Population growth rate of a common understory herb decreases non-linearly across a gradient of deer herbivory

Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Forest Ecology and Management 257 (2009): 1095-1103, doi:10.1016/j.foreco.2008.11.018.Overabundant white-tailed deer (Odocoileus virginianus) are a significant management problem in North America that exert unprecedented herbivory pressure on native understory forest communities. Conserving understory plant populations requires quantifying a sustainable level of deer herbivory. To date, most population projection models consider only deer presence and absence. To estimate population growth rate along a gradient of herbivory, we focused on Trillium grandiflorum because it is a common understory species and a bellwether of deer effects and forest decline. We used matrix population models, and employed both prospective and retrospective analyses using a regression life table response experiment (LTRE). Deer affect size, stage and population dynamics of T. grandiflorum. Because deer target flowering and large non-flowering stages of T. grandiflorum, these individuals do not produce seed in the year they are browsed and are more likely to regress in stage and size in the following growing season relative to non-browsed plants. Importantly, sustained high browse levels result in populations dominated by small, non-flowering individuals. Our LTRE revealed a significant negative and decelerating relationship between herbivory and λ. This non-linearity occurs at the highest herbivory levels because highly browsed populations become dominated by stages that deer do not consume and are thus buffered from rapid decline. However, population extinction is expected when herbivory is greater than the pivotal value of ~15%. Our study demonstrates that levels of deer herbivory commonly experienced by forest understory perennials are sufficient to cause the loss of T. grandiflorum and likely other co-occurring palatable species.We thank the National Science Foundation (DEB-0105000 and DEB-0108208 to SK), McKinley and Darbarker Research Funds and Botany in Action (Phipps Conservatory and Botanical Garden) for funding

Bioenergetic Changes during Differentiation of Human Embryonic Stem Cells along the Hepatic Lineage.

Mitochondrial dysfunction has been demonstrated to result in premature aging due to its effects on stem cells. Nevertheless, a full understanding of the role of mitochondrial bioenergetics through differentiation is still lacking. Here we show the bioenergetics profile of human stem cells of embryonic origin differentiating along the hepatic lineage. Our study reveals especially the transition between hepatic specification and hepatic maturation as dependent on mitochondrial respiration and demonstrates that even though differentiating cells are primarily dependent on glycolysis until induction of hepatocyte maturation, oxidative phosphorylation is essential at all stages of differentiation

Modeling of MnS precipitation during the crystallization of grain oriented silicon steel

The process of manganese sulfide formation in the course of grain-oriented silicon steel solidification process is described in the paper. Fine dispersive MnS inclusions are grain growth inhibitors and apart from AlN inclusions they contribute to the formation of a privileged texture, i.e. Goss texture. A computer simulation of a high-silicon steel ingot solidification with the use of author’s software has been performed. Ueshima model was adapted for simulating the 3 % Si steel ingot solidification. The calculations accounted for the back diffusion effect according to Wołczyński equation. The computer simulation results are presented in the form of plots representing the process of steel components segregation in a solidifying ingot and curves illustrating the inclusion separation process

Population genetic structure of three species in the genus Astrocaryum G. Mey. (Arecaceae).

We assessed the level and distribution of genetic diversity in three species of the economically important palm genus Astrocaryum located in Pará State, in northern Brazil. Samples were collected in three municipalities for Astrocaryum aculeatum: Belterra, Santarém, and Terra Santa; and in two municipalities for both A. murumuru: Belém and Santo Antônio do Tauá and A. paramaca: Belém and Ananindeua. Eight microsatellite loci amplified well and were used for genetic analysis. The mean number of alleles per locus for A. aculeatum, A. murumuru, and A. paramaca were 2.33, 2.38, and 2.06, respectively. Genetic diversity was similar for the three species, ranging from HE = 0.222 in A. aculeatum to HE = 0.254 in A. murumuru. Both FST and AMOVA showed that most of the genetic variation was found within populations for all three species, but high genetic differentiation among populations was found for A. aculeatum. Three loci were not in Hardy-Weinberg equilibrium, with populations of A. paramaca showing a tendency for the excess of heterozygotes (FIS = -0.144). Gene flow was high for populations of A. paramaca (Nm = 19.35). Our results suggest that the genetic diversity within populations followed the genetic differentiation among populations due to high gene flow among the population. Greater geographic distances among the three collection sites for A. aculeatum likely hampered gene flow for this species

