The causes of spatiotemporal variations in erupted fluxes and compositions along a volcanic arc.

Decades of study on volcanic arcs have provided insight into the overarching processes that control magmatism, and how these processes manifest at individual volcanoes. However, the causes of ubiquitous and dramatic intra-arc variations in volcanic flux and composition remain largely unresolved. Investigating such arc-scale issues requires greater quantitative comparison of geophysical and geochemical data, linked through sets of common intensive variables. To work towards these goals, we use observed lava compositions to estimate the heat budget associated with Quaternary volcanism in the Cascades Arc and compare this to the heat required to produce the observed geophysical properties of the crust. Here we show that along-strike volcanic variability in the Quaternary Cascades Arc is primarily related to variations in the flux of basalt into the crust, rather than variations in their crustal storage history. This approach shows promise for studying other large-scale frontier geologic problems in volcanic arcs.

Kinematic variables and water transport control the formation and location of arc volcanoes.

The processes that give rise to arc magmas at convergent plate margins have long been a subject of scientific research and debate. A consensus has developed that the mantle wedge overlying the subducting slab and fluids and/or melts from the subducting slab itself are involved in the melting process. However, the role of kinematic variables such as slab dip and convergence rate in the formation of arc magmas is still unclear. The depth to the top of the subducting slab beneath volcanic arcs, usually approximately 110 +/- 20 km, was previously thought to be constant among arcs. Recent studies revealed that the depth of intermediate-depth earthquakes underneath volcanic arcs, presumably marking the slab-wedge interface, varies systematically between approximately 60 and 173 km and correlates with slab dip and convergence rate. Water-rich magmas (over 4-6 wt% H(2)O) are found in subduction zones with very different subduction parameters, including those with a shallow-dipping slab (north Japan), or steeply dipping slab (Marianas). Here we propose a simple model to address how kinematic parameters of plate subduction relate to the location of mantle melting at subduction zones. We demonstrate that the location of arc volcanoes is controlled by a combination of conditions: melting in the wedge is induced at the overlap of regions in the wedge that are hotter than the melting curve (solidus) of vapour-saturated peridotite and regions where hydrous minerals both in the wedge and in the subducting slab break down. These two limits for melt generation, when combined with the kinematic parameters of slab dip and convergence rate, provide independent constraints on the thermal structure of the wedge and accurately predict the location of mantle wedge melting and the position of arc volcanoes.

Intramural blood flow of skeletal muscle ventricles functioning as aortic counterpulsators.

BACKGROUND: Skeletal muscle ventricles (SMVs) working as aortic counterpulsators have provided long-term left ventricular assistance under experimental conditions. However, gradual deterioration of SMV pump function and rupture have been observed, and this may be related to compromised intramural blood flow during synchronized counterpulsation under systemic working conditions. METHODS: Transformed, double-layered SMVs in 6 sheep were stimulated for 3-minute periods (5 V, 30 Hz, burst duration and delay from QRS both 40% of the cardiac cycle) to work as diastolic counterpulsators in the systemic circulation at a 1:2 (SMV:heart) and 1:1 ratio, and on a mock circulation with low-pressure loading conditions at a 1:2 ratio. Thoracodorsal artery blood flow was monitored by ultrasonic flow probe, and intramural blood flow distribution was investigated by fluorescent microspheres. Thoracodorsal venous lactate concentrations were measured before and after each period of stimulation. RESULTS: Thoracodorsal artery blood flow increased significantly (p < 0.001) after stimulation. The magnitude of augmentation (89%; 95% confidence interval, 36% to 163%) was similar for all working conditions studied. Reactive hyperemia was observed after most 1:1 regimens but was rare after 1:2 regimens. A significant (p < 0.05) 15% increase in serum lactate levels was present after 1:1 regimens only. All regimens of stimulation resulted in a significant increase (p < 0.01) in blood flow to sections in the outer wall of the SMV, but a significant increase (p < 0.05) in blood flow to sections in the inner wall was observed only under low loading conditions. CONCLUSIONS: Skeletal muscle ventricles subjected to 1:1 systemic counterpulsation regimens work under partly anaerobic conditions. High loading conditions may compromise SMV inner wall blood flow.

Difficult intubation: thyromental distance and the atlanto-occipital gap.

Ten patients with a history of difficult intubation and 10 control patients were examined clinically and radiologically. It was shown that thyromental distance can be measured reliably clinically and further support is given to its usefulness as a predictor of difficult intubation. We were unable to demonstrate a conclusive link between thyromental distance and atlanto-occipital or atlanto-axial gaps. A review of X rays in other collections may add to the understanding of these factors in difficult intubation.

Time-shift, trial, and gender effects on vocal perturbation measures.

Three jitter and three shimmer measures were examined for: (1) the stability of the measured values with respect to shifts in sample site (starting point of window in the token) and (2) the effects of trial and gender. The perturbation measures and their coefficients of variation for windows starting from five different but adjacent cycles showed a dependence on sample size. Their variability with regard to shifts in sample site decreased asymptotically with increasing size. The data suggested no statistically significant trial effect except for APQ and no statistically significant gender effect except for absolute jitter. It is speculated that relatively long smoothing windows for shimmer (such as the one used for APQ) would allow the effects of slow vocal modulations (e.g., tremor) to accentuate, especially for lower pitch speakers.

Interactive effects of local smoothing window size and fundamental frequency on shimmer calculation.

Slow amplitude modulation of human voice was approximated by a sinusoidal wave. The theoretical effects of smoothing window size, F0, and modulation frequency on window amplitude average as well as calculated shimmer were mathematically derived. Subsequently, the theoretical predictions were tested using idealized and real voice signals from normal speakers. The theoretical and experimental results suggest that shimmer (when calculated using a smoothing window) is a function of window duration and modulation frequency. Window duration when defined as a constant number of pitch periods varies from speaker to speaker depending on their F0. It may not be desirable to use local smoothing windows with a constant number of cycles for shimmer computation, especially if voices with known low-frequency amplitude modulations but notably different fundamental frequencies are compared.

Effects of auditory feedback and phonetic context on stomal noise in laryngectomized speakers.

Stomal noise intensity during esophageal speech was measured in 7 laryngectomized subjects during amplified monaural auditory feedback and during control conditions without feedback. A significant (5-10 dB) reduction in stomal noise was observed when auditory feedback was applied. The conditions without feedback were designed to provide additional information regarding the effects of the initial phonetic element in the esophageal speech token on stomal noise. During the control conditions, esophageal speech tokens beginning with voiceless consonants resulted in significantly more stomal noise than was present for the other speech tokens. Clinical implications of the findings are discussed.