Statistics for fixed points of the self-power map

The map x -> x^x modulo p is related to a variation of the digital signature scheme in a similar way to the discrete exponentiation map, but it has received much less study. We explore the number of fixed points of this map by a statistical analysis of experimental data. In particular, the number of fixed points can in many cases be modeled by a binomial distribution. We discuss the many cases where this has been successful, and also the cases where a good model may not yet have been found.Comment: 11 pages, 7 figures; replaced theoretical bounds with stronger ones from elsewhere, fixed some typo

High prices for rare species can drive large populations extinct: the anthropogenic Allee effect revisited

Consumer demand for plant and animal products threatens many populations with extinction. The anthropogenic Allee effect (AAE) proposes that such extinctions can be caused by prices for wildlife products increasing with species rarity. This price-rarity relationship creates financial incentives to extract the last remaining individuals of a population, despite higher search and harvest costs. The AAE has become a standard approach for conceptualizing the threat of economic markets on endangered species. Despite its potential importance for conservation, AAE theory is based on a simple graphical model with limited analysis of possible population trajectories. By specifying a general class of functions for price-rarity relationships, we show that the classic theory can understate the risk of species extinction. AAE theory proposes that only populations below a critical Allee threshold will go extinct due to increasing price-rarity relationships. Our analysis shows that this threshold can be much higher than the original theory suggests, depending on initial harvest effort. More alarmingly, even species with population sizes above this Allee threshold, for which AAE predicts persistence, can be destined to extinction. Introducing even a minimum price for harvested individuals, close to zero, can cause large populations to cross the classic anthropogenic Allee threshold on a trajectory towards extinction. These results suggest that traditional AAE theory may give a false sense of security when managing large harvested populations

The Interactive Effects of Multiple Stressors on Lithobates catesbeianus and Anaxyrus americanus

Amphibian populations worldwide have experienced dramatic declines, and many species have already become locally, regionally, or globally extirpated with thousands more being threatened with extinction. These declines have occurred more rapidly in amphibians than any other group of vertebrates, which is especially concerning to scientists because amphibians serve as indicator species of overall environmental health. Major causes for amphibian declines are discussed in Chapter 1 and include: habitat modification and destruction, commercial over-exploitation, introduced species, environmental contaminants, global climate change, and infectious diseases. Chapter 2 discusses the major research aspects of the thesis by examining the interactive effects of multiple stressors on two species of larval amphibians. The study investigated the individual and combined effects of a major environmental contaminant (Glyphosate, commercial Roundup ®), increased temperatures, and predatory cues on survival, growth, and development of tadpoles from two species (Lithobates catesbeianus and Anaxyrus americanus). Glyphosate reduced tadpole survival in both amphibian species and becomes more toxic to tadpoles as temperature increases. Increased temperature reduced survivorship over time in both species; however, survivorship decreased only when temperature interacted with glyphosate. Increased temperature also caused a decrease in growth in L. catesbeianus and an increase in growth and development in A. americanus. Accelerated growth and development caused by temperature may ameliorate the adverse effects of glyphosate by reducing larval period and increasing size at metamorphosis. Glyphosate caused significant anatomical shape variation in L. catebeianus, while increased temperature caused significant anatomical shape variation in A. americanus. The shape variations caused by the different stressors may lead to further developmental and behavioral abnormalities. Predatory cues had no effect on A. americanus survival, and only decreased growth and development at intermediate glyphosate concentrations and temperatures; therefore, the effects of temperature and glyphosate concentration may have been enhanced in the presence of predatory cues. The study highlighted the importance of examining the interactions between multiple stressors on amphibian declines. Chapter 3 focuses on potential solutions for global amphibian declines. Conservation efforts such as educational outreach, effective land management and water quality regulation guidelines, captive breeding programs, and several others are discussed

Pumpable two-part resin cable bolt bonding material tests

The Australian underground mining industry extensively uses thixotropic cementitious grout as a bonding agent for cable bolts. Grout is very effective as a bonding agent but is prone to issues with consistently achieving full column encapsulation and has operational issues impacting production. An economically viable two-part resin bonding agent is being investigated by Jennmar which offers some operational advantages. This paper explores the bond strength evaluation of the two-part resin against cementitious grout

Development, trials and testing of an innovative method to improve strength characteristics of hollow cable bolts

