United States Department of Energy

About: United States Department of Energy is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Coal & Catalysis. The organization has 13656 authors who have published 14177 publications receiving 556962 citations. The organization is also known as: DOE & Department of Energy.

Electronic properties and stabilities of bulk and low-index surfaces of SnO in comparison with Sn O 2 : A first-principles density functional approach with an empirical correction of van der Waals interactions

Abstract: The electronic properties and stabilities of SnO and $\mathrm{Sn}{\mathrm{O}}_{2}$ bulk materials and their low-index surfaces are investigated by density functional theory. An empirical method has been adopted in this study to account for the van der Waals interactions among the Sn-O layers in the bulk and low-index surfaces of SnO. Compared with $\mathrm{Sn}{\mathrm{O}}_{2}$, the structural and electronic properties of SnO bulk and its low-index surfaces present some unique features due to the dual valency of Sn. In SnO, the $s$ orbital of Sn has larger contributions than its $p$ and $d$ orbitals in the first valence band (VB) and the $p$ orbital of Sn has a larger contribution than its $s$ and $d$ orbitals in its conduction band (CB). In $\mathrm{Sn}{\mathrm{O}}_{2}$, the $p$ and $d$ orbitals of Sn play an important role to form the upper part of the VB and its $s$ orbital dominates in forming the lower parts of the VB and the CB. In both oxides, the $s$ orbital of O forms the second VB with lower energy and its $p$ orbitals are involved in forming the first VB and the CB. The calculated bulk modulus and cohesive energy agree well with the experimental measurements. By constructing all possible symmetrical low-index surfaces of SnO and the (111) surface of $\mathrm{Sn}{\mathrm{O}}_{2}$, our results reveal that the calculated surface energies of SnO stoichiometric surfaces are lower than that of the corresponding surfaces of $\mathrm{Sn}{\mathrm{O}}_{2}$ due to different bonding between Sn and O in these two oxides. The calculated stabilities of the low-index stoichiometric surfaces of SnO are in the order $(001)g(101)∕(011)\ensuremath{\ge}(010)∕(100)g(110)g(111)$ while the order in the case of $\mathrm{Sn}{\mathrm{O}}_{2}$ is $(110)g(010)∕(100)g(101)∕(011)g(001)g(111)$. The calculated relationships between surface free energies $[\ensuremath{\gamma}(p,T)]$ and oxygen chemical potentials $[{\ensuremath{\mu}}_{\mathrm{O}}(p,T)]$ indicate that the nonstoichiometric O-terminated (110) and (111) surfaces of SnO could be more stable than their corresponding stoichiometric ones when the ${\ensuremath{\mu}}_{\mathrm{O}}(p,T)$ reaches its higher O-rich bound, and one Sn-terminated nonstoichiometric (111) surface of $\mathrm{Sn}{\mathrm{O}}_{2}$ could be more stable than its stoichiometric ones when the ${\ensuremath{\mu}}_{\mathrm{O}}(p,T)$ falls into its lower O-poor region. During surface formation from the bulk, the stable surface usually has small atom displacements. For both SnO and $\mathrm{Sn}{\mathrm{O}}_{2}$ the atoms on the (111) surface have larger relaxations than on their other low-index surfaces.

Comparative genomics provides insights into the lifestyle and reveals functional heterogeneity of dark septate endophytic fungi.

Abstract: Dark septate endophytes (DSE) are a form-group of root endophytic fungi with elusive functions. Here, the genomes of two common DSE of semiarid areas, Cadophora sp. and Periconia macrospinosa were sequenced and analyzed with another 32 ascomycetes of different lifestyles. Cadophora sp. (Helotiales) and P. macrospinosa (Pleosporales) have genomes of 70.46 Mb and 54.99 Mb with 22,766 and 18,750 gene models, respectively. The majority of DSE-specific protein clusters lack functional annotation with no similarity to characterized proteins, implying that they have evolved unique genetic innovations. Both DSE possess an expanded number of carbohydrate active enzymes (CAZymes), including plant cell wall degrading enzymes (PCWDEs). Those were similar in three other DSE, and contributed a signal for the separation of root endophytes in principal component analyses of CAZymes, indicating shared genomic traits of DSE fungi. Number of secreted proteases and lipases, aquaporins, and genes linked to melanin synthesis were also relatively high in our fungi. In spite of certain similarities between our two DSE, we observed low levels of convergence in their gene family evolution. This suggests that, despite originating from the same habitat, these two fungi evolved along different evolutionary trajectories and display considerable functional differences within the endophytic lifestyle.

The Red-Absorbing Chlorophyll a Antenna States of Photosystem I: A Hole-Burning Study of Synechocystis sp. PCC 6803 and Its Mutants

Abstract: Low temperature (4.2 K) absorption and hole-burned spectra are presented for the trimeric (wild-type, WT) photosystem I complex of the cyanobacterium Synechocystis sp. PCC 6803, its monomeric form, and mutants deficient in the PsaF, K, L, and M protein subunits. High-pressure- and Stark-hole-burning data for the WT trimer are presented as well as its temperature-dependent Qy-absorption and -fluorescence spectra. Taken as a whole, the data lead to assignment of a new and lowest energy antenna Qy-state located at 714 nm at low temperatures. It is this state that is responsible for the fluorescence in the low-temperature limit and not the previously identified antenna Qy-state near 708 nm. The data indicate that the 714 nm state is associated with strongly coupled chlorophyll a molecules (perhaps a dimer) and possesses significant charge transfer character. The red chlorophylls absorbing at 708 and 714 nm do not appear to be directly bound to any of the above protein subunits. The results are consistent with...

Dissolution-Driven Permeability Reduction of a Fractured Carbonate Caprock

Abstract: Geochemical reactions may alter the permeability of leakage pathways in caprocks, which serve a critical role in confining CO2 in geologic carbon sequestration. A caprock specimen from a carbonate formation in the Michigan sedimentary Basin was fractured and studied in a high-pressure core flow experiment. Inflowing brine was saturated with CO2 at 40°C and 10 MPa, resulting in an initial pH of 4.6, and had a calcite saturation index of −0.8. Fracture permeability decreased during the experiment, but subsequent analyses did not reveal calcite precipitation. Instead, experimental observations indicate that calcite dissolution along the fracture pathway led to mobilization of less soluble mineral particles that clogged the flow path. Analyses of core sections via electron microscopy, synchrotron-based X-ray diffraction imaging, and the first application of microbeam Ca K-edge X-ray absorption near edge structure, provided evidence that these occlusions were fragments from the host rock rather than s...