bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dehydration in the tropical tropopause layer: A case study for model evaluation using aircraft observations
Authors: Ueyama Rei , Jensen Eric J. , Pfister Leonhard , Diskin Glenn S. , Bui T. P. , Dean‐Day Jonathan M. 
Published: April 2014

AbstractThe dynamical and microphysical processes that influence water vapor concentrations in the tropical tropopause layer (TTL) are investigated in simulations of ice clouds along backward trajectories of air parcels sampled during three flights of the Airborne Tropical Tropopause Experiment over the central to eastern tropical Pacific in boreal fall 2011. ERA‐Interim reanalysis temperatures interpolated onto the flight tracks have a negligible (−0.09 K) cold bias compared to aircraft measurements of tropical cold point temperature thus permitting case study simulations of TTL dehydration. When the effects of subgrid‐scale waves, cloud microphysical processes, and convection are considered, the simulated water vapor mixing ratios on the final day of 40 day backward trajectories exhibit a mean profile that is within 20–30% of the mean of the aircraft measurements collected during vertical profiling maneuvers between the 350 and 410 K potential temperature levels. Averaged over the three flights, temperature variability driven by subgrid‐scale waves dehydrated the 360–390 K layer by approximately −0.5 ppmv, whereas including homogeneous freezing of aqueous aerosols and subsequent sublimation and rehydration of ice crystals increased water vapor below the 380 K level by about +1 ppmv. The predominant impact of convection was to moisten the TTL, resulting in an average enhancement below the 370 K level by +1 to 5 ppmv. Accurate (to within 0.5–1 ppmv) predictions of TTL water vapor using trajectory models require proper representations of waves, in situ ice cloud formation, and convective influence, which together determine the saturation history of air parcels.
Long‐term changes in lower tropospheric baseline ozone concentrations: Comparing chemistry‐climate models and observations at northern midlatitudes
Authors: Parrish D. D. , Lamarque J.‐F. , Naik V. , Horowitz L. , Shindell D. T. , Staehelin J. , Derwent R. , Cooper O. R. , Tanimoto H. , Volz‐Thomas A. , Gilge S. , Scheel H.‐E. , Steinbacher M. , Fröhlich M. 
Published: April 2014

AbstractTwo recent papers have quantified long‐term ozone (O3) changes observed at northern midlatitude sites that are believed to represent baseline (here understood as representative of continental to hemispheric scales) conditions. Three chemistry‐climate models (NCAR CAM‐chem, GFDL‐CM3, and GISS‐E2‐R) have calculated retrospective tropospheric O3 concentrations as part of the Atmospheric Chemistry and Climate Model Intercomparison Project and Coupled Model Intercomparison Project Phase 5 model intercomparisons. We present an approach for quantitative comparisons of model results with measurements for seasonally averaged O3 concentrations. There is considerable qualitative agreement between the measurements and the models, but there are also substantial and consistent quantitative disagreements. Most notably, models (1) overestimate absolute O3 mixing ratios, on average by ~5 to 17 ppbv in the year 2000, (2) capture only ~50% of O3 changes observed over the past five to six decades, and little of observed seasonal differences, and (3) capture ~25 to 45% of the rate of change of the long‐term changes. These disagreements are significant enough to indicate that only limited confidence can be placed on estimates of present‐day radiative forcing of tropospheric O3 derived from modeled historic concentration changes and on predicted future O3 concentrations. Evidently our understanding of tropospheric O3, or the incorporation of chemistry and transport processes into current chemical climate models, is incomplete. Modeled O3 trends approximately parallel estimated trends in anthropogenic emissions of NOx, an important O3 precursor, while measured O3 changes increase more rapidly than these emission estimates.
Polar summer mesospheric extreme horizontal drift speeds during interplanetary corotating interaction regions (CIRs) and high‐speed solar wind streams: Coupling between the solar wind and the mesosphere
Authors: Lee Young‐Sook , Kirkwood Sheila , Kwak Young‐Sil , Kim Kyung‐Chan , Shepherd Gordon G. 
Published: April 2014

