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Chemotherapy remains a mainstay in the treatment of many types of cancer even though it is associated with debilitating behavioral side effects referred to as "chemobrain," including difficulty concentrating and memory impairment. The predominant hypothesis in the field is that systemic inflammation drives these cognitive impairments, although the brain mechanisms by which this occurs remain poorly understood. Here, we hypothesized that microglia are activated by chemotherapy and drive chemotherapy-associated cognitive impairments. To test this hypothesis, we treated female C57BL/6 mice with a clinically-relevant regimen of a common chemotherapeutic, paclitaxel (6 i.p. doses at 30 mg/kg), which impairs memory of an aversive stimulus as assessed via a contextual fear conditioning (CFC) paradigm. Paclitaxel increased the percent area of IBA1 staining in the dentate gyrus of the hippocampus. Moreover, using a machine learning random forest classifier we identified immunohistochemical features of reactive microglia in multiple hippocampal subregions that were distinct between vehicle- and paclitaxel-treated mice. Paclitaxel treatment also increased gene expression of inflammatory cytokines in a microglia-enriched population of cells from mice. Lastly, a selective inhibitor of colony stimulating factor 1 receptor, PLX5622, was employed to deplete microglia and then assess CFC performance following paclitaxel treatment. PLX5622 significantly reduced hippocampal gene expression of paclitaxel-induced proinflammatory cytokines and restored memory, suggesting that microglia play a critical role in the development of chemotherapy-associated neuroinflammation and cognitive impairments. This work provides critical evidence that microglia drive paclitaxel-associated cognitive impairments, a key mechanistic detail for determining preventative and intervention strategies for these burdensome side effects.

Cancer patients experience circadian rhythm disruptions in activity cycles and cortisol release that correlate with poor quality of life and decreased long-term survival rates. However, the extent to which chemotherapy contributes to altered circadian rhythms is poorly understood. In the present study, we examined the extent to which paclitaxel, a common chemotherapy drug, altered entrained and free-running circadian rhythms in wheel running behavior, circulating corticosterone, and circadian clock gene expression in the brain and adrenal glands of tumor-free mice. Paclitaxel injections delayed voluntary wheel running activity onset in a light-dark cycle (LD) and lengthened the free-running period of locomotion in constant darkness (DD), indicating an effect on inherent suprachiasmatic nucleus (SCN) pacemaker activity. Paclitaxel attenuated clock gene rhythms in multiple brain regions in LD and DD. Furthermore, paclitaxel disrupted circulating corticosterone rhythms in DD by elevating its levels across a 24-hour cycle, which correlated with blunted amplitudes of Arntl, Nr1d1, Per1, and Star rhythms in the adrenal glands. Paclitaxel also shortened SCN slice rhythms, increased the amplitude of adrenal gland oscillations in PER2::luciferase cultures, and increased the concentration of pro-inflammatory cytokines and chemokines released from the SCN. These findings indicate that paclitaxel disrupts clock genes and behavior driven by the SCN, other brain regions, and adrenal glands, which were associated with chemotherapy-induced inflammation. Together, this preclinical work demonstrates that chemotherapy disrupts both central and peripheral circadian rhythms and supports the possibility that targeted circadian realignment therapies may be a novel and non-invasive way to improve patient outcomes after chemotherapy.

The flow regime shapes lotic environments, influencing local instream habitats that limit the distribution, abundance, and long-term persistence of aquatic macroinvertebrates, such as fresh...

Here we present analysis of a novel reactive material system that employs dinitrogen tetroxide (N2O4) as a liquid oxidizer with metal powder fuels. The oxidizer was added to micron scale aluminum and zirconium powders by a remote injection system. When ignited with a high voltage spark, the mixtures were observed to possess reactivity comparable to nanocomposite reactive materials, with open-tube flame expansion velocities from 500 to 1400 m/s depending on fuel/oxidizer ratio and tube diameter. Temperatures were observed to range from 3000 to 3500 K as measured with gray body fits to 16-channel time-resolved pyrometer and time-integrated spectrometer data. These values were significantly below calculated adiabatic flame temperatures, which we attribute to local deviations from stoichiometry and kinetic/energetic limitations similar to those observed in studies of particles burning in high pressures gaseous oxidizers. Al/N2O4 reactivity was found to be most likely limited by the vaporization of the metal from the particle surface and Zr/N2O4 was limited by slower burning and complex interactions involving the solubility of nitrogen and oxygen in the molten Zr. We also discuss the potential for these materials to be used to create an “on/off” reactive material, since N2O4 can be added remotely and driven to evaporate via vacuum or purge of inert gases to return it to a safe condition.

