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At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Intracellular delivery of poly(I:C) induces apoptosis of fibroblast-like synoviocytes via an unknown dsRNA sensor

Fibroblast-like synoviocytes (FLS) express functional membranous and cytoplasmic sensors for double-stranded (ds)RNA. Notably, FLS undergo apoptosis upon transfection with the synthetic dsRNA analog poly(I:C). We here studied the mechanism of intracellular poly(I:C) recognition and subsequent cell death in FLS. FLS responded similarly to poly(I:C) or 3pRNA transfection; however, only intracellular delivery of poly(I:C) induced significant cell death, accompanied by upregulation of pro-apoptotic proteins Puma and Noxa, caspase 3 cleavage, and nuclear segregation. Knockdown of the DExD/H-box helicase MDA5 did not affect the response to intracellular poly(I:C); in contrast, knockdown of RIG-I abrogated the response to 3pRNA. Knockdown of the downstream adaptor proteins IPS, STING, and TRIF or inhibition of TBK1 did not affect the response to intracellular poly(I:C), while knockdown of IFNAR blocked intracellular poly(I:C)-mediated signaling and cell death. We conclude that a so far unknown intracellular sensor recognizes linear dsRNA and induces apoptosis in FLS. - Highlights: • Intracellular poly(I:C) and 3pRNA evoke immune responses in FLS. • Only intracellular delivery of poly(I:C) induces FLS apoptosis. • FLS do not require MDA5 for their response to intracellular poly(I:C). • FLS respond to intracellular poly(I:C) independent of IPS and STING. • An unknown intracellular sensor recognizes linear dsRNA in FLS.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Preservation of rat hearts in subfreezing temperature isochoric conditions to – 8 °C and 78 MPa

Highlights: • A novel method of low-temperature organ preservation is tested using rat hearts. • Isochoric systems allow ice-free preservation at temperatures well below freezing. • Conventional heart preservation employs on-ice storage in atmospheric conditions. • Histological quality is improved in hearts preserved in a −4 °C isochoric system. Isochoric (constant volume) preservation at subfreezing temperatures is being investigated as a novel method for preserving cells and organs. This study is a first initial effort to evaluate the efficacy of this method for heart preservation, and to provide a preliminary outline of appropriate preservation parameters. To establish a baseline for further studies, rat hearts were preserved in a University of Wisconsin (UW) intracellular solution for one hour under isochoric conditions at: 0 °C (atmospheric pressure - 0.1 MPa), - 4 °C (41 MPa), - 6 °C (60 MPa) and – 8 °C (78 MPa). The viability of the heart was evaluated using Langendorff perfusion and histological examination. The physiological performance of hearts preserved at – 4 °C (41 MPa) was comparable to that of a heart preserved on ice at atmospheric pressure, with no statistically significant difference in histological injury score. However, hearts preserved at −4 °C displayed substantially reduced interstitial edema compared to hearts preserved by conventional hypothermic preservation in UW on ice at atmospheric pressure, suggesting significant protection from increased vascular permeability following preservation. Hearts preserved at – 6 °C (60 MPa) suffered injury from cellular swelling and extensive edema, and at – 8 °C (78 MPa) hearts experienced significant morphological disruption. To the best of our knowledge, this is the first publication showing that a mammalian organ can survive low subfreezing temperatures without the use of a cryoprotective additive. Lowering the preservation temperature reduces metabolism and improves preservation quality, and these results suggest that improvements in preservation are possible at subzero temperatures with low to moderate pressures observed at −4 °C. Notably, tissue damage was observed at lower temperatures (−6 °C or below) accompanying further elevation of pressure associated with isochoric preservation that may prove detrimental. Therefore, subfreezing temperature isochoric preservation protocols should optimize, a combination of temperature and pressure that will minimize the negative effects of elevated pressure while retaining the beneficial effect of lower temperatures and reduced metabolism.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Hsa{sub c}irc{sub 0}007534/miR-761/ZIC5 regulatory loop modulates the proliferation and migration of glioma cells

