187 research outputs found
Effect of black carbon and sulfate aerosols on the global radiation budget
Global fields of radiative forcing due to natural and anthropogenic sulfate aerosols, black carbon aerosols, and an external mixture of the two have been calculated with a one-dimensional radiative transfer model developed for estimates of the direct radiative forcing by aerosols. Estimates of solar radiative forcing by different aerosols are presented for January and July, based on calculated three-dimensional, global distributions of sulfate and black carbon mass. We show that the radiative forcing by sulfate is negative, as already known, while the forcing due to black carbon aerosols is mainly positive. Considering both black carbon and sulfate together and assuming an external mixture, we calculate a globally averaged radiative forcing of approximately -0.2 W/m2, with a quite nonuniform geographical distribution. The radiative forcing due to aerosols is highly dependent upon the optical properties of the aerosol, while the surface reflectance and the Sun angle influence the direction of the forcing. Our results show that the presence of black carbon, the main absorbing component of anthropogenic aerosol, may reduce the cooling effect of aerosol, thus leading to an increase in the greenhouse warming
Optical properties of aerosols and clouds: The software package OPAC
The software package OPAC (Optical Properties of Aerosols and Clouds) is described. It easily provides optical properties in the solar and terrestrial spectral range of atmospheric particulate matter. Microphysical and optical properties of six water clouds, three ice clouds, and 10 aerosol components, which are considered as typical cases, are stored as ASCII files. The optical properties are the extinction, scattering, and absorption coefficients, the single scattering albedo, the asymmetry parameter, and the phase function. They are calculated on the basis of the microphysical data (size distribution and spectral refractive index) under the assumption of spherical particles in case of aerosols and cloud droplets and assuming hexagonal columns in case of cirrus clouds. Data are given for up to 61 wavelengths between 0.25 and 40 mu m and up to eight values of the relative humidity. The software package also allows calculation of derived optical properties like mass extinction coefficients and Angstrom coefficients. Real aerosol in the atmosphere always is a mixture of different components. Thus, in OPAC it is made possible to get optical properties of any mixtures of the basic components and to calculate optical depths on the base of exponential aerosol height profiles. Typical mixtures of aerosol components as well as typical height profiles are proposed as default values, but mixtures and profiles for the description of individual cases may also be achieved simply
Bildung und Transport stratosphärischer Aerosolteilchen und ihre Bedeutung für den Strahlungshaushalt
Rezente winterliche Klimaänderungen auf der Nordhemisphäre, Ozonänderungen und zunehmender Treibhauseffekt
Globale Strahlungswirkung atmosphärischer Aerosolteilchen basierend auf dem Globalen Aerosoldatensatz GADS
Hall-like effect induced by spin-orbit interaction
The effect of spin-orbit interaction on electron transport properties of a
cross-junction structure is studied. It is shown that it results in spin
polarization of left and right outgoing electron waves. Consequently, incoming
electron wave of a proper polarization induces voltage drop perpendicularly to
the direct current flow between source and drain of the considered
four-terminal cross-structure. The resulting Hall-like resistance is estimated
to be of the order of 10^-3 - 10^-2 h/e^2 for technologically available
structures. The effect becomes more pronounced in the vicinity of resonances
where Hall-like resistance changes its sign as function of the Fermi energy.Comment: 4 pages (RevTeX), 4 figures, will appear in Phys. Rev. Let
Forward K+ production in subthreshold pA collisions at 1.0 GeV
K+ meson production in pA (A = C, Cu, Au) collisions has been studied using
the ANKE spectrometer at an internal target position of the COSY-Juelich
accelerator. The complete momentum spectrum of kaons emitted at forward angles,
theta < 12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far
below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal
distribution at low kaon momenta and the larger momenta reflect a high degree
of collectivity in the target nucleus.Comment: 4 pages, 3 figure
Self-sustaining smouldering combustion of coal tar for the remediation of contaminated sand:Two-dimensional experiments and computational simulations
This study presents the development and validation of a computational model which simulates the propagation of a smouldering front through a porous medium against unique experiments in coal tar and sand. The model couples a multiphase flow solver in porous media with a perimeter expansion module based on Huygens principle to predict the spread. A suite of two-dimensional experiments using coal tar- contaminated sand were conducted to explore the time-dependent vertical and lateral smouldering front 6 propagation rates and final extent of remediation as a function of air injection rate. A thermal severity analysis revealed, for the first time, the temperature-time relationship indicative of coal tar combustion. The model, calibrated to the base case experiment, then correctly predicts the remaining experiments. This work provides further confidence in a model for predicting smouldering, which eventually is expected to be useful for designing soil remediation schemes for a novel technology based upon smouldering destruction of organic contaminants in soil
A comprehensive score reflecting memory-related fMRI activations and deactivations as potential biomarker for neurocognitive aging
Older adults and particularly those at risk for developing dementia typically show a
decline in episodic memory performance, which has been associated with altered
memory network activity detectable via functional magnetic resonance imaging
(fMRI). To quantify the degree of these alterations, a score has been developed as a
putative imaging biomarker for successful aging in memory for older adults (Functional Activity Deviations during Encoding, FADE; Düzel et al., Hippocampus, 2011; 21:
803–814). Here, we introduce and validate a more comprehensive version of the
FADE score, termed FADE-SAME (Similarity of Activations during Memory Encoding),
which differs from the original FADE score by considering not only activations but
also deactivations in fMRI contrasts of stimulus novelty and successful encoding, and
by taking into account the variance of young adults' activations. We computed both
scores for novelty and subsequent memory contrasts in a cohort of 217 healthy
adults, including 106 young and 111 older participants, as well as a replication cohort
of 117 young subjects. We further tested the stability and generalizability of both
scores by controlling for different MR scanners and gender, as well as by using different data sets of young adults as reference samples. Both scores showed robust agegroup-related differences for the subsequent memory contrast, and the FADE-SAME
score additionally exhibited age-group-related differences for the novelty contrast.
Furthermore, both scores correlate with behavioral measures of cognitive aging,
namely memory performance. Taken together, our results suggest that single-value
scores of memory-related fMRI responses may constitute promising biomarkers for
quantifying neurocognitive aging
Development of the social brain from age three to twelve years
Human adults recruit distinct networks of brain regions to think about the bodies and minds of others. This study characterizes the development of these networks, and tests for relationships between neural development and behavioral changes in reasoning about others' minds ('theory of mind', ToM). A large sample of children (n = 122, 3-12 years), and adults (n = 33), watched a short movie while undergoing fMRI. The movie highlights the characters' bodily sensations (often pain) and mental states (beliefs, desires, emotions), and is a feasible experiment for young children. Here we report three main findings: (1) ToM and pain networks are functionally distinct by age 3 years, (2) functional specialization increases throughout childhood, and (3) functional maturity of each network is related to increasingly anti-correlated responses between the networks. Furthermore, the most studied milestone in ToM development, passing explicit false-belief tasks, does not correspond to discontinuities in the development of the social brain.National Science Foundation (U.S.) (Award 1122374)National Science Foundation (U.S.) (Award 095518)National Institutes of Health (U.S.) (Award R01-MH096914-05
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