74,599 research outputs found

    Interactive Tutorials For Upper Level Quantum Mechanics Courses

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    This thesis explores the ongoing need for interactive tutorials in the upper level undergraduate Quantum Mechanics course. It first summarizes the development and evaluation of tutorials at the introductory physics level by others, and then challenges the belief that upper level students do not need this type of intervention by citing research in student difficulties in learning Quantum Mechanics. Physics Education research shows that there are common student misconceptions that persist even in the upper level undergraduate courses such as Quantum Mechanics. Cognitive research serves as a guide for effective curriculum design. A description of the iterative process for developing and evaluating the tutorials is discussed. The development and evaluation of "The Time Evolution of a Wave Function" Quantum Interactive Learning Tutorial (QuILT) is described in detail. Finally, the success of the QuILT in reducing the common misconceptions about time evolution is discussed

    The private finance initiative (PFI) and finance capital: A note on gaps in the "accountability" debate

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    During recent years, a wide spectrum of research has questioned whether public services/infrastructure procurement through private finance, as exemplified by the UK Private Finance Initiative (PFI), meets minimum standard of democratic accountability. While broadly agreeing with some of these arguments, this paper suggests that this debate is flawed on two grounds. Firstly, PFI is not about effective procurement, or even about a pragmatic choice of procurement mechanisms which can potentially compromise public involvement and input; rather it is about a process where the state creates new profit opportunities at a time when the international financial system is increasingly lacking in safe investment opportunities. Secondly, because of its primary function as investment opportunity, PFI, by its very nature, prioritises the risk-return criteria of private finance over the needs of the public sector client and its stakeholders. Using two case studies of recent PFI projects, the paper illustrates some of the mechanisms through which finance capital exercises control over the PFI procurement process. The paper concludes that recent proposals aimed at “reforming” or “democratising” PFI fail to recognise the objective constraints which this type of state-finance capital nexus imposes on political process

    Design, performance, and calculated error of a Faraday cup for absolute beam current measurements of 600-MeV protons

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    A mobile self-contained Faraday cup system for beam current measurments of nominal 600 MeV protons was designed, constructed, and used at the NASA Space Radiation Effects Laboratory. The cup is of reentrant design with a length of 106.7 cm and an outside diameter of 20.32 cm. The inner diameter is 15.24 cm and the base thickness is 30.48 cm. The primary absorber is commercially available lead hermetically sealed in a 0.32-cm-thick copper jacket. Several possible systematic errors in using the cup are evaluated. The largest source of error arises from high-energy electrons which are ejected from the entrance window and enter the cup. A total systematic error of -0.83 percent is calculated to be the decrease from the true current value. From data obtained in calibrating helium-filled ion chambers with the Faraday cup, the mean energy required to produce one ion pair in helium is found to be 30.76 + or - 0.95 eV for nominal 600 MeV protons. This value agrees well, within experimental error, with reported values of 29.9 eV and 30.2 eV

    An independent distance estimate to the AGB star R Sculptoris

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    For the carbon AGB star R Sculptoris, the uncertain distance significantly affects the interpretation of observations regarding the evolution of the stellar mass loss during and after the most recent thermal pulse. We aim to provide a new, independent measurement of the distance to R Sculptoris, reducing the absolute uncertainty of the distance estimate to this source. R Scl is a semi-regular pulsating star, surrounded by a thin shell of dust and gas created during a thermal pulse approximately 2000 years ago. The stellar light is scattered by the dust particles in the shell at a radius of 19 arcsec. The variation in the stellar light affects the amount of dust-scattered light with the same period and amplitude ratio, but with a phase lag that depends on the absolute size of the shell. We measured this phase lag by observing the star R Scl and the dust-scattered stellar light from the shell at five epochs between June - December 2017. By observing in polarised light, we imaged the shell in the plane of the sky, removing any uncertainty due to geometrical effects. The phase lag gives the absolute size of the shell, and together with the angular size of the shell directly gives the absolute distance to R Sculptoris. We measured a phase lag between the stellar variations and the variation in the shell of 40.0 +/- 4.0 days. The angular size of the shell is measured to be 19.1 arcsec +/- 0.7 arcsec. Combined, this gives an absolute distance to R Sculptoris of 361 +/- 44 pc. We independently determined the absolute distance to R Scl with an uncertainty of 12%. The estimated distance is consistent with previous estimates, but is one of the most accurate distances to the source to date. In the future, using the variations in polarised, dust-scattered stellar light, may offer an independent possibility to measure reliable distances to AGB stars.Comment: accepted by A&A, 8 pages, 8 figure

    Dynamically dominant magnetic fields in the diffuse interstellar medium

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    Observations show that magnetic fields in the interstellar medium (ISM) often do not respond to increases in gas density as would be naively expected for a frozen-in field. This may suggest that the magnetic field in the diffuse gas becomes detached from dense clouds as they form. We have investigated this possibility using theoretical estimates, a simple magneto-hydrodynamic model of a flow without mass conservation and numerical simulations of a thermally unstable flow. Our results show that significant magnetic flux can be shed from dense clouds as they form in the diffuse ISM, leaving behind a magnetically dominated diffuse gas.Comment: 2 pages, 1 figure. In proceedings of IAU Symposium 259: "Cosmic magnetic fields: from planets to stars and galaxies", eds. K.G. Strassmeier, A.G. Kosovichev & J.E. Beckman in pres

    Lithium-drifted silicon detectors as low-energy photon spectrometers

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    Fabrication and testing of lithium-drifted detectors as low energy photon spectrometer
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