Diurnal thermal cycling effects on microwave signatures of thin seaice

To investigate effects of diurnal thermal cycles on C-band polarimetric backscatter and millimeter-wave emission from sea ice, the authors carried out a winter experiment at the outdoor geophysical research facility (GRF) in the cold regions research and engineering laboratory (CRREL), the ice sheet grew from open sea water to a thickness of 10 cm in 2.5 days, during which they took polarimetric backscatter data with a C-band scatterometer, interlaced with brightness temperature measurements at 90 GHz in conjunction with meteorological and sea ice characterizations. The initial ice growth in the late morning was slow due to high insolation. As the air temperature dropped during the night, the growth rate increased significantly. Air temperature changed drastically from about -12 to -36°C between day and night, the diurnal thermal cycle repeated itself the next day and the growth rate varied in the same manner. Ice temperature profiles clearly show the diurnal response in the ice sheet with a lag of 2.5 h behind the time of the maximum short-wave incident solar radiation. The diurnal cycles are also evident in the millimeter-wave brightness temperature data, measured sea ice backscatter revealed substantial diurnal variations up to 6 dB with repeatable cycles in synchronization with the temperature cycles and the brightness temperature modulations, the diurnal cycles in backscatter indicate that the dominant scattering mechanism related to thermodynamic processes in sea ice is reversible, a diurnal backscatter model based on sea ice electrodynamics and thermodynamics explains the observed diurnal signature. This work shows that diurnal effects are important for inversion algorithms to retrieve sea ice geophysical parameters from remote sensing data acquired with a satellite synthetic aperture radar (SAR) or scatterometer on Sun-synchronous orbits     

Triangular ray-tube analysis of dielectric lens antennas

A new method of analysis for the radiation characteristics of dielectric lens antennas with arbitrary inner and outer surfaces is presented. The analysis is based on representing the feed illumination by a contiguous set of ray tubes and including the effects of surface reflections and ray divergence. Radiation patterns and the antenna gain are then computed by evaluating the closed-form expressions developed for the Kirchhoff's integral of the aperture fields. The validity of the analysis method has been demonstrated by comparing the computations with measured results of two different spherical lenses and a shaped lens configurations. The analysis method presented takes into account some of the practical aspects associated with lens design such as surface zoning to reduce the mass and surface matching to minimize the reflection loss     

On-chip high voltage charge pump in standard low voltage CMOS process

An on-chip high voltage tolerant 4VDD charge pump with symmetrical architecture in a standard low voltage 1.8 V 0.18 /spl mu/m CMOS process is presented. For a 250 k/spl Omega/ load, circuit efficiency of the charge pump is approximately 71%. All the MOS transistors satisfy typical voltage stress related reliability requirements for standard low voltage CMOS devices.     

A systematic design method to obtain broadband characteristics for singly-fed electromagnetically coupled patch antennas for circular polarization

We present a systematic, empirical design technique to obtain optimum broadband impedance, axial-ratio (AR) and gain bandwidths for a singly-fed electromagnetically coupled patch antenna for circular polarization. Our investigation has also revealed tradeoffs amongst obtainable AR, impedance bandwidth and AR bandwidth. Using two design examples at different frequency bands and for different senses of circular polarization, we have demonstrated the effectiveness of the proposed knowledge-based tuning method. We have obtained at C-band measured values of impedance bandwidth (VSWR/spl les/2) equal to 43%, 3-dB AR bandwidth of 8%, AR of less than 0.3 dB and a mean gain level of 7 dB. For the Ku-band element, a 40% impedance bandwidth and a 17.3% of 3-dB AR bandwidth have been obtained with a peak gain of 7.2 dBic.     

Hash function based on block cipher

A new 2m-bit iterated hash function based on an m-bit block cipher with a 2m-bit key is presented. The results of security analysis show that the hash function can be expected to have ideal computational security against the five attacks when the underlying cipher is assumed to have no weakness     

The slot-coupled hemispherical dielectric resonator antenna with a parasitic patch: applications to the circularly polarized antenna and wide-band antenna

The aperture-coupled hemispherical dielectric resonator antenna (DRA) with a parasitic patch is studied rigorously. Using the Green's function approach, integral equations for the unknown patch and slot currents are formulated and solved using the method of moments. The theory is utilized to design a circularly polarized (CP) DRA and a wide-band linearly polarized (LP) DRA. In the former, the CP frequency and axial ratio (AR) can easily be controlled by the patch location and patch size, respectively, with the impedance matched by varying the slot length and microstrip stub length. It is important that the AR will not be affected when the input impedance is tuned, and the CP design is therefore greatly facilitated. For the wide-band LP antenna, a maximum bandwidth of 22% can be obtained, which is much wider than the previous bandwidth of 7.5% with no parasitic patches. Finally, the frequency-tuning characteristics of the proposed antenna are discussed. Since the parasitic patch can be applied to any DRAs, the method will find applications in practical DRA designs.     

Diode-HBT-logic circuits monolithically integrable with ECl/CMLcircuits

A novel logic approach, diode-HBT logic (DHL), that is implemented with GaAlAs/GaAs HBTs and Schottky diodes to provide high-density and low-power digital circuit operation is described. This logic family was realized with the same technology used to produce emitter-coupled-logic/current-mode-logic (ECL/CML) circuits. The logic operation was demonstrated with a 19-stage ring oscillator and a frequency divider. A gate delay of 160 ps was measured with 1.1 mW of power per gate. The divider worked properly up to 6 GHz. Layouts of a DHL flip-flop and divider showed that circuit area and transistor count can be reduced by about a factor of 3, relative to ECL/CML circuits. The new logic approach allows monolithic integration of high-speed ECL/CML circuits with high-density DHL circuits with high-density DHL circuits     

Ultraviolet photolysis of CH2I2 in methanol: O-H insertion and HI elimination reactions to form a dimethoxymethane product

Ultraviolet photolysis of low concentrations of CH2I2 in methanol solution found that CH2I2 is converted into dimethoxymethane and some H+ and I- products. Picosecond time-resolved resonance Raman (ps-TR3) experiments observed that the isodiiodomethane (CH2I-I) photoproduct decayed faster as the concentration of methanol increases, suggesting that isodiiodomethane is reacting with methanol. Ab initio calculations indicate isodiiodomethane is able to react with methanol via an O-H insertion/HI elimination to form an iodoether (ICH2-O-CH3) and HI products. The iodoether can then further react via another O-H insertion/HI elimination reaction to form the dimethoxymethane (CH3-O-CH2-O-CH3) observed in the photochemistry experiments. A reaction mechanism consistent with these experimental and theoretical observations is proposed.     

Comparison of the dehalogenation of dihalomethanes (CH2XI, where X = Cl, Br, I) following ultraviolet photolysis in aqueous and NaCl saltwater environments

The ultraviolet photolysis of low concentrations of CH(2)XI (X = Cl, Br, I) were investigated in water and saltwater solutions by photochemistry and picosecond time-resolved resonance Raman spectroscopy. Photolysis in both kinds of solutions formed mostly CH(2)(OH)(2) and HI and HX products. However, photolysis of the CH(2)XI molecules in saltwater resulted in production of some CH(2)XCl products not observed in aqueous solutions without salt present. The appearance of these new products in saltwater solutions is accompanied by a decrease in the amount of CH(2)(OH)(2), HI, and HX products compared to photolysis in aqueous solutions without salt present. The possible implications for photolysis of CH(2)XI and other polyhalomethanes in seawater and other salt aqueous environments compared to nonsaltwater solvated environments is briefly discussed.