Abstract
This work analyses the isothermal flow field of a research burner exploiting both swirl and radially staged combustion air. The burner is composed of two coaxial co-rotating swirling jets, ...and the swirl level of the two jets can be controlled independently of each other. The influence of the swirl levels on the flow field is experimentally investigated under isothermal conditions using the Stereo-PIV technique, and the results evidence significant differences in the mean flow field at the different swirl levels. The vortex breakdown occurs in all the investigated cases, except for the combination of the lowest outer swirl level and the intermediate inner swirl level. Besides, the central recirculating flow region shape and size are affected by the momentum ratio and swirl level of the central jet. When the swirl intensities of the two coaxial jets are at their maximum, LDV measurements evidence on the burner axis tangential velocity fluctuations at a frequency of about 86 Hz; a POD-based phase average of the PIV maps allows recognizing the presence of a Precessing Vortex Core (PVC) which induces a periodic merging of the two jets. Those results can be of significance in the design of double swirl burners and for the control of the combustion process. Nevertheless, further tests are required to extend the current analysis to combustion conditions.
The Background Orientend Schlieren (BOS) is a line of sight optical technique that exploits light refraction arising in inhomogeneous density field to visualize or either measure density gradients. ...The working principle of BOS is quite simple: a background patter appears distorted when observed through an optical inhomogeneous media, by comparing the distorted and undistorted images the apparent local displacement of the background pattern can be measured. The images comparison is carried out using either cross-correlation or optical flow techniques. In the framework of geometric optics and for a 2D refractive index field the measured displacements is proportional to the refractive index gradient. When applicable, the Gladstone-Dale relationship provides the link between the refractive index and the fluid density. The uncertainty in the measured displacements affects the qualitative and quantitative results extracted from BOS images. Spatial and temporal filtering techniques can reduce the uncertainty at the expenses of the spatial and the temporal resolutions. This work describes a modified BOS technique, named Enhanced BOS (EBOS), which is able to reduce the displacement uncertainty without using any spatial or temporal filter. The EBOS technique uses N undistorted images of a grey-scale background pattern taken at slightly different potions, the N reference images are paired with a single distorted background image. Eventually displacement maps obtained from the N image couples are averaged together. The mean displacement map is an improved estimate of the actual displacement field. The EBOS technique can also be used with optical flow techniques anyhow we limited our investigation to image analysis based on cross-correlation technique. The paper reports the results obtained by applying EBOS and BOS techniques to the same test case. The comparison evidence the capability of EBOS to reduce displacement uncertainty respect to BOS by using a limited number of undistorted background images. EBOS and BOS techniques achieve almost the same uncertainty when the number of particles contained in an interrogation area is high, thus EBOS is most advantageous to use when small interrogation area are required.
•Automatic detection of flow structure within schlieren images of supersonic flows.•Accurate Mach number measurements in moderately supersonic flows.•Accurate measurement of position and slope of ...simple waves and oblique shocks.•Quantitative application of schlieren technique in non-ideal compressible flows.•Experimental characterization of highly non-ideal supersonic flows.
This paper presents a technique to automatically detect flow structures recorded in schlieren images of supersonic flows. The method provides position and local slope of the detected lines. Salient flow structures considered are shock waves, expansion fans and Mach waves. If the local flow direction is known, the technique provides local Mach number measurement. Moreover, the peculiarities of schlieren technique make the algorithm suitable for Mach measurements in flows where direct velocity measurements are challenged by difficult insemination and for which calibrated aerodynamic pressure probes are not available. The technique is applied to two test cases. In the first case study, the local Mach number is measured at the axis of a supersonic nozzle operated with siloxane vapor MDM. In the second test case, supersonic flow of MDM was analyzed around a diamond shaped airfoil providing the Mach number upstream/downstream oblique shocks/expansion fans and the slope of oblique shocks/fan edges.
The effects of hydrogen addition on a lean non-premixed natural gas swirl-stabilized flame were investigated. Fuel mixtures containing a volumetric fraction of hydrogen ranging from 0% up to 100% ...were burnt at ambient pressure with swirled air within a quartz chamber in a co-flow configuration. Tests were carried out keeping the sum of the volumetric fuels flow rate constant; thus, the fuel mixture mass flow rate, input thermal power and equivalence ratio decreased as hydrogen fraction was increased.
