Dependence of the normalized radar cross section of water waves onBragg wavelength-wind speed sensitivity

Measurements of the normalized radar cross section (σ°) made by the YSCAT ultrawideband scatterometer during an extended deployment on the Canada Centre for Inland Waters (CCIW) Research Tower located at Lake Ontario are analyzed and compared with anemometer wind measurements to study the sensitivity of σ° to the wind speed as a function of the Bragg wavelength. This paper concentrates on upwind and downwind azimuth angles in the wind speed range of 4.5-12 m/s. While YSCAT collected measurements of σ° at a variety of frequencies and incidence angles, this paper focuses on frequencies of 2.0, 3.05, 5.30, 10.02, and 14.0 GHz and incidence angles within the Bragg regime, 30-50°. Adopting a power law model to describe the relationship between σ° and wind speed, both wind speed exponents and upwind/downwind (u/d) ratios of σ° are found using least squares linear regression. The analysis of the wind speed exponents and u/d ratios show that shorter Bragg wavelengths (Λ<4 cm) are the most sensitive to wind speed and direction. Additionally, vertical polarization (V-pol) σ° is shown to be more sensitive to wind speed than horizontal polarization (H-pol) σ, while the H-pol u/d ratio is larger than the V-pol u/d ratio     

The Kolmogorov complexity, universal distribution, and codingtheorem for generalized length functions

A function h(w) is said to be useful for the coding theorem if the coding theorem remains to be true when the lengths |w| of codewords w in it are replaced with h(w). For a codeword w=a₀a₁...a_m-1 of length m and an infinite sequence Q=(q₀, q₁, q₂, ...) of real numbers such that 0n⩽½, let |w|_Q denote the value Σ_n=0^m-1 (if a_n =0 then -log₂q_n, else -log₂(1-q _n)), that is, -log₂, (the probability that flippings of coins generate x) assuming that the (i+1)th coin generates a tail (or 0) with probability q_i. It is known that if 0n→∞ q_n then |w|_Q is useful for the coding theorem and if lim_n→∞ q _n/(1/(2ⁿ))=0 then |w|_Q is not useful. We introduce several variations of the coding theorem and show sufficient conditions for h(w) not to be useful for these variations. The usefulness is also defined for the expressions that define the Kolmogorov complexity and the universal distribution. We consider the relation among the usefulness for the coding theorem, that for the Kolmogorov complexity, and that for the universal distribution     

Perfect pseudoperiodic binary arrays

Arrays with good correlation properties are required for code-departure imaging, as well as for other applications of two-dimensional signal processing. Since binary arrays with perfect periodic autocorrelation are rather sparse. `pseudoperiodic' binary arrays are discussed. The transmitted binary array is correlated in the receiver with the same array which is surrounded periodically by similar ternary arrays. A construction method is presented that permits the construction of such `pseudoperiodic' binary arrays with perfect correlation properties for all sizes p₁^a1×p ₂^a2 (p₁, p₂ odd prime, a₁, a₂=1, 2, 3...)     

Electrical properties of Si p+-n junctions for sub-0.25μm CMOS fabricated by Ga FIB implantation

p⁺-n junction diodes for sub-0.25-μm CMOS circuits were fabricated using focused ion beam (FIB) Ga implantation into n-Si (100) substrates with background doping of N_b=(5-10)×10 ¹⁵ and N_b⁺=(1-10)×10¹⁷ cm^-3. Implant energy was varied from 2 to 50 keV at doses ranging from 1×10¹³ to 1×10¹⁵ cm^-2 with different scan speeds. Rapid thermal annealing (RTA) was performed at either 600 °C or 700°C for 30 s. Diodes fabricated on N_b⁺ with 10-keV Ga⁺ exhibited a leakage current (^I_R) 100× smaller than those fabricated with 50-keV Ga⁺. Tunneling was determined to be the major current transport mechanism for the diodes fabricated on N_b⁺ substrates. An optimal condition for I_R on N_b⁺ substrates was obtained at 15 keV/1×10¹⁵ cm^-2. Diodes annealed at 600°C were found to have an I_R 1000× smaller than those annealed at 700°C. I-V characteristics of diodes fabricated on N_b substrates with low-energy Ga⁺ showed no implant energy dependence. I-V characteristics were also measured as a function of temperature from 25 to 200°C. For diodes implanted with 15-keV Ga ⁺, the cross-over temperatures between I_diff and I_g-r occurred at 106°C for N_b ⁺ and at 91°C for N_b substrates     

