2,428 research outputs found
Beam Loss in Linacs
Beam loss is a critical issue in high-intensity accelerators, and much effort
is expended during both the design and operation phases to minimize the loss
and to keep it to manageable levels. As new accelerators become ever more
powerful, beam loss becomes even more critical. Linacs for H- ion beams, such
as the one at the Oak Ridge Spallation Neutron Source, have many more loss
mechanisms compared to H+ (proton) linacs, such as the one being designed for
the European Spallation Neutron Source. Interesting H- beam loss mechanisms
include residual gas stripping, H+ capture and acceleration, field stripping,
black-body radiation and the recently discovered intra-beam stripping
mechanism. Beam halo formation, and ion source or RF turn on/off transients,
are examples of beam loss mechanisms that are common for both H+ and H-
accelerators. Machine protection systems play an important role in limiting the
beam loss.Comment: 24 pages, contribution to the 2014 Joint International Accelerator
School: Beam Loss and Accelerator Protection, Newport Beach, CA, USA , 5-14
Nov 201
Simulation and reconstruction study of a future surface scintillator array at the IceCube Neutrino Observatory
A Computer-Assisted Uniqueness Proof for a Semilinear Elliptic Boundary Value Problem
A wide variety of articles, starting with the famous paper (Gidas, Ni and
Nirenberg in Commun. Math. Phys. 68, 209-243 (1979)) is devoted to the
uniqueness question for the semilinear elliptic boundary value problem
-{\Delta}u={\lambda}u+u^p in {\Omega}, u>0 in {\Omega}, u=0 on the boundary of
{\Omega}, where {\lambda} ranges between 0 and the first Dirichlet Laplacian
eigenvalue. So far, this question was settled in the case of {\Omega} being a
ball and, for more general domains, in the case {\lambda}=0. In (McKenna et al.
in J. Differ. Equ. 247, 2140-2162 (2009)), we proposed a computer-assisted
approach to this uniqueness question, which indeed provided a proof in the case
{\Omega}=(0,1)x(0,1), and p=2. Due to the high numerical complexity, we were
not able in (McKenna et al. in J. Differ. Equ. 247, 2140-2162 (2009)) to treat
higher values of p. Here, by a significant reduction of the complexity, we will
prove uniqueness for the case p=3
Metamaterials proposed as perfect magnetoelectrics
Magnetoelectric susceptibility of a metamaterial built from split ring
resonators have been investigated both experimentally and within an equivalent
circuit model. The absolute values have been shown to exceed by two orders of
magnitude that of classical magnetoelectric materials. The metamaterial
investigated reaches the theoretically predicted value of the magnetoelectric
susceptibility which is equal to the geometric average of the electric and
magnetic susceptibilities.Comment: 5 pages, 3 figure
An ecological framework for the analysis of prebiotic chemical reaction networks and their dynamical behavior
It is becoming widely accepted that very early in the origin of life, even
before the emergence of genetic encoding, reaction networks of diverse small
chemicals might have manifested key properties of life, namely self-propagation
and adaptive evolution. To explore this possibility, we formalize the dynamics
of chemical reaction networks within the framework of chemical ecosystem
ecology. To capture the idea that life-like chemical systems are maintained out
of equilibrium by fluxes of energy-rich food chemicals, we model chemical
ecosystems in well-mixed containers that are subject to constant dilution by a
solution with a fixed concentration of food chemicals. Modelling all chemical
reactions as fully reversible, we show that seeding an autocatalytic cycle (AC)
with tiny amounts of one or more of its member chemicals results in logistic
growth of all member chemicals in the cycle. This finding justifies drawing an
instructive analogy between an AC and the population of a biological species.
We extend this finding to show that pairs of ACs can show competitive,
predator-prey, or mutualistic associations just like biological species.
Furthermore, when there is stochasticity in the environment, particularly in
the seeding of ACs, chemical ecosystems can show complex dynamics that can
resemble evolution. The evolutionary character is especially clear when the
network architecture results in ecological precedence (survival of the first),
which makes the path of succession historically contingent on the order in
which cycles are seeded. For all its simplicity, the framework developed here
is helpful for visualizing how autocatalysis in prebiotic chemical reaction
networks can yield life-like properties. Furthermore, chemical ecosystem
ecology could provide a useful foundation for exploring the emergence of
adaptive dynamics and the origins of polymer-based genetic systems
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Metamaterials: optical activity without chirality
We report that the classical phenomenon of optical activity, which is traditionally associated with chirality (helicity) of organic molecules, proteins, and inorganic structures, can be observed in artificial planar media which exhibit neither 3D nor 2D chirality. We observe the effect in the microwave and optical parts of the spectrum at oblique incidence to regular arrays of nonchiral subwavelength metamolecules in the form of strong circular dichroism and birefringence indistinguishable from those of chiral three-dimensional media
N-Cyclopropyl-(20R)-2-Methylene-19,26,27-trinor-25-aza-Vitamin D analogs and their uses
This invention discloses N-cyclopropyl-(20R)-2-methylene-19,26,27-trinor-25-aza-vitamin D analogs, and specifically N-cyclopropyl-(20R)-2-methylene-19,26,27-trinor-25-aza-1.alpha.-hydroxyvi- tamin D.sub.3 and pharmaceutical uses therefor. This compound exhibits relatively high binding activity and pronounced activity in arresting the proliferation of undifferentiated cells and inducing their differentiation to the monocyte thus evidencing use as an anti-cancer agent especially for the treatment or prevention of leukemia, colon cancer, breast cancer, skin cancer or prostate cancer
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