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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Reengineering the RHIC helium cooled current leads for EIC
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Myosin dilated cardiomyopathy mutation S532P disrupts actomyosin interactions, leading to altered muscle kinetics, reduced locomotion, and cardiac dilation in Drosophila
Dilated cardiomyopathy (DCM), a life-threatening disease characterized by pathological heart enlargement, can be caused by myosin mutations that reduce contractile function. To better define the mechanistic basis of this disease, we employed the powerful genetic and integrative approaches available in Drosophila melanogaster. To this end, we generated and analyzed the first fly model of human myosin–induced DCM. The model reproduces the S532P human β-cardiac myosin heavy chain DCM mutation, which is located within an actin-binding region of the motor domain. In concordance with the mutation’s location at the actomyosin interface, steady-state ATPase and muscle mechanics experiments revealed that the S532P mutation reduces the rates of actin-dependent ATPase activity and actin binding and increases the rate of actin detachment. The depressed function of this myosin form reduces the number of cross-bridges during active wing beating, the power output of indirect flight muscles, and flight ability. Further, S532P mutant hearts exhibit cardiac dilation that is mutant gene dose–dependent. Our study shows that Drosophila can faithfully model various aspects of human DCM phenotypes and suggests that impaired actomyosin interactions in S532P myosin induce contractile deficits that trigger the disease.
Metallothionein expression in Eastern mosquitofish ( Gambusia holbrooki ) exposed to 137 Cs and lead: implications for using metallothionein as a metal exposure biomarker
Given the range of threats facing aquatic ecosystems, it is critical we have monitoring tools to quickly and efficiently identify stressors within ecosystems. Metallothionein’s (MTs) are a group of proteins widely used as biomarkers of metal exposure; however, their suitability has been questioned due to their influenceable nature and ability to be induced by various stressors. Through our study, we sought to (1) evaluate induction of MT in eastern mosquitofish (Gambusia holbrooki) exposed to a radionuclide ( 137 Cs) and metal (Pb), (2) assess the influence of in situ 137 Cs pre-exposure on Pb-induced MT expression, and (3) quantify changes in MT concentrations during Pb depuration. We conducted our experiment in three phases using mosquitofish as a model species: Phase I—pre-exposure to 137 Cs in the field, Phase II—exposure to Pb in the lab immediately following 137 Cs exposure, and Phase III—depuration in the laboratory. We quantified MT concentrations over time and assessed differences among treatments. We did not find in situ exposure of mosquitofish to 137 Cs to induce MT, nor did pre-exposure to 137 Cs appear to influence induction of MT following Pb exposure. Metallothionein was rapidly induced in mosquitofish following Pb exposure; however, MT induction was also observed in control fish. Additionally, there was no apparent relationship between MT and Pb body burdens. During depuration, we found MT concentrations to be highly variable among fish demonstrating no clear response. Furthermore, our study demonstrates the high variability exhibited by MT, the need for further validation of MT as a metal exposure biomarker, and the value in additional research on these proteins under varying exposure scenarios, particularly environmentally realistic concentrations.
A semidominant point mutation of Mediator tail subunit MED5b in Arabidopsis leads to altered enrichment of H3K27me3 and reduced expression of targets of MYC2
Abstract The Mediator complex coordinates regulatory input for transcription driven by RNA polymerase II in eukaryotes. reduced epidermal fluorescence4-3 (ref4-3) is a semidominant mutation that results in a single amino acid substitution in the Mediator tail subunit Med5b. Previous characterization of ref4-3 revealed altered expression of a variety of loci in Arabidopsis, including those contributing to phenylpropanoid biosynthesis. Examination of existing RNA-seq data indicated that loci enriched for the transcriptionally repressive chromatin modification H3K27me3 are overrepresented among genes that are misregulated in ref4-3. We used ChIP-seq and RNA-seq to examine the possibility that perturbation of H3K27me3 homeostasis in ref4-3 plants contributed to altered transcript levels. We observed that ref4-3 results in a modest global reduction of H3K27me3 at enriched loci and that this reduction is not dependent on gene expression; however, altered H3K27me3 was not strongly predictive of altered expression in ref4-3 plants. Instead, our analyses revealed a substantial enrichment of targets of the MYC2 transcriptional regulator among genes that exhibit decreased expression in ref4-3. Consistent with previous characterization of ref4-3, we observed that ref4-3-dependent decreased expression of MYC2 targets can be suppressed by loss of another Mediator tail subunit, MED25. This observation is consistent with previous biochemical characterization of MYC2. Our data highlight the diverse and distinct impacts that a single amino acid change in the tail subunit of Mediator can have on transcriptional circuits and raise the prospect that Mediator directly contributes to H3K27me3 homeostasis in plants.
