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Fast Magnetosonic Waves Observed by Van Allen Probes: Testing Local Wave Excitation Mechanism
Get PDFLinear Vlasov theory and particle-in-cell (PIC) simulations for electromagnetic fluctuations in a homogeneous, magnetized, and collisionless plasma are used to investigate a fast magnetosonic wave event observed by the Van Allen Probes. The fluctuating magnetic field observed exhibits a series of spectral peaks at harmonics of the proton cyclotron frequency Omega p and has a dominant compressional component, which can be classified as fast magnetosonic waves. Furthermore, the simultaneously observed proton phase space density exhibits positive slopes in the perpendicular velocity space, partial derivative f(p)/partial derivative v(perpendicular to) > 0, which can be a source for these waves. Linear theory analyses and PIC simulations use plasma and field parameters measured in situ except that the modeled proton distribution is modified to have larger partial derivative f(p)/partial derivative v(perpendicular to) under the assumption that the observed distribution corresponds to a marginally stable state when the distribution has already been scattered by the excited waves. The results show that the positive slope is the source of the proton cyclotron harmonic waves at propagation quasi-perpendicular to the background magnetic field, and as a result of interactions with the excited waves the evolving proton distribution progresses approximately toward the observed distribution.Publishe
Automatically identifying, counting, and describing wild animals in camera-trap images with deep learning
Get PDFHaving accurate, detailed, and up-to-date information about the location and behavior of animals in the wild would improve our ability to study and conserve ecosystems. We investigate the ability to automatically, accurately, and inexpensively collect such data, which could help catalyze the transformation of many fields of ecology, wildlife biology, zoology, conservation biology, and animal behavior into "big data" sciences. Motion-sensor "camera traps" enable collecting wildlife pictures inexpensively, unobtrusively, and frequently. However, extracting information from these pictures remains an expensive, time-consuming, manual task. We demonstrate that such information can be automatically extracted by deep learning, a cutting-edge type of artificial intelligence. We train deep convolutional neural networks to identify, count, and describe the behaviors of 48 species in the 3.2 million-image Snapshot Serengeti dataset. Our deep neural networks automatically identify animals with >93.8% accuracy, and we expect that number to improve rapidly in years to come. More importantly, if our system classifies only images it is confident about, our system can automate animal identification for 99.3% of the data while still performing at the same 96.6% accuracy as that of crowdsourced teams of human volunteers, saving >8.4 y (i.e., >17,000 h at 40 h/wk) of human labeling effort on this 3.2 million-image dataset. Those efficiency gains highlight the importance of using deep neural networks to automate data extraction from camera-trap images, reducing a roadblock for this widely used technology. Our results suggest that deep learning could enable the inexpensive, unobtrusive, high-volume, and even real-time collection of a wealth of information about vast numbers of animals in the wild.PublishedYe
The Role of Breccia Lenses in Regolith Generation From the Formation of Small, Simple Craters: Application to the Apollo 15 Landing Site
Get PDFImpact cratering is likely a primary agent of regolith generation on airless bodies. Regolith production via impact cratering has long been a key topic of study since the Apollo era. The evolution of regolith due to impact cratering, however, is not well understood. A better formulation is needed to help quantify the formation mechanism and timescale of regolith evolution. Here we propose an analytically derived stochastic model that describes the evolution of regolith generated by small, simple craters. We account for ejecta blanketing as well as regolith infilling of the transient crater cavity. Our results show that the regolith infilling plays a key role in producing regolith. Our model demonstrates that because of the stochastic nature of impact cratering, the regolith thickness varies laterally, which is consistent with earlier work. We apply this analytical model to the regolith evolution at the Apollo 15 site. The regolith thickness is computed considering the observed crater size-frequency distribution of small, simple lunar craters (< 381m in radius for ejecta blanketing and <100m in radius for the regolith infilling). Allowing for some amount of regolith coming from the outside of the area, our result is consistent with an empirical result