One of the most intriguing features of some high-temperature cuprate superconductors is the interplay between one-dimensional "striped" spin order and charge order, and superconductivity. We used ...mid-infrared femtosecond pulses to transform one such stripe-ordered compound, nonsuperconducting La₁.₆₇₅Eu₀.₂Sr₀.₁₂₅CuO₄, into a transient three-dimensional superconductor. The emergence of coherent interlayer transport was evidenced by the prompt appearance of a Josephson plasma resonance in the c-axis optical properties. An upper limit for the time scale needed to form the superconducting phase is estimated to be 1 to 2 picoseconds, which is significantly faster than expected. This places stringent new constraints on our understanding of stripe order and its relation to superconductivity.
Two major droughts in the past decade had large impacts on carbon exchange in the Amazon. Recent analysis of vertical profile measurements of atmospheric CO2 and CO by Gatti et al. (2014) suggests ...that the 2010 drought turned the normally close‐to‐neutral annual Amazon carbon balance into a substantial source of nearly 0.5 PgC/yr, revealing a strong drought response. In this study, we revisit this hypothesis and interpret not only the same CO2/CO vertical profile measurements but also additional constraints on carbon exchange such as satellite observations of CO, burned area, and fire hot spots. The results from our CarbonTracker South America data assimilation system suggest that carbon uptake by vegetation was indeed reduced in 2010 but that the magnitude of the decrease strongly depends on the estimated 2010 and 2011 biomass burning emissions. We have used fire products based on burned area (Global Fire Emissions Database version 4), satellite‐observed CO columns (Infrared Atmospheric Sounding Interferometer), fire radiative power (Global Fire Assimilation System version 1), and fire hot spots (Fire Inventory from NCAR version 1), and found an increase in biomass burning emissions in 2010 compared to 2011 of 0.16 to 0.24 PgC/yr. We derived a decrease of biospheric uptake ranging from 0.08 to 0.26 PgC/yr, with the range determined from a set of alternative inversions using different biomass burning estimates. Our numerical analysis of the 2010 Amazon drought results in a total reduction of carbon uptake of 0.24 to 0.50 PgC/yr and turns the balance from carbon sink to source. Our findings support the suggestion that the hydrological cycle will be an important driver of future changes in Amazonian carbon exchange.
Key Points
Amazon carbon budget estimated by CarbonTracker South America
Biospheric uptake decreases by 0.08–0.26 PgC/yr in response to 2010 drought
Amazon biomass burning emissions more than doubled during 2010 drought
The hypothesis of an exogenous origin and delivery of biologically important molecules to early Earth presents an alternative route to their terrestrial in situ formation. Dipeptides like Gly-Gly ...detected in the Murchison meteorite are considered as key molecules in prebiotic chemistry because biofunctional dipeptides present the vital link in the evolutionary transition from prebiotic amino acids to early proteins. However, the processes that could lead to the exogenous abiotic synthesis of dipeptides are unknown. Here, we report the identification of two proteinogenic dipeptides-Gly-Gly and Leu-Ala-formed via electron-irradiation of interstellar model ices followed by annealing the irradiated samples to 300 K. Our results indicate that the radiation-induced, non-enzymatic formation of proteinogenic dipeptides in interstellar ice analogs is facile. Once synthesized and incorporated into the "building material" of solar systems, biomolecules at least as complex as dipeptides could have been delivered to habitable planets such as early Earth by meteorites and comets, thus seeding the beginning of life as we know it.
Computational fluid dynamics (CFD) simulations and isothermal approximation were applied for the interpretation of experimental measurements of the C10H7Br pyrolysis efficiency in the ...high-temperature microreactor and of the pressure drop in the flow tube of the reactor. Applying isothermal approximation allows the derivation of analytical relationships between the kinetic, gas flow, and geometrical parameters of the microreactor, which, along with CFD simulations, accurately predict the experimental observations. On the basis of the obtained analytical relationships, a clear strategy for measuring rate coefficients of (pseudo) first-order bimolecular and unimolecular reactions using the microreactor was proposed. The pressure- and temperature-dependent rate coefficients for the C10H7Br pyrolysis calculated using variable reaction coordinate transition state theory were invoked to interpret the experimental data on the pyrolysis efficiency.
The present laboratory study simulated cosmic-ray-induced grain chemistry of nitrogen-bearing organic molecules in interstellar and cometary ices. Model ices of ammonia (NH3)-methane (CH4) were ...prepared and irradiated at 10 K under contamination-free, ultrahigh vacuum conditions with energetic electrons generated in the track of galactic cosmic-ray particles. The radiolysis-induced processing of nitrogen-bearing molecules was then monitored on line and in situ by a Fourier transform infrared spectrometer and a quadrupole mass spectrometer during the irradiation phase and subsequent warm-up phases. The analogous processing was also achieved in ammonia (NH3) and six hydrocarbon (C n H2n+2; n = 1-6) ices. The formation of cyanide anion (CN--) was commonly observed in both ices at 10 K, the temporal column density fit of which traced back the involvement of methylamine (CH3NH2)-based intermediates. Traces of CH3NH2 were evident at about 110 K through thin ammonia matrices in sublimation. From the point of radiative transfer, we further constrain the formation mechanism of aminoacetonitrile (NH2CH2CN) on icy grains of Sgr B2(N) under a cosmic-ray-induced photon field.
