438 research outputs found
Invasion speeds for structured populations in fluctuating environments
We live in a time where climate models predict future increases in
environmental variability and biological invasions are becoming increasingly
frequent. A key to developing effective responses to biological invasions in
increasingly variable environments will be estimates of their rates of spatial
spread and the associated uncertainty of these estimates. Using stochastic,
stage-structured, integro-difference equation models, we show analytically that
invasion speeds are asymptotically normally distributed with a variance that
decreases in time. We apply our methods to a simple juvenile-adult model with
stochastic variation in reproduction and an illustrative example with published
data for the perennial herb, \emph{Calathea ovandensis}. These examples
buttressed by additional analysis reveal that increased variability in vital
rates simultaneously slow down invasions yet generate greater uncertainty about
rates of spatial spread. Moreover, while temporal autocorrelations in vital
rates inflate variability in invasion speeds, the effect of these
autocorrelations on the average invasion speed can be positive or negative
depending on life history traits and how well vital rates ``remember'' the
past
Composition and Acidification of the Culture Medium Influences Chronological Aging Similarly in Vineyard and Laboratory Yeast
Chronological aging has been studied extensively in laboratory yeast by culturing cells into stationary phase in synthetic complete medium with 2% glucose as the carbon source. During this process, acidification of the culture medium occurs due to secretion of organic acids, including acetic acid, which limits survival of yeast cells. Dietary restriction or buffering the medium to pH 6 prevents acidification and increases chronological life span. Here we set out to determine whether these effects are specific to laboratory-derived yeast by testing the chronological aging properties of the vineyard yeast strain RM11. Similar to the laboratory strain BY4743 and its haploid derivatives, RM11 and its haploid derivatives displayed increased chronological life span from dietary restriction, buffering the pH of the culture medium, or aging in rich medium. RM11 and BY4743 also displayed generally similar aging and growth characteristics when cultured in a variety of different carbon sources. These data support the idea that mechanisms of chronological aging are similar in both the laboratory and vineyard strains
Stress and subjective well-being among first year UK undergraduate students
Transition to university is stressful and successful adjustment is imperative for well-being. Historically research on transitional stress focussed on negative outcomes and ill health. This is the first UK study applying a positive psychology approach to investigate the characteristics that facilitate adjustment among new university students. A range of psychological strengths conceptualised as covitality factors, shown individually to influence the stress and subjective well-being (SWB) relationship were assessed among 192 first year UK undergraduates in week three of their first semester and again six months later. Path analyses revealed that optimism mediated the relationship between stress and negative affect (a component of SWB) over time, and academic self-efficacy demonstrated significant relationships with life satisfaction and positive affect. Contrary to predictions, stress levels remained stable over time although academic alienation increased and self-efficacy decreased. Optimism emerged as a key factor for new students to adjust to university, helping to buffer the impact of stress on well-being throughout the academic year. Incorporating stress management and psycho-educational interventions to develop strengths is discussed as a way of promoting confidence and agency in new students to help them cope better with the stress at university
Cast aluminium single crystals cross the threshold from bulk to size-dependent stochastic plasticity
Metals are known to exhibit mechanical behaviour at the nanoscale different to bulk samples. This transition typically initiates at the micrometre scale, yet existing techniques to produce micrometre-sized samples often introduce artefacts that can influence deformation mechanisms. Here, we demonstrate the casting of micrometre-scale aluminium single-crystal wires by infiltration of a salt mould. Samples have millimetre lengths, smooth surfaces, a range of crystallographic orientations, and a diameter D as small as 6âÎźm. The wires deform in bursts, at a stress that increases with decreasing D. Bursts greater than 200ânm account for roughly 50% of wire deformation and have exponentially distributed intensities. Dislocation dynamics simulations show that single-arm sources that produce large displacement bursts halted by stochastic cross-slip and lock formation explain microcast wire behaviour. This microcasting technique may be extended to several other metals or alloys and offers the possibility of exploring mechanical behaviour spanning the micrometre scale
Dynamic simulations on the mitochondrial fatty acid Beta-oxidation network
