2,299 research outputs found
Neutral Evolution as Diffusion in phenotype space: reproduction with mutation but without selection
The process of `Evolutionary Diffusion', i.e. reproduction with local
mutation but without selection in a biological population, resembles standard
Diffusion in many ways. However, Evolutionary Diffusion allows the formation of
local peaks with a characteristic width that undergo drift, even in the
infinite population limit. We analytically calculate the mean peak width and
the effective random walk step size, and obtain the distribution of the peak
width which has a power law tail. We find that independent local mutations act
as a diffusion of interacting particles with increased stepsize.Comment: 4 pages, 2 figures. Paper now representative of published articl
Magnetic confinement of radiotherapy beam-dose profiles
We have used electron and photon beams from the 50 MV electron microtron at UM Hospital together with a large-bore 3.5T superconducting solenoid to demonstrate the magnetic confinement of HE electron and photon beam-dose profiles for typical radiotherapy beams. The HE electron beams in particular exhibit a large reduction in penumbra when entering a tissue-equivalent phantom and, in addition, confinement of the secondary electrons produced by the primary beam. Likewise photon beams show a similar confinement of the dose from secondary electrons. While the results resemble features predicted from Monte Carlo calculations, there are a number of anomalous details in the actual experimental data which serve to illustrate the problems associated with practical clinical implementations. However the data suggest that in certain cases HE electrons may provide a cost-effective alternate to proton or HI radiotherapy beams and, also, improve the dose profile for HE photon beams. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87615/2/44_1.pd
Resolving the inner jet structure of 1924-292 with the EVENT HORIZON TELESCOPE
We present the first 1.3 mm (230 GHz) very long baseline interferometry model
image of an AGN jet using closure phase techniques with a four-element array.
The model image of the quasar 1924-292 was obtained with four telescopes at
three observatories: the James Clerk Maxwell Telescope (JCMT) on Mauna Kea in
Hawaii, the Arizona Radio Observatory's Submillimeter Telescope (SMT) in
Arizona, and two telescopes of the Combined Array for Research in
Millimeterwave Astronomy (CARMA) in California in April 2009. With the greatly
improved resolution compared with previous observations and robust closure
phase measurement, the inner jet structure of 1924-292 was spatially resolved.
The inner jet extends to the northwest along a position angle of at
a distance of 0.38\,mas from the tentatively identified core, in agreement with
the inner jet structure inferred from lower frequencies, and making a position
angle difference of with respect to the cm-jet. The size of
the compact core is 0.15\,pc with a brightness temperature of
\,K. Compared with those measured at lower frequencies, the
low brightness temperature may argue in favor of the decelerating jet model or
particle-cascade models. The successful measurement of closure phase paves the
way for imaging and time resolving Sgr A* and nearby AGN with the Event Horizon
Telescope.Comment: 6 pages, 4 figures, accepted for publication in ApJ
Chandra Detection of a TypeII Quasar at z=3.288
We report on observations of a TypeII quasar at redshift z=3.288, identified
as a hard X-ray source in a 185 ks observation with the Chandra X-ray
Observatory and as a high-redshift photometric candidate from deep, multiband
optical imaging. CXOJ084837.9+445352 (hereinafter CXO52) shows an unusually
hard X-ray spectrum from which we infer an absorbing column density N(H) =
(4.8+/-2.1)e23 / cm2 (90% confidence) and an implied unabsorbed 2-10 keV
rest-frame luminosity of L(2-10) = 3.3e44 ergs/s, well within the quasar
regime. Hubble Space Telescope imaging shows CXO52 to be elongated with slight
morphological differences between the WFPC2 F814W and NICMOS F160W bands.
