50 research outputs found
Topological entropy and secondary folding
A convenient measure of a map or flow's chaotic action is the topological
entropy. In many cases, the entropy has a homological origin: it is forced by
the topology of the space. For example, in simple toral maps, the topological
entropy is exactly equal to the growth induced by the map on the fundamental
group of the torus. However, in many situations the numerically-computed
topological entropy is greater than the bound implied by this action. We
associate this gap between the bound and the true entropy with 'secondary
folding': material lines undergo folding which is not homologically forced. We
examine this phenomenon both for physical rod-stirring devices and toral linked
twist maps, and show rigorously that for the latter secondary folds occur.Comment: 13 pages, 8 figures. pdfLaTeX with RevTeX4 macro
The EMCCD-Based Speckle Interferometer of the BTA 6-m Telescope: Description and First Results
The description is given for the speckle interferometer of the BTA 6-m
telescope of the SAO RAS based on a new detector with an electron
multiplication CCD. The main components of the instrument are microscope
objectives, interference filters and atmospheric dispersion correction prisms.
The PhotonMAX-512B CCD camera using a back-illuminated CCD97 allows up to 20
speckle images (with 512512 pix resolution) per second storage on the
hard drive. Due to high quantum efficiency (93% in the maximum at 550 nm), and
high transmission of its optical elements, the new camera can be used for
diffraction-limited (0.02) image reconstruction of stars under
good seeing conditions. The main advantages of the new system over the previous
generation BTA speckle interferometer are examined.Comment: 18 pages, 14 figure
Spinor condensates and light scattering from Bose-Einstein condensates
These notes discuss two aspects of the physics of atomic Bose-Einstein
condensates: optical properties and spinor condensates. The first topic
includes light scattering experiments which probe the excitations of a
condensate in both the free-particle and phonon regime. At higher light
intensity, a new form of superradiance and phase-coherent matter wave
amplification were observed. We also discuss properties of spinor condensates
and describe studies of ground--state spin domain structures and dynamical
studies which revealed metastable excited states and quantum tunneling.Comment: 58 pages, 33 figures, to appear in Proceedings of Les Houches 1999
Summer School, Session LXXI
The PHENIX Experiment at RHIC
The physics emphases of the PHENIX collaboration and the design and current
status of the PHENIX detector are discussed. The plan of the collaboration for
making the most effective use of the available luminosity in the first years of
RHIC operation is also presented.Comment: 5 pages, 1 figure. Further details of the PHENIX physics program
available at http://www.rhic.bnl.gov/phenix
Enhancing elementary science learning through organic chemistry modeling and visualization
The scientists of the future will need to begin studying science in great depth, much earlier in life, in order to keep up with the accelerating pace of discovery and technological innovation. For this to be possible, engaging and child-friendly pedagogical approaches need to be developed that leverage the natural enthusiasm of young science learners, as many students lose interest in science well before they encounter the rich subject matter of high school and college. This study provides evidence that a specially-designed chemistry curriculum can allow students 8-11 years old to rapidly learn advanced material while motivating them. The curriculum adhered to a backward design strategy and utilized a visual approach to chemistry learning. It also featured extensive use of hand-held organic chemistry model building and computerized molecular modeling activities. The 5-session study involved 63 students from grades 3-5 from an economically disadvantaged urban school in New Jersey. Despite the technical nature of the program, student motivation for chemistry learning was high, and assessment results showed students’ high-level understanding of the material
Online signal extraction by robust linear regression
Robust filtering, least median of squares, least trimmed squares, repeated median, deepest regression, breakdown point,