<div>Understanding the fundamental physics involved in the high strain rate deformation of high explosives (HE) is critical for developing more efficient, reliable, and safer energetic materials. When HE are impacted at high velocities, several thermo-mechanical processes are activated, which are responsible for the ignition of these materials. These processes occur at different time and length scales, some of them inaccessible by experimentation. Therefore, computational modeling is an excellent alternative to study multiscale phenomena responsible for the ignition and initiation of HE. This thesis aims to develop a continuum model of HMX to study the anisotropic behavior of HE at the mesoscale, including fracture evolution and plastic deformation. This thesis focus on three types of simulations. First, we investigate dynamic fracture and hotspot formation in HMX particles embedded in Sylgard binder undergoing high strain rate compression and harmonic excitation. We use the phase field damage model (PFDM) to simulate dynamic fracture. Also, we implement a thermal model to capture temperature increase due to fracture dissipation and friction at both cracks and debonded HMX/Sylgard interface. In our simulations, we observe that crack patterns are strongly dominated by initial defects such as pre-existing cracks and interface debonding. Regions with initial debonding between HMX particles and the polymer are critical sites where cracks nucleate and propagate. Heating due to friction generates in these regions too and caused the formation of critical hotspots. We also run simulations of a HMX particle under high-frequency harmonic excitation. As expected, higher frequencies and larger amplitudes lead to an increase in the damage growth rate. The simulations suggest that the intensity of the thermal localization can be controlled more readily by modifying the bonding properties between the particle and the binder rather than reducing the content of bulk defects in the particle. </div><div><br></div><div>Second, we present simulations of shock compression in HMX single crystals. For this purpose, we implemented a constitutive model that simulates the elastoplastic anisotropic response of this type of material. The continuum model includes a rate-dependent crystal plasticity model and the Mie-Gruneisen equation of state to obtain the pressure due to shock. Temperature evolves in the material due to plastic dissipation, shock, and thermo-elastic coupling. The model is calibrated with non-reactive atomistic simulations to make sure the model obeys the Rankine-Hugoniot jump conditions. We compare finite element (FE) and molecular dynamic (MD) simulations to study the formation of hot spots during the collapse of nano-size void in a HMX energetic crystal. The FE simulations captured the transition from viscoelastic collapse for relatively weak shocks to a hydrodynamic regime for strong shocks. The overall temperature distributions and the rate of pore collapse are similar to MD simulations. We observe that the void collapse rate and temperature field are strongly dependent on the plasticity model, and we quantify these effects. We also studied the collapse of a micron size void in HMX impacted at different crystal orientations and impact velocities. The simulation results of void collapse are in good agreement with a gas gun void collapse experiment. While the void size and crystal orientation do not affect the area ratio rate, they strongly affect the void collapse regime and temperature. Also, increased plastic activity when the crystal is impacted on the plane (110) renders higher temperature fields.</div><div><br></div><div>Finally, we studied shock compression and dynamic fracture in polycrystalline HMX using the same model implemented for shocks in single crystals. The goal of this study is to understand the role of crystal anisotropy and how it affects other hotspot formation mechanisms such as frictional heating. To simulate fracture, we used a phase field damage model implemented for large deformations. We first perform simulations of sustained shocks in polycrystalline HMX, where the grains are perfectly bonded to understand the effect of plastic deformation and hotspot formation due to plastic heating. Then, we simulate shocks in polycrystalline HMX with dynamic fracture. Simulations capture fracture evolution and frictional heating at cracks. In the polycrystalline case, we study heat generation due to shock and plastic deformation. A heterogeneous temperature field forms when the shock wave travels in the material. Temperature increases more in crystals that showed a higher magnitude of accumulated slip. When weak grain boundaries are included in the simulations, frictional heating becomes the dominant hotspot formation mechanism. As the crystals' interfaces break and crack surface sliding occurs, temperature increases due to friction at cracks. Hotspots tend to form at cracks oriented 45 deg from the shock direction. For this case, crystal anisotropy does not play an important role in temperature generation due to plastic dissipation. However, the random orientation of the crystals creates heterogeneous deformation and stress fields that cause the formation of a higher number of hotspots than the case where all the grains are oriented in the same direction.</div>

