Foraging memory: Retrieving words from one and from two semantic categories

Traditionally applied to an animal's search for food, the concept of foraging has been extended to include the search for information in such places as the Internet and libraries (Pirotti & Card, 1999). The premise behind the research reported here is that memory searching can also be construed as foraging. The goals of this investigation are to uncover mental factors that may affect memory production during memory search and to use this knowledge to guide a prediction of foraging production. Prior to testing, four such mental factors were identified: a time cost when producing an initial item from a different category (switch cost); a production benefit driven by a release of proactive interference (time-out benefit); a production cost caused by the additional mental load of executing an autonomous switching strategy (executive-decision cost); and sub-optimal allocation of time between categories. Experiment 1 tested whether switching between categories leads to a switch cost and/or time-out benefit by having subjects produce items from a category in a continuous three-minute block or multiple blocks that add to three minutes. Experiment 2 addressed the possibility of an "Executive-decision" cost by either allowing subjects to autonomously switch between categories or yoking them to another subject's switch schedule. Experiment 3 tested whether memory foragers divide their time optimally between categories. Data from the first experiment demonstrated that like external foraging, moving from category to category (patch to patch) results in a production downtime. These data also demonstrated that switching production between domains may lead to a time-out benefit. Experiment 2 showed that the execution of an autonomous switching strategy leads to less production then when switching is forced. The third experiment demonstrated that, unlike animals, humans do not have an innate sense of how to divide their time between patches (categories) to maximize gain. Our prediction was derived by having subjects produce category exemplars from a single category alone or from two categories at once. Data from single-category production trials as well as adjustments inspired by Experiment I through 3 were used to predict production from two categories. Though accurate, the flexibility of our prediction is limited. Research needed to allow for greater flexibility is discussed

Interactive Inverse Design Optimization of Fuselage Shape for Low-Boom Supersonic Concepts

This paper introduces a tool called BOSS (Boom Optimization using Smoothest Shape modifications). BOSS utilizes interactive inverse design optimization to develop a fuselage shape that yields a low-boom aircraft configuration. A fundamental reason for developing BOSS is the need to generate feasible low-boom conceptual designs that are appropriate for further refinement using computational fluid dynamics (CFD) based preliminary design methods. BOSS was not developed to provide a numerical solution to the inverse design problem. Instead, BOSS was intended to help designers find the right configuration among an infinite number of possible configurations that are equally good using any numerical figure of merit. BOSS uses the smoothest shape modification strategy for modifying the fuselage radius distribution at 100 or more longitudinal locations to find a smooth fuselage shape that reduces the discrepancies between the design and target equivalent area distributions over any specified range of effective distance. For any given supersonic concept (with wing, fuselage, nacelles, tails, and/or canards), a designer can examine the differences between the design and target equivalent areas, decide which part of the design equivalent area curve needs to be modified, choose a desirable rate for the reduction of the discrepancies over the specified range, and select a parameter for smoothness control of the fuselage shape. BOSS will then generate a fuselage shape based on the designer's inputs in a matter of seconds. Using BOSS, within a few hours, a designer can either generate a realistic fuselage shape that yields a supersonic configuration with a low-boom ground signature or quickly eliminate any configuration that cannot achieve low-boom characteristics with fuselage shaping alone. A conceptual design case study is documented to demonstrate how BOSS can be used to develop a low-boom supersonic concept from a low-drag supersonic concept. The paper also contains a study on how perturbations in the equivalent area distribution affect the ground signature shape and how new target area distributions for low-boom signatures can be constructed using superposition of equivalent area distributions derived from the Seebass-George-Darden (SGD) theory

Variability in Quasar Broad Absorption Line Outflows I. Trends in the Short-Term versus Long-Term Data

Broad absorption lines (BALs) in quasar spectra identify high velocity outflows that likely exist in all quasars and could play a major role in feedback to galaxy evolution. The variability of BALs can help us understand the structure, evolution, and basic physical properties of the outflows. Here we report on our first results from an ongoing BAL monitoring campaign of a sample of 24 luminous quasars at redshifts 1.2<z<2.9, focusing on C IV 1549 BAL variability in two different time intervals: 4 to 9 months (short-term) and 3.8 to 7.7 years (long-term) in the quasar rest-frame. We find that 39% (7/18) of the quasars varied in the short-term, whereas 65% (15/23) varied in the long-term, with a larger typical change in strength in the long-term data. The variability occurs typically in only portions of the BAL troughs. The components at higher outflow velocities are more likely to vary than those at lower velocities, and weaker BALs are more likely to vary than stronger BALs. The fractional change in BAL strength correlates inversely with the strength of the BAL feature, but does not correlate with the outflow velocity. Both the short-term and long-term data indicate the same trends. The observed behavior is most readily understood as a result of the movement of clouds across the continuum source. If the crossing speeds do not exceed the local Keplerian velocity, then the observed short-term variations imply that the absorbers are <6 pc from the central quasar.Comment: 14 pages, 7 figures, accepted for publication in MNRA

Trust in Humans and Robots: Economically Similar but Emotionally Different

Trust-based interactions with robots are increasingly common in the marketplace, workplace, on the road, and in the home. However, a looming concern is that people may not trust robots as they do humans. While trust in fellow humans has been studied extensively, little is known about how people extend trust to robots. Here we compare trust-based investments and emotions from across three nearly identical economic games: human-human trust games, human-robot trust games, and human-robot trust games where the robot decision impacts another human. Robots in our experiment mimic humans: they are programmed to make reciprocity decisions based on previously observed behaviors by humans in analogous situations. We find that people invest similarly in humans and robots. By contrast, the social emotions elicited by the interactions (but not non-social emotions) differed across human and robot trust games, and did so lawfully. Emotional reactions depended on how one’s trust game decision interacted with the partnered agent’s decision, and whether another person was affected economically and emotionally

Deterministic enhancement of coherent photon generation from a nitrogen-vacancy center in ultrapure diamond

The nitrogen-vacancy (NV) center in diamond has an optically addressable, highly coherent spin. However, an NV center even in high quality single-crystalline material is a very poor source of single photons: extraction out of the high-index diamond is inefficient, the emission of coherent photons represents just a few per cent of the total emission, and the decay time is large. In principle, all three problems can be addressed with a resonant microcavity. In practice, it has proved difficult to implement this concept: photonic engineering hinges on nano-fabrication yet it is notoriously difficult to process diamond without degrading the NV centers. We present here a microcavity scheme which uses minimally processed diamond, thereby preserving the high quality of the starting material, and a tunable microcavity platform. We demonstrate a clear change in the lifetime for multiple individual NV centers on tuning both the cavity frequency and anti-node position, a Purcell effect. The overall Purcell factor $F_{\rm P}=2.0$ translates to a Purcell factor for the zero phonon line (ZPL) of $F_{\rm P}^{\rm ZPL}\sim30$ and an increase in the ZPL emission probability from $\sim 3 \%$ to $\sim 46 \%$. By making a step-change in the NV's optical properties in a deterministic way, these results pave the way for much enhanced spin-photon and spin-spin entanglement rates.Comment: 6 pages, 4 figure