AbstractWe report the observation of echo extreme horizontal drift speed (EEHS, ≥ 300 m s−1) during polar mesospheric (80–90 km) summer echoes (PMSEs) by the VHF (52 MHz) radar at Esrange, Sweden, in years of 2006 and 2008. The EEHS occur in PMSEs as correlated with high‐speed solar wind streams (HSSs), observed at least once in 12–17% of all hours of observation for the two summers. The EEHS rate peaks occur either during high solar wind speed in the early part of the PMSE season or during the arrival of interplanetary corotating interaction regions (CIRs) followed by peaks in PMSE occurrence rate after 1–4 days, in the latter part of the 2006 summer. The cause of EEHS rate peaks is likely under the competition between the interval of the CIR and HSS passage over the magnetosphere. A candidate process in producing EEHS is suggested to be localized strong electric field, which is caused by solar wind energy transfer from the interaction of CIR and HSS with the magnetosphere in a sequential manner. We suggest that EEHS are created by strong electric field, estimated as > 10–30 V m−1 at 85 km altitude, exceeding the mesospheric breakdown threshold field.
Lunar dayside current in the terrestrial lobe: ARTEMIS observations
Authors: Zhou X.‐Z. , Angelopoulos V. , Poppe A. R. , Halekas J. S. , Khurana K. K. , Kivelson M. G. , Fatemi S. , Holmström M. 
Published: April 2014

AbstractWe report Acceleration, Reconnection, Turbulence and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) dual‐probe observations of two events in the terrestrial magnetotail lobe, both characterized by upward moving heavy ions of lunar origin at one of the probes that is magnetically connected with the dayside lunar surface. By treating magnetic measurements at the other probe as the unperturbed lobe fields, we obtain background‐subtracted magnetic perturbations (most significantly in Bz) when the first probe moved in the dawn‐dusk direction across flux tubes magnetically connected to the Moon. These magnetic perturbations indicate the presence of field‐aligned current above the lunar surface. By examining possible carriers of field‐aligned current, we find that lunar heavy ions and accompanying electrons both contribute considerably to the current. Observations of the field‐aligned current also suggest that the charging process at the dayside lunar surface and the associated lobe plasma environment, which have traditionally been viewed as a one‐dimensional current balance problem, are actually more complicated. These observations give the first insights into how heavy ions affect the lunar dayside environment in terms of multispecies plasma dynamics.
Ionosphere variability during the 2009 SSW: Influence of the lunar semidiurnal tide and mechanisms producing electron density variability
Authors: Pedatella N. M. , Liu H.‐L. , Sassi F. , Lei J. , Chau J. L. , Zhang X. 
Published: April 2014

AbstractTo investigate ionosphere variability during the 2009 sudden stratosphere warming (SSW), we present simulation results that combine the Whole Atmosphere Community Climate Model Extended version and the thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM). The simulations reveal notable enhancements in both the migrating semidiurnal solar (SW2) and lunar (M2) tides during the SSW. The SW2 and M2 amplitudes reach ∼50 m s−1 and ∼40 m s−1, respectively, in zonal wind at E region altitudes. The dramatic increase in the M2 at these altitudes influences the dynamo generation of electric fields, and the importance of the M2 on the ionosphere variability during the 2009 SSW is demonstrated by comparing simulations with and without the M2. TIME‐GCM simulations that incorporate the M2 are found to be in good agreement with Jicamarca Incoherent Scatter Radar vertical plasma drifts and Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) observations of the maximum F region electron density. The agreement with observations is worse if the M2 is not included in the simulation, demonstrating that the lunar tide is an important contributor to the ionosphere variability during the 2009 SSW. We additionally investigate sources of the F region electron density variability during the SSW. The primary driver of the electron density variability is changes in electric fields. Changes in meridional neutral winds and thermosphere composition are found to also contribute to the electron density variability during the 2009 SSW. The electron density variability for the 2009 SSW is therefore not solely due to variability in electric fields as previously thought.
The origin of Jupiter's outer radiation belt
Authors: Woodfield E. E. , Horne R. B. , Glauert S. A. , Menietti J. D. , Shprits Y. Y. 
Published: April 2014

AbstractThe intense inner radiation belt at Jupiter (>50 MeV at 1.5 RJ) is generally accepted to be created by radial diffusion of electrons from further away from the planet. However, this requires a source with energies that exceed 1 MeV outside the orbit of the moon Io at 5.9 RJ, which has never been explained satisfactorily. Here we test the hypothesis that this source population could be formed from a very soft energy spectrum, by particle injection processes and resonant electron acceleration via whistler mode chorus waves. We use the British Antarctic Survey Radiation Belt Model to calculate the change in the electron flux between 6.5 and 15 RJ; these are the first simulations at Jupiter combining wave particle interactions and radial diffusion. The resulting electron flux at 100 keV and 1 MeV lies very close to the Galileo Interim Radiation Electron model spectrum after 1 and 10 days, respectively. The primary driver for the increase in the flux is cyclotron resonant acceleration by chorus waves. A peak in phase space density forms such that inside L≈9 radial diffusion transports electrons toward Jupiter, but outside L≈9 radial diffusion acts away from the planet. The results are insensitive to the softness of the initial energy spectrum but do depend on the value of the flux at the minimum energy boundary. We conclude by suggesting that the source population for the inner radiation belt at Jupiter could indeed be formed by wave‐particle interactions.
Increasing the credibility of regional climate simulations by introducing subgrid‐scale cloud‐radiation interactions
Authors: Herwehe Jerold A. , Alapaty Kiran , Spero Tanya L. , Nolte Christopher G. 
Published: April 2014

