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Search Results: 1 - 10 of 515 matches for " Verena Tams "
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Quantitative PCR Reveals Strong Spatial and Temporal Variation of the Wasting Disease Pathogen, Labyrinthula zosterae in Northern European Eelgrass (Zostera marina) Beds
Anna-Christina Bockelmann, Verena Tams, Jana Ploog, Philipp R. Schubert, Thorsten B. H. Reusch
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0062169
Abstract: Seagrass beds are the foundation species of functionally important coastal ecosystems worldwide. The world’s largest losses of the widespread seagrass Zostera marina (eelgrass) have been reported as a consequence of wasting disease, an infection with the endophytic protist Labyrinthula zosterae. During one of the most extended epidemics in the marine realm, ~90% of East and Western Atlantic eelgrass beds died-off between 1932 and 1934. Today, small outbreaks continue to be reported, but the current extent of L. zosterae in European meadows is completely unknown. In this study we quantify the abundance and prevalence of the wasting disease pathogen among 19 Z. marina populations in northern European coastal waters, using quantitative PCR (QPCR) with primers targeting a species specific portion of the internally transcribed spacer (ITS1) of L. zosterae. Spatially, we found marked variation among sites with abundances varying between 0 and 126 cells mg?1 Z. marina dry weight (mean: 5.7 L. zosterae cells mg?1 Z. marina dry weight ±1.9 SE) and prevalences ranged from 0–88.9%. Temporarily, abundances varied between 0 and 271 cells mg?1 Z. marina dry weight (mean: 8.5±2.6 SE), while prevalences ranged from zero in winter and early spring to 96% in summer. Field concentrations accessed via bulk DNA extraction and subsequent QPCR correlated well with prevalence data estimated via isolation and cultivation from live plant tissue. L. zosterae was not only detectable in black lesions, a sign of Labyrinthula-induced necrosis, but also occurred in green, apparently healthy tissue. We conclude that L. zosterae infection is common (84% infected populations) in (northern) European eelgrass populations with highest abundances during the summer months. In the light of global climate change and increasing rate of marine diseases our data provide a baseline for further studies on the causes of pathogenic outbreaks of L. zosterae.
Current European Labyrinthula zosterae Are Not Virulent and Modulate Seagrass (Zostera marina) Defense Gene Expression
Janina Brakel, Franziska Julie Werner, Verena Tams, Thorsten B. H. Reusch, Anna-Christina Bockelmann
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0092448
Abstract: Pro- and eukaryotic microbes associated with multi-cellular organisms are receiving increasing attention as a driving factor in ecosystems. Endophytes in plants can change host performance by altering nutrient uptake, secondary metabolite production or defense mechanisms. Recent studies detected widespread prevalence of Labyrinthula zosterae in European Zostera marina meadows, a protist that allegedly caused a massive amphi-Atlantic seagrass die-off event in the 1930's, while showing only limited virulence today. As a limiting factor for pathogenicity, we investigated genotype×genotype interactions of host and pathogen from different regions (10–100 km-scale) through reciprocal infection. Although the endophyte rapidly infected Z. marina, we found little evidence that Z. marina was negatively impacted by L. zosterae. Instead Z. marina showed enhanced leaf growth and kept endophyte abundance low. Moreover, we found almost no interaction of protist×eelgrass-origin on different parameters of L. zosterae virulence/Z. marina performance, and also no increase in mortality after experimental infection. In a target gene approach, we identified a significant down-regulation in the expression of 6/11 genes from the defense cascade of Z. marina after real-time quantitative PCR, revealing strong immune modulation of the host's defense by a potential parasite for the first time in a marine plant. Nevertheless, one gene involved in phenol synthesis was strongly up-regulated, indicating that Z. marina plants were probably able to control the level of infection. There was no change in expression in a general stress indicator gene (HSP70). Mean L. zosterae abundances decreased below 10% after 16 days of experimental runtime. We conclude that under non-stress conditions L. zosterae infection in the study region is not associated with substantial virulence.
