Measurement of river surface currents with coherent microwave systems

River surface currents have been measured using coherent microwave systems from a bridge, a cableway, several riverbanks, a helicopter, and an airplane. In most cases, the microwave measurements have been compared with conventional measurements of near-surface currents and found to be accurate to within about 10 cm/s. In all cases, the basis for the microwave measurement of surface current is the Doppler shift induced in the signal backscattered from the rough water surface. In this paper, we outline the principles of the measurements and the various implementations that have been used to make microwave measurements of surface currents. Continuous-wave (CW) microwave systems have been used from a bridge to make long-term measurements of surface currents; these are compared with current-meter measurements and with time series of stage. A compact CW system has been developed and used on a cableway to measure surface currents at various distances across a river; these measurements have been compared with acoustic ones. Pulsed Doppler radars have been used to measure river surface currents from a riverbank, a helicopter, and an airplane. In the first two cases, comparisons with both current-meter and acoustic measurements have been made. We suggest that the CW system would be preferable to the pulsed Doppler radar to make such measurements from helicopters in the future. Finally, we consider the implications of our experiments for the measurement of surface currents from aircraft or satellites using interferometric synthetic aperture radars (INSARs). We find that a combination along-track, cross-track INSAR is necessary but that significant limitations are inherent in the technique.     

In situ calibration for quantitative ultrasonic imaging

We have considered the necessity of integral in situ calibration of acoustic properties for precision dimensional measurements and image rendering using ultrasound echo time-of-flight methods on living subjects. We have shown that by combining time-of-flight measurements over several paths with external measurements of transmitter and receiver locations generating those paths the relevant acoustic parameters and dimensional measurements can be extracted. It remains to be shown, theoretically and experimentally, that these methods can be successfully combined in a practical system that addresses natural geometries combining the impediments that we have herein addressed only separately     

射频磁控溅射法制备ZnO:Cu薄膜的磁性研究

ZnO films and ZnO：Cu diluted magnetic semiconductor films were prepared by radio frequency mag-netron sputtering on Si （111） substrates, with targets of ZnO and Zn0.99Cu0.01O, respectively. The plasma emission spectra were analyzed by using a grating monochromator during sputtering. The X-ray photoelectron spectroscopy measurements indicate the existence of Zni defect in the films, and the valence state of Cu is 1＋. The X-ray diffraction measurements indicate that the thin films have a hexagonal wurtzite structure and have a preferred orientation along the c-axis. The vibrating sample magnetometer measurements indicate that the sample is ferromagnetic at room temperature, and the origin of the magnetic behavior of the samples is discussed.     

CW and pulsed mode transfer impedance measurements in coaxialcables

Transfer impedance measurements have been performed both in frequency and time domains. CW measurements were performed using a matched triaxial system, a quintaxial system, and stripline injection. For nuclear electromagnetic pulse (NEMP) purposes, measurements up to a maximum frequency of 200 MHz are sufficient. For this frequency range the matched triaxial system was found to be the most convenient. Amplitude and phase measurements in different cables are discussed. Direct and indirect injection was employed in the time domain measurements. A delayed coupling is demonstrated when the diffusion term is dominant in the transfer impedance. In a magnetically shielded cable, hysteresis and saturation effects have been observed. At 5 kA the transfer impedance of the magnetically shielded cable increased by an order of magnitude due to saturation     

Measured spacecraft dynamic effects on atmospheric scienceinstruments

In September 1991, NASA launched the Upper Atmosphere Research Satellite (UARS). In addition to its atmospheric science mission, spacecraft dynamic effects on science measurements were analyzed. The investigation included two in-flight experiments to determine how each onboard instrument, subsystem, and environmental disturbance contributed to the spacecraft dynamic response and how these disturbances affected science measurements. Three case studies are presented that show the impact of spacecraft dynamic response on science measurements. The case studies have demonstrated that the influence of spacecraft dynamic response needs to be examined in most remote-sensing spacecraft that have attitude jitter levels commensurate to instrument pointing requirements. In the first case, correlation of independent atmospheric meridional wind measurements taken by two instruments with the spacecraft dynamic response demonstrated that excessive vibration (exceeding instrument pointing requirements) resulted in wind measurement disagreement. In the second case, solar array disturbances produced a spacecraft response signature on radiometer measurements. The signature explicitly demonstrated that if an instrument has sufficient spatial and temporal resolution, spacecraft dynamic response could impact measurements. In the final case, correlation of an instruments fine Sun-sensor data and CO₂ measurements demonstrated the effect of temporal and spatial sampling resolution and active pointing control on science measurements. The Sun sensor had a frequency modulated characteristic, due to spacecraft vibration and the periodic scanning of another instrument, which was not present on the CO₂ measurements     

