Explosive Opening Research Articles

Reply to comment by Ferlito et al. on “Complex magma dynamics at Mount Etna revealed by seismic, thermal and volcanological data”

Reply to comment by Ferlito et al. on “Complex magma dynamics at Mount Etna revealed by seismic, thermal and volcanological data”

Mechanism of Inspiratory and Expiratory Crackles

Although crackles are frequently heard on auscultation of the chest of patients with common cardiopulmonary disorders, the mechanism of production of these sounds is inadequately understood. The goal of this research was to gain insights into the mechanism of crackle generation by systematic examination of the relationship between inspiratory and expiratory crackle characteristics. Patients with a significant number of both inspiratory and expiratory crackles were examined using a multichannel lung sound analyzer. These patients included 37 with pneumonia, 5 with heart failure, and 13 with interstitial fibrosis. Multiple crackle characteristics were calculated for each crackle, including frequency, amplitude, crackle transmission coefficient, and crackle polarity. Spectral, temporal, and spatial characteristics of expiratory and inspiratory crackles in these patients were found to be similar, but two characteristics were strikingly different: crackle numbers and crackle polarities. Inspiratory crackles were almost twice as numerous as expiratory crackles (n = 3,308 vs 1,841) and had predominately negative polarity (76% of inspiratory crackles vs 31% of expiratory crackles). These observations are quantitatively consistent with the so-called stress-relaxation quadrupole hypothesis of crackle generation. This hypothesis holds that expiratory crackles are caused by sudden airway closure events that are similar in mechanism but opposite in sign and far less energetic than the explosive opening events that generate inspiratory crackles. We conclude that the most likely mechanism of crackle generation is sudden airway closing during expiration and sudden airway reopening during inspiration.

Explosive opening switches of the MOL stand for currents of 50 and 1000 kA

PB50/50 and PB50/1000 explosive opening switches developed at the Efremov Research Institute of Electrophysical Equipment have been chosen as current switches in the MOL (magnetic sharpening liner) experimental stand. The results of studies and updating of these opening switches performed at the Russian State Research Center, Troitsk Institute of Innovation and Fusion Research during starts of the stand’s first amplifying stage and on a separate test bench with a charging current of up to 50 kA are presented.

Variations in tissue resistivity and in the extension of activated neuron domains shape the voltage signal during spreading depression in the CA1 in vivo

Spreading depression (SD), a wave of neuron activity related to migraine and the ischaemic penumbra, features a moving shell of extracellular negative potential shift (V(o)) whose generators are poorly understood. We investigated its subcellular correlates in the hippocampal CA1 in vivo by localizing the neuron domains that generate transmembrane current (I(m)) using field analysis, and the local changes of tissue resistivity, a major determinant of extracellular current flow. A large increase of tissue resistivity occurred in times and dendritic strata displaying large V(o), albeit with different rates. Typically, SD is composed of basal and apical dendritic components. The apical SD lasts much longer, while it becomes gradually restricted to a narrow dendritic region. Strikingly, pyramidal cells displayed a strong surge of inward current only when SD affected a small dendritic region. However, when the V(o) signal covered most of the main neuron axis, only smaller surges of inward current developed at the outer dendritic rims of a wide null current zone. Computational reconstruction showed that this effect was due to strong spatial cancellation of the inward and outward currents in SD-activated isopotential and shunted regions of individual neurons. Consequently, despite former accounts of large conductance increase, the net I(m) is small and the large DeltaV(o) amplitude mostly due to increased tissue resistivity. The particular subcellular evolution indicates an initial explosive opening of conductance along most of the pyramidal neuron followed by a wave-like centripetal closure towards the apical dendrites. The applicability of these mechanisms to SD in other brain regions is discussed.

