5,050 research outputs found
Abundance analyses of helium-rich subluminous B stars
The connection between helium-rich hot subdwarfs of spectral types O and B
(He-sdB) has been relatively unexplored since the latter were found in
significant numbers in the 1980's. In order to explore this connection further,
we have analysed the surface composition of six He-sdB stars, including LB
1766, LB 3229, SB 21 (= Ton-S 137 = BPS 29503-0009), BPS 22940-0009, BPS
29496-0010, and BPS 22956-0094. Opacity-sampled line-blanketed model
atmospheres have been used to derive atmospheric properties and elemental
abundances. All the stars are moderately metal-poor compared with the Sun
([Fe/H] ~ -0.5). Four stars are nitrogen-rich, two of these are carbon-rich,
and at least four appear to be neon-rich. The data are insufficient to rule out
binarity in any of the sample. The surface composition and locus of the N-rich
He-sdBs are currently best explained by the merger of two helium white dwarfs,
or possibly by the merger of a helium white dwarf with a post-sdB white dwarf.
C-rich He-sdBs require further investigation.Comment: Accepted 2010 July
Beta cell differentiation status in Type 2 Diabetes
Type 2 Diabetes (T2D) affects over 415 million people globally and is characterised by cellular stresses including: poor glucose homeostasis, dyslipidaemia, inflammation, hypoxia and ER stress. Studies in mice have shown that exposure to these stresses influences beta cell differentiation status as well as cell survival and may explain the extent of beta cell mass loss that is seen in the disease. To date, studies of altered beta cell differentiation have largely been confined to murine models. I used the EndoC-H1 human beta cell line, along with human pancreatic tissue sections, to better characterise this mechanism in human disease. To elucidate these mechanisms, I firstly established a humanised version of cell culture techniques for the EndoC Ī²H1 cell model and assessed the influence on cell function. Secondly, I evaluated the effects of the diabetic microenvironment on beta cell differentiation and gene expression patterns. Finally, I investigated whether a diabetomimetic microenvironment induced differences in microRNA regulation in the cells. I found that the humanised EndoC-Ī²H1 culture techniques improved glucose sensitive insulin release in the cell model. EndoC-Ī²H1 cells exposed to a Diabetic microenvironment showed some degree of transdifferentiation and this may be due to dysregulation of splicing factor expression. These effects may be compounded by altered microRNA regulation in response to these cell stresses. These data suggest that altered gene regulation caused by a diabetic microenvironment may alter gene regulation to produce a reversible delta-like phenotype in human beta cells
Grid Cells Form a Global Representation of Connected Environments.
The firing patterns of grid cells in medial entorhinal cortex (mEC) and associated brain areas form triangular arrays that tessellate the environment [1, 2] and maintain constant spatial offsets to each other between environments [3, 4]. These cells are thought to provide an efficient metric for navigation in large-scale space [5-8]. However, an accurate and universal metric requires grid cell firing patterns to uniformly cover the space to be navigated, in contrast to recent demonstrations that environmental features such asĀ boundaries can distort [9-11] and fragment [12] gridĀ patterns. To establish whether grid firing is determined by local environmental cues, or provides a coherent global representation, we recorded mEC grid cells in rats foraging in an environment containing two perceptually identical compartments connected via a corridor. During initial exposures to the multicompartment environment, grid firing patterns were dominated by local environmental cues, replicating between the two compartments. However, with prolonged experience, grid cell firing patterns formed a single, continuous representation that spanned both compartments. Thus, we provide the first evidence that in a complex environment, grid cell firing can form the coherent global pattern necessary for them to act as a metric capable of supporting large-scale spatial navigation
On the binary helium star DY Centauri: Chemical composition and evolutionary state
DY Cen has shown a steady fading of its visual light by about 1 magnitude in
the last 40 years suggesting a secular increase in its effective temperature.
We have conducted non-LTE and LTE abundance analyses to determine the star's
effective temperature, surface gravity, and chemical composition using
high-resolution spectra obtained over two decades. The derived stellar
parameters for three epochs suggest that DY Cen has evolved at a constant
luminosity and has become hotter by about 5000 K in 23 years. We show that the
derived abundances remain unchanged for the three epochs. The derived
abundances of the key elements, including F and Ne, are as observed for the
extreme helium stars resulting from a merger of an He white dwarf with a C-O
white dwarf. Thus, DY Cen by chemical composition appears to be also a product
of a merger of two white dwarfs. This appearance seems to be at odds with the
recent suggestion that DY Cen is a single-lined spectroscopic binary.Comment: Accepted to ApJ with 8 Figures and 5 Table
Cultural Customization: An Analysis Of Chinese And Spanish B2C Web Sites
The following paper analyzes the trends in e-commerce, the variations among global e-consumers, and in turn, the imperative for cultural customization of business-to-consumer web sites. A literature review delves into past research done in the field of cultural customization as well as the dimensions and values that distinguish cultures from one another. Furthermore, ten (10) Chinese and ten (10) Spanish B2C web sites from the service, retail and manufacturing sectors are analyzed to view the extent of their cultural customization. The findings conclude that none of the B2C web sites viewed were truly culturally customized, but that there exist advantages for businesses to take the initiative and put forth resources into achieving said status for their respective web sites
On the angular momentum evolution of merged white dwarfs
We study the angular momentum evolution of binaries containing two white
dwarfs which merge and become cool helium-rich supergiants. Our object is to
compare predicted rotation velocities with observations of highly evolved stars
believed to have formed from such a merger, including RCrB and extreme helium
stars. The principal study involves a binary containing a 0.6 solar mass CO
white dwarf, and a 0.3 solar mass He white dwarf. The initial condition for the
angular momentum distribution is defined where the secondary fills its Roche
Lobe. We assume conservation of angular momentum to compute the angular
momentum distribution in a collisionless disk and subsequently in the giant
envelope. At the end of shell-helium burning, the giant contracts to form a
white dwarf. We derive the surface rotation velocity during this contraction.