The unprecedented scientific achievements in combating the COVID-19 pandemic reflect a global response informed by unprecedented access to data. We now have the ability to rapidly generate a diversity of information on an emerging pathogen and, by using high-performance computing and a systems biology approach, we can mine this wealth of information to understand the complexities of viral pathogenesis and contagion like never before. These efforts will aid in the development of vaccines, antiviral medications, and inform policymakers and clinicians. Here we detail computational protocols developed as SARS-CoV-2 began to spread across the globe. They include pathogen detection, comparative structural proteomics, evolutionary adaptation analysis via network and artificial intelligence methodologies, and multiomic integration. These protocols constitute a core framework on which to build a systems-level infrastructure that can be quickly brought to bear on future pathogens before they evolve into pandemic proportions.

The unprecedented scientific achievements in combating the COVID-19 pandemic reflect a global response informed by unprecedented access to data. We now have the ability to rapidly generate a diversity of information on an emerging pathogen and, by using high-performance computing and a systems biology approach, we can mine this wealth of information to understand the complexities of viral pathogenesis and contagion like never before. These efforts will aid in the development of vaccines, antiviral medications, and inform policymakers and clinicians. Here we detail computational protocols developed as SARS-CoV-2 began to spread across the globe. They include pathogen detection, comparative structural proteomics, evolutionary adaptation analysis via network and artificial intelligence methodologies, and multiomic integration. These protocols constitute a core framework on which to build a systems-level infrastructure that can be quickly brought to bear on future pathogens before they evolve into pandemic proportions.

Development of energetic polymers is at the forefront of the energetics research enterprise. Formulations having high energy density as well as robust safety are goals that can be realized with implementation of new energetic polymers that target performance and mechanical properties. Presented herein are a series of oligomers synthesized from the small molecule BIDO (1) as our group's first attempt at making heterocyclic based energetic polymers without sensitive explosophores. Crystallographic investigation of the BIDO core with surrogate addends demonstrated the significant stacking ability of the BIDO core. Synthesis of four unique oligomers (3–6) is presented and characterized by spectroscopic and thermochemical measurements. Polymerization of 6 was demonstrated and tested for Tg and thermal sensitivity, and Shore A hardness. The polymer 7 exhibits a Tg value (−18 °C), close to the operating range of other energetic materials, a Shore A hardness of 81, and thermally stable up to 320 °C.

BackgroundVaricose veins represent a common cause of cardiovascular morbidity, with limited available medical therapies. Although varicose veins are heritable and epidemiologic studies have identified several candidate varicose veins risk factors, the molecular and genetic basis remains uncertain. Here, we analyzed the contribution of common genetic variants to varicose veins using data from the VA Million Veteran Program and other large multi-ancestry biobanks. Among 49,765 individuals with varicose veins and 1,334,301 disease-free controls, we identified 139 risk loci. We identified genetic overlap between varicose veins, other vascular diseases, and dozens of anthropometric factors. Using Mendelian randomization, we prioritized novel therapeutic targets via integration of proteomic and transcriptomic data. Finally, topological enrichment analyses confirmed the biologic roles of endothelial shear flow disruption, inflammation, vascular remodeling, and angiogenesis. These findings may facilitate future efforts to develop non-surgical therapies for varicose veins.