An empirical model and an inversion technique for radar scatteringfrom bare soil surfaces

Polarimetric radar measurements were conducted for bare soil surfaces under a variety of roughness and moisture conditions at L -, C-, and X-band frequencies at incidence angles ranging from 10° to 70°. Using a laser profiler and dielectric probes, a complete and accurate set of ground truth data was collected for each surface condition, from which accurate measurements were made of the rms height, correlation length, and dielectric constant. Based on knowledge of the scattering behavior in limiting cases and the experimental observations, an empirical model was developed for σ°_hh, σ°_vv, and σ° _hv in terms of ks (where k=2π/λ is the wave number and s is the rms height) and the relative dielectric constant of the soil surface. The model, which was found to yield very good agreement with the backscattering measurements of the present study as well as with measurements reported in other investigations, was used to develop an inversion technique for predicting the rms height of the surface and its moisture content from multipolarized radar observations     

Wind vector retrieval using ERS-1 synthetic aperture radar imagery

An automated algorithm intended for operational use is developed and tested for estimating wind speed and direction using ERS-1 SAR imagery. The wind direction comes from the orientation of low frequency, linear signatures in the SAR imagery that the authors believe are manifestations of roll vortices within the planetary boundary layer. The wind direction thus has inherently a 180° ambiguity since only a single SAR image is used. Wind speed is estimated by using a new algorithm that utilizes both the estimated wind direction and σ ₀ values to invert radar cross section models. The authors show that: 1) on average the direction of the roll vortices signatures is approximately 11° to the right of the surface wind direction and can be used to estimate the surface wind direction to within ±19° and 2) utilizing these estimated wind directions from the SAR imagery subsequently improves wind speed estimation, generating errors of approximately ±1.2 m/s, for ERS-1 SAR data collected during the Norwegian Continental Shelf Experiment in 1991     

Comparison of transformation to low-resistivity phase andagglomeration of TiSi2 and CoSi2

The phase transformation and stability of TiSi₂ on n ⁺ diffusions are investigated. Narrower n⁺ diffusions require higher anneal temperatures, or longer anneal times, than wider diffusions for complete transitions from the high-resistivity C49 phase to the low-resistivity C54 phase. A model is presented which explains this in terms of the probability of forming C54 nuclei on narrow diffusions and the influence of diffusion width on C54 grain size. The results are that more C49 and C54 nucleation events are required to completely transform narrow lines. For thin TiSi₂ (40 nm), there is a narrow process window for achieving complete transformation without causing agglomeration of the TiSi₂. The process window decreases with decreasing silicide thickness. A significantly larger process window is achieved with short-time rapid annealing. Similar studies are performed for CoSi₂ on n⁺ and p⁺ diffusions. No linewidth dependence is observed for the transformation from CoSi_x to CoSi₂. There is a broad process window from 575°C to 850°C using furnace annealing, for which the low-resistivity phase is obtained without causing agglomeration     

On ternary complementary sequences

A pair of real-valued sequences A=(a₁,a₂,...,a_N) and B=(b₁,b ₂,...,b_N) is called complementary if the sum R(·) of their autocorrelation functions R_A(·) and R_B(·) satisfies R(τ)=R_A(τ)+R _B(τ)=Σ_i=1^N$ -^τa_ia_i+τ+Σ_j=1 ^N-τb_jb_j+τ=0, ∀τ≠0. In this paper we introduce a new family of complementary pairs of sequences over the alphabet α₃=+{1,-1,0}. The inclusion of zero in the alphabet, which may correspond to a pause in transmission, leads both to a better understanding of the conventional binary case, where the alphabet is α₂={+1,-1}, and to new nontrivial constructions over the ternary alphabet α₃. For every length N, we derive restrictions on the location of the zero elements and on the form of the member sequences of the pair. We also derive a bound on the minimum number of zeros necessary for the existence of a complementary pair of length N over α₃. The bound is tight, as it is met by some of the proposed constructions, for infinitely many lengths     

