Majority Species Research Articles

Hydrogen Deposition on Pt(111) during Electrochemical Hydrogen Evolution from a First-Principles Multiadsorption-Site Study

We study the simultaneous adsorption of H* on Pt(111) for multiple, interacting adsorption sites (i.e., fcc, atop, and hcp) and, over a wide range of electrode potential, examine the equilibrium site coverage during the hydrogen evolution reaction (HER) and oxidation reaction (HOR). We use a first-principles-based cluster expansion (CE) and Monte Carlo simulations. We predict the adsorption isotherm and cyclic voltammogram for −0.9 V 0, we show that traces of weakly adsorbed H*atop and H*hcp are present, and they are expected to be active in the HER. For U < 0, we predict that H*atop takes over as the majority species ca. U = −0.4 V, where a simultaneous decrease in H*fcc occurs—contradicting the general assumption that H*fcc remains the majority species, even at very negative potential. We identify the favorable HER operating potentials by mapping out the coverage of the kinetically activ...

Folding and aggregation of a multi-domain engineered immunotoxin

Engineered immunotoxins with specific targeting mechanisms have potential applications for the treatment of cancer and other diseases; however, their folding behavior is often poorly understood and this presents challenges during process development, manufacturing, and formulation. Folding thermodynamics of an antibody variable domain (VH/VL) genetically fused to a biological toxin payload were characterized at pH 6.0 and pH 8.0 in order to assess the relative domain stabilities, along with time scales on which they fold, and the competition between aggregation and folding. The toxin and VH/VL domains had considerably different unfolding free energies (ΔGUNF), leading to a thermodynamically-distinct intermediate species, with the toxin domain unfolded and the VH/VL folded. The intermediate is the majority species over a range of denaturant concentrations (∼4–6M urea; ∼2–4M guanidine HCl). Thermal unfolding resulted in reversible unfolding of the toxin domain at pH 8, but at pH 6 thermal unfolding was convoluted with aggregation due to irreversible unfolding and aggregation for the VH/VL domain. Chemical unfolding of both domains was more easily reversible, provided that the refold was done stepwise, allowing the antibody domain to fold first at intermediate denaturant concentration, as folding of the VH/VL domain played a key role in aggregation of this antibody fusion protein.

LTE or non-LTE, that is the question

Context. Strontium has proven itself to be one of the most important neutron-capture elements in the study of metal-poor stars. Th anks to the strong absorption lines of Sr, they can be detected eve n in the most metal-poor stars and also in low-resolution spe ctra. However, we still cannot explain the large star-to-star abundance sc atter we derive for metal-poor stars. Aims. Here we compare Galactic chemical evolution (GCE) predictions with improved abundances for Sri and Srii, including updated atomic data, to evaluate possible explanations for the larg e star-to-star scatter at low metallicities. Methods. We have derived abundances under both local thermodynamic equilibrium (LTE) and non-LTE (NLTE) for stars spanning a large interval of metallicities, as well as a broad range of other stellar parameters. Gravities and metallicities are also determined in NLTE. We employed MARCS stellar atmospheres and MOOG for theLTE spectrum synthesis, while MAFAGS and DETAIL were used to derive the NLTE abundances. We verified the consisten cy of the two methods in LTE. Results. We confirm that the ionisation equilibrium between Sr I and Sr II is satisfied under NLTE but not LTE, where the di fference between neutral and ionised Sr is on average ∼ 0.3 dex. We show that the NLTE corrections are of increasing importance as the metallicity decreases. For the stars with [Fe/H] > −3, the Sri NLTE correction is∼ 0.35/0.55 dex in dwarfs/giants, while the Srii NLTE correction is <±0.05 dex. Conclusions. On the basis of the large NLTE corrections to Sri, Sri should not be applied as a chemical tracer under LTE, while it is a good tracer under NLTE. Srii, on the other hand, is a good tracer under both LTE and NLTE (down to [Fe/H]∼ −3), and LTE is a safe assumption for this majority species (if the NLTE corrections are not available). However, the Sr abundance fro m Srii lines depends on determining an accurate surface gravity, which can be obtained from the NLTE spectroscopy of Fe lines or from parallax measurements. We could not explain the star-to-star scatte r (which remains under both LTE and NLTE) by the use of the Galactic chemical evolution model, since Sr yields to date have been too uncertain to draw firm conclusions. At least two nucleosyn thetic production sites seem necessary to account for this large sc atter.

