Comparing the end correction of a spherically baffled piston to infinitely baffled and unbaffled circular radiators (L).

Models of acoustical systems commonly employ end corrections to represent the radiation impedance of a vibrating element. Although several analytic solutions appear in the literature, the end corrections of an infinitely baffled circular piston and an unbaffled semi-infinite circular pipe remain popular in modeling applications. This Letter compares the end correction of these two configurations to that of a radially vibrating cap on a sphere.

Low-frequency radiation from a vibrating cap on a rigid spherical shell with a circular aperture.

Theoretical models based on spherical geometries have long provided essential insights into the directional behavior of sound sources such as loudspeakers and human speech. Because commonly applied models predict omnidirectional radiation at low frequencies and increasing directionality at higher frequencies, they fail to predict the directional characteristics of certain sources with different source geometries. These sources include violins and open-back guitar amplifiers that have openings or ports connecting a cavity or enclosure to the exterior domain.

Directional characteristics of two gamelan gongs.

The distinctive geometry and structural characteristics of Balinese gamelan gongs lead to the instrument's unique sound and musical style. This work presents high-resolution directivity measurements of two types of gamelan gongs to quantify and better understand their acoustic behavior. The measured instruments' structural modes clearly impact their far-field directivity patterns, with the number of directional lobes corresponding to the associated structural mode shapes.

On the low-frequency acoustic center.

Acousticians typically consider the acoustic center of a source to be the point from which sound waves appear to diverge spherically. Many applications require the center's accurate determination, but its deeper significance and means of assessment have often remained ambiguous. This work revisits the acoustic center and shows how a low-frequency sound radiator with omnidirectional far-field directivity has a center defined by its dipole-to-monopole moment ratio.

High-resolution spherical directivity of live speech from a multiple-capture transfer function method.

Although human speech radiation has been a subject of considerable interest for decades, researchers have not previously measured its directivity over a complete sphere with high spatial and spectral resolution using live phonetically balanced passages. The research reported in this paper addresses this deficiency by employing a multiple-capture transfer function technique and spherical harmonic expansions. The work involved eight subjects and 2522 unique sampling positions over a 1.

Glucose-Insulin-Potassium Does Not Reduce Myocardial Infarct Size in an Ischemic/Reperfusion Rabbit Model.

While glucose-insulin-potassium (GIK) has been suggested to be cardioprotective, few studies have assessed its effect on anatomic myocardial infarct size in an ischemia-reperfusion protocol. Anesthetized rabbits were subjected to a 30-minute coronary artery occlusion followed by 4 hours of reperfusion. Rabbits were pretreated with a GIK infusion lasting 90 minutes or placebo.

Is warm retrograde blood cardioplegia better than cold for myocardial protection?

Background: This study tests the hypothesis that continuous normothermic retrograde blood cardioplegia is superior to cold intermittent blood cardioplegia in protecting the left and right side of the heart transmurally during an extended cross-clamping period.

Methods: Twelve anesthetized, open chest dogs were placed on cardiopulmonary bypass and randomized to receive continuous warm (n = 6) or intermittent cold cardioprotection (n = 6) during a 3-hour aortic cross-clamp period. Transmural left ventricular muscle biopsy specimens were taken before the initiation of cardiopulmonary bypass and 90 and 180 minutes after cross-clamping.

Stuttering Reperfusion of Ischemic Myocardium Does Not Exacerbate Myocardial Infarction: Evidence Against Lethal Cell Reperfusion Injury in the Rabbit.

In the clinical setting of acute myocardial infarction, coronary reperfusion may occur intermittently. Whether this intermittent or stuttering reperfusion exacerbates reperfusion cell injury is not known. To investigate whether stuttering reperfusion affects the development of necrosis, anesthetized male rabbits were randomized to either control or stuttering-reperfusion groups.

Acute Ethanol Does Not Protect Against Ischemic/Reperfusion Injury in Rabbit Myocardium.

Moderate use of alcohol has shown protective effects in coronary artery disease, while excessive use has been associated with cardiomyopathy and hypertension. Since alcohol is a vasodilator, we postulated that it might have protective effects when administered acutely in the setting of ischemia/reperfusion. Therefore, we studied the acute effects of alcohol on myocardial infarction in a rabbit model.

Do antioxidant vitamins reduce infarct size following acute myocardial ischemia/reperfusion?

There is controversy concerning the ability of antioxidant vitamins to reduce myocardial infarct size. We sought to determine whether a brief prophylactic treatment of vitamin C or vitamin C plus Trolox (a water-soluble form of vitamin E) could reduce myocardial infarct size in an experimental model. We used an anesthetized open-chest rabbit model in which a branch of the circumflex coronary artery was ligated for 30 minutes followed by 4 hours of reperfusion.

An adenosine A1 receptor agonist, R(-)-N-(2-phenylisopropyl)-adenosine (PIA), but not adenosine itself, acts as a therapeutic preconditioning-mimetic agent in rabbits.

Objective: A preconditioning mimetic agent could be useful therapy for cardiac ischaemic events; stimulation of adenosine receptors has been proposed as a preconditioning mediator. The ability of adenosine-receptor activation to mimic ischaemic preconditioning was tested in an in vivo rabbit model.

Methods: Adenosine (15 mg, a maximally tolerated dose, n = 10) was infused over six minutes via a coronary artery and compared with saline (n = 12) in anaesthetised rabbits.