A double-diamond retrospective on modeling change in attitudes and opinions.

The five decades of results produced by analysts of the General Social Survey (GSS) have enriched our understanding of social change, but some core modeling challenges remain. This article proposes that we more fully engage in the development of targeted models of period-based attitude and opinion change, using counterfactual reasoning, as we continue to model cohort replacement. This shift is also consistent with the recent literature on age, period, and cohort analysis, which argues for attention to age varying period effects. Two outcomes are modeled to provide material for the argument: support for government spending on drug addiction and rehabilitation and the valuation of obedience as a goal for child behavioral development.

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) detection limits for blood on fabric: Orientation and coating uniformity effects.

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to analyze four types of forensically relevant fabrics coated with varying dilutions of blood. The blood was applied in two manners, dip coating with a smooth and uniform layer and drip coating with droplets from pipettes. Spectra of neat and dip coated fabrics were acquired using controlled orientations, and these were compared to spectra collected on samples with random orientations. The improved reproducibility seen in visual inspection of the spectra is confirmed by principal component and linear discriminant projections of the spectra, as well as by statistical hypothesis testing. Principal component regression (PCR), using the regions of the IR spectra associated with the amide A/B, I, II, and III vibrational bands (3500-2800, 1650, 1540, and 1350 cm-1), was employed on the more uniform dip coated spectra to estimate limits of detection for blood on two of the four fabrics - acrylic and nylon. These results demonstrate that detection limits for blood on fabrics can be decreased significantly by controlling for the orientation and face of the fabric samples while collecting spectra. Limits of detection for acrylic and nylon were found to be 196 × and 227 × diluted blood, respectively.

A quantitative method for determining a representative detection limit of the forensic luminol test for latent bloodstains.

The luminol test has been used for over 60 years by forensic investigators for presumptive identification of blood and visualization of blood splatter patterns. Multiple studies have estimated the limit of detection (LD) for bloodstains when luminol is employed, with results ranging from 100× to 5,000,000× dilute. However, these studies typically have not identified and controlled important experimental variables which may affect the luminol LD for bloodstains. Without control of experimental parameters in the laboratory, variables which affect the potential of presumptive bloodstain test methods remain largely unknown, and comparisons required to establish new, more powerful detection methods are simply impossible. We have developed a quantitative method to determine the relationship between the amount of blood present and its reaction with luminol by measuring, under controlled conditions, the resulting chemiluminescent intensity with a video camera, combined with processing of the digital intensity data. The method resulted in an estimated LD for bloodstains on cotton fabric at ∼200,000× diluted blood with a specific luminol formulation. Although luminol is the focus of this study, the experimental protocol used could be modified to study effects of variables using other blood detection reagents.

In Vivo Ambient Serotonin Measurements at Carbon-Fiber Microelectrodes.

The mechanisms that control extracellular serotonin levels in vivo are not well-defined. This shortcoming makes it very challenging to diagnose and treat the many psychiatric disorders in which serotonin is implicated. Fast-scan cyclic voltammetry (FSCV) can measure rapid serotonin release and reuptake events but cannot report critically important ambient serotonin levels. In this Article, we use fast-scan controlled adsorption voltammetry (FSCAV), to measure serotonin's steady-state, extracellular chemistry. We characterize the "Jackson" voltammetric waveform for FSCAV and show highly stable, selective, and sensitive ambient serotonin measurements in vitro. In vivo, we report basal serotonin levels in the CA2 region of the hippocampus as 64.9 ± 2.3 nM (n = 15 mice, weighted average ± standard error). We electrochemically and pharmacologically verify the selectivity of the serotonin signal. Finally, we develop a statistical model that incorporates the uncertainty in in vivo measurements, in addition to electrode variability, to more critically analyze the time course of pharmacological data. Our novel method is a uniquely powerful analysis tool that can provide deeper insights into the mechanisms that control serotonin's extracellular levels.

Attenuated Total Reflection (ATR) Sampling in Infrared Spectroscopy of Heterogeneous Materials Requires Reproducible Pressure Control.

Attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, in which the sample is pressed against an internal reflection element, is a popular technique for rapid IR spectral collection. However, depending on the accessory design, the pressure applied to the sample is not always well controlled. While collecting data from fabrics with heterogeneous coatings, we have observed systematic pressure-dependent changes in spectra that can be eliminated by more reproducible pressure control. We also described a pressure sensor adapted to work with an ATR tower to enable more precise control of pressure during ATR sampling.

