An integrated 2-D model of a lithium ion battery: The effect of material parameters and morphology on storage particle stress

An integrated 2-D model of a lithium ion battery is developed to study the mechanical stress in storage particles as a function of material properties. A previously developed coupled stress-diffusion model for storage particles is implemented in 2-D and integrated into a complete battery system. The effect of morphology on the stress and lithium concentration is studied for the case of extraction of lithium in terms of previously developed non-dimensional parameters. These non-dimensional parameters include the material properties of the storage particles in the system, among other variables. We examine particles functioning in isolation as well as in closely-packed systems. Our results show that the particle distance from the separator, in combination with the material properties of the particle, is critical in predicting the stress generated within the particle. © 2012 Springer-Verlag.

Determination of the rheological parameters of self-compacting concrete matrix using slump flow test

The classification of a concrete mixture as self-compacting (SCC) is performed by a series of empirical characterization tests that have been designed to assess not only the flowability of the mixture but also its segregation resistance and filling ability. The objective of the present work is to correlate the rheological parameters of SCC matrix, yield stress and plastic viscosity, to slump flow measurements. The focus of the slump flow test investigation was centered on the fully yielded flow regime and an empirical model relating the yield stress to material and flow parameters is proposed. Our experimental data revealed that the time for a spread of 500 mm which is used in engineering practice as reference for measurement parameters, is an arbitrary choice. Our findings indicate that the non-dimensional final spread is linearly related to the non-dimensional yield-stress. Finally, there are strong indications that the non-dimensional viscosity of the mixture is associated with the non-dimensional final spread as well as the stopping time of the slump flow; this experimental data set suggests an exponential decay of the final spread and stopping time with viscosity. © Appl. Rheol.

Effect of process parameters on the morphology and nanostructure of roll-to-roll printed P3HT:PCBM thin films for organic photovoltaics

Roll-to-roll (R2R) gravure exhibits significant advantages such as high precision and throughput for the printing of photoactive and conductive materials and the fabrication of flexible organic electronics such as organic photovoltaics (OPVs). Since the photoactive layer is the core of the OPV, it is important to investigate and finally control the process parameters and mechanisms that define the film morphology in a R2R process. The scope of this work is to study the effect of the R2R gravure printing and drying process on the nanomorphology and nanostructure of the photoactive P3HT:PCBM thin films printed on PEDOT:PSS electrodes towards the fabrication of indium tin oxide (ITO)-free flexible OPVs. In order to achieve this, P3HT:PCBM blends of different concentration were R2R printed under various speeds on the PEDOT:PSS layers. Due to the limited drying time during the rolling, an amount of solvent remains in the P3HT:PCBM films and the slow-drying process takes place which leads to the vertical and lateral phase separation, according to the Spectroscopic Ellipsometry and Atomic Force Microscopy analysis. The enhanced slow-drying leads to stronger phase separation, larger P3HT crystallites according to the Grazing Incidence X-Ray Diffraction data and to weaker mechanical response as it was shown by the nanoindentation creep. However, in the surface of the films the P3HT crystallization is controlled by the impinged hot air during the drying, where the more the drying time the larger the surface P3HT crystallites. The integration of the printed P3HT:PCBM and PEDOT:PSS layers in an OPV device underlined the feasibility of fabricating ITO-free flexible OPVs by R2R gravure processes. © 2013 Elsevier B.V.

Effect of the interplay between protein and surface on the properties of adsorbed protein layers.

Although protein adsorption to surface is a common phenomenon, investigation of the process is challenging due to the complexity of the interplay between external factors, protein and surface properties. Therefore experimental approaches have to measure the properties of adsorbed protein layers with high accuracy in order to achieve a comprehensive description of the process. To this end, we used a combination of two biosensing techniques, dual polarization interferometry and quartz crystal microbalance with dissipation. From this, we are able to extract surface coverage values, layer structural parameters, water content and viscoelastic properties to examine the properties of protein layers formed at the liquid/solid interface. Layer parameters were examined upon adsorption of proteins of varying size and structural properties, on surfaces with opposite polarity. We show that "soft" proteins such as unfolded α-synuclein and high molecular weight albumin are highly influenced by the surface polarity, as they form a highly diffuse and hydrated layer on the hydrophilic silica surface as opposed to the denser, less hydrated layer formed on a hydrophobic methylated surface. These layer properties are a result of different orientations and packing of the proteins. By contrast, lysozyme is barely influenced by the surface polarity due to its intrinsic structural stability. Interestingly, we show that for a similar molecular weight, the unfolded α-synuclein forms a layer with the highest percentage of solvation not related to surface coverage but resulting from the highest water content trapped within the protein. Together, these data reveal a trend in layer properties highlighting the importance of the interplay between protein and surface for the design of biomaterials.

