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EN
A novel dispersion-compensating fiber Bragg grating (FBG)-based en/decoder is proposed to compensate both the out-band and in-band dispersion in a time-spreading/wavelength-hopping (TS/WH) optical code-division multiplexing (OCDM) system. The experimental realization of such en/decoders only needs a uniform-pitch phase mask and a sub-micrometer precision moving stage. Such an en/decoder pair with the ability of compensating the dispersion of transmission in 20-km single mode fiber (SMF) is simulated and experimentally fabricated. Both the simulation and experimental results show that the decoded pulse can be recovered without any distortion owing to the elimination of dispersion.
EN
In this paper, the issue of the estimation of wave propagation characteristics in thermal media is dealt with. A formulation, named the Thermal Semi Analytical Finite Element, based on the semi analytical finite element approach coupled with the thermal effect is offered. Temperature variations affect the mechanical properties of the waveguide. The question of dispersion curves and group velocities is studied. This study is expected to be of use in the sensitivity analysis of guided waves for wave propagation in thermal environment. Comparisons between numerical and analytical results are given to show the effectiveness of the proposed approach.
EN
Selective flocculation of hematite with starch is a process well-known in practice. However, the separation of hematite from other minerals depends strongly on the methods of starch digestion performed either as heating-digestion or alkali-digestion (different type and dosage of alkali). The purpose of this study is to identify possible influence of the alkali-digested starch on flocculation of ultra-fine hematite when the starch was digested at different concentrations of sodium hydroxide at room temperature. Adsorption of starch digested with sodium hydroxide at different concentration on hematite was investigated by abstraction and co-precipitation tests. Turbidities tests, settling rates, flocculation/dispersion measurement and Fourier transform infrared spectroscopic analysis (FTIR) have also been conducted. Based on the results of the above mentioned tests it is suggested that the flocculating power of caustic digested starch towards fine particles may be significantly weakened, while its dispersing ability starts to play a role instead, if the concentration of sodium hydroxide is high enough in starch digestion. When the weight ratio of NaOH /starch is lower than 2, incomplete gelatinization of starch granules may lead to coagulation of fine particles of hematite mostly due to non-selective electrostatic attraction. The weight ratio of NaOH /starch from 2 to 4 helps to flocculate mineral surfaces selectively and efficiently, assuring a complete digestion of starch granules and a small amount of acidic functional products on the starch chain. However, much smaller and homogenous short-chain granules resulting from higher concentration of sodium hydroxide (the weight ratio of NaOH /starch is more than 4) used to digest starch may weaken the flocculating capacity of the caustized starch for hematite and lead to its dispersion.
EN
This article presents results of an analysis of impact of a designed discharge of contaminated water into the Dead Vistula (Wisła Martwa) in the region of the Isthmus (Przesmyk) with the aim of determination of a possible effect of the pollution onto protected areas of Natura 2000 (bird habitats and sites, especially the Bird Paradise – Ptasi Raj) nature reserve. The analysis was conducted on the basis of the two-dimensional modelling of unsteady transport of non-degradable dissolved matter. To this end, a numerical model of a section of the Dead Vistula was worked out. Four scenarios of hydro-dynamical conditions (2 – for average weather conditions and 2 – for stormy weather conditions) were selected. To solving the equation of pollution migration the finite volumes method (MOS) was applied. Two localizations of contaminated water discharge outlet were considered, namely: the first from the side of Siennicki Bridge before the Isthmus and the other in the section of the Brave Vistula (Wisła Śmiała) downstream the Isthmus. The obtained results made it possible to assess positively the first localization of the designed discharge outlet. In the other case there is a fear that at unfavourable hydro-meteorological conditions a water pollution may happen over Natura 2000 protected areas.
