Laser power-meter comparison at far-infrared wavelengths and terahertz frequencies

We have evaluated the responsivity of seven different thermal detectors compared to an electrically calibrated photoacoustic reference detector at 119 µm (2.5 THz) and 394 µm (0.76 THz) laser wavelengths. Among the thermal detectors is an electrically calibrated thermopile having a vertically aligned carbon nanotube array as the absorber. We document the uncertainty contributions attributable to the photoacoustic reference detector along with a definition of a calibration factor based on the measurement protocol. The expanded relative uncertainty (k = 2) and a calibration factor of each detector are tabulated

Should we increase instruction time in low achieving schools? Evidence from Southern Italy

AbstractThis paper investigates the short term effects of a large scale intervention, funded by the European Social Fund, which provides additional instruction time to selected classes of lower secondary schools in Southern Italy. Selection is addressed using institutional rules that regulate class formation: first year students are divided into groups distinguished by letters, they remain in the same group across grades at the school, and the composition of teachers assigned to groups is stable over time. Using a difference-in-differences strategy, we consider consecutive cohorts of first year students enrolled in the same group. We compare participating groups to non-participating groups within the same school, as well as to groups in non-participating schools. We find that the intervention raised scores in mathematics for students from the least advantaged backgrounds. We also find that targeting the best students with extra activities in language comes at the cost of lowering performance in mathematics. We go beyond average effects, finding that the positive effect for mathematics is driven by larger effects for the best students

A New Way to Link Development to Institutions, Policies and Geography

The paper aims to examine the role of institutions relative to economic policy and geography in explaining the differential level of development across countries over time. To that end, it attempts to construct a Development Quality Index (DQI) and an Institutional Quality Index (IQI) by using multivariate statistical method of principal components. It shows that (i) higher level of IQI along with economic policy and geography factors lead to a positive improvement in the level of DQI; and (ii) results remain robust for IQI and relatively robust for economic policy and geography even when it is compared across cross-section and panel data estimation for a set of 102 countries over 1980 to 2004. The results strongly indicate that institutions matter in the context of specific economic policy mixes and geography related factors illustrated by disease burden, etc. It demonstrates that relative influence of institutions varies across stages of development

A Far-Infrared Heterodyne Spectrometer for Airborne Astronomy

The design and construction of a novel heterodyne spectrometer for airborne astronomy in the 50 µm - 200 µm wavelength range is described. along with laboratory measurements of its performance. A bulk, extrinsic Ge:Ga photoconductor is used as the mixer. Its low bandwidth, determined by the hole recombination rate, necessitates the use of a continuously tunable local oscillator. This is provided by a far-infrared laser sideband generator, which is based on a GaAs Schottky diode mounted at the feed of a comer-cube antenna, the latter combination acting as a reflective FIR modulator. The first chapter of this thesis describes the astronomical and technical context of the project - in particular, the constraints which the astronomical goals set on the instrument, and the advantages and drawbacks of each of the various broad instrumental strategies that are available for spectrometer design. The chapter's last section provides a very brief overview of our most successful laboratory results, which are described at greater length in chapters 2- 4. In chapter two we describe the performance of Ge:Ga mixers as heterodyne mixers. We report on an extensive series of measurements of bandwidth, photoconductive gain, and direct detection responsivity for a series of highly compensated, NTD detectors grown specifically for this purpose. Chapter two also describes a nunber of experiments on FIR heterodyne performance, made using the direct, attenuated laser, rather than the output of the sideband generator, as the local oscillator. These confirm the expectation that germanium photoconductors are capable of quantum-limited noise performance with quantum efficiencies of ~10%, at much lower LO powers than required for Schottky diodes. Our best achieved noise temperature is TN(DSB) = 655K at PLO = 1.6µW, a factor of &gt; 25 lower than the best reported corresponding figure for Schottky diodes. Chapter 3 describes the operating principles and construction of our FIR laser, which formed a basic tool in nearly all our laboratory experiments. A brief discussion of the Lorenz instability in FIR lasers is also given, in connection with various observations we have made of spontaneous pulsations and excess low-frequency noise on the laser output, and which have recently been the subject of considerable study by other researchers. Chapter four describes FIR laser sideband generation using small-area Schottky diodes and comer-cube antennas. The construction and performance of our corner-cubes is outlined, including the first direct measurement of the main beam efficiency of a corner-cube antenna in the FIR, and a comparison with theory. The construction and measured performance of the rest of the sideband generator is also described. A detailed, quantitative model has been developed for the conversion efficiency obtainable from Schottky diodes in this application. We find that the low conversion efficiency (-39 db) measured in our experiments, and comparable to that found by other researchers, is inherent in the diode and well predicted by the model. For our particular experiment, the model predicts -28 db loss due to the diode, plus approximately -10 db loss due to the antenna coupling efficiency. The dependence of conversion efficiency on diode parameters is studied and guidelines for future optimization derived. Unfortunately, the severe conversion loss we measure, combined with low FIR laser power and (somewhat less significantly) poor optics transmission, leads to our presently available LO power being inadequate to obtain astronomically useful sensitivity, by a large factor.</p

A service oriented architecture for data integration in asset management

The integration of data plays a crucial role in condition monitoring and active data warehousing. It is classified in horizontal and vertical integration which capture different integration scenarios. Horizontal scenarios deal with application providing complementary functionality, whereas vertical scenarios deal with the integration of applications on different abstraction levels. Processing data for effective decision support in condition monitoring is usually performed by different software applications that are integrated in a common business process. In order to execute the business process, data must be exported from one application and imported into another. However, due to heterogeneous underlying data models, the data export and import is not straight forward and a translation of data from one representation into another is required. We propose a Service Oriented Architecture (SOA) based on Web services that allow a seamless integration of asset management tools by providing a common architecture. It supports vertical and horizontal integration and enables the plug-in of new tools without interfering with a running environment.