1,283 research outputs found
Coexistence between fluid and crystalline phases of proteins in photosynthetic membranes
Photosystem II (PSII) and its associated light-harvesting complex II (LHCII)
are highly concentrated in the stacked grana regions of photosynthetic
thylakoid membranes. Within the membrane, PSII-LHCII supercomplexes can be
arranged in disordered packings, ordered arrays, or mixtures thereof. The
physical driving forces underlying array formation are unknown, complicating
attempts to determine a possible functional role for arrays in regulating light
harvesting or energy conversion efficiency. Here we introduce a coarse-grained
model of protein interactions in coupled photosynthetic membranes, focusing on
just two particle types that feature simple shapes and potential energies
motivated by structural studies. Reporting on computer simulations of the
model's equilibrium fluctuations, we demonstrate its success in reproducing
diverse structural features observed in experiments, including extended
PSII-LHCII arrays. Free energy calculations reveal that the appearance of
arrays marks a phase transition from the disordered fluid state to a
system-spanning crystal, which can easily be arrested by thermodynamic
constraints or slow dynamics. The region of fluid-crystal coexistence is broad,
encompassing much of the physiologically relevant parameter regime. Our results
suggest that grana membranes lie at or near phase coexistence, conferring
significant structural and functional flexibility to this densely packed
membrane protein system.Comment: 11 pages, 5 figure
Grtler Instability and Its Control via Surface Suction over an Axisymmetric Cone at Mach 6
The characteristics of Grtler instability over an axisymmetric cone with an aft concave section are studied via linear and nonlinear instability analysis and direct numerical simulations. Several options for the cone geometry have been investigated numerically, subject to a fixed forecone section and constraints on the maximum cone diameter, overall cone length, and minimum N-factor for the most amplified Grtler modes. Computations show that it is possible to design a cone with a peak N-factor of Nmax > 8 at the target Reynolds number of 12.110(exp 6) per meter, corresponding to the maximum quiet Reynolds number in the Boeing/AFOSR Mach-6 Quiet Tunnel at Purdue University. Direct numerical simulations show that an array of roughness elements corresponding to a peak roughness height of 0.1006 mm at the center can excite Grtler vortices that evolve into sufficiently strong streamwise streaks that may break down via high-frequency secondary instability. Thus, the selected axisymmetric configuration of interest should provide an acceptable baseline to investigate the feasibility of several aspects of laminar-flow control via boundary-layer suction. The apparatus that is being used for measurements in the Boeing/AFOSR Quiet Tunnel is described, along with some preliminary experimental results
Semantic Similarity-Based Clustering of Findings From Security Testing Tools
Over the last years, software development in domains with high security
demands transitioned from traditional methodologies to uniting modern
approaches from software development and operations (DevOps). Key principles of
DevOps gained more importance and are now applied to security aspects of
software development, resulting in the automation of security-enhancing
activities. In particular, it is common practice to use automated security
testing tools that generate reports after inspecting a software artifact from
multiple perspectives. However, this raises the challenge of generating
duplicate security findings. To identify these duplicate findings manually, a
security expert has to invest resources like time, effort, and knowledge. A
partial automation of this process could reduce the analysis effort, encourage
DevOps principles, and diminish the chance of human error. In this study, we
investigated the potential of applying Natural Language Processing for
clustering semantically similar security findings to support the identification
of problem-specific duplicate findings. Towards this goal, we developed a web
application for annotating and assessing security testing tool reports and
published a human-annotated corpus of clustered security findings. In addition,
we performed a comparison of different semantic similarity techniques for
automatically grouping security findings. Finally, we assess the resulting
clusters using both quantitative and qualitative evaluation methods.Comment: Accepted to ICNLSP 202
Cohesive Obstacle Management for Directed Flocking in Real-time Strategy Games
