A summer heat wave decreases the immunocompetence of the mesograzer, Idotea baltica

Extreme events associated with global change will impose increasing stress on coastal organisms. How strong biological interactions such as the host-parasite arms-race are modulated by environmental change is largely unknown. The immune system of invertebrates, in particular phagocytosis and phenoloxidase activity response are key defence mechanisms against parasites, yet they may be sensitive to environmental perturbations. We here simulated an extreme event that mimicked the European heat wave in 2003 to investigate the effect of environmental change on the immunocompetence of the mesograzer Idotea baltica. Unlike earlier studies, our experiment aimed at simulation of the natural situation as closely as possible by using long acclimation, a slow increase in temperature and a natural community setting including the animals' providence with natural food sources (Zostera marina and Fucus vesiculosus). Our results demonstrate that a simulated heat wave results in decreased immunocompetence of the mesograzer Idotea baltica, in particular a drop of phagocytosis by 50%. This suggests that global change has the potential to significantly affect host-parasite interaction

Fast and interactive ray-based rendering

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonDespite their age, ray-based rendering methods are still a very active field of research with many challenges when it comes to interactive visualization. In this thesis, we present our work on Guided High-Quality Rendering, Foveated Ray Tracing for Head Mounted Displays and Hash-based Hierarchical Caching and Layered Filtering. Our system for Guided High-Quality Rendering allows for guiding the sampling rate of ray-based rendering methods by a user-specified Region of Interest (RoI). We propose two interaction methods for setting such an RoI when using a large display system and a desktop display, respectively. This makes it possible to compute images with a heterogeneous sample distribution across the image plane. Using such a non-uniform sample distribution, the rendering performance inside the RoI can be significantly improved in order to judge specific image features. However, a modified scheduling method is required to achieve sufficient performance. To solve this issue, we developed a scheduling method based on sparse matrix compression, which has shown significant improvements in our benchmarks. By filtering the sparsely sampled image appropriately, large brightness variations in areas outside the RoI are avoided and the overall image brightness is similar to the ground truth early in the rendering process. When using ray-based methods in a VR environment on head-mounted display de vices, it is crucial to provide sufficient frame rates in order to reduce motion sickness. This is a challenging task when moving through highly complex environments and the full image has to be rendered for each frame. With our foveated rendering sys tem, we provide a perception-based method for adjusting the sample density to the user’s gaze, measured with an eye tracker integrated into the HMD. In order to avoid disturbances through visual artifacts from low sampling rates, we introduce a reprojection-based rendering pipeline that allows for fast rendering and temporal accumulation of the sparsely placed samples. In our user study, we analyse the im pact our system has on visual quality. We then take a closer look at the recorded eye tracking data in order to determine tracking accuracy and connections between different fixation modes and perceived quality, leading to surprising insights. For previewing global illumination of a scene interactively by allowing for free scene exploration, we present a hash-based caching system. Building upon the concept of linkless octrees, which allow for constant-time queries of spatial data, our frame work is suited for rendering such previews of static scenes. Non-diffuse surfaces are supported by our hybrid reconstruction approach that allows for the visualization of view-dependent effects. In addition to our caching and reconstruction technique, we introduce a novel layered filtering framework, acting as a hybrid method between path space and image space filtering, that allows for the high-quality denoising of non-diffuse materials. Also, being designed as a framework instead of a concrete filtering method, it is possible to adapt most available denoising methods to our layered approach instead of relying only on the filtering of primary hitpoints