Detection Limits for Blood on Fabrics Using Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy and Derivative Processing.

Attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR) was used to detect blood stains based on signature protein absorption in the mid-IR region, where intensity changes in the spectrum can be related to blood concentration. Partial least squares regression (PLSR) was applied for multivariate calibrations of IR spectra of blood dilutions on four types of fabric (acrylic, nylon, polyester, and cotton). Gap derivatives (GDs) were applied as a preprocessing technique to optimize the performance of calibration models. We report a much improved IR detection limit (DL) for blood on cotton (2700× in dilution factor units) and the first IR DL reported for blood on nylon (250×). Due to sample heterogeneity caused by fabric hydrophobicity, acrylic fabric produced variable ATR FT-IR spectra that caused poor DLs in concentration units compared to previous work. Polyester showed a similar problem at low blood concentrations that lead to a relatively poor DL as well. However, the increased surface sensitivity and decreased penetration depth of ATR FT-IR make it an excellent choice for detection of small quantities of blood on the front surface of all fabrics tested (0.0010 µg for cotton, 0.0077 µg for nylon, 0.011 µg for acrylic, and 0.0066 µg for polyester).

Fast voltammetry of metals at carbon-fiber microelectrodes: towards an online speciation sensor.

Speciation controls the chemical behavior of trace metals. Thus, there is great demand for rapid speciation analysis in a variety of fields. In this study, we describe the application of fast scan cyclic voltammetry (FSCV) and fast scan adsorption controlled voltammetry (FSCAV) to trace metal speciation analysis. We show that Cu2+ can be detected using FSCAV in different matrices. We find that matrices with different Cu2+ binding ability do not affect the equilibrium of Cu2+ adsorption onto CFMs, and thus are an excellent predictor for free Cu2+ ([Cu2+]free) in solution. We modelled a correlation between the FSCV response, [Cu2+]free and log Kf for 15 different Cu2+ complexes. Using our model, we rapidly predicted, and verified [Cu2+]free and Kf of a real groundwater sample spiked with Cu2+. We thus highlight the potential of fast voltammetry as a rapid trace metal speciation sensor.

Fast voltammetry of metals at carbon-fiber microelectrodes: rapid determination of solution formation constants.

Metal speciation controls the behavior of aqueous metal ions. Fundamental thermodynamic parameters, such as the formation constant (Kf) of metal-ligand equilibria, provide useful speciation information. Although this information can be determined by spectroscopic techniques with high accuracy, it comes at the expense of time and cost. In this work, we studied Cu2+ complexation with different ligands using an ultra-fast method, fast scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes (CFMs). We observed a correlation between the FSCV response and the previously reported Cu2+-ligand equilibrium constants. This relationship allowed us to model a predictive relationship between Kf and 16 model ligands. We hence present an essential proof of principle study that highlights FSCV's capability to prove speciation information in real time.

Variations in enzymatic hydrolysis efficiencies for amitriptyline and cyclobenzaprine in urine.

A collaborative study was conducted to investigate discrepancies in recoveries of two commonly prescribed compounds, amitriptyline and cyclobenzaprine, in patient urine samples when hydrolyzed with different enzymes from different sources. A 2- to 10-fold increase in analyte recoveries was seen for patient samples hydrolyzed using a recombinant ß-glucuronidase (IMCSzyme™) over samples hydrolyzed with ß-glucuronidase from Haliotis rufescens We report outcomes from four commercially available ß-glucuronidase enzymes (IMCSzyme™, Patella vulgata, Helix pomatia and H. rufescens) on patient samples that tested positive for amitriptyline and cyclobenzaprine. Our results confirm reduced hydrolysis of glucuronides by ß-glucuronidases isolated from mollusks, but near complete conversion when using the recombinant enzyme. Our premise is that systematic differences in hydrolysis efficiencies due to varying substrate affinity among enzyme subtypes potentially impacts accuracy and reliability of measurements.

Reversible Gap Derivatives and Their Integration.

Higher-order gap derivatives are sometimes avoided as a preprocessing method for multivariate calibration despite their numerous advantages. One reason that they are avoided is the difficulty in interpreting the complex processed spectra and the regression vectors that arise from common calibration procedures like principal components regression or partial least squares regression. In this report we offer a method of calculating gap derivatives of any order with the aim of retrieving zero-order spectral information via numerical integration. This method is also extended to the integration of the accompanying regression vectors to aid in the interpretation of multivariate calibration models.

