A hybrid genetic algorithm for solving a layout problem in the fashion industry.

As of this writing, many success stories exist yet of powerful genetic algorithms (GAs) in the field of constraint optimisation. In this paper, a hybrid, intelligent genetic algorithm will be developed for solving a cutting layout problem in the Belgian fashion industry. In an initial section, an existing LP formulation of the cutting problem is briefly summarised and is used in further paragraphs as the core design of our GA. Through an initial attempt of rendering the algorithm as universal as possible, it was conceived a threefold genetic enhancement had to be carried out that reduces the size of the active solution space. The GA is therefore rebuilt using intelligent genetic operators, carrying out a local optimisation and applying a heuristic feasibility operator. Powerful computational results are achieved for a variety of problem cases that outperform any existing LP model yet developed.Fashion; Industry;

Code Renewability for Native Software Protection

Software protection aims at safeguarding assets embedded in software by preventing and delaying reverse engineering and tampering attacks. This paper presents an architecture and supporting tool flow to renew parts of native applications dynamically. Renewed and diversified code and data belonging to either the original application or to linked-in protections are delivered from a secure server to a client on demand. This results in frequent changes to the software components when they are under attack, thus making attacks harder. By supporting various forms of diversification and renewability, novel protection combinations become available, and existing combinations become stronger. The prototype implementation is evaluated on a number of industrial use cases

Nanoscale characterization of materials for thin film batteries

The continuing development of mobile electronic devices and the increasing importance of electric vehicles (EV) drives the demand for improved batteries. Further improvements of current batteries are needed to enable novel applications. This requires new device concepts that improve battery safety, power and energy density. A solution might come from the three dimensional (3D) all-solid-state thin film battery. 3D thin film batteries use a nanostructured template in which the battery stack is deposited. By fabricating a thin film battery in a 3D substrate, the total storage capacity is increased whereas the benefit of using a thin film (high power) is retained. In this work the effect of downscaling the battery components is evaluated. Such ultra-thin films are expected to be used in all-solid-state 3D batteries. When nanoscaling battery films, different physical phenomena set in. Examples are an increased Li-ion storage capacity, changes of the electronic conductivity and a shift of the intercalation site energy. The onset of these type of phenomena in different thin film battery materials is studied in detail. The first material investigated for use in 3D thin film batteries was the spinel structured LiMn2O4. This material can store two Li+-ions in its structure, one is inserted at 4 V and one at 3 V vs Li+/Li. Currently only the 4 V region is used due to the volume expansion associated with the intercalation of the second lithium ion (at 3 V). Such volume expansion leads to cracking of the electrode and a loss of contact with the current collector. By nanoscaling LiMn2O4 layers we have shown that the volume changes associated with the insertion of the Li-ion in the 3 V region can be accommodated. By preventing manganese dissolution, layers exhibiting stable cycling were shown, retaining ~100 % of the capacity after 70 cycles. Furthermore, the maximum theoretical capacity was measured in the thinnest films (25 nm), leading to exceptionally high capacities of 1.2 Ah/cm3. Attaining these storage densities has proven impossible in thicker films. Finally, the thin film LiMn2O4 showed exceptional rate performance. The thinnest layers could be charged to 75 % of the theoretical capacity within 18s (or a rate of 200C). LixMg1-2xAl2+xO4 was evaluated for use as a solid electrolyte in battery applications. The material is a lithium doped version of the classic MgAl2O4 spinel. It was anticipated to possess a high Li-ion conductivity (predicted from NMR measurements and modeling). Furthermore, its spinel structure could allow the fabrication of a lattice matched battery. Matching the crystal lattices provides an optimal interface between the battery components and, as such, allows easy transport of lithium. In addition, MgAl2O4 has a wide bandgap which allows the downscaling of the solid electrolyte layers, thus improving the battery's energy density. Investigation of spinel structured LixMg1-2xAl2+xO4 (x= 0 to 0.25) films showed low electronic leakage but also low ionic conductivity. This seemingly contradicted the results of cyclic voltammetry measurements which evidenced lithium plating and stripping and even lithium-platinum alloy formation. To further investigate this discrepancy, potential dependent impedance measurements were performed, showing an increase in conductivity of over 3 orders of magnitude on approaching 0.1 V versus Li+/Li. This is explained by lithium intercalation in the LixMg1-2xAl2+xO4 layers, increasing their ionic conductivity. Once a stable composition is formed, the layer acts as a solid electrolyte. Upon reversing the potential, the lithium is removed from the layer and the original resistance values are regained. In the final part of the thesis, thin films of the solid electrolyte LiPON (nitrogen doped Li3PO4 glass) were investigated. The influence of sputtering conditions, film thickness and substrate material on ionic conductivity were studied. When the amount of incorporated nitrogen is increased, ionic conductivity rises and the activation energy reduces. No influence of layer thickness or substrate material was found on these quantities. In studying the electronic conductivity of LiPON with varying thickness, layers up to 15 nm LiPON were found to be electronically insulating, in contrast with other literature reports. In a next step, the breakdown characteristics of LiPON layers were investigated using I-V measurements. These showed the prevalence of a distinct constant current plateau, attributed to the dissociation of the LiPON layer and the diffusion limited Li-ion transport. During LiPON dissociation, Li+, oxygen or nitrogen gas, and a phosphate-rich compound are generated. Finally, hard breakdown is observed - as a result of the formation of lithium filaments that short the solid electrolyte layer.status: publishe

