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.

Visualization of turbulent flame fronts with planar laser-induced fluorescence.

This report concerns the quantitative time-resolved visualization of reaction zones in laminar, transitional, and turbulent nonpremixed flames. Two-dimensional OH molecular concentrations were measured with planar laser-induced fluorescence excited by a sheet of light (formed from a single tunable ultraviolet laser pulse) and detected with a two-dimensional, image-intensified photodiode array camera. From the resulting data details of instantaneous flame front structures (including positions, shapes, and widths) were obtained.

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.

Diarrheal disease among military personnel during Operation Restore Hope, Somalia, 1992-1993.

The potential for widespread diarrheal disease was regarded as a substantial threat to U.S. troops participating in the early phases of Operation Restore Hope in Somalia. Outpatient surveillance of 20,859 U.S. troops deployed during the first eight weeks, however, indicated that a mean of only 0.8% (range 0.5-1.2%) of personnel sought care for diarrhea each week, and in three epidemiologic surveys, < 3% of troops reported experiencing a diarrheal illness per week. Despite these low overall attack rates, diarrhea accounted for 16% of 381 hospital admissions and 20% of 245 patients admitted with a temperature > or = 38.5 degrees C. Sixty-one specimens were obtained from inpatients and 52 were obtained from outpatients. Shigella sp. were isolated from 33%, enterotoxigenic Escherichia coli from 16%, Giardia lamblia from 4%, and rotavirus from 1% of 113 stool samples obtained from inpatient (61) and outpatient (52) troops with diarrhea. Bacterial isolates obtained in Somalia were resistant to doxycycline (78%), ampicillin (54%), and sulfamethoxazole (49%), but uniformly sensitive to ciprofloxacin. With the exception of 10 Shigella sonnei isolates that were linked epidemiologically to one eating facility, bacterial pathogens occurred sporadically and demonstrated a wide variation of serotypes and antibiotic sensitivity patterns. Additionally, three of 11 paired sera collected from persons with nausea, vomiting, and watery diarrhea demonstrated a four-fold or greater increase in titer to Norwalk virus antibody. These data indicate that large outbreaks of diarrheal disease did not occur; however, highly drug-resistant enteric bacteria, and to a lesser extent viral and parasitic pathogens, were important causes of morbidity among U.S. troops in Somalia.

Dengue fever in U.S. troops during Operation Restore Hope, Somalia, 1992-1993.

Dengue fever (DF) was considered to be a potential cause of febrile illness in U.S. troops deployed to Somalia during Operation Restore Hope in 1992-1993. A prospective study of hospitalized troops with fever and a seroepidemiologic survey of 530 troops were conducted. Among 289 febrile troops hospitalized, 129 (45%) did not have an identified cause of their fever. Dengue (DEN) virus was recovered from 41 (43%) of 96 of these patients by inoculation of admission sera into C6/36 cell cultures. Thirty-nine (41%) of the isolates were identified as DEN-2 and two (2%) as DEN-3 by an indirect immunofluorescent antibody assay. An additional 18 (49%) of 37 culture-negative cases were shown by immunoglobulin M (IgM) antibody capture enzyme-linked immunosorbent assay to have anti-DEN virus antibody. All identified DF cases recovered within 1-2 weeks; no case of dengue hemorrhagic fever or shock syndrome was observed. A seroepidemiologic survey of a unit (n = 494) with 17 culture or serologically identified DF cases and a 13% attack rate of unidentified febrile illness revealed a 7.7% prevalence of anti-DEN virus IgM antibody. Failure to use bed nets was the only identified risk factor for DEN infection (adjusted odds ratio = 2.2, 95% confidence interval = 1.4-3.0). These data indicate that DF was an important cause of febrile illness among US troops in Somalia, and demonstrate the difficulties in preventing DEN infection in troops operating in field conditions.

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.

Long-term recidivism of child molesters.

We examined the long-term recidivism rates of 197 child molesters released from prison between 1958 and 1974. Overall, 42% of the total sample were reconvicted for sexual crimes, violent crimes, or both, with 10% of the total sample reconvicted 10-31 years after being released. Incest offenders were reconvicted at a slower rate than were offenders who selected only boys, with offenders against girls showing a rate intermediate between these two groups. Other factors associated with increased recidivism were (a) never being married and (b) previous sexual offenses. None of the mental health and personality tests used in this study (e.g., the Eysenck Personality Inventory and the Minnesota Multiphasic Personality Inventory) was significantly associated with recidivism.

Preventing disease and non-battle injury in deployed units.

Most military physicians know that disease and non-battle injuries (DNBIs) have historically caused more death during war than battle injury. Most DNBIs are preventable, but many unit surgeons and physician assistants, especially at battalion/squadron and brigade/wing level, may not have had the benefit of preventive medicine training or experience. The authors present a logical and thorough framework that all unit surgeons can use to organize their preventive efforts.

Attrition from a male batterer treatment program: client-treatment congruence and lifestyle instability.

Although patient compliance is a problem for almost all forms of therapy, treatment programs for male batterers face special concerns. Male batterers are often perceived as coming to therapy only because of the external pressures of courts or intimate partners. In the present study, we examined the rates at which male batterers failed to attend treatment following an initial assessment interview. Of the 526 men recommended for treatment, only 218 (41%) attended a single treatment session, and only 132 (25%) completed the brief (10-week) treatment program. The variables associated with attrition fell into two general categories: (a) those associated with lifestyle instability (e.g., moves, unemployment, youthfulness), and (b) those variables indicating a congruence between the clients' self-identified problems and the targets of treatment (e.g., self-admitted problems with spousal assault). Suggestions are provided as to how programs could reduce their attrition rates by attending to the issues of client-treatment congruence and lifestyle instability.

