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1.
The fringing field region of a quadrupole mass filter is modelled using an iterative finite difference technique to solve Laplace's equation for the electrostatic potential. The results are used to formulate an expression f(z) such that the electrostatic potential of the fringing field, F(x, y, z, t) may be written in the form F(x, y, z, t) = f(z) φ(x, y, t), where φ(x, y, t) is the hyperbolic field of the quadrupole. The function f(z) is expressed in the form f(z) = 1 - exp {- az - bz2}), where a and b are constants and z is in units of rO, where 2rO is the spacing of the quadrupole rods. The effect of the distance from the quandrupole rods to the end plate of the quadrupole mass filter, d on f(z) is investigated and the results presented show that for d < 0.125 rO the function f(z) does not alter significantly.  相似文献   

2.
The crystal structures of the tetragonal rare earth (RE) oxychlorides, REOCl (RE=La-Nd, Sm-Ho, and Y) were studied by X-ray powder diffraction measurements, Rietveld analyses, and bond valence calculations. The tetragonal structure (space group P4/nmm, No. 129, Z=2) is stable for all but Er-Lu oxychlorides, which possess a hexagonal structure. The tetragonal structure consists of alternating layers of (REO)nn+ complex cations and Xn anions, where the rare earth is coordinated to four oxygens and four plus one chlorines in a monocapped tetragonal antiprism arrangement. The Rietveld analyses yielded a coherent series of structural parameters. Preferred orientation and microabsorption effects were found significant. The evolution of interatomic distances and bond angles indicated that the reason for the preferred structure changing from tetragonal to hexagonal is the strain in the chlorine layer. The bond valence parameter B for the RE-O bonds had to be recalculated due to the covalent nature of the (REO)nn+ unit. The results obtained with the new parameter confirmed the strains in the chlorine layer to be the cause for the phase transition.  相似文献   

3.
The proteins of SMC family are characterized by having Walker A and B sites. The Escherichia coli RecN protein is a prokaryotic member of SMC family that involved in the induced excision of Tn10 and the repair of the DNA double strand breaks. In this work, the Walker A nucleotide binding site of the E. coli RecN protein was mutated by changing the highly conserved lysine residue 35 to the aspartic acid (D), designated as recNK35D. Reverse genetics was utilized to delete the entire recN gene (ΔrecN108) or introduce the recNK35D gene into the E. coli chromosomal DNA. The recNK35D cells showed decrease in the frequency of excision of Tn10 from gal76::Tn10 after treatment with mitomycin C compared to recN+ cells. The ΔrecN108 cells showed an un-induced increase in the frequency of Tn10 excision from gal76::Tn10 in rec+ background while, recBC sbcBC ΔrecN108 cells are completely deficient in Tn10 excision. The recombination proficiency is reduced in cells carrying recBC sbcBC cells in addition recNK35D mutation. We observed that the Walker A nucleotide binding site is important for the RecN protein. Strains that deleted recN gene are recombination deficient and more sensitive to mitomycin C than strains carrying recNK35D.  相似文献   

4.
The integral enthalpies of solution Δsol H m of L-cysteine and L-asparagine in mixtures of water with ethanol, n-propanol, and isopropanol at a mole fraction of alcohol of up to 0.32 were determined by calorimetry of solution. The standard enthalpies of solution (Δsol H 0) of L-serine and of its transfer (Δtr H 0) from water to a mixed solvent were calculated. The dependences of Δsol H 0 and Δtr H 0 on the composition of water-alcohol mixtures pass through a maximum. The calculated enthalpy coefficients of pair interaction of amino acids with alcohol molecules are positive and increase in the order ethanol, n-propanol, isopropanol. The data obtained were interpreted from the viewpoint of various types of interaction in solution and effect of the amino acid residue on the thermochemical characteristics of solution.  相似文献   

5.
The structural parameters of the effective r g configuration of the LaI3 molecule were calculated using the DFT/B3LYP method. The difference between the calculated values of r e (La-I) and r g (La-I) is mostly due to the anharmonicity of the ν1 and ν2 vibrations and does not exceed the error in determining the distance r g (La-I) in the electron diffraction experiment. Inclusion of the anharmonicity of the ν2 and ν4 deformation vibrations in calculations leads to decreased amplitudes l(I…I) and shrinking effect δ(I…I) compared to the respective values obtained in the harmonic approximation. The LaI3 molecule proved to be more rigid than predicted by B3LYP calculations.  相似文献   