Generation of soft X-ray emission by Z-pinches powered from helical explosive magnetocumulative generators

Results are presented from experiments on the implosion of wire arrays powered from 100-and 200-mm-diameter helical explosive magnetocumulative generators with explosive opening switches. The experiments were performed at load currents of up to 4 MA, the current rise time being 0.3–0.4 μs. The maximum soft X-ray yield of ∼ 100 kJ was achieved at a pinch plasma temperature of 55 eV. A two-dimensional MHD code was developed to simulate the process of liner implosion and the generation of X-ray emission. The results of computer simulations agree satisfactorily with the experimental data.

Exploding pollen in Montrichardia arborescens (Araceae)

Pollen grains of Montrichardia are inaperturate with psilate ornamentation. The pollen wall is formed by a thin ectexine and an extraordinarily thick intine. In living as well as in dead pollen grains contact with water leads to a rapid swelling of the intine followed by an explosive opening of the exine. Within a few seconds a thick tube is formed, which is not the pollen tube. The pollen protoplast is situated at the tip of the tube. These intine tubes are interpreted as pollen connecting tools to keep pollen grains together and adhere them to the cuticle of the hairless pollinators.

Design and testing of the power electronics for the cannon caliber electromagnetic gun system

The University of Texas Center for Electromechanics (UT-CEM) is in the final fabrication and testing phase of a power electronics system required to operate a skid mounted compulsator-driven railgun. Design goals for the self-excited air core compulsator include a 95 MW rectifier/inverter bridge for field coil self-excitation. Initial field coil seed energy is supplied by a 50 kJ capacitive discharge from the field initiation module. The field coil is passively protected from voltage transients by an array of metal oxide varistors. Other system power modules include the gun closing switch and explosive opening switch. This paper presents a brief system overview and detailed design of the rectifier/inverter bridge module with performance data from shots up to 6.

A hybrid computational approach for the analysis of blast resistant connections

The behavior, response and role of reinforcing bars in structural concrete knee-joints under explosive opening loads has been studied numerically. A hybrid finite element (FE)-finite difference (FD) approach was developed for this purpose, in which the connection region was simulated by the FD part of the approach and the adjoining members were represented with the FE code DYNA3D. Nonlinear material models for concrete and steel were employed, and the effect of bar size and location in the connection were studied. The proposed approach is described, and findings, conclusions and recommendations are presented.

Design of a dissipation circuit for a 560 MJ inductive storage supply

The authors report on the design and component testing of a dissipation circuit for a 560 MJ inductive storage supply. This storage supply is charged by a 5 MA battery power supply. This battery upgraded supply (BUS) requires energy management at either the end of a test or as a means of aborting a test in the event of a fault. Energy management is accomplished by diverting the supply current into large dump resistors capable of dissipating the inductively stored energy through resistive heating. After most of the energy has been resistively dissipated, a low residual current exists in the resistor circuit due to the applied battery voltage of the battery power supply. This current is interrupted with final interrupter switches in series with the dump resistors. Both the divert and final interrupt switches are explosive opening switches. Special design features of these components include low-cost extruded aluminium switch elements for use in both the divert and final interrupt positions that have the designed-in capability to open thermally in the event of an explosive switch failure.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dynamic behavior of an explosive opening switch

An investigation into the dynamic behavior of explosive opening switches, which are used in power compression circuits for railgun research, is summarized. During switch operation, a primacord is ignited at one end of the switch, and a detonation wave propagates down the primacord along the length of the switch. It is assumed that all locations along the length of the primacord detonate simultaneously, a line detonation. A 2-D Eulerian hydrocode was executed to simulate the early-time dynamics of the explosive switch. Three different opening switch element geometries were considered: a circular external shape with a round internal hole, a faceted (or hexagonal) external shape with a round internal hole, and a circular external shape with a round internal hole that has four internal notches directed along predetermined shear planes. The results provide insight into the pressures, stresses, and strains experienced at various locations in the switch.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Electromagnetic force, jerk, and electric gun projectiles