Circadian rhythms influence various aspects of biology, including hormonal, immunological, and behavioral processes. These 24-hour oscillations are necessary to optimize cellular functions and to synchronize these processes with the environment. Breast cancer patients and survivors frequently report disruptions in circadian oscillations that adversely affect quality-of-life, including fragmented sleep-wake cycles and flattened cortisol rhythms, which are associated with negative behavioral comorbidities (e.g., fatigue). However, the potential causal role of tumor biology in circadian dysregulation has not been investigated. Here, we examined the extent to which sham surgery, non-metastatic mammary tumors, or mammary tumor removal in mice disrupts circadian rhythms in brain clock gene expression, loco motor behavior (free-running and entrained), and physiological rhythms that have been associated with cancer behavioral comorbidities. Tumors and tumor resection altered time-of-day differences in hypothalamic expression of eight circadian-regulated genes. The onset of activity in entrained running behavior was advanced in tumor-bearing mice, and the amplitude of free-running rhythms was increased in tumor-resected mice. Tumors flattened rhythms in circulating corticosterone and Ly6c(Hi) monocytes which were largely restored by surgical tumor resection. This work implies that tumors alone may directly impact central and/or peripheral circadian rhythmicity in breast cancer patients, and that these effects may persist in cancer survivors, potentially contributing to behavioral comorbidities.

Time-resolved x-ray imaging is used to capture high-resolution images of the Al/Fe2O3 thermite reaction as it proceeds in an extended burn tube. The observed thermite reaction products are generally large, multi-phase composite particles. Image processing algorithms are developed to extract a continuous record of composite particle size as a function of time and distance from the ignition point. Small particles are observed immediately after ignition, followed by a rapid increase in particle size and a gradual decline toward late times. Correlating the dynamic particle size with visible light emission from the reaction, we propose a two-stage mechanism where the combination of early ignition and delayed expansion causes the material closest to the ignition point to undergo substantial coalescence before it begins moving down the tube. We also identify two mechanisms that may contribute to particle size refinement at late times, both based on the collapse of large gas bubbles that are observed preferentially in particles at earlier times. A new approach to extracting burn times from luminous intensity data is explored, and we find that a more nuanced analysis of burn time and luminous intensity may help to improve reactivity assessments when data from in situ studies is unavailable.

While chemotherapy remains a common cancer treatment, it is associated with debilitating side effects (e.g., anorexia, weight loss, and fatigue) that adversely affect patient quality of life and increase mortality. However, the mechanisms underlying taxane chemotherapy-induced side effects, and effective treatments to ameliorate them, are not well-established. Here, we tested the longitudinal relationship between a clinically-relevant paclitaxel regimen, inflammation, and sickness behaviors (loss of body mass, anorexia, fever, and fatigue) in adult, female mice. Furthermore, we sought to identify the extent to which voluntary exercise (wheel running) attenuates paclitaxel-induced sickness behaviors and underlying central pathways. Body mass and food intake decreased following six doses of chemotherapy treatment relative to vehicle controls, lasting less than 5 days after the last dose. Paclitaxel treatment also transiently decreased locomotion (open field test), voluntary wheel running, home-cage locomotion, and core body temperature without affecting motor coordination (rotarod task). Circulating interleukin (IL)-6 and hypothalamic Il1b gene expression remained elevated in chemotherapy-treated mice at least 3 days after the last dose. Exercise intervention did not ameliorate fatigue or inflammation, but hastened recovery from paclitaxel-induced weight loss. Body mass recovery was associated with the wheel running-induced recovery of body composition, paclitaxel-induced alterations to hypothalamic melanocortin signaling, and associated peripheral circulating hormones (ghrelin and leptin). The present findings demonstrate the benefits of exercise on faster recovery from paclitaxel-induced body mass loss and deficits in melanocortin signaling and suggests the development of therapies targeting the melanocortin pathway to reduce paclitaxel-induced weight loss.

Within the suprachiasmatic nucleus (SCN)—the locus of the master circadian clock— transcriptional regulation via the CREB/CRE pathway is implicated in the functioning of the molecular clock timing process, and is a key conduit through which photic input entrains the oscillator. One event driving CRE-mediated transcription is the phosphorylation of CREB at serine 133 (Ser133). Indeed, numerous reporter gene assays have shown that an alanine point mutation in Ser133reduces CREB-mediated transcription. Here, we sought to examine the contribution of Ser133phosphorylation to the functional role of CREB in SCN clock physiology in vivo. To this end, we used a CREB knock-in mouse strain, in which Ser133was mutated to alanine (S/A CREB). Under a standard 12 h light-dark cycle, S/A CREB mice exhibited a marked alteration in clock-regulated wheel running activity. Relative to WT mice, S/A CREB mice had highly fragmented bouts of locomotor activity during the night phase, elevated daytime activity, and a delayed phase angle of entrainment. Further, under free-running conditions, S/A CREB mice had a significantly longer tau than WT mice and reduced activity amplitude. In S/A CREB mice, light-evoked clock entrainment, using both Aschoff type 1 and 6 h “jet lag” paradigms, was markedly reduced relative to WT mice. S/A CREB mice exhibited attenuated transcriptional drive, as assessed by examining both clock-gated and light-evoked gene expression. Finally, SCN slice culture imaging detected a marked disruption in cellular clock phase synchrony following a phase-resetting stimulus in S/A CREB mice. Together, these data indicate that signaling through CREB phosphorylation at Ser133is critical for the functional fidelity of both SCN timing and entrainment.

