Aspect Ratio

In the present study, 1-dimensional (1D) brushite nanomaterials were fabricated through sucrose ester based reverse microemulsion for the first time. X-ray diffraction patterns revealed that the nanomaterials possessed brushite crystal phase with trace amount of hydroxyapatite. The size and morphology of brushite crystals were governed by the changes in the aqueous-to-sucrose ester weight ratio at low initial reactant concentration, giving rise to rod-like and fibre-like 1D nanomaterials. Brushite nanorods and nanofibres with average diameters of 25.53 AE 4.60 nm (aspect ratio $ 6) and 76.18 AE 19.74 nm (aspect ratio $ 40), respectively, had been synthesized. As the reactant concentration increased, it became the key factor in controlling nucleation and crystal growth, rendering the aqueous-to-sucrose ester ratio unimportant. Formation mechanism of various morphologies of brushite crystals is postulated. #

A route to the production of stable non-spherical emulsion droplets has been developed by pushing millimeter-sized liquid droplets stabilized by an excess amount of solid Pickering particles through a narrow capillary. This excess amount allows for the full coverage of the newly created droplets' interface during deformation. Upon exiting the capillary the adhered particles wedge, or ''jam'', on the surface preserving the non-spherical shape. Stable millimeter-sized non-spherical liquid droplets with aspect ratios exceeding 10 and cross-sections in line with capillary dimensions are easily obtained. Post-modification can be performed in conventional reactors. The ability to fabricate non-spherical droplets creates exciting opportunities in areas such as self-healing polymer composites.