Effect of high temperature LiPON electrolyte in all solid state batteries

© 2019 Elsevier B.V. Thin film solid state Li 4 Ti 5 O 12 -based batteries are developed by using amorphous Lithium Phosphorus Oxynitride (LiPON) electrolyte deposited by reactive sputtering at different substrate temperatures (T dep ). Such layers maintain their amorphous character even at higher T dep . The stoichiometry, ionic conductivity, thermal stability and overall effect on full battery stacks were investigated. The ionic conductivity falls down by nearly three orders of magnitude for samples deposited at higher temperatures while no significant compositional variations are found, in contrast with previous reports. This is interpreted as the creation of a highly thermally stable LiPON glass with a closed-packed structure which inhibits Li-ion diffusion. The onset of the glass transition (T g ) and the crystallization temperature (T c ) of LiPON shifts to higher temperatures as T dep increases. Galvanostatic (dis)charge measurements on fully operational thin film batteries show a decrease in capacity and a worsened C-rate performance as LiPON T dep increases. Despite the lower ionic conduction, the improved thermal stability reported here using LiPON whose properties can be properly tuned could open interesting scenarios in future advances in solid-state battery systems and new possibilities in high temperature applications.status: publishe

A hybrid genetic algorithm for solving a layout problem in the fashion industry

As of this writing, many success stories exist yet of powerful genetic algorithms (GAs) in the field of constraint optimisation. In this paper, a hybrid, intelligent genetic algorithm will be developed for solving a cutting layout problem in the Belgian fashion industry. In an initial section, an existing LP formulation of the cutting problem is briefly summarised and is used in further paragraphs as the core design of our GA. Through an initial attempt of rendering the algorithm as universal as possible, it was conceived a threefold genetic enhancement had to be carried out that reduces the size of the active solution space. The GA is therefore rebuilt using intelligent genetic operators, carrying out a local optimisation and applying a heuristic feasibility operator. Powerful computational results are achieved for a variety of problem cases that outperform any existing LP model yet developed.status: publishe

Plasma-assisted and thermal atomic layer deposition of electrochemically active Li2CO3

Thin-film lithium carbonate (Li2CO3) has applications in various electrochemical devices, like Li-ion batteries, gas sensors and fuel cells. ALD of Li2CO3 is of interest for these applications as it allows for uniform and conformal coating of high-aspect ratio structures and particles with very precise thickness control. However, there are few studies that focus on its fabrication and characterization. In this work, plasma-assisted and thermal ALD were adopted to grow ultra-thin, conformal Li2CO3 films between 50 and 300 C using lithium tert-butoxide as a precursor and O2 plasma or H2O/CO2 as co-reactants. More specifically, we focus on the plasma-assisted process by film growth, stability and conductivity studies and emphasize the differences from its more extensively adopted thermal counterpart. Plasma-assisted ALD allows for higher growth per cycle values (0.82 vs. 0.60 °A), lower substrate temperatures and shorter cycle times. The stoichiometry of the films, ranging from Li2CO3 to Li2O, can be controlled by substrate temperature and O2 plasma exposure time. The ionic conductivity for both plasma-assisted and thermal ALD is measured for the first time and is in the order of 1E-10 S/cm after normalizing to the different effective surface areas. The Li-ion conductivities found here are in line with literature values predicted by simulation studies.status: publishe

First-principles material modeling of solid-state electrolytes with the spinel structure

Ionic diffusion through the novel (AlxMg1-2xLix)Al2O4 spinel electrolyte is investigated using first-principles calculations, combined with the Kinetic Monte Carlo algorithm. We observe that the ionic diffusion increases with the lithium content x. Furthermore, the structural parameters, formation enthalpies and electronic structures of (AlxMg1-2xLix)Al2O4 are calculated for various stoichiometries. The overall results indicate the (AlxMg1-2xLix)Al2O4 stoichiometries x = 0.2…0.3 as most promising. The (AlxMg1-2xLix)Al2O4 electrolyte is a potential candidate for the all-spinel solid-state battery stack, with the material epitaxially grown between well-known spinel electrodes, such as LiyMn2O4 and Li4+3yTi5O12 (y = 0…1). Due to their identical crystal structure, a good electrolyte-electrode interface is expected.status: publishe

Nanometer-thin graphitic carbon buffer layers for electrolytic MnO₂ for thin-film energy storage devices

In this study, nanometer thin graphitic carbon coatings were applied as an adhesion layer for the growth of submicron to micron thick electrolytic manganese dioxide (EMD) films for thin-film energy storage devices. The graphitic carbon coating served not only as current collector and adhesion layer between the EMD and the substrate, but also prevented the oxidation of the non-noble TiN substrate during the anodic deposition process. The EMD films consisted of a network of interconnected nanometer-size particles with around 50% porosity. The ability to grow a few hundred nanometer thick EMD film with good adhesion to the current collector is critical for reliable thin-film batteries on high aspect ratio microstructured surfaces. Thin EMD films grown on our graphitic carbon coated TiN substrates showed improved reversible Li-ion intercalation kinetics and increased cycle life compared to similar films deposited on noble metal platinum substrates, thus demonstrating the improved interface properties using the graphitic carbon buffer layer.status: publishe