AuNi alloy nanoparticles supported on reduced graphene oxide as highly efficient electrocatalysts for hydrogen evolution and oxygen reduction reactions

Bimetallic nanoparticles of Au and Ni in the form of alloy nanostructures with varying Ni content are synthesized on reduced graphene oxide (rGO) sheets via a simple solution chemistry route and tested as electrocatalysts towards the hydrogen evolution (HE) and oxygen reduction (OR) reactions using polarization and impedance studies. The AuNi alloy NPs/rGO nanocomposites display excellent electrocatalytic activity which is found to improve with increasing Ni content in the AuNi/rGO alloy nanocomposites. For HER, the best AuNi alloy NPs/rGO electrocatalyst, the one with the highest Ni content, exhibits high activity with an onset overpotential approaching zero versus the reversible hydrogen electrode and an overpotential of only 37 mV at 10 mA cm^?2. Additionally, a low Tafel slope of 33 mV dec^?1 and a high exchange current density of 0.6 mA cm^?2 are measured which are very close to those of commercial Pt/C catalyst. Also, in the ORR tests, this electrocatalyst displays comparable activity to Pt/C. The Koutecky–Levich plots referred to a 4-electron mechanism for the reduction of dissolved O₂ on the AuNi alloy NPs/rGO catalyst. The electrocatalyst thus demonstrates excellent activity towards HER and ORR. Additionally, it exhibits outstanding operational durability and activation after 10,000^th cycles assuring its practical applicability.     

An Experimental Investigation on the Effect of Ferrofluids on the Efficiency of Novel Parabolic Trough Solar Collector Under Laminar Flow Conditions

ABSTRACT

The paper is related to the use of magnetic nanofluids (ferrofluids) in a direct absorption solar parabolic trough collector, which enhances thermal efficiency compared to conventional solar collectors. By applying the right magnetic intensity and magnetic field direction, the thermal conductivity of the fluid increased higher than typical nanofluids. Moreover, the ferrofluids exhibit excellent optical properties. The external magnetic source is installed to alter the thermo-physical properties of the fluid, and the absorber tube does not have selective surface allowing ferrofluids to absorb the incoming solar irradiance directly. In this paper, an experimental investigation of the performance of small scale direct absorption solar collector using ferrofluids as an absorber was conducted. Nanoparticle concentrations of 0.05 vol% at the operational temperatures between 19°C and 40°C were used in the current study. The results show that using ferrofluids as a heat transfer fluid increases the efficiency of solar collectors. In the presence of the external magnetic field, the solar collector efficiency increases to the maximum, 25% higher than the conventional parabolic trough. At higher temperatures, the ferrofluids show much better efficiency than conventional heat transfer fluid. The study indicated that nanofluids, even of low-content, have good absorption of solar radiation, and can improve the outlet temperatures and system efficiencies. The study shows the potential of using ferrofluids in the direct absorption solar collector.     

Pre-design guidelines for passive solar architectural buildings in Kenya

Analyses have been done on the climatic data to obtain physical building design specifications for various regional climatic conditions in Kenya. The main aim is to provide a general and appropriate information at strategic pre-design stages to make better use of passive solar energy in urban planning and, building design for better indoor ‘comfort’ climate and, the health and productivity of the building occupants. It utilizes a computer program, ARCHIPAK together with climatic data (for 8 year period) to get ‘comfort zones’, and ‘control potential zones’(CPZs), for nine stations representing Kenya fairly well by virtue of their geographical locations. The use of the CPZs in building design and the objectives of the pre-design guidelines are discussed for eight major provincial urban centers and the capital City of Nairobi, all with distinctive climatic conditions. Opportunities and limitations of the pre-design guidelines are also discussed.     

A MEMS-based pneumatic micro-conveyor for planar micromanipulation

This paper present a two dimensional pneumatic actuator based on silicon MEMS technology for objects micro-manipulation using tilted air jets. The device is composed of three layers stacked together, two micro-machined silicon wafers and a Pyrex glass wafer. The system is composed of a set of micro-conveyors in about 9 mm × 9 mm area. Each micro-conveyor has four nozzles and can generate tilted air-jets which allow four conveyance directions. An experiment of the conveyance of a silicon chip of 3 mm diameter and weighing approximately 2 mg was performed with pulsed air flow.     

