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Mechanically Tunable Biofabricated Channels Enable Mimicking Arterial Pulsatility and Dynamic Tissue Actuation
Get PDFDynamic alteration of blood vessel geometry is an inherent feature of the circulatory system. However, while the engineering of multiscale, branched, and interconnected blood vessels has been well explored, mimicking the dynamic behavior (e.g., pulsatile blood flow) of native arterial vessels has remained understudied. This is surprising because the natural pulsatile flow and subsequent dynamic deformation of arteries provide physiologically relevant mechanical actuation to proximal cells and tissues, contributing to both tissue homeostasis and disease progression. Yet, many tissue engineering efforts and Organ-on-Chip developments have focused on replicating vessel structure, while overlooking the native mechanical dynamicity that governs arterial tissue function. Here, the development of an on-demand tunable elastic hydrogel is reported, composed of tyramine-conjugated alginate, offering controlled, reversible dilation under physiologically relevant flow. Exploring casted and 3D bioprinted channels, how vessel dilation influences shear stresses in relation to vessel compliance is investigated. This approach is demonstrated to allow for hydrodynamic mechanodeformation and stimulation of engineered tissues. Moreover, it is revealed that pulsatile flow deformation alters compound penetration rates (e.g., nutrients and pharmaceuticals) into surrounding tissues. Finally, the spatially controlled stiffening of engineered blood vessels is demonstrated to locally limit the dilation, modeling blood vessel diseases such as stenosis or aneurysm.</p
A Programmable Resolution Digital-to-Frequency or Period Converter With Sawtooth-Based Jitter Reduction
Get PDFOpen-loop fractional output dividers (FODs) are compact, digital-intensive frequency synthesizers with instantaneous frequency switching capability. Traditional FODs linearly map a digital code to frequency [digital-to-frequency converter (DFC)] or to period [digital-to-period converter (DPC)] with a fixed frequency or period resolution, respectively. This article proposes a flexible FOD that can be reconfigured to a DFC or a DPC with a programmable frequency or period step size. An analog-sawtooth-based phase interpolation approach is used to cancel the digital quantization errors. The interpolation circuit exploits a dual-alternating slope digital-to-time converter (DTC) architecture with a delay that is insensitive to process, voltage, and temperature variations and is tolerant to power supply noise. Fabricated in GlobalFoundries 22-nm FDSOI technology, the proposed FOD prototype produces the output frequencies ranging from 132 to 404 MHz using a 3 GHz input clock while consuming 5.5 mW and occupying an active area of 0.032 mm2. The fractional spurs are below −50 dBc at the nominal condition and below −47 dBc across supply, bias current, and temperature variations after performing a one-time calibration at 0.9 V supply voltage and room temperature
Vegetation optimal temperature modulates global vegetation season onset shifts in response to warming climate
No full textThe warming climate strongly impacts vegetation phenology, altering the terrestrial carbon cycle, biodiversity, and food production. Here, we analyzed satellite observations from 1982 to 2015 and found that approximately one-third of vegetated areas experienced a significant shift in the timing of the start of the growing season (SOS), with 65.5% exhibiting an earlier trend and 34.5% a delay. We revealed that these changes in SOS were significantly associated with temperature variations, with a response depending on the differences between seasonal temperature and optimal growing temperature for vegetation (ΔT). When ΔT < 0 (seasonal temperature below optimal temperature), warming accelerates the photosynthetic process, leading to an earlier SOS. Conversely, when ΔT > 0, vegetation may experience photosynthetic inhibition induced by rising temperature, delaying SOS. Based on these findings, trends of earlier SOS can be expected to gradually decelerate and even potentially transition into delayed shifts with additional warming in the future.</p
A macroscale evapotranspiration benchmark based on spatial and temporal enhancements to the Budyko framework
No full textThe Budyko framework estimates macroscale evapotranspiration (ET) through hydrological partitioning, which determines what proportion of precipitation becomes ET or passes overland as runoff. This method has been widely used for modelling catchment ET and calibrating satellite-based ET algorithms at multi-annual timesteps, as it effectively accounts for how the relationship between water and energy balance changes with climatic aridity. However, substantial deviations from the predictive Budyko curve are observed as the spatiotemporal resolution increases, suggesting that additional environmental controls beside aridity also significantly influence hydrological partitioning over space and time. In this study, we assessed the impact of 14 environmental indicators on hydrological partitioning from the Budyko framework across 45 catchments over central-western Europe. The combination of catchment slope and two climatic factors - cumulative moisture surplus andrainfall erosivity - effectively explained spatial differences in hydrological partitioning (r = 0.83, rRMSE = 11.66 %). Interannual variations in the enhanced vegetation index and the fraction of precipitation falling as snow captured the temporal scatters (r = 0.37, rRMSE = 14.18 %). Based on these findings, we introduced a two-step modification involving a spatial adjustment of curve parameter (w) and a temporal correction of curve scatter (α) into the Budyko model, which led to improved ET prediction (Δr = 0.30, ΔRMSE = -21.62 mm yr-1) compared to the original framework. The revised Budyko model can be further applied to map ET beyondcatchment scale, which facilitates water balance studies at regional scales. The Budyko-predicted ET, independent from existing energy-balance ET (ETEB) products, can also serve as a macroscale water-balance ET benchmark for satellite-based products in data-scarce regions
