Full-coverage film cooling heat transfer study: Summary of data for normal-hole injection and 30 deg slant-hole injection

Heat transfer to a full coverage film cooled turbulent boundary layer over a flat surface was studied. The surface consisted of a discrete hole test section containing 11 rows of holes spaced 5 diameters apart in a staggered array and an instrumented recovery region. Ten diameter spacing was also studied by plugging appropriate holes. Two test sections were used, one having holes normal to the surface and the other having holes angled 30 deg to the surface in the downstream direction. Stanton number data were obtained both in the full coverage region and in the downstream recovery region for a range of blowing ratios, or mass flux ratios, from 0 to 1.3. Initial conditions at the upstream edge of the blowing region were varied from 500 to 5000 for momentum thickness Reynolds number and from 100 to 1800 for enthalpy thickness Reynolds number. The range of Reynolds numbers based on hole diameter and mainstream velocity was 6000 to 22000. Initial boundary layer thicknesses range from 0.5 to 2.0 hole diameters. Air was used as the working fluid. The data were taken for the secondary injection temperature equal to the wall temperature and also equal to the mainstream temperature. Superposition was then used to obtain Stanton number as a continuous function of the injectant temperature. The heat transfer coefficient was defined on the basis of a mainstream-to-wall temperature difference. This definition permits direct comparison of performance between film cooling and transpiration cooling

Ascaroside Signaling Is Widely Conserved among Nematodes

Background: Nematodes are among the most successful animals on earth and include important human pathogens, yet little is known about nematode pheromone systems. A group of small molecules called ascarosides has been found to mediate mate finding, aggregation, and developmental diapause in Caenorhabditis elegans, but it is unknown whether ascaroside signaling exists outside of the genus Caenorhabditis. Results: To determine whether ascarosides are used as signaling molecules by other nematode species, we performed a mass spectrometry-based screen for ascarosides in secretions from a variety of both free-living and parasitic (plant, insect, and animal) nematodes. We found that most of the species analyzed, including nematodes from several different clades, produce species-specific ascaroside mixtures. In some cases, ascaroside biosynthesis patterns appear to correlate with phylogeny, whereas in other cases, biosynthesis seems to correlate with lifestyle and ecological niche. We further show that ascarosides mediate distinct nematode behaviors, such as retention, avoidance, and long-range attraction, and that different nematode species respond to distinct, but overlapping, sets of ascarosides. Conclusions: Our findings indicate that nematodes utilize a conserved family of signaling molecules despite having evolved to occupy diverse ecologies. Their structural features and level of conservation are evocative of bacterial quorum sensing, where acyl homoserine lactones (AHLs) are both produced and sensed by many species of gram-negative bacteria. The identification of species-specific ascaroside profiles may enable pheromone-based approaches to interfere with reproduction and survival of parasitic nematodes, which are responsible for significant agricultural losses and many human diseases worldwide

Communication between oocytes and somatic cells regulates volatile pheromone production in Caenorhabditis elegans

Males of the androdioecious species Caenorhabditis elegans are more likely to attempt to mate with and successfully inseminate C. elegans hermaphrodites that do not concurrently harbor sperm. Although a small number of genes have been implicated in this effect, the mechanism by which it arises remains unknown. In the context of the battle of the sexes, it is also unknown whether this effect is to the benefit of the male, the hermaphrodite, or both. We report that successful contact between mature sperm and oocyte in the C. elegans gonad at the start of fertilization causes the oocyte to release a signal that is transmitted to somatic cells in its mother, with the ultimate effect of reducing her attractiveness to males. Changes in hermaphrodite attractiveness are tied to the production of a volatile pheromone, the first such pheromone described in C. elegans

Mechanical Differences Between Sexes During A Jump Landing

Jump landings are a frequent occurrence in both male and female sports. However, aberrant landing mechanics, such as landing with smaller knee flexion angles (KFA), can increase the likelihood of knee joint injury. Previous research suggests males and females demonstrate different landing mechanics, which could explain the higher incidence of knee injuries in females, such as anterior cruciate ligament (ACL) injury. PURPOSE: The purpose of this study was to compare lower extremity landing biomechanics associated with ACL injury between males and females. We hypothesized that females would land with smaller KFA and greater knee abduction angles (KAA) compared to males. METHODS: Landing biomechanics were assessed in 15 males (23.46±2.75 yrs, 1.77±0.06 m, 77.81±14.01kg) and 15 females (21.24±1.99 yrs, 1.63±0.06 m, 63.15±12.19kg) during a jump landing task. All participants had experience playing sports that required jumping and landing. Separate independent samples t-tests were used to compare KFA at initial contact, knee abduction angle (KAA) at initial contact, peak KFA, and peak KAA between males and females. RESULTS: Males demonstrated larger KFA at initial contact compared to females (16.52±4.55o vs 12.85±4.91o, p=0.04), but smaller KAA at initial contact (3.13±2.07o vs 0.93±052o, po vs 91.88±10.71o, p=0.03) and smaller peak KAA (-2.97±2.0o vs -6.49±4.11o, p=0.004). CONCLUSION: The landing mechanics demonstrated by females may be problematic, as smaller KFA when landing have been associated with higher forces being absorbed, increasing the odds of ACL injury. Furthermore, females also demonstrated greater KAA, which have also been linked with traumatic knee injury. Therefore, females participating in sports involving landing from a jump could benefit from interventions that aim to improve landing kinematics