Magnetic properties of ZnO:Cu thin films prepared by RF magnetron sputtering

ZnO films and ZnO:Cu diluted magnetic semiconductor films were prepared by radio frequency magnetron sputtering on Si (111) substrates, with targets of ZnO and Zn0.99Cu0.01 O, respectively. The plasma emission spectra were analyzed by using a grating monochromator during sputtering. The X-ray photoelectron spectroscopy measurements indicate the existence of Zni defect in the films, and the valence state of Cu is 1. The X-ray diffraction measurements indicate that the thin films have a hexagonal wurtzite structure and have a preferred orientation along the c-axis. The vibrating sample magnetometer measurements indicate that the sample is ferromagnetic at room temperature, and the origin of the magnetic behavior of the samples is discussed.     

Measurement of wall charge and capacitance variation for a single cell in the AC plasma display panel

Real-time dynamic measurements are performed on a single cell in a standard commercially available large plasma panel. The measurements determine cell response to variations in address pulses, sustain waveforms, or priming from neighboring cells. The wall-charge measurement indicates the internal dielectric surface charge and the capacitance measurement indicates the existence of a plasma in the gas volume. These measurements have shown that neighboring on cells can cause a large wall-charge transfer in off cells that results in reduced write and sustain voltage margins. Direct wall-charge measurements allows use of a simple technique for determination of the voltage transfer curve of the plasma cell which greatly aids device characterization. The capacitance measurement has shown that a plasma exists in commercial MgO panels for 10-15 µs after the discharge-current peak. The capacitance and wall-charge measurements can be combined to give simultaneous real-time results.     

Attenuation statistics in Italy as measured by the SIRIO satellite during its five year lifetime

The results of a campaign of attenuation measurements carried out by means of the Italian satellite SIRIO at the two frequencies 11.6 and 17.8 GHz are presented. The campaign lasted five years (1978- 1982) and yielded almost continuous measurements at the lower frequency (acquired in three Italian stations) and measurements for a considerable fraction of time at the higher one (acquired in two of the three stations). The major aim of these measurements was to acquire long-term statistics to be employed in future earth-space radiolink design. This objective has been fully accomplished, owing to the very long life of the satellite, and the acquired data have been already utilized, properly extrapolated in frequency, for designing the domestic satellite system Italsat planned to start in 1987. Year-to-year and site-to-site variation have been found to be very high. Conversely the ratio between equiprobable values of attenuation at the two frequencies has proved to be very similar in the two stations and rather stable across the attenuation range.     

Electrical characteristics of proton-implanted vertical-cavitysurface-emitting lasers

The electrical characteristics of proton-implanted GaAs quantum-well vertical-cavity surface-emitting semiconductor lasers (VCSELs) have been studied. We show that the 2 kT current, observed over many decades in these VCSELs, is primarily due to nonradiative recombination mechanisms. These include surface recombination at the edges of the proton-implanted region and bulk recombination at defects and heterojunction interface traps. The contribution of these mechanisms to the total nonradiative current and the threshold current density has been calculated. Lateral spontaneous emission measurements have been used to prove that the radiative current has a kT behavior in the subthreshold region. Electrical derivative measurements have been used to identify leakage current paths through the proton-implanted region in the low-bias regions. In addition, electrical derivative measurements have been used to measure the variation of series resistance with current near the lasing threshold. From a consideration of the various current paths in the VCSEL, a lumped circuit equivalent model for the VCSEL has been developed     

