14,531 research outputs found
Buy High Sell Low: Redefining Bean Counting in the Coffee Industry for a Sustainable Future
Charles Manz returns to the JVBL providing ‒ together with several fellow researchers/writers ‒ a case study of a socially responsible business within the coffee industry. Familiar CSR concepts are examined such as Fair Trade and sustainability which foster parity in dealing with buyers while maintaining product quality and reasonable income. The practices of Dean’s Beans, a progressive coffee organization, are examined as a notable demonstration of how a business can fiscally succeed while maintaining a commitment to the triple-bottom-line considerations of people, planet, and profits
Addressing student models of energy loss in quantum tunnelling
We report on a multi-year, multi-institution study to investigate student
reasoning about energy in the context of quantum tunnelling. We use ungraded
surveys, graded examination questions, individual clinical interviews, and
multiple-choice exams to build a picture of the types of responses that
students typically give. We find that two descriptions of tunnelling through a
square barrier are particularly common. Students often state that tunnelling
particles lose energy while tunnelling. When sketching wave functions, students
also show a shift in the axis of oscillation, as if the height of the axis of
oscillation indicated the energy of the particle. We find inconsistencies
between students' conceptual, mathematical, and graphical models of quantum
tunnelling. As part of a curriculum in quantum physics, we have developed
instructional materials to help students develop a more robust and less
inconsistent picture of tunnelling, and present data suggesting that we have
succeeded in doing so.Comment: Originally submitted to the European Journal of Physics on 2005 Feb
10. Pages: 14. References: 11. Figures: 9. Tables: 1. Resubmitted May 18 with
revisions that include an appendix with the curriculum materials discussed in
the paper (4 page small group UW-style tutorial
Structure and Dynamics of amorphous Silica Surfaces
We use molecular dynamics computer simulations to study the equilibrium
properties of the surface of amorphous silica. Two types of geometries are
investigated: i) clusters with different diameters (13.5\AA, 19\AA, and
26.5\AA) and ii) a thin film with thickness 29\AA. We find that the shape of
the clusters is independent of temperature and that it becomes more spherical
with increasing size. The surface energy is in qualitative agreement with the
experimental value for the surface tension. The density distribution function
shows a small peak just below the surface, the origin of which is traced back
to a local chemical ordering at the surface. Close to the surface the partial
radial distribution functions as well as the distributions of the bond-bond
angles show features which are not observed in the interior of the systems. By
calculating the distribution of the length of the Si-O rings we can show that
these additional features are related to the presence of two-membered rings at
the surface. The surface density of these structures is around 0.6/nm^2 in good
agreement with experimental estimates. From the behavior of the mean-squared
displacement at low temperatures we conclude that at the surface the cage of
the particles is larger than the one in the bulk. Close to the surface the
diffusion constant is somewhat larger than the one in the bulk and with
decreasing temperature the relative difference grows. The total vibrational
density of states at the surface is similar to the one in the bulk. However, if
only the one for the silicon atoms is considered, significant differences are
found.Comment: 30 pages of Latex, 16 figure
Time-reversible Born-Oppenheimer molecular dynamics
We present a time-reversible Born-Oppenheimer molecular dynamics scheme,
based on self-consistent Hartree-Fock or density functional theory, where both
the nuclear and the electronic degrees of freedom are propagated in time. We
show how a time-reversible adiabatic propagation of the electronic degrees of
freedom is possible despite the non-linearity and incompleteness of the
self-consistent field procedure. Time-reversal symmetry excludes a systematic
long-term energy drift for a microcanonical ensemble and the number of
self-consistency cycles can be kept low (often only 2-4 cycles per nuclear time
step) thanks to a good initial guess given by the adiabatic propagation of the
electronic degrees of freedom. The time-reversible Born-Oppenheimer molecular
dynamics scheme therefore combines a low computational cost with a physically
correct time-reversible representation of the dynamics, which preserves a
detailed balance between propagation forwards and backwards in time.Comment: 4 pages, 4 figure
Ehrenfest dynamics is purity non-preserving: a necessary ingredient for decoherence