The use of hydrogen-enriched natural gas mixtures allowed the burner to operate at overall leaner stable conditions as compared to the case of burning natural gas only; however, an increase in soot,
NO
x
and CO has also been observed. The flame structure was analyzed by still-color photographs and laser sheet visualization; laser Doppler velocimetry (LDV) and thermocouples were used to analyze the flow field and temperature distributions. Measurements of CO and
NO
x
were obtained by probing the exhaust gases and using gas analyzers, while soot was directly identified by the yellow luminosity in the flame photographs and estimated through spectral analysis of spontaneous flame emission.
The present results revealed that hydrogen addition produced: (1) a shorter and narrowed blue flame located closer to the burner head, (2) a central highly luminous yellow plume extending above the visible blue zone, (3) a deeper fuel jet penetration inside the recirculating bubble, and (4) a monotonic increase of both CO and
NO
x
emissions for
H
2
fractions ranging from 0% up to 80%. The latter behavior may be due to quenching of CO oxidation, related to the reduction in the size of the reaction zone, while the temperature increase observed near the flame front and close to the burner head promote the thermal
NO
x
production.
The experimental results revealed that hydrogen addition extended the stability limits of a conventional natural gas non-premixed burner and evidenced a significant change in both the flame structure and the flow field. Improved fuel mixture injection strategies should be explored to improve mixing and minimize pollutant production, without affecting flame stability.
Adolescents are particularly vulnerable to inadequate provision of mental health and addictions care, as services have been traditionally conceptualized to serve the needs of children or adults. ...Additionally, rural communities have been largely excluded from research investigating mental healthcare access and exhibit unique barriers that warrant targeted interventions. Finally, perspectives from the target population will be most important when understanding how to optimize adolescent mental health and addictions care. Therefore, the purpose of this study was to identify what adolescents in a rural town perceive as barriers to accessing mental health services. We conducted a cross-sectional survey study with high school students to generate ranked lists of the top perceived individual-level, community-level, and overall barriers. A total of 243 high school students responded to the survey. Perceived barriers were predominantly at the community level. Overall, the top barriers reported were a lack of awareness and education regarding mental health, resources, and the nature of treatment. Students who had previously accessed mental health services identified primary barriers related to mental health professionals, whereas students who had not accessed care reported fear and uncertainty as primary barriers. Modifiable community-level factors related to (1) mental health literacy and (2) mental healthcare professionals were identified by adolescents as the main perceived barriers to accessing mental health and addiction services in a rural town. The findings of this preliminary study should inform intervention strategies and further rigorous research for this traditionally underserved target population.
Anthropogenic emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) may affect concentration levels and composition of biogenic secondary organic aerosols (BSOA) through photochemical reactions ...with biogenic organic precursors to form organosulfates and nitrooxy organosulfates. We investigated this influence in a field study from 19 May to 22 June, 2011 at two sampling sites in Denmark. Within the study, we identified a substantial number of organic acids, organosulfates and nitrooxy organosulfates in the ambient urban curbside and semi-rural background air. A high degree of correlation in concentrations was found among a group of specific organic acids, organosulfates and nitrooxy organosulfates, which may originate from various precursors, suggesting a common mechanism or factor affecting their concentration levels at the sites. It was proposed that the formation of those species most likely occurred on a larger spatial scale, with the compounds being long-range transported to the sites on the days with the highest concentrations. The origin of the long-range transported aerosols was investigated using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model in addition to modeled emissions of related precursors, including isoprene and monoterpenes using the global Model of Emissions of Gases and Aerosols from Nature (MEGAN) and SO2 emissions using the European Monitoring and Evaluation Program (EMEP) database. The local impacts were also studied by examining the correlation between selected species, which showed significantly enhanced concentrations at the urban curbside site and the local concentrations of various gases, including SO2, ozone (O3), NOx, aerosol acidity and other meteorological conditions. This investigation showed that an inter-play of the local parameters such as the aerosol acidity, NOx, SO2, relative humidity (RH), temperature and global radiation seemed to affect the concentration level of those species, suggesting the influence of aqueous aerosol chemistry. The local impacts, however, seemed minor compared to the regional impacts. The total concentrations of organosulfates and nitrooxy organosulfates, on average, contributed to approximately 0.5–0.8% of PM1 mass at the two sampling sites.
