Solution of inverse problem of light beating spectroscopy using Tikhonov method of regularization for analyzing polydisperse suspensions of nanoparticles

The results of a numerical solution of the inverse problem of light beating spectroscopy using the Tikhonov regularization method are presented. The developed algorithm takes into account the positivity of the solution and the constant background signal. The regularization parameter of the method is determined based on the a priori information on the noise amplitude of the input signal. The results of the reconstruction of model uni-, bi-, and multimodal distributions are presented. For examples of numerically generated spectra, the effects of the measured spectrum noise, background signal, and frequency bandwidth of the signal measurement on the characteristics of the reconstructed distributions are studied.     

Comparison of electric light scattering and birefringence for polydisperse suspensions

Summary A review is made of the existing theoretical expressions, describing the change of the scattered light intensity and the birefringence by application of an electrical field to a colloid solution.Furthermore, the geometrical functions for disc-shaped particles are calculated in this article for the case of electric light scattering and are. presented graphically. In addition, expressions are derived for the average value of the electrical polarizability () for the case of polydisperse solutions.

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Zusammenfassung Es wird ein überblick über die existierenden theoretischen Beziehungen gegeben, die die Änderung der Intensität des Streulichtes und der Doppelbrechung von Kolloidsuspensionen im elektrischen Feld beschreiben.Weiterhin sind die geometrischen Funktionen für scheibchenförmige Teilchen in dieser Arbeit für den Fall der elektrooptischen Lichtstreuung berechnet und grafisch dargestellt. Außerdem werden Beziehungen für den Mittelwert der elektrischen Polarisierbarkeit () für den Fall polydisperser Suspensionen abgeleitet.

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With 1 figure and 1 table     

Using light scattering to evaluate the separation of polydisperse nanoparticles

The analysis of natural and otherwise complex samples is challenging and yields uncertainty about the accuracy and precision of measurements. Here we present a practical tool to assess relative accuracy among separation protocols for techniques using light scattering detection. Due to the highly non-linear relationship between particle size and the intensity of scattered light, a few large particles may obfuscate greater numbers of small particles. Therefore, insufficiently separated mixtures may result in an overestimate of the average measured particle size. Complete separation of complex samples is needed to mitigate this challenge. A separation protocol can be considered improved if the average measured size is smaller than a previous separation protocol. Further, the protocol resulting in the smallest average measured particle size yields the best separation among those explored. If the differential in average measured size between protocols is less than the measurement uncertainty, then the selected protocols are of equivalent precision. As a demonstration, this assessment metric is applied to optimization of cross flow (V_x) protocols in asymmetric flow field flow fractionation (AF⁴) separation interfaced with online quasi-elastic light scattering (QELS) detection using mixtures of polystyrene beads spanning a large size range. Using this assessment metric, the V_x parameter was modulated to improve separation until the average measured size of the mixture was in statistical agreement with the calculated average size of particles in the mixture. While we demonstrate this metric by improving AF⁴V_x protocols, it can be applied to any given separation parameters for separation techniques that employ dynamic light scattering detectors.     

Application of error-ranked singular value decomposition for the determination of potential-derived atomic-centered point charges

The present work provides a detailed investigation on the use of singular value decomposition (SVD) to solve the linear least-squares problem (LLS) for the purposes of obtaining potential-derived atom-centered point charges (PD charges) from the ab initio molecular electrostatic potential (V(QM)). Given the SVD of any PD charge calculation LLS problem, it was concluded that (1) all singular vectors are not necessary to obtain the optimal set of PD charges and (2) the most effective set of singular vectors do not necessarily correspond to those with the largest singular values. It is shown that the efficient use of singular vectors can provide statistically well-defined PD charges when compared with conventional PD charge calculation methods without sacrificing the agreement with V(QM). As can be expected, the methodology outlined here is independent of the algorithm for sampling V(QM) as well as the basis set used to calculate V(QM). An algorithm is provided to select the best set of singular vectors used for optimal PD charge calculations. To minimize the subjective comparisons of different PD charge sets, we also provide an objective criterion for determining if two sets of PD charges are significantly different from one another.     

