
The Boltzmann equation for colourless plasmons in hot QCD plasma. Semiclassical approximation
Within the framework of the semiclassical approximation, we derive the
Boltzmann equation describing the dynamics of colorless plasmons in a hot QCD
plasma. The probability of the plasmon-plasmon scattering at the leading order
in the coupling constant is obtained. This probability is gauge-independent at
least in the class of the covariant and temporal gauges. It is noted that the
structure of the scattering kernel possesses important qualitative difference
from the corresponding one in the Abelian plasma, in spite of the fact that we
focused our study on the colorless soft excitations. It is shown that
four-plasmon decay is suppressed by the power of relative to the process of
nonlinear scattering of plasmons by thermal particles at the soft momentum
scale. It is stated that the former process becomes important in going to the
ultrasoft region of the momentum scale.Comment: 41, LaTeX, minor changes, identical to published versio
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