Cold and hot weather are associated with mortality and morbidity. Although the burden of temperature-associated mortality may shift towards high temperatures in the future, cold temperatures may represent a greater current-day problem in temperate cities. Hot and cold temperature vulnerabilities may coincide across several personal and neighborhood characteristics, suggesting opportunities for increasing present and future resilience to extreme temperatures. We present a narrative literature review encompassing the epidemiology of cold- and heat-related mortality and morbidity, related physiologic and environmental mechanisms, and municipal responses for hot and cold weather, illustrated by Detroit, Michigan, USA, a financially-burdened city in an economically diverse metropolitan area. The Detroit area experiences sharp increases in mortality and hospitalizations with extreme heat, while cold temperatures are associated with more gradual increases in mortality, with no clear threshold. Interventions, such as heating and cooling centers, may reduce but not eliminate temperature-associated health problems. Furthermore, direct hemodynamic responses to cold, sudden exertion, indoor air quality and respiratory epidemics likely contribute to cold-related mortality. Short- and long-term interventions to enhance energy and housing security and housing quality may reduce temperature-related health problems. Extreme temperatures can increase morbidity and mortality in municipalities like Detroit that experience both extreme heat and prolonged cold seasons amidst large socioeconomic disparities. The similarities in physiological and built environment vulnerabilities to both hot and cold weather suggest prioritization of strategies that address both present-day cold and near-future heat concerns.

Improvements in breast cancer therapy/diagnosis have substantially increased the cancer survivor population, although many survivors report persistent mental health issues including fatigue, mood and anxiety disorders, and cognitive impairments. These behavioral symptoms impair quality-of-life and are often associated with increased inflammation. Nocturnal rodent models of cancer are critical to the identification of the neurobiological mechanisms underlying these behavioral changes. Although both behavior and immunity display distinct diurnal patterns, most rodent research in this field is performed during the rodents’ inactive (light) period, which could potentially undermine the conclusions and clinical relevance. Therefore, here we tested the extent to which mammary tumors or tumor resection (“survivors”) in mice affects behavior and neuroinflammation in a nyctohemeral (day versus night)-dependent manner. Indeed, only the dark (active) phase unmasked fatigue-like behavior and altered novel object investigation for both tumor-bearing and -resected mice relative to surgical controls. Several inflammatory markers were expressed in a time-of-day-dependent manner (lower in the dark phase) in the blood and brains of surgical control mice, whereas this temporal pattern was absent (IL-1β, CXCL1, Myd88, Cd4) or reversed (C3) in the respective tissues of tumor-bearing and -resected mice. Taken together, these data indicate that the time of day of assessment significantly modulates various persistent and transient tumor-induced behavioral and immune changes.

The importance of the oxidation state of an oxidizer and its impact on gaseous oxygen and total gas production in nanocomposite thermite combustion was investigated by probing the reaction and ignition properties of aluminum nanoparticles (Al-NPs) with both cupric oxide (CuO) and cuprous oxide (Cu2O) nanoparticles. The gas release and ignition behavior of these materials were tested with >105 K/s temperature jump (T-jump) heating pulses in a high temporal resolution time-of-flight mass spectrometer (ToF-MS) as well as in an argon environment. Reactivity was tested using a constant volume combustion cell with simultaneous pressure and optical measurements. A variety of Cu2O particle sizes ranging from 200 to 1500 nm were synthesized and found to release oxygen at ∼1200 K, which is higher than the values found for a variety of CuO particle sizes (∼1000 K). Both oxides were found to ignite around 1000 K, which implies a consistent ignition mechanism for both through a condensed phase pathway. The higher oxid...