Rapid thermal anneal of gate oxides for low thermal budget TFT's

The performance and reliability of deposited gate oxides for thin film transistors (TFT's) has been studied as a function of rapid thermal annealing (RTA) conditions. The effect of temperature ranging from 700 to 950°C and the annealing ambients including oxygen (O₂), argon (Ar), and nitrous oxide (N₂O) is investigated. Improvement in charge to breakdown (Q_bd) is seen starting from 700°C, with marked increase at 900°C temperature and above. The N₂O and Ar ambients result in higher Q_bd compared to O₂ ambient and we attribute this to reduced interfacial stress. Fourier Transform Infrared spectroscopy (FTIR) is used to qualitatively measure the stress. The bias temperature instability is decreased by RTA. The TFT characteristics are significantly improved with RTA gate oxide. The RTA-Ar anneal at 950°C results in the lowest trap density in TFT's as measured from charge pumping technique     

95-GHz scattering by terrain at near-grazing incidence

This study, consisting of three complimentary topics, examines the millimeter-wave backscattering behavior of terrain at incidence angles extending between 70 and 90°, corresponding to grazing angles of 20° to 0°. The first topic addresses the character of the statistical variability of the radar backscattering cross section per unit area σ_A. Based on an evaluation of an extensive data set acquired at 95 GHz, it was determined that the Rayleigh fading model (which predicts that σ_A is exponentially distributed) provides an excellent fit to the measured data for various types of terrain covers, including bare surfaces, grasses, trees, dry snow, and wet snow. The second topic relates to the angular variability and dynamic range of the backscattering coefficient σ⁰, particularly near grazing incidence. We provide a summary of data reported to date for each of several types of terrain covers. The last topic focuses on bare surfaces. A semi-empirical model for σ⁰ is presented for vertical (VV), horizontal (HH), and cross (HV) polarizations. The model parameters include the incidence angle &thetas;, the surface relative dielectric constant ϵ, and the surface roughness ks, where k=2π/λ and s is the surface root mean square (RMS) height     

Electrical properties of low-temperature pyrolytic SiO2on InP

The first application of a new technique (SiH₄+O₂ at 83-330°C and 2-12 torr) for deposition of SiO₂ on InP is reported. SiO₂ deposited at 150-330°C has breakdown strength of 8-10 MV/cm, resistivity >10¹⁵ Ωcm, and refractive index of 1.45-1.46 comparable to thermal SiO ₂ grown at 1100°C. C/V measurements on Al/SiO₂/InP MIS structures suggest that very low temperature oxides (90-100°C) have the best interfacial properties     

Effect of tree structure on X-band microwave signature ofconifers

Experimental studies are performed on some coniferous trees, Austrian pine, Nordmann spruce, and Norway spruce, to investigate the relation between the tree architecture and radar signal at X-band. For a single tree, the radar cross section (RCS) is measured as a function of the scatterer location at 90° incidence. It is found that the main scatterers are the leafy branches, and the difference between σ_vv and σ_hh is significant at the upper portion of the tree. At the lower portion of the tree σ^o_vv and σ°_hh have almost the same level. For a group of trees the angular trends of σ°_vv and σ°_hh are measured. It is found that the levels of σ°_vv and σ° _hh are of the same order, but their angular trends vary from one tree species to the other, depending on the tree species structure. The experimental results are interpreted with the help of a theoretical model which accounts for the structure of the tree     

Design of active phase shifters based on multichannelheterojunction field effect transistors (MCHFET's)

