On the Contribution of Higher Azimuthal Modes to the Near- and Far-Field of Jet Mixing Noise

The prediction of jet mixing noise is studied using a stochastic realization of the Tam & Auriault source model. The acoustical sources are generated by means of the Random Particle-Mesh Method (RPM), which utilizes turbulence statistics as provided by solu- tions to the Reynolds Averaged Navier-Stokes (RANS) equations. The generated stochas- tic sound sources closely realize the two-point cross-correlation function used in the jet noise model to prescribe the fine-scale sound source. The RPM code is coupled with the DLR CAA solver PIANO. The azimuthal-modal decomposed linearized Euler equations are applied as governing equations. With this approach, it is possible to evaluate jet noise spectra at any position in the near-field. Based on an azimuthal decomposition, 3-D sound radiation from the jet can be reproduced at the computational price of a few axisymmetric 2-D computations. Furthermore, it will be shown, that we are able to verify the imple- mented methodology with the results published for the genuine model. The spectra are correctly predicted in terms of sound pressure levels, Mach scaling exponent and spectral shape. A Strouhal number range of up to St = 10 can be covered using the first six az- imuthal mode components of the broadband source. To reach higher Strouhal numbers more azimuthal modes have to be adopted. The presented results reveal the importance of individual azimuthal contributions to the total spectra. To evaluate the spectra in the far-field, the generated near-field noise is extrapolated with a modal Ffowcs-Williams & Hawkings (FWH) method. For the static single stream jet (Ma = 0.9) two different kinds of extrapolation were used - a simplified extrapolation and the modal FWH method. With this computational case, it was possible to predict a jet noise spectrum in the range of St = 0.01 . . . 20. To investigate the effect of different nozzle configurations on sound gener- ation, different nozzle configurations, i.e. dual-stream nozzles with and without nozzle lip treatments are simulated. Good agreement with experimental data for the noise reduction potential of nozzle lip treatments is found

Population studies of migratory birds in Virgin Islands National Park

The majority of the individual songbirds nesting in the deciduous forests of eastern North America migrate to the West Indies, Central America and South America during the winter. They typically spend more than six months in tropical winter habitats. Until recently relatively little was known about their habitat requirements during the winter, but increasing concern about declining pcpulations of many migratory songbirds combined with widespread alarm about the rapid destruction of tropical forests has led to a flurry of research on this subject (Terborgh, 1989; Askins et al. 1990). In 1987 we initiated a study of the ecology and behavior of migrants in the Virgin Islands, particularly in Virgin Islands NP on St. John. This study has not only yielded information about the winter ecology of migratory birds, but also about the distribution of resident species and (unexpectedly) the impact of a major hurricane on bird populations

Flocking behavior of migratory warblers in winter in the Virgin Islands

We assessed the flocking behavior of birds on St. John and St. Thomas, U.S. Virgin Islands, with systematic surveys along trails in moist forests. Winter residents (species breeding in North America and that winter in the Virgin Islands), all of which were warblers, comprised 91% of the individuals found in 28 flocks but only 49% of solitary individuals. The average flock size was 4.0 individuals of 3.1 species, and did not differ between St. John and St. Thomas even though the average forest tract on St. John (1,000 ha) was much larger than on St. Thomas (62 ha). Northern Parula (Parula americana) and Black-and-white Warbler (Mniotilta varia), the most common species in flocks, occurred in 76% and 79% of the flocks, respectively. Northern Parula flocked significantly more frequently on St. Thomas than on St. John, but no other species showed a difference in flocking behavior between the two islands. Each flock typically included one individual of each species

Resistance and resilience of Virgin Islands bird populations following severe hurricanes

