Search Menu
DOE PAGES title logo U.S. Department of Energy
Office of Scientific and Technical Information
Search Scholarly Publications

42 Search Results

Sorted by Relevance
Save Results
...

  1. Investigating overflow metabolism in heterotrophic cultures of the green alga Chromochloris zofingiensis

    Meagher, Michelle ; Camacho, Dimitrios J. ; Gallaher, Sean D. ; ... - Metabolic Engineering
    Chromochloris zofingiensis is of interest for its ability to perform a reversible trophic switch in the presence of glucose that is characterized by a shutdown of photosynthesis and an accumulation of energy storage metabolites. Previous work has shown that this trophic switch is accompanied by overflow metabolism and the production of lactate in aerobic conditions. This trophic switch is not observed in nutrient replete media. We utilized isotopically assisted metabolic flux analysis to characterize intracellular flux distributions that are associated with different metabolic phenotypes observed in this organism in different media formulations in light and dark conditions. The results ofmore » this analysis showed that low iron cultures have no flux through carbon fixation reactions, and that the carbon flux entering the TCA cycle in these cultures is approximately 40 % lower than that in iron replete cultures grown heterotrophically. This analysis was complemented with transcriptomics data collected for C. zofingiensis grown in iron limited conditions to provide further evidence towards the negative impact of iron limitation on both photosynthetic and respiratory activity. Overflow metabolism allows this alga to compensate for the lower energy production that results from iron limitation. This work highlights how nutrient availability can lead to changes in the metabolism of C. zofingiensis.« less

  2. California annual grass phenology and allometry influence ecosystem dynamics and fire regime in a vegetation demography model

    Gao, Xiulin ; Koven, Charles D. ; Longo, Marcos ; ... - New Phytologist
    Grass-dominated ecosystems cover wide areas of the land surface yet have received far less attention from the Earth System Model (ESM) community. This limits model projections of ecosystem dynamics in response to global change and coupled vegetation–climate dynamics. We used the Functionally Assembled Terrestrial Ecosystem Simulator (FATES), a dynamic vegetation demography model, to determine ecosystem sensitivity to alternate, observed grass allometries and biophysical traits, and evaluated model performance in capturing California C3 annual grasslands structure and fire regimes. Grass allometry, leaf physiology, plant phenology, and plant mortality all drove the seasonal variation in matter and energy exchange and fire dynamicsmore » in California annual grasslands. Allometry influenced grassland structure and function mainly through canopy architecture-mediated space and light competition instead of through carbon partitioning strategy. Regional variation in grassland annual burned area was driven by variation in ecosystem productivity. Our study advances the modeling of grassy ecosystems in ESMs by establishing the importance of grass allometry and plant phenology and mortality in driving C3 annual grassland seasonal dynamics and fire regime. The calibrated annual grass allometry and biophysical traits presented can be applied in future studies to project climate–vegetation–fire feedbacks in annual grass-dominant ecosystems under global change.« less

  3. Probing light quark Yukawa couplings through angularity distributions in Higgs boson decay

    Yan, Bin ; Lee, Christopher - Journal of High Energy Physics (Online)
    We propose to utilize angularity distributions in Higgs boson decay to probe light quark Yukawa couplings at e+e- colliders. Angularities $$τ$$a are a class of 2-jet event shapes with variable and tunable sensitivity to the distribution of radiation in hadronic jets in the final state. Using soft-collinear effective theory (SCET), we present a prediction of angularity distributions from Higgs decaying to quark and gluon states at e+e- colliders to NNLL + $$\mathcal{O}$$(αs) accuracy. Due to the different color structures in quark and gluon jets, the angularity distributions from H → $$q\overline{q}$$ and H → gg show different behaviors and canmore » be used to constrain the light quark Yukawa couplings. We show that the upper limit of light quark Yukawa couplings could be probed to the level of ~ 15% of the bottom quark Yukawa coupling in the Standard Model in a conservative analysis window far away from nonperturbative effects and other uncertainties; the limit can be pushed to ≲ 7 – 9% with better control of the nonperturbative effects especially on gluon angularity distributions and/or with multiple angularities.« less

