1,600 research outputs found
Pinwheel stabilization by ocular dominance segregation
We present an analytical approach for studying the coupled development of
ocular dominance and orientation preference columns. Using this approach we
demonstrate that ocular dominance segregation can induce the stabilization and
even the production of pinwheels by their crystallization in two types of
periodic lattices. Pinwheel crystallization depends on the overall dominance of
one eye over the other, a condition that is fulfilled during early cortical
development. Increasing the strength of inter-map coupling induces a transition
from pinwheel-free stripe solutions to intermediate and high pinwheel density
states.Comment: 10 pages, 4 figure
MYOD-1 in normal colonic mucosa : role as a putative biomarker?
Background
DNA methylation of promoter-associated CpG islands of certain genes may play a role in the development of colorectal cancer. The MYOD-1 gene which is a muscle differentiation gene has been showed to be significantly methylated in colorectal cancer which, is an age related event. However the role of this gene in the colonic mucosa is not understood and whether methylation occurs in subjects without colon cancer. In this study, we have determined the frequency of methylation of the MYOD-1 gene in normal colonic mucosa and investigated to see if this is associated with established colorectal cancer risk factors primarily ageing.
Results
We analysed colonic mucosal biopsies in 218 normal individuals and demonstrated that in most individuals promoter hypermethylation was not quantified for MYOD-1. However, promoter hypermethylation increased significantly with age (p < 0.001 using regression analysis) and this was gender independent. We also showed that gene promoter methylation increased positively with an increase in waist to hip (WHR) ratio – the latter is also a known risk factor for colon cancer development.
Conclusions
Our study suggests that promoter gene hypermethylation of the MYOD-1 gene increases significantly with age in normal individuals and thus may offer potential as a putative biomarker for colorectal cancer
A Quantitative Comparison of SMC, LMC, and Milky Way UV to NIR Extinction Curves
We present an exhaustive, quantitative comparison of all of the known
extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with
our understanding of the general behavior of Milky Way extinction curves. The
R_V dependent CCM relationship and the sample of extinction curves used to
derive this relationship is used to describe the general behavior of Milky Way
extinction curves. The ultraviolet portion of the SMC and LMC extinction curves
are derived from archival IUE data, except for one new SMC extinction curve
which was measured using HST/STIS observations. The optical extinction curves
are derived from new (for the SMC) and literature UBVRI photometry (for the
LMC). The near-infrared extinction curves are calculated mainly from 2MASS
photometry supplemented with DENIS and new JHK photometry. For each extinction
curve, we give R_V = A(V)/E(B-V) and N(HI) values which probe the same dust
column as the extinction curve. We compare the properties of the SMC and LMC
extinction curves with the CCM relationship three different ways: each curve by
itself, the behavior of extinction at different wavelengths with R_V, and
behavior of the extinction curve FM fit parameters with R_V. As has been found
previously, we find that a small number of LMC extinction curves are consistent
with the CCM relationship, but majority of the LMC and all of the SMC curves do
not follow the CCM relationship. For the first time, we find that the CCM
relationship seems to form a bound on the properties of all of the LMC and SMC
extinction curves. This result strengthens the picture of dust extinction
curves exhibit a continuum of properties between those found in the Milky Way
and the SMC Bar. (abridged)Comment: 18 pages, 10 figures, ApJ in pres
Real-Gas Effects and Phase Separation in Underexpanded Jets at Engine-Relevant Conditions
A numerical framework implemented in the open-source tool OpenFOAM is
presented in this work combining a hybrid, pressure-based solver with a
vapor-liquid equilibrium model based on the cubic equation of state. This
framework is used in the present work to investigate underexpanded jets at
engine-relevant conditions where real-gas effects and mixture induced phase
separation are probable to occur. A thorough validation and discussion of the
applied vapor-liquid equilibrium model is conducted by means of general
thermodynamic relations and measurement data available in the literature.
