Essential connectedness and the rigidity problem for Gaussian symmetrization

We provide a geometric characterization of rigidity of equality cases in Ehrhard's symmetrization inequality for Gaussian perimeter. This condition is formulated in terms of a new measure-theoretic notion of connectedness for Borel sets, inspired by Federer's definition of indecomposable current.Comment: 38 page

Fragmentation of Ammonium Nitrate Particles under Thermal Cycling

Ammonium nitrate finds application in explosives and chlorine-free slow-burning propellants. Different phases are known for this ammonium salt, each of them featured by peculiar bulk densities. As a consequence, the variation of storage temperature induces processes of expansion-contraction in the crystals, unless specific stabilization is performed. In this paper, a batch of raw ammonium nitrate particles has been thermally cycled between −30 °C to +60 °C and analyzed. Microscopic observations, particle size measurement, and X-ray microtomography showed that the particles undergo a progressive fragmentation process, with opening of internal cracks and voids. The tested material halved its mass-mean diameter after five thermal cycles. As a term of comparison, a phase-stabilized ammonium nitrate batch was tested under the same conditions, showing no effect

Parallel packing code for propellant microstructure analysis

In recent years, packing codes have become a successful alternative to experimental data collection for microstructure investigation of heterogeneous materials. Composite solid rocket propellants are interesting representatives of this category, consisting of a mix of fuel and oxidizer powders embedded in a polymeric binder. Their macroscopic properties are strictly dependent on the peculiar microstructure, which influences mechanical, combustion, as well as physical features. This work addresses algorithm development, validation, and scalability of POLIPack, a parallel packing code based on the Lubachevsky–Stillinger algorithm, developed at the Space Propulsion Laboratory (SPLab) of Politecnico di Milano. The application can reproduce the organization of spheres of any diameter inside a cube with periodic boundary. In addition to the general code description, the paper identifies a collision condition not addressed by the original Lubachevsky's algorithm (here called back impact), introduces a novel post-impact handling granting a minimum separation velocity between particles, and presents a parallelization approach based on OpenMP shared memory paradigm. Monomodal and bimodal packs have been compared to experimental data through statistic descriptors and packing maps

Evaluating New Liquid Storable Bipropellants: Safety and Performance Assessments

Conventional storable bipropellants make use of hydrazine and its derivatives as fuels and nitrogen tetroxide as an oxidizer. In recent years, the toxicity character of these chemicals pushed the propulsion community towards “green” alternatives. Several candidates have been proposed among existing and newly developed chemicals, highlighting the need for a common and robust selection methodology. This paper aims at reviewing the most important selection criteria in the field of toxicity and discusses how to objectively define a green propellant, considering both the health and environmental hazards caused by the chemicals. Additionally, consistent figures of merit in the field of safety and handling operations and performance are proposed. In particular, operating temperatures, flammability and stability issues are discussed in the framework of physical hazards and storage requirements, while vacuum impulses, adiabatic flame temperature and sooting occurrence of the investigated couples are compared to the UDMH/NTO benchmark case. Hydrogen peroxide and nitrous oxide, and light hydrocarbons, alcohols and kerosene are selected from the open literature as promising green oxidizers and fuels, respectively. The identified methodology highlights merits and limitations of each chemical, as well as the fact that the identification of a universally best suited green couple is quite impractical. On the contrary, the characteristics of each propellant lead to a scenario of several “sub-optimal” couples, each of them opportunely fitting into a specific mission class

Insecticidal Activity of Plant Secondary Metabolites

Dear Colleagues, Plant secondary metabolites display a plethora of biological functions, among which the biochemical defense against insects and other organisms is one of the most important ones. For this purpose, they synthesize alkaloids, terpenoids, and phenolics which act as allelochemicals through highly diverse modes of action leading to major changes on the arthropods’ physiology and behavior. Thus, they represent a complementary and alternative strategy to manage populations of pests and vectors. In this framework, the present Special Issue welcomes original research articles and reviews shedding light on recent advancements about the use of plant secondary metabolites and related formulations against arthropod targets of health and agricultural importance. This Special Issue welcomes contributions on the following topics: - Phytochemical analysis and biological evaluation of plant-borne secondary metabolites; - Lethal and sub-lethal effects of plant-borne insecticides and acaricides; - Repellent effects of plant-borne secondary metabolites on insects and mites; - Modes of action of green insecticides, acaricides, and repellents; - Toxicity of green insecticides and acaricides on non-target species, including aquatic organisms; - Structure–activity relationships characterizing green insecticides and acaricides; - Synergistic and antagonistic studies focusing on green insecticides and acaricides; - Development of insecticidal and acaricidal formulations with extended shelf-life and prolonged bioactivity in the field. Prof. Dr. Filippo Maggi Dr. Giovanni Benelli Guest Editor

Monte Carlo Uncertainty Quantification Using Quasi-1D SRM Ballistic Model

Compactness, reliability, readiness, and construction simplicity of solid rocket motors make them very appealing for commercial launcher missions and embarked systems. Solid propulsion grants high thrust-to-weight ratio, high volumetric specific impulse, and a Technology Readiness Level of 9. However, solid rocket systems are missing any throttling capability at run-time, since pressure-time evolution is defined at the design phase. This lack of mission flexibility makes their missions sensitive to deviations of performance from nominal behavior. For this reason, the reliability of predictions and reproducibility of performances represent a primary goal in this field. This paper presents an analysis of SRM performance uncertainties throughout the implementation of a quasi-1D numerical model of motor internal ballistics based on Shapiro's equations. The code is coupled with a Monte Carlo algorithm to evaluate statistics and propagation of some peculiar uncertainties from design data to rocker performance parameters. The model has been set for the reproduction of a small-scale rocket motor, discussing a set of parametric investigations on uncertainty propagation across the ballistic model

Analysis of food supplement with unusual raspberry ketone content

In recent years food supplement market increased constantly, including slimming products and against obesity. The case of rasberry ketone (RK) is here reported. HPTLC and HPLC-DAD analyses on a marketed product containing raspberry juice evidenced an abnormal quantity of RK, not in accordance with the juice natural content. The reported data confirm the need of adequate controls on marketed food supplements and the necessity of a complete adherence between labelling and real constitution of the product. Practical Applications: Determining the natural origin and assuring the consumers' safety for raspberry-based food supplement