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An effusive eruption at Sinabung Volcano in Indonesia began in December 2013. We use structure-from-motion (SfM) photogrammetric techniques to create digital elevation models (DEMs) of the active lava flow. We build DEMs from photographs taken during two separate time periods and from two separate low-cost handheld cameras and compare them with a pre-eruption DEM to assess the quality and accuracy of photogrammetric DEMs created using different cameras, calculate flow volume and long-term average effusion rate, and document changes in flow morphology. On September 22nd, 2014, the lava flow was 2.9 km long and had a volume of 1.03 ± 0.14 × 108 m3, leading to an estimated time-averaged discharge rate of 4.8 ± 0.6 m3 s−1. Differencing the photogrammetric DEMs shows that during the two-week field campaign, topographic changes of the flow occurred in zones along the flow front and on the upper flank, a finding supported by relatively high temperatures in corresponding thermal images. The deformation can be explained by active advance at the flow front and development of instabilities and collapse on the upper flanks. Large pyroclastic density currents associated with gravitational collapse of upper-flank instabilities in October 2014 and June 2015 were caused by lava growing over ridges that had initially confined the flow to a pre-existing channel. This work demonstrates the ability of SfM photogrammetry to measure or identify the lava flow volume, time-averaged discharge rate, flow emplacement rate and style, as well as the development of gravitational instabilities. Our results show the potential of SfM photogrammetry as a cost- and time-effective method of repeatedly measuring active volcanic features and monitoring hazards at Sinabung and during similar eruptions.

Photonic crystal fibers consisting of a novel hybrid structure providing low values for both dispersion and confinement loss were simulated using finite element method. The studies on different arrangements, polygonal and circular, of air holes as cladding of PCFs have shown that circular PCFs results in a structure with low dispersion, air filling fractions remaining same. Circular PCF with dispersion 103.50 ps/nm.km and confinement loss 5.97 × 10−6 dB/m was restructured by replacing its first ring with octagonal air hole lattice having eight air holes. This hybrid circular-octagon PCF has shown a dispersion of 33.15 ps/nm.km and a confinement loss of 2.52 × 10−6 dB/m. The introduction of air hole defects in the hybrid fiber core with three identical air holes in an equilateral triangular lattice was found to modify dispersion by reducing its value to −11.63 ps/nm.km with confinement loss 9.51 × 10−5 dB/m.

Nanostructured photocatalysts have always offered opportunities to solve issues concerned with the environmental challenges caused by rapid urbanization and industrialization. These materials, due to their tunable physicochemical characteristics, are capable of providing a clean and sustainable ecosystem to humanity. One of the current thriving research focuses of visible-light-driven photocatalysts is on the nanocomposites of titanium dioxide (TiO2) with carbon nanostructures, especially graphene. Coupling TiO2 with graphene has proven more active by photocatalysis than TiO2 alone. It is generally considered that graphene sheets act as an electron acceptor facilitating the transfer and separation of photogenerated electrons during TiO2 excitation, thereby reducing electron-hole recombination. This study briefly reviews the fundamental mechanism and interfacial charge-transfer dynamics in TiO2/graphene nanocomposites. Design strategies of various graphene-based hybrids are highlighted along with some specialized synthetic routes adopted to attain preferred properties. Importantly, the enhancing interfacial charge transfer of photogenerated e¯CB through the graphene layers by morphology orientation of TiO2, predominated exposure of their high energy crystal facets, defect engineering, enhancing catalytic sites in graphene, constructing dedicated architectures, tuning the nanomaterial dimensionality at the interface, and employing the synergism adopted through various modifications, are systematically compiled. Portraying the significance of these photocatalytic hybrids in environmental remediation, important applications including air and water purification, self-cleaning surfaces, H2 production, and CO2 reduction to desired fuels, are addressed.

In this paper, we engineered a Circular PCF having a very low confinement loss and high nonlinear coefficient, from five Circular PCFs of same ring separation value. From the analysis, it is derived that the zero dispersion wavelengths can be shifted by increasing the d/R ratio. Analysis of light propagation fiber characteristics such as confinement loss, effective mode area, non linear coefficient, numerical aperture and chromatic dispersion of silica core circular photonic crystal fibers have been investigated by full vector finite element method. Simulation results show that, the magnitude of confinement loss can be reduced to a value of 5.5012 × 10−6 dB/km at the operating wavelength 1550 nm for the structure with d/R = 0.8 and the corresponding effective mode area is 3.78046 μm2 and nonlinear coefficient is 0.03313 km−1W−1. C-PCFs with small air hole diameter show flat chromatic dispersion response over the wavelength region 1400 nm to 1800 nm. In addition to tight light confinement and Gaussian output over the entire operating wavelengths, we have simulated the Supercontinuum generation in the d/R = 0.8 fiber for different coupled power.

