Strength of webs of I-beams and girders,

Cover title

Reverie

https://digitalcommons.library.umaine.edu/mmb-ps/1620/thumbnail.jp

Fluctuation Induced Instabilities in Front Propagation up a Co-Moving Reaction Gradient in Two Dimensions

We study 2D fronts propagating up a co-moving reaction rate gradient in finite number reaction-diffusion systems. We show that in a 2D rectangular channel, planar solutions to the deterministic mean-field equation are stable with respect to deviations from planarity. We argue that planar fronts in the corresponding stochastic system, on the other hand, are unstable if the channel width exceeds a critical value. Furthermore, the velocity of the stochastic fronts is shown to depend on the channel width in a simple and interesting way, in contrast to fronts in the deterministic MFE. Thus, fluctuations alter the behavior of these fronts in an essential way. These affects are shown to be partially captured by introducing a density cutoff in the reaction rate. Some of the predictions of the cutoff mean-field approach are shown to be in quantitative accord with the stochastic results

Discovering qualitative empirical laws

In this paper we describe GLAUBER, an AI system that models the scientific discovery of qualitative empirical laws. We have tested the system on data from the history of early chemistry, and it has rediscovered such concepts as acids, alkalis, and salts, as well as laws relating these concepts. After discussing GLAUBER we examine the program's relation to other discovery systems, particularly methods for conceptual clustering and language acquisition

Social Media and Social Order

Social Media and Social Order combines a structural analysis of the global impact of social media as contributing to the production of a datafied social order with a series of actor-focused analyses, each examining how roles structured by social media are performed at various sites: enmeshed in European cities, entangled in contested Middle Eastern borders, and embedded in provincial Indian small-town networks. The final section then arcs back to a focus on the general properties of social media networks revealed through two American cases, emphasizing the human costs for the recipients of abuse (legislators of color) and the political costs of participatory propaganda for a deliberative understanding of democracy. A central theme is how the principle of differential treatment embedded in the datafied social order is becoming increasingly widespread across social fields. The book demonstrates how social media are implicated in reshaping social order in ways which align with this principle, including creating new precarious hierarchies of esteem, reinforcing existing social, class and religious hierarchies, opening political discussion to more participants but at the cost of reinforcing local hierarchies and dominant discourses, underlining gendered constructions of national identity, amplifying the abuse received by women and people of color in leadership positions and enmeshing users in the circulation of propaganda which resonates with their preconceptions, thus deepening societal polarization

Syntactic versus lexical therapy for anomia in acquired aphasia: differential effects on narrative and conversation

Background: Previous studies of therapy for acquired anomia have treated nouns in isolation. The effect on nouns in connected speech remains unclear. In a recent study in 2012, we used a novel noun syntax therapy and found an increase in the number of determiner plus noun constructions in narrative after therapy. Aims: Two aims arose from the previous study: to identify the critical ingredient in the noun syntax therapy, specifically whether this is lexical production, or the syntactic context; and to extend the analysis of the effects beyond narrative into conversation. Methods & Procedures: We compared the effects of lexical therapy with those of noun syntax therapy in one individual with aphasia, in a sequential intervention design. We analysed the effects on conversation and on narrative. Outcomes & Results: There was improved picture naming of treated words after both therapies. Lexical therapy had no impact on narrative and conversation, whereas noun syntax therapy led to more noun production, primarily in the context of determiner plus noun combinations. Conclusions & Implications: The results support the claim that greater impact on narrative and conversation can be achieved for some people with aphasia by treating nouns in syntactic contexts

Front Propagation up a Reaction Rate Gradient

We expand on a previous study of fronts in finite particle number reaction-diffusion systems in the presence of a reaction rate gradient in the direction of the front motion. We study the system via reaction-diffusion equations, using the expedient of a cutoff in the reaction rate below some critical density to capture the essential role of fl uctuations in the system. For large density, the velocity is large, which allows for an approximate analytic treatment. We derive an analytic approximation for the front velocity depe ndence on bulk particle density, showing that the velocity indeed diverge s in the infinite density limit. The form in which diffusion is impleme nted, namely nearest-neighbor hopping on a lattice, is seen to have an essential impact on the nature of the divergence

The effects of irradiation on the biological and biomechanical properties of an acellular porcine superflexor tendon graft for cruciate ligament repair

Acellular xenogeneic tissues have the potential to provide ‘off‐the‐shelf’ grafts for anterior cruciate ligament (ACL) repair. To ensure that such grafts are sterile following packaging, it is desirable to use terminal sterilization methods. Here, the effects of gamma and electron beam irradiation on the biological and biomechanical properties of a previously developed acellular porcine superflexor tendon (pSFT) were investigated. Irradiation following treatment with peracetic acid was compared to peracetic acid treatment alone and the stability of grafts following long‐term storage assessed. Irradiation did not affect total collagen content or biocompatibility (determined using a contact cytotoxicity assay) of the grafts, but slightly increased the amount of denatured collagen in and decreased the thermal denaturation temperature of the tissue in a dose dependant fashion. Biomechanical properties of the grafts were altered by irradiation (reduced ultimate tensile strength and Young's modulus, increased failure strain), but remained superior to reported properties of the native human ACL. Long term storage at 4°C had no negative effects on the grafts. Of all the conditions tested, a dose of minimum 25 kGy of gamma irradiation had least effect on the grafts, suggesting that this dose produces a biocompatible pSFT graft with adequate mechanical properties for ACL repair

Decellularization and Characterization of Porcine Superflexor Tendon: A Potential Anterior Cruciate Ligament Replacement

The porcine superflexor tendon (SFT) was identified as having appropriate structure and properties for development of a decellularised device for use in ACL reconstruction. SFTs were decellularised using a combination of freeze thaw and washes in hypotonic buffer and 0.1% (w/v) SDS in hypotonic buffer plus proteinase inhibitors followed by nuclease treatment and sterilisation using peracetic acid. The decellularised biological scaffold was devoid of cells and cell remnants and contained only 13 ng.mg-1 (dry weight) residual total DNA. Immunohistochemistry showed retention of collagens type I and III and tenascin-C. Quantitative analysis of sulphated sugar and hydroxyproline content revealed a loss of glycosaminoglycans compared to native tissue but no loss of collagen. The decellularised SFT was biocompatible in vitro and in vivo following implantation in a mouse subcutaneous model for 12 weeks. Uniaxial tensile testing to failure indicated that the gross material properties of decellularised SFT were not significantly different to native tissue. Decellularised SFTs had an ultimate tensile strength of 61.8 ± 10.3 MPa (± 95 % confidence limits), a failure strain of 0.29 ± 0.04 and a Young’s modulus of the collagen phase of 294.1 ± 61.9 MPa. Analysis of the presence of the alpha-Gal (galactose-α-1,3-galactose) epitope by immunohistochemistry, lectin binding and antibody absorption assay indicated that the epitope was reduced but still present post decellularisation. This is discussed in light of the potential role of non-cellular alpha-Gal in the acceleration of wound healing and tissue regeneration in the presence of antibodies to alpha-Gal