18,249 research outputs found
A faint extended cluster in the outskirts of NGC 5128: evidence of a low mass accretion
We report the discovery of an extended globular cluster in a halo field in
Centaurus A (NGC 5128), situated \sim 38\kpc from the centre of that galaxy,
imaged with the Advanced Camera for Surveys on board the Hubble Space
Telescope. At the distance of the galaxy, the half-light radius of the cluster
is r_h ~ 17pc, placing it among the largest globular clusters known. The faint
absolute magnitude of the star cluster, M_(V,o)=-5.2, and its large size render
this object somewhat different from the population of extended globular
clusters previously reported, making it the first firm detection in the
outskirts of a giant galaxy of an analogue of the faint, diffuse globular
clusters present in the outer halo of the Milky Way. The colour-magnitude
diagram of the cluster, covering approximately the brightest four magnitudes of
the red giant branch, is consistent with an ancient, i.e., older than ~8 Gyr,
intermediate-metallicity, i.e., [M/H] ~-1.0 dex, stellar population. We also
report the detection of a second, even fainter cluster candidate which would
have r_h ~ 9pc, and M_(V,o)=-3.4 if it is at the distance of NGC 5128. The
properties of the extended globular cluster and the diffuse stellar populations
in its close vicinity suggest that they are part of a low mass accretion in the
outer regions of NGC 5128.Comment: 9 pages, MNRAS, in pres
Measurements of PAN, alkyl nitrates, ozone, and hydrocarbons during spring in interior Alaska
Measurements of the atmospheric mixing ratios of ozone, peroxyacetylnitrate (PAN), hydrocarbons, and alkyl nitrates were made in a boreal forest ecosystem in the interior of Alaska from March 15 to May 14, 1993. During this period the mixing ratios of PAN, alkyl nitrates, and nonmethane hydrocarbons (NMHCs) generally decreased due to the influence of both meteorology and OH removal. Mean mixing ratios of ozone, PAN, C2 ‐ C6 alkyl nitrates, and total C2 ‐ C5 NMHC during southerly flow periods were 24.4 parts per billion (ppbv), 132.1 parts per trillion (pptv ), 34 pptv, and 8.2 ppbCv, respectively. During a short period of northerly flow, mixing ratios of PAN and total NMHC were approximately 2 times the southerly flow mixing ratios. PAN is correlated with ozone, and alkyl nitrates are correlated with alkanes. PAN and ozone mixing ratios exhibit similar diurnal variations on a number of days with an early morning minimum and afternoon maximum. This is likely due to a diurnal cycle in the boundary layer ‐ free troposphere exchange and loss processes in the boundary layer for both O3 and PAN. Higher molecular weight (mw) hydrocarbons and alkyl nitrates are observed to decrease more quickly than the lower mw hydrocarbons, consistent with removal by OH as the primary loss process
Investigations into the potential anticancer activity of Maximin H5
Here we report the first major example of anionic amphibian host defence peptides (HDPs) with anticancer activity. Maximin H5 is a C-terminally amidated, anionic host defence peptide (MH5N) from toads of the Bombina genus, which was shown to possess activity against the glioma cell line, T98G (EC50 = 125 μM). The peptide adopted high levels of α-helical structure (57.3%) in the presence of model cancer membranes (DMPC:DMPS in a molar ratio of 10:1). MH5N also showed a strong ability to penetrate these model membranes (Π = 10.5 mN m-1), which correlated with levels of DMPS (R2 > 0.98). Taken with the high ability of the peptide to lyse these membranes (65.7%), it is proposed that maximin H5 kills cancer cells via membranolytic mechanisms that are promoted by anionic lipid. It was also found that C-terminally deaminated maximin H5 (MH5C) exhibited lower levels of α-helical structure in the presence of cancer membrane mimics (44.8%) along with a reduced ability to penetrate these membranes (Π = 8.1 mN m-1) and induce their lysis (56.6%). These data suggested that the two terminal amide groups of native maximin H5 are required for its optimal membranolytic and anticancer activity
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Observations of ozone and related species in the northeast Pacific during the PHOBEA campaigns 2. Airborne observations
