Non-conventional injection molding of poly(lactide) and poly(ε-caprolactone) intended for orthopedic applications

Biodegradable polymers such as poly(lactide) (PLA) and poly(epsilon-caprolactone) (PCL) are increasingly used in biomedical applications as temporary implants. However, melt processing of these materials in particular of PLA is difficult due to the temperature sensitivity. Within this study, PLA and PCL were injection molded conventionally and by using the process shear controled orientation in injection molding (SCORIM) in order to investigate the effect of processing parameters on the physical properties of the moldings. Therefore, flexural testing, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), molecular weight (MW) and orientation measurements were performed. PLA showed high sensitivity to melt temperature. In the case of amorphous poly(DL-lactide), the molecular weight and subsequently the ductility is substantially reduced by processing at higher melt temperatures. In the case of crystallizable poly(L-lactide), higher melt temperatures and shear induced by the SCORIM process resulted in enhanced crystallinity, which compromised the mechanical properties. Generally, SCORIM processing improved the mechanical properties, in particular the ductility, by orientating the molecular structure. PCL was shown to be less sensitive to shear and temperature than PLA. Stress at yield and stiffness are more improved by SCORIM processing. However, the processing temperature in combination with the grade used proved to be influential for the mechanical properties of resulting moldings.     

Correcting ocular spherical aberration with soft contact lenses

Following aberroscopy, aspheric front surface soft contact lenses (SCLs) were custom-made to correct spherical refractive error and ocular spherical aberration (SA) of 18 myopic and five hypermetropic subjects (age, 20.5 +/- 5 yr). On-eye residual aberrations, logMAR visual acuity, and contrast sensitivity were compared with the best-correcting spectacle lens, an equally powered standard SCL, and an SCL designed to be aberration free in air. Custom-made and spherical SCLs reduced SA (p < 0.001; p < 0.05) but did not change total root-mean-square (rms) wave-front aberration (WFA). Aberration-free SCLs increased SA (p < 0.05), coma (p < 0.05), and total rms WFA. Visual acuity remained unchanged with any of the SCL types compared with the spectacle lens correction. Contrast sensitivity at 6 cycles/degree improved with the custom-made SCLs (p < 0.05). Increased coma with aspheric lens designs and uncorrected astigmatism limit the small possible visual benefit from correcting ocular SA with SCLs.     

Sequential switch of biomineral crystal morphology using trivalent ions

Many biominerals are laminated such that crystal shape or habit changes from layer to layer thus yielding exquisitely designed composite materials with tightly controlled properties. Although lamination in biominerals is usually performed using peptides and proteins, here we introduce a new strategy by which sequential addition or depletion of inorganic trivalent ions in a supersaturated solution can be used to switch the surface morphology of calcium oxalate monohydrate (COM) back and forth, resulting in either the growth of flat crystalline sheets or of nanostructures oriented perpendicular to the surface. We propose that the occupation of a Ca(2+) site by Eu(3+) ion switches the orientation of the COM unit cell. The need to compensate the third charge forces coordination of Eu(3+) to an additional oxalate ion ((-)OOC-COO(-)) in an orientation that is not compatible with the initial unit cell. This mechanism of switching the orientation of the unit cell is unique, as it does not involve the use of expensive and thermally labile biomolecules. Suggestions of how to extend this strategy to engineer non-biological nanocomposites are given.     

Pre-equating: a simulation study based on a large scale assessment model

Although post-equating (PE) has proven to be an acceptable method in the scaling and equating of items and forms, there are times when the turn-around period for equating and converting raw scores to scale scores is so small that PE cannot be undertaken within the prescribed time frame. In such cases, pre-equating (PrE) could be considered as an acceptable alternative. Assessing the feasibility of using item calibrations from the item bank (as in PrE) is conditioned on the equivalency of the calibrations and the errors associated with it vis a vis the results obtained via PE. This paper creates item banks over three periods of item introduction into the banks and uses the Rasch model in examining data with respect to the recovery of item parameters, the measurement error, and the effect cut-points have on examinee placement in both the PrE and PE situations. Results indicate that PrE is a viable solution to PE provided the stability of the item calibrations are enhanced by using large sample sizes (perhaps as large as full-population) in populating the item bank.     

Preparation of Pt-Re/Vulcan carbon nanocomposites using a single-source molecular precursor and relative performance as a direct methanol fuel cell electrooxidation catalyst

Pt-Re/Vulcan carbon powder nanocomposites have been prepared with total metal loadings of 18 wt.% and 40 wt.% using a new non-cluster (1:1)-PtRe bimetallic precursor as the source of metal. Pt-Re nanoparticles having an average diameter of ca. 6 nm and atomic stoichiometry near 1:1 are formed. TEM, on-particle HR-EDS, and powder XRD data are consistent with the formation of Pt-Re alloy nanoparticles having a hexagonal unit cell with cell constants of a = 2.77 A and c = 4.47 A. A nanocomposite prepared at higher total metal loading under more rigorous thermal treatment also contains Pt-Re alloy nanoparticles having a fcc unit cell structure (a = 3.95 A). The precise dependence of Pt-Re nanocrystal structure on the thermal history of the nanocomposite specimen has not been investigated in detail. While these Pt-Re/carbon nanocomposites are active as anode catalysts in operating direct methanol fuel cells, the measured performance is less than that of commercial Pt-Ru/carbon catalysts and has marginal practical importance.     

