A second-generation constrained reaction volume shock tube.

We have developed a shock tube that features a sliding gate valve in order to mechanically constrain the reactive test gas mixture to an area close to the shock tube endwall, separating it from a specially formulated non-reactive buffer gas mixture. This second-generation Constrained Reaction Volume (CRV) strategy enables near-constant-pressure shock tube test conditions for reactive experiments behind reflected shocks, thereby enabling improved modeling of the reactive flow field. Here we provide details of the design and operation of the new shock tube. In addition, we detail special buffer gas tailoring procedures, analyze the buffer/test gas interactions that occur on gate valve opening, and outline the size range of fuels that can be studied using the CRV technique in this facility. Finally, we present example low-temperature ignition delay time data to illustrate the CRV shock tube's performance.

Quantum cascade laser absorption sensor for carbon monoxide in high-pressure gases using wavelength modulation spectroscopy.

A tunable quantum cascade laser sensor, based on wavelength modulation absorption spectroscopy near 4.8 µm, was developed to measure CO concentration in harsh, high-pressure combustion gases. The sensor employs a normalized second harmonic detection technique (WMS-2f/1f) at a modulation frequency of 50 kHz. Wavelength selection at 2059.91 cm⁻¹ targets the P(20) transition within the fundamental vibrational band of CO, chosen for absorption strength and relative isolation from infrared water and carbon dioxide absorption. The CO spectral model is defined by the Voigt line-shape function, and key line-strength and line-broadening spectroscopic parameters were taken from the literature or measured. Sensitivity analysis identified the CO-N2 collisional broadening coefficient as most critical for uncertainty mitigation in hydrocarbon/air combustion exhaust measurements, and this parameter was experimentally derived over a range of combustion temperatures (1100-2600 K) produced in a shock tube. Accuracy of the wavelength-modulation-spectroscopy-based sensor, using the refined spectral model, was validated at pressures greater than 40 atm in nonreactive shock-heated gas mixtures. The laser was then free-space coupled to an indium-fluoride single-mode fiber for remote light delivery. The fiber-coupled sensor was demonstrated on an ethylene/air pulse detonation combustor, providing time-resolved (~20 kHz), in situ measurements of CO concentration in a harsh flow field.

Extension of Bacillus endospore gas dynamic heating studies to multiple species and test conditions.

AIMS: Shock wave-induced damage to a variety of Bacillus endospore species is studied for a wide range of postshock temperatures and test times in oxidative and non-oxidative gas environments. METHODS AND RESULTS: Bacillus atrophaeus and Bacillus subtilis endospores are nebulized into an aqueous aerosol, loaded into the Stanford aerosol shock tube (SAST) and subjected to shock waves of controlled strength. Endospores experience uniform test temperatures between 500 and 1000 K and pressures ranging from 2 to 7 atm, for either a short test time (∼2·5 ms) or a relatively long test time (∼45 ms). During this process, the bioaerosol is observed using in situ laser absorption and scattering diagnostics. Additionally, shock-treated samples are extracted for ex situ analysis including viability plating and flow cytometry. For short test times, results are consistent with previous studies; all endospore species begin to lose the ability to form colonies when shock-heated to temperatures above 500 K, while significant breakdown in morphology is observed for postshock temperatures above 700 K. Oxidative bath gases did not affect viability losses or morphological breakdown rates. Experiments with extended postshock test time showed increased viability loss with minimal morphological damage for shocks between 600 and 700 K. CONCLUSIONS: Genetic differences between B. subtilis and B. atrophaeus endospores do not confer noticeable gains in resistance to shock heating. Oxidative environments do not exacerbate shock-induced damage to endospores. Extended test time experiments reinforce our hypothesis that a temperature/time-dependent inactivation mechanism that does not involve morphological breakdown exists at low-to-moderate postshock temperatures. SIGNIFICANCE AND IMPACT OF THE STUDY: The methodology and experiments described in this paper extend the study of the interactions of endospores with shock/blast waves to new species and environmental conditions.

Bacillus endospore resistance to gas dynamic heating.

