COVID-19 as a game-changer? The impact of the pandemic on urban trajectories.

Will the COVID-19 pandemic interrupt the recent European urbanization trends - and if so - what is the magnitude of this sudden shock, and how deaths, births, and net migration contribute to this disruption? Until now, most discussions on the topic have circled either around the anecdotal evidence of city center decline, or contrarian speculations about residential inertia and the forthcoming business-as-usual. Bringing clarity to the uncertainty and confusion surrounding COVID-19, this paper seeks to detect overarching patterns in and the magnitude of its sudden shock to long-term urban trajectories, understood as a reversal of the pre-pandemic population development trend, across European cities in the early 2020s. It reveals that during the first year of COVID-19, population growth in European cities significantly slowed down to -0.3 % per annum, with 28 % of all European cities having experienced a U-turn from population growth to loss. Out-migration was the main driver of such rapid urban shrinkage, while excess mortality associated with COVID-19 has also contributed to population loss in several European city-regions; some, especially, smaller cities suffered from a significant drop in birth rates. Based on the factorial, hierarchical, and temporal dimensions of the COVID-19 crisis, the paper provides a plausible forecast about the future of Europe's post-coronavirus city.

A trait-based typification of urban forests as nature-based solutions.

Urban forests as nature-based solutions (UF-NBS) are important tools for climate change adaptation and sustainable development. However, achieving both effective and sustainable UF-NBS solutions requires diverse knowledge. This includes knowledge on UF-NBS implementation, on the assessment of their environmental impacts in diverse spatial contexts, and on their management for the long-term safeguarding of delivered benefits. A successful integration of such bodies of knowledge demands a systematic understanding of UF-NBS. To achieve such an understanding, this paper presents a conceptual UF-NBS model obtained through a semantic, trait-based modelling approach. This conceptual model is subsequently implemented as an extendible, re-usable and interoperable ontology. In so doing, a formal, trait-based vocabulary on UF-NBS is created, that allows expressing spatial, morphological, physical, functional, and institutional UF-NBS properties for their typification and a subsequent integration of further knowledge and data. Thereby, ways forward are opened for a more systematic UF-NBS impact assessment, management, and decision-making.

Use and design of public green spaces in Serbian cities during the COVID-19 pandemic.

Since December 2019, the global community has been challenged by managing the COVID-19 health crisis. Some governments have restricted the use of public green spaces (PGS), as part of measures for limiting the spread of the virus. Although many scholars studied the changing perception of using PGS during the pandemic, the extent to which the planning and design of new PGS recognize new realities and lessons learned from the ongoing pandemic including requirements for social distancing is less illuminated. Against this background, this article seeks to assess the intersection between the institutional responsibility in planning, designing and managing PSG, and the corresponding perception by PGS users in the two Serbian cities Belgrade and Novi Sad during the ongoing pandemic. Therefore, the paper surveyed 400 respondents about their perception of introduced measures and physical settings of PGS including their specific suggestions concerning which features, if included, would help them remain vigilant during a pandemic. The findings suggest that people have very clear and diverse ideas about the planning, design and management of PGS during a health crisis adapted to their individual needs but also beneficial to the whole local community. In reviewing public green space design competition calls and results published from 2019 to 2021, this study finds that the global lessons learned about the use of public green spaces during the pandemic were not considered by local governments and professionals in Serbia when planning and designing them. In addition, residents are less likely to request changing ways of implementing, designing or managing PGS from their local government. These two aspects are striking in successfully shaping and managing PGS as a crucial resource in cities and communities bouncing back after the COVID-19 pandemic.

The impact of the COVID-19 pandemic on the use of and attitudes towards urban forests and green spaces: Exploring the instigators of change in Belgium.

The COVID-19 pandemic has strongly impacted our society, producing drastic changes in people's routines and daily mobility, and putting public spaces under a new light. This paper starts with the premise that the use of urban forests and green spaces - where and for who they were available and accessible - increased, when social restrictions were most stringent. It takes an explorative approach to examine changes in attitude towards urban forests and urban green spaces in terms of attraction (i.e., as the actual use behaviour), intended use (i.e., intention of going to green spaces), and civic engagement in relation to green spaces. In particular, it analyses the responses to a survey of 1987 respondents in Belgium and statistically examines the relationship between sociodemographic characteristics, urbanisation characteristics, actual and intended green space use, and changes in attitudes towards green spaces and civic engagement. The findings show that highly educated citizens experienced an increase in actual and intended use of green spaces during the pandemic, but that this increase differs among sociodemographic profiles such as impact of age or access to private green, and depends on their local built environment characteristics. In addition, the COVID-19 pandemic has strongly impacted citizens' attitudes, as well as (intended) behaviour and civil engagement with respect to the green spaces in their area.

Compact or spread? A quantitative spatial model of urban areas in Europe since 1990.

