On wavenumber spectra for sound within subsonic jets

This paper clarifies the nature of sound spectra within subsonic jets. Three problems, of increasing complexity, are presented. Firstly, a point source is placed in a two-dimensional plug flow and the sound field is obtained analytically. Secondly, a point source is embedded in a diverging axisymmetric jet and the sound field is obtained by solving the linearised Euler equations. Finally, an analysis of the acoustic waves propagating through a turbulent jet obtained by direct numerical simulation is presented. In each problem, the pressure or density field are analysed in the frequency-wavenumber domain. It is found that acoustic waves can be classified into three main frequency-dependent groups. A physical justification is provided for this classification. The main conclusion is that, at low Strouhal numbers, acoustic waves satisfy the d'Alembertian dispersion relation.Comment: 20 pages, 9 figure

Trident: A three-pronged galaxy survey. I. Lyman alpha emitting galaxies at z~2 in GOODS North

Context. Lyman alpha emitting galaxies (LAEs) are used to probe the distant universe and are therefore important for galaxy evolution studies and for providing clues to the nature of the epoch of reionization, but the exact circumstances under which Lyman alpha escapes a galaxy are still not fully understood. Aims. The Trident project is designed to simultaneously examine Lyman alpha, H-alpha and Lyman Continuum emission from galaxies at redshift z~2, thus linking together these three aspects of ionising radiation in galaxies. In this paper, we outline the strategy of this project and examine the properties of LAEs in the GOODS North field. Methods. We performed a narrowband LAE survey in GOODS North using existing and two custom made filters at the Nordic Optical Telescope with MOSCA. We use complementary broad band archival data in the field to make a careful candidate selection and perform optical to near-IR SED fitting. We also estimate far-infrared luminosities by matching our candidates to detections in Spitzer/MIPS 24{\mu}m and Herschel/PACS catalogs. Results. We find a total of 25 LAE candidates, probing mainly the bright end of the LAE luminosity function with L_Ly {\alpha} ~ 1-15e42 erg/s. They display a range of masses of ~0.5-50e9 M_solar, and average ages from a few tens of Myr to 1 Gyr when assuming a constant star formation history. The majority of our candidates also show signs of recent elevated star formation. Three candidates have counterparts in the GOODS-Herschel far-IR catalogue, with luminosities consistent with ultra-luminous infrared galaxies (ULIRGs). Conclusions. The wide range of parameters derived from our SED fitting, as well as part of our sample being detected as ULIRGs, seems to indicate that at these Lyman alpha luminosities, LAEs do not necessarily have to be young dwarfs, and that a lack of dust is not required for Lyman alpha to escape.Comment: 16 pages, 12 figures. Accepted version for publication in A&

Output frequency response function-based analysis for nonlinear Volterra systems

Analysis of nonlinear systems has been studied extensively. Based on some recently developed results, a new systematic approach to the analysis of nonlinear Volterra systems in the frequency domain is proposed in this paper, which provides a novel insight into the frequency domain analysis and design of nonlinear systems subject to a general input instead of only specific harmonic inputs using input-output experimental data. A general procedure to conduct an output frequency response function (OFRF) based analysis is given, and some fundamental results and techniques are established for this purpose. A case study for the analysis of a circuit system is provided to illustrate this new frequency domain method

Late Frasnian mass extinction: Conodont event stratigraphy, global changes, and possible causes

Several abrupt changes in conodont biofacies are documented to occur synchronously at six primary control sections across the Frasnian-Famennian boundary in Euramerica. These changes occurred within a time-span of only about 100,000 years near the end of the latest Frasnian linguiformis Zone, which is formally named to replace the Uppermost gigas Zone. The conodont-biofacies changes are interpreted to reflect a eustatic rise followed by an abrupt eustatic fall immediately preceding the late Frasnian mass extinction. Two new conodont species are named and described. Ancyrognathus ubiquitus n.sp. is recorded only just below and above the level of late Frasnian extinction and hence is a global marker for that event. Palmatolepispraetriangularis n.sp. is the long-sought Frasnian ancestor of the formerly cryptogenic species, Pa. triangularis, indicator of the earliest Famennian Lower triangularis Zone. The actual extinction event occurred entirely within the Frasnian and is interpreted to have been of brief duration-from as long as 20,000 years to as short as several days. The eustatic rise-and-fall couplet associated with the late Frasnian mass extinction is similar to eustatic couplets associated with the demise of most Frasnian (F2h) reefs worldwide about 1 m.y. earlier and with a latest Famennian mass extinction about 9.5 m.y. later. All these events may be directly or indirectly attributable to extraterrestrial triggering mechanisms. An impact of a small bolide or a near miss of a larger bolide may have caused the earlier demise of Frasnian reefs. An impact of possibly the same larger bolide in the Southern Hemisphere would explain the late Frasnian mass extinction. Global regression during the Famennian probably resulted from Southern-Hemisphere glaciation triggered by the latest Frasnian impact. Glaciation probably was the indirect cause of the latest Famennian mass extinction

