Research in large adaptive antenna arrays

The feasibility of microwave holographic imaging of targets near the earth using a large random conformal array on the earth's surface and illumination by a CW source on a geostationary satellite is investigated. A geometrical formulation for the illuminator-target-array relationship is applied to the calculation of signal levels resulting from L-band illumination supplied by a satellite similar to ATS-6. The relations between direct and reflected signals are analyzed and the composite resultant signal seen at each antenna element is described. Processing techniques for developing directional beam formation as well as SNR enhancement are developed. The angular resolution and focusing characteristics of a large array covering an approximately circular area on the ground are determined. The necessary relations are developed between the achievable SNR and the size and number of elements in the array. Numerical results are presented for possible air traffic surveillance system. Finally, a simple phase correlation experiment is defined that can establish how large an array may be constructed

Random sampling adaptively focusing synthetic aperture radar

A high resolution narrow angle of view imaging radar system is considered that employs an airborne synthetic aperture of 600 meters operating at X-band to produce a beamwidth of approximately 0.05 mr. This system differs from a conventional SAR in that only a smaller number of wavefront samples, spaced randomly over the aperture are processed, and adaptive beamforming with open loop scanning is used. As a result, the processing requirements are reduced to within the capability of present day small computer technology, and the tolerance on flight stability is loosened by about 100:1. The system is described and initial analysis and evaluation results are presented

Study of large adaptive arrays for space technology applications

The research in large adaptive antenna arrays for space technology applications is reported. Specifically two tasks were considered. The first was a system design study for accurate determination of the positions and the frequencies of sources radiating from the earth's surface that could be used for the rapid location of people or vehicles in distress. This system design study led to a nonrigid array about 8 km in size with means for locating the array element positions, receiving signals from the earth and determining the source locations and frequencies of the transmitting sources. It is concluded that this system design is feasible, and satisfies the desired objectives. The second task was an experiment to determine the largest earthbound array which could simulate a spaceborne experiment. It was determined that an 800 ft array would perform indistinguishably in both locations and it is estimated that one several times larger also would serve satisfactorily. In addition the power density spectrum of the phase difference fluctuations across a large array was measured. It was found that the spectrum falls off approximately as f to the minus 5/2 power

A survey thesis of the personal reading preferences of children in the intermediate grades

Thesis (Ed.M.)--Boston Universit

Declining use of combination infliximab and immunomodulator for inflammatory bowel disease in the community setting.

To describe trends of combination therapy (CT) of infliximab (IFX) and immunomodulator (IMM) for inflammatory bowel disease (IBD) in the community setting.A retrospective study was conducted of all IBD patients referred for IFX infusion to our community infusion center between 04/01/01 and 12/31/14. CT was defined as use of IFX with either azathioprine, 6-mercaptopurine, or methotrexate. We analyzed trends of CT usage overall, for Crohn\u27s disease (CD) and ulcerative colitis (UC), and for the subgroups of induction patients. We also analyzed the trends of CT use in these groups over the study period, and compared the rates of CT use prior to and after publication of the landmark SONIC trial.Of 258 IBD patients identified during the 12 year study period, 60 (23.3%) received CT, including 35 of 133 (26.3%) induction patients. Based on the Cochran-Armitage trend test, we observed decreasing CT use for IBD patients overall (P \u3c 0.0001) and IBD induction patients, (P = 0.0024). Of 154 CD patients, 37 (24.68%) had CT, including 20 of 77 (26%) induction patients. The Cochran Armitage test showed a trend towards decreasing CT use for CD overall (P \u3c 0.0001) and CD induction, (P = 0.0024). Overall, 43.8% of CD patients received CT pre-SONIC vs 7.4% post-SONIC (P \u3c 0.0001). For CD induction, 40.0% received CT pre-SONIC vs 10.8% post-SONIC (P = 0.0035). Among the 93 patients with UC, 19 (20.4%) received CT. Of 50 induction patients, 14 (28.0%) received CT. The trend test of the 49 patients with a known year of induction again failed to demonstrate any significant trends in the use of CT (P = 0.6).We observed a trend away from CT use in IBD. A disconnect appears to exist between expert opinion and evidence favoring CT with IFX and IMM, and evolving community practice

