Psychosocial Stress-Induced Analgesia: An Examination of Effects on Heat Pain Threshold and Tolerance and of Neuroendocrine Mediation

Stress-induced analgesia (SIA) is an adaptive response of reduced nociception following demanding acute internal and external stressors. Although a psychobiological understanding of this phenomenon is of importance for stress-related psychiatric and pain conditions, comparably little is known about the psychobiological mechanisms of SIA in humans. The aim of this study was to investigate the effects of acute psychosocial stress on heat pain perception and its possible neuroendocrine mediation by salivary cortisol levels and α-amylase activity in healthy men. Employing an intra-individual assessment of heat pain parameters, acute psychosocial stress did not influence heat pain threshold but significantly, albeit slightly, increased heat pain tolerance. Using linear mixed-model analysis, this effect of psychosocial stress on heat pain tolerance was not mediated by increases of salivary cortisol and state anxiety levels or by the activity of α-amylase. These results show that while psychosocial stress is selectively analgesic for heat pain tolerance, this observed effect is not mediated by stress-induced increases of salivary cortisol and α-amylase activity, as proxies of both the hypothalamus-pituitary-adrenal axis and the autonomic nervous system activation

Modelling an Acoustically Perturbed Rocket Engine Combustion Chamber with Cryogenic Propellant Injection

An experimental combustor, dubbed BKH, has been developed at DLR Lampoldshausen to investigate combustion instability phenomena. The combustor operates with cryogenic liquid oxygen and hydrogen propellants at supercritical pressure conditions analogous to real rocket engines. The BKH combustor has been modelled using a specially developed version of the DLR TAU code with real gas capabilities for supercritical injection. The TAU code CFD results are compared with optical data recorded during BKH experiments. The numerical flame and liquid oxygen distributions match experimental observations. The acoustic field inside the BKH combustor has also been calculated separately with an acoustic solver that uses a realistic acoustic property distribution from the CFD calculations. The resonant modes are successfully predicted using the acoustic solver

Experimental and numerical study of transcritical oxygen-hydrogen rocket flame response to transverse acoustic excitation

The response of a transcritical oxygen-hydrogen flame to transverse acoustic velocity was investigated using a combination of experimental analyses and numerical modelling. The experiment was conducted on a rectangular rocket combustor with shear coaxial injectors and continuously forced transverse acoustic field. Simultaneous high-speed shadowgraph and filtered OH* radiation images were collected and reduced using dynamic mode decomposition in order to characterise the flame response to the acoustic disturbance. CFD modelling of a representative single injector under forcing conditions was carried out to gain insights into the three-dimensional features of the reacting flow field. Invisible in the 2D projection, the model reveals that the excited LOX jet develops into a flattened and widened structure normal to the imposed acoustic velocity. The comparison of co-located structures allowed features in the imaging to be attributed to the deformation and transverse displacement of lower density oxygen surrounding the denser liquid oxygen core by the transverse acoustic velocity

Large Eddy Simulation of Flashing Cryogenic Liquid with a Compressible Volume of Fluid Solver

For the development of new upper orbit thrusters with cryogenic propellants, it is important to understand the dynamics of oxidizer and fuel injection at near vacuum conditions before ignition. Due to the low ambient pressure with respect to the saturation pressure at the injection temperature, the propellants enter a superheated state and evaporate rapidly. This process is called flash evaporation. To simulate such a flashing cryogenic jet a compressible multiphase solver is developed in OpenFOAM. The homogeneous relaxation model (HRM) is chosen to model the phase change. For solving this multiphase problem, a one-fluid approach which solves for the mixture properties and phase fraction is selected. For the equation of state, the open source library CoolProp is used to calculate density, enthalpy and the saturation conditions. Further, the numerical methods to solve and capture the supersonic multiphase flow with a Volume of Fluid (VoF) method is described. The transition from mechanical break up to fully flashing spray and the change from subsonic to supersonic flow is investigated in detail. The numerical results are validated with experiments conducted at DLR Lampoldshausen which provide shadowgraph images. As a first approximation to fuel-oxidizer mixing, cryogenic nitrogen jet experiments at the DLR test bench M3.3 in Lampoldshausen are made and numerically investigated with large eddy simulations. It is noted that the flashing jet becomes supersonic and forms a shock shortly after the nozzle exit. This occurs despite the velocity being lower than the sonic velocities associated with each individual pure phase. The results show that the HRM model can predict the onset of the partial flashing flow, however fully flashing jet with 180 degree spray angle cannot be predicted with standard coefficients of the HRM model

High DeltaV Solid Propulsion System fort Small Satellites

Safe propulsion for orbit adjustment and de-orbit is a critical capability for the deployment of large constellations of small satellites. ‘Rideshare,’ in which a CubeSat or other small satellite is provided a ride to orbit on a large launch vehicle, is the primary method of getting CubeSats into orbit; however, when riding as a secondary payload, there is little or no influence on the final orbit. Therefore, a high Δ V, high thrust propulsion system is an enabling technology permitting the CubeSat to be redirected to a desired orbit, after the initial insertion. End of life deorbiting of small satellites is necessary to reduce the presence of space junk and this will require the use of compact, high performing thrusters. However, there is a catch-22 in that one needs a high-Δ V propulsion to fully realize the potential of small satellites, but as secondary payloads, the risk to the main payload of lifting a highly hazardous propulsion system on a rideshare often precludes it. Given the short lifetime (often the end of a university student project) and often small budgets of these very small satellites, getting to the target orbit in a short time is important to enable basic scientific missions. LANL’s segmented solid-fuel, solid-oxidizer system is uniquely non-detonable and safe, making it the perfect solution. The LANL Segregated Fuel-Oxidizer System (SFOS) is a combination of novel materials that allow for a radically new propulsion design that is unique in its high level of safety and energy density. Inheriting from the development of high-nitrogen/high-hydrogen energetics at LANL that contain little or no oxygen, a segregated tandem system has been designed. The decomposition of solid energetic material provides fuel-rich gasses that are oxidized downstream by reaction with a solid oxidizer grain. Because the fuel and the oxidizer are separated until combustion and both are relatively (or completely) insensitive to shock, the chance of accidental detonation or initiation of the rocket is dramatically reduced. The fuel used is non-detonable and decomposes into gaseous products such as hydrogen and nitrogen upon ignition. Additional safety is gained as the oxidizer doesn’t burn in the absence of fuel and heat. Fuel rich products react with the oxidizer in a diffusion flame above the surface of the oxidizer grain. Thermochemical analysis predicts rocket performances in excess of standard solid propellants and hypergolic propellants. With a theoretical characteristic exhaust velocity (c*) of approximately 1600 m/s and vacuum specific impulse (Isp ) as high as 260 s, this new propulsion system is a competitive, safe, low-cost, non-toxic alternative to existing hydrazine based and composite solid propulsion systems. In this work, we will discuss the fundamental research in the development of this propulsion system, and its integration on to an existing LANL CubeSat platform in arrays to provide multiple orbital maneuvers. Current efforts are focused on the design of 12-50 mm diameter motors, but like any conventional solid propellant system, the size is scalable to different dimensions depending on mission requirements