723 research outputs found

    Physical modelling of DMFC performance heterogeneities and the recovery of reversible cathode degradation

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    In this work, a transient multiphase DMFC model in 2D has been developed with the aim to describe the physical processes inside a DMFC single cell with a focus on performance heterogeneities along the channel. The model featured the spatial discretisation of the ACL and CCL, which proved essential for the investigation of local inhomogeneities in the cell as well as for understanding transient phenomena during the recovery of reversible cathode degradation. The model has been thoroughly validated against experimental performance data from a macro-segmented cell, which also included impedance spectra as well as the overall methanol and water crossover. The local resolution of the cell performance helped to verify the modelling of physical processes for mass and charge transport on the global as well as on the local scale. Such a locally resolved model validation can hardly be found in literature. A very good agreement of the model prediction with the experimental data regarding humidity-related phenomena inside the DMFC cathode as well as general mass transport phenomena and their effect on the cell performance under various operating conditions has been achieved with just one set of model parameters. The simulation study has highlighted the complex interplay of gas and liquid phase inside the DMFC and its impact on material properties and transport processes inside the cell. Furthermore, the importance of interface processes at the PEM boundaries to the catalyst layers as well as inside the catalyst layer on the local cell behaviour could be shown. For the species transport inside the compositional fuel cell structure, the formation and presence of liquid water plays a dominant role. It could be shown that phase-dependent sorption processes at the DMFC membrane interface fundamentally determine the water transfer from anode to cathode and consequently the distribution of liquid water inside the cell. The impact of the individual humidity-related transport mechanisms has been evaluated step by step in this work. The ionomer phases in the cell, i.e the bulk membrane as well as the ionomer thin-film in the CL, proved to be highly sensitive to the local water activity and phase conditions and exhibit a strong resistance to proton transport in the areas of the DMFC with poor humidification. Mass transport resistances in the heterogeneous CL microstructure due to liquid water accumulation could be successfully modelled on the continuum scale by integrating an ionomer-film model. The validated cell model also proved fit to describe the transient processes within the cell during the recovery of reversible cathode degradation during a refresh cycle. Without any adjustments in the model, the dynamics in the local potential for electrons and ions as well as in the membrane in dependence on the conditions inside the DMFC were predicted with a very good accuracy in anode and cathode. With its spatial resolution of the CCL, the model rendered a visualisation of the heterogeneous distribution of species and reactions in the course of the refresh sequence. Also the local formation of H2 in the DMFC anode during the absence of oxygen in the CCL could be successfully described with the model. The simulation study showed that the methanol crossover through the DMFC membrane and the resulting methanol oxidation reactions in the CCL play an essential role during the refresh cycle. Especially the secondary, H2O-activated MOR reaction path in the CCL under oxygen-depleted conditions was identified as relevant for the achievement of low local potentials in the DMFC cathode and thus for the full recovery of the cathode ECSA during the air break. A variation of air stop scenarios was simulated with the model and the impact of the local species distribution on the electrochemical processes within the cell was studied. The variations included settings where the PtOx-surface species in the CCL would get entirely or only partially reduced. In a simulation of a longer air stop, the effect of methanol accumulation during the air stop period could be visualised and its impact on the heterogeneities in the local cell voltage could be explained. Also the processes during an incomplete air stop, where oxygen is only partially depleted in the cathode catalyst layer, could be shown with the model. Two air stop variants resulting in a full recovery of the cathode ECSA were identified and examined. The simulation showed that while a flush with pure nitrogen on the one hand swiftly enables a full reduction of the platinum oxides in the CCL, it on the other hand limits the re-humidification of the membrane. By improving the model’s refresh boundary conditions, i.e. further limiting the diffusion of oxygen into the cell from external during the air stop period (and thus presumably approximating the experimental conditions more closely), the best results in terms of platinum oxide reduction and ionomer rehydration were achieved

