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Search Results: 1 - 10 of 461461 matches for " Kelsey A.; "
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Plastic Additives Decrease Agrin-Induced Acetylcholine Receptor Clusters and Myotube Formation in C2C12 Skeletal Muscle Cell Culture  [PDF]
Kelsey Neufeld, Kelly Ezell, Wade A. Grow
CellBio (CellBio) , 2015, DOI: 10.4236/cellbio.2015.41002
Abstract: Common additives in plastics such as bisphenol A (BPA) or phthalates like di-(2-ethylhexyl) phthalate (DEHP) are environmental estrogens that have been shown to be endocrine disruptors in some experimental animal models. This project used the C2C12 cell culture model to examine how exposure to BPA or DEHP affects two aspects of skeletal muscle development, the fusion of myoblasts into myotubes and agrin-induced clustering of acetylcholine receptors (AChRs). During myotube formation AChRs cluster spontaneously. Treatment with motor neuron derived agrin increases the frequency of AChR clusters through an agrin signaling pathway that also clusters other postsynaptic components of the neuromuscular synapse. For this project C2C12 cells were exposed to BPA or DEHP while myoblasts fused into myotubes. After exposure to 10 μM BPA or 100 μM DEHP the frequency of agrin-induced AChR clusters decreased. In addition, myotube formation decreased as a higher percentage of nuclei remained in myoblasts. Furthermore, BPA or DEHP reduced the amount of the myogenic regulatory factor myogenin. This suggests that BPA and DEHP decrease AChR clustering by reducing myogenin. Moreover, plastic additives like BPA and DEHP may pose a risk for skeletal muscle development in humans.
Mapping schemes realizable by obstructed topological polynomials
Gregory A. Kelsey
Mathematics , 2010,
Abstract: In 1985, Levy used a theorem of Berstein to prove that all hyperbolic topological polynomials are equivalent to complex polynomials. We prove a partial converse to the Berstein-Levy Theorem: given post-critical dynamics that are in a sense strongly non-hyperbolic, we prove the existence of topological polynomials which are not equivalent to any complex polynomial that realize these post-critical dynamics. This proof employs the theory of self-similar groups to demonstrate that a topological polynomial admits an obstruction and produces a wealth of examples of obstructed topological polynomials.
Achievement of Climate Planning Objectives among U.S. Member Cities of the International Council for Local Environmental Initiatives (ICLEI)  [PDF]
Margaret A. Reams, Kelsey W. Clinton, Nina S. N. Lam
Low Carbon Economy (LCE) , 2012, DOI: 10.4236/lce.2012.34018
Abstract:

In an effort to address climate change, many cities have joined the International Council for Local Environmental Initiatives (ICLEI) whose members commit to work toward five specific program objectives designed to reduce greenhouse gas emissions. This study examines the extent to which 257 member cities in the U.S.have been successful in achieving these program milestones and identifies factors that may explain variation in the performance of member cities. Potential influences on milestone attainment include socioeconomic, political and ideological characteristics of residents, length of ICLEI membership, existence of other climate programs within the state, and local environmental pressures. Multiple regression results indicate that length of membership is the strongest predictor of milestone attainment, regardless of local socioeconomic conditions, ideological and political orientations of residents, or other climate-related initiatives within the state. This finding supports the general effectiveness of ICLEI’s network organizational model and its outreach and education efforts. However, member cities facing more “climate stress”, including higher levels of hazardous air pollutants (HAP’s) and greater automobile use among residents are making slower progress. The findings yield insight into the conditions under which cities engaged in climate planning are more likely to succeed in reducing local greenhouse gas emissions-relevant information for planners, community stakeholders and administrators of organizations like ICLEI.

Visual boundaries of Diestel-Leader graphs
Keith Jones,Gregory A. Kelsey
Mathematics , 2013,
Abstract: Diestel-Leader graphs are neither hyperbolic nor CAT(0), so their visual boundaries may be pathological. Indeed, we show that for $d>2$, $\partial\text{DL}_d(q)$ carries the indiscrete topology. On the other hand, $\partial\text{DL}_2(q)$, while not Hausdorff, is $T_1$, totally disconnected, and compact. Since $\text{DL}_2(q)$ is a Cayley graph of the lamplighter group $L_q$, we also obtain a nice description of $\partial\text{DL}_2(q)$ in terms of the lamp stand model of $L_q$ and discuss the dynamics of the action.
