Chemical Descriptors for a Large-Scale Study on Drop-Weight Impact Sensitivity of High Explosives.

The drop-weight impact test is an experiment that has been used for nearly 80 years to evaluate handling sensitivity of high explosives. Although the results of this test are known to have large statistical uncertainties, it is one of the most common tests due to its accessibility and modest material requirements. In this paper, we compile a large data set of drop-weight impact sensitivity test results (mainly performed at Los Alamos National Laboratory), along with a compendium of molecular and chemical descriptors for the explosives under test. These data consist of over 500 unique explosives, over 1000 repeat tests, and over 100 descriptors, for a total of about 1500 observations. We use random forest methods to estimate a model of explosive handling sensitivity as a function of chemical and molecular properties of the explosives under test. Our model predicts well across a wide range of explosive types, spanning a broad range of explosive performance and sensitivity. We find that properties related to explosive performance, such as heat of explosion, oxygen balance, and functional group, are highly predictive of explosive handling sensitivity. Yet, models that omit many of these properties still perform well. Our results suggest that there is not one or even several factors that explain explosive handling sensitivity, but that there are many complex, interrelated effects at play.

Understanding Explosive Sensitivity with Effective Trigger Linkage Kinetics.

We present a simple linear model for ranking the drop weight impact sensitivity of organic explosives that is based explicitly on chemical kinetics. The model is parameterized to specific heats of explosion, Q, and Arrhenius kinetics for the onset of chemical reactions that are obtained from gas-phase Born-Oppenheimer molecular dynamics simulations for a chemically diverse set of 24 molecules. Reactive molecular dynamics simulations sample all possible decomposition pathways of the molecules with the appropriate probabilities to provide an effective reaction barrier. In addition, the calculations of effective trigger linkage kinetics can be accomplished without prior physical intuition of the most likely decomposition pathways. We found that the specific heat of explosion tends to reduce the effective barrier for decomposition in accordance with the Bell-Evans-Polanyi principle, which accounts naturally for the well-known correlations between explosive performance and sensitivity. Our model indicates that sensitive explosives derive their properties from a combination of weak trigger linkages that react at relatively low temperatures and large specific heats of explosion that further reduce the effective activation energy.

Atom Equivalent Energies for the Rapid Estimation of the Heat of Formation of Explosive Molecules from Density Functional Tight Binding Theory.

Atom equivalent energies have been derived from which the gas-phase heat of formation of explosive molecules can be estimated from fast, semiempirical density functional tight binding total energy calculations. The root-mean-square deviation and maximum deviation of the heats of formation from the experimental values for the set of 45 energetic molecules compiled by Byrd and Rice [ J. Phys. Chem. A, 2006, 110, 1005-1013] are 10.4 and 25.5 kcal/mol, respectively, using 4 atom equivalent energies and 7.4 and 15.0 kcal/mol, respectively, using 7 atom equivalent energies. These errors are around a factor of 2-3 larger than those obtained from density functional theory calculations but are smaller than those obtained from other semiempirical electronic structure methods. Heats of formation calculated with density functional tight binding theory using the 4 and 7 atom equivalent energies, the Byrd and Rice scheme, and the atom pair contribution method for a new set of 531 energetic molecules that contain only carbon, hydrogen, nitrogen, and oxygen are provided.

Understanding homeopathic decision-making: a qualitative study.

BACKGROUND: Understanding how homeopaths make clinical decisions is important in terms of optimising patient care, yet currently little is understood about this process. Most current literature investigating decision-making has focussed on conventional medicine; to date only two studies, both quantitative, have explored this area, with both studies investigating this in homeopathy. The aim of this qualitative study was to explore how homeopaths make prescribing decisions primarily during their first consultation with a patient. METHOD: In-depth, semistructured, face to face interviews were carried out with 14 private homeopaths working in private practice. Interpretative phenomenological analysis (IPA) was carried out on the data by 3 researchers. FINDINGS: Cognitive processes that homeopaths used in decision-making emerged from the analysis included the use of pattern recognition (P), hypothetico-deductive reasoning (H) and intuition (I), which led to a precise remedy match (R-M). Four themes emerged from the data: three related to the process of making a decision; one theme to those factors that influence this process. These themes fitted into a decision-making model, which we describe: the P.H.I.RM decision-making model. Two further themes emerged, which contributed to the model: the practitioners' awareness of avoiding major bias and the role of the patient practitioner relationship in influencing decision-making. CONCLUSION: The P.H.I.R-M decision-making model describes how homeopathic practitioners' used an evidence-based process to make decisions. This study also contributes more weight to the accumulating evidence that intuition is a valuable component of decision-making for homeopathic practitioners.