6,659 research outputs found
Orbital-Free Density Functional Theory: Kinetic Potentials and Ab-Initio Local Pseudopotentials
In the density functional (DF) theory of Kohn and Sham, the kinetic energy of
the ground state of a system of noninteracting electrons in a general external
field is calculated using a set of orbitals. Orbital free methods attempt to
calculate this directly from the electron density by approximating the
universal but unknown kinetic energy density functional. However simple local
approximations are inaccurate and it has proved very difficult to devise
generally accurate nonlocal approximations. We focus instead on the kinetic
potential, the functional derivative of the kinetic energy DF, which appears in
the Euler equation for the electron density. We argue that the kinetic
potential is more local and more amenable to simple physically motivated
approximations in many relevant cases, and describe two pathways by which the
value of the kinetic energy can be efficiently calculated. We propose two
nonlocal orbital free kinetic potentials that reduce to known exact forms for
both slowly varying and rapidly varying perturbations and also reproduce exact
results for the linear response of the density of the homogeneous system to
small perturbations. A simple and systematic approach for generating accurate
and weak ab-initio local pseudopotentials which produce a smooth slowly varying
valence component of the electron density is proposed for use in orbital free
DF calculations of molecules and solids. The use of these local
pseudopotentials further minimizes the possible errors from the kinetic
potentials. Our theory yields results for the total energies and ionization
energies of atoms, and for the shell structure in the atomic radial density
profiles that are in very good agreement with calculations using the full
Kohn-Sham theory.Comment: To be published in Phys. Rev.
Regulation of the flowering time of Arabidopsis thaliana by thylakoid ascorbate peroxidase
Flowering time of higher plants is precisely controlled by various exogenous and endogenous factors. Recent researches implied that H2O2 is a potential flowering initiation factor. In order to confirm this hypothesis, thylakoid ascorbate peroxidase (tAPX) overexpressing Arabidopsis, the mutant line containing a T-DNA insertion and the wild type have been analyzed in this study, since APX was an important enzyme scavenging H2O2 in plant cells. It was found that during the vegetative growth stage there was no phenotypic difference among the three lines under common conditions, but 3,3â-diaminobenzidinetetrahydrochloride (DAB) staining showed that the endogenous H2O2 content varied: the mutant line had the highest content; the wild type took the second place, while the tAPX-overexpressing line had the lowest H2O2 content. This trend was in accordance with the bolting and flowering time during the following reproductive growth stage: the mutant bolted and flowered first, followed by the wild type, and the overexpressing line bolted and flowered last. This correlation confirmed the previous hypothesis that âH2O2 is a possible factor in flowering inductionâ.Keywords: Ascorbate peroxidase, Arabidopsis thaliana, flowering time, hydrogen peroxide
Precise Measurement of Gravity Variations During a Total Solar Eclipse
The variations of gravity were measured with a high precision LaCoste-Romberg
D gravimeter during a total solar eclipse to investigate the effect of solar
eclipse on the gravitational field. The observed anomaly m/s during the eclipse implies that there may be a shielding
property of gravitation
Do human neutrophils make hydroxyl radical? Detection of free radicals by human neutrophils activated with a soluble or particulate stimulus using electron paramagnetic resonance spectrometry
