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Acoustics Research Letters Online

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Jan 2003

Volume 4, Issue 1, pp. 1-24

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The focusing of transient response in structural networks: “hot spots”

John Ertel and Joe Dickey

ARLO Volume 4, Issue 1, pp. 1-6 (October 2002); (6 pages)

Online Publication Date: 03 Oct 2002

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When a structural network is driven at a point in one of its systems, other points in other systems may experience anomalously high response. These are termed “hot spots.” The phenomena may be of importance in networks where one or more of the subsystems are fragile. Such networks may be driven in a robust system and break at a hot spot in a fragile system. The phenomena are demonstrated in the calculated spatial/temporal response of simple models of connected one-dimensional wave-bearing systems. © 2003 Acoustical Society of America.
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43.40.Qi Effect of sound on structures, fatigue; spatial statistics of structural vibration
43.40.At Experimental and theoretical studies of vibrating systems
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Radiation damping, efficiency, and directivity for violin normal modes below 4 kHz

George Bissinger and John Keiffer

ARLO Volume 4, Issue 1, pp. 7-12 (October 2002); (6 pages) | Cited 3 times

Online Publication Date: 16 Oct 2002

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Simultaneous modal and acoustical measurements on three violins characterized the physical chain from bridge to sound below 4 kHz via normal mode rms mobility and radiativity, total damping, radiation efficiency, and averaged directivity. The fraction of vibrational energy radiated as sound was estimated as 31%±10% for the 1st corpus bending modes. Radiation efficiencies ranged from ∼0.004 to ∼1, rising with frequency, with lower and upper 1st corpus bending mode values of 0.12±0.03 and 0.11±0.04 respectively. Averaged directivity rose slowly from ∼1 for the lowest modes to ∼2 at 4 kHz. The A1 cavity mode radiates effectively via induced corpus motion. © 2002 Acoustical Society of America.
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43.75.De Bowed stringed instruments
43.40.Yq Instrumentation and techniques for tests and measurement relating to shock and vibration, including vibration pickups, indicators, and generators, mechanical impedance
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A statistical analysis of acoustic emission signals for tool condition monitoring (TCM)

G. Pontuale, F. A. Farrelly, A. Petri, and L. Pitolli

ARLO Volume 4, Issue 1, pp. 13-18 (November 2002); (6 pages) | Cited 5 times

Online Publication Date: 14 Nov 2002

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The statistical properties of acoustic emission signals for tool condition monitoring (TCM) applications in mechanical lathe machining are analyzed in this paper. Time series data and root mean square (RMS) values at various tool wear levels are shown to exhibit features that can be put into relation with aging in both cases. In particular, the histograms of raw data show power-law distributions above a cross-over value, in which newer cutting tools exhibit more numerous larger events compared with more worn-out ones. For practical purposes, statistics based on RMS values are more feasible, and the analysis of these also reveals discriminating age-related features. The assumption that experimental RMS histograms follow a Beta (β) distribution has also been tested. The residuals of the modeling β functions indicate that the search for a more appropriate fitting function for the experimental distribution is desirable. © 2002 Acoustical Society of America.
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43.60.Cg Statistical properties of signals and noise
43.40.Le Techniques for nondestructive evaluation and monitoring, acoustic emission
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Sound transmission in the spermaceti complex of a recently expired sperm whale calf

Bertel Møhl, Peter T. Madsen, Magnus Wahlberg, Whitlow W. L. Au, Paul E. Nachtigall, and Sam H. Ridgway

ARLO Volume 4, Issue 1, pp. 19-24 (December 2002); (6 pages) | Cited 4 times

Online Publication Date: 06 Dec 2002

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Sound pulses were projected into the forehead of a neonate, female sperm whale that died following a stranding and attempts to revive it. Two hydrophones, held against the skin, recorded the sound pulses and their reflections. A consistent reflection was found about 0.8 ms after sound projection. This time corresponded to the expected two-way travel time back and forth within the spermaceti organ. Reflections were also detected at the frontal surface of the junk from sounds projected into the distal sac area. These signals must have traversed rearward along the axis of the spermaceti organ to the frontal sac where they were likely reflected and directed forward to the front of the junk, demonstrating an acoustic continuum between the spermaceti organ and the junk. These results support the basic Norris and Harvey (1972) theory of sound generation in sperm whales and later amendments to that theory (Møhl and Amundin (1991), Møhl (2001)). © 2002 Acoustical Society of America.
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43.80.Ka Sound production by animals: mechanisms, characteristics, populations, biosonar
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