337 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
Association of 3He-Rich Solar Energetic Particles with Large-Scale Coronal Waves
Small 3He-rich solar energetic particle (SEP) events have been commonly
associated with extreme-ultraviolet (EUV) jets and narrow coronal mass
ejections (CMEs) which are believed to be the signatures of magnetic
reconnection involving field lines open to interplanetary space. The elemental
and isotopic fractionation in these events are thought to be caused by
processes confined to the flare sites. In this study we identify 32 3He-rich
SEP events observed by the Advanced Composition Explorer near the Earth during
the solar minimum period 2007-2010 and examine their solar sources with the
high resolution Solar Terrestrial Relations Observatory (STEREO) EUV images.
Leading the Earth, STEREO-A provided for the first time a direct view on
3He-rich flares, which are generally located on the Sun's western hemisphere.
Surprisingly, we find that about half of the 3He-rich SEP events in this survey
are associated with large-scale EUV coronal waves. An examination of the wave
front propagation, the source-flare distribution and the coronal magnetic field
connections suggests that the EUV waves may affect the injection of 3He-rich
SEPs into interplanetary space.Comment: accepted for publication in The Astrophysical Journa
Case studies of multi-day 3He-rich solar energetic particle periods
Context. Impulsive solar energetic particle events in the inner heliosphere
show the long-lasting enrichment of 3He. Aims. We study the source regions of
long-lasting 3He-rich solar energetic particle (SEP) events Methods. We located
the responsible open magnetic field regions, we combined potential field source
surface extrapolations (PFSS) with the Parker spiral, and compared the magnetic
field of the identified source regions with in situ magnetic fields. The
candidate open field regions are active region plages. The activity was
examined by using extreme ultraviolet (EUV) images from the Solar Dynamics
Observatory (SDO) and STEREO together with radio observations from STEREO and
WIND. Results. Multi-day periods of 3He-rich SEP events are associated with ion
production in single active region. Small flares or coronal jets are their
responsible solar sources. We also find that the 3He enrichment may depend on
the occurrence rate of coronal jets.Comment: 7page, 4 figure
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
3He-Rich Solar Energetic Particles in Helical Jets on the Sun
Particle acceleration in stellar flares is ubiquitous in the Universe,
however, our Sun is the only astrophysical object where energetic particles and
their source flares can both be observed. The acceleration mechanism in solar
flares, tremendously enhancing (up to a factor of ten thousand) rare elements
like 3He and ultra-heavy nuclei, has been puzzling for almost 50 years. Here we
present some of the most intense 3He- and Fe-rich solar energetic particle
events ever reported. The events were accompanied by non-relativistic electron
events and type III radio bursts. The corresponding high-resolution,
extreme-ultraviolet imaging observations have revealed for the first time a
helical structure in the source flare with a jet-like shape. The helical jets
originated in relatively small, compact active regions, located at the coronal
hole boundary. A mini-filament at the base of the jet appears to trigger these
events. The events were observed with the two Solar Terrestrial Relations
Observatories STEREO on the backside of the Sun, during the period of increased
solar activity in 2014. The helical jets may be a distinct feature of these
intense events that is related to the production of high 3He and Fe
enrichments.Comment: accepted for publication in The Astrophysical Journa
Hatch Dates, Growth, Survival, and Overwinter Mortality of Ageâ0 Alewives in Lake Michigan: Implications for HabitatâSpecific Recruitment Success
Alewives Alosa pseudoharengus are key components of Laurentian Great Lakes ecosystems and spawn in multiple habitat types. Exploration of alewife early life history dynamics within these different habitats should help identify important recruitment processes. During 2001â2003, we quantified physical (temperature, transparency) and biotic (chlorophyll a, zooplankton densities) habitat factors and collected ageâ0 alewives (using ichthyoplankton nets and trawls) in a nearshore region of Lake Michigan and Muskegon Lake, Michigan (a drowned river mouth lake connected to Lake Michigan). We characterized alewife hatch dates, individual condition, growth, mortality, and sizeâdependent overwinter survival to infer differences in habitatâspecific recruitment success. Temperature, turbidity, chlorophyllâa concentrations, and densities of zooplankton prey were consistently higher in Muskegon Lake than in nearshore Lake Michigan. On average, young alewives in Muskegon Lake hatched earlier, grew faster, were in better condition (based on a biphasic lengthâweight relationship), and had greater survival than alewives in Lake Michigan. By the end of the growing season, young alewives in Muskegon Lake obtained a larger size than those residing in nearshore Lake Michigan, suggesting that they were more likely to survive through winter (a period of intense sizeâselective mortality) and ultimately recruit to the adult population.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141621/1/tafs1298.pd
An easy-to-perform, culture-free Campylobacter point-of-management assay for processing plant applications
Aims Current culture-based methods for detection and determination of Campylobacter levels on processed chickens takes at least two days. Here, we sought to develop a new complete, low-cost and rapid (approximately 2·5 hours) detection system requiring minimal operator input. Methods and Results We observed a strong correlation between culture-based cell counts and our ability to detect either Campylobacter jejuni or Campylobacter coli by Loop mediated isothermal amplification (LAMP) from the same samples. This knowledge was used to develop a rapid and simple five-step assay to quantify Campylobacter, which was subsequently assessed for its specificity, reproducibility and accuracy in quantifying Campylobacter levels from processed chickens. The assay was found to be highly specific for C. jejuni and C. coli and was capable of distinguishing between samples that are either within or exceeding the industry set target of 6,000 Campylobacter colony forming units (cfu) per carcass (equivalent to 12 cfu ml-1 of chicken rinse) with> 90% accuracy relative to culture-based methods. Conclusions Our method can reliably quantify Campylobacter counts of processed chickens with an accuracy comparable to culture-based assays but provides results within hours as opposed to days. Significance and Impact of the Study The research presented here will help improve food safety by providing fast Campylobacter detection that will enable the implementation of real-time risk management strategies in poultry processing plants to rapidly test processed chickens and identify effective intervention strategies. This technology is a powerful tool that can be easily adapted for other organisms and thus could be highly beneficial for a broad range of industries
Probing shock geometry via the charge to mass ratio dependence of heavy ion spectra from multiple spacecraft observations of the 2013 November 4 event
In large Solar Energetic Particle (SEP) events, ions can be accelerated at coronal mass ejection (CME)-driven shocks to very high energies. The spectra of heavy ions in many large SEP events show features such as roll-overs or spectral breaks. In some events when the spectra are plotted in terms of energy/nucleon, they can be shifted relative to each other to make the spectral breaks align. The amount of shift is charge to mass ratio (Q/A) dependent and varies from event to event. This can be understood if the spectra of heavy ions are organized by the diffusion coefficients (Cohen et al. 2005). In the work of Li et al. (2009), the Q/A dependence of the scaling is related to shock geometry when the CME-driven shock is close to the Sun. For events where multiple in-situ spacecraft observations exist, one may expect that different spacecraft are connected to different portions of the CME-driven shock that have different shock geometries, therefore yielding different Q/A dependence. In this work, we examine one SEP event which occurred on 2013 November 4. We study the Q/A dependence of the energy scaling for heavy ion spectra using helium, oxygen and iron ions. Observations from STEREO-A, STEREO-B and ACE are examined. We find that the scalings are different for different spacecraft. We suggest that this is because ACE, STEREO-A and STEREO-B are connected to different parts of the shock that have different shock geometries. Our analysis indicates that studying the Q/A scaling of in-situ particle spectra can serve as a powerful tool to remotely examine the shock geometry for large SEP events
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