140,288 research outputs found
Optimal conservation strategy in fluctuating environments with species interactions: Resource-enhancement of the native species versus extermination of the alien species
No full textAlien species are often a major threat to native species. We consider optimal conservation strategies for a population whose viability is affected both by an alien species (such as a competitor, a predator, or a pathogen) and by random fluctuations of the environment (e.g. precipitation, temperature). We assume that the survivorship of the native population can be improved by providing resources such as food and shelter, and also by an extermination effort that decreases the abundance of the alien species. These efforts decrease the extinction probability of the native population, but they are accompanied by economic costs. We search for the optimal strategy that minimizes the weighted sum of the extinction probability and the economic costs over a single year. We derive conditions under which investment should be made in both resource-enhancement and extermination, and examine how the optimal effort levels change with parameters. When the optimal strategy includes both types of efforts, the optimal extermination effort level turns out to be independent of the density and economic value of the native species, or the variance of the environmental fluctuation. Furthermore, the optimal resource-enhancement effort is then. independent of the density of the alien species. However, the parameter dependencies greatly change if one of the efforts becomes zero. We also examine the situation in which the impact of the alien species is uncertain. The optimal extermination effort increases with the uncertainty of this impact except when the cost of extermination is very high. (c) 2006 Elsevier Ltd. All rights reserved
TANDEM MAGNETIC REFRIGERATOR FOR 1.8-K
No full textA tandem magnetic refrigerator has been developed for continuous operation between 4.2 and 1.8 K. This paper presents the design, computer simulation and construction of the prototype machine. The- regenerative concept is employed in the magnetic refrigerator to obtain a cascaded magnetic Carnot cycle effect along the temperature axis from the cold end to the warm end. Entropy pumping action from the cold heat reservoir to the warm heat reservoir occurs in the active magnetic regenerator. The inherent sources of irreversibility in regenerative magnetic refrigerators, i.e. heat capacity imbalance between magnetic refrigerant and heat transport medium, helium entrainment and dead volume effect, have been minimized by design optimization of the system components. The magnetic system of the tandem refrigerator has two virtually identical units, each consisting of a gadolinium gallium garnet (GGG; Gd3Ga5O12) magnetic core, a superconducting magnet, a warm end heat exchanger and a cold end heat exchanger. These components are united by a cryogenic displacer which shuttles the heat transport medium, subatmospheric He-3 gas, between the two units. The prototype of the designed magnetic refrigerator has operated continuously, producing a net refrigeration rate of 12 mW per magnetic core at 1.8 K
Low-energy excitations in the electron-doped metal phtalocyanine LiO.5MnPc from Li and 1H NMR
No full textNMR and magnetization measurements in Li0.5MnPc (Pc=C32H16N8), recently proposed as a strongly correlated metal, are presented. Two different low-frequency dynamics are evidenced. The first one, probed by 1H nuclei, gives rise to a slowly relaxing magnetization at low temperature and is associated with the freezing of MnPc S=3/2 spins. This dynamics is similar to the one observed in pristine beta-MnPc and originates from Li-depleted chain segments. The second one, evidenced by the 7Li spin-lattice relaxation rate, is associated with the hopping of the electrons along Li-rich chains. The characteristic correlation times for the two dynamics are derived, and the role of the disorder is briefly discussed
A Survey on Indirect Reciprocity
No full textThis survey deals with indirect reciprocity, i.e., with the possibility that altruistic acts are returned, not by the recipient, but by a third party. After briefly sketching how this problem is dealt with in classical game theory, we describe recent work on the assessment on interactions, and the evolutionary stability of strategies for indirect reciprocation. All stable strategies ( the 'leading eight') distinguish between justified and non-justified defections, and therefore are based on non-costly punishment. Next we consider the replicator dynamics of populations consisting of defectors, discriminators and undiscriminating altruists. We stress that errors can destabilise cooperation for strategies not distinguishing justified from unjustified defections, but that a fixed number of rounds, or the assumption of an individual's social network growing with age, can lead to cooperation based on a stable mixture of undiscriminating altruists and of discriminators who do not distinguish between justified and unjustified defection. We describe previous work using agent-based simulations for 'binary-score' and 'full score' models. Finally, we survey the recent results on experiments with the indirect reciprocation game
Low-energy excitations in electron-doped metal phthalocyanines
No full textMagnetization and NMR relaxation measurements in Lix(Mn,Zn)Pc were performed in order to study the evolution of the electronic
properties of metal phthalocyanines upon electron doping. For x = 2 the doubly degenerate lowest unoccupied molecular orbital
(LUMO) is half filled and the electrons are coupled in a singlet state owing to the Jahn–Teller distortions. The effects of the Jahn–Teller distortions on the spin excitations are discussed in the light of NMR relaxation measurements
Quantifying metastatic inefficiency:rare genotypes versus rare dynamics
No full textWe introduce and solve a 'null model' of stochastic metastatic colonization. The model is described by a single parameter ?: the ratio of the rate of cell division to the rate of cell death for a disseminated tumour cell in a given secondary tissue environment. We are primarily interested in the case in which colonizing cells are poorly adapted for proliferation in the local tissue environment, so that cell death is more likely than cell division, i.e. ? 1, we find that the probability of establishment is exponentially rare, as expected, and yet the mean time for such rare events is of the form ~log (N)/(1 - ?) while the standard deviation of colonization times is ~1/(1 - ?). Thus, counter to naive expectation, for ? 1), i.e. the statistics show a duality mapping (1 - ?) --> (? - 1). We conclude our analysis with a study of heterogeneity in the fitness of colonising cells, and describe a phase diagram delineating parameter regions in which metastatic colonization is dominated either by low or high fitness cells, showing that both are plausible given our current knowledge of physiological conditions in human cancer
Persistence of corruption: an evolutionary game theory motivated by illegal logging in tropics
No full textIllegal logging is a serious threat to plantations in the tropics. Here, we study the coupled dynamics of Social-Ecological systems shedding light of two different aspects.
