8,521 research outputs found
Galactic accretion and the outer structure of galaxies in the CDM model
We have combined the semi-analytic galaxy formation model of Guo et al.
(2011) with the particle-tagging technique of Cooper et al. (2010) to predict
galaxy surface brightness profiles in a representative sample of ~1900 massive
dark matter haloes (10^12--10^14 M_sol) from the Millennium II Lambda-CDM
N-body simulation. Here we present our method and basic results focusing on the
outer regions of galaxies, consisting of stars accreted in mergers. These
simulations cover scales from the stellar haloes of Milky Way-like galaxies to
the 'cD envelopes' of groups and clusters, and resolve low surface brightness
substructure such as tidal streams. We find that the surface density of
accreted stellar mass around the central galaxies of dark matter haloes is well
described by a Sersic profile, the radial scale and amplitude of which vary
systematically with halo mass (M_200). The total stellar mass surface density
profile breaks at the radius where accreted stars start to dominate over stars
formed in the galaxy itself. This break disappears with increasing M_200
because accreted stars contribute more of the total mass of galaxies, and is
less distinct when the same galaxies are averaged in bins of stellar mass,
because of scatter in the relation between M_star and M_200. To test our model
we have derived average stellar mass surface density profiles for massive
galaxies at z~0.08 by stacking SDSS images. Our model agrees well with these
stacked profiles and with other data from the literature, and makes predictions
that can be more rigorously tested by future surveys that extend the analysis
of the outer structure of galaxies to fainter isophotes. We conclude that it is
likely that the outer structure of the spheroidal components of galaxies is
largely determined by collisionless merging during their hierarchical assemblyComment: Accepted by MNRAS. Shortened following referee's report, conclusions
unchanged. 21 pages, 15 figure
Symposium in Celebration of the Fixed Target Program with the Tevatron
This document is an abridgement of the commemorative book prepared on the occasion of the symposium "In Celebration of the Fixed Target Program with the Tevatron" held at Fermilab on June 2, 2000. The full text with graphics contains, in addition to the material here, a section for each experiment including a "plain text" description, lists of all physics publications, lists of all degree recipients and a photo from the archives. The full text is available on the web at: http://conferences.fnal.gov/tevft/book
Adding Environmental Gas Physics to the Semi-Analytic Method for Galaxy Formation: Gravitational Heating
We present results of an attempt to include more detailed gas physics
motivated from hydrodynamical simulations within semi-analytic models (SAM) of
galaxy formation, focusing on the role that environmental effects play. The
main difference to previous SAMs is that we include 'gravitational' heating of
the intra-cluster medium (ICM) by the net surplus of gravitational potential
energy released from gas that has been stripped from infalling satellites.
Gravitational heating appears to be an efficient heating source able to prevent
cooling in environments corresponding to dark matter halos more massive than
M. The energy release by gravitational heating can
match that by AGN-feedback in massive galaxies and can exceed it in the most
massive ones. However, there is a fundamental difference in the way the two
processes operate. Gravitational heating becomes important at late times, when
the peak activity of AGNs is already over, and it is very mass dependent. This
mass dependency and time behaviour gives the right trend to recover down-sizing
in the star-formation rate of massive galaxies. Abridged...Comment: replaced by accepted version to ApJ, some sections have been dropped
and text has been added to others to include the referee's comments, several
typos have been correcte
Ground state phase diagram of 2D electrons in a high Landau level: - DMRG study
The ground state phase diagram of 2D electrons in a high Landau level (index
N=2) is studied by the density matrix renormalization group method. Pair
correlation functions are systematically calculated for various filling factors
from v=1/8 to 1/2. It is shown that the ground state phase diagram consists of
three different CDW states called stripe-phase, bubble-phase, and Wigner
crystal. The boundary between the stripe and the bubble phases is determined to
be v_c = 0.38, and that for the bubble phase and Wigner crystal is v_c = 0.24.
