58,204 research outputs found
Moment-Based Relaxation of the Optimal Power Flow Problem
The optimal power flow (OPF) problem minimizes power system operating cost
subject to both engineering and network constraints. With the potential to find
global solutions, significant research interest has focused on convex
relaxations of the non-convex AC OPF problem. This paper investigates
``moment-based'' relaxations of the OPF problem developed from the theory of
polynomial optimization problems. At the cost of increased computational
requirements, moment-based relaxations are generally tighter than the
semidefinite relaxation employed in previous research, thus resulting in global
solutions for a broader class of OPF problems. Exploration of the feasible
space for test systems illustrates the effectiveness of the moment-based
relaxation.Comment: 7 pages, 4 figures. Abstract accepted, full paper in revie
Ion Exchange-Precipitation for Nutrient Recovery from Dilute Wastewater
Regulated phosphorus (P) and nitrogen (N) discharges and the cost of fertilizer provide economic drivers for nutrient removal and recovery from wastewater. This study used ion exchange (IX) in dilute (domestic) wastewater to concentrate nutrients with subsequent recovery by struvite precipitation. This is the first tertiary wastewater treatment study directly comparing P removal using a range of Fe, Cu, and Al-based media followed by clinoptilolite IX columns for N removal and precipitation using the combined regenerants. Phosphate removal prior to breakthrough was 0.5–2.0 g P Lmedia−1, providing effluent concentrations −1 PO4-P and −1 NH4-N for ≥80 bed volumes. Dow-FeCu resin provided effective P removal, efficient neutral pH regeneration and 560 mg P L−1 in the regeneration eluate (≥100× concentration factor). Exchange capacity of clinoptilolite in column mode was 3.9–6.1 g N Lmedia−1 prior to breakthrough. Precipitation using the combined cation and anion regenerants resulted in a maximum of 74% P removal using Dow-FeCu. Precipitates contained impurities, including Al3+, Ca2+, and Fe. Overall, the IX-precipitation recovery process removed ≥98% P and 95% N and precipitates contained 13% P and 1.6% N. This sequential process can satisfy increasingly stringent wastewater standards and offers an effective alternative to traditional treatment technologies that simply remove nutrients. Approximately 84% of total P and 97% of total Kjeldahl N entering a treatment plant can be captured (accounting for primary clarifier removal), whereas most existing technologies target side streams that typically contain only 20–30% of influent P and 15–20% of influent N
High Impedance Detector Arrays for Magnetic Resonance
Resonant inductive coupling is commonly seen as an undesired fundamental
phenomenon emergent in densely packed resonant structures, such as nuclear
magnetic resonance phased array detectors. The need to mitigate coupling
imposes rigid constraints on the detector design, impeding performance and
limiting the scope of magnetic resonance experiments. Here we introduce a high
impedance detector design, which can cloak itself from electrodynamic
interactions with neighboring elements. We verify experimentally that the high
impedance detectors do not suffer from signal-to-noise degradation mechanisms
observed with traditional low impedance elements. Using this new-found
robustness, we demonstrate an adaptive wearable detector array for magnetic
resonance imaging of the hand. The unique properties of the detector glove
reveal new pathways to study the biomechanics of soft tissues, and exemplify
the enabling potential of high-impedance detectors for a wide range of
demanding applications that are not well suited to traditional coil designs.Comment: 16 pages, 12 figures, videos available upon reques
Comments on a Major Range Extension of the Little-Known Acrocera bakeri (Diptera: Acroceridae)
The spider fly Acrocera bakeri Coquillett, 1904 (Diptera: Acroceridae) is reported as a new state record for Wisconsin. This is a major range extension, because this rarely-encountered species was previously known only from the western U.S., specifically Arizona, California, and Nevada. The taxonomic history of the species is briefly discussed and hypotheses are offered for its unexpected presence in Wisconsin
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