Decomposition of triacetone triperoxide is an entropic explosion

Both X-ray crystallography and electronic structure calculations using the cc-pVDZ basis set at the DFT B3LYP level were employed to study the explosive properties of triacetone triperoxide (TATP) and diacetone diperoxide (DADP). The thermal decomposition pathway of TATP was investigated by a series of calculations that identified transition states, intermediates, and the final products. Counterintuitively, these calculations predict that the explosion of TATP is not a thermochemically highly favored event. It rather involves entropy burst, which is the result of formation of one ozone and three acetone molecules from every molecule of TATP in the solid state.     

Stress relaxation behavior of soda-lime glass between the transformation and softening temperatures

The compressive stress relaxation modulus of a container glass composition was investigated over a wide range of strain, time, modulus, and temperature. It is shown that the glass behaves in a linear viscoelastic manner up to a 2% strain level, and that the relaxation modulus is a smooth function of time, with no pseudo-rubbery plateau apparent down to a modulus of 10⁸ dyn/cm². The data cover roughly five decades of modulus, five decades of time, and a temperature range of 150° C above the glass transition, T_g = 536°C. Within experimental error, the effect of temperature on the stress relaxation behavior is to simply shift the modulus-time curves along the time axis with no change in shape. Temperature dependent shift factor data are expressed in terms of the WLF relation, and are shown to be in good agreement with data found in the literature for other silicate compositions. Viscosity data derived from the generated stress relaxation data agree well with data obtained by more direct methods.     

Generating-Tree Isomorphisms for Pattern-Avoiding Involutions

We show that for k ≥ 5 and the permutations τ _k = (k − 1)k(k − 2). . .312 and J _k = k(k − 1). . .21, the generating tree for involutions avoiding the pattern τ _k is isomorphic to the generating tree for involutions avoiding the pattern J _k . This implies a family of Wilf equivalences for pattern avoidance by involutions.     

Effect of temperature and volume on the tensile and adhesive properties of photocurable resins

Knowing the mechanical properties of UV‐curable resins at cryogenic conditions is important to ongoing fusion‐energy research and to emerging aerospace applications. The tensile and interfacial shear strengths of two commercially available UV‐curable resins were measured at room‐temperature and cryogenic conditions for both bulk and reduced (subnanoliter) specimen volumes. The tensile properties of cured specimens are remarkably sensitive to both testing temperature and specimen size. For one type of resin, the cold (?150 °C) tensile strength of subnanoliter specimens is ～9× larger (179 ± 19 MPa) than bulk values at room temperature. The interfacial shear strength between SiC fibers and small volumes of resin volumes is comparable to the bulk, room‐temperature tensile strength, but it varies over a wide range at ?150 °C (15–53 MPa). All resins were fully cured, and an analysis of fractured surfaces revealed microstructural features. The enhanced strength in microscopic specimens may be related to inhomogeneous stress fields that develop during cure. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 936–945     

Partially dynamic vehicle routing—models and algorithms

In this paper we propose a framework for dynamic routing systems based on their degree of dynamism. Next, we consider its impact on solution methodology and quality. Specifically, we introduce the Partially Dynamic Travelling Repairman Problem and describe several dynamic policies to minimize routing costs. The results of our computational study indicate that increasing the dynamic level results in a linear increase in route length for all policies studied. Furthermore, a Nearest Neighbour policy performed, on the average, uniformly better than the other dispatching rules studied. Among these, a Partitioning policy produced only slightly higher average route lengths.     

Representations of Hecke Algebras and Dilations of Semigroup Crossed Products

A family of Hecke C^*-algebras can be realised as crossed productsby semigroups of endomorphisms. It is shown by dilating representationsof the semigroup crossed product that the category of representationsof the Hecke algebra is equivalent to the category of continuousunitary representations of a totally disconnected locally compactgroup.     

Depth-dependent acoustic features of diving sperm whales (Physeter macrocephalus) in the Gulf of Mexico

Three-dimensional dive trajectories of three sperm whales in the Gulf of Mexico have been obtained by measuring the relative arrival times and bearings of the animals' acoustic multipath reflections, using two elements of a towed hydrophone array deployed at an unknown depth and orientation. Within the first 6-12 min of the start of a dive, the intervals between successive "clicks" of all three whales corresponded closely with the two-way travel time of an acoustic pulse traveling vertically between the animals' position and the ocean bottom. The click spectra contained multiple peaks, including a faint band of energy originally centered near 10 kHz. As the animals descended over 500 m in depth, the center frequency of this band shifted to nearly 15 kHz, but subsequently remained near this value during the rest of the dive. This frequency shift is consistent with that expected from energy scattering from an ensemble of incompressible small-scale air-filled resonators, with diameters on the order of 4 mm. One possible candidate for such an ensemble is proposed to reside in the collapsed frontal sac of the animal. A comparison of the received levels for the bottom and direct multipath arrivals indicates that the whales' acoustic directivity must range between 10-30 dB in the 5-20-kHz region.