Kinetics analysis of the curing reaction of fast cure epoxy prepregs

In this article, the curing kinetics of two fast cure flip-chip epoxy encapsulants under both isothermal and nonisothermal conditions are investigated by differential scanning calorimetry. The method allows determination of the most suitable kinetic model and corresponding parameters. The kinetic analysis suggests that the two-parameter autocatalytic model is more appropriate to describe the kinetics of the curing reaction. There are certain differences between the kinetic data from isothermal and that from nonisothermal measurements. The apparent activation energy Ea and pre-exponential factor A of E-AB1 determined from nonisothermal experiments were higher than the isothermal values, whereas the Ea and A of E-RV2 determined from both methods are relatively close. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1501–1508, 1999     

Characterization and properties of polypropylene‐block‐poly(ethylene‐co‐propylene) synthesized by short‐period polymerization

The morphology and mechanical properties of novel block copolymers consisting of isotactic polypropylene (PP) and ethylene–propylene rubber (EPR) synthesized by a short‐period polymerization method were examined using differential scanning calorimetry, atomic force microscopy, dynamic mechanical analysis, and a rheooptical technique. It was found that the novel block copolymers show a single glass transition and EPR segments are trapped into the amorphous region of PP. Furthermore, the rheooptical analysis demonstrates that a drawing process of the EPR‐rich block copolymer induces orientation of the PP lamellae in the EPR matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 958–964, 1999     

Tumor-Specific miRNA Signatures in Combination with CA19-9 for Liquid Biopsy-Based Detection of PDAC

Pancreatic ductal adenocarcinoma (PDAC) is considered one of the most aggressive malignancies and has high mortality and poor survival rates. Therefore, there is an urgent need to discover non-invasive biomarkers for early detection before PDAC reaches the incurable stage. We hypothesized that liquid biopsy of PDAC-derived extracellular vesicles (PDEs) containing abundant microRNAs (miRNAs) could be used for early diagnosis of PDAC because they can be selectively enriched and because they are biologically stable. We isolated PDEs by immunocapture using magnetic beads, and we identified 13 miRNA candidates in 20 pancreatic cancer patients and 20 normal controls. We found that expression of five miRNAs, including miR-10b, miR-16, miR-155, miR-429, and miR-1290, was markedly higher in PDEs. Furthermore, the miRNA signatures along with serum carbohydrate antigen 19-9 (CA19-9) were optimized by logistic regression, and the miRNA signature and CA19-9 combination markers (CMs) were effective at differentiating PDAC patients from normal controls. As a result, the CMs represented a high sensitivity (AUC, 0.964; sensitivity, 100%; specificity, 80%) and a high specificity (AUC, 0.962; sensitivity, 85.71%; specificity, 100%). These findings suggest that five miRNAs expressed in PDEs and CA19-9 are valuable biomarkers for screening and diagnosis of pancreatic cancer by liquid biopsy.     

Evaluation of the Effects of Particle Sizes of Silver Nanoparticles on Various Biological Systems

Seven biological methods were adopted (three bacterial activities of bioluminescence, enzyme, enzyme biosynthetic, algal growth, seed germination, and root and shoot growth) to compare the toxic effects of two different sizes of silver nanoparticles (AgNPs). AgNPs showed a different sensitivity in each bioassay. Overall, the order of inhibitory effects was roughly observed as follows; bacterial bioluminescence activity ≈ root growth > biosynthetic activity of enzymes ≈ algal growth > seed germination ≈ enzymatic activity > shoot growth. For all bacterial activities (bioluminescence, enzyme, and enzyme biosynthesis), the small AgNPs showed statistically significantly higher toxicity than the large ones (p < 0.0036), while no significant differences were observed among other biological activities. The overall effects on the biological activities (except shoot growth) of the small AgNPs were shown to have about 4.3 times lower EC₅₀ (high toxicity) value than the large AgNPs. These results also indicated that the bacterial bioluminescence activity appeared to be an appropriate method among the tested ones in terms of both sensitivity and the discernment of particle sizes of AgNPs.     