    Optical Measurement of Airborne Particles on Unmanned Aircraft

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    Aerosols and clouds are persistent causes of uncertainty in climate and weather models, which is due to their heterogeneous suspension and occurrence within the atmosphere, and complex interactions which are chaotic and exist on small scales. Unmanned aerial vehicles (UAVs) have grown in popularity, and are becoming more commonly used for general atmospheric measurement, particularly measurement of aerosols and clouds. This thesis presents and evaluates a synergy between two UAVs, a multi-rotor: the UH-AeroSAM octocopter and a fixed-wing: the FMI-Talon, and an optical particle instrument: the Universal Cloud and Aerosol Sounding System. Computational fluid dynamics with Lagrangian particle tracking (CFD-LPT) was used as a tool for the characterisation of the velocity fields and particle trajectories around both UAVs. In both instances CFD-LPT was used to develop an operational envelope, with particular attention to angle of attack constraints and size distribution perturbation, for the UAV – instrument synergy. UCASS was the first open path instrument to be used on a UAV, and a good case has been made for its continued use, particularly on fixed-wing UAVs, which exhibit less complex aerodynamics and superior stability in the induced sampling airflow through the instrument

    4D FLOW CMR in congenital heart disease

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    This thesis showed that the use of a cloud-based reconstruction applicationwith advanced eddy currents correction, integrated with interactiveimaging evaluation tools allowed for remote visualization and interpretationof 4D flow data and that was sufficient for gross visualizationof aortic valve regurgitation. Further, this thesis demonstrated that bulkflow and pulmonary regurgitation can be accurately quantified using 4Dflow imaging analyzed. Peak systolic velocity over the pulmonary valvemay be underestimated. However, the measurement of peak systolicvelocity can be optimized if measured at the level of highest velocity inthe pulmonary artery. Also correlated against invasive measurements (inan animal model), this thesis shows that aorta flow and pulmonary flowcan be accurately and simultaneously measured by 4D flow MRI.When applied in clinical practice, 4D flow has extra advantages, of beingable to visualize flow pattern, vorticity and to predict aortic growth. InASD patients it can measure shunt volume directly following the septumframe by frame. In Fontan patients in can visualize better than standardMRI the Fontan circuit and it can measure flow at multiple points alongthe Fontan circuit. We observed in our Fontan population that shunt lesionswere very common, most of the time via veno-venous collaterals.Further using advanced computations, we showed that WSS angle wasthe only independent predictor of aortic growth in BAV patients. We alsoshowed the feasibility of GLS analysis on 4D flow MRI and presented anintegrative approach in which flow and functional data are acquired inone sequence.From the technical point of view, 4D flow MRI has proved to complementthe traditional components of the standard cardiac MR exams, enablingin-depth insights into hemodynamics. At this moment it proved its addedvalue, but in most of the cases it is not able yet to replace the standardexam. This is still due to long scanning times and relatively longpost-processing times.<br/

