Initial '80s Development of Inflated Antennas

State of the art technology was considered in the definition and documentation of a membrane surface suitable for use in a space reflector system for long durations in orbit. Requirements for a metal foil-plastic laminate structural element were determined and a laboratory model of a rigidized element to test for strength characteristics was constructed. Characteristics of antennas ranging from 10 meters to 1000 meters were determined. The basic antenna configuration studied consists of (1) a thin film reflector, (2) a thin film cone, (3) a self-rigidizing structural torus at the interface of the cone and reflector; and (4) an inflation system. The reflector is metallized and, when inflated, has a parabolic shape. The cone not only completes the enclosure of the inflatant, but also holds the antenna feed at its apex. The torus keeps the inflated cone-reflector from collapsing inward. Laser test equipment determined the accuracy of the inflated paraboloids

Optical alignment and spinning of laser-trapped microscopic particles

Light-induced rotation of absorbing microscopic particles by transfer of angular momentum from light to the material raises the possibility of optically driven micromachines. The phenomenon has been observed using elliptically polarized laser beams or beams with helical phase structure. But it is difficult to develop high power in such experiments because of overheating and unwanted axial forces, limiting the achievable rotation rates to a few hertz. This problem can in principle be overcome by using transparent particles, transferring angular momentum by a mechanism first observed by Beth in 1936, when he reported a tiny torque developed in a quartz waveplate due to the change in polarization of transmitted light. Here we show that an optical torque can be induced on microscopic birefringent particles of calcite held by optical tweezers. Depending on the polarization of the incident beam, the particles either become aligned with the plane of polarization (and thus can be rotated through specified angles) or spin with constant rotation frequency. Because these microscopic particles are transparent, they can be held in three-dimensional optical traps at very high power without heating. We have observed rotation rates in excess of 350 Hz.Comment: 4 pages, 4 figure

Optical microrheology using rotating laser-trapped particles

We demonstrate an optical system that can apply and accurately measure the torque exerted by the trapping beam on a rotating birefringent probe particle. This allows the viscosity and surface effects within liquid media to be measured quantitatively on a micron-size scale using a trapped rotating spherical probe particle. We use the system to measure the viscosity inside a prototype cellular structure.Comment: 5 pages, 4 figures. v2: bibliographic details, minor text correction

Property rights and transaction costs : The role of ownership and organization in German public service provision

This paper provides evidence that ownership and organization matters for the efficiency of provision of public services. In particular, we find that pure private ownership is more efficient than pure public ownership, followed by mixed ownership. The delegation of management in different legal forms also has an impact, highlighting the importance of the design of the government-operator relation. We apply a structural approach of production function estimation ensuring precise determination of total factor productivity for a panel of German refuse collection firms in the time period between 2000-2012. We project total factor productivity estimates (TFP) on ownership and organization. Our results are in line with the trade-offs implied by the property rights literature and provide important policy implications regarding the organization of public service provision.Dieses Arbeitspapier liefert dafür Evidenz, dass sowohl die Eigentums als auch Organisationsstruktur für die Bereitstellung öffentlicher Güter wichtig sind. In Einzelnen wird für das Beispiel der deutschen Müllabfuhr dargelegt, dass die Bereitstellung mit Hilfe privater Unternehmen effizienter als durch öffentliche Unternehmen geschieht. Am schlechtesten schneidet bei diesem Effizienzvergleich die privat-öffentliche Mischform ab. Die Art und Weise der Managementorganisation in verschiedenen rechtlichen Organisationsformen hat ebenfalls einen wichtigen Einfluss. Es wird ein struktureller Ansatz zur Schätzung der Produktionsfunktion durchgeführt. Hierzu wird ein Panel deutscher Müllabfuhrunternehmen genutzt. Die ermittelte totale Faktorproduktivität wird danach mit verschiedenen Organisationsformen sowie mit der Eigentümerstruktur erklärt. Die Ergebnisse bestätigen die Vorhersagen der Theorie der Verfügungsrechte und haben somit einen wichtigen Einfluss auf wirtschaftspolitische Entscheidungen