Attractiveness of Male and Female Adults of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) to Conspecifics With and Without Grain

Whether stored-grain insects can communicate with each other inside stored-grain bulks is an important question for the development of pest management programs. Movements of the individual adults of Cryptolestes ferrugineus towards caged adult(s), in the presence or absence of wheat, were studied inside an apparatus (10 cm length), using an infrared camera. The numbers of the caged adults were 1, 20, or 50 of females or males, and 100 or 200 mixed-sex adults. Without grain, both males and females moved towards the caged single male, but not the caged single female. With grain, neither males nor females moved towards the caged single male or female. When 50 males were added to the cage, females did move significantly towards the caged males. There were trends for introduced males and females to move towards caged males at higher densities.

A Pore-Scale Model for Quantifying Airflow Paths through Grain Bulks

A commercial discrete element software package (PFC3D) was used to develop a model to simulate pore structures of grain beds. Based on the simulated structure of a grain bed, an algorithm reported in the literature was adopted and modified to determine airflow paths in the grain bed by treating the grain bed as a series of four-particle tetrahedrons. Critical characteristic parameters of the airflow path were predicted, including path length (tortuosities), width, and local turning angle (change in airflow direction at a location in the grain bed). The predicted tortuosities were in good agreement with the range of tortuosity values reported in the literature for porous beds consisting of spherical particles. The average path width was in the range of 0.83 to 5.93 mm. The local turning angles were mostly in the 0° to 10° range. Keywords: Airflow, Discrete element method, Grain bed, Pore structure, Tortuosity.

Development and Evaluation of a Low-Cost Probe-Type Instrument to Measure the Equilibrium Moisture Content of Grain

Storage of grain in bags is common in Africa, Asia, and many other less developed countries making a bag probing method well-suited for moisture content (MC) measurement. A low-cost meter was developed under a USAID project to reduce post-harvest loss (PHL). The meter, referred to as the PHL meter, measures the MC of maize and other grains based on relative humidity (RH) and temperature (T) measurements obtained by a small digital sensor located in the tip of a tubular probe that can be inserted into bags of grain or other grain bulks. Measurements are used by equilibrium moisture content (EMC) equations programmed into the meter to predict MC. A handheld reader connected to the probe provides a user interface. Keywords: Equilibrium moisture content, Grain storage, Maize, Moisture content, Moisture meter, Post-harvest

Void Nucleation and Growth at Grain Boundaries in Copper Bicrystals With Surface Perturbations

Material failure on the microstructural level is important in determining macroscale behavior. When a material is subjected to dynamic (shock) loading conditions, damage and deformation patterns due to spall failure can provide a basis for connecting micro- to macroscale behavior. By analyzing deformation patterns at and around interfaces and boundaries that are representative of those found in engineering materials at high strain rates, we can develop stronger structures that can withstand impact collisions and rapid crack propagation. The addition of surface perturbations to one side of the samples provides insight on how strain localization occurs during the shock loading process and how the rippled release wave interacts with the boundary. Copper bicrystal samples were grown from two single crystal seeds using the vertical Bridgeman technique. A photolithography process was developed to create periodic surface perturbations on one side of the samples. The square wave ripples had a 150 μm wavelength and 5 μm amplitude. The bicrystals were shocked using laser ablation on the perturbation side at the Trident laser at Los Alamos National Laboratory and monitored using a VISAR (velocity interferometer systems for any reflector) and TIDI (transient imaging displacement interferometry) system. Shock pressures used were around 8–10 GPa. Targets measured 5 mm in diameter and 100 microns thick. The orientations of the grains were [001] and [111] along the shock direction with a 50° misorientation angle for the boundary, which was aligned parallel to the shock direction. Samples were soft recovered and cross-sectioned to perform quantitative characterization of damage using electron backscattering diffraction (EBSD) and Scanning Electron Microscopy (SEM) to gather information on the characteristics of the grain boundary and its surroundings, with emphasis on how the rippled surfaces and material anisotropy affected strain localization and spallation, initial results show that damage indeed localized at the grain boundary and that surface perturbations led to heterogeneity of spall damage distribution in the grain bulks.