3,779 research outputs found
Self-Diffusion of a Polymer Chain in a Melt
Self-diffusion of a polymer chain in a melt is studied by Monte Carlo
simulations of the bond fluctuation model, where only the excluded volume
interaction is taken into account. Polymer chains, each of which consists of
segments, are located on an simple cubic lattice
under periodic boundary conditions, where each segment occupies unit cells. The results for
and 512 at the volume fraction are reported, where
for and L=192 for . The -dependence of the
self-diffusion constant is examined. Here, is estimated from the mean
square displacements of the center of mass of a single polymer chain at the
times larger than the longest relaxation time. From the data for , 384
and 512, the apparent exponent , which describes the apparent power
law dependence of on as , is estimated as
. The ratio seems to be a
constant for and 512, where and
denote the longest relaxation time and the mean square end-to-end distance,
respectively.Comment: 4 pages, 3 figures, submitted to J. Phys. Soc. Jp
Impact of Simulated 1/f Noise for HI Intensity Mapping Experiments
Cosmology has entered an era where the experimental limitations are not due
to instrumental sensitivity but instead due to inherent systematic
uncertainties in the instrumentation and data analysis methods. The field of HI
intensity mapping (IM) is still maturing, however early attempts are already
systematics limited. One such systematic limitation is 1/f noise, which largely
originates within the instrumentation and manifests as multiplicative gain
fluctuations. To date there has been little discussion about the possible
impact of 1/f noise on upcoming single-dish HI IM experiments such as BINGO,
FAST or SKA. Presented in this work are Monte-Carlo end-to-end simulations of a
30 day HI IM survey using the SKA-MID array covering a bandwidth of 950 and
1410 MHz. These simulations extend 1/f noise models to include not just
temporal fluctuations but also correlated gain fluctuations across the receiver
bandpass. The power spectral density of the spectral gain fluctuations are
modelled as a power-law, and characterised by a parameter . It is found
that the degree of 1/f noise frequency correlation will be critical to the
success of HI IM experiments. Small values of ( < 0.25) or high
correlation is preferred as this is more easily removed using current component
separation techniques. The spectral index of temporal fluctuations ()
is also found to have a large impact on signal-to-noise. Telescope slew speed
has a smaller impact, and a scan speed of 1 deg s should be sufficient
for a HI IM survey with the SKA.Comment: 22 pages, 15 figures, 2 table
Collaboratively setting the priorities for health and social care research for older lesbian, gay, bisexual and trans* people
This paper reports on a novel approach to setting research priorities relevant to the needs of older LGBT people. Research is growing in this area and has recognised the negative impact of contemporary and historical discrimination towards non-normative genders and sexualities. The results of a symposium, survey and agreement analysis are presented to identify the levels of priority placed on sixty different research topics. Discussion focuses on the novelty and/or similarity to existing research patterns on LGBT ageing, as well as prioritising topics such as: how to include unheard voices; exploring trans* people’s experiences and preferences around long-term hormone use; and, embedding research findings into policy and practice
Simulations for single-dish intensity mapping experiments
HI intensity mapping is an emerging tool to probe dark energy. Observations
of the redshifted HI signal will be contaminated by instrumental noise,
atmospheric and Galactic foregrounds. The latter is expected to be four orders
of magnitude brighter than the HI emission we wish to detect. We present a
simulation of single-dish observations including an instrumental noise model
with 1/f and white noise, and sky emission with a diffuse Galactic foreground
and HI emission. We consider two foreground cleaning methods: spectral
parametric fitting and principal component analysis. For a smooth frequency
spectrum of the foreground and instrumental effects, we find that the
parametric fitting method provides residuals that are still contaminated by
foreground and 1/f noise, but the principal component analysis can remove this
contamination down to the thermal noise level. This method is robust for a
range of different models of foreground and noise, and so constitutes a
promising way to recover the HI signal from the data. However, it induces a
leakage of the cosmological signal into the subtracted foreground of around 5%.
The efficiency of the component separation methods depends heavily on the
smoothness of the frequency spectrum of the foreground and the 1/f noise. We
find that as, long as the spectral variations over the band are slow compared
to the channel width, the foreground cleaning method still works.Comment: 14 pages, 12 figures. Submitted to MNRA
HI intensity mapping with FAST
We discuss the detectability of large-scale HI intensity fluctuations using
the FAST telescope. We present forecasts for the accuracy of measuring the
Baryonic Acoustic Oscillations and constraining the properties of dark energy.