Correlated phases of population imbalanced Fermi-Fermi mixtures on an optical lattice

We study a two-species fermion mixture with different populations on a square lattice modeled by a Hubbard Hamiltonian with onsite interspecies repulsive interaction. Such a model can be realized in a cold-atom system with fermionic atoms in two different hyperfine states loaded on an optical lattice and with tunable interspecies interaction strength via external fields. For a two-dimensional square lattice, when at least one of the fermion species is close to half-filling, the system is highly affected by lattice effects. With the majority species near half-filling and varying densities for the minority species, we find that several correlated phases emerge as the ground state, including a spin density wave state, a charge density wave state with stripe structure, and various $p$-wave BCS pairing states for both species. We study this system using a functional renormalization group method, determine its phase diagram at weak coupling, discuss the origin and characteristics of each phase, and provide estimates for the critical temperatures.

Elucidating the Role of Subdiffusion and Evanescence in the Target Problem: Some Recent Results

We present an overview of recent results for the classic problem of the survival probability of an immobile target in the presence of a single mobile trap or of a collection of uncorrelated mobile traps. The diffusion exponent of the traps is taken to be either γ = 1, associated with normal diffusive motion, or 0 < 1, corresponding to subdiffusive motion. We consider traps that can only die upon interaction with the target and, alternatively, traps that may die due to an additional evanescence process even before hitting the target. The evanescence reaction is found to completely modify the survival probability of the target. Such evanescence processes are important in systems where the addition of scavenger molecules may result in the removal of the majority species, or ones where the mobile traps have a finite intrinsic lifetime.

Induced superfluidity of imbalanced Fermi gases near unitarity

The induced intraspecies interactions among the majority species, mediated by the minority species, is computed for a population-imbalanced two-component Fermi gas. Although the Feshbach-resonance mediated interspecies interaction is dominant for equal populations, leading to singlet s-wave pairing, we find that in the strongly imbalanced regime the induced intraspecies interaction leads to p-wave pairing and superfluidity of the majority species. Thus, we predict that the observed spin-polaron Fermi liquid state in this regime is unstable to p-wave superfluidity, in accordance with the results of Kohn and Luttinger, below a temperature that, near unitarity, we find to be within current experimental capabilities. Possible experimental signatures of the p-wave state using radio-frequency spectroscopy as well as density-density correlations after free expansion are presented.

Structural and Biochemical Characterization of Human Mitochondrial Branched-chain α-Ketoacid Dehydrogenase Phosphatase

The branched-chain α-ketoacid dehydrogenase phosphatase (BDP) component of the human branched-chain α-ketoacid dehydrogenase complex (BCKDC) has been expressed in Escherichia coli and purified in the soluble form. The monomeric BDP shows a strict dependence on Mn(2+) ions for phosphatase activity, whereas Mg(2+) and Ca(2+) ions do not support catalysis. Metal binding constants for BDP, determined by competition isothermal titration calorimetry, are 2.4 nm and 10 μm for Mn(2+) and Mg(2+) ions, respectively. Using the phosphorylated decarboxylase component (p-E1b) of BCKDC as a substrate, BDP shows a specific activity of 68 nmol/min/mg. The Ca(2+)-independent binding of BDP to the 24-meric transacylase (dihydrolipoyl transacylase; E2b) core of BCKDC results in a 3-fold increase in the dephosphorylation rate of p-E1b. However, the lipoyl prosthetic group on E2b is not essential for BDP binding or E2b-stimulated phosphatase activity. Acidic residues in the C-terminal linker of the E2b lipoyl domain are essential for the interaction between BDP and E2b. The BDP structure was determined by x-ray crystallography to 2.4 Å resolution. The BDP structure is dominated by a central β-sandwich. There are two protrusions forming a narrow cleft ∼10 Å wide, which constitutes the active site. The carboxylate moieties of acidic residues Asp-109, Asp-207, Asp-298, and Asp-337 in the active-site cleft participate in binding two metal ions. Substitutions of these residues with alanine nullify BDP phosphatase activity. Alteration of the nearby Arg-104 increases the K(m) for p-E1b peptide by 60-fold, suggesting that this residue is critical for the recognition of the native p-E1b protein.

