bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic reconnection, buoyancy, and flapping motions in magnetotail explosions
Authors: Sitnov M. I. , Merkin V. G. , Swisdak M. , Motoba T. , Buzulukova N. , Moore T. E. , Mauk B. H. , Ohtani S. 
Published: August 2014

AbstractA key process in the interaction of magnetospheres with the solar wind is the explosive release of energy stored in the magnetotail. Based on observational evidence, magnetic reconnection is widely believed to be responsible. However, the very possibility of spontaneous reconnection in collisionless magnetotail plasmas has been questioned in kinetic theory for more than three decades. In addition, in situ observations by multispacecraft missions (e.g., THEMIS) reveal the development of buoyancy and flapping motions coexisting with reconnection. Never before have kinetic simulations reproduced all three primary modes in realistic 2‐D configurations with a finite normal magnetic field. Moreover, 3‐D simulations with closed boundaries suggest that the tail activity is dominated by buoyancy‐driven instabilities, whereas reconnection is a secondary effect strongly localized in the dawn‐dusk direction. In this paper, we use massively parallel 3‐D fully kinetic simulations with open boundaries to show that sufficiently far from the planet explosive processes in the tail are dominated by reconnection motions. These motions occur in the form of spontaneously generated dipolarization fronts accompanied by changes in magnetic topology which extend in the dawn‐dusk direction over the size of the simulation box, suggesting that reconnection onset causes a macroscale reconfiguration of the real magnetotail. In our simulations, buoyancy and flapping motions significantly disturb the primary dipolarization front but neither destroy it nor change the near 2‐D picture of the front evolution critically. Consistent with recent multiprobe observations, dipolarization fronts are also found to be the main regions of energy conversion in the magnetotail.
Long‐lived plasmaspheric drainage plumes: Where does the plasma come from?
Authors: Borovsky Joseph E. , Welling Daniel T. , Thomsen Michelle F. , Denton Michael H. 
Published: August 2014

AbstractLong‐lived (weeks) plasmaspheric drainage plumes are explored. The long‐lived plumes occur during long‐lived high‐speed‐stream‐driven storms. Spacecraft in geosynchronous orbit see the plumes as dense plasmaspheric plasma advecting sunward toward the dayside magnetopause. The older plumes have the same densities and local time widths as younger plumes, and like younger plumes they are lumpy in density and they reside in a spatial gap in the electron plasma sheet (in sort of a drainage corridor). Magnetospheric‐convection simulations indicate that drainage from a filled outer plasmasphere can only supply a plume for 1.5–2 days. The question arises for long‐lived plumes (and for any plume older than about 2 days): Where is the plasma coming from? Three candidate sources appear promising: (1) substorm disruption of the nightside plasmasphere which may transport plasmaspheric plasma outward onto open drift orbits, (2) radial transport of plasmaspheric plasma in velocity‐shear‐driven instabilities near the duskside plasmapause, and (3) an anomalously high upflux of cold ionospheric protons from the tongue of ionization in the dayside ionosphere, which may directly supply ionospheric plasma into the plume. In the first two cases the plume is drainage of plasma from the magnetosphere; in the third case it is not. Where the plasma in long‐lived plumes is coming from is a quandary: to fix this dilemma, further work and probably full‐scale simulations are needed.
On the day‐to‐day variation of the equatorial electrojet during quiet periods
Authors: Yamazaki Y. , Richmond A. D. , Maute A. , Liu H.‐L. , Pedatella N. , Sassi F. 
Published: August 2014

AbstractIt has been known for a long time that the equatorial electrojet varies from day to day even when solar and geomagnetic activities are very low. The quiet time day‐to‐day variation is considered to be due to irregular variability of the neutral wind, but little is known about how variable winds drive the electrojet variability. We employ a numerical model introduced by Liu et al. (2013), which takes into account weather changes in the lower atmosphere and thus can reproduce ionospheric variability due to forcing from below. The simulation is run for May and June 2009. Constant solar and magnetospheric energy inputs are used so that day‐to‐day changes will arise only from lower atmospheric forcing. The simulated electrojet current shows day‐to‐day variability of ±25%, which produces day‐to‐day variations in ground level geomagnetic perturbations near the magnetic equator. The current system associated with the day‐to‐day variation of the equatorial electrojet is traced based on a covariance analysis. The current pattern reveals return flow at both sides of the electrojet, in agreement with those inferred from ground‐based magnetometer data in previous studies. The day‐to‐day variation in the electrojet current is compared with those in the neutral wind at various altitudes, latitudes, and longitudes. It is found that the electrojet variability is dominated by the zonal wind at 100–120 km altitudes near the magnetic equator. These results suggest that the response of the zonal polarization electric field to variable zonal winds is the main source of the day‐to‐day variation of the equatorial electrojet during quiet periods.
The pattern and variability of winter Kuroshio intrusion northeast of Taiwan
Authors: Liu Xiaohui , Dong Changming , Chen Dake , Su Jilan 
Published: August 2014

