Satellite monitoring of vegetation and geology in semi-arid environments

The possibility of mapping various characteristics of the natural environment of Tanzania by various LANDSAT techniques was assessed. Interpretation and mapping were carried out using black and white as well as color infrared images on the scale of 1:250,000. The advantages of several computer techniques were also assessed, including contrast-stretched rationing, differential edge enhancement; supervised classification; multitemporal classification; and change detection. Results Show the most useful image for interpretation comes from band 5, with additional information being obtained from either band 6 or band 7. The advantages of using color infrared images for interpreting vegetation and geology are so great that black and white should be used only to supplement the colored images

The Inflection Point of the Speed-Density Relation and the Social Force Model

It has been argued that the speed-density digram of pedestrian movement has an inflection point. This inflection point was found empirically in investigations of closed-loop single-file pedestrian movement. The reduced complexity of single-file movement does not only allow a higher precision for the evaluation of empirical data, but it occasionally also allows analytical considerations for micosimulation models. In this way it will be shown that certain (common) variants of the Social Force Model (SFM) do not produce an inflection point in the speed-density diagram if infinitely many pedestrians contribute to the force computed for one pedestrian. We propose a modified Social Force Model that produces the inflection point.Comment: accepted for presentation at conference Traffic and Granular Flow 201

Evolutionary responses of communities to extinctions

Question: What are the evolutionary consequences of extinctions in ecological communities? Can evolution restore pre-extinction communities by replacing lost ecological strategies with similar ones, or will communities change in fundamental ways and never be the same again? Mathematical approach: We develop and explore a new framework based on evolutionary domains of attraction (EDAs), defined as sets of strategy combination from which a particular ESS community can be attained through gradual evolution. The latter dynamics may include three types of evolutionary processes: continuous strategy adaptation in response to directional selection, evolutionary branching in response to disruptive selection, and evolutionarily driven extinction. Key assumptions: We consider gradual frequency-dependent evolution in ecological communities, with evolutionary dynamics being fully determined by the strategy composition of a community's resident species. Results: The EDA approach distinguishes ESS communities that gradual evolution can restore after extinctions from ESS communities for which this option does not exist or is constrained. The EDA approach also offers a natural definition of 'evolutionary keystone species' as species whose removal causes a community to shift from one EDA to another. Our study highlights that environmentally driven extinctions can readily cause such shifts. We explain why the evolutionary attainability of an ESS community through gradual evolution from a single precursor species does not imply its evolutionary restorability after extinctions. This shows that evolution driven by frequency-dependent selection may lead to 'Humpty Dumpty' effects and community closure on an evolutionary time scale. By establishing EDAs for several example food webs, we discover that evolutionarily driven extinctions may be crucially involved in the evolutionary restoration of ESS communities

Constrained simulations of the Antennae Galaxies: Comparison with Herschel-PACS observations

We present a set of hydro-dynamical numerical simulations of the Antennae galaxies in order to understand the origin of the central overlap starburst. Our dynamical model provides a good match to the observed nuclear and overlap star formation, especially when using a range of rather inefficient stellar feedback efficiencies (0.01 < q_EoS < 0.1). In this case a simple conversion of local star formation to molecular hydrogen surface density motivated by observations accounts well for the observed distribution of CO. Using radiative transfer post-processing we model synthetic far-infrared spectral energy distributions (SEDs) and two-dimensional emission maps for direct comparison with Herschel-PACS observations. For a gas-to-dust ratio of 62:1 and the best matching range of stellar feedback efficiencies the synthetic far-infrared SEDs of the central star forming region peak at values of ~65 - 81 Jy at 99 - 116 um, similar to a three-component modified black body fit to infrared observations. Also the spatial distribution of the far-infrared emission at 70 um, 100 um, and 160 um compares well with the observations: >50% (> 35%) of the emission in each band is concentrated in the overlap region while only < 30% (< 15%) is distributed to the combined emission from the two galactic nuclei in the simulations (observations). As a proof of principle we show that parameter variations in the feedback model result in unambiguous changes both in the global and in the spatially resolved observable far-infrared properties of Antennae galaxy models. Our results strengthen the importance of direct, spatially resolved comparative studies of matched galaxy merger simulations as a valuable tool to constrain the fundamental star formation and feedback physics.Comment: 17 pages, 8 figures, 4 tables, submitted to MNRAS, including revisions after first referee report, comments welcom

Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets

The concept of local isotropy in a chemically reacting turbulent wall-jet flow is addressed using direct numerical simulation (DNS) data. Different DNS databases with isothermal and exothermic reactions are examined. The chemical reaction and heat release effects on the turbulent velocity, passive scalar and reactive species fields are studied using their probability density functions (PDF) and higher order moments for velocities and scalar fields, as well as their gradients. With the aid of the anisotropy invariant maps for the Reynolds stress tensor the heat release effects on the anisotropy level at different wall-normal locations are evaluated and found to be most accentuated in the near-wall region. It is observed that the small-scale anisotropies are persistent both in the near-wall region and inside the jet flame. Two exothermic cases with different Damkohler number are examined and the comparison revealed that the Damkohler number effects are most dominant in the near-wall region, where the wall cooling effects are influential. In addition, with the aid of PDFs conditioned on the mixture fraction, the significance of the reactive scalar characteristics in the reaction zone is illustrated. We argue that the combined effects of strong intermittency and strong persistency of anisotropy at the small scales in the entire domain can affect mixing and ultimately the combustion characteristics of the reacting flow

Experimental f-value and isotopic structure for the Ni I line blended with [OI] at 6300A

We have measured the oscillator strength of the Ni I line at 6300.34 \AA, which is known to be blended with the forbidden [O I] $\lambda$6300 line, used for determination of the oxygen abundance in cool stars. We give also wavelengths of the two isotopic line components of $^{58}$Ni and $^{60}$Ni derived from the asymmetric laboratory line profile. These two line components of Ni I have to be considered when calculating a line profile of the 6300 \AA\ feature observed in stellar and solar spectra. We also discuss the labelling of the energy levels involved in the Ni I line, as level mixing makes the theoretical predictions uncertain.Comment: Accepted for publication in ApJLetter