An experimental study was conducted on the response of V-shaped and M-shaped premixed flames to external acoustic excitation. Low emission premixed combustors with anchored V-flames are susceptible to combustion instabilities. V-flames attach to an anchoring rod at the centre of the burner, whereas M-flames attach to the anchoring rod as well as the burner rim. This is in contrast to conical flames which are anchored only on the burner rim. As a consequence, V-and M-shaped flames are more sensitive to external flow perturbations. In the present study, a mixture of propane-air was used. The mixture equivalence ratio was changed to determine the stability range of V-and M-shaped premixed flames. The results indicated that M-shaped flames have a narrower stability range compared to that of V-flames. This limited the equivalence ratios range for acoustic excitation experiments. In order to study the flame response to external acoustic excitations, a loud speaker was placed upstream of the flame to generate acoustic waves in a certain range of frequencies. Pressure fluctuations caused by the acoustically excited flame were measured by a microphone placed downstream of the burner. Flame imaging was done with a CCD high speed camera during acoustic excitations. These images were used for flame response determination. Image processing was accomplished using the MATLAB software to obtain the amplitude and phase of the flame response. Variations of the flame shape and the intensity of light emitted by the flame were examined during a period of excitation for various values of equivalence ratios and flow rates. The results indicated that the vortex shedding and roll-up due to the velocity perturbations play an important role on the flame response. The phase response of flames evolves quasi-linearly with excitation frequency, indicating a certain time delay for the fluctuations to reach the flame surface. Also, in a certain range of excitation frequency, the flame gain response exhibits more sensitivity to variation of the equivalence ratio. Observations of the V-flame behavior during a period of excitation have led to determination of the effects of nonlinear parameters on the flame response.

In the present study, the flame response and the effect of equivalence ratio and inlet temperature on the flame response are numerically investigated using Weller flamelet combustion and LES turbulent models. The results show that with increasing excitation amplitude at a constant frequency, theheat release ratio increases; the increment is smaller at higher frequencies. Due to the combustor geometry, two recirculating zones are formed. Any change in the amplitude and frequency can affect these recirculation zones, especially the central recirculation zone. At the low frequencies (below 50Hz), increasing the excitation amplitude affects flame transfer functioninconsiderably, because of no influence of the recirculation zoneson the heat release. At higher frequencies, an increase in the amplitude has a more influence on value of flame transfer function. It is shown that by increasing the amplitude, up to frequency of 140 Hz, the phase of flame transfer function slightly reduced, while this is intensified with increasing the equivalence ratio or flame inlet temperature. Furthermore, by increasing the equivalence ratio or inlet temperature of the flame, heat release ratio and the flame transfer function are reduced.

Background and Aim: The necessity of maintaining effective cognitive function for the employees of ships is much more than for sedentary and low-risk jobs. The present study was conducted with the aim of comparing the cognitive performance before and after presenting different levels of noise in the employees of light vessels operating in the Persian Gulf. Methods: The current causal-comparative study was conducted in the first half of 1400 in the southern region of the country. The statistical population of the present study was all the employees of light vessels active in the Persian Gulf, and 15 people were placed in three groups with different noise ranges using the available sampling method. Posner's visual attention test was performed in the pre-test for all sample subjects. Then people of different buoyancy classes were then exposed to different noise ranges, and immediately after receiving the noise, the participants' Posner visual attention test was taken again. Data were analyzed using SPSS software. Results: The mean age of the subjects was 23.94 with a standard deviation of 3.25. The results showed that all components of the cognitive function of watchtower staff are different in both situations before and after exposure to sound. The results showed that the correct time response and the number of correct responses of individuals after the presentation of noise had a significant decrease and the reaction of the wrong time and the number of incorrect responses increased significantly. Conclusion: The results showed that exposure to acoustic vibrations at different frequencies affects selective attention and weakens the reaction time of correct responses.

Hydrogen plays a key role in reducing reliance on fossil fuels in various energy production systems. While its use offers a promising alternative to carbon-based fuels, it presents significant challenges. The transition from carbon-rich hydrocarbons to hydrogen-based energy systems requires a thorough understanding of its dynamic effects. This study investigates the impact of hydrogen addition on the dynamic behavior of a partially premixed methane-air counterflow flame through experimental analysis and one-dimensional numerical simulations. The study examines the steady-state flame structure and response without acoustic excitation, assessing the influence of added hydrogen on the flame's heat release rate and thermal region thickness. Employing an acoustically excitable counterflow flame burner setup, the effects of increasing hydrogen content on methane-air flames are explored, and their dynamic response is analyzed using the CH* radical chemiluminescence method. The findings reveal that while hydrogen addition reduces the intensity of CH* radical emission in the absence of acoustic excitation, exposure to acoustic waves amplifies oscillations in the heat release rate and CH* radical emission intensity. This underscores the enhanced flame response function with hydrogen addition. 

Introduction: The hemodynamic response function (HRF), reflecting cerebral blood flow in response to neural activity, plays a crucial role in the analysis of the brain data obtained by functional magnetic resonance imaging (fMRI). In this study, a comparison of two statistical models was performed to evaluate HRF for block design.Materials and Methods: fMRI data from 3 patients with brain tumor were taken using a 3 Tesla scanner. Analysis of fMRI data was performed by the SPM12 toolbox in MATLAB software. The AIC, SBC and MSE indices were used to select the most convenient HRF mode.Results: Based on the simulation data, HRF estimated by canonical HRF model plus time derivations (TD) model was more consistent with simulated HRF. These models were evaluated on real data. The MSE, AIC and SBC indices were obtained for TD-logistic model (IL) models (for TD and logis tic IL models; 0.052, 1235.1, 1223.9 and 0.068, -1091.5, 1049.2, respectively). Based on the average values of T, W, H and model selection indicators, IL model for estimating HRF in healthy regions of the brain and brain tumor is a more appropriate approach.Conclusion: The results of the present study can be helpful for the evaluation and diagnosis of HRF in high-metabolism points. Using the IL model to estimate HRF in the block design may lead to a better estimation of HRF and thus maintaining patient health and quality of life after surgical treatment and non-surgical medical procedures.

This study investigates the stability of a surface flame burner using a photodiode and data acquisition system. The light intensity fluctuations were measured by the photodiode and, using fast Fourier transform, they were transferred from the temporal to the frequency space. To illustrate the dynamic behavior of premixed flames, flames are divided into two regions of cellular flames and surface flames. This classification is dependent on the flow rate and the equivalence ratio. In surface flames, as the flow rate increases, the oscillation frequency also increases because the hot burned gas velocity increases. In cellular flames, as the flow rate increases, oscillation frequency decreases. At identical flow rates, the sharp decrease in the oscillation frequency indicates the appearance of cellular flames so we can find the transition from the surface flame to the cellular flame. At a constant flow rate, with an increase in the equivalence ratio, there is no increase in the oscillation frequency, the transition from the cellular flame to the surface flame occurs. The initiation of the transition from the cellular flame to the surface flame occurs at flow rates of 1. 1, 1. 2, 1. 3, 1. 4, 1. 5, 1. 6 m3/h and at equivalence ratios of 0. 6, 0. 62, 0. 62, 0. 64, 0. 66, and 0. 67, respectively. The location of the transition corresponds to the start of the liftoff zone based on the image processing. This research is innovative because it is possible to evaluate flame stability using a non-intrusive method without disturbing the flame shape and damaging the flame regime.