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1.
The objective of the research outlined in this paper was to develop the analytical approximations for calculating real-gas properties (p-v-T data, thermodynamic functions: internal energy, enthalpy, and entropy, and specific heats) of vapor-phase n-alkanes from C1 (methane) to C14 (normal tetradecane), O2, N2, H2O, CO, CO2, and H2 within the range of pressure 0.05 MPa ≤ p ≤ 20 MPa and temperature 280 K ≤ T ≤ 3000 K aimed for implementation into computational fluid dynamics (CFD)-codes simulating the operation process in modern Diesel engines. The analytical approximations have been developed based on available literature data and on the new equation of state for moderately dense gases. The approximations reported are rather simple and therefore can be used directly in CFD codes. Approximations for mixing rules are also provided.  相似文献   

2.
The zeroth-order theory of intermolecular forces is used to derive additivity relations for rotationally averaged molecular dipole properties and dispersion energy constants by assuming that a molecule is comprised of non-interacting atoms or molecules. Some of the additivity rules are new and others, for example the mixture rule for dipole oscillator strength distributions (DOSDs), Bragg's rule for stopping cross sections and Landolt's rule for molecular refractivities, are well known. The additivity rules are tested by using previously constructed DOSDs and reliable values for the dipole oscillator strength sums Sk , Lk and Ik , and dispersion energy constants C 6, for H, N, O, H2, N2, O2, NO, N2O, NH3 and H2O as models. It is found that additivity is generally unreliable for estimating molecular properties corresponding to k < -2. Generally for k ≥ -2 and for C 6, and if the hydrogen molecule is used to represent the hydrogen atom in the additivity rules, the additivity relations yield results that are reliable to within ?20 per cent and the estimates improve substantially as k increases. The effects of molecule formation on DOSDs is examined by comparing the various molecular DOSDs with the sum of the DOSDs for the atoms making up the molecules. Molecule formation results in a net decrease in the amount of dipole oscillator strength for low excitation energies and a compensating net increase for higher energies in a region extending from the absorption threshold to about 100 eV. This is shown to imply that estimates of the stopping average energy I 0, obtained by using bona fide atomic I 0 values, are lower bounds to the correct molecular I 0 results.  相似文献   

3.
Accurate values for the orientation-averaged long-range dipole-dipole dispersion energy coefficients, C 6(A, B), have been determined for all possible pair interactions involving ground state H, Li, N, O, H2, N2, O2, NH3, H2O, NO, and N2O. The calculations have been carried out by employing dipole oscillator strength distributions for these species that have been constructed (except in the case of H) by using discrete oscillator strength, photo-absorption, and high energy inelastic scattering data and by requiring the distributions to reproduce the Thomas-Reiche-Kuhn sum rule and, in the case of the molecules, available accurate refractivity and dispersion measurements for the relevant dilute gases. These oscillator strength distributions were also used to evaluate the refractivity R(λ), as a function of wavelength λ in the visible and ultra-violet region below the ultra-violet absorption thresholds, and the dipole oscillator strength sums S -2l , l = 1, 2, …, 7, for each atom and molecule. The calculated values of R(λ) provide refractivities for wavelengths, especially in the ultra-violet region, for which accurate experimental data are often not available. The accurate results for C 6(A, B) and for various dipole oscillator strength sums are used to make self-consistent tests of the adequacy of (1) the C 6(A, A) bounds provided by Padé approximant methods and (2) various semi-empirical formulae for C 6(A, B). Some problems that can arise in using other procedures to evaluate the S -2l and C 6(A, B) are discussed briefly.  相似文献   

