401 research outputs found
Quantum control in infinite dimensions
Accurate control of quantum evolution is an essential requirement for quantum
state engineering, laser chemistry, quantum information and quantum computing.
Conditions of controllability for systems with a finite number of energy levels
have been extensively studied. By contrast, results for controllability in
infinite dimensions have been mostly negative, stating that full control cannot
be achieved with a finite dimensional control Lie algebra. Here we show that by
adding a discrete operation to a Lie algebra it is possible to obtain full
control in infinite dimensions with a small number of control operators.Comment: 6 pages Late
Land use inventory through merging of LANDSAT (satellite), aerial photography and map sources
There are no author-identified significant results in this report
The Three-Nucleon System Near the N-d Threshold
The three-nucleon system is studied at energies a few hundred keV above the
N-d threshold. Measurements of the tensor analyzing powers and
for p-d elastic scattering at keV are presented
together with the corresponding theoretical predictions. The calculations are
extended to very low energies since they are useful for extracting the p-d
scattering lengths from the experimental data. The interaction considered here
is the Argonne V18 potential plus the Urbana three-nucleon potential. The
calculation of the asymptotic D- to S-state ratio for H and He, for
which recent experimental results are available, is also presented.Comment: Latex, 11 pages, 2 figures, to be published in Phy.Lett.
Precision Measurements of d(d,p)t and d(d,n)^3He Total Cross Sections at Big-Bang Nucleosynthesis Energies
Recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements have
determined the baryon density of the Universe with a precision of
about 4%. With tightly constrained, comparisons of Big Bang
Nucleosynthesis (BBN) abundance predictions to primordial abundance
observations can be made and used to test BBN models and/or to further
constrain abundances of isotopes with weak observational limits. To push the
limits and improve constraints on BBN models, uncertainties in key nuclear
reaction rates must be minimized. To this end, we made new precise measurements
of the d(d,p)t and d(d,n)^3He total cross sections at lab energies from 110 keV
to 650 keV.
A complete fit was performed in energy and angle to both angular distribution
and normalization data for both reactions simultaneously. By including
parameters for experimental variables in the fit, error correlations between
detectors, reactions, and reaction energies were accurately tabulated by
computational methods. With uncertainties around 2% +/- 1% scale error, these
new measurements significantly improve on the existing data set. At relevant
temperatures, using the data of the present work, both reaction rates are found
to be about 7% higher than those in the widely used Nuclear Astrophysics
Compilation of Reaction Rates (NACRE). These data will thus lead not only to
reduced uncertainties, but also to modifications in the BBN abundance
predictions.Comment: 15 pages, 11 figures, minor editorial change
Evidence for Three Nucleon Force Effects in p-d Elastic Scattering
A new measurement of the p-d differential cross section at Ep= 1 MeV has been
performed. These new data and older data sets at energies below the deuteron
breakup are compared to calculations using the two-nucleon Argonne v18 and the
three-nucleon Urbana IX potentials. A quantitative estimate of the capability
of these interactions to describe the data is given in terms of a chi^2
analysis. The chi^2 per datum drastically improves when the three-nucleon
interaction is included in the Hamiltonian.Comment: 13 pages, 5 figures, to be published in Phys. Rev.
Estimating the burden of minor ailment consultations in general practices and emergency departments through retrospective review of routine data in North East Scotland
Minor ailment attendances in general practices and emergency departments (EDs) place significant burden on health care resources
Study of the Structure of Cold, High-spin Nuclei Using Neutron-Multiplicity Filter
This research was sponsored by the National Science Foundation Grant NSF PHy 87-1440
Bellman equations for optimal feedback control of qubit states
Using results from quantum filtering theory and methods from classical
control theory, we derive an optimal control strategy for an open two-level
system (a qubit in interaction with the electromagnetic field) controlled by a
laser. The aim is to optimally choose the laser's amplitude and phase in order
to drive the system into a desired state. The Bellman equations are obtained
for the case of diffusive and counting measurements for vacuum field states. A
full exact solution of the optimal control problem is given for a system with
simpler, linear, dynamics. These linear dynamics can be obtained physically by
considering a two-level atom in a strongly driven, heavily damped, optical
cavity.Comment: 10 pages, no figures, replaced the simpler model in section
Simplicity and predictability: a phenomenological study of psychological flow in transactional workers
Psychological flow is a positive experience achieved through a near-balance of task challenge and skill capability, creating a merging of awareness and action and leading to an intrinsically rewarding feeling. Flow has typically been documented in persons who participate in work and leisure activities where they can exercise a large degree of creativity and agency over their actions in pursuit of their goals. The objective of the present study is to explore the lived experiences of flow in workers in roles where creativity and agency are typically not expected. An interpretative phenomenological analysis approach was employed to attain this objective. Semi-structured interviews were conducted with 17 adults whose role is to perform transactional work, which by its nature affords less opportunity for creative execution. Common themes about participantsâ flow experiences are documented. Two broad types of flow are described and a connection is made that the present studyâs participants achieve one of those flow types while working. Participantsâ feelings, preferences, and actions are mapped to the nine conventional dimensions of flow. Specific non-task work system factors are discussed relative to their influence on participantsâ attainment of flow. Limitations of the present study and recommended future research are discussed
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