Freshwater gastropods in the family Pleuroceridae are important components of North American freshwater ecosystems that can greatly influence ecological processes and biotic communities. Elimia is the most taxa rich among pleurocerid genera. Elimia comalensisPilsbry, 1890, is the only pleurocerid species that occurs in Texas and is currently known to occupy artesian springs and spring-fed river systems associated with the Edwards Plateau region. Published literature on E. comalensis is limited, and little information is currently present regarding explicit patterns of distribution and abundance within most systems currently occupied. We examined temporal and spatial variation of E. comalensis densities in the upper San Marcos River from 2013 to 2016, as well as interspecific affinities between E. comalensis and two invasive thiarid snails. We observed significant annual differences in E. comalensis densities, with greater mean density occurring under low flow conditions in 2014. We also observed significant differences in densities among sites, with greater density occurring at sites with larger and more complex substratum particles. Elimia comalensis exhibited a strong positive relationship with the thiarid snail Tarebia granifera, although data suggest that interspecific competition is limited as these species co-occur at high densities. As anthropogenic impacts continue to impact Edwards Plateau spring systems, further research on the distribution and population dynamics of ecologically important pleurocerid snails, such as E. comalensis, is needed to aid in the conservation of these unique ecosystems.

While freshwater mussels are often negatively impacted by large reservoirs, the influence of smaller low-head dams on resident mussel fauna is variable. A 2017 planned dewatering of Robinson Lake, a small water-supply reservoir located in the Llano River, Texas, presented an opportunity to quantify the native unionid community. We also compared unionid communities between Robinson Lake and a riverine portion of the mainstem Llano River to assess how impoundments may influence assemblage structure, and we evaluated the conservation implications for two Endangered Species Act (ESA) candidate species. In total, we salvaged and relocated 1,012 live unionids representing five species from Robinson Lake, including ESA-candidate species Lampsilis bracteata and Cyclonaias petrina. Lentic specialists were observed exclusively in Robinson Lake, while lotic specialists and habitat generalists occurred in the Llano River. Though community composition differed, we did observe overlap among sites, suggesting that Robinson Lake contains a subset of the unionid community within nearby riverine reaches, and it supports more lentic-adapted species. Contrary to previous habitat assessments, observations of L. bracteata reproduction in Robinson Lake suggests that this species is able to adapt to lacustrine environments and establish populations within small impoundments, though catch rates suggest higher densities in lotic habitats. As increased utilization of water resources and changing climactic patterns continue to impact spring-fed river systems of the Edwards Plateau region, such impoundments may become important conservation units for L. bracteata during major drought conditions.

A common method for measuring the reactivity of rapidly deflagrating materials has been to loosely pack a desired mixture into an approx. 10 cm long×3 mm diameter acrylic tube, ignite the material on one end, and report the observed self-propagating flame velocity through the material. While this method can yield qualitative information, linking this to quantitative intrinsic properties, such as particle burn time, has remained challenging. In this work, we significantly redesign the traditional burn tube experiment. Between 25 and 250 mg of nanocomposite aluminum/copper oxide (Al/CuO) thermite is loosely packed into the capped end of a 1.8 m long tube, and the remainder of the tube is left unfilled. The material is ignited using a hot wire, resulting in a steadily-propagating luminous front, which extends part, or all, of the way down the length of the tube. We suggest the behavior is a result of “reactive entrainment”, which occurs when the reaction time scale becomes longer than the characteristic momentum relaxation time scale. When this criterion is met, and when there are significant pressure gradients present or produced during the reaction, material will be entrained by the gases before and/or during the reaction; a behavior very different from conventional thermites, which use larger particle sizes. The effect of sample mass and tube diameter on propagation velocity is investigated, and we find a linear scaling with mass and a power law scaling with tube radius (r−1.3) between 1.56 and 4.76 mm radii. For several conditions, we observe the reaction complete; defined by the distance where the propagation velocity decreases to a fixed fraction of its steady value. The ratio of quench distance to propagation velocity was found to approach a constant value of 3.29±0.70 ms, which we suggest is the burn time of the Material. For the range of masses studied in this work, the burn time was found to be independent of mass, implying that it is an intrinsic particle burn time. We expect other quantitative information can be deduced from this experiment, so long as the chosen sample mass and tube dimensions allow one to observe the full extent of reaction.

