•Kidney Exchange Problem (KEP) with preferences of patients over potential donors is studied.•The objective of the he problem is to find maximum cardinality stable exchanges.•Four new Integer ...Programming (IP) models, validated through computational experiments, are proposed for solving the problem.•The trade-off between the stability requirement and the maximization of the number of transplants is evaluated.•To our best knowledge, this is the first time IP models are suggested for finding maximum cardinality stable exchanges in KEP.
Kidney exchange programs (KEPs) represent an additional possibility of transplant for patients suffering from end-stage kidney disease. If a patient has a willing living donor with whom the patient is not compatible, the pair recipient–donor can join a pool of incompatible pairs and, if compatibility between recipient and donor in two or more pairs exists, organs can be exchanged between them. The problem can be modelled as an integer program that in general aims at finding the pairs that should be selected for transplant such that maximum number of transplants is performed.
In this paper, we consider that for each recipient there may exist a preference order over the organs that he/she can receive, since a recipient may be compatible with several donors but the level of compatibility with the recipient might vary for different donors. Under this setting, the aim is to find the maximum cardinality stable exchange, a solution where no blocking cycle exists, i.e., there is no cycle such that all recipients prefer the donor in that cycle rather than that in the exchange. For this purpose we propose four novel integer programming models based on the well-known edge and cycle formulations, and also on the position-indexed formulation. These formulations are adjusted for both finding stable and strongly stable exchanges under strict preferences and for the case when ties in preferences may exist. Furthermore, we study a situation when the stability requirement can be relaxed by addressing the trade-off between maximum cardinality versus number of blocking cycles allowed in a solution. The effectiveness of the proposed models is assessed through extensive computational experiments on a wide set of instances. Results show that the cycle-edge and position-indexed formulations outperform the other two formulations. Another important practical outcome is that targeting strongly stable solutions has a much higher negative impact on the number of transplants (with an average reduction of up to 20% for the bigger instances), when compared to stable solutions.
This paper examines differences in the connectedness between exchange rates and stock prices for companies with different asset currencies on the Hong Kong stock market, and it seeks to explain those ...differences by proposing a hypothesis on asset-denominated currency difference. Under a framework of investor heterogeneity, we establish a dynamic, discrete theoretical model to analyse the connectedness between exchange rates, the stocks of local Hong Kong companies, the stocks of companies from the mainland and foreign exchange interventions. Using monthly data from January 2000 to August 2018, we adopt the time-varying parameter vector auto-regression (TVP-VAR) model to empirically study the dynamic relationships between exchange rates and the prices of both Hong Kong-based and mainland-based stocks. The results show significant differences in the ways that exchange rates and prices for the two types of stocks are linked. The exchange rates are positively correlated with mainland stocks and negatively correlated with Hong Kong stocks. Moreover, foreign exchange intervention is found to be an effective means for stabilising exchange rates, although such intervention tends to increase stock volatility.
Abbreviations: TVP-VAR - time-varying parameter vector auto-regression model; MCMC - Monte Carlo-Markov Chain method.
The Asia-Pacific region remains understudied regarding return connectedness among exchange rate markets. Furthermore, previous studies mostly use average-based estimators to measure return ...connectedness, even though they are not necessarily suitable to quantify connectedness measures during extreme events, i.e. in the tails of the conditional distribution. The aim of this paper is to study the dynamic connectedness among 11 Asia-Pacific exchange rates from September 1994 to August 2019, not only on average but also in the left and right tails. Using mean-based measures of connectedness, the level of return connectedness is on average 32%, indicating a moderate level of connectedness across the currencies under study. However, using a novel quantile-based connectedness framework, the level of connectedness is found to be much higher, reaching around 85% at both the left and right tails of the conditional distribution. This result shows that return connectedness across the 11 exchange rates is much stronger during extreme negative and extreme positive events, suggesting that the application of mean-based models of connectedness in the Asia-Pacific exchange rate markets is too restrictive and inadequate. Furthermore, return connectedness measures are time-varying in all cases, but are less volatile in the tails. A detailed analysis involving the relative tail dependence shows that an asymmetric behaviour is present, indicating that return spillovers differ between periods of extreme market depreciations and periods of extreme market appreciations.