The calculation is repeated for a range of initial mass ratios, and also for
the case of mergers between two helium white dwarfs; the latter will contract
to the helium main-sequence rather than the white dwarf sequence. Assuming
complete conservation of angular momentum, we predict acceptable angular
rotation rates for cool giants and during the initial subsequent contraction.
However such stars will only survive spin-up to reach the white dwarf sequence
(CO+He merger) if the initial mass ratio is close to unity. He+He merger
products must lose angular momentum in order to reach the helium main sequence.
Minimum observed rotation velocities in extreme helium stars are lower than our
predictions by at least one half, indicating that CO+He mergers must lose at
least one half of their angular momentum.Comment: 11 pages, 11 figures, MNRAS in pres
miRNAs responsive to the diabetic microenvironment in the human beta cell line EndoC-Ī²H1 may target genes in the FOXO, HIPPO and Lysine degradation pathways.
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Altered expression of miRNAs is evident in the islets of diabetic human donors, but the effects of specific aspects of the diabetic microenvironment and identity of gene ontology pathways demonstrating target gene enrichment in response to each is understudied. We assessed changes in the miRNA milieu in response to high/low glucose, hypoxia, dyslipidaemia and inflammatory factors in a humanised EndoC-Ī²H1 beta cell culture system and performed miRPath analysis for each treatment individually. The 10 miRNAs demonstrating the greatest dysregulation across treatments were then independently validated and Gene Set Enrichment Analysis to confirm targeted pathways undertaken. 171 of 392 miRNAs displayed altered expression in response to one or more cellular stressors. miRNA changes were treatment specific, but their target genes were enriched in conserved pathways. 5 miRNAs (miR-136-5p, miR299-5p, miR-454-5p, miR-152 and miR-185) were dysregulated in response to multiple stressors and survived validation in independent samples (pāÆ=āÆ0.008, 0.002, 0.012, 0.005 and 0.024 respectively). Target genes of dysregulated miRNAs were clustered into FOXO1, HIPPO and Lysine degradation pathways (pāÆ=āÆ0.02, pāÆ=āÆ5.84āÆĆāÆ10-5 and pāÆ=āÆ3.00āÆĆāÆ10-3 respectively). We provide evidence that the diabetic microenvironment may induce changes to the expression of miRNAs targeting genes enriched in pathways involved in cell stress response and cell survival.Dr Hadwen TrustAnimal Free Research U
Characterisation of amorphous pharmaceutical materials
Small quantities of amorphous content can have a profound influence on the properties of a material,
however their instability means that quantifying amorphous content over time is important for proving
the stability of a drug. Quantifying amorphous content in Ī±-lactose monohydrate by solid state 13C CP
MAS NMR, has been carried out by use of proton saturation recovery relaxation and differentiating
between spectra by partial least squares (PLS), however these techniques have not proved sensitive on
their own, this work investigates their sensitivity in combination. Crystalline Ī±-lactose monohydrate
and a rapidly quenched melt were combined to create a set of calibration mixes, whose spectra were
recorded using proton saturation recovery relaxations ranging from 2 to 60 seconds. This technique
showed a limit of detection of 0.17% (LOD = intercept + 3xSy/x), with a relaxation delay of 15 s and was
able to recognise amorphous materials generated by spray and freeze drying. The atmospheric effects
on the proton saturation recovery relaxation times of different amorphous lactose preparations were
investigated. This found that an oxygen atmosphere reduced the relaxation times, of amorphous
lactose that was prepared from a rapidly quenched melt. The loss of moisture from spray dried and
freeze dried samples to less than 1% removed the significance of this effect.
Lactose is an important excipient in pharmaceuticals and a key ingredient of confectionary, very little
research has been carried out in to the quantification of the isomers of different preparations of
amorphous lactose. This work quantifies the isomer content by Gas Chromatography with Flame
Ionisation Detection (GC-FID) using a DB-17 15m 0.53mm 1.00 Ī¼m column and derivatisation with N-
(trimethylsilyl)imidazole. [Continues.
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