Leibniz University of Hanover

About: Leibniz University of Hanover is a education organization based out in Hanover, Niedersachsen, Germany. It is known for research contribution in the topics: Finite element method & Population. The organization has 14283 authors who have published 29845 publications receiving 682152 citations.

Palladium Doped Porous Titania Photocatalysts: Impact of Mesoporous Order and Crystallinity

Abstract: Herein, we report a facile synthesis method for highly ordered hexagonal P6m mesoporous palladium doped titania nanoarchitectures using the F127 triblock copolymer as a template. The mesoporous Pd/TiO2 nanoarchitectures possess high surface areas of 223 m2g−1 and large pore volumes of 0.42 cm3g−1 at 300 °C that are reduced to 162 m2g−1 and 0.29 cm3g−1, respectively, as a result of calcination at 450 °C with their tunable mesopore diameter ranging from 5.7 to 8.3 nm. Transmission electron microscopy (TEM) measurements evince that the framework of the highly crystalline mesoporous Pd/TiO2 is composed of aligned anatase phase grown along the [101] direction. The Pd nanoparticles are well dispersed and exhibit sizes of about 20 nm and they are separated by 1.95 A, which agrees with the (200) lattice spacing of face-centered cubic Pd. The newly prepared photocatalysts have been compared with Pd photodeposited onto the commercial photocatalyst Sachtleben Hombikat UV-100 by the determination of the rate of HCHO ...

Adaptation of Plants to Adverse Chemical Soil Conditions

Abstract: Publisher Summary This chapter focuses on the various constraints faced by plants in adverse soil conditions such as acidity, poor aeration, alkalinity, and salinity. The low-external input high-efficiency involving adapted genotypes that efficiently uses the nutrients from soil reserves and fertilizer can lead to yields that are only 10–20% below the maximum. Two components that contribute to overall nutrient efficiency include uptake efficiency, which is the amount of nutrient absorbed, and utilization efficiency, which characterizes the efficiency with which the absorbed nutrients are utilized to produce yield. Both of them primarily depend on the nutrient supply by the soil and fertilizers. The main constraints to plant growth in flooded or submerged soils are the low oxygen availability, Fe and Mn toxicity and toxic metabolites of anaerobic decomposition. Adaptation to flooded soils includes aerenchyma formation to transport oxygen to the roots, efficient generation and use of energy and carbohydrate conservation. Plant growth in alkaline or calcareous soils is inhibited by low availability of Fe, Zn, Mn and B and tolerance to such soils is achieved by mobilization of Fe and Zn via exudation of chelating compounds such as organic acid anions in Strategy I plants and phytosiderophores in Strategy II plants. The main constraints to plant growth in saline soils are low osmotic potential and ion toxicity (Na, Cl, sulphate) as well as ion imbalances (low K/Na ratio). The salt tolerance mechanisms can be divided into salt exclusion (reduced uptake, increased efflux) and salt inclusion (compartmentation into the vacuole, release of salts via salt glands, and salt-tolerant enzymes).

Simultaneous Production of Hydrogen and Synthesis Gas by Combining Water Splitting with Partial Oxidation of Methane in a Hollow‐Fiber Membrane Reactor

Abstract: Hydrogen is gaining more and more attention because it is regarded as an important future fuel. Today, hydrogen is mainly produced from nonrenewable natural gas and petroleum. With concerns over worldwide energy demands and global climate change, alternative sources must be found. Obviously, water is recommended as the ideal source for the generation of large amounts of hydrogen. In addition to electrolysis, recently several new processes, such as photovoltaic–photoelectrochemical water splitting and one-step or multistep thermochemical water splitting 6] based on focused solar or nuclear heat, have been developed. Although water dissociation into oxygen and hydrogen is conceptually simple [Eq. (1)], efficient hydrogen production

A New Aerodynamic Parametrization for Real Urban Surfaces

Abstract: This study conducted large-eddy simulations (LES) of fully developed turbulent flow within and above explicitly resolved buildings in Tokyo and Nagoya, Japan. The more than 100 LES results, each covering a 1,000 $$\times $$ 1,000 m $$^{2}$$ area with 2-m resolution, provide a database of the horizontally-averaged turbulent statistics and surface drag corresponding to various urban morphologies. The vertical profiles of horizontally-averaged wind velocity mostly follow a logarithmic law even for districts with high-rise buildings, allowing estimates of aerodynamic parameters such as displacement height and roughness length using the von Karman constant $$=$$ 0.4. As an alternative derivation of the aerodynamic parameters, a regression of roughness length and variable Karman constant was also attempted, using a displacement height physically determined as the central height of drag action. Although both the regression methods worked, the former gives larger (smaller) values of displacement height (roughness length) by 20–25 % than the latter. The LES database clearly illustrates the essential difference in bulk flow properties between real urban surfaces and simplified arrays. The vertical profiles of horizontally-averaged momentum flux were influenced by the maximum building height and the standard deviation of building height, as well as conventional geometric parameters such as the average building height, frontal area index, and plane area index. On the basis of these investigations, a new aerodynamic parametrization of roughness length and displacement height in terms of the five geometric parameters described above was empirically proposed. The new parametrizations work well for both real urban morphologies and simplified model geometries.