AbstractThe radiation schemes in the Weather Research and Forecasting (WRF) model have previously not accounted for the presence of subgrid‐scale cumulus clouds, thereby resulting in unattenuated shortwave radiation, which can lead to overly energetic convection and overpredicted surface precipitation. This deficiency can become problematic when applying WRF as a regional climate model (RCM). Therefore, modifications were made to the WRF model to allow the Kain–Fritsch (KF) convective parameterization to provide subgrid‐scale cloud fraction and condensate feedback to the rapid radiative transfer model–global (RRTMG) shortwave and longwave radiation schemes. The effects of these changes are analyzed via 3 year simulations using the standard and modified versions of WRF, comparing the modeled results with the North American Regional Reanalysis (NARR) and Climate Forecast System Reanalysis data, as well as with available data from the Surface Radiation Network and Clouds and Earth's Radiant Energy System. During the summer period, including subgrid cloudiness estimated by KF in the RRTMG reduces the surface shortwave radiation, leading to less buoyant energy, which is reflected in a smaller diabatic convective available potential energy, thereby alleviating the overly energetic convection. Overall, these changes have reduced the overprediction of monthly, regionally averaged precipitation during summer for this RCM application, e.g., by as much as 49 mm for the southeastern U.S., to within 0.7% of the NARR value of 221 mm. These code modifications have been incorporated as an option available in the latest version of WRF (v3.6).
Zentren der Methanaktivierung auf Oberflächen von Lithium‐dotiertem MgO
Authors: Kwapien Karolina , Paier Joachim , Sauer Joachim , Geske Michael , Zavyalova Ulyana , Horn Raimund , Schwach Pierre , Trunschke Annette , Schlögl Robert 
Published: April 2014

AbstractDie mittels Dichtefunktionaltheorie berechneten Energiebarrieren für die H‐Abstraktion durch Sauerstoffradikale in Li‐dotiertem MgO sind viel kleiner (12±6 kJ mol−1) als die Barrieren, die man bei unterschiedlichen Methanaktivierungsexperimenten findet (80–160 kJ mol−1). Das nährt weitere Zweifel an Lunsfords Hypothese, dass Li+O.−‐Paare die aktiven Zentren sind. Temperaturprogrammierte oxidative Kupplungsreaktionen von Methan (OCM) zeigen, dass bei reinem und Li‐dotiertem MgO die gleichen Zentren für die Reaktion verantwortlich sind. MgO‐Katalysatoren, die durch Sol‐Gel‐Synthese hergestellt wurden, zeigen große Unterschiede zwischen anfänglicher Aktivität und der Aktivität im stationären Zustand. Transmissionselektronenmikroskopie zeigt, dass damit substanzielle morphologische Veränderungen und Restrukturierungen der Oberfläche einhergehen. Berechnungen an (MgO)9‐Clustermodellen ergeben, dass CH4 heterolytisch an Mg2+O2−‐Paaren chemisorbiert wird, die sich an Stufen oder Ecken befinden. Die homolytische Freisetzung von Methylradikalen erfordert jedoch die Anwesenheit von O2 auf der Oberfläche.
Inverse Peptide Synthesis via Activated α‐Aminoesters
Authors: Suppo Jean‐Simon , Subra Gilles , Bergès Matthieu , Marcia de Figueiredo Renata , Campagne Jean‐Marc 
Published: April 2014

AbstractA mild, practical, and simple procedure for peptide‐bond formation is reported. Instead of activation of the carboxylic acid functionality, the reaction involves an unprecedented use of activated α‐aminoesters. The method provides a straightforward entry to dipeptides and was effective when a sensitive cysteine residue was used, as no epimerization was detected in this case. The applicability of this method to iterative peptide synthesis was illustrated by the synthesis of a model tetrapeptide in the challenging reverse N→C direction.
An Enantiospecific Synthesis of Jiadifenolide
Authors: Siler David A. , Mighion Jeffrey D. , Sorensen Erik J. 
Published: April 2014