Value at Risk models with long memory features and their economic performance

We study alternative dynamics for Value at Risk (VaR) that incorporate a slow moving component and information on recent aggregate returns in established quantile (auto) regression models. These models are compared on their economic performance, and also on metrics of first-order importance such as violation ratios. By better economic performance, we mean that changes in the VaR forecasts should have a lower variance to reduce transaction costs and should lead to lower exceedance sizes without raising the average level of the VaR. We find that, in combination with a targeted estimation strategy, our proposed models lead to improved performance in both statistical and economic terms

Ab Initio Liquid Hydrogen Muon Cooling Simulations with ELMS in ICOOL

This paper presents new theoretical results on the passage of muons through liquid hydrogen which have been confirmed in a recent experiment. These are used to demonstrate that muon bunches may be compressed by ionisation cooling more effectively than suggested by previous calculations. Muon cooling depends on the differential cross section for energy loss and scattering of muons. We have calculated this cross section for liquid H2 from first principles and atomic data, avoiding traditional assumptions. Thence, 2-D probability maps of energy loss and scattering in mm-scale thicknesses are derived by folding, and stored in a database. Large first-order correlations between energy loss and scattering are found for H2, which are absent in other simulations. This code is named ELMS, Energy Loss & Multiple Scattering. Single particle trajectories may then be tracked by Monte Carlo sampling from this database on a scale of 1 mm or less. This processor has been inserted into the cooling code ICOOL. Significant improvements in 6-D muon cooling are predicted compared with previous predictions based on GEANT. This is examined in various geometries. The large correlation effect is found to have only a small effect on cooling. The experimental scattering observed for liquid H2 in the MUSCAT experiment has recently been reported to be in good agreement with the ELMS prediction, but in poor agreement with GEANT simulation.Comment: 6 pages, 3 figure

Job Growth in Early Transition: Comparing Two Paths

Small start-up firms are the engine of job creation in early transition and yet little is known about the characteristics of this new sector. We seek to identify patterns of job growth in this sector in terms of niches left from central planning and ask about differences in job creation across two different transition economies: Estonia, which experienced rapid destruction of the pre-existing firms, and the Czech Republic, which reduced the old sector gradually. We find job growth within industries to be quantitatively more important than job growth due to across-industry reallocation. Furthermore, the industrial composition of startups is strikingly similar in the two countries. We offer convergence to "western" industry firm-size distributions as an explanation. We also find regularities in wage evolution across new and old firms, including small differences in job quality across the two transition paths.http://deepblue.lib.umich.edu/bitstream/2027.42/39888/3/wp503.pd

Silicon-based molecular electronics

Molecular electronics on silicon has distinct advantages over its metallic counterpart. We describe a theoretical formalism for transport through semiconductor-molecule heterostructures, combining a semi-empirical treatment of the bulk silicon bandstructure with a first-principles description of the molecular chemistry and its bonding with silicon. Using this method, we demonstrate that the presence of a semiconducting band-edge can lead to a novel molecular resonant tunneling diode (RTD) that shows negative differential resistance (NDR) when the molecular levels are driven by an STM potential into the semiconducting band-gap. The peaks appear for positive bias on a p-doped and negative for an n-doped substrate. Charging in these devices is compromised by the RTD action, allowing possible identification of several molecular highest occupied (HOMO) and lowest unoccupied (LUMO) levels. Recent experiments by Hersam et al. [1] support our theoretical predictions.Comment: Author list is reverse alphabetical. All authors contributed equally. Email: rakshit/liangg/ ghosha/[email protected]