A large number of clinopyroxene (cpx) phenocrysts and hosted melt inclusions (MI) in pyroclasts from several Vesuvius eruptions were analyzed. Assuming that their temperature of homogenization (Thom) reflects that of crystallization of the host mineral and that after homogenization and quenching, composition of the MI represents the melt from which the host crystallized, each cpx-MI pair records equilibrium conditions at Tho m. These data were used to discuss the magma evolution within shallow magma chamber. They formed by means of the periodic arrival of mafic batches, recorded by the MI in diopside (Fs4_7) crystallized at 1150 ø-1200øC. Under open conduit conditions the chambers are small, and each magma pulse induces thermal and compositional variations recorded by oscillatory zoned pyroxenes (Fs4_15). Their MI and Tho m summarize the evolution of the chamber resulting from cycles of magma injection, crystal settling, and magma extraction. The deposits of the explosive eruptions which reopen the conduit reflect variable mixing during magma withdrawal from zoned reservoirs, whose layering was deciphered through MI and Thom in salite (Fs15_30). We suggest that the Vesuvius magma chambers evolve from prolate toward subequant, changing their layering with increasing volume and age: (1) initial stage, high aspect ratio chamber, homogeneous mafic melt (TøC -1100) crystal enriched downward; (2) young stage, medium aspect ratio, continuous gradation from mildly evolved (TøC•-1050) to felsic melt (TøC-850-900); and (3) mature stage, low aspect ratio, twofold chamber with stepwise gradient separating lower, convective, mildly evolved portion (TøC ~ 1050) from upper, stratified, felsic portion (TøC-800-950). tions [Santacroce et al., 1993; Belkin et al., 1993; Villemant et al., 1993]). Eruptions marking reopening of the conduit after quiescent intervals of variable length are explosive, polyphased, and commonly characterized by a main, Plinian-type magmatic phase and initial and final phreatomagmatic phases. The erupted magmas have widely variable compositions (K-latite to K-trachyte; K-phonotephrite to K-alkaliphonolite) and volumes (0.2 to >3x109 m3). Clinopyroxene is a common phenocryst phase of Vesuvius magmas [Santacroce, 1987], frequently hosting melt inclusions (MI). Assuming that (1) the temperature of homogenization (Thom) of these inclusions is the (minimal) temperature of crystallization of the host mineral, and (2) after homogenization and quenching the composition of the included glass is representative of the melt from which the host mineral crystallized, each host-inclusion pair records equilibrium conditions at Tho m . They were used to decipher the main processes driving magma evolution during periods of open or obstructed conduit conditions. Pyroxenes from pyroclasts, rather than from lavas, were studied because they represent a quenched record of the erupted magma. The MI are, in fact, glassy to cryptocrystalline with poor or absent crystallization of the host. In the studied crystals the homogenization process is reversible, showing that posttrapping transformations have been completely recovered and the system can be considered closed. Pyroxenes from lavas contain MI with trapped/daughter crystals [Vaggelli et al., 1993] which are absent in the MI from Vesuvius pyroclasts. They give a Tho m [Vaggelli et al., 1992; Belkin et al., 1996] generally higher than those in pyroclasts. Several factors can cause such behavior. The relatively slow cooling of lava flows could induce nonreversible changes in the MI, thus promoting volatile diffusion and important crystallization. On the other hand, microfracturing of the host, possibly induced by pressure variations due to crystallization and vola-18,277 18,278 CIONI ET AL.: VESUVIUS MAGMA CHAMBERS tile exsolution of the liquid in the MI, would favor an advective loss of volatiles. 2. Analytical Methods More than 300 successful homogenization experiments were carried out on doubly polished wafers. Only glassy or cryptocrystalline MI, with a clear shrinkage bubble and no evidences of heterogeneous trapping [Roedrier, 1984], were chosen. For the high-temperature experimental study of MI a modified Leitz 1350 heating stage and an optical heating stage, designed in the Vernadsky Institute of Geochemistry, Moscow (described by Sobolev et al. [1980], were used. The temperature was measured with a Pt-Pt90Rh•0 thermocouple. The accuracy of measurement was around _10øC (Leitz) and +_5øC (Vernarisky), controlled by the melting point of gold and silver. Experiments were performed in a He atmosphere. The rate of heating was varied as a function of the rate of transformation in the inclusions and ranged from 2 to 40øC/min to the point of complete homogenization of MI, i.e., disappearance of bubbles. At attainment of melt homogenization the samples were quenched (in air with Leitz and in He with the Vernadsky apparatus, for which the effective time of quenching was <1 s). After quenching, the inclusions were glassy, at times containing (experiments with Leitz) very small (1-2 gm)shrinkage bubbles on the wall of the inclusion. Some strongly zoned megacrysts were broken into several chips containing zones of differing composition, and thermometric measurements were carried out separately on inclusions in the different zones. Each fragment was quenched after attainment of homogenization of MI. Each crystal was then mounted in epoxy and gradually ground to the point of exposure of the inclusion. After final polishing, the glass inclusions were analyzed. Quantitative analyses of the MI and of their host minerals were obtained by an Energy Dispersive System on a Scanning Electron Microscope (SEM-EDS) at Dipartimento di Scienze della Terra, University of Pisa (Philips 515 SEM with EDAX9900, Philips XL30 with EDAX DX4), at 20 kV accelerating energy, 200-500 nm beam diameter, 100 s live time (a raster area of about 10x10 gm was analyzed on glass).

We study the pressure and shear stress response of an elastomer constrained by, and adhesively bonded to, a rigid cylinder of ®nite length and subject to dierent end boundary conditions. We ®nd that the pressure and shear distributions are very sensitive to the compressibility of the elastomer as well as the aspect ratio of the cylinder. Notably, a slight change in the Poisson's ratio m has a profound eect on the pressure transmissibility of elastomers. Through this principle, we also propose using such geometries to measure the Poisson's ratio of elastomers, which is vital for engineers or designers who model the mechanical behavior of elastomers (e.g., rubbers or gels). Ó

When a cantilevered plate lies in an axial flow, it is known to exhibit selfsustained oscillations once a critical flow velocity is reached. This flutter instability has been investigated theoretically, numerically and experimentally by different authors, showing that the critical velocity is always underestimated by two-dimensional models. However, it is generally admitted that if the plate is confined in the spanwise direction by walls, three-dimensionality of the flow is reduced and the two-dimensional models can apply. The aim of this article is to quantify this phenomenon by analyzing the effect of the clearance between the plate and the side walls on the flutter instability. To do so, the pressure distribution around an infinite-length plate is first solved in the Fourier space, which allows to develop an empirical model for the pressure jump. This empirical model is then used in real space to compute instability thresholds as a function of the channel clearance, the plate aspect ratio and mass ratio. Our main result shows that, as the value of the clearance is reduced, the convergence towards the two-dimensional limit is so slow that this limit is unattainable experimentally.