11,930 research outputs found
Gaussian processes for choosing laser parameters for driven, dissipative Rydberg aggregates
To facilitate quantum simulation of open quantum systems at finite
temperatures, an important ingredient is to achieve thermalization on a given
time-scale. We consider a Rydberg aggregate (an arrangement of Rydberg atoms
that interact via long-range interactions) embedded in a laser-driven atomic
environment. For the smallest aggregate (two atoms), suitable laser parameters
can be found by brute force scanning of the four tunable laser parameters. For
more atoms, however, such parameter scans are too computationally costly. Here
we apply Gaussian processes to predict the thermalization performance as a
function of the laser parameters for two-atom and four-atom aggregates. These
predictions perform remarkably well using just 1000 simulations, demonstrating
the utility of Gaussian processes in an atomic physics setting. Using this
approach, we find and present effective laser parameters for generating
thermalization, the robustness of these parameters to variation, as well as
different thermalization dynamics
Evolution and turnover in scaling systems
Scaling has been discovered in the long tails of size distributions characterizing a variety of diverse systems, many of which evolve in terms of the size of their components through competition. Such time-invariant macro distributions, however, often obscure the micro-dynamics of change, such as continual turnover in the rank order of the constituents. Here we show how a model drawn from evolutionary theory can explain this change, such that the time spent in the top ranked constituents is finite and also characterized by longtailed distributions. To show the broad applicability of this model, we compare typical model runs to real-world examples including US boysā names, UK Number One for pop albums, journal article keywords, and city sizes
Meteorology and Cimatology: On-Line Weather Studies
Through the Virginia Earth Science Collaborative (VESC), a partnership of nine institutes of higher education, non-profit organizations, and eighty-three school divisions, a 3-credit, graduate-level meteorology course was offered six times between Spring 2006 and Fall 2007. The course, entitled Meteorology, was offered at three locations (Richmond, Abingdon, and Harrisonburg), and a local instructor facilitated each section. Funding for the course development, instructor stipends, and participant expenses (including travel, meals, and tuition) was provided through a competitive Mathematics and Science Partnership (MSP) grant funded through the federal No Child Left Behind legislation of 2001. The framework of the course was the American Meteorological Society\u27s Online Weather Studies program, which provides meteorological content and laboratory investigations, and relies heavily on the use of Internet-accessed, real-time weather data to teach meteorological topics in a distance learning format. The 115 teacher participants were required to complete text readings and written assignments, conduct laboratory investigations, design projects using realātime meteorological data, complete exams, and attend three face-to-face meetings. For the purpose of the VESC grant evaluation, pre-test and post-test data were collected on 110 of the participants which indicated an average 14.7% increase in participantsā content knowledge and use of real-time meteorological products (weather maps, satellite images, station models, etc.) in their instructional delivery
Contracts between Legal Persons
Contract law and the economics of contract have, for the most part, developed independently of each other. In this essay, we briefly review the notion of a contract from the perspective of lawyer, and then use this framework to organize the economics literature on contract. The title, Contracts between Legal Persons, limits the review to that part of contract law that is generic to any legal person. A legal person is any individual, firm or government agency with the right to enter into binding agreements. Our goal is to discuss the role of the law in enforcing these agreements under the hypothesis that the legal persons have well defined goals and objectives.contract law, law and economics, contract breach, contract theory, incomplete contracts
Isospin-breaking interactions studied through mirror energy differences
Background: Information on charge-dependent (i.e., isospin-non-conserving) interactions is extracted from excited states of mirror nuclei.
Purpose: Specifically, the purpose of the study is to extract effective isovector (Vpp 12Vnn) interactions which, in general, can either be of Coulomb or nuclear origin.
Methods: A comprehensive shell-model description of isospin-breaking effects is used to fit data on mirror energy differences in the A = 42\u201354 region. The angular-momentum dependence of isospin-breaking interactions was determined from a systematic study of mirror energy differences.
Results: The results reveal a significant isovector term, with a very strong spin dependence, beyond that expected of a two-body Coulomb interaction.
Conclusions: The isospin-breaking terms that are extracted have a J dependence that is not consistent with the known CSB properties of the bare nucleon-nucleon interaction
Novel battery model of an all-electric personal rapid transit vehicle to determine state-of-health through subspace parameter estimation and a Kalman Estimator
Abstract--The paper describes a real-time adaptive
battery model for use in an all-electric Personal Rapid
Transit vehicle. Whilst traditionally, circuit-based models
for lead-acid batteries centre on the well-known Randlesā
model, here the Randlesā model is mapped to an equivalent
circuit, demonstrating improved modelling capabilities and
more accurate estimates of circuit parameters when used in
Subspace parameter estimation techniques. Combined with
Kalman Estimator algorithms, these techniques are
demonstrated to correctly identify and converge on voltages
associated with the battery State-of-Charge, overcoming
problems such as SoC drift (incurred by coulomb-counting
methods due to over-charging or ambient temperature
fluctuations).
Online monitoring of the degradation of these estimated
parameters allows battery ageing (State-of-Health) to be
assessed and, in safety-critical systems, cell failure may be
predicted in time to avoid inconvenience to passenger
networks.
Due to the adaptive nature of the proposed methodology,
this system can be implemented over a wide range of
operating environments, applications and battery
topologies
Flexible scheme to truncate the hierarchy of pure states
The hierarchy of pure states (HOPS) is a wavefunction-based method which can
be used for numerically modeling open quantum systems. Formally, HOPS recovers
the exact system dynamics for an infinite depth of the hierarchy. However,
truncation of the hierarchy is required to numerically implement HOPS. We want
to choose a 'good' truncation method, where by 'good' we mean that it is
numerically feasible to check convergence of the results. For the truncation
approximation used in previous applications of HOPS, convergence checks are
numerically challenging. In this work we demonstrate the application of the
'-particle approximation' (PA) to HOPS. We also introduce a new
approximation, which we call the '-mode approximation' (MA). We then
explore the convergence of these truncation approximations with respect to the
number of equations required in the hierarchy. We show that truncation
approximations can be used in combination to achieve convergence in two
exemplary problems: absorption and energy transfer of molecular aggregates.Comment: 8 pages, 3 figure
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