AbstractThe variations of the Kuroshio path and velocity northeast of Taiwan are analyzed based on along‐track satellite altimeter data as well as high‐resolution model experiments. Observations reveal that in winter the Kuroshio intrusion into the East China Sea (ECS) at this location is manifested by a secondary maximum current core (SMCC) shoreward of the Kuroshio's main path. The SMCC varies significantly on interannual time scale, and its variability is strikingly out of phase with that of the Kuroshio entering the ECS, meaning that the stronger the Kuroshio, the weaker the SMCC, and vice versa. Model experiments corroborate the observational results and, more importantly, indicate that the Kuroshio intrusion here follows two primary routes, a large anticyclonic loop that separates from the Kuroshio at the northern end of Taiwan and moves forward to form the SMCC, and a straight northward path onto the shelf when the Kuroshio turns sharply eastward along the continental slope of the ECS. The intrusion is controlled by both local forcing and remote effect, with its pattern and variability depending mostly on the local heat flux and the inertia of the Kuroshio Current.
Microspectroscopic imaging and characterization of individually identified ice nucleating particles from a case field study
Authors: Knopf D. A. , Alpert P. A. , Wang B. , O'Brien R. E. , Kelly S. T. , Laskin A. , Gilles M. K. , Moffet R. C. 
Published: August 2014

AbstractThe effect of anthropogenic and biogenic organic particles on atmospheric glaciation processes is poorly understood. We use an optical microscopy setup to identify the ice nuclei (IN) active in immersion freezing (IMF) and deposition ice nucleation within a large population of particles collected on a substrate from an ambient environment in central California dominated by urban and marine aerosols. Multimodal microspectroscopy methods are applied to characterize the physicochemical properties and mixing state of the individual IN and particle populations to identify particle‐type classes. The temperature onsets of water uptake occurred between 235 and 257 K at subsaturated conditions, and the onsets of IMF proceeded at subsaturated and saturated conditions for 235–247 K, relevant for ice nucleation in mixed‐phase clouds. Particles also took up water and nucleated ice between 226 and 235 K and acted as deposition IN with onset temperatures below 226 K, a temperature range relevant to cirrus cloud formation. The identified IN belong to the most common particle‐type classes observed in the field samples: organic coated sea salt and Na‐rich, secondary, and refractory carbonaceous particles. Based on these observations, we suggest that the IN are not always particles with unique chemical composition and exceptional ice nucleation propensity; rather, they are common particles in the ambient particle population. The results suggest that particle‐type abundance and total particle surface area are also crucial factors, in addition to particle‐type ice nucleation efficiency, in determining ice formation within the particle population.
Life in a fishbowl: Prospects for the endangered Devils Hole pupfish (Cyprinodon diabolis) in a changing climate
Authors: Hausner Mark B. , Wilson Kevin P. , Gaines D. Bailey , Suárez Francisco , Scoppettone G. Gary , Tyler Scott W. 
Published: August 2014

AbstractThe Devils Hole pupfish (Cyprinodon diabolis) is a federally listed endangered species living solely within the confines of Devils Hole, a geothermal pool ecosystem in the Mojave Desert of the American Southwest. This unique species has suffered a significant, yet unexplained, population decline in the past two decades, with a record low survey of 35 individuals in early 2013. The species survives on a highly variable seasonal input of nutrients and has evolved in a thermal regime lethal to other pupfish species. The short lifespan of the species (approximately 1 year) makes annual recruitment in Devils Hole critical to the persistence of the species, and elevated temperatures on the shallow shelf that comprises the optimal spawning habitat in the ecosystem can significantly reduce egg viability and increase larval mortality. Here we combine computational fluid dynamic modeling and ecological analysis to investigate the timing of thresholds in the seasonal cycles of food supply and temperature. Numerical results indicate a warming climate most impacts the heat loss from the water column, resulting in warming temperatures and reduced buoyancy‐driven circulation. Observed climate change is shown to have already warmed the shallow shelf, and climate change by 2050 is shown to shorten the window of optimum conditions for recruitment by as much as 2 weeks. While there are many possible reasons for the precipitous decline of this species, the changing climate of the Mojave region is shown to produce thermal and nutrient conditions likely to reduce the success of annual recruitment of young C. diabolis in the future, leading to continued threats to the survival of this unique and enigmatic species.
Epigenetic promoter silencing in Friedreich ataxia is dependent on repeat length
Authors: Chutake Yogesh K. , Lam Christina , Costello Whitney N. , Anderson Michael , Bidichandani Sanjay I. 
Published: August 2014