Engine-relevant simulation cases for two different fuels were defined. Analyses
of the flow field show that the used fuel has a first order effect on the
occurrence of phase separation. In the case of phase separation two different
effects could be revealed causing the single-phase instability, namely the
strong expansion and the mixing of the fuel with the chamber gas. A comparison
of single-phase and two-phase jets disclosed that the phase separation leads to
a completely different penetration depth in contrast to single-phase injection
and therefore commonly used analytical approaches fail to predict the
penetration depth.Comment: Preprint submitted to AIAA Scitech 2018, Kissimmee, Florid
Effects of Climate Change on Fluted Pumpkin Production and Adaptaton Measures Used Among Farmers in Rivers State
The importance of fluted pumpkin crop in rural household economy cannot be over emphasized. Farmers in the South South Nigeria depend greatly on fluted pumpkin for its many uses. The production however is beset with a myriad of constraints of which climate change is one of the most outstanding. The study assessed the effects of climate change and adaptation measures used by fluted pumpkin farmers in Ikwerre Local Government Area(LGA) of Rivers State, Southsouth Nigeria. Multi-stage sampling technique was used to select respondents for the study. Out of the twelve communities that make up Ikwerre LGA, six communities were randomly chosen from which one hundred and eighty fluted pumpkin farmers were proportionately selected. Interview schedule and focus group discussion were used to elicit in depth information from respondents. Data were analyzed using percentage, frequency count and mean. Tables and charts were used in presentation of data. The result of the study showed that 51 percent of the respondents were female, majority were married (77 percent) and were full time farmers (79 percent). Relatively large proportion had no formal education (42 percent) and indicated both consumption and sale (79 percent) as the major aim of production. The respondents perceived that unpredictable climate condition, changes in rainfall pattern, changes in rainfall distribution, reduced yield of fluted pumpkin and reduction of family income were the major effects of climate change on fluted pumpkin production. A combination of fluted pumpkin production with other income generating activities was shown to be the most widely used adaptation strategy by respondents. Based on the results of the study it was recommended that improved extension services that can provide the needed farming inputs (fluted pumpkin seedlings, fertilizers e.t.c) as well as useful and relevant information on climate change and adaptation strategies should be made available to the people
Effects of Climate Change on Fluted Pumpkin Production and Adaptaton Measures Used Among Farmers in Rivers State
The importance of fluted pumpkin crop in rural household economy cannot be over emphasized. Farmers in the South South Nigeria depend greatly on fluted pumpkin for its many uses. The production however is beset with a myriad of constraints of which climate change is one of the most outstanding. The study assessed the effects of climate change and adaptation measures used by fluted pumpkin farmers in Ikwerre Local Government Area(LGA) of Rivers State, Southsouth Nigeria. Multi-stage sampling technique was used to select respondents for the study. Out of the twelve communities that make up Ikwerre LGA, six communities were randomly chosen from which one hundred and eighty fluted pumpkin farmers were proportionately selected. Interview schedule and focus group discussion were used to elicit in depth information from respondents. Data were analyzed using percentage, frequency count and mean. Tables and charts were used in presentation of data. The result of the study showed that 51 percent of the respondents were female, majority were married (77 percent) and were full time farmers (79 percent). Relatively large proportion had no formal education (42 percent) and indicated both consumption and sale (79 percent) as the major aim of production. The respondents perceived that unpredictable climate condition, changes in rainfall pattern, changes in rainfall distribution, reduced yield of fluted pumpkin and reduction of family income were the major effects of climate change on fluted pumpkin production. A combination of fluted pumpkin production with other income generating activities was shown to be the most widely used adaptation strategy by respondents. Based on the results of the study it was recommended that improved extension services that can provide the needed farming inputs (fluted pumpkin seedlings, fertilizers e.t.c) as well as useful and relevant information on climate change and adaptation strategies should be made available to the people
Permeating the social justice ideals of equality and equity within the context of Early Years: challenges for leadership in multi-cultural and mono-cultural primary schools