AbstractA Robinson annulation, van Leusen homologation, and a desymmetrizing CH oxidation enabled an enantiospecific synthesis of the neurotrophic natural product jiadifenolide. From a pulegone‐derived building block, a key propellane intermediate was constructed through the use of simple reagents in a highly diastereoselective fashion. A short series of oxidations of this tricylic framework allowed progression to the natural product.
Organokatalytische atropselektive Aldolkondensation: Synthese axial‐chiraler Biaryle durch Arenbildung
Authors: Link Achim , Sparr Christof 
Published: April 2014

AbstractAxial‐chirale Verbindungen sind in der modernen Synthesechemie von zentraler Bedeutung und für die Arzneimittelentwicklung unentbehrlich. Der Zugang zu Atropisomeren in reiner Form erweist sich jedoch oft als sehr aufwendig. Hier zeigen wir eine atropselektive Synthesemethode, welche die stereochemische Information eines sekundären Amin‐Organokatalysators effizient in die axiale Chiralität von tri‐ortho‐substituierten Biarylen überträgt. Die beschriebene Aldolkondensationskaskade führt während der Dehydratisierung zur Arenbildung und somit zu hoch enantiomerenangereicherten Binaphthylderivaten. Der grundlegende Reaktionsablauf ist mit der aromatischen Polyketid‐Biosynthese verwandt.
anti‐Markovnikov Hydroamination of Alkenes Catalyzed by a Two‐Component Organic Photoredox System: Direct Access to Phenethylamine Derivatives
Authors: Nguyen Tien M. , Manohar Namita , Nicewicz David A. 
Published: April 2014

AbstractDisclosed herein is a general catalytic system for the intermolecular anti‐Markovnikov hydroamination of alkenes. By using an organocatalytic photoredox system, α‐ and β‐substituted styrenes as well as aliphatic alkenes undergo anti‐Markovnikov hydroamination. Heterocyclic amines were also successfully employed as nitrogen nucleophiles, thus providing a direct route to heterocyclic motifs common in medicinal agents.
Nonenzymatic Rubylation and Ubiquitination of Proteins for Structural and Functional Studies
Authors: Singh Rajesh K. , Sundar Adithya , Fushman David 
Published: April 2014

AbstractUncovering the mechanisms that allow conjugates of ubiquitin (Ub) and/or Ub‐like (UBL) proteins such as Rub1 to serve as distinct molecular signals requires the ability to make them with native connectivity and defined length and linkage composition. A novel, effective, and affordable strategy for controlled chemical assembly of fully natural UBL–Ub, Ub–UBL, and UBL–UBL conjugates from recombinant monomers is presented. Rubylation of Ub and Rub1 and ubiquitination of Rub1 was achieved without E2/E3 enzymes. New residue‐specific information was obtained on the interdomain contacts in naturally‐occurring K48‐linked Rub1–Ub and Ub–Rub1, and K29‐linked Rub1–Ub heterodimers, and their recognition by a K48‐linkage‐specific Ub receptor. The disassembly of these heterodimers by major deubiquitinating enzymes was examined and it was discovered that some deubiquitinases also possess derubylase activity. This unexpected result suggests possible crosstalk between Ub and Rub1/Nedd8 signaling pathways.
Tetravinylethylene
Authors: Lindeboom Erik J. , Willis Anthony C. , Paddon‐Row Michael N. , Sherburn Michael S. 
Published: April 2014

AbstractThe first four‐fold cross coupling reaction involving alkenic partners leads to the title hydrocarbon on multi‐gram scale in one step from commercially available precursors. In stark contrast to its close structural relatives, tetravinylethylene is a remarkably robust, bench‐stable compound. The π‐bond rich hydrocarbon is shown to undergo one‐pot sequences of pericyclic reactions leading to the formation of complex systems with four new rings, seven CC bonds and ten stereocenters with a very high level of stereoselectivity. Insights into the reactivity of this and related systems is provided using the accurate composite ab initio MO G4(MP2) method.
Intramolecular Metal‐Free Oxidative Aryl–Aryl Coupling: An Unusual Hypervalent‐Iodine‐Mediated Rearrangement of 2‐Substituted N‐Phenylbenzamides
Authors: Shang Siyun , Zhang‐Negrerie Daisy , Du Yunfei , Zhao Kang 
Published: April 2014