To safely transport and use energetic materials, it is important that their response to mechanical excitation at various temperatures be well understood. In order to better understand the thermomechanical response of these materials, samples of inert and live PBXN-109 are fabricated and excited between 10-20 kHz. The resonance of the system is found using a Laser Doppler Vibrometer and the temperature at the surface of the sample is measured with an infrared camera. Samples are loaded into an environmental chamber and tested at -10, 22, 55, and 120 ˚C. Using multiple procedures, the shift in resonant frequency caused by changing material properties can be predicted and followed to elicit the greatest thermal response. Twelve samples are excited using a fluctuating sinusoidal input at each temperature range. The samples are shown to generate significantly less heat from mechanical excitation as ambient temperature increases. Heating rates are also severely affected by temperature. Samples tested at 120 ˚C heat at a rate of ~0.5 ˚C/min, while samples at -10 ˚C heat at ~ 5.7 ˚C/min. Despite the large difference in heating rates samples tested at higher ambient temperatures reached higher peak temperatures. This indicates that the strong temperature dependence of the material properties is likely key to reducing heating caused by mechanical excitation. It also indicates that proper control of ambient temperature should be considered when transporting or using munition systems to ensure safety and proper functionality.

This study investigated the effect of hearing six background noise conditions (silent baseline, pink noise, monologue, lively conversation, one-sided phone call, and cocktail noise) on acoustic measures of speech production during story retells in people with aphasia. Eleven individuals with aphasia and 11 age- and gender-matched control participants took part in the study. Participants heard the background noise conditions through open-back headphones while they retold six short stories. The examiner calculated mean and standard deviation of intensity, mean and standard deviation of fundamental frequency (F0), and speech rate in words per minute. A Matlab application that identified pauses (i.e., periods of silence greater than 200 ms) computed a speaking time ratio measure (i.e., time speaking versus time pausing). With the exception of the monologue and one-sided phone call condition, both people with aphasia and control participants significantly increase their intensity and F0 in the presence of background noise. Additionally, participants with aphasia have significantly lower speaking time ratios and speaking rates when compared to control participants. Participants make acoustic changes while hearing background noise; speech intensity rises in an effort to increase the signal-to-noise ratio, while mean F0 increases due to a presumed rise in subglottal pressure. Further research is suggested to investigate other acoustic differences, possibly at the segmental level, between speech produced in informational and energetic background noise.

Balancing increased safety against detonation performance is paramount for new explosive energetic materials in the development process. Often these two requirements are in opposition to each other. Sensitivity tests to external stimuli are used to determine how safe an energetic material is to phenomena such as impact, heat, or friction. Meanwhile, detonation performance is assessed by the maximum pressure and shock velocity induced from chemical reactions. Tailoring the performance while maintaining safety of the explosive would be possible with knowledge of the chemical reactions that functional groups provide during detonation. Current knowledge of the chemical reactions that occur during detonation is limited. Several mechanisms have been suggested for first step reactions throughout the detonation process for energetic molecules; however, no single chemical pathway has been irrefutably substantiated by experiments. Alternatively, models can provide insight into the types of reactions that may transpire, but lack direct experimental comparisons. If experiments and models could be compared at the equivalent time and length scales, then measurements could guide the physics and chemistry assumptions present in models. Experiments presented in this document bridge that gap by using an ultrafast laser system to generate shocks in samples and spectroscopically probe vibrational and electronic absorption changes that occur during shock compression. A review of how to turn a benchtop chirped pulse amplifier into a shock physics and chemistry laboratory is first presented. Applications of the spectroscopic techniques developed were then applied to trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN) during shock compression. Mid-infrared absorption results for shock compressed TNT and PETN were compared to current suggestions on chemical pathways and inconsistencies were present for both materials. It is suggested that a carbon-carbon bond breaking mechanism is present for PETN, and a hydrogenic stretch like hydroxyl or amide bond formation mechanism is suggested for TNT based on the MIR absorption measurements. Recommendations for future experimental thrusts are also provided. The results provided in this document could be directly compared to simulations to refine the assumptions present in models.

