Multiple-scale thermo-acoustic stability analysis of a coaxial jet combustor

In this paper, asymptotic multiple-scale methods are used to formulate a mathematically consistent set of thermo-acoustic equations in the low-Mach number limit for linear stability analysis. The resulting sets of nonlinear equations for hydrodynamics and acoustics are two-way coupled. The coupling strength depends on which multiple scales are used. The double-time-double-space (2T-2S), double-time-single-space (2T-1S) and single-time-double-space (1T-2S) limits are revisited, derived and linearized. It is shown that only the 1T-2S limit produces a two-way coupled linearized system. Therefore this limit is adopted and implemented in a finite-element solver. The methodology is applied to a coaxial jet combustor. By using an adjoint method and introducing the intrinsic sensitivity, (i) the interaction between the acoustic and hydrodynamic subsystems is calculated and (ii) the role of the global acceleration term, which is the coupling term from the acoustics to the hydrodynamics, is analyzed. For the confined coaxial jet diffusion flame studied here, (i) the growth rate of the thermo-acoustic oscillations is found to be more sensitive to small changes in the hydrodynamic field around the flame and (ii) increasing the global acceleration term is found to be stabilizing in agreement with the Rayleigh Criterion.This is the accepted manuscript. The final version is available at http://www.sciencedirect.com/science/article/pii/S1540748916300670

Reward-Related Behavioral Paradigms for Addiction Research in the Mouse: Performance of Common Inbred Strains

The mouse has emerged as a uniquely valuable species for studying the molecular and genetic basis of complex behaviors and modeling neuropsychiatric disease states. While valid and reliable preclinical assays for reward-related behaviors are critical to understanding addiction-related processes, and various behavioral procedures have been developed and characterized in rats and primates, there have been relatively few studies using operant-based addiction-relevant behavioral paradigms in the mouse. Here we describe the performance of the C57BL/6J inbred mouse strain on three major reward-related paradigms, and replicate the same procedures in two other commonly used inbred strains (DBA/2J, BALB/cJ). We examined Pavlovian-instrumental transfer (PIT) by measuring the ability of an auditory cue associated with food reward to promote an instrumental (lever press) response. In a separate experiment, we assessed the acquisition and extinction of a simple stimulus-reward instrumental behavior on a touchscreen-based task. Reinstatement of this behavior was then examined following either continuous exposure to cues (conditioned reinforcers, CRs) associated with reward, brief reward and CR exposure, or brief reward exposure followed by continuous CR exposure. The third paradigm examined sensitivity of an instrumental (lever press) response to devaluation of food reward (a probe for outcome insensitive, habitual behavior) by repeated pairing with malaise. Results showed that C57BL/6J mice displayed robust PIT, as well as clear extinction and reinstatement, but were insensitive to reinforcer devaluation. DBA/2J mice showed good PIT and (rewarded) reinstatement, but were slow to extinguish and did not show reinforcer devaluation or significant CR-reinstatement. BALB/cJ mice also displayed good PIT, extinction and reinstatement, and retained instrumental responding following devaluation, but, unlike the other strains, demonstrated reduced Pavlovian approach behavior (food magazine head entries). Overall, these assays provide robust paradigms for future studies using the mouse to elucidate the neural, molecular and genetic factors underpinning reward-related behaviors relevant to addiction research

Mitochondrial dysfunction and biogenesis: do ICU patients die from mitochondrial failure?

Mitochondrial functions include production of energy, activation of programmed cell death, and a number of cell specific tasks, e.g., cell signaling, control of Ca2+ metabolism, and synthesis of a number of important biomolecules. As proper mitochondrial function is critical for normal performance and survival of cells, mitochondrial dysfunction often leads to pathological conditions resulting in various human diseases. Recently mitochondrial dysfunction has been linked to multiple organ failure (MOF) often leading to the death of critical care patients. However, there are two main reasons why this insight did not generate an adequate resonance in clinical settings. First, most data regarding mitochondrial dysfunction in organs susceptible to failure in critical care diseases (liver, kidney, heart, lung, intestine, brain) were collected using animal models. Second, there is no clear therapeutic strategy how acquired mitochondrial dysfunction can be improved. Only the benefit of such therapies will confirm the critical role of mitochondrial dysfunction in clinical settings. Here we summarized data on mitochondrial dysfunction obtained in diverse experimental systems, which are related to conditions seen in intensive care unit (ICU) patients. Particular attention is given to mechanisms that cause cell death and organ dysfunction and to prospective therapeutic strategies, directed to recover mitochondrial function. Collectively the data discussed in this review suggest that appropriate diagnosis and specific treatment of mitochondrial dysfunction in ICU patients may significantly improve the clinical outcome

Adjoint sensitivity analysis of thermo-acoustic/hydrodynamic instabilities in turbulent combustion chambers

In this paper, we de ne a mathematically consistent set of thermo-acoustic equations via asymptotic multiple scale methods in the low-Mach number limit. The nal thermoacoustic equations consist of reacting low-Mach number (LMN) equations for hydrodynamic phenomena and acoustic (AC) equations. The two sets of equations are two-way coupled. The coupling terms depend on which multiple scales are used. We derive and discuss the coupling terms for three distinct limits: double-time-double-space (2T-2S); double-time-single-space (2T-1S); and single-time-double-space (1T-2S). We linearize the thermo-acoustic equations around the mean ow, which is obtained by time averaging Large-Eddy simulations. We show that only 1T-2S provides a two-way coupled linearized system. In the other limits, the coupling from the AC to the LMN is of higher order. We perform global direct and adjoint analysis to identify unstable modes and passivefeedback mechanisms to stabilize/lower the frequency of the oscillation. Preliminary results are shown for a dual-swirl gas turbine combustor and a simpli ed dump combustor

Adjoint sensitivity analysis of thermo-acoustic/hydrodynamic instabilities in turbulent combustion chambers

In this paper, we de ne a mathematically consistent set of thermo-acoustic equations via asymptotic multiple scale methods in the low-Mach number limit. The nal thermoacoustic equations consist of reacting low-Mach number (LMN) equations for hydrodynamic phenomena and acoustic (AC) equations. The two sets of equations are two-way coupled. The coupling terms depend on which multiple scales are used. We derive and discuss the coupling terms for three distinct limits: double-time-double-space (2T-2S); double-time-single-space (2T-1S); and single-time-double-space (1T-2S). We linearize the thermo-acoustic equations around the mean ow, which is obtained by time averaging Large-Eddy simulations. We show that only 1T-2S provides a two-way coupled linearized system. In the other limits, the coupling from the AC to the LMN is of higher order. We perform global direct and adjoint analysis to identify unstable modes and passivefeedback mechanisms to stabilize/lower the frequency of the oscillation. Preliminary results are shown for a dual-swirl gas turbine combustor and a simpli ed dump combustor