Resolving Discrepancies between State-of-the-Art Theory and Experiment for HO2 + HO2 via Multiscale Informatics.

Recent high-level theoretical calculations predict a mild temperature dependence for HO2 + HO2 inconsistent with state-of-the-art experimental determinations that upheld the stronger temperature dependence observed in early experiments. Via MultiScale Informatics analysis of the theoretical and experimental data, we identified an alternative interpretation of the raw experimental data that uses HO2 + HO2 rate constants nearly identical to theoretical predictions─implying that the theoretical and experimental data are actually consistent, at least when considering the raw data from experimental studies. Similar analyses of typical signals from low-temperature experiments indicate that an HOOOOH intermediate─identified by recent theory but absent from earlier interpretations─yields modest effects that are smaller than, but may have contributed to, the scatter in data among different experiments. More generally, the findings demonstrate that modern chemical theories and experiments have progressed to a point where meaningful comparison requires joint consideration of their data simultaneously.

Dissociation-induced depletion of high-energy reactant molecules as a mechanism for pressure-dependent rate constants for bimolecular reactions.

In 1922, Lindemann proposed the now-well-known mechanism for pressure-dependent rate constants for unimolecular reactions: reactant molecules with sufficiently high energies dissociate more quickly than collisions can reestablish the Boltzmann distribution of the internal energies of the molecule during its dissociation at low pressures - yielding pressure-dependent rate constants for unimolecular reactions due to the preferential depletion of the high energy states capable of dissociation. In the last century, incredible progress has been made in achieving a far greater understanding of and quantitative predictions for unimolecular and association reactions. In the modern era, pressure-dependent phenomenological rate constants are now nearly universally used to describe the rates of unimolecular and associative reactions in phenomenological kinetic modeling. However, there is a second, more indirect, implication of Lindemann's mechanism that relates to how these dissociation-induced non-equilibrium distributions impact bimolecular reactions, including non-associative bimolecular reactions - which are generally not considered to have pressure-dependent rate constants. Yet, as we show herein, the same high energy states depleted due to dissociation would otherwise react most rapidly in high-activation-energy bimolecular reactions - yielding a mechanism for pressure-dependent rate constants for bimolecular reactions (including non-associative reactions). Here, we present results from a case study for CH2O dissociation, isomerization, and bimolecular reaction with O2 to explore this question. Results from our master equation calculations indicate that the effect of dissociation-induced non-equilibrium distributions on bimolecular reactions can be substantial - even when chemical timescales are well separated from internal energy relaxational timescales (i.e. when the traditional rate constant description would be thought to apply). This effect is found to be more pronounced - and more complex - for bimolecular reactions involving molecular entities whose chemical timescales are merged with the internal energy relaxational timescales. Finally, we present some ideas for discussion regarding what should be considered as "chemical species" in phenomenological kinetic models.

Understanding and Representing the Distinct Kinetics Induced by Reactive Collisions of Rovibrationally Excited Ephemeral Complexes across Reactive Collider Mole Fractions and Pressures.

Rovibrationally excited ephemeral complexes AB**, formed from the association of two molecules A + B, are generally considered to undergo collisions only with an inert bath gas M that transfer energy-inducing termolecular association reactions A + B (+M) → AB (+M). Recent studies have demonstrated that reactive collisions of AB** with a third molecule C-inducing chemically termolecular reactions A + B + C → products-can also be significant in combustion and planetary atmospheres. Previous studies on systems with reactive collisions have primarily focused on limited ranges of reactive collider mole fraction, XC, and pressure, P, specific to the chosen application. Yet, it remains to be established how such systems, and the rate constants of their emergent phenomenological reactions, behave over the wide XC and P ranges of potential interest-a gap in the present understanding that has impeded the development of broadly applicable rate laws and general treatment of such systems in kinetic modeling. Here, we present results from master equation calculations for HO2** formed from H + O2 and its reactions with H to advance understanding and explore representations of systems with reactive colliders across wide ranges of XC and P. With regard to understanding, we demonstrate that reactive collisions can both (1) increase the overall rate of conversion of reactants to products and (2) alter the branching ratio among final products. With regard to representations in kinetic models, we find that rate constants of all emergent phenomenological reactions-termolecular association A + B (+M), chemically termolecular A + B + C, and bimolecular AB + C-exhibit a rich XC and P dependence. We also present analyses to explore the existence of a unique phenomenological representation (or lack thereof) and assess ways for the distinct effects of reactive collisions to be represented in kinetic models.