6.
The high resolution laser-atomic-beam technique was used to investigate the hyperfine structure in Nd I 4f 46s 2 5 I,5 F,5 S and 4f 45d6s 7 L,7 K,7 I,7 H. The metastable states were populated by an arc discharge burning in the atomic beam. The measured hyperfine constantsA andB of the levels of 4f 46s 2 and 4f 45d6s allow a parametric analysis to be performed using the effective tensor operator formalism. The experimental radial integrals of the 4f and 5d electrons fit with those of the other lanthanides. The 4f radial integrals are in agreement with values of optimized Hartree-Fock-Slater calculations. The spectroscopic quadrupole moments of143Nd and145Nd are deduced from the 4f parameters:Q I =?0.610(21) b and ?0.314(12) b, respectively. TheQ I resulting from the 5d parameter are in satisfactory agreement with these values. The hyperfine anomaly due to thes electron in 4f 45d 6s amounts to about 1%.  相似文献   

7.
Electrical resistivity and Hall effect measurements at 77–373°K are presented for Zn doped ZnO crystals. The crystals have been doped systematically at 600–1100°C in controlled pressures of Zn. The concentration of electrons at room temperature is in the range nRT = 2.5 × 1016, to 3.6 × 1018, cm?3. The donor level ED and the concentrations of donors ND and acceptors NA have been calculated from a best fit to the experimental relationships log n versus 1T and log μH versus log T. At dilute concentrations of donors, two donor levels have been observed, EDI = 0.043–0.045 eV and a deeper level EIID greater than 0.165 eV. The ZnO was found to behave as a metal at ND ~ 6 × 1018, cm?3.At least two different donors have to be assumed in order to explain the experimental results. It is suggested that interstitial Zn is the electrical active donor at higher doping levels. The nature of the other donor is not clear. Neither 1s1 H-type nor 1s2 He-type donors seem to explain all the observations consistently.  相似文献   

8.
The spectrum of four times ionized Xenon (XeV), has been observed in the 500–6800 Å range and 84 new lines have been identified as transitions between levels of 5s5p 3, 5s 25p5d, 5s 25p6s, 5s 25p 2, and 5s 25p6p configurations. Nine new levels belonging to the configuration 5p6p have been determined. The results of this analysis are supported by Hartree-Fock calculations. The configurations are interpreted by fitting the theoretical energy parameters to the observed levels using least-squares techniques.  相似文献   

