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

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

Microwave Dielectric Heating of Drops in Microfluidic Devices

We present a technique to locally and rapidly heat water drops in microfluidic devices with microwave dielectric heating. Water absorbs microwave power more efficiently than polymers, glass, and oils due to its permanent molecular dipole moment that has a large dielectric loss at GHz frequencies. The relevant heat capacity of the system is a single thermally isolated picoliter drop of water and this enables very fast thermal cycling. We demonstrate microwave dielectric heating in a microfluidic device that integrates a flow-focusing drop maker, drop splitters, and metal electrodes to locally deliver microwave power from an inexpensive, commercially available 3.0 GHz source and amplifier. The temperature of the drops is measured by observing the temperature dependent fluorescence intensity of cadmium selenide nanocrystals suspended in the water drops. We demonstrate characteristic heating times as short as 15 ms to steady-state temperatures as large as 30 degrees C above the base temperature of the microfluidic device. Many common biological and chemical applications require rapid and local control of temperature, such as PCR amplification of DNA, and can benefit from this new technique.Comment: 6 pages, 4 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&

Neutral gas in Lyman-alpha emitting galaxies Haro 11 and ESO 338-IG04 measured through sodium absorption

Context. The Lyman alpha emission line of galaxies is an important tool for finding galaxies at high redshift, and thus probe the structure of the early universe. However, the resonance nature of the line and its sensitivity to dust and neutral gas is still not fully understood. Aims. We present measurements of the velocity, covering fraction and optical depth of neutral gas in front of two well known local blue compact galaxies that show Lyman alpha in emission: ESO 338-IG 04 and Haro 11. We thus test observationally the hypothesis that Lyman alpha can escape through neutral gas by being Doppler shifted out of resonance. Methods. We present integral field spectroscopy from the GIRAFFE/Argus spectrograph at VLT/FLAMES in Paranal, Chile. The excellent wavelength resolution allows us to accurately measure the velocity of the ionized and neutral gas through the H-alpha emission and Na D absorption, which traces the ionized medium and cold interstellar gas, respectively. We also present independent measurements with the VLT/X-shooter spectrograph which confirm our results. Results. For ESO 338-IG04, we measure no significant shift of neutral gas. The best fit velocity is -15 (16) km/s. For Haro 11, we see an outflow from knot B at 44 (13) km/s and infalling gas towards knot C with 32 (12) km/s. Based on the relative strength of the Na D absorption lines, we estimate low covering fractions of neutral gas (down to 10%) in all three cases. Conclusions. The Na D absorption likely occurs in dense clumps with higher column densities than where the bulk of the Ly-alpha scattering takes place. Still, we find no strong correlation between outflowing neutral gas and a high Lyman alpha escape fraction. The Lyman alpha photons from these two galaxies are therefore likely escaping due to a low column density and/or covering fraction.Comment: 9 pages, 3 figure

Exploring the work practices of site managers as processes of embodiment

In construction, site managerial work has often been depicted as 'muddling through', skilfully solving problems as these inevitably crop up and trying to be everywhere at the same time. This perspective seems to give precedence to structural conditions in the industry when explaining micro-level practice on construction sites. Recently, however, organisation scholars have highlighted a need to investigate managerial practices as these unfold in everyday work. This means we ought to take into account the actual work activities that influence expectations, meanings and values about what is desirable and necessarily relate to everyday work. The purpose of this paper is to further explore how practice enactment and outcomes are embedded in the lived, everyday work activities of real human beings working on site. The focus is on the work stories of two site managers, a man and a woman, in a large Swedish construction company. Drawing on their stories we take a critical stance towards the established view that certain structural and cultural conditions are strong and sufficient precursors to predict work practice outcomes. We propose instead that practices enacted on site can better be understood as various processes of embodiment