9,448 research outputs found
A statistical analysis of Electromagnetic Ion Cyclotron (EMIC) waves and their correlation to the 11-year solar cycle
This thesis presents a statistical analysis of EMIC waves measured at Halley Research Station from 2008 through 2012. An introduction covering the origin of and theory behind EMIC waves is provided, along with a background covering previous statistical research regarding EMIC waves. Guidelines regarding EMIC wave definition and analysis are described along with examples of how they were used. The data shows an increase in the total number of EMIC waves as well as the number and percentage of EMIC waves with maximum frequency above 1 Hz during the 5-year period. The results suggest that the total number of EMIC waves and the proportion of EMIC waves with maximum frequency above 1 Hz increase with increasing solar activity. A future perspective in EMIC wave research is also provided
Temperature-sensed cryogenic bleed maintains liquid state in transfer line
Inverted tee, installed at a high point in a cryogenic transfer line, is equipped with an insulated bleed line that passes a fixed amount of cryogenic fluid at atmospheric pressure. A sensing device activates a vent valve in the tee stack whenever gaseous nitrogen is present
Inexpensive insulation is effective for cryogenic transfer lines
Matting cover thermally insulates cryogenic-liquid transfer pipelines. The matting consists of layers of commercially available fiber glass tape in which the fibers are randomly oriented in parallel planes
A challenge to the Delta G~0 interpretation of hydrogen evolution
Platinum is a nearly perfect catalyst for the hydrogen evolution reaction,
and its high activity has conventionally been explained by its
close-to-thermoneutral hydrogen binding energy (G~0). However, many candidate
non-precious metal catalysts bind hydrogen with similar strengths, but exhibit
orders-of-magnitude lower activity for this reaction. In this study, we employ
electronic structure methods that allow fully potential-dependent reaction
barriers to be calculated, in order to develop a complete working picture of
hydrogen evolution on platinum. Through the resulting ab initio microkinetic
models, we assess the mechanistic origins of Pt's high activity. Surprisingly,
we find that the G~0 hydrogen atoms are kinetically inert, and that the
kinetically active hydrogen atoms have G's much weaker, similar to that of
gold. These on-top hydrogens have particularly low barriers, which we compare
to those of gold, explaining the high reaction rates, and the exponential
variations in coverages can uniquely explain Pt's strong kinetic response to
the applied potential. This explains the unique reactivity of Pt that is missed
by conventional Sabatier analyses, and suggests true design criteria for
non-precious alternatives
Nonmetallic impurities improve mechanical properties of vapor-deposited tungsten
Mechanical properties of vapor deposited tungsten are improved by selective incorporation of various nonmetallic impurities. Addition of trace quantities of carbon, nitrogen, or oxygen can significantly increase both low and high temperature yield strength without greatly affecting ductile-to-brittle transition temperature
Automated Microbial Metabolism Laboratory Final report
Photosynthesis activity during phosphate soil analysi
"Dressing" lines and vertices in calculations of matrix elements with the coupled-cluster method and determination of Cs atomic properties
We consider evaluation of matrix elements with the coupled-cluster method.
Such calculations formally involve infinite number of terms and we devise a
method of partial summation (dressing) of the resulting series. Our formalism
is built upon an expansion of the product of cluster amplitudes
into a sum of -body insertions. We consider two types of insertions:
particle/hole line insertion and two-particle/two-hole
random-phase-approximation-like insertion. We demonstrate how to ``dress''
these insertions and formulate iterative equations. We illustrate the dressing
equations in the case when the cluster operator is truncated at single and
double excitations. Using univalent systems as an example, we upgrade
coupled-cluster diagrams for matrix elements with the dressed insertions and
highlight a relation to pertinent fourth-order diagrams. We illustrate our
formalism with relativistic calculations of hyperfine constant and
electric-dipole transition amplitude for Cs atom. Finally,
we augment the truncated coupled-cluster calculations with otherwise omitted
fourth-order diagrams. The resulting analysis for Cs is complete through the
fourth-order of many-body perturbation theory and reveals an important role of
triple and disconnected quadruple excitations.Comment: 16 pages, 7 figures; submitted to Phys. Rev.
Estimating the Expected Value of Partial Perfect Information in Health Economic Evaluations using Integrated Nested Laplace Approximation
The Expected Value of Perfect Partial Information (EVPPI) is a
decision-theoretic measure of the "cost" of parametric uncertainty in decision
making used principally in health economic decision making. Despite this
decision-theoretic grounding, the uptake of EVPPI calculations in practice has
been slow. This is in part due to the prohibitive computational time required
to estimate the EVPPI via Monte Carlo simulations. However, recent developments
have demonstrated that the EVPPI can be estimated by non-parametric regression
methods, which have significantly decreased the computation time required to
approximate the EVPPI. Under certain circumstances, high-dimensional Gaussian
Process regression is suggested, but this can still be prohibitively expensive.
Applying fast computation methods developed in spatial statistics using
Integrated Nested Laplace Approximations (INLA) and projecting from a
high-dimensional into a low-dimensional input space allows us to decrease the
computation time for fitting these high-dimensional Gaussian Processes, often
substantially. We demonstrate that the EVPPI calculated using our method for
Gaussian Process regression is in line with the standard Gaussian Process
regression method and that despite the apparent methodological complexity of
this new method, R functions are available in the package BCEA to implement it
simply and efficiently
Geometry of effective Hamiltonians
We give a complete geometrical description of the effective Hamiltonians
common in nuclear shell model calculations. By recasting the theory in a
manifestly geometric form, we reinterpret and clarify several points. Some of
these results are hitherto unknown or unpublished. In particular, commuting
observables and symmetries are discussed in detail. Simple and explicit proofs
are given, and numerical algorithms are proposed, that improve and stabilize
common methods used today.Comment: 1 figur
Effects of additions of nonmetallics on the properties of vapor-deposited tungsten
Nonmetallic additive effects on properties of vapor deposited tungste
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