We analyzed changes in abundance of terrestrial birds on St. John, U.S. Virgin Islands, for a 32 year period during which 3 major hurricanes occurred. Using 1987 as a baseline year, because it followed a 27 year hiatus when no major hurricanes hit the island, we assessed the impact of hurricanes on vegetation structure and bird populations. Bird abundance was determined for 25 m radius circular plots that were surveyed each year of the study along the same transects. Percent cover of trees, shrubs, and herbs was measured in each plot in 1987, 1990, and 2019. All of the survey plots were in moist forest or dry woodland in Virgin Islands National Park. Of 13 common birds, 5 did not show marked and consistent declines in abundance following hurricanes even though the structure of vegetation on the island was heavily modified by storms. Three of these species are insectivores. Seven species declined or showed habitat shifts following Hurricane Hugo in 1989, but 5 of these populations subsequently increased and most recovered to close to their 1987 abundance during the 1990s. Six of these 7 species also declined or showed habitat shifts following Hurricanes Irma and Maria in 2017. The most marked declines in the aftermath of hurricanes in both 1989 and 2017 were for frugivores and nectarivores, especially hummingbirds. Most common bird species in Virgin Islands National Park were either resistant to the effects of severe hurricanes or resilient in the decade following a hurricane. However, more research is needed to assess the status of vulnerable species such as hummingbirds and rare resident species (Bridled Quail-Dove [Geotrygon mystacea] and Puerto Rican Flycatcher [Myiarchus antillarum]). Analizamos los cambios en la abundancia de aves terrestres en St. John, en las Islas V ́ırgenes de los Estados Unidos, por un periodo de 32 an ̃os durante los cuales ocurrieron 3 grandes huracanes. Usando 1987 como el an ̃o base, porque e ́ste siguio ́ a una pausa de 27 an ̃os durante los cuales ningu ́n gran huraca ́n golpeo ́ la isla, determinamos el impacto de huracanes en la estructura de la vegetacio ́n y las poblaciones de aves. La abundancia de aves fue determinada en parcelas circulares de 25 m de radio que fueron muestreadas cada an ̃o a lo largo de los mismos transectos. El porcentaje de cobertura de a ́rboles, arbustos y hierbas fue medido en cada parcela en 1987, 1990 y 2019. Todas las parcelas de muestreo fueron hechos en bosques hu ́medos o arbolados secos del Virgin Islands National Park. De 13 aves comunes, 5 no mostraron declines marcados y consistentes en abundancia despue ́s del paso de huracanes si bien la estructura de la vegetacio ́n en la isla fue fuertemente modificada por estas tormentas. Tres de estas especies fueron insect ́ıvoros. Siete especies declinaron o mostraron cambios de ha ́bitat despue ́s del huraca ́n Hugo en 1989, aunque 5 de estas poblaciones subsecuentemente se incrementaron y la mayor ́ıa se recuperaron cercanamente a sus abundancias de 1987 durante la de ́cada de 1990. Seis de estas 7 especies tambie ́n declinaron o mostraron cambios de ha ́bitat despue ́s de los huracanes Irma y Mar ́ıa en 2017. Los declines ma ́s marcados como secuela de huracanes en 1989 y 2017 fueron para frug ́ıvoros y nectar ́ıvoros, especialmente colibr ́ıes. Las especies ma ́s comunes en el Virgin Islands National Park fueron resistentes a los efectos de huracanes severos o resilientes en la de ́cada posterior a un huraca ́n. Sin embargo, necesitamos ma ́s investigacio ́n para determinar el estatus de especies vulnerables como colibr ́ıes y especies residentes raras (la paloma Geotrygon mystacea y el mosquero Myiarchus antillarum)

Sensation Seeking and Perceived Need for Structure Moderate Soldiers’ Well-Being Before and After Operational Deployment

This study examined associations between sensation seeking and perceived need for structure, and changes in reported well-being among deployed soldiers. Participants (n = 167) were assessed before and after a six-month deployment to south Afghanistan. Results indicated that although well-being declined in the soldier sample as a whole following deployment, the degree of decrease was significantly different among soldiers with different personality profiles. Differences were moderated by soldiers’ level of sensation seeking and perceived need for structure. Results are discussed in terms of a person-environment fit theory in the context of preparation and rehabilitation of deployed military personnel

Exploring efficacy in personal constraint negotiation: an ethnography of mountaineering tourists

Limited work has explored the relationship between efficacy and personal constraint negotiation for adventure tourists, yet efficacy is pivotal to successful activity participation as it influences people’s perceived ability to cope with constraints, and their decision to use negotiation strategies. This paper explores these themes with participants of a commercially organised mountaineering expedition. Phenomenology-based ethnography was adopted to appreciate the social and cultural mountaineering setting from an emic perspective. Ethnography is already being used to understand adventure participation, yet there is considerable scope to employ it further through researchers immersing themselves into the experience. The findings capture the interaction between the ethnographer and the group members, and provide an embodied account using their lived experiences. Findings reveal that personal mountaineering skills, personal fitness, altitude sickness and fatigue were the four key types of personal constraint. Self-efficacy, negotiation-efficacy and other factors, such as hardiness and motivation, influenced the effectiveness of negotiation strategies. Training, rest days, personal health, and positive self-talk were negotiation strategies. A conceptual model illustrates these results and demonstrates the interplay between efficacy and the personal constraint negotiation journey for led mountaineers

Further experiments with the Iowa air blast seed separator for the analysis of small-seeded grasses

In recent years attempts, have been made in Europe and North America to improve seed laboratory machines used for the separation of chaff from heavy seeds in grasses. The most important European contribution is probably the Gilchrist seed separator used at the seed testing station in Edinburgh, Scotland. The Holland (Leendertz) separator has some merit, but its chief weakness as shown by Porter (7) was the inconstant speed of the motor which made it. impossible to deliver the same volume of air through the separator tube each time the valve was opened to a given point. Replacement of the motor by one that operated at constant speed was found by Brown and Porter (1) to correct the defect reasonably well. The use of bolting cloth in place of a metal screen is also a disadvantage. Following the initial work Porter (8) described a new seed separator equipped with a combined motor\u27 and fan unit of standard specifications which made uniform separations of bluegrass, redtop and orchard grass samples either by repeated blowings of the same sub-sample or by a single blowing for each of many replicate sub-samples. He also employed synthetic samples to check the accuracy and uniformity of separation. These results were obtained with samples from the same lot and indicated that for any given lot of seed it was possible to obtain uniform results if care was used in reading the dial opening on the valve or the manometer which indicated pressure in the compression chamber. It is noteworthy that in his experiments Porter (8) showed that if the weight of sample varied from 112 to 2 grams of blue-\u27 grass seed, the dial reading was more dependable than pressure as measured in the compression chamber, and further that pressure as measured in the blowing tube was about as reliable as the dial reading. He showed, however, that with samples having a low weight per bushel the amount of germinable seed removed at a given opening was greater than with samples having a high weight per bushel