Orientador: Jorge de Lucas Junior / Banca: Osmar de Carvalho Bueno / Banca: Tânia Mara Baptista dos Santos / Resumo: Nos últimos anos, verifica-se crescente a produção de resíduos sólidos urbanos associada a um aumento populacional e ao maior consumo de produtos com embalagens que poderiam ser recicladas. Medidas rápidas de valorização e reciclagem devem ser tomadas para que permitam um consumo contínuo de alguma forma racional, diminuindo conseqüentemente, as agressões ambientais. No presente estudo avaliaram-se parâmetros que proporcionem subsídios na tomada de decisões sobre o melhor aproveitamento dos resíduos sólidos urbanos orgânicos, utilizando-se a compostagem ou a biodigestão anaeróbia. O resíduo sólido urbano orgânico (lixo) foi cedido pela empresa CONSTROESTE, localizada no município de São José do Rio Preto-SP, e o experimento foi conduzido no Laboratório de Biodigestão Anaeróbia do Departamento de Engenharia Rural da Faculdade de Ciências Agrárias e Veterinárias - Campus de Jaboticabal da Universidade Estadual Paulista - Unesp. Foram conduzidos ensaios de compostagem e biodigestão anaeróbia, utilizando-se resíduo sólido urbano orgânico coletado no município de São José do Rio Preto - SP, no intuito de avaliar as características químico-minerais, o potencial energético e a interferência da qualidade do resíduo no desenvolvimento dos processos. Avaliaram-se as reduções de sólidos totais e voláteis, produções de biogás e qualidade do biofertilizante durante a biodigestão anaeróbia, que foi conduzida com a utilização ou não de inóculo, e parâmetros como temperatura, umidade, peso, teores de nutrientes, e redução de massa enleirada durante a compostagem e a equivalência energética nos dois processos. Observaram-se reduções de 58,5% nas quantidades de massa seca enleirada e de 40,9% nos teores de carbono orgânico, matéria orgânica compostável e demanda química de oxigênio. Foram verificadas temperaturas acima de 40º C,...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: An increasing production of urban organic wastes is noticed in the last years, associated with the growth of the global population and the increased of resultant consumption. Fast actions of valorization and recycling must be done, in a way that it allows a rational continuous consumption and consequently decreasing environmental aggressions. This work has evaluated some parameters that supply decision making over better use of urban organic wastes through composting or anaerobic digestion processes. The urban organic waste was supplied by Controeste company, in São José do Rio Preto - SP. The experiment was conducted in the Anaerobic Digestion Laboratory - Agricultural Engineering Department - Veterinary and Agricultural Sciences College - Jaboticabal Campus - São Paulo State University - UNESP. Samples of composting and anaerobic digestion were collected done from the wastes in the city of São José do Rio Preto - SP, with the objective of evaluating to the chemical and mineral properties and consequent interference of the residues on the processes. The reductions of total and volatile solids, biogas production and biofertilizer quality werw evaluated during the anaerobic digestion. It was conducted using inoculums or not and parameters such as temperature, humidity, weight, nutrient content and reduction of heap mass during the composting. A reduction the 58.5% in the quantity of heap dry mass, 40.9% in the organic carbon contents, recycling organic material and chemical demand of oxygen was observed. It was registered temperatures above 40ºC in the heaps interior, evidencing the importance of the process of reduction and/or elimination of pathogens.The presence of innocuous in the substrate anticipated the biogas production in the process of anaerobic digestion...(Complete abstract click electronic access below) / Mestre

