1,175 research outputs found
Quasi-single helicity spectra in the Madison Symmetric Torus
Evidence of a self-organized collapse towards a narrow spectrum of magnetic instabilities in the Madison Symmetric Torus [R. N. Dexter, D. W. Kerst, T. W. Lovell, S. C. Prager, and J. C. Sprott, Fusion Technol. 19, 131 (1991)] reversed field pinch device is presented. In this collapsed state, dubbed quasi-single helicity (QSH), the spectrum of magnetic modes condenses spontaneously to one dominant mode more completely than ever before observed. The amplitudes of all but the largest of the m=1 modes decrease in QSH states. New results about thermal features of QSH spectra and the identification of global control parameters for their onset are also discussed
Formation of Liesegang patterns: A spinodal decomposition scenario
Spinodal decomposition in the presence of a moving particle source is
proposed as a mechanism for the formation of Liesegang bands. This mechanism
yields a sequence of band positions x_n that obeys the spacing law
x_n~Q(1+p)^n. The dependence of the parameters p and Q on the initial
concentration of the reagents is determined and we find that the functional
form of p is in agreement with the experimentally observed Matalon-Packter law.Comment: RevTex, 4 pages, 4 eps figure
Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing
Large-scale molecular simulations are performed to investigate tensile
failure of polymer interfaces as a function of welding time . Changes in the
tensile stress, mode of failure and interfacial fracture energy are
correlated to changes in the interfacial entanglements as determined from
Primitive Path Analysis. Bulk polymers fail through craze formation, followed
by craze breakdown through chain scission. At small welded interfaces are
not strong enough to support craze formation and fail at small strains through
chain pullout at the interface. Once chains have formed an average of about one
entanglement across the interface, a stable craze is formed throughout the
sample. The failure stress of the craze rises with welding time and the mode of
craze breakdown changes from chain pullout to chain scission as the interface
approaches bulk strength. The interfacial fracture energy is calculated
by coupling the simulation results to a continuum fracture mechanics model. As
in experiment, increases as before saturating at the average
bulk fracture energy . As in previous simulations of shear strength,
saturation coincides with the recovery of the bulk entanglement density. Before
saturation, is proportional to the areal density of interfacial
entanglements. Immiscibiltiy limits interdiffusion and thus suppresses
entanglements at the interface. Even small degrees of immisciblity reduce
interfacial entanglements enough that failure occurs by chain pullout and
Chronic Peripheral Hyperinsulinemia in Type 1 Diabetic Patients After Successful Combined Pancreas-Kidney Transplantation Does Not Affect Ectopic Lipid Accumulation in Skeletal Muscle and Liver
Onset of entanglement
We have developed a theory of polymer entanglement using an extended
Cahn-Hilliard functional, with two extra terms. One is a nonlocal attractive
term, operating over mesoscales, which is interpreted as giving rise to
entanglement, and the other a local repulsive term indicative of excluded
volume interactions. We show how such a functional can be derived using notions
from gauge theory. We go beyond the Gaussian approximation, to the one-loop
level, to show that the system exhibits a crossover to a state of entanglement
as the average chain length between points of entanglement decreases. This
crossover is marked by critical slowing down, as the effective diffusion
constant goes to zero. We have also computed the tensile modulus of the system,
and we find a corresponding crossover to a regime of high modulus.Comment: 18 pages, with 4 figure
Was Sinn Féin dying? A quantitative post-mortem of the party's decline and the emergence of Fianna Fáil
This article calls for a reappraisal of the consensus surrounding the split within Sinn Féin in 1926 that led to the foundation of Fianna Fáil. It demonstrates that quantitative factors cited to demonstrate Sinn Féin’s “terminal” decline – finances, cumann numbers, and election results – and to explain de Valera’s decision to leave Sinn Féin and establish a rival republican organisation, Fianna Fáil, do not provide sufficient objective grounds to explain the republican leader’s actions. This article demonstrates that Sinn Féin’s election results during the period in question (1923-1926) were encouraging and the decline in finances and cumann numbers can be explained by the fact that the base year used to compare progress was 1923, an election year. Moreover, this article compares the performance of Sinn Féin to the first five years of Fianna Fáil (1926-1931) to show that what has been interpreted as terminal decline can also be attributed to normal inter-election lulls in party activity. Correspondingly, subjective factors – e.g. personal rivalries, differences in ideology, organisational style and levels of patience in terms of achieving political power – were most likely the determining factors rather than organisational decline
Explicit formulae in probability and in statistical physics
We consider two aspects of Marc Yor's work that have had an impact in
statistical physics: firstly, his results on the windings of planar Brownian
motion and their implications for the study of polymers; secondly, his theory
of exponential functionals of Levy processes and its connections with
disordered systems. Particular emphasis is placed on techniques leading to
explicit calculations.Comment: 14 pages, 2 figures. To appear in Seminaire de Probabilites, Special
Issue Marc Yo
The structure of Chariklo's rings from stellar occultations
Two narrow and dense rings (called C1R and C2R) were discovered around the
Centaur object (10199) Chariklo during a stellar occultation observed on 2013
June 3. Following this discovery, we planned observations of several
occultations by Chariklo's system in order to better characterize the physical
properties of the ring and main body. Here, we use 12 successful occulations by
Chariklo observed between 2014 and 2016. They provide ring profiles (physical
width, opacity, edge structure) and constraints on the radii and pole position.
Our new observations are currently consistent with the circular ring solution
and pole position, to within the km formal uncertainty for the ring
radii derived by Braga-Ribas et al. The six resolved C1R profiles reveal
significant width variations from to 7.5 km. The width of the fainter
ring C2R is less constrained, and may vary between 0.1 and 1 km. The inner and
outer edges of C1R are consistent with infinitely sharp boundaries, with
typical upper limits of one kilometer for the transition zone between the ring
and empty space. No constraint on the sharpness of C2R's edges is available. A
1 upper limit of m is derived for the equivalent width of
narrow (physical width <4 km) rings up to distances of 12,000 km, counted in
the ring plane
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