Performance documentation of the engineering model 30-cm diameter thruster

The results of extensive testing of two 30-cm ion thrusters which are virtually identical to the 900 series Engineering Model Thruster in an ongoing 15,000-hour life test are presented. Performance data for the nominal fullpower (2650 W) operating point; performance sensitivities to discharge voltage, discharge losses, accelerator voltage, and magnetic baffle current; and several power throttling techniques (maximum Isp, maximum thrust/power ratio, and two cases in between are included). Criteria for throttling are specified in terms of the screen power supply envelope, thruster operating limits, and control stability. In addition, reduced requirements for successful high voltage recycles are presented

A fast data acquisition system for the study of transient events by high repetition rate time-of-flight mass spectrometry

Recent advances in commercially available data acquisition electronics embodying high speed A/D conversion coupled to increased memory storage have now made practical (at least within time intervals of a third of a millisecond or more) the capturing of all of the data generated by a high repetition rate time-of-flight mass spectrometer producing complete spectra every 25 to 35 microseconds. Such a system was assembled and interfaced with a personal computer for control and management of data. The applications are described for recording time-resolved spectra of individual vapor plumes induced from the pulsed-laser heating of material. Each laser pulse triggers the system to generate automatically a 3-dimensional (3-D) presentation of the time-resolved spectra with m/z labeling of the major mass peaks, plus an intensity versus time display of both the laser pulse and the resulting vapor pulse. The software also permits storing of data and its presentation in various additional forms

An additional study and implementation of tone calibrated technique of modulation

The Tone Calibrated Technique (TCT) was shown to be theoretically free from an error floor, and is only limited, in practice, by implementation constraints. The concept of the TCT transmission scheme along with a baseband implementation of a suitable demodulator is introduced. Two techniques for the generation of the TCT signal are considered: a Manchester source encoding scheme (MTCT) and a subcarrier based technique (STCT). The results are summarized for the TCT link computer simulation. The hardware implementation of the MTCT system is addressed and the digital signal processing design considerations involved in satisfying the modulator/demodulator requirements are outlined. The program findings are discussed and future direction are suggested based on conclusions made regarding the suitability of the TCT system for the transmission channel presently under consideration

Estimating Local Compliance in a Beam from Bending Measurements Part I. Computing "Span Function"

Bending modulus of elasticity measurements have been useful and profitable for decades in the sorting of dimension lumber for its structural quality. Bending and tensile strengths of lumber are known to be correlated with modulus of elasticity. Previous research indicates that bending elasticity on short spans, shorter than can be practically measured with precision, may improve correlation with strength. It is expected, therefore, that the optimal estimation method of the present two-part paper will be applied in the machine stress rating (MSR) process for more accurate sorting of dimension lumber into MSR grades.Using weighting functions called "span functions," the estimation method processes a sequence of bending measurements from overlapping spans, such as those obtained from equipment for MSR lumber production. A span function is specific to the support configuration of a particular bending span and defines how much the local elastic properties along a beam contribute to a measurement. Intuitively, the local elasticity values of a beam near span center affect the measurement more than values near span ends. Span function defines this effect as a function of position along the bending span. In Part I, a procedure is developed for computing span function of a general bending span configuration. Span functions are graphed for bending spans of a production-line machine used in MSR lumber production and for other bending span configurations. In Part II, use of span functions in optimal estimation of local elasticity is described

Estimating Residual Error by Repeated Measurements

Repeated measurements can be used to estimate the residual error of a measurement process. Residual error, defined as the error remaining after all known sources of error have been accounted for, is what causes differences in the measurement outcome when everything about the measurement process is seemingly identical. Four estimators for the amount of residual error are suggested. These estimators are functions of the outcomes from m repeated measurements on each of n items. Assuming a normal distribution for the residual error, two of the estimators are unbiased estimators for the standard deviation of the residual error, and the third is the maximum likelihood estimator for the standard deviation of the residual error. The fourth is not an estimator for standard deviation, but rather it uses the distance between measurement order statistics as an indicator of the amount of residual error. The efficiencies of the first two estimators and the bias of the maximum likelihood estimator are evaluated. Computations use standard statistical methods and are included in appendices.This work, motivated by the study of machines used to measure the modulus of elasticity of dimension lumber, has been used to assess the performance of this machinery. An example using data from more than 10 years ago and some recent data show that the residual error then was about double that of today for well-tuned, high-speed production-line machinery

Synopsis of a computer program designed to interface a personal computer with the fast data acquisition system of a time-of-flight mass spectrometer

Briefly described are the essential features of a computer program designed to interface a personal computer with the fast, digital data acquisition system of a time-of-flight mass spectrometer. The instrumentation was developed to provide a time-resolved analysis of individual vapor pulses produced by the incidence of a pulsed laser beam on an ablative material. The high repetition rate spectrometer coupled to a fast transient recorder captures complete mass spectra every 20 to 35 microsecs, thereby providing the time resolution needed for the study of this sort of transient event. The program enables the computer to record the large amount of data generated by the system in short time intervals, and it provides the operator the immediate option of presenting the spectral data in several different formats. Furthermore, the system does this with a high degree of automation, including the tasks of mass labeling the spectra and logging pertinent instrumental parameters

An Alternive to Critical Point Drying for Preparing Meat Emulsions for Scanning Electron Microscopy

A rapid sample drying technique is described which is useful for the simultaneous preparation of large numbers of samples as an alternative to critical point drying. The cryofractured face of meat emulsions was visualized after appl ying this technique . The fine structure of 1 ipids and proteins were found to be well preser ved in comparison to other reports which used critical point dried meat emulsions. Lipid was readily discerned from the protein matrix by selective fixation of the components in duplicate samples . Stereo imaging was useful in enhancing the texture of the cryofractured surface and as an aid in differentiating the protein matrix from the fat component of meat emulsions