853 research outputs found
The self-assembly of DNA Holliday junctions studied with a minimal model
In this paper, we explore the feasibility of using coarse-grained models to
simulate the self-assembly of DNA nanostructures. We introduce a simple model
of DNA where each nucleotide is represented by two interaction sites
corresponding to the phosphate-sugar backbone and the base. Using this model,
we are able to simulate the self-assembly of both DNA duplexes and Holliday
junctions from single-stranded DNA. We find that assembly is most successful in
the temperature window below the melting temperatures of the target structure
and above the melting temperature of misbonded aggregates. Furthermore, in the
case of the Holliday junction, we show how a hierarchical assembly mechanism
reduces the possibility of becoming trapped in misbonded configurations. The
model is also able to reproduce the relative melting temperatures of different
structures accurately, and allows strand displacement to occur.Comment: 13 pages, 14 figure
Chandra X-ray Sources in the Collapsed-Core Globular Cluster M30 (NGC 7099)
We report the detection of six discrete, low-luminosity (Lx < 10^33 erg/s)
X-ray sources, located within 12 arcsec of the center of the collapsed-core
globular cluster M30 (NGC 7099), and a total of 13 sources within the half-mass
radius, from a 50 ksec Chandra ACIS-S exposure. Three sources lie within the
very small upper limit of 1.9 arcsec on the core radius. The brightest of the
three core sources has a luminosity of Lx (0.5-6 keV) = 6x10^32 erg/s and a
blackbody-like soft X-ray spectrum, which are both consistent with it being a
quiescent low-mass X-ray binary (qLMXB). We have identified optical
counterparts to four of the six central sources and a number of the outlying
sources, using deep Hubble Space Telescope and ground-based imaging. While the
two proposed counterparts that lie within the core may represent chance
superpositions, the two identified central sources that lie outside of the core
have X-ray and optical properties consistent with being CVs. Two additional
sources outside of the core have possible active binary counterparts. We
discuss the X-ray source population of M30 in light of its collapsed-core
status.Comment: 18 pages, 13 figures (8 color), resubmitted to ApJ after
incorporating referee comment
Circadian Rhythms in Resting Metabolic Rate Account for Apparent Daily Rhythms in the Thermic Effect of Food
Acknowledgments We would like to thank Barbara Fielding, Adam Collins, Hayriye Biyikoglu, Alice Brealy, and Paul Jefcoate as well as all the staff at the Surrey Clinical Research Facility for their assistance in running this study. We would also like to thank Graham Horgan from Biomathematics and Statistics Scotland, for input on the modeling and statistical analysis. Financial Support: This study was funded by the Medical Research Council (grant No. MR/P012205/1, The Big Breakfast Study). A.M.J. and P.J.M. acknowledge funding support from the Scottish Government, Rural and Environment Science and Analytical Services Division.Peer reviewedPublisher PD
Stellar Variability in the Globular Cluster Terzan 5
We present the results of a search for variability in and near the core of
the metal-rich, obscured globular cluster Terzan 5, using NICMOS on HST. This
extreme cluster has approximately solar metallicity and a central density that
places it in the upper few percent of all clusters. It is estimated to have the
highest interaction rate of any galactic globular cluster. The large extinction
towards Terzan 5 and the severe stellar crowding near the cluster center
present a substantial observational challenge. Using time series analysis we
discovered two variable stars in this cluster. The first is a RRab Lyrae
variable with a period of ~0.61 days, a longer period than that of field stars
with similar high metallicities. This period is, however, shorter than the
average periods of RR Lyraes found in the metal-rich globular clusters NGC
6441, NGC 6388 and 47 Tuc. The second variable is a blue star with a 7-hour
period sinusoidal variation and a likely orbital period of 14 hours. This star
is probably an eclipsing blue straggler, or (less likely) the infrared
counterpart to the low mass X-ray binary known in Terzan 5. Due to the extreme
