Current Scaling Technique Research Articles

Estimation of Aerodynamic Coefficients in a Small Subsonic Wind Tunnel

To apply the experimental data measured in a wind tunnel for a scaled aircraft to a free-flying model, conditions of dynamical similarity must be met or scaling procedures introduced. The scaling methods should correct the wind tunnel data regarding model support, wall interference, and lower Reynolds number. To include the necessary corrections, the current scaling techniques use computational fluid dynamics (CFD) in combination with measurements in cryogenic wind tunnels. There are a few methods that enable preliminary calculations of typical corrections considering specific measurement conditions and volume limitation of test section. The purpose of this paper is to present one possible approach to estimating corrections due to sting interference and difference in Reynolds number between the real airplane in cruise regime and its 1:100 model in the small wind tunnel AT-1. The analysis gives results for correction of axial and normal force coefficients. The results of this analysis indicate that the Reynolds number effects and the problem of installation of internal force balance are quite large. Therefore, the wind tunnel AT-1 has limited usage for aerodynamic coefficient determination of transport airplanes, like Dash 8 Q400 analyzed in this paper.

Tensile Failure Properties of the Perinatal, Neonatal, and Pediatric Cadaveric Cervical Spine

Biomechanical tensile testing of perinatal, neonatal, and pediatric cadaveric cervical spines to failure. To assess the tensile failure properties of the cervical spine from birth to adulthood. Pediatric cervical spine biomechanical studies have been few due to the limited availability of pediatric cadavers. Therefore, scaled data based on human adult and juvenile animal studies have been used to augment the limited pediatric cadaver data. Despite these efforts, substantial uncertainty remains in our understanding of pediatric cervical spine biomechanics. A total of 24 cadaveric osteoligamentous head-neck complexes, 20 weeks gestation to 18 years, were sectioned into segments (occiput-C2 [O-C2], C4-C5, and C6-C7) and tested in tension to determine axial stiffness, displacement at failure, and load-to-failure. Tensile stiffness-to-failure (N/mm) increased by age (O-C2: 23-fold, neonate: 22 ± 7, 18 yr: 504; C4-C5: 7-fold, neonate: 71 ± 14, 18 yr: 509; C6-C7: 7-fold, neonate: 64 ± 17, 18 yr: 456). Load-to-failure (N) increased by age (O-C2: 13-fold, neonate: 228 ± 40, 18 yr: 2888; C4-C5: 9-fold, neonate: 207 ± 63, 18 yr: 1831; C6-C7: 10-fold, neonate: 174 ± 41, 18 yr: 1720). Normalized displacement at failure (mm/mm) decreased by age (O-C2: 6-fold, neonate: 0.34 ± 0.076, 18 yr: 0.059; C4-C5: 3-fold, neonate: 0.092 ± 0.015, 18 yr: 0.035; C6-C7: 2-fold, neonate: 0.088 ± 0.019, 18 yr: 0.037). Cervical spine tensile stiffness-to-failure and load-to-failure increased nonlinearly, whereas normalized displacement at failure decreased nonlinearly, from birth to adulthood. Pronounced ligamentous laxity observed at younger ages in the O-C2 segment quantitatively supports the prevalence of spinal cord injury without radiographic abnormality in the pediatric population. This study provides important and previously unavailable data for validating pediatric cervical spine models, for evaluating current scaling techniques and animal surrogate models, and for the development of more biofidelic pediatric crash test dummies.

A Micropower Low-Noise Neural Recording Front-End Circuit for Epileptic Seizure Detection

This paper describes a micropower low-noise neural front-end circuit capable of recording epileptic fast ripples (FR). The front-end circuit consisting of a preamplifier followed by a 6th-order bandpass filter is designed for signal sensing in a future epileptic deep brain stimulator. A current-splitting technique is combined with an output-branch current scaling technique in a folded-cascode amplifier structure to improve the noise and power tradeoff in the preamplifier. In measurements, the preamplifier exhibits 39.4 dB DC gain, 0.36 Hz to 1.3 kHz of -3 dB bandwidth, and 3.07 μVrms total input-referred noise while consuming 2.4 μW from a 2.8 V power supply provided by an on-chip regulator circuit. A noise efficiency factor (NEF) of 3.09 is achieved with minimal power consumption and is one of the lowest published to date. The 6th-order follow-the-leader feedback elliptic bandpass filter passes FR signals and provides -110 dB/decade attenuation to out-of-band frequency components. In measurements, the entire front-end circuit achieves a mid-band gain of 38.5 dB, a bandwidth from 250 to 486 Hz, and a total input-referred noise of 2.48 μVrms while consuming 4.5 μW from the 2.8 V power supply. The front-end NEF achieved is 7.6. To the authors' knowledge, the proposed epileptic seizure- detection system is the first to achieve the FR-recording functionality. The chip is fabricated in a standard 0.6 μm CMOS process. Die size is 0.45 mm2.

A 10-bit 60-MS/s Low-Power CMOS Pipelined Analog-to-Digital Converter

A 10-bit 60-MS/s low-power CMOS pipelined analog-to-digital converter (ADC) is proposed. At the front-end, a timing-skew-insensitive double-sampled Miller-capacitance-based sample-and-hold circuit is employed to enhance the dynamic performance of the pipelined ADC. Bootstrapped switch achieves rail-to-rail signal swing at low-voltage power supply. Employing double sampling and bias current scaling techniques, very competitive power consumption can be achieved. The prototype chips have been fabricated and experimental results confirm the feasibility of this new technique.

Highly linear programmable balanced current scaling technique in moderate inversion

A technique to achieve highly linear current scaling in CMOS technologies is proposed. It is based on two balanced electronically programmable current mirrors operating in moderate inversion. The scaling factor can be continuously adjusted in a wide range. This technique can be employed to achieve or to extend gain adjustment in amplifiers. As an application example, a variable-gain differential current amplifier and a tunable transconductor are presented. Measurement results of the transconductor implemented in a 0.5-/spl mu/m CMOS technology validate in silicon the proposed approach.

Current scaling technique for high dynamic rangeswitched-current delta-sigma modulators

Thermal noise at the input usually imposes a fundamental limitation on the dynamic range of switched-current (SI) delta-sigma modulators. The authors present a technique for increasing the dynamic range of SI modulators without a drastic increase in power dissipation and chip area.

Scaled Physical Modeling of Steam-Injection Experiments

Summary Scaled model experiments are valuable aids to steamflood design and numerical simulation. Current scaling techniques, however, have limitations. Because the techniques require porous media and pressure conditions different from those in the field studied, pressure-dependent properties and porous media characteristics are not scaled accurately. This paper discusses scaling techniques that allow field porous media and pressure conditions to be used. The ability of scaling approaches to predict such parameters as oil production rate, temperature distribution, and pressure conditions is considered. The new approaches provide scaling options for steam processes that use additives (PVT properties must be scaled), that use pressure cycles (fluid compressibilities must be scaled), and that require use of the same porous medium as found in the field.