Increased Accuracy in the Measurement of the Dielectric Constant of Seawater at 1.413 GHz

This paper describes the latest results for the measurements of the dielectric constant at 1.413 GHz by using a resonant cavity technique. The purpose of these measurements is to develop an accurate relationship for the dependence of the dielectric constant of sea water on temperature and salinity which is needed by the Aquarius inversion algorithm to retrieve salinity. Aquarius is the major instrument on the Aquarius/SAC-D observatory, a NASA/CONAE satellite mission launched in June of20ll with the primary mission of measuring global sea surface salinity to an accuracy of 0.2 psu. Aquarius measures salinity with a 1.413 GHz radiometer and uses a scatterometer to compensate for the effects of surface roughness. The core part of the seawater dielectric constant measurement system is a brass microwave cavity that is resonant at 1.413 GHz. The seawater is introduced into the cavity through a capillary glass tube having an inner diameter of 0.1 mm. The change of resonance frequency and the cavity Q value are used to determine the real and imaginary parts of the dielectric constant of seawater introduced into the thin tube. Measurements are automated with the help of software developed at the George Washington University. In this talk, new results from measurements made since September 2010 will be presented for salinities 30, 35 and 38 psu with a temperature range of O C to 350 C in intervals of 5 C. These measurements are more accurate than earlier measurements made in 2008 because of a new method for measuring the calibration constant using methanol. In addition, the variance of repeated seawater measurements has been reduced by letting the system stabilize overnight between temperature changes. The new results are compared to the Kline Swift and Meissner Wentz model functions. The importance of an accurate model function will be illustrated by using these model functions to invert the Aquarius brightness temperature to get the salinity values. The salinity values will be compared to co-located in situ data collected by Argo buoys

Characterization and mitigation of process variation in digital circuits and systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 155-166).Process variation threatens to negate a whole generation of scaling in advanced process technologies due to performance and power spreads of greater than 30-50%. Mitigating this impact requires a thorough understanding of the variation sources, magnitudes and spatial components at the device, circuit and architectural levels. This thesis explores the impacts of variation at each of these levels and evaluates techniques to alleviate them in the context of digital circuits and systems. At the device level, we propose isolation and measurement of variation in the intrinsic threshold voltage of a MOSFET using sub-threshold leakage currents. Analysis of the measured data, from a test-chip implemented on a 0. 18[mu]m CMOS process, indicates that variation in MOSFET threshold voltage is a truly random process dependent only on device dimensions. Further decomposition of the observed variation reveals no systematic within-die variation components nor any spatial correlation. A second test-chip capable of characterizing spatial variation in digital circuits is developed and implemented in a 90nm triple-well CMOS process. Measured variation results show that the within-die component of variation is small at high voltages but is an increasing fraction of the total variation as power-supply voltage decreases. Once again, the data shows no evidence of within-die spatial correlation and only weak systematic components. Evaluation of adaptive body-biasing and voltage scaling as variation mitigation techniques proves voltage scaling is more effective in performance modification with reduced impact to idle power compared to body-biasing.(cont.) Finally, the addition of power-supply voltages in a massively parallel multicore processor is explored to reduce the energy required to cope with process variation. An analytic optimization framework is developed and analyzed; using a custom simulation methodology, total energy of a hypothetical 1K-core processor based on the RAW core is reduced by 6-16% with the addition of only a single voltage. Analysis of yield versus required energy demonstrates that a combination of disabling poor-performing cores and additional power-supply voltages results in an optimal trade-off between performance and energy.by Nigel Anthony Drego.Ph.D