Solution of the mean spherical approximation for polydisperse multi-Yukawa hard-sphere fluid mixture using orthogonal polynomial expansions

The Blum-Hoye [J. Stat. Phys. 19 317 (1978)] solution of the mean spherical approximation for a multicomponent multi-Yukawa hard-sphere fluid is extended to a polydisperse multi-Yukawa hard-sphere fluid. Our extension is based on the application of the orthogonal polynomial expansion method of Lado [Phys. Rev. E 54, 4411 (1996)]. Closed form analytical expressions for the structural and thermodynamic properties of the model are presented. They are given in terms of the parameters that follow directly from the solution. By way of illustration the method of solution is applied to describe the thermodynamic properties of the one- and two-Yukawa versions of the model.     

Simultaneous spectrophotometric determinations of cobalt, nickel and copper using partial least squares based on singular value decomposition

The partial least squares modeling based on singular value decomposition was applied for the simultaneous spectrophotometric determination of Co(II), Ni(II) and Cu(II) as their ammonium 2-amino-1-cyclohexan-1-dithiocarbamate complexes. The latent variable calculation in this partial least squares modeling is not an iterative technique. The detection limits for Co(II), Ni(II) and Cu(II) were 0.072, 0.021 and 0.063 mug/ml, respectively. The application of the method was confirmed by analysis of these metals in sample alloys.     

A method for monitoring the composition of suspensions

The concentrations of particulates in dispersion media, as well as of true solutions, were analyzed by ratiometric method. The error in determination of the concentrations was estimated for the ratiometric, as well as for the conventional procedure based on the calibration connection equations.     

Electrical impedance spectroscopy for detection of bacterial cells in suspensions using interdigitated microelectrodes

In this study, we present a new, simple and rapid impedance method to detect bacterial cells by making use of the impedance properties of bacterial cell suspensions using interdigitated microelectrodes. It was found that bacterial cell suspensions in deionized (DI) water with different cell concentrations could generate different electrical impedance spectral responses, whereas cell suspensions in phosphate buffered saline (PBS) solution could not produce any significant differences in impedance spectra in response to different cell concentrations. In DI water suspensions, impedance at 1 kHz decreased with the increasing cell concentrations in the suspensions. The impedance of cell suspensions in DI water was discussed and found that it was resulted from the cell wall charges and the release of ions or other osmolytes from the cells. A linear relationship between the impedance and the logarithmic value of the cell concentration was found in the cell concentration range from 10⁶ to 10¹⁰ cfu/ml, which can be expressed by a regression equation of Z (kΩ) = −2.06 log C (cells/20 μl) + 5.23 with R² = 0.98. The detection limit was calculated to be 3.45 × 10⁶ cfu/ml, which is comparable with many label-free immunosensors for detection of pathogenic bacteria reported in the literature. To achieve the selectivity of this method, we also demonstrated the feasibility of integrating magnetic separation to this impedance method. This study has demonstrated that bacterial cell concentration can be inferred by measuring the impedance of cell suspensions in DI water. This new detection mechanism could be an alternative to current impedance methods that have been reported for the detection of bacterial cells, e.g. impedance microbiology and electrical/electrochemical impedance biosensors.     

Glutathione-capped CuO nanoparticles for the determination of cystine using resonance Rayleigh scattering spectroscopy

Microchimica Acta - A porous hydrophilic affinity bead consisting of graphene oxide and chitosan (pGC) with the honeycomb-biomimetic microchannels has been synthesized and applied as...     

Dynamics of hard sphere suspensions using dynamic light scattering and X-ray photon correlation spectroscopy: dynamics and scaling of the intermediate scattering function

Intermediate scattering functions are measured for colloidal hard sphere systems using both dynamic light scattering and x-ray photon correlation spectroscopy. We compare the techniques, and discuss the advantages and disadvantages of each. Both techniques agree in the overlapping range of scattering vectors. We investigate the scaling behavior found by Segré and Pusey [Phys. Rev. Lett. 77, 771 (1996)] but challenged by Lurio et al. [Phys. Rev. Lett. 84, 785 (2000)]. We observe a scaling behavior over several decades in time but not in the long-time regime. Moreover, we do not observe long-time diffusive regimes at scattering vectors away from the peak of the structure factor and so question the existence of long-time diffusion coefficients at these scattering vectors.     

