139 research outputs found
Determination of the Suitability of Arkansas River Water for Municipal, Industrial and Agricultural Use: Volume 3 Treatability Study
Volume III of the overall report for the project to determine the suitability of the Arkansas River for municipal, agricultural and industrial water supplies contains the treatability data. These data include the results of the granular activated carbon, ozonation and packed tower aeration studies. The research project was conducted under contract with the Arkansas Soil and Water Conservation Commission. Funding was provided by the Corps of Engineers, the Environmental Protection Agency, the City of Little Rock, Rockefeller Foundation and the Ozark Society. Additionally, the U.S. Geological Survey contributed financially by matching the cost of sample collection. The City of Little Rock provided funding for sampling the Little Rock site. Funding for the Lee Creek site was provided by the Environmental Protection Agency
Development of the cryogenic system of AEgIS at CERN
The AEgIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) experiment is located at the antiproton decelerator complex of CERN. The main goal of the experiment is to perform the first direct measurement of the Earthâs gravitational acceleration on antihydrogen atoms within 1% precision. The antihydrogen is produced in a cylindrical Penning trap by combining antiprotons with positrons. To reach the precision of 1%, the antihydrogen has to be cooled to 100 mK to reduce its random velocity. A dilution refrigerator is selected to deliver the necessary cooling capacity of 100 ÎŒW at 50 mK. The AEgIS cryogenic system basically consists of cryostats for a 1-T and for a 5-T superconducting magnet, a central region cryostat, a dilution refrigerator cryostat and a measurement cryostat with a MoirĂ© deflectometer to measure the gravitational acceleration. In autumn 2012, the 1-T cryostat, 5-T cryostat and central region cryostat were assembled and commissioned. The apparatus is cooled down in eight days using 2500 L of liquid helium and liquid nitrogen. During operation, the average consumption of liquid helium is 150 Lâday-1 and of liquid nitrogen 5 L·day-1. The temperature sensors at the Penning traps measured 12 K to 18 K, which is higher than expected. Simulations show that this is caused by a bad thermalization of the trap wiring. The implementation of the sub-kelvin region is foreseen for mid-2015. The antihydrogen will be cooled down to 100 mK in an ultra-cold trap consisting of multiple high-voltage electrodes made of sapphire with gold plated electrode sectors
Annihilation of low energy antiprotons in silicon
The goal of the AEIS experiment at the Antiproton
Decelerator (AD) at CERN, is to measure directly the Earth's gravitational
acceleration on antimatter. To achieve this goal, the AEIS
collaboration will produce a pulsed, cold (100 mK) antihydrogen beam with a
velocity of a few 100 m/s and measure the magnitude of the vertical deflection
of the beam from a straight path. The final position of the falling
antihydrogen will be detected by a position sensitive detector. This detector
will consist of an active silicon part, where the annihilations take place,
followed by an emulsion part. Together, they allow to achieve 1 precision on
the measurement of with about 600 reconstructed and time tagged
annihilations.
We present here, to the best of our knowledge, the first direct measurement
of antiproton annihilation in a segmented silicon sensor, the first step
towards designing a position sensitive silicon detector for the
AEIS experiment. We also present a first comparison with
Monte Carlo simulations (GEANT4) for antiproton energies below 5 MeVComment: 21 pages in total, 29 figures, 3 table
Measuring the free fall of antihydrogen
After the first production of cold antihydrogen by the ATHENA and ATRAP experiments ten years ago, new second-generation experiments are aimed at measuring the fundamental properties of this anti-atom. The goal of AEGIS (Antimatter Experiment: Gravity, Interferometry, Spectroscopy) is to test the weak equivalence principle by studying the gravitational interaction between matter and antimatter with a pulsed, cold antihydrogen beam. The experiment is currently being assembled at CERN's Antiproton Decelerator. In AEGIS, antihydrogen will be produced by charge exchange of cold antiprotons with positronium excited to a high Rydberg state (n > 20). An antihydrogen beam will be produced by controlled acceleration in an electric-field gradient (Stark acceleration). The deflection of the horizontal beam due to its free fall in the gravitational field of the earth will be measured with a moire deflectometer. Initially, the gravitational acceleration will be determined to a precision of 1%, requiring the detection of about 105 antihydrogen atoms. In this paper, after a general description, the present status of the experiment will be reviewed
Measuring 129Xe transfer across the bloodâbrain barrier using MR spectroscopy
Purpose
This study develops a tracer kinetic model of xenon uptake in the human brain to determine the transfer rate of inhaled hyperpolarized 129Xe from cerebral blood to gray matter that accounts for the effects of cerebral physiology, perfusion and magnetization dynamics. The 129Xe transfer rate is expressed using a tracer transfer coefficient, which estimates the quantity of hyperpolarized 129Xe dissolved in cerebral blood under exchange with depolarized 129Xe dissolved in gray matter under equilibrium of concentration.
Theory and Methods
Timeâresolved MR spectra of hyperpolarized 129Xe dissolved in the human brain were acquired from three healthy volunteers. Acquired spectra were numerically fitted with five Lorentzian peaks in accordance with known 129Xe brain spectral peaks. The signal dynamics of spectral peaks for gray matter and red blood cells were quantified, and correction for the 129Xe T1 dependence upon blood oxygenation was applied. 129Xe transfer dynamics determined from the ratio of the peaks for gray matter and red blood cells was numerically fitted with the developed tracer kinetic model.
Results
For all the acquired NMR spectra, the developed tracer kinetic model fitted the data with tracer transfer coefficients between 0.1 and 0.14.
Conclusion
In this study, a tracer kinetic model was developed and validated that estimates the transfer rate of HP 129Xe from cerebral blood to gray matter in the human brain
Cooling of electrically insulated high voltage electrodes down to 30 mK
AEgIS [1] is an antimatter experiment, using high voltage electrodes at 100 mK. In this work two possible principles to cool these electrodes with a dilution refrigerator are described: the Rod and the Sandwich. The metallic Rod is electrically insulated by a ceramic and connects a single electrode directly with a heat exchanger placed in the mixing chamber. The Sandwich consists of an elec-trically insulating sapphire plate, at both sides covered with indium. The total thermal resistivities of the Rod and of different Sandwich samples are measured between (30 and 130) mK. The lowest resistivity of the Sandwich is achieved with indium vapour deposited on polished sapphire (26 cm2K4/W at 30 mK). The resistivity of the Rod is significantly lower (0.5 cm2K4/W at 30 mK)
Cooling of electrically insulated high voltage electrodes down to 30 mK: Dynamic measurements
AEgIS [1] is an antimatter experiment, using high voltage electrodes at 100 mK. Two possible principles to cool these electrodes with a dilution refrigerator are investigated: the Rod and the Sandwich. Both designs are described in detail in [2]. The Sandwich design is discussed in the present work. It consists of an electrically insulating sapphire plate covered with indium on both sides. Dynamic measurements are performed in order to estimate the influence of time depending heat loads on different Sandwich designs. From these data the Sandwichâs thermal diffusivity is derived and compared to previous measurements using a static heat load. The lowest resistivity of the Sandwich is achieved with an indium vapor deposition onto polished sapphire (26 cm2K4/W at 30 mK). The same sandwich shows the best, i.e. highest thermal diffusivity (0.23 mm2/s at 70 mK). However, the results of the static and the dynamic measurements show some interesting and contrary tendencies
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