High-velocity impact on composite sandwich structures: A theoretical model

A theoretical energy-based model to capture the ballistic response of sandwich structures made of composite material peels and a crushable foam core was developed. The model was based on the wave propagation theory and it was split in six stages with their corresponding energy-absorption mechanisms. The division of the stages was based on the physical interpretation of the perforation process involving reasonable hypotheses and simplifications. The energy-absorption was analysed at velocities below, near and above the ballistic limit within all the stages showing the general trends in terms of their relative importance. The time and velocity at each stage was separately analysed within a wide range of velocities in order to see the stage contribution to the energy-absorption. The model was validated against experimental results obtained in the literature showing a good agreement in terms of the impact-residual velocity curve. © 2021 The Author(s

Quality and safety considerations in breast cancer screening

Breast cancer is a leading cause of premature mortality among United States women. Early detection has been shown to reduce breast cancer morbidity, mortality and cost of treatment. The relative safety of breast cancer screening has been viewed in terms of benefits and harms. The quality and safety of breast cancer screening depends on both technical and human factors. Focusing on quality and safety considerations, we review two imaging modalities recommended for primary breast cancer screening: mammography and magnetic resonance imaging, and the use of ultrasound (US) for supplemental breast cancer screening

A numerical–analytical study to determine a suitable distribution of plies in sandwich structures subjected to high-velocity impact

This work presents a study that was undertaken to find the configuration that corresponds to the highest ballistic limit for composite sandwich structures made of glass fibre-reinforced polymer (GFRP) sandwich skins and a crushable foam. To this end, a new three-dimensional finite element (FE) model was implemented. The model accounts for the constitutive response of the GFRP sandwich skins and the crushable foam by means of two subroutines. A previously developed analytical model was used to support and complete the results of the FE model. Experimental data were also used to validate both models in the vicinity of the ballistic limit for the neutral configuration (same number of plies on the front and rear face skins). Thus, the most appropriate configuration to improve the ballistic limit for a structure with the same material (same number of plies) was obtained by testing different distributions of laminae. The ballistic limit was then estimated for all the possible configurations and the energy-absorption mechanisms were analysed to reveal new insights into the behaviour of these structures when the neutral configuration is varied. In addition, the damaged areas of the specimens were compared between the experiments and the model. As a result, the most suitable configuration turned out to be associated with thicker rear face skins, which produce higher ballistic limits. The largest fraction of the energy was absorbed by the out-of-plane mechanisms, this behaviour being maintained in all the configurations. Experimental observations established that the damaged area of the front face skin was smaller than the damage produced in the rear face skin and that bending effects were notable in the latter. The affected areas were proved to have a round shape, presenting the largest size in the vicinity of the ballistic limit

Elasto-mammography: Theory, Algorithm, and Phantom Study

A new imaging modality framework, called elasto-mammography, is proposed to generate the elastograms of breast tissues based on conventional X-ray mammography. The displacement information is extracted from mammography projections before and after breast compression. Incorporating the displacement measurement, an elastography reconstruction algorithm is specifically developed to estimate the elastic moduli of heterogeneous breast tissues. Case studies with numerical breast phantoms are conducted to demonstrate the capability of the proposed elasto-mammography. Effects of noise with measurement, geometric mismatch, and elastic contrast ratio are evaluated in the numerical simulations. It is shown that the proposed methodology is stable and robust for characterization of the elastic moduli of breast tissues from the projective displacement measurement

Co supported on N and S dual-doped reduced graphene oxide as highly active oxygen-reduction catalyst for direct ethanol fuel cells

Oxygen reduction reaction (ORR) is one of the key features for the efficient functioning of several energy conversion devices such as fuel cells, appearing the necessity of development of new low-cost catalyst materials. Heteroatom-doped carbon materials have attracted attention in this field due to its physicochemical and electronic properties. In this work, a nitrogen and sulfur doped material with anchored Co3O4 nanoparticles (Co/SN-rGO) is proposed as cathode catalyst for direct ethanol fuel cells (DEFCs) and results are compared with different doped graphene nanomaterials (GMs). The effect of the heteroatoms and cobalt oxide nanoparticles in the final efficiency was studied. Synthesized materials were characterized and the activity of Co/SN-rGO and GMs for the ORR was studied. Co/SN-rGO presents high ORR performance in terms of onset potential (Eonset), 0.86 V (vs RHE) and half-wave potential (E1/2) 0.72 V (vs RHE). Tafel analysis shows 60 mV dec-1 at low overpotential for potential dependent ORR mechanism. Besides, when Co/SN-rGO performance is evaluated in a DEFC using a fuel cell test station, main results indicate higher catalytic activity, stability, and ethanol tolerance of Co/SN-rGO in comparison to a carbon-supported Pt catalystThis work has been developed in the framework of the projects PID2020-117586RB-100, PID2020-112594RB-C33, PID2020- 116712RBC21 funded by MCIN/AEI/10.13039/501100011033, and ProID2021010098 funded by the Gobierno de Canarias (FEDER). S. Fajardo acknowledge the MCIN for the pre-doctoral grant (PRE2018- 085718). The authors thank SEGAI-ULL for the collaboratio

Sexual Size Dimorphism, Ovipositioning, and Hatching in Leiocephalus macropus asbolomus (Squamata: Leiocephalidae) in Alexander von Humboldt National Park in Eastern Cuba

The endemic Antillean family Leiocephalidae includes 28 currently recognized extant species in the genus Leiocephalus. These are distributed across Hispaniola, Cuba, and various islands and cays in the Bahamas. Sexual size dimorphism (SSD)  is a fundamental and widespread biological phenomenon generally attributed to sexual differences  in relationships between body size, survival, fecunditty, and mating success. Six species with 40 subspecies are known from Cuba. Few data are available regarding SSD and reproduction. Herein we report new life-history data and the sexual size dimorphism index (SSDI) in Leiocephalus macropus asbolomus. Fieldwork was performed  during mid-August 2009 iin La Melba (Alexander von Humboldt National Park), HolguinProvince, Cuba. All males were larger in size then females and the SSDI (1.44) is the highest reported ffor any species of Leiocephalus. Egg measurments averaged 18.2 x 12.7 mml mean clutch size was 3. Eggs took 61-72 days to hatch; mean incubation time was 66.5 days, and mean hatchling SVL was 30.1 mm. &nbsp