Policymakers around the world are enforcing mobility restriction policies such as lockdowns, facemask requirements and social distancing to curb the spread of Covid-19. While these policies are ...effective in preventing the spread of virus, the economic implications are not well understood. We contribute to the literature by examining the impact of these policies on the offline retail sector. Specifically, we measure the effects of these policies on the daily number of shoppers passing by, which we refer to as ‘footfall’, along major shopping streets in Netherlands. We rely on unique proprietary Wifi data to accurately measure footfall. Our findings imply that all these policies attribute to a non-trivial reduction in footfall levels along shopping streets. While lockdowns led to a 50% reduction in footfall along major shopping streets, shopping streets faced with facemask regulations also experience a 25% drop in human traffic. A reduction in footfall translates into a substantial reduction in retail income of between 12% and 25%.
We study the economic effects of place-based policies in the housing market, by investigating the effects of a place-based program on prices of surrounding owner-occupied properties. The program ...improved the quality of public housing in 83 impoverished neighborhoods throughout the Netherlands. We combine a first-difference approach with a fuzzy regression-discontinuity design to address the fundamental issue that these neighborhoods are endogenously treated. Improvements in public housing induced surrounding housing prices to increase by 3.5%. The program's external benefits are sizable and at least half of the value of investments in public housing.
When selling a home, through the choice of the list price, sellers make a trade‐off between achieving a quick sale at a low price or waiting for higher bids. This list‐price setting decision is ...governed by a discount rate. Using data on housing sales in the Netherlands, we derive gross discount rates under bilateral bargaining and bidding wars. The estimated discount rates are 25%–35%, which are considerably higher than long‐run housing market discount rates and may result from the seller's unfamiliarity with the selling process. The rates are higher for sellers that already moved and have a low education.
Balance training aims to improve balance and transfer acquired skills to real-life tasks. How older adults adapt gait to different conditions, and whether these adaptations are altered by balance ...training, remains unclear. We hypothesized that reorganization of modular control of muscle activity is a mechanism underlying adaptation of gait to training and environmental constraints. We investigated the transfer of standing balance training, shown to enhance unipedal balance control, to gait and adaptations in neuromuscular control of gait between normal and narrow-base walking in twenty-two older adults (72.6 ± 4.2 years). At baseline, after one, and after ten training sessions, kinematics and EMG of normal and narrow-base treadmill walking were measured. Gait parameters and temporal activation profiles of five muscle synergies were compared between time-points and gait conditions. Effects of balance training and an interaction between training and gait condition on step width were found, but not on synergies. After ten training sessions step width decreased in narrow-base walking, while step width variability decreased in both conditions. Trunk center of mass displacement and velocity, and the local divergence exponent, were lower in narrow-base compared to normal walking. Activation duration in narrow-base compared to normal walking was shorter for synergies associated with dominant leg weight acceptance and non-dominant leg stance, and longer for the synergy associated with non-dominant heel-strike. Time of peak activation associated with dominant leg stance occurred earlier in narrow-base compared to normal walking, while it was delayed in synergies associated with heel-strikes and non-dominant leg stance. The adaptations of synergies to narrow-base walking may be interpreted as related to more cautious weight transfer to the new stance leg and enhanced control over center of mass movement in the stance phase. The improvement of gait stability due to standing balance training is promising for less mobile older adults.
There are many graph problems that can be solved in linear or polynomial time with a dynamic programming algorithm when the input graph has bounded treewidth. For combinatorial optimization problems, ...this is a useful approach for obtaining fixed-parameter tractable algorithms. Starting from trees and series-parallel graphs, we introduce the concepts of treewidth and tree decompositions, and illustrate the technique with the Weighted Independent Set problem as an example. The paper surveys some of the latest developments, putting an emphasis on applicability, on algorithms that exploit tree decompositions, and on algorithms that determine or approximate treewidth and find tree decompositions with optimal or close to optimal treewidth. Directions for further research and suggestions for further reading are also given.
Dried blood spot (DBS) analysis has been introduced more and more into clinical practice to facilitate Therapeutic Drug Monitoring (TDM). To assure the quality of bioanalytical methods, the design, ...development and validation needs to fit the intended use. Current validation requirements, described in guidelines for traditional matrices (blood, plasma, serum), do not cover all necessary aspects of method development, analytical- and clinical validation of DBS assays for TDM. Therefore, this guideline provides parameters required for the validation of quantitative determination of small molecule drugs in DBS using chromatographic methods, and to provide advice on how these can be assessed. In addition, guidance is given on the application of validated methods in a routine context. First, considerations for the method development stage are described covering sample collection procedure, type of filter paper and punch size, sample volume, drying and storage, internal standard incorporation, type of blood used, sample preparation and prevalidation. Second, common parameters regarding analytical validation are described in context of DBS analysis with the addition of DBS-specific parameters, such as volume-, volcano- and hematocrit effects. Third, clinical validation studies are described, including number of clinical samples and patients, comparison of DBS with venous blood, statistical methods and interpretation, spot quality, sampling procedure, duplicates, outliers, automated analysis methods and quality control programs. Lastly, cross-validation is discussed, covering changes made to existing sampling- and analysis methods. This guideline of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology on the development, validation and evaluation of DBS-based methods for the purpose of TDM aims to contribute to high-quality micro sampling methods used in clinical practice.