•Study extreme spillovers across Asia-Pacific currencies via quantile-based analyses.•Applying mean-based models of connectedness is too restrictive and inadequate.•Return spillovers are stronger at the tails of the distribution than at the mean.•Total return connectedness index is time-varying but is less volatile at the tails.•Relative tail dependence analysis shows evidence of an asymmetric behaviour.
•DOC removal up to 50% was achieved during long-term continuous operation.•Increasing raw water sulphate from 12 to 60 mg/L led to 19% lower DOC removal.•Secondary ion exchange was confirmed to ...involve DOC removal and sulphate release.•DOC affinity was constant, despite increasing resin loading and changes in counter-ion.
Biological ion exchange (BIEX) offers removal of dissolved organic carbon (DOC) with greatly reduced regeneration frequency. In the present work, a strong base anionic exchange resin was operated without regeneration and using inlet water with either Low (12 mg L−1) or High (60 mg L−1) sulphate and DOC of 2.75 or 5.0 mg L−1. Filters operated continuously for 226 days (16,500 bed volumes) and achieved DOC removal varying from 32% to 50%. Initially, sulphate and DOC were retained by the resin with chloride being released. During this period, DOC removal occurred due to traditional mechanisms, referred to as primary ion exchange. Following this initial period, DOC removal continued even though the conventionally defined resin capacity was exhausted (based on chloride loading). During the later period, no chloride release was observed, but instead sulphate was released. Although suggested by others, the present study is the first to confirm the direct exchange in charge equivalence of anions removed (DOC and nitrate) to released (sulphate) during the secondary ion exchange mechanism. Further, increasing inlet sulphate from 12 to 60 mg L−1 resulted in a 19% decrease in DOC removal. Finally, percent DOC removal was affected only by an increase of inlet DOC but not changes to the counter ion or after DOC loading on the resin increased to 1/3 of total capacity. This work promotes BIEX as a viable alternative to biological activated carbon and a leading solution for low-maintenance DOC removal.
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Building upon a Behavioural Equilibrium Exchange Rate model, estimated at a quarterly frequency since 1999 on a broad sample of 57 countries, this paper assesses both the size and the persistence of ...real effective exchange rate misalignments of countries that have adopted the euro and of those outside the euro area. The euro area is indeed a poignant example of a currency union in which the nominal exchange rate is irrevocably fixed; the non-euro area economies considered include countries with either flexible or pegged currencies. While misalignments are found to be smaller in the euro area than in the rest of the world, they are also more persistent; however, the persistence in the euro area has decreased after the global financial crisis. Finally, it is found that improvements in the quality of institutions – observed in particular after 2009 within the euro area – reduce the persistence of misalignments.
We document how product quality responds to exchange rate movements and quantify the extent to which these quality changes affect the aggregate pass-through into export prices. We analyze the ...substantial sudden appreciation of the Swiss franc post removal of the 1.20-CHF-per-euro lower bound in 2015 using export data representing a large share of the universe of goods exports from Switzerland. We find that firms upgrade the quality of their products after the appreciation. Furthermore, they disproportionately remove lower-quality products from their product ranges. This quality upgrading and quality sorting effect accounts for a substantial share of the total pass-through one year after the appreciation. We cross-check our results with the microdata underlying the Swiss export price index, which includes an adjustment factor for quality based on firms' reported product replacements, and obtain similar results.
The main aim of this paper is to investigate the volatility determinants of crude oil and foreign exchange markets and jump spillover between them. We consider currencies of two major oil-importing ...countries (India and China) over the sample period of January 1, 2013 to October 31, 2019. We find evidence of positive return spillover from the oil to the foreign exchange market; however, there is a lack of return spillover in the other direction. Oil jumps appear to have a negative impact on exchange rate conditional volatility, and the latter responds asymmetrically to disentangled (positive and negative) oil price jumps. We also report disentangled exchange rate jumps' significant impact on conditional oil price volatility. These results, however, are asymmetric based on the nature of jumps and alternative oil price series. Finally, we do not find evidence of co-jump between the oil and foreign exchange markets. These results have important implications for investors and policymakers.
