Electrical properties study of multi-walled carbon nanotubes/hybrid-glass nanocomposites

Electrical properties of multi-walled carbon nanotubes (MWNTs)/hybrid-glass nanocomposites prepared by the fast-sol–gel reaction were investigated in light of percolation theory. A good correlation was found between the experimental results and the theory. We obtained a percolation threshold ? _c  = 0.22 wt%, and a critical exponent of t = 1.73. These values are reported for the first time for a silica-based system. The highest conductivity measured on the MWNT/hybrid-glass nanocomposites was σ ≈ 10^?3(Ω cm)^?1 for 2 wt% carbon nanotube (CNT) loading. The electrical conductivity was at least 12 orders of magnitude higher than that of pure silica. Electrostatic force microscopy and conductive-mode atomic force microscopy studies demonstrated conductivity at the micro-level, which was attributed to the CNT dispersed in the matrix. It appears that the dispersion in our MWNT/hybrid-glass system yields a particularly low percolation threshold compared with that of a MWNT/silica-glass system. Materials with electrical conductivities described in this work can be exploited for anti-static coating.     

\hbox {FeF}_{3} catalyzed cascade C–C and C–N bond formation: synthesis of differentially substituted triheterocyclic benzothiazole functionalities under solvent-free condition

A series of diverse polyfunctionalized triheterocyclic benzothiazoles were easily prepared in excellent yields via the Biginelli reaction of 2-aminobenzothiazole with substituted benzaldehydes and $\upalpha $ -methylene ketones using $\hbox {FeF}_{3}$ as an expeditious catalyst under solvent-free conditions. The protocol provides a practical and straightforward approach toward highly functionalized triheterocyclic benzothiazole derivatives in excellent yields. The reaction was conveniently promoted by $\hbox {FeF}_{3}$ and the catalyst could be recovered easily after the reaction and reused without any loss of its catalytic activity. The advantageous features of this methodology are high atom economy, operational simplicity, shorter reaction time, convergence, and facile automation.     

Visible-light triggered photochemical reaction for the synthesis of dumbbell-like bis aminomethyl-1, 2 dihydrofullerene dimers via addition of α-amino radicals

Research on Chemical Intermediates - Single electron transfer-mediated photochemical reaction of C60 fullerene with simple bis-α-silyl tertiary alkyl/benzyl amines has been developed for the...     

Optimizing buffer size for the retrial queue: two state space collapse results in heavy traffic

We study a single server queueing model with admission control and retrials. In the heavy traffic limit, the main queue and retrial queue lengths jointly converge to a degenerate two-dimensional diffusion process. When this model is considered with holding and rejection costs, formal limits lead to a free boundary curve that determines a threshold on the main queue length as a function of the retrial queue length, above which arrivals must be rejected. However, it is known to be a notoriously difficult problem to characterize this curve. We aim instead at optimizing the threshold on the main queue length independently of the retrial queue length. Our main result shows that in the small and large retrial rate limits, this problem is governed by the Harrison–Taksar free boundary problem, which is a Bellman equation in which the free boundary consists of a single point. We derive the asymptotically optimal buffer size in these two extreme cases, as the scaling parameter and the retrial rate approach their limits.     

Efficient Direct‐Methanol Fuel Cell Based on Graphene Quantum Dots/Multi‐walled Carbon Nanotubes Composite

Direct‐methanol fuel cells are proton‐exchange fuel cell in which methanol is used as the fuel. The important advantage of these fuel cells is the simplicity of transport and storage of methanol. In this study, methanol fuel cell electrocatalysts including graphene quantum dots (GQDs), functionalized multi‐walled carbon nanotubes (f‐MWCNTs) and GQDs/f‐MWCNTs composite were synthesized. The structures of synthesized electrocatalysts were highlighted by scanning electron microscope (SEM), raman spectroscopy, UV–vis spectroscopy, fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and x‐ray diffraction (XRD) method. After that, the effective surface areas (ESA) of GQDs, f‐MWCNTs and GQDs/f‐MWCNTs were calculated. Finally, GQDs/f‐MWCNTs composite modified glassy carbon electrode (GQDs/f‐MWCNTs/GCE) showed highest current signals for methanol oxidation than those of comparable GQDs/GCE and f‐MWCNTs/GCE.     

Exponential stability for nonlinear filtering

We study the a.s. exponential stability of the optimal filter w.r.t. its initial conditions. A bound is provided on the exponential rate (equivalently, on the memory length of the filter) for a general setting both in discrete and in continuous time, in terms of Birkhoff's contraction coefficient. Criteria for exponential stability and explicit bounds on the rate are given in the specific cases of a diffusion process on a compact manifold, and discrete time Markov chains on both continuous and discrete-countable state spaces. A similar question regarding the optimal smoother is investigated and a stability criterion is provided.     

Fabrication of bimetallic Pt/Pd nanoparticles on 2-thiolbenzimidazole functionalized reduced graphene oxide for methanol oxidation

In this study, an electrocatalyst based on 2-thiolbenzimidazole (TBI) functionalized reduced graphene oxide (rGO) with platinum and palladium nanoparticles (Pt-PdNPs) was synthesized. The successful synthesis of nanomaterials and the prepared glassy carbon electrode (GCE) surfaces were confirmed by transmission electron microscope, X-ray photo electron spectroscopy, scanning electron microscope, electrochemical impedance spectroscopy and X-ray diffraction method. The effective surface areas of TBIrGO/GCE, PdNPs/TBIrGO/GCE, PtNPs/TBIrGO/GCE and Pt-PdNPs/TBIrGO/GCE were calculated to be 324, 578, 667 and 1189 cm²/mg, respectively. According to the results, the electrochemical surface area of the Pt-PdNPs/TBIrGO is 3.67, 2.06 and 1.78 times higher than those of TBIrGO, PdNPs/TBIrGO and PtNPs/TBIrGO, respectively. The Pt-PdNPs/TBIrGO/GCE also exhibited higher peak current for methanol oxidation than those of comparable TBIrGO/GCE, PdNPs/TBIrGO/GCE, PtNPs/TBIrGO/GCE modified GCEs, thus providing evidence for its higher electro-catalytic activity.