4.
Using First-principle calculations, we have studied the structural, electronic and elastic properties of M2TlC, with M = Ti, Zr and Hf. Geometrical optimization of the unit cell is in good agreement with the available experimental data. The effect of high pressures, up to 20 GPa, on the lattice constants shows that the contractions are higher along the c-axis than along the a axis. We have observed a quadratic dependence of the lattice parameters versus the applied pressure. The band structures show that all three materials are electrical conductors. The analysis of the site and momentum projected densities shows that bonding is due to M d-C p and M d-Tl p hybridizations. The M d-C p bonds are lower in energy and stiffer than M d-Tl p bonds. The elastic constants are calculated using the static finite strain technique. We derived the bulk and shear moduli, Young’s modulus and Poisson’s ratio for ideal polycrystalline M2TlC aggregates. We estimated the Debye temperature of M2TlC from the average sound velocity. This is the first quantitative theoretical prediction of the elastic properties of Ti2TlC, Zr2TlC, and Hf2TlC compounds that requires experimental confirmation.   相似文献   

5.
R P Singh  R N Singh 《Pramana》1988,30(3):217-223
The infrared and laser Raman spectra of 2, 3 dichloro aniline and 2, 6 dichloro aniline have been recorded. The vibrational spectra have been analysed assumingC s andC 2v point groups for 2, 3 dichloro aniline and 2, 6 dichloro aniline respectively. Assignments for fundamental vibrations, combination and overtone frequencies and internal modes of vibration of amino group have been proposed.  相似文献   

6.
A calculated exhaustive set of vibrational state energies in 12C2H2, 13C2H2 and 12C2D2 has been used to analyse the evolution of the integrated number of states with increasing vibrational energy N(E) up to 15000 cm?1, 12000cm?1 and 10000 cm?1 in each isotopomer, respectively. The regular contribution to N(E) was modelled analytically and numerical parameters were fitted. The other expected contribution to N(E), which is of oscillatory nature, was quantified and is discussed using energyand time-dependent theories. Related periods of oscillation and temporal recurrences are interpreted consistently in terms of the constant of the motion Nr = 5v2 + 3v2 + 5v3 + v4 + v5 and of an average vibrational quantum. More pragmatically, the vibrational dynamics appear to be dominated by the bending vibrations, i.e., by the slowest oscillators.  相似文献   

7.
We present measurements of the resistivity tensor components ρa (T) and ρc (T) of high-quality Tl2Ba2Ca2Cu3O10 single crystals wit Tc = 118 … 121 K. The in-plane resistivity ρa as well as the out-of-plane resistivity ρc show a metal-like temperature dependence with an anisotropy ratio ρca of up to 103. The coherence length ξc (0) = 0.15 nm could be determined from an analysis of the fluctuation conductivity above Tc. From measurements of the ac-susceptibility in magnetic fields up to 10 Tesla the temperature dependence of the depinning line could be obtained. The diffusion coefficient of the flux lines obtained from the frequency dependence of the depinning temperature shows a thermally activated behaviour of the flux motion in the field range 0.1 T ? B ? 10 T.  相似文献   

8.
A comprehensive investigation of the structural, elastic, and lattice dynamical properties for ZrMo2 and HfMo2 with C14, C15, C36, and CeCu2 phases are conducted using density functional total energy calculations. The results have showed that C15 phase for both materials is energetically more stable than C14, C36 and CeCu2 phases. We have also estimated the mechanical behaviours of these compounds, including mechanical stability, bulk modulus, Young's modulus, shear modulus, Poisson's ratio, ductility, and anisotropy. Additionally, the lattice dynamical properties are analyzed and discussed exhaustively for these phases. The calculated properties agree well with available experimental and theoretical data.  相似文献   

9.
The rotational spectra of formaldehyde, H212C16O and its isotopic species H213C16O, H212C18O, and H213C18O have been investigated in the ground vibrational state in the frequency region between 8 and 460 GHz. For most cases in which measurements of the a-type R- and Q-branch transitions already existed the accuracy of the line position has been improved to about 10 kHz. For H212C16O and H213C16O a large number of ΔKa = ±2 transitions were measured with similar accuracy. These new data when combined with all other available data and appropriate weightings lead to a set of ground state parameters which for the first time are compatible with infrared and ultraviolet data. The rotational constants (and 3σ standard deviations) obtained using Watson's A-reduced Hamiltonian are:
  相似文献   

10.

