First principles study of the ZrX2 (X = H,D and T) compounds

The Zr–H system is of particular importance for the solid state storage of hydrogen isotopes in the form of zirconium hydride. Here we report the structural, electronic, vibrational and thermodynamic properties of ZrH₂, ZrD₂ and ZrT₂ using density functional theory (DFT). The structural optimization was carried out by the plane-wave based pseudo-potential method under the generalized gradient approximation (GGA) scheme. The electronic structure of the ZrH₂ compound was illustrated explicitly. The vibrational, thermodynamic, and the effect of isotopes on ZrX₂ (X = H, D, T) compounds were evaluated by the frozen phonon method. Both the Raman and infrared active vibrational modes of ZrX₂ at Γ-point showed significant isotopic effect on ZrX₂ compounds. For example, the phonon energy gap between optical and acoustic modes reduces for ZrT₂ than ZrD₂ and ZrH₂. The formation energies of ZrX₂ compounds, including the ZPE contributions, were estimated to be −143.68, −147.87 and −150.01 kJ/(mole of compound) for X = H, D and T, respectively.     

Fines removal in a continuous plug flow crystallizer by optimal spatial temperature profiles with controlled dissolution

This work presents a systematic study for obtaining the optimal temperature profile in a continuous plug flow crystallizer (PFC). The proposed PFC consists of multiple segments where the temperature of each segment can be controlled individually. An optimization problem is formulated for a target crystal size distribution (without fines) with the temperature of the segments as decision variables. The results indicate that for the crystallization kinetics considered, dissolution steps are necessary for the reduction of fines due to nucleation. A systematic study on the form of growth and dissolution kinetics suggested that the key factor that determines whether the dissolution steps will be successful in reducing fines, without compromising the final size of the crystals from seed, is the size dependence of the growth and dissolution kinetics. Best fines removal is achieved when the larger crystals grow faster than the smaller ones and the smaller crystals dissolve faster than the larger ones. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4582–4594, 2013     

Processing of coal fines in a water-only cyclone

It is reported in the literature that a water-only cyclone (WOC), a centrifugal gravity concentrator, is an alternative to froth flotation to treat coal fines (below 0.5 mm). This unit overcomes the inherent limitations of froth flotation and the dense-medium cyclone techniques as it requires no chemicals or artificial medium. The literature dealing with WOC performance to treat coal fines is also limited and as a result it is not well established how the design variables affect the performance of a WOC while treating coal fines. Therefore, an attempt has been made to develop regression models based on factorial design of experiments to quantify the effects of major design variables of a WOC on the beneficiation characteristics of a typical coal fine sample. Further attempts have been made to provide possible explanations on the observed trends of the data based on simple hydrodynamic analyses.     

Barrier properties of electron‐beam‐modified EPDM rubber

EPDM rubber was surface‐ and bulk‐modified with varying concentrations of trimethylol propane triacrylate (TMPTA) in the presence of a constant electron‐beam irradiation dose of 100 kGy and over a wide range of irradiation doses from 0 to 200 kGy at a fixed TMPTA concentration (10%). The permeation rate and absorption of three homologous nonpolar solvents, namely, n‐hexane, n‐heptane, and n‐octane, along with an aromatic solvent, toluene, and a polar solvent, trichloroethylene, through unirradiated, unmodified control, and modified rubber membranes (≈150 μm) were studied. It was found that both the permeation rate and absorption decrease progressively with increase in the TMPTA concentration up to 10% for both the surface‐ and bulk‐modified rubbers. With increase in the radiation dose, there also is an initial drop in the values up to 50 kGy for the control and surface‐modified rubbers and up to about 100 kGy for the bulk‐modified one. The control rubber shows the highest absorption and permeation for all the solvents except trichloroethylene, followed by the bulk‐modified rubber membrane. Trichloroethylene is, however, absorbed and permeated most by the surface‐modified sample. The observations are explained in terms of the structural modifications of the rubber, crosslinking, changes in the relevant thermodynamic properties such as surface energy, the penetrant size, and the transport mechanism of the penetrants. The influence of temperature on the permeability characteristics of the control and modified rubbers was also studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 784–795, 2000     

n- to p- type carrier reversal in nanocrystalline indium doped ZnO thin film gas sensors

Selectivity has been the central issue in the research area of semiconducting metal oxide gas sensors and still remains a challenge for the researchers. In the present work, we report a promising hydrogen (reducing gas) sensing characteristics of nanocrystalline indium doped zinc oxide thin film sensing elements. At sensor operating temperature in the range (200–300) °C, ‘n’ to ‘p’ type carrier reversal is detected in the measured resistance transients. Furthermore, for a given operating temperature the type of carriers remain unaltered for each concentrations of gas. Thus, temperature plays a crucial role for this transition irrespective of the gas concentration. However, such carrier reversal is not observed in NO₂ (oxidizing gas) environment even with the variation of operating temperature and gas concentration. This is attributed to the gas sensing mechanism related to the surface conductivity and the underlying variations of the carrier type. It is argued that, it can pave the way for selective detection of hydrogen at lower operating temperatures.     

Highly efficient electroosmotic flow through functionalized carbon nanotube membranes

Carbon nanotube membranes with inner diameter ranging from 1.5-7 nm were examined for enhanced electroosmotic flow. After functionalization via electrochemical diazonium grafting and carbodiimide coupling reaction, it was found that neutral caffeine molecules can be efficiently pumped via electroosmosis. An electroosmotic velocity as high as 0.16 cm s(-1) V(-1) has been observed. Power efficiencies were 25-110 fold improved compared to related nanoporous materials, which has important applications in chemical separations and compact medical devices. Nearly ideal electroosmotic flow was seen in the case where the mobile cation diameter nearly matched the inner diameter of the single-walled carbon nanotube resulting in a condition of using one ion is to pump one neutral molecule at equivalent concentrations.     

Performance of line codes in optical direct detection continuous phase frequency shift keying transmission system impaired by polarization mode dispersion

Small deviations from perfect circular symmetry in the core region of single mode fiber (SMF) cause optical pulses to become broadened as they propagate. This phenomenon is referred to as polarization mode dispersion (PMD), which leads to intersymbol interference and becomes a major impediment for the high speed long-haul fiber-optic links. We present here the theoretical complement for evaluating the performance of a line-coded continuous phase frequency shift keying (CPFSK) optical transmission system with a direct detection receiver. The analysis is carried out for two different line-coding schemes, i.e. alternate mark inversion (AMI) and order-1 coding, to investigate the effectiveness of the line coding in counteracting the effect of PMD in a CPFSK direct detection transmission system in the presence of group velocity dispersion (GVD) and receiver noise in a single mode fiber. The average bit error rate (BER) performances are evaluated without and compared to that of line codes at a bit rate of 10 Gb s^?1 considering Maxwellian distribution for the mean differential group delay (DGD). We found that the amount of power penalty improvement of line-coded systems is within 0.65 to 2.25 dB with respect to NRZ data at a BER of 10^?9.