Colorimetric assay for determination of trimethylamine-nitrogen (TMA-N) in fish by combining headspace-single-drop microextraction and microvolume UV–vis spectrophotometry

In this work, headspace-single-drop microextraction has been used in combination with microvolume UV–vis spectrophotometry to enhance the determination of trimethylamine-nitrogen (TMA-N) in fish samples. TMA-N is often used for monitoring fish freshness, but due to the low analytical sensitivity usually achieved, its determination must be performed after certain time of storage in some fish species. The proposed methodology, based on the extraction and subsequent complexation of volatile TMA-N onto a picric acid-containing xylene microdrop exposed to the headspace, involves an important improvement of sensitivity (detection limit 6 × 10⁻⁴ mg TMA-N per 100 g of fish), a miniaturization of the AOAC Official Method (971.14) and a simple approach for routine labs. This method is well suited to determination of TMA-N in different species of frozen and fresh fish samples from markets and to study the evolution of TMA-N concentration in farmed turbot at the earliest stages of deterioration.     

Quantum dot-based headspace single-drop microextraction technique for optical sensing of volatile species

Core-shell CdSe/ZnS quantum dots (QDs) dispersed in a droplet of organic solvent have been applied for the first time as luminescent probes for the selective detection of volatile species. Luminescence quenching caused by volatile species was examined after their trapping onto a drop using the headspace single-drop microextraction (HS-SDME) approach along with microvolume fluorospectrometry. The novel method is characterized by low reagent and sample consumption, especially regarding QDs, a reduction about 500-fold for each analysis being attained in comparison with luminescent probing in aqueous phase using conventional luminescence spectrometers with 1 cm quartz cells for measurement. To assess QDs as luminescent probes along with HS-SDME, 14 volatile species were tried. Strong luminescence quenching (i.e., I(0)/I > 2.5) was observed for species such as CH(3)Hg(+) and Se(IV) after hydridation with NaBH(4). Moderate luminescent quenching (I(0)/I ≈ 2) was observed for species such as Hg(II) after its conversion into Hg(0), H(2)S, and methylcyclopentadienyl-manganese tricarbonyl (MMT). Small luminescence quenching effects (i.e., 1< I(0)/I <2) were caused by other hydride forming species such as As(III), Sb(III), Te(IV), and Bi(III), as well as SnBu(4), volatile amines, and endosulfan. Detection limits of 6.3 × 10(-9) and 1.6 × 10(-7) M were obtained for Se(IV) and CH(3)Hg(+), respectively. Repeatability expressed as relative standard deviation (N = 7) was about 5%. QD-HS-SDME-μvolume-fluorospectrometry allows one to carry out matrix separation, preconcentration, and confinement of QDs, hence achieving a selective, sensitive, fast, environmentally friendly, and miniaturized luminescence assay.     

Cactus stem (Opuntia ficus‐indica Mill): anatomy,physiology and chemical composition with emphasis on its biofunctional properties

Cactus stem (Opuntia ficus‐indica Mill) is native to Mesoamerica and marketed in different forms such as fresh, frozen or pre‐cooked. Worldwide, this vegetable is recognized for its pharmaceutical actions, including its antioxidant, diuretic, anticarcinogenic, anti‐inflammatory, anti‐diabetic, and anti‐hypercholesterolemic properties, as well as their antiviral and antispermatogenic effects. However, not all of these properties have been associated with its chemical composition; therefore, this review aims to present and integrate information available on the physiology and anatomy of cactus stem and its chemical composition, focusing on some of the many factors that determine its biofunctionality. © 2017 Society of Chemical Industry     

Perspective correct occlusion‐capable augmented reality displays using cloaking optics constraints

Perspective‐correct occlusion‐capable augmented reality displays are generalized using an optical cloak constraint for ray transfer analysis or simulations; any ray entering the optical system exits at the height and angle as if it passed through empty space. We analyze several systems with two‐lens, three‐lens, and four‐lens looped groups in inline, folded, and looped configurations. We design and demonstrate a four‐lens folded optical cloak and a three‐lens inverted cloak with an erecting prism.     

A Dynamic-compensation Approach to Impedance Control of Robot Manipulators

This paper presents an impedance–control strategy with dynamic compensation for interaction control of robot manipulators. The proposed impedance controller has been developed considering that the equilibrium point of the closed-loop system, composed by the combination of the controller and the full nonlinear robot dynamics is, locally, asymptotically stable in agreement with Lyapunov’s direct method. The performance of the proposed controller is verified through simulation and experimental results obtained from the implementation of an interaction task involving a two degree-of-freedom, direct-drive robot.     

A more Efficient Starch Degradation by the Combination of Hydrolase and Transferase Activities of α‐Amylase and Cyclomaltodextrin Glucanotransferase

α‐Amylases catalyze the hydrolysis of internal α‐(1→4) linkages of glucose polymers as their main reaction; however, some α‐amylases catalyze transfer reactions in addition to hydrolysis. It has been observed that those α‐amylases capable of transferring glycoside residues are also those that generate low molecular weight products from their action on starch (i.e. saccharifying α‐amylases). In this paper the product profiles of a liquefying α‐amylase, a cyclomaltodextrin glucanotransferase and both enzymes acting together on starch and maltodextrins are compared. The increase in glucose and maltose concentration, when both enzymes act together, is due to the combined action of the transfer and hydrolytic activity of CGTase and the liquefying α‐amylase, respectively.     

Analysis of distributed power control under constant and time-varying delays

This work studies the distributed power control algorithm proposed in 1993 by Foschini-Miljanic, standardised for universal mobile telecommunication systems. Continuous and discrete time versions of this algorithm are analysed. First, the stability of the distributed power allocation schemes was studied, where sufficient conditions to guarantee stability and convergence to a desired quality of service were provided. In this study, the channel gains are assumed to be slowly time-varying or piece-wise constant. For closed-loop control, a proportional controller is then employed under integral action in order to achieve good tracking despite time-varying and unknown channel gains. Next, the effects of constant and time-varying time delays in the closed-loop structure are studied. Explicit stability regions for the control gains in the Foschini-Miljanic scheme are derived for both the continuous and discrete-time versions of the algorithm, under constant and time-varying delays. For time-varying scenario, the resulting stability regions do not impose limitations on the rate change of the time-varying profiles. A comprehensive evaluation using simulations is performed to validate the analytical derivations described in the paper.