Experimental study and numerical modeling of brittle fracture of carbonate rock under uniaxial compression

The brittle carbonate rock taken from the Tarim Oilfield is tested in laboratory under uniaxial compression. The acoustic emission (AE) is used to monitor the microcracking activity in rock during the experiment. Moreover, the 3D tomograms of carbonate rock after uniaxial compression are obtained by using CT imaging technology, which indicates that microcracks mutually interconnect and eventually form macroscopic fractures after failure. The PFC2D is used to model the behavior of brittle rock including microcracks propagation. The stress–strain curve and cracks distribution in rock model are obtained from the PFC simulation. The numerical results agree with the experimental test well.     

Size control of phase‐separated liquid crystal droplets in a polymer matrix based on the phase diagram

When a mixture of liquid crystal (LC) and photo reactive monomer is irradiated by UV light, polymerization occurs and LC droplets form through phase separation, producing polymer dispersed LCs (PDLCs). Although size control of LC droplets and reduced amounts of LC in PDLC films are important in applications, precise size control of LC droplets at a low LC fraction has not yet been accomplished. In this study, the phase diagrams of the LC/initial monomer and the LC/polymer during polymerization were used to control LC droplet size at various LC fractions. Both the relative position of the sample in the initial phase diagram and the shift of the phase separation line during polymerization were shown to be important in determining the size of LC droplets. Our results are expected to provide a new strategy for precise size control of LC droplets especially at a low LC fraction range, which would be a great help for PDLC applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Comparison of scale factor estimators for ultrasonic temperature monitoring: Application to structural health monitoring

In Structural Health Monitoring (SHM) of materials, estimating the effects of environmental and operational conditions such as temperature is important. Indeed, temperature changes induce modifications of the mechanical properties of the material and therefore cause a dilation of the acoustic signals characterized by a scale factor. This paper described four scale factor estimators able to monitor changes in temperature: The short-time cross-correlation (STXC) method, the stretching method (STRE), the Minimum Variance Based Estimator method (MVBE) and the Scale Transform Based Estimator method (STBE). The first two methods have already been assessed in the literature while the latter two have been specifically developed for this study. First, closed-form for the Cramer-Rao bound on the estimates of the scale factor, from a simplified deterministic signal, are derived and simplified expressions are given. Then, a statistical evaluation of the quality of estimates is conducted through Monte-Carlo simulations using synthetic signals, based on a model taking into account the influence of temperature. A raw estimate of the computational complexity of signal processing methods also completes this evaluation phase. Finally, the experimental validation of estimation methods is conducted on an aluminum plate subjected to temperatures variations in a controlled thermal environment. The temperature estimates are then faced with an analytical model describing the material behavior.     

Vibrational spectroscopy in the development of surface hydrophilic elastomer latex (SHEL)

An illustrative example is given to show how various vibrational spectroscopy techniques coupled with two-dimensional (2D) correlation analysis can be effectively utilized in the development of a novel and functional material. Surface-hydrophilic elastomer latex (SHEL) is a material exhibiting rather unusual permanently water-wettable surface feature despite having a soft and rubbery bulk property, which can be successfully analyzed with vibrational spectroscopy. 2D photoacoustic (PAS) IR spectra of a SHEL film indicate the localized surface segregation of long-chain ethoxylate moiety of the oligomeric surfactant used in the preparation of this material. The accumulation of the hydrophilic long-chain ethoxylate produces the high energy polar surface over the hydrophobic bulk phase of SBR copolymer. The persistence of very low water contact angle, even after repeated washing of a SHEL film with an excess amount of water, indicates permanent covalent attachment of long-chain ethoxylate group to the SBR copolymer. 2D Raman spectra generated from the process monitoring of the emulsion copolymerization of SHEL reveal the mechanism of the covalent attachment of long-chain ethoxylate. The reaction involves a separate step of oleyl moiety of the block surfactant reacting with 1,3-butadiene prior to the onset of copolymerization to produce the SBR latex product.     

A rapid and simple HPTLC assay for therapeutic drug monitoring of capecitabine in colorectal cancer patients

Capecitabine is a prodrug of 5‐flurouracil, employed as a broad spectrum chemotherapeutic agent. It is also used as monotherapy or a combination chemotherapy agent for the treatment of colorectal cancer. Capecitabine is administered in combination with oxaliplatin and hence it is essential to determine that co‐administration does not affect its metabolism. To determine the plasma concentration of capecitabine a simple HPTLC method was developed and validated. Blood samples from 12 patients with colorectal cancer were collected and analyzed by the HPTLC method with a reference internal standard. Out of these 12 patients, six were treated with capecitabine monotherapy and another six were treated with capecitabine + oxaliplatin combination therapy. The results of analysis indicated that there was no significant drug–drug interaction and the co‐administration of oxaliplatin did not affect the metabolism of capecitabine. This method is sensitive, robust and specific and allows analysis of multiple samples simultaneously, making it suitable for therapeutic drug monitoring of capecitabine.     

Analysis of Organic Compounds in Antarctic Snow and Their Origin

Abstract

Organic compounds extractable with n-hexane were identified and quantitatively determined in pack, surface and deep snow samples taken at different depths and collected at several altitudes above sea level from Antarctica during the 1993/94 Italian expedition. The comparison between the composition of organic compounds in snow and the ones in pack and sea-water samples pointed out that the three matrices substantially contain the same biogenic and anthropogenic organic compounds. The contribution of marine aerosol to organic content in the snow is confirmed by the enrichment ratios calculated for the more representative classes of identified compounds (n-alkanes, phthalates and low molecular weight alkylbenzenes). The changes in the composition of organic compounds in snow as the altitude increases seem to depend on the dimensional spectrum of the aerosol. Thus, smallest particles, richest in surfactant material, reach the highest altitudes.     