Using electron paramagnetic resonance spectrometry and the spin trap 5,5-dimethyl-1-oxide (DMPO), neutrophil free radical production in response to phorbol myristate acetate and opsonized zymosan was investigated. Using phorbol myristate acetate and zymosan (3 mg/ml), the superoxide spin-trapped adduct 2-2-dimethyl-5-hydroperoxy-1-pyrrolidinyloxyl (DMPO-OOH) and the hydroxyl spin-trapped adduct 2-2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO-OH) were detected. Only DMPO-OH was observed with zymosan (0.5 mg/ml). Hydroxyl radical production in the presence of dimethylsulfoxide (Me2SO) and DMPO yields 2,2,5-trimethyl-1-pyrrolidinyloxyl. The only 2,2-trimethyl-1-pyrrolidinyloxyl detected following neutrophil stimulation was that expected from DMPO-OOH degradation. Superoxide dismutase but not catalase inhibited generation of all three spin-trapped adducts. These data indicate that DMPO-OH arose from DMPO-OOH degradation and does not represent hydroxyl radical production. Under certain conditions DMPO-OH is the predominant spin-trapped adduct resulting from neutrophil superoxide production, perhaps due to cellular bioreduction of DMPO-OOH to DMPO-OH. Cytochalasin B, which prevents phagosome closure, inhibited zymosan-stimulated neutrophil oxygen consumption and electron paramagnetic resonance superoxide detection. No hydroxyl radical was detected. Spin trapping with DMPO appears to detect intraphagosomal free-radical formation
Purification, Cloning, Characterization and Essential Amino Acid Residues Analysis of a New iota-Carrageenase from Cellulophaga sp QY3
Îč-Carrageenases belong to family 82 of glycoside hydrolases that degrade sulfated galactans in the red algae known as Îč-carrageenans. The catalytic mechanism and some substrate-binding residues of family GH82 have been studied but the substrate recognition and binding mechanism of this family have not been fully elucidated. We report here the purification, cloning and characterization of a new Îč-carrageenase CgiA_Ce from the marine bacterium Cellulophaga sp. QY3. CgiA_Ce was the most thermostable carrageenase described so far. It was most active at 50°C and pH 7.0 and retained more than 70% of the original activity after incubation at 50°C for 1 h at pH 7.0 or at pH 5.0â10.6 for 24 h. CgiA_Ce was an endo-type Îč-carrageenase; it cleaved Îč-carrageenan yielding neo-Îč-carrabiose and neo-Îč-carratetraose as the main end products, and neo-Îč-carrahexaose was the minimum substrate. Sequence analysis and structure modeling showed that CgiA_Ce is indeed a new member of family GH82. Moreover, sequence analysis of Îč-carrageenases revealed that the amino acid residues at subsites â1 and +1 were more conserved than those at other subsites. Site-directed mutagenesis followed by kinetic analysis identified three strictly conserved residues at subsites â1 and +1 of Îč-carrageenases, G228, Y229 and R254 in CgiA_Ce, which played important roles for substrate binding. Furthermore, our results suggested that Y229 and R254 in CgiA_Ce interacted specifically with the sulfate groups of the sugar moieties located at subsites â1 and +1, shedding light on the mechanism of Îč-carrageenan recognition in the family GH82
Vision-related Quality of Life and Emotional Impact in Children with Strabismus: a Prospective Study
The potential impact of the surgical correction of strabismus on vision-related quality of life (VRQOL) and the symptoms of anxiety and depression in children with strabismus remain unclear. The present study included 60 children with strabismus: 30 with heterophoria and 30 with heterotropia. A healthy age- and gender-matched control group (n = 60) was also recruited. The psychological instruments that were used were the short-form 25-item National Eye Institute Visual Functioning Questionnaire (NEI-VFQ-25) and the Hospital Anxiety and Depression Scale (HADS). The results demonstrated that eight of the 12 NEI-VFQ-25 subscales were significantly impaired in children with strabismus compared with matched controls. Compared with pre-operative values, significant improvements were noted after surgery in the NEI-VFQ-25 summary score, and the anxiety and depression scores. This study demonstrated that the NEI-VFQ-25 instrument can be used in strabismus children and that surgical interventions can improve VRQOL, anxiety and depression in strabismus patients
The Magnetic Field Structure of Mercuryâs Magnetotail
In this study, we use the magnetic field data measured by MErcury Surface, Space ENvironment, GEochemistry, and Ranging from 2011 to 2015 to investigate the average magnetic field morphology of Mercuryâs magnetotail in the down tail 0â3 RM (RMÂ =Â 2,440Â km, Mercuryâs radius). It is found that Mercury has a terrestrialâlike magnetotail; the magnetic field structure beyond 1.5 RM down tail is stretched significantly with typical lobe field 50Â nT. A crossâtail current sheet separating the antiparallel field lines of lobes is present in the equatorial plane. The magnetotail width in northâsouth direction is about 5 RM, while the transverse width is about 4 RM. Thus, the magnetotail