A novel non-enzymatic hydrogen peroxide sensor based on single walled carbon nanotubes–manganese complex modified glassy carbon electrode

A simple procedure was developed to prepare a glassy carbon (GC) electrode modified with single wall carbon nanotubes (SWCNTs) and phenazine derivative of Mn-complex. With immersing the GC/CNTs modified electrode into Mn-complex solution for a short period of time 20–100 s, a stable thin layer of the complex was immobilized onto electrode surface. Modified electrode showed a well defined redox couples at wide pH range (1–12). The surface coverages and heterogeneous electron transfer rate constants (k_s) of immobilized Mn-complex were approximately 1.58 × 10⁻¹⁰ mole cm⁻² and 48.84 s⁻¹. The modified electrode showed excellent electrocatalytic activity toward H₂O₂ reduction. Detection limit, sensitivity, linear concentration range and k_cat for H₂O₂ were, 0.2 μM and 692 nA μM⁻¹ cm⁻², 1 μM to 1.5 mM and 7.96(±0.2) × 10³ M⁻¹ s⁻¹, respectively. Compared to other modified electrodes, this electrode has many advantageous such as remarkable catalytic activity, good reproducibility, simple preparation procedure and long term stability.     

Self-assembled micelles of well-defined pentaerythritol-centered amphiphilic A4B8 star-block copolymers based on PCL and PEG for hydrophobic drug delivery

Biodegradable star-shaped poly(?-caprolactone) (PCL) with four arms were synthesized by ring-opening polymerization (ROP) from a symmetric pentaerythritol core via the ‘‘core-first’’ strategy. Subsequently, two samples of the amphiphilic A₄B₈ star-block copolymers with symmetrical topologies [4s(PCL-b-2sPEG)] were synthesized by a macromolecular coupling reaction between carboxyl-terminated poly(ethylene glycol) (PEG) and 4-arm star-shaped PCL macromers with eight -OH end groups. The latter was prepared by attaching 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoic acid (HHMPA) to 4sPCL using a simple two-step reaction sequence. The in vitro cytotoxicity test indicated no apparent cytotoxicity. The amphiphilic star-block copolymers are capable of self-assembling into spherical micelles in water at room temperature, and they possess low critical micelle concentrations (CMCs) of 2∼8 mg/L in aqueous solution which was determined by fluorescence spectroscopy using pyrene as a probe. Transmission electron microscopy (TEM) measurement demonstrated that the micelles exhibit a spherical shape with a size range of 30∼50 nm in diameter. In addition, the hydrophobic and anticancer drug, quercetin, is loaded effectively in the polymeric micelles, suggesting that these new materials are appropriate candidates as hydrophobic drug nanocarriers.     

Facile synthesis of monodisperse thermally immiscible Ag-Ni alloy nanoparticles at room temperature

Ag and Ni are immiscible, mainly due to their large lattice mismatch. This paper reports on their nanoscale formation of solid solution at room temperature by simple reduction reactions which lead to the amorphous Ag-Ni alloy nanoparticles (ANPs) with mono-disperse distribution. Microscopic and spectroscopic studies confirmed dependence of the alloy composition on size of nanoparticles. In the presence of different ligands such as sodium citrate, polyvinyl alcohol and potassium carbonate a mixture of silver oxide and Ag-Ni ANPs was achieved. Stoichiometry of the Ag-Ni ANPs was also found to be strongly dependent on ligands of the reduction reaction and further study shows without any ligand 100% Ag-Ni ANPs was observed in the system. Using Tetrakis hydroxymethyl phosphonium chloride resulted in construction of near-uniform ANPs in the easily controllable conditions of the present alloying procedure. Nanoparticles having up to 65% Ni were observed for the first time in this research.     

A single-chip dual-band tri-mode CMOS transceiver for IEEE 802.11a/b/g wireless LAN

A single-chip dual-band tri-mode CMOS transceiver that implements the RF and analog front-end for an IEEE 802.11a/b/g wireless LAN is described. The chip is implemented in a 0.25-/spl mu/m CMOS technology and occupies a total silicon area of 23 mm/sup 2/. The IC transmits 9 dBm/8 dBm error vector magnitude (EVM)-compliant output power for a 64-QAM OFDM signal. The overall receiver noise figure is 5.5/4.5 dB at 5 GHz/2.4 GHz. The phase noise is -105 dBc/Hz at a 10-kHz offset and the spurs are below -64 dBc when measured at the 5-GHz transmitter output.     

Seismic performance of stiffness-based designed buckling-restrained braced frame and special moment-resisting frame dual systems

Conventional procedure for designing dual systems, proposed in seismic regulations, encompasses some limitations such as not putting a required minimum stiffness value for the secondary system. This research investigates the stiffness limit value required for the secondary system for designing buckling-restrained braced frame (BRBF) and special moment-resisting frame (SMRF) dual systems. Non-linear static and time history analyses were carried out on the sample dual structures with different heights and different relative stiffness ratios of the primary system to the secondary system. A stiffness-based designing approach is employed to ensure that the designed system comprises the predefined relative stiffness ratios. It is demonstrated that the suitable stiffness combination ratio is gained when the BRBF and SMRF subsystems have 65% and 35% of the total stiffness, respectively. Implementation of the suitable relative stiffness ratio in the dual systems designed according to the presented approach, leads to a uniform plasticity profile in the height of structures.     