AIM: To develop a novel laboratory procedure for the study of shock wave-induced damage to Bacillus endospores. METHODS AND RESULTS: Bacillus atrophaeus endospores are nebulized into an aerosol, loaded into the stanford aerosol shock tube and subjected to shock waves of controlled strength. Endospores experience uniform test temperatures between 500 and 1000K and pressures ranging from 2 to 7atm, for a relatively short time (2-3ms). During this process, the bioaerosol is observed using in situ laser absorption and scattering diagnostics. Additionally, shock-treated samples are extracted for ex situ analysis including viability plating, flow cytometry and SEM imaging. Measurements indicate that endospores lose the ability to form colonies when heated to test temperatures above 500K while significant breakdown in morphology is observed at test temperatures above 750K. CONCLUSION: These results demonstrate the disruption of essential biochemical pathways or biomolecules prior to the onset of significant endospore morphological deterioration. SIGNIFICANCE AND IMPACT OF THE STUDY: This novel laboratory approach to study the interaction of endospores with shock waves provides an experimental means to investigate the mechanisms of endospore resistance to rapid heating. In addition, this methodology allows for the direct simulation of a blast wave-bioaerosol interaction in an atmospheric environment.

Measurements of CO(2) concentration and temperature at high pressures using 1f-normalized wavelength modulation spectroscopy with second harmonic detection near 2.7 microm.

Tunable diode lasers (TDL) near 2.7 mum are used to measure high-resolution direct absorption and wavelength modulation with second harmonic (WMS-2f) spectra at high pressures for two CO(2) transitions near 3633.08 and 3645.20 cm(-1), belonging to the nu(1)+ nu(3) vibrational band. Important factors influencing the design of a high-pressure TDL sensor and the variation of WMS-2f line shape with changes in pressure and laser parameters are discussed. Measurements of line strength and line broadening parameters are carried out for the 3645.20 cm(-1) transition in an atmospheric-pressure, high-temperature cell. A room-temperature high-pressure cell is then used to measure the pressure shift for both CO(2) transitions. Deviation of the direct absorption and wavelength modulation spectroscopy (WMS) spectra from the Lorentzian profile is studied in a high-density (9.2 amagats) CO(2)-Ar mixture. The WMS spectra are shown to be negligibly affected by non-Lorentzian effects up to 10 atm and room temperature, in contrast with direct absorption. Measurements of CO(2) concentration and temperature are carried out in nonreactive shock-tube experiments (P approximately 8-12 atm, T~800-1200 K) to validate the accuracy and precision of wavelength-modulation-spectroscopy-based sensing. CO(2) time histories are then measured in heptane ignition experiments and compared with reaction kinetics mechanisms to demonstrate the use of this sensor in high-pressure combustion systems.

Does Static-99 predict recidivism among older sexual offenders?

Static-99 (Hanson & Thornton, 2000) is the most commonly used actuarial risk tool for estimating sexual offender recidivism risk. Recent research has suggested that its methods of accounting for the offenders' ages may be insufficient to capture declines in recidivism risk associated with advanced age. Using data from 8 samples (combined size of 3,425 sexual offenders), the present study found that older offenders had lower Static-99 scores than younger offenders and that Static-99 was moderately accurate in estimating relative recidivism risk in all age groups. Older offenders, however, had lower sexual recidivism rates than would be expected based on their Static-99 risk categories. Consequently, evaluators using Static-99 should considered advanced age in their overall estimate of risk.

A structured approach to evaluating change among sexual offenders.

Presently, there are no established scales that evaluate change in risk among sexual offenders. The Sex Offender Need Assessment Rating (SONAR) was developed to fill this gap. The SONAR includes five relatively stable factors (intimacy deficits, negative social influences, attitudes tolerant of sex offending, sexual self-regulation, general self-regulation) and four acute factors (substance abuse, negative mood, anger, victim access). The psychometric properties of the scale were examined using data previously collected by Hanson and Harris (1998, 2000). Overall, the scale showed adequate internal consistency and moderate ability to differentiate between recidivists and nonrecidivists (r = .43; ROC area of .74). SONAR continued to distinguish between the groups after controlling for well-established risk indicators, such as age, and scores on the Static-99 (Hanson & Thornton, 2000) and the Violence Risk Appraisal Guide (Quinsey, Harris, Rice, & Cormier, 1998).

