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Martin S.,German Aerospace Center | Lucka K.,OWI Oel Waerme Institute GmbH | Worner A.,German Aerospace Center | Vetter A.,Thuringer Landesanstalt fur Landwirtschaft
Chemie-Ingenieur-Technik | Year: 2011

Although there have been recent technical improvements, still there are numerous hurdles that stand against a widespread introduction of hydrogen- and fuel cell technology to the market. Besides the reduction of the production costs particular attention should be paid to the hydrogen infrastructure. Also the particular hydrogen production method is of importance. To evaluate the production of the secondary energy carrier hydrogen in a positive way, its production from renewable energy sources is of vital importance. Assuming that from 2020onwards an increasing amount of fuel cell powered vehicles is introduced to the market, the reforming of biofuels is a promising option. The presented evaluations of theoretical potentials show that in 2020 6-8% of the current fuel consumption could be covered by sustainably produced hydrogen. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Rucknagel J.,Martin Luther University of Halle Wittenberg | Brandhuber R.,Bayerische Landesanstalt fur Landwirtschaft | Hofmann B.,Martin Luther University of Halle Wittenberg | Lebert M.,Ingenieurburo fur Bodenphysik | And 4 more authors.
Soil and Tillage Research | Year: 2010

Mechanical precompression stress is a yardstick for the strength and compressibility of soils. The default method for the estimation of precompression stress is the graphic method according to Casagrande. It involves a subjective perception by the engineer who not only determines the point of the highest curvature visually, but decides also which points are to be used for generating the virgin compression line. In order to avoid such subjective approaches, mathematical models for the determination of precompression stress have been developed emanating from the Casagrande method. These models estimate the smallest radius of the curvature based on the minimum of the second numerical derivative. The paper has the aim to quantify the variance of subjectivity implied by the person executing the graphic method, the variance of different model approaches and the accuracy of the latter in handling the graphic values. Additionally we wanted to investigate the effect of different parameters on the ordinate of the diagram and the effect of the first load step on the precompression stress. To understand these relationships, stress/bulk density functions and stress/void ratio functions measured on 13 sites were analysed by five experienced but independent engineers and by use of three mathematical models. The mean errors of precompression stress estimations by the different testers were 0.01-0.12 and by the models 0.10-0.87 on a logarithmic scale. Expressed in kPa, increasing mean errors were observed with rising precompression stress, due to delogarithmization. For the graphical determination, they reached approx. 10-20 kPa at precompression stress levels of 60-150 kPa in typical subsoils; this means 15% on average. The handling of graphically obtained values by help of mathematical models disclosed considerable deviations between them. In the logarithmic variant, the mean absolute errors varied from 0.09 (9 kPa) to 0.40 (30 kPa) and the determination coefficients from 0.71 to 0.96. Another influence on the level of precompression stress has been observed when different variables were plotted on the ordinate of the graph. The graphically obtained values of precompression stress and those shown in the dry bulk density graph exceed the values calculated on the basis of the void ratio by the factor 1.2-1.5. Furthermore, it can be stated that in soil-compression tests with an initial load of 25 kPa higher precompression stress values were obtained than with lower initial loads (5 kPa), if the precompression values were low. © 2009 Elsevier B.V. All rights reserved. Source


Rucknagel J.,Martin Luther University of Halle Wittenberg | Gotze P.,Martin Luther University of Halle Wittenberg | Hofmann B.,Martin Luther University of Halle Wittenberg | Christen O.,Martin Luther University of Halle Wittenberg | Marschall K.,Thuringer Landesanstalt fur Landwirtschaft
Geoderma | Year: 2013