Design criteria of active phase shifters based on GaAs/AlGaAs multichannel (MC) HFET in the frequency range 4-60 GHz are presented. The phase characteristics of MCHFET devices were studied using the computer aided design program TOUCHSTONE. The dependence of transmission phase on various intrinsic elements in the equivalent circuit model as a function of control gate bias was also studied. There are limited gate bias ranges which correspond to the active regions of the two conducting wells for which a quasi-linear continuous phase shift for analog applications was achieved. Continuously varying the gate bias from V_gs=-1.9 V to V_gs=-0.6 V results in a quasilinear phase shift of 10°, 15°, 21°, and 29° at f=12, 20, 30, and 60 GHz, respectively. Similarly, varying the gate bias from V_gs =-0.4 V to V_gs=0.7 V a quasi-linear phase shift of 21°, 26°, 27°, and 23° at f=12, 20, 30, and 60 GHz, respectively, was achieved. The gain variation was less than 3 dB in these bias regions. With digital applications in mind, a maximum differential phase shift of around 50° was obtained by switching the gate bias discretely. The transmission phase of single gate MCHFET mostly depends on variation of gate source capacitance with gate bias rather than on other intrinsic elements. The dependence of phase shift on various geometrical and structural parameters is also presented. To test the practicality of the device, other scattering parameters (e.g., S₁₁, S₂₂, S₁₂) and the noise figure (NF) were finally studied     

Accuracy of scatterometer-derived winds using the Cramer-Rao bound

A wind scatterometer makes measurements of the normalized radar-backscatter coefficient σ° of the ocean surface. To retrieve the wind, a geophysical model function (GMF), which relates σ° to the near-surface wind, is used. The wind vector can be estimated using maximum-likelihood techniques from several σ° measurements made at different azimuth angles. The probability density of the measured σ° is assumed to be Gaussian with a variance that depends on the true σ° and therefore, depends on the wind through the GMF. With this model for wind estimation, the Cramer-Rao (C-R) bound is derived for wind estimation, and its implications for wind retrieval are discussed. As part of this discussion, the role of geophysical modeling error is considered and shown to play a significant role in the performance of near-surface wind estimates. The C-R bound is illustrated using parameters from the ERS AMI, NSCAT, and Sea Winds scatterometers     

Electroless Ni-Cu-P barrier between Si/Ti/Al pad and Sn-Pbflip-chip solder bumps

This work investigates the barrier effect of the electroless Ni-Cu-P deposit between Al conductor and Sn-Pb solder bump, as well as the interfacial reaction with the Sn-Pb solder. For the Ni-Cu-P/63Sn-37Pb system, a (Ni, Cu)₃Sn₄ compound with three different morphologies: fine-grain, whisker, and polygon are formed at the Ni-Cu-P/63Sn-37Pb interface after reflow at 220°C for 15 s. These (Ni, Cu)₃Sn₄ crystals transform into polygon shape with smooth appearance during 150°C aging. For the Ni-Cu-P/95Pb-5Sn system, equiaxial (Ni, Cu)₃Sn₄ crystals are formed at the Ni-Cu-P/95Pb-5Sn interface after reflow at 350°C for 15 s, and they also transform into polygon shape during 150°C aging. In addition, the Ni-Cu-P deposit will crystallize to form Ni₅ P₂ during 350°C reflow. The growth of the (Ni, Cu)₃ Sn₄ compound by solid state reaction is a diffusion controlled process for both Ni-Cu-P/63Sn-37Pb and Ni-Cu-P/95Pb-5Sn systems. A 4 μm Ni-Cu-P deposit can provide adequate barrier function between an Al conductor and two Sn-Pb solders under 150°C aging for 1000 h     

Matrix-geometric solutions of M/G/1-type Markov chains: a unifyinggeneralized state-space approach

We present an algorithmic approach to find the stationary probability distribution of M/G/1-type Markov chains which arise frequently in performance analysis of computer and communication networks. The approach unifies finite- and infinite-level Markov chains of this type through a generalized state-space representation for the probability generating function of the stationary solution. When the underlying probability generating matrices are rational, the solution vector for level k, x_k, is shown to be in the matrix-geometric form x_k+1=gF^kH, k⩾0, for the infinite-level case, whereas it takes the modified form x_k+1=g₁F^k₁H₁+g ₂F^K-k-1₂H₂, 0⩽k⩽K, for the finite-level case. The matrix parameters in the above two expressions can be obtained by decomposing the generalized system into forward and backward subsystems, or, equivalently, by finding bases for certain generalized invariant subspaces of a regular pencil λE-A. We note that the computation of such bases can efficiently be carried out using advanced numerical linear algebra techniques including matrix-sign function iterations with quadratic convergence rates or ordered generalized Schur decomposition. The simplicity of the matrix-geometric form of the solution allows one to obtain various performance measures of interest easily, e.g., overflow probabilities and the moments of the level distribution, which is a significant advantage over conventional recursive methods     