Attacks and Countermeasures in Fingerprint Based Biometric Cryptosystems
Benjamin Tams
Computer Science , 2013,
Abstract: We investigate implementations of biometric cryptosystems protecting fingerprint templates (which are mostly based on the fuzzy vault scheme by Juels and Sudan in 2002) with respect to the security they provide. We show that attacks taking advantage of the system's false acceptance rate, i.e. false-accept attacks, pose a very serious risk --- even if brute-force attacks are impractical to perform. Our observations lead to the clear conclusion that currently a single fingerprint is not sufficient to provide a secure biometric cryptosystem. But there remain other problems that can not be resolved by merely switching to multi-finger: Kholmatov and Yanikoglu in 2007 demonstrated that it is possible to break two matching vault records at quite a high rate via the correlation attack. We propose an implementation of a minutiae fuzzy vault that is inherently resistant against cross-matching and the correlation attack. Surprisingly, achieving cross-matching resistance is not at the cost of authentication performance. In particular, we propose to use a randomized decoding procedure and find that it is possible to achieve a GAR=91% at which no false accepts are observed on a database generally used. Our ideas can be adopted into an implementation of a multibiometric cryptosystem. All experiments described in this paper can fully be reproduced using software available for download.
Decodability Attack against the Fuzzy Commitment Scheme with Public Feature Transforms
Benjamin Tams
Computer Science , 2014,
Abstract: The fuzzy commitment scheme is a cryptographic primitive that can be used to store biometric templates being encoded as fixed-length feature vectors protected. If multiple related records generated from the same biometric instance can be intercepted, their correspondence can be determined using the decodability attack. In 2011, Kelkboom et al. proposed to pass the feature vectors through a record-specific but public permutation process in order to prevent this attack. In this paper, it is shown that this countermeasure enables another attack also analyzed by Simoens et al. in 2009 which can even ease an adversary to fully break two related records. The attack may only be feasible if the protected feature vectors have a reasonably small Hamming distance; yet, implementations and security analyses must account for this risk. This paper furthermore discusses that by means of a public transformation, the attack cannot be prevented in a binary fuzzy commitment scheme based on linear codes. Fortunately, such transformations can be generated for the non-binary case. In order to still be able to protect binary feature vectors, one may consider to use the improved fuzzy vault scheme by Dodis et al. which may be secured against linkability attacks using observations made by Merkle and Tams.
Security of the Improved Fuzzy Vault Scheme in the Presence of Record Multiplicity (Full Version)
Johannes Merkle,Benjamin Tams
Computer Science , 2013,
Abstract: Dodis et al. proposed an improved version of the fuzzy vault scheme, one of the most popular primitives used in biometric cryptosystems, requiring less storage and leaking less information. Recently, Blanton and Aliasgari have shown that the relation of two improved fuzzy vault records of the same individual may be determined by solving a system of non-linear equations. However, they conjectured that this is feasible for small parameters only. In this paper, we present a new attack against the improved fuzzy vault scheme based on the extended Euclidean algorithm that determines if two records are related and recovers the elements by which the protected features, e.g., the biometric templates, differ. Our theoretical and empirical analysis demonstrates that the attack is very effective and efficient for practical parameters. Furthermore, we show how this attack can be extended to fully recover both feature sets from related vault records much more efficiently than possible by attacking each record individually. We complement this work by deriving lower bounds for record multiplicity attacks and use these to show that our attack is asymptotically optimal in an information theoretic sense. Finally, we propose remedies to harden the scheme against record multiplicity attacks.
The Effect of Variable Electricity Tariffs in the Household on Usage of Household Appliances  [PDF]
Rainer Stamminger, Verena Anstett
Smart Grid and Renewable Energy (SGRE) , 2013, DOI: 10.4236/sgre.2013.44042
Abstract: Demand side management (DSM) has been discussed and investigated widely as a strategy to also influence residential energy consumption. Flexible energy tariffs are often proposed as a possible tool of DSM. However, real-life experience with this tool is rare. It was therefore the objective of this study to investigate under more realistic conditions how consumers are able and willing to adjust their residential energy consumption under the conditions of flexible energy tariffs with and without the support of intelligent smart appliances. Sixty-seven households in Germany within an experimental design with fictive tariff model (August 11 to July 12) driven by RWE Effizienz GmbH, as the energy utility, and Miele & Cie.KG, as the appliance manufacturer, were equipped with intelligent smart meters and 41 of them also with smart appliances (washing-machine and tumble-dryer). As a first part of the experiment, the energy tariff changed per hour and day by day, depending on the forecast of the availability of renewable energy in Germany between 10 €-Cent and 40 €-Cent per kWh. Consumers could respond to this change by adjusting the operation of their energyconsuming appliances either by themselves or—with the smart appliances—by a programmed start at low tariffs. The behaviour of the 41 consumers with smart appliances and their motivation are intensively investigated and analysed during this running two year project including several questionnaires. The consumers had to fill out daily a diary about the usage of their washing-machine, tumble-dryer, dishwasher and ironing devices. These data were matched with the actual tariff. This did allow identifying if and to which extend the consumers adjust their household activities depending on availability of solar and wind energy. These data were also used to calculate the cost savings by using the flexible tariff. In comparison to the costs of the fixed tariff of 25 €-Cent per kWh savings of 25% were realised on average. The results of a first phase already show that flexible tariffs are able to influence the operation of household appliances towards a flexible demand.
