Electrical observation of a tunable band gap in bilayer graphene nanoribbons at room temperature

We investigate the transport properties of double-gated bilayer graphene nanoribbons at room temperature. The devices were fabricated using conventional CMOS-compatible processes. By analyzing the dependence of the resistance at the charge neutrality point as a function of the electric field applied perpendicular to the graphene surface, we show that a band gap in the density of states opens, reaching an effective value of ~sim50 meV. This demonstrates the potential of bilayer graphene as FET channel material in a conventional CMOS environment.Comment: 3 pages, 3 figure

Inhibitory control in mind and brain 2.0: blocked-input models of saccadic countermanding.

The interactive race model of saccadic countermanding assumes that response inhibition results from an interaction between a go unit, identified with gaze-shifting neurons, and a stop unit, identified with gaze-holding neurons, in which activation of the stop unit inhibits the growth of activation in the go unit to prevent it from reaching threshold. The interactive race model accounts for behavioral data and predicts physiological data in monkeys performing the stop-signal task. We propose an alternative model that assumes that response inhibition results from blocking the input to the go unit. We show that the blocked-input model accounts for behavioral data as accurately as the original interactive race model and predicts aspects of the physiological data more accurately. We extend the models to address the steady-state fixation period before the go stimulus is presented and find that the blocked-input model fits better than the interactive race model. We consider a model in which fixation activity is boosted when a stop signal occurs and find that it fits as well as the blocked input model but predicts very high steady-state fixation activity after the response is inhibited. We discuss the alternative linking propositions that connect computational models to neural mechanisms, the lessons to be learned from model mimicry, and generalization from countermanding saccades to countermanding other kinds of responses

Population Characteristics of Co-Managed White Bass and Hybrid Striped Bass in Lake McConaughy, Nebraska

White Bass (Morone chrysops) and Hybrid Striped Bass (M. saxatillis × M. chrysops) populations often coexist in the same waterbody and are known to achieve different lengths, have differing reproductive success, and provide different opportunities for anglers. However, comparative population dynamics from systems where Moronids are managed with the same regulation is often lacking. This study aimed to assess the recruitment, mortality, and growth of these species from seasonal samples collected at Lake McConaughy in 2015 and fall 2016. White Bass demonstrated highly variable recruitment in Lake McConaughy despite stocking efforts (mean recruitment variability index = 0.157). Hybrid Striped Bass year class strength was also variable, but RVI was not calculated as the number of missing year classes exceed the number of present year classes. Total annual mortality estimates for Hybrid Striped Bass (39.7%) and White Bass (41.4%) were consistent with values reported in other populations, but both species were observed to achieve uncommon longevity. Both species exhibited sexual size dimorphism, and growth was moderate and consistent with average values presented for North American populations. This study provides insight into the population dynamics of two species with trophy potential managed by the same regulation in Lake McConaughy. Differences in growth patterns indicate the current regulation affects each species differently, and managers may be able to utilize this to inform decisions about management of coexisting Moronid populations

Food Habits of Fall-Collected Age-0 Walleyes in Eastern South Dakota Glacial Lakes

Food habits of age-0 fishes can influence their growth and survival prior to the first winter (Hoxmeier et al. 2006, Shoup and Wahl 2011). Ontogenetic diet shifts in juvenile piscivorous fishes result in a transition in consumption from zooplankton to macroinvertebrates and eventually fish throughout development (Mittelbach and Persson 1998). Certain food items may be more energetically beneficial to fishes than others as consumption of prey fishes may lead to faster growth rates of predators, decreased overwinter starvation, avoidance of competition, and reduced predation risk (Werner and Gilliam 1984). By the time age-0 walleyes (Sander vitreus) have reached lengths of 60–80 mm total length (TL), their diets are predominantly composed of fish (Priegel 1969, Quist et al. 2002, Galarowicz and Wahl 2005). Previous studies have examined age-0 walleye food habits in South Dakota in a limited number of waters at various times and the majority of fall diets were composed of fish (Beck et al. 1998, Blackwell et al. 1999). Fathead minnows (Pimephales promelas), rainbow smelt (Osmerus mordax), yellow perch (Perca flavescens), darters (Etheostoma spp.), and gizzard shad (Dorosoma cepedianum) have all been documented as regionally important prey fish species for juvenile walleyes (Jackson et al. 1992, Beck et al. 1998, Blackwell et al. 1999, Pelham et al. 2001, Uphoff 2012). Although generalized feeding ecology of walleye during early life stages has been investigated, previous studies have only examined food habits in either a controlled setting or limited number of waters, thereby potentially overlooking spatial differences in feeding ecology. Therefore, this study examined food habits of age-0 walleye collected during fall across a range of eastern South Dakota glacial lakes