A Quality-Centered Analysis of Eye Tracking Data in Foveated Rendering

This work presents the analysis of data recorded by an eye tracking device in the course of evaluating a foveated rendering approach for head-mounted displays (HMDs). Foveated ren- dering methods adapt the image synthesis process to the user’s gaze and exploiting the human visual system’s limitations to increase rendering performance. Especially, foveated rendering has great potential when certain requirements have to be fulfilled, like low-latency rendering to cope with high display refresh rates. This is crucial for virtual reality (VR), as a high level of immersion, which can only be achieved with high rendering performance and also helps to reduce nausea, is an important factor in this field. We put things in context by first providing basic information about our rendering system, followed by a description of the user study and the collected data. This data stems from fixation tasks that subjects had to perform while being shown fly-through sequences of virtual scenes on an HMD. These fixation tasks consisted of a combination of various scenes and fixation modes. Besides static fixation targets, moving tar- gets on randomized paths as well as a free focus mode were tested. Using this data, we estimate the precision of the utilized eye tracker and analyze the participants’ accuracy in focusing the displayed fixation targets. Here, we also take a look at eccentricity-dependent quality ratings. Comparing this information with the users’ quality ratings given for the displayed sequences then reveals an interesting connection between fixation modes, fixation accuracy and quality ratings

Konfigurierbare Softwarekomponenten zur Unterstützung dynamischer Lern- und Arbeitsumgebungen für virtuelle Gemeinschaften

Die Kontexte, in denen Mitglieder virtueller Gemeinschaften zusammen lernen und arbeiten, werden von einer Vielzahl von Faktoren beeinflusst: Während heutige Lernumgebungen oftmals mehrere didaktische Konzepte und ihre flexible Kombinierbarkeit (blended learning) berücksichtigen müssen, treten wechselnde Anforderungen an Arbeitsumgebungen virtueller Gemeinschaften häufig durch eine Steigerung des Sozialisierungsgrades und dem damit verbundenen Wunsch nach mehr Selbstadministration bzw. –regulation auf. Somit ist die Notwendigkeit zur Unterstützung dynamischer Kontexte zwar jeweils unterschiedlich begründet, führt aber bei der Umsetzung beider Systemklassen zu derselben konzeptionellen Herausforderung: Die technologische Infrastruktur muss möglichst reaktions- und anpassungsfähig bzgl. Kommunikation, Interaktion und Zusammenarbeit gestalten werden, um sowohl der individuellen als auch der kollektiven Entwicklungsdynamik ihrer Benutzer Rechnung zu tragen

Unterstützung selbst verwalteter Gruppenprozesse in virtuellen Gemeinschaften durch skalierbare Architekturkonzepte am Beispiel der Sifa-Community

Der Aufbau der Sifa-Community, einer virtuellen Gemeinschaft für Fachkräfte für Arbeitssicherheit (Sifas), findet im Rahmen der vom Hauptverband der Berufsgenossenschaften beauftragten „Langzeitstudie zur Wirksamkeit der Tätigkeit von Fachkräften für Arbeitssicherheit“ (Sifa-Langzeitstudie) statt. Diese Langzeitstudie ist angelegt als 8-Jahres-Längsschnitt in Form einer repräsentativen Online-Befragung von Sifas aus allen Wirtschaftszweigen der gesetzlichen Unfallversicherungen und wird durch eine vertiefende Befragung in ausgewählten Unternehmen begleitet. Zwischen 2005 und 2011 werden über 4000 Sifas zu vier Erhebungszeitpunkten mit einem Online-Fragebogen über ihre Einstellungen und Erfahrungen in ihrem Tätigkeitsgebiet als Sifa befragt. Die Längsschnittstudie ist unter www.Sifa-langzeitstudie.de erreichbar. Die Sifa-Community, die seit Juni 2005 im Testbetrieb online ist, soll in erster Linie den Erhalt und die Motivation der Stichprobe über die Laufzeit der Studie hinweg unterstützen. Durch die exklusiv angebotenen Möglichkeiten der Information und Kommunikation haben die 4000 Studien-Teilnehmer die Möglichkeit, berufsbezogene Informationen individualisiert abzurufen und über berufsbezogene Fragen und Probleme mit räumlich entfernten Arbeitskollegen zu diskutieren. In der Ausschreibung der Langzeitstudie wurde darüber hinaus die Entwicklung von Konzepten gefordert, die die Fortführung der projektbezogenen Internetplattform über die Förderdauer hinaus sichern können. Dem versuchen die Autoren Rechnung zu tragen, indem eine funktionierende, zu großen Teilen selbst verwaltete virtuelle Gemeinschaft entwickelt wird, die auch nach Abschluss der Befragungen alle Fachkräfte für Arbeitssicherheit zur Verfügung stehen kann (Kahnwald & Köhler, 2005). Die Community ist unter www.Sifacommunity. de erreichbar