Highlights: • Hsa{sub c}irc{sub 0}007534 knockdown inhibited glioma cell proliferation and migration. • Hsa{sub c}irc{sub 0}007534 regulated cell proliferation and migration by sponging miR-761. • ZIC5 was a target of miR-761. • Hsa{sub c}irc{sub 0}007534 promoted glioma cell proliferation and migration via upregulating ZIC5 expression by sponging miR-761. Increasing evidences demonstrate the essential roles of circular RNAs (circRNAs) in human cancers. However, the study about the functions of circRNAs in glioma remains very limited. In the present study, we found that circRNA hsa{sub c}irc{sub 0}007534 was highly expressed in glioma tissues compared to normal brain tissues. Furthermore, we found that knockdown of hsa{sub c}irc{sub 0}007534 significantly inhibited the proliferation and migration of glioma cells. In mechanism, we showed that hsa{sub c}irc{sub 0}007534 could sponge miR-761 to repress its availability in glioma cells. We found that inhibition of miR-761 could rescue the suppressed proliferation and migration of glioma cells by hsa{sub c}irc{sub 0}007534 knockdown. Moreover, we explored the downstream mechanism and found that ZIC5 was a target of miR-761. We showed that hsa{sub c}irc{sub 0}007534 promoted the expression of ZIC5 by inhibiting miR-761 in glioma cells. And restoration of ZIC5 expression significantly reversed the effects of hsa{sub c}irc{sub 0}007534 knockdown on glioma cell proliferation and migration. In summary, our results demonstrated that hsa{sub c}irc{sub 0}007534 serves as an oncogene in glioma via promoting ZIC5 expression by repressing miR-761 availability. Our results suggested that hsa{sub c}irc{sub 0}007534/miR-761/ZIC5 regulatory loop might be a promising therapeutic target for glioma treatment.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Role of c-Myb in the regulation of natural killer cell activity

Highlights: • c-Myb activity was downregulated by TGF-β in natural killer cells. • Celastrol, a c-Myb inhibitor, decreased NK-92 activity at low concentrations. • Celastrol downregulated NKG2D and granzyme B expression. • c-Myb knockdown downregulated NK-92 cytotoxicity and IFN-γ secretion. The regulation of natural killer (NK) cell activity is an important research goal for the development of immunotherapies. In this study, we identified transcription factors affecting NK cell activity. In particular, we screened transcription factors affected by interleukin-2 (IL-2) and transforming growth factor-beta (TGF-β) by protein/DNA arrays using primary NK cells. We found that celastrol, a c-Myb inhibitor, inhibited NK-92 cells more strongly than any other inhibitors of transcription factor candidates. In addition, c-Myb and c-Myb-related signaling molecules, e.g., Nemo-like kinase (NLK) and c-Myc, were regulated by the activation status of NK cells, suggesting that c-Myb is a key regulator of NK cell activity. We also found that celastrol inhibits NK-92-cell-mediated cytotoxicity via the downregulation of NKG2D and granzyme B. Knockdown studies also showed that c-Myb is important for NK cell activation. In particular, the knockdown of c-Myb did not significantly affect NK cell proliferation and survival but decreased the secretion of IFN-γ and the cytotoxicity of NK cells. Our data demonstrate that c-Myb plays a critical role in the activation of NK cells and therefore is a therapeutic target for cancer and viral diseases.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

On the densification of cubic ZrO{sub 2} nanocondensates by capillarity force and turbostratic C–Si–H multiple shell

