Combining motility and bioluminescent signalling aids mate finding in deep-sea fish: a simulation study

We present a model to estimate the mean time required for mate finding among deep-sea fish as a function of motility and the extent of bioluminescent signalling. This model differs from those of previous works in 3 important ways by including (1) sex differences in motility, (2) a maximum detection range of bioluminescent signals derived from a recently published mechanistic model based on physical principles and the physiology of vision, and (3) a novel consideration of the likelihood of individuals passing within detection range only in the interval between flashes and hence, failing to detect the signaller. We argue that the flash rates required for effective detection are low, with rates of less than 1 per minute being entirely plausible, and that predation pressure may further encourage low flash rates. Further, even at high flash frequencies, the energetic cost of bioluminescent signalling is argued to be a trivial fraction of resting metabolic rates. Using empirically derived estimates for parameter values, we estimate that a female will be detected and reached by a male within 2 to 4 h of beginning to signal. Hence, we argue that mate finding may not seriously restrict reproductive success in species that can exploit this signalling system. We further argue that where male motility allows bioluminescent signalling, this may have some advantages over chemical-based signalling. Bioluminescent signalling may, therefore, be more important to mate finding in the deep sea (relative to chemical signals) than some previous works have suggested

Do agonistic behaviours bias baited remote underwater video surveys of fish?

Marine environments require monitoring to determine the effects of impacts such as climate change, coastal development and pollution and also to assess the effectiveness of conservation measures. Marine protected areas (MPAs) are being established globally and require periodic monitoring to determine whether their objectives are being met. Baited underwater video systems are becoming a popular method for monitoring change within protected fish populations, because they are less damaging to habitats than bottom trawling and allow for more statistical powerful comparisons to determine spatial and temporal patterns in the relative abundances, lengths and biomass of demersal and pelagic fishes. However, much remains uncertain about how interactions between the fish and bait and between the fish themselves affect the results obtained. Agonistic behaviours are frequently observed around the bait of the camera and potentially bias fish density estimates by altering the number and size classes seen at cameras. Here we counted the number of agonistic behaviours between pink snappers (Pagrus auratus), the size of fish involved and whether the fish left the field of view following such behaviours. The study consisted of 20 baited underwater video deployments inside a New Zealand marine reserve and 20 in adjacent open areas. We observed a significant relationship between the peak number of fish observed at the camera and the total number of agonistic behaviours, as well as the number of both aggressor and subordinate fish leaving the camera field of view following interactions. The slope of the latter relationship and thus the absolute numbers of fish leaving were higher for subordinate fish. As subordinates were significantly smaller than aggressors, the apparent size frequency distribution is likely skewed away from smaller size classes. The staying time of the fish and thus the maximum number of fish present at the camera will be reduced by agonistic behaviours and the absolute magnitude of this effect appears to be greater at high fish densities. Our results suggest that an overall effect of these phenomena is to underestimate the differences in abundance between MPAs and open areas, but also to overestimate differences in average size

The impact of active workstations on workplace productivity and performance: a systematic review

Active workstations have been recommended for reducing sedentary behavior in the workplace. It is important to understand if the use of these workstations has an impact on worker productivity. The aim of this systematic review was to examine the effect of active workstations on workplace productivity and performance. A total of 3303 articles were initially identified by a systematic search and seven articles met eligibility criteria for inclusion. A quality appraisal was conducted to assess risk of bias, confounding, internal and external validity, and reporting. Most of the studies reported cognitive performance as opposed to productivity. Five studies assessed cognitive performance during use of an active workstation, usually in a single session. Sit-stand desks had no detrimental effect on performance, however, some studies with treadmill and cycling workstations identified potential decreases in performance. Many of the studies lacked the power required to achieve statistical significance. Three studies assessed workplace productivity after prolonged use of an active workstation for between 12 and 52 weeks. These studies reported no significant effect on productivity. Active workstations do not appear to decrease workplace performance

Chemical etching and organometallic chemical vapor deposition on varied geometries of GaAs