9.
In semi-arid regions, browse plant species are used as feed and for medicinal purposes for both animals and humans. The limitation of the utilization of these species to medicinal purposes or as feed for livestock is a lack of knowledge on the concentration level of phytochemicals and other bioactive compounds found in these plants. The study sought to assay the qualitative and quantitative bioactive constituents of some browse species found in the savannah biome of South Africa, viz. Adansonia digitate, Androstachys johnsonii, Balanites maughamii, Berchemia discolor, Berchemia zeyheri, Bridelia mollis hutch, Carissa edulis, Catha edulis, Colophospermum mopane, Combretum Imberbe, Combretum molle, Combretum collinum, Dalbergia melanoxylon, Dichrostachys cinerea, Diospros lycioides, Diospyros mespiliformis, Euclea divinorum, Flueggea virosa, Grewia flava, Grewia flavescens, Grewia monticola, Grewia occidentalis, Melia azedarach, Peltophorum africanum, Prosopis velutina, Pseudolachnostylis maprouneifolia, Pterocarpus rotundifolius, Schinus molle, Schotia brachypetala, Sclerocarya birrea, Searsia lancea, Searsia leptodictya, Searsia pyroides, Senegalia caffra, Senegalia galpinii, Senegalia mellifera, Senegalia nigrescens, Senegalia polyacantha, Strychnos madagascariensis, Terminalia sericea, Trichilia emetic, Vachellia erioloba, Vachellia hebeclada, Vachellia karroo, Vachellia nilotica, Vachellia nilotica subsp. Kraussiana, Vachellia rechmanniana, Vachellia robusta, Vachellia tortilis, Vachellia tortilis subsp. raddiana, Vangueria infausta, and Ziziphus mucronata. These browse species’ leaf samples were harvested from two provinces (Limpopo and North-West) of South Africa. The Limpopo province soil type was Glenrosa, Mispah, and Lithosols (GM-L), and the soil types in the North-West Province were Aeolian Kalahari Sand, Clovelly, and Hutton (AKS-CH). The harvested browse samples were air dried at room temperature for about seven days and ground for analysis. The methanol and distilled water extracts of the browse species leaves showed the presence of common phytoconstituents, including saponins, flavonoids, tannins, phenols, cardio glycosides, terpenoids, and phlobatannins, as major active compounds in browse species leaves. In the quantitative analysis, phytochemical compounds, such as soluble phenols, insoluble tannins, and condensed tannins, were quantified for common species found in both sites. Two-way ANOVA and multivariate analysis were used to test soil type and species effect on soluble phenols, insoluble tannins, and condensed tannins of woody species. Dichrostachys cinerea (0.1011% DM) in GM-L soil type and Z. mucronata (0.1009% DM) in AKS-CH soil type showed the highest (p < 0.05) concentration of soluble phenols. In AKS-CH soil type, D. cinerea (0.0453% DM) had the highest insoluble tannins concentration, while V. hebeclada had the lowest (0.0064% DM) insoluble tannins content. Vacchelia hebeclada had lower (p < 0.05) condensed tannins concentration levels than all other browse plants in both soil types. Under multivariate analysis tests, there was a significant effect (p < 0.001) of soil type, species, and soil type x species interaction on soluble phenols, insoluble tannins, and condensed tannins of woody species. In this study, most of the woody species found in GM-L soil type showed a lower amount of tannins than those harvested in AKS-CH soil type. There is a need to identify the amount of unquantified phytochemicals contained in these browse species and valorize the high-bioactive-compound browse species to enhance and maximize browsing of these browse species for animal production.  相似文献   

10.
11.
The visoelastic photoelastic behaviour of cross-linked polymethacrylic acid, swollen to equilibrium in variously concentrated aqueous NaCl solutions (cx = 0.05-1.5 M), was studied. In the rubber-like region, stress and birefringence relaxation at various elongations (λ) can be separated into the deformation- and time-dependent parts. Both the extrapolated equilibrium modulus (Gr) and the interaction parameter (χ) strongly depend on the degree of swelling of the gel. One of the most interesting findings is that the exponent of the volume fraction of the polymer (ν2) in the dependence of the modulus Ge on ν2 is much higher than 1/3 as predicted by the theory of Gaussian networks, if the concentration of the crosslinking agent c is low. The same is true for the Mooney-Rivlin constant (C1) even if the ratio C2C1 approaches zero at lower ν2. The values of the stress-optical coefficient (Ce) increase with both increasing swelling and decreasing content of the cross-linking agent in the gel; the most pronounced increase in Ce is connected with the largest decrease in Ge. The same dependence of Ce on the modulus in the dry state (Gd), irrespective of the concentration of the cross-linking agent and cs, suggests the conclusive role played by the macroform contribution to birefringence. The effects found are probably due to the disappearance of the secondary structure of PMA chains with increasing swelling and concentration of the cross-linking agent.  相似文献   

12.
We have investigated the magnetic structure of HoB12, ErB12 and TmB12 by neutron diffraction on isotopically enriched single-crystalline samples. Results in zero field as well as in magnetic field up to 5 T reveal modulated incommensurate magnetic structures in these compounds. The basic reflections can be indexed with q=(1/2±δ, 1/2±δ, 1/2±δ), where δ=0.035 both for HoB12 and TmB12 and with q=(3/2±δ, 1/2±δ, 1/2±δ), where δ=0.035, for ErB12. In an applied magnetic field, new phases are observed. The complex magnetic structure of these materials seems to result from the interplay between the RKKY and dipole-dipole interaction. The role of frustration due to the fcc symmetry of dodecaborides and the crystalline electric field effect is also considered.  相似文献   