Development of energy-efficient passive solar building design in Nicosia Cyprus

Analyses have been done on different techniques of passive solar control using local climatic data (for 25-year period) to obtain physical building design. Our main aim is to provide general and appropriate information at strategic pre-design stages to make better use of passive solar energy in urban planning and building design for better indoor ‘comfort’ climate. It utilizes manual analysis techniques or Mahoney tables and ACHIPAK to develop ‘comfort zones’, and ‘control potential zones’, for the Capital City of Nicosia (Cyprus). The use of the control potential zones (CPZs) in pre-design of buildings and their objectives are discussed. Opportunities and limitations of the pre-design guidelines are also discussed.     

Recovering metal values hydrometallurgically from spent dry battery cells

A hydro-pyrometallurgical method was used to recover metal values from spent dry battery cells. Water-soluble ingredients were filtered, and solid residue was sorted by magnetic separation and water flotation. Parameters affecting the recovery efficiency were also studied. Results revealed that metallic parts, carbon rods, and paper were safely recovered; pure NH₄Cl, MnO₂, and ZnCl₂ salts were obtained. Maximum recovery efficiencies reached 93 percent for manganese and 99.5 percent for zinc and NH₄. For more information, contact M.A. Barakat, Central Metallurgical Research and Development Institute, Extractive Metallurgy Department, P.O. Box 87, Helwan, Cairo, Egypt; telephone 202-5010-647; fax 202-5010-639; e-mail rucmrdi@rusys.eg.net.     

Integrated solar energy systems for rural electrification in Kenya

In sub-Saharan Africa where population is projected to increase by 124% in the next 20 years, grid extension has advanced more slowly than in any other major regions; only about a third of the urban residents, and a mere 8% of the rural population, are served by grid electricity. Today, it is estimated that nearly two billion people worldwide remain without access to electricity or the immediate prospect of grid electrification. The situation in Kenya is no different. About 80% urban and 99.5% rural households, respectively, in Kenya have no access to electricity and its services. The annual electricity demand currently stands at 6% and increasing. However, we have shown that Kenya is well endowed with abundant renewable energy (RE) potential, especially solar energy resources. In our study, we have observed that Kenya gets an annual average exposure to sunshine of about 10 h per day in most regions, and an annual mean radiation of 6.98 kW h/m², which if harnessed efficiently could contribute to improve quality of life in rural and poor urban sector in Kenya.     

Arteritis and fatal subarachnoid hemorrhage complicating occult Candida meningitis: unusual presentation in pediatric acquired immunodeficiency syndrome

We report the case of an 11-month-old child with acquired immunodeficiency syndrome, who despite treatment for systemic candidiasis developed undetected Candida meningitis. This uncommon manifestation of candidiasis was accompanied by basilar granulomatous inflammation and fibrosis of meninges with arteritis, vascular invasion by fungi, and terminal subarachold hemorrhage. To our knowledge, this constellation of findings has not been reported previously in pediatric acquired immunodeficiency syndrome.     

Decoupling without prediction of linear systems with delays: A structural approach

We exhibit, using a new structural approach specific for linear systems with delays, a necessary and sufficient condition for static row-by-row decoupling without prediction. Moreover, the decoupling problem is analyzed through two different concepts: the total one (without any time assumption), and the partial one (in a temporal mean), which can be considered if the total one has no solution.     

Thiol-yne reaction on boron-doped diamond electrodes: application for the electrochemical detection of DNA-DNA hybridization events

Boron-doped diamond (BDD) interfaces were chemically functionalized through the catalyst free thiol-yne reaction. Different thiolated precursors (e.g., perfluorodecanethiol, 6-(ferrocenyl)-hexanethiol, DNA) were successfully "clicked" to alkynyl-terminated BDD by irradiating the interface at 365 nm for 30 min. Thiolated oligonucleotide strands were immobilized using the optimized reaction conditions, and the surface concentration was tuned to obtain a surface coverage of 3.1 × 10(12) molecules cm(-2). Electrochemical impedance spectroscopy (EIS) was employed to follow the kinetics of hybridization and dehybridization events. The sensitivity of the oligonucleotide modified BDD interface was assayed, and a detection limit of 1 nM was obtained.