5,325 research outputs found
Nucleation and growth of single wall carbon nanotubes
The nucleation and growth of single wall carbon nanotubes from a
carbon-saturated catalytic particle surrounded by a single sheet of graphene is
described qualitatively by using a very restricted number of elementary
processes, namely Stone-Wales defects and carbon bi-interstitials. Energies of
the different configurations are estimated by using a Tersoff energy
minimization scheme. Such a description is compatible with a broad variety of
size or helicity of the tubes. Several mechanisms of growth of the embryos are
considered: one of them is made more favourable when the tubes embryos are
arranged in an hexagonal network in the graphene plane. All the proposed
mechanisms can be indefinitely repeated for the growth of the nanotubes.Comment: Solid state communications, in pres
Gravity-Yang-Mills-Higgs unification by enlarging the gauge group
We revisit an old idea that gravity can be unified with Yang-Mills theory by
enlarging the gauge group of gravity formulated as gauge theory. Our starting
point is an action that describes a generally covariant gauge theory for a
group G. The Minkowski background breaks the gauge group by selecting in it a
preferred gravitational SU(2) subgroup. We expand the action around this
background and find the spectrum of linearized theory to consist of the usual
gravitons plus Yang-Mills fields charged under the centralizer of the SU(2) in
G. In addition, there is a set of Higgs fields that are charged both under the
gravitational and Yang-Mills subgroups. These fields are generically massive
and interact with both gravity and Yang-Mills sector in the standard way. The
arising interaction of the Yang-Mills sector with gravity is also standard.
Parameters such as the Yang-Mills coupling constant and Higgs mass arise from
the potential function defining the theory. Both are realistic in the sense
explained in the paper.Comment: 61 pages, no figures (v2) some typos correcte
Enhancing the heavy Higgs signal with jet-jet profile cuts
The jet-jet profile, or detailed manner, in which transverse energy and mass
are distributed around the jet-jet system resulting from the hadronic decay of
a boson in the process Higgs at a proton-proton collider energy of
40\tev is carefully examined. Two observables are defined that can be used to
help distinguish the -jet-jet signal from Higgs decay from the
``ordinary'' QCD background arising from the large transverse momentum
production of single bosons plus the associated jets. By making cuts on
these observables, signal to background enhancement factors greater than
can be obtained.Comment: 16 pages, Univ. Florida IFT-93-
Sivers and Boer-Mulders functions in Light-Cone Quark Models
Results for the naive-time-reversal-odd quark distributions in a light-cone
quark model are presented. The final-state interaction effects are generated
via single-gluon exchange mechanism. The formalism of light-cone wave functions
is used to derive general expressions in terms of overlap of wave-function
amplitudes describing the different orbital angular momentum components of the
nucleon. In particular, the model predictions show a dominant contribution from
S- and P-wave interference in the Sivers function and a significant
contribution also from the interference of P and D waves in the Boer-Mulders
function. The favourable comparison with existing phenomenological
parametrizations motivates further applications to describe azimuthal
asymmetries in hadronic reactions.Comment: references and explanations added; version to appear in Phys. Rev.
Full one-loop electroweak radiative corrections to single Higgs production in e+ e-
We present the full electroweak radiative corrections to
single Higgs production in \epemt. This takes into account the full one-loop
corrections as well as the effects of hard photon radiation. We include both
the fusion and Higgs-strahlung processes. The computation is performed with the
help of {\tt GRACE-loop} where we have implemented a generalised non-linear
gauge fixing condition. The latter includes 5 gauge parameters that can be used
for checks on our results. Besides the UV, IR finiteness and gauge parameter
independence checks it proves also powerful to test our implementation of the
5-point function. We find that for a 500GeV machine and a light Higgs of mass
150GeV, the total correction is small when the results are
expressed in terms of . The total correction decreases
slightly for higher energies. For moderate centre of mass energies the total
decreases as the Higgs mass increases, reaching -10% for
GeV and GeV. In order to quantify the genuine weak
corrections we have subtracted the universal virtual and bremsstrahlung
correction from the full . We find, for GeV, a
weak correction slowly decreasing from -2% to -4% as the energy increases from
GeV to TeV after expressing the tree-level results in
terms of Comment: 16 pages, 3 figures. Only correction is a reference to a web-pag
Dynamics of Phase Transitions: The 3D 3-state Potts model
In studies of the QCD deconfining phase transition or cross-over by means of
heavy ion experiments, one ought to be concerned about non-equilibrium effects
due to heating and cooling of the system. In this paper we extend our previous