The horofunction boundary of the lamplighter group $L_2$ with the Diestel-Leader metric
Keith Jones,Gregory A. Kelsey
Mathematics , 2014,
Abstract: We fully describe the horofunction boundary $\partial_h L_2$ with the word metric associated with the generating set $\{t, at\}$ (i.e the metric arising in the Diestel-Leader graph $\text{DL}_2(2)$). The visual boundary of $L_2$ with this metric is a subset of $\partial_h L_2$. The height function on $\text{DL}_2(2)$ provides a natural stratification of $\partial_h L_2$. Further, the height function and its negation are themselves non-Busemann functions in $\partial_h L_2$ and are global fixed points of the action of $L_2$.
Evidence of positive selection at codon sites localized in extracellular domains of mammalian CC motif chemokine receptor proteins
Kelsey J Metzger, Michael A Thomas
BMC Evolutionary Biology , 2010, DOI: 10.1186/1471-2148-10-139
Abstract: In mammals, the majority of chemokine receptor genes are clustered together; in humans, seven of the ten genes are clustered in the 3p21-24 chromosome region. Gene conversion events, or exchange of DNA sequence between genes, have been reported in chemokine receptor paralogs in various mammalian lineages, especially between the cytogenetically closely located pairs CCR2/5 and CCR1/3. Datasets of mammalian orthologs for each gene were analyzed separately to minimize the potential confounding impact of analyzing highly similar sequences resulting from gene conversion events.Molecular evolution approaches and the software package Phylogenetic Analyses by Maximum Likelihood (PAML) were utilized to investigate the signature of selection that has acted on the mammalian CC chemokine receptor (CCR) gene family. The results of neutral vs. adaptive evolution (positive selection) hypothesis testing using Site Models are reported. In general, positive selection is defined by a ratio of nonsynonymous/synonymous nucleotide changes (dN/dS, or ω) >1.Of the ten mammalian CC motif chemokine receptor sequence datasets analyzed, only CCR2 and CCR3 contain amino acid codon sites that exhibit evidence of positive selection using site based hypothesis testing in PAML. Nineteen of the twenty codon sites putatively indentified as likely to be under positive selection code for amino acid residues located in extracellular domains of the receptor protein products.These results suggest that amino acid residues present in intracellular and membrane-bound domains are more selectively constrained for functional signal transduction and homo- or heterodimerization, whereas amino acid residues in extracellular domains of these receptor proteins evolve more quickly, perhaps due to heightened selective pressure resulting from ligand-binding and pathogen interactions of extracellular domains.Chemotactic or chemoattractant cytokine (chemokine) proteins are a unique division of cytokines characterized by
Barriers to hospital births: why do many Bolivian women give birth at home?
Otis,Kelsey E.; Brett,John A.;
Revista Panamericana de Salud Pública , 2008, DOI: 10.1590/S1020-49892008000700006
Abstract: objectives: this study investigated the low rates of hospital/health center births recorded in yapacaní, bolivia, that persist despite the national maternal-infant insurance program designed to ensure equitable access to free center-based health care services for pregnant women. the purpose of this study was to identify the multilevel factors inhibiting access to and utilization of public health centers for labor and delivery. methods: qualitative research methods were used, including participant observation, semistructured interviews of 62 community members, and key informant interviews with eight regional experts. data were coded and analyzed using the grounded theory approach. results: from the semistructured interview data, five reasons for the low rate of institutional births and their frequency were identified: (1) fear or embarrassment related to receiving care at a public health care center (37%); (2) poor quality of care available at the health care centers (22%); (3) distance from or other geographic issues preventing timely travel to health care services (21%); (4) economic constraints preventing travel to or utilization of health care services (14%); and (5) the perception that health care services are not necessary due to the experience of "easy birth" (6%). conclusions: the reasons for the low rate of births in public health centers exist within the context of deficient resources, politics, and cultural differences that all influence the experience of women and their partners at the time of birth. these large scale, contextual issues must be taken into account to improve access to quality health care services for all bolivian women at the time of birth. resources at the national level must be carefully targeted to ensure that governmental services will successfully instill confidence in bolivian women and facilitate their overcoming the cultural, geographic, economic, and logistical barriers to accessing "free" services.
