Graphene coating assisted injection molding of ultra‐thin thermoplastics

High strength light weight parts are critical for the development of new technologies, particularly electronic devices, such as laptop computers, smart phones, and tablet devices. Injection molded plastics and composites are excellent choices for mass producing such parts. As the part thickness decreases from traditional injection molding (>2 mm thickness) to thin wall molding (～1 mm thickness), and lastly, to ultra‐thin wall molding (<0.5 mm thickness), avoiding incomplete filling (short shots) becomes more challenging. Even though, methods exist today for molding thin‐wall plastic parts (i.e., fast heating/fast cooling injection molding), they require multiple steps resulting in a noncost efficient process. In this article, we demonstrate the technical feasibility of using graphene coating to facilitate flow, by promoting slip at the mold walls. We evaluate the influence of coated and uncoated mold inserts on fiber orientation. We present experimental results using un‐reinforced polypropylene and a 40% by weight carbon fiber reinforced polycarbonate/acrylonitrile butadiene styrene. POLYM. ENG. SCI., 55:1374–1381, 2015. © 2015 Society of Plastics Engineers     

Different bacterial models for in vitro induction of non‐cavitated enamel caries‐like lesions: Microhardness and polarized light miscroscopy analyses

The aim of this study was to compare different bacterial models for in vitro induction of non‐cavitated enamel caries‐like lesions by microhardness and polarized light microscopy analyses. One hundred blocks of bovine enamel were randomly divided into four groups (n = 25) according to the bacterial model for caries induction: (A) Streptococcus mutans, (B) S. mutans and Lactobacillus acidophilus, (C) S. mutans and L. casei, and (D) S. mutans, L. acidophilus, and L. casei. Within each group, the blocks were randomly divided into five subgroups according to the duration of the period of caries induction (4–20 days). The enamel blocks were immersed in cariogenic solution containing the microorganisms, which was changed every 48 h. Groups C and D presented lower surface hardness values (SMH) and higher area of hardness loss (ΔS) after the cariogenic challenge than groups A and B (P < 0.05). As regards lesion depth, under polarized light microscopy, group A presented significantly lower values, and groups C and D the highest values. Group B showed a higher value than group A (P < 0.05). Groups A and B exhibited subsurface caries lesions after all treatment durations, while groups C and D presented erosion‐type lesions with surface softening. The model using S. mutans, whether or not it was associated with L. acidophilus, was less aggressive and may be used for the induction of non‐cavitated enamel caries‐like lesions. The optimal period for inducing caries‐like lesions was 8 days. Microsc. Res. Tech. 78:444–451, 2015. © 2015 Wiley Periodicals, Inc.     

The effect of radiopacifiers agents on pH,calcium release,radiopacity, and antimicrobial properties of different calcium hydroxide dressings

The aim of this study was to evaluate the antimicrobial activity, pH level, calcium ion release, and radiopacity of calcium hydroxide pastes associated with three radiopacifying agents (iodoform, zinc oxide, and barium sulfate). For the pH and calcium release tests, 45 acrylic teeth were utilized and immersed in ultrapure water. After 24 h, 72 h, and 7 days the solution was analyzed by using a pH meter and an atomic absorption spectrophotometer. Polyethylene tubes filled with the pastes were used to perform the radiopacity test. For the antimicrobial test, 25 dentin specimens were infected intraorally in order to induce the biofilm colonization and treated with the pastes for 7 days. The Live/Dead technique and a confocal microscope were used to obtain the ratio of live cells. Parametric and nonparametric statistical tests were performed to show differences among the groups (P < 0.05). The pH analysis at 7 days showed significant differences (P < 0.05) among the groups. No differences among the pastes were found in the calcium release test on the 7th day (P > 0.05). The calcium hydroxide/iodoform samples had the highest radiopacity and antimicrobial activity against the biofilm‐infected dentin in comparison to the other pastes (P < 0.05). Calcium hydroxide mixed with 17% iodoform and 35% propylene glycol into a paste had the highest pH, calcium ion release, radiopacity, and the greatest antimicrobial action versus similar samples mixed with BaSO4 or ZnO. Microsc. Res. Tech. 78:620–625, 2015. © 2015 Wiley Periodicals, Inc.     

Effects of Phonon Confinement on Anomalous Thermalization,Energy Transfer,and Upconversion in Ln3+‐Doped Gd2O3 Nanotubes

There is a growing interest in understanding how size‐dependent quantum confinement affects the photoluminescence efficiency, excited‐state dynamics, energy‐transfer and thermalization phenomena in nanophosphors. For lanthanide (Ln³⁺)‐doped nanocrystals, despite the localized 4f states, confinement effects are induced mostly via electron–phonon interactions. In particular, the anomalous thermalization reported so far for a handful of Ln³⁺‐doped nanocrystals has been rationalized by the absence of low‐frequency phonon modes. This nanoconfinement may further impact on the Ln³⁺ luminescence dynamics, such as phonon‐assisted energy transfer or upconversion processes. Here, intriguing and unprecedented anomalous thermalization in Gd₂O₃:Eu³⁺ and Gd₂O₃:Yb³⁺,Er³⁺ nanotubes, exhibiting up to one order of magnitude larger than previously reported for similar materials, is reported. This anomalous thermalization induces unexpected energy transfer from Eu³⁺ C₂ to S₆ crystallographic sites, at 11 K, and ²H_11/2 → ⁴I_15/2 Er³⁺ upconversion emission; it is interpreted on the basis of the discretization of the phonon density of states, easily tuned by varying the annealing temperature (923–1123 K) in the synthesis procedure, and/or the Ln³⁺ concentration (0.16–6.60%).     