The interaction between the solar wind and the partially ionized gas of the local interstellar medium (ISM) creates a bubble known as the heliosphere. Classically, the shape of the heliosphere has been regarded as comet-like, with a long tail pointed in the direction opposite the Sun’s motion through the ISM. In this view, the solar magnetic field was assumed to have a negligible effect on the global structure of the heliosphere. Recent advances in numerical modeling have revealed the importance of the solar magnetic field in its ability to confine and collimate the solar wind plasma, and the shape of the heliosphere has been called into question. Energetic neutral atoms (ENAs) are created throughout the heliosphere via charge exchange. The separate contributions of the solar magnetic field topology and the solar wind structure to ENA observations is largely unexplored. The Interstellar Boundary Explorer (IBEX) has been providing a global perspective of the heliosphere through ENA maps with energies ranging from 0.2 to 6 keV. In this dissertation, three-dimensional magnetohydrodynamic simulations of the heliosphere are used as input to an ENA model designed to produce synthetic ENA maps. I compare modeled ENA maps with IBEX observations to investigate how different heliospheric conditions and properties affect ENAs created in the heliosphere, and therefore how ENA observations can be used to understand the heliosphere. First, I investigate the effect of the solar wind collimation by the solar magnetic field on ENA maps in the case of a solar wind without latitudinal variation. I find that even in the absence of variations of the solar wind, two lobes of strong ENA flux form at high latitudes, similar to what is observed by IBEX at high energies. Second, I test the effect of a latitudinally-varying solar wind on ENAs both with and without the inclusion of the solar magnetic field. I show that the latitudinal variations of the solar wind during solar minimum creates a structured ENA profile with latitude, corresponding to the profile observed at 1 AU, but that the solar magnetic field significantly enhances ENA flux in the region where the solar wind is confined. Lastly, I investigate the effect of the solar cycle on ENAs and how changing solar wind conditions (e.g. density, temperature, velocity) affect the heliosphere over time. I demonstrate that, given changes in the solar cycle, there is a significant evolution in the modeled ENA flux due to the changes in the solar wind profile and the solar magnetic field, which is also seen by ENA observations.

Auditory maskers, whether intelligible speech or unintelligible noise, can make it difficult to hear and/or process a target sentence. These maskers can present challenges to peripheral processing as well as central processing. Change in pupil size is a physiological index of listening effort and can be measured using eye tracking technology. The aim of the study was to compare listening effort, as measured by changes in pupil size in individuals with normal hearing, between the conditions of Intelligible Speech Masker (ISM), Speech Shaped, Speech Envelope-Modulated Noise Maskers (SSSNM), and Stationary Noise Masker (SNM). Spatial separation between target and maskers was used throughout all conditions. The study design used adaptive tracks that varied the Target to Masker Ratios (TMRs) in each of the 3 conditions in order to identify the TMR corresponding to the 75% correct point on the psychometric function for each participant. Once the TMR corresponding to the 75% correct point was identified, this TMR was held constant for 24 trials while pupil size was recorded. The results show that the ISM condition elicited a higher degree of listening effort compared to either of the noise conditions (SNM and SSSNM). These results reveal that more effort is required to ignore background speech than to ignore background noise at equivalent TMRs. Understanding the amount of effort that young, normal-hearing listeners must exert in these different types of situations will provide a foundation for later measuring the amount of effort that individuals with hearing loss and/or cognitive-linguistic deficits (e.g., aphasia) must exert in the same situations. / 2023-05-19T00:00:00Z

This research aims to contribute to the safe methodology for additive manufacturing (AM) of energetic materials. Coating formulation processes were investigated to find a suitable method that may enable selective laser sintering (SLS) as the safe method for fabrication of high explosive (HE) compositions. For safety and convenience reasons, the concept demonstration was conducted using inert explosive simulants with properties quasi-similar to the real HE. Coating processes for simulant RDX-based microparticles by means of PCL and 3,4,5- trimethoxybenzaldehyde (as TNT simulant) are reported. These processes were evaluated for uniformity of coating the HE inert simulant particles with binder materials to facilitate the SLS as the adequate binding and fabrication method. The critical constraints being the coating effectiveness required, spherical particle morphology, micron size range (>20 μm) and a good powder deposition and flow, and performance under SLS to make the method applicable for HEs. Of the coating processes investigated, suspension system and single emulsion methods gave required particle near spherical morphology, size and uniform coating. The suspension process appears to be suitable for the SLS of HE mocks and potential formulation methods for active HE composites. The density was estimated to be comparable with the current HE compositions and plastic bonded explosives (PBXs) such as C4 and PE4, produced from traditional methods. The formulation method developed and the understanding of the science behind the processes paves the way toward safe SLS of the active HE compositions and may open avenues for further research and development of munitions of the future. / Dissertation (MSc (Applied Science:Chemical Technology))--University of Pretoria, 2019. / Chemical Engineering / MSc (Applied Science:Chemical Technology) / Unrestricted