    Development of DNA origami-based tools for cancer treatment

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    DNA has been used as material for the assembly of objects at different scales. Particularly, the introduction of DNA origami has been inspiring the design and construction of many different versions of DNA nanostructures for, especially, biomedical applications. DNA origami nanostructures are showing unique advantages, including structural homogeneity, addressability, biocompatibility, and capacity to carry pharmaceuticals or biomolecules, for the development of future cancer therapeutics. To fully unlock their potential, however, they need to be tailored based on physiological and pathological molecular environments which they interact with. In this thesis, we develop a few functionalized DNA origami nanostructures to investigate specific questions of cancer biology or to overcome challenges of cancer immunotherapy. In PAPER I, we compare the physical characteristics of a compact lattice-based rod and a wireframe-styled rod and revealed how they interact with cell spheroid tissue models (CSTMs). Our data indicate that the wireframe structure, which has a lower local material density in design, has higher local deformability than the lattice-based structure. We reveal that these physical differences play important roles in the interaction between DNA origami nanostructures and human cancer cells, showing that wireframe rods are more likely to stay on the cell membrane, rather than being internalized, and this facilitates their deeper penetration into CSTMs. These observations tell us that DNA origami design methods should be carefully considered in DNA origami-based drug delivery applications. In PAPER II, to explore the nanoscale clustering effect of death receptor 5 (DR5) on human breast cancer cells, we develop flat sheet-like DNA origami nanostructures and functionalize them with the tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)- mimicking peptides which can recognize and bind with DR5, in differently sized hexagonal patterns. Experiments of cancer cells and DNA origami incubation show that apoptosis can be precisely controlled when we vary the size of peptide patterns between the range of 6 nm to 26 nm. Interestingly, our data indicate that the interpeptide distance for effective apoptosis is sub-10 nm. Our findings highlight the potency of precise spatial patterning of ligands on apoptosis signaling. In PAPER III, to limit cytotoxicity of the sub-10 nm peptide pattern, which we have screened out in the work of PAPER II, only to tumors, we design a three-dimensional DNA origami nanostructure containing a 6 nm wide and 12 nm deep cavity and use it to hide but display the peptide pattern according to the acidity of the tissue microenvironment. Peptide display is achieved by the protonation-triggered formation of the DNA triplex, during which a singlestranded DNA extension from the complementary strand of a mini-scaffold DNA wraps back to the mini-scaffold duplex. By varying the AT percentage in the mini-scaffold DNA, we can control the triggering pH for the formation of the DNA triplex. We demonstrate the safety of the DNA origami under physiological pH (pH 7.4) for non-cancer cells and its cytotoxicity to cancer cells under the pH of solid tumors (pH 6.5). In PAPER IV, to mimic functions of T cell engagers but mitigate corresponding adverse effects mainly caused by “on-target, off-tumor” immune activation and cytokine release syndrome, we develop a wireframe DNA origami based-nanorobot: a double-layered barrellike origami with antibodies inside under its closed status. When the DNA nanorobot presents as its open configuration, internal antibodies get exposed, functioning to engage T cells with cancer cells and activate T cell immune killing. By spatiotemporally controlling the opening of the DNA nanorobot via signals from cancer cells, tumor microenvironment, or external stimulus, we aim to selectively redirect the cytotoxicity of T cells to solid cancers and substantially mitigate corresponding adverse effects of current T cell engagers-based cancer immunotherapy

    Endogenous UMIs as quantifiable reporter elements – validation studies & applications in rAAV vectorology

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    In the creation of recombinant adeno-associated viral (rAAV) vectors, terminal DNA elements known ITRs (inverted terminal repeats) of the direct the intracellular synthesis and packaging of nonviral DNA. The need to clonally amplify ITR sequences in one form or another thereby underlies the existence of all rAAV clinical products and research materials worldwide. Their tendency to form strong nonduplex structures raises problems. The genetic precursors to rAAV vectors – typically prokaryotic plasmids – are known to possess heterogenous ITR sequences as a result of replicational instability, the effects of which on vector yield and efficacy are unclear and have not been systematically explored. To shed much-needed light on this decades-old problem, I utilised unique molecular identifiers (UMIs) as reporter elements for different rAAV plasmid preparations, so that massively parallel sequencing could be used to analyse their DNA and RNA derivatives through the course of production and in vivo gene transfer. The range of vector potencies observed, while not calamitous, definitively erases the notion that this problem can be further overlooked. The success of this unconventional strategy proved to be an equally notable outcome, offering unprecedented insights into population kinetics, and achieving quantitative consistency between biological replicates comparable to q/dPCR measurement replicates of single samples. This triggered concerted efforts to formally investigate the capabilities of UMIs used in this fashion. The probabilistic principles underlying the technique were formalised and empirically validated, confirming precision capabilities akin if not superior to dPCR and qPCR at equivalent levels of stringency. Experiments also revealed a pattern of measurement bias with potentially adverse implications for other areas of count analysis including differential gene expression

    TROPOMI/S5P Total Column Water Vapor validation against AERONET ground-based measurements

