Driving piezochromism and metallicity in van der Waals materials under compression

Complex chalcogenides provide an important platform to explore the interplay between structure, charge, and spin across pressure-induced phase transitions. Where much of the previous research has been focused on tuning these materials towards the single-layer limit, we instead explore the modification of bond lengths and bond angles under compression. In the first project we revealed piezochromism in MnPS3. We combined high pressure optical spectroscopy and first-principles calculations to analyze the dramatic color change (green → yellow → red → black) that takes place as the charge gap shifts across the visible and into the near infrared region, moving systematically toward closure at a rate of approximately -50 meV/GPa. The discovery of deterministically controlled piezochromism at room temperature provides an exciting opportunity to seek out this functionality in other complex chalcogenides. NiPS3 is the second platform of investigation in this dissertation. By combining a variety of high pressure experimental techniques including synchrotron-based infrared spectroscopy, Raman scattering, x-ray diffraction, and an in-depth symmetry analysis with first-principles calculations we revealed five different states of matter up to 39 GPa. Bringing together the appearance of a polar high pressure phase from symmetry analysis and the insulator-metal transition with the appearance of a Drude, we suggest the development of a room temperature polar metal above 23 GPa. By providing a platform to access this uncommon state of matter, this research will further the development and understanding of polar metals more broadly. In our final project, we compared the prototypical parent compound FePS3 with chemically-similar CrPS4. We found that these materials displayed markedly different symmetry progressions and high pressure states of matter under pressure. CrPS4 in fact drives toward P2/m - a symmetry not observed in any of the other systems. These differences are attributed to the structural differences including the van der Waals gap size, layer corrugation, and character of the P-P linkage, as well as the orbital occupation of the transition metals. The structure-property relations in these compounds demonstrate the importance of structural and electronic contributions in the determination of the different symmetry breaking within these materials under compression

Biological control agent attack timing and population variability, but not density, best explain target weed density across an environmental gradient

© 2020, The Author(s). Spatial variation in plant–herbivore interactions can be important in pest systems, particularly when insect herbivores are used as biological control agents to manage invasive plants. The geographic ranges of the invasive plant alligatorweed (Alternanthera philoxeroides) and its biological control agent the alligatorweed flea beetle (Agasicles hygrophila) do not completely overlap in the southeastern USA, producing spatial heterogeneity in interaction strength that may be related to latitude-correlated environmental gradients. We studied this system near the range margin of the alligatorweed flea beetle to test whether spatial variation in alligatorweed density was best explained by agent mean or maximum density, variability in agent density, agent attack timing, or a combination of biological control and environmental (i.e., weather) variables. The pattern that emerged was that mean agent and host densities were negatively and positively associated with latitude, respectively. Variability in agent density increased with latitude and was positively correlated with host density. We further discovered that agent first attack timing was negatively correlated with winter and spring temperatures and spring and summer precipitation, and positively correlated with seasonal temperature extremes, which was then directly influential on agent density and variability in density, and indirectly on host density. This study demonstrates that, contrary to common wisdom, weather-related timing of agent activity and population variability, but not agent mean density, contribute to the spatial heterogeneity observed in alligatorweed populations

Comparison of Heteranthera Dubia (Jacq.) MacM.-associated Macroinvertebrates Between Georgraphical Regions in the United States

Macroinvertebrates associated with the aquatic plant, water stargrass (Heteranthera dubia), were sampled from 12 waterbodies in four regions of the United States from June to August 2005. Taxa richness, evenness, and diversity were lowest in the Lower Midwest (LMW) region, and higher in Northern sites, especially the Upper Midwest (UMW), and Northeast (NE). While relative abundance varied from site to site and region to region, utilization of the plant by functional groups remained fairly constant. Collector-gatherers consistently comprised the largest portion of invertebrates sampled. The shredder/ herbivore functional group comprised an average of 17 % of total groups. Through an exhaustive literature review, it was found that shredder/ herbivores of water stargrass have not been reported in the literature. Because of this, the herbivore group was analyzed separately and consisted of 2,383 specimens representing 23 species. The most common groups were Rhopalosiphum sp., Nectopsyche spp. and chironomids. No differences were found in herbivore diversity or evenness between sampling regions, but species richness was significantly different

