Magnesia supported Au and Ag catalysts for the preparation of few-layer graphene–metal nanocomposites: relationship between catalyst structure and the properties of graphene composites

Magnesia supported Au, Ag, and Au–Ag nanostructured catalysts were prepared, characterized, and used to synthesize few-layer graphene–metal nanoparticle (Gr–MeNP) composites. The catalysts have a mezoporous structure and a mixture of MgO and MgO·H₂O as support. The gold nanoparticles (AuNPs) are uniformly dispersed on the surface of the Au/MgO catalysts, and have a uniform round shape with a medium size of ~8 nm. On the other hand, the silver nanoparticles (AgNPs) present on the Ag/MgO catalyst have an irregular shape, larger diameters, and less uniform dispersion. The Au–Ag/MgO catalyst contains large Au–Ag bimetallic particles of ~20–30 nm surrounded by small (5 nm) AuNPs. Following the RF-CCVD process and the dissolution of the magnesia support, relative large, few-layer, wrinkled graphene sheets decorated with metal nanoparticles (MeNPs) are observed. Graphene–gold (Gr–Au) and graphene–silver (Gr–Ag) composites had 4–7 graphitic layers with a relatively large area and similar crystallinity for samples prepared in similar experimental conditions. Graphene–gold–silver composites (Gr–Au–Ag) presented graphitic rectangles with round, bent edges, higher crystallinity, and a higher number of layers (8–14). The MeNPs are encased in the graphitic layers of all the different samples. Their size, shape, and distribution depend on the nature of the catalyst. The AuNPs were uniformly distributed, had a size of about 15 nm, and a round shape similar to those from Au/MgO catalyst. In Gr–Ag, the AgNPs have a round shape, very different from that of the Ag/MgO catalyst, large size distribution and are not uniformly distributed on the surface. Agglomerations of AgNPs together with large areas of pristine few-layer graphene were observed. In Gr–Au–Ag composites, almost exclusively large bimetallic particles of about 25–30 nm, situated at the edge of graphene rectangles have been found.     

Electrochemical study of azo-azulene compounds

An electrochemical study of several azo-azulene compounds (Az-NN-Y, where Y = substituted phenyl, pyridine, thiazole) was performed with cyclic and differential pulse voltammetry, as well as rotating-disk electrode methods. The objective of this work was to characterize their electrochemical properties and establish the influence of donor and acceptor substituents on azulene and azo group behaviour. Calculations were performed, using quantum mechanics-based methods, to correlate electrochemical reactivity with structure. Satisfactory correlations were found between experimental oxidation and reduction potentials as well as calculated ionization potentials and LUMOs.     

Experimental Results Regarding an Anthropomorphic Original Gripper with Two-Finger Tests during Grasping Objects with Varied Shapes

The paper presents theoretical and experimental results on an original anthropomorphic gripping concept. Compared to the existing anthropomorphic grippers, this gripper is very simple, yet it has the advantage of high performance in terms of gripping possibilities and a very low manufacturing cost. Source of inspiration was the human hand, which is able to catch objects by only using two fingers. The analyzed anthropomorphic gripper has two fingers, with two phalanxes each, and is based on a new mechanism with articulated bars. The kinematic analysis performed on the gripping mechanism reveals the optimal displacement in the translational coupling, which was experimentally validated. The gripping possibilities were increased by attaching clamping jaws to each phalanx. The clamping jaws have been attached by means of spherical couplings, thus offering the possibility to catch objects with any type of surface. By carrying out gripping tests with different objects, we underline the importance of a safe use of the two-fingered anthropomorphic grippers in different applications. Due to the innovative mechanical structure, the gripper can insure the minimal gripping conditions, whilst the complexity of the objects that can be gripped make it suitable for the use in robots.     

Polarisation stabilisation of vertical cavity surface emitting lasers by minimally invasive focused electron beam triggered chemistry

Local electron triggered reactions of functional surface adsorbates were used as a maskless, dry, and minimally invasive nanolithography concept to stabilize the polarisation of individual vertical cavity surface emitting lasers (VCSELs) on a wafer in a post-processing step. Using a 30 keV focused electron beam of a scanning electron microscope and injecting volatile organo-metallic (CH(3))(2)Au(tfa) molecules, polarisation gratings were directly written on VCSELs by dissociating the surface adsorbed molecules. The electron triggered adsorbate dissociation resulted in electrically conductive Au-C nano-composite material, with gold nanocrystals embedded in a carbonaceous matrix. A resistivity of 2500 μ?cm was measured at a typical composition of 30 at.% Au. This material proved successful in suppressing polarisation switching when deposited as line gratings with a width of 200 nm, a thickness of 50 nm, and a pitch of 500 nm and 1 μm. Refractive index measurements suggest that the optical attenuation by the deposited Au-C material is much lower than by pure Au thus giving a low emission power penalty while keeping the polarisation stable.     

