Theory and modeling of laser-driven flyer plate experiments to study explosives under a microscope

Studying liquid and solid high-explosive materials requires precise characterization of thermodynamics and chemical kinetics to capture the reactive behavior. Although high explosives have been studied for many decades, there is currently no reactive continuum scale model for characterizing reactive materials in the micrometer length scale and nanosecond time-scale. The Dlott research group at the University of Illinois Urbana-Champaign has developed a novel, tabletop experimental set-up, which has provided high-quality experimental data. In the research described herein, we (1) present a computational framework for modeling and simulating microscopic size, laser-driven flyer impact experiments at 0.5 – 4.5 km/s, (2) identify and develop effective material models for inert and reactive materials, and (3) utilize this framework to present deeper understanding of reactive behavior for a classical reactive material, liquid nitromethane. We present a computational approach using a multi-material, arbitrary Lagrangian-Eulerian code termed ALE3D to model the nanosecond/micrometer dynamics of the launch of 0.5 - 4.5 km/s laser-driven metal flyer plates and the impact with stationary targets of Pyrex and fused silica glasses, and Lexan and Plexiglas polymers, producing pressures in the target in the 5 - 20 GPa range. The simulations are compared to experimental results where the flyer velocity profile and the velocity profile imparted to the target material were measured with high-speed velocimetry. The experimental flyer launch by a high-intensity pulsed laser is modeled by depositing heat into a thin vaporizable layer under the flyer plate. This model produces a flyer plate that has not been exposed to the laser pulse, allowing us to compare the properties of the real flyer to a simulated ideal flyer. Simulations of target impact are in good agreement with experiment except at the highest impact velocities where the shock release process in experiment is slower than in the simulation. In addition, we observe the spallation influence in the metal flyer at these hyper-velocity speeds. We utilize the same computational framework with the multi-physics ALE3D code to model the nanosecond/micrometer dynamics of the 1.60 – 4.30 km/s laser-driven flyer plate and the impact with stationary target containing pure, liquid nitromethane, sandwiched between a metal lid and a transparent Pyrex window. Basically, in this specific case, we extend the inert example above by incorporating a reactive material target to be studied. Shock compressed, nitromethane chemical reactivity is modeled using the CHEETAH, thermochemical code within ALE3D. The reactive model parameters are obtained from past studies in literature, and assessed to capture the reactivity in liquid nitromethane within the experimental time duration. Simulation results show good agreement when compared to experimental data for the incoming PDV velocity profiles and the downstream comparison of velocity profiles at 25 μm, 40 μm, 64 μm, 90 μm, and 170 μm downstream. We also present pressure, density, and temperature results. As part of this research, we developed a novel framework for studying reactive materials at the microscopic scale with fast-time chemical kinetics. We show careful characterization of the inert material behavior at high impact, as well as, the material behavior under shock compressive reactive behavior. This framework can be utilized to studying other liquid and solid materials to further understand the reactive dynamics at the point where physics and chemistry merge together

On the mechanistic difference between in-phase and out-of-phase thermo-mechanical fatigue crack growth

The crack driving mechanisms in a coarse grained nickel-base superalloy RR1000 when subjected to in- and out of phase thermo mechanical fatigue are investigated. It is found that the difference in fatigue crack growth rate between these two load conditions is accounted for by the different mechanical conditions at the crack tip region, rather than oxidation effects. This is based on digital image correlation and finite element analyses of the mechanical strain field at the crack tip, which demonstrate that in phase leads to larger crack tip deformation and crack opening. Notably, it is demonstrated that in- and out of phase crack growth rates coincide when correlated to the crack tip opening displacement

Effects of spermidine supplementation on cognition and biomarkers in older adults with subjective cognitive decline (SmartAge)—study protocol for a randomized controlled trial

Background: Given the global increase in the aging population and age-related diseases, the promotion of healthy aging is one of the most crucial public health issues. This trial aims to contribute to the establishment of effective approaches to promote cognitive and brain health in older individuals with subjective cognitive decline (SCD). Presence of SCD is known to increase the risk of objective cognitive decline and progression to dementia due to Alzheimer’s disease. Therefore, it is our primary goal to determine whether spermidine supplementation has a positive impact on memory performance in this at-risk group, as compared with placebo. The secondary goal is to examine the effects of spermidine intake on other neuropsychological, behavioral, and physiological parameters. Methods: The SmartAge trial is a monocentric, randomized, double-blind, placebo-controlled phase IIb trial. The study will investigate 12 months of intervention with spermidine-based nutritional supplementation (target intervention) compared with 12months of placebo intake (control intervention). We plan to recruit 100 cognitively normal older individuals with SCD from memory clinics, neurologists and general practitioners in private practice, and the general population. Participants will be allocated to one of the two study arms using blockwise randomization stratified by age and sex with a 1:1 allocation ratio. The primary outcome is the change in memory performance between baseline and post-intervention visits (12 months after baseline). Secondary outcomes include the change in memory performance from baseline to follow-up assessment (18months after baseline), as well as changes in neurocognitive, behavioral, and physiological parameters (including blood and neuroimaging biomarkers), assessed at baseline and post-intervention. Discussion: The SmartAge trial aims to provide evidence of the impact of spermidine supplementation on memory performance in older individuals with SCD. In addition, we will identify possible neurophysiological mechanisms of action underlying the anticipated cognitive benefits. Overall, this trial will contribute to the establishment of nutrition intervention in the prevention of Alzheimer’s disease

