Correlated EoM and Distributions for A=6 Nuclei

Energy spectra and electromagnetic transitions of nuclei are strongly depending from the correlations of the bound nucleons. Two particle correlations are responsible for the scattering of model particles either to low momentum- or to high momentum-states. The low momentum states form the model space while the high momentum states are used to calculate the G-matrix. The three and higher order particle correlations do not play a role in the latter calculation especially if the correlations induced by the scattering operator are of sufficient short range. They modify however, via the long tail of the nuclear potential, the Slater determinant of the A particles by generating excited Slater's determinants. In this work the influence of the correlations on the level structure and ground state distributions of even open shell nuclei is analyzed via the boson dynamic correlation model BDCM. The model is based on the unitary operator $e^S$ ({\it S} is the correlation operator) formalism which in this paper is presented within a non perturbative approximation. The low lying spectrum calculated for $^6$Li reproduce very well the experimental spectrum while for $^6$He a charge radius slightly larger than that obtained within the isotopic-shift (IS) theory has been calculated. Good agreement between theoretical and experimental results has been obtained without the introduction of a genuine three body force.Comment: 25 pages 4 figures. To be published in the Progress Theoretical Physic

Extended Cluster Model for Light, and Medium Nuclei

The structures, the electromagnetic transitions, and the beta decay strengths of exotic nuclei are investigated within an extended cluster model. We start by deriving an effective nuclear Hamiltonian within the $S_2$ correlation operator. Tensor forces are introduced in a perturbative expansion which includes up to the second order terms. Within this Hamiltonian we calculate the distributions and the radii of A=3,~4 nuclei. For exotic nuclei characterized by n valence protons/neutrons we excite the structure of the closed shell nuclei via mixed modes formed by considering correlations operators of higher order. Good results have been obtained for the calculated transitions and for the beta decay transition probabilities.Comment: 8-pages, 5-figure

Accounting for the effect of horizontal gradients in limb measurements of scattered sunlight

Limb measurements provided by the SCanning Imaging Absorption spectrometer for Atmospheric CHartographY (SCIAMACHY) on the ENVISAT satellite allow retrieving stratospheric profiles of various trace gases on a global scale, among them BrO for the first time. For limb observations in the UV/VIS spectral region the instrument measures scattered light with a complex distribution of light paths: the light is measured at different tangent heights and can be scattered or absorbed in the atmosphere or reflected by the ground. By means of spectroscopy and radiative transfer modelling these measurements can be inverted to retrieve the vertical distribution of stratospheric trace gases. <br></br> The fully spherical 3-D Monte Carlo radiative transfer model "Tracy-II" is applied in this study. The Monte Carlo method benefits from conceptual simplicity and allows realizing the concept of full spherical geometry of the atmosphere and also its 3-D properties, which is important for a realistic description of the limb geometry. Furthermore it allows accounting for horizontal gradients in the distribution of trace gases. <br></br> In this study the effect of horizontally inhomogeneous distributions of trace gases along flight/viewing direction on the retrieval of profiles is investigated. We introduce a tomographic method to correct for this effect by combining consecutive limb scanning sequences and utilizing the overlap in their measurement sensitivity regions. It is found that if horizontal inhomogenity is not properly accounted for, typical errors of 20% for NO<sub>2</sub> and up to 50% for OClO around the altitude of the profile peak can arise for measurements close to the Arctic polar vortex boundary in boreal winter

Extending differential optical absorption spectroscopy for limb measurements in the UV

Methods of UV/VIS absorption spectroscopy to determine the constituents in the Earth's atmosphere from measurements of scattered light are often based on the Beer-Lambert law, like e.g. Differential Optical Absorption Spectroscopy (DOAS). While the Beer-Lambert law is strictly valid for a single light path only, the relation between the optical depth and the concentration of any absorber can be approximated as linear also for scattered light observations at a single wavelength if the absorption is weak. If the light path distribution is approximated not to vary with wavelength, also linearity between the optical depth and the product of the cross-section and the concentration of an absorber can be assumed. These assumptions are widely made for DOAS applications for scattered light observations. <br><br> For medium and strong absorption of scattered light (e.g. along very long light-paths like in limb geometry) the relation between the optical depth and the concentration of an absorber is no longer linear. In addition, for broad wavelength intervals the differences in the travelled light-paths at different wavelengths become important, especially in the UV, where the probability for scattering increases strongly with decreasing wavelength. <br><br> However, the DOAS method can be extended to cases with medium to strong absorptions and for broader wavelength intervals by the so called air mass factor modified (or extended) DOAS and the weighting function modified DOAS. These approaches take into account the wavelength dependency of the slant column densities (SCDs), but also require a priori knowledge for the air mass factor or the weighting function from radiative transfer modelling. <br><br> We describe an approach that considers the fitting results obtained from DOAS, the SCDs, as a function of wavelength and vertical optical depth and expands this function into a Taylor series of both quantities. The Taylor coefficients are then applied as additional fitting parameters in the DOAS analysis. Thus the variability of the SCD in the fit window is determined by the retrieval itself. <br><br> This new approach provides a description of the SCD the exactness of which depends on the order of the Taylor expansion, and is independent from any assumptions or a priori knowledge of the considered absorbers. <br><br> In case studies of simulated and measured spectra in the UV range (332–357 nm), we demonstrate the improvement by this approach for the retrieval of vertical profiles of BrO from the SCIAMACHY limb observations. The results for BrO obtained from the simulated spectra are closer to the true profiles, when applying the new method for the SCDs of ozone, than when the standard DOAS approach is used. For the measured spectra the agreement with validation measurements is also improved significantly, especially for cases with strong ozone absorption. <br><br> While the focus of this article is on the improvement of the BrO profile retrieval from the SCIAMACHY limb measurements, the novel approach may be applied to a wide range of DOAS retrievals

Monte Carlo modeling of photon propagation reveals highly scattering coral tissue

Corals are very efficient at using solar radiation, with photosynthetic quantum efficiencies approaching theoretical limits. Here, we investigated potential mechanisms underlying such outstanding photosynthetic performance through extracting inherent optical properties of the living coral tissue and skeleton in a massive faviid coral. Using Monte Carlo simulations developed for medical tissue optics it is shown that for the investigated faviid coral, the coral tissue was a strongly light scattering matrix with a reduced scattering coefficient of µs’ =10 cm-1 (at 636 nm). In contrast, the scattering coefficient of the coral skeleton was µs’ =3.4 cm-1, which facilitated the efficient propagation of light to otherwise shaded coral tissue layers, thus supporting photosynthesis in lower tissues. Our study provides a quantification of coral tissue optical properties in a massive faviid coral and suggests a novel light harvesting strategy, where tissue and skeletal optics act in concert to optimize the illumination of the photosynthesizing algal symbionts embedded within the living coral tissue

Microenvironment and photosynthesis of zooxanthellae in scleractinian corals studied with microsensors for O2, pH and light

During experimental Light-dark cycles, O-2 in the tissue of the colonial scleractinian corals Favia sp. and Acropora sp. reached >250% of air saturation after a few minutes in Light. Immediately after darkening, O-2 was depleted rapidly, and within 5 min the O-2 concentration at the tissue surface reached 6 times higher at a saturating irradiance of 350 mu Ein m(-2) s(-1) than the dark respiration measured under identical hydrodynamic conditions (flow rate of 5 to 6 cm s(-1))