Plastic solar cells bear the potential for large‐scale power generation based on materials that provide the possibility of flexible, lightweight, inexpensive, efficient solar cells. Since the ...discovery of the photoinduced electron transfer from a conjugated polymer to fullerene molecules, followed by the introduction of the bulk heterojunction (BHJ) concept, this material combination has been extensively studied in organic solar cells, leading to several breakthroughs in efficiency, with a power conversion efficiency approaching 5 %. This article reviews the processes and limitations that govern device operation of polymer:fullerene BHJ solar cells, with respect to the charge‐carrier transport and photogeneration mechanism. The transport of electrons/holes in the blend is a crucial parameter and must be controlled (e.g., by controlling the nanoscale morphology) and enhanced in order to allow fabrication of thicker films to maximize the absorption, without significant recombination losses. Concomitantly, a balanced transport of electrons and holes in the blend is needed to suppress the build‐up of the space–charge that will significantly reduce the power conversion efficiency. Dissociation of electron–hole pairs at the donor/acceptor interface is an important process that limits the charge generation efficiency under normal operation condition. Based on these findings, there is a compromise between charge generation (light absorption) and open‐circuit voltage (VOC) when attempting to reduce the bandgap of the polymer (or fullerene). Therefore, an increase in VOC of polymer:fullerene cells, for example by raising the lowest unoccupied molecular orbital level of the fullerene, will benefit cell performance as both fill factor and short‐circuit current increase simultaneously.
A review of the processes and limitations that govern the device operation of polymer:fullerene bulk heterojunction solar cells is presented, with respect to the charge‐carrier transport and photogeneration mechanism. Dissociation of electron–hole pairs at the donor/acceptor interface is an important process that limits the charge generation efficiency (see figure).
The trap-assisted recombination of electrons and holes in organic semiconductors is investigated. The extracted capture coefficients of the trap-assisted recombination process are thermally activated ...with an identical activation energy as measured for the hole mobility μ(p). We demonstrate that the rate limiting step for this mechanism is the diffusion of free holes towards trapped electrons in their mutual Coulomb field, with the capture coefficient given by (q/ε)μ(p). As a result, both the bimolecular and trap-assisted recombination processes in organic semiconductors are governed by the charge carrier mobilities, allowing predictive modeling of organic light-emitting diodes.
The photocurrent in conjugated polymer-fullerene blends is dominated by the dissociation efficiency of bound electron-hole pairs at the donor-acceptor interface. A model based on Onsager's theory of ...geminate charge recombination explains the observed field and temperature dependence of the photocurrent in PPV:PCBM blends. At room temperature only 60% of the generated bound electron-hole pairs are dissociated and contribute to the short-circuit current, which is a major loss mechanism in photovoltaic devices based on this material system.
The effect of controlled thermal annealing on charge transport and photogeneration in bulk‐heterojunction solar cells made from blend films of regioregular poly(3‐hexylthiophene) (P3HT) and ...methanofullerene (PCBM) has been studied. With respect to the charge transport, it is demonstrated that the electron mobility dominates the transport of the cell, varying from 10–8 m2 V–1 s–1 in as‐cast devices to ≈3 × 10–7 m2 V–1 s–1 after thermal annealing. The hole mobility in the P3HT phase of the blend is dramatically affected by thermal annealing. It increases by more than three orders of magnitude, to reach a value of up to ≈ 2 × 10–8 m2 V–1 s–1 after the annealing process, as a result of an improved crystallinity of the film. Moreover, upon annealing the absorption spectrum of P3HT:PCBM blends undergo a strong red‐shift, improving the spectral overlap with solar emission, which results in an increase of more than 60 % in the rate of charge‐carrier generation. Subsequently, the experimental electron and hole mobilities are used to study the photocurrent generation in P3HT:PCBM devices as a function of annealing temperature. The results indicate that the most important factor leading to a strong enhancement of the efficiency, compared with non‐annealed devices, is the increase of the hole mobility in the P3HT phase of the blend. Furthermore, numerical simulations indicate that under short‐circuit conditions the dissociation efficiency of bound electron–hole pairs at the donor/acceptor interface is close to 90 %, which explains the large quantum efficiencies measured in P3HT:PCBM blends.
The effect of controlled thermal annealing on charge transport and photogeneration in bulk‐heterojunction solar cells made from blend films of poly(3‐hexylthiophene) (P3HT) and methanofullerene is investigated. The hole mobility in the P3HT phase of the blend is dramatically affected by annealing (see Figure). An increase in this hole mobility is the most important factor leading to a strong enhancement of the efficiency.
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