7,783 research outputs found
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
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&
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
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
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