During late March and April of 1999 the University of Wyoming's King Air research aircraft measured atmospheric concentrations of NO, O3, peroxyacetyl nitrate (PAN), CO, CH4, VOCs, aerosols, and J(NO2) off the west coast of the United States. During 14 flights, measurements were made between 39°-48° N latitude, 125°-129° W longitude, and at altitudes from 0-8 km. These flights were part of the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOBEA) experiment, which included both ground-based and airborne measurements. Flights were scheduled when meteorological conditions minimized the impact of local pollution sources. The resulting measurements were segregated by air mass source region as indicated by back isentropic trajectory analysis. The chemical composition of marine air masses whose 5-day back isentropic trajectories originated north of 40° N latitude or west of 180° W longitude (WNW) differed significantly from marine air masses whose 5-day back isentropic trajectories originated south of 40° N latitude and east of 180° W longitude (SW). Trajectory and chemical analyses indicated that the majority of all encountered air masses, both WNW and SW, likely originated from the northwestern Pacific and have characteristics of emissions from the East Asian continental region. However, air masses with WNW back trajectories contained higher mixing ratios of NO, NOx, O3, PAN, CO, CH4, various VOC pollution tracers, and aerosol number concentration, compared to those air masses with SW back trajectories. Calculations of air mass age using two separate methods, photochemical and back trajectory, are consistent with transport from the northwestern Pacific in 8-10 days for air masses with WNW back trajectories and 16-20 days for air masses with SW back trajectories. Correlations, trajectory analysis, and comparisons with measurements made in the northwestern Pacific during NASA's Pacific Exploritory Mission-West Phase B (PEM-West B) experiment in 1994 are used to investigate the data. These analyses provide evidence that anthropogenically influenced air masses from the northwestern Pacific affect the overall chemical composition of the northeastern Pacific troposphere. Copyright 2001 by the American Geophysical Union
Investigation of hydrophobic moment and hydrophobicity properties for transmembrane α-helices
Integral membrane proteins are the primary targets of novel drugs but are largely without solved structures. As a consequence, hydrophobic moment plot methodology is often used to identify putative transmembrane α-helices of integral membrane proteins, based on their local maximum mean hydrophobic moment (<μH>) and the corresponding mean hydrophobicity (<H>). To calculate these properties, the methodology identifies an optimal eleven residue window (L = 11), assuming an amino acid angular frequency, θ, fixed at 100°. Using a data set of 403 transmembrane α-helix forming sequences, the relationship between <μH> and <H>, and the effect of varying of L and / or θ on this relationship, was investigated. Confidence intervals for correlations between <μH> and <H> are established. It is shown, using bootstrapping procedures that the strongest statistically significant correlations exist for small windows where 7 ≤ L ≤ 16. Monte Carlo analysis suggests that this correlation is dependent upon amino acid residue primary structure, implying biological function and indicating that smaller values of L give better characterisation of transmembrane sequences using <μH>. However, varying window size can also lead to different regions within a given sequence being identified as the optimal window for structure / function predictions. Furthermore, it is shown that optimal periodicity varies with window size; the optimum, based on <μH> over the range of window sizes, (7 ≤ L ≤ 16), was at θ = 102° for the transmembrane α-helix data set
The Chemical Enrichment History of the Small Magellanic Cloud and Its Gradients
We present stellar metallicities derived from Ca II triplet spectroscopy in
over 350 red giant branch stars in 13 fields distributed in different positions
in the SMC, ranging from 1\arcdeg\@ to 4\arcdeg\@ from its center.
In the innermost fields the average metallicity is [Fe/H] . This value
decreases when we move away towards outermost regions. This is the first
detection of a metallicity gradient in this galaxy. We show that the
metallicity gradient is related to an age gradient, in the sense that more
metal-rich stars, which are also younger, are concentrated in the central
regions of the galaxy.Comment: 30 pages, 13 figures, accepted for publication in Astronomical
Journa
Establishing comprehensive oral assessments for children with safeguarding concerns.