ObjectiveFriedreich ataxia (FRDA) is caused by an expanded GAA triplet‐repeat (GAA‐TR) mutation in the FXN gene. Patients are typically homozygous for expanded alleles containing 100 to 1,300 triplets, and phenotypic severity is significantly correlated with the length of the shorter of the 2 expanded alleles. Patients have a severe deficiency of FXN transcript, which is predominantly caused by epigenetic silencing of the FXN promoter. We sought to determine whether the severity of FXN promoter silencing is related to the length of the expanded GAA‐TR mutation in FRDA.MethodsPatient‐derived lymphoblastoid cell lines bearing a range of expanded alleles (200–1,122 triplets) were evaluated for FXN transcript levels by quantitative reverse transcriptase polymerase chain reaction. FXN promoter function was directly measured by quantitative analysis of transcriptional initiation via metabolic labeling of newly synthesized transcripts in living cells.ResultsFXN transcriptional deficiency was significantly correlated with the length of the shorter of the 2 expanded alleles, which was noted both upstream (R2 = 0.84, p = 0.014) and downstream (R2 = 0.89, p = 0.002) of the expanded GAA‐TR mutation, suggesting that FXN promoter silencing in FRDA is related to repeat length. A bilinear regression model revealed that length dependence was strongest when the shorter of the 2 expanded alleles contained <400 triplets. Direct measurement of FXN promoter activity in patients with expanded alleles containing <400 versus >400 triplets in the shorter of the 2 expanded alleles revealed a significantly greater deficiency in individuals with longer GAA‐TR alleles (p < 0.05).InterpretationFXN promoter silencing in FRDA is dependent on the length of the expanded GAA‐TR mutation. Ann Neurol 2014;76:522–528
Schwefel(VI)‐fluorid‐Austausch (SuFEx): Eine weitere gute Anwendung für die Click‐Chemie
Authors: Dong Jiajia , Krasnova Larissa , Finn M. G. , Sharpless K. Barry 
Published: August 2014

AbstractArylsulfonylchloride (z. B. Ts‐Cl) sind die am häufigsten eingesetzten SVI‐Elektrophile in der organischen Synthesechemie, und auch die Stammverbindung, das Sulfurylchlorid (O2SVICl2), wurde zur Synthese von Sulfaten und Sulfamiden genutzt. Allerdings wird die gewünschte Halogenidsubstitution oftmals durch die Zersetzung des Schwefelelektrophils in SIV‐Spezies und Cl− verhindert, denn die SVI‐Cl‐Bindung ist äußerst reduktionsanfällig. Mit Schwefel(VI)‐fluoriden (z. B. R‐SO2‐F und SO2F2) verläuft die Umsetzung hingegen ausschließlich über den Substitutionsweg. Wie es bei der Click‐Chemie zumeist der Fall ist, wurden viele entscheidende Aspekte der Reaktivität von Schwefel(VI)‐fluoriden vor langer Zeit in Deutschland entdeckt.6a Überraschenderweise gerieten diese außerordentlichen Arbeiten in der Mitte des 20. Jahrhunderts ziemlich abrupt aus dem Blickfeld. In diesem Aufsatz versuchen wir, dieser Chemie neues Leben einzuhauchen. Insbesondere stützen wir uns dabei auch auf John Hyatts unbeachtet gebliebene Veröffentlichung über CH2CH‐SO2‐F aus dem Jahr 1979.98 Wir tragen mehrere neue Beobachtungen bei, einschließlich dem Befund, dass das ansonsten sehr stabile Gas SO2F2 eine exzellente Reaktivität unter den richtigen Umständen aufweist. Wir zeigen auch, dass Protonen oder Siliciumzentren den Austausch von S‐F‐Bindungen gegen S‐O‐Bindungen aktivieren können und dass der Sulfat‐Konnektor überraschend hydrolysestabil ist. Anwendungen dieser kontrollierbaren Ligationschemie auf kleine Moleküle, Polymere und Biomoleküle werden diskutiert.
Chemical Probing of the Human Sirtuin 5 Active Site Reveals Its Substrate Acyl Specificity and Peptide‐Based Inhibitors
Authors: Roessler Claudia , Nowak Theresa , Pannek Martin , Gertz Melanie , Nguyen Giang T. T. , Scharfe Michael , Born Ilona , Sippl Wolfgang , Steegborn Clemens , Schutkowski Mike 
Published: August 2014