Changes in urban residential density represent an important issue in terms of land consumption, the conservation of ecosystems, air quality and related human health problems, as well as the consequential challenges for urban and regional planning. It is the decline of residential densities, in particular, that has often been used as the very definition of sprawl, describing a phenomenon that has been extensively studied in the United States and in Western Europe. Whilst these studies provide valuable insights into urbanization processes, only a handful of them have reflected the uneven dynamics of simultaneous urban growth and shrinkage, using residential density changes as a key indicator to uncover the underlying dynamics. This paper introduces a contrasting analysis of recent developments in both de- and re-concentration, defined as decreasing or increasing residential densities, respectively. Using a large sample of European cities, it detects differences in density changes between successional population growth/decline. The paper shows that dedensification, found in some large cities globally, is not a universal phenomenon in growing urban areas; neither the increasing disproportion between a declining demand for and an increasing supply of residential areas nor actual concentration processes in cities were found. Thus, the paper provides a new, very detailed perspective on (de)densification in both shrinking and growing cities and how they specifically contribute to current land take in Europe.

Quantitative thermophoretic study of disease-related protein aggregates.

Amyloid fibrils are a hallmark of a range of neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. A detailed understanding of the physico-chemical properties of the different aggregated forms of proteins, and of their interactions with other compounds of diagnostic or therapeutic interest, is crucial for devising effective strategies against such diseases. Protein aggregates are situated at the boundary between soluble and insoluble structures, and are challenging to study because classical biophysical techniques, such as scattering, spectroscopic and calorimetric methods, are not well adapted for their study. Here we present a detailed characterization of the thermophoretic behavior of different forms of the protein α-synuclein, whose aggregation is associated with Parkinson's disease. Thermophoresis is the directed net diffusional flux of molecules and colloidal particles in a temperature gradient. Because of their low volume requirements and rapidity, analytical methods based on this effect have considerable potential for high throughput screening for drug discovery. In this paper we rationalize and describe in quantitative terms the thermophoretic behavior of monomeric, oligomeric and fibrillar forms of α-synuclein. Furthermore, we demonstrate that microscale thermophoresis (MST) is a valuable method for screening for ligands and binding partners of even such highly challenging samples as supramolecular protein aggregates.

Understanding the similarity in thermophoresis between single- and double-stranded DNA or RNA.

Thermophoresis is the movement of molecules in a temperature gradient. For aqueous solutions its microscopic basis is debated. Understanding thermophoresis for this case is, however, important since it proved very useful to detect the binding affinity of biomolecules and since thermophoresis could have played an important role in early molecular evolution. Here we discuss why the thermophoresis of single- and double-stranded oligonucleotides - DNA and RNA - is surprisingly similar. This finding is understood by comparing the spherical capacitor model for single-stranded species with the case of a rod-shaped model for double-stranded oligonucleotides. The approach describes thermophoresis of DNA and RNA with fitted effective charges consistent with electrophoresis measurements and explains the similarity between single- and double-stranded species. We could not confirm the sign change for the thermophoresis of single- versus double-stranded DNA in crowded solutions containing polyethylene glycol [Y. T. Maeda, T. Tlusty, and A. Libchaber, Proc. Natl. Acad. Sci. USA 109, 17972 (2012)], but find a salt-independent offset while the Debye length dependence still satisfies the capacitor model. Overall, the analysis documents the continuous progress in the microscopic understanding of thermophoresis.

Detection of thermoresponsive polymer phase transition in dilute low-volume format by microscale thermophoretic depletion.

Environmentally responsive polymers are becoming increasingly important in the biomaterials field for use as diagnostic reagents, drug carriers, and tissue engineering scaffolds. Characterizing polymer phase transitions by cloud point curves typically requires large milliliter volumes of sample at high micromolar solution concentrations. Here we present a method based on quantification of thermophoretic Soret diffusion that allows determination of polymer phase transitions using only ~1 µL of liquid at dilute nanomolar concentrations, effectively reducing the amount of sample required by a factor of 10(6). We prepared an oligo(ethylene glycol) (OEG) methyl ether methacrylate copolymer via RAFT polymerization. End-group modification with fluorescent BODIPY-maleimide provided a dye-labeled pOEG-BODIPY conjugate with a lower critical solution temperature (LCST) in the range of ~25-35 °C. Thermophoresis measurements in dilute solution demonstrated a marked change in polymer thermodiffusion in the vicinity of the LCST. We measured the temperature dependence of thermodiffusion and transformed these data sets into sigmoidal curves characterizing the phase transition of the polymer. Finite element modeling suggested a correction to the measured values that brought the transition temperatures measured by thermophoresis into accord with the cloud point curves. Our results demonstrate that observation of polymer thermodiffusion in a low volume dilute format is a facile method for determining polymer phase transition temperatures.

DNA concentration modulation on supported lipid bilayers switched by surface acoustic waves.

Spatially addressable arrays of molecules embedded in or anchored to supported lipid bilayers are important for on-chip screening and binding assays; however, methods to sort or accumulate components in a fluid membrane on demand are still limited. Here we apply in-plane surface acoustic shear waves (SAWs) to laterally accumulate double-stranded DNA segments electrostatically bound to a cationic supported lipid bilayer. The fluorescently labeled DNA segments are found to segregate into stripe patterns with a spatial frequency corresponding to the periodicity of the standing SAW wave (~10 µm). The DNA molecules are accumulated 10-fold in the regions of SAW antinodes. The superposition of two orthogonal sets of SAW sources creates checkerboard like arrays of DNA demonstrating the potential to generate arrayed fields dynamically. The pattern relaxation time of 0.58 s, which is independent of the segment length, indicates a sorting and relaxation mechanism dominated by lipid diffusion rather than DNA self-diffusion.