Modelling the effects of COVID-19 on travel mode choice behaviour in India

The COVID-19 pandemic has resulted in unprecedented changes in the activity patterns and travel behaviour around the world. Some of these behavioural changes are in response to restrictive measures imposed by the Government (e.g. full or partial lock-downs), while others are driven by perceptions of own safety and/or commitment to slow down the spread (e.g. during the preceding and following period of a lock-down). Travel behaviour amidst the stricter of these measures is quite straightforward to predict as people have very limited choices, but it is more challenging to predict the behavioural changes in the absence of restrictive measures. The limited research so far has demonstrated that different socio-demographic groups of different countries have changed travel behaviour in response to COVID-19 in different ways. However, no studies to date have either (a) investigated the changes in travel behaviour in the context of the Global South, or (b) modelled the relationship between changes in transport mode usage and traveller characteristics in order to quantify the associated heterogeneity. In this paper, we address these two gaps by developing mathematical models to quantify the effect of the socio-demographic characteristics of the travellers on the mode-specific trip frequencies before (January 2020) and during the early stages of COVID-19 spread in India (March 2020). Primary data collected from 498 respondents participating in online surveys have been used to estimate multiple discrete choice extreme value (MDCEV) models in this regard. Results indicate – a) significant inertia to continue using the pre-COVID modes, and b) high propensity to shift to virtual (e.g. work from home, online shopping, etc.) and private modes (e.g. car, motorcycle) from shared ones (e.g. bus and ride-share options). The extent of inertia varies with the trip purpose (commute and discretionary) and trip lengths. The results also demonstrate significant heterogeneity based on age, income, and working status of the respondents. The findings will be directly useful for planners and policy-makers in India as well as some other countries of the Global South in better predicting the mode-specific demand levels and subsequently, making better investment and operational decisions during similar disruptions

Physical insights into unstart dynamics of a hypersonic mixed compression intake

Hypersonic air-breathing cruise vehicles powered by supersonic combustion ramjet engines are the potential candidate for future space and defense applications. The air intake of the scramjet engine is a vital component that uses shock waves to compress the air to pressure and temperatures suitable for supersonic combustion. Understanding the unstart dynamics of such intakes is of prime importance for the seamless operation of scramjet intakes. While the unstart dynamics in supersonic intakes are studied widely by various researchers, only a few such studies are reported in hypersonic intakes. The mechanisms associated with the same are not clearly understood. In the current work, a design optimization framework is established by coupling (a) oblique-shock theory and Non-dominated Sorting Genetic Algorithm II (NSGA-II) and (b) Computational fluid dynamics (CFD) and NSGA - II to minimize total pressure loss and maximize intake exit temperature of planar mixed compression intake at a design Mach number of 6. The ramp and cowl angles constitute the design space. The intake with maximum exit temperature is chosen to study its unstart dynamics using a combination of experiments in a hypersonic wind tunnel (M = 6 and Re = 8.86 × 106/m) and unsteady numerical investigations using the open-source suite SU2. The intake model is equipped with a movable cowl and flap to study the internal contraction and throttling induced unstart. Simultaneous pressure measurements and schlieren flow visualization are carried out to study unsteady flow physics associated with intake unstart. The dynamic content in the flow is analyzed using Fast Fourier Transform (FFT) and spectrogram of the unsteady pressure signal and Dynamic Mode Decomposition (DMD) of the schlieren images and density contours. In this work, two different modes of shock oscillation during unstart are observed when the flap is moved while the cowl is held stationary. At ICR = 1.19, the intake shows started behavior for throttling ratio up to 0.31, and a dual behavior, where it remains started in dynamic flap runs but unstarted in fixed flap runs for throttling ratios of 0.35 and 0.42. The intake exhibits a staged evolution to a large amplitude oscillatory unstart for throttling ratios of 0.55 and 0.69, with frequencies of 950 and 1100 Hz, respectively. A staged evolution (5 stages) to a subsonic spillage oscillatory unstart is detailed using corroborative evidence from both time-resolved schlieren and pressure measurements. The ramp side separation bubble drives the high amplitude oscillatory unstart. At ICR = 1.37, the shear layer emanating from the triple point of shock interaction drives the low amplitude oscillatory unstart with a dominant frequency of about 3.7 kHz for a throttling ratio of 0.69. A criterion for demarcating the modes of unstart is evolved using current and previous data. The actual shock on lip condition during started operation demarcates the two modes of oscillatory unstart. Unsteady numerical computations are performed to study the effect of enthalpy on the unstart frequency. The frequency of unstart varies linearly with stagnation acoustic speed and is an appropriate velocity scale. During unstart, the extent of the subsonic region is the appropriate length scale to be used in the quarter-wave resonance model to estimate unstart frequency pertaining to high mechanical blockag

Review—Metal Organic Framework Based Nanomaterials for Electrochemical Sensing of Toxic Heavy Metal Ions: Progress and Their Prospects

Heavy metal ions, which have harmful effects on living organisms, are extremely toxic to the environment. Therefore, with quick response time and low cost analytical instrument, it is of immense demand to assess the toxic levels of heavy metal ions. A promising and systematic way of perceiving the selective determination of metal ions in polluted water is electrochemical detection. Recent developments in metal organic frameworks (MOF) have ignited a considerable interest in the metal ion sensor field as an interesting class of electrode material. This paper reviews the MOF-based material as an electrode detection platform for toxic heavy metal ions. The rapidly evolving MOF has a 3D structure with tunable pore sizes, and a high specific area containing a large number of ions makes it ideal for ion exchange capture of toxic metal ions. The toxicity levels in the atmosphere of heavy metal ions such as arsenic, lead, mercury and cadmium and recent advances in the use of MOF as an active electrode material for estimating these metal ions are discussed. The key advantages and disadvantages of electrochemical sensors based on MOF have also been evaluated, and the potential prospect of improving performance is also presented. Thus, the compiled review work could provide a torchlight and a pathway for more metal ion sensor research that gives science research and community research a vast dimension.</jats:p