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Now showing 1 - 10 of 164
  • (2006) Tarnopolsky, Alex Z.; Fletcher, Neville H.; Hollenberg, Lloyd C. L.; Lange, Benjamin D.; Smith, John; Wolfe, Joseph
    Journal Article
    The didjeridu, or yidaki, is a simple tube about 1.5 m long, played with the lips, as in a tuba, but mostly producing just a tonal, rhythmic drone sound. The acoustic impedance spectra of performers' vocal tracts were measured while they played and compared with the radiated sound spectra. When the tongue is close to the hard palate, the vocal tract impedance has several maxima in the range 1-3 kHz. These maxima, if sufficiently large, produce minima in the spectral envelope of the sound because the corresponding frequency components of acoustic current in the flow entering the instrument are small. In the ranges between the impedance maxima, the lower impedance of the tract allows relatively large acoustic current components that correspond to strong formants in the radiated sound. Broad, weak formants can also be observed when groups of even or odd harmonics coincide with bore resonances. Schlieren photographs of the jet entering the instrument and high speed video images of the player's lips show that the lips are closed for about half of each cycle, thus generating high levels of upper harmonics of the lip frequency. Examples of the spectra of 'circular breathing' and combined playing and vocalization are shown.

  • (2005) Smith, J.R.; Wolfe, Joseph; Bavu, E.
    Journal Article
    Bowing a string with a non-zero radius exerts a torque, which excites torsional waves. In general, torsional standing waves have higher fundamental frequencies than do transverse standing waves, and there is generally no harmonic relationship between them. Although torsional waves have little direct acoustic effect, the motion of the bow-string contact depends on the sum of the transverse speed v of the string plus the radius times the angular velocity (rw). Consequently, in some bowing regimes, torsional waves could introduce non-periodicity or jitter to the transverse wave. The ear is sensitive to jitter so, while quite small amounts of jitter are important in the sounds of (real) bowed strings, modest amounts of jitter can be perceived as unpleasant or unmusical. It follows that, for a well bowed string, aperiodicities produced in the transverse motion by torsional waves (and other effects) must be small. Is this because the torsional waves are of small amplitude or because of strong coupling between the torsional and transverse waves? We measure the torsional and transverse motion for a string bowed by an experienced player over a range of tunings. The torsional wave spectrum shows a series of harmonics of the translational fundamental, with strong formants near the natural frequencies for torsion. The peaks in rw, which occur near the start and end of the 'stick' phase in which the bow and string move together, are only several times smaller than v during this phase. We present sound files of the transverse velocity and the rotational velocity due to the torsional wave. Because the torsional waves occur at exact harmonics of the translational fundamental and because of similarities in the temporal envelope, the sound of the torsional signal alone clearly suggests the sound of a bowed string with the pitch of the translational fundamental. However, the harmonics that fall near the torsional resonances are so strong that they may be heard as distinct notes.

  • (2006) Inta, R.A.; Smith, J.R.; Wolfe, Joseph
    Journal Article
    This is a report on the first three years of a long-term experiment designed to measure how two very similar violins change with time. After being constructed 'in parallel,' one is stored under controlled conditions in a museum and is played infrequently, while the other is played regularly by a professional musician. Vibro-acoustic measurements were performed on the instruments and parts thereof during and after construction. Playing and listening tests by a panel of experienced violinists were conducted at completion, after three years with no adjustment, and then after minor adjustments were made to the played violin only. Panels of players and listeners rated the two violins at all stages, and all results are consistent with the null hypothesis: at present there is no significant preference for either instrument over a range of categories.

  • (2005) Smith, J.R.; Tarnopolsky, A.; Wolfe, Joseph; Fletcher, N
    Journal Article
    The effect of evanescent mode generation, due to geometrical mismatch, in acoustic impedance measurements is investigated. The particular geometry considered is that of a impedance probe with an annular flow port and a central microphone, but the techniques are applicable to other geometries. It is found that the imaginary part of the measured impedance error is proportional to frequency, and that the sign of the error is positive for measurements made on tubes with diameter much larger than that of the inlet port,,but negative for tubes with diameter close to that of the inlet. The result is a distortion of the measured frequencies of the impedance minima of the duct while the maxima are largely unaffected. There is, in addition, a real resistive component to the error that varies approximately as the square root of the frequency. Experiment confirms the results of the analysis and calculations, and a calibration procedure is proposed that allows impedance probes that have been calibrated on a semi-infinite tube of one diameter to be employed for measurements on components with an inlet duct of some very different diameter. © 2005 Acoustical Society of America.