AbstractSirtuins are NAD+‐dependent deacetylases acting as sensors in metabolic pathways and stress response. In mammals there are seven isoforms. The mitochondrial sirtuin 5 is a weak deacetylase but a very efficient demalonylase and desuccinylase; however, its substrate acyl specificity has not been systematically analyzed. Herein, we investigated a carbamoyl phosphate synthetase 1 derived peptide substrate and modified the lysine side chain systematically to determine the acyl specificity of Sirt5. From that point we designed six potent peptide‐based inhibitors that interact with the NAD+ binding pocket. To characterize the interaction details causing the different substrate and inhibition properties we report several X‐ray crystal structures of Sirt5 complexed with these peptides. Our results reveal the Sirt5 acyl selectivity and its molecular basis and enable the design of inhibitors for Sirt5.
Antifreezes Act as Catalysts for Methane Hydrate Formation from Ice
Authors: McLaurin Graham , Shin Kyuchul , Alavi Saman , Ripmeester John A. 
Published: August 2014

AbstractContrary to the thermodynamic inhibiting effect of methanol on methane hydrate formation from aqueous phases, hydrate forms quickly at high yield by exposing frozen water–methanol mixtures with methanol concentrations ranging from 0.6–10 wt % to methane gas at pressures from 125 bars at 253 K. Formation rates are some two orders of magnitude greater than those obtained for samples without methanol and conversion of ice is essentially complete. Ammonia has a similar catalytic effect when used in concentrations of 0.3–2.7 wt %. The structure I methane hydrate formed in this manner was characterized by powder X‐ray diffraction and Raman spectroscopy. Steps in the possible mechanism of action of methanol were studied with molecular dynamics simulations of the Ih (0001) basal plane exposed to methanol and methane gas. Simulations show that methanol from a surface aqueous layer slowly migrates into the ice lattice. Methane gas is preferentially adsorbed into the aqueous methanol surface layer. Possible consequences of the catalytic methane hydrate formation on hydrate plug formation in gas pipelines, on large scale energy‐efficient gas hydrate formation, and in planetary science are discussed.
Near‐IR‐Triggered, Remote‐Controlled Release of Metal Ions: A Novel Strategy for Caged Ions
Authors: Atilgan Ahmet , Tanriverdi Eçik Esra , Guliyev Ruslan , Uyar T. Bilal , Erbas‐Cakmak Sundus , Akkaya Engin U. 
Published: August 2014

AbstractA ligand incorporating a dithioethenyl moiety is cleaved into fragments which have a lower metal‐ion affinity upon irradiation with low‐energy red/near‐IR light. The cleavage is a result of singlet oxygen generation which occurs on excitation of the photosensitizer modules. The method has many tunable factors that could make it a satisfactory caging strategy for metal ions.
Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base
Authors: Scott Daniel J. , Fuchter Matthew J. , Ashley Andrew E. 
Published: August 2014

AbstractIn recent years ‘frustrated Lewis pairs’ (FLPs) have been shown to be effective metal‐free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional‐group tolerance restricts the range of solvents in which FLP‐mediated reactions can be performed, with all FLP‐mediated hydrogenations reported to date carried out in non‐donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C6Cl5)x(C6F5)3−x (x=0–3) are capable of heterolytic H2 activation in the strong‐donor solvent THF, in the absence of any additional Lewis base. This allows metal‐free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal‐free catalytic hydrogenation of furan heterocycles. The air‐stability of the most effective borane, B(C6Cl5)(C6F5)2, makes this a practically simple reaction method.
Au@Pt Nanoparticle Encapsulated Target‐Responsive Hydrogel with Volumetric Bar‐Chart Chip Readout for Quantitative Point‐of‐Care Testing
Authors: Zhu Zhi , Guan Zhichao , Jia Shasha , Lei Zhichao , Lin Shuichao , Zhang Huimin , Ma Yanli , Tian Zhong‐Qun , Yang Chaoyong James 
Published: August 2014

