Purpose: We developed a better method of accounting for the effects of heterogeneity in convolution algorithms. We integrated this method into our GPU‐accelerated, multi‐energetic ...convolution/superposition (C/S) implementation. In doing so, we have created a new dose algorithm: heterogeneity compensated superposition (HCS). Methods: Convolution in the spherical density‐scaled distance space, a.k.a. C/S, has proven to be a good estimator of the dose deposited in a homogeneous volume. However, near heterogeneities electron disequilibrium occurs, leading to faster fall‐off and re‐buildup than predicted by C/S. We propose to filter the actual patient density in a position and direction sensitive manner, allowing the dose deposited near interfaces to be increased or decreased relative to traditional C/S. We implemented the effective density function as a multivariate first‐order recursive filter. We compared HCS against traditional C/S using the ICCR 2000 Monte‐Carlo accuracy benchmark, 23 similar accuracy benchmarks and 5 patient cases. For the patient cases, we created custom routines capable of using the discrete material mappings used by Monte‐Carlo. C/S normally considers each voxel to be a mixture of materials based on a piecewise‐linear density look‐up table. Results: Multi‐energetic HCS increased the dosimetric accuracy for the vast majority of voxels; in many cases near Monte‐Carlo results were achieved. HCS improved the mean Van Dyk error by 0.79 (% of Dmax or mm) on average for the patient volumes; reducing the mean error from 1.93%|mm to 1.14%|mm. We found a mean error difference of up to 0.30 %|mm between linear and discrete material mappings. Very low densities (i.e. <0.1 g / cm3) remained problematic, but may be solvable with a better filter function. Conclusions: We have developed a novel dose calculation algorithm based on the principals of C/S that better accounts for the electron disequilibrium caused by patient heterogeneity. This work was funded in part by the National Science Foundation under Grant No. EEC9731748, in part by Johns Hopkins University internal funds and in part by Elekta.
Ultrasonic-assisted pulse electrodeposition of nanocrystalline nickel (NC-Ni) coatings from Watts bath on copper substrate was investigated. Direct (DC), pulsed (PC), and pulse reversed (PRC) current ...electrodeposition techniques were employed to electrodeposit NC-Ni coatings in the absence and presence of ultrasound wave with a nominal power ranging from 95 W to 200 W and their surface morphology, hardness, and crystalline microstructure were compared. We observed that as the ultrasound power increases, the cathodic efficiency and the microhardness increase, whereas the crystallite size and surface roughness decrease for NC-Ni electrodeposited by the three techniques in the same way. However, the effect of pulse waveform is dominant. The finest crystallite size (24 nm) and highest hardness (585 HV) were achieved for NC Ni coatings PC electrodeposited using an ultrasound with 200 W nominal power. It is believed that the coating produced by PC and PRC techniques develops a preferential orientation in (111) and (100) planes, respectively. The application of ultrasound wave and increasing its nominal power changes the preferential orientation of all obtained coatings to (111) planes. The corrosion behavior of NC Ni coatings, as investigated by potentiodynamic polarization and electrochemical impedance spectroscopy in NaOH solution, demonstrates the effect of nanocrystalline on the passivation and corrosion resistance of NC-Ni coatings.
•Ultrasonic-assisted pulse electrodeposition of nanocrystalline nickel (NC-Ni) coatings from Watts bath was exploited.•Effect of ultrasound wave with different nominal power ranging from 95 W to 200 W was studied.•Effect of direct, pulse and pulse-reverse current on nucleation and growth of nickel films was studied.•Increasing ultrasound power boosts cathodic efficiency and microhardness while decreasing crystallite size and surface roughness.•NC Ni coatings in NaOH solution show that corrosion behavior is influenced by crystallite size and morphology
Hull cell depositions are industrially used to monitor electrolytes and study the influence of additives. By combining the Hull cell deposition and a numerical simulation based on the boundary ...element method via a curve-fitting approach allows to obtain kinetic parameters (e.g. transfer coefficient, exchange current density) and assessing the effects of additives without losing the visual information and the opportunity to get the structural and physical properties of the metal deposition (reverse determination). In an acidic copper electrolyte, an additive based on polyethylene glycol decreases the effective exchange current density,
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by up to two orders of magnitude, while the transfer coefficient is hardly influenced. By adding another additive based on bis-(3-sulfopropyl)disulphide, the effect is counteracted and
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increases in dependence on the ratio of both additives. The combined approach enables obtaining more information about visual and structural effects and the deposition kinetics from one experimental analysis.
Controlling electrochemical deposition of lithium sulfide (Li2S) is a major challenge in lithium–sulfur batteries as premature Li2S passivation leads to low sulfur utilization and low rate ...capability. In this work, the solvent's roles in controlling solid Li2S deposition are revealed, and quantitative solvent‐mediated Li2S growth models as guides to solvent selection are developed. It is shown that Li2S electrodeposition is controlled by electrode kinetics, Li2S solubility, and the diffusion of polysulfide/Li2S, which is dictated by solvent's donicity, polarity, and viscosity, respectively. These solvent‐controlled properties are essential factors pertaining to the sulfur utilization, energy efficiency and reversibility of lithium–sulfur batteries. It is further demonstrated that the solvent selection criteria developed in this study are effective in guiding the search for new and more effective electrolytes, providing effective screening and design criteria for computational and experimental electrolyte development for lithium–sulfur batteries.
