Local Phonon Density of States in an Elastic Substrate

The local, eigenfunction-weighted acoustic phonon density of states (DOS) tensor is calculated for a model substrate consisting of a semi-infinite isotropic elastic continuum with a stress-free surface. On the surface, the local DOS is proportional to the square of the frequency, as for the three-dimensional Debye model, but with a constant of proportionality that is considerably enhanced compared to the Debye value, a consequence of the Rayleigh surface modes. The local DOS tensor at the surface is also anisotropic, as expected. Inside the substrate the local DOS is both spatially anisotropic and non-quadratic in frequency. However, at large depths, the local DOS approaches the isotropic Debye value. The results are applied to a Si substrate.Comment: 7 pages, 2 figures, RevTe

Improved procedures for valuation of the contribution of recreation to national economic development

Improved procedures are presented for evaluating the contribution of recreation to national economic development. These procedures are to replace those outlined in the Principles and Standards for Planning Water and Related Land Resources. Desirable criteria for valuation procedures are specified. Variation procedures currently used by federal agencies make almost exclusive use of the “interim unit day value approach,” sometimes augmented by point systems. This approach has little theoretical or empirical justification and does not encourage efficient allocation of resources. Revision and modification of the “interim unit day value approach” and the use of point systems is not a useful method of developing improved procedures. Rather, it is recommended that models be developed to predict individual willingness-to-pay for many types of recreation as functions of site characteristics, the characteristics of the individual user (including the history of the previous use), the availability of substitute activities and sites, and the location of the individual in relation to the resources under study. The total value of the resource would then be a function of these variables, the number of users, and the distribution of users within the market area. These functions may be derived from regional travel cost demand functions (which would also provide estimates of use) or could be explicit willingness-to-pay functions derived from the survey method (which must be supplemented by a use estimate). Examples of the desired models are provided along with guidelines for their development and use. Needs for further research are identified.U.S. Department of the InteriorU.S. Geological SurveyOpe

Facilitation of Learning Spatial Relations among Goal Locations does not Require Visual Exposure to the Configuration of Goal Locations

Human participants searched in a virtual-environment open-field search task for four hidden goal locations arranged in a diamond configuration located in a 5 x 5 matrix. Participants were randomly assigned to one of three groups: Pattern Only, Landmark + Pattern, or Cues + Pattern. All participants experienced a Training phase followed by a Testing phase. During Training, visual cues were coincident with goal locations for the Cues + Pattern group, and a single visual cue at a non-goal location maintained a consistent spatial relationship with the goal locations for the Landmark + Pattern group. All groups were then tested in the absence of visual cues. Presence of the visual cue(s) during Training facilitated acquisition of the task, but the Landmark + Pattern group and the Cues + Pattern group did not differ when their visual cues were removed during Testing and performed superior to the Pattern Only group. Results suggest learning based upon the spatial relations among locations may not be susceptible to cue-competition effects and facilitation of learning spatial relations by visual cues does not require visual exposure to the configuration of goal locations

Quantitative analysis of Hedgehog gradient formation using an inducible expression system

BACKGROUND: The Hedgehog (Hh) family of secreted growth factors are morphogens that act in development to direct growth and patterning. Mutations in human Hh and other Hh pathway components have been linked to human diseases. Analysis of Hh distribution during development indicates that cholesterol modification and receptor mediated endocytosis affect the range of Hh signaling and the cellular localization of Hh. RESULTS: We have used an inducible, cell type-specific expression system to characterize the three-dimensional distribution of newly synthesized, GFP-tagged Hh in the developing Drosophila wing. Following induction of Hh-GFP expression in posterior producing cells, punctate structures containing Hh-GFP were observed in the anterior target cells. The distance of these particles from the expressing cells was quantified to determine the shape of the Hh gradient at different time points following induction. The majority of cholesterol-modified Hh-GFP was found associated with cells near the anterior/posterior (A/P) boundary, which express high levels of Hh target genes. Without cholesterol, the Hh gradient was flatter, with a lower percentage of particles near the source and a greater maximum distance. Inhibition of Dynamin-dependent endocytosis blocked formation of intracellular Hh particles, but did not prevent movement of newly synthesized Hh to the apical or basolateral surfaces of target cells. In the absence of both cholesterol and endocytosis, Hh particles accumulated in the extracellular space. Staining for the Hh receptor Ptc revealed four categories of Hh particles: cytoplasmic with and without Ptc, and cell surface with and without Ptc. Interestingly, mainly cholesterol-modified Hh is detected in the cytoplasmic particles lacking Ptc. CONCLUSION: We have developed a system to quantitatively analyze Hh distribution during gradient formation. We directly demonstrate that inhibition of Dynamin-dependent endocytosis is not required for movement of Hh across target cells, indicating that transcytosis is not required for Hh gradient formation. The localization of Hh in these cells suggests that Hh normally moves across both apical and basolateral regions of the target cells. We also conclude that cholesterol modification is required for formation of a specific subset of Hh particles that are both cytoplasmic and not associated with the receptor Ptc

