Shock wave focusing using geometrical shock dynamics

A finite-difference numerical method for geometrical shock dynamics has been developed based on the analogy between the nonlinear ray equations and the supersonic potential equation. The method has proven to be an efficient and inexpensive tool for approximately analyzing the focusing of weak shock waves, where complex nonlinear wave interactions occur over a large range of physical scales. The numerical results exhibit the qualitative behavior of strong, moderate, and weak shock focusing observed experimentally. The physical mechanisms that are influenced by aperture angle and shock strength are properly represented by geometrical shock dynamics. Comparison with experimental measurements of the location at which maximum shock pressure occurs shows good agreement, but the maximum pressure at focus is overestimated by about 60%. This error, though large, is acceptable when the speed and low cost of the method is taken into consideration. The error is primarily due to the under prediction of disturbance speed on weak shock fronts. Adequate resolution of the focal region proves to be particularly important to properly judge the validity of shock dynamics theory, under-resolution leading to overly optimistic conclusions

Seismic detection of sonic booms

The pressure signals from a sonic boom will produce a small, but detectable, ground motion. The extensive seismic network in southern California, consisting of over 200 sites covering over 50 000 square kilometers, is used to map primary and secondary sonic boom carpets. Data from the network is used to analyze three supersonic overflights in the western United States. The results are compared to ray-tracing computations using a realistic model of the stratified atmospheric at the time of the measurements. The results show sonic boom ground exposure under the real atmosphere is much larger than previously expected or predicted by ray tracing alone. Finally, seismic observations are used to draw some inferences on the origin of a set of "mystery booms" recorded in 1992–1993 in southern California

Rapid evaporation at the superheat limit

In an experimental investigation of the transient processes that occur when a single droplet of butane at the superheat limit vaporizes explosively, short-exposure photographs and fast-response pressure measurements have been used to construct a description of the complete explosion process. It is observed that only a single bubble forms within the drop during each explosion, and that the growth proceeds on a microsecond time scale. An interfacial instability driven by rapid evaporation has been observed on the surface of the bubbles. It is suggested that the Landau mechanism of instability, originally described in connection with the instability of laminar flames, also applies to rapid evaporation at the superheat limit. The photographic evidence and the pressure data are used to estimate the evaporative mass flux across the liquid-vapour interface after the onset of instability. The ;ate of evaporation is shown to be two orders of magnitude greater than would be predicted by conventional bubble-growth theories that do not account for the effects of instability. An estimate of the mean density within the bubbles during the evaporative stage indicates that it is more than one half of the critical density of butane. Additional interesting dynamical effects that are observed include a series of toroidal waves that form on the interface between the butane vapour and the external host liquid in the bubble column apparatus after the bubble has grown large enough to contact the outer edge of the drop, and violent oscillations of the bubble that occur on a millisecond time scale, after evaporation of the liquid butane is complete, that cause the disintegration of the bubble into a cloud of tiny bubbles by Rayleigh-Taylor instability

An investigation of shock strengthening in a conical convergent channel

The behaviour of an initially plane, strong shock wave propagating into a conical convergence is investigated experimentally and theoretically. In the experiment a 10° half-angle cone is mounted on the end of a pressure-driven shock tube. Shock waves with initial Mach numbers varying from 6.0 to 10·2 are generated in argon a t a pressure of 1·5 Torr. During each run local shock velocities a t several positions along the cone axis are measured using a thin multi-crystal piezoelectric probe inserted from the vertex. This technique produces accurate velocity data for both the incident and reflected shock waves. In the corresponding analysis, a simplified characteristics method is used to obtain an approximate solution of the axisymmetric diffraction equations derived by Whitham (1959). Both the shock velocity measurements and the axisymmetric diffraction solution confirm that the incident shock behaviour is dominated by cyclic diffraction processes which originate at the entrance of the cone. Each diffraction cycle is characterized by Mach reflexion on the cone wall followed by Mach reflexion on the axis, These cycles evidently persist until the shock reaches the cone vertex, where the measured velocity has increased by as much as a factor of three. Real-gas effects, enhanced in the experiment by increasing the initial Mach number and decreasing the pressure, apparently alter the shock wave behaviour only in the region near the vertex. Velocity measurements for the reflected shock within the cone show that the shock velocity is nearly constant throughout most of the convergence length

Problems of LNG spill hazard assessment

It is apparent from the literature on LNG spills that there is a considerable lack of knowledge in many areas of technical importance to the safety assessment of LNG receiving terminals. For this reason, a thorough critical review of the state-of-the-art regarding the technical aspects of LNG spill evaluation is in preparation. The purpose of this review is to focus attention on these aspects of the problem that are least understood and which are crucial to a proper assessment of the hazards. It is realized that ERDA has already conducted an LNG Safety and Control Workship, the outcome of which was a set of conclusions and recommendations regarding the safety and control issues of LNG operations

