295 research outputs found
“Improbable Allies”—The North Korean Downing of a U.S. Navy EC-121 and U.S.-Soviet Cooperation during the Cold War
In April 1969, North Korea shot down a USN reconnaissance plane. Soviet surface ships were first on the scene and contributed to a joint U.S.-USSR search-and-rescue/recovery operation—a rare example of cooperation between traditional Cold War adversaries
Systematic Assessment of a High Impact Course Design Institute
Herein, we describe an intensive, week long course design institute (CDI) designed to introduce participants to the scholarly and evidence driven process of learning focused course design. Impact of this intervention is demonstrated using a multifaceted approach: (a) post CDI satisfaction and perception surveys, (b) pre /post CDI surveys probing pedagogical confidence and perceptions regarding importance of syllabi components, and (c) pre /post CDI syllabi analysis using a reliable syllabus rubric validated for higher education courses. The combined results of these qualitative and quantitative studies indicate that participants value the CDI experience, believe they learn basic principles of learning focused course design, report they are more confident enacting learning focused concepts in the classroom, believe they are better able to design learning focused syllabi, and they actually design more learning focused courses/syllabi
Proper ferroelastic phase transitions in thin epitaxial films with symmetry-conserving and symmetry-breaking misfit strains
We study how the ferroelastic domain structure sets in in an epitaxial film
of a material with second order proper ferroelastic transition. The domain
structures considered are similar to either or
structures in perovskite ferroelectrics. If the "extrinsic" misfit
strain, not associated with the transition, does not break the symmetry of the
high-temperature phase, the phase transition in the film occurs at somewhat
lower temperature compared to the bulk. The loss of stability then occurs with
respect to a sinusoidal strain wave, which evolves into the domain structure
with practically the same geometry and approximately the same period. In the
presence of the symmetry-breaking component of the misfit strain ("extrinsic"
misfit) the character of the phase transition is qualitatively different. In
this case it is a {\em topological} transition between single-domain and
multi-domain states, which starts from a low density of the domain walls.Comment: 7 pages, 2 figures, REVTeX 3.
Perturbation theory in a framework of iteration methods
In a previous paper (J. Phys. A 36, 11807 (2003)), we introduced the
`asymptotic iteration method' for solving second-order homogeneous linear
differential equations. In this paper, we study perturbed problems in quantum
mechanics and we use the method to find the coefficients in the perturbation
series for the eigenvalues and eigenfunctions directly, without first solving
the unperturbed problem.Comment: 13 page
Surface polaritons on left-handed cylinders: A complex angular momentum analysis
We consider the scattering of electromagnetic waves by a left-handed cylinder
-- i.e., by a cylinder fabricated from a left-handed material -- in the
framework of complex angular momentum techniques. We discuss both the TE and TM
theories. We emphasize more particularly the resonant aspects of the problem
linked to the existence of surface polaritons. We prove that the long-lived
resonant modes can be classified into distinct families, each family being
generated by one surface polariton propagating close to the cylinder surface
and we physically describe all the surface polaritons by providing, for each
one, its dispersion relation and its damping. This can be realized by noting
that each surface polariton corresponds to a particular Regge pole of the
matrix of the cylinder. Moreover, for both polarizations, we find that there
exists a particular surface polariton which corresponds, in the large-radius
limit, to the surface polariton which is supported by the plane interface.
There exists also an infinite family of surface polaritons of
whispering-gallery type which have no analogs in the plane interface case and
which are specific to left-handed materials.Comment: published version. v3: reference list correcte
Excess-noise-enhanced parametric down conversion
We calculate the influence of excess noise on parametric down conversion in an unstable optical parametric oscillator (OPO), using a quantum quasimode description. We find a strongly enhanced pair photon generation rate below threshold as compared to a conventional stable cavity setup of comparable gain and loss. In addition, the oscillation threshold is lowered due to the influence of the excess noise and the squeezing properties of the emitted light are significantly changed. In general, the maximal quantum-noise suppression in one quadrature component is reduced, which poses strong limitations for the practical usefulness of a geometrically unstable OPO source. The analytical results from our quasimode description are in good agreement with numerical simulations using a positive-P representation of the field in mode space and in position space
- …