A turbostratic C–Si–H lamellar phase with 0.35–0.39 nm interspacing and ZrO{sub 2} condensates having cubic (c), tetragonal and monoclinic structures stabilized by increasing particle size were synthesized by pulsed laser ablation on Zr plate in TEOS and characterized by X-ray/electron diffraction and optical spectroscopy. The c-ZrO{sub 2} phase ca. 10% denser than the ambient lattice was stabilized as 3–10 nm sized cubo-octahedral nanoparticles but as abnormal large-sized (up to 30 nm) ones when encapsulated by the C{sub 1−x}Si{sub x}:H multiple shell with defective graphite-like structure units to exert an effective compressive stress. The potential application of such core–shell nanostructure with enhanced binding of Zr and O ions and implication for natural dynamic occurrence of the C{sub 1−x}Si{sub x}:H phase are addressed. - Graphical abstract: Lattice image of a typical cubic-ZrO{sub 2} particle densified by the turbostratic Si{sub x}C{sub 1−x}:H shell. Highlights: ► Turbostratic C–Si–H lamellar phase and ZrO{sub 2} condensates were synthesized by PLA. ► The c-ZrO{sub 2} phase ca. 10% denser than the ambient lattice was stabilized as 3–10 nm. ► The c-ZrO{sub 2} particles up to 30 nm were densified when encapsulated by the C{sub 1−x}Si{sub x}:H multiple shell. ► Tight ion binding of the c-ZrO{sub 2} due to capillarity force and turbostratic shell.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Synthesis of g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction with enhanced photocatalytic performance

Graphical abstract: g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction photocatalyst with visible-light response was prepared by a facile coprecipitation method. The results show that g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} possesses a much higher activity for the decomposition of RhB than that of the pure Ag{sub 3}PO{sub 4} particles. The most mechanism is that g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction photocatalyst can efficiently separate the photogenerated electron–hole pairs, enhancing the photocatalytic activity of g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} composites. - Highlights: • g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction showed much higher activity than that of Ag{sub 3}PO{sub 4}. • The high activity could be attributed to g-C{sub 3}N{sub 4} for modifying Ag{sub 3}PO{sub 4}. • More ·OH radicals may be significant reason to improve Ag{sub 3}PO{sub 4} activity. - Abstract: g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction photocatalyst with visible-light response was prepared by a facile coprecipitation method. The photocatalysts were characterized by X-ray powder diffraction, transmission electron microscopy, UV–vis absorption spectroscopy and Fourier transform infrared spectroscopy. The photocatalytic activities of the obtained samples were tested by using Rhodamine B (RhB) as the degradation target under visible light irradiation. g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} decomposed RhB more effectively than the pure Ag{sub 3}PO{sub 4} particles did, and 2 wt.% g-C{sub 3}N{sub 4} had the highest activity. Furthermore, 2 wt.% g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} degraded high-concentration RhB more potently than unmodified Ag{sub 3}PO{sub 4} did, probably because g-C{sub 3}N{sub 4}/Ag{sub 3}PO{sub 4} heterojunction photocatalyst enhanced the photocatalytic activity by efficiently separating the photogenerated electron–hole pairs.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Scalable production of Cu@C composites for cross-coupling catalysis

Highlights: • Cu@C core–shell composite was prepared by reduction of [Cu(NH{sub 3}){sub 4}]{sup 2+} with glucose. • The carbon shell in Cu@C can be tuned to the different degree of carbonization. • The Cu@C composites were utilized to catalyze the C−N cross coupling reaction. • The catalytic ability of Cu@C depends on the degree of shell-carbonization. - Abstract: A novel Cu@C core–shell microstructure was prepared by reduction of [Cu(NH{sub 3}){sub 4}]{sup 2+} with glucose using a mild hydrothermal process. The carbon shell of such Cu@C composite can be tuned to different carbonization degrees just through varying the calcination conditions. The structural properties of as-prepared Cu@C were investigated in detail by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron micrographs (TEM) and Raman spectra. In addition, these Cu@C composites were firstly used to catalyze the C−N cross coupling of amines with iodobenzene. Among them, the catalytic ability of Cu@C composites increased as their surface carbon’s carburization degree improved.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

In situ high-energy X-ray diffraction investigation of the micromechanical behavior of Fe-0.1C-10Mn-0/2Al steel at room and elevated temperatures

