Phase unwrapping for 2-D blind deconvolution of ultrasound images

In most approaches to the problem of two-dimensional homomorphic deconvolution of ultrasound images, the estimation of a corresponding point-spread function (PSF) is necessarily the first stage in the process of image restoration. This estimation is usually performed in the Fourier domain by either successive or simultaneous estimation of the amplitude and phase of the Fourier transform (FT) of the PSE This paper addresses the problem of recovering the FT-phase of the PSF, which is an important reconstruction problem by itself. The purpose of this paper is twofold. First, it provides a theoretical framework, establishing that the FT-phase of the PSF can be effectively estimated by a proper smoothing of the FT-phase of the appropriate radio-frequency (RF) image. Second, it presents a novel approach to the estimation of the FT-phase of the PSF, by solving a continuous Poisson equation over a predefined smooth subspace, in contrast to the discrete Poisson equation solver used for the classical least mean squares phase unwrapping algorithms, followed by a smoothing procedure. The proposed approach is possible due to the distinct properties of the FT-phases, among which the most important property is the availability of precise values of their partial derivatives. This property overcomes the main disadvantage of the discrete schemes, which routinely use wrapped (principal) values of the phase in order to approximate its partial derivatives. Since such an approximation is feasible subject to the restriction that the partial phase differences do not exceed pi in absolute value, the discrete schemes perform satisfactory only for few practical situations. The proposed approach is shown to be independent of this restriction and, thus, it performs for a wider class of the phases with significantly lower errors. The main advantages of the novel method over the algorithms based on discrete schemes are demonstrated in a series of computer simulations and for in vivo measurements.     

Comparison of the effectiveness of four linearizing techniques used in SiGe HBT LNA at 1900 MHz and low-bias voltage

In this article, four linearizing techniques are compared with each other when they are used in a common-emitter SiGe HBT LNA. Finally, when all of them are employed together, improved linearity of the LNA is observed and more than 10 dBm of IIP3 and −5 dBm of 1-dB gain input compression point are realized when the circuit is fed with 2.4 V. © 2004 Wiley Periodicals, Inc. Int J RF and Microwave CAE 14, 144–152, 2004.     

On the structure and properties of high-nitrogen low-carbon non-austenitic steels

Phase transformations, when cooling and heating non-austenitic high-nitrogen low-carbon steels containing chromium and other alloying elements, as well as structure and mechanical properties of these steels were analyzed. It was confirmed that these steels have high temperature chromium diffusion controlled pearlitic type transformation and martensitic type transformation. Experimental high nitrogen steels after quenching and tempering provide mechanical properties of about the same level as high strength commercial alloyed steels. Features of nitrogen as an alloying element in steels discussed allow the supposition of a possible reduction of the consumption of nickel, manganese, molybdenum or tungsten in high strength alloyed steels.     

The optical absorption edge of rare earth sesquisulfides and alkaline earth - rare earth sulfides

Optical band gaps were measured by diffuse reflectance spectroscopy on a series of Ln₂S₃ compounds of α, δ, ε and τ structure types and on a series of ternary sulfides MLn₂S₄ (M = Sr, Cd, Mg) of Th₃P₄, CaFe₂O₄ and spinel structure types. Sharp absorption edges are observed with band gaps ranging from 2.2 to 3.5 eV. Systematic changes occur with rare earth radii. Analysis of some of the absorption edges suggests direct forbidden transitions.     

Flow stress,subgrain size,and subgrain stability at elevated temperature

Well defined subgrain boundaries dominate the microstructural changes occurring during plastic flow of polycrystalline metals at elevated temperature. The quantitative influence of subgrain size on elevated-temperature plastic flow is considered. Based on the results of tests under constant-stress and constant-structure conditions, an equation is developed which predicts the creep rate as a function of subgrain size, stress, diffusion coefficient, and elastic modulus. In general, the subgrain size is a unique function of the current modulus-compensated flow stress, but if fine subgrains can be introduced and stabilized, large increases in creep strength may result. The applicability of the phenomenological relation developed to the behavior of dispersion-strengthened materials (where the second-phase particles may predetermine the effective subgrain size) is discussed. When subgrain effects are included, it is shown that the creep rate is less dependent on stacking fault energy than has been previously thought. This paper is based on a presentation made at a symposium on “Mechanical-Thermal Processing and Dislocation Substructure Strengthening,” held at the Annual Meeting in Las Vegas, Nevada, on February 23, 1976, under the sponsorship of the TMS/IMD Heat Treating Committee.     

Nanoexplosion synthesis of multimetal oxide ceramic nanopowders

Herein we demonstrate a unique processing technique for engineering multicomponent ceramic nanopowders with precise morphologies by "nanoblast" calcination/deagglomeration. Multiple "nanoexplosions" of C(3)H(6)N(6)O(6) nanoparticles embedded in preliminary engineered nanoreactors break apart the agglomerates because of the highly energetic impacts of the blast waves. Also, the solid-solubility of one component into the other is enhanced by the extremely high local temperature generated during the nanoexplosions. We applied this technique to produce nanosized agglomerate-free ceria-gadolinia solid solution powder with an average aggregate size of 42 nm. The described method opens the door to the synthesis of a wide range of multimetal oxide ceramic and metal-ceramic composite nanopowders, with precise stoichiometries and uniform morphologies.     

Hypoxia in the Baltic Sea and basin-scale changes in phosphorus biogeochemistry

Deep-water oxygen concentrations in the Baltic Sea are influenced by eutrophication, but also by saltwater inflows from the North Sea. In the last two decades, only two major inflows have been recorded and the lack of major inflows is believed to have resulted in a long-term stagnation of the deepest bottom water. Analyzing data from 1970 to 2000 at the basin scale, we show that the estimated volume of water with oxygen, <2 mL L(-1), was actually at a minimum at the end of the longest so-called stagnation period on record. We also show that annual changes in dissolved inorganic phosphate water pools were positively correlated to the area of bottom covered by hypoxic water, but not to changes in total phosphorus load, thus addressing the legacy of eutrophication on a basinwide scale. The variations in phosphorus pools that have occurred during the past decades do not reflect any human action to reduce inputs. The long residence time and internally controlled variation of the large P pool in the Baltic Sea has important implications for management of both N and P inputs into this eutrophicated enclosed basin.     

Van der Waals SnSe2(1−x)S2x Alloys: Composition‐Dependent Bowing Coefficient and Electron–Phonon Interaction

The design of advanced functional materials with customized properties often requires the use of an alloy. This approach has been used for decades, but only recently to create van der Waals (vdW) alloys for applications in electronics, optoelectronics, and thermoelectrics. A route to engineering their physical properties is by mixing isoelectronic elements, as done for the SnSe_2(1?x)S_2x alloy. Here, by experiment and first‐principles modeling, it is shown that the value of x can be adjusted over a wide range, indicating good miscibility of the SnS₂ and SnSe₂ compounds. The x‐dependence of the indirect bandgap energy from E_ind = 1.20 eV for SnSe₂ to E_ind = 2.14 eV for SnS₂, corresponds to a large bowing coefficient b ≈ 1 eV, arising from volume deformation and charge exchange effects due to the different sizes and orbital energies of the S‐ and Se‐atoms. This also causes composition‐dependent phonon energy modes, electron–phonon interaction, and temperature dependence of E_ind. The alloys are exfoliable into thin layers with properties that depend on the composition, but only weakly on the layer thickness. This work shows that the electronic and vibrational properties of the SnSe_2(1?x)S_2x alloy and its thin layers provide a versatile platform for development and exploitation.