More Like this

1. Nucleation in a liquid droplet

   https://doi.org/10.1039/D0CP00559B  

   Yang, Fuqian (May 2020, Physical Chemistry Chemical Physics)

   null (Ed.)

   The droplet-based microreactors in microfluidic systems have been used to synthesize nanocrystals of a variety of metals and semiconductors, which involves the nucleation and growth processes. Considering the limited numbers of solvent atoms and solute atoms/particles in a stationary droplet, we derive analytical expressions of the changes of the Gibbs free energy and the Helmholtz free energy for the concurrent formation of multiple microclusters of the same size in the liquid droplet. Both the changes of the Gibbs free energy and the Helmholtz free energy are dependent on the ratio of the number of microclusters to the solvent atoms and the interface energy between the solution and the microclusters. Using the change of the free energy, which is an approximation of the Gibbs free energy and the Helmholtz free energy, we obtain the critical nucleation number of the solute atoms/particles in the microclusters for the concurrent nucleation of multiple nuclei of the same size. The critical nucleation number of the solute atoms/particles is dependent on the ratio of the number of nuclei in the droplet to the solvent atoms, and the maximum change of the free energy for the concurrent nucleation of multiple nuclei of the same size increases with the increase of the ratio of the number of the nuclei in the droplet to the number of the solvent atoms. 

   more » « less
2. Effect of external shear flow on sperm motility

   https://doi.org/10.1039/c9sm00717b  

   Kumar, Manish; Ardekani, Arezoo M. (August 2019, Soft Matter)

   The trajectory of sperm in the presence of background flow is of utmost importance for the success of fertilization, as sperm encounter background flow of different magnitude and direction on their way to the egg. Here, we have studied the effect of an unbounded simple shear flow as well as a Poiseuille flow on the sperm trajectory. In the presence of a simple shear flow, the sperm moves on an elliptical trajectory in the reference frame advecting with the local background flow. The length of the major-axis of this elliptical trajectory decreases with the shear rate. The flexibility of the flagellum and consequently the length of the major axis of the elliptical trajectories increases with the sperm number. The sperm number is a dimensionless number representing the ratio of viscous force to elastic force. The sperm moves downstream or upstream depending on the strength of background Poiseuille flow. In contrast to the simple shear flow, the sperm also moves toward the centerline in a Poiseuille flow. Far away from the centerline, the cross-stream migration velocity of the sperm increases as the transverse distance of the sperm from the centerline decreases. Close to the centerline, on the other hand, the cross-stream migration velocity decreases as the sperm further approaches the center. The cross-stream migration velocity of the sperm also increases with the sperm number. 

   more » « less
3. Localized Defects in Cold Die-Compacted Metal Powders

   https://doi.org/10.3390/jmmp6060155  

   Torresani, Elisa; Ischia, Gloria; Molinari, Alberto (December 2022, Journal of Manufacturing and Materials Processing)

   In powder metallurgy (PM), the compaction step is fundamental to determining the final properties of the sintered components. The deformation and defectiveness introduced in the powder material during uniaxial die compaction can be correlated to the activation and enhancement of the dislocation pipe diffusion, a lattice diffusion mechanism during the sintering process. Its coefficient depends on the dislocation density. The powder particles are mostly deformed along the direction of the compaction (longitudinal direction) rather than along the compaction plane; consequently, the contact areas perpendicular to the direction of the compaction present a higher density of dislocations and lattice defects. This high density intensifies the shrinkage along the direction of compaction. To demonstrate the influence of uniaxial cold compaction on the material’s stress state the powder particles and their contacts were modeled using spheres made of pure copper. These spheres are compacted in a die at different pressures to better analyze the system’s response at the grade of deformation and the consequent influence on the material’s behavior during the sintering. In the different zones of the sphere, the micro-hardness was measured and correlated to the concentration of dislocations using the model for indentation size effect (ISE). After the compaction, the spheres were more deformed along the longitudinal than the transversal direction. The results obtained using hardness indentation show differences in the dislocation density between the undeformed and deformed spheres and, in the case of the compacted sphere, between the contact area along the longitudinal and the transversal direction. 