Site of Blood Vessel Damage and Relevance of CD18 in a Murine Model of Immune Complex-Mediated Vasculitis

How neutrophils (polymorphonuclear neutrophils, PMNs) damage vessels in leukocytoclastic vasculitis (LcV) mediated by immune complexes (ICs) is unclear. If degradative enzymes and oxygen radicals are released from PMNs while adhering to the inner side of the vessel wall, they could be washed away by the blood stream or neutralized by serum protease inhibitors. We investigated if in LcV PMNs could damage vessels from the tissue side after transmigration. We used CD18-deficient (CD18−/−) mice because the absence of CD18 excludes transmigration of PMNs. When eliciting the Arthus reaction in ears of CD18−/− mice, deposition of ICs was not sufficient to recruit PMNs or to induce IC-mediated LcV. Injection of PMNs intradermally in CD18−/− mice allowed us to investigate if bypassing diapedesis and placing PMNs exclusively on the abluminal side leads to vascular destruction. We found that injected PMNs gathered around perivascular ICs, but did not cause vessel damage. Only intravenous injection of wild-type PMNs could re-establish the Arthus reaction in CD18−/− mice. Thus, PMNs cause vessel damage during diapedesis from the luminal side, but not from the perivascular space. We suggest that in order to shield the cytotoxic products from the blood stream, ICs induce particularly tight interactions between them, PMNs and endothelial cells

Salinity change impairs pipefish immune defence

a b s t r a c t Global change is associated with fast and severe alterations of environmental conditions. Superimposed onto existing salinity variations in a semi-enclosed brackish water body such as the Baltic Sea, a decrease in salinity is predicted due to increased precipitation and freshwater inflow. Moreover, we predict that heavy precipitation events will accentuate salinity fluctuations near shore. Here, we investigated how the immune function of the broad-nosed pipefish (Syngnathus typhle), an ecologically important teleost with sex-role reversal, is influenced by experimentally altered salinities (control: 18 PSU, lowered: 6 PSU, increased: 30 PSU) upon infection with bacteria of the genus Vibrio. Salinity changes resulted in increased activity and proliferation of immune cells. However, upon Vibrio infection, individuals at low salinity were unable to mount specific immune response components, both in terms of monocyte and lymphocyte cell proliferation and immune gene expression compared to pipefish kept at ambient salinities. We interpret this as resource allocation trade-off, implying that resources needed for osmoregulation under salinity stress are lacking for subsequent activation of the immune defence upon infection. Our data suggest that composition of small coastal fish communities may change due to elevated environmental stress levels and the incorporated consequences thereof

Specific immune priming in the invasive ctenophore Mnemiopsis leidyi

Specific immune priming enables an induced immune response upon repeated pathogen encounter. As a functional analogue to vertebrate immune memory, such adaptive plasticity has been described, for instance, in insects and crustaceans. However, towards the base of the metazoan tree our knowledge about the existence of specific immune priming becomes scattered. Here, we exposed the invasive ctenophore Mnemiopsis leidyi repeatedly to two different bacterial epitopes (Gram-positive or -negative) and measured gene expression. Ctenophores experienced either the same bacterial epitope twice (homologous treatments) or different bacterial epitopes (heterologous treatments). Our results demonstrate that immune gene expression depends on earlier bacterial exposure. We detected significantly different expression upon heterologous compared with homologous bacterial treatment at three immune activator and effector genes. This is the first experimental evidence for specific immune priming in Ctenophora and generally in non-bilaterian animals, hereby adding to our growing notion of plasticity in innate immune systems across all animal phyla