Chapter One - Detonation Performance and Sensitivity: A Quest for Balance

Machine learning approaches for predicting impact sensitivity and detonation performances of energetic materials

Background: Many studies have been conducted on tutor performance in problem-based curricula. In the past, the implicit assumption behind these studies was that tutor performance is a relatively stable characteristic. More recent studies demonstrate that a tutor's performance may be dependent on other circumstances, such as the level of structure in the curricular materials. The aim of this study was to investigate whether a tutor's performance is also dependent on the tutorial group's productivity. Purpose: The idea is that low-productive tutorial groups require much more input from a tutor than high-productive groups. In the problem-based curriculum under investigation, most tutors guide 2 tutorial groups within the same unit. A salient finding in this problem-based curriculum was that some tutors who guide 2 tutorial groups within the same unit have discrepancies in their tutor performance across the 2 groups. This finding might be explained by differences in both tutorial groups. In this study, first the scope of the discrepancy phenomena was studied. Second, the relation between the tutor's performance and the tutorial group's productivity was studied. Methods: The data set for this study included 136 tutors who, in total, ran 272 tutorial groups (each tutor ran 2 groups per unit). The analyses were conducted at the tutorial group level. Students were asked to judge the performance of their tutor. Low, medium, and high levels of tutor performance were distinguished. Tutors who were qualified as "low level of performance" in one tutorial group and "medium level of performance" in the other tutorial group were considered to have a discrepancy in their tutor performance: "discrepancy tutors." The same holds for tutors with medium level of performance in one group and high level of performance in the other group or low level of performance in one group and high level of performance in the other group. All other tutors were considered "nondiscrepancy tutors." The nondiscrepancy tutors had equal levels of performance in both groups: a low, medium, or high level. For each type of tutor (discrepancy tutors and nondiscrepancy tutors) the average tutorial group's productivity score was computed. Results: The results show that 39% of the tutors were classified as discrepancy tutors. In addition, it was found that a discrepancy tutor with a low level of tutor performance in one group also had a low productivity score in this group, whereas a high level of tutor performance corresponds with a high level of the tutorial group's productivity. Furthermore, the results show that nondiscrepancy tutors with a high level of tutor performance receive high tutor performance scores, irrespective of the tutorial group's level of productivity. Conclusions: These findings demonstrate that the tutorial group's productivity is another influencing factor in determining tutor performance. Low-productive groups require much more input from a tutor than high-productive groups. Nondiscrepancy tutors with consistent low levels of tutor performance and discrepancy tutors lack certain competencies that are needed when being confronted with a low-productive tutorial group. Nondiscrepancy tutors with a high level of tutor performance, on the contrary, know how to deal with low-productive tutorial groups, due to which their tutor performance is high irrespective of the tutorial group's productivity. Thus, a tutor's performance seems to be part tutor specific and part situation specific (i.e., dependent on the group's productivity).

Computational design of high energy density materials with zero oxygen balance: A combination of furazan and piperazine rings

Magnetic Resonance Colonography for the Detection of Colorectal Neoplasia

Covering the Cover

We designed a series of energetic compounds based on the CL‐20 molecular skeleton, and the properties including molecular geometric structures, electronic structures, density, heat of formation, detonation performances, and impact sensitivity were evaluated using density functional theory (DFT). The results indicate that five molecules have higher density values than that of Octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX; 1.91 g/cm3) and A4 has a larger density value (2.07 g/cm3) than that of CL‐20 (2.04 g/cm3). In addition, most of the molecules have better detonation performances and stability than those of CL‐20, with A4 showing much greater detonation velocity (9.93 km/s) and pressure (47.32 GPa) than those of CL‐20 with a h50 value of 14.02 cm. Taking both excellent detonation performance and low sensitivity into consideration, all seven compounds except for A3 and A5 are considered as potential energetic compounds. These theoretically calculated results would be conducive to the design and synthesis of novel nitramine energetic compounds.

The search for coplanar high‐energy insensitive explosives is a new direction in the research of energetic materials. A series of coplanar compounds based on the [1,2,4]triazolo[4,3‐b][1,2,4]triazine skeleton (ATTZ) were designed and studied using density functional theory. The research content includes density, detonation performance, shock sensitivity, bond‐dissociation energy, thermodynamic properties, and electrostatic potential. The formation of intramolecular hydrogen bonds between the energetic groups connected by these coplanar compounds and the introduction of coordinated oxygen on the parent to improve detonation performance are the highlights of this study. The results show that most of the compounds have good density, low sensitivity, and excellent detonation performance. And compound A11 shows a high density (d = 1.93 g/cm3), detonation velocity (D = 9.12 km/s1), and explosion pressure (P = 38.41 GPa), with the bond dissociation energy value of 253.4 kJ/mol. Designing coplanar compounds is an efficient approach to explore high‐energy insensitive explosives.