crowding and overlapping Airy profile of the IR PSF, we fall short of our
original goal of detecting CVs via Palpha emission and detecting variable
infrared emission from the location of the binary MSP in Terzan 5.Comment: 17 pages including 12 figures. Accepted for publication in Ap
Modelling multiscale aspects of colorectal cancer
Colorectal cancer (CRC) is responsible for nearly half a million deaths annually world-wide [11]. We present a series of mathematical models describing the dynamics of the intestinal epithelium and the kinetics of the molecular pathway most commonly mutated in CRC, the Wnt signalling network. We also discuss how we are coupling such models to build a multiscale model of normal and aberrant guts. This will enable us to combine disparate experimental and clinical data, to investigate interactions between phenomena taking place at different levels of organisation and, eventually, to test the efficacy of new drugs on the system as a whole
HST-NICMOS Observations of Terzan 5: Stellar Content and Structure of the Core
We report results from HST-NICMOS imaging of the extremely dense core of the
globular cluster Terzan 5. This highly obscured bulge cluster has been
estimated to have one of the highest collision rates of any galactic globular
cluster, making its core a particularly conducive environment for the
production of interacting binary systems. We have reconstructed high-resolution
images of the central 19"x19" region of Terzan 5 by application of the drizzle
algorithm to dithered NIC2 images in the F110W, F187W, and F187N near-infrared
filters. We have used a DAOPHOT/ALLSTAR analysis of these images to produce the
deepest color-magnitude diagram (CMD) yet obtained for the core of Terzan 5. We
have also analyzed the parallel 11"X11" NIC1 field, centered 30" from the
cluster center and imaged in F110W and F160W, and an additional NIC2 field that
is immediately adjacent to the central field. This imaging results in a clean
detection of the red-giant branch and horizontal branch in the central NIC2
field, and the detection of these plus the main-sequence turnoff and the upper
main sequence in the NIC1 field. We have constructed an H versus J-H CMD for
the NIC1 field. We obtain a new distance estimate of 8.7 kpc, which places
Terzan 5 within less than 1 kpc of the galactic center. We have also determined
a central surface-density profile which results in a maximum likelihood
estimate of 7.9" +/- 0.6" for the cluster core radius. We discuss the
implications of these results for the dynamical state of Terzan 5.Comment: 17 pages, 9 figures, accepted for publication in ApJ, for May 20,
200
Regulation of pituitary MT1 melatonin receptor expression by gonadotrophin-releasing hormone (GnRH) and early growth response factor-1 (Egr-1) : in vivo and in vitro studies
Copyright: © 2014 Bae et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was funded by the UK Biotechnology and Biological Sciences Research Council (BBSRC; grant BB/F020309/1; http://www.bbsrc.ac.uk/home/home.aspx). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD
Unacylated ghrelin, leptin, and appetite display diurnal rhythmicity in lean adults
Constant routine and forced desynchrony protocols typically remove the effects of behavioral/environmental cues to examine endogenous circadian rhythms, yet this may not reflect rhythms of appetite regulation in the real world. It is therefore important to understand these rhythms within the same subjects under controlled diurnal conditions of light, sleep, and feeding. Ten healthy adults (9âM/1 F, means ±SD: age, 30â±â10âyr; body mass index, 24.1â±â2.7âkg·m-2) rested supine in the laboratory for 37âh. All data were collected during the final 24âh of this period (i.e., 0800-0800 h). Participants were fed hourly isocaloric liquid meal replacements alongside appetite assessments during waking before a sleep opportunity from 2200 to 0700 h. Hourly blood samples were collected throughout the 24-h period. Dim light melatonin onset occurred at 2318 ± 46 min. A diurnal rhythm in mean plasma unacylated ghrelin concentration was identified (P = 0.04), with the acrophase occurring shortly after waking (0819), falling to a nadir in the evening with a relative amplitude of 9%. Plasma leptin concentration also exhibited