The authors define jerk in terms of electromagnetic parameters and give simple examples of stress amplification with increasing acceleration rate. For a given barrel caliber and length, railgun and projectile structural limitations produce a family of curves which define a range of allowed muzzle energies. Maps of ideal performance are presented based on idealized current waveforms modified to observe railgun and projectile structural limitations. The authors also describe a modification to explosive opening switches which allows control of the developed voltage of the switch and therefore the rate of rise of current in the railgun. Experimental data demonstrating this capability on a 60-MJ power supply are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Non-arcing commutation in explosive opening switches

The authors examine the commutation performance of the RAP switch in the Air Force Armament Technology Battery Power System. The system stores over 10 MJ at up to 2.5 MA in an inductor. The RAP switch is used to commutate the current into a railgun load. The RAP switch develops several hundred volts before it completely opens and arcs. The authors have developed an analytic description of the nonarcing opening powers and show that it is primarily resistive and that current diffusion plays a central role. Experimental results which validate the theoretical model are also presented. It is shown how the effect can be exploited to achieve higher nonarcing impedance, therefore reducing the destructive effects of arcs on the opening switch. >

An explosive opening superconducting switch

A superconducting YBCO tube was tested as an opening switch to demonstrate novel switching concepts for inductive energy storage. The tube was connected in series with a 1.2-mH inductor and a 4800- mu F capacitor bank which was charged to a predetermined level and discharged through the circuit. No measurable dissipation was observed for test discharges of 8-ms duration, with maximum pulse amplitude increasing for each test while the YBCO was superconducting at 77 K. At the highest current pulse maximum of 95 A, the switch was opened by exploding a short length of detonating cord inserted into the center of the tube. The current decreased to zero, and the voltage increased to maximum in approximately 160 mu s, resulting in a voltage gain of over 25 for current commutation purposes.

Renewal of explosive activity at Vesuvius: models for the expected tephra fallout

One of the major problems concerning the assessment of volcanic hazard at Vesuvius is to determine the type and size of the eruptive event that will characterize the volcano when it becomes active once again. During its history, Somma-Vesuvius has exhibited different types of activity, ranging from quiet lava emission to moderate strombolian activity, to catastrophic plinian eruptions. Available data support a behavior model characterized by the increasing size and explosiveness of the eruptions with increasing repose time, as a consequence of a roughly constant periodic supply of deep basic magma to a shallow magma chamber and differentiation and mixing in the chamber. After the A.D. 79 eruption, a homogeneous HK (high potassium) nature of erupted products was reflected by a magma alimentation rate roughly estimated at 1.5–2.0 millions of cubic meters per year. Assuming no major changes have occurred in the feeding system of the volcano after its last eruption in 1944, a volume of 40–70 × 10 6 m 3 magma could be considered presently available for a renewal of activity at Vesuvius. The emission of such a mass of magma during a single eruption would result into the largest event since the highly disruptive 1631 subplinian eruption. Presently, no possibility exists to forecast the eruptive character of such an eruption, and either a “ultrastrombolian” or a “subplinian” case appear equally possible. The latter possibility implies the highest potential hazard. This paper provides the numerical simulations of the main eruptive phenomenon that probably will occur during this “maximum expected event”: the fallout of tephra from a high, sustained eruption column. After the initial explosive opening of the vent, the scenario consists of the formation of a high convective column with lee-side fallout of pumice and lithic fragments, accompanied and followed by column collapses generating pyroclastic flows and surges. The column behavior was numerically simulated by using the Wilson and Walker column model with the following input parameters: mass eruption rate between 0.4 and 2.0 × 10 7 kg s −1, gas content between 5 and 10 wt.%, lithic content 20 wt.%, basal radius of the column larger than the minimum value for subsonic initial velocity of the jet. The resulting maximum column height and maximum gas thrust height were respectively 11–16 km and below 1000 m. The tephra fallout was modeled by a continuity equation solved on a nonuniform three-dimensional grid. The input parameters to the model are: seasonal wind velocity profiles; eddy diffusion coefficients of 3000 m 2 s −1 (horizontal) and 50 m 2 s −1 (vertical); particles whose nature and grain size are inferred after data on pyroclastic deposits from ancient Vesuvius eruptions distributed along a vertical linear source. The hazard implications of the different modeled cases are briefly discussed.