myo-Inositol trispyrophosphate: a novel allosteric effector of hemoglobin with high permeation selectivity across the red blood cell plasma membrane

myo‐Inositol trispyrophosphate (ITPP), a novel membrane‐permeant allosteric effector of hemoglobin (Hb), enhances the regulated oxygen release capacity of red blood cells, thus counteracting the effects of hypoxia in diseases such as cancer and cardiovascular ailments. ITPP‐induced shifting of the oxygen–hemoglobin equilibrium curve in red blood cells (RBCs) was inhibited by DIDS and NAP‐taurine, indicating that band 3 protein, an anion transporter mainly localized on the RBC membrane, allows ITPP entry into RBCs. The maximum intracellular concentration of ITPP, determined by ion chromatography, was 5.5×10^?3 M , whereas a drop in concentration to the limit of detection was observed in NAP‐taurine‐treated RBCs. The dissociation constant of ITPP binding to RBC ghosts was found to be 1.72×10^?5 M . All data obtained indicate that ITPP uptake is mediated by band 3 protein and is thus highly tissue‐selective towards RBCs, a feature of major importance for its potential therapeutic use.     

Synthesis and characterization of Cu core Pt–Ru shell nanoparticles for the electro-oxidation of alcohols

Cu@Pt–Ru core–shell supported electrocatalysts have been synthesized by a two-step process via a galvanic displacement reaction. XRD diffraction and EDX analysis, and cyclic voltammetry measurements revealed the presence of nanoparticles composed by a Cu-rich Pt–Cu core surrounded by a Pt-rich Pt–Ru shell. Cyclic voltammetry and chronoamperometric measurements showed that as-synthesized core–shell materials exhibit superior catalytic activity towards methanol and ethanol electro-oxidation compared to a commercial Pt–Ru/C catalyst with higher Pt loading. This behavior can be associated with the lattice mismatch between the Pt-rich shell and the Cu rich core, which in turn produces lattice-strain, surface ligand effects and a large amount of surface defect sites. In addition, the core–shell electrodes displayed a better catalytic activity and lower onset potentials for ethanol oxidation than for methanol oxidation.     

Influence of workpiece hardness on EDM performance

The aim of this research is to show the influence of the hardness of the alloy steel on the material removal rate and on the workpiece surface roughness.The Taguchi methodology was used to study that influence. The result of the verification test for workpiece surface roughness was a strong confirmation. This type of outcome allows the use of the additive model to predict the workpiece surface roughness with an average error of 0.4%.The result of the verification test for material removal rate was a poor confirmation due to an interaction of parameters. This type of outcome does not allow the additive model to predict the material removal rate with accuracy. Therefore, a linear regression model was developed for material removal rate using workpiece hardness and its interactions, among other variables. This model predicts the material removal rate with an average error of 1.06%.These results show that workpiece hardness and its interactions have influence on the material removal rate and on the workpiece surface roughness.     

Carbon nanotube junctions obtained by pulsed liquid injection chemical vapour deposition

The effect of substrate surface roughness on the synthesis of carbon nanotube (CNT) junctions is studied. CNTs were obtained by a pulsed liquid injection chemical vapour deposition system (PLICVD) and grown on quartz substrates with different roughnesses. Nickel particles were used as catalyst and acetone as the carbon precursor. Results shown that CNTs growth depend strongly on the substrate irregularity. When roughness is present, the presence of CNT junctions are increased. On the quartz surface, without any modification of roughness, CNTs are not obtained. Thus, a growth mechanism for CNT junctions, based on the substrate roughness is suggested. This method represents an important alternative to produce CNTs for applying them in nanoelectronic devices.     

Reliability and validity of self-reported burnout in college students: A cross randomized comparison of paper-and-pencil vs. online administration

Internet data collection is becoming increasingly popular in all research fields dealing with human perceptions, behaviors and opinions. Advantages of internet data collection, when compared to the traditional paper-and-pencil format, include reduced costs, automatic database creation, and the absence of researcher-related bias effects, such as availability and complete anonymity. However, the validity and reliability of internet gathered data must be established, in comparison to the usual paper-and-pencil accepted formats, before an inferential analysis can be done. In this study, we compared questionnaire data gathered from the internet with that from the traditional paper-and-pencil in a sample of college students. The questionnaires used were the Maslach Burnout Inventory - Student Survey (MBI-SS), the Oldenburg Burnout Inventory (OBI-SS) and the Copenhagen Burnout Inventory (CBI-SS). Data was gathered through a within-subject cross randomized and counterbalanced design, on both internet and paper-and-pencil formats. The results showed no interference in the application order, and a good reliability for both formats. However, concordance between answers was generally higher in the paper-and-pencil format than on the internet. The factorial structure was invariant in the three burnout inventories. Data gathered in this study supports the Internet as a convenient, user-friendly, comfortable and secure data gathering method which does not affect the accepted factorial structures existent in the paper format of the three burnout inventories used.     

Variable-order fractional derivatives and their numerical approximations

This paper addresses the different possible definitions of variable-order derivatives and their numerical approximations; both approximations based upon the definitions and approximations consisting of non-linear transfer functions (in particular combining existing approximations of constant-order fractional derivatives, such as the Crone approximation, with fuzzy logic) are considered. There are different possible configurations, implementing variable-order fractional derivatives both with and without memory of past values of the time-dependent differentiation order.