Deterministic and statistical characterization of rigid frame porous materials from impedance tube measurements.

A method to characterize macroscopically homogeneous rigid frame porous media from impedance tube measurements by deterministic and statistical inversion is presented. Equivalent density and bulk modulus of the samples are reconstructed with the scattering matrix formalism, and are then linked to its physical parameters via the Johnson-Champoux-Allard-Lafarge model. The model includes six parameters, namely the porosity, tortuosity, viscous and characteristic lengths, and static flow and thermal permeabilities. The parameters are estimated from the measurements in two ways. The first one is a deterministic procedure that finds the model parameters by minimizing a cost function in the least squares sense. The second approach is based on statistical inversion. It can be used to assess the validity of the least squares estimate, but also presents several advantages since it provides valuable information on the uncertainty and correlation between the parameters. Five porous samples with a range of pore properties are tested, and the pore parameter estimates given by the proposed inversion processes are compared to those given by other characterization methods. Joint parameter distributions are shown to demonstrate the correlations. Results show that the proposed methods find reliable parameter and uncertainty estimates to the six pore parameters quickly with minimal user input.

Real-time near-field acoustic holography for continuously visualizing nonstationary acoustic fields.

Near-field acoustic holography (NAH) is an effective tool for visualizing acoustic sources from pressure measurements made in the near-field of sources using a microphone array. The method involving the Fourier transform and some processing in the frequency-wavenumber domain is suitable for the study of stationary acoustic sources, providing an image of the spatial acoustic field for one frequency. When the behavior of acoustic sources fluctuates in time, NAH may not be used. Unlike time domain holography or transient method, the method proposed in the paper needs no transformation in the frequency domain or any assumption about local stationary properties. It is based on a time formulation of forward sound prediction or backward sound radiation in the time-wavenumber domain. The propagation is described by an analytic impulse response used to define a digital filter. The implementation of one filter in forward propagation and its inverse to recover the acoustic field on the source plane implies by simulations that real-time NAH is viable. Since a numerical filter is used rather than a Fourier transform of the time-signal, the emission on a point of the source may be rebuilt continuously and used for other post-processing applications.

Gunshot injuries of the spine - a review of 49 cases managed at the Groote Schuur Acute Spinal Cord Injury Unit : trauma

The Acute Spinal Injury Unit; relocated from Conradie Hospital to Groote Schuur Hospital in mid-2003; admitted 162 patients in the first year of its existence. A large number of these injuries were the result of interpersonal violence; particularly gunshot wounds. Aim. To review patients with gunshot injuries to the spine; with reference to neurological injury; associated injuries; need for surgery and complications. Methods. A comprehensive database is maintained to collect data on all spinal injury admissions. These data; as well as case notes and X-rays; were reviewed for all gunshot spine patients admitted to the Acute Spinal Injury Unit over a year. Forty-nine patients were identified. Thirty-eight were male and 11 female with an average age of 27.5 years (range 15 - 51 + 8.53). The average stay in the acute unit was 30 (4 - 109 + 28) days. Results. The spinal injury was complete in 38 and incomplete in 8; with 3 having no neurological deficit. The level was cervical in 13; thoracic in 24 and lumbar in 12. Only 9 patients improved neurologically. The spine was considered stable in 43 cases. Stabilisation was performed in the 6 unstable cases. The bullets were removed in 11 cases as they were in the canal. There were 55 significant associated injuries; viz. 14 haemo-pneumothoraces; 16 abdominal visceral injuries; 3 vascular injuries; 4 injuries of the brachial plexus and 3 of the oesophagus; 2 tracheal injuries; 1 soft palate injury and 11 non-spinal fractures. Complications included 3 deaths and discitis in 3 cases; pneumonia in 6 and pressure sores in 6. Conclusion. Gunshot injuries of the spine are a prevalent and resource-intensive cause of paralysis. There is a high incidence of permanent severe neurological deficit; but usually the spine remains mechanically stable. Most of the management revolves around the associated injuries and consequences of the neurological deficit

Gunshot injuries of the spine--a review of 49 cases managed at the Groote Schuur Acute Spinal Cord Injury Unit.

UNLABELLED: The Acute Spinal Injury Unit, relocated from Conradie Hospital to Groote Schuur Hospital in mid-2003, admitted 162 patients in the first year of its existence. A large number of these injuries were the result of interpersonal violence, particularly gunshot wounds. AIM: To review patients with gunshot injuries to the spine, with reference to neurological injury, associated injuries, need for surgery and complications. METHODS: A comprehensive database is maintained to collect data on all spinal injury admissions. These data, as well as case notes and X-rays, were reviewed for all gunshot spine patients admitted to the Acute Spinal Injury Unit over a year. Forty-nine patients were identified. Thirty-eight were male and 11 female with an average age of 27.5 years (range 15-51 +/- 8.53). The average stay in the acute unit was 30 (4-109 +/- 28) days. RESULTS: The spinal injury was complete in 38 and incomplete in 8, with 3 having no neurological deficit. The level was cervical in 13, thoracic in 24 and lumbar in 12. Only 9 patients improved neurologically. The spine was considered stable in 43 cases. Stabilisation was performed in the 6 unstable cases. The bullets were removed in 11 cases as they were in the canal. There were 55 significant associated injuries, viz. 14 haemo-pneumothoraces, 16 abdominal visceral injuries, 3 vascular injuries, 4 injuries of the brachial plexus and 3 of the oesophagus, 2 tracheal injuries, 1 soft palate injury and 11 non-spinal fractures. Complications included 3 deaths and discitis in 3 cases, pneumonia in 6 and pressure sores in 6. CONCLUSION: Gunshot injuries of the spine are a prevalent and resource-intensive cause of paralysis. There is a high incidence of permanent severe neurological deficit, but usually the spine remains mechanically stable. Most of the management revolves around the associated injuries and consequences of the neurological deficit.