The circadian timing system influences the functional properties of most, if not all, physiological processes. Central to the mammalian timing system is the suprachiasmatic nucleus (SCN) of the hypothalamus. The SCN functions as a ‘master clock’ that sets the phasing of ancillary circadian oscillator populations found throughout the body. Further, via an entraining input from the retina, the SCN ensures that the clock oscillators are synchronized to the daily light/dark cycle. A critical component of the SCN timing and entrainment systems is the p44/42 mitogen-activated protein kinase (ERK/MAPK) pathway. Here, we examined the expression and function of phosphoprotein-enriched in astrocytes (PEA-15), an ERK scaffold protein that serves as a key regulator of MAPK signaling. A combination of immunolabeling and Western blotting approaches revealed high levels of PEA-15 within the SCN. PEA-15 expression was enriched in distinct subpopulations of SCN neurons, including arginine vasopressin (AVP)-positive neurons of the SCN shell region. Further, expression profiling detected a significant circadian oscillation in PEA-15 expression within the SCN. Brief photic stimulation during the early subjective night led to a significant increase in PEA-15 phosphorylation, an event that can trigger ERK/PEA-15 dissociation. Consistent with this, co-immunoprecipitation assays revealed that PEA-15 is directly bound to ERK in the SCN, and that photic stimulation leads to their dissociation. Finally, we show that PEA-15 regulates ERK/MAPK-dependent activation of the core clock gene period1. Together, these data raise the prospect that PEA-15 functions as a key regulator of the SCN timing system.

Circadian modulation of learning and memory efficiency is an evolutionarily conserved phenomenon, occurring in organisms ranging from invertebrates to higher mammalian species, including humans. While the suprachiasmatic nucleus (SCN) of the hypothalamus functions as the master mammalian pacemaker, recent evidence suggests that forebrain regions, including the hippocampus, exhibit oscillatory capacity. This finding, as well as work on the cellular signaling events that underlie learning and memory, has opened promising new avenues of investigation into the precise cellular, molecular, and circuit-based mechanisms by which clock timing impacts plasticity and cognition. In this review, we examine the complex molecular relationship between clock timing and memory, with a focus on hippocampal-dependent tasks. We evaluate how the dysregulation of circadian timing, both at the level of the SCN and at the level of ancillary forebrain clocks, affects learning and memory. Further, we discuss experimentally validated intracellular signaling pathways (e.g., ERK/MAPK and GSK3β) and potential cellular signaling mechanisms by which the clock affects learning and memory formation. Finally, we examine how long-term potentiation (LTP), a synaptic process critical to the establishment of several forms of memory, is regulated by clock-gated processes.

This study explores the reaction between Al and Bi2O3 nanoparticles under high heating rate conditions with temperature-jump/time of flight mass spectrometry (T-Jump/TOFMS), high speed imaging, and rapid sample heating within a scanning electron microscope (SEM). Comparison of rapid heating of Al/Bi2O3 thermite and neat Bi2O3 shows that initiation of the Al/Bi2O3 reaction occurs at a much lower temperature than the point where oxygen is released from the neat Bi2O3 powder. Thus, without the presence of a gas phase oxidizer, it can be concluded that a condensed phase initiation mechanism must be at play in the Al/Bi2O3 nanothermite. C/Bi2O3 heating experiments were used for a mechanistic comparison between two different fuel types since the carbon represents a nonvolatile fuel in contrast to the aluminum. This formulation showed a similar condensed phase initiation as was seen with the aluminum nanothermite. Qualitative comparison of high speed imaging for Al/Bi2O3 and Al/CuO indicates that the initiation ...

