17 research outputs found
Characterization of a high strain composite material
L'Garde has designed and developed a high-strain composite material consisting of car- bon FIbers embedded in a silicone matrix. The behavior of this material is significantly different from standard composites and the paper presents special test methods to measure the properties of this material. It is found that rule of mixtures estimates are quite accurate for the longitudinal moduli in tension and bending, but less accurate for compression. The Poisson's ratio prediction is also not accurate. Regarding the strength of the composite, it is found that conservative predictions of tensile and compressive strengths can be obtained respectively from the Weibull distribution of the strength of a single fiber combined with a simple bundle theory, and the elastic fiber microbuckling stress
Evaluación de la degradación por termoxidación de termoplásticos empleados en aplicaciones agrícolas
Maternal Perception of Child Weight Among Mexicans in California and Mexico
The prevalence of childhood overweight is high in Mexican immigrant communities in the United States. Understanding mother’s perceptions of child weight in immigrants’ country of origin may help to understand this high prevalence. The goal of this study was to examine and compare mothers’ perception of weight in Mexico (MX) and in an immigrant community in California (CA). We assessed perceptions of child weight using a pictorial scale with 314 mothers of 5-year-old children in MX and 60 mothers of 5 year-old-children in CA. We compared maternal reports with children’s objectively measured weight. Using chi-square and Analysis of Variance, we investigated associations of maternal perception of and satisfaction with weight according to socio-demographic characteristics. Mothers were more likely to underestimate their children’s weight in CA than in MX. On average, CA mothers wanted their children to be smaller than they currently were and mothers in MX wanted their children to be bigger than they currently were. This differed by weight status in CA with mothers of normal weight and at-risk-for-overweight children wanting them to be bigger and mothers of overweight children wanting them to be smaller. In order for programs to be effective, mothers must be able to recognize their children as overweight and want to address it. Because underestimation of weight and a desire for a larger size is common in this population, programs to address overweight may be more effective if they focus on alternative benefits of weight control strategies, such as healthy child development
Experimental and Numerical Analysis of a Concentrated Strain Deployable Truss of Solid Rods
Interplay of Degradation, Dissolution and Stabilization of Clarithromycin and Its Amorphous Solid Dispersions
Clarithromycin (CLA) is an aminomacrolide
antibiotic whose physical
properties are fascinating and challenging. It has very poor solubility
at neutral intestinal pH, but much better solubility under acidic
conditions due to amine protonation. The improved solubility in an
acid environment is confounded by the poor chemical stability of clarithromycin
that is quite labile toward acid-catalyzed degradation. This creates
a complex system under gastrointestinal (GI) conditions: dissolution
in the stomach, degradation, potential for precipitation in the small
intestine, and interplay with the formulation components. We report
herein a study of amorphous solid dispersion (ASD) of CLA with carboxyl-containing
cellulose derivatives, which have recently been shown to be excellent
ASD matrices for maximizing oral bioavailability. This approach was
intended to improve CLA solubility in neutral media while minimizing
release in an acid environment, and thereby increase its uptake from
the small intestine. Amorphous polymer/CLA nanoparticles were also
prepared by high-shear mixing in a multi-inlet vortex mixer (MIVM).
Different extents of release were observed at low pH from the various
formulations. Thus the solubility increase from nanosizing was deleterious
to the concentration of intact CLA obtained upon reaching small intestine
conditions; the high extent of release at gastric pH led to complete
degradation of CLA. Using pH-switch experiments, it was possible to
separate the effects of loss of CLA from solution by crystallization
vs. that from chemical degradation. It was found that the hydrophobic
cellulose derivative cellulose acetate adipate propionate (CAAdP)
was effective at protecting CLA from dissolution in the stomach, and
preventing CLA decomposition at low pH; 54% of CLA in CAADP ASD was
released intact, vs. 0% and 6% from HPMCAS and CMCAB ASDs, respectively.
We conclude that protection against degradation is central to enhancing
overall release of <i>intact</i> CLA from ASD formulations;
the formulations studied herein have great promise for simultaneous
CLA solubility enhancement and protection from loss to chemical degradation,
thereby reducing dose requirements and potentially decreasing colonic
exposure to CLA (reduced colonic exposure is expected to minimize
killing of beneficial colonic bacteria by CLA)