a diurnal rhythm (P < 0.01), with the acrophase occurring shortly after lights-out (0032 h) and the lowest concentrations at midday. The amplitude for this rhythm was 25%. Diurnal rhythms were established in all dimensions of appetite except for sweet preference (P = 0.29), with both hunger (2103 h) and prospective food consumption (1955 h) reaching their peak in the evening before falling to their nadir shortly after waking. Under controlled diurnal conditions, simultaneous measurement of leptin, unacylated ghrelin, and subjective appetite over a 24-h period revealed rhythmicity in appetite regulation in lean, healthy humans.NEW & NOTEWORTHY Simultaneous assessment of subjective appetite, unacylated ghrelin, and leptin was carried out over a continuous 37-h protocol for the first time under conditions of controlled light, sleep, and feeding in healthy, lean adults. Rhythms were observed in unacylated ghrelin, leptin, and components of subjective appetite, such as hunger, prospective consumption, and fullness. Concurrent measurement of rhythms in these variables is important to fully understand the temporal relationships between components of appetite as well as the influence of diurnal factors such as sleep, light, and feeding
Discovery of Two Gravitationally Lensed Quasars with Image Separations of 3 Arcseconds from the Sloan Digital Sky Survey
We report the discovery of two doubly-imaged quasars, SDSS
J100128.61+502756.9 and SDSS J120629.65+433217.6, at redshifts of 1.838 and
1.789 and with image separations of 2.86'' and 2.90'', respectively. The
objects were selected as lens candidates from the Sloan Digital Sky Survey
(SDSS). Based on the identical nature of the spectra of the two quasars in each
pair and the identification of the lens galaxies, we conclude that the objects
are gravitational lenses. The lenses are complicated; in both systems there are
several galaxies in the fields very close to the quasars, in addition to the
lens galaxies themselves. The lens modeling implies that these nearby galaxies
contribute significantly to the lens potentials. On larger scales, we have
detected an enhancement in the galaxy density near SDSS J100128.61+502756.9.
The number of lenses with image separation of ~3'' in the SDSS already exceeds
the prediction of simple theoretical models based on the standard
Lambda-dominated cosmology and observed velocity function of galaxies.Comment: 24 pages, 9 figures, accepted for publication in Ap
Unravelling the Structure of Magnus' Pink Salt
A combination of multinuclear ultra-wideline solid-state NMR, powder X-ray diffraction (pXRD), X-ray absorption fine structure experiments, and first principles calculations of platinum magnetic shielding tensors has been employed to reveal the previously unknown crystal structure of Magnusâ pink salt (MPS), [Pt(NH3)4][PtCl4], study the isomeric Magnusâ green salt (MGS), [Pt(NH3)4][PtCl4], and examine their synthetic precursors K2PtCl4 and Pt(NH3)4Cl2·H2O. A simple synthesis of MPS is detailed which produces relatively pure product in good yield. Broad 195Pt, 14N, and 35Cl SSNMR powder patterns have been acquired using the WURST-CPMG and BRAIN-CP/WURST-CPMG pulse sequences. Experimentally measured and theoretically calculated platinum magnetic shielding tensors are shown to be very sensitive to the types and arrangements of coordinating ligands as well as intermolecular PtâPt metallophilic interactions. High-resolution 195Pt NMR spectra of select regions of the broad 195Pt powder patterns, in conjunction with an array of 14N and 35Cl spectra, reveal clear structural differences between all compounds. Rietveld refinements of synchrotron pXRD patterns, guided by first principles geometry optimization calculations, yield the space group, unit cell parameters, and atomic positions of MPS. The crystal structure has P-1 symmetry and resides in a pseudotetragonal unit cell with a distance of >5.5 Ă
between Pt sites in the square-planar Pt units. The long PtâPt distances and nonparallel orientation of Pt square planes prohibit metallophilic interactions within MPS. The combination of ultra-wideline NMR, pXRD, and computational methods offers much promise for future investigation and characterization of Pt-containing systems
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