  4. Enhanced Production of Λ b 0 Baryons in High-Multiplicity p p Collisions at s = 13     TeV

    Aaij, R. ; Abdelmotteleb, A. S. W. ; Abellan Beteta, C. ; ... - Physical Review Letters
    The production rate of Λ b 0 baryons relative to B 0 mesons in p p collisions at a center-of-mass energy s = 13     TeV is measured by the LHCb experiment. The ratio of Λ b 0 to B 0 production cross sections shows a significant dependence on both the transverse momentum and the measured charged-particle multiplicity. At low multiplicity, the ratio measured at LHCb is consistent with the valuemore » measured in e + e − collisions, and increases by a factor of ∼ 2 with increasing multiplicity. At relatively low transverse momentum, the ratio of Λ b 0 to B 0 cross sections is higher than what is measured in e + e − collisions, but converges with the e + e − ratio as the momentum increases. These results imply that the evolution of heavy b quarks into final-state hadrons is influenced by the density of the hadronic environment produced in the collision. Comparisons with several models and implications for the mechanisms enforcing quark confinement are discussed. © 2024 CERN, for the LHCb Collaboration 2024 CERN« less

  5. Adiabatic and post-adiabatic hyperspherical treatment of the huge ungerade proton-hydrogen scattering length

    Singh, Shayamal ; Greene, Chris H. - Canadian Journal of Physics
    While the hydrogen molecular ion is the simplest molecule in nature and very well studied in all of its properties, it remains an interesting system to use for explorations of fundamental questions. One such question treated in this study relates to finding an optimal adiabatic representation of the physics, i.e., the best adiabatic description that minimizes the role of nonadiabatic effects. As a test case explored here in detail, we consider the ungerade symmetry of $$H$$$^{+}_{2}$$, which is known to have a huge scattering length of order 750 Bohr radii, and an incredibly weakly bound excited state. We show thatmore » a hyperspherical adiabatic description does an excellent job of capturing the main physics. Furthermore, our calculation yields a competitive scattering length and shows that nonadiabatic corrections are small and can even be adequately captured using the post-adiabatic theory of Klar and Fano.« less

  6. Centrality-dependent modification of hadron and jet production in electron-nucleus collisions

    Li, Hai Tao ; Liu, Ze Long ; Vitev, Ivan - Physics Letters. B

  7. SPLENDAQ: A Detector-Agnostic Data Acquisition System for Small-Scale Physics Experiments

    Watkins, Samuel Linton - Journal of Low Temperature Physics
    Many scientific applications from rare-event searches to condensed matter system characterization to high-rate nuclear experiments require time-domain triggering on a raw stream of data, where the triggering is generally threshold-based or randomly acquired. When carrying out detector R &D, there is a need for a general data acquisition (DAQ) system to quickly and efficiently process such data. In the SPLENDOR collaboration, we are developing the Python-based SPLENDAQ package for this exact purpose—it offers two main features for offline analysis of continuous data: a threshold triggering algorithm based on the time-domain optimal filter formalism and an algorithm for randomly choosing nonoverlappingmore » segments for noise measurements. Further, combined with the commercially available Moku platform, developed by Liquid Instruments, we have a full pipeline of event building off raw data with minimal setup. Here, we review the underlying principles of this detector-agnostic DAQ package and give concrete examples of its utility in various applications.« less

