Reconstructing the electron in a fractionalized quantum fluid

The low energy physics of the fractional Hall liquid is described in terms quasiparticles that are qualitatively distinct from electrons. We show, however, that a long-lived electron-like quasiparticle also exists in the excitation spectrum: the state obtained by the application of an electron creation operator to a fractional quantum Hall ground state has a non-zero overlap with a complex, high energy bound state containing an odd number of composite-fermion quasiparticles. The electron annihilation operator similarly couples to a bound complex of composite-fermion holes. We predict that these bound states can be observed through a conductance resonance in experiments involving a tunneling of an external electron into the fractional quantum Hall liquid. A comment is made on the origin of the breakdown of the Fermi liquid paradigm in the fractional hall liquid.Comment: 5 pages, 2 figure

First Steps Toward Change in Teacher Preparation for Elementary Science

Unless introductory undergraduate science classes for prospective elementary teachers actively incorporate the philosophy of inquiry-based learning called for in K-l2 science education refom little will change in elementary science education. Thus, at James Madison University, we have developed a new integrated science core curriculum called Understanding our World [1]. This course sequence was not only designed to fulfill general education science requirements. but also to focus on content areas our students will need to know as teachers. The objectives of these courses are based on the National Science Education Standards and Virginia’s Science Standards of Learning, including earth and space science, chemistry, physics, life sciences, and environmental science [2,3]. As an integrated package, this course sequence addresses basic science content, calculation skills, the philosophy and history of science, the process of how science is done, the role of science in society, and applications of computers and technology in science. Keeping in mind that students tend to teach in the same way they were taught, Understanding our World core classes embrace the concepts associated with reform in elementary math and science

Demonstration of efficient nonreciprocity in a microwave optomechanical circuit

The ability to engineer nonreciprocal interactions is an essential tool in modern communication technology as well as a powerful resource for building quantum networks. Aside from large reverse isolation, a nonreciprocal device suitable for applications must also have high efficiency (low insertion loss) and low output noise. Recent theoretical and experimental studies have shown that nonreciprocal behavior can be achieved in optomechanical systems, but performance in these last two attributes has been limited. Here we demonstrate an efficient, frequency-converting microwave isolator based on the optomechanical interactions between electromagnetic fields and a mechanically compliant vacuum gap capacitor. We achieve simultaneous reverse isolation of more than 20 dB and insertion loss less than 1.5 dB over a bandwidth of 5 kHz. We characterize the nonreciprocal noise performance of the device, observing that the residual thermal noise from the mechanical environments is routed solely to the input of the isolator. Our measurements show quantitative agreement with a general coupled-mode theory. Unlike conventional isolators and circulators, these compact nonreciprocal devices do not require a static magnetic field, and they allow for dynamic control of the direction of isolation. With these advantages, similar devices could enable programmable, high-efficiency connections between disparate nodes of quantum networks, even efficiently bridging the microwave and optical domains.Comment: 9 pages, 6 figure

The Importance of Broad Emission-Line Widths in Single Epoch Black Hole Mass Estimates

Estimates of the mass of super-massive black holes (BHs) in distant active galactic nuclei (AGNs) can be obtained efficiently only through single-epoch spectra, using a combination of their broad emission-line widths and continuum luminosities. Yet the reliability and accuracy of the method, and the resulting mass estimates, M_BH, remain uncertain. A recent study by Croom using a sample of SDSS, 2QZ and 2SLAQ quasars suggests that line widths contribute little information about the BH mass in these single-epoch estimates and can be replaced by a constant value without significant loss of accuracy. In this Letter, we use a sample of nearby reverberation-mapped AGNs to show that this conclusion is not universally applicable. We use the bulge luminosity (L_Bulge) of these local objects to test how well the known M_BH - L_Bulge correlation is recovered when using randomly assigned line widths instead of the measured ones to estimate M_BH. We find that line widths provide significant information about M_BH, and that for this sample, the line width information is just as significant as that provided by the continuum luminosities. We discuss the effects of observational biases upon the analysis of Croom and suggest that the results can probably be explained as a bias of flux-limited, shallow quasar samples.Comment: 10 text pages + 4 Figures + 1 Table. Accepted for publication in ApJ Letter

Reverberation Mapping and the Physics of Active Galactic Nuclei

Reverberation-mapping campaigns have revolutionized our understanding of AGN. They have allowed the direct determination of the broad-line region size, enabled mapping of the gas distribution around the central black hole, and are starting to resolve the continuum source structure. This review describes the recent and successful campaigns of the International AGN Watch consortium, outlines the theoretical background of reverberation mapping and the calculation of transfer functions, and addresses the fundamental difficulties of such experiments. It shows that such large-scale experiments have resulted in a ``new BLR'' which is considerably different from the one we knew just ten years ago. We discuss in some detail the more important new results, including the luminosity-size-mass relationship for AGN, and suggest ways to proceed in the near future.Comment: Review article to appear in Astronomical Time Series, Proceedings of the Wise Observatory 25th Ann. Symposium. 24 pages including 7 figure

Cusp energetic ions: A bow shock source

Recent interpretations of cusp energetic ions observed by the POLAR spacecraft have suggested a new energization process in the cusp [Chen et al., 1997; 1998]. Simultaneous enhancement of H+, He+2, and O\u3e+2 fluxes indicates that they are of solar wind origin. In the present study, we examine H+ and He+2 energy spectra from 20 eV to several 100 keV measured by the Hydra, Toroidal Imaging Mass-Angle Spectrograph (TIMAS), and Charge and Mass Magnetospheric Ion Composition Experiment (CAMMICE) on POLAR. The combined spectrum for each species is shown to be continuous with a thermal distribution below 10 keV/e and an energetic component above 20 keV/e. Energetic ions with comparable fluxes and a similar spectral shape are commonly observed downstream from the Earth\u27s quasi-parallel (Q∥) bow shock. In addition to the similarity in the ion spectra, electric and magnetic field noise and turbulence detected in the cusp by the Plasma Wave Instrument (PWI) and Magnetic Field Experiment (MFE) onboard POLAR are similar to the previously reported observations at the bow shock. The waves appear to be coincidental to the cusp energetic ions rather than causal. We suggest that these ions are not accelerated locally in the cusp. Rather, they are accelerated at the Q∥ bow shock and enter the cusp along open magnetic field lines connecting both regions

The degradation of MgB2 under ambient environment

The superconductivities of samples prepared by several procedures were found to degrade under ambient environment. The degradation mechanism was studied by measuring the change of surface chemical composition of dense MgB2 pellets (prepared by hot isostatic pressure, HIPed) under atmospheric exposure using X-ray Photoelectron Spectroscopy (XPS). Results showed that samples with poor connectivity between grains and with smaller grain sizes degrade with time when exposed to ambient conditions. In these samples, the Tc did not change with time, but the superconducting transition became broader and the Meissner fraction decreased. In contrast, our well-sintered and the HIPed samples remained stable for several months under ambient condition. The degradation was found to be related to surface decomposition as observed by XPS. We observed the formation of oxidized Mg, primarily in the form of a Mg hydroxide, the increase of C and O contents, and the reduction of B concentration in the surface layer of MgB2 samples.Comment: 15 pages, 3 figure