The micromechanical behavior of medium-Mn transformation-induced-plasticity (TRIP) steels with nominal chemical compositions of Fe-0.1C-10Mn (mass%) (0Al steel) and Fe-0.1C-10Mn-2Al (mass%) (2Al steel) fabricated by intercritical annealing 600 degrees C for 1 h and 650 degrees C for 1 h, respectively, was investigated using in situ high-energy X-ray diffraction (HE-XRD) with uniaxial tensile tests at 25 degrees C and 100 degrees C. We found that Liiders band propagation promoted lower volume fraction of austenite transformation to martensite in 0Al steel than 2Al steel at 25 degrees C while higher volume fraction of austenite transformation to martensite in 0Al steel than 2Al steel at 100 degrees C. Portevin-Le Chatelier (PLC) band propagation promoted higher volume fraction of austenite transformation to martensite in 0Al steel than 2Al steel during deformation at 25 degrees C and 100 degrees C. Moreover, the addition of Al obviously suppresses the formation of intermediate epsilon martensite during tensile deformation, thus the zigzag change in lattice strain of austenite was completely depressed in 2Al steel. Due to the controlled stability of metastable austenite, the 2Al steel demonstrated the best combination of ultimate tensile strength and total elongation at 25 degrees C.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Theoretical Kinetics Analysis for $\dot{H}$ Atom Addition to 1,3-Butadiene and Related Reactions on the $\dot{C}$ 4 H 7 Potential Energy Surface

The oxidation chemistry of the simplest conjugated hydrocarbon, 1,3-butadiene, can provide a first step in understanding the role of poly-unsaturated hydrocarbons in combustion and, in particular, an understanding of their contribution towards soot formation. Based on our previous work on propene and the butene isomers (1-, 2- and isobutene), it was found that the reaction kinetics of H-atom addition to the C=C double bond plays a significant role in fuel consumption kinetics and influences the predictions of high-temperature ignition delay times, product species concentrations and flame speed measurements. In this study, the rate constants and thermodynamic properties for $\dot{H}$-atom addition to 1,3-butadiene and related reactions on the $\dot{C}$ 4 H 7 potential energy surface have been calculated using two different series of quantum chemical methods and two different kinetic codes. Excellent agreement is obtained between the two different kinetics codes. The calculated results including zero point energies, single point energies, rate constants, barrier heights and thermochemistry are systematically compared among the two quantum chemical methods. 1-methylallyl ($\dot{C}$ 4 H 7 1-3) and 3-buten-1- yl ($\dot{C}$ 4 H 7 1-4) radicals and C 2 H 4 + $\dot{C}$2H3 are found to be the most important channels and reactivity promoting products, respectively. We calculated that terminal addition is dominant (> 80%) compared to internal $\dot{H}$-atom addition at all temperatures in the range 298 – 2000 K. However, this dominance decreases with increasing temperature. The calculated rate constants for the bimolecular reaction C 4 H 6 + $\dot{H}$ → products and C 2 H 4 + $\dot{C}$ 2 H 3 → products are in excellent agreement with both experimental and theoretical results from the literature. For selected C 4 species the calculated thermochemical values are also in good agreement with literature data. In addition, the rate constants for H-atom abstraction by $\dot{H}$ atoms have also been calculated, and it is found that abstraction from the central carbon atoms is the dominant channel (> 70%) at temperatures in the range 298 – 2000 K. Lastly, by incorporating our calculated rate constants for both H-atom addition and abstraction into our recently developed 1,3-butadiene model, we show that laminar flame speed predictions are significantly improved, emphasizing the value of this study.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Ni-Doping Effects on Oxygen Removal from an Orthorhombic Mo 2 C (001) Surface: A Density Functional Theory Study

Density functional theory (DFT) calculations were used in this paper to investigate the effect of Ni dopants on the removal of chemisorbed oxygen (O*) from the Mo-terminated (T Mo ) and C-terminated (T C ) Mo 2 C(001) surfaces. The removal of adsorbed oxygen from the catalytic site is essential to maintain the long-term activity and selectivity of the carbide catalysts in the deoxygenation process related to bio-oil stabilization and upgrading. In this contribution, the computed reaction energetics and reaction barriers of O* removal were compared among undoped and Ni-doped Mo 2 C(001) surfaces. The DFT calculations indicate that selected Ni-doped surfaces such as Ni adsorbed on T Mo and T C Mo 2 C(001) surfaces enable weaker binding of important reactive intermediates (O*, OH*) compared to the undoped counterparts, which is beneficial for the O* removal from the catalyst surface. This study thus confirms the promoting effect of the Ni dopant on O* removal reaction on the T Mo Mo 2 C(001) and T C Mo 2 C(001) surfaces. Finally, this computational prediction has been confirmed by the temperature-programmed reduction profiles of Mo 2 C and Ni-doped Mo 2 C catalysts, which had been passivated and stored in an oxygen environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Ethanol Conversion to C 4+ Olefins over Bimetallic Copper- And Lanthanum-Containing Beta Zeolite Catalysts