  8. Role of carbon treating in piperazine oxidation

    Wu, Yuying ; Rochelle, Gary T. - International Journal of Greenhouse Gas Control
    Bench-scale experiments were performed to test the effects of carbon treating (8 × 30 mesh, lignite-based granular activated carbon from Nowata Filtration) on the oxidation of aqueous piperazine (PZ) at conditions of CO2 capture. The combined mitigation with carbon treating and N2 sparging was also tested. When carbon treating is applied, the UV–Vis absorbance at 320 nm, the NH3 production rate, and the accumulation rate of dissolved Fe concentration and total formate concentration decrease. The effects of carbon treating last even when the carbon is bypassed, which is possibly due to the removal of catalytic degradation products. Therefore, it ismore » better to apply carbon treating in the early stages of oxidation. Combining carbon treating and nitrogen sparging is more effective in oxidation mitigation than applying the methods separately. The amount of Fe removed by the carbon bed is greater than the result calculated from the solvent inventory and concentration difference of Fe in solvent, indicating that Fe colloids or other “soluble” Fe will dissolve into the solvent and replace the dissolved Fe that is adsorbed and removed. Furthermore, the carbon removes the degradation products that can complex with Fe3+, even if they are not complexed. Since the source of Fe includes fly ash and corrosion, removing the complexing agents instead of all the available Fe is a more feasible target.« less

  9. Deep underground measurement of B 11 ( α , n ) N 14

    Borgwardt, Tyler C. ; deBoer, Richard James ; Boeltzig, Axel ; ... - Physical Review. C
    The primordial elemental abundance composition of the first stars leads to questions about their modes of energy production and nucleosynthesis. The formation of 12C has been thought to occur primarily through the 3α process, however, alternative reaction chains may contribute significantly, such as 7Li (α, γ)11B (α,n)14N. This reaction sequence cannot only bypass the mass A = 8 stability gap, but could also be a source of neutrons in the first star environment. However, the efficiency of this reaction chain depends on the possible enhancement of its low energy cross section by α-cluster resonances near the reaction threshold. A newmore » study of the reaction 11B(α,n) 14N has been undertaken at the CASPAR underground facility at beam energies from 300–700 keV. A 4π neutron detector in combination with pulse shape discrimination at low background conditions resulted in the ability to probe energies lower than previously measured. Further, resonance strengths were determined for both the resonance at a laboratory energy of 411 keV, which was measured for the second time, and for a new resonance at 337 keV that has been measured for the first time. This resonance, found to be significantly weaker than previous estimates, dominates the reaction rate at lower temperatures (T < 0.2 KG) and reduces the reaction rate in first star environments.« less

  10. A comparative study of solute trapping in Fe-(33–45 at%) Cu alloys manufactured by laser directed energy deposition

    Yin, Daniel ; Misra, Amit - Journal of Alloys and Compounds
    The high cooling rates in laser directed energy deposition (DED-LB) of alloys lead to substantial amounts of solute trapping as solute atoms cannot diffuse away from the solid/liquid interface before it advances. In some concentrated alloys, this results in supersaturated solid phases that form nanoscale hierarchical microstructures when the solute atoms precipitate out during reheating from subsequent laser passes. We choose the Iron-Copper (Fe-Cu) binary alloy as model system as it is chemically homogeneous in the liquid phase and has negligible solid solubility at room temperature. Two alloys with nominal compositions in atomic (at.) %, Fe67Cu33 and Fe55Cu45, were manufacturedmore » using DED-LB. Scanning transmission electron microscopy (STEM), energy dispersive spectroscopy (EDS) and wavelength dispersive spectroscopy (WDS) were used to characterize the nanostructures and heterogeneous chemical compositions. A non-equilibrium solute partitioning model was used to compute the supersaturated chemistries of the constituent phases and validated with experimentally measured compositions. The measured phase compositions of the two alloys were very similar, at roughly 12 at.% Cu and 4 at.% Fe in the α(bcc)-Fe and ε(fcc)-Cu phases respectively, despite having different processing parameters and mechanical behavior. This indicates that the total thermal history, that depends on both the processing parameters and laser scan pattern, plays a stronger role on the final microstructure evolution than just the initial quantity of trapped solute. In addition, we find that current non-equilibrium solute partitioning models applied on the continuum scale fall short of predicting accurate quantitative phase compositions in concentrated alloys, although the qualitative trends are captured correctly.« less
...
Search for:
All Records
Subject
Ga Fe atomic exchange
Refine by:
Article Type
Availability
Journal
more less
Creator / Author
more less
Publication Date
Research Organization
more less