DNA Barcoding the Dioscorea in China, a Vital Group in the Evolution of Monocotyledon: Use of matK Gene for Species Discrimination

Background Dioscorea is an important plant genus in terms of food supply and pharmaceutical applications. However, its classification and identification are controversial. DNA barcoding is a recent aid to taxonomic identification and uses a short standardized DNA region to discriminate plant species. In this study, the applicability of three candidate DNA barcodes (rbcL, matK, and psbA-trnH) to identify species within Dioscorea was tested.Methodology/Principal FindingsOne-hundred and forty-eight individual plant samples of Dioscorea, encompassing 38 species, seven varieties and one subspecies, representing majority species distributed in China of this genus, were collected from its main distributing areas. Samples were assessed by PCR amplification, sequence quality, extent of specific genetic divergence, DNA barcoding gap, and the ability to discriminate between species. matK successfully identified 23.26% of all species, compared with 9.30% for rbcL and 11.63% for psbA-trnH. Therefore, matK is recommended as the best DNA barcoding candidate. We found that the combination of two or three loci achieved a higher success rate of species discrimination than one locus alone. However, experimental cost would be much higher if two or three loci, rather than a single locus, were assessed.ConclusionsWe conclude that matK is a strong, although not perfect, candidate as a DNA barcode for Dioscorea identification. This assessment takes into account both its ability for species discrimination and the cost of experiments.

Quantum dynamics of impurities in a one-dimensional Bose gas

Using a species-selective dipole potential, we create initially localized impurities and investigate their interactions with a majority species of bosonic atoms in a one-dimensional configuration during expansion. We find an interaction-dependent amplitude reduction of the oscillation of the impurities' size with no measurable frequency shift, and study it as a function of the interaction strength. We discuss possible theoretical interpretations of the data. We compare, in particular, with a polaronic mass shift model derived following Feynman variational approach.

Electromagnetically induced transparency spectroscopy

We propose a method based on the electromagnetically induced transparency (EIT) phenomenon for the detection of molecules which exist as a small minority in the presence of a majority of absorbers. The EIT effect we employ effectively eliminates the absorption of the majority species in the spectral region where it overlaps with the absorption of the minority species. The method can also be used to enhance local-modes transitions which overlap spectrally with a background of other local-modes transitions of the same molecule. The general theory is applied to the case of sparse and congested background spectra within the same molecule and to the recording of the spectra of isotopomers (of chlorine and methanol) that are in minority relative to other isotopomers which constitute the majority of molecules present.