shows elongation along the northâsouth direction. At the crossâtail current sheet center, the normal component of magnetic field (10â20Â nT) is much larger than the crossâtail component. The lobeâfieldâaligned component of magnetic field over current sheet can be well fitted by Harris sheet model. The curvature radius of field lines at sheet center usually reaches a minimum around midnight (100â200Â km) with stronger current density (40â50Â nA/m2), while the curvature radius increases toward both flanks (400â600Â km) with the decreased current density (about 20Â nA/m2). The halfâthickness of current sheet around midnight is about 0.25 RM or 600Â km, and the inner edge of current sheet is located at the down tail about 1.5 RM. Our results about the field structure in the near Mercuryâs tail show an evident dawnâdusk asymmetry as that found in the Earthâs magnetotail, but reasons should be different. Possible reasons are discussed.Key PointsThe magnetic field distribution, configuration, and current density in Mercuryâs magnetotail are quantitatively addressedMercuryâs magnetotail is elongated along the southânorth direction, which is probably due to the effect of the dipole offset or the induction effect of coreThe magnetic structure of tail current sheet shows a clear dawnâdusk asymmetry with smaller Bz and less flaring field on the dusksidePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142544/1/jgra54041.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142544/2/jgra54041_am.pd
Pyridine functionalized carbon nanotubes: unveiling the role of external pyridinic nitrogen sites for oxygen reduction reaction.
Pyridinic nitrogen has been recognized as the primary active site in nitrogen-doped carbon electrocatalysts for the oxygen reduction reaction (ORR), which is a critical process in many renewable energy devices. However, the preparation of nitrogen-doped carbon catalysts comprised of exclusively pyridinic nitrogen remains challenging, as well as understanding the precise ORR mechanisms on the catalyst. Herein, a novel process is developed using pyridyne reactive intermediates to functionalize carbon nanotubes (CNTs) exclusively with pyridine rings for ORR electrocatalysis. The relationship between the structure and ORR performance of the prepared materials is studied in combination with density functional theory calculations to probe the ORR mechanism on the catalyst. Pyridinic nitrogen can contribute to a more efficient 4-electron reaction pathway, while high level of pyridyne functionalization result in negative structural effects, such as poor electrical conductivity, reduced surface area, and small pore diameters, that suppressed the ORR performance. This study provides insights into pyridine-doped CNTs-functionalized for the first time via pyridyne intermediates-as applied in the ORR and is expected to serve as valuable inspiration in designing high-performance electrocatalysts for energy applications
A universal pH range and a highly efficient Mo2C-based electrocatalyst for the hydrogen evolution reaction
Electrochemical water splitting is a promising approach to generate âgreenâ hydrogen. The efficiency of this process relies on the effectiveness of the electrocatalysts used. The electro-kinetics of the hydrogen evolution reaction (HER) is highly pH dependent and conventional catalysts typically are expensive and rare platinum-based materials. The development of low-cost, multi-component electrocatalysts, where each of the components has a synergistic effect, can be an effective approach to improve kinetics. Herein, a series of transition metal (Fe, Mn, Co, and Ni)-modified molybdenum carbides in a nitrogen-doped carbon matrix (TM-Mo2C@NCF) are synthesised to maximise exposed active sites. Among them, Fe-Mo2C@NCF delivers the best-in-class HER performance over a wide range of electrolytes. Tafel slopes of 76, 109 and 110 mV decâ1 and overpotentials of 65, 130 and 129 mV at 10 mA cmâ2 were obtained in 1.0 M KOH, 1.0 M phosphate buffer solution (PBS) and 0.5 M H2SO4, respectively. The computational study further indicates that the synergistic electronic modulation co-activated by Fe and N dopants in Fe-Mo2C@NCF can reduce the Gibbs free energy of H adsorption (ÎGH*) and render the MoâMo bridge site the most energetically favorable adsorption site for the H* intermediate, which contributes to an increased HER performance
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