The effect of phase angle on crack growth mechanisms under thermo-mechanical fatigue loading

The current paper describes TMF crack growth behaviour in an advanced nickel-based superalloy. Changes in behaviour are examined which occur as a function of the phase angle between applied stress and temperature. The fractography of the failed specimens reveals changes from transgranular to intergranular growth between high and low phase angle tests as a result of the onset of high temperature damage mechanisms. More targeted testing has also been undertaken to isolate the contributions of these mechanisms, with specific transitions in behaviour becoming clear in 90° diamond cycles, where dynamic crack growth and oxidation strongly interact

DevTMF – Towards code of practice for thermo-mechanical fatigue crack growth

The current paper presents work on identification and evaluation of a range of factors influencing accuracy and comparability of data generated by three laboratories carrying out stress-controlled thermo-mechanical fatigue crack growth tests. It addresses crack length measurements, heating methods and temperature measurement techniques. It also provides guidance for pre-cracking and use of different specimen geometries as well as Digital Image Correlation imaging for crack monitoring. The majority of the tests have been carried out on a coarse grain polycrystalline nickel-base superalloy using two phase angles, Out-of-Phase and In-Phase cycles with a triangular waveform and a temperature range of 400–750 °C

Effects of Spermidine Supplementation on Cognition and Biomarkers in Older Adults With Subjective Cognitive Decline : Decline A Randomized Clinical Trial

IMPORTANCE Developing interventions against age-related memory decline and for older adults experiencing neurodegenerative disease is one of the greatest challenges of our generation. Spermidine supplementation has shown beneficial effects on brain and cognitive health in animal models, and there has been preliminary evidence of memory improvement in individuals with subjective cognitive decline. OBJECTIVE To determine the effect of longer-term spermidine supplementation on memory performance and biomarkers in this at-risk group. DESIGN, SETTING, AND PARTICIPANTS This 12-month randomized, double-masked, placebocontrolled phase 2b trial (the SmartAge trial) was conducted between January 2017 and May 2020. The study was a monocenter trial carried out at an academic clinical research center in Germany. Eligible individuals were aged 60 to 90 years with subjective cognitive decline who were recruited from health care facilities as well as through advertisements in the general population. Data analysis was conducted between January and March 2021. INTERVENTIONS One hundred participants were randomly assigned (1:1 ratio) to 12 months of dietary supplementation with either a spermidine-rich dietary supplement extracted from wheat germ (O.9 mg spermidine/d) or placebo (microcrystalline cellulose). Eighty-nine participants (89%) successfully completed the trial intervention. MAIN OUTCOMES AND MEASURES Primary outcome was change in memory performance from baseline to 12-month postintervention assessment (intention-to-treat analysis), operationalized by mnemonic discrimination performance assessed by the Mnemonic Similarity Task. Secondary outcomes included additional neuropsychological, behavioral, and physiological parameters. Safety was assessed in all participants and exploratory per-protocol, as well as subgroup, analyses were performed. RESULTS A total of 100 participants (51 in the spermidine group and 49 in the placebo group) were included in the analysis (mean [SD] age, 69 [5] years; 49 female participants [49%]). Over 12 months, no significant changes were observed in mnemonic discrimination performance (between-group difference, -0.03; 95% CI, -0.11 to 0.05; P = .47) and secondary outcomes. Exploratory analyses indicated possible beneficial effects of the intervention on inflammation and verbal memory. Adverse events were balanced between groups. CONCLUSIONS AND RELEVANCE In this randomized clinical trial, longer-term spermidine supplementation in participants with subjective cognitive decline did not modify memory and biomarkers compared with placebo. Exploratory analyses indicated possible beneficial effects on verbal memory and inflammation that need to be validated in future studies at higher dosage.Peer reviewe

Dietary spermidine for lowering high blood pressure

Loss of cardiac macroautophagy/autophagy impairs heart function, and evidence accumulates that an increased autophagic flux may protect against cardiovascular disease. We therefore tested the protective capacity of the natural autophagy inducer spermidine in animal models of aging and hypertension, which both represent major risk factors for the development of cardiovascular disease. Dietary spermidine elicits cardioprotective effects in aged mice through enhancing cardiac autophagy and mitophagy. In salt-sensitive rats, spermidine supplementation also delays the development of hypertensive heart disease, coinciding with reduced arterial blood pressure. The high blood pressure-lowering effect likely results from improved global arginine bioavailability and protection from hypertension-associated renal damage. The polyamine spermidine is naturally present in human diets, though to a varying amount depending on food type and preparation. In humans, high dietary spermidine intake correlates with reduced blood pressure and decreased risk of cardiovascular disease and related death. Altogether, spermidine represents a cardio- and vascular- protective autophagy inducer that can be readily integrated in common diets