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Test-Particle Simulations of Linear and Nonlinear Interactions Between a 2-D Whistler-Mode Wave Packet and Radiation Belt Electrons
Get PDFUsing test-particle simulations, we describe (in 2-D) the interaction of an ensemble of electrons with a discrete whistler-mode wave packet, which propagates with a moderate wave-normal angle with respect to the background magnetic field. We evaluate both the average transport coefficients used in quasi-linear diffusion transport and also the full nonlinear wave-particle interactions. The magnitude of the calculated diffusion coefficients is found to increase proportionally to the wave amplitude squared, in agreement with quasi-linear diffusion theory. Cyclotron resonance of counterstreaming electrons (n = 1 harmonic number) is more important for pitch angle scattering than Landau resonance. Landau resonance of costreaming electrons (n = 0) is comparable to cyclotron resonance for energy diffusion and advection. Strong acceleration of high pitch angle, costreaming electrons arises in nonlinear wave-particle interactions with high-amplitude waves. In our simulations with zero parallel electric field, the energy source for electron acceleration is the wave's perpendicular electric field, in both the cyclotron and Landau resonances. The Landau resonance can happen even with zero parallel electric field, if the wave packet propagates with a finite wave-normal angle. This resonance between the particle's azimuthal velocity and the wave fields leads to trapping and substantial parallel acceleration.PublishedYe
Equatorial Evolution of the Fast Magnetosonic Mode in the Source Region: Observation-Simulation Comparison of the Preferential Propagation Direction
Get PDFRecent analysis of an event observed by the Van Allen Probes in the source region outside the plasmapause has shown that fast magnetosonic waves (also referred to as equatorial noise) propagate preferentially in the azimuthal direction, implying that wave amplification should occur during azimuthal propagation. To demonstrate this, we carry out 2-D particle-in-cell simulations of the fast magnetosonic mode at the dipole magnetic equator with the simulation box size, the magnetic field inhomogeneity, and the plasma parameters chosen from the same event recently analyzed. The self-consistently evolving electric and magnetic field fluctuations are characterized by spectral peaks at harmonics of the local proton cyclotron frequency. The azimuthal component of the electric field fluctuations is larger than the radial component, indicating wave propagation mainly along the azimuthal direction. Because the simulation box is within the source region, this also implies wave amplification mainly during azimuthal propagation. The excellent agreement between the wave polarization properties of the present simulations and the recently reported observations is clear evidence that the main wave amplification occurs during azimuthal propagation in the source region.PublishedYe
The Librarian's Dilemma
Get PDFLibrarians who work with incarcerated individuals face
the dilemma of being asked to participate in a restrictive
system while also adhering to universally accepted
intellectual freedom standards. Prison librarians often
face dual mistrust: the population they are serving
distrusts them in their position of authority, while the
prison hierarchy often dismisses their authority since
prison administrators have ultimate power over prison
library collection development and censorship decisions.
In addition to this lack of control, librarians are often
expected to simultaneously fulfill the duties of librarians
in traditional spaces, by providing information and
access to materials; act as a social worker, by providing
rehabilitation and reentry programs; and to work as a
government employee, assisting staff in maintaining
order and discipline within the institution. All of this
frequently happens in conditions with limited budgets,
chronic understaffing, insufficient space, and lack of
support from prison administrators and the Department
of Corrections. The mission of libraries is to provide
free and open access to information, thereby creating
a dissonance in prison library space. We address how
librarians navigate questions of censorship in prisons
and discuss whether intellectual freedom can exist in the
current U.S. penal system
Seasonal Shifts in Reproduction Depend on Prey Availability for an Income Breeder
Get PDFThe evolution of reproductive strategies depends on local environmental conditions. When environments are seasonal, selection favors individuals that align changes in key reproductive traits with seasonal shifts in habitat quality. Offspring habitat quality can decline through the season, and increased maternal provisioning to late-produced offspring may compensate. This shift, however, may depend on environmental factors that influence reproduction and are, themselves, subject to temporal changes (e.g., food abundance). We studied the brown anole lizard (Anolis sagrei) to demonstrate how prey abundance modifies seasonal changes in key reproductive traits. We bred lizards in controlled laboratory conditions across the reproductive season and manipulated the availability of food by