To assess responsive neurostimulation (RNS) efficacy in pediatric patients with drug-resistant epilepsy, comparing response (≥ 50% reduction in seizure frequency) rates between patients with two or ...fewer seizure foci and those with multifocal or generalized epilepsy. This study seeks to address the gap in knowledge regarding RNS effectiveness in pediatric populations.PURPOSETo assess responsive neurostimulation (RNS) efficacy in pediatric patients with drug-resistant epilepsy, comparing response (≥ 50% reduction in seizure frequency) rates between patients with two or fewer seizure foci and those with multifocal or generalized epilepsy. This study seeks to address the gap in knowledge regarding RNS effectiveness in pediatric populations.A systematic review and meta-analysis included data from PubMed, Embase, and Web of Science through November 2023, including 17 retrospective studies and a case series of 24 patients from our practice for a total of 105 aggregated patients. The inclusion criteria of patients were age ≤ 18 and diagnosis of DRE. Exclusion criteria were nonhuman subjects and cases where RNS was not utilized to treat DRE. Study inclusion criteria were detailing the use of RNS and comparing patients with ≤ 2 foci with other focalities. Study exclusion criteria were failure to specify RNS lead placement or type of epilepsy. The risk of bias was assessed using the ROBINS-I tool for all non-randomized studies. Effect sizes and variances were aggregated to provide a comprehensive measure of RNS efficacy, and heterogeneity among the studies was assessed using I2 statistics and Cochran's Q test to evaluate the consistency of the findings. Statistical analyses were conducted using IBM SPSS. We analyzed demographics, epilepsy history, treatment outcomes, and RNS details using descriptive and inferential statistics, including Wilcoxon-Mann-Whitney, Fisher's exact, and chi-squared tests. This systematic review was not registered.METHODSA systematic review and meta-analysis included data from PubMed, Embase, and Web of Science through November 2023, including 17 retrospective studies and a case series of 24 patients from our practice for a total of 105 aggregated patients. The inclusion criteria of patients were age ≤ 18 and diagnosis of DRE. Exclusion criteria were nonhuman subjects and cases where RNS was not utilized to treat DRE. Study inclusion criteria were detailing the use of RNS and comparing patients with ≤ 2 foci with other focalities. Study exclusion criteria were failure to specify RNS lead placement or type of epilepsy. The risk of bias was assessed using the ROBINS-I tool for all non-randomized studies. Effect sizes and variances were aggregated to provide a comprehensive measure of RNS efficacy, and heterogeneity among the studies was assessed using I2 statistics and Cochran's Q test to evaluate the consistency of the findings. Statistical analyses were conducted using IBM SPSS. We analyzed demographics, epilepsy history, treatment outcomes, and RNS details using descriptive and inferential statistics, including Wilcoxon-Mann-Whitney, Fisher's exact, and chi-squared tests. This systematic review was not registered.Seventeen retrospective studies and a single-institution case series, encompassing 105 pediatric patients, were analyzed. Effect sizes and confidence intervals were calculated to quantify treatment effects. Analyses revealed that RNS reduces seizure frequency across a spectrum of pediatric epilepsy syndromes, irrespective of the seizures' focal, multifocal, or generalized origins. The effectiveness of RNS was not influenced by the patient's sex, age at epilepsy onset, or presence of neurological and psychiatric comorbidities. Prior vagus nerve stimulation surgery and the presence of an epileptic syndrome were factors associated with a lower likelihood of near-complete seizure remission with RNS, underscoring the complexities of treating patients with generalized epilepsies or previous interventional failures. The necessity of further research into individualized surgical strategies for patients was underscored by the mixed results of comparisons of electrode characteristics with responder rates. Limitations of our study include its reliance on retrospective studies, which introduces potential bias and limits the ability to infer causality.RESULTSSeventeen retrospective studies and a single-institution case series, encompassing 105 pediatric patients, were analyzed. Effect sizes and confidence intervals were calculated to quantify treatment effects. Analyses revealed that RNS reduces seizure frequency across a spectrum of pediatric epilepsy syndromes, irrespective of the seizures' focal, multifocal, or generalized origins. The effectiveness of RNS was not influenced by the