A Novel Idea of Coherent Acoustic Wave-Induced Atmospheric Refractivity Fluctuation and Its Applications

The physical mechanism of generating the lasting tropospheric refractivity fluctuation with a stable array-distributed structure by coherent acoustic waves is investigated. An example of the quantitative calculation of atmospheric refractive index is given and analyzed. Based on the theory of electromagnetic wave propagation and scattering in the troposphere, the feasibility to purposefully affect radio wave propagation is qualitatively demonstrated by the experiment of the coherent acoustic source-induced laser interference fringe change. The potential application aspects of synthetically controlling the radio wave propagation by the artificial refractivity fluctuation structure are preliminarily proposed. This chapter will promote the development of the coherent acoustic wave-induced tropospheric refractivity fluctuation, and it has the important theoretical significance and potential application value to purposely apply the positive or negative effects on radio wave propagation

Ultrasonographic abdominal adipose tissue thickness for the prediction of gestational diabetes mellitus: A meta-analysis

Obesity has been linked to the risk of gestational diabetes mellitus (GDM). The meta-analysis aimed to assess the predictive role of ultrasonographic measurements of the abdominal adipose tissue thickness for GDM in pregnant women. Cohort studies evaluating the association between abdominal subcutaneous and/or visceral adipose thickness (SAT and/or VAT) and subsequent risk of GDM were retrieved from PubMed, Embase, and Web of Science databases. Only studies with SAT/VAT measured before the diagnosis of GDM were included. Random-effects models incorporating the influence of potential heterogeneity were used to pool the results. A total of 13 studies involving 5616 pregnant women were included. Pooled results showed that both a high abdominal SAT (odds ratio [OR] for per 1-cm increment: 1.23, 95% confidence interval [CI]: 1.07 to 1.41, P = 0.003, I2 = 13%; OR for high versus low category: 3.42, 95% CI: 2.31 to 5.07, P < 0.001, I2 = 0%) and VAT (OR for per 1-cm increment: 1.54, 95% CI: 1.16 to 2.06, P = 0.003, I2 = 63%; OR for high versus low category: 5.73, 95% CI: 3.39 to 9.77, P < 0.001, I2 = 31%) at early stages of pregnancy were associated with a higher subsequent risk of GDM. Subgroup analysis based on study design, timing of ultrasound examination, GDM diagnostic criteria, and study quality score showed consistent results. In conclusion, ultrasound-measured abdominal adipose tissue thickness may be useful for predicting the subsequent risk of GDM in pregnant women

Numerical Analysis of Isothermal Elastohydrodynamic Lubrication of Cylindrical Gears with Variable Hyperbolic Circular Arc and Tooth Trace

In this study on cylindrical gears with variable hyperbolic circular arc and tooth trace (VH-CATT), the tooth surface equation of the VH-CATT gear is obtained according to the theory of meshing and differential geometry. The data points of the tooth surface are obtained using MATLAB. Then, based on the data points, a model of a VH-CATT gear pair was built using UG. Considering the geometric features, contact form, relative velocity, entrainment velocity, load, etc., an isothermal elastohydrodynamic lubrication model of a VH-CATT gear pair is established. On the basis of the existing elastohydrodynamic lubrication (EHL) theory, an isothermal EHL numerical solution of a VH-CATT gear is obtained by utilizing the multigrid method. The distribution of dimensionless pressure and film thickness under the effect of various loads and at different speeds of a VH-CATT gear pair are discussed. The results show that both loading and speed have impact on oil film pressure and oil film thickness. The second pressure peaks and the minimum film thickness of the VH-CATT gear pair are greatly affected by the entrainment velocity and load. Based on the results of the study, we can provide a guide to creating a tribological design of VH-CATT gears and provide a theoretical basis and the application of value engineering in industrial applications of VH-CATT gear pairs under high speed and heavy load