山东中新世山旺组葛属(豆科)小叶的形态及其古生态学意义

葛属Pueraria是豆科蝶形花亚科、菜豆族大豆亚族中最大的、具有三小叶复叶的属，其大多数种为攀援性藤本植物，分布于东亚、南亚、东南亚和大洋洲。化石记录表明，葛属早在中新世就已出现在东亚、巴尔干半岛和高加索地区的亚热带和温带植物群中，目前已知有3个化石种，即中国山旺中新世的荚果化石山旺葛藤P. shanwangensis、山旺和日本数个中、上新世产地的叶、小叶化石鲁葛藤P. miothunbergiana以及克罗地亚和格鲁吉亚阿布哈兹中新世的小叶化石大葛藤P. maxima。本文基于对中新世山旺组最近采集的葛属小叶印痕化石的观察和对现生种葛P. montana小叶的形态比较，研究了该属化石种的小叶形态和发育变异。结果表明，现生种葛与化石种鲁葛藤和大葛藤的小叶都具有不甚发育的间二级脉，这个特征在先前报道的鲁葛藤小叶化石中未见保存。另外，它们的主脉和二级脉远轴侧有时都会分别发出两条挨得很近、角度不同的二级脉和二级脉梳脉，这个特征过去在葛属中则被忽视了。总体上，葛属小叶化石的叶脉特征在中新世广阔的欧亚中纬度地区显示了高度的相似性。目前，仅在中国中新世山旺植物群和日本中新世高峰山组植物群中发现了与现生的葛小叶相似的、具有裂瓣的鲁葛藤小叶化石，但现生葛比化石葛的小叶更大些、似乎发育了更多具有裂瓣的小叶，这可能与中新世以来大气二氧化碳浓度的变化有关。现生葛长在荫蔽生境以及攀援于支持物(如藤架或其他木本植物)上的植株比生于开阔生境以及蔓生的植株发育了更多的、具有裂瓣的小叶，这可能有效促进了整株植物的叶片和冠层中的光照截取和通风散热。据此推测，中国和日本中、上新世的鲁葛藤居群可能比克罗地亚和阿布哈兹中新世的大葛藤居群的生态耐受性更加宽泛，东亚的居群既生于荫蔽的、更多依赖森林的生境中，也长在开阔的、较少依赖森林生境中，甚至蔓生。 Pueraria DC. is the largest papilionoid legume, trifoliolate genus of the subtribe Glycininae in the tribe Phaseoleae, the majority species of which are climbing lianas distributed in East Asia, South Asia, Southeast Asia, and Oceania. The known three fossil species of Pueraria described from the subtropical and temperate floras of the Balkan Peninsula, the Caucasus, and eastern Asia respectively are P. shanwangensis (fruit) from the Miocene Shanwang of China, P. miothunbergiana (leaf and leaflet) from the Miocene of Shanwang and numerous localities in the Mio-Pliocene of Japan, and P. maxima (leaflet) from the Miocene of Croatia and Georgian Abkhazia. On the basis of observations on the newly collected Pueraria leaflet impres-sions and comparisons with the leaflets of living P. montana, the morphology and developmental variation of Pueraria leaflet fossils are studied. The result shows that the leaflets of both living species P. montana and fossil species P. miothunbergiana and P. maxima bear poorly developed intersecondary veins, which were not observed in former reports on P. miothunbergiana. Also, two adjacent secondary veins or agrophic veins at different angles are sometimes diverged respectively from the primary vein (midvein) and the exmedial side of secondary veins in both extant and fossil Pueraria leaflets, which is a feature that has long been neglected. Overall, the venation of fossil Pueraria leaflets that are widely occurred across the Miocene of middle lati-tudes in Eurasia is highly similar, but the lobed leaflets similar to those of living P. montana are only discov-ered from the Miocene Shanwang flora of China and Takamine flora of Japan. Extant P. montana bears larger leaflets than fossil Pueraria and seems to have developed more lobed leaflets than fossil P. miothunbergiana does, which might have been related to the change of atmospheric CO2 concentrations since the Miocene onwards. Living individuals of P. montana growing in shady, closed habitats as well as climbing on supports (e.g., pergolas or other woody plants) develop more lobed leaflets than those inhabiting open habitats and trailing, which may efficiently enhance light interception and heat dissipation within leaves and canopies. It is inferred that populations of P. miothunbergiana lived in the Mio-Pliocene of China and Japan may have wider ecological tolerances than those of P. maxima occurred in the Miocene of Croatia and Abkhazia, so the eastern Asian populations may not only live in shady habitats more relied on forests, but also grow in open habitats less relied on forests or even sprawl.

Universal COI primers for DNA barcoding amphibians

DNA barcoding is a proven tool for the rapid and unambiguous identification of species, which is essential for many activities including the vouchering tissue samples in the genome 10K initiative, genealogical reconstructions, forensics and biodiversity surveys, among many other applications. A large-scale effort is underway to barcode all amphibian species using the universally sequenced DNA region, a partial fragment of mitochondrial cytochrome oxidase subunit I COI. This fragment is desirable because it appears to be superior to 16S for barcoding, at least for some groups of salamanders. The barcoding of amphibians is essential in part because many species are now endangered. Unfortunately, existing primers for COI often fail to achieve this goal. Herein, we report two new pairs of primers (➀, ➁) that in combination serve to universally amplify and sequence all three orders of Chinese amphibians as represented by 36 genera. This taxonomic diversity, which includes caecilians, salamanders and frogs, suggests that the new primer pairs will universally amplify COI for the vast majority species of amphibians.

