15,607 research outputs found
A proof of anomalous invasion speeds in a system of coupled Fisher-KPP equations
This article is concerned with the rigorous validation of anomalous spreading
speeds in a system of coupled Fisher-KPP equations of cooperative type.
Anomalous spreading refers to a scenario wherein the coupling of two equations
leads to faster spreading speeds in one of the components. The existence of
these spreading speeds can be predicted from the linearization about the
unstable state. We prove that initial data consisting of compactly supported
perturbations of Heaviside step functions spreads asymptotically with the
anomalous speed. The proof makes use of a comparison principle and the explicit
construction of sub and super solutions
Lattice Design in High-energy Particle Accelerators
This lecture gives an introduction into the design of high-energy storage
ring lattices. Applying the formalism that has been established in transverse
beam optics, the basic principles of the development of a magnet lattice are
explained and the characteristics of the resulting magnet structure are
discussed. The periodic assembly of a storage ring cell with its boundary
conditions concerning stability and scaling of the beam optics parameters is
addressed as well as special lattice insertions such asdrifts, mini beta
sections, dispersion suppressors, etc. In addition to the exact calculations
that are indispensable for a rigorous treatment of the matter, scaling rules
are shown and simple rules of thumb are included that enable the lattice
designer to do the first estimates and get the basic numbers 'on the back of an
envelope'.Comment: 40 pages, contribution to the CAS - CERN Accelerator School: Advanced
Accelerator Physics Course, Trondheim, Norway, 18-29 Aug 2013. arXiv admin
note: substantial text overlap with arXiv:1303.651
Workforce Development and the Disadvantaged: New Directions for 2009 and Beyond
Assesses the 1998 Workforce Investment Act's successes and limitations. Outlines the changes needed, such as increasing funding and consolidating programs, for a more effective public workforce training system, especially for the young and hard-to-employ
Reconnecting Young Black Men: What Policies Would Help?
The term "disconnected youth" refers to young people who have been out of school and out of work for considerable periods of time – like a year or more. They are not temporarily "idle" but are fully disconnected from the mainstream worlds of schooling and work. They may be incarcerated or on parole or probation; they might be aging out of foster care or still attached to their nuclear families. But, overwhelmingly, they come from low-income families and often grow up in poor and relatively segregated neighborhoods. Of all racial and gender groups, young black men are by far the most likely to become "disconnected" from school and work. In the year 2000 – when the labor market was very tight – over 17 percent of all young black men between the ages of 16 and 24 were disconnected, while the comparable percentages for other race/gender groups were much lower. Indeed, this figure implies that one out of every six young black men was disconnected from both school and work at that time
Introduction to Transverse Beam Dynamics
In this chapter we give an introduction to the transverse dynamics of the
particles in a synchrotron or storage ring. The emphasis is more on qualitative
understanding rather than on mathematical correctness, and a number of
simulations are used to demonstrate the physical behaviour of the particles.
Starting from the basic principles of how to design the geometry of the ring,
we review the transverse motion of the particles, motivate the equation of
motion, and show the solutions for typical storage ring elements. Following the
usual treatment in the literature, we present a second way to describe the
particle beam, using the concept of the emittance of the particle ensemble and
the beta function, which reflects the overall focusing properties of the ring.
The adiabatic shrinking due to Liouville's theorem is discussed as well as
dispersive effects in the most simple case.Comment: 19 pages, contribution to the CAS-CERN Accelerator School: Ion
Sources, Senec, Slovakia, 29 May - 8 June 2012, edited by R. Bailey,
CERN-2013-00
Introduction to Longitudinal Beam Dynamics
This chapter gives an overview of the longitudinal dynamics of the particles
in an accelerator and, closely related to that, the issue of synchronization
between the particles and the accelerating field. Beginning with the trivial
case of electrostatic accelerators, the synchronization condition is explained
for a number of driven accelerators like Alvarez linacs, cyclotrons and finally
synchrotrons and storage rings, where it plays a crucial role. In the case of
the latter, the principle of phase focusing is motivated qualitatively as well
as on a mathematically more correct level and the problem of operation below
and above the transition energy is discussed. Throughout, the main emphasis is
more on physical understanding rather than on a mathematically rigorous
treatment.Comment: 15 pages, contribution to the CAS-CERN Accelerator School: Ion
Sources, Senec, Slovakia, 29 May - 8 June 2012, edited by R. Bailey,
CERN-2013-00
Higher-order Modes and Heating
This chapter gives a basic introduction to the problem of wake fields created
in the beam-surrounding environment and the resulting heating effects of
machine components. The concepts are introduced and scaling rules derived that
are exemplified by several observations from operation of the LHC and other
machines.Comment: 14 pages, contribution to the CAS-CERN Accelerator School:
Superconductivity for Accelerators, Erice, Italy, 24 April - 4 May 2013,
edited by R. Baile
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