An axiomatization of the nucleolus of the assignment game

[cat] En el domini dels jocs bilaterals d’assignació, es presenta una axiomàtica del nucleolus com l´unica solució que compleix les propietats de consistència respecte del joc derivat definit per Owen (1992) i monotonia de les queixes dels sectors respecte de la seva cardinalitat. Com a conseqüència obtenim una caracterització geomètrica del nucleolus mitjançant una propietat de bisecció més forta que la que satisfan els punts del kernel (Maschler et al, 1979).

Buy-and-Hold Strategies and Comonotonic Approximations

[cat] En aquest article estudiem estratègies “comprar i mantenir” per a problemes d’optimitzar la riquesa final en un context multi-període. Com que la riquesa final és una suma de variables aleatòries dependents, on cadascuna d’aquestes correspon a una quantitat de capital que s’ha invertit en un actiu particular en una data determinada, en primer lloc considerem aproximacions que redueixen l’aleatorietat multivariant al cas univariant. A continuació, aquestes aproximacions es fan servir per determinar les estratègies “comprar i mantenir” que optimitzen, per a un nivell de probabilitat donat, el VaR i el CLTE de la funció de distribució de la riquesa final. Aquest article complementa el treball de Dhaene et al. (2005), on es van considerar estratègies de reequilibri constant.

A note on the coincidence between Stackelberg and Nash equilibria in a differential game between government and firms

[cat] A Navas i Marín Solano es va demostrar la coincidència entre els equilibris de Nash i de Stackelberg per a una versi´o modificada del joc diferencial proposat por Lancaster (1973). Amb l’objectiu d’obtenir una solució interior, es van imposar restriccions importants sobre el valors dels paràmetres del model. En aquest treball estenem aquest resultat, en el límit en que la taxa de descompte és igual a zero, eliminant les restriccions i considerant totes les solucions possibles.

The assignment game: core bounds for mixed-pair coalitions

In the assignment game framework, we try to identify those assignment matrices in which no entry can be increased without changing the coreof the game. These games will be called buyer¿seller exact games and satisfy the condition that each mixed¿pair coalition attains the corresponding matrix entry in the core of the game. For a given assignment game, a unique buyerseller exact assignment game with the same core is proved to exist. In order to identify this matrix and to provide a characterization of those assignment games which are buyer¿seller exact in terms of the assignment matrix, attainable upper and lower core bounds for the mixed¿pair coalitions are found. As a consequence, an open question posed in Quint (1991) regarding a canonical representation of a ¿45o¿lattice¿ by means of the core of an assignment game can now be answered

Early antifungal intervention strategies in ICU patients.

PURPOSE OF REVIEW: Despite progress in the understanding of the pathophysiology of invasive candidiasis, and the development of new classes of well tolerated antifungals, invasive candidiasis remains a disease difficult to diagnose, and associated with significant morbidity and mortality. Early antifungal treatment may be useful in selected groups of patients who remain difficult to identify prospectively. The purpose of this review is to summarize the recent development of risk-identification strategies targeting early identification of ICU patients susceptible to benefit from preemptive or empirical antifungal treatment. RECENT FINDINGS: Combinations of different risk factors are useful in identifying high-risk patients. Among the many risk factors predisposing to invasive candidiasis, colonization has been identified as one of the most important. In contrast to prospective surveillance of the dynamics of colonization (colonization index), integration of clinical colonization status in risk scores models significantly improve their accuracy in identifying patients at risk of invasive candidiasis. SUMMARY: To date, despite limited prospective validation, clinical models targeted at early identification of patients at risk to develop invasive candidiasis represent a major advance in the management of patients at risk of invasive candidiasis. Moreover, large clinical studies using such risk scores or predictive rules are underway.

Mating frequency of ant queens with alternative dispersal strategies, as revealed by microsatellite analysis of sperm

In social Hymenoptera (ants, bees, and wasps), the number of males that mate with the same queen affects social and genetic organization of the colony. However, the selective forces leading to single mating in certain conditions and multiple mating in others remain enigmatic. In this study, I investigated whether queens of the wood ant Formica paralugubris adopting different dispersal strategies varied in their mating frequency (the number of males with whom they mated). The frequency of multiple mating was determined by using microsatellite markers to genotype the sperm stored in the spermatheca of queens, and the validity of this method was confirmed by analysing mother-offspring combinations obtained from experimental single-queen colonies. Dispersing queens, which may found new colonies, did not mate with more males than queens that stayed within polygynous colonies, where the presence of numerous reproductive individuals ensured a high level of genetic diversity. Hence, this study provides no support to the hypotheses that multiple mating is beneficial because it increases genetic variability within colonies. Most of the F. paralugubris queens mated with a single male, whatever their dispersal strategy and life history. Moreover, multiple mating had little effect on colony genetic structure: the effective mating frequency was 1.11 when calculated from within-brood relatedness, and 1.13 when calculated from the number of mates detected in the sperm. Hence, occasional multiple mating by F. paralugubris queens may have no adaptive significance.