We report ethanol conversion to C 4+ olefins remains a critical yet nonselective process for producing renewable middle distillates. Here, Cu–La/Beta catalysts composed of copper and lanthanum incorporated onto a dealuminated Beta support are reported for ethanol conversion to C 4+ olefins (73% selectivity, ~98% ethanol conversion, 623 K,<4% C 1 –C 3 hydrocarbons) which particularly favors C 5+ olefin formation (43% selectivity) as a distinction from the benchmarking Cu–Y/Beta catalyst. Monometallic Cu/Beta or La/Beta samples are insufficient to catalyze the C 4+ olefin formation and primarily form dehydration products (e.g., ethylene and diethyl ether), indicating the necessity of both Cu and La species for butene and C 5+ olefin formation. Increasing the bulk La loading at a fixed Cu content yields higher C 5+ olefins until the La/Cu molar ratio reaches 3.6. These findings indicate Cu–La/Beta as an effective ethanol conversion catalyst that facilitates multiple C–C bond formation events required for synthesizing C 5+ olefins (i.e., hexenes and octenes).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Controlled monodefluorination and alkylation of C(sp 3 )–F bonds by lanthanide photocatalysts: importance of metal–ligand cooperativity

The controlled functionalization of a single fluorine in a CF 3 group is difficult and rare. Photochemical C–F bond functionalization of the sp 3 -C–H bond in trifluorotoluene, PhCF 3 , is achieved using catalysts made from earth-abundant lanthanides, (Cp Me4 ) 2 Ln(2-O-3,5- t Bu 2 -C 6 H 2 )(1-C{N(CH) 2 N( i Pr)}) (Ln = La, Ce, Nd and Sm, Cp Me4 = C 5 Me 4 H). The Ce complex is the most effective at mediating hydrodefluorination and defluoroalkylative coupling of PhCF 3 with alkenes; addition of magnesium dialkyls enables catalytic C–F bond cleavage and C–C bond formation by all the complexes. Mechanistic experiments confirm the essential role of the Lewis acidic metal and support an inner-sphere mechanism of C–F activation. Computational studies agree that coordination of the C–F substrate is essential for C–F bond cleavage. The unexpected catalytic activity for all members is made possible by the light-absorbing ability of the redox non-innocent ligands. The results described herein underscore the importance of metal–ligand cooperativity, specifically the synergy between the metal and ligand in both light absorption and redox reactivity, in organometallic photocatalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Structure, stability, and electronic property of carbon-doped gold clusters Au{sub n}C{sup −} (n = 1–10): A density functional theory study

The equilibrium geometric structures, relative stabilities, and electronic properties of Au{sub n}C{sup −} and Au{sub n+1}{sup −} (n = 1–10) clusters are systematically investigated using density functional theory with hyper-generalized gradient approximation. The optimized geometries show that one Au atom capped on Au{sub n−1}C{sup −} clusters is a dominant growth pattern for Au{sub n}C{sup −} clusters. In contrast to Au{sub n+1}{sup −} clusters, Au{sub n}C{sup −} clusters are most stable in a quasi-planar or three-dimensional structure because C doping induces the local non-planarity while the rest of the structure continues to grow in a planar mode, resulting in an overall non-2D configuration. The relative stability calculations show that the impurity C atom can significantly enhance the thermodynamic stability of pure gold clusters. Moreover, the effect of C atom on the Au{sub n}{sup −} host decreases with the increase of cluster size. The HOMO-LUMO gap curves show that the interaction of the C atom with Au{sub n}{sup −} clusters improves the chemical stability of pure gold clusters, except for Au{sub 3}{sup −} and Au{sub 4}{sup −} clusters. In addition, a natural population analysis shows that the charges in corresponding Au{sub n}C{sup −} clusters transfer from the Au{sub n}{sup −} host to the C atom. Meanwhile, a natural electronic configuration analysis also shows that the charges mainly transfer between the 2s and 2p orbitals within the C atom.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

