A characterization of graphs of radius-rr flip-width at most 22

The $r$-flip-width of a graph, for $r\in \mathbb{N}\cup \{\infty\}$, is a graph parameter defined in terms of a variant of the cops and robber game, called a flipper game, and it was introduced by Toru\'{n}czyk [Flip-width: Cops and robber on dense graphs, arXiv:2302.00352]. We prove that for every $r\in (\mathbb{N}\setminus \{1\})\cup \{\infty\}$, the class of graphs of $r$-flip-width at most $2$ is exactly the class of ($C_5$, bull, gem, co-gem)-free graphs, which are known as totally decomposable graphs with respect to bi-joins.Comment: 14 pages, 1 figur

The impact of weight misperception on health-related quality of life in Korean adults (KNHANES 2007–2014): a community-based cross-sectional study

Weight perception, especially misperception, might affect health-related quality of life (HRQoL); however, related research is scarce and results remain equivocal. We examined the association between HRQoL and weight misperception by comparing obesity level as measured by body mass index (BMI) and weight perception in Korean adults

Flame surface properties of neutrally stable premixed flames in isotropic turbulence.

An experimental and theoretical investigation of free turbulent premixed flames propagating in isotropic turbulence at neutrally-stable preferential diffusion conditions is described. Experiments were limited to the wrinkled thin laminar flamelet regime and involved mixtures of hydrogen, air and nitrogen ignited within a fan-stirred combustion chamber. Test conditions included turbulence intensities relative to the laminar flame speed in the range 0-1.6, and turbulence Reynolds numbers in the range 0-4195. Measurements included two-point laser velocimetry, flash schlieren photography and flame tomography. Turbulence properties in the unburned gas were characterized by laser velocimetry. Flame surface statistics measured by flame tomography included mean and r.m.s. fluctuations of the flame radius, the fractal dimensions and turbulent/laminar flame perimeters as a function of time from ignition. Flame surface properties were numerically simulated using a two-dimensional flame propagation and advection algorithm combined with a statistical time series simulation of unburned gas velocities along the flame surface. The simulation provided for mean velocities generated by flame propagation, as well as the probability density functions and temporal and spatial correlations of velocity fluctuations within the unburned gas. For neutral preferential diffusion conditions, measurements showed progressively increasing flame radius fluctuations, flame surface fractal dimensions and turbulent/laminar flame perimeters with increasing mean flame radius. Additionally, the rate of increase of these properties all increased with increased turbulence intensities relative to the laminar flame speed. This implies that models and computations of turbulent premixed turbulent flame properties for free premixed turbulent flames must account for both relative turbulence intensities and the distance or time of propagation from the point of ignition. Simulated flame properties for neutral preferential diffusion conditions duplicated measured trends with respect to relative turbulent intensities and distance or time from the point of ignition. However, the effects of turbulence were underestimated due to the limitations of a two-dimensional simulation.Ph.D.Aerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/105394/1/9124038.pdfDescription of 9124038.pdf : Restricted to UM users only

Preparation and Performance Evaluation of Platinum Barium Hexaaluminate Catalyst for Green Propellant Hydroxylamine Nitrate Thrusters

Spacecraft have monopropellant thruster systems for attitude control in the vacuum of space. Hydroxylamine nitrate is a green propellant that has high performance and low toxicity. Owing to the high adiabatic decomposition temperature of the hydroxylamine nitrate propellant, it is necessary to develop a catalyst with high thermal stability. We used a platinum barium hexaaluminate catalyst for green propellant hydroxylamine nitrate thrusters. Barium hexaaluminate support was prepared by a wet impregnation method and heat treatment. Platinum, the active material, was coated on catalyst supports. The Brunauer–Emmett–Teller specific surface was also investigated. X-ray diffraction and scanning electron microscope imagery were used to confirm the formation of barium hexaaluminate. A hydroxylamine nitrate propellant blended with methanol was used for performance evaluation via firing tests of the thruster. The catalytic decomposition performance of each test was evaluated by calculating the characteristic velocity efficiency using the pressure of the chamber at the end of the catalyst bed and the mass flow rate of the propellant. As the catalyst bed was preheated to 350 °C, the characteristic velocity efficiency was 71.9%. Test results revealed that the platinum barium hexaaluminate catalyst is feasible for a hydroxylamine nitrate thruster

Combustion Characteristics of Multi-Element Swirl Coaxial Jet Injectors under Varying Momentum Ratios

The combustion characteristics of a staged combustion cycle engine with an oxidizer-rich preburner were experimentally studied at different momentum ratios of multi-element injectors. Propellants were simultaneously supplied as a liquid–liquid–liquid system, and an injector was designed in which a swirl coaxial jet is sprayed. The injector burned the propellants in the inner chamber which had a temperature greater than 2000 K. To cool the combustion gas, a liquid oxidizer was supplied to the cooling channel outside the injector. To prevent the turbine blades from melting, the temperature of the combustion gas was maintained below 700 K. To confirm the combustion characteristics at different momentum ratios of the high-temperature combustion gas inside the injector and the low-temperature liquid oxidizer outside the injector, three types of injectors were designed and manufactured with different momentum ratios: MR 3.0, MR 3.3, and MR 3.7. In this study, the results of the combustion test for each type were compared for 30 s. For ORPB-A, a combustion pressure of 18.5 MPaA, fuel mass flow rate of 0.26 kg/s, oxidizer mass flow rate of 15.3 kg/s, and turbine inlet temperature of 686 K were obtained in the combustion stability period of 29.0–29.5 s. The combustion efficiency was 98% for MR 3.0 (ORPB-A), which was superior to that for other momentum ratios. In addition, during the combustion test for MR 3.0, the fluctuations in the characteristic velocity, combustion pressure, and propellant mass flow rate were low, indicating that combustion was stable. The three types of combustion instability were all less than 0.8%, thus confirming that the combustion stability was excellent