Browsing by Subject "PERFORMANCE"

Now showing 1 - 11 of 11

Open Access
A Brain to Spine Interface for Transferring Artificial Sensory Information.
(Scientific reports, 2020-01-21) Yadav, Amol P; Li, Daniel; Nicolelis, Miguel AL
Lack of sensory feedback is a major obstacle in the rapid absorption of prosthetic devices by the brain. While electrical stimulation of cortical and subcortical structures provides unique means to deliver sensory information to higher brain structures, these approaches require highly invasive surgery and are dependent on accurate targeting of brain structures. Here, we propose a semi-invasive method, Dorsal Column Stimulation (DCS) as a tool for transferring sensory information to the brain. Using this new approach, we show that rats can learn to discriminate artificial sensations generated by DCS and that DCS-induced learning results in corticostriatal plasticity. We also demonstrate a proof of concept brain-to-spine interface (BTSI), whereby tactile and artificial sensory information are decoded from the brain of an "encoder" rat, transformed into DCS pulses, and delivered to the spinal cord of a second "decoder" rat while the latter performs an analog-to-digital conversion during a sensory discrimination task. These results suggest that DCS can be used as an effective sensory channel to transmit prosthetic information to the brain or between brains, and could be developed as a novel platform for delivering tactile and proprioceptive feedback in clinical applications of brain-machine interfaces.
Open Access
A Modular Multilevel Series/Parallel Converter for a Wide Frequency Range Operation
(IEEE Transactions on Power Electronics, 2019-10-01) Li, Z; Ricardo Lizana, F; Yu, Z; Sha, S; Peterchev, AV; Goetz, SM
When providing ac output, modular multilevel converters (MMCs) experience power fluctuation in the phase arms. The power fluctuation causes voltage ripple on the module capacitors, which grows with the output power and inversely to the output frequency. Thus, low-frequency operations of MMCs, e.g., for motor drives, require injecting common-mode voltages and circulating currents, and strict dc voltage output relative to ground is impossible. To address this problem, this paper introduces a novel module topology that allows parallel module connectivity in addition to the series and bypass states. The parallel state directly transfers power across the modules and arms to cancel the power fluctuations and hence suppresses the capacitor voltage ripple. The proposed series/parallel converter can operate at a wide frequency range down to dc without common-mode voltages or circulating currents; it also allows sensorless operation and full utilization of the components at higher output frequencies. We present detailed simulation and experiment results to characterize the advantages and limitations of the proposed solution.
Open Access
Competing for global capital or local voters? The politics of business location incentives
(Public Choice, 2015-09) Jensen, NM; Malesky, EJ; Walsh, M
© 2015, Springer Science+Business Media New York. The competition for global capital has led to interjurisdictional competition between countries, states and cities as to who can offer the most attractive incentives to firms. In this study, we examine the domestic politics of this competition by focusing on incentive use in the United States from 1999 to 2012. We define incentives as the targeted tax deductions or exemptions that are used to lure businesses into a locality. Drawing on data from municipal incentive programs, we examine how electoral competition shapes the use and oversight of targeted incentives. We find evidence that cities with elected mayors provide larger incentives than non-elected city managers by taking advantage of exogeneity in the assignment of city government institutions and a database of over 2000 investment incentives from 2010 to 2012. We also find that elected mayors enjoy more lax oversight of incentive projects than their appointed counterparts. Our results have important implications for the study of interjurisdictional competition and the role of electoral institutions in shaping economic policy.
Open Access
Earthworms modify plant biomass and nitrogen capture under conditions of soil nutrient heterogeneity and elevated atmospheric CO2 concentrations
(Soil Biology and Biochemistry, 2014-01-01) García-Palacios, Pablo; Maestre, Fernando T; Bradford, Mark A; Reynolds, James F
Earthworms modify the way roots respond to soil nutrient patchiness. However, few studies have evaluated the joint effects of earthworms and soil heterogeneity on plant community biomass and species dominance, and none of them have assessed the influence of different patch features and environmental conditions on such effects. We evaluated how soil nutrient heterogeneity, earthworms (Eisenia fetida), organic material quality (15N-labelled leaves and roots of contrasting C: N ratios) and elevated atmospheric CO2 concentrations (phytotron chambers) affected the resource-use strategy, biomass and species dominance of mixtures formed by Lolium perenne L. and Plantago lanceolata L. Soil heterogeneity decreased N capture from the organic material, especially in the presence of earthworms. Mixtures experienced a 26 and 36% decrease in shoot and root biomass when earthworms were added to the heterogeneous microcosms, but only with high quality organic material. The dominance of L. perenne was lower under conditions of elevated CO2, nutrient heterogeneity and earthworms. Our data suggest that earthworms can neutralize positive plant growth responses to soil heterogeneity by exacerbating decreases in the supply of N to the plant. Specifically, earthworms foraging for high quality patches may stimulate microbial N immobilization, translating into lower N capture by plants. Increases in casting activity under elevated CO2, and hence in microbial N immobilization, may also explain why earthworms modulated the effects of soil heterogeneity and CO2 concentrations on plant community structure. We show that earthworms, absent from most soil nutrient heterogeneity studies, mediate plant biomass responses to nutrient patchiness by affecting N capture. Future plant-foraging behaviour studies should consider the roles played by soil engineers such as earthworms, so that results can be better extrapolated to natural communities. © 2014 Elsevier Ltd.
Open Access
Extreme events reveal an alimentary limit on sustained maximal human energy expenditure.