The dental profession is well placed to contribute important information in child protection cases but no previous research has been reported that assesses the volume or impact of this information. Comprehensive oral assessment clinics were introduced and established as an integral part of comprehensive medical assessments for children with welfare concerns in Greater Glasgow and Clyde. An assessment protocol and standardised paperwork for comprehensive oral assessments were developed to enhance information sharing and patient access to appropriate care. Two cases are presented and discussed to demonstrate the value of dental input
Origin of the unusually low nitrogen abundances in young populations of the Large Magellanic Cloud
It is a longstanding problem that HII regions and very young stellar
populations in the Large Magellanic Cloud (LMC) have the nitrogen abundances
([N/H]) by a factor of ~7 lower than the solar value. We here discuss a new
scenario in which the observed unusually low nitrogen abundances can be closely
associated with recent collision and subsequent accretion of HI high velocity
clouds (HVCs) that surround the Galaxy and have low nitrogen abundances. We
show that if the observed low [N/H] is limited to very young stars with ages
less than ~10^7 yr, then the collision/accretion rate of the HVCs onto the LMC
needs to be ~ 0.2 M_sun/yr (corresponding to the total HVC mass of 10^6-10^7
M_sun) to dilute the original interstellar medium (ISM) before star formation.
The required accretion rate means that even if the typical mass of HVCs
accreted onto the LMC is ~ 10^7 M_sun, the Galaxy needs to have ~2500 massive
HVCs within the LMC's orbital radius with respect to the Galactic center. The
required rather large number of massive HVCs drives us to suggest that the HVCs
are not likely to efficiently dilute the ISM of the LMC and consequently lower
the [N/H]. We thus suggest the transfer of gas with low [N/H] from the Small
Magellanic Cloud (SMC) to the LMC as a promising scenario that can explain the
observed low [N/H].Comment: 24pages, 6 figures, accepted in Ap
Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. I. Abundances and Velocities for a Sample of Clusters
We have obtained near-infrared spectra covering the Ca II triplet lines for a
number of stars associated with 16 SMC clusters using the VLT + FORS2. These
data compose the largest available sample of SMC clusters with
spectroscopically derived abundances and velocities. Our clusters span a wide
range of ages and provide good areal coverage of the galaxy. Cluster members
are selected using a combination of their positions relative to the cluster
center as well as their abundances and radial velocities. We determine mean
cluster velocities to typically 2.7 km/s and metallicities to 0.05 dex (random
errors), from an average of 6.4 members per cluster. (continued in paper)Comment: 68 pages, 15 figures, Accepted to AJ Reason for the replacement:
section 7 and fig. 9 have been modified according referee suggestion
Age and Mass for 920 LMC Clusters Derived from 100 Million Monte Carlo Simulations
We present new age and mass estimates for 920 stellar clusters in the Large
Magellanic Cloud (LMC) based on previously published broad-band photometry and
the stellar cluster analysis package, MASSCLEANage. Expressed in the generic
fitting formula, d^{2}N/dM dt ~ M^{\alpha} t^{\beta}, the distribution of
observed clusters is described by \alpha = -1.5 to -1.6 and \beta = -2.1 to
-2.2. For 288 of these clusters, ages have recently been determined based on
stellar photometric color-magnitude diagrams, allowing us to gauge the
confidence of our ages. The results look very promising, opening up the
possibility that this sample of 920 clusters, with reliable and consistent age,
mass and photometric measures, might be used to constrain important
characteristics about the stellar cluster population in the LMC. We also
investigate a traditional age determination method that uses a \chi^2
minimization routine to fit observed cluster colors to standard infinite mass
limit simple stellar population models. This reveals serious defects in the
derived cluster age distribution using this method. The traditional \chi^2
minimization method, due to the variation of U,B,V,R colors, will always
produce an overdensity of younger and older clusters, with an underdensity of
clusters in the log(age/yr)=[7.0,7.5] range. Finally, we present a unique
simulation aimed at illustrating and constraining the fading limit in observed
cluster distributions that includes the complex effects of stochastic
variations in the observed properties of stellar clusters.Comment: Accepted for publication in The Astrophysical Journal, 37 pages, 18
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