Ecological similarities and differences among littoral species of Ceriodaphnia
The occurrence of six littoral species of Ceriodaphnia (C. affinis, C. laticaudata, C. megops,C. reticulata, C. rotunda and C. setosa)living at the same time and locality is described.Basic population characteristics were studied in allspecies coexisting in the field, except for C. setosa, which was too scarce. Abundances,proportions of gamogenetic individuals, mean bodylengths and clutch sizes were compared among species.Dissolved oxygen, temperature, chlorophyll-a and totalseston volume were measured and related to populationchanges. C. laticaudata and C. rotundawere closely similar to each other in many featuresand showed significant differences to other species.C. reticulata and C. megops seem to besimilar in some features, while C. affinis wasecologically different.
Growth and reproduction of the cladoceran Ceriodaphnia dubia from a forested floodplain swamp
Microcrustaceans are abundant in many freshwater wetlands, including forested floodplain swamps, but little has been done to assess their secondary production and functional role in these systems. Since standard cohort approaches to estimating secondary production are impossible with continuously growing and reproducing microcrustaceans, it is necessary to obtain independent determinations of their growth and reproductive characteristics under environmental conditions encountered in their natural habitat throughout the year. The growth and reproduction of Ceriodaphnia dubia fed natural swamp seston were measured at 10, 15, 20, and 25”C-temperatures which span much of the annual temperature range in southeastern floodplain swamps. Somatic biomass growth rates were as high as 61% d-r. Total growth rates (somatic tissue and egg mass) reached 95% d-r. Both somatic growth rates and total growth rates could be described as functions of individual size and temperature. High egg production, particularly in the larger instars, resulted in individuals maintaining high total growth rates (>20% d-l at most temperatures) over the lifespan. Lifetime egg production accounted for ~50% of biomass produced by individuals at all temperatures and > 80% for temperatures 120°C. Somatic growth rates for C. dubia fed swamp seston were within the range of literature estimates for other species of Ceriodaphnia under various food conditions.
Rubik's for cryptographers
Hard mathematical problems are at the core of security arguments in cryptography. In this paper, we study mathematical generalizations of the famous Rubik’s cube puzzle, namely the factorization, representation and balance problems in non-Abelian groups. These problems arise naturally when describing the security of Cayley hash functions, a class of cryptographic hash functions with very interesting properties. The factorization problem is also strongly related to a famous long-standing conjecture of Babai, at the intersection of group theory and graph theory. A constructive proof of Babai’s conjecture would make all Cayley hash functions insecure, but on the other hand it would have many positive applications in graph theory and computer science. In this paper, we classify existing attacks against Cayley hash functions and we review known results on Babai’s conjecture. Despite recent cryptanalytic progress on particular instances, we show that the factorization, representation and balance problems presumably remain good sources of cryptographic hard problems. Our study demonstrates that Cayley hash functions deserve further interest by the cryptography community.