Bath Gas Mixture Effects on Multichannel Reactions: Insights and Representations for Systems beyond Single-Channel Reactions.

Nearly all studies of and available data for pressure-dependent reactions focus on pure bath gases. Of the comparatively fewer studies on bath gas mixtures, important to combustion and planetary atmospheres, nearly all focus on single-channel reactions. The present study explores, and seeks reliable representations of, bath gas mixture effects on multichannel reactions. Analytical and numerical solutions of the master equation here reveal several unique manifestations of mixture effects for multichannel reactions, including behavior completely opposite to trends observed for single-channel reactions. The most common way of evaluating mixture rate constants from data for pure components, the classic linear mixture rule, is found to yield errors exceeding a factor of ∼10. A new linear mixture rule based on the reduced pressure, instead of the absolute pressure, is found to be accurate within ∼30% for rate constants (and ∼50% for the branching ratio). A new nonlinear mixture rule that additionally incorporates analytically derived activity coefficients is found to be accurate within ∼10% for rate constants and branching ratios. These new mixture rules are therefore recommended for use in fundamental and applied chemical kinetics investigations of reacting mixtures, including reacting flow codes and experimental interpretations of third-body efficiencies.

Parenting styles are associated with overall child dietary quality within low-income and food-insecure households.

OBJECTIVE: To examine the association between parenting styles and overall child dietary quality within households that are low-income and food-insecure. DESIGN: Child dietary intake was measured via a 24 h dietary recall. Dietary quality was assessed using the Healthy Eating Index-2005 (HEI-2005). Parenting styles were measured and scored using the Parenting Styles and Dimensions Questionnaire. Linear regressions were used to test main and interaction associations between HEI-2005 scores and parenting styles. SETTING: Non-probability sample of low-income and food-insecure households in South Carolina, USA. PARTICIPANTS: Parent-child dyads (n 171). Parents were ≥18 years old and children were 9-15 years old. RESULTS: We found a significant interaction between authoritative and authoritarian parenting style scores. For those with a mean authoritarian score, each unit increase in authoritative score was associated with a higher HEI-2005 score (b = 3·36, P < 0.05). For those with an authoritarian score that was 1 sd above the mean authoritarian score, each unit increase in authoritative score was associated with a higher HEI-2005 score (b = 8.42, P < 0.01). For those with an authoritarian score that was -1 sd below the mean authoritarian score, each unit increase in authoritative score was associated with a lower HEI-2005 score; however, this was not significant (b = -1·69, P > 0·05). Permissive parenting style scores were negatively associated with child dietary quality (b = -2·79, P < 0·05). CONCLUSIONS: Parenting styles should be considered an important variable that is associated with overall dietary quality in children living within low-income and food-insecure households.

Severity of household food insecurity and lifetime racial discrimination among African-American households in South Carolina.

OBJECTIVES: In 2014, 30% of African-American households with children had low or very low food security, a rate double that of white households with children. A household has low food security if its members experience food shortages and reductions in food quality attributable to a lack of household resources or access and very low food security if its members also experience reductions in food intake and disrupted eating patterns. Households that are either low or very low food secure are known collectively as food insecure. We examined the association between the severity of household food insecurity and reports of lifetime racial discrimination among a sample of food-insecure African-American households in South Carolina. DESIGN: Data were collected from 154 African-American respondents. Food insecurity was measured using the US Department of Agriculture's Household Food Security Survey Module. Lifetime racial discrimination was measured using the Perceived Ethnic Discrimination Questionnaire-Community Version (PEDQ-CV). We used logistic regression to test the association between severity of food insecurity (low vs. very low food secure), PEDQ-CV score and PEDQ-CV subscales. All models were adjusted for demographic and socioeconomic variables. RESULTS: A one-unit increase in the frequency of lifetime racial discrimination was associated with a 5% increase in the odds of being very low food secure (odds ratio (OR) 1.05, P < .05). More reports of discrimination that were stigmatizing or devaluing (OR 1.16, P < .05), took place at a workplace or school (OR 1.15, P < .05) or were threatening or aggressive (OR 1.39, P < .05) increased the odds of being very low food secure. More reports of racial discrimination that were excluding or rejecting did not significantly increase the odds of being very low food secure (OR 1.07, P > .05). CONCLUSIONS: Severity of household food insecurity is associated with lifetime racial discrimination among African-American households in South Carolina.