Knowledge Transformation in Purchasing and Supply Management:A Process Perspective
No full textTo succeed in the face of constantly changing business challenges, Purchasing and Supply Management (PSM) needs to develop strong knowledge management (KM) mechanisms to equip individuals with accurate, reliable, and up-to-date knowledge and has, therefore, become a significant factor in building competence in this area. Although inter-organizational processes within the context of supply chains and supplier development have previously been studied, little is known about the transformative nature of the PSM function itself. Following a process perspective and drawing on the SECI model of knowledge creation, we contextualize the construct of knowledge assets in PSM and conceptualize mechanisms behind their conversion. Based on thirty-four interviews with PSM practitioners, we show how PSM knowledge is curated and study the applications of KM dynamics within the PSM practice. Our work also highlights barriers to this process and provides recommendations for improving PSM practices and strengthening learning capabilities
Protoplasts under stress:Investigating the effect of compression on protoplasts using microfluidics
No full textProtoplasts are plant cells which have had their cell walls enzymatically removed. They can be isolated from almost any plant tissue of many different plant species. The key feature of protoplasts is that they can be induced to regenerate from a single cell back into a full plant. The regeneration of a protoplast into a specific tissue type or a whole plant is a complex, time and labor-consuming task with a yield that is not easy to predict, as all the factors affecting the regeneration efficiency, both internal and external, are not yet fully understood. The complexity of the regeneration process makes it difficult to investigate the sub-processes happening therein. There are phenomena that still bear exploration even in the early, single-cell stage of regeneration. In this thesis, we investigated whether the application of mechanical compression on a single protoplast in a finely controlled microfluidic environment can affect their divisions and cell wall regeneration. Microfluidics served here as an engineering tool, that enabled us to reproducibly apply stimuli to cultured cells and closely observe the result. In this thesis, microfluidic platforms were used to investigate the initial divisions of freshly isolated protoplasts of Nicotiana tabacum, a widely used model plant species. Uniquely, our devices allowed us to affect these protoplasts with mechanical compression without also introducing other known factors of influence like osmotic stress. Our microfluidic device was designed to be compatible with high-content imaging platforms, allowing us to generate large time-resolved image datasets of cell behavior. Due to the large quantities of data generated on this platform and the sometimes subtle effects that compression has on the regeneration process, we recognized a strong need for automated tools for data analysis. Additionally, such a rich dataset could serve as the input for a prediction model that would make it possible to predict the outcome of the regeneration of a single protoplast based on its initial image. Such a model would be of great value both for fundamental biology, as it can help identify specific features crucial for the regeneration success, and the crop industry, as then it can significantly improve the efficiency of the regeneration process
Nanofabrication of 3D Photonic Band Gap Crystals from Silicon to Control the Emission of Light
No full textEffect of load and twist on filament packing in three-strand aramid fibre ropes: a micro-CT study
No full textThis study investigates how varying rope and strand twists influence the filament packing fraction in three-strand Aramid fibre ropes. Micro-computed tomography (micro-CT) scanning was used to visualize and quantify filament arrangements under different twist configurations and loads. High-resolution CT-scan image segmentation enabled the calculation of local filament packing fractions. Results indicate that twist parameters strongly affect how tightlyfilaments pack inside strands, particularly when a tensile load is applied. Higher twist levels often lead to a more compact internal structure, whereas lower twist levels introduce voids and an uneven arrangement. Under tensile loading, additional compaction is observed, especially at strand-to-strand interfaces. The findings help in understanding how twist geometry and applied tensile load redistribute filaments in a three-strand configuration, providing insights intoload sharing, potential filament slip, and internal damage – all critical factors in assessing rope performance and service life
Planning Under Uncertainties with Closed-Loop Sensitivity:Recent Results and Perspectives
No full textThis paper presents a comprehensive summary of recent advancements in motion planning under parametric uncertainties, focusing on the application of closed-loop state sensitivity. This concept provides a framework for quantifying how deviations in model parameters affect the behavior of a system in closed-loop, facilitating the generation of robust trajectories. Various methods have been proposed to improve the resilience of robotic systems to model inaccuracies. However, these approaches often face challenges such as computational complexity and limitations in real-time applications. This paper synthesizes key results from several recent works, highlighting the development of techniques that optimize trajectory robustness while reducing computational overhead. Additionally, we outline the practical applications of these methods, discussing their validation through simulations and experiments on robotic systems subject to non-negligible uncertainties in their models.</p