<p>Abstract</p> <p>Background</p> <p>The oxidation of fatty acids in mitochondria plays an important role in energy metabolism and genetic disorders of this pathway may cause metabolic diseases. Enzyme deficiencies can block the metabolism at defined reactions in the mitochondrion and lead to accumulation of specific substrates causing severe clinical manifestations. Ten of the disorders directly affecting mitochondrial fatty acid oxidation have been well-defined, implicating episodic hypoketotic hypoglycemia provoked by catabolic stress, multiple organ failure, muscle weakness, or hypertrophic cardiomyopathy. Additionally, syndromes of severe maternal illness (HELLP syndrome and AFLP) have been associated with pregnancies carrying a fetus affected by fatty acid oxidation deficiencies. However, little is known about fatty acids kinetics, especially during fasting or exercise when the demand for fatty acid oxidation is increased (catabolic stress).</p> <p>Results</p> <p>A computational kinetic network of 64 reactions with 91 compounds and 301 parameters was constructed to study dynamic properties of mitochondrial fatty acid β-oxidation. Various deficiencies of acyl-CoA dehydrogenase were simulated and verified with measured concentrations of indicative metabolites of screened newborns in Middle Europe and South Australia. The simulated accumulation of specific acyl-CoAs according to the investigated enzyme deficiencies are in agreement with experimental data and findings in literature. Investigation of the dynamic properties of the fatty acid β-oxidation reveals that the formation of acetyl-CoA â substrate for energy production â is highly impaired within the first hours of fasting corresponding to the rapid progress to coma within 1â2 hours. LCAD deficiency exhibits the highest accumulation of fatty acids along with marked increase of these substrates during catabolic stress and the lowest production rate of acetyl-CoA. These findings might confirm gestational loss to be the explanation that no human cases of LCAD deficiency have been described.</p> <p>Conclusion</p> <p>In summary, this work provides a detailed kinetic model of mitochondrial metabolism with specific focus on fatty acid β-oxidation to simulate and predict the dynamic response of that metabolic network in the context of human disease. Our findings offer insight into the disease process (e.g. rapid progress to coma) and might confirm new explanations (no human cases of LCAD deficiency), which can hardly be obtained from experimental data alone.</p
Measurement of the Forward-Backward Asymmetry in the B -> K(*) mu+ mu- Decay and First Observation of the Bs -> phi mu+ mu- Decay
We reconstruct the rare decays , , and in a data sample
corresponding to collected in collisions at
by the CDF II detector at the Fermilab Tevatron
Collider. Using and decays we report the branching ratios. In addition, we report
the measurement of the differential branching ratio and the muon
forward-backward asymmetry in the and decay modes, and the
longitudinal polarization in the decay mode with respect to the squared
dimuon mass. These are consistent with the theoretical prediction from the
standard model, and most recent determinations from other experiments and of
comparable accuracy. We also report the first observation of the {\mathcal{B}}(B^0_s \to
\phi\mu^+\mu^-) = [1.44 \pm 0.33 \pm 0.46] \times 10^{-6}27 \pm 6B^0_s$ decay observed.Comment: 7 pages, 2 figures, 3 tables. Submitted to Phys. Rev. Let
Measurements of the properties of Lambda_c(2595), Lambda_c(2625), Sigma_c(2455), and Sigma_c(2520) baryons
We report measurements of the resonance properties of Lambda_c(2595)+ and
Lambda_c(2625)+ baryons in their decays to Lambda_c+ pi+ pi- as well as
Sigma_c(2455)++,0 and Sigma_c(2520)++,0 baryons in their decays to Lambda_c+
pi+/- final states. These measurements are performed using data corresponding
to 5.2/fb of integrated luminosity from ppbar collisions at sqrt(s) = 1.96 TeV,
collected with the CDF II detector at the Fermilab Tevatron. Exploiting the
largest available charmed baryon sample, we measure masses and decay widths
with uncertainties comparable to the world averages for Sigma_c states, and
significantly smaller uncertainties than the world averages for excited
Lambda_c+ states.Comment: added one reference and one table, changed order of figures, 17
pages, 15 figure
Search for a New Heavy Gauge Boson Wprime with Electron + missing ET Event Signature in ppbar collisions at sqrt(s)=1.96 TeV
We present a search for a new heavy charged vector boson decaying
to an electron-neutrino pair in collisions at a center-of-mass
energy of 1.96\unit{TeV}. The data were collected with the CDF II detector
and correspond to an integrated luminosity of 5.3\unit{fb}^{-1}. No
significant excess above the standard model expectation is observed and we set
upper limits on . Assuming standard
model couplings to fermions and the neutrino from the boson decay to
be light, we exclude a boson with mass less than
1.12\unit{TeV/}c^2 at the 95\unit{%} confidence level.Comment: 7 pages, 2 figures Submitted to PR
X-ray emission from the Sombrero galaxy: discrete sources
We present a study of discrete X-ray sources in and around the
bulge-dominated, massive Sa galaxy, Sombrero (M104), based on new and archival
Chandra observations with a total exposure of ~200 ks. With a detection limit
of L_X = 1E37 erg/s and a field of view covering a galactocentric radius of ~30
kpc (11.5 arcminute), 383 sources are detected. Cross-correlation with Spitler
et al.'s catalogue of Sombrero globular clusters (GCs) identified from HST/ACS
observations reveals 41 X-rays sources in GCs, presumably low-mass X-ray
binaries (LMXBs). We quantify the differential luminosity functions (LFs) for
both the detected GC and field LMXBs, whose power-low indices (~1.1 for the
GC-LF and ~1.6 for field-LF) are consistent with previous studies for
elliptical galaxies. With precise sky positions of the GCs without a detected
X-ray source, we further quantify, through a fluctuation analysis, the GC LF at
fainter luminosities down to 1E35 erg/s. The derived index rules out a
faint-end slope flatter than 1.1 at a 2 sigma significance, contrary to recent
findings in several elliptical galaxies and the bulge of M31. On the other
hand, the 2-6 keV unresolved emission places a tight constraint on the field
LF, implying a flattened index of ~1.0 below 1E37 erg/s. We also detect 101
sources in the halo of Sombrero. The presence of these sources cannot be
interpreted as galactic LMXBs whose spatial distribution empirically follows
the starlight. Their number is also higher than the expected number of cosmic
AGNs (52+/-11 [1 sigma]) whose surface density is constrained by deep X-ray
surveys. We suggest that either the cosmic X-ray background is unusually high
in the direction of Sombrero, or a distinct population of X-ray sources is
present in the halo of Sombrero.Comment: 11 figures, 5 tables, ApJ in pres
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