Quantitative solvent‐mediated Li2S growth models and property–performance relationships of solvents are developed for solvent selection in Li–S batteries. An effective solvent, propionitrile, is identified as a promising alternative solvent based on guidelines developed in this study.
Abstract
The production of precious metals from Cu-rich sources such as ore products or secondary sources is slow and complex largely due to limited solubility in aqueous electrolytes. This results ...in sequential processing with various electrolytes and chemistries, where first Cu is electrorefined, followed by Ag, followed by Au and the platinum group metals. These are separate processes, often conducted in separate electrorefining and electrowinning facilities. The chemical properties of molten sulfides, and their ability to operate at a temperature where liquid metal cathodes are used, suggest the possibility of an alternative, streamlined processing route for Cu and precious metals. Unfortunately, little thermodynamic or electrochemical information is available regarding the behavior of Cu and precious metal sulfides in molten sulfide electrolytes. Herein, the relative activity of the Cu2S-Ag2S pseudobinary dissolved in a BaS-La2S3 supporting electrolyte is measured at 1523 K. It was found that the supporting electrolyte favors mixing with Ag2S over Cu2S. Molten sulfide electrolysis of Cu and Ag was conducted, with results in good agreement with the thermodynamic model. It is found that the Ag-Cu cathode chemistry will influence the electrochemical selectivity in the Ag-Cu-Ba-La-S system.
We offer an explanation for how dendrite growth can be inhibited when Li metal pouch cells are subjected to external loads, even for cells using soft, thin separators. We develop a contact mechanics ...model for tracking Li surface and sub-surface stresses where electrodes have realistically (micron-scale) rough surfaces. Existing models examine a single, micron-scale Li metal protrusion under a fixed local current density that presses more or less conformally against a separator or stiff electrolyte. At the larger, sub-mm scales studied here, contact between the Li metal and the separator is heterogeneous and far from conformal for surfaces with realistic roughness: the load is carried at just the tallest asperities, where stresses reach tens of MPa, while most of the Li surface feels no force at all. Yet, dendrite growth is suppressed over the entire Li surface. To explain this dendrite suppression, our electrochemical/mechanics model suggests that Li avoids plating at the tips of growing Li dendrites if there is sufficient local stress; that local contact stresses there may be high enough to close separator pores so that incremental Li+ ions plate elsewhere; and that creep ensures that Li protrusions are gradually flattened. These mechanisms cannot be captured by single-dendrite-scale analyses.
The renaissance of aqueous Zn ion batteries has drawn intense attention to Zn metal anode issues, including dendrites growth, dead Zn, low efficiency, and other parasitic reactions. However, against ...the widely used 2D Zn foil, in fact, the Zn powder anode is a more practical choice for Zn-based batteries in industrial applications, but the related solutions are rarely investigated. Herein, we focus on the Zn powder anode and disclose its unknown failure mechanism different from Zn foils. By utilization of 2D flexible conductive Ti3C2Tx MXene flakes with hexagonal close-packed lattice as electrons and ions redistributor, a stable and highly reversible Zn powder anode without dendrite growth and low polarization is constructed. Low lattice mismatch (∼10%) enables a coherent heterogeneous interface between the (0002) plane of deposited Zn and (0002) plane of the Ti3C2Tx MXene. Thus, the Zn2+ ions are induced to undergo rapid uniform nucleation and sustained reversible stripping/plating with low energy barriers via the internally bridged shuttle channels. Paired with cyano group iron hexacyanoferrate (FeHCF) cathode, the FeHCF//MXene@Zn full battery delivers superior cycle durability and rate capability, whose service life with a CE of near 100% touches 850% of bare Zn powder counterparts. The proposed Ti3C2Tx MXene redistributor strategy concerning high-speed electrons/ions channel, low-barrier heterogeneous interface, is expected to be widely applied to other alkali metal anodes.
This work describes a method developed for the precise determination of Cm in a solution. The method is based on accurate spiking of a 244Cm solution having a known isotopic vector but unknown ...concentration, with a Pu reference standard. The specific 244Cm activity and concentration is determined through an alpha spectrometric measurement of the 244Cm/Pu alpha peak ratio. The alpha ratio is determined after removing interferences from 241Am and 238Pu in the 244Cm peak and by modelling 244Cm tailing into the 239Pu region of interest. The precision of the method was experimentally determined comparing 20 samples prepared from the same spiked solution by direct alpha planchette deposition with or without addition of a surfactant. The 20 samples were measured in 5 different alpha detectors belonging to two different alpha spectrometry systems. A total of 90 measurements yielded a combined measurement and evaluation precision of the Cm/Pu alpha ratio of 0.27% (k = 2). This result was compared to measurements of the Cm/Pu alpha ratio in 7 samples prepared by electrodeposition. The comparison indicated that sample preparation by electrodeposition gives a slightly increased uncertainty. Finally, the overall uncertainties involved in the analysis method are discussed and an uncertainty budget is estimated. The method is robust and by minimising uncertainties in the individual steps, the concentration of Cm can be determined with an overall uncertainty less than 0.670% with a coverage factor of 2 standard deviations.
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