The Hamburg University of Applied science is an institution of higher education and applied research located in Hamburg, Germany. Formerly known as Fachhochschule Hamburg the Hamburg University of Applied science was founded in 1970. In terms of student enrollment, the HAW is the second largest university in Hamburg, with a student body of 14,928 . Wikipedia.
Marmol F.G.,NEC Europe Ltd. |
Sorge C.,University of Paderborn |
Ugus O.,Hamburg University of Applied Sciences |
Perez G.M.,University of Murcia
IEEE Communications Magazine | Year: 2012
The recent deployment of smart grids has proven to bring numerous advantages in terms of energy consumption reduction in both homes and businesses. A more accurate measurement of up-to-date electricity necessities through smart meters utilization leads to an enhancement in the ability of monitoring, controlling and predicting energy use. Nevertheless, it has associated drawbacks related to the privacy of customers as well, since such management might reveal their personal habits and behavior, which electrical appliances they are using at each moment, whether they are at home or not, and so on. In this article we present a privacy enhanced architecture for smart metering aimed to tackle this threat by means of a new and novel protocol encrypting individual measurements while allowing the electricity supplier to access the aggregation of the corresponding decrypted values. The technique being used is named additively homomorphic encryption, and enables the direct connection and exchange of data between electricity suppliers and final users, while preserving the privacy of the latter. © 1979-2012 IEEE.
Lewandowski D.,Hamburg University of Applied Sciences
Aslib Proceedings: New Information Perspectives | Year: 2011
Purpose: The purpose of this paper is to test major web search engines on their performance on navigational queries, i.e. searches for homepages. Design/methodology/approach: In total, 100 user queries are posed to six search engines (Google, Yahoo!, MSN, Ask, Seekport, and Exalead). Users described the desired pages, and the results position of these was recorded. Measured success and mean reciprocal rank are calculated. Findings: The performance of the major search engines Google, Yahoo!, and MSN was found to be the best, with around 90 per cent of queries answered correctly. Ask and Exalead performed worse but received good scores as well. Research limitations/implications: All queries were in German, and the German-language interfaces of the search engines were used. Therefore, the results are only valid for German queries. Practical implications: When designing a search engine to compete with the major search engines, care should be taken on the performance on navigational queries. Users can be influenced easily in their quality ratings of search engines based on this performance. Originality/value: This study systematically compares the major search engines on navigational queries and compares the findings with studies on the retrieval effectiveness of the engines on informational queries. © Emerald Group Publishing Limited.
Lewandowski D.,Hamburg University of Applied Sciences |
Spree U.,Hamburg University of Applied Sciences
Journal of the American Society for Information Science and Technology | Year: 2011
This paper aims to review the fiercely discussed question of whether the ranking of Wikipedia articles in search engines is justified by the quality of the articles. After an overview of current research on information quality in Wikipedia, a summary of the extended discussion on the quality of encyclopedic entries in general is given. On this basis, a heuristic method for evaluating Wikipedia entries is developed and applied to Wikipedia articles that scored highly in a search engine retrieval effectiveness test and compared with the relevance judgment of jurors. In all search engines tested, Wikipedia results are unanimously judged better by the jurors than other results on the corresponding results position. Relevance judgments often roughly correspond with the results from the heuristic evaluation. Cases in which high relevance judgments are not in accordance with the comparatively low score from the heuristic evaluation are interpreted as an indicator of a high degree of trust in Wikipedia. One of the systemic shortcomings of Wikipedia lies in its necessarily incoherent user model. A further tuning of the suggested criteria catalog, for instance, the different weighing of the supplied criteria, could serve as a starting point for a user model differentiated evaluation of Wikipedia articles. Approved methods of quality evaluation of reference works are applied to Wikipedia articles and integrated with the question of search engine evaluation. © 2010 ASIS&T.
Lewandowski D.,Hamburg University of Applied Sciences
Online Information Review | Year: 2010
Abstract Purpose - The purpose of this paper is to measure the coverage of Google Scholar for Library and Information Science (LIS) journal literature as identified by a list of core LIS journals from a study by Schlogl and Petschnig. Design/methodology/approach - The paper checked every article from 35 major LIS journals from the years 2004 to 2006 for availability in Google Scholar. It also collected information on the type of availability - whether a certain article was available as a PDF for a fee, as a free PDF or as a preprint. Findings - The paper found that only some journals are completely indexed by Google Scholar, that the ratio of versions available depends on the type of publisher, and that availability varies a lot from journal to journal. Google Scholar cannot substitute for abstracting and indexing services in that it does not cover the complete literature of the field. However, it can be used in many cases to easily find available full texts of articles already identified using another tool. Originality/value - The study differs from other Google Scholar coverage studies in that it takes into account not only whether an article is indexed in Google Scholar at all, but also the type of availability. © Emerald Group Publishing Limited.
Winkler W.,Hamburg University of Applied Sciences
Applied Energy | Year: 2011
The necessary reduction of the human footprint demanded by Sustainable Development can be measured by the entropy flow of the society to the environment. The classic tools of process evaluation as e.g. exergetic or life cycle analysis are able to evaluate existing solutions. But their use during the design phase is quite limited because of lacking information about the system and its components. They may be helpful for evolutionary development strategies on a long term only. But reversible process structures can be used as benchmarks already in the conceptual design phase to introduce the demands of the second law. It can be shown that basic human demands on housing, mobility, communication, and infrastructure and industry can be principally supplied by reversible process structures. Because the process logic is a virtual one, real processes can be engineered with a reversible structure however its components produce irreversible entropy flows. Hybrid cars are the most common examples here. The use of exergetic efficiencies allows a transfer of the results of reversible structures to real technology easily. The here presented methodology of sustainable engineering can be summarized by three design rules as using reversible structures, considering technology by exergetic efficiencies, and minimizing components' entropy export. The still increasing utilization of electricity in upcoming technologies is very helpful for introducing reversible structures within hybrid technologies. © 2011 Elsevier Ltd.