Mentorship in Sobriety: An Alternative to Twelve Step Support for Deaf People

For individuals seeking recovery from alcohol and other drug addiction/dependence, the most common source of support is Twelve Step programs. Some people who experience problems as the result of alcohol or other drug use seek help directly from these programs. Others turn to Twelve Step programs as a source of ongoing support after having completed chemical dependency treatment. For years, deaf recovering people, like their hearing counterparts have been referred to Twelve Step meetings. Frequently, Twelve Step meetings, related literature, and sponsorship are not accessible to Deaf individuals pursuing recovery. The authors suggest there may be alternatives to traditional Twelve Step groups that would provide Deaf recovering people with fellowship, information, and support. This paper proposes an alternative model of support for deaf people using mentors who are members of the Deaf community

Drug Abuse Resistance Education (D.A.R.E): Special Consideration for Students who are Deaf or Hard of Hearing

Prevention programing in the area of alcohol and other drug abuse had made significant progress in the past several years. From the scare tactics and testimonials of recovering addicts we have progressed to efforts aimed at building self-esteem and teaching refusal skills. Students who are deaf or hard of hearing often continue to experience a lack of quality prevention services. Because information from the media is often inaccessible to these students and because school and community-based programs often do not take into account the special cultural and communication considerations of this population, their knowledge and skill base often lag behind that of their hearing peers. This project is an attempt to make one proactive prevention program accessible, meaningful and beneficial for students who are deaf or hard of hearing

Passion or delusion: middle managers constructing new meanings of work

Recently, organization scholars have called for a need to re-think managerial leadership so as to take into account the "mundane", the key activity of which is "influencing expectations, meanings, and values about what is desirable and necessary related to everyday work" (Sveningsson et. al., 2012: 84). In other words, mundane leaders can be seen as sense makers (Weick, 1995) and sense givers (Gioia and Chittipeddi 1991). Managerial leadership has also been described as event-driven actions arising mostly from unforeseen happenings (Holmberg and Tyrstrup, 2010). A study of site managers in construction depicted their leadership as a "muddling through", i.e. they skilfully solve problems as these inevitably crop up, and they try to be everywhere at the same time Styhre, 2012). We argue that muddling through also puts high demands on site managers' abilities and possibilities of coping with and balancing their work, family and personal life. The purpose of this paper is to explore what mundane leadership and muddling through actually mean for managerial leaders in construction from a wider perspective than their work. In other words, what does muddling through mean in terms of coping with work and family and life in general. This paper contributes empirical examples from 37 in-depth interviews with site managers, foremen and supervisor in a large number of construction organisations. We draw on practice theories to explore and analyse the data, and argue that mundane leaders are indeed both organizational sense makers and sense givers, the linkers of the strategic with the operational, the cohesion that generates coherence. All the site managers interviewed were passionate about their work, but deplored organisational and institutional constraints, which mostly obstructed rather than supported or facilitated their work. Sense-making and sense-giving roles demand presence, flexibility, experience, hindsight, judgment and improvisation, which in turn, and over time, often result in exhaustion and stress, and leave little energy over for family and life outside work. We conclude that the "mundane" activities of middle managers are far from trivial; they demand leadership competences that require fostering and nurturing. Today there is little support for middle-managerial leaders and little training of the competences that they need the nmost

Workaholics on site! Sustainability of site managers' work situations?

Site-managerial practice in construction has been depicted as a 'muddling through', being everywhere at the same time and skilfully solving problems as these crop up. The purpose of this paper is to explore work patterns and related well-being implications of site managers in construction. Drawing on the work-life stories of 21 site managers, which have been analysed using narrative analysis we argue that muddling through put high demands on these managers' abilities and possibilities of coping with and balancing their work situations. In all the accounts, several features of workaholism were identified as driving forces, often leading to negative well-being symptoms. The site managers were passionate about their work, but deplored organisational and institutional constraints, which mostly obstructed rather than supported or facilitated their work. This resulted in periods of exhaustion and stress, leaving little energy over for family and life outside work. We conclude that the warnings we perceive concerning the unsustainable work situations of site managers warrant further research