Discussion of the paper “Accelerated growth of calcium silicate hydrates” by Luc Nicoleau

Some of the limitations of the model recently used by Nicoleau in a recent article [Accelerated growth of calcium silicate hydrates: experiments and simulations, Cement Concr. Res. 21 (2011) 1339 -1348.] are discussed.     

Kinetics of structure II gas hydrate formation for propane and ethane using an in-situ particle size analyzer and a Raman spectrometer

The kinetics of structure II gas hydrates, formed from pure propane and a mixture of propane and ethane, were investigated and intrinsic rate constants were regressed from the experimental data. The experiments were conducted in a semi-batch stirred tank reactor equipped with an in-situ particle size analyzer and connected to an external Raman spectrometer. Experiments were conducted with pure propane at temperatures ranging from 274 to 276 K and pressures ranging from 0.39 to 0.43 MPa. The intrinsic rate constant for ethane in structure II was subsequently regressed from experimental data on the formation of hydrates formed from an equimolar mixture of propane and ethane at 274 K and 0.35 MPa. Raman spectroscopy was used to verify that ethane was present only in the large sII cavity.     

Tunable infrared plasmonic devices using graphene/insulator stacks

The collective oscillation of carriers--the plasmon--in graphene has many desirable properties, including tunability and low loss. However, in single-layer graphene, the dependence on carrier concentration of both the plasmonic resonance frequency and magnitude is relatively weak, limiting its applications in photonics. Here, we demonstrate transparent photonic devices based on graphene/insulator stacks, which are formed by depositing alternating wafer-scale graphene sheets and thin insulating layers, then patterning them together into photonic-crystal-like structures. We show experimentally that the plasmon in such stacks is unambiguously non-classical. Compared with doping in single-layer graphene, distributing carriers into multiple graphene layers effectively enhances the plasmonic resonance frequency and magnitude, which is different from the effect in a conventional semiconductor superlattice and is a direct consequence of the unique carrier density scaling law of the plasmonic resonance of Dirac fermions. Using patterned graphene/insulator stacks, we demonstrate widely tunable far-infrared notch filters with 8.2 dB rejection ratios and terahertz linear polarizers with 9.5 dB extinction ratios. An unpatterned stack consisting of five graphene layers shields 97.5% of electromagnetic radiation at frequencies below 1.2 THz. This work could lead to the development of transparent mid- and far-infrared photonic devices such as detectors, modulators and three-dimensional metamaterial systems.     

Metal ions modulate the plastic nature of Mycobacterium tuberculosis chaperonin-10

Chaperonin-10s possess a highly flexible segment of ~10 residuesthat covers their dome-like structure and closes the centralcavity of the chaperonin assembly. The dome loop is believedto contribute to the plasticity of their oligomeric structure.We have exploited the presence of a single tryptophan residueoccurring in the dome loop of Mycobacterium tuberculosis chaperonin-10(cpn-10), and through intrinsic fluorescence measurements showthat in the absence of metal ions, the tryptophan is almostfully solvent exposed at neutral pH. The dome loop, however,assumes a closed conformation in the presence of metal ions,or at low pH. These changes are fully reversed in the presenceof chelating agents such as EDTA, confirming the role of cationsin modulating the metastable states of cpn-10.     

120 keV Ar ion-induced red and blue shift of SPR Wavelength of Au nanoparticles in fullerene C60

Journal of Materials Science: Materials in Electronics - Au nanoparticles are synthesized in a fullerene C60 matrix using the thermal co-evaporation technique. Fullerene C60 is chosen due to its...     

Rigorous design of high pressure natural gas pipelines using bwr equation of state

A model is presented for the prediction of pressure and temperature profiles in a high pressure gas pipeline. Using the BWR equation of state to predict the properties of the gas, an analytical approach reduces the problem to two nonlinear equations which can be solved numerically. Rigorous thermodynamic treatment of the energy and flow equations results in a model which yields good agreement with published data for high pressure natural gas pipelines. The model is also shown to predict frictional heating during the adiabatic flow of dense phase hydrocarbons.     