  • (2005) Tarnopolsky, A.; Fletcher, N.; Hollenberg, L.; Lange, B.; Smith, J.; Wolfe, Joseph
    Journal Article
    The Australian didgeridoo (or yidaki in the Yolngu language of northern Australia) is a simple musical instrument that, at the lips of an experienced player, is capable of a spectacular variety of timbres - considerably greater than those that can be coaxed from orchestral instruments, for example. To understand this phenomenon, we simultaneously measured the sound produced by the didgeridoo and the acoustic impedance of the player's vocal tract. We find that the maxima in the envelope of the sound spectrum are associated with minima in the impedance of the vocal tract, as measured just inside the lips. This acoustic effect is similar to the production of vowel sounds made during human speech or singing, although the mechanism is different, and leads to the surprising conclusion that experienced players are subconsciously using their glottis to accentuate the instrument's tonal variation.

  • (2007) Longmore, Steven; Burton, Michael; Barnes, P; Wong, Tony; Purcell, Cormac; Ott, J
    Journal Article
    We present observations of the (1,1), (2,2), (4,4) and (5,5) inversion transitions of para-ammonia (NH3) and 24-GHz continuum, taken with the Australia Telescope Compact Array towards 21 southern Galactic hot molecular cores traced by 6.7-GHz methanol maser emission. We detect NH3(1,1) emission towards all 21 regions and 24-GHz continuum emission towards 12 of the regions, including six with no reported 8-GHz continuum counterparts. In total, we find the 21 regions contain 41 NH3(1,1) cores but around half of the regions only contain a single core. We extract characteristic spectra for every core at each of the NH3 transitions and present both integrated intensity maps and channel maps for each region. NH3(2,2) emission was detected towards all NH3(1,1) cores. NH3(4,4) emission was detected in 13 of the NH3(1,1) cores with NH3(5,5) emission coincident with 11 of these. The NH3(4,4) and (5,5) emission is always unresolved and found at the methanol maser position. An analysis of the NH3(1,1) and (2,2) line ratios suggests that the cores with NH3(4,4) and (5,5) emission are warmer than the remaining cores rather than simply containing more ammonia. The coincidence of the maser emission with the higher spatial resolution NH3(4,4) and (5,5) emission indicates that the methanol masers are found at the warmest part of the core. In all cores detected at NH3(4,4) (with the exception of G12.68-0.18 core 4), the measured linewidth increases with transition energy. The NH3(1,1) spectra of several cores show an emission and absorption component slightly offset in velocity but it is unclear whether or not this is due to systematic motion of the gas. We observe large asymmetries in the NH3(1,1) hyperfine line profiles and conclude that this is due to non-local thermodynamic equilibrium conditions arising from a number of dense, small clumps within the beam, rather than systematic motions of gas in the cores. Assuming that the 24-GHz continuum emission is optically-thin bremsstrahl

  • (2007) Urquhart, J; Busfield, A; Hoare, M; Lumsden, S; Oudmaijer, R; Moore, T; Gibb, A; Purcell, Cormac; Burton, Michael; Marechal, L
    Journal Article
    Context. The Red MSX Source ( RMS) survey is an ongoing multi-wavelength observational programme designed to return a large, well-selected sample of massive young stellar objects (MYSOs). We have identified similar to 2000 MYSOs candidates located within our Galaxy by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. The aim of our follow- up observations is to identify other contaminating objects such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe) and distinguish between genuine MYSOs and nearby low- mass YSOs. Aims. A critical part of our follow- up programme is to conduct (CO)-C-13 molecular line observations in order to determine kinematic distances to all of our MYSO candidates. These distances will be used in combination with far- IR and (sub) millimetre fluxes to determine bolometric luminosities which will allow us to identify and remove nearby low- mass YSOs. In addition these molecular line observations will help in identifying evolved stars which are weak CO emitters. Methods. We have used the 22 m Mopra telescope, the 15 m JCMT and the 20 m Onsala telescope to conduct molecular line observations towards 854 MYSOs candidates located in the 3rd and 4th quadrants. These observations have been made at the J = 1 - 0 ( Mopra and Onsala) and J = 2 - 1 (JCMT) rotational transition frequency of (CO)-C-13 molecules and have a spatial resolution of similar to 20`- 40`, a sensitivity of T-A* A similar or equal to 0.1 K and a velocity resolution of similar to 0.2 km s(-1). Results. We detect (CO)-C-13 emission towards a total of 752 of the 854 RMS sources observed (similar to 88%). In total 2132 emission components are detected above 3s level (typically T*(A) = 0.3 K). Multiple emission profiles are observed towards the majority of these sources - 461 sources (similar to 60%) - with an average of similar to 4 molecular clouds detected along the line of sight. These multiple emission features make it di. cult t