The Thermodynamics Of Formation Of A 3-strand, Dna 3-way Junction Complex

Isothermal titration calorimetry (ITC) is used to study the thermodynamics of assembly of the three DNA oligonucleotides S1 (5\u27GCCTGCCACCGC), S2 (5\u27-GCGGTGCGTCCG), and S3AA (5\u27-CGGACGAAGCAGGC) to form a three-way junction (TWJ) complex consisting of three double-helical arms radiating from a junction region having two unpaired adenosines in one strand (S3AA). The thermodynamics of assembly were measured for three different orders of addition of the component oligonucleotides at four temperatures between 10 and 25 degrees C. At each temperature studied, the overall values of Delta H, Delta S degrees, and Delta G degrees for assembly of the complex from the component single strands were found to be independent of the order of addition. The enthalpy of binding, Delta H, was found to be linearly dependent on temperature. From the temperature dependence of Delta H, the change in heat capacity Delta C-p, for the overall assembly of three strands to form the junction complex was calculated and found to be-1.6 kcal mol(-1) K-1. This work represents the first attempt to evaluate the thermodynamics of DNA TWJ formation by ITC

Small Scale Detonation Studies: Direct impulse measurements for detonations and deflagrations

This report is an account of research carried out from January to June 2000 on the feasibility of detonation initiation and impulse generation for small-scale pulse detonation engines. The initial work was focussed on the direct measurement of impulse using the ballistic pendulum technique for single detonations initiated in a tube with one end open to the atmosphere through a thin diaphragm. Three tubes were used: (1) 38-mm diameter by 1.5 m long. (2) 75-mm diameter by 0.6 m long. (3) 75-mm diameter by 1 m long. At the closed end of the tube, combustion was initiated by a low energy, less than 50 mJ, capacitor discharge system. A fast flame or detonation was created by transition to detonation. The effect of spirals and orifice plates was examined on propane- and ethylene-oxygen-nitrogen mixtures with varying initial pressure, equivalence ratio, and dilution amounts. A simple model for the impulse in prompt detonations was developed and calibrated. The results of our experiments were compared with this model

Studies of sonic booms with seismic networks

Seismographs are sufficiently sensitive to detect ground motions induced by atmospheric pressure waves, so seismic networks have the potential to monitor sonic booms over large areas of the United States. They are especially well suited for the analysis of long‐range sonic‐boom propagation. Ground motion or displacement data provide accurate arrival times and useful estimates of wave amplitude and waveform. The instrumentation is most sensitive to the disturbance produced by the arrival of sonic booms at the measuring station, thus serving as sonic‐boom event recorders, but seismographs have also detected seismic waves remotely generated by anomalous coupling of sonic boom into soil. Direct and indirect sonic booms from aircraft operations are routinely detected by the Southern California Seismic Network which consists of 250 seismic stations covering 50 000 sq km. Indirect booms from space shuttle landings has been observed at ranges of hundreds of kilometers from the flight path. Data from the network identified ‘‘mystery booms’’ heard in 1992–93 to be long‐range indirect sonic booms from offshore operations. Sonic booms generated by space shuttle reentry at Mach 20 and by meteoritic entries into the atmosphere have been detected by seismic networks in the Northwest and Canada

Dynamics of gas-driven eruptions: Experimental simulations using CO_2-H_2O-polymer system

We report exploratory experiments simulating gas-driven eruptions using the CO_2 - H_2O system at room temperature as an analog of natural eruptive systems. The experimental apparatus consists of a test cell and a large tank. Initially, up to 1.0 wt % of CO_2 is dissolved in liquid water under a pressure of up to 735 kPa in the test cell. The experiment is initiated by suddenly reducing the pressure of the test cell to a typical tank pressure of 10 kPa. The following are the main results: (1) The style of the process depends on the decompression ratio. There is a threshold decompression ratio above which rapid eruption occurs. (2) During rapid eruption, there is always fragmentation at the liquid-vapor interface. Fragmentation may also occur in the flow interior. (3) Initially, the top of the erupting column ascends at a constant acceleration (instead of constant velocity). (4) Average bubble radius grows as t^(2/3). (5) When viscosity is 20 times that of pure water or greater, a static foam may be stable after expansion to 97% vesicularity. The experiments provide several insights into natural gas-driven eruptions, including (1) the interplay between bubble growth and ascent of the erupting column must be considered for realistic modeling of bubble growth during gas-driven eruptions, (2) buoyant rise of the bubbly magma is not necessary during an explosive volcanic eruption, and (3) CO_2-driven limnic eruptions can be explosive. The violence increases with the initial CO_2 content dissolved in water

Development of Phage-Based Single Chain Fv Antibody Reagents for Detection of Yersinia pestis

detection. by flow cytometry and whole-cell ELISA. strains, whereas phage displayed scFvs were found to be easy to purify/label and remarkably stable. Furthermore direct fluorescent labeling of phage displaying scFv allowed for an easy one-step flow cytometry assay. Slight cross-reactivity was observed when fixed cells were used in ELISA. F1 antigen. We describe implementation of different methods for phage-based immunoassay. Based on the success of these methods and the proven stability of phage, we indicate that the use of phage-displayed, rather than phage-free proteins, might generally overcome the shortcomings of scFv antibodies