Hydrogen generation from hydrolysis of sodium borohydride by cubic Co–La–Zr–B nano particles as novel catalyst

Cubic Co–La–Zr–B nano particles were prepared in situ for the first time from the reduction of Co(II), La(III) and Zr(IV) chloride by sodium borohydride in methanol under reflux condition. Poly N-vinyl-2-pyrrolidone (PVP) as stabilizing agent was used for preparation of Co–La–Zr–B nano particles. Obtained powders were characterized by XRD, BET, ICP, SEM, TEM and UV–vis techniques. XRD patterns declare that under argon atmosphere only metalboride phase has been crystallized and it was not seen any oxide phase of metals. TEM image depicts that PVP stabilized nano particles are square shaped particles that containing many nanoclusters. Cubic Co–La–Zr–B nano particles were also confirmed by SEM image. Co–La–Zr–B is highly active catalysts for hydrogen generation from the hydrolysis of sodium borohydride. The reported work also includes the full experimental details for the collection of a wealth of kinetic data to determine the activation energy (E_a = 53 kJ mol⁻¹) and effects of the catalyst dosage, amount of NaBH₄, and temperature on the rate of the catalytic hydrolysis of sodium borohydride. Catalytic hydrolysis of NaBH₄ is first order with respect to the catalyst concentration and also first order to the NaBH₄ concentration in the case of cubic Co–La–Zr–B nano particles.     

Analysis of ultrasonic assisted machining (UAM) on regenerative chatter in turning

Ultrasonic assisted machining (UAM) is an advanced technology for improving the machining process, especially for hard materials. This paper presents an experimental and theoretical study toward the effect of UAM on chatter. Theoretical explanation of the effect of UAM on chatter is not fully presented in the available literature yet. In this paper, considering fixed tool geometry, theoretical dynamic equations for UAM are represented. The approach is demonstrated by deriving dynamic formulation of UAM in turning, considering both turning equation and Merchants ultrasonic machining equations. A time domain analysis is fulfilled on each machining condition to verify whether it has a stable vibration or an unstable chatter vibration. Subsequently, an experimental setup is designed and manufactured to investigate UAM effect on regenerative chatter. Special conical shape for workpiece is designed to experimentally generate different points of stability lobe. The generated oscillation by a piezoelectric actuator is transferred, amplified, and concentrated on the tip of the tool by appropriate design of a cutting tool, which is vibrated in its bending mode. The obtained results are encouraging, and indicating good agreement between experimental and theoretical results.     

Development and characterization of a new nickel(II) ion selective optode based on 2-amino-1-cyclopentene-dithiocarboxylic acid

A highly sensitive and selective optical membrane sensor was prepared for the determination of ultra trace amount of Ni²⁺ ions. The plasticized PVC membrane incorporating dibuthylphthalate and 2-amino-1-cyclopentene-dithiocarboxylic acid (ACDA) as a chromoionophore works on the basis of a cation-exchange mechanism and shows a significant absorbance signal change on exposure to acidic solution containing nickel(II) ion. The sensor displays a calibration response for Ni²⁺ ion over a wide concentration range of 3.1 × 10⁻⁸-8.0 × 10⁻³ M, and a response time of 3 min. In addition to high stability, reproducibility and relatively long working lifetime, the sensor possesses good selectivity for nickel(II) ion over several common diverse ions. The sensor was successfully applied to determine the traces of Ni²⁺ ion in some water samples.     

Microstructure and Corrosion Properties of CP-Ti Processed by Laser Powder Bed Fusion under Similar Energy Densities

In this work, two types of CP Ti cubes with similar volumetric energy densities (VED) but different process parameters were produced using laser powder bed fusion (LPBF) method. The corrosion behavior of the fabricated specimens was investigated by conducting electrochemical impedance spectroscopy (EIS) and polarization experiments in simulated body fluid (SBF) solution at 37 °C. The results indicated that the microstructure and porosities, which are of great importance for biomedical applications, can be controlled by changing the process parameters even under constant energy densities. The sample produced with a lower laser power (E1) was featured with a higher level of porosity and thinner alpha laths, as compared with the sample fabricated with a higher laser power (E2). Moreover, results obtained from the bioactivity tests revealed that the sample produced with a higher laser power conferred a slight improvement in the bioactivity due to the higher amount of porosity. Lower laser power and hence higher porosity level promoted the formation of bone-like apatite on the surface of the printed specimens. The potentiodynamic polarization tests revealed inferior corrosion resistance for the fabricated sample with higher porosity. Moreover, the EIS results after different immersion times indicated that a stable oxide film was formed on the surface of samples for all immersion times. After 1 and 3 days of immersion, superior passivation behavior was observed for the sample fabricated with lower laser power. However, very similar impedance and phase values were observed for all the samples after 14 days of immersion.     

Cross‐level fragility analysis of modularized suspended buildings based on experimentally validated numerical models

Suspended buildings typically have a core as the primary and suspended floors as the secondary structures. These configurations offer visual transparency, smaller vertical components, and seismic attenuation via the primary–secondary structure interaction. Such attenuation is further enhanced by the modularization of the suspended segment which allows large drifts but prevents them from causing damage. Previously conducted shake‐table tests have confirmed these features. However, how the component performance contributes to system performance has not been quantitated. To address this gap, fragility analyses are conducted for 10‐story experimentally validated models with optimized supplemental dampers and inter‐module stiffness. Multiple limit state functions are proposed to provide a full account of damage sources. Additionally, a mapping rule from the component‐level to the system‐level limit states is developed which captures the influence of damage distribution on system‐level limit states. Results for the uncontrolled suspended building indicate that for the PGV of 0.5 m/s, the failure probabilities of the repairable and life safety limit states are 97% and 83%, respectively. These probabilities are 92% and 27% for the frame structure with viscous dampers, 58% and 5% for the passive‐controlled modularized suspended building system (MSBS), and 45% and 3% for MSBS with optimal vertical distributions of modularized secondary structure.