Many arable soils have significant horizon-specific gravel content levels. Just how these influence compaction behaviour, and in particular precompression stress as an important criterion of a soil's susceptibility to compaction, has yet to be sufficiently clarified. This article is intended to contribute towards answering this question.Firstly, three different fine earths, from the "Clay", "Silt Loam" and "Sandy Loam" soil texture classes were mixed with staggered proportions (0, 10, 20, 30, 40% by volume) of a quartz gravel (the shape of which was subrounded to rounded, average weighted diameter 6. mm). Soil core samplers were filled with the mixtures at a typical density for a natural site. In the case of the 30% by volume variant only, in addition to the quartz gravel an angular to subangular limestone gravel with the same size graduation was also used. The tests were supplemented by 20 samples from a natural site; the gravel content of these varied between 0.1 and 23.5% by volume. All of the disturbed and natural samples were adjusted to a water content at a matric potential of -. 6. kPa. Subsequently, an oedometer test was used to apply loads to them in stages (5-550. kPa). Precompression stress was calculated using the resulting stress-bulk density functions.While fine earth bulk density remained constant, the staggered addition of quartz gravel led to an increase in the whole soil density after packing, and thus also to a vertical shift in overall stress-bulk density functions. However, the stress-density functions of the fine earth do show that the overall compaction of fine earth decreased as gravel content increased. In the case of low gravel content levels of no more than 10% by volume, the increase in precompression stress (log) in the disturbed samples was, on the whole, very low. In the disturbed samples, however, as gravel content increased precompression stress (log) increased exponentially. Contrary to this, a continuous linear increase in precompression stress (log) could be observed with increasing gravel content in the natural samples. The angular to subangular shape of the gravel only resulted in greater precompression stress (log) in the "Silt Loam".At gravel-rich sites, gravel content influences soil compaction behaviour and precompression stress very strongly. For this reason, it is essential that it be considered when assessing such sites' risk of compaction damage. © 2013 The Authors. Source


Haag N.L.,University of Hohenheim | Nagele H.-J.,University of Hohenheim | Reiss K.,University of Hohenheim | Biertumpfel A.,Thuringer Landesanstalt fur Landwirtschaft | Oechsner H.,University of Hohenheim
Biomass and Bioenergy | Year: 2015

The growing number of biogas plants in Germany has greatly increased the demand for maize silage, the predominant crop used for biogas production. With a share of 80% among the energy crops, maize silage is currently subject to major concerns such as competition between food and fuel, environmental issues and sustainability. Alternative substrates cannot compete with the specific methane yield (SMY) of maize and are therefore disadvantaged. The cup plant is considered suitable to provide a solution however little data is available. To support the search for alternative crops, batch and continuous laboratory tests were carried out in order to determine the SMY of cup plant silage. The mean SMY in the batch test was measured at 0.251±0.0141m3 N/kg oDM and at 0.227±0.0158m3 N/kg oDM in the continuous test. The results show that the methane yield per ha of cup plant lies in the range between grass and maize silage. The cup plant proved to have no negative effects on process stability for the ratio fed into the digester. Although cup plant cannot currently compete with maize silage, further research in plant breeding will help to increase dry matter yields, SMY potential and promote the positive environmental effect such as a diverse energy crop rotation. s © 2015 Elsevier Ltd. Source


Scholz H.,Anhalt University of Applied Sciences | Beyer B.,Anhalt University of Applied Sciences | Anacker G.,Thuringer Landesanstalt fur Landwirtschaft | Wahner M.,Anhalt University of Applied Sciences
Archiv fur Tierzucht | Year: 2010

Data of 1841 lactations of 353 Holstein Friesian dairy cows and data according to their reproductive fertility and diseases were analysed over a period of five years in a breeding farm in Thüringen (Germany). As a result the lowest success of first service has been achieved at a lactation (ranged) between 9 000 and 11 000 kg. The time between calving and the following first service varied according to the first disease in last lactation. With rising milk yield the frequency of diseases and the success of first service tend to decrease. Cows achieving a 305 day milk yield of more than 11 000 kg showed with 56% the lowest frequency of diseases. In average 60% of all dairy cows need to be treated once in a lactation. The diseases of highest prevalence are in the field of reproductive fertility and udder health. For heifers a decreased success of first service has been detected if they showed an increased prevalence of illness. © Leibniz Institute for Farm Animal Biology, Dummerstorf Germany. Source

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