Time‐Warped Foveated Rendering for Virtual Reality Headsets

Rendering in real time for virtual reality headsets with high user immersion is challenging due to strict framerate constraints as well as due to a low tolerance for artefacts. Eye tracking‐based foveated rendering presents an opportunity to strongly increase performance without loss of perceived visual quality. To this end, we propose a novel foveated rendering method for virtual reality headsets with integrated eye tracking hardware. Our method comprises recycling pixels in the periphery by spatio‐temporally reprojecting them from previous frames. Artefacts and disocclusions caused by this reprojection are detected and re‐evaluated according to a confidence value that is determined by a newly introduced formalized perception‐based metric, referred to as confidence function. The foveal region, as well as areas with low confidence values, are redrawn efficiently, as the confidence value allows for the delicate regulation of hierarchical geometry and pixel culling. Hence, the average primitive processing and shading costs are lowered dramatically. Evaluated against regular rendering as well as established foveated rendering methods, our approach shows increased performance in both cases. Furthermore, our method is not restricted to static scenes and provides an acceleration structure for post‐processing passes.     

Management Options to Improve Water Quality in Lake Peipsi: Insights from Large Scale Models and Remote Sensing

Nutrient pollution causes frequent blooms of potentially harmful cyanobacteria in Lake Peipsi (Estonia/Russia). Although external nutrient loading has reduced since the 1990s, lake water quality has barely improved, and eutrophication is still considered a threat to lake biota and water usage. To understand the recovery dynamics of the lake it is necessary to analyse the effects of land use and lake management on water quality to develop mitigation strategies. Comprehensive analysis has thus far failed due to information gaps inherent to conventional monitoring strategies. We show how two large-scale hydrological models using Earth observation data provide spatial information on pollution and can help explain the causes of past and current lake eutrophication. WaterGAP3.2 provides valid estimates of present and probable future phosphorus concentration in the lake water, based on past hydrological conditions. WaterWorld models spatial potential water quality and a scenario of optimal pollution reduction. Remotely sensed optical water quality data can be used to analyse recent, spatial water quality dynamics. The spatial and temporal algae distributions and can help explain eutrophication causes at Lake Peipsi and its catchment, adding value to in situ monitoring and supporting river basin management with large scale data.

     

CFRP/titanium hybrid material for improving composite bolted joints

The structural joining remains an essential challenge for the development of composite aerospace structures: every structural interconnection means a disturbance of an optimized structure resulting in an increase in overall structural weight. The lightweight potential of advanced, high-performance fiber composite materials is affected more strongly by mechanical fastening techniques than by conventional metallic materials due to the low shear and bearing capabilities of CFRP materials. Local embedding of thin titanium layers into the composite laminate in the coupling region results in a considerable improvement in structural efficiency of bolted and riveted joints in CFRP structures. This improvement is not only obvious in the increase in shear and bearing capabilities, but also in the resulting possibilities for a design no longer burdenend by local material thickening, excentricities and additionally excited local bending stresses.

This report displays experimental results demonstrating the advantageous influence of titanium hybridization on specific characteristics of CFRP-materials, thus proving the mechanical potential of CFRP/titanium hybrid materials when used as an advanced reinforcement technique for highly loaded composite joints.     

Corneal oxygen uptake: A review of polarographic techniques, applications, and variables.

Factors that influence the polarographic measurement of the oxygen uptake of the cornea are reviewed. These factors include the technique, electrode assembly, oxygen reservoir, membrane material and thickness, oxygen tension of the corneal environment, duration of exposure to environmental conditions and time to application of the probe all influencing measured oxygen uptake rates. Subject factors include lid position, palpebral aperture size, blinking, corneal thickness, and corneal integrity. Contact lens wear influences corneal oxygen uptake, with lens material and design parameters influencing rates obtained both under static (without blinking) and dynamic (with blinking) conditions. Measurement of corneal oxygen uptake rates remains an excellent method to quantify the oxygen supply in contact lens systems that include the contact lens, the tears, and the cornea, in which oxygen flux is influenced by the thickness and diffusion characteristics of each component.     

Is Trendelenburg a wise choice?

