Showing 301 - 310 of 734 Items
Using landscape metrics to characterize towns along an urban-rural gradient
Date: 2021-10-01
Creator: Abigail Kaminski, Dana Marie Bauer, Kathleen P. Bell, Cynthia S. Loftin, Erik J., Nelson
Access: Open access
- Context: Urban-rural gradients are useful tools when examining the influence of human disturbances on ecological, social and coupled systems, yet the most commonly used gradient definitions are based on single broad measures such as housing density or percent forest cover that fail to capture landscape patterns important for conservation. Objectives: We present an approach to defining urban–rural gradients that integrates multiple landscape pattern metrics related to ecosystem processes important for natural resources and wildlife sustainability. Methods: We develop a set of land cover composition and configuration metrics and then use them as inputs to a cluster analysis process that, in addition to grouping towns with similar attributes, identifies exemplar towns for each group. We compare the outcome of the cluster-based urban-rural gradient typology to outcomes for four commonly-used rule-based typologies and discuss implications for resource management and conservation. Results: The resulting cluster-based typology defines five town types (urban, suburban, exurban, rural, and agricultural) and notably identifies a bifurcation along the gradient distinguishing among rural forested and agricultural towns. Landscape patterns (e.g., core and islet forests) influence where individual towns fall along the gradient. Designations of town type differ substantially among the five different typologies, particularly along the middle of the gradient. Conclusions: Understanding where a town occurs along the urban-rural gradient could aid local decision-makers in prioritizing and balancing between development and conservation scenarios. Variations in outcomes among the different urban-rural gradient typologies raise concerns that broad-measure classifications do not adequately account for important landscape patterns. We suggest future urban-rural gradient studies utilize more robust classification approaches.
Arginine methylation of yeast mRNA-binding protein Npl3 directly affects its function, nuclear export, and intranuclear protein interactions
Date: 2005-09-02
Creator: Anne E. McBride, Jeffrey T. Cook, Elizabeth A. Stemmler, Kate L. Rutledge, Kelly A., McGrath, Jeffrey A. Rubens
Access: Open access
- Arginine methylation can affect both nucleocytoplasmic transport and protein-protein interactions of RNA-binding proteins. These effects are seen in cells that lack the yeast hnRNP methyltransferase (HMT1), raising the question of whether effects on specific proteins are direct or indirect. The presence of multiple arginines in individual methylated proteins also raises the question of whether overall methylation or methylation of a subset of arginines affects protein function. We have used the yeast mRNA-binding protein Npl3 to address these questions in vivo. Matrix-assisted laser desorption/ionization Fourier transform mass spectrometry was used to identify 17 methylated arginines in Npl3 purified from yeast: whereas 10 Arg-Gly-Gly (RGG) tripeptides were exclusively dimethylated, variable levels off methylation were found for 5 RGG and 2 RG motif arginines. We constructed a set of Npl3 proteins in which subsets of the RGG arginines were mutated to lysine. Expression of these mutant proteins as the sole form of Npl3 specifically affected growth of a strain that requires Hmtl. Although decreased growth generally correlated with increased numbers of Arg-to-Lys mutations, lysine substitutions in the N terminus of the RGG domain showed more severe effects. Npl3 with all 15 RGG arginines mutated to lysine exited the nucleus independent of Hmtl, indicating a direct effect of methylation on Npl3 transport. These mutations also resulted in a decreased, methylation-independent interaction of Npl3 with transcription elongation factor Tho2 and inhibited Npl3 self-association. These results support a model in which arginine methylation facilitates Npl3 export directly by weakening contacts with nuclear proteins. © 2005 by The American Society for Biochemistry and Molecular Biology, Inc.
