On the trophic fate of Phaeocystis pouchetii: VII. Sterols and fatty acids reveal sedimentation of Phaocystis-derived organic matter via krill fecal strings

As part of a joint project on the fate of phytoplankton in Balsfjorden in Northern Norway, we investigated the trophic fate and sedimentation potential of Phaeocystis pouchetii by tracing the transition of biomarker patterns from a phytoplankton bloom to sediment traps and during a gut passage experiment. The phytoplankton biomass during the spring bloom 1996 was dominated by colonial P. pouchetii (ca. 85 %) and four members of the diatom family Thalassiosiraceae (ca. 10%). Particulate organic carbon in sediment traps largely consisted of fecal material from the Arctic krill Thysanoessa sp.. Sterol and fatty acid biomarker patterns in the phytoplankton bloom could be reproduced by combining the individual biomarker patterns of the isolated phytoplankters P. pouchetii and Thalassiosira decipiens in a ratio of ca. 75:25. In a laboratory experiment, Arctic krill (Thysanoessa raschii) fed with similar efficiency on Phaeocystis colonies and the Thalassiosiraceae. During gut passage, the abundance of Thalassiosiraceae biomarkers in fecal strings increased relative to Phaeocystis biomarkers, while biomarkers from krill became dominant. This transition of biomarker patterns due to gut passage in T. raschii closely resembled the biomarker transition from the surface bloom to material in sediment traps at 40-170 m depth, which was mainly composed of krill fecal strings. We conclude that krill grazed efficiently on Phaeocystis colonies in Balsfjorden, and caused sedimentation of Phaeocystis-derived organic matter below the euphotic zone via fecal strings. Hence, both transfer to higher trophic levels and sedimentation of Phaeocystis-derived organic matter can be more effective than commonly believed

Structure and stability of graphene nanoribbons in oxygen, carbon dioxide, water, and ammonia

We determine, by means of density functional theory, the stability and the structure of graphene nanoribbon (GNR) edges in presence of molecules such as oxygen, water, ammonia, and carbon dioxide. As in the case of hydrogen-terminated nanoribbons, we find that the most stable armchair and zigzag configurations are characterized by a non-metallic/non-magnetic nature, and are compatible with Clar's sextet rules, well known in organic chemistry. In particular, we predict that, at thermodynamic equilibrium, neutral GNRs in oxygen-rich atmosphere should preferentially be along the armchair direction, while water-saturated GNRs should present zigzag edges. Our results promise to be particularly useful to GNRs synthesis, since the most recent and advanced experimental routes are most effective in water and/or ammonia-containing solutions.Comment: accepted for publication in PR

Structure, Stability, Edge States and Aromaticity of Graphene Ribbons

We determine the stability, the geometry, the electronic and magnetic structure of hydrogen-terminated graphene-nanoribbons edges as a function of the hydrogen content of the environment by means of density functional theory. Antiferromagnetic zigzag ribbons are stable only at extremely-low ultra-vacuum pressures. Under more standard conditions, the most stable structures are the mono- and di-hydrogenated armchair edges and a zigzag edge reconstruction with one di- and two mono-hydrogenated sites. At high hydrogen-concentration ``bulk'' graphene is not stable and spontaneously breaks to form ribbons, in analogy to the spontaneous breaking of graphene into small-width nanoribbons observed experimentally in solution. The stability and the existence of exotic edge electronic-states and/or magnetism is rationalized in terms of simple concepts from organic chemistry (Clar's rule)Comment: 4 pages, 3 figures, accepted for publication by Physical Review Letter

Expression Patterns of BDNF with Central Anorexigenic Signaling Pathways Involving PACAP in the Hypothalamic Ventromedial Nuclei

