Validating Sample Average Approximation Solutions with Negatively Dependent Batches

Sample-average approximations (SAA) are a practical means of finding approximate solutions of stochastic programming problems involving an extremely large (or infinite) number of scenarios. SAA can also be used to find estimates of a lower bound on the optimal objective value of the true problem which, when coupled with an upper bound, provides confidence intervals for the true optimal objective value and valuable information about the quality of the approximate solutions. Specifically, the lower bound can be estimated by solving multiple SAA problems (each obtained using a particular sampling method) and averaging the obtained objective values. State-of-the-art methods for lower-bound estimation generate batches of scenarios for the SAA problems independently. In this paper, we describe sampling methods that produce negatively dependent batches, thus reducing the variance of the sample-averaged lower bound estimator and increasing its usefulness in defining a confidence interval for the optimal objective value. We provide conditions under which the new sampling methods can reduce the variance of the lower bound estimator, and present computational results to verify that our scheme can reduce the variance significantly, by comparison with the traditional Latin hypercube approach

The eyes have it?-intra- and inter-observer reproducibility of the PD-L1 companion diagnostic assay

No abstract available

Understanding communication patterns in HPCG

Conjugate Gradient (CG) algorithms form a large part of many HPC applications, examples include bioinformatics and weather applications. These algorithms allow numerical solutions to complex linear systems. Understanding how distributed implementations of these algorithms use a network interconnect will allow system designers to gain a deeper insight into their exacting requirements for existing and future applications. This short paper documents our initial investigation into the communication patterns present in the High Performance Conjugate Gradient (HPCG) benchmark. Through our analysis, we identify patterns and features which may warrant further investigation to improve the performance of CG algorithms and applications which make extensive use of them. In this paper, we capture communication traces from runs of the HPCG benchmark at a variety of different processor counts and then examine this data to identify potential performance bottlenecks. Initial results show that there is a fall in the throughput of the network when more processes are communicating with each other, due to network contention

Counselling the spirit

Stephen Wright explains how a good ‘spiritual director’ can guide you to enlightenment. A ‘spiritual director’ may be able to help practitioners become more insightful, rounded nurses

Spirituality, nursing and mental health

I was 10 years old and playing football in the street; snotty nosed kids in dirty T-shirts and worn old shorts. Brian stood on the pavement alone, just watching with a lonely, longing look on his face. Nobody spoke to him, and he spoke to no one. He had come from a few streets away and wandered into our patch, an odd thing to do in those days – kids kept pretty much to the streets near home. He might just as well have wandered over from a foreign country. He went to the same school as me, but was in a different year. One of my teammates called out his name together with a dirty word and told him to ‘Get lost’. They put me in goal, the place where the least useful player could be safely stored, there being no skill required but to stand around a lot and (hopefully) block the ball anyway you could if it came your way

Limitations for change detection in multiple Gabor targets

We investigate the limitations on the ability to detect when a target has changed, using Gabor targets as simple quantifiable stimuli. Using a partial report technique to equalise response variables, we show that the log of the Weber fraction for detecting a spatial frequency change is proportional to the log of the number of targets, with a set-size effect that is greater than that reported for visual search. This is not a simple perceptual limitation, because pre-cueing a single target out of four restores performance to the level found when only one target is present. It is argued that the primary limitation on performance is the division of attention across multiple targets, rather than decay within visual memory. However in a simplified change detection experiment without cueing, where only one target of the set changed, not only was the set size effect still larger, but it was greater at 2000 msec ISI than at 250 msec ISI, indicating a possible memory component. The steepness of the set size effects obtained suggests that even moderate complexity of a stimulus in terms of number of component objects can overload attentional processes, suggesting a possible low-level mechanism for change blindness

Microflare Heating of a Solar Active Region Observed with NuSTAR, Hinode/XRT, and SDO/AIA

NuSTAR is a highly sensitive focusing hard X-ray (HXR) telescope and has observed several small microflares in its initial solar pointings. In this paper, we present the first joint observation of a microflare with NuSTAR and Hinode/XRT on 2015 April 29 at ~11:29 UT. This microflare shows heating of material to several million Kelvin, observed in Soft X-rays (SXRs) with Hinode/XRT, and was faintly visible in Extreme Ultraviolet (EUV) with SDO/AIA. For three of the four NuSTAR observations of this region (pre-, decay, and post phases) the spectrum is well fitted by a single thermal model of 3.2-3.5 MK, but the spectrum during the impulsive phase shows additional emission up to 10 MK, emission equivalent to A0.1 GOES class. We recover the differential emission measure (DEM) using SDO/AIA, Hinode/XRT, and NuSTAR, giving unprecedented coverage in temperature. We find the pre-flare DEM peaks at ~3 MK and falls off sharply by 5 MK; but during the microflare's impulsive phase the emission above 3 MK is brighter and extends to 10 MK, giving a heating rate of about $2.5 \times 10^{25}$ erg s$^{-1}$. As the NuSTAR spectrum is purely thermal we determined upper-limits on the possible non-thermal bremsstrahlung emission. We find that for the accelerated electrons to be the source of the heating requires a power-law spectrum of $\delta \ge 7$ with a low energy cut-off $E_{c} \lesssim 7$ keV. In summary, this first NuSTAR microflare strongly resembles much more powerful flares.Comment: Accepted for publication in ApJ. 14 pages with 12 figures and 1 tabl