Bacterial protein export involves the translocation of precursor proteins across the inner cytoplasmic membrane. Over 100 proteins are exported from Escherichia coli. This study showed that energy in the form of ATP and membrane gradient energy is essential for the export of leucine specific binding protein and (3-lactamase precursors. Ionophores or combinations of ionophores (SF6847, valinomycin/nigericin and valinomycin/monensin) which dissipate protonmotive force inhibit protein export. Valinomycin alone also inhibits export, but not as well as reagents which dissipate protonmotive force. Nigericin or monensin alone slightly stimulate protein export. These results suggest that the transmembrane electrical potential ( DY) is the component of membrane gradient energy necessary for precursor protein export. ATP is necessary for the export of precursors. In the absence of ATP, in vitro export of leucine specific binding protein and B-lactamase precursors is not observed. An upper limit of l0μM was determined for the effective Km for ATP during in vitro protein export. It was also shown that ATP is consumed during the export process. The SecA protein was shown to contain an ATPase activity that is stimulated by the presence of inverted membranes and purified LSBP precursors. Vanadate and diethylstilbestrol, inhibitors of ATPases, inhibit in vitro protein export. Vanadate also inhibits SecA ATPase activity which depends on membranes and precursors. Vanadate is a specific inhibitor of P-type ion translocating ATPases. This study showed primary sequence homology between part of the SecA protein and the phosphorylation sequence of P-type ATPases. Sequence homology, vanadate inhibition of SecA ATPase activity, and vanadate inhibition of in vitro protein export suggest that SecA may function by a mechanism similar to the E1E2 mechanism found in P-type ATPases. Phosphorylation of two proteins with apparent sizes of 62 and 37 kDa is observed to occur in an export-associated fashion. This phosphorylation is dependent on membranes and precursors, is sensitive to hydroxylamine, and is sensitive to inhibitors of protein export, including valinomycin/nigericin and vanadate. Furthermore, phosphorylation of the 62 kDa protein is dependent on the presence of SecA. The phosphate linkage appears to be an acyl phosphate based on hydroxylamine sensitivity and reduction of the acyl phosphate linkage by NaCNBH3. Both proteins appear to be peripherally associated with the cytoplasmic face of the inner membrane, which is also consistent with a possible role in the bacterial protein export process.

10ABSTRACTEnergetic materials are widely used as rocket propellants and explosives in the field of aerospace and defense. Understanding the nature of impact in polymer-bonded explosives is crucial safety and transportation of energetic materials. The formation of hotpots in energetic materials leads to unexpected initiations, posing a safety hazard. An attempt was made to study the mechanical behavior of energetic materials under different shapes of impactors. In particular, the likelihood of hotspot formations was discussed in spherical and Spherical Impactors(SI). Spherical and planar-shaped impactors were modeled with a cohesive finite element frame work to simulate the behavior of granular energetic materials with cyclo-tetramethylene-tetranitramine(HMX) embedded in a hydroxyl-polybutadiene binder. Temperature distribution and stresses induced around crystals on expanding stress profile of SI and uniform pressure profile from a SI are compared to determine the possibility of detonation.<div><br></div><div>In this work, the dependence of sample morphology on induced stresses in the microstructure is highlighted by using three different microstructures. A digitized polymer-bonded-explosive microstructure was analyzed for possible initiations with different impact velocities. The effect of the shape of grains and volume fractions on the likeliness of hotspot formation were studied using rounded and sharp-edged idealized crystals. Impactor behavior on samples was compared based on force chains, temperature profiles, and stress distributions</div>