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Search Results: 1 - 10 of 248592 matches for " Peter C. Breen "
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Regional differences in expression of VEGF mRNA in rat gastrocnemius following 1 hr exercise or electrical stimulation
Tom D Brutsaert, Timothy P Gavin, Zhenxing Fu, Ellen C Breen, Kechun Tang, Odile Mathieu-Costello, Peter D Wagner
BMC Physiology , 2002, DOI: 10.1186/1472-6793-2-8
Abstract: Total muscle VEGF mRNA (via Northern blot) was upregulated 3.5-fold with both exercise and with electrical stimulation (P = 0.015). Quantitative densitometry of the VEGF mRNA signal via in situ hybridization reveals significant regional differences (P ≤ 0.01) and protocol differences (treadmill, electrical stimulation, and control, P ≤ 0.05). Mean VEGF mRNA signal was higher in the oxidative region in both treadmill run (~7%, N = 4 muscles, P ≤ 0.05) and electrically stimulated muscles (~60%, N = 4, P ≤ 0.05). These regional differences were not significantly different from control muscle (non-exercised, non-stimulated, N = 2 muscles), although nearly so for electrically stimulated muscle (P = 0.056).Moderately higher VEGF mRNA signal in oxidative muscle regions is consistent with regional differences in capillary density. However, it is not possible to determine if the VEGF mRNA signal difference is important in either the maintenance of regional capillarity differences or exercise induced angiogenesis.The adaptations of skeletal muscle to endurance-type training are well characterized. They include increases in mitochondrial volume density and increases in the activity of enzymes involved in oxidative phosphorylation to produce ATP [1]. The increased metabolic capacity of trained muscle is accompanied by an angiogenic response which increases capillary density and/or capillary to fiber ratio [2,3], preserving the functional match between oxygen delivery and metabolic demand within the muscle. The angiogenic response in skeletal muscle is thought to be mediated by a number of angiogenic factors including, most importantly, vascular endothelial growth factor (VEGF). VEGF is a 45 kDA heparin-binding homodimeric glycoprotein with a predominant specificity to vascular endothelial cells [4-7]. Recent investigations demonstrate that VEGF increases vascular permeability [4], endothelial cell proliferation in vitro[8], and angiogenesis in vivo[9]. We have previously demons
The ERI-6/7 Helicase Acts at the First Stage of an siRNA Amplification Pathway That Targets Recent Gene Duplications
Sylvia E. J. Fischer,Taiowa A. Montgomery,Chi Zhang,Noah Fahlgren,Peter C. Breen,Alexia Hwang,Christopher M. Sullivan,James C. Carrington,Gary Ruvkun
PLOS Genetics , 2011, DOI: 10.1371/journal.pgen.1002369
Abstract: Endogenous small interfering RNAs (siRNAs) are a class of naturally occuring regulatory RNAs found in fungi, plants, and animals. Some endogenous siRNAs are required to silence transposons or function in chromosome segregation; however, the specific roles of most endogenous siRNAs are unclear. The helicase gene eri-6/7 was identified in the nematode Caenorhabditis elegans by the enhanced response to exogenous double-stranded RNAs (dsRNAs) of the null mutant. eri-6/7 encodes a helicase homologous to small RNA factors Armitage in Drosophila, SDE3 in Arabidopsis, and Mov10 in humans. Here we show that eri-6/7 mutations cause the loss of 26-nucleotide (nt) endogenous siRNAs derived from genes and pseudogenes in oocytes and embryos, as well as deficiencies in somatic 22-nucleotide secondary siRNAs corresponding to the same loci. About 80 genes are eri-6/7 targets that generate the embryonic endogenous siRNAs that silence the corresponding mRNAs. These 80 genes share extensive nucleotide sequence homology and are poorly conserved, suggesting a role for these endogenous siRNAs in silencing of and thereby directing the fate of recently acquired, duplicated genes. Unlike most endogenous siRNAs in C. elegans, eri-6/7–dependent siRNAs require Dicer. We identify that the eri-6/7–dependent siRNAs have a passenger strand that is ~19 nt and is inset by ~3–4 nts from both ends of the 26 nt guide siRNA, suggesting non-canonical Dicer processing. Mutations in the Argonaute ERGO-1, which associates with eri-6/7–dependent 26 nt siRNAs, cause passenger strand stabilization, indicating that ERGO-1 is required to separate the siRNA duplex, presumably through endonucleolytic cleavage of the passenger strand. Thus, like several other siRNA–associated Argonautes with a conserved RNaseH motif, ERGO-1 appears to be required for siRNA maturation.