CO2 induced phase transitions in diamine-appended metal-organic frameworks
Date: 2015-06-15
Creator: Bess Vlaisavljevich, Samuel O. Odoh, Sondre K. Schnell, Allison L. Dzubak, Kyuho, Lee, Nora Planas, Jeffrey B. Neaton, Laura Gagliardi, Berend Smit
Access: Open access
- Using a combination of density functional theory and lattice models, we study the effect of CO2 adsorption in an amine functionalized metal-organic framework. These materials exhibit a step in the adsorption isotherm indicative of a phase change. The pressure at which this step occurs is not only temperature dependent but is also metal center dependent. Likewise, the heats of adsorption vary depending on the metal center. Herein we demonstrate via quantum chemical calculations that the amines should not be considered firmly anchored to the framework and we explore the mechanism for CO2 adsorption. An ammonium carbamate species is formed via the insertion of CO2 into the M-Namine bonds. Furthermore, we translate the quantum chemical results into isotherms using a coarse grained Monte Carlo simulation technique and show that this adsorption mechanism can explain the characteristic step observed in the experimental isotherm while a previously proposed mechanism cannot. Furthermore, metal analogues have been explored and the CO2 binding energies show a strong metal dependence corresponding to the M-Namine bond strength. We show that this difference can be exploited to tune the pressure at which the step in the isotherm occurs. Additionally, the mmen-Ni2(dobpdc) framework shows Langmuir like behavior, and our simulations show how this can be explained by competitive adsorption between the new model and a previously proposed model.
On influence, stable behavior, and the most influential individuals in networks: A game-theoretic approach
Date: 2014-01-01
Creator: Mohammad T. Irfan, Luis E. Ortiz
Access: Open access
- We introduce a new approach to the study of influence in strategic settings where the action of an individual depends on that of others in a network-structured way. We propose network influence games as a game-theoretic model of the behavior of a large but finite networked population. In particular, we study an instance we call linear-influence games that allows both positive and negative influence factors, permitting reversals in behavioral choices. We embrace pure-strategy Nash equilibrium, an important solution concept in non-cooperative game theory, to formally define the stable outcomes of a network influence game and to predict potential outcomes without explicitly considering intricate dynamics. We address an important problem in network influence, the identification of the most influential individuals, and approach it algorithmically using pure-strategy Nash-equilibria computation. Computationally, we provide (a) complexity characterizations of various problems on linear-influence games; (b) efficient algorithms for several special cases and heuristics for hard cases; and (c) approximation algorithms, with provable guarantees, for the problem of identifying the most influential individuals. Experimentally, we evaluate our approach using both synthetic network influence games and real-world settings of general interest, each corresponding to a separate branch of the U.S. Government. Mathematically, we connect linear-influence games to important models in game theory: potential and polymatrix games. © 2014 Published by Elsevier B.V.
APPSSAT: Approximate probabilistic planning using stochastic satisfiability
Date: 2005-01-01
Creator: Stephen M. Majercik
Access: Open access
- We describe APPSSAT, an approximate probabilistic contingent planner based on ZANDER, a probabilistic contingent planner that operates by converting the planning problem to a stochastic satisfiability (SSAT) problem and solving that problem instead [1]. The values of some of the variables in an SSAT instance are probabilistically determined; APPSSAT considers the most likely instantiations of these variables (the most probable situations facing the agent) and attempts to construct an approximation of the optimal plan that succeeds under those circumstances, improving that plan as time permits. Given more time, less likely instantiations/situations are considered and the plan is revised as necessary. In some cases, a plan constructed to address a relatively low percentage of possible situations will succeed for situations not explicitly considered as well, and may return an optimal or near-optimal plan. This means that APPSSAT can sometimes find optimal plans faster than ZANDER. And the anytime quality of APPSSAT means that suboptimal plans could be efficiently derived in larger time-critical domains in which ZANDER might not have sufficient time to calculate the optimal plan. We describe some preliminary experimental results and suggest further work needed to bring APPSSAT closer to attacking real-world problems. © Springer-Verlag Berlin Heidelberg 2005.