Phosphorolytic degradation of leaf starch via plastidic α-glucan phosphorylase leads to optimized plant growth and water use efficiency over the diel phases of Crassulacean acid metabolism
In plants with Crassulacean acid metabolism (CAM), it has been proposed that the requirement for nocturnal provision of phosphoenolpyruvate as a substrate for CO 2 uptake has resulted in a re-routing of chloroplastic starch degradation from the amylolytic route to the phosphorolytic route. To test this hypothesis, we generated and characterized four independent RNAi lines of the obligate CAM species Kalanchoë fedtschenkoi with a >10-fold reduction in transcript abundance of plastidic α-glucan phosphorylase (PHS1). The rPHS1 lines showed diminished nocturnal starch degradation, reduced dark CO 2 uptake, a reduction in diel water use efficiency (WUE), and an overall reduction in growth. A re-routing of starch degradation via the hydrolytic/amylolytic pathway was indicated by hyperaccumulation of maltose in all rPHS1 lines. Further examination indicated that whilst operation of the core circadian clock was not compromised, plasticity in modulating net dark CO 2 uptake in response to changing photoperiods was curtailed. The data show that phosphorolytic starch degradation is critical for efficient operation of the CAM cycle and for optimizing WUE. This finding has clear relevance for ongoing efforts to engineer CAM into non-CAM species as a means of boosting crop WUE for a warmer, drier future.
Disc tearing leads to low and high frequency quasi-periodic oscillations in a GRMHD simulation of a thin accretion disc
Black hole X-ray binaries (BHXRBs) display a wide range of variability phenomena, from long duration spectral state changes to short-term broad-band variability and quasi-periodic oscillations (QPOs). A particularly puzzling aspect is the production of QPOs, which – if properly understood – could be used as a powerful diagnostic tool of black hole accretion and evolution. In this work, we analyse a high-resolution 3D general relativistic magnetohydrodynamic simulation of a geometrically thin accretion disc, which is tilted by 65° with respect to the black hole spin axis. We find that the Lense–Thirring torque from the rapidly spinning 10 M ⊙ black hole causes several sub-discs to tear off within ~10–20 gravitational radii. Tearing occurs in cycles on time-scales of seconds. During each tearing cycle, the inner sub-disc precesses for 1–5 periods before it falls into the black hole. We find a precession frequency of ~3 Hz, consistent with observed low-frequency QPOs. In addition, we find a high frequency QPO (HFQPO) with centroid frequency of ~55 Hz in the power spectra of the mass-weighted radius of the inner disc and the radial mass flux. This signal is caused by radial epicyclic oscillations of a dense ring of gas at the tearing radius, which suggests a corresponding modulation of the X-ray light curve and may thus explain some of the observed HFQPOs.