The thioreduction component CcmG confers efficiency and the heme ligation component CcmH ensures stereo-specificity during cytochrome c maturation

In many Gram-negative bacteria, including Rhodobacter capsulatus, cytochrome c maturation (Ccm) is carried out by a membrane-integral machinery composed of nine proteins (CcmA to I). During this process, the periplasmic thiol-disulfide oxidoreductase DsbA is thought to catalyze the formation of a disulfide bond between the Cys residues at the apocytochrome c heme binding site (CXXCH). Subsequently, a Ccm-specific thioreductive pathway involving CcmG and CcmH reduces this disulfide bond to allow covalent heme ligation. Currently, the sequence of thioredox reactions occurring between these components and apocytochrome c, and the identity of their active Cys residues are unknown. In this work, we first investigated protein-protein interactions among the apocytochrome c, CcmG, and the heme ligation components CcmF, CcmH, and CcmI. We found that they all interact with each other, forming a CcmFGHI-apocytochrome c complex. Using purified wild-type CcmG, CcmH, and apocytochrome c, as well as their respective Cys mutant variants we determined the rates of thiol-disulfide exchange reactions between selected pairs of Cys residues from these proteins. We established that CcmG can efficiently reduce the disulfide bond of apocytochrome c and also resolve a mixed disulfide bond formed between apocytochrome c and CcmH. We further show that C45 of CcmH and C34 of apocytochrome c are most likely to form this mixed disulfide bond, which is consistent with the stereo-specificity of the heme-apocytochrome c ligation reaction. We conclude that CcmG confers efficiency, and CcmH ensures stereo-specificity during Ccm, and present a comprehensive model for thioreduction reactions that lead to heme-apocytochrome c ligation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

C{sub 60} in photodissociation regions

Recent studies have confirmed the presence of buckminsterfullerene (C{sub 60}) in different interstellar and circumstellar environments. However, several aspects regarding C{sub 60} in space are not yet well understood, such as the formation and excitation processes, and the connection between C{sub 60} and other carbonaceous compounds in the interstellar medium, in particular polycyclic aromatic hydrocarbons (PAHs). In this paper, we study several photodissociation regions (PDRs) where C{sub 60} and PAHs are detected and the local physical conditions are reasonably well constrained to provide observational insights into these questions. C{sub 60} is found to emit in PDRs where the dust is cool (T{sub d} = 20-40 K) and even in PDRs with cool stars. These results exclude the possibility for C{sub 60} to be locked in grains at thermal equilibrium in these environments. We observe that PAH and C{sub 60} emission are spatially uncorrelated and that C{sub 60} is present in PDRs where the physical conditions (in terms of radiation field and hydrogen density) allow for full dehydrogenation of PAHs, with the exception of Ced 201. We also find trends indicative of an increase in C{sub 60} abundance within individual PDRs, but these trends are not universal. These results support models where the dehydrogenation of carbonaceous species is the first step toward C{sub 60} formation. However, this is not the only parameter involved and C{sub 60} formation is likely affected by shocks and PDR age.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