Hadamard Renormalisation of the Stress Energy Tensor on the Horizons of a Spherically Symmetric Black Hole Space-Time
Cormac Breen,Adrian C. Ottewill
Physics , 2011, DOI: 10.1103/PhysRevD.85.064026
Abstract: We consider a quantum field which is in a Hartle-Hawking state propagating in a general spherically symmetric black hole space-time. We make use of uniform approximations to the radial equation to calculate the components of the stress tensor, renormalized using the Hadamard form of the Green's function, on the horizons of this space-time. We then specialize these results to the case of the `lukewarm' Reissner-Nordstrom-de Sitter black hole and derive some conditions on the stress tensor for the regularity of the Hartle-Hawking state.
Extended Green-Liouville asymptotics and vacuum polarization for lukewarm black holes
Cormac Breen,Adrian C. Ottewill
Physics , 2010, DOI: 10.1103/PhysRevD.82.084019
Abstract: We consider a quantum field on a lukewarm black hole spacetime. We introduce a new uniform approximation to the radial equation, constructed using an extension of Green-Liouville asymptotics. We then use this new approximation to construct the renormalized vacuum polarization in the Hartle-Hawking vacuum. Previous calculations of the vacuum polarization rely on the WKB approximation to the solutions of the radial equation, however the nonuniformity of the WKB approximations obscures the results of these calculations near both horizons. The use of our new approximation eliminates these obscurities, enabling us to obtain explicitly finite and easily calculable values of the vacuum polarization on the two horizons.
Hadamard Renormalization of the Stress Energy Tensor in a Spherically Symmetric Black Hole Space-Time with an Application to Lukewarm Black Holes
Cormac Breen,Adrian C. Ottewill
Physics , 2011, DOI: 10.1103/PhysRevD.85.084029
Abstract: We consider a quantum field which is in a Hartle-Hawking state propagating in a spherically symmetric black hole space-time. We calculate the components of the stress tensor, renormalized using the Hadamard form of the Green's function, in the exterior region of this space-time. We then specialize these results to the case of the `lukewarm' Riessner-Nordstrom-de Sitter black hole.
Carbon dioxide kinetics and capnography during critical care
Cynthia T Anderson, Peter H Breen
Critical Care , 2000, DOI: 10.1186/cc696
Abstract: Carbon dioxide is produced in the tissues by aerobic plus/minus anaerobic metabolism (Fig. 1a), transported in blood to the lung by venous return (essentially equal to cardiac output [QT]), and eliminated from the lung by minute ventilation (VE) [1]. In this model the lung is a simple mixing chamber and the alveolar fractional carbon dioxide (FACO2) is given byFACO2 = ?CO2,ti/?A + FICO2 (1)where ?CO2,ti is the tissue carbon dioxide production, ?A is alveolar ventilation, and FICO2 is the inspired FCO2. If one assumes no diffusion defect for carbon dioxide, then the partial carbon dioxide tension (PCO2) of arterial blood (PaCO2) leaving the lung is the perfusion-weighted average alveolar PCO2 (PACO2). Note that pulmonary shunt will add mixed venous blood with high PCO2 (PVCO2) to arterial blood and slightly increase PaCO2 [2]. ?A is the product of respiratory frequency and expired tidal volume (VT). Expired VT is composed of alveolar VT and total physiologic dead space (VDphy). The fraction VDphy/VT is given byVDphy/VT = (PaCO2 - P?CO2)/PaCO2 (2)where P?CO2 is the mixed expired PCO2 [2]. In turn, VDphy is partitioned into anatomic dead space (VDana; conducting airways that do not participate in gas exchange) and alveolar dead space (VDalv; ventilated alveolar units that are devoid of perfusion; Fig. 2). VDalv/VTalv is given byVDalv/VTalv = (PaCO2 - PACO2)/PaCO2 (3)where PACO2 is the alveolar PCO2, estimated either from PETCO2 or P?CO2 [2] (see below). The PaCO2-PETCO2 gradient results from the presence of VDalv or high alveolar ventilation-to-blood flow (VA/Q) lung regions (see also Capnography during weaning from mechanical ventilation, below).The normal capnogram is the measurement of PCO2 at the airway opening during the ventilatory cycle (Fig. 1b) [1]. Phase I (inspiratory baseline) reflects inspired gas, which is normally devoid of carbon dioxide. Phase II (expiratory upstroke) is the transition between VDana, which does not participate in gas exchange, and alve
A Preliminary Examination of Risk in the Pharmaceutical Supply Chain (PSC) in the National Health Service (NHS)  [PDF]
Liz Breen
Journal of Service Science and Management (JSSM) , 2008, DOI: 10.4236/jssm.2008.12020
Abstract: The effective management of pharmaceuticals in the National Health Service (NHS) is critical to patient welfare thus any risks attached to this must be identified and controlled. At a very basic level, risks in the pharmaceutical supply chain are associated with product discontinuity, product shortages, poor performance, patient safety/dispensing errors, and technological errors (causing stock shortages in pharmacies) to name but a few, all of which incur risk through disruption to the system. Current indications suggest that the pharmaceutical industry and NHS practitioners alike have their concerns as to the use of generic supply chain strategies in association with what is perceived to be a specialist product (pharmaceuticals). The aim of the study undertaken was to gain a more realistic understanding of the nature and prevalence of risk in the Pharmaceutical Supply Chain (PSC) to be used as a basis for a more rigorous research project incorporating in-vestigation in the UK, Europe and USA. Data was collected via a workshop forum held in November 2005. The outputs of the workshop indicated that there were thirty-five prevalent risks. The risks were rated using risk assessment catego-ries such as impact, occurrence and controllability. The findings indicated that the risks identified are similar to those prevalent in industrial supply chains, regardless of the idiosyncrasies of pharmaceuticals. However, the group consen-sus was that caution must be applied in how such risks are addressed, as there are aspects of the product that highlight its uniqueness e.g. criticality.
