Fouling mechanisms in constant flux crossflow ultrafiltration

Four fouling models due to Hermia (complete pore blocking, intermediate pore blocking, cake filtration and standard pore blocking), have long been used to describe membrane filtration and fouling in constant transmembrane pressure (ΔP) operation of membranes. A few studies apply these models to constant flux dead-end filtration systems. However, these models have not been reported for constant flux crossflow filtration, despite the frequent use of this mode of membrane operation in practical applications. We report derivation of these models for constant flux crossflow filtration. Of the four models, complete pore blocking and standard pore blocking were deemed inapplicable due to contradicting assumptions and relevance, respectively. Constant flux crossflow fouling experiments of dilute latex bead suspensions and soybean oil emulsions were conducted on commercial poly (ether sulfone) flat sheet ultrafiltration membranes to explore the models’ abilities to describe such data. A model combining intermediate pore blocking and cake filtration appeared to give the best agreement with the experimental data. Below the threshold flux, both the intermediate pore blocking model and the combined model fit the data well. As permeate flux approached and passed the threshold flux, the combined model was required for accurate fits. Based on this observation, a physical interpretation of the threshold flux is proposed: the threshold flux is the flux below which cake buildup is negligible and above which cake filtration becomes the dominant fouling mechanism

3D Visual Perception for Self-Driving Cars using a Multi-Camera System: Calibration, Mapping, Localization, and Obstacle Detection

Cameras are a crucial exteroceptive sensor for self-driving cars as they are low-cost and small, provide appearance information about the environment, and work in various weather conditions. They can be used for multiple purposes such as visual navigation and obstacle detection. We can use a surround multi-camera system to cover the full 360-degree field-of-view around the car. In this way, we avoid blind spots which can otherwise lead to accidents. To minimize the number of cameras needed for surround perception, we utilize fisheye cameras. Consequently, standard vision pipelines for 3D mapping, visual localization, obstacle detection, etc. need to be adapted to take full advantage of the availability of multiple cameras rather than treat each camera individually. In addition, processing of fisheye images has to be supported. In this paper, we describe the camera calibration and subsequent processing pipeline for multi-fisheye-camera systems developed as part of the V-Charge project. This project seeks to enable automated valet parking for self-driving cars. Our pipeline is able to precisely calibrate multi-camera systems, build sparse 3D maps for visual navigation, visually localize the car with respect to these maps, generate accurate dense maps, as well as detect obstacles based on real-time depth map extraction

Can we constrain interior structure of rocky exoplanets from mass and radius measurements?

We present an inversion method based on Bayesian analysis to constrain the interior structure of terrestrial exoplanets, in the form of chemical composition of the mantle and core size. Specifically, we identify what parts of the interior structure of terrestrial exoplanets can be determined from observations of mass, radius, and stellar elemental abundances. We perform a full probabilistic inverse analysis to formally account for observational and model uncertainties and obtain confidence regions of interior structure models. This enables us to characterize how model variability depends on data and associated uncertainties. We test our method on terrestrial solar system planets and find that our model predictions are consistent with independent estimates. Furthermore, we apply our method to synthetic exoplanets up to 10 Earth masses and up to 1.7 Earth radii as well as to exoplanet Kepler-36b. Importantly, the inversion strategy proposed here provides a framework for understanding the level of precision required to characterize the interior of exoplanets. Our main conclusions are: (1) observations of mass and radius are sufficient to constrain core size; (2) stellar elemental abundances (Fe, Si, Mg) are key constraints to reduce degeneracy in interior structure models and to constrain mantle composition; (3) the inherent degeneracy in determining interior structure from mass and radius observations does not only depend on measurement accuracies but also on the actual size and density of the exoplanet. We argue that precise observations of stellar elemental abundances are central in order to place constraints on planetary bulk composition and to reduce model degeneracy. [...]Comment: 19 pages, 18 figures, accepted in Astronomy & Astrophysics (no changes to previous version

The effectiveness and feasibility of psychological interventions for populations under ongoing threat: a systematic review