The effect of aluminum size on confined flame propagation velocities in thermite composites was investi- gated between 108 mm and 80 nm, and in all cases using nanometric copper oxide as the oxidizer. It was found that the velocity exhibited two distinct regimes; between 108 and 3.5 mm the velocity scaled as the particle diameter to the � 0.56 power, and becomes invariant of size below this. One explanation for the invariance is that the pressure- driven flow reaches some peak velocity, controlled by the pressure gradient, pore size, and fluid viscosity. Another ex- planation is that the system becomes limited by the inter- nal gas heating rate, defined by the intrinsic kinetic time scale, and which can significantly impact the effective parti- cle heating time. The particle heating time was calculated as a function of particle size, and as a function of gas heat- ing rates ranging from 10 5 Ks � 1 to infinity. It was found that at any finite gas heating rate, there exists a critical par- ticle diameter below which all sizes take the same amount of time to heat. This is a direct artifact of the characteristic thermal relaxation time scale; if the heating rate is not suffi- ciently fast, then the particle will rapidly equilibrate with the gas at each time step. The inverse of thermal relaxation time was used to calculate a critical heating rate defining a transition point, and which exhibits a dp 2 scaling. This scaling sets a constraint on the kinetics, which must at least scale with dp 2 to remain in the size-dependent regime.

PressurizationratesincreasebyafactorofabouttwowiththeadditionofAlH3,whereasburntubevelocitiesincrease by about 25%. The enhancement in pressurization rate appears to primarily be a result of the increased pressure associated with the AlH3 decomposition in the nanocomposite thermite system and an enhancement in convective heat transfer. Similar experiments were conducted with micron-scale aluminum in place of the aluminum hydride, whichresultedinareductionofallthepreviouslymentionedparameterswithrespecttothebaselinenanoaluminum– copper-oxide thermite. The addition of any amount of alane to iron oxide based thermite resulted in a reduction in performance in pressure cell testing. The performanceofBi2O3 basedthermite was largelyunaffected by alaneuntil alanebecamethemajorityfuelcomponent.Theseresultshavebeenfoundtocorrelatewithchangesinthecombustion mechanism through equilibrium calculations.

In this study we investigate the role of gas phase oxygen on ignition of nanothermite reactions. By separately evaluating the temperature at which ten oxidizers release gas phase species, and the temperature of ignition in an aluminum based thermite, we found that ignition occurred prior to, after or simultaneous to the release of gas phase oxygen depending on the oxidizer. For some nanothermites formulations, we indeed saw a correlation of oxygen release and ignition temperatures. However, when combined with in situ high heating stage microscopy indicating reaction in the absence of O2, we conclude that the presence of free molecular oxygen cannot be a prerequisite to initiation for many other nanothermites. This implies that for some systems initiation likely results from direct interfacial contact between fuel and oxidizer, leading to condensed state mobility of reactive species. Initiation of these nanothermite reactions is postulated to occur via reactive sintering, where sintering of the particles can commence at the Tammann temperature which is half the melting temperature of the oxidizers. These results do not imply that gas phase oxygen is unimportant when full combustion commences.

This work investigated Ag2O as a potential oxidizer in antimicrobial energetic systems. Ultrafine Ag2O was synthesized, and its performance in nanoaluminum-based thermite systems was evaluated using a constant volume combustion cell. The Ag2O alone was found to be a relatively poor oxidizer, but it performed well when blended with more reactive oxidizers, CuO and AgIO3. Time-resolved mass spectrometry was used to investigate the reaction mechanism in more detail. Post-reaction analysis confirmed the production of Ag, but it was seen to exist in a matrix with Cu in the Al/CuO/Ag2O ternary system. The product in surface contact with Al2O3 suggested a reactive sintering mechanism occurred. The results indicate that Ag2O, while a poor oxidizer itself, can be integrated into more reactive systems to produce high yields of biocidal silver. The morphology of the final product, however, indicates that a large amount of the silver may not be surface-exposed, a result which would negatively impact the biocidal activity. 2012 Published by Elsevier Inc. on behalf of The Combustion Institute.

This study investigates the use of metal oxides as an oxygen carrier in chemical looping combustion applications. The initiation and decomposition of C/CuO and C/Fe2O3 are investigated using a time-resolved T-jump/ time-of-flight mass spectrometer (T-Jump/TOFMS). Heating of the metal oxide nanopowders produces gaseous O2, but when mixed with the fuel (carbon), gaseous O2 forms temporally after the primary combustion product, CO2. This indicates condensed phase reaction between the metal oxide and carbon as the predominant reaction mechanism rather than gas phase release of O2 and subsequent burning of carbon, at least in the initiation phase. In situ heating TEM, and SEM are used to further investigate the reaction. The oxidation rate of carbon in the present experiment is estimated to be 3 to 5 orders of magnitude greater than that predicted using the Nagle Strickland-Constable model. The activation energy of C/CuO, C/Fe2O3, and C/Bi2O3 are determined using the Ozawa iso- conversion method and are found to be 110, 170, and 230 kJ/mol, respectively. The condensed phase nature of this reaction is compared to our previous studies on aluminum nanothermites and is considered to be further evidence toward a reactive sintering initiation mechanism.