AbstractHypervalent‐iodine‐mediated oxidative coupling of the two aryl groups in either 2‐acylamino‐N‐phenyl‐benzamides or 2‐hydroxy‐N‐phenylbenzamides, with concomitant insertion of the ortho‐substituted N or O atom into the tether, has been described for the first time. This unusual metal‐free rearrangement reaction involves an oxidative C(sp2)C(sp2) aryl–aryl bond formation, cleavage of a C(sp2)C(O) bond, and a lactamization/lactonization. Furthermore, unsymmetrical diaryl compounds can be easily obtained by removing the tether within the cyclized product.
Pullulan Encapsulation of Labile Biomolecules to Give Stable Bioassay Tablets
Authors: Jahanshahi‐Anbuhi Sana , Pennings Kevin , Leung Vincent , Liu Meng , Carrasquilla Carmen , Kannan Balamurali , Li Yingfu , Pelton Robert , Brennan John D. , Filipe Carlos D. M. 
Published: April 2014

AbstractA simple and inexpensive method is reported for the long‐term stabilization of enzymes and other unstable reagents in premeasured quantities in water‐soluble tablets (cast, not compressed) made with pullulan, a nonionic polysaccharide that forms an oxygen impermeable solid upon drying. The pullulan tablets dissolve in aqueous solutions in seconds, thereby facilitating the easy execution of bioassays at remote sites with no need for special reagent handling and liquid pipetting. This approach is modular in nature, thus allowing the creation of individual tablets for enzymes and their substrates. Proof‐of‐principle demonstrations include a Taq polymerase tablet for DNA amplification through PCR and a pesticide assay kit consisting of separate tablets for acetylcholinesterase and its chromogenic substrate, indoxyl acetate, both of which are highly unstable. The encapsulated reagents remain stable at room temperature for months, thus enabling the room‐temperature shipping and storage of bioassay components.
Accelerating Diffusion‐Ordered NMR Spectroscopy by Joint Sparse Sampling of Diffusion and Time Dimensions
Authors: Urbańczyk Mateusz , Koźmiński Wiktor , Kazimierczuk Krzysztof 
Published: April 2014

AbstractDiffusion‐ordered multidimensional NMR spectroscopy is a valuable technique for the analysis of complex chemical mixtures. However, this method is very time‐consuming because of the costly sampling of a multidimensional signal. Various sparse sampling techniques have been proposed to accelerate such measurements, but they have always been limited to frequency dimensions of NMR spectra. It is now revealed how sparse sampling can be extended to diffusion dimensions.
Direct Umpolung of Glycals and Related 2,3‐Unsaturated N‐Acetylneuraminic Acid Derivatives Using Samarium Diiodide
Authors: Le Tien Xuan , Papin Caroline , Doisneau Gilles , Beau Jean‐Marie 
Published: April 2014

AbstractThe umpolung of glycals with samarium diiodide offers a simple route to novel carbohydrate‐derived nucleophilic reagents in a single step using a readily available reductant. The corresponding allyl samarium reagent that arises from the hexose series reacts with ketones at the C3 position with high stereoselectivity; carbon–carbon bond formation takes place only anti to the substituent at the C4 position of the dihydropyran ring. For the sialic acid series, the completely regio‐ and stereoselective coupling process of the samarium reagent occurs at the anomeric carbon atom and provides a new approach to the α‐C‐glycosides of N‐acetyl neuraminic acid.
Reversible Click Reactions with Boronic Acids to Build Supramolecular Architectures in Water
Authors: Arzt Matthias , Seidler Christiane , Ng David Y. W. , Weil Tanja 
Published: April 2014

AbstractThe interaction of boronic acids with various bifunctional reagents offers great potential for the preparation of responsive supramolecular architectures. Boronic acids react with 1,2‐diols yielding cyclic boronate esters that are stable at pH>7.4 but can be hydrolyzed at pH<5.0. The phenylboronic acid (PBA)–salicylhydroxamic acid (SHA) system offers ultra‐fast reaction kinetics and high binding affinities. This Focus Review summarizes the current advances in exploiting the bioorthogonal interaction of boronic acids to build pH‐responsive supramolecular architectures in water.
Synthesis, Crystal Packing, and Ambipolar Carrier Transport Property of Twisted Dibenzo[g,p]chrysenes
Authors: Ueda Yasuyuki , Tsuji Hayato , Tanaka Hideyuki , Nakamura Eiichi 
Published: April 2014

AbstractA versatile method for the synthesis of dibenzo[g,p]chrysene (DBC) derivatives based on regio‐ and stereoselective stannyllithiation to diarylacetylenes is described. This method affords a variety of DBCs possessing both electron‐donating and electron‐withdrawing functional groups. These twisted molecules take brickwork packing structures in single crystals. Thus, ambipolar carrier transport properties with mobility values of up to 10−3 cm2 V−1 s−1 in the amorphous state were achieved. Functional groups on DBC frameworks are considered to increase carrier mobility through the enhancement of intermolecular interactions in the brickwork packing structures.