A novel use of carbon nanotube networks (CNT) as a semi-transparent layer for better charge collector in GaAs solar cells in order to improve the overall cell performance is presented. The different photovoltaic behaviors have been investigated considering substrate thickness, cell width, dependence between CNT work function and transmittance. CNT layer thickness is found to be optimized at 100 nm for AM1.5G. The sheet resistivity is evaluated at 128 Ω/□. The performance parameters of a cell with and without the CNT network are compared. The CNT networks allow for a greater area of charge collection on the surface of solar cells as well as serve as a lower resistance path for charge carriers with minimum voltage loss to travel to the top contact. This model thus significantly improves the power conversion efficiency from 26.04% to 29.18% under AM1.5G. The addition of a CNT layer was shown to minimize the voltage drop and maintain high maximum power levels at 34.4 mW/cm 2 for cells with larger width. EQE of the cell is well above 90%. The model has been validated with various reported experimental works. CNT layers with lower sheet resistance and better light transmission can therefore greatly improve the efficiency of solar cells.

The presence of toxic contaminants like dyestuff in water causes an environmental threat and pores challenge to discrete it out from the water. Nowadays, to overcome challenges of conventional processes as well as to remove these contaminants mesoporous materials are used for degradation. In this work, porous rock like CeO2/SiO2 monolith was synthesized via sol-gel method and analyzed by FTIR, SEM with EDAX, TGA as well as BET isotherm. The efficiency of CeO2/SiO2 monolith was investigated towards the removal of Congo Red (CR) and Reactive Orange (RO 84) using sunlight with different parameters. The maximum degradation of dyes was achieved at 70 and 50 min with a removal percentage of 90 and 80% respectively. Langmuir-Hinshelwood kinetic model well describes the photodegradation capacity. The photocatalytic degradation of dyes CR and RO 84 exhibited pseudo-first-order kinetics. The time of flight mass spectrometer identified degraded products. The findings from this study suggest that CeO2/SiO2 monolith is a promising material for water treatment with excellent reusability and can be employed as an alternative photocatalyst for dye degradation.

A unique design of a pure silica hybrid photonic crystal fiber consisting of three circular rings and one octagonal ring lattices of air holes bounding silica core has been simulated for the generation of wide super continuum spectrum extending from ultraviolet to near infrared. Further modifications of the fiber core with elliptical air hole, manipulated the dispersion profile of the fundamental mode and it generated two zero dispersion wavelengths. The insertion of air hole enhanced the value of nonlinear coefficient, typically from 75 W−1km−1to 466 W−1km−1 (at 1550 nm) for an optimum PCF with ellipticity 0.93, keeping the single mode guidance. Numerical aperture of the fibers was found to increase substantially from 0.56 to 0.86 correspondingly to the ellipticity 0.72 to 0.93 at 1550 nm. Pumping with femtosecond pulses in the anomalous dispersion regime made the spectrum broad. At 1000 W pump, a bandwidth of ≈1472 nm (491 to 1963 nm) was obtained for a fiber of 1 m length with pulse duration of 200 fs. The characteristics of the proposed fiber indicate that it can find numerous applications in a variety of fields, especially in ophthalmology, dentistry and imaging using optical coherence tomography.

The mode properties of solid-core photonic crystal fibers (PCFs) having square, pentagonal, hexagonal, octagonal, nonagonal, decagonal, and dodecagonal lattice formats with uniform air-filling fractions (AFFs) have been evaluated by a full-vector finite-element method using the software COMSOL Multiphysics 4.3. Irrespective of the hole-to-hole spacing for a particular type of lattice, the ratio of air-hole radii of two PCFs having different AFFs is a constant. The ratio of air-hole radii of a pair of PCFs consisting of different lattice types is also found to be constant if the AFF is the same. With dependence on value of AFF used the effect of the order of lattice on the mode area of PCFs exhibit a reversal characteristic while approaching higher order. The effective nonlinear coefficient has been found to be maximized for octagonal PCFs. A reduction in confinement loss to the order of 10 − 6 has been observed for higher order PCFs with increased AFF. The variation of the effective area with AFF indicates that it almost reaches saturation for higher ordered structures, but its magnitude is found to decrease with increasing AFF. A flattened dispersion is observed for square PCFs over a wide wavelength range.