We discuss the evolution of purity in mixed quantum/classical approaches to
electronic nonadiabatic dynamics in the context of the Ehrenfest model. As it
is impossible to exactly determine initial conditions for a realistic system,
we choose to work in the statistical Ehrenfest formalism that we introduced in
Ref. 1. From it, we develop a new framework to determine exactly the change in
the purity of the quantum subsystem along the evolution of a statistical
Ehrenfest system. In a simple case, we verify how and to which extent Ehrenfest
statistical dynamics makes a system with more than one classical trajectory and
an initial quantum pure state become a quantum mixed one. We prove this
numerically showing how the evolution of purity depends on time, on the
dimension of the quantum state space , and on the number of classical
trajectories of the initial distribution. The results in this work open new
perspectives for studying decoherence with Ehrenfest dynamics.Comment: Revtex 4-1, 14 pages, 2 figures. Final published versio
Multihazard hurricane fragility model for wood structure homes considering hazard parameters and building attributes interaction.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).Predicting building damage as a function of hurricane hazards, building attributes, and the interaction between hazard and building attributes is a key to understanding how significant interaction reflects variation hazard intensity effect on damage based on building attribute levels. This paper develops multihazard hurricane fragility models for wood structure homes considering interaction between hazard and building attributes. Fragility models are developed for ordered categorical damage states (DS) and binary collapse/no collapse. Exterior physical damage and building attributes from rapid assessment in coastal Mississippi following Hurricane Katrina (2005), high-resolution numerical hindcast hazard intensities from the Simulating WAves Nearshore and ADvanced CIRCulation (SWAN+ADCIRC) models, and base flood elevation values are used as model input. Leave-one-out cross-validation (LOOCV) is used to evaluate model prediction accuracy. Eleven and forty-nine combinations of global damage response variables and main explanatory variables, respectively, were investigated and evaluated. Of these models, one DS and one collapse model met the rejection criteria. These models were refitted considering interaction terms. Maximum 3-s gust wind speed and maximum significant wave height were found to be factors that significantly affect damage. The interaction between maximum significant wave height and number of stories was the significant interaction term for the DS and collapse models. For every 0.3 m (0.98 ft) increase in maximum significant wave height, the estimated odds of being in a higher rather than in a lower damage state for DS model were found to be 1.95 times greater for one- rather than for two-story buildings. For every 0.3 m (0.98 ft) increase in maximum significant wave height, the estimated odds of collapse were found to be 2.23 times greater for one- rather than for two-story buildings. Model prediction accuracy was 84% and 91% for DS and collapse models, respectively. This paper does not consider the full hazard intensity experienced in Hurricane Katrina; rather, it focuses on single-family homes in a defined study area subjected to wind, wave, and storm surge hazards. Thus, the findings of this paper are not applicable for events with hazards that exceed those experienced in the study area, from which the models were derived.ECU Open Access Publishing Support Fun
Optimality program in segment and string graphs
Planar graphs are known to allow subexponential algorithms running in time
or for most of the paradigmatic
problems, while the brute-force time is very likely to be
asymptotically best on general graphs. Intrigued by an algorithm packing curves
in by Fox and Pach [SODA'11], we investigate which
problems have subexponential algorithms on the intersection graphs of curves
(string graphs) or segments (segment intersection graphs) and which problems
have no such algorithms under the ETH (Exponential Time Hypothesis). Among our
results, we show that, quite surprisingly, 3-Coloring can also be solved in
time on string graphs while an algorithm running
in time for 4-Coloring even on axis-parallel segments (of unbounded
length) would disprove the ETH. For 4-Coloring of unit segments, we show a
weaker ETH lower bound of which exploits the celebrated
Erd\H{o}s-Szekeres theorem. The subexponential running time also carries over
to Min Feedback Vertex Set but not to Min Dominating Set and Min Independent
Dominating Set.Comment: 19 pages, 15 figure
Retirement Finance
Exam paper for second semester Retirement Financ
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