Electrochemical detection of nitrate,nitrite and ammonium for on-site water quality monitoring

This review examines the most recent electrochemical developments for nitrate, nitrite and ammonium detection for on-site water monitoring. There remains a high demand for effective field-based detection of the dissolved inorganic nitrogen (DIN) analytes to aid in mitigating nitrogen loading. Electrochemical approaches show increasing potential to fill this role as advancements in nanotechnology continually improve analytical performance and on-site applicability. However, translating these improvements into the field still faces the resonating challenges of reaching analytical proficiency (selectivity, sensitivity, robustness, stability), practical end-user functionality, minimal matrix interferences and cost effectiveness. Herein, we elaborate on these challenges via a critical evaluation of current studies and examine how realistic the prospects of on-site nitrate, nitrite and ammonium are. We also present recommendations in addressing these gaps to conclude the review.     

AuPt Bipyramid Nanoframes as Multifunctional Platforms for In Situ Monitoring of the Reduction of Nitrobenzene and Enhanced Electrocatalytic Methanol Oxidation

Multifunctional metal nanostructures with a hollow feature, especially for nanoframes, are highly attractive owing to their high surface-to-volume ratios. However, pre-grown metal nanocrystals are always involved during the preparation procedure, and a synthetic strategy without the use of a pre-grown template is still a challenge. In this article, a template-free strategy is reported for the preparation of novel AuPt alloy nanoframes through simply mixing HAuCl₄ and H₂PtCl₆ under mild conditions. The alloy nanostructures show a bipyramid-frame hollow architecture with the existence of only the ten ridges and absence of their side faces. This is the first report of bipyramid-like nanoframes and a template-free method under mild conditions. This configuration merges the plasmonic features of Au and highly active catalytic sites of Pt in a single nanostructure, making it an ideal multifunctional platform for catalyzing and monitoring the catalytic reaction in real time. The superior catalytic activity is demonstrated by using the reduction of nitrobenzene to the corresponding aminobenzene as a model reaction. More importantly, the AuPt nanoframes can track the reduction process on the basis of the SERS signals of the reactants, intermediates, and products, which helps to reveal the reaction mechanism. In addition, the AuPt nanoframes show much higher electrocatalytic properties toward the methanol oxidation reaction than commercial Pt/C electrocatalysts.     

A simple,rapid and reliable liquid chromatography–mass spectrometry method for determination of methotrexate in human plasma and its application to therapeutic drug monitoring

A simple, rapid and reliable liquid chromatography–electrospray ionization tandem mass spectrometry method was established and validated for the determination of methotrexate in human plasma. After a straightforward protein precipitation by acetonitrile–water (70:30, v/v), methotrexate (MTX) and p‐aminoacetophenone (used as internal standard, IS) were separated on a Column C₁₈ column (50 × 2.1 mm, 3 µm; Column Technology, Fremont, CA, USA) using a gradient elution with mobile phase of acetonitrile and 0.03% acetic acid aqueous solution at a flow rate of 0.5 mL/min. The total chromatographic runtime was 5 min for each injection. Quantification detection was performed in a triple‐quadruple tandem mass spectrometer under positive mode monitoring the following mass transitions: m/z 455.3 → 308.3 for MTX and m/z 136.1 → 94.4 for IS. The calibration curve was linear over the range of 0.05–25.0 µmol/L with a lower limit of quantification of 0.05 µmol/L. The intra‐ and interday precisions were <5.2%, the accuracy varied from ?4.1 to 4.5%. The recovery was >94%. The LC‐MS/MS method showed an excellent agreement with the existing HPLC‐UV method using Passing–Bablok regression and Bland–Altman difference plot analysis. The validated LC‐MS/MS can be successfully applied to the routine therapeutic drug monitoring of MTX in clinical laboratories. Copyright © 2015 John Wiley & Sons, Ltd.     

Sustainable alternative in environmental monitoring using carbon nanoparticles as optical probes

Environmental monitoring is getting more important nowadays due to the greater stress faced by the natural environment in the era of urbanisation and industrialisation. To accomplish the task, rapid and reliable analytical probes are essentially needed to perform the monitoring at real time basis with high sensitivity and accuracy. In view of this, analytical probes developed using carbon nanoparticles are one of the latest alternatives that are proven with capability to detect various analytes of the environment. Carbon nanoparticles portray good fluorescence property that enables the integration onto optical sensing transducers. Further engineering via surface functionalization can be performed in the interest to improve the selectivity and sensitivity of the probes. There are several advantages of using carbon nanoparticles and the most significant benefit is the sustainability prospect as compared to other groups of fluorophores. Carbon nanoparticles can be synthesised with greener approach via simple pyrolysis or hydrolysis processes that involve minimum use of toxic or harmful starting precursors, besides able to tap on using renewable resources such as carbon rich agricultural wastes. The synthesis is often performed under mild condition and produces less or no side chemical products. Carbon nanoparticles by nature show low toxicity effect to the environment. This review focuses specifically of the sustainable significances, advantages and achievements in adopting carbon nanoparticles as an alternative for environmental monitoring.