Genetic variation in parasites has important consequences for host–parasite interactions. Prior studies of the ecologically important parasite Metschnikowia bicuspidata have suggested low genetic variation in the species. Here, we collected M. bicuspidata from two host species (Daphnia dentifera and Ceriodaphnia dubia) and two regions (Michigan and Indiana, USA). Within a lake, outbreaks tended to occur in one host species but not the other. Using microsatellite markers, we identified six parasite genotypes grouped within three distinct clades, one of which was rare. Of the two main clades, one was generally associated with D. dentifera, with lakes in both regions containing a single genotype. The other M. bicuspidata clade was mainly associated with C. dubia, with a different genotype dominating in each region. Despite these associations, both D. dentifera- and C. dubia-associated genotypes were found infecting both hosts in lakes. However, in lab experiments, the D. dentifera-associated genotype infected both D. dentifera and C. dubia, but the C. dubia-associated genotype, which had spores that were approximately 30% smaller, did not infect D. dentifera. We hypothesize that variation in spore size might help explain patterns of cross-species transmission. Future studies exploring the causes and consequences of variation in spore size may help explain patterns of infection and the maintenance of genotypic diversity in this ecologically important system.

Surface albedo typically dominates the mass balance of mountain glaciers, though long-term trends and patterns of glacier albedo are seldom explored. We calculated broadband shortwave albedo for glaciers in the central Chilean Andes (33–34°S) using end-of-summer Landsat scenes between 1986 and 2020. We found a high inter-annual variability of glacier-wide albedo that is largely a function of the glacier fractional snow-covered area and the total precipitation of the preceding hydrological year (up to 69% of the inter-annual variance explained). Under the 2010–2020 ‘Mega Drought’ period, the mean albedo, regionally averaged ranging from ~0.25–0.5, decreased by −0.05 on average relative to 1986–2009, with the greatest reduction occurring 3500–5000 m a.s.l. In 2020, differences relative to 1986–2009 were −0.14 on average as a result of near-complete absence of late summer snow cover and the driest hydrological year since the Landsat observation period began (~90% reduction of annual precipitation relative to the 1986–2009 period). We found statistically significant, negative trends in glacier ice albedo of up to −0.03 per decade, a trend that would have serious implications for the future water security of the region, because glacier ice melt acts to buffer streamflow shortages under severe drought conditions.

Using an ensemble of close- and long-range remote sensing, lake bathymetry and regional meteorological data, we present a detailed assessment of the geometric changes of El Morado Glacier in the Central Andes of Chile and its adjacent proglacial lake between 1932 and 2019. Overall, the results revealed a period of marked glacier down wasting, with a mean geodetic glacier mass balance of −0.39 ± 0.15 m w.e.a−1 observed for the entire glacier between 1955 and 2015 with an area loss of 40% between 1955 and 2019. We estimate an ice elevation change of −1.00 ± 0.17 m a−1 for the glacier tongue between 1932 and 2019. The increase in the ice thinning rates and area loss during the last decade is coincident with the severe drought in this region (2010–present), which our minimal surface mass-balance model is able to reproduce. As a result of the glacier changes observed, the proglacial lake increased in area substantially between 1955 and 2019, with bathymetry data suggesting a water volume of 3.6 million m3 in 2017. This study highlights the need for further monitoring of glacierised areas in the Central Andes. Such efforts would facilitate a better understanding of the downstream impacts of glacier downwasting.

Evidence from the Piovego, the fraud magistracy of early modern Venice, offers a critical perspective on the documentary record of credit and the ways in which this was used in practice. Although it was formally illegal to charge interest on personal loans, a variety of legal fictions were employed to evade the ban. Such fictions significantly reduced the transparency and certainty of exchange, pushing personal loans into a world of semi-legality. This was a ‘baroque economy’, in which people were aware of the potential discrepancy between surface form and underlying substance, and private agreements might be contested on grounds of substantive fairness. The ‘hidden transcripts’ presented by litigants indicate that the formal record must be interpreted through a ‘thick description’ that considers its role as a resource in a broader process of negotiation. Far from being a ‘market’, characterized by price competition, choice, and transparency, the informal economy of credit was embedded in long-term power relationships. Rather than celebrating intermediaries such as brokers and notaries as facilitators of ‘market’ relations, we need to understand them as part of a hierarchical network of power and wealth, embedded in long-term relationships.