An Improved-Efficiency Compact Lamp for the Thermal Infrared.

A major type of infrared camera is sensitive to wavelengths in the 8-14 µm band and is mainly used for thermal imaging. Such cameras can also be used for general broadband infrared reflectance imaging when provided with a suitable light source. We report the design and properties of an infrared lamp using a heated alumina emitter suitable for active thermal infrared imaging, as well as comparisons to existing commercial light sources for this purpose. We find that the alumina lamp is a broadband non-blackbody source with a lower out-of-band emission intensity and therefore higher electrical efficiency for this application than existing commercial sources.

Minimally invasive identification of degraded polyester-urethane magnetic tape using attenuated total reflection Fourier transform infrared spectroscopy and multivariate statistics.

Audio recordings are a significant component of the world's modern cultural history and are retained for future generations in libraries, archives, and museums. The vast majority of tapes contain polyester-urethane as the magnetic particle binder, the degradation of which threatens the playability and integrity of these often unique recordings. Magnetic tapes with stored historical data are degrading and need to be identified prior to digitization and/or preservation. We demonstrate the successful differentiation of playable and nonplayable quarter-inch audio tapes, allowing the minimally invasive triage of tape collections. Without such a method, recordings are put at risk during playback, which is the current method for identifying degraded tapes. A total of 133 quarter-inch audio tapes were analyzed by attenuated total reflectance Fourier transform-infrared spectroscopy (ATR FT-IR). Classification of IR spectra in regards to tape playability was accomplished using principal component analysis (PCA) followed by quadratic discriminant analysis (QDA) and K-means cluster analysis. The first principal component suggests intensities at the following wavenumbers to be representative of nonplayable tapes: 1730 cm(-1), 1700 cm(-1), 1255 cm(-1), and 1140 cm(-1). QDA and cluster analysis both successfully identified 93.78% of nonplayable tapes in the calibration set and 92.31% of nonplayable tapes in the test set. This application of IR spectra assessed with multivariate statistical analysis offers a path to greatly improve efficiency of audio tape preservation. This rapid, minimally invasive technique shows potential to replace the manual playback test, a potentially destructive technique, ultimately allowing the safe preservation of culturally valuable content.

Chemical contrast observed in thermal images of blood-stained fabrics exposed to steam.

Thermal imaging is not ordinarily a good way to visualize chemical contrast. In recent work, however, we observed strong and reproducible images with chemical contrasts on blood-stained fabrics, especially on more hydrophobic fabrics like acrylic and polyester.

Detection limits for blood on four fabric types using infrared diffuse reflection spectroscopy in mid- and near-infrared spectral windows.

Detection limits (DL) for blood on four fabric types were estimated for calibrations derived using partial least squares regression applied to infrared (IR) diffuse reflection spectra. Samples were prepared by dip-coating acrylic, cotton, nylon, and polyester fabrics from solutions of diluted rat blood. While DLs often appear in terms of dilution factor in the forensic community, mass percentage, coverage (mass per unit area), or film thickness are often more relevant when comparing experimental methods. These alternate DL units are related to one another and presented here. The best IR diffuse reflection DLs for blood on acrylic and cotton fabrics were in the mid-IR spectral window corresponding to the protein Amide I/II absorption bands. These DLs were dilution by a factor of 2300 (0.019% w/w blood solids) for acrylic and a factor of 610 (0.055% w/w blood solids) for cotton. The best DL for blood on polyester was found in the mid-IR spectral window corresponding to the protein Amide A absorption band at dilution by a factor of 900 (0.034% w/w blood solids). Because of the similarity between the IR spectra of blood solids and nylon fabrics, no satisfactory IR DLs were determined for the calibration of blood on nylon. We compare our values to DLs reported for blood detection using the standard luminol method. The most commonly reported luminol DLs are of the order of 1000-fold dilution, which we estimate are a factor of 2-7 lower than our reported IR DLs on a coverage basis.

Optimization of gap derivatives for measuring blood concentration of fabric using vibrational spectroscopy.

