Oesophageal pH-Impedance for the Diagnosis of Gastro-Oesophageal Reflux Disease: Validation of General Population Reference Values in Children with Chronic Neurological Impairments

Diagnosis of gastro-oesophageal reflux disease (GORD) in children with chronic neurological impairment (NI) remains a clinical challenge. The study aimed to validate the relevance of the reference values used to assess gastro-oesophageal reflux (GOR) in children with NI and to determine the optimal cut-off level of the pH-impedance parameter with the best predictive value for outcomes associated with endoscopic assessments of the oesophagus. Sixty-seven children (32 male, 35 female; age: interquartile range, 5 years 6 months–14 years 10 months; median, 11 years 3 months) with NI were prospectively recruited for the study. The exclusion criteria were previous fundoplication and lack of consent for the study. All patients underwent evaluations for GOR disease, including pH-impedance and gastroscopy. Based on endoscopy, oesophagitis was diagnosed in 22/67 children (32.8%); 9/67 (13.4%) were classified as having Hetzel–Dent grade III or IV. GOR was present in 18/67 children (26.9%), as determined by pH-impedance. Patients with endoscopic lesions had a significantly higher number of total reflux (p = 0.0404) and acidic episodes (p = 0.0219). The total number of reflux episodes, with a cut-off level of 44 episodes, was the pH-impedance parameter most strongly predictive of the presence of lesions in gastroscopy (specificity: 50%, sensitivity: 73%). These findings suggest that endoscopic lesions may be present in children with chronic NI with a low number of GOR episodes, as recorded by pH-impedance. The use of standardised reference norms determined for the general population may underestimate GOR episodes in this group of patients.

Reflection of Plane Waves from Surface of a Generalized Thermo-Viscoelastic Porous Solid Half-Space with Impedance Boundary Conditions

A phenomenon of reflection of plane waves from a thermally insulated surface of a solid half-space is studied in context of Lord-Shulman theory of generalized thermo-viscoelasticity with voids. The governing equations of generalized thermo-viscoelastic medium with voids are specialized in x–z plane. The plane wave solution of these equations shows the existence of three coupled longitudinal waves and a shear vertical wave in a generalized thermo-viscoelastic medium with voids. For incident plane wave (longitudinal or shear), three coupled longitudinal waves and a shear vertical wave reflect back in the medium. The mechanical boundary conditions at free surface of solid half-space are considered as impedance boundary conditions, in which the shear force tractions are assumed to vary linearly with the tangential displacement components multiplied by the frequency. The impedance corresponds to the constant of proportionality. The appropriate potentials of incident and reflected waves in the half-space will satisfy the required impedance boundary conditions. A non-homogeneous system of four equations in the amplitude ratios of reflected waves is obtained. These amplitude ratios are functions of material parameters, impedance parameter, angle of incidence, thermal relaxation and speeds of plane waves. Using relevant material parameters for medium, the amplitude ratios are computed numerically and plotted against certain ranges of impedance parameter and the angle of incidence.

A new method using medians to calibrate single-parameter spatial interaction models

I present a method for calibrating the impedance parameter of a gravity spatial interaction model using only the median travel time as a measure of observed traveler behavior. Complete information about the spatial structure of origins, destinations, and travel times between origins and destinations is also required. Using Monte Carlo simulation techniques on stylized cities, I attempt to recover true (a priori known) impedance values with this method for a range of impedance values for both negative exponential and power impedance functions. The results are compared with estimates obtained by other fast methods. The proposed method proves to provide a fairly accurate estimate of the impedance parameter, with a mean percent error typically below 20% and often below 10% for common impedance values. The proposed method is an improvement over existing calibration methods in several respects. First, it allows for the estimation of the impedance parameter directly without lengthy iterative calculations. Second, because it only requires median travel times, it can be calibrated with smaller samples (n~200), allowing the construction of gravity models for specific modes and/or travel purposes. And third, the method does not require expensive travel demand software and so can be implemented more widely in practice.

Unit-Cell-Based Domain Decomposition Method for Efficient Simulation of a Truncated Electromagnetic Bandgap Structure in High-Speed PCBs

In this paper, we present a unit-cell-based domain decomposition method (UC-DDM) for rapid and accurate simulation of predicting the parallel plate noise (PPN) suppression of a truncated electromagnetic bandgap (EBG) structure in high-speed printed circuit boards (PCBs). The proposed UC-DDM divides the analysis domain of the truncated EBG structure into UCs as sub-domains. Solving a sub-domain is based on a novel UC model, yielding an analytical expression for the impedance parameter (Z-parameter) of the UC. The novel UC model is derived using a spatial decomposition technique, which results in the modal decomposition of quasi-transverse electromagnetic (TEM) and transverse magnetic (TM) modes. In addition, we analytically derive a impedance-parameter recombination method (ZRM) to obtain the analytical solution of a finite EBG array from the sub-domain results. The proposed UC-DDM is verified through comparison with full-wave simulation results for various EBG arrays. Comparison between the UC-DDM and a full-wave simulation of a truncated EBG structure reveals that a substantial improvement in computation time with high accuracy is achieved. It is demonstrated that the simulation time of the proposed method is only 0.1% of that of a full-wave simulation without accuracy degradation.

Diagonal Mode van der Pauw Stress Sensors: Proof of Diagonal-Mode Conjecture

The conjecture discussed in our previous paper [Jaeger, R. C., Motalab, M., Hussain, S., and Suhling, J. C., 2014, “Four-Wire Bridge Measurements of Silicon van der Pauw Stress Sensors,” ASME J. Electron. Packag., 136(4), p. 041014; Jaeger, R. C., Motalab, M., Hussain, S., and Suhling, J. C., 2018, Erratum: “Four-Wire Bridge Measurements of Silicon van der Pauw Stress Sensors,” ASME J. Electron. Packag., 140(1), p. 017001] was backed up by measurements and simulation results, but not mathematically proven. A proof based upon two-port impedance parameter reciprocity is presented with additional experimental confirmation.