EN
This paper presents a soft glass spiral photonic crystal fiber with circular air holes for achieving high birefringence, large nonlinearity and large negative dispersion. The material used here for designing the fiber is soft glass (SF-57). A central defect air hole is being introduced in the core for achieving high birefringence and for different ellipticity ratios the effect of various optical properties of a photonic crystal fiber are studied. The structure proposed has a high birefringence in the order of 10–2, high nonlinearity of 5828 W–1km–1 and high negative dispersion of –1546.6 ps/nm•km at 0.850 μm. A numerical approach based on the finite element method is used for the design and simulation of the structure. Due to the optimization in the cladding air holes, the fiber can be used as polarization maintaining fibers, in dispersion compensation and other nonlinear applications.
EN
This work is concerned with the propagation of rapidly oscillating electromagnetic (EM) signal in a Lorentz dispersive medium. The problem considered here is 1-dimensional and its exact solution is described by a contour integral defined in a complex frequency plane. With the use of uniform asymptotic techniques, approximate representation for the total field consisting of the Sommerfeld and Brillouin precursors and the main signal is obtained. The effect of the rate of envelope changes, as well as of carrier frequency on the shape of the total signal is examined.
EN
The present article illustrates the modeling and optimization of a dual-slot waveguide for the application of a refractive index biosensor. The nanometer scale waveguide structure uses the silicon-on-insulator platform for the consideration of higher sensitivity and compactness of a resonator biosensor. The modal analysis is performed using the finite difference method based on full vector eigenmode calculation. The maximum field penetration in the lower index region is found for the quasi-TE mode. The sensitivity is maximized through the optimization of the waveguide dimension by relating effective refractive index with the dispersion of a waveguide. The biosensor showed the maximum calculated sensitivity of 461.327 nm/RIU and a limit-of-detection of 2.601 × 10–6 RIU (where RIU denotes refractive index unit).
EN
The deepest regression method is such a method of estimation of regression parameters that the maximal regression depth characterises the obtained model. In this paper the deeepest regression method is presented and the simulation analysis (Monte Carlo experiments) of dispersion of linear regression parameter estimates is conducted in case of data sets with different numbers of outliers. On the basis of the results of Monte Carlo experiments the characteristics of distribution of regression parameter estimates are determined and compared with the results of analogous experiments conducted with the use of the least square method.
PL
Metoda najgłębszej regresji polega na oszacowaniu parametrów liniowej funkcji regresji w taki sposób, aby uzyskanemu modelowi odpowiadała największa głębia regresyjna. W pracy przedstawiono charakterystykę metody najgłębszej regresji i przeprowadzono symulacyjną analizę (metodami Monte Carlo) zróżnicowania ocen parametrów modelu regresji liniowej uzyskanych tą metodą dla zbiorów danych zawierających różną liczbę obserwacji nietypowych. Na podstawie przeprowadzonych eksperymentów Monte Carlo wyznaczono charakterystyki rozkładu ocen parametrów i dokonano porównania otrzymanych wyników z wynikami analogicznych eksperymentów, w których do estymacji parametrów wykorzystano metodę najmniejszych kwadratów.
EN
The paper presents an opto-electronic system for antenna beam control and results of model system measurements.
EN
To implement the spectral Talbot effect in sampled fiber Bragg gratings (SFBGs), a hybrid technique based on a chirp effect and phase shifts is proposed. Firstly, the general phase condition is derived as the principle of this hybrid technique, and it also can be used to demonstrate other reported techniques, including the linear chirp, the periodical chirp, and the multiple phase shift technique. According to the general phase condition and the equivalent chirp coefficient in the Talbot effect, multi-channel dispersion compensators are designed with different arrangements of chirp coefficient and phase shifts. Moreover, the dispersion value can be tuned in these devices by dynamically adjusting the phase shifts of the hybrid technique. Numerical simulations are carried out to confirm the performance of such devices realized by using the hybrid technique.
11
Content available remote Contaminant transport in the surf zone
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EN
Dispersion of dissolved contaminants introduced at various locations within and just outside the surf zone are investigated. It is shown that the Longuet-Higgins model of surf-zone hydrodynamics adequately describes the distribution of longshore currents measured at the laboratory scale. Relations are derived between the longitudinal and transverse dispersion coefficients and the influencing parameters. The maximum longitudinal dispersion coefficients are associated with tracer releases near the breaker line, and longitudinal dispersion coefficients generally increase with travel time for distances up to at least 10 surf-zone widths. In contrast, transverse dispersion coefficients remain relatively constant for increasing travel time. The longitudinal and transverse dispersion coefficients can be significantly influenced by assumed values of local turbulent diffusion and cross-shore shear dispersion.