System Test of the ATLAS Muon Spectrometer in the H8 Beam at the CERN SPS

An extensive system test of the ATLAS muon spectrometer has been performed in the H8 beam line at the CERN SPS during the last four years. This spectrometer will use pressurized Monitored Drift Tube (MDT) chambers and Cathode Strip Chambers (CSC) for precision tracking, Resistive Plate Chambers (RPCs) for triggering in the barrel and Thin Gap Chambers (TGCs) for triggering in the end-cap region. The test set-up emulates one projective tower of the barrel (six MDT chambers and six RPCs) and one end-cap octant (six MDT chambers, A CSC and three TGCs). The barrel and end-cap stands have also been equipped with optical alignment systems, aiming at a relative positioning of the precision chambers in each tower to 30-40 micrometers. In addition to the performance of the detectors and the alignment scheme, many other systems aspects of the ATLAS muon spectrometer have been tested and validated with this setup, such as the mechanical detector integration and installation, the detector control system, the data acquisition, high level trigger software and off-line event reconstruction. Measurements with muon energies ranging from 20 to 300 GeV have allowed measuring the trigger and tracking performance of this set-up, in a configuration very similar to the final spectrometer. A special bunched muon beam with 25 ns bunch spacing, emulating the LHC bunch structure, has been used to study the timing resolution and bunch identification performance of the trigger chambers. The ATLAS first-level trigger chain has been operated with muon trigger signals for the first time

A low-skew, low jitter receiver circuit for on-chip optical clock distribution

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 127-130).by Nigel Anthony Drego.S.M

Numerical Modelling of the Magnetohydrodynamic Reconnection Shock Structure at the Terrestrial Magnetopause

The magnetic reconnection process is known to govern the transfer of solar wind plasma into the terrestrial magnetosphere. Numerical simulations were employed to qualitatively analyse the plasma flow and magnetic field across an MHD shock structure separating magnetosheath plasma from plasma in the magnetosphere at the onset as well as for the duration of continuing magnetic reconnection. The one-dimensional time-dependent Riemann problem was re-visited in this numerical study in order to qualitatively analyse the development of the MHD discontinuities for non-viscous and non-resistive conditions and thereby provide further in-sight into the initial development of discontinuities at an arbitrary reconnection site along the terrestrial magnetopause where the resistivity could be considered very small or negligible in comparison to the diffusion region. The two-dimensional steady-state Riemann problem was also numerically solved to obtain the ideal MHD 2D shock structure that is independent of time. The goal of modelling the 2D MHD shock structure was to obtain a greater understanding into the behaviour of the plasma flow and the magnetic field across the MHD discontinuities for ongoing magnetic reconnection conditions that occur at an arbitrary point on the dayside terrestrial magnetopause transition layer in the direction of the sub-solar point towards the cusp. The 1D as well as 2D models were solved by employing a Galerkin method of weighted residuals and a streamline diffusion technique was also employed to linearize the nonlinear ideal MHD equations governing the model. For a symmetric case with uniform plasma parameter conditions and exactly anitparallel magnetic fields in the tangential direction (z) across two equally divided plasma regions in the defined domain, four discontinuities were obtained in the solution for the 1D model as well as the 2D which were a pair of symmetric slow shocks and a pair of symmetric fast shocks. These results are in agreement with solution obtained by Lin & Lee (1993) for a similar 1D Riemann problem with symmetric conditions. On the other hand for an asymmetric case, the same two plasma regions had non-uniform plasma conditions and anitparallel magnetic fields in the tangential direction (z) with different magnitude. Five discontinuities were found to exist in the solution of the 1D as well as the 2D models which were a pair of asymmetric slow shocks, a pair of asymmetric fast shocks and a contact discontinuity. When the results obtained in this study are applied to the Earth's magnetosphere, MHD shocks and the contact discontinuity may be present at the magnetopause-boundary layer region with magnetic reconnection and a non-zero normal (x- direction) component of the magnetic field (in this case Bx= 0.3). Therefore, magnetic reconnection can occur under ideal MHD conditions devoid of resistivity and viscosity at an arbitrary point along the dayside magnetopause transition layer with the formation of five discontinuities about this layer for asymmetric conditions similar to those that are present in the terrestrial magnetosphere.Validerat; 20130220 (ysko