A computer controlled signal preprocessor for laser fringe anemometer applications

The operation of most commercially available laser fringe anemometer (LFA) counter-processors assumes that adjustments are made to the signal processing independent of the computer used for reducing the data acquired. Not only does the researcher desire a record of these parameters attached to the data acquired, but changes in flow conditions generally require that these settings be changed to improve data quality. Because of this limitation, on-line modification of the data acquisition parameters can be difficult and time consuming. A computer-controlled signal preprocessor has been developed which makes possible this optimization of the photomultiplier signal as a normal part of the data acquisition process. It allows computer control of the filter selection, signal gain, and photo-multiplier voltage. The raw signal from the photomultiplier tube is input to the preprocessor which, under the control of a digital computer, filters the signal and amplifies it to an acceptable level. The counter-processor used at Lewis Research Center generates the particle interarrival times, as well as the time-of-flight of the particle through the probe volume. The signal preprocessor allows computer control of the acquisition of these data.Through the preprocessor, the computer also can control the hand shaking signals for the interface between itself and the counter-processor. Finally, the signal preprocessor splits the pedestal from the signal before filtering, and monitors the photo-multiplier dc current, sends a signal proportional to this current to the computer through an analog to digital converter, and provides an alarm if the current exceeds a predefined maximum. Complete drawings and explanations are provided in the text as well as a sample interface program for use with the data acquisition software

Filter induced errors in laser anemometer measurements using counter processors

Simulations of laser Doppler anemometer (LDA) systems have focused primarily on noise studies or biasing errors. Another possible source of error is the choice of filter types and filter cutoff frequencies. Before it is applied to the counter portion of the signal processor, a Doppler burst is filtered to remove the pedestal and to reduce noise in the frequency bands outside the region in which the signal occurs. Filtering, however, introduces errors into the measurement of the frequency of the input signal which leads to inaccurate results. Errors caused by signal filtering in an LDA counter-processor data acquisition system are evaluated and filters for a specific application which will reduce these errors are chosen

Laser anemometry techniques for turbine applications

Laser anemometry offers a nonintrusive means for obtaining flow field information. Current research at NASA Lewis Research Center is focused on instrumenting a warm turbine facility with a laser anemometer system. In an effort to determine the laser anemometer system best qualified for the warm turbine environment, the performance of a conventional laser fringe anemometer and a two spot time of flight system were compared with a new, modified time of flight system, called a Four Spot laser anemometer. The comparison measurements were made in highly turbulent flows near walls. The Four Spot anemometer uses elliptical spots to increase the flow acceptance angle to be comparable to that of a Laser Fringe Anemometer. Also, the Four Spot uses an optical code that vastly simplifies the pulse detection processor. The results of the comparison measurements will exemplify which laser anemometer system is best suited to the hostile environment typically encountered in warm rotating turbomachinery

A computer program to calculate the resistivity of a thin film deposited on a conductive substrate from four-point probe measurements

A series of FORTRAN-77 programs is described which correct for the effect of a conducting substrate when a linear four-point probe is used to measure the resistivity of a thin film. The resistivity of the film is given in terms of the thicknesses of the film and substrate, the known resistivity of the substrate, and the measured delta V/I. A full development is given as well as a complete description of the operation of the programs. The programs themselves can be obtained through COSMIC, and are identified as LEW No. 14381

An optical method for determining level in two-phase cryogenic fluids

A method was evaluated to measure the liquid-gas and the liquid-slush interfaces in two-phase cryogen systems using optical means. This method makes use of the attenuation of a directed light beam caused by the difference in the index of refraction between the solid particles and the surrounding liquid. Preliminary experimental results obtained in slush nitrogen are shown. The possibility of extending this technique to include a measure of solid fraction is also discussed

Steric Effects on the Formation of Manganese Oxide Clusters and 2-Dimensional Ammonium Formate Architectures

It has been demonstrated by the Beatty group that altering the identity of the ortho-substituent of a dianiline counterion affects the assembly and dimensionality of a cadmium-chloride layer from 2-D to 0-D. This work seeks to extend this finding to metal oxide and organic hydrogen-bonded materials. By systematically increasing the ortho­-substituent’s size on the benzoate building block of reported manganese oxide clusters, of formula MnxOy(O2C-R)zLw (where R = Alkyl, L = neutral monodentate ligand), we aim to impact the self-assembly of these materials relative to their parent forms; establishing a structure/function relationship of each material through measurement of their magnetization. The formation of 2-dimensional hydrogen-bonded ammonium formate layers will be investigated in the same manner. By maintaining the formate anion, but altering the identity of the ammonium cation, typically a substituted benzylamine, a novel series of 2-D layered structures will be closely compared in order to determine the impact of substituents on the formation of these lamellar materials. With respect to the ammonium formate compounds, the size of the ortho-substituent is considered as well as the position of substituent around the ring. Additionally, these ammonium formate compounds will also be compared to analogous ammonium-3,5-pyrazoledicarboxylate structures (HPzDCA) to evaluate the impacts of the anion on the formation of these layered materials. We have found that with metal oxides, solvothermal methods, in addition to a bulky ortho-phenyl substituted benzoate, were required to alter the crystal structure of the Mn12-type complex to a Mn13-supercubane-type structure. We also found that lowering the site-specific symmetry of distorted MnIII ions impacted the magnetization of the Mn12-type substituted compounds. With ammonium formates, we have found that, by modifying the substituent in a series of benzylamines, the shape and orientation of the layer sheets and the interlayer pillars are drastically altered as per hydrogen bonding, and CH/π interactions. When compared to analogous HPzDCA compounds, the size of the anion (the mono-anion of 3,5-pyrazoledicarboxylic acid versus the formate ion) influences the shape of the layer. The smaller formate ion allows for enhanced flexibility in the hydrophilic sheet, as well as increased packing density of the ammonium cation