Current views of psychological therapies for trauma typically assume the traumatic event to be in the past. Yet, individuals who live in contexts of ongoing organized violence or experience intimate partner violence (IPV) may continue to be (re)exposed to related traumatic events or have realistic fears of their recurrence. This systematic review considers the effectiveness, feasibility, and adaptations of psychological interventions for individuals living with ongoing threat. PsychINFO, MEDLINE, and EMBASE were searched for articles that examined psychological interventions in contexts of ongoing threat of either IPV or organized violence and used trauma-related outcome measures. The search was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Data on study population, ongoing threat setting and design, intervention components, evaluation methods, and outcomes were extracted, and study quality was assessed using the Mixed-Method Appraisal Tool. Eighteen papers featuring 15 trials were included (12 on organized violence and 3 on IPV). For organized violence, most studies showed moderate to large effects in reducing trauma-related symptoms when compared to waitlists. For IPV, findings were varied. Most studies made adaptations related to culture and ongoing threat and found that providing psychological interventions was feasible. The findings, albeit preliminary with mixed methodological quality, showed psychological treatments can be beneficial and should not be withheld in the context of ongoing organized violence and IPV. Clinical and research recommendations are discussed

Spatiotemporal Mapping of Photocurrent in a Monolayer Semiconductor Using a Diamond Quantum Sensor

The detection of photocurrents is central to understanding and harnessing the interaction of light with matter. Although widely used, transport-based detection averages over spatial distributions and can suffer from low photocarrier collection efficiency. Here, we introduce a contact-free method to spatially resolve local photocurrent densities using a proximal quantum magnetometer. We interface monolayer MoS2 with a near-surface ensemble of nitrogen-vacancy centers in diamond and map the generated photothermal current distribution through its magnetic field profile. By synchronizing the photoexcitation with dynamical decoupling of the sensor spin, we extend the sensor's quantum coherence and achieve sensitivities to alternating current densities as small as 20 nA per micron. Our spatiotemporal measurements reveal that the photocurrent circulates as vortices, manifesting the Nernst effect, and rises with a timescale indicative of the system's thermal properties. Our method establishes an unprecedented probe for optoelectronic phenomena, ideally suited to the emerging class of two-dimensional materials, and stimulates applications towards large-area photodetectors and stick-on sources of magnetic fields for quantum control.Comment: 19 pages, 4 figure

Video shot boundary detection: seven years of TRECVid activity

Shot boundary detection (SBD) is the process of automatically detecting the boundaries between shots in video. It is a problem which has attracted much attention since video became available in digital form as it is an essential pre-processing step to almost all video analysis, indexing, summarisation, search, and other content-based operations. Automatic SBD was one of the tracks of activity within the annual TRECVid benchmarking exercise, each year from 2001 to 2007 inclusive. Over those seven years we have seen 57 different research groups from across the world work to determine the best approaches to SBD while using a common dataset and common scoring metrics. In this paper we present an overview of the TRECVid shot boundary detection task, a high-level overview of the most significant of the approaches taken, and a comparison of performances, focussing on one year (2005) as an example

Nonlinearities in stock return prediction: A Blended Approach

Our prior research indicates that there are periods within which nonlinear stock selection models outperform their linear counterparts in the South African equity market. In order to explore the nonlinearities in stock return prediction, we propose a blended stock selection technique that has the potential of diversifying the risk of inaccurate forecasts of the linear and nonlinear models. The proposed technique has an objective of optimizing the Qian and Hua (2003) information ratio, which constitutes to the maximization of the forecasting accuracy per unit of forecasting volatility. The blended stock selection model is found to outperform the respective linear and nonlinear models in an out-of-sample fractile analysis on a risk-adjusted basis for South African stocks over the period from 2002 to 2007.Department of HE and Training approved lis

Resilient Market Timing Strategies For Global Equities

The systemic impact of the global financial crisis of 2008 reveals that there are periods of uncertainty during which most asset classes experience substantial drawdown, rendering diversification an ineffective risk management tool. The desired exposures to risky assets such as stocks, bonds and commodities during these periods of systemic risk should be zero. This paper tests the effectiveness of two market timing strategies that intend to provide early signals for portfolio protection during turbulent times: a filter rule strategy based on the portfolio drawdown (DD) and drawup (DU) thresholds; and an exponential moving average (EMA) strategy based on the crossover of the fast moving average (FMA) and the slow moving average (SMA) of the fund values. The pre-specified market timing strategies are tested on the total return index of the Morgan Stanley Capital International World (MSCI World) Index since the inception of the index in 1997 through 2008. Both the optimal filter rule strategy and the optimal EMA strategy achieve Sharpe ratios that are higher than the Sharpe ratio of the unprotected MSCI World Index. The comparison of the historical risk-return characteristics reveals that the timing of protection is more accurate for the EMA strategy. As is the case for all market timing strategies, the signals provided by the protection mechanism lag the actual economic events. Thus, the market timing strategies tend to be more effective for prolonged economic downturn