Graphene modelocked VECSELs

In the past decade, passively modelocked optically pumped vertical external cavity surface emitting lasers (OPVECSELs), sometimes referred to as semiconductor disk lasers (OP-SDLs), impressively demonstrated the potential for generating femtosecond pulses at multi-Watt average output powers with gigahertz repetition rates. Passive modelocking with a semiconductor saturable absorber mirror (SESAM) is well established and offers many advantages such as a flexible design of the parameters and low non-saturable losses. Recently, graphene has emerged as an attractive wavelength-independent alternative saturable absorber for passive modelocking in various lasers such as fiber or solid-state bulk lasers because of its unique optical properties. Here, we present and discuss the modelocked VECSELs using graphene saturable absorbers. The broadband absorption due to the linear dispersion of the Dirac electrons in graphene makes this absorber interesting for wavelength tunable ultrafast VECSELs. Such widely tunable modelocked sources are in particularly interesting for bio-medical imaging applications. We present a straightforward approach to design the optical properties of single layer graphene saturable absorber mirrors (GSAMs) suitable for passive modelocking of VECSELs. We demonstrate sub-500 fs pulses from a GSAM modelocked VECSEL. The potential for broadband wavelength tuning is confirmed by covering 46 nm in modelocked operation using three different VECSEL chips and up to 21 nm tuning in pulsed operation is achieved with one single gain chip. A linear and nonlinear optical characterization of different GSAMs with different absorption properties is discussed and can be compared to SESAMs. © 2014 SPIE.

Enlarging regions of stable running with segmented legs

In human and animal running spring-like leg behavior is found, and similar concepts have been demonstrated by various robotic systems in the past. In general, a spring-mass model provides self-stabilizing characteristics against external perturbations originated in leg-ground interactions and motor control. Although most of these systems made use of linear spring-like legs. The question addressed in this paper is the influence of leg segmentation (i.e. the use of rotational joint and two limb-segments) to the self-stability of running, as it appears to be a common design principle in nature. This paper shows that, with the leg segmentation, the system is able to perform self-stable running behavior in significantly broader ranges of running speed and control parameters (e.g. control of angle of attack at touchdown, and adjustment of spring stiffness) by exploiting a nonlinear relationship between leg force and leg compression. The concept is investigated by using a two-segment leg model and a robotic platform, which demonstrate the plausibility in the real world. ©2008 IEEE.

Effect of the interplay between protein and surface on the properties of adsorbed protein layers

Although protein adsorption to surface is a common phenomenon, investigation of the process is challenging due to the complexity of the interplay between external factors, protein and surface properties. Therefore experimental approaches have to measure the properties of adsorbed protein layers with high accuracy in order to achieve a comprehensive description of the process. To this end, we used a combination of two biosensing techniques, dual polarization interferometry and quartz crystal microbalance with dissipation. From this, we are able to extract surface coverage values, layer structural parameters, water content and viscoelastic properties to examine the properties of protein layers formed at the liquid/solid interface. Layer parameters were examined upon adsorption of proteins of varying size and structural properties, on surfaces with opposite polarity. We show that "soft" proteins such as unfolded α-synuclein and high molecular weight albumin are highly influenced by the surface polarity, as they form a highly diffuse and hydrated layer on the hydrophilic silica surface as opposed to the denser, less hydrated layer formed on a hydrophobic methylated surface. These layer properties are a result of different orientations and packing of the proteins. By contrast, lysozyme is barely influenced by the surface polarity due to its intrinsic structural stability. Interestingly, we show that for a similar molecular weight, the unfolded α-synuclein forms a layer with the highest percentage of solvation not related to surface coverage but resulting from the highest water content trapped within the protein. Together, these data reveal a trend in layer properties highlighting the importance of the interplay between protein and surface for the design of biomaterials. © 2014 The Authors.

Parameters influencing the maximum controllable current in gate commutated thyristors

The model of interconnected numerical device segments can give a prediction on the dynamic performance of large area full wafer devices such as the Gate Commutated Thyristors (GCTs) and can be used as an optimisation tool for designing GCTs. In this study the authors evaluate the relative importance of the shallow p-base thickness, its peak concentration, the depth of the p-base and the buffer peak concentration. © The Institution of Engineering and Technology 2014.