3,677 research outputs found
An Audible Demonstration Of The Speed Of Sound In Bubbly Liquids
The speed of sound in a bubbly liquid is strongly dependent upon the volume fraction of the gas phase, the bubble size distribution, and the frequency of the acoustic excitation. At sufficiently low frequencies, the speed of sound depends primarily on the gas volume fraction. This effect can be audibly demonstrated using a one-dimensional acoustic waveguide, in which the flow rate of air bubbles injected into a water-filled tube is varied by the user. The normal modes of the waveguide are excited by the sound of the bubbles being injected into the tube. As the flow rate is varied, the speed of sound varies as well, and hence, the resonance frequencies shift. This can be clearly heard through the use of an amplified hydrophone and the user can create aesthetically pleasing and even musical sounds. In addition, the apparatus can be used to verify a simple mathematical model known as Wood's equation that relates the speed of sound of a bubbly liquid to its void fraction. (c) 2008 American Association of Physics Teachers.Mechanical Engineerin
Cassiopeia A: dust factory revealed via submillimetre polarimetry
If Type-II supernovae - the evolutionary end points of short-lived, massive
stars - produce a significant quantity of dust (>0.1 M_sun) then they can
explain the rest-frame far-infrared emission seen in galaxies and quasars in
the first Gyr of the Universe. Submillimetre observations of the Galactic
supernova remnant, Cas A, provided the first observational evidence for the
formation of significant quantities of dust in Type-II supernovae. In this
paper we present new data which show that the submm emission from Cas A is
polarised at a level significantly higher than that of its synchrotron
emission. The orientation is consistent with that of the magnetic field in Cas
A, implying that the polarised submm emission is associated with the remnant.
No known mechanism would vary the synchrotron polarisation in this way and so
we attribute the excess polarised submm flux to cold dust within the remnant,
providing fresh evidence that cosmic dust can form rapidly. This is supported
by the presence of both polarised and unpolarised dust emission in the north of
the remnant, where there is no contamination from foreground molecular clouds.
The inferred dust polarisation fraction is unprecedented (f_pol ~ 30%) which,
coupled with the brief timescale available for grain alignment (<300 yr),
suggests that supernova dust differs from that seen in other Galactic sources
(where f_pol=2-7%), or that a highly efficient grain alignment process must
operate in the environment of a supernova remnant.Comment: In press at MNRAS, 10 pages, print in colou
Growth and Empowerment for Indigenous Australians in Substance Abuse Treatment
This paper describes psychosocial outcomes of an Indigenous residential substance abuse rehabilitation centre in Australia, examines the sensitivity to change of the new Growth and Empowerment Measure (GEM), and explores the degree to which service users value cultural components of the treatment program. Participants were 57 Indigenous and 46 non-Indigenous male clients from Oolong House. Intake, 8-weeks, and 16-weeks (program completion) measures of Kessler 10 Psychological Distress Scale (K10), Drug Taking Confidence Questionnaire (DTCQ-8), and GEM were completed. The Treatment Component Evaluation (TCE) was completed at 16-weeks. There were significant improvements for participants, with a decrease in psychological distress and increases in refusal self-efficacy and empowerment. Effect sizes for GEM were medium to large across the time-points (r00.61 to 0.70 for all four subscales from baseline to 8-weeks; r00.44 to 0.70 for three subscales from 8-weeks to 16-weeks), indicating sensitivity to change. Indigenous participants rated cultural components of treatment significantly more helpful than did non-Indigenous participants. Implications for future research and substance abuse interventions for Indigenous Australians are discussed
Precision control of thermal transport in cryogenic single-crystal silicon devices
We report on the diffusive-ballistic thermal conductance of multi-moded
single-crystal silicon beams measured below 1 K. It is shown that the phonon
mean-free-path is a strong function of the surface roughness
characteristics of the beams. This effect is enhanced in diffuse beams with
lengths much larger than , even when the surface is fairly smooth, 5-10
nm rms, and the peak thermal wavelength is 0.6 m. Resonant phonon
scattering has been observed in beams with a pitted surface morphology and
characteristic pit depth of 30 nm. Hence, if the surface roughness is not
adequately controlled, the thermal conductance can vary significantly for
diffuse beams fabricated across a wafer. In contrast, when the beam length is
of order , the conductance is dominated by ballistic transport and is
effectively set by the beam area. We have demonstrated a uniformity of 8%
in fractional deviation for ballistic beams, and this deviation is largely set
by the thermal conductance of diffuse beams that support the
micro-electro-mechanical device and electrical leads. In addition, we have
found no evidence for excess specific heat in single-crystal silicon membranes.
