Long-term cycling behavior of asymmetric activated carbon/MnO2 aqueous electrochemical supercapacitor

Activated carbon–MnO₂ hybrid electrochemical supercapacitor cells have been assembled and characterized in K₂SO₄ aqueous media. A laboratory cell achieved 195,000 cycles with stable performance. The maximal cell voltage was 2 V associated with 21 ± 2 F g⁻¹ of total composite electrode materials (including activated carbon and MnO₂, binder and conductive additive) and an equivalent serie resistance (ESR) below 1.3 Ω cm². Long-life cycling was achieved by removing dissolved oxygen from the electrolyte, which limits the corrosion of current collectors. Scaling up has been realized by assembling several electrodes in parallel to build a prismatic cell. A stable capacity of 380 F and a cell voltage of 2 V were maintained over 600 cycles. These encouraging results show the interest of developing such devices, including non-toxic and safer components as compared to the current organic-based devices.     

Wavelength‐Emission Tuning of ZnO Nanowire‐Based Light‐Emitting Diodes by Cu Doping: Experimental and Computational Insights

The band‐gap engineering of doped ZnO nanowires is of the utmost importance for tunable light‐emitting‐diode (LED) applications. A combined experimental and density‐functional theory (DFT) study of ZnO doping by copper (Zn²⁺ substitution by Cu²⁺) is presented. ZnO:Cu nanowires are epitaxially grown on magnesium‐doped p‐GaN by electrochemical deposition. The heterojunction is integrated into a LED structure. Efficient charge injection and radiative recombination in the Cu‐doped ZnO nanowires are demonstrated. In the devices, the nanowires act as the light emitters. At room temperature, Cu‐doped ZnO LEDs exhibit low‐threshold emission voltage and electroluminescence emission shifted from the ultraviolet to violet–blue spectral region compared to pure ZnO LEDs. The emission wavelength can be tuned by changing the copper content in the ZnO nanoemitters. The shift is explained by DFT calculations with the appearance of copper d states in the ZnO band‐gap and subsequent gap reduction upon doping. The presented data demonstrate the possibility to tune the band‐gap of ZnO nanowire emitters by copper doping for nano‐LEDs.     

Chemical Coupling of Carbon Nanotubes and Silicon Nanoparticles for Improved Negative Electrode Performance in Lithium‐Ion Batteries

Multi‐walled carbon nanotube (MWCNT)/silicon nanocomposites obtained by a grafting technique using the diazonium chemistry are used to prepare silicon negative electrodes for lithium‐ion batteries. The covalent bonding of the two compounds is obtained via mono‐ and multi‐layers of phenyl bridges, leading to an ideal dispersion of MWCNTs and silicon nanoparticles that are bound together. The presence of MWCNTs close to silicon nanoparticles enhances the electronic pathway to the active material particles and probably helps to prevent silicon decrepitation upon repeated lithium insertion/extraction by improving the mechanical stability of the electrode at a nanoscale level. This effect results in the enhancement of cycling ability and capacity, which are demonstrated by comparing the nanocomposite electrode to a simple mixture of the two compounds. This technique can be applied to other carbon conductive additives together with silicon or other nanosized active compounds.     

Failure analysis defect location on a real case 55 nm memory using dynamic power supply emulation

Static and dynamic techniques for defect location are well established in the failure analysis flow of a failing integrated circuit. When a circuit shows an overconsumption on power supply, the useful static techniques are laser stimulation (OBIRCH, TIVA, LIVA, etc.) or photoemission. When the electrical signature is a soft fail, a functional fault or a timing issue the analyst will use dynamic techniques like dynamic laser mapping (SDL, xVM, LVI, etc.), dynamic photoemission or internal probing (Ebeam, TRE, LVP, etc.) by applying a looping test sequence which emulates the fail.In this paper we will present a real case analysis on a circuit showing a static signature (over consumption) and also a functional fault. Both static and dynamic location techniques have been used for the defect location, plus a non conventional approach by applying a clocked power supply sequence to the circuit. A comparison is done between the different signatures and we show that dynamic power supply emulation can bring some additional information on the defect location which is not detected with the conventional static/dynamic approach.     

