505 research outputs found
beta-Cu2V2O7: a spin-1/2 honeycomb lattice system
We report on band structure calculations and a microscopic model of the
low-dimensional magnet beta-Cu2V2O7. Magnetic properties of this compound can
be described by a spin-1/2 anisotropic honeycomb lattice model with the
averaged coupling \bar J1=60-66 K. The low symmetry of the crystal structure
leads to two inequivalent couplings J1 and J1', but this weak spatial
anisotropy does not affect the essential physics of the honeycomb spin lattice.
The structural realization of the honeycomb lattice is highly non-trivial: the
leading interactions J1 and J1' run via double bridges of VO4 tetrahedra
between spatially separated Cu atoms, while the interactions between structural
nearest neighbors are negligible. The non-negligible inter-plane coupling
Jperp~15 K gives rise to the long-range magnetic ordering at TN~26 K. Our model
simulations improve the fit of the magnetic susceptibility data, compared to
the previously assumed spin-chain models. Additionally, the simulated ordering
temperature of 27 K is in remarkable agreement with the experiment. Our study
evaluates beta-Cu2V2O7 as the best available experimental realization of the
spin-1/2 Heisenberg model on the honeycomb lattice. We also provide an
instructive comparison of different band structure codes and computational
approaches to the evaluation of exchange couplings in magnetic insulators.Comment: 11 pages, 10 figures, 2 tables: revised version, extended description
of simulation result
Attached intertidal diatoms have stronger photoprotective capacity compared to motile diatoms
POB4 USE OF GROWTH CURVE ANALYSES FOR DISCRETE EVENT SIMULATION: A CASE STUDY OF POOLED CLINICAL TRIALS OF THE EFFECTS OF RIMONABANT ON CARDIOMETABOLIC RISK FACTORS IN OBESE PATIENTS
Photoprotection capacity differs among microphytobenthic diatoms inhabiting intertidal mudflats: Possible consequences on their spatial distribution related to the light environment
Silencing of the Violaxanthin De-Epoxidase Gene in the Diatom Phaeodactylum tricornutum Reduces Diatoxanthin Synthesis and Non-Photochemical Quenching
Diatoms are a major group of primary producers ubiquitous in all aquatic ecosystems. To protect themselves from photooxidative damage in a fluctuating light climate potentially punctuated with regular excess light exposures, diatoms have developed several photoprotective mechanisms. The xanthophyll cycle (XC) dependent non-photochemical chlorophyll fluorescence quenching (NPQ) is one of the most important photoprotective processes that rapidly regulate photosynthesis in diatoms. NPQ depends on the conversion of diadinoxanthin (DD) into diatoxanthin (DT) by the violaxanthin de-epoxidase (VDE), also called DD de-epoxidase (DDE). To study the role of DDE in controlling NPQ, we generated transformants of P. tricornutum in which the gene (Vde/Dde) encoding for DDE was silenced. RNA interference was induced by genetic transformation of the cells with plasmids containing either short (198 bp) or long (523 bp) antisense (AS) fragments or, alternatively, with a plasmid mediating the expression of a self-complementary hairpin-like construct (inverted repeat, IR). The silencing approaches generated diatom transformants with a phenotype clearly distinguishable from wildtype (WT) cells, i.e. a lower degree as well as slower kinetics of both DD de-epoxidation and NPQ induction. Real-time PCR based quantification of Dde transcripts revealed differences in transcript levels between AS transformants and WT cells but also between AS and IR transformants, suggesting the possible presence of two different gene silencing mediating mechanisms. This was confirmed by the differential effect of the light intensity on the respective silencing efficiency of both types of transformants. The characterization of the transformants strengthened some of the specific features of the XC and NPQ and confirmed the most recent mechanistic model of the DT/NPQ relationship in diatoms
Ecological niche predicts photoprotection capacity of microphytobenthic diatoms inhabiting intertidal mudflats
Content in fatty acids and carotenoids in phytoplankton blooms during the seasonal sea ice retreat in Hudson Bay complex, Canada.
The Hudson Bay complex (HBC) is home to numerous indigenous communities that traditionally have relied
heavily on its marine resources. The nutritional quality and stocks of the entire HBC food web depend in
large part on the phytoplankton production of bioactive molecules (long chain polyunsaturated fatty acids
and carotenoids) and their transfer through trophic levels. The purpose of this study was thus to
determine which molecules were produced during spring phytoplankton blooms, as well as the
environmental factors driving this production. We investigated 21 stations in 5 sub-regions of the HBC.
At the time of sampling, the sub-regions studied had different environmental settings (e.g., ice cover,
nutrients, seawater salinity and temperature) conditioning their bloom stages. Pre- and post-bloom stages
were associated with relatively low concentrations of bioactive molecules (either fatty acids or
carotenoids). In contrast, the highest concentrations of bioactive molecules (dominated by
eicosapentaenoic acid and fucoxanthin) were associated with the diatom bloom that typically occurs at
the ice edge when silicates remain available. Interestingly, the large riverine inputs in eastern Hudson Bay
led to a change in protist composition (larger contribution of Dinophyceae), resulting in lower while more
diverse content of bioactive molecules, whether fatty acids (e.g., aa-linolenic acid) or carotenoids
(e.g., peridinin). As greater stratification of the HBC is expected in the future, we suggest that
a mixotrophic/heterotrophic flagellate-based food web would become more prevalent, resulting in
a smaller supply of bioactive molecules for the food web
OPENCoastS: An open-access service for the automatic generation of coastal forecast systems
info:eu-repo/semantics/publishedVersio
Coincidence measurement of residues and light particles in the reaction 56Fe+p at 1 GeV per nucleon with SPALADIN
The spallation of Fe in collisions with hydrogen at 1 A GeV has been
studied in inverse kinematics with the large-aperture setup SPALADIN at GSI.
Coincidences of residues with low-center-of-mass kinetic energy light particles
and fragments have been measured allowing the decomposition of the total
reaction cross-section into the different possible de-excitation channels.
Detailed information on the evolution of these de-excitation channels with
excitation energy has also been obtained. The comparison of the data with
predictions of several de-excitation models coupled to the INCL4 intra-nuclear
cascade model shows that only GEMINI can reasonably account for the bulk of
collected results, indicating that in a light system with no compression and
little angular momentum, multifragmentation might not be necessary to explain
the data.Comment: 4 pages, 5 figures, revised version accepted in Phys. Rev. Let
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