Research on Damage Characteristics of Brick Masonry under Explosion Load

As the main structural component of partition wall or load-bearing wall, brick masonry has been widely used in construction engineering. However, brick and mortar are all brittle materials prone to crack. Nowadays, fireworks, gas stoves, high-pressure vessels, and other military explosives may explode to damage nearby structures. Many explosion casualties had shown that the load-bearing capacity of brick masonry decreased dramatically and cracks or fragments appeared. Previous studies mainly focused on noncontact explosion in which shock wave is the main damage element. In fact, the response and damage effect of brick masonry wall under contact explosion are more complex, which attracts more attention now. In order to explore the damage characteristics of brick masonry under explosion load, a series of simulations and verification experiments are conducted. RHT and MO granular material models are introduced to describe the behaviour of brick and masonry, respectively, in simulation. The combination effect of front compressive wave and back tensile wave are main factors influencing the breakage of masonry wall. The experimental results are well in accordance with the simulation results. The front cross section dimension of crater is closely related to the radius of spherical explosive charge. A power function predictive model is developed to express the relationship between the radius of hole and the radius of explosive. Furthermore, with increasing the quantity of explosive charge, the number and ejection velocity of fragments are all increased. The relationship between maximum ejection velocity and the quantity of explosive also can be expressed as a power function model.

“HEAD/TAIL PLASMON” PRODUCED BY A GAUSSIAN EJECTION VELOCITY PULSE

We present an analytic model of a collimated ejection with a “single pulse” Gaussian ejection velocity. This flow produces a dense “head” (the leading working surface) joined to the outflow source by a “tail” of lower velocity material. For times greater than the duration of the ejection pulse, this tail develops a linear radial velocity vs. position structure. This “head/tail plasmon” structure is interesting for modelling astrophysical “bullets” joined to their outflow sources by structures with “Hubble law” radial velocity dependencies. We study the case of a Gaussian ejection velocity law with a constant and a Gaussian ejection density history, We compare these two cases, and find that the main effect of the different ejection density histories is to change the mass and the density stratification of the plasmon tail.

Abstract 16058: Abnormal P Wave Morphology is Associated With Decreased Left Atrial Appendage Ejection Velocity

Introduction: P-wave abnormalities measured during periods of sinus rhythm have been associated stroke in people with atrial fibrillation (AF). The majority of AF-related strokes occur from left atrial appendage (LAA) thromboembolism. Electrical and mechanical dysfunction of the left atrium (LA) and left atrial appendage (LAA) can lower the threshold for thromboembolism and stroke. Hypothesis: We aimed to determine whether P-wave abnormalities are associated with decreased LAA ejection velocity (LAAV) on transesophageal echocardiography (TEE). Methods: We conducted a retrospective cross-sectional study. We reviewed patients at a tertiary care medical center who had underwent TEE in sinus rhythm and had an interpretable sinus rhythm ECG within 12 months of TEE. Participants were excluded for history of complex congenital heart disease, age<18, cardiac transplantation, and atrial pacing. Logistic regression analysis was used to estimate the odds ratios of LAAV<40 cm/s for P-wave abnormalities—advanced interatrial block (aIAB), abnormal P-wave terminal force in V1 (aPTFV1), prolonged P-wave duration (PPWD), and abnormal P-wave axis (aPWA). Results: In our final cohort of 169 patients, the odds ratios of aIAB and aPTFV1 for LAAV<40 cm/s after adjustment for CHA 2 DS 2 VASc variables, heart rate during TEE, history of atrial arrhythmias, and left atrial volume index were 2.81 (1.07-7.53) and 2.48 (1.13-5.60), respectively. Conclusions: P-wave abnormalities are independently associated with low LAAV, which may explain their association with AF-related stroke. Further research is needed to determine if incorporation of P-wave analysis will aid AF-related stroke prediction algorithms.

Differences in kinematic parameters between male and female hammer throw finalists of the World Championship in Daegu in 2011

Background and Study Aim. Hammer throwing is the most complex athletic throwing discipline with rotational trajectory and strong effect of several different forces that try to disable the projected throwing trajectory. Kinematic parameters are an important segment in the analysis of athletic disciplines, including hammer throw. They are an indicator of influence and often a difference between competitors of different or the same rank of the competition. The aim of the study was to determine the spatial and temporal differences of kinematic parameters between male and female elite hammers. Material and Methods. The study was conducted on sample of 16 Daegu World Championship finalists in 2011, to analyse differences in kinematic parameters between male and female throwers hammer. To obtain the required results, t-test for small independent samples was applied. Results. The data obtained in the study were given as Mean and Standard deviation. Statistically significant differences between male and female finalists were confirmed in the rate of ejection (t=3.684; p<0.004) and the speed of the fourth turn (t=4.396; p<0.002). The male finalists achieved an average ejection velocity of 27.91m/s and the female finalists 27.17m/s, with an average turn speed of 4.67m/s (male) and 4.03m/s (female). Conclusions. The research has shown that significant differences were made between male and female finalists in Daegu in 2011. The causes of differences can be found in length of training, different training process, technical mastery, competitor experience, morphological profile, motor and anatomical structures, movement technique and biomechanical parameters, which were not taken into the research.