The 70 t Sumo is a resin point-anchored, pre-tensioned, post-grouted hollow cable bolt for tunnel roof support, particularly in poor ground conditions. An innovative ancillary product to the 70 t Sumo is the Booster cable, which is designed to reinforce the Sumo and enhance the systems shear and tensile performance. The Booster cable is an 11 mm 7-wire PC strand with a nominal breaking load of 15 tonnes, which is inserted into the hollow centre tube of the 70 t Sumo after grouting, while the grout is still pliable. Theoretically, the Booster can increase the tensile and shear capacity of the 70 t Sumo by up to 20%. The Booster reinforced 70 t Sumo is useful in high demand conditions where additional support strength is required without the need to install new support. This paper will present results from laboratory tests undertaken to quantify the tensile and shear characteristics of the 70 t Sumo reinforced with the Booster cable. A case study of a support trial using Booster reinforced 70 t Sumo cable bolts at a Dendrobium is also presented in this paper. The Booster cable successfully reduced 70 t Sumo cable bolt densities by 25%, from four cables per meter to three

Cotranslational Pulling Forces Alter Outcomes of Protein Synthesis

As nascent proteins are synthesized by the ribosome, interactions between the nascent protein and its environment can create pulling forces that are transmitted to the ribosome's catalytic center. These forces can affect the rate and outcomes of translation. We use atomistic and coarse-grained simulation to characterize the origins of pulling forces, the propagation of force to catalytic center of the ribosome, and the effects of force on synthetic outcomes. We uncover a novel form of pulling force-mediated regulation in which the forces generated by the integration of a transmembrane helix induce frameshifting in a viral polyprotein. Computational force measurements of hundreds of mutant viral sequences in combination with deep mutational scanning experiments reveal the structural and sequence-level features that enable this powerful regulatory mechanism. Force measurements are also used to provide a molecular picture for complex pulling force experiments on multispanning membrane proteins. In particular, we identify signatures of cotranslational helix packing interactions and the translocation of surface helices. To understand how forces are propagated through the nascent protein in the ribosomal exit tunnel, we ran and analyzed hundreds of microseconds of atomistic molecular dynamics with an applied pulling force on the nascent protein. The simulations reveal how the secondary structure of nascent proteins and their interactions with the ribosome control force propagation. The inhibition of force transduction by nascent protein-ribosome interactions explains how amino acids tens of angstroms away from the catalytic center of the ribosome can still influence the force-induced restart of stalled ribosomes.</p

Studies in biological surface science: microfluidics, photopatterning and artificial bilayers

Herein is presented the collective experimental record of research performed in the Laboratory for Biological Surface Science. These investigations are generally classified under the category of bioanalytical surface science and include the following projects. Chapters III and IV describe the creation of a microfluidic device capable of generating fixed arrays of concentration gradients. Experimental results were matched with computational fluid dynamics simulations to predict analyte distributions in these systems. Chapters V and VI demonstrate the discovery and utility of photobleaching fluorophores for micropatterning applications. Bleached fluorophores were found to rapidly attach to electron rich surfaces and this property was used to pattern enzymes inside microfluidic channels in situ. Finally, Chapter VII exhibits a method by which solid supported lipid bilayers can be dried and preserved by specifically bound proteins. The intrinsic property of lateral lipid mobility was maintained during this process and a mechanism by which the protein protects the bilayer was suggested

PinR mediates the generation of reversible population diversity in Streptococcus zooepidemicus

Opportunistic pathogens must adapt to and survive in a wide range of complex ecosystems. Streptococcus zooepidemicus is an opportunistic pathogen of horses and many other animals, including humans. The assembly of different surface architecture phenotypes from one genotype is likely to be crucial to the successful exploitation of such an opportunistic lifestyle. Construction of a series of mutants revealed that a serine recombinase, PinR, inverts 114 bp of the promoter of SZO_08560, which is bordered by GTAGACTTTA and TAAAGTCTAC inverted repeats. Inversion acts as a switch, controlling the transcription of this sortase-processed protein, which may enhance the attachment of S. zooepidemicus to equine trachea. The genome of a recently sequenced strain of S. zooepidemicus, 2329 (Sz2329), was found to contain a disruptive internal inversion of 7 kb of the FimIV pilus locus, which is bordered by TAGAAA and TTTCTA inverted repeats. This strain lacks pinR and this inversion may have become irreversible following the loss of this recombinase. Active inversion of FimIV was detected in three strains of S. zooepidemicus, 1770 (Sz1770), B260863 (SzB260863) and H050840501 (SzH050840501), all of which encoded pinR. A deletion mutant of Sz1770 that lacked pinR was no longer capable of inverting its internal region of FimIV. The data highlight redundancy in the PinR sequence recognition motif around a short TAGA consensus and suggest that PinR can reversibly influence the wider surface architecture of S. zooepidemicus, providing this organism with a bet-hedging solution to survival in fluctuating environments