The crossed beam reactions of the phenyl radical (C6H5, X2A1) with 1,3-butadiene (C4H6, X1Ag) and D6-1,3-butadiene (C4D6, X1Ag) as well as of the D5-phenyl radical (C6D5, X2A1) with ...2,3-D2-1,3-butadiene and 1,1,4,4-D4-1,3-butadiene were carried out under single collision conditions at collision energies of about 55 kJ mol–1. Experimentally, the bicyclic 1,4-dihydronaphthalene molecule was identified as a major product of this reaction (58 ± 15%) with the 1-phenyl–1,3-butadiene contributing 34 ± 10%. The reaction is initiated by a barrierless addition of the phenyl radical to the terminal carbon atom of the 1,3-butadiene (C1/C4) to form a bound intermediate; the latter underwent hydrogen elimination from the terminal CH2 group of the 1,3-butadiene molecule leading to 1-phenyl-trans-1,3-butadiene through a submerged barrier. The dominant product, 1,4-dihydronaphthalene, is formed via an isomerization of the adduct by ring closure and emission of the hydrogen atom from the phenyl moiety at the bridging carbon atom through a tight exit transition state located about 31 kJ mol–1 above the separated products. The hydrogen atom was found to leave the decomposing complex almost parallel to the total angular momentum vector and perpendicularly to the rotation plane of the decomposing intermediate. The defacto barrierless formation of the 1,4-dihydronaphthalene molecule involving a single collision between a phenyl radical and 1,3-butadiene represents an important step in the formation of polycyclic aromatic hydrocarbons (PAHs) and their partially hydrogenated counterparts in combustion and interstellar chemistry.
Optical pulses at THz and mid-infrared frequencies tuned to specific vibrational resonances modulate the lattice along chosen normal mode coordinates. In this way, solids can be switched between ...competing electronic phases and new states are created. Here, we use vibrational modulation to make electronic interactions (Hubbard-U) in Mott-insulator time dependent. Mid-infrared optical pulses excite localized molecular vibrations in ET-F2TCNQ, a prototypical one-dimensional Mott-insulator. A broadband ultrafast probe interrogates the resulting optical spectrum between THz and visible frequencies. A red-shifted charge-transfer resonance is observed, consistent with a time-averaged reduction of the electronic correlation strength U. Secondly, a sideband manifold inside of the Mott-gap appears, resulting from a periodically modulated U. The response is compared to computations based on a quantum-modulated dynamic Hubbard model. Heuristic fitting suggests asymmetric holon-doublon coupling to the molecules and that electron double-occupancies strongly squeeze the vibrational mode.
The classification of chemical reactions based on shared characteristics is at the heart of the chemical sciences, and is well exemplified by Langmuir's concept of
isovalency
, in which 'two ...molecular entities with the same number of valence electrons have similar chemistries'. Within this account we further investigate the ramifications of the
isovalency
of four radicals with the same X
2
Σ
+
electronic structure - cyano (CN), boron monoxide (BO), silicon nitride (SiN), and ethynyl (C
2
H), and their reactions with simple prototype hydrocarbons acetylene (C
2
H
2
) and ethylene (C
2
H
4
). The fact that these four reactants own the same X
2
Σ
+
electronic ground state should dictate the outcome of their reactions with prototypical hydrocarbons holding a carbon-carbon triple and double bond. However, we find that other factors come into play, namely, atomic radii, bonding orbital overlaps, and preferential location of the radical site. These doublet radical reactions with simple hydrocarbons play significant roles in extreme environments such as the interstellar medium and planetary atmospheres (CN, SiN and C
2
H), and combustion flames (C
2
H, BO).
The classification of chemical reactions based on shared characteristics is at the heart of the chemical sciences, and is well exemplified by Langmuir's concept of
isovalency
, in which 'two molecular entities with the same number of valence electrons have similar chemistries'.
Carbon monoxide is the second most abundant molecule on icy grains in the interstellar medium. It also exists on Pluto, Triton, comets, and possibly in other icy bodies of the outer solar system like ...Kuiper Belt objects. With the intense radiation fields that permeate virtually all unprotected regions of space, carbon monoxide ices can be processed through energetic particle bombardment (planetary magnetospheric particles, solar wind, Galactic cosmic ray particles, and UV photons). In the present study we have investigated the effects by condensing a 1 km layer of carbon monoxide ice on a substrate at 10 K and irradiated the sample with energetic (keV) electrons. These simulate the energetic electrons trapped in magnetospheres of planets and reproduce the irradiation effects of typical Galactic cosmic ray particles. A series of new carbon-chain ( sub(C)3, C sub(6)) and carbon oxide species were observed including the linear isomers of C sub(2)O, C sub(3)O, C sub(4)O, C sub(5)O, C sub(6/7)O, CO sub(2), C sub(3)O sub(2), C sub(4)O sub(2), and C sub(5)O sub(2). A reaction model was proposed that outlines different reaction pathways to each of these products. Using this model, the kinetics of each route of reaction was quantified, and from this, the mechanisms and dynamics of the reactions can be understood. This work should aid in the astronomical detection of new molecular species in solar system ices as well as building up a comprehensive reaction model to describe the chemical inventory of ices on interstellar dust grains.
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