2,092 research outputs found
Uniqueness of Lagrangian self-expanders
No full textIn mean curvature flow an important class of solutions are the self-expanders, which move simply by dilations under the flow and provide models for smoothing of singular con-
figurations. In K¨ahler–Einstein manifolds mean curvature flow preserves Lagrangian submanifolds,providing the notion of Lagrangian mean curvature flow. I will describe joint
work with Neves [12] showing that Lagrangian self-expanders in Cn asymptotic to pairs of planes are locally unique if n > 2 and unique if n = 2
Consideration of Interference Correlation Properties in a JD-CDMA Mobile Radio System with Coherent Receiver Antenna Diversity
No full textIn code division multiple access (CDMA) mobile radio systems, both intersymbol interference and multiple access interference arise which can be combatted by using Joint Detection (JD) techniques, to reduce the degradation in performance resulting from time variance, coherent receiver antenna diversity (CRAD) can be used. The application of JD techniques offers the possibility to exploit the knowledge of noise covariances at the receiver. If only intercell (cochannel) interference is considered, the noise covariances in the uplink receiver of a multiple receiver antenna CDMA mobile radio system depend mainly on the directions of arrival (DOAs) of the interfering signals and the receiver antenna placement. Therefore, if the interferer DOAs are known at the base station, these covariances could be estimated. In this thesis, a realistic model of the uplink of a JD CDMA mobile radio system with CRAD is described in which the above mentioned interference cancelling method is used. Simulation results according to this model are given and evaluated.Applied SciencesElectrical EngineeringTelecommunications and Traffic Control Systems Grou
Stability of torsion-free G_2 structures along the Laplacian flow
No full textWe prove that torsion-free G2 structures are (weakly) dynamically stable along the Laplacian flow for closed G2 structures. More precisely, given a torsion-free G2 structure φ¯¯¯ on a compact 7-manifold M, the Laplacian flow with initial value in [φ¯¯¯], sufficiently close to φ¯¯¯, will converge to a point in the Diff0(M)-orbit of φ¯¯¯. We deduce, from fundamental work of Joyce, that the Laplacian flow starting at any closed G2 structure with sufficiently small torsion will exist for all time and converge to a torsion-free G2 structure
Dairy farmers’ perceptions toward the implementation of on-farm Johne’s disease prevention and control strategies
No full textmplementation of specific management strategies on dairy farms is currently the most effective way to reduce the prevalence of Johne’s disease (JD), an infectious chronic enteritis of ruminants caused by Mycobacterium avium subspecies paratuberculosis (MAP). However, dairy farmers often fail to implement recommended strategies. The objective of this study was to assess perceptions of farmers participating in a JD prevention and control program toward recommended practices, and explore factors that influence whether or not a farmer adopts risk-reducing measures for MAP transmission. Semi-structured interviews were conducted with 25 dairy farmers enrolled in a voluntary JD control program in Alberta, Canada. Principles of classical grounded theory were used for participant selection, interviewing, and data analysis. Additionally, demographic data and MAP infection status were collected and analyzed using quantitative questionnaires and the JD control program database. Farmers’ perceptions were distinguished according to 2 main categories: first, their belief in the importance of JD, and second, their belief in recommended JD prevention and control strategies. Based on these categories, farmers were classified into 4 groups: proactivists, disillusionists, deniers, and unconcerned. The first 2 groups believed in the importance of JD, and proactivists and unconcerned believed in proposed JD prevention and control measures. Groups that regarded JD as important had better knowledge about best strategies to reduce MAP transmission and had more JD risk assessments conducted on their farm. Although not quantified, it also appeared that these groups had more JD prevention and control practices in place. However, often JD was not perceived as a problem in the herd and generally farmers did not regard JD control as a “hot topic” in communications with their herd veterinarian and other farmers. Recommendations regarding how to communicate with farmers and motivate various groups of farmers according to their specific perceptions were provided to optimize adoption of JD prevention and control measures and thereby increase success of voluntary JD control programs
Laplacian flow for closed G2 structures: real analyticity
No full textLet φ(t),t∈[0,T0] be a solution to the Laplacian flow for closed G2 structures on a compact 7-manifold M. We show that for each fixed time t∈(0,T0],(M,φ(t),g(t)) is real analytic, where g(t) is the metric induced by φ(t). Consequently, any Laplacian soliton is real analytic and we obtain unique continuation results for the flow
Spacelike Mean Curvature Flow
No full textWe prove long-time existence and convergence results for spacelike solutions to mean curvature flow in the pseudo-Euclidean space Rn,m, which are entire or defined on bounded domains and satisfying Neumann or Dirichlet boundary conditions. As an application, we prove long-time existence and convergence of the G2-Laplacian flow in cases related to coassociative fibrations
Laplacian flow for closed G₂ structures: real analyticity
No full textLet φ(t),t∈[0,T0] be a solution to the Laplacian flow for closed G2 structures on a compact 7-manifold M. We show that for each fixed time t∈(0,T0],(M,φ(t),g(t)) is real analytic, where g(t) is the metric induced by φ(t). Consequently, any Laplacian soliton is real analytic and we obtain unique continuation results for the flow
Laplacian flow for closed G2 structures: Shi-type estimates, uniqueness and compactness
No full textWe develop foundational theory for the Laplacian flow for closed G2 structures which will be essential for future study. (1). We prove Shi-type derivative estimates for the Riemann curvature tensor Rm and torsion tensor T along the flow, i.e. that a bound on
Λ(x,t)=(|∇T(x,t)|2g(t)+|Rm(x,t)|2g(t))12
will imply bounds on all covariant derivatives of Rm and T. (2). We show that Λ(x,t) will blow up at a finite-time singularity, so the flow will exist as long as Λ(x,t) remains bounded. (3). We give a new proof of forward uniqueness and prove backward uniqueness of the flow, and give some applications. (4). We prove a compactness theorem for the flow and use it to strengthen our long time existence result from (2) to show that the flow will exist as long as the velocity of the flow remains bounded. (5). Finally, we study soliton solutions of the Laplacian flow
SU(2)² -invariant G₂ -instantons
No full textWe initiate the systematic study of G₂-instantons with SU(2)² -symmetry. As well as developing foundational theory, we give existence, non-existence and classification results for these instantons. We particularly focus on R⁴ x S³ with its two explicitly known distinct holonomy G₂ metrics, which have different volume growths at infinity, exhibiting the different behaviour of instantons in these settings. We alsogive an explicit example of sequences of G₂-instantons where “bubbling” and “removable singularity” phenomena occur in the limit
Knowledge gaps that hamper prevention and control of Mycobacterium avium subspecies paratuberculosis infection
No full textIn the last decades, many regional and country‐wide control programmes for Johne's disease (JD ) were developed due to associated economic losses, or because of a possible association with Crohn's disease. These control programmes were often not successful, partly because management protocols were not followed, including the introduction of infected replacement cattle, because tests to identify infected animals were unreliable, and uptake by farmers was not high enough because of a perceived low return on investment. In the absence of a cure or effective commercial vaccines, control of JD is currently primarily based on herd management strategies to avoid infection of cattle and restrict within‐farm and farm‐to‐farm transmission. Although JD control programmes have been implemented in most developed countries, lessons learned from JD prevention and control programmes are underreported. Also, JD control programmes are typically evaluated in a limited number of herds and the duration of the study is less than 5 year, making it difficult to adequately assess the efficacy of control programmes. In this manuscript, we identify the most important gaps in knowledge hampering JD prevention and control programmes, including vaccination and diagnostics. Secondly, we discuss directions that research should take to address those knowledge gaps
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