A ‘head/tail’ plasmon model with a Hubble law velocity profile

ABSTRACT We present a model of a hypersonic, collimated, ‘single pulse’ outflow, produced by an event with an ejection velocity that first grows, reaches a peak, and then decreases again to zero velocity in a finite time (simultaneously, the ejection density can have an arbitrary time-variability). We obtain a flow with a leading ‘head’ and a trailing ‘tail’ that for times greater than the width of the pulse develops a linear, ‘Hubble law’ velocity versus position. We present an analytical model for a simple pulse with a parabolic ejection velocity versus time and time-independent mass-loss rate, and compare it to an axisymmetric gasdynamic simulation with parameters appropriate for fast knots in planetary nebulae. This ‘head/tail plasmon’ flow might be applicable to other high-velocity clumps with ‘Hubble law’ tails.

Exploring velocity limits in the thermonuclear supernova ejection scenario for hypervelocity stars and the origin of US 708

Context. Hypervelocity stars (HVS) are a class of stars moving at velocities that are high enough to make them gravitationally unbound from the Galaxy. In recent years, ejection from a close binary system in which one of the components undergoes a thermonuclear supernova (SN) has emerged as a promising candidate production mechanism for the least massive specimens of this class. The explosion mechanisms leading to thermonuclear supernovae, which include the important Type Ia and related subtypes, remain unclear. Aims. This study presents a thorough theoretical analysis of candidate progenitor systems of thermonuclear SNe in the single degenerate helium donor scenario in the relevant parameter space leading to the ejection of HVS. The primary goal is to investigate the previously indeterminate characteristics of the velocity spectra for the ejected component, including possible maxima and minima, as well as the constraints arising from stellar evolution and initial masses. Furthermore, this paper addresses the question of whether knowledge of the ejection velocity spectra may aid in the reconstruction of the terminal state of the supernova progenitor, with a focus on the observed object, US 708. Methods. This study presents the results of 390 binary model sequences computed with the Modules for Experiments in Stellar Astrophysics framework, investigating the evolution of supernova progenitors composed of a helium-rich hot subdwarf and an accreting white dwarf, while avoiding assumption of a specific explosion mechanism as much as possible. The detailed evolution of the donor star as well as gravitational wave radiation and mass transfer-driven orbital evolution were fully taken into account. The results were then correlated with an idealized kinematic analysis of the observed object US 708. Results. This work shows that the ejection velocity spectra reach a maximum in the range of 0.19 M⊙ < MHVS < 0.25 M⊙. Depending on the local Galactic potential, all donors below 0.4 M⊙ are expected to become HVSs. The single degenerate helium donor channel is able to account for runaway velocities up to ∼1150 km s−1 with a Chandrasekhar mass accretor, exceeding 1200 km s−1 when super-Chandrasekhar mass detonations are taken into account. Results show that the previously assumed mass of 0.3 M⊙ for US 708, combined with proper motions that have been obtained more recently, favor a sub-Chandrasekhar mass explosion with a terminal WD mass between 1.1 M⊙ and 1.2 M⊙, while a Chandrasekhar mass explosion requires a mass of > 0.34 M⊙ for US 708. This mechanism may be a source of isolated runaway extremely low-mass white dwarfs. Conclusions. The presence of clear ejection velocity maxima that are terminal accretor mass-dependent, but simultaneously initial-condition independent, provides constraints on the terminal state of a supernova progenitor. Depending on the accuracy of astrometry, it is possible to discern certain types of explosion mechanisms from the inferred ejection velocities alone, with current proper motions allowing for a sub- Chandrasekhar mass SN to explain the origins of US 708. However, more robust reconstructions of the most likely SN progenitor state will require a greater number of observed objects than are currently available.

Investigation of aerodynamics of separator delivery from cavity

The ejection test technology is studied in a sub-transonic supersonic wind tunnel using a single cylinder to provide ejection velocity. The angular velocity adjusting device of ejection mechanism is designed, which can adjust the ejection velocity and angular velocity of the model independently. When the ejection cylinder moves downward, the angular velocity adjusting mechanism works at the same time, so that the model has the preset ejection velocity and angular velocity at the moment of leaving the ejection frame. The ejection velocity error is less than 5%, the angular velocity error is less than 10%, and the repetition rate is more than 95%. The new technology has been verified by wind tunnel tests under complex aerodynamic conditions of sub-transonic supersonic and multi-body interference. All parameters have reached or surpassed the existing technical specifications. It has served for model tests many times and met the needs of wind tunnel test research on ejection of embedded weapons in aircraft.