Search results for "Radiative Transfer"

Electromagnetic transitions of heavy baryons in theSU(2Nf)⊗O(3)symmetry

2001

We apply heavy quark symmetry to the radiative decays of heavy baryons. Even with this symmetry in place there are too many couplings to make a meaningful set of predictions. We show that if, in addition, light-diquark symmetries are applied, the number of electromagnetic couplings among S wave and P wave states as well as those between P wave to S wave transitions can be reduced significantly. Using this constituent quark model picture a number of predictions are made that will be testable in the near future.

Superradiance and Exciton (De)localization in Light-Harvesting Complex II from Green Plants?

2002

Fluorescence quantum yield and fluorescence lifetime measurements were performed on trimeric light-harvesting complex II (LHCII) from spinach in the temperature range 7−293 K. From the results the radiative rate was calculated, which is related to the amount of delocalization of excitations over different pigments because of intermolecular interactions. The emitting dipole strength of LHCII is very similar to that of unbound Chl a, and it appears to be almost independent of temperature. The apparent increase of the radiative rate upon lowering the temperature can largely be explained by the shrinking of the sample. It is concluded that at all temperatures the amount of exciton delocalizatio…

Atomic Radiative Lifetimes Measured by Pulsed Laser Spectroscopy in the Uv/Vuv Spectral Region

1998

Abstract Experimental lifetime measurements on free atoms and ions performed by using pulsed laser excitation in the ultraviolet and vacuum-ultraviolet spectral regions are presented. Different methods of laser pulse generation, atomization and light detection are described. A short summary of results obtained is also given. Future possibilities in determination of lifetimes and transition probabilities in the short wavelengths region are discussed.

Non-Leptonic Kaon Decays and the Chiral Anomaly

1994

32 páginas, 3 figuras, 4 tablas.-- El PDF es el artículo publicado en el CERN en Junio de 1993.

Microphysical and radiative changes in cirrus clouds by geoengineering the stratosphere

2013

[1] In the absence of tangible progress in reducing greenhouse gas emissions, the implementation of solar radiation management has been suggested as measure to stop global warming. Here we investigate the impacts on northern midlatitude cirrus from continuous SO2emissions of 2–10 Mt/a in the tropical stratosphere. Transport of geoengineering aerosols into the troposphere was calculated along trajectories based on ERA Interim reanalyses using ozone concentrations to quantify the degree of mixing of stratospheric and tropospheric air termed “troposphericity”. Modeled size distributions of the geoengineered H2SO4-H2O droplets have been fed into a cirrus box model with spectral microphysics. Th…

Regional and seasonal radiative forcing by perturbations to aerosol and ozone precursor emissions

2016

Abstract. Dedicated model simulations by four general circulation and chemistry-transport models are used to establish a matrix of specific radiative forcing, defined as the radiative forcing per unit change in mass emitted, as a function of the near-term climate forcer emitted, its source region, and the season of emission. Emissions of eight near-term climate forcers are reduced: sulphur dioxide, the precursor to sulphate aerosols; black carbon aerosols; organic carbon aerosols; ammonia, a precursor to nitrate aerosols; methane; and nitrogen oxides, carbon monoxide, and volatile organic compounds, the precursors to ozone and to secondary organic aerosols. The focus is on two source region…

Large-scale random features for kernel regression

2015

Kernel methods constitute a family of powerful machine learning algorithms, which have found wide use in remote sensing and geosciences. However, kernel methods are still not widely adopted because of the high computational cost when dealing with large scale problems, such as the inversion of radiative transfer models. This paper introduces the method of random kitchen sinks (RKS) for fast statistical retrieval of bio-geo-physical parameters. The RKS method allows to approximate a kernel matrix with a set of random bases sampled from the Fourier domain. We extend their use to other bases, such as wavelets, stumps, and Walsh expansions. We show that kernel regression is now possible for data…

Radiative emission due to atomic self-dressing in QED

2002

We study the radiative emission due to the self-dressing of a two-level atom, initially in its bare ground state, interacting with the zero-point electromagnetic field. Evolution in time leads to the formation of a dressed ground state of lower energy. This energy difference between bare and dressed ground state is taken into account by the emission of real photons. In order to describe this aspect of the self-dressing process we study the transition probability amplitude from the initial bare state to an asymptotic state consisting of the atom in its dressed ground state plus some real photons. Adopting nonperturbative techniques based on the resolvent method we find that the bare-dressed …

2017

Abstract. We present a sensitivity study on transatlantic dust transport, a process which has many implications for the atmosphere, the ocean and the climate. We investigate the impact of key processes that control the dust outflow, i.e., the emission flux, convection schemes and the chemical aging of mineral dust, by using the EMAC model following Abdelkader et al. (2015). To characterize the dust outflow over the Atlantic Ocean, we distinguish two geographic zones: (i) dust interactions within the Intertropical Convergence Zone (ITCZ), or the dust–ITCZ interaction zone (DIZ), and (ii) the adjacent dust transport over the Atlantic Ocean (DTA) zone. In the latter zone, the dust loading show…

The ACRIDICON-CHUVA campaign: Studying tropical deep convective clouds and precipitation over Amazonia using the new German research aircraft HALO

2016

Abstract Between 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitatio…