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1.
Using first-principles calculations based on density functional theory, we demonstrate that Si60 fullerene cage can be stabilized by exohydrogenated method. In contrast to previous theoretical studies that Si60 fullerene geometry construction will be seriously distorted when it is bare or encapsulated by metal atom clusters, exohydrogenated scheme shows that Si60H60 cage will be able to keep perfect fullerene structure similar to C60. 相似文献
2.
The structures and stabilities of As2-doped Sin (n = 1-7) clusters have been investigated at the B3LYP level of theory, incorporating the 6-311+G∗ basis set. An isosceles triangle is predicted to be the lowest-energy structure of the As2Si cluster, whereas the global minimum of As2Si2 possesses an As-As-butterfly structure. The ground state structures for As2Si3, As2Si4 and As2Si5 are all bipyramids: trigonal, tetragonal and pentagonal, respectively, which could have important applications as building blocks to synthesize silicon nanowires. The most stable isomer of As2Si6 possesses a tricapped trigonal bipyramid structure. The lowest energy structure of As2Si7 can be viewed as a substitutional structure of the tricapped trigonal prism Si9 isomer. In the majority of the lowest energy isomers, the two As atoms tend to be separated from each other, in order to maximize the number of Si-As bonds, and therefore locate at the axial vertex or face-capping atomic positions, especially for As2Si4-As2Si7. According to results of the incremental binding energies, the HOMO-LUMO gaps and the vertical ionization potentials, the As2Si3 and As2Si6 clusters are relatively stable compared to their neighbors. Natural bond orbital analyses suggest that delocalized electrons and multi-centered bonds play an important role in stabilizing the low-energy As2Sin structures. 相似文献
3.
Jasper Kunow Beatrix Schwörer Karl O. Stetter Rudolf K. Thauer 《Archives of microbiology》1993,160(3):199-205
Archaeoglobus fulgidus, a sulfate-reducing Archaeon with a growth temperature optimum of 83°C, uses the 5-deazaflavin coenzyme F420 rather than pyridine nucleotides in catabolic redox processes. The organism does, however, require reduced pyridine nuclcotides for biosynthetic purposes. We describe here that the Archaeon contains a coenzyme F420-dependent NADP reductase which links anabolism to catabolism. The highly thermostable enzyme was purfied 3600-fold by affinity chromatography to apparent homogeneity in a 60% yield. The native enzyme with an apparent molecular mass of 55 kDa was composed of only one type of subunit of apparent molecular mass of 28 kDa. Spectroscopic analysis of the enzyme did not reveal the presence of any chromophoric prosthetic group. The purified enzyme catalyzed the reversible reduction of NADP (apparent K
M 40 M) with reduced F420 (apparent K
M 20M) with a specific activity of 660 U/mg (apparent V
max) at pH 8.0 (pH optimum) and 80°C (temperature optimum). It was specific for both coenzyme F420 and NADP. Sterochemical investigations showed that the F420-dependent NADP reductase was Si face specific with respect to C5 of F420 and Si face specific with respect to C4 of NADP.Abbreviations F420
coenzyme F420
- F420H2
1,5-dihydrocoenzyme F420
- H4MPT
tetrahydromethanopterin
- CH=H4MPT
N5, N10-methylenetetrahydromethanopterin
- MFR
methanofuran
- HPLC
high performance liquid chromatography
- methylene-H4MPT dehydrogenase
N5, N10-methylenetetrahydromethanopterin dehydrogenase
- 1 U =
1 mol/min 相似文献
4.
Javad Beheshtian Ali Ahmadi Peyghan Zargham Bagheri 《Journal of molecular modeling》2013,19(2):833-837
Adsorption of arsenic ions, As (III and V), on the surface of fullerene-like B12N12 cage has been explored in vacuum and aqueous phase using density functional theory in terms of Gibbs free energies, enthalpies, geometry, and density of state analysis. It was found that these ions can be strongly chemisorbed on the surface of the cluster in both vacuum and aqueous phase, resulting in significant changes in its electronic properties so that the cluster transforms from a semi-insulator to a semiconductor. The solvent significantly affects the geometry parameters and electronic properties of the As/B12N12 complexes and the interaction between components is considerably weaker in the aqueous phase than that in the vacuum. 相似文献
5.
The structure and stability of 22 B36N36 cage molecules containing four-membered (F
4), five-membered (F
5), six-membered (F
6), eight-membered (F
8) and 12-membered (F
12) rings have been computed at the B3LYP/6-31G* level of density functional theory. The most stable structure (1) has T
d symmetry with six F
4 and 32 F
6 rings, following the isolated square rule, while the fullerene-like structures (12 F
5 and 26 F
6) and also structures with F
8 and F
12 are much higher in energy.
Figure
The T
d symmetrical structure (1) with six F
4 and thirty-two F
6 rings is the most stable B36N36 cage. 相似文献
6.
The effect of tree height on crown level stomatal conductance 总被引:19,自引:6,他引:13
Variation in stomatal conductance is typically explained in relation to environmental conditions. However, tree height may also contribute to the variability in mean stomatal conductance. Mean canopy stomatal conductance of individual tree crowns (GSi) was estimated using sap flux measurements in Fagus sylvatica L., and the hypothesis that GSi decreases with tree height was tested. Over 13 d of the growing season during which soil moisture was not limiting, GSi decreased linearly with the natural logarithm of vapour pressure deficit (D), and increased exponentially to saturation with photosynthetic photon flux density (Qo). Under conditions of D = 1 kPa and saturating Qo, GSi decreased by approximately 60% with 30 m increase in tree height. Over the same range in height, sapwood‐to‐leaf area ratio (AS:AL) doubled. A simple hydraulic model explained the variation in GSi based on an inverse relationship with height, and a linear relationship with AS:AL. Thus, in F. sylvatica, adjustments in AS:AL partially compensate for the negative effect of increased flow‐path length on leaf conductance. Furthermore, because stomata with low conductance are less sensitive to D, gas exchange of tall trees is reduced less by high D. Despite these compensations, decreasing hydraulic conductance with tree height in F. sylvatica reduces carbon uptake through a corresponding decrease in stomatal conductance. 相似文献
7.
A Low Resistance Calcium/Reduced Titania Passivated Contact for High Efficiency Crystalline Silicon Solar Cells
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Thomas G. Allen James Bullock Quentin Jeangros Christian Samundsett Yimao Wan Jie Cui Aïcha Hessler‐Wyser Stefaan De Wolf Ali Javey Andres Cuevas 《Liver Transplantation》2017,7(12)
Recent advances in the efficiency of crystalline silicon (c‐Si) solar cells have come through the implementation of passivated contacts that simultaneously reduce recombination and resistive losses within the contact structure. In this contribution, low resistivity passivated contacts are demonstrated based on reduced titania (TiOx) contacted with the low work function metal, calcium (Ca). By using Ca as the overlying metal in the contact structure we are able to achieve a reduction in the contact resistivity of TiOx passivated contacts of up to two orders of magnitude compared to previously reported data on Al/TiOx contacts, allowing for the application of the Ca/TiOx contact to n‐type c‐Si solar cells with partial rear contacts. Implementing this contact structure on the cell level results in a power conversion efficiency of 21.8% where the Ca/TiOx contact comprises only ≈6% of the rear surface of the solar cell, an increase of 1.5% absolute compared to a similar device fabricated without the TiOx interlayer. 相似文献
8.
K.-D. Kim 《Molecular simulation》2013,39(12):825-830
In this paper, a novel device structure (Si1 ? x Ge x /Si/Si1 ? x Ge x hetero-structure), which is named as “center-channel (CC) double-gate (DG) MOSFET,” is proposed. Device performance of the proposed FET structure was investigated with our two-dimensional quantum-mechanical simulator which produces a self-consistent solution of Poisson–Schrödinger equations and the current continuity equation. The CC operation of CC-NMOS is confirmed from the electron density distribution and the band lineups as well as the lowest energy wave function. Current–voltage characteristics including the trans-conductance (G m) of CC-MOSFET are carefully compared with those of the conventional DG-NMOS to evaluate the distinct feature of the proposed FET structure. Our simulation revealed that the proposed FET demonstrates the enhanced (about (~1.6 × ) current drive and 60% G m. Finally, the short-channel effects of CC and DG MOSFET, both of which demonstrate excellent sub-threshold behaviors and open the possibility of device scaling down to sub-20 nm. 相似文献
9.
Zhidan Zeng Qingfeng Zeng Nian Liu Artem R. Oganov Qiaoshi Zeng Yi Cui Wendy L. Mao 《Liver Transplantation》2015,5(12)
Li15Si4, the only crystalline phase that forms during lithiation of the Si anode in lithium‐ion batteries, is found to undergo a structural transition to a new phase at 7 GPa. Despite the large unit cell of Li15Si4 (152 atoms in the unit cell), ab initio evolutionary metadynamics (using the USPEX code) successfully predicts the atomic structure of this new phase (β‐Li15Si4), which has an orthorhombic structure with an Fdd2 space group. In the new β‐Li15Si4 phase Si atoms are isolated by Li atoms analogous to the original cubic phase (α‐Li15Si4), whereas the atomic packing is more efficient owing to the higher Si? Li coordination number and shorter Si? Li, Li? Li bonds. β‐Li15Si4 has substantially larger elastic moduli compared with α‐Li15Si4, and has a good electrical conductivity. As a result, β‐Li15Si4 has superior resistance to deformation and fracture under stress. The theoretical volume expansion of Si would decrease 25% if it transforms to β‐Li15Si4, instead of α‐Li15Si4, during lithiation. Moreover, β‐Li15Si4 can be recovered back to ambient pressure, providing opportunities to further investigate its properties and potential applications. 相似文献
10.
Jian-Ying Li Li-Min Liu Bo Jin Hua Liang Hai-Jun Yu Hong-Chang Zhang Shi-Jin Chu Ru-Fang Peng 《Journal of molecular modeling》2013,19(4):1705-1710
The applications of endohedral non-metallic fullerenes are limited by their low production rate. Recently, an explosive method developed in our group shows promise to prepare He@C60 at fairly high yield, but the mechanism of He inserting into C60 cage at explosive conditions was not clear. Here, ab initio molecular dynamics analysis has been used to simulate the collision between C60 molecules at high-temperature and high-pressure induced by explosion. The results show that defects formed on the fullerene cage by collidsion can effectively decrease the reaction barrier for the insertion of He into C60, and the self-healing capability of the defects was also observed. Figure
Simulation of He@C60 formation by explosive method. Ab initio molecular dynamics has been used to simulate collision of C60. Defects caused by fullerenes reaction in explosion are shown by theory. The defects decrease the reaction barrier for He inserting into C60 cage. The method provides a promising technique to synthesized He@C60 相似文献
11.
Sheka EF 《Journal of molecular modeling》2012,18(4):1409-1420
The cyanation of C60 to C60(CN)18 and the aziridination of C60 to C60(NH)9 were studied by an unrestricted broken spin symmetry Hartree–Fock approach implemented in semiempirical codes based on the
AM1 technique. The calculations focused on the successive addition of CN and NH moieties to the fullerene cage following the
identification of the target cage atoms as those with the highest atomic chemical susceptibilities calculated at each step.
The results obtained were analyzed from the viewpoint of the parallelism between these derivatives as well as C60 fluorides and hydrides. The difference between the first-stage C60 chlorination and other sterically free processes is discussed. 相似文献
12.
Sheka EF 《Journal of molecular modeling》2011,17(8):1973-1984
Hydrogenation from C60 to C60H60 was studied by an unrestricted broken spin symmetry Hartree–Fock approach implemented in semiempirical codes based on the
AM1 technique. The calculations focused on the successive addition of hydrogen molecules to the fullerene cage following the
identification of the cage target atoms by calculating the highest atomic chemical susceptibility at each step. The results
obtained are analyzed from energy, symmetry, and composition perspectives. 相似文献
13.
Grigory V. Andrievsky Vadim I. Bruskov Artem A. Tykhomyrov Sergey V. Gudkov 《Free radical biology & medicine》2009,47(6):786-793
Aqueous solutions of highly stable supramolecular donor–acceptor complexes of chemically nonmodified pristine C60 fullerene molecules with H2O molecules (hydrated C60 fullerene–C60HyFn) and their labile nano-sized clusters were examined for their antioxidant effects on removal of hydroxyl radicals (OH) and protecting DNA against oxidative damage induced by ionizing radiation in vitro. The suppressing influence of C60HyFn on the formation of OH-radicals in water exposed to X-rays at doses of 1–7 Gy was assessed by determination of oxidation levels of coumarin-3-carboxylic acid. C60HyFn demonstrates apparent antiradical activity in vitro in the range of concentrations of 10−11–10−6 M. Paradoxically, the OH-removing efficacy of C60HyFn was in reverse correlation with fullerene concentration. It was hypothesized that the antiradical action of C60HyFn in water medium generally is due to a “nonstoichiometric” mechanism, supposedly to a hydrated free radical recombination (self-neutralization), which is catalyzed by specific water structures ordered by C60HyFn. With the use of 8-oxoguanine as a marker of oxidative damage to DNA, it has been demonstrated that C60HyFn in concentrations of 10−7–10−6 M protects nucleic acids against radical-induced damage. The second part of the present study was aimed to evaluate the overall radioprotective efficacy of C60HyFn in doses of 0.1 or 1 mg/kg b.w. injected intraperitoneally to mice either 1 h before or 15 min after lethal dose exposure of the X-ray (7 Gy) irradiation. Survival rate of the mice was observed at 30 day intervals after irradiation, while the weight gains of experimental animals were monitored as well. The most significant protective effect was demonstrated when 1 mg/kg dosage of C60HyFn was administered before irradiation. The outcome of the substance testing is 15% survival rate of irradiated animals at 30 days of observation, and prevention of noticeable weight loss characteristic for radiation impact, versus unprotected control animals. In conclusion, results of the study obviate that the apparent protective action of C60HyFn in vivo is determined by its considerable ability to decrease X-ray-generated reactive oxygen species. Based on the results and that neat C60 is nontoxic, actually in the hydrated form, without side effects and with sufficient radioprotective effects in low doses, C60HyFn may be considered as a novel antioxidant agent, which substantially diminishes the harmful effects of ionizing radiation. 相似文献
14.
Approaching the Minimum Thermal Conductivity in Rhenium‐Substituted Higher Manganese Silicides
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Xi Chen Steven N. Girard Fei Meng Edgar Lara‐Curzio Song Jin John B. Goodenough Jianshi Zhou Li Shi 《Liver Transplantation》2014,4(14)
Higher manganese silicides (HMS) made of earth‐abundant and non‐toxic elements are regarded as promising p‐type thermoelectric materials because their complex crystal structure results in low lattice thermal conductivity. It is shown here that the already low thermal conductivity of HMS can be reduced further to approach the minimum thermal conductivity via partial substitution of Mn with heavier rhenium (Re) to increase point defect scattering. The solubility limit of Re in the obtained RexMn1‐xSi1.8 is determined to be about x = 0.18. Elemental inhomogeneity and the formation of ReSi1.75 inclusions with 50?200 nm size are found within the HMS matrix. It is found that the power factor does not change markedly at low Re content of x ≤ 0.04 before it drops considerably at higher Re contents. Compared to pure HMS, the reduced lattice thermal conductivity in RexMn1‐xSi1.8 results in a 25% increase of the peak figure of merit ZT to reach 0.57 ± 0.08 at 800 K for x = 0.04. The suppressed thermal conductivity in the pure RexMn1‐xSi1.8 can enable further investigations of the ZT limit of this system by exploring different impurity doping strategies to optimize the carrier concentration and power factor. 相似文献
15.
In Situ Grain Boundary Functionalization for Stable and Efficient Inorganic CsPbI2Br Perovskite Solar Cells
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Zhaobing Zeng Jing Zhang Xinlei Gan Hongrui Sun Minghui Shang Dagang Hou Chaojie Lu Renjie Chen Yuejin Zhu Liyuan Han 《Liver Transplantation》2018,8(25)
The phase instability and large energy loss are two obstacles to achieve stable and efficient inorganic‐CsPbI3?xBrx perovskite solar cells. In this work, stable cubic perovskite (α)‐phase CsPbI2Br is successfully achieved by Pb(Ac)2 functioning at the grain boundary under low temperature. Ac? strongly coordinates with CsPbI2Br to stabilize the α‐phase and also make the grain size smaller and film uniform by fast nucleation. PbO is formed in situ at the grain boundary by decomposing Pb(Ac)2 at high‐temperature annealing. The semiconducting PbO effectively passivates the surface states, reduces the interface recombination, and promotes the charge transport in CsPbI2Br perovskite solar cells. A 12% efficiency and good stability are obtained for in situ PbO‐passivated CsPbI2Br solar cells, while Pb(Ac)2‐passivated device exhibits 8.7% performance and the highest stability, much better than the control device with 8.5% performance and inferior stability. This article highlights the extrinsic ionic grain boundary functionalization to achieve stable and efficient inorganic CsPbI3?xBrx materials and the devices. 相似文献
16.
Toshihiko Ogura 《Biochemical and biophysical research communications》2009,385(4):624-202
We introduced a novel X-ray microscope system based on scanning electron microscopy using thin film, which enables the measurement of unstained biological samples without damage. An unstained yeast sample was adsorbed under a titanium (Ti)-coated silicon nitride (Si3N4) film 90 nm thick. The X-ray signal from the film was detected by an X-ray photodiode (PD) placed below the sample. With an electron beam at 2.6 kV acceleration and 6.75 nA current, the yeast image is obtained using the X-ray PD. The image is created by soft X-rays from the Ti layer. The Ti layer is effective in generating the characteristic 2.7-nm wavelength X-rays by the irradiation of electrons. Furthermore, we investigated the electron trajectory and the generation of the characteristic X-rays within the Ti-coated Si3N4 film by Monte Carlo simulation. Our system can be easily utilized to observe various unstained biological samples of cells, bacteria, and viruses. 相似文献
17.
2015年12月—2016年10月,每月小潮日原位定期向闽江口塔礁洲淡水感潮野慈姑(Sagittaria trifolia L.)湿地施加剂量为60、120 kg S hm~(-2)a~(-1)的K_2SO_4溶液(分别记做S-60和S-120),探讨模拟硫酸根(SO_4~(2-))沉降对河口淡水感潮湿地甲烷(CH4)排放通量及间隙水SO_4~(2-)浓度的影响。对照、S-60和S-120处理组CH_4排放通量年均值分别为(7.88±1.00)mg h~(-1)m~(-2)、(6.55±0.97)mg h~(-1)m~(-2)和(6.66±1.49)mg h~(-1)m~(-2)。在年尺度上,两个高强度模拟SO_4~(2-)沉降处理组均未显著降低闽江口淡水感潮野慈姑湿地CH_4排放通量(P0.05),即高强度SO_4~(2-)沉降不会对河口淡水感潮湿地CH_4排放通量产生类似于其对泥炭湿地和水稻田的显著抑制效应。在年尺度以及秋、冬季,两个施加K_2SO_4溶液处理显著增加了野慈姑湿地10 cm深度土壤间隙水SO_4~(2-)浓度。对于各个处理组,温度较高的夏、秋季CH_4排放通量均显著高于温度相对较低的冬、春季(P0.05)。不同处理组CH_4排放通量均与土壤温度呈显著正相关关系,温度仍然是影响亚热带河口淡水感潮湿地CH_4排放通量的重要环境因子。 相似文献
18.
