Theory of a general class of dissipative processes

General theory of dissipative periodic processes for systems defined by partial, functional, or neutral differential equation

Liner radius fluctuations in a high-gain Cherenkov free-electron laser

Phase shifts in the propagating electromagnetic field of a Cherenkov free-electron laser (CFEL) can affect its gain. The phase velocity of an electromagnetic wave varies, for example, when the lined waveguide is inhomogeneous along its length. In this paper, we study quantitatively the saturated power of a particular CFEL at both weak and strong electron-beam pumping when the inner radius of the liner contains fluctuations along the waveguide. We show that the gain bandwidth of the CFEL is substantially broadened when the CFEL is pumped with a high-current beam. We also show that the design of a CFEL needs to include optimization with respect to sensitivity to liner fluctuations, especially for weakly pumped CFELs, that is, CFELs that use a low-current electron-beam density. This optimization can be relaxed for more strongly pumped CFELs

Electronic structure of the ferromagnetic superconductor UCoGe from first principles

The superconductor UCoGe is analyzed with electronic structure calculations using Linearized Augmented Plane Wave method based on Density Functional Theory. Ferromagnetic and antiferromagnetic calculations with and without correlations (via LDA+U) were done. In this compound the Fermi level is situated in a region where the main contribution to DOS comes from the U-5f orbital. The magnetic moment is mainly due to the Co-3d orbital with a small contribution from the U-5f orbital. The possibility of fully non-collinear magnetism in this compound seems to be ruled out. These results are compared with the isostructural compound URhGe, in this case the magnetism comes mostly from the U-5f orbital

Breakup of Shearless Meanders and "Outer" Tori in the Standard Nontwist Map

The breakup of shearless invariant tori with winding number $\omega=[0,1,11,1,1,...]$ (in continued fraction representation) of the standard nontwist map is studied numerically using Greene's residue criterion. Tori of this winding number can assume the shape of meanders (folded-over invariant tori which are not graphs over the x-axis in $(x,y)$ phase space), whose breakup is the first point of focus here. Secondly, multiple shearless orbits of this winding number can exist, leading to a new type of breakup scenario. Results are discussed within the framework of the renormalization group for area-preserving maps. Regularity of the critical tori is also investigated.Comment: submitted to Chao

Energy landscapes, ideal glasses, and their equation of state

Using the inherent structure formalism originally proposed by Stillinger and Weber [Phys. Rev. A 25, 978 (1982)], we generalize the thermodynamics of an energy landscape that has an ideal glass transition and derive the consequences for its equation of state. In doing so, we identify a separation of configurational and vibrational contributions to the pressure that corresponds with simulation studies performed in the inherent structure formalism. We develop an elementary model of landscapes appropriate to simple liquids which is based on the scaling properties of the soft-sphere potential complemented with a mean-field attraction. The resulting equation of state provides an accurate representation of simulation data for the Lennard-Jones fluid, suggesting the usefulness of a landscape-based formulation of supercooled liquid thermodynamics. Finally, we consider the implications of both the general theory and the model with respect to the so-called Sastry density and the ideal glass transition. Our analysis shows that a quantitative connection can be made between properties of the landscape and a simulation-determined Sastry density, and it emphasizes the distinction between an ideal glass transition and a Kauzmann equal-entropy condition.Comment: 11 pages, 3 figure

The loss of anisotropy in MgB2 with Sc substitution and its relationship with the critical temperature

The electrical conductivity anisotropy of the sigma-bands is calculated for the (Mg,Sc)B2 system using a virtual crystal model. Our results reveal that anisotropy drops with relatively little scandium content (< 30%); this behaviour coincides with the lowering of Tc and the reduction of the Kohn anomaly. This anisotropy loss is also found in the Al and C doped systems. In this work it is argued that the anisotropy, or 2D character, of the sigma-bands is an important parameter for the understanding of the high Tc found in MgB2

Research in the general area of non-linear dynamical systems Final report, 8 Jun. 1965 - 8 Jun. 1967

Nonlinear dynamical systems research on systems stability, invariance principles, Liapunov functions, and Volterra and functional integral equation

The effect of the GLP-1 analogue Exenatide on functional connectivity within an NTS-based network in women with and without obesity.

ObjectiveThe differential effect of GLP-1 agonist Exenatide on functional connectivity of the nucleus tractus solitaries (NTS), a key region associated with homeostasis, and on appetite-related behaviours was investigated in women with normal weight compared with women with obesity.MethodsFollowing an 8-h fast, 19 female subjects (11 lean, 8 obese) participated in a 2-d double blind crossover study. Subjects underwent functional magnetic resonance imaging at fast and 30-min post subcutaneous injection of 5 μg of Exenatide or placebo. Functional connectivity was examined with the NTS. Drug-induced functional connectivity changes within and between groups and correlations with appetite measures were examined in a region of interest approach focusing on the thalamus and hypothalamus.ResultsWomen with obesity reported less hunger after drug injection. Exenatide administration increased functional connectivity of the left NTS with the left thalamus and hypothalamus in the obese group only and increased the correlation between NTS functional connectivity and hunger scores in all subjects, but more so in the obese.ConclusionsObesity can impact the effects of Exenatide on brain connectivity, specifically in the NTS and is linked to changes in appetite control. This has implications for the use of GLP-1 analogues in therapeutic interventions

Labyrinthine Island Growth during Pd/Ru(0001) Heteroepitaxy

Using low energy electron microscopy we observe that Pd deposited on Ru only attaches to small sections of the atomic step edges surrounding Pd islands. This causes a novel epitaxial growth mode in which islands advance in a snakelike motion, giving rise to labyrinthine patterns. Based on density functional theory together with scanning tunneling microscopy and low energy electron microscopy we propose that this growth mode is caused by a surface alloy forming around growing islands. This alloy gradually reduces step attachment rates, resulting in an instability that favors adatom attachment at fast advancing step sections