Results of micron-spaced geometries produced by wet chemical etching and subsequent OMCVD growth on various GaAs surfaces are presented. The polar lattice increases the complexity of the process. The slow-etch planes defined by anisotropic etching are not always the same as the growth facets produced during MOCVD deposition, especially for deposition on higher-order planes produced by the hex groove etching

Distance from a fishing community explains fish abundance in a no-take zone with weak compliance

There are numerous examples of no-take marine reserves effectively conserving fish stocks within their boundaries. However, no-take reserves can be rendered ineffective and turned into ‘paper parks’ through poor compliance and weak enforcement of reserve regulations. Long-term monitoring is thus essential to assess the effectiveness of marine reserves in meeting conservation and management objectives. This study documents the present state of the 15-year old no-take zone (NTZ) of South El Ghargana within the Nabq Managed Resource Protected Area, South Sinai, Egyptian Red Sea. Previous studies credited willing compliance by the local fishing community for the increased abundances of targeted fish within the designated NTZ boundaries compared to adjacent fished or take-zones. We compared benthic habitat and fish abundance within the NTZ and the adjacent take sites open to fishing, but found no significant effect of the reserve. Instead, the strongest evidence was for a simple negative relationship between fishing pressure and distance from the closest fishing village. The abundance of targeted piscivorous fish increased significantly with increasing distance from the village, while herbivorous fish showed the opposite trend. This gradient was supported by a corresponding negative correlation between the amount of discarded fishing gear observed on the reef and increasing distance from the village. Discarded fishing gear within the NTZ suggested decreased compliance with the no-take regulations. Our findings indicate that due to non-compliance the no-take reserve is no longer functioning effectively, despite its apparent initial successes and instead a gradient of fishing pressure exists with distance from the nearest fishing community

When Is It Feasible to Use the Software Acquisition Pathway?…and when should you start?

Symposium PresentationApproved for public release; distribution is unlimited

When is it Feasible (or Desirable) to use the Software Acquisition Pathway?

Excerpt from the Proceedings of the Nineteenth Annual Acquisition Research SymposiumDoD Instruction 5000.87 establishes a Software Acquisition Pathway (SWP) “for the efficient and effective acquisition, development, integration, and timely delivery of secure software” (Office of the Under Secretary of Defense for Acquisition and Sustainment, 2020, p. 1). Under SWP, programs are required to deliver a Minimum Viable Capability Release (MVCR) deployed to an operational environment within 1 year of initial funding. This MVCR must be secure and suitable for operational deployment and must enhance warfighting capability. This paper discusses the challenge of determining for a software development effort whether the minimum capabilities that meet these criteria and enable ongoing agile development can plausibly be developed, tested, and operationally deployed in less than a year. We use a standard software cost and schedule model to derive bounds on the size of software that can be developed and ready to field in 12 months. The study concludes that many DoD software acquisitions will require too much development effort for the MVCR to comply with the SWP deadline if SWP is used from program initiation. We propose some criteria the Under Secretary of Defense for Acquisition and Sustainment might use to determine whether the SWP is appropriate for a particular new or existing program or software development project. We also consider development strategies that might improve the chances of success in using the SWP, including how non-SWP programs and projects should be architected if the intent is to later transition to SWP.Approved for public release; distribution is unlimited

Experimental determination of Apery-like identities for zeta(2n+2)

We document the discovery of two generating functions for the Riemann zeta values zeta(2n+2), analogous to earlier work for zeta(2n+1) and zeta(4n+3). This continues work initiated by Koecher and pursued further by Borwein, Bradley and others.Comment: 15 pages, AMSLaTeX, Proof of Theorem 1 improve

Solution of an infection model near threshold

We study the Susceptible-Infected-Recovered model of epidemics in the vicinity of the threshold infectivity. We derive the distribution of total outbreak size in the limit of large population size $N$. This is accomplished by mapping the problem to the first passage time of a random walker subject to a drift that increases linearly with time. We recover the scaling results of Ben-Naim and Krapivsky that the effective maximal size of the outbreak scales as $N^{2/3}$, with the average scaling as $N^{1/3}$, with an explicit form for the scaling function