Singlet Oxygen Leads to Structural Changes to Chloroplasts during their Degradation in the Arabidopsis thaliana plastid ferrochelatase two Mutant
Abstract During stress, chloroplasts produce large amounts of reactive oxygen species (ROS). Chloroplasts also contain many nutrients, including 80% of a leaf’s nitrogen supply. Therefore, to protect cells from photo-oxidative damage and to redistribute nutrients to sink tissues, chloroplasts are prime targets for degradation. Multiple chloroplast degradation pathways are induced by photo-oxidative stress or nutrient starvation, but the mechanisms by which damaged or senescing chloroplasts are identified, transported to the central vacuole and degraded are poorly defined. Here, we investigated the structures involved with degrading chloroplasts induced by the ROS singlet oxygen (1O2) in the Arabidopsis thaliana plastid ferrochelatase two (fc2) mutant. Under mild 1O2 stress, most fc2 chloroplasts appeared normal, but had reduced starch content. A subset of chloroplasts was degrading, and some protruded into the central vacuole via ‘blebbing’ structures. A 3D electron microscopy analysis demonstrated that up to 35% of degrading chloroplasts contained such structures. While the location of a chloroplast within a cell did not affect the likelihood of its degradation, chloroplasts in spongy mesophyll cells were degraded at a higher rate than those in palisade mesophyll cells. To determine if degrading chloroplasts have unique structural characteristics, allowing them to be distinguished from healthy chloroplasts, we analyzed fc2 seedlings grown under different levels of photo-oxidative stress. A correlation was observed among chloroplast swelling, 1O2 signaling and the state of degradation. Finally, plastoglobule (PG) enzymes involved in chloroplast disassembly were upregulated while PGs increased their association with the thylakoid grana, implicating an interaction between 1O2-induced chloroplast degradation and senescence pathways.
Manipulation of Lignin Monomer Composition Combined with the Introduction of Monolignol Conjugate Biosynthesis Leads to Synergistic Changes in Lignin Structure
Abstract The complexity of lignin structure impedes efficient cell wall digestibility. Native lignin is composed of a mixture of three dominant monomers, coupled together through a variety of linkages. Work over the past few decades has demonstrated that lignin composition can be altered through a variety of mutational and transgenic approaches such that the polymer is derived almost entirely from a single monomer. In this study, we investigated changes to lignin structure and digestibility in Arabidopsis thaliana in near-single-monolignol transgenics and mutants and determined whether novel monolignol conjugates, produced by a FERULOYL-CoA MONOLIGNOL TRANSFERASE (FMT) or a p-COUMAROYL-CoA MONOLIGNOL TRANSFERASE (PMT), could be integrated into these novel polymers to further improve saccharification efficiency. Monolignol conjugates, including a new conjugate of interest, p-coumaryl p-coumarate, were successfully integrated into high-H, high-G and high-S lignins in A. thaliana. Regardless of lignin composition, FMT- and PMT-expressing plants produced monolignol ferulates and monolignol p-coumarates, respectively, and incorporated them into their lignin. Through the production and incorporation of monolignol conjugates into near-single-monolignol lignins, we demonstrated that substrate availability, rather than monolignol transferase substrate preference, is the most important determining factor in the production of monolignol conjugates, and lignin composition helps dictate cell wall digestibility.
Leading the way out: how a plant myosin facilitates vesicle tethering during exocytosis
Exocytosis is a process by which molecules, such as lipids, proteins, and polysaccharides, are delivered to the plasma membrane (PM) and the extracellular space via vesicular transport. Precise orchestration of this process ensures the spatiotemporal specificity of cargo delivery and therefore plays a vital role in cell growth, function, and response to environmental cues (reviewed in Wu and Guo, 2015; Ravikumar et al., 2017). Lastly, while sophisticated mechanisms for exocytosis have been described in animal and yeast cells, the extent of conservation of these mechanisms in plant systems is far less clear.
Complete Next-to-Leading-Order Standard-Model-Effective-Field-Theory Electroweak Corrections to Higgs Decays
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Beyond leading twist: 𝜌 meson decay constants and distribution amplitudes in a self-consistent light-front quark model
In this study, we present a comprehensive analysis of decay constants and chiral-even and chiral-odd distribution amplitudes (DAs) up to twist 4 for the 𝜌 meson in the standard light-front quark model (LFQM) based on the Bakamjian-Thomas (BT) construction. For the 𝜌 meson, which possesses both longitudinal (ℎ=0) and transverse (ℎ =±1) polarizations, two types of decay constants, 𝑓$^{∥}_{𝜌}$ and 𝑓$^{⊥}_{𝜌}$, arises accordingly. We demonstrate that these decay constants can be self-consistently extracted from both local (𝑧𝜇 =0) and nonlocal (𝑧𝜇 ≠0) matrix elements ⟨0|$\overline{𝑞}$(𝑧)Γ𝑞(−𝑧)|𝜌(𝑃,ℎ)⟩, with Γ=(𝛾 𝜇 ,𝜎 𝜇𝜈 ,𝛾 𝜇 𝛾 5 ,𝟏), in a manner independent of current components, polarizations, and reference frames. In particular, we emphasize the role of nonlocal matrix elements involving axial-vector and scalar currents, where mixing between 𝑓$^{∥}_{𝜌}$ and 𝑓$^{⊥}_{𝜌}$ occurs. We show that this mixing is consistently resolved through the BT construction, ensuring the proper extraction of these decay constants.
