252 research outputs found
A Tractable Approach to the Firm Location Decision Problem
The conditional logit model based on random utility maximization has provided an adequate framework to model firm location decisions. However, in practice, the implementation of this methodology presents problems when one has to handle complex choice scenarios with a large number of spatial alternatives. We posit the Poisson regression as a tractable solution to these problems. We demonstrate that by taking advantage of an equivalence relation between the likelihood function of the conditional logit and the Poisson regression we can, under certain circumstances, easily estimate a conditional logit model regardless of the number of choices. This insight should be particularly useful for studies of economic location
Localization for Yang-Mills Theory on the Fuzzy Sphere
We present a new model for Yang-Mills theory on the fuzzy sphere in which the
configuration space of gauge fields is given by a coadjoint orbit. In the
classical limit it reduces to ordinary Yang-Mills theory on the sphere. We find
all classical solutions of the gauge theory and use nonabelian localization
techniques to write the partition function entirely as a sum over local
contributions from critical points of the action, which are evaluated
explicitly. The partition function of ordinary Yang-Mills theory on the sphere
is recovered in the classical limit as a sum over instantons. We also apply
abelian localization techniques and the geometry of symmetric spaces to derive
an explicit combinatorial expression for the partition function, and compare
the two approaches. These extend the standard techniques for solving gauge
theory on the sphere to the fuzzy case in a rigorous framework.Comment: 55 pages. V2: references added; V3: minor corrections, reference
added; Final version to be published in Communications in Mathematical
Physic
Recommended from our members
Permafrost Formation in a Meandering River Floodplain
Permafrost influences 25% of land in the Northern Hemisphere, where it stabilizes the ground beneath communities and infrastructure and sequesters carbon. However, the coevolution of permafrost, river dynamics, and vegetation in Arctic environments remains poorly understood. As rivers meander, they erode the floodplain at cutbanks and build new land through bar deposition, creating sequences of landforms with distinct formation ages. Here we mapped these sequences along the Koyukuk River floodplain, Alaska, analyzing permafrost occurrence, and landform and vegetation types. We used radiocarbon and optically stimulated luminescence (OSL) dating to develop a floodplain age map. Deposit ages ranged from modern to 10 ka, with more younger deposits near the modern channel. Permafrost rapidly reached 50% areal extent in all deposits older than 200 years then gradually increased up to ∼85% extent for deposits greater than 4 Kyr old. Permafrost extent correlated with increases in black spruce and wetland abundance, as well as increases in permafrost extent within wetland, and shrub and scrub vegetation classes. We developed an inverse model to constrain permafrost formation rate as a function of air temperature. Permafrost extent initially increased by ∼25% per century, in pace with vegetation succession, before decelerating to <10% per millennia as insulating overbank mud and moss slowly accumulated. Modern permafrost extent on the Koyukuk floodplain therefore reflects a dynamic balance between widespread, time-varying permafrost formation and rapid, localized degradation due to cutbank erosion that might trigger a rapid loss of permafrost with climatic warming
High-impact firms in South Carolina
This study analyzes private-sector firms and employment change in South Carolina from a new perspective. For years, it has been widely believed that small businesses create almost all jobs in the United States. Recent research has suggested that a small number of fast-growing firms (many small and medium-sized) are responsible for a majority of the employment gains in the United States. The research presented in this study assesses the scope of South Carolina’s small-business and high-impact job creation over the past two decades
The economic impact of South Carolina 's automotive cluster
This executive summary highlights the results of an in-depth, comprehensive economic study of South Carolina’s automotive and ground transportation cluster. The study shows that the auto cluster plays a unique role in economic development. Notably, few other sectors of the economy have the real potential to scale up employment, which is the most pressing economic imperative in South Carolina today. Automotive and ground transportation-related businesses contribute to approximately 5.4 percent of the state’s employment base, according to 2008 data compiled by the Division of Research. Importantly, the employment multipliers for each job created in South Carolina are unparalleled. For the automotive-related sectors examined in this study, the job impacts are higher than any other specific sector or industry
Human metabolism and elimination of the anthocyanin, cyanidin-3-glucoside: a 13C-tracer study
