High-Frequency Microstrip Cross Resonators for Circular Polarization EPR Spectroscopy

In this article we discuss the design and implementation of a novel microstrip resonator which allows for the absolute control of the microwaves polarization degree for frequencies up to 30 GHz. The sensor is composed of two half-wavelength microstrip line resonators, designed to match the 50 Ohms impedance of the lines on a high dielectric constant GaAs substrate. The line resonators cross each other perpendicularly through their centers, forming a cross. Microstrip feed lines are coupled through small gaps to three arms of the cross to connect the resonator to the excitation ports. The control of the relative magnitude and phase between the two microwave stimuli at the input ports of each line allows for tuning the degree and type of polarization of the microwave excitation at the center of the cross resonator. The third (output) port is used to measure the transmitted signal, which is crucial to work at low temperatures, where reflections along lengthy coaxial lines mask the signal reflected by the resonator. EPR spectra recorded at low temperature in an S= 5/2 molecular magnet system show that 82%-fidelity circular polarization of the microwaves is achieved over the central area of the resonator.Comment: Published in Review of Scientific Instrument

When, where and how to perform efficiency estimation

In this paper we compare two flexible estimators of technical efficiency in a cross-sectional setting: the nonparametric kernel SFA estimator of Fan, Li and Weersink (1996) to the nonparametric bias corrected DEA estimator of Kneip, Simar andWilson (2008). We assess the finite sample performance of each estimator via Monte Carlo simulations and empirical examples. We find that the reliability of efficiency scores critically hinges upon the ratio of the variation in efficiency to the variation in noise. These results should be a valuable resource to both academic researchers and practitioners.Bootstrap; Nonparametric kernel; Technical efficiency

When, Where and How to Perform Efficiency Estimation

In this paper we compare two flexible estimators of technical efficiency in a cross-sectional setting: the nonparametric kernel SFA estimator of Fan, Li and Weersink (1996) to the nonparametric bias corrected DEA estimator of Kneip, Simar and Wilson (2008). We assess the finite sample performance of each estimator via Monte Carlo simulations and empirical examples. We find that the reliability of efficiency scores critically hinges upon the ratio of the variation in efficiency to the variation in noise. These results should be a valuable resource to both academic researchers and practitioners.nonparametric kernel, technical efficiency, bootstrap

Biases in approximating log production

Most empirical work in economic growth assumes either a Cobb-Douglas production function expressed in logs or a log-approximated constant elasticity of substitution specification. Estimates from each are likely biased due to logging the model and the latter can also suffer from approximation bias. We illustrate this with a successful replication of Masanjala and Papagerogiou (2004) and then estimate both models in levels to avoid these biases. Our estimation in levels gives results in line with conventional wisdom.Nonparametric, Kmenta Approximation, Levels, Logs, PPML

When, where and how to perform efficiency estimation

In this paper we compare two flexible estimators of technical efficiency in a cross-sectional setting: the nonparametric kernel SFA estimator of Fan, Li and Weersink (1996) to the nonparametric bias corrected DEA estimator of Kneip, Simar and Wilson (2008). We assess the finite sample performance of each estimator via Monte Carlo simulations and empirical examples. We find that the reliability of efficiency scores critically hinges upon the ratio of the variation in efficiency to the variation in noise. These results should be a valuable resource to both academic researchers and practitioners.Bootstrap, Nonparametric Kernel, Technical Efficiency

Fabrication of Nano-Gapped Single-Electron Transistors for Transport Studies of Individual Single-Molecule Magnets

Three terminal single-electron transistor devices utilizing Al/Al2O3 gate electrodes were developed for the study of electron transport through individual single-molecule magnets. The devices were patterned via multiple layers of optical and electron beam lithography. Electromigration induced breaking of the nanowires reliably produces 1-3 nm gaps between which the SMM can be situated. Conductance through a single Mn12(3-thiophenecarboxylate) displays the coulomb blockade effect with several excitations within +/- 40 meV.Comment: 10 pages, 5 figure

Design evolution of the orbiter reaction control subsystem

The challenges of space shuttle orbiter reaction control subsystem development began with selection of the propellant for the subsystem. Various concepts were evaluated before the current Earth storable, bipropellant combination was selected. Once that task was accomplished, additional challenges of designing the system to satisfy the wide range of requirements dictated by operating environments, reusability, and long life were met. Verification of system adequacy was achieved by means of a combination of analysis and test. The studies, the design efforts, and the test and analysis techniques employed in meeting the challenges are described