3,603 research outputs found
Sustainability in irrigated agriculture
Irrigated farmingAgricultureIrrigation efficiencySustainability
X-ray Lines from Dark Matter: The Good, The Bad, and The Unlikely
We consider three classes of dark matter (DM) models to account for the
recently observed 3.5 keV line: metastable excited state DM, annihilating DM,
and decaying DM. We study two examples of metastable excited state DM. The
first, millicharged composite DM, has both inelasticity and photon emission
built in, but with a very constrained parameter space. In the second example,
up-scattering and decay come from separate sectors and is thus less
constrained. The decay of the excited state can potentially be detectable at
direct detection experiments. However we find that CMB constraints are at the
border of excluding this as an interpretation of the DAMA signal. The
annihilating DM interpretation of the X-ray line is found to be in tension with
CMB constraints. Lastly, a generalized version of decaying DM can account for
the data with a lifetime exceeding the age of the Universe for masses GeV.Comment: 14 pages, 4 figures; updated to match JCAP published versio
Non-linear elastic effects in phase field crystal and amplitude equations: Comparison to ab initio simulations of bcc metals and graphene
We investigate non-linear elastic deformations in the phase field crystal
model and derived amplitude equations formulations. Two sources of
non-linearity are found, one of them based on geometric non-linearity expressed
through a finite strain tensor. It reflects the Eulerian structure of the
continuum models and correctly describes the strain dependence of the
stiffness. In general, the relevant strain tensor is related to the left
Cauchy-Green deformation tensor. In isotropic one- and two-dimensional
situations the elastic energy can be expressed equivalently through the right
deformation tensor. The predicted isotropic low temperature non-linear elastic
effects are directly related to the Birch-Murnaghan equation of state with bulk
modulus derivative for bcc. A two-dimensional generalization suggests
. These predictions are in agreement with ab initio results for
large strain bulk deformations of various bcc elements and graphene. Physical
non-linearity arises if the strain dependence of the density wave amplitudes is
taken into account and leads to elastic weakening. For anisotropic deformations
the magnitudes of the amplitudes depend on their relative orientation to the
applied strain.Comment: 16 page
A pedestrian approach to the high energy limits of branes and other gravitational systems
In this article we study limits of models that contain a dimensionful
parameter such as the mass of the relativistic point-particle. The limits are
analogous to the massless limit of the particle and may be thought of as high
energy limits. We present the ideas and work through several examples in a
(hopefully) pedagogical manner. Along the way we derive several new results.Comment: 19 pages, 1 figur
Fixed point distribution on Hilbert scheme of points
Let be a closed field of characteristic zero. We prove that all
monomial ideals sit in the curvilinear component of the Hilbert scheme of
points of the affine space , answering a
long-standing question about the distribution of torus-fixed points among
punctual components. This result confirms that the punctual Hilbert scheme is
connected, a property previously established only for the full Hilbert scheme
in 1966 by Hartshorne.Comment: 28 page
SLO Mixed Use Neighborhood Development
This project involved developing and delivering conceptual and schematic architectural and engineering design documents for two parcels at the corner of Broad St. and Branch St. in downtown San Luis Obispo. Sixteen residential units, shared common spaces, outdoor pool, three office units, shared conference room, restaurant, cafes, and other commercial spaces are incorporated into this development. This package includes description, selection, configuration, and sizing information of the gravity, lateral, foundation, and parking system used on this project
Beyond the local approximation to exchange and correlation: the role of the Laplacian of the density in the energy density of Si
We model the exchange-correlation (XC) energy density of the Si crystal and
atom as calculated by variational Monte Carlo (VMC) methods with a gradient
analysis beyond the local density approximation (LDA). We find the Laplacian of
the density to be an excellent predictor of the discrepancy between VMC and LDA
energy densities in each system. A simple Laplacian-based correction to the LDA
energy density is developed by means of a least square fit to the VMC XC energy
density for the crystal, which fits the homogeneous electron gas and Si atom
without further effort.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
About the Dirac Equation with a potential
An elementary treatment of the Dirac Equation in the presence of a
three-dimensional spherically symmetric -potential is
presented. We show how to handle the matching conditions in the configuration
space, and discuss the occurrence of supercritical effects.Comment: 8 pages, 1 postscript figure, Latex, Revise
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