(Science advances, 2019-06-05) Thurber, Caitlin; Dugas, Lara R; Ocobock, Cara; Carlson, Bryce; Speakman, John R; Pontzer, Herman
The limits on maximum sustained energy expenditure are unclear but are of interest because they constrain reproduction, thermoregulation, and physical activity. Here, we show that sustained expenditure in humans, measured as maximum sustained metabolic scope (SusMS), is a function of event duration. We compiled measurements of total energy expenditure (TEE) and basal metabolic rate (BMR) from human endurance events and added new data from adults running ~250 km/week for 20 weeks in a transcontinental race. For events lasting 0.5 to 250+ days, SusMS decreases curvilinearly with event duration, plateauing below 3× BMR. This relationship differs from that of shorter events (e.g., marathons). Incorporating data from overfeeding studies, we find evidence for an alimentary energy supply limit in humans of ~2.5× BMR; greater expenditure requires drawing down the body's energy stores. Transcontinental race data suggest that humans can partially reduce TEE during long events to extend endurance.
Open Access
The awakening of the attention: Evidence for a link between the monitoring of mind wandering and prospective goals.
(Journal of experimental psychology. General, 2018-03) Seli, Paul; Smilek, Daniel; Ralph, Brandon CW; Schacter, Daniel L
Across 2 independent samples, we examined the relation between individual differences in rates of self-caught mind wandering and individual differences in temporal monitoring of an unrelated response goal. Rates of self-caught mind wandering were assessed during a commonly used sustained-attention task, and temporal goal monitoring was indexed during a well-established prospective-memory task. The results from both samples showed a positive relation between rates of self-caught mind wandering during the sustained-attention task and rates of checking a clock to monitor the amount of time remaining before a response was required in the prospective-memory task. This relation held even when controlling for overall propensity to mind-wander (indexed by intermittent thought probes) and levels of motivation (indexed by subjective reports). These results suggest the possibility that there is a common monitoring system that monitors the contents of consciousness and the progress of ongoing goals and tasks. (PsycINFO Database Record
Open Access
The effect of market competition on bribery in emerging economies: An empirical analysis of Vietnamese firms
(World Development, 2020-07-01) Malesky, EJ; Nguyen, TV; Bach, TN; Ho, BD
© 2020 Elsevier Ltd Studies of firm bribery have not fully examined how market competition conditions the effects of social norms on firms’ bribe payments. We suggest that firms pay bribes to obtain abnormal rents and/or to conform to accepted rules of corruption. These motivations operate differently, depending on the level of market competition. Using data from an annual survey of 10,000 Vietnamese firms between 2006 and 2017, we find that in environments characterized by open competition, bribery is positively associated with long-standing norms in the business social context, while in closed-competition environments, bribe payments are functions of rents that accrue from uncertainty in policy-making.
Open Access
The Socially and Spatially Bounded Relationships of Entrepreneurial Activity: Olav Sorenson -- Recipient of the 2018 Global Award for Entrepreneurship Research
(Small Business Economics, 2018) Rickne, Annika; Ruef, M; Wennberg, Karl
This article reviews the academic contributions of Olav Sorenson, recipient of the 2018 Global Award for Entrepreneurship Research. His work has advanced scholarly understanding of how entrepreneurship and innovation are strongly embedded in socially and spatially bounded relationships. Based on meticulous empirical studies using a broad range of methods, he has challenged conventional models of new firms’ location choices, explained patterns of and determinants of knowledge diffusion, and considered how social networks can lead to economic advantages. This article discusses Sorenson’s work specifically focusing on three themes—(i) the geography of entrepreneurial activity, (ii) social capital, and (iii) the evolution of learning and innovation—highlighting scholarly contributions and insights for management practice and public policy.
Open Access
Trajectories of functional ability over the life course: a conceptual model of the interaction of stressor-induced functional loss and resilience.
(System dynamics review, 2018-10) Matchar, David B; Ansah, John P; Koh, Victoria; Whitson, Heather E
Understanding the factors that influence functional ability over the life course is integral to identifying clinical and public health policies to facilitate successful aging. The World Health Organization has advocated a conceptual framework to clarify the policy discussion. We have sought to translate this general framework into an explicit system dynamics model of the interaction of physiological loss, stressors and endogenous responses to produce a familiar variety of trajectories of functional ability over the life courses. Simulation experiments were implemented for both a 30-month duration with only one major stressor; and for the life course with an initial major stressor and subsequent stressors determined by the level of functional ability. For both contexts, variations in the few parameters in the scenarios led to a realistic range of trajectories of function over time.
Open Access
Validation of algorithmic CT image quality metrics with preferences of radiologists
(MEDICAL PHYSICS, 2019-11-01) Cheng, Yuan; Abadi, Ehsan; Smith, Taylor Brunton; Ria, Francesco; Meyer, Mathias; Marin, Daniele; Samei, Ehsan
Open Access
Water turnover among human populations: Effects of environment and lifestyle.
(American journal of human biology : the official journal of the Human Biology Council, 2020-01) Swanson, Zane S; Pontzer, Herman
OBJECTIVES:To discuss the environmental and lifestyle determinants of water balance in humans and identify the gaps in current research regarding water use across populations. METHODS:We investigated intraspecific variation in water turnover by comparing data derived from a large number of human populations measured using either dietary survey or isotope tracking. We also used published data from a broad sample of mammalian species to identify the interspecific relationship between body mass and water turnover. RESULTS:Water facilitates nearly all physiological tasks and water turnover is strongly related to body size among mammals (r2=0.90). Within humans, however, the effect of body size is small. Instead, water intake and turnover vary with lifestyle and environmental conditions. Notably, despite living physically active lives in conditions that should increase water demands, the available measures of water intake and turnover among small-scale farming and pastoralist communities are broadly similar to those in less active, industrialized populations. CONCLUSIONS:More work is required to better understand the environmental, behavioral, and cultural determinants of water turnover in humans living across a variety of ecosystems and lifestyles. The results of such work are made more vital by the climate crisis, which threatens the water security of millions around the globe.