一种新的激光衍射粒度测试技术的研究

介绍了一种基于衍射的粒度测试新技术，其反演方法采用Shifrin变换，接受器件采用线性CCD。理论分析和对样品测试表明：该法仅需要很少的预知信息；可测得的直方图分布形式为详细的粒径连续分布；峰值粒径测量精度提高，其相对误差在3％左右。     

Model-based estimation with boundary side information or boundary regularization [cardiac emission CT

The authors have previously developed a model-based strategy for joint estimation of myocardial perfusion and boundaries using ECT (emission computed tomography). They have also reported difficulties with boundary estimation in low contrast and low count rate situations. Here they propose using boundary side information (obtainable from high resolution MRI and CT images) or boundary regularization to improve both perfusion and boundary estimation in these situations. To fuse boundary side information into the emission measurements, the authors formulate a joint log-likelihood function to include auxiliary boundary measurements as well as ECT projection measurements. In addition, they introduce registration parameters to align auxiliary boundary measurements with ECT measurements and jointly estimate these parameters with other parameters of interest from the composite measurements. In simulated PET O-15 water myocardial perfusion studies using a simplified model, the authors show that the joint estimation improves perfusion estimation performance and gives boundary alignment accuracy of <0.5 mm even at 0.2 million counts. They implement boundary regularization through formulating a penalized log-likelihood function. They also demonstrate in simulations that simultaneous regularization of the epicardial boundary and myocardial thickness gives comparable perfusion estimation accuracy with the use of boundary side information.     

Frequency-dependent electrical characteristics of GaAs MESFETs

Output resistance and transconductance of GaAs MESFETs have been observed to change significantly at very low frequencies. Extensive measurements of these characteristics as a function of device bias are reported. Direct measurements of the dispersive behavior between DC and 100 kHz and over a broad temperature range have been made on ion-implanted monolithic microwave IC (MMIC) devices. Conductance deep level transient spectroscopy (DLTS) and microwave S-parameter measurements have also been made to investigate this behavior. These measurements reveal that surface or channel-substrate interface traps in the material are most likely to be responsible for the observed behavior. A new equivalent-circuit model which accounts for many of the observed characteristics is developed. Unlike previously proposed equivalent circuits, the model does not rely on physically unrealistic circuit element values in order to obtain accurate performance predictions. The bias dependence of circuit element values is computed for one device. Effects not described by the model are also discussed     

LPE and VPE In1-xGaxAsyP1-y/InP: Transport properties, defects, and device considerations

The electrical properties of In1-xGaxAsyP1-yalloys lattice matched to InP, grown by liquid-phase and vapor-phase epitaxial techniques, have been determined by various measurements. Several electron and hole traps, with activation energies varying from 0.26 to 0.82 eV, have been identified by transient capacitance and photocapacitance measurements and their density and capture cross section have been measured. The 0.82 electron trap has emission and capture properties identical to the dominant 0.83 eV electron trap present in bulk and VPE GaAs. Hall measurements were made on the alloys in the temperature range of 20-600 K. Analysis of the mobility data has yielded the values of several transport parameters including the alloy scattering potentialDelta Uas a function of composition. The maximum value ofDelta U simeq 0.8eV corresponding to the bandgapE_{g} simeq 0.95eV. Photo-Hall measurements at low temperatures show the presence of donor- and acceptor-like defects in the LPE and VPE alloys, respectively. These centers exhibit persistent photoconductivity at low temperatures and have a high barrier energy (∼0.2 eV) associated with electron capture. Defects, which are possibly located in the interconduction-valley region, have been identified from analysis of Hall data forT > 400K. The strong temperature dependence of the threshold current in injection lasers and the large leakage currents near breakdown in avalanche photodiodes have been discussed in the fight of the defects identified in the present investigation.     