Photoluminescence Detection of 2,4,6-Trinitrotoulene (TNT) Binding on Single Cell Diatom Biosilica

T. pseudonana biosilica and live cells was explored as a biosensor for detection of the explosive compound 2,4,6-trinitrotoluene (TNT) in aqueous solution. The diatom frustule is an intricately nanostructured, highly porous biogenic silica material derived from the shells of microscopic algae called diatoms. This material emits strong visible blue photoluminescence (PL) upon UV excitation. PL-active frustule biosilica was isolated from cultured cells of the marine diatom T. pseudonana, exposed to varying concentrations of TNT, and the PL response was observed using PL spectroscopy. This process was repeated for live T. pseudonana cells. Both experiments showed distinct trends and an attempt at explanation was made. Key Words: Diatom, Trinitrotoluene, Photoluminescenc

An ABC Transporter Is Required for Secretion of Peptide Sex Pheromones in Enterococcus faecalis

ABSTRACT Enterococci are leading causes of hospital-acquired infection in the United States and continue to develop resistances to new antibiotics. Many Enterococcus faecalis isolates harbor pheromone-responsive plasmids that mediate horizontal transfer of even large blocks of chromosomal genes, resulting in hospital-adapted strains over a quarter of whose genomes consist of mobile elements. Pheromones to which the donor cells respond derive from lipoprotein signal peptides. Using a novel bacterial killing assay dependent on the presence of sex pheromones, we screened a transposon mutant library for functions that relate to the production and/or activity of the effector pheromone. Here we describe a previously uncharacterized, but well-conserved, ABC transporter that contributes to pheromone production. Using three distinct pheromone-dependent mating systems, we show that mutants defective in expressing this transporter display a 5- to 6-order-of-magnitude reduction in conjugation efficiency. In addition, we demonstrate that the ABC transporter mutant displays an altered biofilm architecture, with a significant reduction in biofilm biomass compared to that of its isogenic parent, suggesting that pheromone activity also influences biofilm development. The conservation of this peptide transporter across the Firmicutes suggests that it may also play an important role in cell-cell communication in other species within this important phylum

DNA assays for genetic discrimination of three Phragmites australis subspecies in the United States

Premise: To genetically discriminate subspecies of the common reed (Phragmites australis), we developed real-time quantitative (qPCR) assays for identifying P. australis subsp. americanus, P. australis subsp. australis, and P. australis subsp. berlandieri. Methods and Results: Utilizing study-generated chloroplast DNA sequences, we developed three novel qPCR assays. Assays were verified on individuals of each subspecies and against two non-target species, Arundo donax and Phalaris arundinacea. One assay amplifies only P. australis subsp. americanus, one amplifies P. australis subsp. australis and/or P. australis subsp. berlandieri, and one amplifies P. australis subsp. americanus and/or P. australis subsp. australis. This protocol enhances currently available rapid identification methods by providing genetic discrimination of all three subspecies. Conclusions: The newly developed assays were validated using P. australis samples from across the United States. Application of these assays outside of this geographic range should be preceded by additional testing

Biogeographical comparison of the emergent macrophyte, Sagittaria platyphylla in its native and introduced ranges

Understanding why some plant species become invasive is important to predict and prevent future weed threats and identify appropriate management strategies. Many hypotheses have been proposed to explain why plants become invasive, yet few studies have quantitatively compared plant and population parameters between native and introduced range populations to gain an objective perspective on the causes of plant invasion. The present study uses a biogeographical field survey to compare morphological and reproductive traits and abundance between the native range (USA) and two introduced ranges (Australia and South Africa) of Sagittaria platyphylla (Engelm.) J.G. Sm (Alismataceae), a highly invasive freshwater macrophyte. Introduced and native populations differed in sexual reproductive output with the number of achenes per fruiting head and individual achene weight found to be 40% and 50% greater in introduced populations respectively. However, no other morphological traits were found to be consistently different between the native and both introduced ranges, especially after taking into account differences in environmental conditions between the three ranges. Although populations in introduced regions were larger and occupied greater percentage cover, no differences in plant density were evident. Our results suggest that, apart from sexual reproduction, many of the trait patterns observed in S. platyphylla are influenced by environmental and habitat conditions within the native and invaded ranges. We conclude that the enemy release hypothesis best explains the results observed for sexual reproduction. In particular, we hypothesise that a release from natural enemies, specifically a pre-dispersal seed predator, may induce reproductive plasticity in S. platyphylla

