1,410 research outputs found
Factors controlling Macondo oil biodegraqdation on a rapidly eroding coastal headlands beach
Fourchon Beach, located along the southeast Louisiana coast, was affected by the oil leaking from the British Petroleum’s Deepwater Horizon Oil rig explosion in 2010. The oil, labeled MC252 oil, came ashore in a stable emulsion form, contaminating the sand, salt pan, marsh and mangroves along the beach. A unique oil form, labeled SSRB (small surface residue ball) was formed from the MC252 oil and a combination of environmental factors. The SSRB is an aggregate of sand and emulsified oil, and forms a large portion of the oil still present on the supratidal zone of Fourchon Beach. SSRBs have not been properly studied and their fate is largely unknown. For this research, various experiments were conducted to examine the biodegradability potential of SSRBs. First, an assessment of the subenvironments where the SSRBs were located was conducted. The environments appeared unfavorable for biodegradation to occur, with low organic matter and high salinities. Then, a characterization of the SSRBs’ physical and biochemical conditions was performed. Results indicated that their characteristics were closely dependent on the subenvironments in which they were located. Nonetheless; certain features pointing towards biodegradation were also found: microorganisms capable of degrading oil hydrocarbons and sources of nutrients and electron acceptors. Also, n-alkanes were substantially depleted in SSRBs sampled. Furthermore, a δ13C analysis in a respiration study indicated some biodegradation of crude oil, from respiration of oil instead of organic matter present. The implementation of these experiments helped identify and better understand the SSRBs and their biodegradability potential. This information obtained may offer us new solutions to challenges in environmental and waste cleanup. Also, help us determine how the oil spill has affected the supratidal area along Fourchon Beach, Louisiana and how best to proceed with cleanup efforts
B- and C-type low molecular weight glutenin subunits in tetraploid wheat germplasm
General knowledge acquisition entails the extraction of statistical regularities from the environment. At high levels of complexity, this may involve the extraction, and consolidation, of associative regularities across event memories. The underlying neural mechanisms would likely involve a hippocampo-neocortical dialog, as proposed previously for system-level consolidation. To test these hypotheses, we assessed possible differences in consolidation between associative memories containing cross-episodic regularities and unique associative memories. Subjects learned face-location associations, half of which responded to complex regularities regarding the combination of facial features and locations, whereas the other half did not. Importantly, regularities could only be extracted over hippocampus-encoded, associative aspects of the items. Memory was assessed both immediately after encoding and 48 h later, under fMRI acquisition. Our results suggest that processes related to system-level reorganization occur preferentially for regular associations across episodes. Moreover, the build-up of general knowledge regarding regular associations appears to involve the coordinated activity of the hippocampus and mediofrontal regions. The putative cross-talk between these two regions might support a mechanism for regularity extraction. These findings suggest that the consolidation of cross-episodic regularities may be a key mechanism underlying general knowledge acquisition
Gradual transition from insulator to semimetal of CaEuB with increasing Eu concentration
The local environment of Eu (, ) in
CaEuB () is investigated by
means of electron spin resonance (ESR). For the spectra show
resolved \textit{fine} and \textit{hyperfine} structures due to the cubic
crystal \textit{electric} field and nuclear \textit{hyperfine} field,
respectively. The resonances have Lorentzian line shape, indicating an
\textit{insulating} environment for the Eu ions. For , as increases, the ESR lines broaden due to local
distortions caused by the Eu/Ca ions substitution. For , the lines broaden further and the spectra gradually change from
Lorentzian to Dysonian resonances, suggesting a coexistence of both
\textit{insulating} and \textit{metallic} environments for the Eu ions.
In contrast to CaGdB, the \textit{fine} structure is still
observable up to . For the \textit{fine} and
\textit{hyperfine} structures are no longer observed, the line width increases,
and the line shape is purely Dysonian anticipating the \textit{semimetallic}
character of EuB. This broadening is attributed to a spin-flip scattering
relaxation process due to the exchange interaction between conduction and
Eu electrons. High field ESR measurements for
reveal smaller and anisotropic line widths, which are attributed to magnetic
polarons and Fermi surface effects, respectively.Comment: Submitted to PR
Site specific spin dynamics in BaFe2As2: tuning the ground state by orbital differentiation
The role of orbital differentiation on the emergence of superconductivity in
the Fe-based superconductors remains an open question to the scientific
community. In this investigation, we employ a suitable microscopic spin probe
technique, namely Electron Spin Resonance (ESR), to investigate this issue on
selected chemically substituted BaFeAs single crystals. As the
spin-density wave (SDW) phase is suppressed, we observe a clear increase of the
Fe 3 bands anisotropy along with their localization at the FeAs plane. Such
an increase of the planar orbital content interestingly occurs independently on
the chemical substitution responsible for suppressing the SDW phase. As a
consequence, the magnetic fluctuations combined with the resultant particular
symmetry of the Fe 3 bands are propitious ingredients to the emergence of
superconductivity in this class of materials.Comment: 6 pages, 5 figure
Fermion soliton stars
A real scalar field coupled to a fermion via a Yukawa term can evade no-go
theorems preventing solitonic solutions. For the first time, we study this
model within General Relativity without approximations, finding static and
spherically symmetric solutions that describe fermion soliton stars. The Yukawa
coupling provides an effective mass for the fermion, which is key to the
existence of self-gravitating relativistic solutions. We systematically study
this novel family of solutions and present their mass-radius diagram and
maximum compactness, which is close to (but smaller than) that of the
corresponding Schwarzschild photon sphere. Finally, we discuss the ranges of
the parameters of the fundamental theory in which the latter might have
interesting astrophysical implications, including compact (sub)solar and
supermassive fermion soliton stars for a standard gas of degenerate neutrons
and electrons, respectively.Comment: 16 pages, 5 figure
Distinct high-T transitions in underdoped BaKFeAs
In contrast to the simultaneous structural and magnetic first order phase
transition previously reported, our detailed investigation on an
underdoped BaKFeAs single crystal unambiguously
revealed that the transitions are not concomitant. The tetragonal (:
I4/mmm) - orthorhombic (: Fmmm) structural transition occurs at
110 K, followed by an adjacent antiferromagnetic (AFM) transition
at 102 K. Hysteresis and coexistence of the and
phases over a finite temperature range observed in our NMR
experiments confirm the first order character of the structural transition and
provide evidence that both and are strongly correlated. Our
data also show that superconductivity (SC) develops in the phase
below = 20 K and coexists with long range AFM. This new observation,
, firmly establishes another similarity between the hole-doped
BaFeAs via K substitution and the electron-doped iron-arsenide
superconductors.Comment: 4 pages, 3 figure
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