Prediction of combustion instability limit cycle oscillations by combining flame describing function simulations with a thermoacoustic network model

Accurate prediction of limit cycle oscillations resulting from combustion instability has been a long-standing challenge. The present work uses a coupled approach to predict the limit cycle characteristics of a combustor, developed at Cambridge University, for which experimental data are available (Balachandran, Ph.D. thesis, 2005). The combustor flame is bluff-body stabilised, turbulent and partially-premixed. The coupled approach combines Large Eddy Simulation (LES) in order to characterise the weakly non-linear response of the flame to acoustic perturbations (the Flame Describing Function (FDF)), with a low order thermoacoustic network model for capturing the acoustic wave behaviour. The LES utilises the open source Computational Fluid Dynamics (CFD) toolbox, OpenFOAM, with a low Mach number approximation for the flow-field and combustion modelled using the PaSR (Partially Stirred Reactor) model with a global one-step chemical reaction mechanism for ethylene/air. LES has not previously been applied to this partially-premixed flame, to our knowledge. Code validation against experimental data for unreacting and partially-premixed reacting flows without and with inlet velocity perturbations confirmed that both the qualitative flame dynamics and the quantitative response of the heat release rate were captured with very reasonable accuracy. The LES was then used to obtain the full FDF at conditions corresponding to combustion instability, using harmonic velocity forcing across six frequencies and four forcing amplitudes. The low order thermoacoustic network modelling tool used was the open source OSCILOS (http://www.oscilos.com). Validation of its use for limit cycle prediction was performed for a well-documented experimental configuration, for which both experimental FDF data and limit cycle data were available. The FDF data from the LES for the present test case was then imported into the OSCILOS geometry network and limit cycle oscillations of frequency 342 Hz and normalised velocity amplitude of 0.26 were predicted. These were in good agreement with the experimental values of 348 Hz and 0.21 respectively. This work thus confirms that a coupled numerical prediction of limit cycle behaviour is possible using an entirely open source numerical framework

Relationship Between Physical Conditioning and Plasma High Density Lipoprotein-Cholesterol Concentration

Five subjects (three females and two males) took part in an exercise regimen in order to determine if aerobic exercise results in an increase in high-density lipoprotein-cholesterol levels (HDL-C) in the plasma. The exercise regimen consisted of running three miles a day, five days per week for six months. Running speed was at such a pace that the subjects attained a minimum of 60% of their maximal heart rate reserve (MHRR). Before the training program began the following parameters were measured in all of the subjects: height, weight, percent body fat, maximal oxygen consumption (Vₒ₂ max), vital capacity, resting heart rate, resting blood pressure, HDL-C, plasma triglycerides (TG), and plasma cholesterol (TC). These same measurements were retaken every two months and at the conclusion of the study. The exercise protocol produced significant changes in Vₒ₂ max and resting heart rate. None of the other parameters were significantly changed. The results of this study have shown that aerobic exercise does not cause significant changes in HDL-C levels

A semi-analytical model for the acoustic impedance of finite length circular holes with mean flow

The acoustic response of a circular hole with mean flow passing through it is highly relevant to Helmholtz resonators, fuel injectors, perforated plates, screens, liners and many other engineering applications. A widely used analytical model [M. S. Howe. On the theory of unsteady high Reynolds number flow through a circular aperture, Proc. of the Royal Soc. A. 366, 1725 (1979), 205223] which assumes an infinitesimally short hole was recently shown to be insufficient for predicting the impedance of holes with a finite length. In the present work, an analytical model based on the Green’s function method is developed to take the hole length into consideration for “short” holes. The importance of capturing the modified vortex noise accurately is shown. The vortices shed at the hole inlet edge are convected to the hole outlet and further downstream to form a vortex sheet. This couples with the acoustic waves and this coupling has the potential to generate as well as absorb acoustic energy in the low frequency region. The impedance predicted by this model shows the importance of capturing the path of the shed vortex. When the vortex path is captured accurately, the impedance predictions agree well with previous experimental and CFD results, for example predicting the potential for generation of acoustic energy at higher frequencies. For “long” holes, a simplified model which combines Howe’s model with plane acoustic waves within the hole is developed. It is shown that the most important effect in this case is the acoustic non-compactness of the hole

Pharm.D. students\u27 opinions on peer mentoring

Background A peer-to-peer student mentoring pilot program was implemented at the University of Rhode Island (URI) College of Pharmacy (COP) in the Fall of 2013, to supplement a well-established, formal, faculty-to-student mentoring program for students beginning their first professional (P1) year. This added one or two students in their third professional (P3) year to each advising group. The goals of the program were to improve academic success for P1 students, enhance leadership, and promote strong communication and camaraderie within the COP. Objective This study aims to evaluate differences in opinions of the previous faculty-mentored (FM) classes (P3 class and P4 class) compared to those with a peer mentor (the current P1 class and P2 class). Methods A 16-question survey was electronically administered to all URI pharmacy students during the Fall of 2014. The responses to the questions evaluated demographics, students’ level of professional involvement, and students’ attitudes towards their mentoring experiences. Information was stratified based on the students’ mentoring program during their P1 year. The FM group (class of 2015 and 2016; P4 and P3, respectively) only experienced a formal faculty-to-student mentoring program and their cumulative responses are compared to the classes of 2017 and 2018 (P2 and P1, respectively), those with the peer-to-peer student mentoring program added to faculty mentoring (PFM). Descriptive statistics were used to compare students’ opinions on confidence, preparedness, time management skills, and level of support provided by faculty and peer mentors in the beginning of their first professional year. This study was designated exempt by the URI Institutional Review Board (IRB). Results Most students were 18-23 years old, lived off-campus, and were female. Overall, students in the PFM group reported being more realistic about the time commitment required during P1 year, more comfortable to reaching out to both faculty mentors and other students for help, having more opportunity to interact with students farther in the PharmD program, and more outreach from faculty mentors. Students in the PFM group reported feeling more anxious than the FM group (75% vs 51%, respectively) and less balanced regarding academic life and social life, organization membership, and extracurricular activities (48% vs 55%, respectively). Discussion/Conclusion PharmD students that had a peer mentor in addition to a faculty mentor reported being more realistic about the time commitment required during P1 year, more comfortable to reaching out to both faculty mentors and other students for help, having more opportunity to interact with students farther in the PharmD program, and more outreach from faculty mentors. Limitations to the study include: recall bias for FM group students and their corresponding experience compared to PFM group students, and P1 students of the PFM group only experienced a few months of the program. Areas of research for the peer mentoring program include anxiety lowering strategies, creating more opportunities to meet peer mentors, and providing advice or activities to balance responsibilities

Microscopic Anatomy of the Digestive Tract of the White Amur, Ctenopharyngodon idella Val.

The digestive tract of the amur is like that of other vertebrates in that it is composed of four layers: mucosa, submucosa, muscularis externa and serosa. The mucosa is composed of pseudostratified epithelial tissue and an extremely thin lamina propria and muscularis mucosa. Goblet cells are found throughout this layer of the gut, being most numerous In the posterior part. The submucosa is composed of dense irregular connective tissue. The muscularis externa consists of an inner and an outer layer of smooth muscle fibers. However, in the esophageal region this layer also contains some striated muscle. The serosa is composed of a thin layer of dense irregular connective tissue and a single layer of simple squamous mesothelium