Lifetime Trauma and Depressive Symptomatology Among Older American Indians: The Native Elder Care Study.

We examined the association between lifetime traumatic events with or without trauma response symptoms and depressive symptomatology in American Indians aged ≥ 55 years from a tribe in the Southeastern US (N = 362). Twenty-three percent of the sample experienced a traumatic event without trauma-response symptoms, whereas 14% experienced a traumatic event with at least one trauma-response symptom. After adjustment for sociodemographic characteristics and social support, participants who experienced a traumatic event with one or more trauma-response symptoms had higher odds of clinically relevant depressive symptomatology compared to (1) those who never experienced a traumatic event [odds ratio (OR) 3.2, p < 0.05], (2) and those who experienced a traumatic event without further symptoms (OR 3.7, p < 0.05). Our results suggest that mental health providers who serve older American Indians should consider the experience of traumatic events followed with response symptoms as a potential risk factor for further disruptions in psychological functioning.

Single stab injuries.

Determining the manner of death in cases involving multiple stab injuries from a knife is generally straightforward. The medico-legal investigation of a stabbing death caused by a single stab injury from a knife comprises a smaller but potentially more problematic subset of forensic cases. We reviewed our institute's experience with single stab injuries and endeavored to identify features identified at the post-mortem examination which may aid in the differentiation between cases of homicide, suicide and accidental death. The single stab injury was to the left chest in the majority of deaths from homicide and from suicide. Clothing was nearly always involved in cases of homicide, but was also seen in cases of suicide. The knife was found in situ in 9 of the 11 cases of suicide involving a chest injury, but was not seen in any of the cases of homicide. There were no cases of an accidental single stab death from a knife in our records. Clinical data on accidental stab injuries was sought via a search of the medical records of a major tertiary referral hospital. A single non-fatal case of an accidental single stab injury from a knife was identified after the conclusion of our study period. Accidental stab injuries from a knife causing injury or death are rare.

Severity of Household Food Insecurity Is Positively Associated with Mental Disorders among Children and Adolescents in the United States.

BACKGROUND: Household food insecurity and mental disorders are both prevalent conditions among children and adolescents (i.e., youth) in the United States. Although some research has examined the association between the 2 conditions, it is not known whether more severe food insecurity is differently associated with mental disorders in youth. OBJECTIVE: We investigated the association between severity of household food insecurity and mental disorders among children (aged 4-11 y) and adolescents (aged 12-17 y) using valid and reliable measures of both household food security status and mental disorders. METHODS: We analyzed cross-sectional data on 16,918 children and 14,143 adolescents whose families participated in the 2011-2014 National Health Interview Survey. The brief Strengths and Difficulties Questionnaire and the 10-item USDA Household Food Security Survey Module were used to measure mental disorders and food security status, respectively. Multinomial logistic regressions were used to test the association between household food security status and mental disorders in youth. RESULTS: There was a significant linear trend in ORs, such that as severity of household food insecurity increased so did the odds of youth having a mental disorder (P < 0.001). Other selected results included the following: compared with food-secure households, youth in marginally food-secure households had higher odds of having a mental disorder with impairment [child OR: 1.26 (95% CI: 1.05, 1.52); adolescent OR: 1.33 (95% CI: 1.05, 1.68)]. In addition, compared with food-secure households, youth in very-low-food-secure households had higher odds of having a mental disorder with severe impairment [child OR: 2.55 (95% CI: 1.90, 3.43); adolescent OR: 3.44 (95% CI: 2.50, 4.75)]. CONCLUSIONS: The severity of household food insecurity is positively associated with mental disorders among both children and adolescents in the United States. These results suggest that improving household food security status has the potential to reduce mental disorders among US youth.

Perceived and geographic food access and food security status among households with children.