The FAST -beam L-band receivers (-- GHz) can provide
constraints on the matter power spectrum and dark energy equation of state
parameters () that are comparable to the BINGO and CHIME
experiments. For one year of integration time we find that the optimal survey
area is . However, observing with larger frequency coverage
at higher redshift (-- GHz) improves the projected errorbars on the
HI power spectrum by more than confidence level. The combined
constraints from FAST, CHIME, BINGO and Planck CMB observations can provide
reliable, stringent constraints on the dark energy equation of state.Comment: 7 pages, 3 figures, submitted to "Frontiers in Radio Astronomy and
FAST Early Sciences Symposium 2015" conference proceedin
Planktonic algae and cyanoprokaryotes as indicators of ecosystem quality in the Mooi River system in the North-West Province, South Africa
An ecologically healthy Mooi River system is important for maintaining the quality of potable water of Potchefstroom and surrounding areas. However, this system is under constant threat from anthropogenic pollution arising from both agricultural and mining activities in its catchment. A survey of planktonic algal and cyanoprokaryote assemblages in Klerkskraal, Boskop and Potchefstroom reservoirs was undertaken during 1999–2000 and 2010–2011. In all three dams, total algal and cyanoprokaryote concentrations were lower during the second survey (2010–2011), suggesting an improvement in ecosystem health. However, results also show a change from a Chrysophyceae-dominated community to one dominated by Bacillariophyceae. Increased numbers of diatom species that usually occur in eutrophic impoundments (Melosira varians, Cyclotella meneghiniana and Aulacoseira granulata) indicate an increase in the trophic status of the reservoirs, especially that of Boskop Dam, a trend mirrored by increases in conductivity as well as phosphorus and ammonium concentrations in all three reservoirs. It can therefore be concluded that although the ecosystem health of the Mooi River system is currently still good, further increases in nutrients such as phosphorus can cause proliferation of problem species (detected in enrichment cultures) and a deterioration of its water quality.Keywords: Mooi River reservoirs, algal communities, cyanoprokaryotes, water qualit
In Vivo Time- Resolved Microtomography Reveals the Mechanics of the Blowfly Flight Motor
Dipteran flies are amongst the smallest and most agile of flying animals. Their wings are driven indirectly by large power muscles, which cause cyclical deformations of the thorax that are amplified through the intricate wing hinge. Asymmetric flight manoeuvres are controlled by 13 pairs of steering muscles acting directly on the wing articulations. Collectively the steering muscles account for <3% of total flight muscle mass, raising the question of how they can modulate the vastly greater output of the power muscles during manoeuvres. Here we present the results of a synchrotron-based study performing micrometre-resolution, time-resolved microtomography on the 145 Hz wingbeat of blowflies. These data represent the first four-dimensional visualizations of an organism's internal movements on sub-millisecond and micrometre scales. This technique allows us to visualize and measure the three-dimensional movements of five of the largest steering muscles, and to place these in the context of the deforming thoracic mechanism that the muscles actuate. Our visualizations show that the steering muscles operate through a diverse range of nonlinear mechanisms, revealing several unexpected features that could not have been identified using any other technique. The tendons of some steering muscles buckle on every wingbeat to accommodate high amplitude movements of the wing hinge. Other steering muscles absorb kinetic energy from an oscillating control linkage, which rotates at low wingbeat amplitude but translates at high wingbeat amplitude. Kinetic energy is distributed differently in these two modes of oscillation, which may play a role in asymmetric power management during flight control. Structural flexibility is known to be important to the aerodynamic efficiency of insect wings, and to the function of their indirect power muscles. We show that it is integral also to the operation of the steering muscles, and so to the functional flexibility of the insect flight motor
Effect of the altitudinal variation of the gravitational acceleration on the thermosphere simulation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95479/1/jgra19341.pd
Franck-Condon Factors and Radiative Lifetime of the A^{2}\Pi_{1/2} - X^{2}\Sigma^{+} Transition of Ytterbium Monoflouride, YbF
The fluorescence spectrum resulting from laser excitation of the
A^{2}\Pi_{1/2} - X^{2}\Sigma^{+} (0,0) band of ytterbium monofluoride, YbF, has
been recorded and analyzed to determine the Franck-Condon factors. The measured
values are compared with those predicted from Rydberg-Klein-Rees (RKR)
potential energy curves. From the fluorescence decay curve the radiative
lifetime of the A^{2}\Pi_{1/2} state is measured to be 28\pm2 ns, and the
corresponding transition dipole moment is 4.39\pm0.16 D. The implications for
laser cooling YbF are discussed.Comment: 5 pages, 5 figure
Structure-Guided Design and Optimization of Covalent VHL-Targeted Sulfonyl Fluoride PROTACs.
Proteolysis-targeting chimeras (PROTACs) are heterobifunctional molecules that have emerged as a therapeutic modality to induce targeted protein degradation (TPD) by harnessing cellular proteolytic degradation machinery. PROTACs which ligand the E3 ligase in a covalent manner have attracted intense interest; however, covalent PROTACs with a broad protein of interest (POI) scope have proven challenging to discover by design. Here, we report the structure-guided design and optimization of Von Hippel-Lindau (VHL) protein-targeted sulfonyl fluorides which covalently bind Ser110 in the HIF1α binding site. We demonstrate that their incorporation in bifunctional degraders induces targeted protein degradation of BRD4 or the androgen receptor without further linker optimization. Our study discloses the first covalent VHL ligands which can be implemented directly in bifunctional degrader design, expanding the substrate scope of covalent E3 ligase PROTACs
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