providing some breeding pairs high prey availability and some low. Halfway through the season, we switched half of the breeding pairs to the opposite treatment. We measured growth of male and female lizards as well as latency to oviposit, fecundity, egg size, egg content (yolk, water, shell mass), and egg quality (steroid hormones, yolk caloric content) over this period. Higher prey availability enhanced lizard growth and some key reproductive traits (egg size, fecundity) but not others (egg content and quality). Moreover, we found that seasonal patterns of reproduction were modified by prey treatment in ways that have consequences for offspring survival. Our results demonstrate that seasonal changes in reproduction are dependent on fluctuations in local environmental conditions. Moreover, researchers must account for seasonal shifts in environmental factors and reproductive traits (and their interactions) when designing experiments and drawing conclusions about how the environment influences reproduction.PublishedYe
Supporting the Proliferation of Data-Sharing Scholars in the Research Ecosystem
Get PDFLibrarians champion the value of openness in scholarship and have been powerful advocates for the sharing of research data. College and university administrators have recently joined in the push for data sharing due to funding mandates. However, the researchers who create and control the data usually determine whether and how data is shared, so it is worthwhile to look at what they are incentivized to do. The current scholarly publishing landscape plus the promotion and tenure process create a “prisoner’s dilemma” for researchers as they decide whether or not to share data, consistent with the observation that researchers in general are eager for others to share data but reluctant to do so themselves. If librarians encourage researchers to share data and promote openness without simultaneously addressing the academic incentive structure, those who are intrinsically motivated to share data will be selected against via the promotion and tenure process. This will cause those who are hostile to sharing to be disproportionately recruited into the senior ranks of academia. To mitigate the risk of this unintended consequence, librarians must advocate for a change in incentives alongside the call for greater openness. Highly-cited datasets must be given similar weight to highly-cited articles in promotion and tenure decisions in order for researchers to reap the rewards of their sharing. Librarians can help by facilitating data citation to track the impact of datasets and working to persuade higher administration of the value of rewarding data sharing in tenure and promotion.publishedN
A Note on Realism in Adam Bede with Reference to Two Novels by George Sand
No full textArticle from the George Eliot Review, digitized and hosted by the George Eliot Review Online.Publishe
No Change in the Recent Lunar Impact Flux Required Based on Modeling of Impact Glass Spherule Age Distributions
Get PDFThe distributions of Ar-40/Ar-39-derived ages of impact glass spherules in lunar regolith samples show an excess at 10 crater radii from the crater, consistent with terrestrial microtektite observations. We suggest that the observed excess of young ages for lunar impact glasses is likely due to limitations of the regolith sampling strategy of the Apollo program, rather than reflecting a change in the lunar impact rate.PublishedYe
DAVIS: A direct algorithm for velocity-map imaging system
Get PDFIn this work, we report a direct (non-iterative) algorithm to reconstruct the three-dimensional (3D) momentum-space picture of any charged particles collected with a velocity-map imaging system from the two-dimensional (2D) projected image captured by a position-sensitive detector. The method consists of fitting the measured image with the 2D projection of a model 3D velocity distribution defined by the physics of the light-matter interaction. The meaningful angle-correlated information is first extracted from the raw data by expanding the image with a complete set of Legendre polynomials. Both the particle's angular and energy distributions are then directly retrieved from the expansion coefficients. The algorithm is simple, easy to implement, fast, and explicitly takes into account the pixelization effect in the measurement. Published by AIP Publishing.PublishedYe
DAVIS: A direct algorithm for velocity-map imaging system
Get PDFIn this work, we report a direct (non-iterative) algorithm to reconstruct the three-dimensional (3D) momentum-space picture of any charged particles collected with a velocity-map imaging system from the two-dimensional (2D) projected image captured by a position-sensitive detector. The method consists of fitting the measured image with the 2D projection of a model 3D velocity distribution defined by the physics of the light-matter interaction. The meaningful angle-correlated information is first extracted from the raw data by expanding the image with a complete set of Legendre polynomials. Both the particle’s angular and energy distributions are then directly retrieved from the expansion coefficients. The algorithm is simple, easy to implement, fast, and explicitly takes into account the pixelization effect in the measurement.PublishedYe