THE SURVEY OF LINES IN M31 (SLIM): INVESTIGATING THE ORIGINS OF [C II] EMISSION

The [C II] 158 μm line is one of the strongest emission lines observed in star-forming galaxies and has been empirically measured to correlate with the star-formation rate (SFR) globally and on kiloparsec scales. However, because of the multiphase origins of [C II], one might expect this relation to break down at small scales. We investigate the origins of [C II] emission by examining high spatial resolution observations of [C II] in M31 with the Survey of Lines in M31. We present five ∼700 × 700 pc (3' × 3') fields mapping the [C II] emission, Hα emission, and the ancillary infrared (IR) data. We spatially separate star-forming regions from diffuse gas and dust emission on ∼50 pc scales. We find that the [C II]-SFR correlation holds even at these scales, although the relation typically has a flatter slope than found at larger (kiloparsec) scales. While the Hα emission in M31 is concentrated in the SFR regions, we find that a significant amount (∼20%-90%) of the [C II] emission comes from outside star-forming regions and that the total IR emission (TIR) has the highest diffuse fraction of all SFR tracers. We find a weak correlation of the [C II]/TIR to dust color in each field and find a large-scale trend of increasing [C II]/TIR with galactocentric radius. The differences in the relative diffuse fractions of [C II], Hα, and IR tracers are likely caused by a combination of energetic photon leakage from H II regions and heating by the diffuse radiation field arising from older (B-star) stellar populations. However, we find that by averaging our measurements over kiloparsec scales, these effects are minimized, and the relation between [C II] and SFR found in other nearby galaxy studies is retrieved.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

On the [C ii]–SFR relation in high redshift galaxies

After two Atacama Large Millimeter/submillimeter Array (ALMA) observing cycles, only a handful of [C ii] 158 μm emission line searches in z > 6 galaxies have reported a positive detection, questioning the applicability of the local [C ii]–star formation rate (SFR) relation to high-z systems. To investigate this issue we use the Vallini et al. (V13) model,based on high-resolution, radiative transfer cosmological simulations to predict the [C ii] emission from the interstellar medium of a z ≈ 7 (halo mass M{sub h} = 1.17 × 10{sup 11} M{sub ⊙}) galaxy. We improve the V13 model by including (a) a physically motivated metallicity (Z) distribution of the gas, (b) the contribution of photodissociation regions (PDRs), and (c) the effects of cosmic microwave background (CMB) on the [C ii] line luminosity. We study the relative contribution of diffuse neutral gas to the total [C ii] emission (F{sub diff}/F{sub tot}) for different SFR and Z values. We find that the [C ii] emission arises predominantly from PDRs: regardless of the galaxy properties, F{sub diff}/F{sub tot} ≤ 10%, since at these early epochs the CMB temperature approaches the spin temperature of the [C ii] transition in the cold neutral medium (T{sub CMB} ∼ T{sub s}{sup CNM} ∼ 20 K). Our model predicts a high-z [C ii]–SFR relation, consistent with observations of local dwarf galaxies (0.02 < Z/Z{sub ⊙} < 0.5). The [C ii] deficit suggested by actual data (L{sub Cii} < 2.0 × 10{sup 7} L{sub ⊙} in BDF3299 at z ≈ 7.1) if confirmed by deeper ALMA observations, can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites. The deviation from the local [C ii]–SFR would then imply a modified Kennicutt–Schmidt relation in z > 6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities (Z < 0.1 Z{sub ⊙}).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Possibility of 14 C cluster as a building block of medium-mass nuclei

The possibility of the 14 C cluster being a basic building block of medium-mass nuclei is discussed. Although α cluster structures have been widely discussed in the light N ≈ Z mass region, the neutron-to-proton ratio deviates from unity in the nuclei near β-stability line and in neutron-rich nuclei. Thus, more neutron-rich objects with N > Z could become the building blocks of cluster structures in such nuclei. The 14 C nucleus is strongly bound and can be regarded as such a candidate. In addition, the path to the lowest shell-model configuration at short relative distances is closed for the 14 C+ 14 C structure, contrary to the case of the 12 C+ 12 C structure; this allows an appreciable separation distance between the 14 C clusters. The recent development of the antisymmetrized quasicluster model (AQCM) allows us to utilize a j j-coupling shell-model wave function for each cluster in a simplified way. The AQCM results for the 14 C+ 14 C structure in 28 Mg are compared with the ones of cranked relativistic mean field (CRMF) calculations. Although theoretical frameworks of these two models are quite different, they give similar results for the nucleonic densities and rotational properties of the structure under investigation. The existence of a linear chain three- 14 C cluster structure in 42 Ar has also been predicted in AQCM. Furthermore, these results confirm the role of the 14 C cluster as a possible building block of cluster structures in medium-mass nuclei.

20 ≤ A ≤ 38↗