The ideology and commitment of social justice principles is central to Early Years practice, however, the term social justice in education is complex and remains contested. This paper explores the ideology of social justice through links between equality and equity and how it is embedded within Early Years, and what remain the potential challenges for leadership. Interviews in English multi-cultural and mono-cultural primary schools were conducted. Findings showed that the ideology of social justice, equality and equity was interpreted differently. Multi-cultural schools appear to use a greater variety of activities to embed social justice principles that involved their diverse communities more to enrich the curriculum. In mono-cultural schools leadership had to be more creative in promoting equality and equity given the smaller proportion of their diverse pupil and staff population. Tentative conclusions suggest that the vision for permeating equality and equity in Early Years, at best, is at early stages
The linewidth-size relationship in the dense ISM of the Central Molecular Zone
The linewidth (sigma) - size (R) relationship has been extensively measured
and analysed, in both the local ISM and in nearby normal galaxies. Generally, a
power-law describes the relationship well with an index ranging from 0.2-0.6,
now referred to as one of "Larson's Relationships." The nature of turbulence
and star formation is considered to be intimately related to these
relationships, so evaluating the sigma-R correlations in various environments
is important for developing a comprehensive understanding of the ISM. We
measure the sigma-R relationship in the Central Molecular Zone (CMZ) of the
Galactic Centre using spectral line observations of the high density tracers
N2H+, HCN, H13CN, and HCO+. We use dendrograms, which map the hierarchical
nature of the position-position-velocity (PPV) data, to compute sigma and R of
contiguous structures. The dispersions range from ~2-30 km/s in structures
spanning sizes 2-40 pc, respectively. By performing Bayesian inference, we show
that a power-law with exponent 0.3-1.1 can reasonably describe the sigma-R
trend. We demonstrate that the derived sigma-R relationship is independent of
the locations in the PPV dataset where sigma and R are measured. The uniformity
in the sigma-R relationship suggests turbulence in the CMZ is driven on the
large scales beyond >30 pc. We compare the CMZ sigma-R relationship to that
measured in the Galactic molecular cloud Perseus. The exponents between the two
systems are similar, suggestive of a connection between the turbulent
properties within a cloud to its ambient medium. Yet, the velocity dispersion
in the CMZ is systematically higher, resulting in a coefficient that is nearly
five times larger. The systematic enhancement of turbulent velocities may be
due to the combined effects of increased star formation activity, larger
densities, and higher pressures relative to the local ISM.Comment: 11 pages, 8 figures, Accepted for publication in MNRA
H-AMR: A New GPU-accelerated GRMHD Code for Exascale Computing With 3D Adaptive Mesh Refinement and Local Adaptive Time-stepping
General-relativistic magnetohydrodynamic (GRMHD) simulations have
revolutionized our understanding of black-hole accretion. Here, we present a
GPU-accelerated GRMHD code H-AMR with multi-faceted optimizations that,
collectively, accelerate computation by 2-5 orders of magnitude for a wide
range of applications. Firstly, it involves a novel implementation of a
spherical-polar grid with 3D adaptive mesh refinement that operates in each of
the 3 dimensions independently. This allows us to circumvent the Courant
condition near the polar singularity, which otherwise cripples high-res
computational performance. Secondly, we demonstrate that local adaptive
time-stepping (LAT) on a logarithmic spherical-polar grid accelerates
computation by a factor of compared to traditional hierarchical
time-stepping approaches. Jointly, these unique features lead to an effective
speed of zone-cycles-per-second-per-node on 5,400 NVIDIA V100 GPUs
(i.e., 900 nodes of the OLCF Summit supercomputer). We demonstrate its
computational performance by presenting the first GRMHD simulation of a tilted
thin accretion disk threaded by a toroidal magnetic field around a rapidly
spinning black hole. With an effective resolution of
,,, cells, and a total of billion
cells and timesteps, it is among the largest astrophysical
simulations ever performed. We find that frame-dragging by the black hole tears
up the disk into two independently precessing sub-disks. The innermost sub-disk
rotation axis intermittently aligns with the black hole spin, demonstrating for
the first time that such long-sought alignment is possible in the absence of
large-scale poloidal magnetic fields.Comment: 10 pages, 5 figures, submitted to MNRAS, for the YouTube playlist,
see https://youtu.be/rIOjKUfzcv
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