This allows for the precise control of the device heat capacity with normal
metal films. We discuss the results in the context of the design and
fabrication of large-format arrays of far-infrared and millimeter wavelength
cryogenic detectors
The effect of infrared beak treatment on the welfare of turkeys reared to 12 weeks of age
This study aimed to determine the effects of infrared beak treatment on the behavior and welfare of male and female turkeys reared to 12 wk of age. To do this, poults (236 males and 324 females) were assigned to one of 2 beak treatments: infrared beak treated on day of hatch (IR) or sham untreated control (C). Data collected included heterophil/lymphocyte (H/L) ratio, pecking force, feather cover, behavioral expression, and beak histology. Data were analyzed as a 2 × 2 factorial of beak treatment and gender, in a completely randomized design and analyzed using PROC MIXED (SAS 9.4). H/L ratio (indicative of a stress response) did not differ between treated and control poults during early life, except at 20 d of age when H/L ratio was higher for C poults than IR poults. Pecking force, measured as a method of monitoring pain, was different only at 1 wk of age, when IR poults pecked with more force than C poults. Feather cover was better in IR poults at 12 wk of age. Differences in behavior between treatments were minor over the 12-wk period. Overall, infrared beak treatment of commercial turkeys had minimal negative impacts on behavior and welfare. The results suggest that stress may be reduced in flocks that are beak treated and that the procedure itself does not cause a pain response
Transition phenomena in unstably stratified turbulent flows
We study experimentally and theoretically transition phenomena caused by the
external forcing from Rayleigh-Benard convection with the large-scale
circulation (LSC) to the limiting regime of unstably stratified turbulent flow
without LSC whereby the temperature field behaves like a passive scalar. In the
experiments we use the Rayleigh-B\'enard apparatus with an additional source of
turbulence produced by two oscillating grids located nearby the side walls of
the chamber. When the frequency of the grid oscillations is larger than 2 Hz,
the large-scale circulation (LSC) in turbulent convection is destroyed, and the
destruction of the LSC is accompanied by a strong change of the mean
temperature distribution. However, in all regimes of the unstably stratified
turbulent flow the ratio varies slightly (even in the range
of parameters whereby the behaviour of the temperature field is different from
that of the passive scalar). Here are the integral scales of
turbulence along x, y, z directions, T and \theta are the mean and fluctuating
parts of the fluid temperature. At all frequencies of the grid oscillations we
have detected the long-term nonlinear oscillations of the mean temperature. The
theoretical predictions based on the budget equations for turbulent kinetic
energy, turbulent temperature fluctuations and turbulent heat flux, are in
agreement with the experimental results.Comment: 14 pages, 14 figures, REVTEX4-1, revised versio
Scalable background-limited polarization-sensitive detectors for mm-wave applications
We report on the status and development of polarization-sensitive detectors
for millimeter-wave applications. The detectors are fabricated on
single-crystal silicon, which functions as a low-loss dielectric substrate for
the microwave circuitry as well as the supporting membrane for the
Transition-Edge Sensor (TES) bolometers. The orthomode transducer (OMT) is
realized as a symmetric structure and on-chip filters are employed to define
the detection bandwidth. A hybridized integrated enclosure reduces the
high-frequency THz mode set that can couple to the TES bolometers. An
implementation of the detector architecture at Q-band achieves 90% efficiency
in each polarization. The design is scalable in both frequency coverage, 30-300
GHz, and in number of detectors with uniform characteristics. Hence, the
detectors are desirable for ground-based or space-borne instruments that
require large arrays of efficient background-limited cryogenic detectors.Comment: 7 pages, 3 figures, Presented at SPIE Astronomical Telescopes and
Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors
and Instrumentation for Astronomy VII. To be published in Proceedings of SPIE
Volume 915
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