The purpose of this study was to introduce additional rules to directed flocking which allowed a flock to navigate obstacles while maintaining cohesion. These rules were chaining, memory, navigation markers, and dynamic leadership. Validation and performance tests were conducted to determine how effective the new rules were and how many units in a flock could be used in a real-time setting.Computer Science Departmen
SPATIAL-TEMPORAL VARIABILITY OF AIR TEMPERATURES IN SERBIA IN THE PERIOD 1961–2010
The aim of this paper is to examine the spatial and temporal variability of the average monthly, seasonal and annual air temperatures in Serbia. Therefore, data from 64 climatologic stations were analyzed in the period from 1961 to 2010. Based on the data, on the position of the stations (their latitude, longitude, altitude), and the characteristics of the terrain in their vicinity (inclination and terrain exposure in a radius of 10 km around the station), a regression model was constructed based on which air temperatures are interpolated for the territory of Serbia. The rootmean-square error (RMSE) of the regression model ranged from 0.2 ºC in January, February and November to 1.1 ºC in August. Spatial distribution of air temperatures is shown (maps of mean monthly, mean seasonal and mean annual air temperatures are made), and the Sen's procedure was used to calculate trends of air temperatures (maps of average monthly, mean seasonal and mean annual trends of air temperatures). The Mann-Kendall test was used to test the significance of air temperature trends. Apart from the southeast, the whole territory of Serbia has practically experienced a statistically significant rise in the average annual air temperature, with the highest increase in the summer and winter months
Stilfiguren aus der Distanz gelesen. Zur automatischen Detektion von Wortstellungsfiguren und deren Nutzen für die qualitative Analyse
Im Projekt ›Anomaly-based large-scale analysis of style and genre reflected in the use of stylistic devices in medieval literature‹ befragen wir mittelhochdeutsche Texte der Trois Matières danach, welche Aussagen zu Textähnlichkeiten sich aufgrund des Gebrauchs von Stilmitteln der Wortstellung, wie etwa Parallelismus und Chiasmus, sowie der Tropen, wie etwa der Metapher, treffen lassen. Der hier vorliegende Artikel stellt die aktuellen Ergebnisse unserer bisherigen Parallelismus- und Chiasmusdetektion in 30 mittelhochdeutschen Texten vor. Es wird zu diskutieren sein, ob unsere Ergebnisse eine Korrelation des Stils mit der gemeinhin nach Stoffkreis definierten Gattung bezeugen, ob andere Faktoren wie Verfasserschaft oder Abfassungszeit eine übergeordnete Rolle spielen und ob darüberhinausgehende Aussagen zu den Ähnlichkeitsverhältnissen der Texte getroffen werden können
A surface acoustic wave-driven micropump for particle uptake investigation under physiological flow conditions in very small volumes
Static conditions represent an important shortcoming of many in vitro experiments on the cellular uptake of nanoparticles. Here, we present a versatile microfluidic device based on acoustic streaming induced by surface acoustic waves (SAWs). The device offers a convenient method for introducing fluid motion in standard cell culture chambers and for mimicking capillary blood flow. We show that shear rates over the whole physiological range in sample volumes as small as 200 mu L can be achieved. A precise characterization method for the induced flow profile is presented and the influence of flow on the uptake of Pt-decorated CeO2 particles by endothelial cells (HMEC-1) is demonstrated. Under physiological flow conditions the particle uptake rates for this system are significantly lower than at low shear conditions. This underlines the vital importance of the fluidic environment for cellular uptake mechanisms
Space station propulsion system technology
Two propulsion systems have been selected for the space station: O/H rockets for high thrust applications and the multipropellant resistojets for low thrust needs. These thruster systems integrate very well with the fluid systems on the station. Both thrusters will utilize waste fluids as their source of propellant. The O/H rocket will be fueled by electrolyzed water and the resistojets will use stored waste gases from the environmental control system and the various laboratories. This paper presents the results of experimental efforts with O/H and resistojet thrusters to determine their performance and life capability
Characterization of 2D PSII Crystalline Arrays in Thylakoid Membranes Highly Efficient in Photo-Protective Energy Dissipation by Atomic Force Microscopy
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