Summary Reasons for performing study: It has long been recognised that the production of abnormal respiratory sounds by horses during exercise is frequently associated with upper airway obstructions. Respiratory acoustic measurements have shown promise in investigation of upper airway disorders in man and, more recently, in horses with experimentally‐induced obstructions. Objectives: To evaluate sounds from exercising horses with naturally occurring dynamic obstructions of the upper respiratory tract and to compare these with those from normal horses in order to determine whether different obstructions produce characteristic spectral patterns. Methods: The audio signal, airflow and videoendoscopic images were recorded simultaneously during an incremental exercise test on a high‐speed treadmill. Results: Spectral analysis of the audio signal showed marked differences between control and clinically afflicted horses. Dorsal displacement of the soft palate was characterised by a narrow low frequency (20–80 Hz) peak during expiration. Horses with dynamic laryngeal collapse produced inspiratory sounds characterised by a broad band high frequency spectral component in the range 1.1–2.7 kHz. Conclusions and potential relevance: Spectral analysis of respiratory sounds in horses has potential as a diagnostic technique for field use especially when facilities for highspeed treadmill assessment are not practicable.
Positronium annihilation spectroscopy has been used to study capillary condensation o^ nitrogen adsorbed in mesoporous VYCOR glass. The temperature and pressure dependences of the relative change in the 2y:2y annihilation ratio are reported. Both isobars and isotherms exhibit features which are associated with a shifted gas-liquid transition. The isotherm data suggest that pore filling occurs via progressive layer formation at the pore surface followed by an abrupt gas-liquid phase transition at some pressure below the bulk saturated vapor pressure. Such a picture is consistent with the theoretical treatment of adsorption in individual pores. PACS numbers: 64.7aFx, 36.10.Dr, 78.70.Bj Although the adsorption of gases on porous substrates has been the subject of investigation [l] since the beginning of this century, it is only in recent years that any fundamental understanding of the underlying physical processes has emerged. One striking phenomenon that is observed for a wide variety of substrates is the capillary condensation of the adsorbed gas to a dense liquidlike state filling the pores at a pressure which is less than the bulk saturated vapor pressure (Psat). Theory suggests that this phenomenon corresponds to a shift of the bulk condensation transition arising from finite-size effects. Adsorption isotherm measurements [1,2] (adsorbed mass versus pressure) register the transition as a rapid increase in the mass adsorbed, with accompanying pronounced hysteresis. Neutron scattering studies of water vapor in porous VYCOR glass [3] exhibit hysteresis which has also been associated with a shifted gas-liquid phase transition. However, the precise nature of capillary condensation and the interpretation of the associated hysteresis in real porous materials remain rather controversial issues [2]. Here we present the first data which demonstrate definitively that positron and/or positronium annihilation spectroscopy [4] can be used to study capillary condensation in mesoporous materials and provide direct information about the pore environment.Under favorable circumstances [4(a)], i.e., in nonmetallic materials such as glasses and polymers and many liquids and gases, a positron will form positronium (Ps). Statistically, three-quarters of the Ps will be ortho-Ps (o-Ps) and one-quarter para-Ps (/7-Ps). In a vacuum, the o-Ps decays via the emission of 3/ photons and has a lifetime of ^140 ns. p-Ps has a lifetime of 125 ps and annihilates into 2/ photons. In anything other than vacuum (< IxlO"^ Pa) o-Ps has, because of its relatively long lifetime, a finite probability of interacting [4(b),4(c)] with the surrounding medium. The consequence of such an interaction is to facilitate 2/-photon decay, a process called quenching [4(b),4(c)], and to shorten the o-Ps lifetime. The extent to which a surrounding medium facilitates <9-Ps quenching will obviously depend on the density of the medium. The probability of such quenching can be monitored by measuring the relative changes in the 3y:2y annihilation ratio.A fraction of pos...
Results are presented on a new cone-shaped positron moderator which shows a high moderator efficiency (i.e., conversion of beta decay to emitted slow positrons). The moderator efficiencies for the cone moderators studied were found to be up to 0.14% compared to thin-foil measurements of 0.06% in the same experimental system including identical source and holder. These moderators are rugged and easily fabricated, however, they have a lower brightness than single-crystal foil moderators. Comparison of various geometries is presented as well as suggestions for further improvements to increase the total efficiencies.
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