2,295 research outputs found
On oscillatorlike Hamiltonians and squeezing
Generalizing a recent proposal leading to one-parameter families of
Hamiltonians and to new sets of squeezed states, we construct larger classes of
physically admissible Hamiltonians permitting new developments in squeezing.
Coherence is also discussed.Comment: 15 pages, Late
Numerical Simulations of Shock Wave-Driven Jets
We present the results of numerical simulations of shock wave-driven jets in
the solar atmosphere. The dependence of observable quantities like maximum
velocity and deceleration on parameters such as the period and amplitude of
initial disturbances and the inclination of the magnetic field is investigated.
Our simulations show excellent agreement with observations, and shed new light
on the correlation between velocity and deceleration and on the regional
differences found in observations.Comment: 7 pages, 11 figures, submitted to Ap
Millimeter-Wave Spectra, ab Initio Calculations, and Structures of Fluorophosphane and Chlorophosphane
The structures of fluorophosphane, PH2F, and chlorophosphane, PH2Cl, have been calculated ab initio at the SCF, MP2, CCSD, and CCSD(T) levels using a quadruple ζ polarized basis set. Equilibrium and ground state rotational constants as well as centrifugal distortion constants have been predicted for several isotopomers of PH2F and PH2Cl. Theoretical CCSD(T) geometries were also determined for the series of PHnX3-n (X = F, Cl; n = 0−3) molecules using a triple ζ polarized basis set. The millimeter-wave spectra of the short-lived molecules PH2F, PH2Cl, and their perdeuterated species were measured in the frequency range 100−470 GHz. For PH2F and PH2Cl, accurate ground state parameters have been obtained by a combined fit of the millimeter-wave data and the infrared ground state combination differences. The ro, rz, and re structures of PH2F and PH2Cl, as well as PH3, PCl3, and PHF2 have been determined. The experimental results are found in excellent agreement with their ab initio predictions
Solar Physics - Plasma Physics Workshop
A summary of the proceedings of a conference whose purpose was to explore plasma physics problems which arise in the study of solar physics is provided. Sessions were concerned with specific questions including the following: (1) whether the solar plasma is thermal or non-themal; (2) what spectroscopic data is required; (3) what types of magnetic field structures exist; (4) whether magnetohydrodynamic instabilities occur; (5) whether resistive or non-magnetohydrodynamic instabilities occur; (6) what mechanisms of particle acceleration have been proposed; and (7) what information is available concerning shock waves. Very few questions were answered categorically but, for each question, there was discussion concerning the observational evidence, theoretical analyses, and existing or potential laboratory and numerical experiments
Walking the tightrope with an e-portfolio:imbalance between support and autonomy hampers self-directed learning
Teacher coaching is essential to support self-directed learning, but requires a lot of time and energy. This mixed-methods study investigated the effects of using an e-portfolio with a self-coaching protocol and limited teacher coaching on the development of self-directed learning skills and motivation. With regard to self-directed learning, students' overestimation of performance on learning tasks grew over time, while their ability to formulate points for improvement did not change significantly. With regard to motivation, students' controlled (i.e. largely extrinsic) motivation increased while their autonomous (i.e. largely intrinsic) motivation decreased. Thematic analysis of interviews demonstrated students needed more support and feedback from their teacher. The use of suboptimal cues for performance assessment and an imperfect balance between autonomy and support hampered self-directed learning and motivation. We recommend providing just-in-time feedback about performance on learning tasks and giving students some autonomy over the choice of learning tasks, to enhance reflection and motivation
Detection of Gravitational Redshift on the Solar Disk by Using Iodine-Cell Technique
With an aim to examine whether the predicted solar gravitational redshift can
be observationally confirmed under the influence of the convective Doppler
shift due to granular motions, we attempted measuring the absolute spectral
line-shifts on a large number of points over the solar disk based on an
extensive set of 5188-5212A region spectra taken through an iodine-cell with
the Solar Domeless Telescope at Hida Observatory. The resulting heliocentric
line shifts at the meridian line (where no rotational shift exists), which were
derived by finding the best-fit parameterized model spectrum with the observed
spectrum and corrected for the earth's motion, turned out to be weakly
position-dependent as ~ +400 m/s near the disk center and increasing toward the
limb up to ~ +600 m/s (both with a standard deviation of sigma ~ 100 m/s).
Interestingly, this trend tends to disappear when the convectiveshift due to
granular motions (~-300 m/s at the disk center and increasing toward the limb;
simulated based on the two-component model along with the empirical
center-to-limb variation) is subtracted, finally resulting in the averaged
shift of 698 m/s (sigma = 113 m/s). Considering the ambiguities involved in the
absolute wavelength calibration or in the correction due to convective Doppler
shifts (at least several tens m/s, or more likely up to <~100 m/s), we may
regard that this value is well consistent with the expected gravitational
redshift of 633 m/s.Comment: 28 pages, 12 figures, electronic materials as ancillary data (table3,
table 4, ReadMe); accepted for publication in Solar Physic
Goitre and Iodine Deficiency in Europe
The prevalence of endemic iodine-deficiency goitre in Europe has been reduced in many areas by the introduction of iodination programmes. Recent reports, however, show that goitre remains a significant problem and that its prevalence has not decreased in a number of European countries. Hetzel1 has pointed out that the high global prevalence of iodine-deficiency disorders could be eradicated within 5-10 years by introduction of an iodised salt programme. The current World Health Organisation recommendations for iodine intake are between 150 and 300 μg/da
On realizations of nonlinear Lie algebras by differential operators
We study realizations of polynomial deformations of the sl(2,R)- Lie algebra
in terms of differential operators strongly related to bosonic operators. We
also distinguish their finite- and infinite-dimensional representations. The
linear, quadratic and cubic cases are explicitly visited but the method works
for arbitrary degrees in the polynomial functions. Multi-boson Hamiltonians are
studied in the context of these ``nonlinear'' Lie algebras and some examples
dealing with quantum optics are pointed out.Comment: 21 pages, Latex; New examples added in Sect.
Invariant vector fields and the prolongation method for supersymmetric quantum systems
The kinematical and dynamical symmetries of equations describing the time
evolution of quantum systems like the supersymmetric harmonic oscillator in one
space dimension and the interaction of a non-relativistic spin one-half
particle in a constant magnetic field are reviewed from the point of view of
the vector field prolongation method. Generators of supersymmetries are then
introduced so that we get Lie superalgebras of symmetries and supersymmetries.
This approach does not require the introduction of Grassmann valued
differential equations but a specific matrix realization and the concept of
dynamical symmetry. The Jaynes-Cummings model and supersymmetric
generalizations are then studied. We show how it is closely related to the
preceding models. Lie algebras of symmetries and supersymmetries are also
obtained.Comment: 37 pages, 7 table
- …