High-pressure spectroscopic investigation of multiferroic Ni3TeO6

We combined diamond anvil cell techniques, infrared and Raman spectroscopies, and lattice dynamics calculations to explore the high pressure properties of multiferroic Ni3TeO6. Using a frequency trend analysis, we trace a subtle decrease in compressibility near 4 GPa to a minimum in the O-Ni2-O bond angle. This unique behavior emanates from the proximity of the Ni2 center in the Ni3-Ni2-Ni1-Te chain to a flexible pocket that is intrinsic to the crystal structure. At the same time, predicted trends in the superexchange pathways are consistent with greater antiferromagnetic character under compression, in line with both phase stability calculations and direct susceptibility measurements. These findings highlight opportunities for local structure control of corundumlike materials

Integrating Invasive Weed Biological Control in Aquatic Ecosystem Restoration Projects

A primary goal of many aquatic ecosystem restoration (AER) projects is to alter and improve plant communities by increasing relative abundance of native species while reducing invasive species abundance, establishment, and spread. Biological control or the use of host-specific pathogens, predators, or herbivores from the native range of a target invader, has been used for invasive plant control, but underutilized as part of integrated pest management (IPM) in government-sponsored AER programs. Weed biological control should be vetted and integrated where possible in all project phases—planning, design, implementation, and maintenance. Using a publicly-funded AER framework—U.S. Army Corps of Engineers or USACE—we define and describe biological control, how it can be seamlessly incorporated at various project stages, a list of common invasive plants that have approved biological controls, and regulatory issues surrounding implementation. Our aim is to illustrate to project managers, planners, environmental personnel, and economists how regulatory agency-approved biological control agents can be a valuable component of AER projects to assist in meeting vegetation community restoration trajectory goals

Melt analysis of mismatch amplification mutation assays (melt-MAMA): a functional study of a cost-effective SNP genotyping assay in bacterial models.

Single nucleotide polymorphisms (SNPs) are abundant in genomes of all species and biologically informative markers extensively used across broad scientific disciplines. Newly identified SNP markers are publicly available at an ever-increasing rate due to advancements in sequencing technologies. Efficient, cost-effective SNP genotyping methods to screen sample populations are in great demand in well-equipped laboratories, but also in developing world situations. Dual Probe TaqMan assays are robust but can be cost-prohibitive and require specialized equipment. The Mismatch Amplification Mutation Assay, coupled with melt analysis (Melt-MAMA), is flexible, efficient and cost-effective. However, Melt-MAMA traditionally suffers from high rates of assay design failures and knowledge gaps on assay robustness and sensitivity. In this study, we identified strategies that improved the success of Melt-MAMA. We examined the performance of 185 Melt-MAMAs across eight different pathogens using various optimization parameters. We evaluated the effects of genome size and %GC content on assay development. When used collectively, specific strategies markedly improved the rate of successful assays at the first design attempt from ~50% to ~80%. We observed that Melt-MAMA accurately genotypes across a broad DNA range (~100 ng to ~0.1 pg). Genomic size and %GC content influence the rate of successful assay design in an independent manner. Finally, we demonstrated the versatility of these assays by the creation of a duplex Melt-MAMA real-time PCR (two SNPs) and conversion to a size-based genotyping system, which uses agarose gel electrophoresis. Melt-MAMA is comparable to Dual Probe TaqMan assays in terms of design success rate and accuracy. Although sensitivity is less robust than Dual Probe TaqMan assays, Melt-MAMA is superior in terms of cost-effectiveness, speed of development and versatility. We detail the parameters most important for the successful application of Melt-MAMA, which should prove useful to the wider scientific community