343 research outputs found
Suppression of inhomogeneous broadening in rf spectroscopy of optically trapped atoms
We present a novel method for reducing the inhomogeneous frequency broadening
in the hyperfine splitting of the ground state of optically trapped atoms. This
reduction is achieved by the addition of a weak light field, spatially
mode-matched with the trapping field and whose frequency is tuned in-between
the two hyperfine levels. We experimentally demonstrate the new scheme with Rb
85 atoms, and report a 50-fold narrowing of the rf spectrum
Maximally-localized Wannier functions for entangled energy bands
We present a method for obtaining well-localized Wannier-like functions (WFs)
for energy bands that are attached to or mixed with other bands. The present
scheme removes the limitation of the usual maximally-localized WFs method (N.
Marzari and D. Vanderbilt, Phys. Rev. B 56, 12847 (1997)) that the bands of
interest should form an isolated group, separated by gaps from higher and lower
bands everywhere in the Brillouin zone. An energy window encompassing N bands
of interest is specified by the user, and the algorithm then proceeds to
disentangle these from the remaining bands inside the window by filtering out
an optimally connected N-dimensional subspace. This is achieved by minimizing a
functional that measures the subspace dispersion across the Brillouin zone. The
maximally-localized WFs for the optimal subspace are then obtained via the
algorithm of Marzari and Vanderbilt. The method, which functions as a
postprocessing step using the output of conventional electronic-structure
codes, is applied to the s and d bands of copper, and to the valence and
low-lying conduction bands of silicon. For the low-lying nearly-free-electron
bands of copper we find WFs which are centered at the tetrahedral interstitial
sites, suggesting an alternative tight-binding parametrization.Comment: 13 pages, with 9 postscript figures embedded. Uses REVTEX and epsf
macro
Innovations in air sampling to detect plant pathogens
Many innovations in the development and use of air sampling devices have occurred in plant pathology since the first description of the Hirst spore trap. These include improvements in capture efficiency at relatively high air-volume collection rates, methods to enhance the ease of sample processing with downstream diagnostic methods and even full automation of sampling, diagnosis and wireless reporting of results. Other innovations have been to mount air samplers on mobile platforms such as UAVs and ground vehicles to allow sampling at different altitudes and locations in a short space of time to identify potential sources and population structure. Geographical Information Systems and the application to a network of samplers can allow a greater prediction of airborne inoculum and dispersal dynamics. This field of technology is now developing quickly as novel diagnostic methods allow increasingly rapid and accurate quantifications of airborne species and genetic traits. Sampling and interpretation of results, particularly action-thresholds, is improved by understanding components of air dispersal and dilution processes and can add greater precision in the application of crop protection products as part of integrated pest and disease management decisions. The applications of air samplers are likely to increase, with much greater adoption by growers or industry support workers to aid in crop protection decisions. The same devices are likely to improve information available for detection of allergens causing hay fever and asthma or provide valuable metadata for regional plant disease dynamics
Gutzwiller-Correlated Wave Functions: Application to Ferromagnetic Nickel
Ferromagnetic Nickel is the most celebrated iron group metal with pronounced
discrepancies between the experimental electronic properties and predictions of
density functional theories. In this work, we show in detail that the recently
developed multi-band Gutzwiller theory provides a very good description of the
quasi-particle band structure of nickel. We obtain the correct exchange
splittings and we reproduce the experimental Fermi-surface topology. The
correct (111)-direction of the magnetic easy axis and the right order of
magnitude of the magnetic anisotropy are found. Our theory also reproduces the
experimentally observed change of the Fermi-surface topology when the magnetic
moment is oriented along the (001)-axis. In addition to the numerical study, we
give an analytical derivation for a much larger class of variational
wave-functions than in previous investigations. In particular, we cover cases
of superconductivity in multi-band lattice systems.Comment: 35 pages, 3 figure
DDW Order and its Role in the Phase Diagram of Extended Hubbard Models
We show in a mean-field calculation that phase diagrams remarkably similar to
those recently proposed for the cuprates arise in simple microscopic models of
interacting electrons near half-filling. The models are extended Hubbard models
with nearest neighbor interaction and correlated hopping. The underdoped region
