Nickel–Cobalt Diselenide 3D Mesoporous Nanosheet Networks Supported on Ni Foam: An All‐pH Highly Efficient Integrated Electrocatalyst for Hydrogen Evolution

Novel 3D Ni_1?x Co_x Se₂ mesoporous nanosheet networks with tunable stoichiometry are successfully synthesized on Ni foam (Ni_1?x Co_x Se₂ MNSN/NF with x ranging from 0 to 0.35). The collective effects of special morphological design and electronic structure engineering enable the integrated electrocatalyst to have very high activity for hydrogen evolution reaction (HER) and excellent stability in a wide pH range. Ni_0.89Co_0.11Se₂ MNSN/NF is revealed to exhibit an overpotential (η₁₀) of 85 mV at ?10 mA cm^?2 in alkaline medium (pH 14) and η₁₀ of 52 mV in acidic solution (pH 0), which are the best among all selenide‐based electrocatalysts reported thus far. In particular, it is shown for the first time that the catalyst can work efficiently in neutral solution (pH 7) with a record η₁₀ of 82 mV for all noble metal‐free electrocatalysts ever reported. Based on theoretical calculations, it is further verified that the advanced all‐pH HER activity of Ni_0.89Co_0.11Se₂ is originated from the enhanced adsorption of both H⁺ and H₂O induced by the substitutional doping of cobalt at an optimal level. It is believed that the present work provides a valuable route for the design and synthesis of inexpensive and efficient all‐pH HER electrocatalysts.     

Optimal PID-type fuzzy logic controller for a multi-input multi-output active magnetic bearing system

The performance of the fuzzy controllers depends highly on the proper selection of some design parameters which is usually tuned iteratively via a trial and error process based primarily on engineering intuition. With the recent developments in the area of global optimization, it has been made possible to obtain the optimal values of the design parameters systematically. Nevertheless, it is well known that unless a priori knowledge is available about the optimization search-domain, most of the available time-domain objective functions may result in undesirable solutions. It is consequently important to provide guidelines on how these parameters affect the closed-loop behavior. As a result, some alternative objective functions are presented for the time-domain optimization of the fuzzy controllers, and the design parameters of a PID-type fuzzy controller are tuned by using the proposed time-domain objective functions. Finally, the real-time application of the optimal PID-type fuzzy controller is investigated on the robust stabilization of a laboratory active magnetic bearing system. The experimental results show that the designed PID-type fuzzy controllers provide much superior performances than the linear on-board controllers while retaining lower profiles of control signals.     

A new approach to adaptive robust control

A new approach is given for the design of adaptive robust control in the frequency domain. Starting with an initial model of a stable plant and a robust stabilizing controller, the new (windsurfer) approach allows the bandwidth of the closed-loop system to be increased progressively through an iterative control-relevant system identification and control design procedure. The method deals with both undermodelling and measurement noise issues. Encouraging results are obtained in the simulations that illustrate the new idea.     

DNS performance and the effectiveness of caching

This paper presents a detailed analysis of traces of domain name system (DNS) and associated TCP traffic collected on the Internet links of the MIT Laboratory for Computer Science and the Korea Advanced Institute of Science and Technology (KAIST). The first part of the analysis details how clients at these institutions interact with the wide-area domain name system, focusing on client-perceived performance and the prevalence of failures and errors. The second part evaluates the effectiveness of DNS caching. In the most recent MIT trace, 23% of lookups receive no answer; these lookups account for more than half of all traced DNS packets since query packets are retransmitted overly persistently. About 13% of all lookups result in an answer that indicates an error condition. Many of these errors appear to be caused by missing inverse (IP-to-name) mappings or NS records that point to nonexistent or inappropriate hosts. 27% of the queries sent to the root name servers result in such errors. The paper also presents the results of trace-driven simulations that explore the effect of varying time-to-live (TTL) and varying degrees of cache sharing on DNS cache hit rates. Due to the heavy-tailed nature of name accesses, reducing the TTL of address (A) records to as low as a few hundred seconds has little adverse effect on hit rates, and little benefit is obtained from sharing a forwarding DNS cache among more than 10 or 20 clients. These results suggest that client latency is not as dependent on aggressive caching as is commonly believed, and that the widespread use of dynamic low-TTL A-record bindings should not greatly increase DNS related wide-area network traffic.     

Polyurethane wood adhesive from palm oil-based polyester polyol

Polyurethane (PU) adhesives for wood bonding were prepared from palm oil-based polyester polyol in a solventless condition that reduces the risk of volatile organic compounds to human health and the environment. The polyester polyol was synthesized from epoxidized palm olein prior to reacting with polymeric 4,4′-methylene diphenyl diisocyanate (pMDI) and toluene 2,4-diisocyanate (TDI) to produce wood-bonding PU adhesives. The effect of glycerol cross-linker, dibutyltin dilaurate catalyst and NCO/OH ratio on lap shear strength and pot life of the PU adhesives were studied. The green strength of the PU adhesives was achieved on day 4 for TDI-based adhesives and day 5 for pMDI-based adhesives. The newly formulated PU adhesives have superior chemical resistance in cold water, hot water, acidic medium and alkaline medium by only showing light deterioration (2–8%) in lap shear strength. The PU adhesives prepared from pMDI exhibited higher lap shear strength and thermal stability as compared to adhesives prepared from TDI adduct. Both adhesives have improved mechanical performance (two folds higher in lap shear strength) as compared to commercial wood bonding adhesives.     

Effect of bubble interaction on interphase mass transfer in gas fluidized beds

A non-interfering technique has been used to measure the concentration of ozone in pairs of bubbles injected into a bed of inactive 390 μm glass beads fluidized by ozone-free air. The transfer of the ozone tracer from the bubble phase to the dense phase is enhanced when compared to the transfer from isolated bubbles in the same particles and the same column. Bubble growth is also greater for the case where pairs of bubbles are introduced than when bubbles are present in isolation. Enhancement of interphase mass transfer for interacting bubbles in the present work and in previous studies incr with particle size and can be explained in terms of enhancement of the throughflow (or convective) component of transfer while the diffusive component unaltered. This mechanism leads to new equations for estimating interphase mass transfer in freely bubbling fluidized beds.