Each transition is of first order.Comment: 4 pages, 6 figure
Vanishing Hall Constant in the Stripe Phase of Cuprates
The Hall constant R_H is considered for the stripe structures. In order to
explain the vanishing of R_H in LNSCO at x = 1/8, we use the relation of R_H to
the Drude weight D as well as direct numerical calculation, to obtain results
within the t-J model, where the stripes are imposed via a charge potential and
a staggered magnetic field. The origin of R_H ~ 0 is related to a maximum in D
and the minimal kinetic energy in stripes with a hole filling ~ 1/2. The same
argument indicates on a possibility of R_H ~ 0 in the whole range of static
stripes for x < 1/8.Comment: RevTeX, 4 pages, 5 figure
Removal of a frameshift between the hsdM and hsdS genes of the EcoKI Type IA DNA restriction and modification system produces a new type of system and links the different families of Type I systems
The EcoKI DNA methyltransferase is a trimeric protein comprised of two modification subunits (M) and one sequence specificity subunit (S). This enzyme forms the core of the EcoKI restriction/modification (RM) enzyme. The 3ā² end of the gene encoding the M subunit overlaps by 1 nt the start of the gene for the S subunit. Translation from the two different open reading frames is translationally coupled. Mutagenesis to remove the frameshift and fuse the two subunits together produces a functional RM enzyme in vivo with the same properties as the natural EcoKI system. The fusion protein can be purified and forms an active restriction enzyme upon addition of restriction subunits and of additional M subunit. The Type I RM systems are grouped into families, IA to IE, defined by complementation, hybridization and sequence similarity. The fusion protein forms an evolutionary intermediate form lying between the Type IA family of RM enzymes and the Type IB family of RM enzymes which have the frameshift located at a different part of the gene sequence
A model for the evolution of prokaryotic DNA restriction-modification systems based upon the structural malleability of Type I restriction-modification enzymes
Restriction Modification (RM) systems prevent the invasion of foreign genetic material into bacterial cells by restriction and protect the host's genetic material by methylation. They are therefore important in maintaining the integrity of the host genome. RM systems are currently classified into four types (I to IV) on the basis of differences in composition, target recognition, cofactors and the manner in which they cleave DNA. Comparing the structures of the different types, similarities can be observed suggesting an evolutionary link between these different types. This work describes the ādeconstructionā of a large Type I RM enzyme into forms structurally similar to smaller Type II RM enzymes in an effort to elucidate the pathway taken by Nature to form these different RM enzymes. Based upon the ability to engineer new enzymes from the Type I āscaffoldā, an evolutionary pathway and the evolutionary pressures required to move along the pathway from Type I RM systems to Type II RM systems are proposed. Experiments to test the evolutionary model are discussed
Relative effectiveness of insulin pump treatment over multiple daily injections and structured education during flexible intensive insulin treatment for type 1 diabetes: cluster randomised trial (REPOSE).