Insulin Clearance in Obesity and Type 2 Diabetes

Plasma insulin clearance is an important determinant of plasma insulin concentration. In this review, we provide an overview of the factors that regulate insulin removal from plasma and discuss the interrelationships among plasma insulin clearance, excess adiposity, insulin sensitivity, and type 2 diabetes (T2D). We conclude with the perspective that the commonly observed lower insulin clearance rate in people with obesity, compared with lean people, is not a compensatory response to insulin resistance but occurs because insulin sensitivity and insulin clearance are mechanistically, directly linked. Furthermore, insulin clearance decreases postprandially because of the marked increase in insulin delivery to tissues that clear insulin. The commonly observed high postprandial insulin clearance in people with obesity and T2D likely results from the relatively low insulin secretion rate, not an impaired adaptation of tissues that clear insulin.     

Surface modification of polyimide and polysulfone membranes by ion beam for gas separation

The surface carbonization of polyimide (PI) and polysulfone (PSf) by ion beam has been performed to adapt the carbon molecular sieve properties on the skin of the polymeric membranes without the deformation of the membrane structure. In order to control the structure of membrane skin and to improve gas transport properties, the irradiation conditions, such as the dosage and the source of ion beams, have been varied. The ideal separation factor of CO₂ over N₂ through the surface‐modified PI and PSf membranes increased threefold compared to those of the untreated, pristine membranes, whereas the permeability decreased with almost two orders of magnitude. This appears to be due to the fact that the structure of membrane skin has been changed to a barrier layer. The formation of barrier layer was confirmed by comparing the calculated values of a simple resistance model with the experimental results, and the estimated permeability of this barrier was 10⁻⁴ barrer. It was concluded that ion beam irradiation could provide a useful tool for improving selectivity for gas separation membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1554–1560, 2000     

Mode I fracture resistance characteristics of graphite/epoxy laminated composites

Mode I crack resistance behavior of fiber‐reinforced (graphite/epoxy) composites laminated unidirectionally and anti‐symmetrically was studied. Double cantilever beam (DCB) specimens of stacking sequences, [O₁₂//O₁₂] and [(O/90)_3s//(90/O)_3s] were used where // represents the initial crack location. Resistance curves (R‐curves) were constructed for three initial crack lengths in order to determine the effects of initial crack length on the resistance behavior. The resistance force, G_R, for a crack increment was determined from the compliance calibration method. The results show that for the case of [(O/90)_3s//(90/O)_3s], the initial crack deviated from the midplane and propagated in a zigzag fashion within 13^th(90‐deg), while the crack propagated along the midplane for a [O₁₂//O₁₂] case. The results also show that for both cases, G_R was affected by the initial crack length before G_R was stabilized. However, G_R was not affected by initial crack length when G_R was stabilized for each case.     

Smart structure for composite repair

This paper reports on an experimental study aimed at assessing the feasibility of detecting damage in a bonded composite structure by means of surface mounted PZT sensor/actuator elements. A boron/epoxy composite patch repair is artificially degraded through the introduction of teflon inserts at the bond line. PZT elements attached to the patch and host structure are then excited and sensed in both transfer function and self-impedance configurations and the measurements examined to assess whether bond degradation is detectable. These measurements indicate that both methods offer good prospect of detecting debonds however, some limitations have been identified.     

Sorting spermatozoa by morphology using magnetophoresis

The chances of successful fertilisation, be it in natural pregnancy, or in vivo and in vitro assisted reproduction, are significantly dependent on the percentage of morphologically normal spermatozoa. Here, we propose sorting spermatozoa by magnetophoresis and shear flow to reduce the percentage of abnormal sperm cells for assisted reproduction. By applying resistive force theory, we develop a theoretical model to compute the swimming velocity as a function of the sperm physical parameters, as well as magnetic field properties. As spermatozoa parameters vary, we implement a statistical approach and run a Monte Carlo simulation to obtain the swimming velocity displayed in box-and-whisker plots. The difference between the velocity of conditionally satisfactory spermatozoa and morphologically abnormal spermatozoa can be enlarged through various combinations of magnetophoresis and shear flow. There exists a clear trend that by using a greater magnetic force or flow rate in the direction against the sperm heading, the percentage of conditionally satisfactory sperm obtainable can be increased, although at the expense of a lower yield. It has been demonstrated that spermatozoa subjected to magnetic fields exhibit uncompromised fertilisation capability. Therefore, sorting by magnetophoresis has the potential to increase the chances of conception in assisted reproduction technology.