The comparisons of anthropometric characteristics among four peoples in East Asia

This study presents comparisons of ethnic difference in anthropometric characteristics among four peoples, i.e., Chinese, Japanese, Korean, and Taiwanese, in East Asia. Anthropometric data from the four East Asian countries were compared. The means of 33 body dimensions and 31 bodily proportions are presented. Also, 15 segmental proportions are illustrated. The results of statistical analyses showed that there is a significant morphological difference among these peoples in the same region. The Mainland Chinese body shape has a narrower body with mid-range limbs. The Japanese body shape is wider with shorter limbs. The Korean body shape is mid-range among the four peoples, but the upper limbs are longer. The Taiwanese body shape has wide shoulder and narrow hip with large hands and long legs. The ethnic diversity in bodily proportions should be considered as well as the mean dimensions.     

In vivo synchrotron study of thallium speciation and compartmentation in Iberis intermedia

Thallium (TI) is a metal of great toxicological concern and its prevalence in the natural environment has steadily increased as a result of manufacturing and combustion practices. Due to its low natural abundance and increasing demand, TI is the fourth most expensive metal, thus, recovery and reuse could be a profitable endeavor. The hyperaccumulator Iberis intermedia was examined via in vivo micro-X-ray absorption near edge (micro-XANES) and micro-X-ray fluorescence (micro-XRF) spectroscopies to determine the speciation and distribution of TI within leaves of the plant. I. intermedia plants were cultivated under controlled conditions in 0, 10, and 20 mg TI kg(-1) soil leading to a shoot concentration of up to 13 430 mg TI kg(-1) dry weight plant mass during 10 weeks of growth. Live plant leaves were examined by micro-XANES and micro-XRF which determined aqueous TI(I) to be the model species distributed primarily throughout the vascular network. A direct relationship of vein size to TI concentration was observed. The high uptake of TI and high potential biomass of I. intermedia, combined with knowledge of TI speciation and compartmentation within the plant, are discussed in terms of accumulation/tolerance mechanisms, consequences for potential food chain contamination, and phytomining strategies to reclaim TI-contaminated soils, sediments, and waters.     

Activities of the enzymes of hepatic gluconeogenesis in periparturient dairy cows with induced fatty liver

The objective was to measure the activities of all the enzymes essential for hepatic gluconeogenesis in dairy cows with induced fatty liver. We aimed to induce severe fatty liver in ten experimental cows by overfeeding them during the dry period while seven control cows were maintained on a restricted diet. To induce a marked negative energy balance, the experimental cows were deprived of feed for 8 h immediately after parturition. In addition, the experimental cows were given a restricted amount of diet during the first 5 d of lactation. Liver samples were collected 1 week before and 1, 2 and 4 weeks after parturition. Before parturition, liver triacylglycerol concentrations did not differ between the two groups. After parturition, the experimental cows developed marked fatty liver as indicated by a higher level of triacylglycerols in the liver compared with the control cows. Before parturition, all gluconeogenic enzymes in the liver were lower in experimental cows than in control cows. Phosphoenolpyruvate carboxykinase, pyruvate carboxylase and propionyl-CoA carboxylase were significantly lower and fructose 1,6-bisphosphatase and glucose 6-phosphatase tended to be lower in the experimental cows. The activities of two crucial enzymes for gluconeogenesis in ruminants, i.e., phosphoenolpyruvate carboxykinase and propionyl-CoA carboxylase, remained low throughout the sampling period post partum. Activities of pyruvate carboxylase and glucose 6-phosphatase in the experimental cows post partum were upgraded to values similar to those of the control cows. The results showed that the capacity for hepatic gluconeogenesis before parturition was lower in cows with induced fatty liver than in control cows. After parturition, the low activities of crucial gluconeogenic enzymes indicated insufficient production of glucose. It is suggested that the low gluconeogenic capacity leads successively to low blood glucose concentrations, low insulin levels and high rates of mobilization of fatty acid, causing severe hepatic lipidosis.     

On the variability of manual spike sorting

The analysis of action potentials, or "spikes," is central to systems neuroscience research. Spikes are typically identified from raw waveforms manually for off-line analysis or automatically by human-configured algorithms for on-line applications. The variability of manual spike "sorting" is studied and its implications for neural prostheses discussed. Waveforms were recorded using a micro-electrode array and were used to construct a statistically similar synthetic dataset. Results showed wide variability in the number of neurons and spikes detected in real data. Additionally, average error rates of 23% false positive and 30% false negative were found for synthetic data.     

Nonlinear modeling of the dynamic effects of arterial pressure and CO2 variations on cerebral blood flow in healthy humans

The effect of spontaneous beat-to-beat mean arterial blood pressure fluctuations and breath-to-breath end-tidal CO2 fluctuations on beat-to-beat cerebral blood flow velocity variations is studied using the Laguerre-Volterra network methodology for multiple-input nonlinear systems. The observations made from experimental measurements from ten healthy human subjects reveal that, whereas pressure fluctuations explain most of the high-frequency blood flow velocity variations (above 0.04 Hz), end-tidal CO2 fluctuations as well as nonlinear interactions between pressure and CO2 have a considerable effect in the lower frequencies (below 0.04 Hz). They also indicate that cerebral autoregulation is strongly nonlinear and dynamic (frequency-dependent). Nonlinearities are mainly active in the low-frequency range (below 0.04 Hz) and are more prominent in the dynamics of the end-tidal CO2-blood flow velocity relationship. Significant nonstationarities are also revealed by the obtained models, with greater variability evident for the effects of CO2 on blood flow velocity dynamics.