Planar perovskite solar cells (PSCs) made entirely via solution processing at low temperatures (<150°C) offer promise for simple manufacturing, compatibility with flexible substrates, and perovskite-based tandem devices. However, these PSCs require an electron-selective layer that performs well with similar processing. We report a contact-passivation strategy using chlorine-capped TiO2 colloidal nanocrystal film that mitigates interfacial recombination and improves interface binding in low-temperature planar solar cells. We fabricated solar cells with certified efficiencies of 20.1 and 19.5% for active areas of 0.049 and 1.1 square centimeters, respectively, achieved via low-temperature solution processing. Solar cells with efficiency greater than 20% retained 90% (97% after dark recovery) of their initial performance after 500 hours of continuous room-temperature operation at their maximum power point under 1-sun illumination (where 1 sun is defined as the standard illumination at AM1.5, or 1 kilowatt/square meter).

https://science.sciencemag.org/content/sci/early/2017/02/01/science.aai9081.full.pdf

Efficient and stable solution-processed planar perovskite solar cells via contact passivation.

The photovoltaics of organic–inorganic lead halide perovskite materials have shown rapid improvements in solar cell performance, surpassing the top efficiency of semiconductor compounds such as CdTe and CIGS (copper indium gallium selenide) used in solar cells in just about a decade. Perovskite preparation via simple and inexpensive solution processes demonstrates the immense potential of this thin-film solar cell technology to become a low-cost alternative to the presently commercially available photovoltaic technologies. Significant developments in almost all aspects of perovskite solar cells and discoveries of some fascinating properties of such hybrid perovskites have been made recently. This Review describes the fundamentals, recent research progress, present status, and our views on future prospects of perovskite-based photovoltaics, with discussions focused on strategies to improve both intrinsic and extrinsic (environmental) stabilities of high-efficiency devices. Strategies and challenges regardi...

Halide Perovskite Photovoltaics: Background, Status, and Future Prospects

Multi-Criteria Decision Aid (MCDA) or Multi-Criteria Decision Making (MCDM) methods have received much attention from researchers and practitioners in evaluating, assessing and ranking alternatives across diverse industries. Among numerous MCDA/MCDM methods developed to solve real-world decision problems, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) continues to work satisfactorily across different application areas. In this paper, we conduct a state-of-the-art literature survey to taxonomize the research on TOPSIS applications and methodologies. The classification scheme for this review contains 266 scholarly papers from 103 journals since the year 2000, separated into nine application areas: (1) Supply Chain Management and Logistics, (2) Design, Engineering and Manufacturing Systems, (3) Business and Marketing Management, (4) Health, Safety and Environment Management, (5) Human Resources Management, (6) Energy Management, (7) Chemical Engineering, (8) Water Resources Management and (9) Other topics. Scholarly papers in the TOPSIS discipline are further interpreted based on (1) publication year, (2) publication journal, (3) authors' nationality and (4) other methods combined or compared with TOPSIS. We end our review paper with recommendations for future research in TOPSIS decision-making that is both forward-looking and practically oriented. This paper provides useful insights into the TOPSIS method and suggests a framework for future attempts in this area for academic researchers and practitioners.

Review: A state-of the-art survey of TOPSIS applications

The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

/pdf/validity-of-cubic-law-for-fluid-flow-in-a-deformable-rock-2ynq4id3hq.pdf

VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

Time is divided by geologists according to marked shifts in Earth's state. Recent global environmental changes suggest that Earth may have entered a new human-dominated geological epoch, the Anthropocene. Here we review the historical genesis of the idea and assess anthropogenic signatures in the geological record against the formal requirements for the recognition of a new epoch. The evidence suggests that of the various proposed dates two do appear to conform to the criteria to mark the beginning of the Anthropocene: 1610 and 1964. The formal establishment of an Anthropocene Epoch would mark a fundamental change in the relationship between humans and the Earth system.

Defining the Anthropocene

Mountainous regions of India experience recurrent slope failures due to rapid urbanization. The main causes of slope failure are high precipitation aided by unplanned construction of cut slopes. Such slope failures are further aggravated because of the presence of low strength, highly jointed, stratified rocks rich in clay minerals. In general, effect of weathering is more pronounced in these rocks, which causes long-term time-dependent deterioration of the rocks as well as joint strength. In this regard, the present investigation deals with the causes, behavior, and mechanism of slope failure by examining a section in the North Eastern Himalayas. A detailed field investigation was carried out for examining the existing condition of slope, slope material, and joint parameters. Laboratory experiments like compressive and tensile strength tests along and across the lamination planes along with slake durability index tests were conducted to characterize the material and investigate the role of weathering in strength degradation. Later, numerical simulation was performed employing distinct element method to investigate the failure behavior, mechanism, and also the effect of water pressure in destabilizing the slope. The experimental result indicates directional strength variations parallel and perpendicular to bedding plane, which makes the rock incompetent to sustain external load. The presence of orthogonal joint sets accelerates the process of block detachment. Significant slaking was observed which further deteriorates and fragments the rock at deeper level. Numerical simulation shows that failure plane is dominantly planar (along the bedding parallel joints) and surficial.