   more » « less
4. Anatomy of the petrosal and middle ear of the brown rat, Rattus norvegicus (Berkenhout, 1769) (Rodentia, Muridae)

   https://doi.org/https://doi.org/10.2992/007.086.0101  

   Wible, John R.; Shelley, Sarah L. (March 2020, Annals of Carnegie Museum)

   The anatomy of the petrosal and associated middle ear structures are described and illustrated for the brown rat, Rattus norvegicus (Berkenhout, 1769). Although the middle ear in this iconic mammal has been treated by prior authors, there has not been a comprehensive, well-illustrated contribution using current anatomical terminology. Descriptions are based on specimens from the osteological collections of the Section of Mammals, Carnegie Museum of Natural History, and a CT scanned osteological specimen from the Texas Memorial Museum. The petrosal, ectotympanic, malleus, incus, stapes, and inner ear were segmented from the CT scans. The petrosal of the brown rat is only loosely attached to the cranium, primarily along its posterior border; it is separated from the basisphenoid, alisphenoid, and squamosal by a large piriform fenestra that transmits various neurovascular structures including the postglenoid vein. The extent of the piriform fenestra broadly exposes the tegmen tympani of the petrosal in lateral view. The floor of the middle ear is formed by the expanded ectotympanic bulla, which is tightly held to the petrosal with five points of contact. The surfaces of the petrosal affording contact with the ectotympanic bulla are the rostral tympanic process, the epitympanic wing, the tegmen tympani, two of the three parts of the caudal tympanic process, and the tympanohyal, with the ectotympanic fused to the last. The ectotympanic in turn is fused to the elongate rostral process of the malleus, which is only discoverable through the study of juvenile specimens. In addition to osteology, the major nerves, arteries, and veins of the petrosal are described and illustrated based on the literature and osteological correlates. The petrosal of the brown rat is compared with those of several Eocene rodents to put the extant form in the context of early members of the rodent lineage. Comparisons benefitted from CT scans of the middle Eocene ischromyoid Paramys delicatus Leidy, 1871, from the western United States, affording the first description of the endocranial surface of the petrosal in an Eocene rodent. The petrosals in the Eocene fossils are more tightly held in the cranium, but the ectotympanic contacts the petrosal through the same five points, with some modifications. The most unexpected discovery in Paramys delicatus was the presence of a prominent tentorial process of the parietal in contact with the reduced crista petrosa. 

   more » « less
5. The large landscape of supernova, GRB, and cocoon interactions

   https://doi.org/10.1093/mnras/stac742  

   De Colle, Fabio; Kumar, Pawan; Hoeflich, Peter (March 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Long gamma-ray bursts (LGRBs) are associated to the collapse of a massive star and the formation of a relativistic jet. As the jet propagates through the star, it forms an extended, hot cocoon. The dynamical evolution of the jet/cocoon system and its interaction with the environment has been studied extensively both analytically and numerically. On the other hand, the role played by the supernova (SN) explosion associated with LGRBs in determining the outcome of the system has been barely considered. In this paper, we discuss the large landscape of outcomes resulting from the interaction of the SN, jet, and cocoon. We show that the outcome depends mainly on three time-scales: the times for the cocoon and SN shock wave to break through the surface of the progenitor star, and the time needed for the cocoon to engulf completely the progenitor star. The delay between the launch of the SN shock moving through the progenitor star and the jet can be related to these three time-scales. Depending on the ordering of these time-scales, the jet-cocoon might propagate inside the SN ejecta or the other way around, and the outcome for the properties of the explosion would be different. We discuss the imprint of the complex interaction between the jet-cocoon and the SN shock on the emergent thermal and non-thermal radiation. 

   more » « less