23,279 research outputs found
Water resource problems of energy projects in the Colorado River Basin
The successful development of western coal and oil shale deposits
is dependent, to a significant degree, on the availability of adequate
water supplies. EQL is involved in a study of the aggregate effects
of various energy activities in the upper Colorado River Basin on
downstream water quantity and quality. These activities will tend
to reduce the available water in the river, and could increase its
salinity, which is already so high as to interfere with downstream
domestic and agricultural use
Re-entrant magnetic field induced charge and spin gaps in the coupled dual-chain quasi-one dimensional organic conductor Perylene[Pt(mnt)]
An inductive method is used to follow the magnetic field-dependent
susceptibility of the coupled charge density wave (CDW) and spin-Peierls (SP)
ordered state behavior in the dual chain organic conductor
Perylene[Pt(mnt)]. In addition to the coexisting SP-CDW state phase
below 8 K and 20 T, the measurements show that a second spin-gapped phase
appears above 20 T that coincides with a field-induced insulating phase. The
results support a strong coupling of the CDW and SP order parameters even in
high magnetic fields, and provide new insight into the nature of the magnetic
susceptibility of dual-chain spin and charge systems.Comment: 6 pages, 6 figure
Modal expansions and non-perturbative quantum field theory in Minkowski space
We introduce a spectral approach to non-perturbative field theory within the
periodic field formalism. As an example we calculate the real and imaginary
parts of the propagator in 1+1 dimensional phi^4 theory, identifying both
one-particle and multi-particle contributions. We discuss the computational
limits of existing diagonalization algorithms and suggest new quasi-sparse
eigenvector methods to handle very large Fock spaces and higher dimensional
field theories.Comment: new material added, 12 pages, 6 figure
Transonic static and dynamic stability characteristics of a finned projectile configuration
Static and dynamic stability tests were made of a finned projectile configuration with the aft-mounted fins arranged in a cruciform pattern. The tests were made at free stream Mach numbers of 0.7, 0.9, 1.1, and 1.2 in the Langley 8-foot transonic pressure tunnel. Some of the parameters measured during the tests were lift, drag, pitching moment, pitch damping, and roll damping. Configurations tested included the body with undeflected fins, the body with various fin deflections for control, and the body with fins removed. Theoretical estimates of the stability derivatives were made for the fins on configuration
Extending the Real-Time Maude Semantics of Ptolemy to Hierarchical DE Models
This paper extends our Real-Time Maude formalization of the semantics of flat
Ptolemy II discrete-event (DE) models to hierarchical models, including modal
models. This is a challenging task that requires combining synchronous
fixed-point computations with hierarchical structure. The synthesis of a
Real-Time Maude verification model from a Ptolemy II DE model, and the formal
verification of the synthesized model in Real-Time Maude, have been integrated
into Ptolemy II, enabling a model-engineering process that combines the
convenience of Ptolemy II DE modeling and simulation with formal verification
in Real-Time Maude.Comment: In Proceedings RTRTS 2010, arXiv:1009.398
Efficient Cosmological Parameter Estimation with Hamiltonian Monte Carlo
Traditional Markov Chain Monte Carlo methods suffer from low acceptance rate,
slow mixing and low efficiency in high dimensions. Hamiltonian Monte Carlo
resolves this issue by avoiding the random walk. Hamiltonian Monte Carlo (HMC)
is a Markov chain Monte Carlo (MCMC) technique built upon the basic principle
of Hamiltonian mechanics. Hamiltonian dynamics allows the chain to move along
trajectories of constant energy, taking large jumps in the parameter space with
relatively inexpensive computations. This new technique improves the acceptance
rate by a factor of 4 and boosts up the efficiency by at least a factor of D in
a D-dimensional parameter space. Therefor shorter chains will be needed for a
reliable parameter estimation comparing to a traditional MCMC chain yielding
the same performance. Besides that, the HMC is well suited for sampling from
non-Gaussian and curved distributions which are very hard to sample from using
the traditional MCMC methods. The method is very simple to code and can be
easily plugged into standard parameter estimation codes such as CosmoMC. In
this paper we demonstrate how the HMC can be efficiently used in cosmological
parameter estimation
Conjecturing-Based Computational Discovery of Patterns in Data
Modern machine learning methods are designed to exploit complex patterns in
data regardless of their form, while not necessarily revealing them to the
investigator. Here we demonstrate situations where modern machine learning
methods are ill-equipped to reveal feature interaction effects and other
nonlinear relationships. We propose the use of a conjecturing machine that
generates feature relationships in the form of bounds for numerical features
and boolean expressions for nominal features that are ignored by machine
learning algorithms. The proposed framework is demonstrated for a
classification problem with an interaction effect and a nonlinear regression
problem. In both settings, true underlying relationships are revealed and
generalization performance improves. The framework is then applied to
patient-level data regarding COVID-19 outcomes to suggest possible risk
factors.Comment: 25 pages, 6 figure
Low temperature structural phase transition and incommensurate lattice modulation in the spin gap compound BaCuSi2O6
Results of high resolution x-ray diffraction experiments are presented for
single crystals of the spin gap compound BaCuSiO in the temperature
range from 16 to 300 K. The data show clear evidence of a transition from the
room temperature tetragonal phase into an incommensurately modulated
orthorhombic structure below 100 K. This lattice modulation is
characterized by a resolution limited wave vector {\bf
q}=(0,0.13,0) and its 2 and 3 harmonics. The phase
transition is first order and exhibits considerable hysteresis. This
observation implies that the spin Hamiltonian representing the system is more
complex than originally thought.Comment: 4 pages, 4 figure
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