Photoproduction of pion pairs off nucleons

In the absence of a solution for Quantum Chromodynamics (QCD) in the low energy regime, so called effective models are being used to describe the nucleon and its excited states. These models include the basic symmetries from QCD, but on the other hand, compared to quarks and gluons, use higher lying degrees of freedom. Experimental contributions are mandatory to validate these models and fix free parameters. Today still most of the world-data in this field was obtained by meson-induced excitation of the nucleon. Even though numerous excited states of the nucleon could be identified, the number of model predicted states is much higher. This is known as the missing resonance problem. One explanation could be that some excited states just couple weakly to pion-N (kaon-N) and hence the excitation via photons was proposed to further test the model predictions. During the last 15 years, much experimental effort was made at various photoproduction facilities like MAMI, ELSA, JLab or ESRF and a large number of states could be confirmed, but the missing resonance problem could not be solved. Higher lying resonances (M > 1.6 GeV) decay preferably via sequential decays with many meson final states, and especially double pion decay channels are assumed to dominate in this region. The reactions investigated in this work, namely g+p(n)->pion^0+pion^0+p(n), g+n(p)->pion^0+pion^0+n(p), g+p->pion^0+pion^0+p, g+p(n)->pion^++pion^0+n(n), g+n(p)->pion^-+pion^0+p(p), g+p->pion^++pion^0+n thus form the primary source of information on photocouplings of higher lying resonances. This work explores neutral and mixed-charge double pion production channels up to invariant masses of the final state center-of-mass system of about 1.9 GeV and presents unpolarized as well as single-polarized observables. All results have high precision, are compared to different model predictions, and will considerably constrain future model analyses in the field of double pion photoproduction and beyond. The data of this work were taken at MAMI in four different experiments with liquid hydrogen and deuterium targets in 2007 and 2009 and include over 600 hours of beam time. A longitudinally polarized electron beam was used to produce circularly polarized bremsstrahlung photons with energies up 1.4 GeV. The reaction products, charged pions, photons and nucleons, were detected in the combined calorimeter consisting of Crystal Ball and TAPS. Total and differential cross sections, invariant mass distributions of N-pion and pion-pion and beam helicity asymmetries were computed in the fully reconstructed final state center-of-mass system. Effects from Fermi motion in the deuteron target could be reliably defolded leading to a good agreement between free and quasifree proton data, and thus the neutron results can be interpreted as a good approximation of free neutron data. Beam-helicity asymmetries for g+n(p)->pion^0+pion^0+n(p) and g+n(p)->pion^-+pion^0+p(p) have been measured for the first time and published together with the results from the proton data. Especially for the mixed-charge results, the available model calculations fail to reproduce the data, and for the neutral channel data, an unexpected similarity for proton and neutron results was observed. Total and differential cross sections as well as invariant mass distributions of N-pion and pion-pion for g+n(p)->pion^-+pion^0+p(p) have also been measured for the first time and previous results for g+p(n)->pion^++pion^0+n(n) could be reproduced and extended into the third resonance region

Comparison of Single Leg Performance Tests in Athletes With and Without ACL Reconstruction

Anterior cruciate ligament (ACL) injury rates among collegiate athletes continue to rise across 15 different men\u27s and women\u27s sports. Re-injury in ACL-reconstructed athletes occurs in 6-13% of reconstructed knees, and 2-6% sustain a ACL injury to the opposite leg. Strength and power have been found to be useful measures of muscle function. Clearance for sport participation following reconstruction and rehabilitation used to be based on a length of time rather than objective measurements of functional movements. Patients typically return to sport between 6 to 9 months postoperatively, which is now being questioned as to whether or not it is an adequate amount of time to ensure safe functional movement patterns in patients. The Functional Movement Screen (FMS) and Y-Balance Test are emerging screening tests used to objectively assess functional movement and dynamic balance. These tests are often used to identify patients who may be at an increased risk of injury, and help with return to sport decision-making. Therefore, the overall objective of this project was to assess bilateral lower extremity differences that an athlete may possess from an anterior cruciate ligament (ACL) tear, despite being cleared by a medical professional following a rehabilitation program. The project assessed each athlete comparing the leg that underwent ACL reconstructive surgery and the non-torn leg within five different arenas- strength, power, speed, balance and force. The main hypothesis was that there would be a significant deficit in strength, power, speed, balance and force in the lower extremity that has underwent reconstructive surgery. The purpose of this research was to clearly identify an athlete\u27s areas of weakness in their reconstructed knee to help prevent re-injury in the future