This paper presents a new methodology for computing a time-frequency map for nonstationary signals using the continuous-wavelet transform (CWT). The conventional method of producing a time-frequency map using the short time Fourier transform (STFT) limits time-frequency resolution by a predefined window length. In contrast, the CWT method does not require preselecting a window length and does not have a fixed time-frequency resolution over the time-frequency space. CWT uses dilation and translation of a wavelet to produce a time-scale map. A single scale encompasses a frequency band and is inversely proportional to the time support of the dilated wavelet. Previous workers have converted a time-scale map into a time-frequency map by taking the center frequencies of each scale. We transform the time-scale map by taking the Fourier transform of the inverse CWT to produce a time-frequency map. Thus, a time-scale map is converted into a time-frequency map in which the amplitudes of individual frequencies rather than frequency bands are represented. We refer to such a map as the time-frequency CWT (TFCWT). We validate our approach with a nonstationary synthetic example and compare the results with the STFT and a typical CWT spectrum. Two field examples illustrate that the TFCWT potentially can be used to detect frequency shadows caused by hydrocarbons and to identify subtle stratigraphic features for reservoir characterization.

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IntroductIon 1 rama Mohana r. turaga and Kalyan Bhaskar E lectronic waste (e-waste), that is, waste arising from end-of-life electronic products such as computers and mobile phones, is one of the fastest growing waste streams in the world today. Annual global production of e-waste is estimated to surpass 50 million tons in 2020. 2 India is among the top five e-waste producing countries in the world with estimated annual production of 2 million tons. Like some of the other developing countries, e-waste management in India is dominated by the informal sector with estimates of more than 90 per cent of the waste being processed in this sector. E-waste contains several precious metals, rare earth metals, ferrous and non-ferrous metals, plastic, wood and glass. Unscientific practices in the processing of e-waste are associated with several environmental and health externalities. 3 In response to these concerns, many developed and devel-1 The earlier versions of the articles in this colloquium (except for the article by Hitesh Sharma) were written for the report 'E-waste Roadmap 2023 for India', an initiative under the India E-waste Program of the International Finance Corporation (IFC). The programme was supported by the Government of Japan and the Korea Green Growth Trust Fund of the World Bank. We gratefully acknowledge the contribution of Neeta Misra, Sarina Bolla and Kalyan Bhaskar, the editors of the 'E-waste Roadmap 2023 for India' report, who worked with a team of experts on e-waste in India and were responsible for the editing of the initial versions of many of the articles in the colloquium.

Enhancing upconversion, temperature sensing and cathodoluminescence in the CaMoO4:Er3+/Yb3+ nanophosphor via K+/Na+ simultaneous codoping.