Depth profile analysis of a cycled lithium ion manganese oxide battery electrode via the valence state of manganese, with soft X-ray emission spectroscopy

A 50-μm thick lithium manganese oxide (parent material LiMn₂O₄) battery electrode (positive electrode; cathode) was charged, slightly discharged and then sliced with a scotch tape test-type method. A selected number of slices was then subject to synchrotron soft X-ray emission spectroscopy near the Mn L_α,β emission lines in order to determine changes in the oxidation state of the manganese as a function of sampling depth. The emission spectra showed a minute yet noticeable and systematic chemical shift of up to 0.25 eV between the layer near the current collector and the layer near the electrolyte separator. The average manganese oxidation state near the separator was smaller than the average oxidation state in the interior of the electrode, or near the current collector. Since the data provide an oxidation state depth profile of the cathode, a Li⁺ depth profile can be inferred. This method provides information on the spatial chemical inhomogeneity of electrodes prior to and after electrochemical cycling, and thus can aid in degradation studies.     

Heat-treated wood as chromium adsorption material

Heavy metals adsorption with lignocellulosic materials has been heavily researched in the last years. Since heat activation has been used with good results to increase the adsorption capacity of some materials, heat-treated wood might be a better adsorbent. This hypothesis is the basis of the present study. The adsorption tests were made with powdered pine wood, heat-treated at 190–210?°C. All the heat-treated samples showed a significantly higher adsorption compared to untreated wood. The maximum adsorption was obtained at pH 3 for heat-treated wood at 210?°C. The kinetics of the adsorption process fitted a pseudo-second-order reaction (R² 0.990–0.996). Adsorption fitted well both the Langmuir and the Freundlich model, but the Freundlich model presented higher R² (0.988–0.998). The q_max values estimated by the Langmuir plotting were in the range 15.6–19.4 mg/g and the n values from Freundlich isotherms between 1.87 and 2.39. Heat-treated wood was a better adsorption material than untreated wood for chromium adsorption. This can be a good application for the sawdust produced by the processing of heat-treated wood at primary and secondary wood processing mills or for the recycling of heat-treated wood at the end of product life.     

A model for non-local bonding in bipartite systems

We hypothesize a non-local model for two-component quantum systems based on a non-linear but non-perturbatively solvable operator equation. The equation introduces a meta-structure, which conforms with quantum mechanics but constrains the range of admissible states of the system. According to the proposed model the composite system as a whole may bind into a non-local molecule with an energy gap different than that of free components.     

Modeling of heat and fluid flow in granular layers using high-order compact schemes and volume penalization method

Abstract

The article presents a novel computational algorithm for modeling of heat and mass transfer processes around neighboring solid objects and inside granular layers. It is based on a volume penalization approach formulated in the framework of an immersed boundary technique, which allows using Cartesian computational meshes for modeling of solid objects with virtually arbitrarily complex shapes and in any form of contact (point-to-point, point-to-surface, etc.). The spatial discretization is performed using a high-order compact discretization/interpolation method on the meshes in which the locations of velocity, density, and temperature are partially staggered with respect to the locations of pressure nodes. Compared to the conventional collocated node arrangement, the present approach has a stabilizing effect, which is very desirable in case of a sudden change of geometry inside the computational grids, especially when high-order discretization is applied. The formulated algorithm is verified based on the following test cases: (i) three hot solid spherical objects immersed in a stream of cold flow; (ii) two granular beds with hundreds of hot solid objects placed in a flowing cold fluid. The results are compared to the solutions obtained using ANSYS-Fluent software and experimental data. In all the cases, the agreement of the results is very good.     

Electrocombustion of humic acid and removal of algae from aqueous solutions

This paper reports experiments involving the electrochemical combustion of humic acid (HA) and removal of algae from pond water. An electrochemical flow reactor with a boron-doped diamond film anode was used and constant current experiments were conducted in batch recirculation mode. The mass transfer characteristics of the electrochemical device were determined by voltammetric experiments in the potential region of water stability, followed by a controlled current experiment in the potential region of oxygen evolution. The average mass transfer coefficient was 5.2 × 10⁻⁵ m s⁻¹. The pond water was then processed to remove HA and algae in the conditions in which the reaction combustion occurred under mass transfer control. To this end, the mass transfer coefficient was used to estimate the initial limiting current density applied in the electrolytic experiments. As expected, all the parameters analyzed here—solution absorbance at 270 nm, total phenol concentration and total organic carbon concentration—decayed according to first-order kinetics. Since the diamond film anode successfully incinerated organic matter, the electrochemical system proved to be predictable and programmable.     

Digital micromirror device as a spatial illuminator for fluorescence lifetime and hyperspectral imaging

Time-domain fluorescence lifetime imaging (FLIM) and hyper-spectral imaging (HSI) are two advanced microscopy techniques widely used in biological studies. Typically both FLIM and HSI are performed with either a whole-field or raster-scanning approach, which often prove to be technically complex and expensive, requiring the user to accept a compromise among precision, speed, and spatial resolution. We propose the use of a digital micromirror device (DMD) as a spatial illuminator for time-domain FLIM and HSI with a laser diode excitation source. The rather unique features of the DMD allow both random and parallel access to regions of interest (ROIs) on the sample, in a very rapid and repeatable fashion. As a consequence both spectral and lifetime images can be acquired with a precision normally associated with single-point systems but with a high degree of flexibility in their spatial construction. In addition, the DMD system offers a very efficient way of implementing a global analysis approach for FLIM, where average fluorescence decay parameters are first acquired for a ROI and then used as initial estimates in determining their spatial distribution within the ROI. Experimental results obtained on phantoms employing fluorescent dyes clearly show how the DMD method supports both spectral and temporal separation for target identification in HSI and FLIM, respectively.     

Medium frequency magnetron self-sputtering of copper

It is well known that the magnetron self-sustained sputtering (SSS) process can be achieved in the direct current (DC) operation mode (DC-SSS) if certain conditions are fulfilled: high self-sputtering yield of the target material (theoretically Y>1), appropriate magnetron source design, high target power density to ensure high ionization level of the sputtered material. The main disadvantage of the DC-SSS process is the instability related to possibility of an arc formation. The author postulates that magnetron plasma pulsing can minimize this problem.In this paper, voltage and current waveforms of medium frequency (MF) powered magnetron source are analysed. A simple electrical model, explaining dynamics of MF magnetron discharge is presented. The method to achieve MF magnetron SSS process is proposed and experimentally verified. The results of MF magnetron SSS (MF-SSS) process are presented for the first time (to the author's knowledge). The experiments were performed using a planar magnetron source equipped with a copper target of 50 mm in diameter and 6 mm thick. The magnetron source was powered by a resonant (110 kHz) power supply. The target power density during MF-SSS process was about 490 W/cm².