Solution decomposition of the layered double hydroxide of Co with Fe: phase segregation of normal and inverse spinels

The nitrate-intercalated layered double hydroxide of Co with Fe decomposes on hydrothermal treatment to yield an oxide residue at a temperature as low as 180 degrees C. The oxide product is phase segregated into a Co(3)O(4)-type normal spinel and a CoFe(2)O(4)-type inverse spinel. Phase segregation is facilitated as decomposition in a solution medium takes place by dissolution of the precursor hydroxide followed by reprecipitation of the oxide phases. In contrast, thermal decomposition takes place at 400 degrees C. This temperature is inadequate to induce diffusion in the solid state whereby phase segregation into the thermodynamically stable individual spinels is suppressed. The result is a single-phase metastable mixed spinel oxide. This is rather uncommon in that a hydrothermal treatment yields thermodynamically stable products where as thermal decomposition yields a metastable product.     

Functionalization of self-organized TiO2 nanotubes with Pd nanoparticles for photocatalytic decomposition of dyes under solar light illumination

Self-organized, vertically oriented TiO2 nanotube arrays prepared by the sonoelectrochemical anodization method are functionalized with palladium (Pd) nanoparticles of approximately 10 nm size. A simple incipient wetness method is adopted to distribute the Pd nanoparticles uniformly throughout the TiO2 nanotubular surface. This functionalized material is found to be an excellent heterogeneous photocatalyst that can decompose nonbiodegradable azo dyes (e.g., methyl red and methyl orange) rapidly (150-270 min) and efficiently (100%) under ambient conditions using simulated solar light in the absence of any external oxidative radicals such as hydrogen peroxide.     

New approach for evaluation optical absorption measurements of charge transfer complexes between dimethoxynaphthalenes and tetracyanoethylene: singular value decomposition method

Singular-value decomposition (SVD) method is a numerical multidimensional technique appropriate for evaluation of optical absorption measurements of 1:1 charge transfer complexes (CTCs). Matrix algebra of the absorption data for different solutions and wavenumbers is primarily used for evaluation of the equilibrium constant and to obtain some general expressions to illustrate physical significance of the results obtained. The influence of the ratio of the concentrations of donor and acceptor is examined. It can lead to information about the stoichiometry of the complex formed in solution. Calculations on data for CTCs between dimethoxynaphthalene (DMNs) and tetracyanoethylene (TCNE) in CH2Cl2 at various temperatures are described. The results suggest that there is a noticeable difference in the K4, caused by substitutions at alpha- and beta-positions, because the alpha-position of naphthalene exhibits relatively high electron density compared with the corresponding beta-position. There is a linear correlation between the donor HOMO energy and charge-transfer absorption maxima.     

Two-way photoswitching using one type of near-infrared light, upconverting nanoparticles, and changing only the light intensity

Only one type of lanthanide-doped upconverting nanoparticle (UCNP) is needed to reversibly toggle photoresponsive organic compounds between their two unique optical, electronic, and structural states by modulating merely the intensity of the 980 nm excitation light. This reversible "remote-control" photoswitching employs an excitation wavelength not directly absorbed by the organic chromophores and takes advantage of the fact that designer core-shell-shell NaYF(4) nanoparticles containing Er(3+)/Yb(3+) and Tm(3+)/Yb(3+) ions doped into separate layers change the type of light they emit when the power density of the near-infrared light is increased or decreased. At high power densities, the dominant emissions are ultraviolet and are appropriate to drive the ring-closing, forward reactions of dithienylethene (DTE) photoswitches. The visible light generated from the same core-shell-shell UCNPs at low power densities triggers the reverse, ring-opening reactions and regenerates the original photoisomers. The "remote-control" photoswitching using NIR light is as equally effective as the direct switching with UV and visible light, albeit the reaction rates are slower. This technology offers a highly convenient and versatile method to spatially and temporally regulate photochemical reactions using a single light source and changing either its power or its focal point.     

Solution of the excluded volume problem for biaxial particles

We report the solution of the excluded volume problem for a pair of biaxial hard molecules; namely, sphero-platelets. As an application of this result we study the isotropic to nematic liquid crystal transition for a fluid composed of these particles in the Onsager limit (length δ breadth or width). We show that the range of stability of the isotropic phase decreases with increasing particle biaxiality.