The evolution of surface magnetic fields in young solar-type stars

The surface rotation rates of young solar-type stars decrease rapidly with age from the end of the pre-main sequence though the early main sequence. This suggests that there is also an important change in the dynamos operating in these stars, which should be observable in their surface magnetic fields. Here we present early results in a study aimed at observing the evolution of these magnetic fields through this critical time period. We are observing stars in open clusters and stellar associations to provide precise ages, and using Zeeman Doppler Imaging to characterize the complex magnetic fields. Presented here are results for six stars, three in the in the beta Pic association (~10 Myr old) and three in the AB Dor association (~100 Myr old).Comment: To appear in the proceedings of IAU symposium 302: Magnetic fields throughout stellar evolution. 2 pages, 3 figure

Chart system simplifies identification of complex design assemblies

Identification breakdown chart that lists the component parts required for any specific end item is used to identify rapidly and accurately, from numerous drawings, all the component parts of a complex design assembly. Cylindrical and complex configurations are depicted as continuous flat surfaces for ready identification

A homomorphism between link and XXZ modules over the periodic Temperley-Lieb algebra

We study finite loop models on a lattice wrapped around a cylinder. A section of the cylinder has N sites. We use a family of link modules over the periodic Temperley-Lieb algebra EPTL_N(\beta, \alpha) introduced by Martin and Saleur, and Graham and Lehrer. These are labeled by the numbers of sites N and of defects d, and extend the standard modules of the original Temperley-Lieb algebra. Beside the defining parameters \beta=u^2+u^{-2} with u=e^{i\lambda/2} (weight of contractible loops) and \alpha (weight of non-contractible loops), this family also depends on a twist parameter v that keeps track of how the defects wind around the cylinder. The transfer matrix T_N(\lambda, \nu) depends on the anisotropy \nu and the spectral parameter \lambda that fixes the model. (The thermodynamic limit of T_N is believed to describe a conformal field theory of central charge c=1-6\lambda^2/(\pi(\lambda-\pi)).) The family of periodic XXZ Hamiltonians is extended to depend on this new parameter v and the relationship between this family and the loop models is established. The Gram determinant for the natural bilinear form on these link modules is shown to factorize in terms of an intertwiner i_N^d between these link representations and the eigenspaces of S^z of the XXZ models. This map is shown to be an isomorphism for generic values of u and v and the critical curves in the plane of these parameters for which i_N^d fails to be an isomorphism are given.Comment: Replacement of "The Gram matrix as a connection between periodic loop models and XXZ Hamiltonians", 31 page

Congenital dislocation of the hip, with late diagnosis after 1year of age: Update and management

SummaryWhen congenital dislocation of the hip (CDH) is diagnosed only after walking age, management is greatly complicated. In view of the increasing number of such cases treated by members of the French Society of Paediatric Orthopaedics (SOFOP) in recent years, a 3-part study was conducted within the Society to shed light on the reasons for late diagnosis, to give an update on treatment strategies currently implemented in France, and to report long-term outcomes

AN ANALYSIS OF DRIVERS BEHIND AMERICAN ARMS ACQUISITIONS TO JAPAN AND TAIWAN

Arms acquisitions are an important instrument used to carry out a country’s national defense and foreign policy strategies. For nations with rich histories of arms acquisitions, investigating the motives that encourage purchasing arms offers a look into the state’s security perspectives. Within the Indo-Pacific, several countries that are closely aligned with the United States - namely Japan and Taiwan - have engaged in large volume arms sales with the U.S. in the 21st century. This thesis investigates the factors that have encouraged Japan and Taiwan to purchase American arms in an effort to determine the motives that sustain long-term arms commitments. It examines various domestic and international drivers that have both encouraged and challenged purchases of U.S. made defensive technologies. This thesis argues that both Japan and Taiwan are influenced to pursue arms acquisitions by their long-standing partnerships with the United States, as well as geopolitical security concerns especially the threat of the PRC. However, unique domestic considerations such as Japan’s antimilitarism ideology and Taiwan’s distinctive Cross-Strait relations have played significant roles in hampering arms acquisitions. When combined, these factors offer insights into the complexities of arms acquisitions and suggest that external factors have the greater influence on arms acquisitions versus internal factors.Lieutenant, United States NavyApproved for public release. Distribution is unlimited

Refined conformal spectra in the dimer model

Working with Lieb's transfer matrix for the dimer model, we point out that the full set of dimer configurations may be partitioned into disjoint subsets (sectors) closed under the action of the transfer matrix. These sectors are labelled by an integer or half-integer quantum number we call the variation index. In the continuum scaling limit, each sector gives rise to a representation of the Virasoro algebra. We determine the corresponding conformal partition functions and their finitizations, and observe an intriguing link to the Ramond and Neveu-Schwarz sectors of the critical dense polymer model as described by a conformal field theory with central charge c=-2.Comment: 44 page

Numerical Simulations of Dynamos Generated in Spherical Couette Flows

We numerically investigate the efficiency of a spherical Couette flow at generating a self-sustained magnetic field. No dynamo action occurs for axisymmetric flow while we always found a dynamo when non-axisymmetric hydrodynamical instabilities are excited. Without rotation of the outer sphere, typical critical magnetic Reynolds numbers $Rm_c$ are of the order of a few thousands. They increase as the mechanical forcing imposed by the inner core on the flow increases (Reynolds number $Re$). Namely, no dynamo is found if the magnetic Prandtl number $Pm=Rm/Re$ is less than a critical value $Pm_c\sim 1$. Oscillating quadrupolar dynamos are present in the vicinity of the dynamo onset. Saturated magnetic fields obtained in supercritical regimes (either $Re>2 Re_c$ or $Pm>2Pm_c$) correspond to the equipartition between magnetic and kinetic energies. A global rotation of the system (Ekman numbers $E=10^{-3}, 10^{-4}$) yields to a slight decrease (factor 2) of the critical magnetic Prandtl number, but we find a peculiar regime where dynamo action may be obtained for relatively low magnetic Reynolds numbers ($Rm_c\sim 300$). In this dynamical regime (Rossby number $Ro\sim -1$, spheres in opposite direction) at a moderate Ekman number ($E=10^{-3}$), a enhanced shear layer around the inner core might explain the decrease of the dynamo threshold. For lower $E$ ($E=10^{-4}$) this internal shear layer becomes unstable, leading to small scales fluctuations, and the favorable dynamo regime is lost. We also model the effect of ferromagnetic boundary conditions. Their presence have only a small impact on the dynamo onset but clearly enhance the saturated magnetic field in the ferromagnetic parts. Implications for experimental studies are discussed