Combining checkpointing and data compression for large scale seismic inversion

Seismic inversion and imaging are adjoint-based optimization problems that processes up to terabytes of data, regularly exceeding the memory capacity of available computers. Data compression is an effective strategy to reduce this memory requirement by a certain factor, particularly if some loss in accuracy is acceptable. A popular alternative is checkpointing, where data is stored at selected points in time, and values at other times are recomputed as needed from the last stored state. This allows arbitrarily large adjoint computations with limited memory, at the cost of additional recomputations. In this paper we combine compression and checkpointing for the first time to compute a realistic seismic inversion. The combination of checkpointing and compression allows larger adjoint computations compared to using only compression, and reduces the recomputation overhead significantly compared to using only checkpointing

Laser Ultrasonic Thermoelastic/Ablation Generation with Laser Interferometric Detection in Graphite/Polymer Composites

Ultrasonic signals have been generated and detected in graphite/polymer composites by optical methods. A Doppler interferometric technique was used for detection. The output voltage of this type of interferometer is proportional to the surface velocity of a sample area which is illuminated by cw laser light. Ultrasonic signals were generated by thermoelastic and ablation processes which occur as a consequence of laser pulses incident on the opposite surface of the sample. The evolution of the magnitude and shape of the detected signals was measured as a function of the pulse energy of the generating laser. Low-energy laser pulses generated ultrasound without causing obvious surface damage. At higher energies surface damage was observable in post inspection but could also be detected by observing (through protective goggles) bright flashes near the illuminated area. The energy at which these processes first occur is qualitatively referred to as the ablation threshold. Changes in the observed waveform were evident at energies above the ablation threshold. The higher-energy waveforms were found to consist of a superposition of a thermoelastic component and an ablatic component, whose relative magnitudes changed with laser power. A delay in the initiation of the ablatic wave relative to the thermoelastic wave was observed to be of the order of 0.3 μs, consistent with observations in pure polymer. [1] Photoelectric detection measurements of the ablation plume also showed a clear threshold and a time scale for growth of the ablation products with a characteristic time scale on the order of 0.3 μs

Evaluation of the effect of solar radiations on the growth of potential water borne and food borne pathogens during solar eclipse

On new moon day when Moon passes between Earth and Sun solar eclipse can be seen from Earth. Although solar eclipse is a fascinating astronomical event, even in today’s fast, modern and civilized life, people have not been able to go away with superstitious beliefs related to outer space activity behind solar eclipse. These misbelieves eventually lead to great socio-economic losses due to discarding of cooked food and drinking water that was exposed to the eclipse directly or indirectly. So considering these misbelieves a study was conducted to see possible biological effects of solar radiations during solar eclipse on bacteria responsible for water borne and food borne diseases. E. coli, S. aureus, B. subtilis, S. typhi, which are known water and food borne pathogens, were exposed to solar radiations throughout the eclipse period. The effect of these radiations on the survival and growth rate of these organisms was assessed by suitable method and compared with that on control day. When such comparison was made, it indicated that there was no statistically significant effect of solar eclipse on the survival and the growth rate of these organisms. Hence, we insist dumping the cooked food or drinking water after solar eclipse should be avoided

Full-waveform inversion, Part 3: Optimization

This tutorial is the third part of a full-waveform inversion (FWI) tutorial series with a step-by-step walkthrough of setting up forward and adjoint wave equations and building a basic FWI inversion framework. For discretizing and solving wave equations, we use Devito (http://www.opesci.org/devito-public), a Python-based domain-specific language for automated generation of finite-difference code (Lange et al., 2016). The first two parts of this tutorial (Louboutin et al., 2017, 2018) demonstrated how to solve the acoustic wave equation for modeling seismic shot records and how to compute the gradient of the FWI objective function using the adjoint-state method. With these two key ingredients, we will now build an inversion framework that can be used to minimize the FWI least-squares objective function