13.
The hydrogenation properties of the LaNi5 (CaCu5 type, hP6, P6/mmm) and Pd substituted derivatives LaNi5−xPdx compounds have been studied in the whole homogeneity range of the solid solution (0.25≤x≤1.5). The pressure versus hydrogen content isotherms show several plateaus and an increase of the plateau pressure as a function of palladium concentration. The volume increase of the Pd substituted alloys should have resulted in a lowering, and not an increase, of the plateau pressure, according to the conventional models based on the size effect. In order to elucidate the origin of this anomalous behavior, both an experimental and a theoretical ab initio electronic structure investigation have been carried out. Experimentally, the nature and the structural properties of the hydrides have been studied by both in situ and ex situ neutron diffraction. The crystal structures of the three hydride phases are reported (LaNi3.5Pd1.5D1.96, filled-up CaCu5 type, P6/mmm; LaNi4PdD2.72, LaNi2(Ni0.75Pt0.25)3H2.61 type, oI128, Ibam; LaNi4.75Pd0.25D5.67, partly ordered CaCu5 type, P6mm). In addition, the phase diagram of LaNi5−xPdx-H system has been investigated. The electronic and thermodynamic properties of both intermetallic compounds and the hydrides have been studied by ab initio electronic structure calculations. The theoretical results are in good agreement with our experimental data, and show that electronic interactions play a major role in the hydrogenation behavior of these Pd substituted intermetallic compounds, and that these effects cannot be accounted for by a simplistic model based on the size effect alone.  相似文献   

14.
An analytic expression for the total energy of metallic clusters composed ofN identical atoms of valencev and with net chargeQ is obtained by means of a variational solution of the Thomas-Fermi-Weizsäcker energy density functional within the spherical jellium model. The minimum energy is given as an expansion in decreasing powers of the cluster radiusR=r s Z 1/3, withZ=vN andr s the radius per electron of the bulk metal. The coefficients are obtained as functions ofr s . Terms of volume (R 3), surface (R 2), curvature (R), constant (R 0), (1/R) and (1/R 2) are clearly separated in the formula, as well as the different contributions (kinetic, coulombic and exchange-correlation) to each of them. The asymptotic values (R→∞) for the work functions,W(r s ), and surface energies σ(r s ), are compared to analogous semiclassical and Kohn-Sham calculations of jellium-like surfaces and to the experimental values. The size dependent behaviour of chemical potentials, μ(R), electron affinities,AF(R), and ionization potentials,IP(R), are easily obtained for any kind of metallic clusters. In particular we discuss the Coulomb and quantum corrections to the coefficients β, δ in the asymptotic formulae:IP?W+β/R andAF?W+δ/R.  相似文献   

15.
In this paper, elastic behaviors of non-Gaussian polymethylene (PM) chains with chain length N=100 are investigated by rotational isomeric state model. Here the tetrahedral lattice of PM chain and the non-local interaction of Sutherland potential are adopted. In the metropolis movement of PM chain, a four-bond movement model is used. The average energy and average Helmholtz free energy with various elongation ratios λ are calculated by Monte Carlo simulation method. The average energy increases with elongation ratio λ and the average Helmholtz free energy decreases with elongation ratio λ. The elastic force f and the energy contribution to elastic force fu can be obtained from f=∂〈A〉/∂r and f=∂〈U〉/∂r. We find that the elastic force f increases with elongation ratio λ and the energy contribution fu decreases with elongation ratio λ, and fu is less than zero. The ratio fu/f is close to −0.21 for λ?1.25, and −0.04 to −0.35 for λ>1.25 at T=364 K. In our calculation, the rubber elasticity may be discussed in terms of the chemical structure of polymer chains.  相似文献   

16.
The fluorescence of a series of copolymers of 2-naphthyl methacrylate (2-NM) and methyl methacrylate (MMA) with various contents of 2-NM (obtained in chloroform, carbon tetrachloride and acetonitrile) was investigated. A linear dependence between the ratio of the excimer to monomer emission intensities (ID/IM) and the diad fraction (fnn) of 2-NM monomer units was established. The relationship between ID/IM and fnn · In (In = the mean sequence length of 2-NM units) fits a logarithmic curve. The results indicate that the excimer emission is determined mainly by the nearest neighbour naphthalene-containing monomer units in the copolymer chain. The copolymers obtained in acetonitrile have higher values of ID/IM than those obtained in chloroform and carbon tetrachloride. This difference is due to the higher content of mm-triads in copolymers from acetonitrile, confirmed by 1H-NMR analysis of the samples of poly(methyl methacrylate) formed from copolymers of 2-NM and MMA.  相似文献   

