Chewed Out: An Experimental Link between Food Material Properties and Repetitive Loading of the Masticatory Apparatus in Mammals

Using a model organism (rabbits) that resembles a number of mammalian herbivores in key aspects of its chewing behaviors, we examined how variation in dietary mechanical properties a ects food breakdown during mastication. Such data have implications for understanding phenotypic variation in the mammalian feeding apparatus, particularly with respect to linking jaw form to diet-induced repetitive loading. Results indicate that chewing frequency (chews/s) is independent of food properties, whereas chewing investment (chews/g) and chewing duration(s), which are proportional to repetitive loading of the jaws, are positively related to food sti ness and toughness. In comparisons of displacement-limited and stress-limited fragmentation indices, which respectively characterize the intraoral breakdown of tough and sti foods, increases in chewing investment and duration are linked solely to sti ness. This suggests that sti er foods engender higher peak loads and increased cyclical loading. Our ndings challenge conventional wisdom by demonstrating that toughness does not, by itself, underlie increases in cyclical loading and loading duration. Instead, tough foods may be associated with such jaw-loading patterns because they must be processed in greater volumes owing to their lower nutritive quality and for longer periods of time to increase oral exposure to salivary chemicals

Low toxicity high temperature PMR polyimide

In-situ polymerization of monomer reactants (PMR) type polyimides constitute an important class of ultra high performance composite matrix resins. PMR-15 is the best known and most widely used PMR polyimide. An object of the present invention is to provide a substantially improved high temperature PMR-15 system that exhibits better processability, toughness, and thermo-oxidative stability than PMR-15, as well as having a low toxicity. Another object is to provide new PMR polyimides that are useful as adhesives, moldings, and composite matrices. By the present invention, a new PMR polyimide comprises a mixture of the following compounds: 3,4'-oxydianiline (3,4'-ODA), NE, and BTDE which are then treated with heat. This PMR was designated LaRC-RP46 and has a broader processing window, better reproducibility of high quality composite parts, better elevated temperature mechanical properties, and higher retention of mechanical properties at an elevated temperature, particularly, at 371 C

2-factors in 32\frac{3}{2}-tough plane triangulations

In 1956, Tutte proved the celebrated theorem that every 4-connected planar graph is hamiltonian. This result implies that every more than $\frac{3}{2}$-tough planar graph on at least three vertices is hamiltonian and so has a 2-factor. Owens in 1999 constructed non-hamiltonian maximal planar graphs of toughness arbitrarily close to $\frac{3}{2}$. In fact, the graphs Owens constructed do not even contain a 2-factor. Thus the toughness of exactly $\frac{3}{2}$ is the only case left in asking the existence of 2-factors in tough planar graphs. This question was also asked by Bauer, Broersma, and Schmeichel in a survey. In this paper, we close this gap by showing that every maximal $\frac{3}{2}$-tough planar graph on at least three vertices has a 2-factor

Indentation as a Technique to Assess the Mechanical Properties of Fallback Foods

A number of living primates feed partyear on seemingly hard food objects as a fallback. We ask here how hardness can be quantified and how this can help understand primate feeding ecology. We report a simple indentation methodology for quantifying hardness, elastic modulus, and toughness in the sense that materials scientists would define them. Suggested categories of fallback foods—nuts, seeds, and root vegetables— were tested, with accuracy checked on standard materials with known properties by the same means. Results were generally consistent, but the moduli of root vegetables were overestimated here. All these properties are important components of what fieldworkers mean by hardness and help understand how food properties influence primate behavior. Hardness sensu stricto determines whether foods leave permanent marks on tooth tissues when they are bitten on. The force at which a food plastically deforms can be estimated from hardness and modulus. When fallback foods are bilayered, consisting of a nutritious core protected by a hard outer coat, it is possible to predict their failure force from the toughness and modulus of the outer coat, and the modulus of the enclosed core. These forces can be high and bite forces may be maximized in fallback food consumption. Expanding the context, the same equation for the failure force for a bilayered solid can be applied to teeth. This analysis predicts that blunt cusps and thick enamel will indeed help to sustain the integrity of teeth against contacts with these foods up to high loads

Deformation Mechanisms in Bioinspired Multilayered Materials

Learning lessons from nature is the key element in the design of tough and light composites

On the Performance of Carbon Nanotubes on Sintered Alumina-Zirconia Ceramics

The alumina (Al2O3) and zirconia (ZrO2) ceramic monoliths and their combination are used in both technical and biomedical applications due to their combination of excellent chemical, physical, and mechanical properties. Pressureless sintering (PLS), reaction bonding (RB), hot pressing (HP), hot isostatic pressing (HIP), and spark plasma sintering (SPS) are the sintering methods more commonly used. The high brittleness, the low fracture toughness, and low thermal stability that possess these ceramics are its Achilles heel for numerous engineering applications. The incorporation of a second phase such as carbon nanotubes (CNTs) into the ceramic matrix has been attempted to overcome these drawbacks but the obtained results are still controversial considering that the homogeneous dispersion of CNTs and the interfacial bonding between two different ceramic materials remains as a difficult task leading to little or even no improvement in mechanical properties. Besides, the role of CNTs in the sintering of ceramic materials is not clear in the scientific literature taking into account parameters such as materials used and particularly inconsistencies in dispersion and mixing of the CNTs. We discuss how the CNTs can affect the sintering behavior and microstructural evolution of alumina and zirconia ceramics and the combination of them

PREDICTORS OF ACADEMIC PERFORMANCE: THE ROLES OF SELF-COMPASSION, COPING, MENTAL TOUGHNESS, GRIT, AND SELF-REPORTED STRESSORS ON PHYSICS FINAL EXAM PERFORMANCE

The intersection of stress, persistence and success in college-aged students is progressively gaining attention in research. Analyzing how students succeed and what factors contribute to their success, failure, and ultimately the completion of their degree, is vitally important for educators and administrators in higher education to understand. Historically utilized factors such as grade point average (GPA), standardized test scores (college admissions and Advance Placement (AP) exams), and previous academic achievement (pre-requisite courses) are not the only predictors of academic performance. This study aimed to quantify contributions and inter-relationships of student perceptions, coping style, stress, mental toughness (MT), and other potential factors that correlate with academic performance. Thirty-five Physics I students provided baseline and day-of final exam self-reported assessments of such factors. Exploratory analysis, utilizing multiple regressions, suggests that self-reported stress is a reliable predictor of academic performance on a Physics I final exam and additional constructs such as MT, self-compassion, stress appraisals, coping strategies and grit contribute as well. Implications for the findings of this study can inform higher education’s approach to admissions, retention, and stress mitigation of college students