Managing small natural features: A synthesis of economic issues and emergent opportunities
Date: 2017-07-01
Creator: Dana Marie Bauer, Kathleen P. Bell, Erik J. Nelson, Aram J.K. Calhoun
Access: Open access
- Small natural features (SNFs), landscape elements that influence species persistence and ecological functioning on a much larger scale than one would expect from their size, can also offer a greater rate of return on conservation investment compared to that of larger natural features or more broad-based conservation. However, their size and perceived lack of significance also makes them more vulnerable to threats and destruction. We examine the management of SNFs and conservation of the associated ecosystem services they generate from an economics perspective. Using the economic concept of market failure, we identify three key themes that explain prevailing threats to SNFs and characterize impediments to and opportunities for SNF management: (1) the degree to which benefits derived from the feature spillover, beyond the feature itself (spatially and temporally); (2) the availability and quality of information about the feature and those who most directly influence its management; and (3) the existence and enforcement of property rights and legal standing of the feature. We argue that the efficacy of alternative SNF management approaches is highly case dependent and relies on four key components: (1) the specific ecosystem services of interest; (2) the amount of redundancy of the SNF on the landscape and the level of connectivity required by the SNF in order to provide ecosystem services; (3) the particular market failures that need correcting and their scope and extent; and (4) the magnitude and distribution of management costs.
In and out of the spectacle: The Beijing olympics and Yiyun Li's The Vagrants
Date: 2011-01-01
Creator: Belinda Kong
Access: Open access
Position effects influence transvection in drosophila melanogaster
Date: 2019-01-01
Creator: Thomas D. King, Justine E. Johnson, Jack R. Bateman
Access: Open access
- Transvection is an epigenetic phenomenon wherein regulatory elements communicate between different chromosomes in trans, and is thereby dependent upon the three-dimensional organization of the genome. Transvection is best understood in Drosophila, where homologous chromosomes are closely paired in most somatic nuclei, although similar phenomena have been observed in other species. Previous data have supported that the Drosophila genome is generally permissive to enhancer action in trans, a form of transvection where an enhancer on one homolog activates gene expression from a promoter on a paired homolog. However, the capacity of different genomic positions to influence the quantitative output of transvection has yet to be addressed. To investigate this question, we employed a transgenic system that assesses and compares enhancer action in cis and in trans at defined chromosomal locations. Using the strong synthetic eye-specific enhancer GMR, we show that loci supporting strong cis-expression tend to support robust enhancer action in trans, whereas locations with weaker cis-expression show reduced transvection in a fluorescent reporter assay. Our subsequent analysis is consistent with a model wherein the chromatin state of the transgenic insertion site is a primary determinant of the degree to which enhancer action in trans will be supported, whereas other factors such as locus-specific variation in somatic homolog pairing are of less importance in influencing position effects on transvection.
Estimating the impact of Critical Habitat designation on the values of developed and undeveloped parcels (2nd version, current as of 7/29/2022)
Date: 2022-07-29
Creator: Saleh Mamun, Erik Nelson, Christoph Nolte
Access: Open access
- We use differences-in-differences (DD) estimators to measure the impact that Endangered Species Act (ESA)’s Critical Habitat (CH) rule had on developed and undeveloped parcel prices throughout the US between 2000 and 2019. In a national-level analysis we found that, on average, the price of parcels “treated” with CH were not statistically different than the prices of nearby parcels in listed species range space but not “treated” by CH. CH’s null impact on developed parcel prices is surprising given homeowner’s documented willingness to pay for property surrounded by protected open space. CH’s null impact on undeveloped parcel prices is surprising as previous research had indicated that the impact of CH on undeveloped parcel prices was negative due to the additional regulatory costs and development uncertainty the CH regulation imposes on land developers. When we used relevant subsets of CH areas to measure CH’s impact on parcel prices, we did occasionally find results that were consistent with expectations. We reach two conclusions. First, the impact of the economic impact of the CH rule, holding the impact of other ESA sections constant, cannot be reduced to a simple, consistent narrative. Second, CH’s relatively minor impact on parcel prices suggests that the rule does not have much regulatory “bite.”