Studies of the kinetics of electrophoretic deposition (EPD) processes have generally focused on electrode geometries that yield analytical solutions, such as infinite parallel planes and concentric cylinders. In this article, we construct a finite element model for EPD of material onto a planar strip electrode, which shows excellent qualitative agreement to experimental results in a similar system. Notably, we demonstrate that the presence of the edges of the electrode lead to a singularity in the electric field that significantly affects the morphology of the deposit at short times or for thin deposits.

One of the open questions in understanding the reactivity of nanometric metal/metal oxide particulate composites is the relative role of gas–solid vs. condensed state reactions. This work is an investigation of several nano-Al based thermites subjected to very rapid heating rates. The ignition temperature of thermites, as measured by the onset of optical emission, was measured using a rapidly heated Pt wire. Generally, ignition was seen to occur above the melting temperature of aluminum. The exception was Al/Bi2O3 which ignited slightly below this point. Samples were also rapidly heated in situ within electron microscopes to provide direct imaging before and after heating. The sintering of aggregated and/or agglomerated particles into characteristically larger structures was experimentally observed in all cases, and the fuel and oxidizer were found to be in surface contact suggesting that a condensed-phase reactive sintering mechanism had occurred. High resolution image sequences of thermites ignited on the Pt wire were collected using a real time phase contrast imaging technique at the Advanced Photon Source of Argonne National Lab. The results suggest that reactive sintering occurs on a fast timescale, and relatively early in the reaction, leading to rapid melting and coalescence of aggregated particles. This dramatically changes the initial size and morphology of the constituents before the remainder of the material burns. The results question the idea that a decrease in particle size will necessarily lead to an enhancement in reactivity, since large amounts of sintering occurs early in the reaction, and alters the morphology. It is suggested that improvements in reactivity can be achieved by designing architectures to improve the interfacial contact upon sintering, as well as by selecting oxidizers based on their ability to liberate and transport oxygen in the condensed phase, while producing volatile species to assist in convective energy transport.

In this work, high-oxygen-content strong oxidizer perchlorate salts were successfully incorporated into current nanothermite composite formulations. The perchlorates were encapsulated within mild oxidizer particles through a series of thermal decomposition, melting, phase segregation, and recrystallization processes, which occurred within confined aerosol droplets. This approach enables the use of hygroscopic materials by stabilizing them within a matrix. Several samples, including Fe2O3/KClO4, CuO/KClO4 and Fe2O3/NH4ClO4 composite oxidizer particles, have been created. The results show that these composite systems significantly outperform the single metal oxide system in both pressurization rate and peak pressure. The ignition temperatures for these mixtures are significantly lower than those of the metal oxides alone, and time-resolved mass spectrometry shows that O2 release from the oxidizer also occurs at a lower temperature and with high flux. The results are consistent with O2 release being the controlling factor in determining the ignition temperature. High-speed imaging clearly shows a much more violent reaction. The results suggest that a strategy of encapsulating a very strong oxidizer, which may not be environmentally compatible, within a more stable weak oxidizer offers the opportunity to both tune reactivity and employ materials that previously could not be considered.

The authors investigated the ignition and reaction of Al/AgIO3 thermites for potential use in biocidal applications. Rapid-heating wire experiments were performed to measure the ignition temperature and investigate the thermal decomposition of the oxidizer using a T-Jump/TOF Mass Spectrometer and an optical emission setup. Combustion experiments inside a constant-volume pressure cell were also carried out, and the relative performance was compared with other thermite systems. The ignition temperature in air at atmospheric pressure was found to be 1215 ± 40 K. The AgIO3 was found to significantly outperform CuO and Fe2O3 oxidizers in pressurization tests, and this is attributed to the enhanced gas release as the AgIO3 thermally decomposes to release iodine in addition to oxygen. The reacted product was collected to investigate the final state of the products. Transmission electron microscopy and X-ray diffraction were performed to show that the major Ag product species was AgI, and not elemental Ag and I2....