291 research outputs found
Role of surface states in STM spectroscopy of (111) metal surfaces with Kondo adsorbates
A nearly-free-electron (NFE) model to describe STM spectroscopy of (111)
metal surfaces with Kondo impurities is presented. Surface states are found to
play an important role giving a larger contribution to the conductance in the
case of Cu(111) and Au(111) than Ag(111) surfaces. This difference arises from
the farther extension of the Ag(111) surface state into the substrate. The
different line shapes observed when Co is adsorbed on different substrates can
be explained from the position of the surface band onset relative to the Fermi
energy. The lateral dependence of the line shape amplitude is found to be
bulk-like for R|| < 4 Amstrongs and surface-like at larger distances, in
agreement with experimental data.Comment: 4 pages, 3 eps figure
Towards a microscopic description of dimer adsorbates on metallic surfaces
Despite the experimental successes of Scanning Tunneling Microscopy (STM) and
the interest in more complex magnetic nanostructures, our present understanding
and theoretical description of STM spectra of magnetic adatoms is mainly
phenomenological and most often ignores many-body effects. Here, we propose a
theory which includes a microscopic description of the wave functions of the
substrate and magnetic adatoms together with quantum many-body effects. To test
our theory, we have computed the STM spectra of magnetic Cobalt monomers and
dimers adsorbed on metallic Copper surfaces and succesfully compared our
results to recent available experimental data.Comment: 4 pages, 2 figures, discussion of calculation of RKKY interaction and
connection to NRG included. Extended discussion on calculations of the
one-electron parameters of Anderson model. Typos correcte
Double layer in ionic liquids: Overscreening vs. crowding
We develop a simple Landau-Ginzburg-type continuum theory of solvent-free
ionic liquids and use it to predict the structure of the electrical double
layer. The model captures overscreening from short-range correlations, dominant
at small voltages, and steric constraints of finite ion sizes, which prevail at
large voltages. Increasing the voltage gradually suppresses overscreening in
favor of the crowding of counterions in a condensed inner layer near the
electrode. The predicted ion profiles and capacitance-voltage relations are
consistent with recent computer simulations and experiments on room-temperature
ionic liquids, using a correlation length of order the ion size.Comment: 4 pages + supplementary informatio
Nonequilibrium thermodynamics of interacting tunneling transport: variational grand potential, density-functional formulation, and nature of steady-state forces
The standard formulation of tunneling transport rests on an open-boundary
modeling. There, conserving approximations to nonequilibrium Green function or
quantum-statistical mechanics provide consistent but computational costly
approaches; alternatively, use of density-dependent ballistic-transport
calculations [e.g., Phys. Rev. B 52, 5335 (1995)], here denoted `DBT', provide
computationally efficient (approximate) atomistic characterizations of the
electron behavior but has until now lacked a formal justification. This paper
presents an exact, variational nonequilibrium thermodynamic theory for fully
interacting tunneling and provides a rigorous foundation for frozen-nuclei DBT
calculations as a lowest order approximation to an exact nonequilibrium
thermodynamics density functional evaluation. The theory starts from the
complete electron nonequilibrium quantum statistical mechanics and I identify
the operator for the nonequilibrium Gibbs free energy. I demonstrate a minimal
property of a functional for the nonequilibrium thermodynamic grand potential
which thus uniquely identifies the solution as the exact nonequilibrium density
matrix. I also show that a uniqueness-of-density proof from a closely related
study [Phys. Rev. B 78, 165109 (2008)] makes it possible to provide a
single-particle formulation based on universal electron-density functionals. I
illustrate a formal evaluation of the thermodynamics grand potential value
which is closely related to the variation in scattering phase shifts and hence
to Friedel density oscillations. This paper also discusses the difference
between the here-presented exact thermodynamics forces and the often-used
electrostatic forces. Finally the paper documents an inherent adiabatic nature
of the thermodynamics forces and observes that these are suited for a
nonequilibrium implementation of the Born-Oppenheimer approximation.Comment: 37 pages, 3 Figure
Whole exome sequencing identifies genetic variants in inherited thrombocytopenia with secondary qualitative function defects
Inherited thrombocytopenias are a heterogeneous group of disorders characterised
by abnormally low platelet counts which can be associated with abnormal bleeding.