from the Apollo 15 seismic experiment. Finally, we find that the timescale of regolith growth is longer than that of crater equilibrium, implying that even if crater equilibrium is observed on a cratered surface, it is likely that the regolith thickness is still evolving due to additional impact craters. Plain Language Summary Impact cratering likely generates much of the regolith (the surface layer made up of a mixture of rocks, rock fragments, sand, and dust) observed on airless planetary surfaces. However, the way that the regolith layer evolves and thickens over time due to impact cratering events is not well understood. When a small, simple crater forms into hard rock, regolith is produced by fracturing the target rock and is deposited in the crater's ejecta blanket and within its transient crater cavity. Here we discuss an analytically derived stochastic model that describes the evolution of regolith developed by simple craters. Our results indicate that the regolith deposited on crater interiors is particularly important to consider when describing the distribution of regolith. Our model also indicates that the regolith thickness varies from one location to another. We apply this model to the regolith at the Apollo 15 landing site by considering the size distribution of observed small, simple lunar craters. Allowing for some regolith coming from outside of the area of the landing site, our result is consistent with an empirical result from the Apollo 15 seismic experiment.PublishedYe
Genomic responses to selection for tame/aggressive behaviors in the silver fox (Vulpes vulpes)
Get PDFAnimal domestication efforts have led to a shared spectrum of striking behavioral and morphological changes. To recapitulate this process, silver foxes have been selectively bred for tame and aggressive behaviors for more than 50 generations at the Institute for Cytology and Genetics in Novosibirsk, Russia. To understand the genetic basis and molecular mechanisms underlying the phenotypic changes, we profiled gene expression levels and coding SNP allele frequencies in two brain tissue specimens from 12 aggressive foxes and 12 tame foxes. Expression analysis revealed 146 genes in the prefrontal cortex and 33 genes in the basal forebrain that were differentially expressed, with a 5% false discovery rate (FDR). These candidates include genes in key pathways known to be critical to neurologic processing, including the serotonin and glutamate receptor pathways. In addition, 295 of the 31,000 exonic SNPs show significant allele frequency differences between the tame and aggressive populations (1% FDR), including genes with a role in neural crest cell fate determination.PublishedYe
Electronic Theses and Dissertations: Limited Shelf Life or Long Tail?
No full textWhen we make theses and dissertations available electronically, we do so because we believe that these documents have value for researchers. We do not know, however, if this value has a time limit or if it will be sustained. The answer to this question has an impact on workflow: Do we upload items as soon as they become available, or in batches every semester/quarter, or even in batches on an annual basis? It also has an impact on embargo policy: If ETDs have a limited window of interest, then shorter embargo times are preferable. There is a financial impact as well: Retrospective digitization of print theses and dissertations is an appropriate use of limited resources if, and only if, these older documents will be used by researchers. This study examines Google Analytics page views data for ETDs in the repository of a land-grant research university. Views of bibliographic pages for individual ETDs were tracked as an indicator of researcher interest in those titles. Bib page views for each ETD uploaded from August 2009 through July 2012 were recorded on a monthly basis, starting with the month in which it was uploaded and continuing through mid-August 2018. Data are presented for all ETDs in the study group, viewed as a whole, and for the sub-groups of unrestricted and embargoed ETDs. Data are also presented for ETDs from 5 AU Colleges: Engineering, Liberal Arts, Agriculture, Sciences & Mathematics, and Education
Relationships among hosts, habitats, and ticks throughout Alabama