Fruit juice-induced endothelium-dependent relaxations in isolated porcine coronary arteries: evaluation of different fruit juices and purees and optimization of a red fruit juice blend

Numerous studies have indicated that several polyphenol-rich sources such as red wine and green tea are potent inducers of endothelium-dependent relaxations in isolated arteries. As various fruits and berries are known to contain high levels of polyphenols, the aim of the present study was to assess the ability of selected pure fruit juices and purees as well as blends to cause endothelium-dependent relaxations in isolated arteries. Vascular reactivity was assessed using porcine coronary artery rings, and fruit juices, purees and blends were characterized for their content in vitamin C, total phenolic, sugar and antioxidant activity. Fruit juices and purees caused variable concentration-dependent relaxations, with blackcurrant, aronia, cranberry, blueberry, lingonberry, and grape being the most effective fruits. Several blends of red fruits caused endothelium-dependent relaxations. Relaxations to blend D involved both a NO- and an EDHF-mediated components. The present findings indicate that some berries and blends of red fruit juices are potent inducers of endothelium-dependent relaxations in the porcine coronary artery. This effect involves both endothelium-derived NO and EDHF, and appears to be dependent on their polyphenolic composition rather than on the polyphenolic content.     

Simple method for the layer-by-layer surface modification of multiwall carbon nanotubes

A simplified method for the surface modification of multiwall carbon nanotubes (MWCNTs) using the layer-by-layer (LbL) technique is proposed. In this approach, the minimum polyelectrolyte content was added to the solution in order to eliminate the tedious centrifugation step. The one pot LbL deposition of poly (diallyldimethylammonium chloride) (PDADMAC), and poly (sodium 4-styrenesulfonate), (PSS) is presented. UV–Vis spectroscopy and zeta potential measurements were used to determine the minimum PDADMAC and PSS concentration needed for the deposition of each polyelectrolyte layer. The deposition cycle was repeated until six layers of PDADMAC/PSS were deposited. The film growth was confirmed by transmission electron microcopy and was found to increase as a function of the number of deposited layers with a final thickness of 18 nm. Evidence of the alternate deposition of oppositely charged polyelectrolytes was further investigated by measurement of the zeta potential values which were found to reverse from positive to negative as a function of the number of deposited layers thus confirming the overcompensation of the surface charge at each adsorption step. This simple method could be useful for the fast preparation of large volumes of MWCNTs solutions in a single batch without the need for centrifugation step.     

Safety management and risk assessment in chemical laboratories

The present paper highlights a new safety management program, MICE (Management, Information, Control and Emergency), which has been specifically adapted for the academic environment. The process starts with an exhaustive hazard inventory supported by a platform assembling specific hazards encountered in laboratories and their subsequent classification. A proof of concept is given by a series of implementations in the domain of chemistry targeting workplace health protection. The methodology is expressed through three examples to illustrate how the MICE program can be used to address safety concerns regarding chemicals, strong magnetic fields and nanoparticles in research laboratories. A comprehensive chemical management program is also depicted.     

Effect of heating rate on bond failure of rebars into concrete using polymer adhesives to simulate exposure to fire

The high bonding capacity of polymer adhesives has encouraged their application for anchoring steel bars into concrete for structural purposes. However, high temperatures have the effect of weakening the bond and endangering the construction under a fire situation. This paper evaluates bond resistance to temperature by means of pull-out tests performed with a constant tensile load on the steel bar and a progressive temperature increase of the bond throughout the test until a failure temperature is reached. Two testing programs were performed using separate heating technologies: electric oven and gas furnace, which mainly differ by their heating speed, in order to assess the influence on bond failure at high temperature. The study describes thermal characteristics and phenomena such as vaporization in different concrete zones near the anchor in both of the testing devices (electric and gas).     

Identification of odour‐active compounds in muscle of brown trout (Salmo trutta) as affected by dietary lipid sources

The effect of fatty acid composition on odour‐active compounds in brown trout (Salmo trutta) muscle was evaluated. The fillets were obtained from three groups of fish fed experimental diets containing either fish oil (FO), soybean oil (SO) or linseed oil (LO). Muscle fatty acid composition was shown to be influenced by diet. Thirty‐one odorous compounds were detected by gas chromatography/olfactometry (frequency‐of‐detection method). Most of these compounds were formed by the oxidation of unsaturated fatty acids. Independently of diet, (E)‐2‐pentenal, (E)‐2‐pentenol and (E)‐2‐hexenol contribute strongly to the odour of brown trout. (E,Z)‐2,4‐Heptadienal was detected with high frequency in fish fed diets containing high levels of n‐3 PUFAs (FO and LO groups). Hexanal, (E)‐2‐hexenal and 2‐nonanol seem to contribute most to the odour of fish fed diets containing vegetable oils. Many odorous compounds were derived from the oxidation of mono‐ and di‐unsaturated fatty acids, which could be promoted by high levels of PUFAs. © 2002 Society of Chemical Industry