[1] We examined the roles of profit-sharing in plantation management strategy in a dynamic game model. The model assumes that the owner chooses the age of the trees to be harvested and the local people choose their level of monitoring effort to prevent illegal logging with surveillance. After the trees are removed, the owner hires local people to replant young trees. Dynamic optimization analysis revealed that, under the pressure of illegal logging, the owner may find it profitable to share harvesting profits with the local people to enhance their surveillance effort. The profit-sharing rate optimal to the owner depends on the rate of natural disturbance, faster future discount rate, and a higher cost of replanting.
[2] Cooperation can be sustained by institutions that punish free-riders. Such institutions, however, tend to be subverted by corruption if they are not closely watched. Monitoring can uphold the enforcement of binding agreements ensuring cooperation, but this usually comes at a price. The temptation to skip monitoring and take the institutionâ s integrity for granted leads to outbreaks of corruption and the breakdown of cooperation. We model the corresponding mechanism by means of evolutionary game theory, using analytical methods and numerical simulations, and find that it leads to sustained or damped oscillations. The results confirm the view that corruption is endemic and transparency a major factor in reducing it.
Lee, J-H., Y. Kubo, T. Fujiwara, R.M. Septianad, S. Riyantod, and Y. Iwasa. 2018. Profit sharing as a management strategy for a state-owned teak plantation at high risk for illegal logging. Ecological Economics 149, 140-148.
Lee, J-H, Y. Iwasa, U. Dieckmann, and K. Sigmund. 2019 Social evolution leads to persistent corruption. PNAS 116, 13276-13281.Non UBCUnreviewedAuthor affiliation: Kwansei Gakuin UniversityFacult
Cordilura remmi Elberg 1972
No full textCordilura remmi Elberg, 1972 [Japanese name: Higenaga-okuro-funbae] (Figs 17–20) Cordilura remmi Elberg, 1972. Type locality: Sakhalin Island, environment of South Sakhalinsk, USSR [Russia]. Phrosia remmi: Šifner, 2008. Cordilura remmi: Ozerov & Krivosheina, 2014. Material examined. [Hokkaido] 1♂, Atsunai, Japan, 22. vii. 1951, leg. Y. Nishijima; 1 ♂, Hokkaido Univ. Forest., Teshiogawa, Otoi-neppu, 4. viii. 2016, leg. S. Shinonaga; 1♀, Tokachi-mitsumata, Tokachi, 22. ix. 1996, leg. M. Iwasa; 1♀, Asahikawa, 16. vii. 1957, leg. R. Kano; 1♀, Mani Spa, Kurisawacho-nishimanzi, Iwamizawa City, 24. vi. 2014, leg. D. Kato. Diagnosis. C. remmi Elberg (Fig. 17) can be recognized by long postpedicel which is about 3 times as long as wide (Fig. 18), shining body, black thorax and abdomen, black femora and brown tibiae and tarsi, and male surstylus (Figs 19, 20) which is apically bifurcated into anterior and posterior lobes. Length (♂ ♀). Body, 9.0–10.0 mm; wing, 7.2–7.3 mm. Distribution. Japan (Hokkaido), Russia (Amur Oblast, Jewish Autonomus Oblast, Kamchatka Kray, Khabarovsk Kray, Primorskiy Kray, Sakhalin Oblast (the Kuril Is., Sakhalin Is.), Zabaikalskiy Kray (Ozerov & Krivosheina, 2014). New to Japan. Remarks. According to Ozerov & Krivosheina (2017), this species is closely related to C. negrobovi Ozerov & Krivosheina, but is distinguished from it by the structures of male sternite V and surstylus.Published as part of Iwasa, Mtsuhiro, 2020, Contribution to the knowledge of the genus Cordilura Fallén (Diptera, Scathophagidae) from Japan, with descriptions of three new species, pp. 471-484 in Zootaxa 4748 (3) on pages 477-478, DOI: 10.11646/zootaxa.4748.3.4, http://zenodo.org/record/370107
Spatially-localized time dependent solutions including turbulence and their interactions in 2D Kolmogorov flow
No full textIn 2D Kolmogorov flow in small aspect ratio domains, spatially-localized solutions such as kink, traveling or time-dependent kink-antikink pars coexist. However, the conservation of the flow rate in the y direction strongly restrict combination of localized solutions and their positioning. We find that by adding a homogeneous flow U y their positioning is controlled and each of localized solutions including a spatially-localized chaos is isolated. Numerical results suggest that these isolated solutions can be elements constructing a whole flow
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