The memory space: Exploring future uses of Web 2.0 and mobile internet through design interventions.

The QuVis Quantum Mechanics Visualization project aims to address challenges of quantum mechanics instruction through the development of interactive simulations for the learning and teaching of quantum mechanics. In this article, we describe evaluation of simulations focusing on two-level systems developed as part of the Institute of Physics Quantum Physics resources. Simulations are research-based and have been iteratively refined using student feedback in individual observation sessions and in-class trials. We give evidence that these simulations are helping students learn quantum mechanics concepts at both the introductory and advanced undergraduate level, and that students perceive simulations to be beneficial to their learning.Comment: 15 pages, 5 figures, 1 table; accepted for publication in the American Journal of Physic

From single particle to superfuid excitations in a dissipative polariton gas

Using angle-resolved heterodyne four-wave-mixing technique, we probe the low momentum excitation spectrum of a coherent polariton gas. The experimental results are well captured by the Bogoliubov transformation which describes the transition from single particle excitations of a normal fluid to sound-wave-like excitations of a superfluid. In a dense coherent polariton gas, we find all the characteristics of a Bogoliubov transformation, i.e. the positive and negative energy branch with respect to the polariton gas energy at rest, sound-wave-like shapes for the excitations dispersion, intensity and linewidth ratio between the two branches in agreement with the theory. The influence of the non-equilibrium character of the polariton gas is shown by a careful analysis of its dispersion.Comment: 4 pages, 3 figure

2D Fourier Transform Spectroscopy of exciton-polaritons and their interactions

We investigate polariton-polariton interactions in a semiconductor microcavity through two-dimensional Fourier transform (2DFT) spectroscopy. We observe, in addition to the lower-lower and the upper-upper polariton self-interaction, a lower-upper cross-interaction. This appears as separated peaks in the on-diagonal and off-diagonal part of 2DFT spectra. Moreover, we elucidate the role of the polariton dispersion through a fine structure in the 2DFT spectrum. Simulations, based on lower-upper polariton basis Gross-Pitaevskii equations including both self and cross-interactions, result in a 2DFT spectra in qualitative agreement with experiments

Laue diffraction lenses for astrophysics: From theory to experiments

Based on the laws of X-ray diffraction in crystals, Laue lenses offer a promising way to achieve the sensitivity and angular resolution leap required for the next generation of hard X-ray and gamma-ray telescopes. The present paper describes the instrumental responses of Laue diffraction lenses designed for nuclear astrophysics. Different possible geometries are discussed, as well as the corresponding spectral and imaging capabilities. These theoretical predictions are then compared with Monte-Carlo simulations and experimental results (ground and stratospheric observations from the CLAIRE project)

The unidentified TeV source (TeVJ2032+4130) and surrounding field: Final HEGRA IACT-System results

The unidentified TeV source in Cygnus is now confirmed by follow-up observations from 2002 with the HEGRA stereoscopic system of Cherenkov Telescopes. Using all data (1999 to 2002) we confirm this new source as steady in flux over the four years of data taking, extended with radius 6.2 arcmin (+-1.2 arcmin (stat) +-0.9 arcmin (sys)) and exhibiting a hard spectrum with photon index -1.9. It is located in the direction of the dense OB stellar association, Cygnus OB2. Its integral flux above energies E>1 TeV amounts to \~5% of the Crab assuming a Gaussian profile for the intrinsic source morphology. There is no obvious counterpart at radio, optical nor X-ray energies, leaving TeVJ2032+4130 presently unidentified. Observational parameters of this source are updated here and some astrophysical discussion is provided. Also included are upper limits for a number of other interesting sources in the FoV, including the famous microquasar Cygnus X-3.Comment: 7 pages, 3 figures. Accepted for publication in Astronomy & Astrophysic

Simultaneous X-Ray and TeV Gamma-Ray Observations of the TeV Blazar Markarian 421 during February and May 2000

In this paper we present the results of simultaneous observations of the TeV blazar Markarian 421 (Mrk 421) at X-ray and TeV Gamma-ray energies with the Rossi X-Ray Timing Explorer (RXTE) and the stereoscopic Cherenkov Telescope system of the HEGRA (High Energy Gamma Ray Astronomy) experiment, respectively. The source was monitored from February 2nd to February 16th and from May 3rd to May 8th, 2000. We discuss in detail the temporal and spectral properties of the source. Remarkably, the TeV observations of February 7th/8th showed statistically significant evidence for substantial TeV flux variability on 30 min time scale. We show the results of modeling the data with a time dependent homogeneous Synchrotron Self-Compton (SSC) model. The X-ray and TeV gamma-ray emission strengths and energy spectra together with the rapid flux variability strongly suggest that the emission volume is approaching the observer with a Doppler factor of 50 or higher. The different flux variability time scales observed at X-rays and TeV Gamma-rays indicate that a more detailed analysis will require inhomogeneous models with several emission zones.Comment: Accepted for Publication in ApJ, 21 Pages, 5 Figure