Effects of temperature in relation to sheet metal stamping

The demand to reduce the use of lubricants and increase tool life in sheet metal stamping has resulted in increased research on the sliding contact between the tool and the sheet materials. Unlubricated sliding wear tests for soft carbon steel sliding on D2 tool steel were performed using a pin-on-disk tribometer. The results revealed that temperature has an influencing role in the wear of tool steel and that material transfer between tool and sheet can be minimized at a certain temperature range in sheet metal stamping

A Method for Identifying Personalized Representations in Web Archives

Web resources are becoming increasingly personalized — two different users clicking on the same link at the same time can see content customized for each individual user. These changes result in multiple representations of a resource that cannot be canonicalized in Web archives. We identify characteristics of this problem by presenting a potential solution to generalize personalized representations in archives. We also present our proof-of-concept prototype that analyzes WARC (Web ARChive) format files, inserts metadata establishing relationships, and provides archive users the ability to navigate on the additional dimension of environment variables in a modified Wayback Machine

Parasite resistance and immunity across female castes in a social insect

[EN] Living in a social group increases the risks of parasitism, especially in highly-related groups. In homogenous groups, with no reproductive division of labour, the impact of parasitism is unlikely to vary with host identity. Many social systems, however, do exhibit division of reproductive labour, most famously in social insects with their reproductive queens and generally infertile workers. In such systems, the impact of parasitism will differ for each group. Consequently, we predict that susceptibility to parasites will vary to reflect such differential impact. We tested this prediction using a trypanosome-bumble bee system, where Crithidia bombi infects both gynes and workers of Bombus terrestris. We studied both susceptibility to the parasite and relevant measures of the immune function. As predicted, gynes were significantly less susceptible to the parasite than workers, but while gynes and workers expressed different immune profiles, how these link to differential susceptibility remains unclear. In conclusion, our results suggest that differential selection pressures exerted by parasites may produce multiple phenotypes from a single genotype in order to maximise fitness in a social group context. Significance statement Social insect colonies dominate terrestrial ecology, and as such are targets for parasites. How they defend themselves against such threats is a key question. Here, we show that bumble bee gynes - the reproductive individuals that overwinter and found colonies in this annual social system - are more resistant to a parasite that disproportionately affects reproductive fitness than their sister workers. Differential patterns of susceptibility may help to explain the success of these social insects.This study was supported by an Enterprise Ireland grant to M. J. F. B., a Ulysses grant to M. J. F. B. and Y. M., and Y. M. was supported by the Centre National de la Recherche Scientifique (C.N.R.S.). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.Ruiz-González, MX.; Kelly, M.; Moret, Y.; Brown, MJF. (2022). Parasite resistance and immunity across female castes in a social insect. Behavioral Ecology and Sociobiology. 76(4):1-8. https://doi.org/10.1007/s00265-022-03162-01876

Experimental Analysis of Reinforcement Learning Techniques for Spectrum Sharing Radar

In this work, we first describe a framework for the application of Reinforcement Learning (RL) control to a radar system that operates in a congested spectral setting. We then compare the utility of several RL algorithms through a discussion of experiments performed on Commercial off-the-shelf (COTS) hardware. Each RL technique is evaluated in terms of convergence, radar detection performance achieved in a congested spectral environment, and the ability to share 100MHz spectrum with an uncooperative communications system. We examine policy iteration, which solves an environment posed as a Markov Decision Process (MDP) by directly solving for a stochastic mapping between environmental states and radar waveforms, as well as Deep RL techniques, which utilize a form of Q-Learning to approximate a parameterized function that is used by the radar to select optimal actions. We show that RL techniques are beneficial over a Sense-and-Avoid (SAA) scheme and discuss the conditions under which each approach is most effective.Comment: Accepted for publication at IEEE Intl. Radar Conference, Washington DC, Apr. 2020. This is the author's version of the wor