We report a molecular simulation study to investigate the decomposition of CH4 hydrate. The decomposition is revealed to be stepwise from the outer to inner layers. Upon decomposition, the number of 51262 cages drops faster than that of 512 cages. CH4 molecules are released, dissolved in water, then enter gas phase; meanwhile, CH4 bubbles may form particularly at a high temperature. Based on the variations of potential energy, order parameter, cage number and density profile of CH4 at different temperatures (300, 330, 345 and 360 K) and NaCl concentrations (0, 0.6 and 1.8 M), the effects of temperature and salt are comprehensively examined. With increasing temperature, the decomposition in pure water is accelerated, whereas two opposite effects are observed in NaCl solution. At 330 K, the decomposition is retarded at a higher NaCl concentration, as attributed to the reduced CH4 solubility in NaCl solution and the participation of ions in cage formation; at 360 K, however, the decomposition is accelerated when NaCl concentration increases due to bubble formation. This simulation study provides microscopic insights into hydrate decomposition, which might be useful towards the optimisation of operating conditions for CH4 production from CH4 hydrate. 相似文献
19.
Cholinergic muscarinic receptors, when stimulated by arecoline, can activate cytosolic phospholipase A2 (cPLA2) to release arachidonic acid (AA) from membrane phospholipid. This signal can be imaged in the brain in vivo using quantitative
autoradiography following the intravenous injection of radiolabeled AA, as an increment in a regional brain AA incorporation
coefficient k*. Arecoline increases k* significantly in brain regions having muscarinic M1,3,5 receptors in wild-type but not in cyclooxygenase (COX)-2 knockout mice. To further clarify the roles of COX enzymes in the
AA signal, in this paper we imaged k* following arecoline (5 mg/kg i.p.) or saline in each of 81 brain regions of unanesthetized rats pretreated 6 h earlier with
the non-selective COX inhibitor flurbiprofen (FB, 60 mg/kg s.c.) or with vehicle. Baseline values of k* were unaffected by FB treatment, which however reduced by 80% baseline brain concentrations of prostaglandin E2 (PGE2) and thromboxane B2 (TXB2), eicosanoids preferentially derived from AA via COX-2 and COX-1, respectively. In vehicle-pretreated rats, arecoline increased the brain PGE2 but not TXB2 concentration, as well as values for k* in 77 of the 81 brain regions. FB-pretreatment prevented these arecoline-provoked changes. These results and those reported
in COX-2 knockout mice suggest that the AA released in brain following muscarinic receptor-mediated activation is lost via COX-2 to PGE2 but not via COX-1 to TXB2, and that increments in k* following arecoline largely represent replacement by unesterified plasma AA of this loss. 相似文献
20.
Spectral‐converting study of Ba9–3(m+n)/2ErmYbnY2Si6O24 (m = 0.005 – 0.2, n = 0 – 0.3) orthosilicate phosphors
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Optical materials composed of Ba9–3(m+n)/2ErmYbnY2Si6O24 (m = 0.005–0.2, n = 0–0.3) were prepared using a solid‐state reaction. The X‐ray diffraction patterns of the obtained phosphors were examined to index the peak positions. The photoluminescence (PL) excitation and emission spectra of the Er3+‐activated phosphors and the critical emission quenching as a function of Er3+ content in the Ba9–3m/2ErmY2Si6O24 structure were monitored. The spectral conversion properties of Er3+ and Er3+–Yb3+ ions doped in Ba9Y2Si6O24 phosphors were elucidated under diode‐laser irradiation at 980 nm. Up‐conversion emission spectra and the dependence of the emission intensity on pump power for the Ba8.55Er0.1Yb0.2Y2Si6O24 phosphor were investigated. The desired up‐conversion of the emitted light, which passed through the green, yellow, orange and red regions of the spectrum, was achieved through the use of appropriate Er3+ and/or Yb3+ concentrations in the host structure and 980 nm excitation light. The up‐conversion mechanism in the phosphors is described by an energy‐level schematic. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献