The Spectral Energy Distributions of Infant Super Star Clusters in Henize 2-10 from 7mm to 6cm
Kelsey E. Johnson,Henry A. Kobulnicky
Physics , 2003, DOI: 10.1086/378585
Abstract: We present observations from our continuing studies of the earliest stages of massive star cluster evolution. In this paper, radio observations from the Very Large Array at 0.7cm, 1.3cm, 2cm, 3.6cm, and 6cm are used to map the radio spectral energy distributions and model the physical properties of the ultra-young embedded super star clusters in Henize 2-10. The 0.7cm flux densities indicate that the young embedded star clusters that are powering the radio detected ``ultradense HII regions'' (UDHIIs) have masses greater than \~10^5 Msun. We model the radio spectral energy distributions as both constant density HII regions and HII regions with power-law electron density gradients. These models suggest the UDHIIs have radii ranging between ~2-4pc and average electron densities of ~10^3-10^4 cm^-3 (with peak electron densities reaching values of ~10^5-10^6 cm^-3). The pressures implied by these densities are P/k_B~10^7-10^10 cm^-3 K, several orders of magnitude higher than typical pressures in the Galactic ISM. The inferred HII masses in the UDHIIs are \~2-8x10^3 Msun; these values are <5% of the embedded stellar masses, and anonamously low when compared to optically visible young clusters. We suggest that these low HII mass fractions may be a result of the extreme youth of these objects.
Signatures of the Youngest Starbursts: Optically-thick Thermal Bremsstrahlung Radio Sources in Henize 2-10
Henry A. Kobulnicky,Kelsey E. Johnson
Physics , 1999, DOI: 10.1086/308075
Abstract: VLA radio continuum imaging reveals compact (<8 pc) ~1 mJy radio sources in the central 5" starburst region of the blue compact galaxy Henize 2-10. We interpret these radio knots as extremely young, ultra-dense HII regions. We model their luminosities and spectral energy distributions, finding that they are consistent with unusually dense HII regions having electron densities, 1500 cm^-3 < n_e < 5000 cm^-3, and sizes of 3-8 pc. Since these H II regions are not visible in optical images, we propose that the radio data preferentially reveal the youngest, densest, and most highly obscured starforming events. Energy considerations imply that each of the five \HII regions contains ~750 O7V equivalent stars, greater than the number found in 30 Doradus in the LMC. The high densities imply an over-pressure compared to the typical interstellar medium so that such objects must be short-lived (<0.5 Myr expansion timescales). We conclude that the radio continuum maps reveal the very young (<0.5 Myr) precursors of ``super starclusters'' or ``proto globular clusters'' which are prominent at optical and UV wavelengths in He 2-10. If the ultra-dense HII regions are typical of those which we predict will be found in other starbursting systems, then super starclusters spend 15% of their lifetime in heavily-obscured environments, similar to Galactic ultra-compact HII regions. This body of work leads us to propose that massive extragalactic star clusters (i.e. proto globular clusters) with ages <10^6 yr may be most easily identified by finding compact radio sources with optically-thick thermal bremsstrahlung spectral signatures.
Cost and Emissions Implications of Coupling Wind and Solar Power  [PDF]
Seth Blumsack, Kelsey Richardson
Smart Grid and Renewable Energy (SGRE) , 2012, DOI: 10.4236/sgre.2012.34041
Abstract: We assess the implications on long-run average energy production costs and emissions of CO2 and some criteria pollutants from coupling wind, solar and natural gas generation sources. We utilize five-minute meteorological data from a US location that has been estimated to have both high-quality wind and solar resources, to simulate production of a coupled generation system that produces a constant amount of electric energy. The natural gas turbine is utilized to provide fill-in energy for the coupled wind/solar system, and is compared to a base case where the gas turbine produces a constant power output. We assess the impacts on variability of coupled wind and solar over multiple time scales, and compare this variability with regional demand in a nearby load center, and find that coupling wind and solar does decrease variability of output. The cost analysis found that wind energy with gas back-up has a lower levelized cost of energy than using gas energy alone, resulting in production savings. Adding solar energy to the coupled system increases levelized cost of energy production; this cost is not made up by any reductions in emissions costs.
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