Exposure to superfluous information reduces cooperation and increases antisocial punishment in reputation-based interactions

Human cooperation is often based on reputation gained from previous interactions with third parties. Such reputation can be built on generous or punitive actions, and both, one's own reputation and the reputation of others have been shown to influence decision making in experimental games that control for confounding variables. Here we test how reputation-based cooperation and punishment react to disruption of the cognitive processing in different kinds of helping games with observers. Saying a few superfluous words before each interaction was used to possibly interfere with working memory. In a first set of experiments, where reputation could only be based on generosity, the disruption reduced the frequency of cooperation and lowered mean final payoffs. In a second set of experiments where reputation could only be based on punishment, the disruption increased the frequency of antisocial punishment (i.e. of punishing those who helped) and reduced the frequency of punishing defectors. Our findings suggest that working memory can easily be constraining in reputation-based interactions within experimental games, even if these games are based on a few simple rules with a visual display that provides all the information the subjects need to play the strategies predicted from current theory. Our findings also highlight a weakness of experimental games, namely that they can be very sensitive to environmental variation and that quantitative conclusions about antisocial punishment or other behavioral strategies can easily be misleading.

Drug targeting strategies for photodynamic therapy.

In human pathologies, therapeutic treatments are often limited by the lack of selectivity of drugs and their elevated effective concentrations. Targeting these agents to a defined tissue could enhance their selectivity and then diminish their side effects when compared to drugs that accumulate in the entire body. Targeting could also improve treatment efficiency by allowing a localized high concentration of the agents. Based on the different behaviors and patterns of expression between diseased and normal cells, strategies for targeting can be explored. For example, receptors, proteases or trans-membrane carriers could be different or differently expressed. Many therapeutic procedures rely on this fact, including photodynamic therapy (PDT). PDT is already used in the treatment of some cancers, of inflammatory diseases and others diseases such as age-related macular degeneration or acne. PDT relies on the activation of a photosensitizer (PS) by visible light which results in the production of cytotoxic reactive oxygen species. In PDT, the general distribution of PS to the whole body leads to generalized photosensitization and poor acceptance of treatments by patients. One way to avoid these effects is to improve the targeting of PSs to diseased tissues using modification of PS with peptides or proteins that will target specific receptors or enzymes. PSs could also be functionalized with non-proteic ligands such as organometalics to achieve targeted and/or combined therapies. Alternatively, PSs could be encapsulated in nanoparticles bearing targeting agents which will decrease concentration of free circulating PS and improve photodynamic efficiency. These different approaches will be discussed in the present review with an emphasis on the use of peptides and proteins.

