3,748 research outputs found
Stochastic Acceleration of He and He in Solar Flares by Parallel Propagating Plasma Waves: General Results
We study the acceleration in solar flares of He and He from a thermal
background by parallel propagating plasma waves with a general broken power-law
spectrum that takes into account the turbulence generation processes at large
scales and the thermal damping effects at small scales. The exact dispersion
relation for a cold plasma is used to describe the relevant wave modes. Because
low-energy -particles only interact with small scale waves in the
He-cyclotron branch, where the wave frequencies are below the
-particle gyro-frequency, their pitch angle averaged acceleration time
is at least one order of magnitude longer than that of He ions, which
mostly resonate with relatively higher frequency waves in the proton-cyclotron
(PC) branch. The -particle acceleration rate starts to approach that of
He beyond a few tens of keV nucleon, where -particles can
also interact with long wavelength waves in the PC branch. However, the He
acceleration rate is always smaller than that of He. Consequently, the
acceleration of He is suppressed significantly at low energies, and the
spectrum of the accelerated -particles is always softer than that of
He. The model gives reasonable account of the observed low-energy He
and He fluxes and spectra in the impulsive solar energetic particle events
observed with the {\it Advanced Composition Explorer}. We explore the model
parameter space to show how observations may be used to constrain the model.Comment: 29 pages, 11 Figures, Submitted to Ap
Buying time: a rationale for examining the use of circadian rhythm and sleep interventions to delay progression of mild cognitive impairment to Alzheimer’s disease
CsrA impacts survival of Yersinia enterocolitica by affecting a myriad of physiological activities.
BackgroundA previous study identified a Yersinia enterocolitica transposon mutant, GY448, that was unable to export the flagellar type three secretion system (T3SS)-dependent phospholipase, YplA. This strain was also deficient for motility and unable to form colonies on Lauria-Bertani agar medium. Preliminary analysis suggested it carried a mutation in csrA. CsrA in Escherichia coli is an RNA-binding protein that is involved in specific post-transcriptional regulation of a myriad of physiological activities. This study investigated how CsrA affects expression of the flagellar regulatory cascade that controls YplA export and motility. It also explored the effect of csrA mutation on Y. enterocolitica in response to conditions that cue physiological changes important for growth in environments found both in nature and the laboratory.ResultsThe precise location of the transposon insertion in GMY448 was mapped within csrA. Genetic complementation restored disruptions in motility and the YplA export phenotype (Yex), which confirmed this mutation disrupted CsrA function. Mutation of csrA affected expression of yplA and flagellar genes involved in flagellar T3SS dependent export and motility by altering expression of the master regulators flhDC. Mutation of csrA also resulted in increased sensitivity of Y. enterocolitica to various osmolytes, temperatures and antibiotics.ConclusionsThe results of this study reveal unique aspects of how CsrA functions in Y. enterocolitica to control its physiology. This provides perspective on how the Csr system is susceptible to adaptation to particular environments and bacterial lifestyles
A resonant feature near the Perseus arm revealed by red clump stars
We investigate the extinction together with the radial velocity dispersion
and distribution of red clump stars in the anti-center direction using spectra
obtained with Hectospec on the MMT. We find that extinction peaks at
Galactocentric radii of about 9.5 and 12.5 kpc, right in front of the locations
of the Perseus and Outer arms and in line with the relative position of dust
and stars in external spiral galaxies. The radial velocity dispersion peaks
around 10kpc, which coincides with the location of the Perseus arm, yields an
estimated arm-interarm density contrast of 1.3-1.5 and is in agreement with
previous studies. Finally, we discover that the radial velocity distribution
bifurcates around 10-11 kpc into two peaks at +27 km/s and -4 km/s. This seems
to be naturally explained by the presence of the outer Lindblad resonance of
the Galactic bar, but further observations will be needed to understand if the
corotation resonance of the spirals arms also plays a role.Comment: 8 pages, 2 figures, accepted for publication in ApJ
Stochastic Acceleration of 3He and 4He by Parallel Propagating Plasma Waves
Stochastic acceleration of He and He from a thermal background by
parallel propagating turbulent plasma waves with a single power-law spectrum of
the wavenumber is studied. In the model, both ions interact with several
resonant modes. When one of these modes dominates, the acceleration rate is
reduced considerably. At low energies, this happens for He, but not for
He where contributions from the two stronger modes are comparable so that
acceleration of He is very efficient. As a result, the acceleration of
He is suppressed by a barrier below keV nucleon and there
is a prominent quasi-thermal component in the He spectra, while almost all
the injected He ions are accelerated to high energies. This accounts for
the large enrichment of He at high energies observed in impulsive solar
energetic particle events. With reasonable plasma parameters this also provides
a good fit to the spectra of both ions. Beyond MeV nucleon, the
spectrum of He is softer than that of He, which is consistent with the
observed decrease of the He to He ratio with energy. This study also
indicates that the acceleration, Coulomb losses and diffusive escape of the
particles from the acceleration site {\it all} play important roles in shaping
the ion spectra. This can explain the varied spectral shapes observed recently
by the {\it Advanced Composition Explorer}.Comment: 14 pages, 4 figures, Submitted to Apj
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A three-stage continuous culture approach to study the impact of probiotics, prebiotics and fat intake on faecal microbiota relevant to an over 60s population
This study aimed to determine the impact of fat intake combined with Bacillus coagulans or trans- galactooligosaccharides (B-GOS) on bacterial composition and immune markers in an in vitro model. A three-stage continuous gut model system was used to simulate specific human colonic regions. Peripheral blood mononuclear cells were exposed to cell free supernatants and subsequent levels of inflammatory cytokines were measured by flow cytometry. Although fat addition decreased bifidobacteria from 8.76 ± 0.12 to 8.63 ± 0.13 and from 8.83 ± 0.08 to 8.67 ± 0.07 in pre- and probiotic models respectively, the changes were not significant. Fat addition also did not impact on cytokines induced by LPS. Under high fat conditions, numbers of bifidobacteria significantly increased by B. coagulans or B-GOS. In addition, B. coagulans or B-GOS significantly suppressed TNF-a production induced by LPS. Under high fat conditions, both B. coagulans and B-GOS led to potentially beneficial effects by targeting specific bacterial groups and modulating immune markers
Commentary: Is there a role for diabetes-specific nutrition formulas as meal replacements in type 2 diabetes?
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