Experimental validation of surface scattering and emission models

Multifrequency polarimetric scattering and emissivity measurements have been carried out on three experimental dielectric models, characterized by random surfaces with different statistics. The results of the measurements have been compared with simulations obtained through physical models based on the classical approximations of physical optics (PO), geometrical optics (GO), small perturbation (SP), and integral equation model (IEM). The comparison of experimental data with theory has shown that, even when the parameters of the observed surface are well determined and known, some discrepancy may exist between models and measurements. Except for a few cases, this discrepancy is quite small and may be insignificant for many practical applications. The IEM has been proven to have a wider range of applicability with respect to other tested approximations     

Optics characterization of a 900-GHz HEB receiver for the ASTE telescope: design,measurement and tolerance analysis

The optics of a 900-GHz HEB receiver for the ASTE telescope have been analyzed by quasi-optical analysis and Physical Optics simulations in combination with beam pattern measurements. The disagreement between simulations and measurements has motivated an extensive campaign of Monte Carlo analyses to find out the cause of such a difference in results. Monte Carlo analyses have considered fabrication and assembly tolerances in all components in the RF chain, as well as some non-expected fabrication errors. This strategy has allowed determining the defective component. In short, the use of all available analyses techniques together with measurements has allowed singling out an underperforming element in an astronomical receiver. The change of this component will improve the optical efficiency and ease astronomical observations. These ideas can be of interest for any quasi-optical receiver at THz frequencies.     

Electro-thermal characterization of a differential temperature sensor in a 65 nm CMOS IC: Applications to gain monitoring in RF amplifiers

This paper reports on the design solutions and the different measurements we have done in order to characterize the thermal coupling and the performance of differential temperature sensors embedded in an integrated circuit implemented in a 65 nm CMOS technology. The on-chip temperature increases have been generated using diode-connected MOS transistors behaving as heat sources. Temperature measurements performed with the embedded sensor are corroborated with an infra-red camera and a laser interferometer used as thermometer. A 2 GHz linear power amplifier (PA) is as well embedded in the same silicon die. In this paper we show that temperature measurements performed with the embedded temperature sensor can be used to monitor the PA DC behavior and RF activity.     

Defects in molecular beam epitaxial GaAs grown at low temperatures

We have utilized a variable energy positron beam and infrared transmission spectroscopy to study defects in GaAs epilayers grown at low temperatures (LT-GaAs) by molecular beam epitaxy. We have measured the Doppler broadening of the positron-electron annihilation gamma ray spectra as a function of positron implantation energy. From these measurements, we have obtained results for the depth profiles of Ga monovacancies in unannealed LT-GaAs and Ga monovacancies and arsenic cluster related defects in annealed LT-GaAs. We have also studied the effects of the Si impurities in annealed LT-GaAs. The infrared transmission measurements on unannealed LT-GaAs furnish a broad defect band, related to As antisites, centered at 0.370 eV below the conduction band.     

Near field vector beam measurements at 1 THz

We have performed near-field vector beam measurements at 1.03 THz to characterize and align the receiver optics of a superconducting receiver. The signal source is a harmonic generator mounted on an X-Y translation stage. We model the measured two-dimensional complex beam pattern by a fundamental Gaussian mode, from which we derive the position of the beam center, the beam radius and the direction of propagation. By performing scans in the planes separated by 400 mm, we have confirmed that our beam pattern measurements are highly reliable.     

On the scattering mechanism of power lines at millimeter-waves

The radar signature of power lines is of high importance in the design of systems for helicopter collision avoidance. Laboratory measurements have been reported previously, but field measurements at millimeter waves are missing. The present contribution describes measurements done in ground-based configuration with a real aperture scanning-beam radar operating simultaneously at 35 and 94 GHz. By scanning, an aspect angle interval of 60/spl deg/ was covered, including the broadside aspect. The narrow beam width allowed to discriminate between different wires separated horizontally. While these measurements were done under a very shallow incidence angle, assisting measurements were done with the same radar mounted into an aircraft using synthetic aperture radar techniques. The results for shallow and steep incidence are compared and show the significant influence of this parameter on the signature of the power line. Additionally the measurement results are compared with those from model calculations.     

Microwave scatterometry in support of space-borne scientificmissions

The interpretation of satellite radar observations of the Earth's surface requires models to link the observations to physical processes. These models require validation through surface measurements. This paper describes a mobile radar scatterometer designed to complement the vertical incidence measurements of satellite radar altimeters. The instrument has been successfully deployed in Antarctica and an Australian desert to make measurements contemporaneous with satellite observations. The key findings from these field experiments are briefly described and results which have implications for synthetic aperture radar studies of similar terrain are presented