Neumann L.,Hamburg University of Applied Sciences |
Scherer P.,Hamburg University of Applied Sciences
Bioresource Technology | Year: 2011
The influence of compost as inoculum during continuous anaerobic digestion of fodder beet silage was studied over 330 days. Two simultaneously driven mesophilic fermentors (Inoc-1/Inoc-2) were inoculated with manure and sewage sludge. Only the digester Inoc-2 was inoculated additionally with compost. After 160 days fermentor Inoc-2 reached a hydraulic retention time (HRT) around 15 days whereas Inoc-1 remained at a HRT of 40d. After changing the substrate feed from one to three times a day both digesters stabilised at a shorter HRT; Inoc-2 at 10 days and Inoc-1 around 20 days. An additional inoculation of fermentor Inoc-1 by compost shortened the HRT to 10 days and revealed a minor increased gas production of about 6%. Fluorescence in situ hybridization indicated that probably an archaeal population shift was responsible for the observed stimulations. An addition of compost induced a methanogenic community change towards hydrogenotrophic methanogens. © 2010 Elsevier Ltd.
Demirel B.,Hamburg University of Applied Sciences |
Demirel B.,Bogazici University |
Scherer P.,Hamburg University of Applied Sciences
Biomass and Bioenergy | Year: 2011
The availability of trace metals as micro-nutrients plays a very significant role on the performance and stability of agricultural biogas digesters, which are operated with energy crops, animal excreta, crop residues, organic fraction of municipal solid wastes or any other type of organic waste. The unavailability of these elements in biogas digesters is probably the first reason of poor process efficiency without any other obvious reason, despite proper management and control of other operational and environmental parameters. However, trace metal requirements of biogas digesters operated with solid biomass are not often reported in literature. Therefore, the aim of this article is to review the previous and current literature about the trace metal requirements of anaerobic biogas digesters operated with solid organic substrates for production of methane. © 2010 Elsevier Ltd.
Biallas G.,Hamburg University of Applied Sciences
International Journal of Fatigue | Year: 2013
Fatigue crack growth thresholds ΔKth were determined for friction stir welded butt joints made from aluminium alloys AA2024 and AA6013. Plotting the thresholds as a function of load ratio R showed distinctly higher amounts for welded joints as compared to those for parent material at small load ratios, but differences became smaller with increasing load ratio, until thresholds became finally identical for the highest R values. Applying Döker's concept of two controlling parameters, namely ΔK and K max , and plotting ΔKth versus Kmax, however, revealed that the effective threshold ΔKth ,eff determined at very high R ratios was nearly independent on the alloy and, simultaneously, was identical for parent material and respective welded joints. Thus, differences in threshold behaviour were only caused by the second threshold Kmax,th, which was significantly higher for welded joints as compared to parent material. Differences in Kmax,th coincided with compressive residual stresses determined by cut-compliance measurements in terms of stress intensity factors Krs acting at the crack tip. Based on the analytical approach described by Döker , only one characteristic Krs value was needed to calculate all thresholds of welded joints for 0 ≤ R ≤ 1 provided a base material master curve is available. © 2012 Elsevier Ltd. All rights reserved.
Gheorghiu V.,Hamburg University of Applied Sciences
SAE Technical Papers | Year: 2010
Most recent implementations of the Atkinson cycle are not ideal from the point of view of thermal conversion efficiency (TCE). For example, Toyota has put a gasoline engine in its Prius II which should achieve high efficiency by using a modified Atkinson cycle based on variable intake valve timing management. Firstly, this implementation of the Atkinson cycle is not the ideal solution because some of the air is first sucked from the intake manifold into the cylinder and subsequently returned back there. Consequently, the oscillating air stream reduces the thermal conversion efficiency of this cycle to a considerable extent. Secondly, this implementation of the Atkinson cycle only reaches low levels of indicated mean pressure (IMEP) and, thirdly, it is not suitable for part load engine operating points (EOP) because of the lower TCE. For these reasons, this implementation of the Atkinson cycle is only suitable for hybrid vehicles, where the engine - because it is not directly linked mechanically to the wheels - works only in its best EOP. This paper analyzes the losses in TCE of internal combustion engine (ICE) - especially for the Atkinson cycles - in detail, and a proposal is made for their reduction for aspirated and especially for high pressure supercharged engines. Copyright © 2010 SAE International.
Hamburg University of Applied Sciences | Date: 2011-03-03
The invention relates to a method for thermochemically converting organic waste material having high molecular weight into liquid combustible materials and fuels, comprising the following steps: feeding organic waste material into a reactor, heating the organic waste material to a temperature between 250 C. and 500 C. while avoiding exceeding critical coking temperatures in the reactor, feeding biogenic substances to the reactor, collecting and condensing the gases and vapors released from the mixture of organic waste material and biogenic substances, collecting the condensate and letting phases form, and removing the phase(s) containing liquid combustible materials and fuels.