Psychosocial factors and their predictive value in chiropractic patients with low back pain: a prospective inception cohort study
Jennifer M Langworthy, Alan C Breen
Chiropractic & Manual Therapies , 2007, DOI: 10.1186/1746-1340-15-5
Abstract: A prospective inception cohort study of patients presenting to a UK chiropractic practice for new episodes of non-specific low back pain (LBP) was conducted. Baseline questionnaires asked about age, gender, occupation, work status, duration of current episode, chronicity, aggravating features and bothersomeness using Deyo's 'Core Set'. Psychological factors (fear-avoidance beliefs, inevitability, anxiety/distress and coping, and co-morbidity were also assessed at baseline. Satisfaction with care, number of attendances and pain impact were determined at 6 weeks. Predictors of poor outcome were sought by the calculation of relative risk ratios.Most patients presented within 4 weeks of onset. Of 158 eligible and willing patients, 130 completed both baseline and 6-week follow-up questionnaires. Greatest improvements at 6 weeks were in interference with normal work (ES 1.12) and LBP bothersomeness (ES 1.37). Although most patients began with moderate-high back pain bothersomeness scores, few had high psychometric ones. Co-morbidity was a risk for high-moderate interference with normal work at 6 weeks (RR 2.37; 95% C.I. 1.15–4.74). An episode duration of >4 weeks was associated with moderate to high bothersomeness at 6 weeks (RR 2.07; 95% C.I. 1.19 – 3.38) and negative outlook (inevitability) with moderate to high interference with normal work (RR 2.56; 95% C.I. 1.08 – 5.08).Patients attending a private UK chiropractic clinic for new episodes of non-specific LBP exhibited few psychosocial predictors of poor outcome, unlike other patient populations that have been studied. Despite considerable bothersomeness at baseline, scores were low at follow-up. In this independent health sector back pain population, general health and duration of episode before consulting appeared more important to outcome than psychosocial factors.Recovery from persistent low back pain is determined not solely by clinical factors but also by the individual's psychological state [1]. Such psychologic
Gravothermal oscillations in two-component models of star clusters
Philip G. Breen,Douglas C. Heggie
Physics , 2011, DOI: 10.1111/j.1365-2966.2011.20036.x
Abstract: In this paper, gravothermal oscillations are investigated in two-component clusters with a range of different stellar mass ratios and total component mass ratios. The critical number of stars at which gravothermal oscillations first appeared is found using a gas code. The nature of the oscillations is investigated and it is shown that the oscillations can be understood by focusing on the behaviour of the heavier component, because of mass segregation. It is argued that, during each oscillation, the re-collapse of the cluster begins at larger radii while the core is still expanding. This re-collapse can halt and reverse a gravothermally driven expansion. This material outside the core contracts because it is losing energy both to the cool expanding core and to the material at larger radii. The core collapse times for each model are also found and discussed. For an appropriately chosen case, direct N -body runs were carried out, in order to check the results obtained from the gas model, including evidence of the gravothermal nature of the oscillations and the temperature inversion that drives the expansion.
Gravothermal oscillations in multi-component models of star clusters
Philip G. Breen,Douglas C. Heggie
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.21688.x
Abstract: In this paper, gravothermal oscillations are investigated in multi-component star clusters which have power law initial mass functions (IMF). For the power law IMFs, the minimum masses ($m_{min}$) were fixed and three different maximum stellar masses ($m_{max}$) were used along with different power-law exponents ($\alpha$) ranging from 0 to -2.35 (Salpeter). The critical number of stars at which gravothermal oscillations first appear with increasing $N$ was found using the multi-component gas code SPEDI. The total mass ($M_{tot}$) is seen to give an approximate stability condition for power law IMFs with fixed values of $m_{max}$ and $m_{min}$ independent of $\alpha$. The value $M_{tot}/m_{max} \simeq 12000$ is shown to give an approximate stability condition which is also independent of $m_{max}$, though the critical value is somewhat higher for the steepest IMF that was studied. For appropriately chosen cases, direct N-body runs were carried out in order to check the results obtained from SPEDI. Finally, evidence of the gravothermal nature of the oscillations found in the N-body runs is presented.
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