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    Water vapor plays an important role in the greenhouse effect, rendering it an atmospheric constituent that requires continuous and global monitoring by different types of remote sensing instruments. The TROPOspheric Monitoring Instrument Sentinel-5 Precursor (TROPOMI/S5P) Total Column Water Vapor (TCWV) is a new product retrieved from the visible blue spectral range (435–455 nm), using an algorithm that was originally developed for the GOME-2/MetOp sensors. For the purposes of this work, 2.5 years of continuous satellite observations at high spatial resolution are validated against co-located (in space and in time) precipitable water Level 2.0 (quality-assured) ground-based measurements from the NASA AERONET (AErosol RObotic NETwork). The network uses Cimel Sun photometers located at approximately 1300 stations globally to monitor precipitable water among other products. Based on data availability, 369 of the stations were used in this study. The two datasets, satellite- and ground-based, were co-located, and the relative differences of the comparisons were calculated and statistically analyzed. The Pearson correlation coefficient of the two products is found to be 0.91, and the mean bias of the overall relative percentage differences is of the order of −2.7 %. For the Northern Hemisphere midlatitudes (30–60∘ N), where the density of the ground-based stations is high, the mean relative bias was found to be −1.8 %, while in the tropics (±15∘) the TROPOMI TCWV product has a relative dry bias of up to −10 %. The effect of various algorithm and geophysical parameters, such as air mass factor, solar zenith angle, clouds and albedo, is also presented and discussed. It was found that the cloud properties affect the validation results, leading the TCWV to a dry bias of −20 % for low cloud heights (cloud top pressure (CTP) &gt;800 hPa). Moreover, cloud albedo introduces a wet bias of 15 % when it is below 0.3 and a dry bias up to −25 % when the clouds are more reflective. Overall, the TROPOMI/S5P TCWV product, on a global scale and for moderate albedo and cloudiness, agrees well at -2.7±4.9 % with the AERONET observations but probably within about −8 % to −13 % with respect to the “truth”.</p

    Optical and hyperspectral image analysis for image-guided surgery

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    RaBit: Parametric Modeling of 3D Biped Cartoon Characters with a Topological-consistent Dataset

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    Assisting people in efficiently producing visually plausible 3D characters has always been a fundamental research topic in computer vision and computer graphics. Recent learning-based approaches have achieved unprecedented accuracy and efficiency in the area of 3D real human digitization. However, none of the prior works focus on modeling 3D biped cartoon characters, which are also in great demand in gaming and filming. In this paper, we introduce 3DBiCar, the first large-scale dataset of 3D biped cartoon characters, and RaBit, the corresponding parametric model. Our dataset contains 1,500 topologically consistent high-quality 3D textured models which are manually crafted by professional artists. Built upon the data, RaBit is thus designed with a SMPL-like linear blend shape model and a StyleGAN-based neural UV-texture generator, simultaneously expressing the shape, pose, and texture. To demonstrate the practicality of 3DBiCar and RaBit, various applications are conducted, including single-view reconstruction, sketch-based modeling, and 3D cartoon animation. For the single-view reconstruction setting, we find a straightforward global mapping from input images to the output UV-based texture maps tends to lose detailed appearances of some local parts (e.g., nose, ears). Thus, a part-sensitive texture reasoner is adopted to make all important local areas perceived. Experiments further demonstrate the effectiveness of our method both qualitatively and quantitatively. 3DBiCar and RaBit are available at gaplab.cuhk.edu.cn/projects/RaBit.Comment: CVPR 2023, Project page: https://gaplab.cuhk.edu.cn/projects/RaBit

    Strategies to Improve Antineoplastic Activity of Drugs in Cancer Progression

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    The aim of this Special Issue is to collect reports regarding all the recent strategies, directed at the improvement of antineoplastic activity of drugs in cancer progression, engaging all the expertise needed for the development of new anticancer drugs: medicinal chemistry, pharmacology, molecular biology, and computational and drug delivery studies
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