In Situ Combustion Measurements of CO(2) by Use of a Distributed-Feedback Diode-Laser Sensor Near 2.0 mum.

High-resolution absorption measurements of CO(2) were made in a heated static cell and in the combustion region above a flat-flame burner for the development of an in situ CO(2) combustion diagnostic based on a distributed-feedback diode laser operating near 2.0 mum. Calculated absorption spectra of high-temperature H(2)O and CO(2) were used to find candidate transitions for CO(2) detection, and the R(50) transition at 1.997 mum (the nu(1) + 2nu(2) + nu(3) band) was selected on the basis of its line strength and its isolation from interfering high-temperature water absorption. Measurements of spectroscopic parameters such as the line strength, the self-broadening coefficient, and the line position were made for the R(50) transition, and an improved value for the line strength is reported. The combustion-product populations of CO(2) in the combustion region above a flat-flame burner were determined in situ to verify the measured spectroscopic parameters and to demonstrate the feasibility of the diode-laser sensor.

Ammonia Monitoring Near 1.5 mum with Diode-Laser Absorption Sensors.

We investigated ammonia spectroscopy near 1.5 mum to select transitions appropriate for trace ammonia detection in air-quality and combustion emissions-monitoring applications using diode lasers. Six ammonia features were selected for these trace-gas detection applications based on their transition strengths and isolation from interfering species. The strengths, positions, and lower-state energies for the lines in each of these features were measured and compared with values published in the literature. Ammonia slip was measured in the exhaust above an atmospheric pressure premixed ethylene-air burner to demonstrate the feasibility of the in situ diode-laser sensor.

Measurements of NH(3) and CO(2) with Distributed-Feedback Diode Lasers Near 2.0 mum in Bioreactor Vent Gases.

Measurements of NH(3) and CO(2) were made in bioreactor vent gases with distributed-feedback diode-laser sensors operating near 2 mum. Calculated spectra of NH(3) and CO(2) were used to determine the optimum transitions for interrogating with an absorption sensor. For ammonia, a strong and isolated absorption transition at 5016.977 cm(-1) was selected for trace gas monitoring. For CO(2), an isolated transition at 5007.787 cm(-1) was selected to measure widely varying concentrations [500 parts per million (ppm) to 10%], with sufficient signal for low mole fractions and without being optically thick for high mole fractions. Using direct absorption and a 36-m total path-length multipass flow-through cell, we achieved a minimum detectivity of 0.25 ppm for NH(3) and 40 ppm for CO(2). We report on the quasi-continuous field measurements of NH(3) and CO(2) concentration in bioreactor vent gases that were recorded at NASA Johnson Space Center with a portable and automated sensor system over a 45-h data collection window.

Diode-Laser Absorption Sensor for Line-of-Sight Gas Temperature Distributions.

Line-of-sight diode-laser absorption techniques have been extended to enable temperature measurements in nonuniform-property flows. The sensing strategy for such flows exploits the broad wavelength-scanning abilities (>1.7 nm approximately 30 cm(-1)) of a vertical cavity surface-emitting laser (VCSEL) to interrogate multiple absorption transitions along a single line of sight. To demonstrate the strategy, a VCSEL-based sensor for oxygen gas temperature distributions was developed. A VCSEL beam was directed through paths containing atmospheric-pressure air with known (and relatively simple) temperature distributions in the 200-700 K range. The VCSEL was scanned over ten transitions in the R branch of the oxygen A band near 760 nm and optionally over six transitions in the P branch. Temperature distribution information can be inferred from these scans because the line strength of each probed transition has a unique temperature dependence; the measurement accuracy and resolution depend on the details of this temperature dependence and on the total number of lines scanned. The performance of the sensing strategy can be optimized and predicted theoretically. Because the sensor exhibits a fast time response (~30 ms) and can be adapted to probe a variety of species over a range of temperatures and pressures, it shows promise for industrial application.