Correlates of battering among 997 men: family history, adjustment, and attitudinal differences.

In order to identify the characteristics associated with physical abuse of female partners, a detailed questionnaire was administered to 997 men who were recruited from either a forensic out-patient clinic (780) or from a community based employment center (217). This questionnaire sampled family and personal history, criminal behavior, psychopathology, and attitudes towards violence. Based upon self-report, the sample was divided into 184 non-abusive men, 517 moderately abusive men, and 296 severely abusive men. The full sample (997) was randomly divided into two subsamples and then, using a cross-validation design, group differences were identified in both subsamples on 46 of the 93 variables examined in this study. All significant effects were linear, such that the average scores of the severely abusive men were worse than the scores of the abusive men who, in turn, scored worse than the non-abusive men. In general, both groups of abusive men reported high rates of violence during childhood (both as victims and perpetrators), antisocial personality disorder, subjective distress, marital maladjustment, attitudes tolerant of spouse assault, and a range of impulsive behaviors (impulsive violence, substance abuse, motor vehicle accidents). The factors that correlated with abuse in the total sample also correlated with abuse in the community sample.

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.

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.

Thematic analysis of daily events as a method of personality assessment.

I examined how themes in emotionally meaningful daily events can be used as a personality assessment technique. Eighty-eight student participants recorded their most positive and most negative experiences each day for 2 weeks. Common themes were identified in these events by the participants and judges. The convergent validity of the daily events measures was demonstrated through comparisons with a diverse set of personality measures of achievement and affiliation motivation, including a projective test (the Thematic Apperception Test), self-report questionnaires, and peer reports. Results suggest that a thematic analysis of daily life events may be a useful means of assessing the specific daily concerns and stressors experienced by individuals.

Semiconductor laser-based measurements of quench rates in an atmospheric pressure plasma by using saturated-fluorescence spectroscopy.

Plasma diagnostics based on saturated fluorescence and absorption spectroscopy with a semiconductor (diode) laser are developed to probe the 4s(3)P(1) ? 4p(3)D(2) transition (8425 A) of argon in an atmospheric pressure plasma produced by an inductively coupled plasma torch. Spatially resolved measurements of saturation intensity, nonradiative collisional transfer (quench) rate, and fluorescence yield (Stern-Volmer factor) are inferred from variations of spectral profile characteristics (line shape, line-center value, and frequency-integrated signal) with laser intensity. The results obtained by using fluorescence and absorption spectroscopy are mutually consistent in the analytical region 10 mm above the induction coil. The measured quench rates compare favorably with computed rates from a multilevel collisional radiative model that assumes a suprathermal electron population relative to the local thermodynamic equilibrium value at the kinetic temperature.

Laser diode wavelength-modulation spectroscopy for simultaneous measurement of temperature, pressure, and velocity in shock-heated oxygen flows.

Wavelength modulation at 10 MHz of an AlGaAs laser diode, superposed on repetitive linear scans of wavelength, is applied to measure second-harmonic absorption line shapes of oxygen in the A band. Theoretical expressions of the harmonic line shapes, including the effect of laser amplitude modulation and varying modulation depth, are presented. A least-squares fit of the experimental line shapes to theoretical second-harmonic line shapes permits simultaneous determination of the temperature and the pressure. The use of high-repetition-rate (10-kHz) linear scans of the studied wavelength region permits application of the technique to high-speed unidimensional transient flows generated in a shock tube; velocity is derived from the Doppler shift of the absorption profiles.

Absorption measurements of water-vapor concentration, temperature, and line-shape parameters using a tunable InGaAsP diode laser.

A tunable diode laser diagnostic based on spectrally resolved laser absorption has been developed to detect water vapor. The system uses a distributed feedback InGaAsP diode laser, emitting at ~ 1.38 µm. The diode laser is tuned in wavelength by modulation of the current, resulting in 1-cm(-1) tuning at 80-Hz repetition rate. The directly measured absorption spectra yield values for water-vapor concentration and temperature, as well as a collision-broadening line shape. To our knowledge, we accurately determined required data for H(2)O line strengths and self-broadening coefficients for several spectral lines in a static cell filled with pure water vapor. The temperature and concentration of the water vapor present in laboratory room air and in the postflame gases above a methane-air flat flame burner have also been measured. These results agree well with calculated values and independent measurements.

Simultaneous planar measurements of velocity and pressure fields in gas flows using laser-induced fluorescence.

The development of a nonintrusive spectroscopic technique is reported which permits simultaneous spatially resolved measurements of two velocity components and pressure in a plane of a compressible gaseous flow field. The technique is based on the detection of fluorescence from an absorption line excited with a narrowbandwidth laser. Doppler shift and pressure broadening of the line are exploited to extract velocity and pressure information, respectively. The fluorescence is detected at a 90 degrees angle with an image-intensified 100 x 100 element photodiode-array camera which is interfaced with a laboratory computer. Results of the implementation in a Mach 1.5 underexpanded supersonic jet are presented.