12
Content available A Physical Model of the Nonlinear Sitar String
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EN
The acoustic properties of the sitar string are studied with the aid of a physical model. The nonlinearity of the string movement caused by the bridge acting as an obstacle to the vibrating string is of special interest. Comparison of the model’s audio output to recordings of the instrument shows interesting similarities. The effects dispersion and bridge have on the sound of the instrument are demonstrated in the model.
13
Content available remote Surface modification of nano-TiN by using silane coupling agent
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EN
Titanium nitride (TiN) nano-particles were subjected to graft modification by silane coupling agent (KH-570) via a direct blending method. The hydroxyl groups on the surface of TiN nano-particles can interact with silanol groups [–Si–OCH3] of KH-570 forming an organic coating layer. The covalent bonds (Ti–O–Si) formation was testified by Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectroscopy (XPS). Through transmission electron micrograph (TEM) observations, it was found that KH-570 could improve the dispersibility of nano-TiN particles in ethyl acetate. Thermo gravimetric analysis (TGA) and contact angle measurements indicated that KH-570 molecules were adsorbed or anchored on the surface of nano-TiN particle and the net efficiency of it was 22.76 %, which facilitated to hinder the aggregation of nano-TiN particles.
14
Content available On elastodynamics of biperiodic composite media
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EN
The aim of this paper is twofold. First, we formulate a mathematical model for the analysis of waves propagating in a linear-elastic composite, which in every plane normal to a certain straight line has an identical periodic structure. Secong, we apply the derived model equations to the investigations of waves propagating across a laminated medium with periodically folded laminae. Lower and higher propagation speeds for the longtudinal and transversal waves are calculated and for the long waves represented in the form of simple asymptotic formulas.
PL
W artykule przedstawiono dwa problemy. Po pierwsze, sformułowano matematyczny model umożliwiający badanie propagacji fal w liniowo-sprężystych kompozytach, dla których każda płaszczyzna prostopadła do pewnej prostej ma taką samą dwuwymiarową strukturę periodyczną. Po drugie, otrzymany model zastosowano do analizy propagacji fal w laminacie o periodycznie pofałdowanych warstwach. Dla przypadku tego wyznaczono niższą i wyższą prędkość fazową propagacji, które w przypadku fal długich dają się wyrazić za pomocą prostych formuł asymptotycznych.
EN
A new model for water treatment and waste disposal reactors was developed. The startpoint to this model is a "triangular" approximation in the shape of the real flow-through curve. This approximation is defined by some characteristic points of time, which are strongly related to the characteristic velocities of wastewater. Combination of this simplified function with the kinetic equation of the reaction of the 1st order yields the sequence of the governing equations. Three practical examples show that the proposed "rational" model gives much better results than the traditional plug-flow model.
EN
In this paper, we investigated the transient electron population and the transient behaviour of the dispersion, absorption and refractive property of weak probe light in a four-level InGaN/GaN quantum dot nanostructure. In order to achieve the wave functions and their corresponding energy levels of the mentioned quantum dot nanostructure, the Schrödinger and Poisson equations is solved selfconsistently for carriers (here electron) in quantum dot. Our findings show that the properties of transient processes can be dramatically affected by parameters such as intensity, detuning and relative phase of applied fields. Our proposed scheme provides a realistic model for transient control of refraction index properties in a quantum dot nanostructure. These results may have potential applications in high speed optical switch for quantum information technologies.
