On the estimation of wind comfort in a building environment by micro-scale simulation

A three-dimensional micro-scale model is used to study some aspects of wind comfort in a built-up area. The equations for calculating the mean wind have been extended by a Markov approach for short-term wind fluctuations. The model components have been successfully verified against wind tunnel measurements and observations of a field experiment. The simulated time series are used to estimate wind comfort measures. It turns out that the frequency of exceedance of prescribed thresholds depends strongly on the specification of the gust duration time. It was also possible to calculate the spatial distribution of a gust factor g depending on local wind characteristics. The simulated range is much broader than a value of g = 3-3.5 commonly used for wind comfort assessments. Again, the order of magnitude and the bandwidth of g depends strongly on the definition of a gust.DF

Observations and numerical simulations of the train-induced air flow in a subway station

This article presents observations and model simulations of wind and temperature in a subway station. The measurements are taken from an experiment with three ultrasonic anemometers at different levels in the underground facility. The available observations indicate a wind regime with a continuous background flow and train-induced ventilation with very effective air exchange between the platform level and the street level. Model simulations with a resolution of less than 1m were performed with running trains in accordance with a regular timetable. The results demonstrate the applicability of the model to the complex underground geometry. Calculated time series of wind and temperature are very comparable to the observations. The findings of a parameter study indicate the necessity to record all details of train movements in order to define appropriate initial and boundary conditions for the model and to explain the observations correctly.DF

Analysis of the different faces of a nocturnal urban heat island

The measurements of an urban-rural observation network in Hannover obtained over almost four years were used to analyse a canopy layer urban heat island (UHIUCL). Especially during the summer months, the UHIUCL was pronounced on numerous nights with maximum values of more than 6 K. We have demonstrated that the choice of rural reference station is important to describe a UHIUCL in detail. The time evolution of UHIUCL differed greatly from night to night and four main types could be identified with comparable frequencies of occurrence. The difference between these types was the appearance of the maximum urban heat island intensity during very different times of the night. The main drivers for the development of a specific type were the rural winds and rural temperature changes caused by turbulent mixing within the near-surface inversion

On the range of boundary layer model results depending on inaccurate input data

A one-dimensional boundary layer model was used to study the effects of uncertain input data on 2-m temperature and 10-m wind. Based on a very large number of numerical results, it can be demonstrated, that even a small degree of ambiguity can have significant implications, especially for temperature. In 50 % of all 6,000 simulations for flat terrain and randomly chosen sets of input data within narrow limits, temperature uncertainty was more than 2 K, and in 14 % of all cases more than 4 K, with a maximum of 9 K. Effect on wind speed is much smaller and depends mostly on surface roughness length. For a forest scenario, the results for temperature of 18,000 simulations are in the same order, with 25 % of the ensemble show temperature uncertainties of more than 2 K, and 6 % of more than 4 K, while wind speed above a forest is much more affected than for the bare soil case. In addition, the contribution of uncertainties of individual input data was estimated

Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films

We correlate simultaneously recorded magnetotransport and spatially resolved magneto optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films micropatterned into Hall bars. Room temperature MOKE images reveal the nucleation and propagation of domains in an externally applied magnetic field and are used to extract a macrospin corresponding to the mean magnetization direction in the Hall bar. The anisotropic magnetoresistance calculated using this macrospin is in excellent agreement with magnetoresistance measurements. This suggests that the magnetotransport in Heusler compounds can be adequately simulated using simple macrospin models, while the magnetoresistance contribution due to domain walls is of negligible importance

Os pais da Igreja enquanto apologetas da teologia natural e da filosofia da religião na modernidade nascente

A filosofia da religião moderna se desenvolveu a partir de reflexões prévias que nem sempre são bem conhecidas. Até que ela assumisse um ponto de vista crítico, no sentido iluminista, a abordagem filosófica da tradição teológica foi arduamente discutida. Durante a Renascença, a filosofia antiga e tradições especulativas foram comparadas aos Pais da Igreja a partir do ponto de vista de uma philosophia perennis. Nesse processo, os limites da abordagem geral prepararam o caminho para a modernidade

Existence of temperature on the nanoscale

We consider a regular chain of quantum particles with nearest neighbour interactions in a canonical state with temperature $T$. We analyse the conditions under which the state factors into a product of canonical density matrices with respect to groups of $n$ particles each and under which these groups have the same temperature $T$. In quantum mechanics the minimum group size $n_{min}$ depends on the temperature $T$, contrary to the classical case. We apply our analysis to a harmonic chain and find that $n_{min} = const.$ for temperatures above the Debye temperature and $n_{min} \propto T^{-3}$ below.Comment: Version that appeared in PR

Local charge and spin currents in magnetothermal landscapes

A scannable laser beam is used to generate local thermal gradients in metallic (Co2FeAl) or insulating (Y3Fe5O12) ferromagnetic thin films. We study the resulting local charge and spin currents that arise due to the anomalous Nernst effect (ANE) and the spin Seebeck effect (SSE), respectively. In the local ANE experiments, we detect the voltage in the Co2FeAl thin film plane as a function of the laser spot position and external magnetic field magnitude and orientation. The local SSE effect is detected in a similar fashion by exploiting the inverse spin Hall effect in a Pt layer deposited on top of the Y3Fe5O12. Our findings establish local thermal spin and charge current generation as well as spin caloritronic domain imaging

Density and Stability in Ultracold Dilute Boson-Fermion Mixtures

We analyze in detail recent experiments on ultracold dilute 87Rb-40K mixtures in Hamburg and in Florence within a mean-field theory. To this end we determine how the stationary bosonic and fermionic density profiles in this mixture depend in the Thomas-Fermi limit on the respective particle numbers. Furthermore, we investigate how the observed stability of the Bose-Fermi mixture with respect to collapse is crucially related to the value of the interspecies s-wave scattering length.Comment: Author Information under http://www.theo-phys.uni-essen.de/tp/ags/pelster_dir

Urban Climate Under Change [UC]2 – A National Research Programme for Developing a Building-Resolving Atmospheric Model for Entire City Regions

Large cities and urban regions are confronted with rising pressure by environmental pollution, impacts of climate change, as well as natural and health hazards. They are characterised by heterogeneous mosaics of urban structures, causing modifications of atmospheric processes on different temporal and spatial scales. Planning authorities need reliable, locally relevant information on urban atmospheric processes, providing fine spatial resolutions in city quarters or street canyons, as well as projections of future climates, specifically downscaled to individual cities. Therefore, building-resolving urban climate models for entire city regions are required as tool for urban development and planning, air quality control, as well as for design of actions for climate change mitigation and adaptation. To date, building-resolving atmospheric models covering entire large cities are mostly missing. The German research programme “Urban Climate Under Change” ([UC]2) aims at developing a new urban climate model, to acquire three-dimensional observational data for model testing and validation, and to test its practicability and usability in collaboration with relevant stakeholders to provide a scientifically sound and practicable instrument to address the above mentioned challenges. This article provides an outline of the collaborative activities of the [UC]2 research programme