l-Lactic acid biosensor based on multi-layered graphene

Pristine graphene platelets and graphene oxide were used as electrode modifiers, aiming the investigation of their electrochemical efficacy towards β-nicotinamide adenine dinucleotide (NADH). The electrochemical detection of NADH is one of the most studied areas of bioelectroanalysis because of the ubiquity of NAD(P)H-based enzymatic reactions in nature. Commercially available graphene and laboratory prepared graphene oxide were used to modify glassy carbon electrodes and the behaviour of such modified electrodes against potassium ferricyanide (III) and NADH was reported. Relying on the graphene-modified transducer, l-lactic dehydrogenase (l-LDH) was successfully immobilised in a 1 % Nafion^® membrane. The developed biosensor, working at +250 mV versus Ag/AgCl reference electrode, was used to assess l-lactic acid in four different types of yogurts, revealing an l-lactic acid concentration ranging between 0.3 and 0.6 %.     

COMMENTS ON π-ELECTRON CONJUGATION IN THE FIVE-MEMBERED RING OF BENZO-DERIVATIVES OF CORANNULENE

Cyclic conjugation in corannulene and its benzo-derivatives is studied by means of the π-electron contents and the energy effects of individual rings, with particular attention to the structural effects influencing the magnitude of cyclic conjugation in the 5-membered ring. Two main general regularities were observed: (a) the PCP effect (6-membered rings connected by a single bond to the 5-membered ring increase in it the intensity of cyclic conjugation), and (b), the linear effect (6-membered rings separated from the 5-membered ring by another 6-membered ring, but not in PCP constellation, decrease the magnitude of cyclic conjugation in the 5-membered ring).     

Polymer-Biologically Active Principle Conjugates Obtained by Esterification of Poly(Vinyl Alcohol)

The paper deals with the study of some polymer-biologically active principle systems characterized by the controlled release of the bioactive component by hydrolyze followed by diffusion. The systems were obtained by coupling the 2-mercapto-benzotiazolyl-acetic acid and N-(m-nitrobenzoyl)-L-methionine on poly(vinyl alcohol) by means of esteric bonds in the presence of diciclohexylcarbodiimide as an activator. The influence of some coupling process parameters on the reaction efficiency was studied, such as the drug/support and activator/support ratios. The coupling products with a maximum content of biologically active compound were characterized by spectral measurements, also as regards the capacity of bioactive compound release under the conditions simulating those within the gastro-intestinal tract. The antibacterial activity of the conjugates against Staphylococcus aureus, Eschrichia coli, Sarcina lutea, and Bacillus subtilis was determined.     

Development of a stability intelligent control system for turning

This paper presents a stability control system based on a new strategy, with application in turning. It works by permanent assessment of the system operating point position relative to the stability limit, and process parameter permanent, in-process modification such as this point is always placed in the stable domain zone that gives the highest process performance. In the case of turning, here approached: (1) this zone is the stability limit proximity; (2) the system operating point position is determined by assessing a cutting force monitored signal feature; and (3) this position is changed by modifying the cutting edge setting angle, the feed rate, and the cutting speed, as it follows: when the risk of overpassing the stability limit is imminent, the setting angle is increased, followed by a feed rate diminishing and then by a worked piece rotation speed reduction, while immediately after surpassing the risk, the three variables modification is reversed, this way the chatter onset being permanently avoided and the performance kept in every moment at the highest possible level. The system was experimentally implemented on a transversal lathe. The results of tests on dedicatedly designed specimens are showing a machining productivity significant increase, in conditions of a stable cutting process. The system is simple, and it can be easily added to the existing CNC machine tools, without important modifications.     

Long-term memory for the terrorist attack of September 11: Flashbulb memories, event memories, and the factors that influence their retention.

More than 3,000 individuals from 7 U.S. cities reported on their memories of learning of the terrorist attacks of September 11, as well as details about the attack, 1 week, 11 months, and/or 35 months after the assault. Some studies of flashbulb memories examining long-term retention show slowing in the rate of forgetting after a year, whereas others demonstrate accelerated forgetting. This article indicates that (a) the rate of forgetting for flashbulb memories and event memory (memory for details about the event itself) slows after a year, (b) the strong emotional reactions elicited by flashbulb events are remembered poorly, worse than nonemotional features such as where and from whom one learned of the attack, and (c) the content of flashbulb and event memories stabilizes after a year. The results are discussed in terms of community memory practices. (PsycINFO Database Record (c) 2010 APA, all rights reserved)