17
Content available remote Particle simulations of dispersion using observed meandering and turbulence
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EN
A Lagrangian stochastic particle model driven by observed winds from a net-work of 13 sonic anemometers is used to simulate the transport of contaminates due to meandering of the mean wind vector and diffusion by turbulence. The turbulence and the meandering motions are extracted from the observed velocity variances using a variable averaging window width. Such partitioning enables determination of the separate contributions from turbulence and meandering to the total dispersion. The turbulence is described by a Markov Chain Monte Carlo process based on the Langevin equation using the observed turbulence variances. The meandering motions, not the turbulence, are primarily responsible for the 1-h averaged horizontal dispersion as measured by the travel time dependence of the particle position variances. As a result, the 1-h averaged horizontal concentration patterns are often characterized by streaks and multi-modal distributions. Time series of concentration at a fixed location are highly nonstationary even when the 1-h averaged spatial distribution is close to Gaussian. The results show that meandering dominates the travel-time dependence of the horizontal dispersion under all atmospheric conditions: weak and strong winds, and unstable and stable stratification.
18
Content available remote Flow and transport in channels with submerged vegetation
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EN
This paper reviews recent work on flow and transport in channels with submerged vegetation, including discussions of turbulence structure, mean velocity profiles, and dispersion. For submerged canopies of sufficient density, the dominant characteristic of the flow is the generation of a shear-layer at the top of the canopy. The shear-layer generates coherent vortices by Kelvin-Helmholtz (KH) instability. These vortices control the vertical exchange of mass and momentum, influencing both the mean velocity profile, as well as the turbulent diffusivity. For flexible canopies, the passage of the KH vortices generates a progressive wave along the canopy interface, termed monami. The KH vortices formed at the top of the canopy penetrate a distance ? e into the canopy. This penetration scale segregates the canopy into an upper layer of rapid transport and a lower layer of slow transport. Flushing of the upper canopy is enhanced by the energetic shear-scale vortices. In the lower layer turbulence is limited to length-scales set by the stem geometry, and the resulting transport is significantly slower than that of the upper layer.
19
Content available Five-wavelength laser microrefractometer
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EN
Corresponding author: In this paper, the design and testing of a five-wavelength laser microrefractometer are presented. Five semiconductor lasers are used for the spectral region of 405–1320 nm. The presented device is based on the critical angle method. In this case, the critical angle of total internal reflection is determined with the help of a CCD camera detecting the disappearance of the diffraction pattern, created by a metal diffraction grating. The samples of a thin liquid layer (< 10 μm) are placed between a flint-glass prism and a chromium diffraction grating. The refractive indices of two matching liquid products of Cargille Laboratories are investigated for the approbation of the presented device. The measured values of the refractive indices are used for the dispersion curves construction. The obtained values of the refractive indices are compared with the catalog data given by the manufacturer.
EN
A low-grade copper ore from Mpanda Mineral Field (MMF), Tanzania containing 0.90% Cu, 10.40% Fe and 58.3% SiO2 was subjected to beneficiation adopting selective dispersion, flocculation and flotation techniques. Based on the mineralogical characterization of the sample chalcopyrite, pyrite and quartz were identified as the major minerals. The isoelectric point of MMF ore was observed to be at pH 2.7, signifying that the ore was highly siliceous. The addition of sodium trisilicate and xanthan gum shifted the zeta potential of ore to more electronegative values. Adsorption of xanthan gum on chalcopyrite and silica indicated that the maximum adsorption was at pH 2.3 for chalcopyrite and the adsorption isotherm exhibited L2 type of the Giles classification. On the contrary, no adsorption of xanthan gum on silica was observed. The ground ore was selectively dispersed and flocculated at pH 9.7 using 30 ppm of sodium trisilicate and 30 ppm of xanthan gum. The grade of CuFeS2 was improved to 19.8% after 3 desliming stages. Flotation of the flocculated portion was carried out at pH 10.30 using 30 g/t of potassium amyl xanthate and potassium ethyl xanthate (1:1) , 40 g/t of Na2S as a sulphidising agent and methyl iso-butyl carbinol (MIBC) as a frother yielding a rougher concentrate with silica and chalcopyrite grades of 8.4% and 23.5% respectively with corresponding recoveries of 4.8% and 92.8% respectively. Additionally, rougher concentrate was subjected to cleaner flotation yielding silica and chalcopyrite grades of 1.8% and 29.2 % respectively and with recoveries of 1.2% and 89.1% respectively.
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