Phase Coherence Imaging for Near-Surface Defects in Rails Using Cross-Correlation of Ultrasonic Diffuse Fields

In this paper, phase coherence imaging is proposed to improve spatial resolution and signal-to-noise ratio (SNR) of near-surface defects in rails using cross-correlation of ultrasonic diffuse fields. The direct signals acquired by the phased array are often obscured by nonlinear effects. Thus, the output image processed by conventional post-processing algorithms, like total focus method (TFM), has a blind zone close to the array. To overcome this problem, the diffuse fields, which contain spatial phase correlations, are applied to recover Green’s function. In addition, with the purpose of improving image quality, the Green’s function is further weighted by a special coherent factor, sign coherence factor (SCF), for grating and side lobes suppression. Experiments are conducted on two rails and data acquisition is completed by a commercial 32-element phased array. The quantitative performance comparison of TFM and SCF images is implemented in terms of the array performance indicator (API) and SNR. The results show that the API of SCF is significantly lower than that of TFM. As for SNR, SCF achieved a better SNR than that of TFM. The study in this paper provides an experimental reference for detecting near-surface defects in the rails

Order Flow in the South: Anatomy of the Brazilian FX Market

Using a unique dataset that covers 100% of the Brazilian FX retail market, this paper contributes to the microstructure approach to exchange rates in at least four ways. First, we find a strict link between currency flows in the FX market and the Balance of Payments. Second, we develop an identication strategy in order to properly estimate the effect of customer order fl?ows on the exchange rate and ?find that dealers from the Brazilian FX market charge a premium of 0.03% in order to provide US$10 million of overnight liquidity. Third, we identify the nature of the feedback trading as "stabilizing"?: a 1$ 111 million and the commercial fl?ow by US$46 million. Finally, we find that the central bank sells in average US$ 28 million for each 1% depreciation in the exchange rate (lean-against-the-wind), and US$23 million for US$ 100 million of financial customer flow (liquidity provision)

Commercially available order flow data and exchange rate movements : Caveat emptor

Research suggests that customer order flow should help predict exchange rates. We make two contributions. First, we provide a review of the recent literature on order flow and exchange rate movements. Second, we critically evaluate the practical value of customer order flow data that are commercially available to the wider market, as well as the forecasting properties of inter-dealer order flow. In line with microstructure theory, we find little evidence that the latter can forecast exchange rates, but our results also cast considerable doubt on the practical value to market practitioners of commercially available customer order flow data