The faint end of the galaxy luminosity function

We present and discuss optical measurements of the faint end of the galaxy luminosity function down to M_R = -10 in five different local environments of varying galaxy density and morphological content. The environments we studied, in order of decreasing galaxy density, are the Virgo Cluster, the NGC 1407 Group, the Coma I Group, the Leo Group and the NGC 1023 Group. Our results come from a deep wide-angle survey with the NAOJ Subaru 8 m Telescope on Mauna Kea and are sensitive down to very faint surface-brightness levels. Galaxies were identified as group or cluster members on the basis of their surface brightness and morphology. The faintest galaxies in our sample have R ~ 22.5. There were thousands of fainter galaxies but we cannot distinguish cluster members from background galaxies at these faint limits so do not attempt to determine a luminosity function fainter than M_R = -10. In all cases, there are far fewer dwarfs than the numbers of low mass halos anticipated by cold dark matter theory. The mean logarithmic slope of the luminosity function between M_R = -18 and M_R = -10 is alpha ~ -1.2, far shallower than the cold dark matter mass function slope of alpha ~ -1.8. We would therefore need to be missing about 90 per cent of the dwarfs at the faint end of our sample in all the environments we study to achieve consistency with CDM theory.Comment: 23 pages, 26 figs, MNRAS in pres

AN EXPLORATION OF THE NEUROPHYSIOLOGICAL AND COGNITIVE CONTRIBUTORS TO MOVEMENT CORRECTION BEHAVIOR IN YOUNGER AND OLDER ADULTS

Making online movement corrections is an important part of navigating dynamic environments where unexpected obstructions can occur. Failure to engage in these corrections can result in injury and, in some cases, death. Observations of movement corrections demonstrate that younger adults tend to follow the minimal intervention principle when correcting their movements. The objective of the current work is to study differences in how older and young adults make online movement corrections and explore the cognitive and physiological contributors to successful online movement corrections. Experiment 1 shows older adults are as likely as young adults to choose hand paths that require the least effort following a visual perturbation; however, they also commit more collisions and have slower movement speeds. Regression analyses show success rates and movement times on the obstacle avoidance task are related to measures of executive control and processing speed. Additionally, perturbations elicited P3b components often associated with executive control. These ERP responses were different following medium and large perturbations for young adults; however, they were not different for older adults. Experiment 2 shows that whether responding to visual or haptic/proprioceptive feedback impacted young adults’ obstacle avoidance performance when the optimal path was ambiguous. P3bs observed in Experiment 2 were also affected by the difference in the modality of feedback. When these findings are evaluated with the experiment’s other findings showing 1) greater P3b related activity for collision trials than non-collision trials, 2) very little differences between P3bs from trials with inward and outward movement corrections, and 3) EMG indicators of movement correction onset occur before the P3b peak, it suggests that the neural activity observed in this study has more to do with monitoring the movement corrections than path selection. The regression models from Experiment 2 also show the top-down processing of visual feedback is associated with a greater number of cognitive variables; yet some level of executive control is still associated with participants\u27 tendency to make optimal reaching movements following physical perturbations

Linear Programming Applied to Sheep Ranching in Utah

The study was initiated to determine how sheep ranches were physically and economically organized in 1964 and to select range and livestock management alternatives which would be profitable to sheep ranches. With data collected from the ranches three model ranches, representing the three most prominent strata, were constructed. These strata were determined by number of breeding ewes that were on the ranch and by the season of grazing on government land, i.e., winter, summer, or year around. After the building of these three ranches, each of them was linear programmed to find the profit maximizing combination of resources both before and following the addition of private and public capital. Capital was added in small increments, and the internal rate of return was calculated for each increment to determine the profitability of each investment. As an added tool, the capitalized value of the ranch resources was obtained showing the value of one more unit of each resource to the ranch concerned

Minimizing Bias in Biomass Allometry: Model Selection and Log‐Transformation of Data

Nonlinear regression is increasingly used to develop allometric equations for forest biomass estimation (i.e., as opposed to the traditional approach of log‐transformation followed by linear regression). Most statistical software packages, however, assume additive errors by default, violating a key assumption of allometric theory and possibly producing spurious models. Here, we show that such models may bias stand‐level biomass estimates by up to 100 percent in young forests, and we present an alternative nonlinear fitting approach that conforms with allometric theory

Carbon Dynamics and Land-Use Choices: Building a Regional-Scale Multidisciplinary Model

Policy enabling tropical forests to approach their potential contribution to global-climate-change mitigation requires forecasts of land use and carbon storage on a large scale over long periods. In this paper, we present an integrated modeling methodology that addresses these needs. We model the dynamics of the human land-use system and of C pools contained in each ecosystem, as well as their interactions. The model is national scale, and is currently applied in a preliminary way to Costa Rica using data spanning a period of over fifty years. It combines an ecological process model, parameterized using field and other data, with an economic model, estimated using historical data to ensure a close link to actual behavior. These two models are linked so that ecological conditions affect land-use choices and vice versa. The integrated model predicts land use and its consequences for C storage for policy scenarios. These predictions can be used to create baselines, reward sequestration, and estimate the value in both environmental and economic terms of including C sequestration in tropical forests as part of the efforts to mitigate global climate change. The model can also be used to assess the benefits from costly activities to increase accuracy and thus reduce errors and their societal costs.carbon, sequestration, climate change, land use, modelling

The endophenotype concept in psychiatric genetics

The idea that some phenotypes bear a closer relationship to the biological processes that give rise to psychiatric illness than diagnostic categories has attracted considerable interest. Much effort has been devoted to finding such endophenotypes, partly because it is believed that the genetic basis of endophenotypes will be easier to analyse than that of psychiatric disease. This belief depends in part on the assumption that the effect sizes of genetic loci contributing to endophenotypes are larger than those contributing to disease susceptibility, hence increasing the chance that genetic linkage and association tests will detect them. We examine this assumption by applying meta-analytical techniques to genetic association studies of endophenotypes. We find that the genetic effect sizes of the loci examined to date are no larger than those reported for other phenotypes. A review of the genetic architecture of traits in model organisms also provides no support for the view that the effect sizes of loci contributing to phenotypes closer to the biological basis of disease is any larger than those contributing to disease itself. While endophenotype measures may afford greater reliability, it should not be assumed that they will also demonstrate simpler genetic architecture

Comparing Fixed-amount and Progressive-amount DRO Schedules for Tic Suppression in Youth with Chronic Tic Disorders

Chronic tic disorders (CTDs) involve motor and/or vocal tics that often cause substantial distress and impairment. Differential reinforcement of other behavior (DRO) schedules of reinforcement produce robust, but incomplete, reductions in tic frequency in youth with CTDs; however, a more robust reduction may be needed to affect durable clinical change. Standard, fixed‐amount DRO schedules have not commonly yielded such reductions, so we evaluated a novel, progressive‐amount DRO schedule, based on its ability to facilitate sustained abstinence from functionally similar behaviors. Five youth with CTDs were exposed to periods of baseline, fixed‐amount DRO (DRO‐F), and progressive‐amount DRO (DRO‐P). Both DRO schedules produced decreases in tic rate and increases in intertic interval duration, but no systematic differences were seen between the two schedules on any dimension of tic occurrence. The DRO‐F schedule was generally preferred to the DRO‐P schedule. Possible procedural improvements and other future directions are discussed