To determine the current level of use, characteristics, and perceived value of the clinicopathologic conference (CPC), we sent a 22-item survey questionnaire to the program directors of internal medicine residency training programs. Of the 278 residency training programs that returned questionnaires, 221 (80%) indicated that they held CPCs regularly. The conference received a mean rating (Likert scale 1 = best to 5 = worst) of 2.2 (95% confidence interval 2.2, 2. 3) for both its perceived educational value and its popularity. The CPC remains widely used in internal medicine training programs. Although relatively few programs have rigorous guidelines for preparation and evaluation of their presentations, the CPC is generally viewed as being popular and having sound educational value.     

Non‐linear adaptive control of a heat exchanger

In this contribution, two methods for adaptation of non‐linear adaptive controllers are presented and compared, namely the data‐driven and the knowledge‐based adaptation. A dynamic Takagi–Sugeno fuzzy model is utilized to model the non‐linear process behaviour. Based on this model, a non‐linear predictive controller is designed to control the process. In the presence of time‐variant process behaviour and changing unmodelled disturbances, high control performance can be achieved by performing an on‐line adaptation of the fuzzy model. First, a local weighted recursive least‐squares algorithm is used for adaptation. It exploits the local linearity of the Takagi–Sugeno fuzzy model. In the second approach, process knowledge that is obtained from theoretical insights is utilized to design a knowledge‐based adaptation strategy. Both approaches are compared and their effectiveness and real‐world applicability are demonstrated by application to temperature control of a heat exchanger. Copyright © 2001 John Wiley & Sons, Ltd.     

Multifunctional heat exchangers derived from three-dimensional micro-lattice structures

A micro-scale cross-flow heat exchanger is constructed from a hollow nickel micro-lattice structure, which is fabricated by conformally electroplating nickel onto a sacrificial polymer micro-lattice formed from self-propagating photopolymer waveguides. The periodic unit cell of the hollow nickel micro-lattice structure tested here includes lattice members with a diameter <1 mm and a nominal pore size <9 mm. The heat transfer performance of the micro-lattice-based heat exchanger is analyzed in terms of thermal conductance per unit volume, which is equal to the value of overall heat transfer coefficient multiplied by surface area to volume ratio. Calculated values range from 0.84 to 1.58 W/cm³K for Reynolds number ranges of between 3400 ± 200 and 6500 ± 500 for hot water flow inside the hollow lattice members and 85 ± 6 and 240 ± 20 for cold water flow around the lattice members. Based on a developed correlation, the experimental heat transfer data is used to predict the thermal performance of larger and smaller micro-lattice-based heat exchangers, as well as various micro-lattice feature dimensions that are tunable with the fabrication process (node-to-node spacing, inner diameter, etc.). The micro-lattice heat exchanger was tested under quasi-static compression and the results illustrate the multifunctional capability for load bearing and energy absorption applications. This work demonstrates a multifunctional heat exchanger with a fully-scalable fabrication process which is useful for size and weight constrained heat transfer applications, including those in the automotive and aerospace industries.     

Phase transfer methodology for the synthesis of substituted stilbenes under Knoevenagel condensation condition

This work describes the use of phase transfer catalyst (PTC) for the Knoevenagel condensation in the synthesis of several substituted stilbenes derived from weak acidic substrates such as p-nitro toluene (pK_a = 20.4) and phenylacetonitrile (pK_a = 21.9) with benzaldehyde using TBAB (tetrabutylammonium bromide) or 18-crown-6 as PTCs, respectively. Reaction of p-nitro toluene with benzaldehyde suffered from the competitive Cannizzaro reaction along with Knoevenagel condensation. Nevertheless, the problem has been solved and the novel procedure yielded >90% of isolated p-nitro stilbene. Utilizing a solid potassium carbonate as base and crown-ether as PTC proved to be the best reaction conditions for phenylacetonitrile and benzaldehyde, which showed 100% conversion of phenylacetonitrile to the corresponding stilbene (1,2-diphenyl-1′-nitrile ethene). To explore the role of PTC, we carried out a thorough kinetic investigation of these reactions. This includes modifying the catalyst nature and structure, the stirring rate, temperature effect and varying the concentration of the reactants and catalysts. Here, we prove for the first time that the PTC extraction mechanism taking place in a solid–liquid system for the carbonate anion. We conclude that it behaves as a typical second order reaction.