Reducing numerical diffusion for incompressible flow calculations

A number of approaches for improving the accuracy of incompressible, steady-state flow calculations are examined. Two improved differencing schemes, Quadratic Upstream Interpolation for Convective Kinematics (QUICK) and Skew-Upwind Differencing (SUD), are applied to the convective terms in the Navier-Stokes equations and compared with results obtained using hybrid differencing. In a number of test calculations, it is illustrated that no single scheme exhibits superior performance for all flow situations. However, both SUD and QUICK are shown to be generally more accurate than hybrid differencing

Electron Scattering in AlGaN/GaN Structures

We present data on mobility lifetime, $\tau_t$, quantum lifetime, $\tau_q$, and cyclotron resonance lifetime, $\tau_{CR}$, of a sequence of high-mobility two-dimensional electron gases in the AlGaN/GaN system, covering a density range of $\sim1-4.5\times10^{12}$cm$^{-2}$. We observe a large discrepancy between $\tau_q$ and $\tau_{CR}$ ($\tau_q\sim\tau_{CR}$/6) and explain it as the result of density fluctuations of only a few percent. Therefore, only $\tau_{CR}$ --and not $\tau_q$ -- is a reliable measure of the time between electron scattering events in these specimens. The ratio $\tau_t / \tau_{CR}$ increases with increasing density in this series of samples, but scattering over this density range remains predominantly in the large-angle scattering regime

Turbofan aft duct suppressor study. Contractor's data report of mode probe signal data

Acoustic modal distributions were measured in a fan test model having an annular exhaust duct for comparison with theoretically predicted acoustic suppression values. This report contains the amplitude and phase data of the acoustic signals sensed by the transducers of the two mode probes employed in the measurement. Each mode probe consisted of an array of 12 transducers sensing the acoustic field at three axial positions and four radial positions

Turbofan aft duct suppressor study

Suppressions due to acoustic treatment in the annular exhaust duct of a model fan were theoretically predicted and compared with measured suppressions. The predictions are based on the modal analysis of sound propagation in a straight annular flow duct with segmented treatment. Modal distributions of the fan noise source (fan-stator interaction only) were measured using in-duct modal probes. The flow profiles were also measured in the vicinity of the modal probes. The acoustic impedance of the single degree of freedom treatment was measured in the presence of grazing flow. The measured values of mode distribution of the fan noise source, the flow velocity profile and the acoustic impedance of the treatment in the duct were used as input to the prediction program. The predicted suppressions, under the assumption of uniform flow in the duct, compared well with the suppressions measured in the duct for all test conditions. The interaction modes generated by the rotor-stator interaction spanned a cut-off ratio range from nearly 1 to 7

Experimental validation of flexibility provision by highly distributed demand portfolio

The wide scale deployment and utilization of demand side management for the provision of frequency balancing service provision is hindered by the lack of proof of performance evaluation of such mechanisms. In this paper, the pre-qualification testing approaches for performance evaluation of frequency balancing service provision by highly distributed demand portfolio are discussed. Preliminary experimental results and challenges that arise of the pre-qualification tests conducted on a highly distributed flexible resource portfolio being managed by a multi-agent based demand side management technology are presented and the need for expansion of present day testing procedures discussed

Prevalence, Awareness and Control of Hypertension in Chennai - The Chennai Urban Rural Epidemiology Study (CURES – 52)

Objective : To study the prevalence, awareness and control of hypertension in Chennai representing Urban South India. Methods : The Chennai Urban Rural Epidemiology Study (CURES) is one of the largest epidemiological studies on diabetes carried out in India, where 26,001 individuals aged ≥ 20 years were screened using systematic random sampling method. Every tenth subject recruited in Phase 1 of CURES was requested to participate in Phase 3 of CURES and the response rate was 2,350/26,001 or 90.4%. An oral glucose tolerance test was performed in all individuals except self-reported diabetic subjects. Anthropometric measurements and lipid estimations were done in all subjects. Hypertension was diagnosed in all subjects who were on drug treatment for hypertension or if the blood pressure ≥ 140/90 mmHg. Results : Hypertension was present in 20% [men:23.2% vs. women:17.1%, p<0.001] of the study population. Isolated systolic hypertension (Systolic BP ≥ 140 and Diastolic BP<90 mmHg) was present in 6.6% while isolated diastolic hypertension (DBP ≥ 90 and SBP<140 mmHg) was present in 4.2% of the population. Among the elderly population (aged ≥ 60 years), 25.2% had isolated systolic hypertension. Age, body mass index, smoking, serum cholesterol and triglycerides were found to be strongly associated with hypertension. Among the total hypertensive subjects, only 32.8% were aware of their blood pressure, of these, 70.8% were under treatment and 45.9% had their blood pressure under control. Conclusion : Hypertension was present in one-fifth of this urban south Indian population and isolated systolic hypertension was more common among elderly population. Majority of hypertensive subjects still remain undetected and the control of hypertension is also inadequate. This calls for urgent prevention and control measures for hypertensio

Non-parabolicity of the conduction band of wurtzite GaN

Using cyclotron resonance, we measure the effective mass, $m$*, of electrons in AlGaN/GaN heterostructures with densities, $n_{2D}\sim 1-6\times10^{12}$cm$^{-2}$. From our extensive data, we extrapolate a band edge mass of $(0.208\pm0.002) m_e$. By comparing our $m$* data with the results of a multi-band \textbf{k.p} calculation we infer that the effect of remote bands is essential in explaining the observed conduction band non-parabolicity (NP). Our calculation of polaron mass corrections -- including finite width and screening - suggests those to be negligible. It implies that the behavior of $m*(n_{2D})$ can be understood solely in terms of NP. Finally, using our NP and polaron corrections, we are able to reduce the large scatter in the published band edge mass values

Acoustic phonon scattering in a low density, high mobility AlGaN/GaN field effect transistor

We report on the temperature dependence of the mobility, $\mu$, of the two-dimensional electron gas in a variable density AlGaN/GaN field effect transistor, with carrier densities ranging from 0.4$\times10^{12}$ cm$^{-2}$ to 3.0$\times10^{12}$ cm$^{-2}$ and a peak mobility of 80,000 cm$^{2}$/Vs. Between 20 K and 50 K we observe a linear dependence $\mu_{ac}^{-1} = \alpha$T indicating that acoustic phonon scattering dominates the temperature dependence of the mobility, with $\alpha$ being a monotonically increasing function of decreasing 2D electron density. This behavior is contrary to predictions of scattering in a degenerate electron gas, but consistent with calculations which account for thermal broadening and the temperature dependence of the electron screening. Our data imply a deformation potential D = 12-15 eV.Comment: 3 pages, 2 figures, RevTeX. Submitted to Appl Phys Let

Realization of Programmable BPSK Demodulator-Bit Synchronizer using Multirate Processing

This paper presents the design and implementation of programmable BPSK demodulator and bit synchronizer. The demodulator is based on the Costas loop design whereas the bit synchronizer is based on Gardner timing error detector. The advantage of this design is that it offers programmability using multi-rate processing and does not rely on computation of filter coefficients, NCO angle input for each specific data rate and thus avoids computational complexities. The algorithm and its application were verified on Matlab-Simulink and was implemented on ALTERA platform. A 32 kHz BPSK demodulator–bit synchronizer pair catering for data rates from 1 kbps to 8 kbps was implemented.DOI:http://dx.doi.org/10.11591/ijece.v4i3.556