Two-dimensional phase unwrapping of subsampled phase-shifted interferograms

Abstract

A novel procedure for phase recovery from undersampled phaseshifted interferograms is described. First, synthetic interferograms are used to calculate the wrapped phase differences along two orthogonal directions. Second, they are unwrapped to recover the true Laplacian of the phase. The final step is to integrate the unwrapped phase differences to obtain the required phase. This method may be used with either path-independent or path-dependent phase unwrapping algorithms. The technique overcomes the sensitivity to noise of previous algorithms when low pass filtering techniques are applied during the calculation of the phase differences and least square methods are employed in the final step of phase integration.     

On telescope performance evaluation

Abstract

We analyse the imaging performance of synthetic-aperture optical systems (diluted aperture and segmented aperture) using the modulation transfer function. We select a single figure-of-merit, the functional cut-off frequency, over the traditional cut-off frequency, as the most useful one for assessing the optical performance of an instrument for its imaging capacity. A simplified aperture layout is proposed with the performance equivalent to that of the Keck telescope, incorporating a smaller number of segments. The detailed analysis in the spatial frequency plane leads us to observe that the central ring of the hexagons in the Keck telescope does not contribute to its resolution.     

How the online social networks are used: dialogues-based structure of MySpace

Quantitative study of collective dynamics in online social networks is a new challenge based on the abundance of empirical data. Conclusions, however, may depend on factors such as user''s psychology profiles and their reasons to use the online contacts. In this study, we have compiled and analysed two datasets from MySpace. The data contain networked dialogues occurring within a specified time depth, high temporal resolution and texts of messages, in which the emotion valence is assessed by using the SentiStrength classifier. Performing a comprehensive analysis, we obtain three groups of results: dynamic topology of the dialogues-based networks have a characteristic structure with Zipf''s distribution of communities, low link reciprocity and disassortative correlations. Overlaps supporting ‘weak-ties’ hypothesis are found to follow the laws recently conjectured for online games. Long-range temporal correlations and persistent fluctuations occur in the time series of messages carrying positive (negative) emotion; patterns of user communications have dominant positive emotion (attractiveness) and strong impact of circadian cycles and interactivity times longer than 1 day. Taken together, these results give a new insight into the functioning of online social networks and unveil the importance of the amount of information and emotion that is communicated along the social links. All data used in this study are fully anonymized.     

Growth of Dense Single Crystals of Potassium Sodium Niobate by a Combination of Solid-State Crystal Growth and Hot Pressing

(K_0.5Na_0.5)NbO₃ (KNN) is a potential lead-free replacement for Pb(Zr, Ti)O₃ (PZT) piezoceramics, but its piezoelectric properties are inferior to those of PZT. By growing single crystals of KNN, it may be possible to improve the piezoelectric properties. Recently, single crystals of KNN were grown by the solid-state crystal growth (SSCG) method, but the crystals were very porous. In this paper, a method of growing dense single crystals by SSCG in a hot press will be described. (110)-oriented single seed crystals of KTaO₃ were buried in KNN powder, with 0.5 mol% of K₄CuNb₈O₂₃ added as a sintering aid. After consolidation by uniaxial and isostatic pressing, the tablets were hot pressed in a two-stage treatment. During hot pressing, dense single crystals of KNN grew using the KTaO₃ seed crystal as a template. The effect of hot pressing on single crystal growth will be discussed.     

Modeling of kinetics of pertechnetate removal by amino-functionalized glycidyl methacrylate copolymer

Technetium-99 comprises a significant health risk, since edible plants can bioaccumulate and convert it to more lipophilic species that cannot be excreted through urine. Batch kinetics of pertechnetate removal from aqueous solutions by two samples of crosslinked poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) functionalized with diethylene triamine (PGME-deta) was investigated at the optimum pH value of 3.0, and the initial solution activity of 325 MBq dm⁻³. PGME-deta was characterized by elemental analysis, mercury intrusion porosimetry, and scanning electron microscopy. Five kinetic models (pseudo-first, pseudo-second order, Elovich, Bangham, and intraparticle diffusion) were used to determine the best-fit equation for pertechnetate sorption. After 24 h, PGME-deta samples sorbed more than 98% of pertechnetate present, with maximum sorption capacity of 25.5 MBq g⁻¹, showing good potential for remediation of slightly contaminated groundwater.     