CO(2) Imaging with Saturated Planar Laser-Induced Vibrational Fluorescence.

We present new vibrational (infrared) planar laser-induced fluorescence (PLIF) imaging techniques for CO(2) that use a simple, inexpensive, high-pulse-energy transversely excited atmospheric CO(2) laser to saturate a CO(2) absorption transition at 10.6 mum. Strong excitation by use of a CO(2) laser provides increased signal levels at flame temperatures and simplifies image interpretation. Because rotational energy transfer and intramodal vibrational energy transfer are fast, vibrational distributions can be approximated by use of a simple three-temperature model. Imaging results from a 425 K unsteady transverse CO(2) jet and a laminar coflowing CO/H(2) diffusion flame with temperatures near 1500 K are presented. If needed, temperature-insensitive signal levels can be generated with a two-laser technique. These results illustrate the potential for saturated infrared PLIF in a variety of flows.

Rapid temperature tuning of a 1.4-mum diode laser with application to high-pressure H(2)O absorption spectroscopy.

Enhanced wavelength tuning of a distributed-feedback InGaAsP diode laser is demonstrated by use of rapid temperature cycling. The laser-active region is cycled from -10 to +50 degrees C (scanning the output from 1399 to 1403 nm) at kilohertz rates by pulsed heating with an auxiliary 532-nm laser. Such 4-nm scans represent a ten-fold increase in the wavelength-scanning range offered by standard current-tuning techniques and thus extend the capabilities of scan-wavelength sensors and systems. As an example application, we demonstrate absorption spectroscopy of H(2)O vapor at a pressure of 10 atm.

A cautionary note regarding Nicholaichuk et al. (2000).

The treatment outcome study by Nicholaichuk, Gordon, Gu, and Wong (2000) used a novel method for identifying a comparison group of untreated sex offenders (i.e., drawing from existing criminal history records). A potential problem with their approach is that older records would be expected to include a disproportionate numbers of recidivists. Such an artifact is identified in Nicholaichuk et al.'s (2000) study; nevertheless, their data continue to suggest a small, positive effect for treatment even after eliminating the cases in which bias is most likely.

Improving risk assessments for sex offenders: a comparison of three actuarial scales.

The study compared the predictive accuracy of three sex offender risk-assessment measures: the RRASOR (Hanson, 1997), Thornton's SACJ-Min (Grubin, 1998), and a new scale, Static-99, created by combining the items from the RRASOR and SACJ-Min. Predictive accuracy was tested using four diverse datasets drawn from Canada and the United Kingdom (total n = 1301). The RRASOR and the SACJ-Min showed roughly equivalent predictive accuracy, and the combination of the two scales was more accurate than either original scale. Static-99 showed moderate predictive accuracy for both sexual recidivism (r = 0.33, ROC area = 0.71) and violent (including sexual) recidivism (r = 0.32, ROC area = 0.69). The variation in the predictive accuracy of Static-99 across the four samples was no more than would be expected by chance.

Multiplexed continuous-wave diode-laser cavity ringdown measurements of multiple species.

Rapid cavity ringdown measurements of multiple broadband absorbing species (methanol and isopropanol) in gas mixtures have been recorded with two multiplexed continuous-wave distributed-feedback diode lasers operating near 1.4 mum. A measurement sensitivity of 2.4 x 10(-9) cm(-1) for a 4.3-s averaging time was achieved in a 39.5-cm-long static cell with 99.94% reflectivity mirrors. This corresponds to a water-vapor detection limit of less than 2 ppb (parts in 10(9)) for the strong H(2)O lines near 1.4 mum. The shot-to-shot noise of the decay time constant tau was approximately 0.3-0.7%, and ringdown acquisition rates as great as 900 Hz were achieved.

In situ combustion measurements of CO with diode-laser absorption near 2.3 microm.