Incentivizing High Quality Crowdwork

We study the causal effects of financial incentives on the quality of crowdwork. We focus on performance-based payments (PBPs), bonus payments awarded to workers for producing high quality work. We design and run randomized behavioral experiments on the popular crowdsourcing platform Amazon Mechanical Turk with the goal of understanding when, where, and why PBPs help, identifying properties of the payment, payment structure, and the task itself that make them most effective. We provide examples of tasks for which PBPs do improve quality. For such tasks, the effectiveness of PBPs is not too sensitive to the threshold for quality required to receive the bonus, while the magnitude of the bonus must be large enough to make the reward salient. We also present examples of tasks for which PBPs do not improve quality. Our results suggest that for PBPs to improve quality, the task must be effort-responsive: the task must allow workers to produce higher quality work by exerting more effort. We also give a simple method to determine if a task is effort-responsive a priori. Furthermore, our experiments suggest that all payments on Mechanical Turk are, to some degree, implicitly performance-based in that workers believe their work may be rejected if their performance is sufficiently poor. Finally, we propose a new model of worker behavior that extends the standard principal-agent model from economics to include a worker's subjective beliefs about his likelihood of being paid, and show that the predictions of this model are in line with our experimental findings. This model may be useful as a foundation for theoretical studies of incentives in crowdsourcing markets.Comment: This is a preprint of an Article accepted for publication in WWW \c{opyright} 2015 International World Wide Web Conference Committe

Shear-induced anisotropic decay of correlations in hard-sphere colloidal glasses

Spatial correlations of microscopic fluctuations are investigated via real-space experiments and computer simulations of colloidal glasses under steady shear. It is shown that while the distribution of one-particle fluctuations is always isotropic regardless of the relative importance of shear as compared to thermal fluctuations, their spatial correlations show a marked sensitivity to the competition between shear-induced and thermally activated relaxation. Correlations are isotropic in the thermally dominated regime, but develop strong anisotropy as shear dominates the dynamics of microscopic fluctuations. We discuss the relevance of this observation for a better understanding of flow heterogeneity in sheared amorphous solids.Comment: 6 pages, 4 figure

Assessment of Smallmouth Bass Growth and Mortality in Nebraska Waters

Smallmouth bass (Micropterus dolomieu) have been introduced across Nebraska into a variety of waterbodies. However, an estimate of smallmouth bass growth and mortality in Nebraska waters has not been produced. The objectives of this study were to use historic sampling data to describe the growth of smallmouth bass in Nebraska lakes in relation to other regional models, growth among waterbody types (reservoirs, Interstate 80 [I-80] lakes, and rivers), estimates of age at quality, preferred, and memorable lengths, and mortality for Nebraska smallmouth bass populations. Mean length ± SE of Nebraska smallmouth bass at age 7 was 383 ± 21 mm, which is similar to national and regional values. Mean lengths at age of smallmouth bass in I-80 lakes and reservoirs were similar, but lengths were larger in rivers than in I-80 lakes and reservoirs at ages 3–5. Mean total annual mortality measured 0.41 (± 0.06 SE). These growth and mortality rates allow biologists to set appropriate management objectives and assess local sampling results with proper perspectives

The novel chemokine receptor CXCR7 regulates trans-endothelial migration of cancer cells

<p>Abstract</p> <p>Background</p> <p>Migration of metastatic tumor cells from the bloodstream into lymph nodes is thought to be facilitated by expression of the chemokine receptors CCR7, CXCR4 and, for B cell-derived tumors, CXCR5. Expression of their respective chemokine ligands (CCL19, CCL21, CXCL12 and CXCL13) by endothelial cells inside the lymph nodes facilitates the trans-endothelial migration (TEM) of these cells through high endothelial venules into the lymph node parenchyma. It is known that CXCR7, a second CXCL12 receptor, regulates TEM of CXCR4+CXCR7+ tumor cells towards a CXCL12 source. In this study, we set out to assess the potential stimulation by CXCL12 of tumor cell TEM towards other chemokines and whether CXCR7 might be able to regulate such effects.</p> <p>Methods</p> <p>The human Burkitt's lymphoma cell line NC-37, which expresses CXCR4, CXCR5, CXCR7 and CCR7, was selected as a model system. TEM of these cells through a human HUVEC endothelial cell monolayer was used as the main model system for these studies. Regulation of their TEM behavior by various concentrations of the various cognate chemokines for the above-mentioned receptors, placed in either the source or target wells of modified Boyden chamber migration plates, was assessed by quantifying the number of cells migrated under each experimental condition.</p> <p>Results</p> <p>Exposure of CXCR4⁺CXCR7⁺cancer cells to CXCL12 greatly potentiated their TEM towards the chemokines CCL19 and CXCL13. This CXCL12-potentiated TEM was inhibited by the second CXCR7 chemokine ligand, CXCL11, as well as CXCR7-specific small molecule antagonists and antibodies. In contrast, the CXCR4 antagonist AMD3100 was less effective at inhibiting CXCL12-potentiated TEM. Thus, CXCR7 antagonists may be effective therapeutic agents for blocking CXCL12-mediated migration of CXCR4⁺CXCR7⁺tumor cells into lymph nodes, regardless of whether the cancer cells follow a CXCL12 gradient or whether serum CXCL12 stimulates their migration towards CCR7 and CXCR5 chemokines in the lymph nodes.</p

Colloidal aggregation in microgravity by critical Casimir forces

By using the critical Casimir force, we study the attractive strength dependent aggregation of colloids with and without gravity by means of Near Field scattering. Significant differences were seen between microgravity and ground experiments, both in the structure of the formed fractal aggregates as well as the kinetics of growth. Ground measurements are severely affected by sedimentation resulting in reaction limited behavior. In microgravity, a purely diffusive behavior is seen reflected both in the measured fractal dimensions for the aggregates as well as the power law behavior in the rate of growth. Formed aggregates become more open as the attractive strength increases.Comment: 4 pages, 3 figure