study of Glauber dynamics of 2D Potts models to the 3D 3-state Potts model,
which serves as an effective model for some QCD properties. We investigate the
linear theory of spinodal decomposition in some detail. It describes the early
time evolution of the 3D model under a quench from the disordered into the
ordered phase well, but fails in 2D. Further, the quench leads to competing
vacuum domains, which are difficult to equilibrate, even in the presence of a
small external magnetic field. From our hysteresis study we find, as before, a
dynamics dominated by spinodal decomposition. There is evidence that some
effects survive in the case of a cross-over. But the infinite volume
extrapolation is difficult to control, even with lattices as large as .Comment: 12 pages; added references, corrected typo
Evapotranspiration Based Irrigation Trials Examine Water Requirement, Nitrogen Use, and Yield of Romaine Lettuce in the Salinas Valley
Cool season vegetables require adequate soil moisture to assure that maximum yield and quality are achieved. On California’s central coast, where the majority of cool season vegetables are produced in the US, long-term overpumping of irrigation water has reduced groundwater levels and led to environmental degradation. Two evapotranspiration (ET) based irrigation field trials were performed near Salinas CA (USA) to determine if ET-based irrigation scheduling could conserve water while producing romaine lettuce (cv. Sun Valley) of commercially viable yield. Sprinklers were used for seed germination and crop establishment. Four drip irrigation treatments were then imposed using a randomized complete block design with six replications. The CropManage decision-support model was used to estimate the full (100%) crop water requirement based mainly on ET replacement. Other treatments included 50% 75% and 150% of the full water requirement. The 100% treatment received 185 mm of water in 2015 and 247 mm in 2016, both of which were well below prior guidance and grower reports. Yields from the 100% and 150% treatments were not significantly different and were similar to industry average, while yields were significantly lower for the 50% and 75% treatments. The 100% treatment had the highest water use efficiency, and the 100% and 150% treatments together had the highest nitrogen recovery efficiency. Irrigation of romaine near the 100% ET replacement level can potentially reduce environmental impacts associated with nitrate leaching and surface runoff
Glauber dynamics of phase transitions: SU(3) lattice gauge theory
Motivated by questions about the QCD deconfining phase transition, we studied
in two previous papers Model A (Glauber) dynamics of 2D and 3D Potts models,
focusing on structure factor evolution under heating (heating in the gauge
theory notation, i.e., cooling of the spin systems). In the present paper we
set for 3D Potts models (Ising and 3-state) the scale of the dynamical effects
by comparing to equilibrium results at first and second order phase transition
temperatures, obtained by re-weighting from a multicanonical ensemble. Our
finding is that the dynamics entirely overwhelms the critical and non-critical
equilibrium effects.
In the second half of the paper we extend our results by investigating the
Glauber dynamics of pure SU(3) lattice gauge on
lattices directly under heating quenches from the confined into the deconfined
regime. The exponential growth factors of the initial response are calculated,
which give Debye screening mass estimates. The quench leads to competing vacuum
domains of distinct triality, which delay equilibration of pure gauge
theory forever, while their role in full QCD remains a subtle question. As in
spin systems we find for pure SU(3) gauge theory a dynamical growth of
structure factors, reaching maxima which scale approximately with the volume of
the system, before settling down to equilibrium. Their influence on various
observables is studied and different lattice sizes are simulated to illustrate
an approach to a finite volume continuum limit. Strong correlations are found
during the dynamical process, but not in the deconfined phase at equilibrium.Comment: 12 pages, 18 figure
POD for optimal control of the Cahn-Hilliard system using spatially adapted snapshots
The present work considers the optimal control of a convective Cahn-Hilliard
system, where the control enters through the velocity in the transport term. We
prove the existence of a solution to the considered optimal control problem.
For an efficient numerical solution, the expensive high-dimensional PDE systems
are replaced by reduced-order models utilizing proper orthogonal decomposition
(POD-ROM). The POD modes are computed from snapshots which are solutions of the
governing equations which are discretized utilizing adaptive finite elements.
The numerical tests show that the use of POD-ROM combined with spatially
adapted snapshots leads to large speedup factors compared with a high-fidelity
finite element optimization
The Symplectic Penrose Kite
The purpose of this article is to view the Penrose kite from the perspective
of symplectic geometry.Comment: 24 pages, 7 figures, minor changes in last version, to appear in
Comm. Math. Phys
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