The acceptance of no-till crop production systems has been limited due to expected problems with weed management. Field experiments were established at two locations in Ontario in 1988 and one location in 1989. Band or broadcast applications of preemergence (PRE) combinations of high or low label rates of atrazine with or without metolachlor or inter-row cultivation, were evaluated for their effectiveness in controlling annual weeds in no-till corn. At each location, different herbicide and cultivation combinations were required to achieve adequate weed control. Corn grain yield was equivalent regardless of whether herbicides were applied as a band or broadcast treatment at all three sites. At two of the three sites, one cultivation combined with herbicides applied as a band was adequate to maintain weed control and corn grain yields. Selective application of herbicides in bands represented an approximate 60% reduction in total herbicide applied into the environment. The integration of a shallow post-plant inter-row cultivation combined with the soil conservation attributes of no-till, would enhance the sustainability of a modified no-till corn production system.

Field experiments evaluating 11 cereal cover crops were established at two locations in Ontario over a two-year period. Cover crops were interseeded into a ridge-tillage corn crop and evaluated in terms of biomass production and winter annual, biennial, and perennial weed species suppression. Seedling establishment and aboveground biomass production of cover crops were variable between locations and years. At both locations over two years, ‘Danko’ winter rye, ‘OAC Halton’ winter barley and ‘Rodeo’ spring barley were the most consistent cover crops in biomass production. However, cover crop residues had no significant effect on weed biomass or density due to a high degree of spatial variability present in the weed populations. Corn grain yields were not reduced by the presence of inter-seeded cover crops when compared with the bare ground control treatment.

Studies were conducted in 1997 and 1998 to evaluate the efficacy and economics of glyphosate-resistant and nontransgenic soybean systems. The three highest yielding glyphosate-resistant and nontransgenic soybean cultivars were chosen each year for three Mississippi locations based on Mississippi Soybean Variety Trials. Treatments within each cultivar/herbicide system included nontreated, low input (one-half of the labeled rate), medium input (labeled rate), and high input level (labeled rate plus an additional postemergence application). In 1997, all systems controlled hemp sesbania by more than 80% but nontransgenic systems controlled hemp sesbania more than the glyphosate-resistant systems in most instances in 1998. High input levels usually controlled pitted morningglory more than low or medium inputs in 1997. In 1998, both systems controlled pitted morningglory by 90% or more at Shelby; however, at other locations control was less than 85%. Soybean yield in 1997 at Shelby was more with the glyphosate-resistant system than with the nontransgenic systems at medium and high input levels, primarily because of early-season injury to a metribuzin-sensitive cultivar in the nontransgenic system. In 1998, soybean yield at Shelby was more with the nontransgenic system than the glyphosate-resistant system, regardless of input level, due to poor late-season hemp sesbania control with glyphosate. Net returns were often more with the glyphosate-resistant system at Shelby in 1997. Within the glyphosate-resistant system, there were no differences in net return between input levels. Within the nontransgenic system, low input level net returns were higher compared to medium and high input levels due to higher soybean yield and less herbicide cost. At Brooksville, using high input levels, the glyphosate-resistant systems net returns were $55.00/ha more than the nontransgenic system. Net returns were higher with the nontransgenic system compared to the glyphosate-resistant system at Shelby in 1998, regardless of input level.

Contemporary research on prehispanic Maya landscapes has focused on caves as core features of the cultural geography. Investigations within a number of large caves have suggested that they served as the loci for important rituals, legitimized inhabitants’ claims to their territory, and helped establish the authority of a site’s ruling elite. The ubiquity and centrality of caves in the Maya worldview raises questions about what happened in regions where large caves did not naturally form. Recent investigations at the site of Maax Na in northern Belize suggest that small caves, despite their diminutive size, still functioned to establish legitimacy and uphold power. The results serve to demonstrate the pervasive power of key ideological concepts in shaping the cultural landscape and indicate the need to take these into account in documenting landmarks at Maya sites, as even the less imposing ones may have been important to their inhabitants.