Strategies of "Pseudomonas aeruginosa" to overcome copper limitation

Summary Copper is an important trace element and micronutrient for living organisms as it is the cofactor of several enzymes involved in diverse biological redox processes such as aerobic respiration, denitrification and photosynthesis. Despite its importance, copper may be poorly bioavailable in soils and aquatic environments, as well as in the human body, especially at physiological or alkaline pH. In this work, we have investigated the strategies that the versatile bacterium and opportunistic pathogen Pseudomonas aeruginosa has evolved to face and overcome copper limitation. The global response of the P. aeruginosa to copper limitation was assessed under aerobic conditions. Numerous iron uptake functions (including the siderophores pyoverdine and pyochelin) were down-regulated whereas expression of cioAB (encoding an alternative, copper-independent, cyanide-resistant ubiquinol oxidase) was up-regulated. Wild type P. aeruginosa was able to grow aerobically in a defined glucose medium depleted of copper by a copper chelator, whereas a cioAB mutant did not grow. Thus, P. aeruginosa relies on the CioAB enzyme to cope with severe copper deprivation. A quadruple cyo cco1 cco2 cox mutant, which was deleted for all known heme-copper terminal oxidases of P. aeruginosa, grew aerobically, albeit more slowly than did the wild type, indicating that the CioAB enzyme is capable of energy conservation. However, the expression of a cioA'-'lacZ fusion was less dependent on the copper status in the quadruple mutant than in the wild type, suggesting that copper availability might affect cioAB expression indirectly, via the function of the heme-copper oxidases. These results suggest that the CioAB enzyme can be used as a by-pass strategy to overcome severe copper limitation and perform aerobic respiration even if virtually no copper is available. The PA0114 gene, which encodes a protein of the SCOT/SenC family, was found to be important for copper acquisition and aerobic respiration in low copper conditions. A PA0114 (sent) mutant grew poorly in low copper media and had low terminal oxidase activity with TMPD (N,N,N',N'-tetramethyl-p-phenylenediamine), but expressed the CioAB enzyme at elevated levels. Addition of copper reversed these phenotypes, suggesting that periplasmic copper capture by the SenC protein is another strategy that helps P. aeruginosa to adapt to copper deprivation. RESUME Le cuivre est un micronutriment important pour les organismes vivants. Il représente le cofacteur de plusieurs enzymes impliquées dans une multitude de processus biologiques tels que la respiration aérobie, la dénitrification et la photosynthèse. Malgré son importance, le cuivre peut être peu disponible dans les sols, les environnements aquatiques et le corps humain, spécialement à pH physiologique ou alcalin. Dans ce travail nous avons étudié les stratégies développées par la bactérie pathogène opportuniste Pseudomonas aeruginosa PAO1 afm de faire face et de surmonter le manque de cuivre. La réponse globale de P. aeruginosa à la carence de cuivre a été analysée dans des conditions aérobie. Les résultats obtenus ont montré que plusieurs gènes impliqués dans l'acquisition du fer, tels que les gènes codant pour les sidérophores (pyoverdine et pyochéline), étaient réprimés, tandis que l'expression de l'opéron cioAB, codant pour l'oxydase terminale insensible au cyanure (CIO), était augmentée. La souche sauvage P. aeruginosa est capable de croître dans un milieu où la concentration en cuivre est limitée, due à la présence d'un chélateur spéciftque de cuivre, tandis que le mutant cioAB ne croît pas dans ces conditions. Nous avons conclu que P. aeruginosa nécessite l'oxydase terminale CIO pour faire face à la carence en cuivre. Un quadruple mutant affecté dans toutes les oxydases dépendantes du cuivre (cyo ccol cco2 cox) et appartenant aux oxydases de type hème-cuivre, peut croître en aérobie, néanmoins plus lentement que la souche sauvage, ce qui montre que l'enzyme CIO est capable de conserver l'énergie. L'expression de la fusion rapportrice cioA'-'IacZ chez le quadruple mutant est moins dépendante de la disponibilité de cuivre que chez la souche sauvage. Ces résultats suggèrent que la disponibilité de cuivre influence l'expression de cioAB d'une façon indirecte, par le biais des oxydases terminales de type héme-cuivre. Il est donc possible qu'en cas de carence de cuivre, P. aeruginosa utilise l'enzyme CIO comme stratégie afin de surmonter ce manque et de réaliser la respiration aérobie. Nous avons démontré que le gène PA0114, codant pour une protéine appartenant à la famille SCO1/SenC, est important dans l'acquisition et dans la respiration aérobie dans des environnements où le cuivre est présent en faible concentration. En ces conditions, la croissance du mutant senC est faible; de plus, l'activité des oxydases terminales en présence du donneur d'électrons TMPD (N,N,N,N'-tetraméthyl-p-phénylenediamine) est basse. Toutefois, l'addition de cuivre au milieu de culture permet de restaurer le phénotype du type sauvage. Ces résultats montrent que la protéine SenC est capable d'acquérir le cuivre et représente donc une autre stratégie chez P. aeruginosa pour s'adapter à un manque de cuivre.

Cardiovascular risk estimation and eligibility for statins in primary prevention comparing different strategies

Recommendations for statin use for primary prevention of coronary heart disease (CHD) are based on estimation of the 10-year CHD risk. It is unclear which risk algorithm and guidelines should be used in European populations. Using data from a population-based study in Switzerland, we first assessed 10-year CHD risk and eligibility for statins in 5,683 women and men 35 to 75 years of age without cardiovascular disease by comparing recommendations by the European Society of Cardiology without and with extrapolation of risk to age 60 years, the International Atherosclerosis Society, and the US Adult Treatment Panel III. The proportions of participants classified as high-risk for CHD were 12.5% (15.4% with extrapolation), 3.0%, and 5.8%, respectively. Proportions of participants eligible for statins were 9.2% (11.6% with extrapolation), 13.7%, and 16.7%, respectively. Assuming full compliance to each guideline, expected relative decreases in CHD deaths in Switzerland over a 10-year period would be 16.4% (17.5% with extrapolation), 18.7%, and 19.3%, respectively; the corresponding numbers needed to treat to prevent 1 CHD death would be 285 (340 with extrapolation), 380, and 440, respectively. In conclusion, the proportion of subjects classified as high risk for CHD varied over a fivefold range across recommendations. Following the International Atherosclerosis Society and the Adult Treatment Panel III recommendations might prevent more CHD deaths at the cost of higher numbers needed to treat compared with European Society of Cardiology guidelines.