Imbalanced ultracold Fermi gas in the weakly repulsive regime: Renormalization-group approach forp-wave superfluidity

We theoretically study a possible new pairing mechanism for a two-dimensional population imbalanced Fermi gas with short-range repulsive interactions which can be realized on the upper branch of a Feshbach resonance. We use a well-controlled renormalization group approach, which allows an unbiased study of the instabilities of imbalanced Fermi liquid without assumption of a broken symmetry and gives a numerical calculation of the transition temperature from microscopic parameters. Our results show a leading superfluid instability in the p-wave channel for the majority species. The corresponding mechanism is that there are effective attractive interactions for the majority species, induced by the particle-hole susceptibility of the minority species, where the mismatch of the Fermi surfaces of the two species plays an important role. We also propose an experimental protocol for detecting the p-wave superfluidity and discuss the corresponding experimental signatures.

Time-resolved mass spectroscopic studies of an atmospheric-pressure helium microplasma jet

Using molecular beam mass spectroscopy, time-resolved measurements of the ionic species in the plasma plume of an atmospheric-pressure helium microplasma jet are made for a range of excitation frequencies (5, 10 and 25 kHz) and source–instrument orifice distances (1, 7 and 11 mm). Ionic species can only be observed in the visible plasma plume, with the main positive species being (65.26%) and (21.11%), and a few percentages of N+, O+, NO+and He+. For the negative ions, the majority species are (22.68%), (H2O) (10.49%) and a large range of minority species observed, namely , , , and clusters, , , (CO3) and . The flux of ions created from air species, such as NO+ and , is seen to be maximized at a distance of several millimeters from the nozzle, whereas the He+ concentration continually decreases with distance from the exit orifice. The time-resolved measurements (time resolution down to 2 µs) show that positive ions appear twice in one full period of the voltage waveform, correlated directly with positive and negative current peaks. The rise and fall times of the positive ions are typically tens of μs. In contrast, the appearance of negative ions is correlated only with the negative part of discharge current, with one main peak in the detected ionic flux seen per cycle. The rise time of the negative ions is about 10 µs, independent of mass; however, we observed longer decay times, from 100 to 150 µs, increasing with mass. With increased driving frequency, the time modulation in the ionic fluxes is reduced, particularly for the negative species that show almost constant fluxes at 25 kHz throughout the cycle. The observations can be understood through a simple picture of the interaction of the He jet and the moist ambient air. The results indicate that the discrete plasma ‘bullets’ and their afterglow tail, that forms the jet, carry an associated positive or negative current depending on the time of their creation in the voltage cycle.

Postsynthetic Modification of a Metal–Organic Framework for Stabilization of a Hemiaminal and Ammonia Uptake

In our study, we show by solid-state (15)N NMR measurements that an important zirconium metal-organic framework (UiO-66) with amino-functionalized links is composed of a mixture of amino and -NH(3)(+)Cl(-) salt functionalities rather than all amino functionality to give a composition of Zr(6)O(4)(OH)(4)(BDC-NH(2))(4)(BDC-NH(3)(+)Cl(-))(2) (UiO-66-A). UiO-66-A was postsynthetically modified to form a mixture of three functionalities, where the hemiaminal functionality is the majority species in UiO-66-B and aziridine is the majority functionality in UiO-66-C. UiO-66-A-C are all porous with surface areas ranging from 780 to 820 m(2)/g and have chemical stability, as evidenced by reversible ammonia uptake and release showing capacities ranging from 134 to 193 cm(3)/g.

Solid Base CaO Catalyzed Methanolysis of Lignite

Solid base CaO was prepared and characterized, which was used to catalyze depolymerization of lignite in supercritical methanol. Methanolysis products were analyzed by gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR). The results showed that the solubility of methanolysis products in organic solvent increased, the majority species of methanolysis products were aliphatic hydrocarbon and oxygenated compounds such as alkyl substitution phenol. CaO can catalyze selective depolymerization of lignite with the reaction of cleavage of ether bond under given condition.