  • (2007) Walsh, Andrew; Chapman, J; Burton, Michael; Wardle, M; Millar, Tom
    Journal Article
    We report on Australia Telescope Compact Array observations of the massive star-forming region G305.2+0.2 at 1.2 cm. We detected emission in five molecules towards G305A, confirming its hot core nature. We determined a rotational temperature of 26 K for methanol. A non-local thermodynamic equilibrium excitation calculation suggests a kinematic temperature of the order of 200 K. A time-dependent chemical model is also used to model the gas-phase chemistry of the hot core associated with G305A. A comparison with the observations suggest an age of between 2 x 10(4) and 1.5 x 10(5) yr. We also report on a feature to the south-east of G305A which may show weak Class I methanol maser emission in the line at 24.933 GHz. The more evolved source G305B does not show emission in any of the line tracers, but strong Class I methanol maser emission at 24.933 GHz is found 3 arcsec to the east. Radio continuum emission at 18.496 GHz is detected towards two H II regions. The implications of the non-detection of radio continuum emission towards G305A and G305B are also discussed.

  • (2005) Rathborne, Jill; Burton, Michael
    Journal Article
    The SPIREX telescope, located at the Amundsen-Scott South Pole Station, was a prototype system developed to exploit the excellent conditions for IR observing at the South Pole. Observations over two winter seasons achieved remarkably deep, high-resolution, wide-field images in the 3-5 mu m wavelength regime. Several star forming complexes were observed, including NGC 6334, Chamaeleon I, eta Chamaeleontis, the Carina Nebula, 30 Doradus, RCW 57, RCW 38, as well as the Galactic Center. Images were obtained of lines at 2.42 mu m H-2, 3.29 mu m PAH and 4.05 mu m Br alpha, as well as 3.5 mu m L-band and 4.7 mu m M-band continuum emission. These data, combined with near-IR, mid-IR, and radio continuum maps, reveal the environments of these star forming sites, as well as any protostars lying within them. The SPIREX project, its observing and reduction methods, and some sample data are summarized here.

  • (2004) Burton, Michael; Lazendic, J; Yusef-Zadeh, F; Wardle, M
    Journal Article
    We present infrared (Anglo-Australian Telescope, United Kingdom Infrared Telescope) and radio (Very Large Array, Swedish-ESO Submillimetre Telescope) observations of the Eye of the Tornado, a compact source apparently near the head of the Tornado Nebula. The near-infrared Brgamma and He I lines are broad (full width at half maximum of 40 and 30 km s(-1), respectively) and have a line centre at V(LSR)similar to-205 km s(-1). This corresponds to a feature at the same velocity in the (CO)-C-12 J= 1-0 line profile. The kinematic velocity derived from Galactic rotation places the Eye at the distance of the Galactic Centre (i.e. 8.5 kpc) and separated (probably foreground) from the Tornado Nebula. Four knots of emission are seen in the Brgamma line and at 6 and 20 cm. Together with the flat radio spectral index, we confirm that the Eye contains ionized gas, but that this is embedded within a dense molecular core. The spectral energy distribution can be modelled as a two-component blackbody + greybody, peaking at far-infrared wavelengths. The knots are ultracompact H II regions, and the core contains a luminous (similar to2 x 10(4) L-.), embedded, massive young stellar source. We also propose a geometrical model for the Eye to account for both its spectral energy distribution and its morphology.