Increased temperature in urban ground as source of sustainable energy

This paper is part of the Proceedings of the 10th International Conference on Urban Regeneration and Sustainability (Sustainable City 2015). http://www.witconferences.comDensely urbanized areas are characterized by special microclimatic conditions with typically elevated temperatures in comparison with the rural surrounding. This phenomenon is known as the urban heat island (UHI) effect, but not restricted exclusively to the atmosphere. We also find significant warming of the urban subsurface and shallow groundwater bodies. Here, main sources of heat are elevated ground surface temperatures, direct thermal exploitation of aquifers and heat losses from buildings and other infrastructure. By measuring the shallow groundwater temperature in several European cities, we identify that heat sources and associated transport processes interact at multiple spatial and temporal scales. The intensity of a subsurface UHI can reach the values of above 4 K in city centres with hotspots featuring temperatures up to +20°C. In comparison with atmospheric UHIs, subsurface UHIs represent long-term accumulations of heat in a relatively sluggish environment. This potentially impairs urban groundwater quality and permanently influences subsurface ecosystems. From another point of view, however, these thermal anomalies can also be seen as hidden large-scale batteries that constitute a source of shallow geothermal energy. Based on our measurements, data surveys and estimated physical ground properties, it is possible to estimate the theoretical geothermal potential of the urban groundwater bodies beneath the studied cities. For instance, by decreasing the elevated temperature of the shallow aquifer in Cologne, Germany, by only 2 K, the obtained energy could supply the space-heating demand of the entire city for at least 2.5 years. In the city of Karlsruhe, it is estimated that about 30% of annual heating demand could be sustainably supplied by tapping the anthropogenic heat loss in the urban aquifer. These results reveal the attractive potential of heated urban ground as energy reservoir and storage, which is in place at many places worldwide but so far not integrated in any city energy plans.This work was supported by the Swiss National Science Foundation (SNSF) under grant number 200021L 144288, and the German Research Foundation (DFG), under grant number BL 1015/4-1

Coulomb effects in semiconductor quantum dots

Coulomb correlations in the optical spectra of semiconductor quantum dots are investigated using a full-diagonalization approach. The resulting multi-exciton spectra are discussed in terms of the symmetry of the involved states. Characteristic features of the spectra like the nearly equidistantly spaced s-shell emission lines and the approximately constant p-shell transition energies are explained using simplified Hamiltonians that are derived taking into account the relative importance of various interaction contributions. Comparisons with previous results in the literature and their interpretation are made.Comment: 7 pages, 2 figure

Division, adjoints, and dualities of bilinear maps

The distributive property can be studied through bilinear maps and various morphisms between these maps. The adjoint-morphisms between bilinear maps establish a complete abelian category with projectives and admits a duality. Thus the adjoint category is not a module category but nevertheless it is suitably familiar. The universal properties have geometric perspectives. For example, products are orthogonal sums. The bilinear division maps are the simple bimaps with respect to nondegenerate adjoint-morphisms. That formalizes the understanding that the atoms of linear geometries are algebraic objects with no zero-divisors. Adjoint-isomorphism coincides with principal isotopism; hence, nonassociative division rings can be studied within this framework. This also corrects an error in an earlier pre-print; see Remark 2.11

Arithmetic behaviour of the sums of three squares

AbstractLet n ≠ 4a(8b + 7) be an integer. We deal with the problem of the solvability of the equation n = x12 + x22 + x32 in integers x1, x2, x3 prime to n. By a theorem of Vila (Arch. Math. 44 (1985), 424–437), the existence of such a solution implies that every central extension of the alternating group An, for n ≡ 3 (mod 8), can be realized as a Galois group over Q

Electric field control and optical signature of entanglement in quantum dot molecules

The degree of entanglement of an electron with a hole in a vertically coupled self-assembled dot molecule is shown to be tunable by an external electric field. Using atomistic pseudopotential calculations followed by a configuration interaction many-body treatment of correlations, we calculate the electronic states, degree of entanglement and optical absorption. We offer a novel way to spectroscopically detect the magnitude of electric field needed to maximize the entanglement.Comment: 4 pages, 6 figure

Insurance-related instruments for disaster risk reduction (2011 Global Assessment Report on Disaster Risk Reduction)

Strategies and measures for disaster risk reduction (DRR) are not being implemented at the scale called for by the Hyogo Framework of Action. Part of the problem is that, from the perspective of decision makers with resource constraints, it is risky to invest in something that reaps benefits only in the case of a relatively unlikely event (such as a hurricane or a drought). People and institutions are understandably prone to invest in choices that yield less uncertain benefits. DRR, in itself, can be perceived as a risky endeavor - especially from the financial perspective. One way to circumvent this problem is by promoting DRR through incentives and other features embedded in market-based financial instruments, which offer financial stability or reliable access to funds to help cope with the consequences of extreme events. Since not all risks can be cost-effectively reduced, especially those that occur only very rarely, forward-thinking DRR stakeholders tend to seek options for financing the remaining or residual risks. Insurance and other disaster risk sharing approaches can serve households, national governments and humanitarian or development organizations, not only to complement ex ante DRR by ensuring or accelerating financing for post-disaster activities (like relief, recovery and reconstruction), but also as a conduit for ex ante DRR, guiding investment decisions that would result in fewer losses if a disaster materializes in the future. The objective of this paper is to assist disaster risk reduction stakeholders analyze whether - and how - insurance and other market-based risk transfer instruments can help increase resilience to disasters