Experimental heat capacities of carbon dioxide-methane mixtures at elevated pressures

The heat exchanger method of determining the ratio of heat capacity at a pressure to the heat capacity at a low pressure was used to obtain data on two binary mixtures of methane and carbon dioxide containing 14.49 and 42.30 mole % methane. The data were obtained at pressures up to 2,250 psi in the temperature range of ambient to 150°C and are expected to be accurate within ± 0.5 % in the regions removed from the pressure maxima and within ± 1 % in regions close to the maxima. Heat capacities of the two binary mixtures were calculated using the BWR equation of state, the generalized correlations of Curl and Pitzer and Yen and Alexander, and the method of Orentlicher and Prausnitz. The calculated values were compared with the experimental values.     

Metal recovery from coal ash via chlorination — A thermodynamic study

Coal ash can become an important mineral substitute for the recovery of several metals, especially aluminum and titanium. A plausible route for the recovery could be via high temperature chlorination in the presence of a reducing agent. The thermodynamics of the reaction system for the free energy computations consisted of 135 chemical species containing 12 elements, namely Al, C, Ca, CI, Fe, K, Mg, Na, O, S, Si and Ti. The results indicate that the chlorination route is feasible over a wide temperature range.     

SERS biodetection using gold-silica nanoshells and nitrocellulose membranes

We have developed a rapid, reproducible, easy to execute, surface enhanced Raman scattering (SERS) method for detection of low volumes and total amounts of biological antigens using an analyte capture system derived from methods commonly used in Western blotting. Our method is a "half-sandwich" assay with an antigen detection scheme that employs a nitrocellulose (NC) membrane with 200 nm pore size to capture subnanograms of analyte and concentrate them in a small area from applied volumes as low as one microliter. The SERS probes used for detection consist of gold-silica nanoshells modified with a two-component mixed monolayer system. One component consists of a poly(ethylene glycol) (PEG)-modified Raman-active chromophore bound to the gold surface which allows for SERS detection and imparts particle stability. The second component uses (ortho-pyridyl) disulfide-PEG-succinimidyl ester to couple the recognition antibody to the particle surface. By controlling the reaction time and concentration of thiols, a mixed monolayer is prepared on the nanoshell surface with the ability to recognize low concentrations of analyte and generate reproducible SERS signals. Using this strategy, we have achieved SERS signals that are proportional to antigen present on the membrane allowing detection of total antigen amounts as low as 1.25 ng for some cases. The performance of this new SERS bioassay has been tested with a variety of potential antigens, demonstrating the potential for multiplexed detection of analytes.     

A novel multi-walled carbon nanotube modified sensor for the selective determination of epinephrine in smokers

Epinephrine (EP), an important neurotransmitter, energizes and speeds up the various body systems and plays an important role during the time of stress and low blood sugar level. There is a close relation between the release of epinephrine and smoking. Edge plane pyrolytic graphite electrode modified with multi-walled carbon nanotubes (MWNTs/EPPGE) has been used as a sensor for the efficient quantitative determination of epinephrine in body fluids of smokers and nonsmokers in resting stage at physiological pH 7.2 by using cyclic voltammetry (CV) and square wave voltammetry (SWV). The oxidation of epinephrine occurred in a well-defined peak having peak potential (E_p) ∼150 mV at pH 7.2. The limit of detection (3σ/slope) and limit of quantification were found to be 0.15 × 10⁻⁹ and 0.48 × 10⁻⁹ M using proposed sensor, respectively. The modified electrode was also utilized for the analysis of commercial sample of epinephrine in order to examine the accuracy of the proposed method. The analytical performance of the modified electrode has been evaluated for quantification of EP in real samples even in the presence of common coexisting biomolecules such as uric acid, ascorbic acid, dopamine and norepinephrine. The voltammetric response of the developed nanosensor towards epinephrine determination in body fluids is fast, sensitive and selective having desirable reproducibility and stability. A comparison of results with high performance liquid chromatography (HPLC) shows a good agreement.