Optical and near-infrared spectroscopy of CXO52 show high-ionization emission
lines with velocity widths ~1000 km/s and flux ratios similar to a Seyfert2
galaxy or radio galaxy. The latter are the only class of high-redshift TypeII
luminous AGN which have been extensively studied to date. Unlike radio
galaxies, however, CXO52 is radio quiet, remaining undetected at radio
wavelengths to fairly deep limits, f(4.8GHz) < 40 microJy. High-redshift TypeII
quasars, expected from unification models of active galaxies and long-thought
necessary to explain the X-ray background, are poorly constrained
observationally with few such systems known. We discuss recent observations of
similar TypeII quasars and detail search techniques for such systems: namely
(1) X-ray selection, (2) radio selection, (3) multi-color imaging selection,
and (4) narrow-band imaging selection. Such studies are likely to begin
identifying luminous, high-redshift TypeII systems in large numbers. We discuss
the prospects for these studies and their implications to our understanding of
the X-ray background.Comment: 28 pages, 5 figures; to appear in The Astrophysical Journa
Intensity of Th and Pa scavenging partitioned by particle chemistry in the North Atlantic Ocean
Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Marine Chemistry 170 (2015): 49-60, doi:10.1016/j.marchem.2015.01.006.The natural radionuclides 231Pa and 230Th are incorporated into the marine sediment record by
scavenging, or adsorption to various particle types, via chemical reactions that are not fully
understood. Because these isotopes have potential value in tracing several oceanographic
processes, we investigate the nature of scavenging using trans-Atlantic measurements of
dissolved (<0.45 μm) and particulate (0.8-51 μm) 231Pa and 230Th, together with major particle
composition. We find widespread impact of intense scavenging by authigenic Fe/Mn
(hydr)oxides, in the form of hydrothermal particles emanating from the Mid-Atlantic ridge and
particles resuspended from reducing conditions near the seafloor off the coast of West Africa.
Biogenic opal was not found to be a significant scavenging phase for either element in this
sample set, essentially because of its low abundance and small dynamic range at the studied
sites. Distribution coefficients in shallow (< 200 m) depths are anomalously low which suggests
either the unexpected result of a low scavenging intensity for organic matter or that, in water
masses containing abundant organic-rich particles, a greater percentage of radionuclides exist in
the colloidal or complexed phase. In addition to particle concentration, the oceanic distribution
of particle types likely plays a significant role in the ultimate distribution of sedimentary 230Th
and 231Pa.Cruise management for GA03 was funded by the U. S. National Science Foundation to W.
Jenkins (OCE-0926423), E. Boyle (OCE-0926204), and G. Cutter (OCE-0926092). Radionuclide
studies were supported by NSF (OCE-0927064 to LDEO, OCE-0926860 to WHOI, OCE-
0927757 to URI, and OCE-0927754 to UMN). Additional support came from the European
Research Council (278705) to LFR and the Ford Foundation Predoctoral Fellowship to SMV.
Particle studies were supported by NSF OCE-0963026 to PJL
Pseudomonas aeruginosa Adaptation to Lungs of Cystic Fibrosis Patients Leads to Lowered Resistance to Phage and Protist Enemies
Pathogenic life styles can lead to highly specialized interactions with host species, potentially resulting in fitness trade-offs in other ecological contexts. Here we studied how adaptation of the environmentally transmitted bacterial pathogen, Pseudomonas aeruginosa, to cystic fibrosis (CF) patients affects its survival in the presence of natural phage (14/1, ΦKZ, PNM and PT7) and protist (Tetrahymena thermophila and Acanthamoebae polyphaga) enemies. We found that most of the bacteria isolated from relatively recently intermittently colonised patients (1-25 months), were innately phage-resistant and highly toxic for protists. In contrast, bacteria isolated from long time chronically infected patients (2-23 years), were less efficient in both resisting phages and killing protists. Moreover, chronic isolates showed reduced killing of wax moth larvae (Galleria mellonella) probably due to weaker in vitro growth and protease expression. These results suggest that P. aeruginosa long-term adaptation to CF-lungs could trade off with its survival in aquatic environmental reservoirs in the presence of microbial enemies, while lowered virulence could reduce pathogen opportunities to infect insect vectors; factors that are both likely to result in poorer environmental transmission. From an applied perspective, phage therapy could be useful against chronic P. aeruginosa lung infections that are often characterized by multidrug resistance: chronic isolates were least resistant to phages and their poor growth will likely slow down the emergence of beneficial resistance mutations
Associations between cardiorespiratory fitness, physical activity and clustered cardiometabolic risk in children and adolescents: the HAPPY study