We determine elemental abundances of He, N, O, Ne, S, and Ar in Magellanic Cloud planetary nebulae (PNe) using direct methods and a large set of observed ions, minimizing the need for ionization correction factors. In contrast to prior studies, we find a clear separation between Type I and non-Type I PNe in these low-metallicity environments, and no evidence that the O-N nucleosynthesis cycle is active in low-mass progenitors. We find that the S/O abundance ratio is anomalously low compared to H ii regions, confirming the “sulfur anomaly” found for Galactic PNe. We also found that Ne/O is elevated in some cases, raising the possibility that Ne yields in low-mass AGB stars may be enhanced at low metallicity.

High-current-density cathodes are required for the development of high-power mm-wave and upper mm-wave devices, as well as for other electron beam applications. To address this need, a current amplifier stage is being developed that will multiply a primary electron-beam current (via the secondary-electron multiplication process) and then emit the amplified beam so as to achieve a current gain of 50-100. Diamond is a particularly promising current amplification source due to the negative electron affinity present at stable hydrogenated surfaces. As such, we are fabricating current amplifiers using single-crystal CVD diamond grown at NRL, with our growth effort focused on reducing the impurity concentration in the epitaxial diamond and on fabricating microns-thick freestanding films. The current amplification characteristics of the diamond films are examined using secondary-electron-emission measurements in both reflection and transmission configurations. In our initial study of an 8.3-µm-thick CVD diamond film, the single-crystal diamond is shown to have superior transport and emission properties compared to similar polycrystalline material. While transmission gains have been obtained under field-free conditions from the unbiased diamond film, we are striving to increase the gain by increasing the transport efficiency in a biased amplifier structure. Towards this end, recent efforts have focused on optimizing the bonding and metallization processes as needed to establish and control the internal electric field. In addition, Monte Carlo simulations are being used to predict the optimal material and device parameters needed to achieve high amplifier gain and low energy spread.

New poly(fluorene-thiophene) alternating copolymers are described in which either the dioctylfluorene or bithiophene units in poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) are replaced by other fluorene or thiophene-based groups, respectively. Improvements in solubility are realized when the bithiophene unit of F8T2 is replaced by dihexylterthiophene or dihexylpentathiophene units. Melting temperatures are also lowered by 50 – 100°C in these polymers when compared to F8T2. Replacement of the bithiophene unit of F8T2 with a dihexylpentathiophene unit also results in a significant improvement in hysteresis (< 2 V vs. 3.5 – 5 V for F8T2). Initial results are also reported on the thermal cleavage of the C8 side groups of F8T2, which yields an insoluble polymeric semiconductor film that continues to exhibit transistor switching characteristics as part of a bottom gate device.

We recently developed an integrated imaging platform that combines single molecule evanescent wave fluorescence imaging (and spectroscopy) with in situ scanning probe microscopy. The advantages, challenges, and potential represented by this coupled tool will be described in the context of the structure-function characteristics of nanostructured biomaterials and thin lipid films.

We recently developed an integrated imaging platform that combines single molecule evanescent wave fluorescence imaging (and spectroscopy) with in situ scanning probe microscopy. The advantages, challenges, and potential represented by this coupled tool will be described in the context of the structure-function characteristics of nanostructured biomaterials and thin lipid films.

In this work, the deposition of silicon carbide lines using a tetramethylsilane (TMS) precursor was investigated. Effects of target temperatures on the morphology and crystal structure of the deposits were examined. It was found that the morphology of the SALD SiC depends strongly on the target temperature. The contour of the cross section of the SiC deposits changes from a triangle to trapezoid to volcano shape and the surface morphology of the deposited lines changes from smooth to rough to porous as the target temperature increases. A critical target temperature was found to be about 700°C to initiate deposition of SiC under the current experimental configurations. X-ray diffraction analyses show that the SALD SiC formed at 1000°C contains both crystalline and amorphous phases. The results are briefly discussed.