OBJECTIVE: To examine the association of both perceived and geographic neighbourhood food access with food security status among households with children. DESIGN: This was a cross-sectional study in which participants' perceptions of neighbourhood food access were assessed by a standard survey instrument, and geographic food access was evaluated by distance to the nearest supermarket. Multinomial logistic regression models were used to examine the associations. SUBJECTS: The Midlands Family Study included 544 households with children in eight counties in South Carolina, USA. Food security status among participants was classified into three categories: food secure (FS), food insecure (FI) and very low food security among children (VLFS-C). RESULTS: Compared with FS households, VLFS-C households had lower odds of reporting easy access to adequate food shopping. VLFS-C households also had lower odds of reporting neighbourhood access to affordable fruits and vegetables compared with FS households and reported worse selection of fruits and vegetables, quality of fruits and vegetables, and selection of low-fat products. FI households had lower odds of reporting fewer opportunities to purchase fast food. None of the geographic access measures was significantly associated with food security status. CONCLUSIONS: Caregivers with children who experienced hunger perceived that they had less access to healthy affordable food in their community, even though grocery stores were present. Approaches to improve perceived access to healthy affordable food should be considered as part of the overall approach to improving food security and eliminating child hunger.

New Insights into Low-Temperature Oxidation of Propane from Synchrotron Photoionization Mass Spectrometry and Multiscale Informatics Modeling.

Low-temperature propane oxidation was studied at P = 4 Torr and T = 530, 600, and 670 K by time-resolved multiplexed photoionization mass spectrometry (MPIMS), which probes the reactants, intermediates, and products with isomeric selectivity using tunable synchrotron vacuum UV ionizing radiation. The oxidation is initiated by pulsed laser photolysis of oxalyl chloride, (COCl)2, at 248 nm, which rapidly generates a ∼1:1 mixture of 1-propyl (n-propyl) and 2-propyl (i-propyl) radicals via the fast Cl + propane reaction. At all three temperatures, the major stable product species is propene, formed in the propyl + O2 reactions by direct HO2 elimination from both n- and i-propyl peroxy radicals. The experimentally derived propene yields relative to the initial concentration of Cl atoms are (20 ± 4)% at 530 K, (55 ± 11)% at 600 K, and (86 ± 17)% at 670 K at a reaction time of 20 ms. The lower yield of propene at low temperature reflects substantial formation of propyl peroxy radicals, which do not completely decompose on the experimental time scale. In addition, C3H6O isomers methyloxirane, oxetane, acetone, and propanal are detected as minor products. Our measured yields of oxetane and methyloxirane, which are coproducts of OH radicals, suggest a revision of the OH formation pathways in models of low-temperature propane oxidation. The experimental results are modeled and interpreted using a multiscale informatics approach, presented in detail in a separate publication (Burke, M. P.; Goldsmith, C. F.; Klippenstein, S. J.; Welz, O.; Huang H.; Antonov I. O.; Savee J. D.; Osborn D. L.; Zádor, J.; Taatjes, C. A.; Sheps, L. Multiscale Informatics for Low-Temperature Propane Oxidation: Further Complexities in Studies of Complex Reactions. J. Phys. Chem A. 2015, DOI: 10.1021/acs.jpca.5b01003). The model predicts the time profiles and yields of the experimentally observed primary products well, and shows satisfactory agreement for products formed mostly via secondary radical-radical reactions.

Multiscale Informatics for Low-Temperature Propane Oxidation: Further Complexities in Studies of Complex Reactions.

The present paper describes further development of the multiscale informatics approach to kinetic model formulation of Burke et al. (Burke, M. P.; Klippenstein, S. J.; Harding, L. B. Proc. Combust. Inst. 2013, 34, 547-555) that directly incorporates elementary kinetic theories as a means to provide reliable, physics-based extrapolation of kinetic models to unexplored conditions. Here, we extend and generalize the multiscale informatics strategy to treat systems of considerable complexity-involving multiwell reactions, potentially missing reactions, nonstatistical product branching ratios, and non-Boltzmann (i.e., nonthermal) reactant distributions. The methodology is demonstrated here for a subsystem of low-temperature propane oxidation, as a representative system for low-temperature fuel oxidation. A multiscale model is assembled and informed by a wide variety of targets that include ab initio calculations of molecular properties, rate constant measurements of isolated reactions, and complex systems measurements. Active model parameters are chosen to accommodate both "parametric" and "structural" uncertainties. Theoretical parameters (e.g., barrier heights) are included as active model parameters to account for parametric uncertainties in the theoretical treatment; experimental parameters (e.g., initial temperatures) are included to account for parametric uncertainties in the physical models of the experiments. RMG software is used to assess potential structural uncertainties due to missing reactions. Additionally, branching ratios among product channels are included as active model parameters to account for structural uncertainties related to difficulties in modeling sequences of multiple chemically activated steps. The approach is demonstrated here for interpreting time-resolved measurements of OH, HO2, n-propyl, i-propyl, propene, oxetane, and methyloxirane from photolysis-initiated low-temperature oxidation of propane at pressures from 4 to 60 Torr and temperatures from 300 to 700 K. In particular, the multiscale informed model provides a consistent quantitative explanation of both ab initio calculations and time-resolved species measurements. The present results show that interpretations of OH measurements are significantly more complicated than previously thought-in addition to barrier heights for key transition states considered previously, OH profiles also depend on additional theoretical parameters for R + O2 reactions, secondary reactions, QOOH + O2 reactions, and treatment of non-Boltzmann reaction sequences. Extraction of physically rigorous information from those measurements may require more sophisticated treatment of all of those model aspects, as well as additional experimental data under more conditions, to discriminate among possible interpretations and ensure model reliability.