Explosive opening switch work at Westinghouse

An explosive switch that commutated 315 kA into a resistor and a second version designed to switch up to 1 MA into an HPG (homopolar generator) -driven railgun system are presented. These switches are located very near the load and consist of a set of main busbars in a low-inductance configuration shorted by a thinner switch busbar. Linear-shaped charges are used to sever this switch busbar at several locations when a preselected current level is attained, commutating the current into the load. The feasibility of multishot explosive switches for electromagnetic-launch systems is also considered.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Explosive flower opening in ornithophily: a study of pollination mechanisms in some Central African Loranthaceae

In many ornithophilous Loranthaceae pollination is accompanied by an explosive opening of the flowers, and diverse mechanisms have evolved in different genera to bring this about. These are described for the African genera Erianthemum, Englerina, Tapinanthus, Globimetula, Vanwykia and Plicosepalus. In many genera tensions within the stamens cause the tubular corolla to split along the petal junctions to form window-like fenestrae. The flowers are pollinated mainly by sunbirds which insert their beaks through the fenestrae in search of the abundant nectar. This action causes the tube to split and the stamens to coil inwards explosively. In Globimetula and many species of Tapinanthus pigment is secreted along the edges of the specialized petal segments of the head, the spathulae. Probing along these secretory junctions causes the spathulae to reflex; further probing splits the corolla tube, and allows the stamens to coil inwards explosively. In Globimetula reflexure of the petals exposes the central column of stamens, between which secondary fenestrae are developed. In Plicosepalus curvature of the corolla tube is connected with a more specialized fenestral structure; flower opening is not explosive, and the open flowers continue to be visited regularly by sunbirds. In Vanwykia an early stage in the development of explosive flower-opening is found.

Foraging Strategies and Energetics of East African Sunbirds at Mistletoe Flowers

Sunbirds (Nectariniidae) feeding on nectar of the mistletoe, Phragmanthera dshallensis, in central Kenya encounter two types of flowers. Closed flowers, which have not been visited previously and must be opened by the feeding bird, contain more nectar and require more feeding time than open flowers. Open flowers result from the visitation and explosive opening of closed flowers. Closed flowers are rarer overall than open flowers, although occasionally a local area may have a majority of closed flowers. The different-sized sunbird species tend to take different proportions of open and closed flowers; generally there is a positive relation between bird size and percentage of closed flowers taken. We examined benefits and costs for each bird species feeding in local patches of mistletoe. The benefits were the same for each species. The time costs varied inversely with bird size. These differences were reduced by the lower energetic costs of the smaller species. For all species the caloric benefit to cost ratio (= foraging efficiency) increased with increasing proportions of closed flowers visited. However the foraging efficiency difference between 0% and 100% closed flowers was greatest for kilimensis, indicating that kilimensis gained more by preferentially moving to patches with high proportions of closed flowers. The data on percentage closed flowers actually taken indicate that those species which should derive greater energy benefits by taking higher proportions of closed flowers tend to do so. Complete specialization on closed flowers, however, apparently is prevented by increasing search costs within and between patches. The sunbird foraging behavior is consistent with predictions based on maximizing foraging efficiencies as a function of relative energy value of the two flower types.

Crackles and wheezes.

This is an essay on the genesis of adventitious lung sounds, based on clinical and experimental observations. Crackling is usually due to the explosive opening of airways in territories of the lung deflated to residual volume. Wheezing is generated by air passing at high velocity through an airway narrowed to the point of closure. The pitch of the wheeze is largely determined by the linear velocity of this jet of air and is independent of the calibre and length of the airway. The clinical interpretation of adventitious sounds is discussed in the light of these observations.