ObjectiveĀ To compare the effectiveness of insulin pumps with multiple daily injections for adults with type 1 diabetes, with both groups receiving equivalent training in flexible insulin treatment.DesignĀ Pragmatic, multicentre, open label, parallel group, cluster randomised controlled trial (Relative Effectiveness of Pumps Over MDI and Structured Education (REPOSE) trial).SettingĀ Eight secondary care centres in England and Scotland.ParticipantsĀ Adults with type 1 diabetes who were willing to undertake intensive insulin treatment, with no preference for pumps or multiple daily injections. Participants were allocated a place on established group training courses that taught flexible intensive insulin treatment ("dose adjustment for normal eating," DAFNE). The course groups (the clusters) were then randomly allocated in pairs to either pump or multiple daily injections.InterventionsĀ Participants attended training in flexible insulin treatment (using insulin analogues) structured around the use of pump or injections, followed for two years.Main outcome measuresĀ The primary outcomes were a change in glycated haemoglobin (HbA1c) values (%) at two years in participants with baseline HbA1c value of ā„7.5% (58 mmol/mol), and the proportion of participants achieving an HbA1c value of <7.5%. Secondary outcomes included body weight, insulin dose, and episodes of moderate and severe hypoglycaemia. Ancillary outcomes included quality of life and treatment satisfaction.ResultsĀ 317 participants (46 courses) were randomised (156 pump and 161 injections). 267 attended courses and 260 were included in the intention to treat analysis, of which 235 (119 pump and 116 injection) had baseline HbA1c values of ā„7.5%. Glycaemic control and rates of severe hypoglycaemia improved in both groups. The mean change in HbA1c at two years was -0.85% with pump treatment and -0.42% with multiple daily injections. Adjusting for course, centre, age, sex, and accounting for missing values, the difference was -0.24% (-2.7 mmol/mol) in favour of pump users (95% confidence interval -0.53 to 0.05, P=0.10). Most psychosocial measures showed no difference, but pump users showed greater improvement in treatment satisfaction and some quality of life domains (dietary freedom and daily hassle) at 12 and 24 months.ConclusionsĀ Both groups showed clinically relevant and long lasting decreases in HbA1c, rates of severe hypoglycaemia, and improved psychological measures, although few participants achieved glucose levels currently recommended by national and international guidelines. Adding pump treatment to structured training in flexible intensive insulin treatment did not substantially enhance educational benefits on glycaemic control, hypoglycaemia, or psychosocial outcomes in adults with type 1 diabetes. These results do not support a policy of providing insulin pumps to adults with poor glycaemic control until the effects of training on participants' level of engagement in intensive self management have been determined.Trial registrationĀ Current Controlled Trials ISRCTN61215213.This research was funded by the UK Health Technology
Assessment Programme (project No 08/107/01) and will be published in
full in Health Technology Assessment. See the HTA programme website
for further project information. (http://www.nets.nihr.ac.uk/). This report
presents independent research commissioned by the National Institute
for Health Research (NIHR). We also acknowledge financial support from
the Research and Development Programmes of the Department of
Health for England and the Scottish Health and Social Care Directorates
who supported the costs of consumables, and of Medtronic UK, which
provided the insulin pumps for the trial. These funders had no
involvement in the design of the protocol; the collection, analysis, and
interpretation of the data; the writing of this paper; or the decision to
submit this article for publication. The views and opinions expressed
herein are those of the authors and do not necessarily reflect those of
the HTA, NIHR, NHS, the Department of Health, or Medtronic UK
A Comparison of Two Ovine Lumbar Intervertebral Disc Injury Models for the Evaluation and Development of Novel Regenerative Therapies
Ā© The Author(s) 2018. Study Design: Large animal research. Objective: Lumbar discectomy is the most commonly performed spinal surgical procedure. We investigated 2 large animal models of lumbar discectomy in order to study the regenerative capacity of mesenchymal stem cells following disc injury. Methods: Twelve adult ewes underwent baseline 3-T magnetic resonance imaging (MRI) followed by lumbar intervertebral disc injury by either drill bit (n = 6) or annulotomy and partial nucleotomy (APN) (n = 6). Necropsies were performed 6 months later. Lumbar spines underwent 3-T and 9.4-T MRI prior to histological, morphological and biochemical analysis. Results: Drill bit-injured (DBI) and APN-injured discs demonstrated increased Pfirrmann grades relative to uninjured controls (P <.005), with no difference between the 2 models. Disc height index loss was greater in the APN group compared with the DBI group (P <.005). Gross morphology injury scores were higher in APN than DBI discs (P <.05) and both were higher than controls (P <.005). Proteoglycan was reduced in the discs of both injury models relative to controls (P <.005), but lower in the APN group (P <.05). Total collagen of the APN group disc regions was higher than DBI and control discs (P <.05). Histology revealed more matrix degeneration, vascular infiltration, and granulation in the APN model. Conclusion: Although both models produced disc degeneration, the APN model better replicated the pathobiology of human discs postdiscectomy. We therefore concluded that the APN model was a more appropriate model for the investigation of the regenerative capacity of mesenchymal stem cells administered postdiscectomy
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