Spatially and temporally resolved temperature measurements of plasma generated in percussion drilling with a diode-pumped Nd:YAG laser

Results of spectroscopic temperature measurements of the laser-induced plasma generated during percussion drilling with a high power diode-pumped, pulsed Nd:YAG laser are presented. SAE 52100 steel was drilled with varying average powers. Helium and oxygen were each used as the shield gas. Emission spectra were collected with a monochrometer and an intensified charge coupled detector connected to the optical multichannel analyzer. The plasma electron temperatures were calculated from the relative intensities of the spectral lines. The spatial and temporal temperature distributions are presented. Both drilling times and spatial distributions indicate energy absorption by the plasma. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71333/2/JAPIAU-84-8-4122-1.pd

A computerized Langmuir probe system

For low pressure plasmas it is important to record entire single or double Langmuir probe characteristics accurately. For plasmas with a depleted high energy tail, the accuracy of the recorded ion current plays a critical role in determining the electron temperature. Even for high density Maxwellian distributions, it is necessary to accurately model the ion current to obtain the correct electron density. Since the electron and ion current saturation values are, at best, orders of magnitude apart, a single current sensing resistor cannot provide the required resolution to accurately record these values. We present an automated, personal computer based data acquisition system for the determination of fundamental plasma properties in low pressure plasmas. The system is designed for single and double Langmuir probes, whose characteristics can be recorded over a bias voltage range of ±70 V with 12 bit resolution. The current flowing through the probes can be recorded within the range of 5 nA–100 mA. The use of a transimpedance amplifier for current sensing eliminates the requirement for traditional current sensing resistors and hence the need to correct the raw data. The large current recording range is realized through the use of a real time gain switching system in the negative feedback loop of the transimpedance amplifier

High-contrast Doppler-free transmission spectroscopy

By applying Doppler-free saturated absorption spectroscopy in the regime of high integrated sample absorption, high-contrast Doppler-free laser transmission signals can be obtained as demonstrated in experiments on the sodium D lines. Natural linewidth background-free signals are observed

Non-normal impact of earth penetrators

A brief literature review of the general subject of projectile penetration into soil media is presented. Particular emphasis is placed on projectiles impacting soil targets at other than normal incidence and/or at an angle of attack, for which lateral accelerations exist and can dominate the structural response. Comparisons of predicted lateral accelerations with recent earth penetrator experiments are then made using a 3 degree-of-freedom rigid-body approach developed elsewhere to determine the external penetrator loading. Agreement between experimental and calculated accelerations is favorable, but the need to include flexible-body response is indicated. Finally a scheme to incorporate a spherical-cavity-expansion analytical procedure into a detailed finite element model of the penetrator is developed to account for flexible-body response

Cardiovascular and Stride Frequency Differences During Land and Aquatic Treadmill Walking

This study examined heart rate (HR) and stride frequency (SF) values of 30 college-aged males and females during dry-land (DL) and aquatic walking (AW). Aquatic walking trials were completed in an underwater treadmill with the water depth at waist level; the water temperature (31℃ ± 0.1℃) and room temperature (26.6℃ ± 0.1℃) were maintained at thermoneutral levels throughout the study. During each walking condition, HR and SF were recorded at treadmill speeds of 1 mph, 2 mph, and 3 mph. Participants were instructed to walk with their hands at their sides swinging as they would when walking on dry-land unless they felt the need to use the handrails to steady themselves. Heart rate monitors were used to record cardiovascular changes, and strides were measured from consecutive left and right toe strikes. Results of the study indicated HR was significantly higher during DL than AW at 1 mph (p \u3c .001) and 3 mph (p \u3c .001) but was not significantly different (p = .64) at 2 mph. The SF of the participants was significantly lower (p \u3c .001) during AW than DL at all speeds. When comparing sex, females had significantly higher HR at 1 mph (p = .012), 2 mph (p = .007), and 3 mph (p \u3c .001) than males for DL conditions. No differences in HR were found during the AW conditions (F = 0.66, p = 0.44, ηp2 = 0.02). No differences in SF were observed between males and females in both DL (F = 2.96, p = 0.06, ηp2 = 0.09) and AW (F = 1.03, p = 0.32, ηp2 = 0.036) conditions. As a result, AW increased HR values similar to those of DL, but without the added stress to the lower extremities due to the buoyancy of the water. Thus, AW provided an exercise medium capable of meeting the ACSM intensity guidelines for PA and allowed adults to be physically active presumably with less stress on the lower body

Extraction-scintillation medium and method of use

An extraction-scintillation medium of substantially free-flowing, porous, solid particulate matter having one or more fluors retained within the particulate matter and an extraction agent adsorbed on or bound to the surface of the particulate matter. The medium is capable of extracting one of a selected radionuclide from an aqueous stream and permits transmission of light therethrough, which light is emitted from the one or more fluors in response to radiation absorbed thereby from the selected radionuclide. A sensor system using the extraction-scintillation medium for real-time or near real-time detection of the selected radionuclide is also disclosed

Laser spectroscopy using beam-overlap modulation

A new Doppler-free laser spectroscopy method is demonstrated that employs modulation of the position of a laser beam rather than the commonly used intensity or polarization modulation. The technique is applicable in saturated absorption as well as fluorescence measurements, as is illustrated in experiments on sodium and iodine lines. A particular feature of the method is that Doppler- and background-free fluorescence spectra can be recorded without using intermodulation techniques

Bolt preload selection for pulsed-loaded vessel closures

Bounding, closed-form solutions are developed for selecting the bolt preload for a square, flat plate closure subjected to a pressure pulse load. The solutions consider the limiting case in which preload is primarily dependent on closure bending response as well as the limiting case in which preload depends on elastic bolt response. The selection of bolt preload is illustrated. Also presented in the paper is a detailed finite element analysis of dynamically loaded, bolted circular closure. The responses of the structure, closure, and bolts are included, and results are obtained for various preloads. The analysis illustrates a method of bolt preload modeling for use in general finite element computer programs

Detection of damage in axial (membrane) systems

In a recent paper, two methods of damage identification (Modified Damage Index and Change-in-Flexibility) were applied to detection of damage in an 8-DOF vibrating system. The goal of the work was to detect damage (reduction in stiffness of one or more of the elements) as well as to locate the particular damaged elements (S). However, the investigation was limited to numerical simulations only. In this paper, a physical, spring-mass model of a similar, degenerate 8-DOF system (7 normal modes plus a rigid-body mode) was constructed. Experiments were then performed and the modal properties of the system were determined in undamaged and damaged states. Excitation was provided either by an impact hammer or by an electromechanical shaker. Damage was induced by replacing one of the springs with a spring of lower stiffness. The Modified Damage Index method clearly isolated the location of damage for a variety of damage locations and levels of damage. The Change-in-Flexibility method, however, was found to be less reliable. The ability of the method to locate damage depended strongly on location and the level of damage as well as the number of modes included