EXPERIMENTAL STUDY OF CLINICAL INDICATORS OF INTRATISSUE PRESSURE IN DEEP CIRCULAR BURNS AND ITS DYNAMICS DEPENDING ON THE NATURE AND VOLUME OF SURGERY

The purpose of research. To improve in the experiment the optimal variants of surgical tactics to eliminate the phenomena of compartment syndrome in circular deep burns on the basis of studying the dynamics of intratissue pressure. Materials and methods. An experiment to study the effectiveness of treatment of deep circular burns of III degree, accompanied by compartment-syndrome with objectification of intra-tissue pressure was performed on 18 male WAG rats weighing 190.0-200.0 g, which were divided into three groups depending from the nature and scope of surgery. Research results and their discussion. Based on the assessment of the dependence of the level of intratissue pressure in the tissues on the timing of modeling of deep circular burns in the experiment and tactics and volume of surgical treatment, a clear dependence of indicators in all groups of experimental animals. The primary necrectomy performed in the III main group due to the radical surgical intervention allowed to completely normalize the intratissue pressure within 24 hours. Conclusions. 1. Clinical indicators of intratissue pressure at deep circular burns depending on time of modeling of a thermal trauma and character and volume of surgical intervention are defined in experiment. 2. It is established that primary necrectomy due to radical excision of necrotized tissues and rapid decompression contributes to the nor malization of intratissue pressure.

Hearing Aids Performance in Hypobaric Environments

OBJECTIVE: High altitudes imply exposure to a decreased ambient air pressure. Such a situation may also alter the performance of acoustic transducers using vibrating diaphragms due to air rarefaction. This study aimed at analyzing the performance at high altitude of hearing aids (HAs) where mechano-electric and electro-mechanic transducers are used. METHODS: A hypobaric chamber was used to perform two separated experimental sessions. In the first one two commercial models of HAs were exposed to a simulated altitude of 25,000 ft (7620 m) and to a subsequent rapid decompression profile, with a rapid climb (< 3 s) from 8000 (2438 m) to 25,000 ft. The second session separately analyzed the performance of microphone and receiver at an altitude of 9000 and 15,000 ft (2743 and 4572 m). Before and after the first session, the HAs were tested with an electronic ear while a dedicated recording system was used in the second session. RESULTS: No HA damage or dysfunction was detected during the first session. In the second one, the microphone showed a mild decrease of its output, while the receiver exhibited a much higher reduction of its output. CONCLUSION: Our findings highlight the safe use of HAs even under extreme environmental pressure changes. For altitudes exceeding 10,000 ft (3048 m), a recalibration of the HAs output via a dedicated program may be suggested. Lucertini M, Sanjust F, Manca R, Cerini L, Lucertini L, Sisto R. Hearing aids performance in hypobaric environments. Aerosp Med Hum Perform. 2021; 92(9):738743.

The products of primary magma fragmentation finally revealed by pumice agglomerates

Following rapid decompression in the conduit of a volcano, magma breaks into ash- to block-sized fragments, powering explosive sub-Plinian and Plinian eruptions that may generate destructive pyroclastic falls and flows. It is thus crucial to assess how magma breaks up into fragments. This task is difficult, however, because of the subterranean nature of the entire process and because the original size of pristine fragments is modified by secondary fragmentation and expansion. New textural observations of sub-Plinian and Plinian pumice lapilli reveal that some primary products of magma fragmentation survive by sintering together within seconds of magma break-up. Their size distributions reflect the energetics of fragmentation, consistent with products of rapid decompression experiments. Pumice aggregates thus offer a unique window into the previously inaccessible primary fragmentation process and could be used to determine the potential energy of fragmentation.