AbstractPoint‐of‐care testing (POCT) with the advantages of speed, simplicity, portability, and low cost is critical for the measurement of analytes in a variety of environments where access to laboratory infrastructure is lacking. While qualitative POCTs are widely available, quantitative POCTs present significant challenges. Here we describe a novel method that integrates an Au core/Pt shell nanoparticle (Au@PtNP) encapsulated target‐responsive hydrogel with a volumetric bar‐chart chip (V‐Chip) for quantitative POCT. Upon target introduction, the hydrogel immediately dissolves and releases Au@PtNPs, which can efficiently catalyze the decomposition of H2O2 to generate a large volume of O2 to move of an ink bar in the V‐Chip. The concentration of the target introduced can be visually quantified by reading the traveling distance of the ink bar. This method has the potential to be used for portable and quantitative detection of a wide range of targets without any external instrument.
A New Class of Organocatalysts: Sulfenate Anions
Authors: Zhang Mengnan , Jia Tiezheng , Yin Haolin , Carroll Patrick J. , Schelter Eric J. , Walsh Patrick J. 
Published: August 2014

AbstractSulfenate anions are known to act as highly reactive species in the organic arena. Now they premiere as organocatalysts. Proof of concept is offered by the sulfoxide/sulfenate‐catalyzed (1–10 mol %) coupling of benzyl halides in the presence of base to generate trans‐stilbenes in good to excellent yields (up to 99 %). Mechanistic studies support the intermediacy of sulfenate anions, and the deprotonated sulfoxide was determined to be the resting state of the catalyst.
Bacterial Imprinting at Pickering Emulsion Interfaces
Authors: Shen Xiantao , Svensson Bonde Johan , Kamra Tripta , Bülow Leif , Leo Jack C. , Linke Dirk , Ye Lei 
Published: August 2014

AbstractThe tendency of bacteria to assemble at oil–water interfaces can be utilized to create microbial recognition sites on the surface of polymer beads. In this work, two different groups of bacteria were first treated with acryloyl‐functionalized chitosan and then used to stabilize an oil‐in‐water emulsion composed of cross‐linking monomers that were dispersed in aqueous buffer. Polymerization of the oil phase followed by removal of the bacterial template resulted in well‐defined polymer beads bearing bacterial imprints. Chemical passivation of chitosan and cell displacement assays indicate that the bacterial recognition on the polymer beads was dependent on the nature of the pre‐polymer and the target bacteria. The functional materials for microbial recognition show great potential for constructing cell–cell communication networks, biosensors, and new platforms for testing antibiotic drugs.
Gold‐Catalyzed 1,2‐Acyloxy Migration/Intramolecular [3+2] 1,3‐Dipolar Cycloaddtion Cascade Reaction: An Efficient Strategy for Syntheses of Medium‐Sized‐Ring Ethers and Amines
Authors: Zhao Changgui , Xie Xingang , Duan Shuangshuang , Li Huilin , Fang Ran , She Xuegong 
Published: August 2014

AbstractA highly efficient strategy for the formation of medium‐sized‐ring ethers and amines based on a gold‐catalyzed cascade reaction, involving enynyl ester isomerization and intramolecular [3+2] cyclization, has been developed. Various multisubstituted medium‐sized‐ring unsaturated ethers and amines were obtained through this transformation. This method represents one of the relatively few transition metal catalyzed intramolecular cycloaddition reactions for medium‐sized ring synthesis.
Carbon Dioxide as a Protecting Group: Highly Efficient and Selective Catalytic Access to Cyclic cis‐Diol Scaffolds
Authors: Laserna Victor , Fiorani Giulia , Whiteoak Christopher J. , Martin Eddy , Escudero‐Adán Eduardo , Kleij Arjan W. 
Published: August 2014

AbstractThe efficient and highly selective formation of a wide range of (hetero)cyclic cis‐diol scaffolds using aminotriphenolate‐based metal catalysts is reported. The key intermediates are cyclic carbonates, which are obtained in high yield and with high levels of diastereo‐ and chemoselectivity from the parent oxirane precursors and carbon dioxide. Deprotection of the carbonate structures affords synthetically useful cis‐diol scaffolds with different ring sizes that incorporate various functional groups. This atom‐efficient method allows the simple construction of diol synthons using inexpensive and accessible precursors and green metal catalysts and showcases the use of CO2 as a temporary protecting group.