Get PDFTicks are the foremost parasites of wildlife and humans in the United States, and may transmit pathogens associated with Lyme disease, Ehrlichiosis, spotted fever Rickettsiosis, and others. Despite the high occurrence of several species of ticks throughout Alabama, little is known about their distribution or the degree to which they carry pathogens. Consequently, the probability of encountering infected ticks in the state is unknown. For this project, we environmental and climatic factors that affect tick and pathogen distribution and risk, and determined relationships among habitats, ticks, pathogens, and hosts. Ticks were trapped for one year (5/16-5/17) on 105 plots in deciduous, coniferous, pasture, early successional, and residential areas throughout Alabama. Hourly forest floor temperature and relative humidity were recorded on the same sites. In preliminary pathogen screenings, minimum infection rates in lone star ticks ranged from 0% to 3% for Ehrlichia spp. and 17% to 49% for Rickettsia amblyommii. Interestingly, the minimum infection rate of Rickettsia parkeri in Gulf coast ticks was 18%, and no ticks tested positive for Borrelia spp. Additionally, during the summers of 2015 to 2017, 762 ticks were collected from 125 white-tailed deer in 19 counties, and 3,302 ticks were collected from 626 deer on 12 Wildlife Management Areas during two successive winters from 2015-2017. Pathogen screening for these samples is in progress. Preliminary analyses show that across all locations and land uses, minimum and range of humidity and temperature are the primary drivers of overall tick abundance, and forest floor characteristics and sandy soils have significant effects. Additionally, while only 11% (n=61) of ticks captured on traps were black-legged ticks, 88% (n=2,894) were collected from deer between November to February, elucidating a deer’s critical role in their survival and movement, and suggesting traditional sampling methods for this species are ineffective in the Southeast.Analyses in progressN
Global Pyrogenic Carbon Production During Recent Decades Has Created the Potential for a Large, Long-Term Sink of Atmospheric CO2
Get PDFFires play an important role in the terrestrial biosphere carbon cycle, not only through direct carbon release but also contributing to a potential long-term storage as pyrogenic carbon (PyC). PyC is formed through fires, and, because it may resist further biological and chemical degradation, is more stable in soil and sediment than original biomass. At the global scale, contributions of fires to both atmospheric CO2 emissions and PyC accumulation are potentially large but difficult to estimate. Our analysis was based on existing simulation results from two different modeling approaches (Global Fire Emissions Database version 4 [GFED4s] and Terrestrial Ecosystem Model version 6 [TEM6]) that used global area burned data to provide recent, retrospective estimates of CO2 emissions from vegetation combustion, together with published, biome- and continental-scale conversion ratios that relate CO2 emissions to PyC production (PyC/CO2) during combustion. The estimates of global CO2 emissions from fires differed substantially between the two models' results. GFED4s estimated 2,041TgC/year during the 2000-2016 time period, whereas the TEM6 estimate was considerably lower at 643TgC/year from 2000 to 2010. Global PyC production estimates from fires were 153.418.7 and 49.54.9TgC/year based on the emission estimates from GFED4s and TEM6, respectively. Our results suggest that African tropical savanna fires produced the largest amount of CO2 emissions and PyC among global biomes, the most significant interannual variations in CO2 emissions and PyC production were found in tropical forests, and the magnitude of PyC produced by fires each year represented a potentially significant long-term sink of atmospheric CO2.Publishe
Chemokine C-C motif ligand 33 is a key regulator of teleost fish barbel development
Get PDFBarbels are important sensory organs in teleosts, reptiles, and amphibians. The majority of similar to 4,000 catfish species, such as the channel catfish (Ictalurus punctatus), possess abundant whisker-like barbels. However, barbel-less catfish, such as the bottlenose catfish (Ageneiosus marmoratus), do exist. Barbeled catfish and barbel-less catfish are ideal natural models for determination of the genomic basis for barbel development. In this work, we generated and annotated the genome sequences of the bottlenose catfish, conducted comparative and subtractive analyses using genome and transcriptome datasets, and identified differentially expressed genes during barbel regeneration. Here, we report that chemokine C-C motif ligand 33 (ccl33), as a key regulator of barbel development and regeneration. It is present in barbeled fish but absent in barbel-less fish. The ccl33 genes are differentially expressed during barbel regeneration in a timing concordant with the timing of barbel regeneration. Knockout of ccl33 genes in the zebrafish (Danio rerio) resulted in various phenotypes, including complete loss of barbels, reduced barbel sizes, and curly barbels, suggesting that ccl33 is a key regulator of barbel development. Expression analysis indicated that paralogs of the ccl33 gene have both shared and specific expression patterns, most notably expressed highly in various parts of the head, such as the eye, brain, and mouth areas, supporting its role for barbel development.PublishedYe