High Crystal Number Densities From Mechanical Damage

Laboratory experiments investigating syn-eruptive crystallization are fundamental for interpreting crystal and vesicle textures in pyroclasts. Previous experiments have advanced our understanding by varying decompression and cooling pathways, volatile components, and melt composition. However, they have largely failed to produce the high crystal number densities seen in many cryptodome and dome samples. This is feasibly due to the relatively simple decompression pathways employed in experimental studies. In this study, we approach the problem by exploring non-linear decompression pathways. We present two series of experiments: (1) decompression from low initial starting pressure and (2) a compression-and-release step after the initial decompression. The purpose of each series was to simulate (1) decompression of magma that stalls during ascent and (2) pressure cycling that occurs in non-erupted magma during episodic explosive activity. The experiments were carried out on a synthetic rhyodacite (SiO2 = 69 wt%) held initially at 50 MPa and 885°C then decompressed at rates of 0.026 and 0.05 MPa s−1 to 10 MPa A subset of experiments was then subjected to a compression step to 110 MPa followed by near-instantaneous release back to 10 MPa. A substantial volume fraction of dendritic microlites (ϕxtl = 0.27–0.32, Na = 4.79 × 103 mm–2) formed during the initial hold at 50 MPa; additional crystallization during subsequent decompression to ≥ 10 MPa was minimal, as evidenced by only small increases in crystallinity (ϕxtl = 0.28–0.33) and comparable crystal number densities (4.11–7.81 × 103 mm–2). Samples that underwent recompression followed by a second decompression showed no increase in crystal volume fraction but did show extensive disruption of the initial dendritic, box-work microlite structures that produced high number densities (Na = 43.5–87.2 × 103 mm–2) of small individual crystals. The disruption was driven by a combination of rapid vesiculation, expansion and resulting shear along the capsule walls. From these results, we suggest that high crystal number densities may be a signature of rapid deformation occurring after magma stalling in the subsurface, perhaps related to pressure cycling and accompanying rapid changes in vesicularity during repeated small and shallow-sourced explosions. We compare our experiments to pyroclasts from shallow intrusions that preceded the 18 May 1980 eruption of Mount St Helens. These pyroclasts were erupted both prior to 18 May, during episodic precursory explosive activity, and by the 18 May initial lateral blast. The pattern of precursory activity indicates multiple episodes of pressurization (prior to explosive events) and rapid decompression (during explosive events) that we use to illustrate the significance of our experimental results.

Research and Verification of Key Techniques in the Simulation of Space Extremely Rapid Decompression in Millisecond

The research of rapid decompression with its effect assessment and protection technology is the problem that must be faced by the future exploration projects such as near space exploration, deep space exploration, and long-term lunar or Mars base. A new reusable quick opening mechanism which can be opened in millisecond is designed to meet the testing requirement of ground simulator for extremely rapid decompression, and the testing results show that the quick opening mechanism can be opened within 0.1 s. The mathematical formulation is also developed, and the comparisons with the results from the literature demonstrate its validity. The CFD simulation and the verification system are established for the airflow in the rapid decompression process under different opening degrees. The simulation results show that the effect of the opening on the decompression process is very obvious and the decompression time corresponding to 50%, 75%, and 100% opening is 479.1 ms, 320.7 ms, and 290.1 ms, respectively. The testing results also show a consistent trend which is 583 ms, 450 ms, and 384 ms, respectively, to reach the equilibrium state.