Experimental (XAS, STEM, TPR, and XPS) and Theoretical (DFT) Characterization of Supported Rhenium Catalysts

A high surface area supported Re-based catalyst, fundamental to heterogeneous catalysis, is studied in the oxidic and reduced states using a combination of experimental (XAFS, STEM, TPR, and XPS) and theoretical (DFT and X-ray spectroscopy simulations) approaches. In the calcined dried catalyst, the Re species is present as an isolated trioxo(oxoaluminate) Re(VII) species. The temperature at which the Re undergoes reduction is a function of the hydrogen partial pressure and temperature ramp rate, but the maximum rate of reduction occurs in the range 300−400 °C. Following reduction at 500 or 700 °C in dry hydrogen, the Re is present as a mixture of species: unreduced trioxo(oxoaluminate) Re(VII) species, Re nanoclusters, and isolated Re atoms. By using a multifaceted approach, it is apparent that the majority species is an isolated Re adatom bound to the alumina support. DFT calculations identify several likely adsorption sites for these Re adatoms on the [110] surface of γ-Al2O3. The final extended X-ray absorption fine structure (EXAFS) model taking into account these three species is used to identify the dominant adsorption site for Re on the alumina surface. FEFF8 X-ray absorption near-edge spectroscopy (XANES) calculations of unsupported and alumina-supported Re nanoclusters provide interpretation of the shape and edge position of the Re L3-edge XANES after reduction. The presence of moisture during reduction strongly affects the mobility of the Re on the alumina leading to agglomeration. Subsequent air exposure of a reduced catalyst readily reoxidizes the reduced Re. The power of using a combination of analysis tools provides insight into the behavior of dispersed Re on supported alumina under oxidizing and reducing conditions relevant to heterogeneous catalysis.

Adsorption and reaction of SO2 on clean and oxygen precovered Pd(100)—a combined HR-XPS and DF study

We studied the adsorption and reactivity of SO(2) on clean and oxygen precovered Pd(100) with high resolution X-ray photoelectron spectroscopy and density functional calculations. Upon adsorption at 120 K two different SO(2) species were detected, which were identified as upright-standing and flat-lying molecules by comparing the calculated core level shifts. In agreement with the relative stabilities determined by the calculations the intensities of the photoelectron spectra indicate that the majority species are upright-standing SO(2). Upon heating the quantitative analysis of the data indicates desorption of SO(3) and formation of atomic sulfur. On the oxygen precovered surface small amounts of SO(3) are formed already upon SO(2) adsorption at low temperatures. Upon heating stepwise oxidation of SO(2) to SO(3) and, eventually, to SO(4) is found. Two different SO(4) species were detected, which are assigned to SO(4) bound in the proximity of or remote from oxygen adatoms, according to core level shift estimates.

Two new species of Paratanytarsus (Diptera: Chironomidae) from southeast of Brazil

The adults and immature stages of Paratanytarsus corbii sp. n. and the male adult of Paratanytarsus silentii sp. n. are described and illustrated. P. corbii larvae were collected on sediment and aquatic vegetation of the headwater of the Anhumas Reservoir (Américo Brasiliense, SP) and reared in laboratory to obtain the pupal exuviae and associated adults. The adult males of P. silentii were obtained from Malaise net put over the Córrego do Silêncio located in Parque Estadual do Jaraguá (São Paulo, SP). The shape of the anal point and the absence of anal point crests are the main characteristics that distinguish P. corbii and P. silentii males from the majority species of the genus. The arrangement of spines on tergites III–V separates the pupae of P. corbii from other species. The length of pedicels and the pecten epipharyngis design are diagnostic for the larvae of P. corbii.

Comment on “Normal Phase of an Imbalanced Fermi Gas”

Recently Mora and Chevy [Phys. Rev. Lett. 104, 230402 (2010), arXiv:1003.0213v2], in studying the energy of an atomic Fermi gas consisting of a majority species, 1, and a minority species, 2, showed that, due to interatomic interactions, the energy density E of the gas has a contribution of the form E^(2)= f n_2^2 /2, where n_i is the density of species i. They attribute this term to a `modification of the single polaron properties due to Pauli blocking'. In this Comment, we demonstrate that E^(2) may equivalently be understood in terms of the familiar interaction between minority atoms induced by the majority component.