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-amino acid polypeptide belonging to the secretin super family of peptides. PACAP binds to its type 1 receptor (PAC1R) with greater affinity than for the receptors for vasoactive intestinal polypeptides (VIP), VPAC1 and VPAC2. Although mRNA for PACAP and its receptor PAC1R are found throughout the central nervous system, they are abundantly expressed in the hypothalamic ventromedial nuclei (VMN). In male Sprague Dawley rats, infusions of PACAP into the VMN produce a robust decrease in food intake with concomitant increased energy expenditure, decreased body weight, and significantly elevated brain-derived neurotrophic factor (BDNF) mRNA expression in the VMN. This latter effect of PACAP on BDNF mRNA expression has been shown to occur in other brain regions. Exogenous BDNF in the VMN regulates energy homeostasis in a manner similar to that of PACAP with decreased feeding and increased metabolism. Although the physiological responses to individual PACAP and BDNF infusions in the VMN lead to decreased feeding behavior and body weight loss, the anatomical distribution of these two cell signals in the VMN has not been established. PACAP-induced changes in BDNF mRNA expression in the VMN may reveal an important interaction with PACAP signaling in the control of feeding behavior. In the present study, we have employed double-labeled fluorescent in-situ hybridization (FISH) to examine the expression patterns of PACAP, PAC1R and BDNF mRNA containing neuronal cells. In the VMN, PACAP mRNA expressing cells co-express BDNF, PAC1R, and VGLUT2. BDNF mRNA expressing cells co-express PAC1R and PACAP. Coupled with previous behavioral data demonstrating PACAP- and BDNF-induced changes in feeding behavior, the co-expression of BDNF with PACAP and PAC1R mRNA in the VMN suggest a potential functional relationship between the two signaling peptides in the regulation of energy homeostasis. The specific and integrated contributions of PACAP and BDNF in the VMN towards regulating energy homeostasis and feeding behavior still remain to be studied

Appearance of Flat Bands and Edge States in Boron-Carbon-Nitride Nanoribbons

Presence of flat bands and edge states at the Fermi level in graphene nanoribbons with zigzag edges is one of the most interesting and attracting properties of nanocarbon materials but it is believed that they are quite fragile states and disappear when B and N atoms are doped at around the edges. In this paper, we theoretically investigate electronic and magnetic properties of boron-carbon-nitride (BCN) nanoribbons with zigzag edges where the outermost C atoms on the edges are alternately replaced with B and N atoms using the first principles calculations. We show that BCN nanoribbons have the flat bands and edge states at the Fermi level in both H_2 rich and poor environments. The flat bands are similar to those at graphene nanoribbons with zigzag edges, but the distributions of charge and spin densities are different between them. A tight binding model and the Hubbard model analysis show that the difference in the distribution of charge and spin densities is caused by the different site energies of B and N atoms compared with C atoms.Comment: 5 pages; 3 figure

Experimentally Engineering the Edge Termination of Graphene Nanoribbons

The edges of graphene nanoribbons (GNRs) have attracted much interest due to their potentially strong influence on GNR electronic and magnetic properties. Here we report the ability to engineer the microscopic edge termination of high quality GNRs via hydrogen plasma etching. Using a combination of high-resolution scanning tunneling microscopy and first-principles calculations, we have determined the exact atomic structure of plasma-etched GNR edges and established the chemical nature of terminating functional groups for zigzag, armchair and chiral edge orientations. We find that the edges of hydrogen-plasma-etched GNRs are generally flat, free of structural reconstructions and are terminated by hydrogen atoms with no rehybridization of the outermost carbon edge atoms. Both zigzag and chiral edges show the presence of edge states.Comment: 16+9 pages, 3+4 figure

Carbon Footprint Calculator Customized for Rice Products: Concept and Characterization of Rice Value Chains in Southeast Asia

In this study, we developed user-friendly software (CF-Rice) for calculating the carbon footprints (CF) of rice products. The approach follows the principles of Life Cycle Assessment while incorporating more flexibility for activities specific to rice production. The graphical user interface provides empirical emission and conversion factors obtained from the literature and from primary research studies of rice value chains. CF-Rice also allows the entering of new values for specific processes or practices. Data outputs distinguish among the contributions of individual stages of the value chain as well as different greenhouse gases (GHG), namely, CH$_{4}$, N$_{2}$O and CO$_{2}$. The new tool was then applied to a scenario assessment of rice production in the regional context of Southeast Asia. The CF baseline of a typical rice value chain in the region accounted for a value of around 2300 g CO$_{2}$e/kg$_{Prod}$. The CF can be reduced by about 27.4% through water-saving practices alone and can further be reduced up to 37.3% through interventions that increase product recovery rates and, thus, reduce food losses. In contrast, straw incorporation into the soil increased the CF by 26.0%. The tool is well suited for impact assessments of advanced practices and technologies of rice value chains