Slope failure in stratified rocks: a case from NE Himalaya, India

Detection of volatile organic compounds (VOCs) is rapidly becoming a necessity as they have significant percentage in the indoor air pollution. Therefore, use of highly sensitive, small and portable VOC sensors ranges from households, offices to large industries. This paper deals with the use of a highly responsive semiconductor, i.e. SnO2, in VOC sensors. A hitherto unreported strategy of using hollow cage-frame-type nanostructures is proposed. These hollow particles supersede the response characteristics of solid or even the porous nanostructures, which are mostly used till date. VOCs such as: ethanol, methanol, acetone, toluene and formaldehyde can be easily detected using SnO2 hollow structures as the chemically active component of the sensor. The fabricated sensors exhibit high selectivity for each VOCs, at different operating temperature. The sensing mechanism of hollow nanostructures is also described in detail. The work can initiate significant activity on VOC sensing using hollow structures, which has remained ignored till now.

Hierarchical SnO2 nanostructures for potential VOC sensor

Today, nearly all publications related to supercapacitors suggest their use in electric vehicles and mobile technologies They only report the performance under static conditions, which is far from reality as vibrations cannot be ignored in the above mentioned applications Over the last few years, there have been some studies trying to understand the effect of external vibrations on the performance of Li-ion cells Such studies, still being ignored for supercapacitors, can have a direct impact on their industrial applications In this paper, the results establish that supercapacitors will also have a significant variation in specific capacitance, if they are operated under the influence of external vibrations Actually, the external vibrations can lead to a loss of >50% in the specific capacitance of supercapacitors Intriguingly, pseudocapacitors are affected far more than EDLCs These results can also be explained theoretically by consideration of the cavitation collapse induced by the external energy, which leads to thermal activation of molecules or generation of radicals near the electrode–electrolyte interface This directly impacts the rate constants of electron transfer reactions in solution, near the electrodes The results can tilt the advantage in favour of carbon based electric double layer capacitors in applications, where external vibrations are envisaged

External vibrations can destroy the specific capacitance of supercapacitors – from experimental proof to theoretical explanations

Jharia coalfield is a chief storehouse of prime coking coal in India. Earlier,many shallow seams were exploited by surface mining but when this method became uneconomical the mine operators resorted to underground method. However, due to various geotechnical problems, it was not possible to fully extract coal by underground method. Opencast mining is now being planned for extraction of coal locked in partially worked coal seam for ensuring maximum recovery. The major problem envisaged in conducting opencast mining insuch areas will be the stability of slope. In this paper, the technique adopted for simulation of 144 10 thick section of rock mass in equivalent material model is outlined. Old shallow surface excavation upto 33.0 m and later on underground workings were simulated in coal seam II/III. The span of the void was 160 m. An opencast excavation was conducted for recovering locked coal. The behaViour of slopes are reported here.

Prediction of instability of slopes in an opencast mine over old surface and underground workings

The fracture properties along with the other physico-mechanical parameters of rock greatly influence the elastic property of rocks (e. g. p-wave velocity). A neural network model based on back-propagation algorithm (algorithm used to train neural network) is designed to predict the compressional wave velocity in rocks. Optimization of the network architecture is done using a systematic approach with different networks. In this network each parameters were varied one by one and other parameters using genetic algorithm were fixed. The networks were then trained and results were compared. Combination of parameters giving best results was selected. Fracture roughness coefficient and some important physico-mechanical properties were taken as input parameters and on the bases of these input parameters the model predicts the output (p-wave velocity). The mean average percentage error in prediction is found to be negligible (1.081%) and generalization capability of the neural network model is established to be excellent. A useful concept of sensitivity analysis is adopted to set the hierarchy of influence of input factors over the velocity of primary wave in rock mass. The results of the present investigation provide functional and vital information for planning and design of excavation in rock mass.

Trilok Singh

Papers

Slope failure in stratified rocks: a case from NE Himalaya, India

Hierarchical SnO2 nanostructures for potential VOC sensor

External vibrations can destroy the specific capacitance of supercapacitors – from experimental proof to theoretical explanations

Prediction of instability of slopes in an opencast mine over old surface and underground workings

A Neuro-Genetic approach for prediction of compressional wave velocity of rock and its sensitivity analysis