Pluralizar o universal: guerra e paz na obra de Hannah Arendt
Stolcke, Verena;
Mana , 2002, DOI: 10.1590/S0104-93132002000100004
Abstract: every theory has its own biography. hannah arendt's work on totalitarianism was born from her experiences as a german jew, exiled from her own country. central to her nonconformist thought is the notion of pariah, inspiring a political philosophy in which she seeks to reconcile intellectual freedom with political commitment. behind this philosophy lies a humanist anthropology whose nucleus is a conception of shared human experience, the diversity of which resides precisely in an original creative freedom. as a result, her work challenges exclusive identities and borders - products of the modern nation state - and in place proposes a civic culture and a form of justice transcending national limits.
Los mestizos no nacen sino que se hacen
Stolcke,Verena;
Av?? , 2009,
Abstract: en este ensayo se analiza el proceso de construcción de la categoría social de l@s mestiz@s en los inicios de la colonización de hispano-américa desde una perspectiva semánticohistórica y antropológica, así como las diferencias en su afianzamiento y gestión política en distintos contextos geopolíticos de la colonial. partiendo de sus investigaciones previas, donde desarrolló una interpretación del racismo como doctrina legitimadora de la desigualdad socioeconómica junto con las formas de dominación y control socio-sexual, en especial de las mujeres, la autora explora los mecanismos utilizados por la administración colonial para distinguir formalmente a l@s mestiz@s de otros grupos sociales así como los criterios de identificación empleados para ello, examinando el significado cambiante de la doctrina peninsular de limpieza de sangre.
O enigma das interse??es: classe, "ra?a", sexo, sexualidade: a forma??o dos impérios transatlanticos do século XVI ao XIX
Stolke, Verena;
Revista Estudos Feministas , 2006, DOI: 10.1590/S0104-026X2006000100003
Abstract: this article approaches the intersections developed under the colonial spanish empire among gender relations, feminine sexuality concepts, family honor and state regulation. the way the multiple moral, social, juridical and religious norms in relation to sexuality and relations between women and men interacted with the social/political inequalities in the iberian colonial experience will be analyzed. the new world provides a particularly clear example of the dynamic intersections between contemporary ideas and ideals about sex/gender and race/ethnicity and social class that became manifest on the new identification systems, classification and social discrimination forged in the consolidation of the iberian american colonial society. it also becomes an example of the consequences that the sexual morality and the prevailing gender stereotypes have had in all the aspects of women's lives.
La mujer es puro cuento: la cultura del género
Stolke, Verena;
Revista Estudos Feministas , 2004, DOI: 10.1590/S0104-026X2004000200005
Abstract: the term gender has become the feminist shorthand, in the 1970s, to signal the cultural construction rather than biological basis of women's unequal treatment and domination by men. in the past three decades the term has become as ubiquitous as ambiguous in feminist theorizing but, surprisingly, there is no semantic history of the origins, changing approaches and meanings of the concept. in this article i show that us sexologists and psychologists introduced gender in the 1950s in their endeavour to distinguish anatomical sex from social gender. this biomedical construction of gender is relevant for the epistemological difficulties in feminist theory with the link between gender and sex. in this article i address three related issues: 1) the habit among feminist scholars to explicitly or implicitly root gender in sex differences, 2) the heterosexual dualism that characterized the original medical notion of social gender and persists in much feminist theorizing until the late 1980s, and 3) the unquestioned cartesian dichotomy between nature and culture that runs like a red thread through the controversy over sex and gender. the article is inevitably open-ended. as i suggest, developments in biotechnology may open new vistas on what is the fundamental anthropological dilemma, namely, how to reconcile culture with nature.
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