An Analysis of Horizontal Forces Between Sports

Different sports have various demands that athletes must meet to perform at the requisite level. For example, hockey athletes produce primarily horizontal forces due to skating. However, in basketball, there are a combination of horizontal forces from running and vertical forces from frequent jumping. Therefore, utilizing forces exclusively in one direction as a metric to compare athletes of different sports could provide a limited analysis. PURPOSE: The purpose of this investigation was to compare the relationship between horizontal and vertical forces between athletes who participate in the 4 major sports in the US by using a ratio of horizontal and vertical forces produced, called Fmax ratios. We hypothesized that athletes who move primary horizontally, like hockey players, would have greater Fmax ratios than athletes who participate in sports that involve jumping, like basketball. METHODS: Kinetic data were collected on 28 male athletes (8 baseball, 8 basketball, 6 hockey, 3 football, 22.4±4.53 yrs., 1.86±0.08m, 86.39±8.64kg) who participate in the 4 major US sports. All athletes had their horizontal forces measured using a DynaSpeed MUSCLELAB system. Athletes ran at various %’s of bodyweight using the DynaSpeed, and regression was used to predict peak horizontal forces. To measure vertical forces, athletes performed a countermovement jump on a force platform. Fmax ratios were calculated by dividing peak horizontal force by peak vertical force. A one-way ANOVA was used to compare Fmax ratios between athletes of the 4 major US sports. RESULTS: No differences were found in Fmax ratios between sports (Baseball = 0.22±0.03, Basketball = 0.20±0.02, Hockey = 0.21±0.02, Football = 0.20±0.01, p=0.34). CONCLUSION: Results contradict our hypothesis as no mean differences were found between any sports. Furthermore, an exploratory analysis found no differences in horizontal forces between groups. This suggests that regardless of predominant direction utilized in sport, athletes of different sports still produce the same magnitude of horizontal forces as well as ratios. Future studies that investigate Fmax ratios should aim to measure horizontal and vertical forces simultaneously rather than separately to best capture sport specificity

Turbulent boundary layer on a full-coverage film-cooled surface: An experimental heat transfer study with normal injection

Heat transfer behavior was studied in a turbulent boundary layer with full-coverage film cooling through an array of discrete holes and with injection normal to the wall surface. Stanton numbers were measured for a staggered hole pattern with pitch-to-diameter ratios of 5 and 10, an injection mass flux ratio range of 0.1 to 1.0, and a range of Reynolds number 170 thousand to 5 million. Air was used as the working fluid with the mainstream velocity varied from .14 to 33.5 m/sec (30 to 110 ft/sec). The data were taken for secondary injection temperatures equal to the wall temperature and also equal to the mainstream temperature. By use of linear superposition theory, the data may be used to obtain Stanton number as a continuous function of the injectant temperature. The heat transfer coefficient is defined on the basis of a mainstream-to-wall temperature difference. This difinition permits direct comparison of performance between film cooling and transpiration cooling

The Effects Of A Heel Lift On Squat Biomechanics

The barbell squat is an effective exercise for improving lower extremity function. During the descent of a squat, the hip and knee joints flex while the ankle joint dorsiflexes. The hip and knee joints then extend and the ankle joint plantarflexes when standing up. During the squat, some athletes use shoes with an elevated heel or other means of heel elevation to achieve lower squat depth. Research has suggested that use of heel elevation may improve range of motion (ROM) of the lower extremity joints and improve stability of the movement during deep squats, especially with an external load. PURPOSE: The purpose of this study was to compare lower extremity biomechanics during the back squat exercise in a heel-lift (HL) vs non-heel lift (NHL) condition. We hypothesized that the HL condition would result in greater peak knee flexion angles (KFA) and greater net knee joint moments (NJM). METHODS: 25 healthy participants (13 male, 12 female, 23.6±3.14 yrs., 1.70±0.08 m, 72.24±12.86kg) who had back squatted at least once per week for the last three months were recruited for data collection. 2 visits were required from each participant with the first visit involving back squat one-repetition-maximum (1RM) testing (101.62±41.40kg). During the second visit, participants underwent 3-D biomechanical analyses for the back squat with and without heel lift. Participants performed three repetitions at 75% 1RM for each condition in a randomized order, with a five-minute rest period. Squat velocity was controlled for by using a metronome set to 20 beats per minute. The 2nd of the three repetitions was used for analysis. Paired samples T-tests were used to compare peak knee NJM and peak KFA between the HL and NHL conditions. RESULTS: No differences were found between HL and NHL for knee NJM (2.79±0.96 Nm/kg-1vs 2.7±0.79 Nm/kg-1, p=0.72) or peak KFA (126.03±15.73o vs 125.8±15.39o, p=0.83) CONCLUSION: Results contradict our hypothesis, as the HL did not increase the participants KFA or knee NJM. These results suggest that shoe type used during the back squat exercise may be left up to user preference as to what is comfortable for them. Future studies may aim to see if adding a HL influences lower extremity biomechanics when the load is closer to 1RM, or in other squat variations