•Examines the intraday dynamics of crude oil and exchange rates of India and China•Oil jumps have a negative impact on exchange rate conditional volatility.•There is no co-jump between the oil and foreign exchange markets.
DUAL-DONOR ORGAN EXCHANGE Ergin, Haluk; Sönmez, Tayfun; Ünver, M. Utku
Econometrica,
September 2017, Letnik:
85, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Owing to the worldwide shortage of deceased-donor organs for transplantation, living donations have become a significant source of transplant organs. However, not all willing donors can donate to ...their intended recipients because of medical incompatibilities. These incompatibilities can be overcome by an exchange of donors between patients. For kidneys, such exchanges have become widespread in the last decade with the introduction of optimization and market design techniques to kidney exchange. A small but growing number of liver exchanges have also been conducted. Over the last two decades, a number of transplantation procedures emerged where organs from two living donors are transplanted to a single patient. Prominent examples include dual-graft liver transplantation, lobar lung transplantation, and simultaneous liver-kidney transplantation. Exchange, however, has been neither practiced nor introduced in this context. We introduce dual-donor organ exchange as a novel transplantation modality, and through simulations show that living-donor transplants can be significantly increased through such exchanges. We also provide a simple theoretical model for dual-donor organ exchange and introduce optimal exchange mechanisms under various logistical constraints.
Low‐cost solution‐processed lead chalcogenide colloidal quantum dots (CQDs) have garnered great attention in photovoltaic (PV) applications. In particular, lead selenide (PbSe) CQDs are regarded as ...attractive active absorbers in solar cells due to their high multiple‐exciton generation and large exciton Bohr radius. However, their low air stability and occurrence of traps/defects during film formation restrict their further development. Air‐stable PbSe CQDs are first synthesized through a cation exchange technique, followed by a solution‐phase ligand exchange approach, and finally absorber films are prepared using a one‐step spin‐coating method. The best PV device fabricated using PbSe CQD inks exhibits a reproducible power conversion efficiency of 10.68%, 16% higher than the previous efficiency record (9.2%). Moreover, the device displays remarkably 40‐day storage and 8 h illuminating stability. This novel strategy could provide an alternative route toward the use of PbSe CQDs in low‐cost and high‐performance infrared optoelectronic devices, such as infrared photodetectors and multijunction solar cells.
Highly air‐stable PbSe colloidal quantum dots (CQDs) are produced via an in situ chloride and cadmium passivation technique. A high‐quality film is fabricated using solution‐phase ligand exchange and a one‐step deposition method. By using a PbS‐EDT (EDT = 1,2‐ethanedithiol) hole‐transporting layer, a PbI2‐capped PbSe‐CQD‐based photovoltaic device shows a record efficiency of 10.68% with impressive air and light soaking stability.
A gas-free continuously regenerated-anion impurity removal device (CR-ARD) is described for ion chromatography (IC). It is a sandwiched configuration consisting of three channels. The central eluent ...channel is isolated from two outer regenerant channels by stacked anion exchange membranes (sAEM) and a bipolar membrane (BPM) plus stacked cation exchange membranes (BPM-sCEM), in which the anion exchange side of BPM is facing the central channel. The sAEM side is an anode with respect to the cathode of the BPM-sCEM side. The central channel is packed with strongly basic anion exchange resins in hydroxide form. The application of an electrical voltage to the device causes enhanced water splitting at the interface of BPM to occur and the potential drives the hydroxide ions through the resin phase toward the anode, thereby enabling continuous regeneration of the resin and avoiding any off-line regeneration. Meanwhile, nonhydroxide anionic impurities (basically carbonate) are transported toward the anode through the sAEM. It does not produce gas in the eluent channel, and no degasser is required afterward. It shows a strong ability to remove anionic impurities, as indicated by effective removal of 5 mM CO3 2– injected sample plug (25 μL, 125 pmol) or continuous removal of 600 μM KNO3 solution at 1 mL/min (10 nmol/s) over 300 min. Much improved peak integration at the gradient mode and a higher signal-to-noise ratio at the isocratic mode can be achieved by CR-ARD. To our knowledge, this is the first account of gas-free CR-ARD.
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