BACKGROUND: Evidence suggests that the consumption of anthocyanin-rich foods beneficially affects cardiovascular health; however, the absorption, distribution, metabolism, and elimination (ADME) of anthocyanin-rich foods are relatively unknown. OBJECTIVE: We investigated the ADME of a (13)C5-labeled anthocyanin in humans. DESIGN: Eight male participants consumed 500 mg isotopically labeled cyanidin-3-glucoside (6,8,10,3',5'-(13)C5-C3G). Biological samples were collected over 48 h, and (13)C and (13)C-labeled metabolite concentrations were measured by using isotope-ratio mass spectrometry and liquid chromatography-tandem mass spectrometry. RESULTS: The mean +/- SE percentage of (13)C recovered in urine, breath, and feces was 43.9 +/- 25.9% (range: 15.1-99.3% across participants). The relative bioavailability was 12.38 +/- 1.38% (5.37 +/- 0.67% excreted in urine and 6.91 +/- 1.59% in breath). Maximum rates of (13)C elimination were achieved 30 min after ingestion (32.53 +/- 14.24 mug(13)C/h), whereas (13)C-labeled metabolites peaked (maximum serum concentration: 5.97 +/- 2.14 mumol/L) at 10.25 +/- 4.14 h. The half-life for (13)C-labeled metabolites ranged between 12.44 +/- 4.22 and 51.62 +/- 22.55 h. (13)C elimination was greatest between 0 and 1 h for urine (90.30 +/- 15.28 mug/h), at 6 h for breath (132.87 +/- 32.23 mug/h), and between 6 and 24 h for feces (557.28 +/- 247.88 mug/h), whereas the highest concentrations of (13)C-labeled metabolites were identified in urine (10.77 +/- 4.52 mumol/L) and fecal samples (43.16 +/- 18.00 mumol/L) collected between 6 and 24 h. Metabolites were identified as degradation products, phenolic, hippuric, phenylacetic, and phenylpropenoic acids. CONCLUSION: Anthocyanins are more bioavailable than previously perceived, and their metabolites are present in the circulation fo
Chronic Supplementation With a Mitochondrial Antioxidant (MitoQ) Improves Vascular Function in Healthy Older Adults.
UNLABELLED: Excess reactive oxygen species production by mitochondria is a key mechanism of age-related vascular dysfunction. Our laboratory has shown that supplementation with the mitochondrial-targeted antioxidant MitoQ improves vascular endothelial function by reducing mitochondrial reactive oxygen species and ameliorates arterial stiffening in old mice, but the effects in humans are unknown. Here, we sought to translate our preclinical findings to humans and determine the safety and efficacy of MitoQ. Twenty healthy older adults (60-79 years) with impaired endothelial function (brachial artery flow-mediated dilation 7.60 m/s; n=11). Plasma oxidized LDL (low-density lipoprotein), a marker of oxidative stress, also was lower after MitoQ versus placebo (P0.1). These findings in humans extend earlier preclinical observations and suggest that MitoQ and other therapeutic strategies targeting mitochondrial reactive oxygen species may hold promise for treating age-related vascular dysfunction. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02597023.This work was supported by National Institutes of Health (NIH)
awards AG049451, AG000279, AG053009, Colorado CTSA UL1
TR001082, and an industry contract with MitoQ Limited (MitoQ
Limited provided MitoQ and some financial support). M.P. Murphy
is supported by UK MRC MC_U105663142 and as a Wellcome Trust
Investigator (110159/Z/15/Z)
A process-based model of conifer forest structure and function with special emphasis on leaf lifespan
We describe the University of Sheffield Conifer Model (USCM), a process-based approach for simulating conifer forest carbon, nitrogen, and water fluxes by up-scaling widely applicable relationships between leaf lifespan and function. The USCM is designed to predict and analyze the biogeochemistry and biophysics of conifer forests that dominated the ice-free high-latitude regions under the high pCO2 “greenhouse” world 290–50 Myr ago. It will be of use in future research investigating controls on the contrasting distribution of ancient evergreen and deciduous forests between hemispheres, and their differential feedbacks on polar climate through the exchange of energy and materials with the atmosphere. Emphasis is placed on leaf lifespan because this trait can be determined from the anatomical characteristics of fossil conifer woods and influences a range of ecosystem processes. Extensive testing of simulated net primary production and partitioning, leaf area index, evapotranspiration, nitrogen uptake, and land surface energy partitioning showed close agreement with observations from sites across a wide climatic gradient. This indicates the generic utility of our model, and adequate representation of the key processes involved in forest function using only information on leaf lifespan, climate, and soils
Long-Term Potentiation: One Kind or Many?
Do neurobiologists aim to discover natural kinds? I address this question in this chapter via a critical analysis of classification practices operative across the 43-year history of research on long-term potentiation (LTP). I argue that this 43-year history supports the idea that the structure of scientific practice surrounding LTP research has remained an obstacle to the discovery of natural kinds
- …