of the phase diagram features density-wave (DDW) order. In a
certain regime of temperature and doping, DDW order coexists with
antiferromagnetic (AF) order. For larger doping, it coexists with
superconductivity (DSC). While phase diagrams of this form
are robust, they are not inevitable. For other reasonable values of the
coupling constants, drastically different phase diagrams are obtained. We
comment on implications for the cuprates.Comment: 7 pages, 3 figure
Prognostic impact of proliferative index determined by quantitative image analysis and the International Prognostic Index in patients with mantle cell lymphoma
Background: The proliferative index (PI) is a powerful prognostic factor in mantle cell lymphoma (MCL); however, its utility is hampered by interobserver variability. The mantle cell international prognostic index (MIPI) has been reported to have prognostic importance. In this study, we determined the prognostic value of the PI as determined by quantitative image analysis in MCL
Dynamical mean-field approach to materials with strong electronic correlations
We review recent results on the properties of materials with correlated
electrons obtained within the LDA+DMFT approach, a combination of a
conventional band structure approach based on the local density approximation
(LDA) and the dynamical mean-field theory (DMFT). The application to four
outstanding problems in this field is discussed: (i) we compute the full
valence band structure of the charge-transfer insulator NiO by explicitly
including the p-d hybridization, (ii) we explain the origin for the
simultaneously occuring metal-insulator transition and collapse of the magnetic
moment in MnO and Fe2O3, (iii) we describe a novel GGA+DMFT scheme in terms of
plane-wave pseudopotentials which allows us to compute the orbital order and
cooperative Jahn-Teller distortion in KCuF3 and LaMnO3, and (iv) we provide a
general explanation for the appearance of kinks in the effective dispersion of
correlated electrons in systems with a pronounced three-peak spectral function
without having to resort to the coupling of electrons to bosonic excitations.
These results provide a considerable progress in the fully microscopic
investigations of correlated electron materials.Comment: 24 pages, 14 figures, final version, submitted to Eur. Phys. J. for
publication in the Special Topics volume "Cooperative Phenomena in Solids:
Metal-Insulator Transitions and Ordering of Microscopic Degrees of Freedom
Wetting films on chemically heterogeneous substrates
Based on a microscopic density functional theory we investigate the
morphology of thin liquidlike wetting films adsorbed on substrates endowed with
well-defined chemical heterogeneities. As paradigmatic cases we focus on a
single chemical step and on a single stripe. In view of applications in
microfluidics the accuracy of guiding liquids by chemical microchannels is
discussed. Finally we give a general prescription of how to investigate
theoretically the wetting properties of substrates with arbitrary chemical
structures.Comment: 56 pages, RevTeX, 20 Figure
Organic matter chemistry controls greenhouse gas emissions from permafrost peatlands
Large tracts of arctic and subarctic peatlands are underlain by permafrost. These peatlands store large quantities of carbon (C), and are currently under severe threat from climate change. The aim of this study was to determine the size and organic chemistry of the easily degradable C pool in permafrost peatlands and link the functional organic chemistry to temperature and moisture controls of greenhouse gas emissions. First, we used a combination of field measurements and laboratory experiments to assess the influence of increased temperature and flooding on CO₂ and CH₄ emissions from sixteen permafrost peatlands in subarctic Sweden and Canada. Second, we determined the variation in organic matter chemistry and the associated microbial community composition of the peat active layer, with depth using quantitative ¹³C solid-state NMR and molecular biomarkers respectively. We demonstrate that the peat organic chemistry strongly controls CO₂ release from peat and that ca. 35 and 26% of the peat organic matter, at the Swedish and Canadian peatlands sites, respectively, is easily degradable by heterotrophic microorganisms. In contrast to CO₂, CH₄ emissions were decoupled from peat functional organic chemistry. We show a strong relationship between the microbial community structure and the peat organic chemistry suggesting that substrate type and abundance is an important driver of microbial composition in sub-arctic peatlands. Despite considerable variation in peat chemistry and microbial community composition with depth the temperature sensitivity was comparable throughout the active layer. Our study shows that functional organic chemistry controls both soil respiration rates and the composition of the microbial community. Furthermore, if these peatlands collapse and flood on thawing, they are unlikely to become large emitters of CH₄ without additional input of labile substrates
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