Via simulating the contribution of spin-orbit interaction to nuclear masses by orthogonal Chebyshev polynomials, the mass excesses are calculated for a group of atomic nuclei characterized by the isospins of Tz = 51/2, 26, 53/2, 55/2, 28, and 57/2 and by the presence of restored Wigner’s spin-isospin SU(4) symmetry. The root-mean-square deviation of the results of these calculations from their experimental counterparts is σ = 140 keV. The potential of the proposed method is discussed.

  相似文献   

11.
12.
In this article, the isomerisation mechanisms of HN(NO2)2 to O2NNN(O)OH without and with catalyst X (X = H2O, (H2O)2, (H2O)3, HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2) have been investigated theoretically at the CBS-QB3 level of theory. Our results show that the catalyst X (X = H2O, (H2O)2, (H2O)3, HCOOH, H2SO4 and CH3CH2COOH) shows different positive catalytic effects on reducing the apparent activation energy of the isomerisation reaction processes. Such different catalytic effects are mainly related to the number of hydrogen bonds and the size of the ring structure in X (X = H2O, (H2O)2 and (H2O)3)-assisted transition states, as well as different values of pKa for H2SO4, HCOOH and CH3CH2COOH. Very interesting is also the fact that H2SO4-assisted reaction is the most favourable for the hydrogen transfer from HN(NO2)2 to O2NNN(O)OH, due to the smallest pKa (?3.0) value of H2SO4 than H2O, HCOOH, H2SO4 and CH3CH2COOH, and also because of the largest ∠X???H???Y (the angle between the hydrogen bond donor and acceptor) involved in H2SO4-assisted transition state. Compared to the self-catalysis of the isomerisation mechanisms of HN(NO2)2 to O2NNN(O)OH, the apparent activation energy of H2SO4-assisted channel also reduces by 9.6 kcal?mol?1, indicating that H2SO4 can affect the isomerisation of HN(NO2)2 to O2NNN(O)OH, most obvious among all the catalysts H2O, (H2O)2, (H2O)3, HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2.  相似文献   

13.
We report anisotropic thermal expansion of the parent, AEFe2As2 (AE = Ba, Sr, and Ca), compounds. Above the structural/antiferromagnetic phase transition anisotropy of the thermal expansion coefficients is observed, with the coefficient along the a-axis being significantly smaller than the coefficient for the c-axis. The high temperature (200 K ≤ T ≤ 300 K) coefficients themselves have similar values for the compounds studied. The sharp anomalies associated with the structural/antiferromagnetic phase transitions are clearly seen in the thermal expansion measurements. For all three pure compounds, the ‘average’ a-value increases and the c-lattice parameter decreases on warming through the transition, with the smallest change in the lattice parameters observed for SrFe2As2. The data are in general agreement with the literature data from X-ray and neutron diffraction experiments.  相似文献   

14.
Substitution of Ca by Y in TlCaBa2Cu2O y does not favour superconductivity, but substitution of Tl by Pb or of Ca by Ln (Ln = Y or rare earth) in TlCaSr2Cu2O y results in high Tc superconductivity (Tc π 60–90 K). TlCa1-xLn x Sr2Cu2O y is a new series of high Tc superconductors, but the x = 0.0 composition does not exhibit bulk superconductivity.  相似文献   

15.
The quadrupole moments (Θ) of the molecules P2, S2 and Cl2 have been computed at the SCF, CASSCF and CASSCF + 1 + 2 levels of theory, using augmented correlation consistent basis sets. The convergence of Θ as a function of basis set and level of theory is discussed. The variation of Θ from the separated atoms to the equilibrium region is reported. Θ is written as the sum of a sigma and pi contribution, and inaccuracies in the SCF values for P2 and S2 are due to the poor representation of the pi system in the SCF theory. A reference state dependent quadrupole moment density, - ½(3cos2 θ- 1)r 2δη(r; R), is defined whose integral is the mole2 cular quadrupole moment, and the spatial distributions of the density and its relationship to the density difference δη(r; R) are examined.  相似文献   