Potential Hawksbill Prey Item Distribution Among Dive Sites in a Marine Protected Area in Roatán, Bay Islands, Honduras

The Bay Islands of Honduras consist of three different islands, one of which is the island of Roatán on which the Roatán Marine Park (RMP), a marine protected area, is located at the west end. The RMP has only recently become an important area for sea turtle populations. The marine park is patrolled daily by park rangers to prevent illegal fishing practices, and the take of sharks and turtles, creating safe foraging areas for many marine megafauna. Hawksbills have been observed foraging within the park, yet the prey species they utilize are essentially unknown. We observed hawksbill foraging behavior for 15 – 20 min intervals and collected small samples of prey we observed turtles ingesting. Potential hawksbill prey items were surveyed by random transects over the reef at 13 individual dive sites. Six to seven transects per site were conducted by laying a 30 meter rope marked every five meters with colored string and a number, over a section of the reef. We placed a 1m2 quadrat at each of the six markers, taking photographs from approximately one meter above each quadrat. Photos were sorted by dive site and transect number, taken into Photoshop CS6 for editing, and then imported into Coral Point Count with Excel extensions (CPCe) to identify presence/absence of species of coral, gorgonians, macroalgae, sponges, and zooanthids. Within the RMP, 13 individual sites have been analyzed to date and revealed a combined average mean of 13.44% ± 3.93 SD for the presence of hard and soft coral, 5.09% ± 2.17 SD gorgonian, 27.60% ± 7.54 SD brown, green and red macroalgae, 2.14% ± 1.21 SD sponge, and 0.26% ± 0.36 SD zooanthids. Also within our study transects we found 19.91% ± 6.51 SD dead coral with algae, and 0.01% ± 0.02 SD diseased corals. Thirty-five individual turtles were observed foraging, and of these, 14(40%) were observed eating only algae during the time observed, while 11(31%) were observed eating only sponge, and 10(29%) were observed eating both sponge and algae. We suggest that due to the high percent presence of macroalgae, the low percentage of sponges, and the high percentage of turtles observed consuming algae among the six dive sites, macroalgae may be an important prey item for turtles at this location. A possible cause for this may be the high percentage of dead corals within our study dive sites on which macroalage are growing. Continued management of the RMP through daily patrols may facilitate reef habitat improvement and potential hawksbill population recovery in this area

Sightings Records of Hawksbills in a Marine Protected Area of Honduras

The Protective Turtle Ecology Center for Training, Outreach, and Research, Inc. (ProTECTOR) works to increase the conservation of, and research on sea turtles in the country of Honduras. Efforts were made this summer to record the sightings of sea turtles in Roatán, specifically in the area of West End and the Roatán Marine Park (RMP). We worked in tandem with 13 dive shops in West End from June 9 – August 8, 2014 to collect dive sightings data. We prepared turtle sighting record sheets that prompted observers to record their name, the dive site and depth of each turtle sighting, along with the specific species spotted, and whether the turtle was a juvenile or adult. We also gave divers training on how to differentiate between species and between adult and juvenile turtles. The data collection sheet provided representative artwork detailing differences in shell shape and color, as well as head scute patterns among the three species (hawksbills, loggerheads, and greens) likely to be sighted in the area. We collected sighting records from 5 dive shops on Mondays and Thursdays, 4 dives shops on Tuesdays and Fridays, and 2 dive shops once weekly, due to low diving frequency. Approximately 720 turtle sightings were recorded in the two months of data collection ranging from a maximum of 80 turtles observed at one site to minimum of 1 turtle observed at one site. The majority of turtle sightings were recorded at Overheat Reef, Bikini Bottom, and Half Moon Bay Wall with 80, 59, and 41 turtle sightings recorded, respectively, over the two month span in which we collected dive sightings from the shops. When compared to sighting records of the previous year, ArcGIS mapping showed a significant increase in the number of dive sites with turtle sightings and a subsequent increase in sightings at the same dive sites. The amount of dive sites where turtles were spotted increased from 20 dive sites in the previous year to 51 dive sites in 2014. Taken together, the data suggests an increase in turtles present in the off shore areas of West End between 2013 and 2014