Reduction of oxide charge and interface-trap density in MOScapacitors with ITO gates

The electrical properties of MOS capacitors with an indium tin oxide (ITO) gate are studied in terms of the number density of the fixed oxide charge and of the interface traps N_f and N _it, respectively. Both depend on the deposition conditions of ITO and the subsequent annealing procedures. The fixed oxide charge and the interface-trap density are minimized by depositing at a substrate temperature of 240°C at low power conditions and in an oxygen-rich ambient. Under these conditions, as-deposited ITO films are electrically conductive. The most effective annealing procedure consists of a two-step anneal: a 45-s rapid thermal anneal at 950°C in N₂, followed by a 30 min anneal in N₂/20% H₂ at 450°C. Typical values obtained for N_it and N_f are 4.2×10¹⁰ cm^-2 and 2.8×10¹⁰ cm^-2, respectively. These values are further reduced to 1.9×10¹⁰ cm^-2 and ≲5×10⁹ cm^-2, respectively, by depositing approximately 25 nm polycrystalline silicon on the gate insulation prior to the deposition of ITO     

Seasat over-land scatterometer data. I. Global overview of theKu-band backscatterer coefficients

Statistics on the backscatter coefficient σ⁰ from the Ku-band Seasat-A Satellite Scatterometer (SASS) collected over the world's land surfaces are presented. This spaceborne scatterometer provided data on σ⁰ between latitude 80° S and 80° N at incidence angles up to 70°. The global statistics of vertical (V) and horizontal (H) polarization backscatter coefficients for 10° bands in latitude are presented for incidence angles between 20° and 70° and compared with the Skylab and ground spectrometer results. Global images of the time-averaged V polarization σ⁰ at a 45° incidence angle and its dependence on the incidence angle are presented and compared to a generalized map of the terrain type. Global images of the differences between the V an H polarization backscatter coefficients are presented and discussed. The most inhomogeneous region, which contains the deserts of North Africa and the Arabian Peninsula, is studied in greater detail and compared with the terrain type     

Natural type selection in adaptive lossy compression

Consider approximate (lossy) matching of a source string ~P, with a random codebook generated from reproduction distribution Q, at a specified distortion d. Previous work determined the minimum coding rate R₁=R(P, Q, d) for this setting. We observe that for a large word length and with high probability, the matching codeword is typical with a distribution Q₁ which is different from Q. If a new random codebook is generated ~Q₁, then the source string will favor codewords which are typical with a new distribution Q₂, resulting in a minimum coding rate R₂=R(P, Q₁, d), and so on. We show that the sequences of distributions Q₁, Q ₂,... and rates R₁, R₂,..., generated by this procedure, converge to an optimum reproduction distribution Q*, and the rate-distortion function R(P, d), respectively. We also derive a fixed rate-distortion slope version of this natural type selection process. In the latter case, an iteration of the process stochastically simulates an iteration of the Blahut-Arimoto (1972) algorithm for rate-distortion function computation (without recourse to prior knowledge of the underlying source distribution). To strengthen these limit statements, we also characterize the steady-state error of these procedures when iterating at a finite string length. Implications of the main results provide fresh insights into the workings of lossy variants of the Lempel-Ziv algorithm for adaptive compression     

Viscosity of GeO2-doped silica glasses

The viscosity of GeO₂-doped silica glasses is experimentally evaluated and found to be expressed as a function of the monoexponential form η₀ exp(-AΔe), where η₀ is the viscosity of pure silica glass, A is a positive constant, and Δe is an equivalent relative-index difference that is introduced for a silica glass with nonuniform dopant distribution in its cross section. The constant A for GeO₂-doped silica glasses is found to be about 0.5, which is much smaller than that for fluorine-doped silica glasses and has almost no temperature dependence between 1400°C and 2200°C