In situ measurements of CO concentration were recorded with tunable diode-laser absorption spectroscopy techniques in both the exhaust and the immediate post-flame regions of an atmospheric-pressure flat-flame burner operating on ethylene air. Two room-temperature cw single-mode InGaAsSb/AlGaAsSb diode lasers operating near 2.3 microm were tuned over individual transitions in the CO first overtone band (v' = 2 <-- v" = 0) to record high-resolution absorption line shapes in the exhaust duct [79 cm above the burner, approximately 470 K; R(15) transition at 4311.96 cm(-1)] and the immediate postflame zone [1.5 cm above the burner, 1820-1975 K; R(30) transition at 4343.81 cm(-1)]. The CO concentration was determined from the measured absorption and the gas temperature, which was monitored with type-S thermocouples. For measurements in the exhaust duct, the noise-equivalent absorbance was approximately 3 x 10(-5) (50-kHz detection bandwidth, 50-sweep average, 0.1-s total measurement time), which corresponds to a CO detection limit of 1.5 ppm m at 470 K. Wavelength modulation spectroscopy techniques were used to improve the detection limit in the exhaust to approximately 0.1 ppm m (approximately 500-Hz detection bandwidth, 20-sweep average, 0.4-s total measurement time). For measurements in the immediate postflame zone, the measured CO concentrations in the fuel-rich flames were in good agreement with chemical equilibrium predictions. These experiments demonstrate the utility of diode-laser absorption sensors operating near 2.3 microm for in situ combustion emission monitoring and combustion diagnostics.

Shock-tube study of high-pressure H2O spectroscopy.

Water-vapor absorption features near 7117, 7185, and 7462 cm(-1) were probed at pressures to 65 atm (1 atm = 760 Torr) and temperatures to 1800 K in shock-heated mixtures of H(2)O in N(2) and Ar with a diode-laser source. Calculated absorbances based on Voigt line shapes and measured line parameters were in good agreement, within 10%, with measured absorbances at 7185.4 and 7117.4 cm(-1). We obtained temperature-dependent N(2) and Ar shift parameters for H(2)O absorption features by shifting the calculated spectra to match the recorded absorption scan. Absorbance simulations based on line parameters from HITRAN and HITEMP were found to be similar over the range of temperatures 600-1800 K and were within 25% of the measurements. The combined use of Toth's [Appl. Opt. 36, 4851 (1994)] line positions and strengths and HITRAN broadening parameters resulted in calculated absorption coefficients that were within 15% of the measurements at all three probed wavelengths.

Predicting relapse: a meta-analysis of sexual offender recidivism studies.

Evidence from 61 follow-up studies was examined to identify the factors most strongly related to recidivism among sexual offenders. On average, the sexual offense recidivism rate was low (13.4%; n = 23,393). There were, however, subgroups of offenders who recidivated at high rates. Sexual offense recidivism was best predicted by measures of sexual deviancy (e.g., deviant sexual preferences, prior sexual offenses) and, to a lesser extent, by general criminological factors (e.g., age, total prior offenses). Those offenders who failed to complete treatment were at higher risk for reoffending than those who completed treatment. The predictors of nonsexual violent recidivism and general (any) recidivism were similar to those predictors found among nonsexual criminals (e.g., prior violent offenses, age, juvenile deliquency). Our results suggest that applied risk assessments of sexual offenders should consider separately the offender's risk for sexual and nonsexual recidivism.

Measurements and modeling of acetone laser-induced fluorescence with implications for temperature-imaging diagnostics.

Recent determinations of the temperature dependence of acetone fluorescence have permitted the application of acetone planar laser-induced fluorescence imaging, which was already popular for mapping concentration, to the measurement of temperature. With a view toward developing temperature-imaging diagnostics, we present atmospheric-pressure fluorescence and absorption results acquired with excitation at eight wavelengths across the absorption feature of acetone and at temperatures from 300 to 1000 K. Modeling of the fluorescence yield of acetone is shown to be useful in explaining both these results and the variation of acetone fluorescence with pressure and composition that was observed in several studies. The model results in conjunction with the photophysics data provide guidance for the application of temperature diagnostics over a range of conditions while also suggesting useful multiparameter imaging approaches.