Technische Universität Darmstadt

About: Technische Universität Darmstadt is a education organization based out in Darmstadt, Germany. It is known for research contribution in the topics: Neutron & Finite element method. The organization has 17316 authors who have published 40619 publications receiving 937916 citations. The organization is also known as: Darmstadt University of Technology & University of Darmstadt.

Stable isotope enrichment (δ15N and δ13C) in a generalist predator (Pardosa lugubris, Araneae: Lycosidae): effects of prey quality

Abstract: Analysis of the natural variations in stable isotope ratios in animal tissue may be a powerful tool to reveal the trophic position and feeding preferences of generalist predators such as lycosid spiders. In the present study, changes in 15N/14N and 13C/12C ratios in the lycosid spider Pardosa lugubris (Araneae: Lycosidae), fed with prey of different quality, were investigated. Experimental food chains included three trophic levels: prey media, prey organism and predator. In order to analyse the time course of stable isotope enrichment, different life stages of P. lugubris feeding on Drosophila melanogaster were studied. The 15N content of hatchlings of P. lugubris was significantly lower than that of their mothers, indicating the existence of nitrogen pools with different 15N signatures in female P. lugubris. With duration of feeding and progressing development, age and body weight, the 15N content in spiderlings increased. Starvation resulted in 15N and 13C enrichment in P. lugubris. Being fed with prey of different quality resulted in varying patterns of stable isotope enrichment. 15N but not 13C content consistently increased when fed on high quality prey (Heteromurus nitidus, D. melanogaster and a mixed diet consisting of H. nitidus and D. melanogaster). In contrast, low quality prey (Rhopalosiphum padi, Folsomia candida and a mixed diet consisting of H. nitidus, D. melanogaster and F. candida) resulted in deviations from postulated patterns of stable isotope enrichment with 15N content being similar to that of starving spiderlings. When fed on high quality prey, 15N enrichment of P. lugubris was close to ca. 3‰. It is concluded that the analysis of variations in the natural abundance of stable isotopes is particularly helpful in revealing the trophic structure of terrestrial food webs in which polyphagous feeders predominate, as is the case in litter and soil.

A man-in-the-middle attack on UMTS

Abstract: In this paper we present a man-in-the-middle attack on the Universal Mobile Telecommunication Standard (UMTS), one of the newly emerging 3G mobile technologies. The attack allows an intruder to impersonate a valid GSM base station to a UMTS subscriber regardless of the fact that UMTS authentication and key agreement are used. As a result, an intruder can eavesdrop on all mobile-station-initiated traffic.Since the UMTS standard requires mutual authentication between the mobile station and the network, so far UMTS networks were considered to be secure against man-in-the-middle attacks. The network authentication defined in the UMTS standard depends on both the validity of the authentication token and the integrity protection of the subsequent security mode command.We show that both of these mechanisms are necessary in order to prevent a man-in-the middle attack. As a consequence we show that an attacker can mount an impersonation attack since GSM base stations do not support integrity protection. Possible victims to our attack are all mobile stations that support the UTRAN and the GSM air interface simultaneously. In particular, this is the case for most of the equipment used during the transition phase from 2G (GSM) to 3G (UMTS) technology.

Numerical Experiments on the Breaking of Solitary Internal Wavesover a Slope–Shelf Topography

Abstract: A theoretical study of the transformation of large amplitude internal solitary waves (ISW) of permanent form over a slope–shelf topography is considered using as basis the Reynolds equations. The vertical fluid stratification, amplitudes of the propagating ISWs, and the bottom parameters were taken close to those observed in the Andaman and Sulu Seas. The problem was solved numerically. It was found that, when an intense ISW of depression propagates from a deep part of a basin onto the shelf with water depth Hs, a breaking event will arise whenever the wave amplitude am is larger than 0.4(Hs − Hm), where Hm is the undisturbed depth of the isopycnal of maximum depression. The cumulative effect of nonlinearity in a propagating ISW leads to a steepening and overturning of a rear wave face over the inclined bottom. Immediately before breaking the horizontal orbital velocity at the site of instability exceeds the phase speed of the ISW. So, the strong breaking is caused by a kinematic instability of t...

Dehydration of d-fructose to hydroxymethylfurfural in sub- and supercritical fluids

Abstract: Hydroxymethylfurfural (HMF) is a key intermediate in the biomass-based chemical product line. Unfortunately, only unsatisfying yields of HMF are achieved by the dehydration of d -fructose in supercritical water (SCW). Previously, we reported on the dehydration of d -fructose to HMF in sub- and supercritical acetone/water mixtures. The use of this reaction media resulted in higher yields of HMF (77% selectivity, 99% conversion). In this work, we conducted the reaction in sub- and supercritical methanol (scMeOH) and subcritical acetic acid (scAcOH) and obtained the resulting furfural-ether (5-methoxymethylfurfural, MMF, 79% selectivity, 99% conversion) and -ester (5-acetoxymethylfurfural, AMF, 38% selectivity, 98% conversion). Further investigations on the reaction mechanism via NMR spectroscopy gave a possible explanation for the higher yields of the furfurals when using the above-mentioned solvents compared to water. Finally, a continuous production process for HMF and MMF is proposed.