Modelling spiral waves in Xenopus laevis oocyte

An investigation was made into the spiral waves solutions for the Atri et al model, a partial differential equation model for Ca²⁺ dynamics in the Xenopus laevis oocyte. Spiral wave solutions, both stable and unstable, were found to exist in the oscillatory regime for this model. The spiral wave solutions were found to have a period that decreased as the initial IP₃ bolus increased. Increasing the initial IP₃ bolus also lead to destabilisation of the spiral waves solutions. After the break up of spiral wave solutions complex spatio-temporal patterns occurred. In some cases spirals reformed after breaking up

Comparative studies of the reproductive strategies of New Zealand grapsid crabs (Brachyura: Grapsidae) and the effects of parasites on their reproductive success.

The reproductive strategies of four intertidal grapsid crabs, Hemigrapsus sexdentatus, H. crenulatus, Cyclograpsus lavauxi, and Helice crassa, were studied in the field and laboratory, with emphasis on mating behaviour, duration of female receptivity, and sperm competition. Mating occurred in all species during the intermoult on the days prior to oviposition, when the gonopore opercula of females became temporarily mobile. Female Helice crassa mated up to three weeks after oviposition, but in all other species mating typically ceased at egg-laying. Male Hemigrapsus spp. used a female-centered competition strategy in which they searched for and defended receptive females until they laid eggs. In contrast, male C. lavauxi searched for and intercepted receptive females only for the duration of copulation and then pursued other receptive females (a mating system termed encounter rate competition with pure search and interception). Male Helice crassa searched for receptive females in their immediate neighbourhood and mated with them briefly on the substrate or in the burrow after which the female left (a mating system termed encounter rate competition with neighbourhoods of dominance). The mating season was short and highly synchronous for Hemigrapsus sexdentatus and Cyclograpsus lavauxi and asynchronous for Hemigrapsus crenulatus and Helice crassa. In the laboratory, the mean duration of receptivity for females housed with three males varied between 4.1 and 12.4 days, and the copulation frequency of females varied before oviposition between 2.1 and 24.3 times (mean) depending on the species. Female Hemigrapsus spp. Isolated from males stayed receptive significantly longer than females held continuously with males. This suggests that females are able to control the duration of their receptivity, and therefore the time available for mating, according to the absence or presence of males. The operational sex ratio (OSR) had no effect on the duration of female receptivity, but female Hemigrapsus crenulatus mated more often when several males were competing for access. Therefore, male-male competition increased the number of matings per female and hence sperm competition within the female spermathecae. Larger males mated significantly more often than smaller males in all species. However, male size did not affect ejaculate size, meaning that small and large males transferred similar-sized ejaculates, e.g., in Hemigrapsus spp. Males of the two Hemigrapsus species followed a different strategy of sperm allocation. Male H. crenulatus, which are typically confronted with a high mating frequency of the female and a long, asynchronous mating season, distributed similar-sized ejaculates, irrespective of female size. By contrast, male H. sexdentatus, which experience a comparatively lower risk of sperm competition during a short, synchronised mating season, invested larger ejaculates for larger females than for smaller females. In addition, the size of the first and second ejaculates transferred to a female by a male H. crenulatus were not significantly different, whereas the first was larger than the second for H. sexdentatus. A parasitological survey was undertaken of the four grapsid crabs and the presence, seasonal variation and relationship with host gender and size of parasites determined. Four internal parasites were discovered: Nectonema zealandica n. sp. (Nematomorpha: Nectonematoidea), Portunion sp. (Isopoda: Entoniscidae), Profilicollis novaezelandensis n. sp. and Profilicollis antarcticus (Acanthocephala: Polymorphidae). Portunion sp. castrated its female hosts, but not the males thereby creating a more male-biased sex ratio. Males parasitized with Portunion sp. were equally successful during male-male competition and the number of matings they achieved. The above findings are important for our current understanding of mating strategies in Grapsidae, which are more diverse than previously thought. Females with a restricted duration of sexual receptivity have some control over their receptive period and can therefore influence the OSR and the extent of male-male competition. As females mated multiple times during their receptive period, sperm competition is a common feature in Grapsidae. However, males employed different tactics in regards to sperm competition such as longer mating duration (e.g., C. lavauxi), high number of matings (Helice crassa), or post-copulatory mate guarding until oviposition (Hemigrapsus spp.)

Do fund managers in the Chinese mutual fund market deliver positive risk-adjusted returns? Yes, but it is mainly observed for local fund managers

A bootstrap and a subsequent injected alpha analysis were conducted on 1,221 Chinese mutual funds that were active at some point between July 2001 and July 2021. The results show that most active managers achieve a positive risk-adjusted return. Additionally, we find that this phenomenon is primarily attributable to local (i.e., Chinese) fund managers. We argue that one explanation for the different levels of risk-adjusted returns observed is the information asymmetry between foreign and local fund managers. Additional results support this view, as fund managers primarily investing in small- to mid-cap and value stocks provide a superior performance, which inherently exhibit greater information asymmetry. The findings are contrary to those from similar studies in developed markets, where only a few active managers demonstrate actual skill in their performance

Microkinetic Modeling of the Oxidation of Methane Over PdO Catalysts—Towards a Better Understanding of the Water Inhibition Effect

Water, which is an intrinsic part of the exhaust gas of combustion engines, strongly inhibits the methane oxidation reaction over palladium oxide-based catalysts under lean conditions and leads to severe catalyst deactivation. In this combined experimental and modeling work, we approach this challenge with kinetic measurements in flow reactors and a microkinetic model, respectively. We propose a mechanism that takes the instantaneous impact of water on the noble metal particles into account. The dual site microkinetic model is based on the mean-field approximation and consists of 39 reversible surface reactions among 23 surface species, 15 related to Pd-sites, and eight associated with the oxide. A variable number of available catalytically active sites is used to describe light-off activity tests as well as spatially resolved concentration profiles. The total oxidation of methane is studied at atmospheric pressure, with space velocities of 160,000 h−1 in the temperature range of 500–800 K for mixtures of methane in the presence of excess oxygen and up to 15% water, which are typical conditions occurring in the exhaust of lean-operated natural gas engines. The new approach presented is also of interest for modeling catalytic reactors showing a dynamic behavior of the catalytically active particles in general

Surface Reaction Kinetics of Steam- and CO₂-Reforming as Well as Oxidation of Methane over Nickel-Based Catalysts

An experimental and kinetic modeling study on the Ni-catalyzed conversion of methane under oxidative and reforming conditions is presented. The numerical model is based on a surface reaction mechanism consisting of 52 elementary-step like reactions with 14 surface and six gas-phase species. Reactions for the conversion of methane with oxygen, steam, and CO₂ as well as methanation, water-gas shift reaction and carbon formation via Boudouard reaction are included. The mechanism is implemented in a one-dimensional flow field description of a fixed bed reactor. The model is evaluated by comparison of numerical simulations with data derived from isothermal experiments in a flow reactor over a powdered nickel-based catalyst using varying inlet gas compositions and operating temperatures. Furthermore, the influence of hydrogen and water as co-feed on methane dry reforming with CO₂ is also investigated

Do Fund Managers Expect Mean Averting Returns?

Abstract This paper finds that fund managers do not expect mean reverting returns, as suggested by theory and empirical evidence, but mean averting returns. The degree of mean aversion is positively related to preferences for non-fundamental information and loss aversion