Derivatives are common preprocessing tools, typically implemented as Savitzky-Golay (SG) smoothing derivatives. This work discusses the implementation and optimization of fourth-order gap derivatives (GDs) as an alternative to SG derivatives for processing infrared spectra before multivariate calibration. Gap derivatives approximate the analytical derivative by calculating finite differences of spectra without curve fitting. Gap derivatives offer an advantage of tunability for spectral data as the distance (gap) over which this finite difference is calculated can be varied. Gap selection is a compromise between signal attenuation, noise amplification, and spectral resolution. A method and discussion of the importance of fourth derivative gap selections are presented as well as a comparison to SG preprocessing and lower-order GDs in the context of multivariate calibration. In most cases, we found that optimized GDs led to calibration models performing comparably to or better than SG derivatives, and that optimized fourth-order GDs behaved similarly to matched filters.

Feeding the pipeline: Gender, occupational plans, and college major selection.

In this article, we analyze gender differences in college major selection for respondents to the Education Longitudinal Study (2002-2006), focusing on educational pathways through college that lead to science, engineering, or doctoral-track medicine occupations and to non-doctoral track clinical and health sciences occupations. We show that gender differences in college major selection remain substantial, even for a cohort in which rates of enrollment in postsecondary education are more than ten percent higher for young women than for young men. Consistent with other recent research, we demonstrate that neither gender differences in work-family goals nor in academic preparation explain a substantial portion of these differences. However, the occupational plans of high school seniors are strong predictors of initial college major selection, a finding that is revealed only when occupational plans are measured with sufficient detail, here by using the verbatim responses of students. We also find that the association between occupational plans and college major selection is not attributable to work-family orientation or academic preparation. Finally, we find gender differences in the associations between occupational plans and college major selection that are consistent with prior research on STEM attrition, as well as with the claim that attrition also affects the selection of majors that are gateways into doctoral-track medicine. We discuss the implications of the predictive power of occupational plans formed in adolescence for understanding sex segregation and for policies intended to create a gender-balanced STEM and doctoral-level medical workforce.

Automated QuEChERS tips for analysis of pesticide residues in fruits and vegetables by GC-MS.

This paper reports the development of an automated method of QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) using pipet tips fitted with filtration screens and containing primary-secondary amine, magnesium sulfate, and graphitized carbon black. These tips are referred to as "QuEChERS Tips". Using loosely contained sorbent, dispersive solid phase extraction (dSPE) cleanup was performed with the QuEChERS Tips and automation. The main advantage of the QuEChERS Tips is that they are readily automated because this dSPE method does not require centrifugation. High recoveries (70-117%) and good reproducibilities (<12%) are shown for over 200 pesticides using automated QuEChERS Tips and GC-MS in various sample matrices.

Coating effects on mid-infrared reflection spectra of fabrics.

Polymer films of varying thicknesses were deposited onto cotton and polyester fabric samples by dip-coating from solution. Scanning electron microscopy (SEM) images of the coated fabric samples were used to evaluate the quality of the polymer coating. The samples were analyzed by infrared diffuse reflection spectroscopy to determine the relationship between film thickness and the effect of the coating on the spectroscopy of the two fabrics. Effects observed in four limiting cases are examined: (Case I) weak coating absorption on a fabric with weak absorption at the same frequency; (Case II) strong coating absorption in a spectral region of weak fabric absorption; (Case III) weak coating absorption in a spectral region of strong fabric absorption; and (Case IV) strong coating absorption in a spectral region of strong fabric absorption. In the first case, effects were dominated by reduced scattering as the coating is added. In the second case, the strong coating absorption that was observed at low coverages plateaus at higher coverage due to depth of penetration effects. In the third and fourth cases, reduced Fresnel diffuse reflection is measured as the coating is added, consistent with the reduction of scattering observed in the first case.

Multimode imaging in the thermal infrared for chemical contrast enhancement. Part 1: Methodology.

We combine a thermal light source with a conventional thermal infrared camera, alternating current (AC) detection methods, and chemical filtering of the infrared (IR) light to generate several imaging modalities in a simple manner. We demonstrate that digital lock-in amplifier techniques can increase the chemical contrast in an active thermal infrared image using both reflectance and thermal re-emission. We show this method is useful for visualizing thin coatings on fabrics that are invisible to the eye. We also take advantage of a "like-detects-like" chemical filtering approach to chemical selectivity for the purpose of chemical identification using a broadband thermal detector.