16.
The elementary representations (ER) of SU (2, 2) induced from the three non-trivial parabolic subgroups P0, P1, P2 are explicitly constructed in two equivalent realizations. We exhibit a one-to-one correspondence between the P0 and P2 induced representations. The corresponding representations are equivalent. We also exhibit a two-to-one correspondence between the P1 ERs and a subset of the P0 ERs; however, the corresponding representations are only partially equivalent. The Knapp-Stein integral intertwining operators are explicitly given for all representations in consideration.  相似文献   

17.
H. Wu  X. Cheng  L. Cai 《哲学杂志》2013,93(23):3373-3383
The equilibrium structure of the compound Li2O2 has been obtained via minimization of the total energy within the local density approximation (LDA) based on density functional theory (DFT). The calculated lattice parameters are in excellent agreement with available values. The elastic properties of Li2O2 are investigated. Values of all independent elastic constants (C 11, C 12, C 13, C 33 and C 44) as well as bulk moduli in the a and c directions are predicted. Our calculated elastic properties suggest that the compound Li2O2 is slightly anisotropic but can be considered as an isotropic material compared with other highly anisotropic materials. The electronic properties, including the density of states and energy band structure, are obtained and we find that this compound behaves as a semiconductor.  相似文献   

18.
The thermal expansion along the principal crystallographic axes of the (NH4)2WO2F4 and (NH4)2MoO2F4 oxyfluorides has been studied. The anomalous behavior of α i (T) due to the phase transitions has been revealed at T 1 = 271.4 K and T 2 ≈ 180 K for the molybdate and at T 1 = 201.5 K and T 2 ≈ 161 K for the tungstate. The quantities dT/dp and dT/dσ i , which characterize the dependence of the phase transition temperatures on the hydrostatic and uniaxial pressures, have been determined from analyzing the results of studies of the thermal expansion and heat capacity with the use of the Pippard relations. The p-T and α i -T phase diagrams reflect different characters of the influence of the pressure on the stability of the initial and distorted phases of the oxyfluorides. The magnitudes of the extensive and intensive barocaloric effects determined in the vicinity of the structural phase transitions are as follows: ΔS BCE varies from approximately −10 to −17 J/mol K and ΔT AD ≈ 8−17 K for the molybdate and ΔS BCE varies from approximately −10 to −17 J/mol K and ΔT AD ≈ 8−13 K for the tungstate.  相似文献   

19.
We report on a comparative crystal chemical study of the Tl2–xBa2Ca n Cu n+1O2n+6(n=0, 1, 2) high-T c superconductors. Superconducting properties were determined by DC-conductivity and-susceptibility measurements. An X-ray diffraction analysis reveals the nonstoichiometry of the compounds as a link between structural and superconducting behavior. A comparison of the different structures gives evidence that T1 deficiency in the TlO double layers increases with increasingn; this deficiency causes apparent Cu valences larger than 2+in the superconducting phases thus maintaining the charge balance. By extracting appropriate chemical formulas and performing a bond strength calculation we obtained the mixed-valent oxidation state of copper for the superconducting tetragonal phases as being 2.17+(n=0), 2.25+(n=1) and 2.31+(n=2) respectively; for the non-superconducting orthorhombic phase Tl2–xBa2CuO6–y a Cu valence of about 2+is suggested.  相似文献   

20.
Yaar  I.  MayTal-Beck  S.  Berant  Z. 《Hyperfine Interactions》2001,136(3-8):777-781
The Hf z coordinate and the value of the electric field gradient (efg) main component (V zz ), were calculated for three Hf2X compounds (X = Pd, Ag, Cd) on a first-principle basis, using the full potential linear augmented plane wave (LAPW) method. Exchange and correlation effects were treated either by the local spine density approximation (LSDA) or by the more advanced generalized gradient approximation (GGA). The calculated V zz values, in the Hf site, were in very good agreement with available 181Hf TDPAC experimental results. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

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