Clustering of cardiometabolic risk factors can occur during childhood and predisposes individuals to cardiometabolic disease. This study calculated clustered cardiometabolic risk in 100 children and adolescents aged 10-14 years (59 girls) and explored differences according to cardiorespiratory fitness (CRF) levels and time spent at different physical activity (PA) intensities. CRF was determined using a maximal cycle ergometer test, and PA was assessed using accelerometry. A cardiometabolic risk score was computed as the sum of the standardised scores for waist circumference, blood pressure, total cholesterol/high-density lipoprotein ratio, triglycerides and glucose. Differences in clustered cardiometabolic risk between fit and unfit participants, according to previously proposed health-related threshold values, and between tertiles for PA subcomponents were assessed using ANCOVA. Clustered risk was significantly lower (p < 0.001) in the fit group (mean 1.21 ± 3.42) compared to the unfit group (mean -0.74 ± 2.22), while no differences existed between tertiles for any subcomponent of PA. Conclusion These findings suggest that CRF may have an important cardioprotective role in children and adolescents and highlights the importance of promoting CRF in youth
The HEARTS partner forum—supporting implementation of HEARTS to treat and control hypertension
Cardiovascular diseases (CVD), principally ischemic heart disease (IHD) and stroke, are the leading causes of death (18. 6 million deaths annually) and disability (393 million disability-adjusted life-years lost annually), worldwide. High blood pressure is the most important preventable risk factor for CVD and deaths, worldwide (10.8 million deaths annually). In 2016, the World Health Organization (WHO) and the United States Centers for Disease Control (CDC) launched the Global Hearts initiative to support governments in their quest to prevent and control CVD. HEARTS is the core technical package of the initiative and takes a public health approach to treating hypertension and other CVD risk factors at the primary health care level. The HEARTS Partner Forum, led by WHO, brings together the following 11 partner organizations: American Heart Association (AHA), Center for Chronic Disease Control (CCDC), International Society of Hypertension (ISH), International Society of Nephrology (ISN), Pan American Health Organization (PAHO), Resolve to Save Lives (RTSL), US CDC, World Hypertension League (WHL), World Heart Federation (WHF) and World Stroke Organization (WSO). The partners support countries in their implementation of the HEARTS technical package in various ways, including providing technical expertise, catalytic funding, capacity building and evidence generation and dissemination. HEARTS has demonstrated the feasibility and acceptability of a public health approach, with more than seven million people already on treatment for hypertension using a simple, algorithmic HEARTS approach. Additionally, HEARTS has demonstrated the feasibility of using hypertension as a pathfinder to universal health coverage and should be a key intervention of all basic benefit packages. The partner forum continues to find ways to expand support and reinvigorate enthusiasm and attention on preventing CVD. Proposed future HEARTS Partner Forum activities are related to more concrete information sharing between partners and among countries, expanded areas of partner synergy, support for implementation, capacity building, and advocacy with country ministries of health, professional societies, academy and civil societies organizations. Advancing toward the shared goals of the HEARTS partners will require a more formal, structured approach to the forum and include goals, targets and published reports. In this way, the HEARTS Partner Forum will mirror successful global partnerships on communicable diseases and assist countries in reducing CVD mortality and achieving global sustainable development goals (SDGs)
Microevolution of Helicobacter pylori during prolonged infection of single hosts and within families
Our understanding of basic evolutionary processes in bacteria is still very limited. For example, multiple recent dating estimates are based on a universal inter-species molecular clock rate, but that rate was calibrated using estimates of geological dates that are no longer accepted. We therefore estimated the short-term rates of mutation and recombination in Helicobacter pylori by sequencing an average of 39,300 bp in 78 gene fragments from 97 isolates. These isolates included 34 pairs of sequential samples, which were sampled at intervals of 0.25 to 10.2 years. They also included single isolates from 29 individuals (average age: 45 years) from 10 families. The accumulation of sequence diversity increased with time of separation in a clock-like manner in the sequential isolates. We used Approximate Bayesian Computation to estimate the rates of mutation, recombination, mean length of recombination tracts, and average diversity in those tracts. The estimates indicate that the short-term mutation rate is 1.4×10−6 (serial isolates) to 4.5×10−6 (family isolates) per nucleotide per year and that three times as many substitutions are introduced by recombination as by mutation. The long-term mutation rate over millennia is 5–17-fold lower, partly due to the removal of non-synonymous mutations due to purifying selection. Comparisons with the recent literature show that short-term mutation rates vary dramatically in different bacterial species and can span a range of several orders of magnitude
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