Can forensic pathologists diagnose pulmonary thromboembolism on postmortem computed tomography pulmonary angiography?

Postmortem computed tomography (CT) scanning is a routine examination in the medicolegal death investigation of every deceased person admitted to the Victorian Institute of Forensic Medicine. Pulmonary CT angiography is a standard clinical investigation for suspected pulmonary thromboembolism. To the best of our knowledge, a study of postmortem CT pulmonary angiography has not been previously reported in the English-speaking forensic literature. We present our findings on 13 cases of suspected massive pulmonary thromboembolism where forensic pathologists assessed postmortem CT pulmonary angiography, which were then correlated with conventional postmortem examinations.

Reformulation and solution of the master equation for multiple-well chemical reactions.

We consider an alternative formulation of the master equation for complex-forming chemical reactions with multiple wells and bimolecular products. Within this formulation the dynamical phase space consists of only the microscopic populations of the various isomers making up the reactive complex, while the bimolecular reactants and products are treated equally as sources and sinks. This reformulation yields compact expressions for the phenomenological rate coefficients describing all chemical processes, i.e., internal isomerization reactions, bimolecular-to-bimolecular reactions, isomer-to-bimolecular reactions, and bimolecular-to-isomer reactions. The applicability of the detailed balance condition is discussed and confirmed. We also consider the situation where some of the chemical eigenvalues approach the energy relaxation time scale and show how to modify the phenomenological rate coefficients so that they retain their validity.

Estimating the Number, Distribution, and Predictors of Food Pantries in the US.

OBJECTIVE: To estimate the number, distribution, and predictors of food pantries across counties in the US in 2020. DESIGN: A cross-sectional, secondary data analysis of geocoded food pantry locations and social, demographic, and economic characteristics at the county level. PARTICIPANTS: Publicly disclosed food pantry locations were collected from websites in all counties. Pantry locations were merged with data from the American Community Survey 2015-2019. MAIN OUTCOME MEASURES: The number of food pantries per county. ANALYSIS: A negative binomial regression estimated the association between the number of pantries per county and community characteristics. RESULTS: We found 48,581 food pantries from publicly disclosed websites, covering 98% of counties. The mean and median number of pantries per county were 15.5 and 6, respectively. Selected characteristics positively associated with the number of pantries per county were income inequality, percentage of noncitizens, and percentage of single-parent households. Selected characteristics negatively associated with the number of pantries per county were percent with a high school education or less, percent of households in poverty, and rurality. CONCLUSIONS AND IMPLICATIONS: The US has an extensive network of food pantries. Future work could assess the potential causal pathways between pantry placement and county-level characteristics.

The use of postmortem computed tomography in the diagnosis of intentional medication overdose.

The recognition of a well defined basal layer of radio dense material on the postmortem computed tomography (CT) images, in the setting of typical scene findings of an intentional medication overdose and unremarkable external examination of the deceased's body can, in certain circumstances, permit such cases to be managed without routine full autopsy examination. Preliminary toxicological analysis can be targeted to such cases to provide further supportive evidence of intentional medication overdose. In cases where the scene findings are ambiguous or have been contaminated the postmortem CT images may alert the pathologist of the possibility of overdose in an otherwise apparently natural death. We reviewed 61 cases of documented intentional therapeutic medication overdose and 61 control cases. In the majority of the cases of confirmed intentional therapeutic medication overdose the CT images showed no diagnostic features. However, in many cases a well defined basal layer of radio-opaque material was clearly seen to line the gastric mucosa. The postmortem CT pattern which we believe to be highly suggestive of intentional medication overdose must be differentiated from other causes of increased radio density in the stomach which include CT artefacts.