Modelling of non-metallic particles motion process in foundry alloys

The behaviour of non-metallic particles in the selected composites was analysed, in the current study. The calculations of particles floating in liquids differing in viscosity were performed. Simulations based on the Stokes equation were made for spherical SiC particles and additionally the particle size influence on Reynolds number was analysed.The movement of the particles in the liquid metal matrix is strictly connected with the agglomerate formation problem.Some of collisions between non-metallic particles lead to a permanent connection between them. Creation of the two spherical particles and a metallic phase system generates the adhesion force. It was found that the adhesion force mainly depends on the surface tension of the liquid alloy and radius of non-metallic particles

Modelling of the crystallization front – particles interactions in ZnAl/(SiC)p composites

The presented work focuses on solid particle interactions with the moving crystallization front during a solidification of the metal matrix composite. The current analyses were made for silicon carbide particles and ZnAl alloy with different additions of aluminium. It was found, that the chemical composition of the metal matrix influences the behaviour of SiC particles. At the same time calculations of the forces acting on a single particle near the crystallization front were performed. For each alloy type the critical conditions that determine whether particle will be absorbed or pushed, were specified

Testing the limits of SMILES-based de novo molecular generation with curriculum and deep reinforcement learning

Deep reinforcement learning methods have been shown to be potentially powerful tools for de novo design. Recurrent-neural-network-based techniques are the most widely used methods in this space. In this work we examine the behaviour of recurrent-neural-network-based methods when there are few (or no) examples of molecules with the desired properties in the training data. We find that targeted molecular generation is usually possible, but the diversity of generated molecules is often reduced and it is not possible to control the composition of generated molecular sets. To help overcome these issues, we propose a new curriculum-learning-inspired recurrent iterative optimization procedure that enables the optimization of generated molecules for seen and unseen molecular profiles, and allows the user to control whether a molecular profile is explored or exploited. Using our method, we generate specific and diverse sets of molecules with up to 18 times more scaffolds than standard methods for the same sample size; however, our results also point to substantial limitations of one-dimensional molecular representations, as used in this space. We find that the success or failure of a given molecular optimization problem depends on the choice of simplified molecular-input line-entry system (SMILES)

Occurrence of airborne spores of fungi causing grain mould over a sorghum crop

Airborne spores of Fusarium, Curvularia and Alternaria species which cause sorghum grain mould were monitored over rainy season crops of the grain-mould susceptible sorghum hybrid CSH 1 using a Hirst spore trap. Spore trapping began at the flowering stage (GS 61) and was continued beyond grain maturity (GS 92). Spores of all three fungal genera were present during the post-flowering stages. However, more spores were trapped after the hard dough stage (GS 87) than at earlier growth stages. Spore content in the air increased after grain maturity (GS 92) under moist or humid conditions. Fusarium spores were most prevalent before dawn, whereas most spores of Alternaria and Curvularia were trapped during the day. The frequency of Fusarium and Alternaria spores in the two years differed while that of Curvularia was similar in both years. The predominant species isolated from surface-sterilized moulded grain on malt-streptomycin agar were A. tenuissima, F. moniliforme, C. lunata and Phoma sorghina. These results prove that spores of mould causal fungi were naturally available in the air and initiated grain mould epidemics under suitable weather conditions

Time of flight measurements based on FPGA using a breast dedicated PET

In this work the implementation of a Time-to-Digital Converter (TDC) using a Nutt delay line FPGA-based and applied on a Positron Emission Tomography (PET) device is going to be presented in order to check the system’s suitability for Time of Flight (TOF) measurements. In recent years, FPGAs have shown great advantages for precise time measurements in PET. The architecture employed for these measurements is described in detail. The system developed was tested on a dedicated breast PET prototype, composed of LYSO crystals and Positive Sensitive Photomultipliers (PSPMTs). Two distinct experiments were carried out for this purpose. In the first test, system linearity was evaluated in order to calibrate the time measurements, providing a linearity error of less than 2% and an average time resolution of 1.4 ns FWHM. The second set of measurements tested system resolution, resulting in a FWHM as good as 1.35 ns. The results suggest that the coincidence window for the current PET can be reduced in order to minimize the random events and thus, achieve better image qualityAguilar, A.; García Olcina, R.; Martos, J.; Soret, J.; Torres-Pais, J.; Benlloch Baviera, JM.; González Martínez, AJ.... (2014). Time of flight measurements based on FPGA using a breast dedicated PET. Journal of Instrumentation. 9:0-8. doi:10.1088/1748-0221/9/05/C05012S08