Global Bayesian analysis of J/𝜓 photoproduction on proton and lead targets
We perform a global Bayesian analysis of diffractive J/𝜓 production in 𝛾 + 𝑝 and 𝛾 + Pb collisions using a color glass condensate (CGC) based calculation framework. As past calculations have shown that CGC-based models typically overpredict the J/𝜓 production in 𝛾 + Pb collisions at high center of mass energy, we address the question of whether it is possible to describe coherent and incoherent diffractive J/𝜓 data from 𝛾 + 𝑝 collisions at Hadron–Electron Ring Accelerator (HERA) and the LHC, and from 𝛾 + Pb collisions at the LHC simultaneously. Our results indicate that a simultaneous description of 𝛾 + 𝑝 and 𝛾 + Pb data is challenging, with results improving when an overall 𝐾-factor—scaling 𝛾 + 𝑝 and 𝛾 + Pb cross sections to absorb model uncertainties—is introduced.
Electric-field-dependent g factor for the ground state of lead monofluoride, PbF
The electric field dependent g–factor and the electron electric dipole moment (eEDM)-induced Stark splittings for the lowest rotational levels of 207,208 PbF are calculated. Observed and calculated Zeeman shifts for 207 PbF are found to be in very good agreement. Furthermore, it is shown that the 207 PbF hyperfine sublevels provide a promising system for the eEDM search and related experiments.
Rapid charge redistribution leading to core hollowing in a high-intensity ion beam
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Finite-size effects in lead scandium tantalate relaxor thin films
Large electromechanical effects in relaxor ferroelectrics are generally attributed to the collective response of an ensemble of correlated, nanometer-sized polar structures induced by chemical and charge disorder. Here, we study finite-size effects on such polar order (i.e., how it evolves when sample dimensions approach the polarization correlation length) in 7–70-nm-thick films of the relaxor ferroelectric PbSc 0.5 Ta 0.5 O 3 . Temperature-dependent polarization studies reveal a linear suppression of the polarization and nonlinearity associated with relaxor order as the film thickness decreases to ≈ 30 nm. Below this thickness, however, the suppression rapidly accelerates, and polarization is completely absent by film thicknesses of ≈ 7 nm, despite the continued observation of a broad peak in dielectric permittivity and frequency dispersion. Diffuse-scattering measurements reveal the diffuse-scattering symmetry, and analysis suggests the films have a polarization correlation length of ≈ 23 nm. Finally, taken together, it is apparent that reduction of sample size and the resulting distribution of polar structures drive suppression and eventual quenching of the electrical response of relaxors, which may be attributed to increasing dipole-dipole and dipole-interface interactions.
Self-consistency in GWΓ formalism leading to quasiparticle-quasiparticle couplings
Within many-body perturbation theory, Hedin's formalism offers a systematic way to iteratively compute the self-energy Σ of any dynamically correlated interacting system, provided one can evaluate the interaction vertex Γ exactly. This is, however, impossible, in general, for it involves the functional derivative of Σ with respect to the Green's function. Here, we analyze the structure of this derivative, splitting it into four contributions and outlining the type of quasiparticle interactions that each of them generate. Moreover, we show how, in the implementation of self-consistency, the action of these contributions can be classified into two: A quantitative renormalization of previously included interaction terms and the inclusion of qualitatively distinct interaction terms through successive functional derivatives of Γ itself. Implementing this latter type of self-consistency can extend the validity of perturbative approximations based on Hedin's equations toward the high interaction limit, as we show in the example of the Hubbard dimer. Furthermore, our analysis also provides a unifying perspective on the perturbation theory landscape, showing how the T-matrix approach is completely contained in Hedin's formalism.
Magneto-optical studies of hybrid organic/inorganic perovskite: The case of methyl-ammonium lead bromide
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