patient's sex, age at epilepsy onset, or presence of neurological and psychiatric comorbidities. Prior vagus nerve stimulation surgery and the presence of an epileptic syndrome were factors associated with a lower likelihood of near-complete seizure remission with RNS, underscoring the complexities of treating patients with generalized epilepsies or previous interventional failures. The necessity of further research into individualized surgical strategies for patients was underscored by the mixed results of comparisons of electrode characteristics with responder rates. Limitations of our study include its reliance on retrospective studies, which introduces potential bias and limits the ability to infer causality.RNS is a safe and effective treatment in pediatric patients with DRE across demographic, comorbidity, and focality variability. FDA age and focality restrictions, along with patient and physician hesitancy, may be limiting the potential for effective treatment of pediatric DRE with RNS. Prospective randomized trials are recommended to validate these findings.DISCUSSIONRNS is a safe and effective treatment in pediatric patients with DRE across demographic, comorbidity, and focality variability. FDA age and focality restrictions, along with patient and physician hesitancy, may be limiting the potential for effective treatment of pediatric DRE with RNS. Prospective randomized trials are recommended to validate these findings.
► Air staging is applied to swirling flames to reduce nitrogen oxides emissions. ► Full benefits of air staged combustion in swirling flames depend on fuel injection method. ► Radial injection in the ...secondary airflow resulted in a dramatic reduction of NOx. ► Radial injection enables a more efficient and faster centrifugal mixing of reactants.
In the framework of a research program to investigate air staging applied to swirling flames, an experimental investigation aimed at studying pollutant emissions is reported. Staged combustion is accepted as an effective way to reduce nitrogen oxides in gas turbine combustors and, in the present study, is applied to a swirled flame fueled by natural gas, to analyze the potential for further reducing nitrogen oxides emissions in a coaxial, non-premixed combustor under overall lean conditions. The results indicate that the full benefits of air staged combustion in swirling flames depend mainly on the method of fuel injection. The most common method of axial injection of a premixed jet into a co-axial swirling airflow does not realize the required fast mixing. By radial injection of the premixed first stage in the secondary co-axial airflow, more efficient and faster centrifugal mixing is achieved, and hence shorter residence time and higher combustion intensity. This fuel injection strategy results in a more stable flame and dramatic reduction of NOx emissions when the first stage equivalence ratio is approaching the stoichiometric value. Still photographs of the flame and isothermal flow patterns are also reported to help correlate flame morphology and mixing features with nitrogen oxides emission.
The kidney is an organ playing an important role in ion regulation in both freshwater (FW) and seawater (SW) fish. The mechanisms of ion regulation in the fish kidney are less well studied than that ...of their gills, especially at the level of transporter proteins. We have found striking differences in the pattern of Na
+
/K
+
/2Cl
-
cotransporter (NKCC) expression between species. In the killifish kidney, NKCC is apically localized in the distal and collecting tubules and basolaterally localized in the proximal tubules. However, in the SW killifish gill, NKCC is basolaterally co-localized with Na
+
/K
+
-ATPase, whereas in FW, NKCC immunoreactivity is primarily apical, although still colocalized within the same mitochondria-rich cell with basolateral Na
+
/K
+
-ATPase. Rainbow trout kidney has NKCC only in the apical membrane of the distal and collecting tubules in both environments, with no signal being detected in the proximal tubule. On the other hand, in the trout gill, NKCC is found basolaterally in both FW and SW environments. An important observation is that, in the gills of rainbow trout, the trailing edge of the filament possesses mostly Na
+
/K
+
-ATPase-positive but NKCC-negative mitochondria-rich cells, whereas in the region between and at the roots of the gill lamellae, most mitochondria-rich cells exhibit both Na
+
/K
+
-ATPase- and NKCC-positive immunoreactivity. These results suggest that the differential localization of transporters between the two species represents differences in function between these two euryhaline fishes with different life histories and strategies.
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