Multiscale analysis of the intensity fluctuation in a time series of dynamic speckle patterns

We propose the application of a method based on the discrete wavelet transform to detect, identify, and measure scaling behavior in dynamic speckle. The multiscale phenomena presented by a sample and displayed by its speckle activity are analyzed by processing the time series of dynamic speckle patterns. The scaling analysis is applied to the temporal fluctuation of the speckle intensity and also to the two derived data sets generated by its magnitude and sign. The application of the method is illustrated by analyzing paint-drying processes and bruising in apples. The results are discussed taking into account the different time organizations obtained for the scaling behavior of the magnitude and the sign of the intensity fluctuation.     

Application of the Schlieren pulsed method for the observation of simple and multiple scattering of ultrasonic waves

The Schlieren pulsed method uses short-term lighting triggered by an acoustic pulse. This allows for an observation of elastic deformation fields in pulsed regime and for an evaluation of the evolution of the pulse in the interior of homogenous and heterogeneous media. In this paper we apply the Schlieren pulsed method to determine the conditions of the change from simple to multiple scattering. An ultrasound transducer put in water emits a wide-band pulse. The pulse goes through a region of parallel cylindrical wires, uniformly spaced and perpendicular to the acoustic beam. Varying the width of the zone of the scatterer cylinders, it is possible to optically observe the transmitted acoustic field and to calculate the transmission coefficient. By studying the behavior of this coefficient in function of the medium width, we obtained the zone in which the transition between simple and multiple scattering happens.     

EMVS: Event-Based Multi-View Stereo—3D Reconstruction with an Event Camera in Real-Time

Event cameras are bio-inspired vision sensors that output pixel-level brightness changes instead of standard intensity frames. They offer significant advantages over standard cameras, namely a very high dynamic range, no motion blur, and a latency in the order of microseconds. However, because the output is composed of a sequence of asynchronous events rather than actual intensity images, traditional vision algorithms cannot be applied, so that a paradigm shift is needed. We introduce the problem of event-based multi-view stereo (EMVS) for event cameras and propose a solution to it. Unlike traditional MVS methods, which address the problem of estimating dense 3D structure from a set of known viewpoints, EMVS estimates semi-dense 3D structure from an event camera with known trajectory. Our EMVS solution elegantly exploits two inherent properties of an event camera: (1) its ability to respond to scene edges—which naturally provide semi-dense geometric information without any pre-processing operation—and (2) the fact that it provides continuous measurements as the sensor moves. Despite its simplicity (it can be implemented in a few lines of code), our algorithm is able to produce accurate, semi-dense depth maps, without requiring any explicit data association or intensity estimation. We successfully validate our method on both synthetic and real data. Our method is computationally very efficient and runs in real-time on a CPU.     

Inverse Analysis of Impact Test Data: Experimental Study on Polymeric Materials Displaying Brittle Behaviour

This paper deals with the influence of the testing equipment on impact load measurements. A previously developed method of analysis and processing of the experimental data based on a refined analogical model of the impact event and inverse problem techniques is used. This method makes it possible to obtain the mechanical response of the material, notwithstanding the disturbance of the dynamic effects associated to the test. Results from tests carried out both on falling weight and swing pendulum instrumented testing machines are compared. It is shown that this method can give an accurate estimation of the actual bending force in impact testing independent of the testing equipment.     

Design Guidelines For Conjugated Polymers With Light‐Activated Anticancer Activity

Multifunctional materials that simultaneously provide therapeutic action and image the results provide new strategies for the treatment of various diseases. Here, it is shown that water soluble conjugated polymers with a molecular design centered on the polythiophene?porphyrin dyad are effective for killing neighboring cells. Following photoexcitation, energy is efficiently transferred from the polythiophene backbone to the porphyrin units, which readily produce singlet oxygen (¹O₂) that is toxic for the cells. Due to the light‐harvesting ability of the electronically delocalized backbone and the efficient energy transfer amongst optical partners, the polythiophene?porphyrin dyad shows a higher ¹O₂ generation efficiency than a small molecule analog. The fluorescent properties of these polymers can also serve to distinguish amongst living and dead cells. Polymers can be designed with folic acid grafted onto the polymer side chain that can specifically kill folate receptor‐overexpressed cells, thereby providing an important demonstration of anticancer specificity through molecular design.     

The Effect of Cook‐Off on the Bulk Permeability of a Plastic Bonded Explosive

Plastic bonded explosives when exposed to prolonged heating environments undergo a variety of changes that affect their bulk chemical, thermophysical, and mechanical properties. During slow heating conditions, referred to as cook‐off, the thermal behavior of the polymeric binder plays an important role in the transformations of these composite energetic materials. The recently introduced Darcian flow hypothesis for PBX‐9501 implies that, during preignition, temperature gradients will lead to pressure gradients which in turn will drive convection of decomposition gases throughout the explosive, thus affecting ignition time and location. Here, we focus on the cook‐off behavior of PBX‐9501 and investigate its effects on bulk permeability to gases produced as a result of thermal decomposition. The concept of Darcian convection through porous media is defined and illustrated in detail by the derivation of the governing equations for a permeameter. Based on a systematic analysis involving: 1) our current understanding about binder behavior as a function of temperature, 2) the physics of the gas permeameter apparatus, 3) the concept of liquid drainage by gas, and 4) the experimental record of four permeameter experiments with cooked PBX‐9501, we conclude that samples heated up to 186 °C were not permeable in the Darcy‐flow sense.     

Small-scale experiments of self-sustaining decomposition of NPK fertilizer and application to events aboard the Ostedijk in 2007

Small-scale experiments to investigate the self-sustaining decomposition (SSD) behaviour of NPK 16.16.16 fertilizer have been undertaken. These experiments show that this material will undergo self-sustaining decomposition and are used to give insight into the behaviour of the reaction. A three-step decomposition process is observed leading to a self-sustained reaction reaching temperatures of 200–350 °C. The measured heat of reaction is 0.73–1.8 MJ/kg. Measurements are applied to the events that occurred aboard the ship Ostedijk in 2007 in which a SSD reaction occurred. The mass loss rate from the cargo was calculated to range from 0.5 kg/s on the first day to 12 kg/s on the last day. From this measurement, the maximum fire size was estimated to be in the range 5.8–29 MW.