Next generation sequencing has previously been employed in these disorders for the
confirmation of suspected genetic abnormalities, and more recently in the discovery
of novel disease causing genes. However its full potential has not previously been
utilised. Over the past 6 years we have sequenced the exomes from 55 patients,
including 37 index cases and 18 additional family members, all of whom were
recruited to the UK Genotyping and Phenotyping of Platelets study. All patients had
inherited or sustained thrombocytopenia of unknown aetiology with platelet counts
varying from 11-186x109
/L. Of the 51 patients phenotypically tested, 37 (73%), had
an additional secondary qualitative platelet defect. Using whole exome sequencing
analysis we have identified “pathogenic” or “likely pathogenic” variants in 46%
(17/37) of our index patients with thrombocytopenia. In addition, we report variants
of uncertain significance in 12 index cases which include novel candidate genetic
variants in previously unreported genes in four index cases. These results
demonstrate that whole exome sequencing is an efficient method for elucidating
potential pathogenic genetic variants in inherited thrombocytopenia. Whole exome
sequencing also has the added benefit of discovering potentially pathogenic genetic
variants for further study in novel genes not previously implicated in inherited
thrombocytopenia
Airborne lidar observations of wind, water vapor, and aerosol profiles during the NASA Aeolus calibration and validation (Cal/Val) test flight campaign
Lidars are uniquely capable of collecting high-precision and high spatiotemporal resolution observations that have been used for atmospheric process studies from the ground, aircraft, and space for many years. The Aeolus mission, the first space-borne Doppler wind lidar, was developed by the European Space Agency (ESA) and launched in August 2018. Its novel Atmospheric LAser Doppler INstrument (ALADIN) observes profiles of the component of the wind vector and aerosol/cloud optical properties along the instrument's line-of-sight (LOS) direction on a global scale. A total of two airborne lidar systems have been developed at NASA Langley Research Center in recent years that collect measurements in support of several NASA Earth Science Division focus areas. The coherent Doppler Aerosol WiNd (DAWN) lidar measures vertical profiles of LOS velocity along selected azimuth angles that are combined to derive profiles of horizontal wind speed and direction. The High Altitude Lidar Observatory (HALO) measures high resolution profiles of atmospheric water vapor (WV) and aerosol and cloud optical properties. Because there are limitations in terms of spatial and vertical detail and measurement precision that can be accomplished from space, airborne remote sensing observations like those from DAWN and HALO are required to fill these observational gaps and to calibrate and validate space-borne measurements.
Over a 2-week period in April 2019, during their Aeolus Cal/Val Test Flight campaign, NASA conducted five research flights over the eastern Pacific Ocean with the DC-8 aircraft. The purpose was to demonstrate the following: (1) DAWN and HALO measurement capabilities across a range of atmospheric conditions, (2) Aeolus Cal/Val flight strategies and comparisons of DAWN and HALO measurements with Aeolus, to gain an initial perspective of Aeolus performance, and (3) ways in which atmospheric dynamic processes can be resolved and better understood through simultaneous observations of wind, WV, and aerosol profile observations, coupled with numerical model and other remote sensing observations. This paper provides a brief description of the DAWN and HALO instruments, discusses the synergistic observations collected across a wide range of atmospheric conditions sampled during the DC-8 flights, and gives a brief summary of the validation of DAWN, HALO, and Aeolus observations and comparisons.</p
Transforming medical professionalism to fit changing health needs
<p>Abstract</p> <p>Background</p> <p>The professional organization of medical work no longer reflects the changing health needs caused by the growing number of complex and chronically ill patients. Key stakeholders enforce coordination and remove power from the medical professions in order allow for these changes. However, it may also be necessary to initiate basic changes to way in which the medical professionals work in order to adapt to the changing health needs.</p> <p>Discussion</p> <p>Medical leaders, supported by health policy makers, can consciously activate the self-regulatory capacity of medical professionalism in order to transform the medical profession and the related professional processes of care so that it can adapt to the changing health needs. In doing so, they would open up additional routes to the improvement of the health services system and to health improvement. This involves three consecutive steps: (1) defining and categorizing the health needs of the population; (2) reorganizing the specialty domains around the needs of population groups; (3) reorganizing the specialty domains by eliminating work that could be done by less educated personnel or by the patients themselves. We suggest seven strategies that are required in order to achieve this transformation.</p> <p>Summary</p> <p>Changing medical professionalism to fit the changing health needs will not be easy. It will need strong leadership. But, if the medical world does not embark on this endeavour, good doctoring will become merely a bureaucratic and/or marketing exercise that obscures the ultimate goal of medicine which is to optimize the health of both individuals and the entire population.</p
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