Chapter 8 - Some molecular and crystalline factors that affect the sensitivities of explosives

Magnetic Resonance Colonography for the Detection of Colorectal Neoplasia in Asymptomatic Adults

Pattern sensitivity was proposed earlier as a property to guide simulation-based test generation for combinational or full-scan circuits. Sensitivity is a binary property, i.e., a pattern is either sensitive or not. In this work, we replace the binary sensitivity property by a property that assumes a range of values, called the level of sensitivity. We demonstrate that patterns with high levels of sensitivity tend to detect more faults than patterns with low levels of sensitivity, and therefore, it is important to consider the level of sensitivity of test patterns during test generation. We also describe a procedure for generating sensitive patterns with high levels of sensitivity.

A series of high energy density compounds are designed by altering the triazole, tetrazine, oxadiazole rings and energetic groups (such as −CN, −N3, −NH2, −NHNH2, −NO2, −NHNO2, −C(NO2)3, −CH(NO2)2) into 2,4,5‐trinitro‐imidazole skeleton. Their structures are optimized by density functional theory (DFT) methods at B3LYP/6‐311G (d,p) method. Based on the optimized structures, the impact of different rings and energetic groups on their energy gaps, heats of formation, detonation performance and sensitivities are investigated. The results show that compound F4 possesses the highest values of heats of formation due to their high nitrogen content. However, compound F2 possesses the highest values of detonation pressure and detonation velocity which indicates that the detonation performance are determined by values of density rather than those of heats of formation. Taking both detonation performance and impact sensitivities into consideration, compounds B4, C4, F4, I4, J4 and J8 are screened as high energy density compounds due to their excellent detonation performance and acceptable sensitivities compared to those of RDX. Finally, the distribution of frontier molecular orbital, the electrostatic potential area distribution, thermodynamic properties and weak interactions of the screened compounds are fully investigated.

The aim of the author's own research was: (a) defining the level of meaning in life and the level of religious experience (God's presence and God's absence) in groups of students with high and low levels of conscience sensitivity and (b) showing the connection between meaning in life and the level of religious experience (God's presence and God's absence) in groups of students with high and low levels of conscience sensitivity. The study was conducted in 2009–2010 among university students in Kraków. The subject group consisted of students of several non-Catholic public and state universities. All participants were Polish born, culturally homogeneous, and stemmed from families of average affluence. The age of the respondents ranged from 21 to 25. Two-hundred and forty sets of correctly completed questionnaires were used for the results analysis.

Lone pair/π-hole interactions in the edge-to-face stacking of the criss-cross construction molecule: Towards thermally stability, low sensitivity, and high detonation performance

Abstractπ-Stacking is common in materials, but different π–π stacking modes remarkably affect the properties and performances of materials. In particular, weak interactions, π-stacking and hydrogen bonding often have a significant impact on the stability and sensitivity of high-energetic compounds. A fused [5,7,5]-tricyclic energetic compound with a conjugated structure has been designed and synthesized. 4H-[1,2,5]Oxadiazolo[3,4-e][1,2,4]triazolo[3,4-g][1,2,4]triazepin-8-amine is obtained in 48% yield from 3-amino-4-carboxy-1,2,5-oxadiazole through an efficient two-step reaction. Owing to its layered planar structure and weak π interactions between layers, 4H-[1,2,5]oxadiazolo[3,4-e][1,2,4]triazolo[3,4-g][1,2,4]triazepin-8-amine exhibits high thermal stability (T d = 318 °C), low sensitivity (IS = 40 J, FS = 360 N), and relatively excellent detonation performance (D = 7059 ms–1, P = 20.2 GPa). This detonation performance is superior to that of the conventional explosive TNT. The developed procedure provides a new method for the synthesis of fused ring compounds.

Ammonium perchlorate (AP) has been widely used as an oxidizer in propellants and military mixed explosives in recent years. However, its high characteristic signal, environmental pollution, and poor detonation performance have prompted the industry to seek alternatives to AP. Ammonium nitrate (AN) is a suitable substitute due to its low characteristic signal, lack of pollution, and excellent detonation performance. However, its room-temperature phase transition and hygroscopicity affect its practical use. In this work, we prepared mixed crystal coprecipitation (MCC) materials of AN and potassium perchlorate (KP) using the evaporative solvent method. The characterization of AN/KP MCCs was carried out by combining TG-DSC, XRD, FT-IR, and SEM analysis, revealing that the formation of MCCs by AN and KP is due to ion exchange between the two components. AN/KP MCCs not only solve the problem of room-temperature phase transition in AN but also reduce its hygroscopicity. Furthermore, AN/KP MCCs have mechanical sensitivity, explosive performance, and specific impulse similar to pure AN, but compared to AN, AN/KP MCCs have higher density, effective oxygen content, and thermal stability. Compared with existing oxidizers AN, AP, and KP, AN/KP MCCs with high density, low sensitivity, high oxygen content, and high safety have obvious advantages and have good prospects in the application of oxidizers in solid propellants and military mixed explosives.