Bubbles and element clusters in rock melts: A chicken and egg problem

&lt;p&gt;The nucleation and growth dynamics of gas bubbles and crystals play a vital function in determining the eruptive behaviour of a magma. Their rate and relative timing, among other factors, are controlled by the magma&amp;#8217;s ascent rate. Investigating the kinetics of decompression-induced degassing and crystallization processes can thus give us insight into the rheology of magmas. For example, the rapid decompression of magmas inhibits microlite crystallization and bubble nucleation during ascent leading to crystallization and degassing at shallow levels. This results in a drastic increase in viscosity and an over pressured system, which can lead to violent eruptions. Although many experiments and numerical simulations of magma decompression have been carried out, nascent and initial bubble nucleation remain poorly understood. It is widely accepted that there are two ways bubbles can nucleate within a melt: heterogeneous (on a pre-existing surface) and homogeneous nucleation (within the melt), where homogeneous nucleation requires a higher volatile supersaturation. It has since been tentatively suggested that homogeneous nucleation is simply a variety of heterogeneous nucleation where nucleation occurs on the surface of submicroscopic crystals. However, evidence of these crystals is equivocal. Thus, we have combined novel 2D and 3D structural and chemical microscopy techniques including scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) mapping, and atom probe tomography (APT) to investigate the presence of sub-nanometer scale chemical heterogeneities in the vicinity of gas bubbles within an experimental andesitic melt. The combined STEM and EELS data reveal a heterogeneous distribution of bubbles within the melt ranging between 20-100 nm in diameter, some of which have Fe and/or Ca element clusters at the bubble-melt interface. Element clusters enriched in Fe, Ca, and Na are also observed heterogeneously distributed within the melt. The reconstructed APT data reveals bubbles as low ionic density regions overlain by a Na-, Ca-, and K-rich cluster and heterogeneously distributed Fe clusters within the bulk of the melt. Based on these observations, our data demonstrate the existence of nano-scale chemical heterogeneities within the melt and at the bubble-melt interface of bubbles that were previously interpreted to be nucleated homogeneously within the melt, therefore contributing to the proposed hypothesis that homogeneous nucleation could in fact be a variety of heterogeneous nucleation. These results highlight the need to redefine homogeneous nucleation and revisit whether bubbles or crystals occur first within volcanic melts.&amp;#160;&lt;/p&gt;

From permanent flank sliding to catastrophic collapse and explosive eruptions at basaltic volcanoes: the role of shallow intrusive magma bodies.

&lt;p&gt;Caldera collapses and flank failures, eventually associated with violent explosive eruptions, punctuate the history of volcanoes worldwide and represent major highly hazardous events in their evolution. Nevertheless, their link to magma transfer and storage in the plumbing system, together with the nature of weakness zones responsible for volcano collapses still need to be fully elucidated. We performed rapid decompression experiments on a set of basaltic rocks (lavas, dolerite dikes, gabbros) from Piton de la Fournaise, La R&amp;#233;union, spanning a very large range of petrophysical properties. Samples derived from the most recent &amp;#160;caldera-related explosive breccias of this volcano. Petrophysical measurements revealed a corresponding variability in density, porosity, P-wave velocity (dry and wet), and uniaxial compressive strength. The large variation in P-wave velocity and strength is interpreted to be the result of the wide ranges in texture (porosity/vesicularity) and lithology. Notably, some of the dense gabbroic units that have remained intact despite likely having experienced several natural cycles of heating and cooling are comparatively weak. We infer that volcano instability should not be interpreted solely in terms of altered rock units. On one side, the interface between shallow intrusive bodies and the vesicular lava pile represents a potential interface for repeated sill emplacement, which favour flank sliding. On the other side, weak shallow seated granular intrusive rocks with variable amounts of interstitial melt respond in a brittle fashion to rapid decompression during caldera and flank collapse events. The large petrophysical heterogeneity of crustal rocks together with the occurrence of shallow intrusive bodies must be considered when interpreting monitoring data and assessing potential hazards related to the stability of basaltic volcanoes.&lt;/p&gt;

Poirierite, a dense metastable polymorph of magnesium iron silicate in shocked meteorites

A dense magnesium iron silicate polymorph with a structure intermediate between olivine, ringwoodite, and wadsleyite was theoretically predicted about four decades ago. As this group of minerals constitute the major component of shocked meteorites, constraining their transitional forms and behaviour is of potential importance for understanding impact events on their parent bodies. Here we use high-resolution transmission electron microscopy techniques and single-crystal X-ray diffraction analyses to identify naturally occurring examples of this mineral – recently named poirierite – in shocked chondritic meteorites. We observe nanoscale lamellar poirierite topotactically intergrown within wadsleyite, and additionally within ringwoodite as recently reported. Our results confirm the intermediate structure of poirierite and suggest it might be a relay point in the shear transformations between its polymorphs. We propose that poirierite formed during rapid decompression at relatively low temperature in retrograde shock metamorphism of the meteorites.