261 research outputs found
Entomopathogenic Nematodes in Pest Management
The definition âbiological controlâ has been used in different fields of biology, most notably entomology and plant pathology. It has been used to describe the use of live predatory insects, entomopathogenic nematodes (EPNs) or microbial pathogens to repress populations of various pest insects in entomology. EPNs are among one of the best biocontrol agents to control numerous economically important insect pests, successfully. Many surveys have been conducted all over the world to get EPNs that may have potential in management of economically important insect pests. The term âentomopathogenicâ comes from the Greek word entomon means insect and pathogenic means causing disease and first occurred in the nematology terminology in reference to the bacterial symbionts of Steinernema and Heterorhabditis. EPNs differ from other parasitic or necromenic nematodes as their hosts are killed within a relatively short period of time due to their mutualistic association with bacteria. They have many advantages over chemical pesticides are in operator and end-user safety, absence of withholding periods, minimising the treated area by monitoring insect populations, minimal damage to natural enemies and lack of environmental pollution. Improvements in mass-production and formulation technology of EPNs, the discovery of numerous efficient isolates and the desirability of increasing pesticide usage have resulted in a surge of scientific and commercial interest in these biological control agents
Asymptotic Freedom and Large Spin Antiferromagnetic Chains
Building on the mapping of large- spin chains onto the O() nonlinear
model with coupling constant , and on general properties of that
model (asymptotic freedom, implying that perturbation theory is valid at high
energy, and Elitzur's conjecture that rotationally invariant quantities are
infrared finite in perturbation theory), we use the Holstein-Primakoff
representation to derive analytic expressions for the equal-time and dynamical
spin-spin correlations valid at distances smaller than or
at energies larger than , where is the Heisenberg
exchange coupling. This is supported by comparing the static correlations with
quantum Monte Carlo simulations for .Comment: 5 pages, 2 figures, Supplemental Material 10 page
Novel families of AKLT states with arbitrary self-conjugate edge states
Using the Matrix Product State framework, we generalize the
Affleck-Kennedy-Lieb-Tasaki (AKLT) construction to one-dimensional spin liquids
with global color symmetry, finite correlation lengths, and edge
states that can belong to any self-conjugate irreducible representation (irrep)
of . In particular, spin- AKLT states with edge
states of arbitrary spin are constructed, and a general
formula for their correlation length is given. Furthermore, we show how to
construct local parent Hamiltonians for which these AKLT states are unique
ground states. This enables us to study the stability of the edge states by
interpolating between exact AKLT Hamiltonians. As an example, in the case of
spin- physical degrees of freedom, it is shown that a quantum phase
transition of central charge separates the Symmetry Protected
Topological (SPT) phase with spin- edge states from a topologically
trivial phase with spin- edge states. We also address some specificities of
the generalization to with , in particular regarding the
construction of parent Hamiltonians. For the AKLT state of the
model with the -box symmetric representation, we prove that the edge states
are in the -dimensional adjoint irrep, and for the model with
adjoint irrep at each site, we are able to construct two different
reflection-symmetric AKLT Hamiltonians, each with a unique ground state which
is either even or odd under reflection symmetry and with edge states in the
adjoint irrep. Finally, examples of two-column and adjoint physical irreps for
with even and with edge states living in the antisymmetric
irrep with boxes are given, with a conjecture about the general formula
for their correlation lengths.Comment: 37 pages, 14 figures, 4 table
A locally modified second-order finite element method for interface problems
The locally modified finite element method, which is introduced in [Frei,
Richter: SINUM 52(2014), p. 2315-2334] is a simple fitted finite element method
that is able to resolve weak discontinuities in interface problems. The method
is based on a fixed structured coarse mesh, which is then refined into
sub-elements to resolve an interior interface. In this work, we extend the
locally modified finite element method to second order using an isoparametric
approach in the interface elements. Thereby we need to take care that the
resulting curved edges do not lead to degenerate sub-elements. We prove optimal
a priori error estimates in the -norm and in a modified energy norm, as
well as a reduced convergence order of in the standard
-norm. Finally, we present numerical examples to substantiate the
theoretical findings
Numerical Investigation of Multiphase Flow in Pipelines
We present and analyze reliable numerical techniques
for simulating complex flow and transport phenomena related to
natural gas transportation in pipelines. Such kind of problems
are of high interest in the field of petroleum and environmental
engineering. Modeling and understanding natural gas flow and
transformation processes during transportation is important for the
sake of physical realism and the design and operation of pipeline
systems. In our approach a two fluid flow model based on a system
of coupled hyperbolic conservation laws is considered for describing
natural gas flow undergoing hydratization. The accurate numerical
approximation of two-phase gas flow remains subject of strong
interest in the scientific community. Such hyperbolic problems are
characterized by solutions with steep gradients or discontinuities, and
their approximation by standard finite element techniques typically
gives rise to spurious oscillations and numerical artefacts. Recently,
stabilized and discontinuous Galerkin finite element techniques
have attracted researchersâ interest. They are highly adapted to the
hyperbolic nature of our two-phase flow model. In the presentation
a streamline upwind Petrov-Galerkin approach and a discontinuous
Galerkin finite element method for the numerical approximation of
our flow model of two coupled systems of Euler equations are
presented. Then the efficiency and reliability of stabilized continuous
and discontinous finite element methods for the approximation is
carefully analyzed and the potential of the either classes of numerical
schemes is investigated. In particular, standard benchmark problems
of two-phase flow like the shock tube problem are used for the
comparative numerical study
Haldane Gap of the Three-Box Symmetric Chain
Motivated by the recent generalization of the Haldane conjecture to
chains [M. Lajk\'o et al., Nucl. Phys. B924, 508 (2017)]
according to which a Haldane gap should be present for symmetric
representations if the number of boxes in the Young diagram is a multiple of
three, we develop a density matrix renormalization group algorithm based on
standard Young tableaus to study the model with three boxes directly in the
representations of the global symmetry. We show that there is
a finite gap between the singlet and the symmetric sector
where is the antiferromagnetic
Heisenberg coupling, and we argue on the basis of the structure of the low
energy states that this is sufficient to conclude that the spectrum is gapped.Comment: 6 pages, 4 figures, + Supplemental Material 12 pages, 15 figure
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