Academic literature on the topic 'Repeated cross-sectional studies'

This chapter focuses on cross-sectional and longitudinal studies. cross-sectional studies involve the analysis of usually quantitative data collected at a single snapshot in time. The unit of observation might be people or countries, and those are measured only once, all at approximately the same time. In contrast, longitudinal studies (also referred to as repeated measures studies) involve analysis on multiple occasions over time, where the same individuals (or countries) — the panel — are measured on each occasion. As such, the unit of observation is occasions, and there are multiple occasions/measures of each individual. A subcategory of longitudinal studies is event-history/survival/duration analysis, where the dependent variable is binary and the focus is on causes of changes between the two states of the outcome. Note that in comparison, time series analysis typically involves fewer individuals (often only one) and a larger number of time points. A third type of study, situated in between longitudinal and cross-sectional studies, is repeated cross-sectional analysis, which involves the analysis of multiple cross-sectional data sets over time, and different individuals are measured in each wave of the survey. Here, the unit of observation is individuals, and there are multiple individuals measured in each survey wave.

In this study, with a focus on the rotating stall phenomenon in the vaneless diffuser of a centrifugal compressor, 2D-PIV is conducted to better understand the flow structure. Although many studies have reported concerning this problem, most data is obtained through experiments under lower speed conditions, using a simplified model or equipment. Unlike such studies, a ship board turbocharger compressor with a higher impeller rotation speed is selected as an application for the present measurement. In the measurement, an ensemble-averaged phase locking technique is also selected to compensate f

In oil and gas installations, whether on-shore or off-shore, pipes are the primary vessel for the conveyance of either crude or products from one location to another. Under use, the pipes are subjected to both internal and external temperature fluctuations while repeated operational start-up and shut-down procedures triggers vibrations of these pipes, propagates internal waves and results in finite and irreversible longitudinal extension of the pipe over time. This longitudinal extension which is sometimes accompanied by pipe buckling is known as ratcheting and has also been described by some

Intermittent gas and liquid two-phase flow was generated in a 6 m × 67 mm diameter pipe mounted rotatable frame (vertical up to −20°). Air and a 5 mPa s silicone oil at atmospheric pressure were studied. Gas superficial velocities between 0.17 and 2.9 m/s and liquid superficial velocities between 0.023 and 0.47 m/s were employed. These runs were repeated at 7 angles making a total of 420 runs. Cross sectional void fraction time series were measured over 60 seconds for each run using a Wire Mesh Sensor and a twin plane Electrical Capacitance Tomography. The void fraction time series data were a