Report and recommendations on multimedia materials for teaching and learning electricity and magnetism

This paper presents the results of a peer review of multimedia materials for teaching and learning electricity and magnetism prepared as a part of the annual activities undertaken by an international group of scientists associated with Multimedia Physics in Teaching and Learning. The work promotes the use of valuable and freely accessible information technology materials for different levels of teaching, mostly higher education. The authors discuss the process of selecting resources and the rubrics used in the rating process. The reviews of high-quality learning resources are presented along with descriptions of valuable didactical feature

Is the giant radio galaxy M 87 a TeV gamma-ray emitter?

For the first time an excess of photons above an energy threshold of 730 GeV from the giant radio galaxy M 87 has been measured at a significance level above 4 σ. The data have been taken during the years 1998 and 1999 with the HEGRA stereoscopic system of 5 imaging atmospheric Cherenkov telescopes. The excess of 107.4 ± 26.8 events above 730 GeV corresponds to an integral flux of 3.3% of the Crab flux or Nγ (E > 730 GeV) = (0.96 ± 0.23) × 10-12 phot cm-2 s-1. M 87 is located at the center of the Virgo cluster of galaxies at a relatively small redshift of z = 0.00436 and is a promising candidate among the class of giant radio galaxies for the emission of TeV γ-radiation. The detection of TeV γ-rays from M 87 - if confirmed - would establish a new class of extragalactic source in this energy regime since all other AGN detected to date at TeV energies are BL Lac type objects.F. A. Aharonian ...G. P. Rowell...et al

The Energy Spectrum of TeV Gamma-Rays from the Crab Nebula as measured by the HEGRA system of imaging air Cherenkov telescopes

The Crab Nebula has been observed by the HEGRA (High-Energy Gamma-Ray Astronomy) stereoscopic system of imaging air Cherenkov telescopes (IACTs) for a total of about 200 hrs during two observational campaigns: from September 1997 to March 1998 and from August 1998 to April 1999. The recent detailed studies of system performance give an energy threshold and an energy resolution for gamma-rays of 500 GeV and ~ 18%, respectively. The Crab energy spectrum was measured with the HEGRA IACT system in a very broad energy range up to 20 TeV, using observations at zenith angles up to 65 degrees. The Crab data can be fitted in the energy range from 1 to 20 TeV by a simple power-law, which yields dJg/dE = (2.79+/-0.02 +/- 0.5) 10^{-7} E^{-2.59 +/- 0.03 +/- 0.05}, ph m^{-2} s^{-1} TeV^{-1} The Crab Nebula energy spectrum, as measured with the HEGRA IACT system, agrees within 15% in the absolute scale and within 0.1 units in the power law index with the latest measurements by the Whipple, CANGAROO and CAT groups, consistent within the statistical and systematic errors quoted by the experiments. The pure power-law spectrum of TeV gamma-rays from the Crab Nebula constrains the physics parameters of the nebula environment as well as the models of photon emission.Comment: to appear in ApJ, 29 pages, 6 figure

The TeV Energy Spectrum of Mkn 501 Measured with the Stereoscopic Telescope System of HEGRA during 1998 and 1999

During 1997, the BL Lac object Mkn 501 went into an extraordinary state of high X-ray and TeV gamma-ray activity, lasting more than 6 months. In this paper we report on the TeV emission characteristics of the source in the subsequent years of 1998 and 1999 as measured with the Stereoscopic Cherenkov Telescope System of HEGRA (La Palma, Canary Islands). Our observations reveal a 1998-1999 mean emission level at 1 TeV of 1/3 of the flux of the Crab Nebula, a factor of 10 lower than during the year of 1997. A dataset of 122 observations hours with the HEGRA telescope system makes it possible to assess for the first time the Mkn 501 TeV energy spectrum for a mean flux level substantially below that of the Crab Nebula with reasonable statistical accuracy. Excluding the data of a strong flare, we find evidence that the 1998--1999 low-flux spectrum is substantially softer (by 0.44+-0.1(stat) in spectral index) than the 1997 time averaged spectrum. The 500 GeV to 10 TeV energy spectrum can well be described by a power law model with exponential cutoff: dN/dE ~ E^(-alpha) exp(-E/E0) with alpha=2.31+-0.22(stat), and E0=5.1 (-2.3+7.8)(stat) TeV. Within statistical accuracy, also a pure power law model gives an acceptable fit to the data: dN/dE ~ E^(-Gamma) with Gamma=2.76+-0.08(stat). After presenting the 1998-1999 TeV characteristics of the source we discuss the implications of the results.Comment: Accepted for publication in The Astrophysical Journal, Part 1, on August 4th, 200