17.
Electrons, electron holes, or excitations in finite or infinite ‘multimer systems’ may be localized or delocalized. In the theory of Hush, localization depends on the ratio Δ/λ (Δ/2 = coupling; λ = reorganization energy). The latter theory has been extended to the infinite system [S. Larsson, A. Klimkāns, Mol. Cryst. Liq. Cryst. 355 (2000) 217]. The metal/insulator transition often takes place abruptly as a function of Δ/λ. It is argued that localization in a system with un-filled bands cannot be determined on the basis of Mott–Hubbard U alone, but depends on the number of accessible valence states, reorganization energy λ and coupling Δ (=2t). In fact U = 0 does not necessarily imply delocalization. The analysis here shows that there are many different situations for an insulator to metal transition. Charge transfer in doped NiO is characterized by Ni2+ − Ni3+ exchange while charge transfer in pure NiO is characterized by a disproportionation 2Ni2+ → Ni+ + Ni3+. In spite of the great differences between these two cases, U has been applied without discrimination to both. The relevant localization parameters appear to be Δ and λ in the first case, with only two oxidation states, and U, Δ and λ in the second case with three oxidation states. The analysis is extended to insulator-metal transitions, giant magnetic resistance (GMR) and high Tc superconductivity (SC). λ and Δ can be determined quite accurately in quantum mechanical calculations involving only one and two monomers, respectively.  相似文献   

18.
The experimental ionization constants were used to calculate and analyze the effective short-range potential d ij for HCl, HBr, and HI in n-alcohols from methanol to octanol at 5–55°C. Changes in the d ij and Δ ij G* = N A d ij values depending on temperature, solvent, and anions were explained in terms of the Samoilov concept of short-range solvation. The character of changes in Δ ij G* was shown to be determined by the ratio between the contributions of ion-molecular and intermolecular non-Coulomb interactions, which were, in turn, determined by the structural state of the solvent and solvation of electrolyte particles in solutions of hydrogen halides.  相似文献   

19.
By comparing UV spectra of β-alkoxy-α,β-unsaturated ketones of established steric structure, spectral constants characteristic of the cis/trans configuration change and s-cis/s-trans and O-s-cis/O-s-trans conformation changes have been evaluated. These are: Δλcistrans = 0, Δλs-ciss-trans = 8 nm and ΔλO-s-transO-s-cis = 6 nm. A comparison of cis-s-cis enol ethers with the parent enols yielded the increment for the intramolecular (“chelating”) H-bond, Δγchel = 24 nm. The methanol-induced bathochromic shift has been found to depend strongly on s-cis/s-trans isomerism. The substituent increments have been shown to be dependent on the degree of substitution in the reference molecule. The results obtained have been summarized in a set of spectral increments complementing the basic system of Woodward and the Fiesers.  相似文献   

20.
The effect of 60Co (γ-ray) irradiation on the electrical and dielectric properties of Au/Polyvinyl Alcohol (Ni,Zn-doped)/n-Si Schottky barrier diodes (SBDs) has been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and 1 MHz. The real capacitance and conductance values were obtained by eliminating series resistance (Rs) effect in the measured capacitance (Cm) and conductance (Gm) values through correction. The experimental values of the dielectric constant ′), dielectric loss ″), loss tangent (tanδ), ac electrical conductivity (σac) and the real (M′) and imaginary (M″) parts of the electrical modulus were found to be strong functions of radiation and applied bias voltage, especially in the depletion and accumulation regions. In addition, the density distribution of interface states (Nss) profile was obtained using the high-low frequency capacitance (CHF-CLF) method for before and after irradiation. The Nss-V plots give two distinct peaks for both cases, namely before radiation and after radiation, and those peaks correspond to two different localized interface states regions at M/S interface. The changes in the dielectric properties in the depletion and accumulation regions stem especially from the restructuring and reordering of the charges at interface states and surface polarization whereas those in the accumulation region are caused by series resistance effect.  相似文献   

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