131 research outputs found
Weekly report for R.V. Polarstern expedition ANT-XXIII/5, report no. 1 (16.04.2006), english version
Grothendieck ring of varieties, D- and L-equivalence, and families of quadrics
We discuss a conjecture saying that derived equivalence of smooth projective simply connected varieties implies that the difference of their classes in the Grothendieck ring of varieties is annihilated by a power of the affine line class. We support the conjecture with a number of known examples, and one new example. We consider a smooth complete intersection X of three quadrics in P5 and the corresponding double cover YâP2 branched over a sextic curve. We show that as soon as the natural Brauer class on Y vanishes, so that X and Y are derived equivalent, the difference [X]â[Y] is annihilated by the affine line class
Metabolism and foraging strategies of midâlatitude mesozooplankton during cyanobacterial blooms as revealed by fatty acids, amino acids, and their stable carbon isotopes
Increasing sea surface temperatures (SST) and blooms of lipidâpoor, filamentous cyanobacteria can change mesozooplankton metabolism and foraging strategies in marine systems. Lipid shortage and imbalanced diet may challenge the buildâup of energy pools of lipids and proteins, and access to essential fatty acids (FAs) and amino acids (AAs) by copepods. The impact of cyanobacterial blooms on individual energy pools was assessed for key species temperate Temora longicornis and boreal Pseudoâ/Paracalanus spp. that dominated field mesozooplankton communities isolated by seaâsonal stratification in the central Baltic Sea during the hot and the cold summer. We looked at (a) total lipid and protein levels, (b) FA trophic markers and AA composition, and (c) compoundâspecific stable carbon isotopes (δ13C) in bulk mesozooplankton and in a subset of parameters in particulate organic matter. Despite lipidâpoor cyanobacterial blooms, the key species were largely able to cover both energy pools, yet a tendency of lipid reduction was observed in surface animals. Omniâ and carânivory feeding modes, FA trophic makers, and δ13C patterns in essential compounds emphasized that cyanobacterial FAs and AAs have been incorporated into mesoâzooplankton mainly via feeding on mixoâ and heterotrophic (dinoâ) flagellates and detrital complexes during summer. Foraging for essential highly unsaturated FAs from (dinoâ) flagellates may have caused night migration of Pseudoâ/Paracalanus spp. from the deep subhalocline waters into the upper waters. Only in the hot summer (SST>19.0°C) was T. longicornis submerged in the colder subthermocline water (~4°C). Thus, the continuous warming trend and simultaneous feeding can eventually lead to competition on the preferred diet by key copepod species below the thermocline in stratified systems. A comparison of δ13C patterns of essential AAs in surface mesoâzooplankton across subâbasins of low and high cyanobacterial biomasses revealed the potential of δ13CâAA isoscapes for studies of commercial fish feeding trails across the Baltic Sea food webs
Open Problems on Central Simple Algebras
We provide a survey of past research and a list of open problems regarding
central simple algebras and the Brauer group over a field, intended both for
experts and for beginners.Comment: v2 has some small revisions to the text. Some items are re-numbered,
compared to v
Weekly report for R.V. Polarstern expedition ANT-XXIII/5, report no. 5 (14.05.2006), english version
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