Synthesis, structural and magnetic properties of nanostructured Ca0.9Gd0.1MnO3 obtained by modified glycine nitrate procedure (MGNP)

Ca_0.9Gd_0.1MnO₃ nanopowders with perovskite type crystal structure were synthesized by modified glycine nitrate procedure. Nanopowders were prepared by combining glycine with metal nitrates and/or metal acetates in their appropriate stoichiometric ratios. Modification of the procedure was performed by partial replacement of nitrates by acetates, in order to control the burn-up reaction. Obtained Ca_0.9Gd_0.1MnO₃ powders were calcinated in the temperature interval from 850 °C to 950 °C for 10 min. Properties such as phase evolution, lattice parameters, chemical composition and magnetic properties were monitored by DTA, X-ray diffraction, SEM/EDS and magnetic measurements. Magnetic measurements performed at the sample with the smallest crystallite size showed that a 10% of Gd³⁺ substituted Ca²⁺ ions changes antiferromagnetic properties of CaMnO₃ by the introduction of ferromagnetic interaction due to a double exchange between Mn³⁺ and Mn⁴⁺ ions. Presence of competing interactions and their randomness lead to a formation of a spin glass state below Neel temperature T_N = 110 K. From the high temperature magnetic susceptibility measurements effective magnetic moment of manganese ions is determined which lies between the values for Mn³⁺ and Mn⁴⁺ ions.     

Synthesis and characterization of novel urethane‐siloxane copolymers with a high content of PCL‐PDMS‐PCL segments

Novel polyurethane copolymers derived from 4,4′‐methylenediphenyl diisocyanate (MDI), 1,4‐butanediol (BD) and α,ω‐dihydroxy‐[poly(caprolactone)‐poly (dimethylsiloxane)‐poly(caprolactone)] (α,ω‐dihydroxy‐(PCL‐PDMS‐PCL); = 6100 g mol^?1) were synthesized by a two‐step polyaddition reaction in solution. In the synthesis of the polyurethanes, the PCL blocks served as a compatibilizer between the nonpolar PDMS blocks and the polar comonomers, MDI and BD. The synthesis of thermoplastic polyurethanes (TPU) with high soft segment contents was optimized in terms of the concentrations of the reactants, the molar ratio of the NCO/OH groups, and the time and temperature of the polyaddition reaction. The structure, composition, and hard MDI/BD segment length of the synthesized polyurethane copolymers were determined by ¹H, ¹³C‐NMR, and two‐dimensional correlation (COSY, HSQC, and HMBC) spectroscopy, while the hydrogen bonding interactions in the copolymers were analyzed by FT‐IR spectroscopy. The influence of the reaction conditions on the structure, molecular weight, thermal, and some physical properties was studied at constant composition of the reaction mixture. A change in the molar ratio of the NCO/OH groups and the reaction conditions modified not only the molecular weight of the synthesized polyurethanes, but also the microstructure and therefore the thermal and physical properties of the copolymers. It was demonstrated that only PCL segments with high soft segment contents crystallize, thereby showing spherulitic morphology. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Endotoxin and biogenic amine levels in Atlantic mackerel (Scomber scombrus), sardine (Sardina pilchardus) and Mediterranean hake (Merluccius merluccius) stored at 22 °C

Whole Atlantic mackerel (Scomber scombrus), sardine (Sardina pilchardus) and Mediterranean hake (Merluccius merluccius) from the Croatian Adriatic were stored at 22 °C and changes in histamine, putrescine, tyramine and cadaverine levels were monitored in relation to bacterial endotoxin. After 12 h, histamine levels in sardine were above the legal limit of 50 mg kg^?1, set by the US Food and Drug Administration, and an increase in putrescine content preceded the increase in histamine. After 24 h, histamine contents in mackerel and sardine reached 1090 ± 101 and 577 ± 275 mg kg^?1, respectively, which exceeded the toxic threshold of 500 mg kg^?1. At the same time, the putrescine content was also high in both fish (353–420 mg kg^?1). The time-course of endotoxin production was similar in all fish species stored at 22 °C. A high correlation was found between endotoxin and histamine, and between endotoxin and putrescine in mackerel and sardine. On the other hand, high endotoxin levels in hake, after 24 h, were associated with the low histamine and putrescine content (40–60 mg kg^?1).     

Crystallization of Zirconium-Rich PLZT Thin Films Below 500°C

The general problem of processing zirconium-rich lead-lanthanum-zirconate-titanate (PLZT) thin films at the commonly used temperatures between 600 and 650 C is lead-oxide loss, leading to the formation of a non-ferroelectric, surface pyrochlore-type phase. To avoid lead-oxide losses due to sublimation and/or the interaction of the film with the substrate, it is desirable that the annealing temperatures are as low as possible. Our goal was to study and prepare perovskite PLZT 9.5/65/35 (Pb 0.858 La 0.095 Zr 0.65 Ti 0.35 O 3 ) thin films below 500 C. At 400 C the growth of the perovskite phase follows the parabolic law typical of diffusion controlled processes. During prolonged annealing growth continues until the limiting stoichiometry of the perovskite phase with regard to the PbO is reached. We conclude that, even at this low temperature the amount of PbO in the film is the critical factor in the crystallization of the perovskite phase.